Fatigue Resistance and Failure Mode of Adhesively Restored Custom Metal–Composite Resin Premolar Implant Abutments Luís Leonildo Boff, MDS, PhD1/Elisa Oderich, MDS, PhD1/ Antônio Carlos Cardoso, MDS, PhD2/Pascal Magne, DMD, PhD3 Purpose: To evaluate the fatigue resistance and failure mode of composite resin and porcelain onlays and crowns bonded to premolar custom metal–composite resin premolar implant abutments. Materials and Methods: Sixty composite resin mesostructures were fabricated with computer assistance with two preparation designs (crown vs onlay) and bonded to a metal implant abutment. Following insertion into an implant with a tapered abutment interface (Titamax CM), each metal–composite resin abutment was restored with either composite resin (Paradigm MZ100) or ceramic (Paradigm C) (n = 15) and attached with adhesive resin (Optibond FL) and a preheated light-curing composite resin (Filtek Z100). Cyclic isometric chewing (5 Hz) was then simulated, starting with 5,000 cycles at a load of 50 N, followed by stages of 200, 400, 600, 800, 1,000, 1,200, and 1,400 N (25,000 cycles each). Samples were loaded until fracture or to a maximum of 180,000 cycles. The four groups were compared using life table survival analysis (log-rank test). Previously published data using zirconia abutments of the same design were included for comparison. Results: Paradigm C and MZ100 specimens fractured at average loads of 1,133 N and 1,266 N, respectively. Survival rates ranged from 20% to 33.3% (ceramic crowns and onlays) to 60% (composite resin crowns and onlays) and were significantly different (pooled data for restorative material). There were no restoration failures, but there were adhesive failures at the connection between the abutment and the mesostructure. The survival of the metal–composite resin premolar abutments was inferior to that of identical zirconia abutments from a previous study (pooled data for abutment material). Conclusions: Composite resin onlays/ crowns bonded to metal–composite resin premolar implant abutments presented higher survival rates than comparable ceramic onlays/crowns. Zirconia abutments outperformed the metal–composite resin premolar abutments. Int J Oral Maxillofac Implants 2014;29:364–373. doi: 10.11607/jomi.2836 Key words: adhesion, ceramic, composite resin, computer-aided design/computer-assisted manufacture, fatigue resistance, implant abutment, premolar
1Visiting
Scholar, Department of Restorative Sciences, Herman Ostrow School of Dentistry, University of Southern California, USA; Assistant Professor and Researcher, Department of Dentistry, Federal University of Santa Catarina, Florianópolis, SC, Brazil. 2 Titular Professor, Science of Health Center, University of Santa Catarina, Florianópolis, SC, Brazil. 3 Tenured Associate Professor and Don and Sybil Harrington Foundation Professor of Esthetic Dentistry, Division of Restorative Sciences, The Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, California, USA. Correspondence to: Dr Pascal Magne, University of Southern California, Division of Restorative Sciences, The Herman Ostrow School of Dentistry, 925 W. 34th Street, Los Angeles, CA 90089-7792, USA. Fax: +213-821-5324. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
R
estorations for posterior implants require a strong and reliable material to withstand normal masticatory function. Titanium abutments and metal-ceramic crowns are traditionally used because of their mechanical properties.1–4 With an increasing trend for esthetic materials, zirconia abutments and all-ceramic restorations have been used as a substitute for metal, even in posterior areas of the arches. These new materials are not associated with the grayish appearance of the cervical soft tissue encountered around metal abutments and have been increasingly recommended to fabricate custom abutments.5–8 Zirconia (yttria-stabilized tetragonal zirconia polycrystal) appears to fulfill the requirements of strength and biocompatibility needed for implant abutments.9 However, reliable performance of the abutment itself does not guarantee the strength of the restoration. For single crowns sup-
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Fig 1 Correlation Mode in CEREC3. (Left) Impression of solid metal abutment. (Center) Correlation of metal abutment with final design from zirconia abutment from previous study.27 (Right) Final mesostructure to be milled (onlay design).
ported by implants, systematic reviews have revealed a slightly inferior 5-year survival rate for all-ceramic systems (91.2%) compared to metal-ceramic systems (95.4%).10 Survival rates can be expected to decline when bruxism is present because parafunctional habits play a significant role in the frequency of complications.11 The stiffness of ceramic in the absence of a periodontal ligament (PDL) results in a nonresilient monobloc structure. In contrast to natural tooth abutments, the inherent rigidity of the bone-implant-restoration assembly has been associated with a higher incidence of mechanical complications, including fracture of the veneering material, abutment or screw loosening, and loss of retention.12 Other drawbacks of zirconia are the difficulty of bonding to it13–15 and the risk of propagating microfractures while trimming prefabricated abutments.16–18 A decade ago, composite resin blocks (Paradigm MZ100, 3M/ESPE) were introduced for use with computer-aided design/computer-assisted manufacture (CAD/CAM) systems as an alternative to machinable ceramics.19,20 The blocks were manufactured from the original Filtek Z100 restorative material (3M/ESPE); this contains patented spheroidal zirconia-silica fillers (85% by weight) that provide restorations with excellent behavior under dynamic loading21–26 while maintaining a relatively low elastic modulus. This unique combination of strength and resilience has been incorporated into a new implant abutment/restoration concept in an attempt to mimic the behavior of natural teeth (the “biomimetic principle”).25 In this concept, the resilient component (to simulate the PDL) is integrated into the restoration. This concept was successfully applied to restore zirconium abutments in the anterior dentition15 and yielded outstanding results in the posterior dentition (100% survival of abutments and restorations).27 Interestingly, when considering the dynamic response to impact loading (measured energy absorption; Periometer, Perimetrics
LL), composite resin restorations bonded to zirconia abutments seemed to respond in a similar fashion to natural teeth with a simulated PDL.28 In the past, however, the use of resilient crowns over rigid abutments did not prove to provide significant stress relief to the bone.29–41 Therefore, a more efficient shockabsorption effect might be obtained with a larger volume of resilient material, for example, if the abutment itself were made of it. Hence, it has been proposed to fabricate anterior single-unit implant-supported restorations using Paradigm MZ100 composite resin abutments25 associated with adhesively retained nonretentive veneers.15,42 In the anterior dentition, the results demonstrated that survival of composite resin abutments did not differ from that of zirconia abutments. There are no data available for such an approach to restoring implants in the posterior dentition. A significant effect of the abutment and restorative material is expected, given the increased volume of those elements in the posterior dentition. It is also not known whether a posterior CAD/CAM composite resin custom abutment will withstand repeated mechanical loading in a moist environment and prevent early restoration failure. The aim of the present study was to assess in vitro the fatigue resistance and failure mode of onlays and crowns bonded to CAD/CAM metal–composite resin premolar implant abutments. The influence of the restoration material (ceramic vs composite resin) was also evaluated. The null hypothesis considered was that the abutment-restoration adhesive interface would not fail before the abutment itself failed and that the restorative material (ceramic vs composite resin) would influence the fatigue resistance and failure mode of the assembly. Previously published data using zirconia custom premolar abutments with the same design,27 generated randomly and simultaneously under strictly identical laboratory and testing conditions, were included for comparison. The International Journal of Oral & Maxillofacial Implants 365
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Fig 2 Restoration designs and dimensions for (left) an onlay and (right) a crown.
Fig 3 CAD/CAM (left) composite resin crown and (right) onlay designs, with the accompanying custom composite resin mesostructures and solid metal abutments.
MATERIALS AND METHODS Sixty implants with an internal tapered abutment interface (Titamax CM, 4.0 mm diameter, 11 mm length, Neodent) were embedded in a standard position in autopolymerizing acrylic resin (Palapress, Heraeus Kulzer), which is considered a suitable material for bone simulation because of its similar elastic modulus.43 The Cerec 3 system (version 3.60, Sirona Dental Systems) was used in Correlation Mode (Fig 1) to design two CAD/CAM custom abutments by combining the optical impressions of two different custom zirconia premolar abutments (onlay and crown designs) from a previous study27 and that of a solid metal abutment (CM Universal Post, 4.5 mm diameter, 4.5 mm height, 2.5 mm neck, Neodent). Both abutments followed the natural emergence profile of a maxillary second premolar and included clearance for either a crown or an onlay restoration. The metal abutment was used as an interface with the implant platform to connect the CAD/CAM composite resin mesostructure to the implant. Thirty identical CAD/CAM composite resin pre-
molar abutments (Paradigm MZ100, 3M/ESPE) were milled for each preparation design. Following the same methodology, 30 identical crowns and 30 identical onlays were fabricated. Thirty restorations (15 crowns and 15 onlays) were milled in composite resin (Paradigm MZ100, 3M/ESPE), and in a similar fashion 30 of the same restorations were milled in glass-ceramic (Paradigm C, 3M/ESPE) (Fig 2). All mesostructures and restorations (Fig 3) were milled with the sprue located at the palatal surface. The porcelain restorations were initially polished using the intraoral Dialite porcelain adjustment polishing kit (Brasseler), and the composite resin restorations were polished using the Q-Polishing System (Kit ref. 4477, Komet) and silicon carbide–impregnated polishing brushes (Occlubrush, Kerr-Hawe). With a coarse round diamond bur (801-023, Brasseler), a circular hole (future access for screw tightening) was created in the occlusal surface of the CAD/CAM composite resin mesostructure. The fitting surfaces of the metal solid abutment and the composite resin mesostructure were subjected to the same surface treatment, ie, airborne-particle abrasion with 27-µm silica-modified aluminum oxide (Cojet, 3M/ESPE) at 0.2 MPa for 10 seconds at a distance of 10 mm, application of a silane (Ultradent) for 20 seconds, and drying at 100°C for 1 minute using a standard oven (ERC Dental Burn Out Oven, Model 500S, Dental Tech). For convenience and to ensure precise positioning during the assembly, the metal abutment was set into an implant analog and the screw-access channel was filled with expanded polytetrafluoroethylene tape. The two parts were luted together with adhesive resin (Optibond FL, Bottle 2, Kerr) and composite resin (Filtek Z100, 3M/ ESPE; preheated for 5 minutes in Calset, Addent). After removal of the excess composite resin, all surfaces were light polymerized for 60 seconds at 1,000 mW/ cm2 (Valo, Ultradent). Surface treatment of porcelain restorations (crowns and onlays) included airborne-particle abrasion with 50-µm aluminum oxide at 0.2 MPa, followed by etching with 9% hydrofluoric acid (Porcelain Etch, Ultradent)
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for 45 seconds and rinsing with water for 20 seconds. Postetching cleaning was done with 35% phosphoric acid (Ultra-Etch, Ultradent) with a gentle brushing motion for 1 minute, followed by rinsing with water for 20 seconds. After final cleaning by immersion in distilled water in an ultrasonic bath for 2.5 minutes and oil-free air drying, intaglio surfaces were silanated (Silane, Ultradent) and heat dried at 100°C for 1 minute. The same surface treatment was applied to the fitting surfaces of the composite resin abutments and composite resin restorations (crowns and onlays) without hydrofluoric acid treatment. Each metal–composite resin abutment was inserted into an implant, and 15 N/cm of torque was applied to the abutment screw. Expanded polytetrafluoroethylene tape was used to cover the abutment screw and fill part of the access channel. Each restoration was bonded individually to its abutment using adhesive resin (Optibond FL, Bottle 2, Kerr) and composite resin (Filtek Z100, 3M/ESPE; preheated for 5 minutes in Calset, Addent). After all excess composite resin was removed, each surface was light polymerized for 60 seconds at 1,000 mW/cm2 (Valo, Ultradent). All margins were covered with an air-blocking barrier (K-Y Jelly, Personal Products Company) and were light polymerized for an additional 10 seconds per surface. Unlimited time to bond the restoration reduced considerably the time needed to remove excess adhesive resin, which was carefully eliminated with hand instruments (scaler, blade); specimens were stored in distilled water for 24 hours before testing. An artificial chewing device actuated by closedloop servo hydraulics (Mini Bionix II, MTS Systems) was used to simulate masticatory forces (Fig 4). The chewing cycle was replicated by an isometric contraction (with load control), which was applied through a 7-mm-diameter cylindric composite resin antagonist (Filtek Z100, 3M/ESPE) to reproduce in every specimen two equidistant contact points (standard position). A new antagonist was fabricated for each specimen. The load chamber was filled with distilled water to submerge the sample during testing. Cyclic loading was applied at a frequency of 5 Hz. A loading protocol was used; this began with a “warm-up” at 50 N for 5,000 cycles and was followed by stages of 200, 400, 600, 800, 1,000, 1,200, and 1,400 N for a maximum of 25,000 cycles each. Samples were loaded until fracture or to a maximum of 180,000 cycles. The fatigue machine was set and calibrated to stop automatically when any movement greater than 0.3 mm was detected inside the load chamber. The number of endured cycles and the failure mode of each specimen were recorded. After the testing, each sample was evaluated by transillumination (Microlux, Addent) with the aid of an optical microscope
Fig 4 Close-up view of specimen and cylindric composite resin antagonist before testing.
(Leica MZ 125, Leica Mycrosystems) at 10:1 magnification (two-examiner agreement). Failure mode analyses were repeated by each examiner with an interval of 7 days, and the data presented were mean values. In the case of a disagreement, a third calibrated examiner was prepared to collaborate in this study. To prevent visual fatigue, the examiners stopped for an interval after every 10 specimens analyzed. A visual distinction was made between cohesive fractures of the abutment, screw, or implant, as well as cohesive fracture of the restorations and/or adhesive failure of the restoration/mesostructure/abutment interfaces. The fatigue resistance of the four groups was compared using the Kaplan-Meier survival analysis (MedCalc Software, version 12.3.0). At each time interval (defined by each load step), the number of specimens that started the interval intact and the number of specimens that fractured during the interval were counted to allow the calculation of survival probability at each interval. The influences of the restoration materials (composite or ceramic) and the different restoration designs (crown or onlay) on the fracture strength of the metal–composite resin premolar abutments were analyzed with the log-rank test at a significance level of .05. Additional computations were carried out to compare the findings of this study with simultaneously generated data using zirconia premolar abutments of the same design that had been tested in identical laboratory/testing conditions.
RESULTS The fatigue resistance and survival rates of composite resin and porcelain onlays and crowns bonded to custom metal–composite resin premolar implant abutments are presented in Tables 1 to 3 and Fig 5. The Paradigm C (ceramic) onlays and crowns fractured at The International Journal of Oral & Maxillofacial Implants 367
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Table 1 Fatigue Resistance of Composite Resin and Ceramic Onlays Bonded to CAD/CAM Composite Resin Abutments
Table 2 Fatigue Resistance of Composite Resin and Ceramic Crowns Bonded to CAD/CAM Composite Resin Abutments
Veneer material/ specimen
Veneer material/ specimen
Maximum load (N)
Cycles
Failure mode
Ceramic (Paradigm C)
Maximum load (N)
Cycles
Failure mode
Ceramic (Paradigm C)
CO_01
1,400
180,000
No failure
CC_01
1,400
157,926
Mostly adhesive
CO_02
1,000
109,183
Mostly cohesive
CC_02
1,400
170,246
Mostly adhesive
CO_03
1,400
158,577
Mostly adhesive
CC_03
1,400
180,000
No failure
CO_04
1,200
143,396
Mostly adhesive
CC_04
1,400
155,243
Mostly adhesive
CO_05
1,200
150,722
Mostly adhesive
CC_05
1,200
136,158
Mostly adhesive
CO_06
1,000
106,447
Mostly adhesive
CC_06
1,400
166,367
Mostly adhesive
CO_07
1,200
135,275
Mostly adhesive
CC_07
1,400
158,048
Mostly adhesive
CO_08
1,400
180,000
No failure
CC_08
1,400
180,000
No failure
CO_09
1,200
130,297
Mostly adhesive
CC_09
1,200
151,453
Mostly cohesive
CO_10
1,400
180,000
No failure
CC_10
1,200
130,549
Mostly adhesive
CO_11
1,000
125,149
Mostly adhesive
CC_11
1,000
105,013
Mostly cohesive
CO_12
1,400
180,000
No failure
CC_12
1,000
110,676
Mostly adhesive
CO_13
1,400
162,597
Mostly adhesive
CC_13
1,400
180,000
No failure
CO_14
1,400
180,000
No failure
CC_14
1,000
126,426
Mostly adhesive
CO_15
1,200
151,482
Mostly adhesive
CC_15
800
85,217
Mostly cohesive
Average
1,253
Average
Composite resin (Paradigm MZ100)
1,240
Composite resin (Paradigm MZ100)
CRO_01
1,400
180,000
No failure
CRC_01
1,400
180,000
No failure
CRO_02
1,400
180,000
No failure
CRC_02
1,400
180,000
No failure
CRO_03
1,400
180,000
No failure
CRC_03
1,400
180,000
No failure
CRO_04
1,000
113,010
Mostly adhesive
CRC_04
1,400
180,000
No failure
CRO_05
1,000
118,410
Mostly adhesive
CRC_05
1,400
180,000
No failure
CRO_06
1,400
180,000
No failure
CRC_06
1,400
155,890
Mostly adhesive
CRO_07
1,400
180,000
No failure
CRC_07
1,400
156,273
Mostly adhesive
CRO_08
1,400
180,000
No failure
CRC_08
1,000
105,595
Mostly adhesive
CRO_09
1,000
105,129
Mostly adhesive
CRC_09
1,200
151,989
Mostly adhesive
CRO_10
1,400
180,000
No failure
CRC_10
1,400
171,737
Mostly adhesive
CRO_11
1,200
134,274
Mostly adhesive
CRC_11
800
83,691
Mostly cohesive
CRO_12
1,400
180,000
No failure
CRC_12
1,400
180,000
No failure
CRO_13
1,000
105,196
Mostly adhesive
CRC_13
1,400
180,000
No failure
CRO_14
800
88,894
Mostly cohesive
CRC_14
1,400
180,000
No failure
CRO_15
1,400
180,000
No failure
CRC_15
1,400
180,000
No failure
Average
1,240
Average
1,320
Table 3 Survival Rates of Ceramic and Composite Resin Implant-Supported Restorations
Table 4 Failure Modes of Composite and Ceramic Onlays and Crowns Bonded to CAD/CAM Composite Abutments
Material
Onlays
Restoration and material
Crowns
Total failure
Partial failure
Paradigm C
20%
33.3%
Paradigm C onlays
90%
10%
Paradigm MZ100
60%
60%
Paradigm MZ100 onlays
83.3%
17.7%
Paradigm C crowns
75%
25%
Paradigm MZ100 crowns
75%
25%
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100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Survival probability (%)
Fig 5a Life table survival analysis of CAD/CAM composite resin implant abutments restored with adhesive restorations: composite resin (Paradigm MZ100) onlays (CRO) and crowns (CRC) and ceramic (Paradigm C) onlays (CO) and crowns (CC).
Crowns Onlays
100 75 50 25 0
50
200
400
Survival probability (%)
CC CO CRO CRC
600 800 1,000 1,200 1,400 Load (N)
Paradigm C Paradigm MZ100
100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Fig 5b Life table survival analysis of onlays vs crowns (MZ100 = composite resin; C = ceramic) bonded to CAD/CAM composite resin implant abutment (pooled data).
Survival probability (%)
Survival probability (%)
Boff et al
Zir abutments CR abutments
100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Fig 5c Life table survival analysis of CAD/CAM composite resin implant abutments restored with Paradigm MZ100 and Paradigm C adhesive restorations (pooled data).
Fig 5d Life table survival analysis (pooled data) of CAD/CAM composite resin (CR) vs zirconia (Zir) abutments (120 samples).
average loads of 1,253 N and 1,240 N, respectively. Five ceramic onlays and three ceramic crowns withstood all 180,000 loading cycles without damage (33.3% and 20% survival rates, respectively); for MZ100 (composite resin) onlays and crowns, specimens fractured at average loads of 1,240 N and 1,320 N, respectively. Nine composite resin onlays and nine crowns survived the testing (60% survival rate for each). There was no significant difference in the survival of the four groups (P = .24). Pooled data for the restoration design (porcelain and composite resin combined) did not demonstrate a significant difference between onlays and crowns (P = .9). However, pooled data for the restoration material (onlays and crowns combined) revealed superior survival probability for Paradigm MZ100 compared to Paradigm C (P = .027). All data from the present study were pooled for comparison with existing data from a previous study,27 which presented an identical experimental design (same operators, implant brand, and model) using zirconia abutments instead of metal–composite resin (60 specimens, 30 of which were restored with ceramic onlays and crowns and 30 of which were restored with composite resin onlays and crowns). A significant differ-
ence in survival probability was found when comparing abutments (zirconia was superior to metal–composite resin, P = .0035) and restoration material (Paradigm MZ100 was superior to Paradigm C, P = .0001). The four groups demonstrated similar failure modes (Table 4), with 100% of the failures involving the restoration and the abutment. There were no exclusively cohesive failures—solely adhesive failures or screw loosening/fractures. The fractures were predominantly adhesive at the metal-resin interface (75% to 90% of the fractured specimens), with complete metal abutment exposure (when more than 75% of the metal abutment surface was exposed, it was classified as totally adhesive) (Fig 6a). The partially adhesive fractures (less than 75% of the metal abutment surface was exposed) were observed only in 10% to 25% of the failures and were associated with a lower failure load (800 to 1,200 N) (Fig 6b).
DISCUSSION The present study evaluated in vitro the fatigue resistance and failure modes of onlays and crowns bonded The International Journal of Oral & Maxillofacial Implants 369
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Boff et al
Fig 6 (a) Composite resin onlay presenting predominantly adhesive failure and (b) composite crown presenting partially cohesive failure type.
a
b
to CAD/CAM metal–composite resin premolar implant abutments and the influence of veneer material selection on fatigue resistance. The null hypothesis was accepted, as the abutment/restoration adhesive interface did not fail before the abutment itself, and the restorative material (ceramic vs composite resin) showed a significant influence on the fatigue resistance of the assembly. Furthermore, identical zirconia abutments from a previous study (data pooled for ceramic and composite onlays and crowns) presented a superior survival rate compared to metal–composite resin premolar abutments in this study. During their life cycle, teeth are subjected to many cycles of relatively low forces and may eventually undergo a sudden high-force impact, eg, trauma. In vitro tests mimicking clinical fatigue are relevant but time-consuming. They contrast with load-to-failure tests, which yield quick results but are also less clinically relevant. The loading protocol used in this study represents a good balance between the traditional fatigue tests and load-to-failure experiments. Originally introduced by Fennis et al44 and later used in numerous other studies,21–23,45 the approach can be considered an “accelerated fatigue test” that covers a wide range of clinically relevant situations (normal and high loads). The first part of the test fell within the range of normal bite forces in the posterior region, namely, up to 600 N.46,47 The second part comprised a range of loads that may be encountered in bruxism, trauma (high extrinsic loads), or masticatory accidents (under chewing loads but delivered to a small area as the result of a hard foreign body such as a stone or seed, for example). Another modification applied in this study was the replacement of the traditional stainless steel antagonist with a composite resin cylinder, as has been suggested in similar fatigue studies.22,26,27 Compared to metal as an antagonist, composite resin prevents localized intense point loads and unrealistic surface damage to specimens.48 Confounding variables were avoided by the
fabrication of both abutments and restorations with CAD/CAM technology. Composite resin and ceramic restorations performed well, considering that all samples survived the normal range of forces in the first half of this test (up to 600 N). Paradigm C and MZ100 specimens fractured at average loads of 1,133 to 1,266 N. Based on these data, it is difficult to conclude that adhesively restored polymer implant abutments are contraindicated on posterior teeth. These results are similar to those of a previous study, in which metal–composite resin abutments restored with Paradigm C and MZ100 easily survived normal bite forces in the anterior region (100 N).25 A further confirmation is the similar performance of ceramic restorations bonded either to zirconia27 or to metal–composite resin premolar abutments on posterior implants (33.3% vs 26.7% survival rates, respectively). The four groups in this study showed similar failure modes, with 100% of the failures involving restorations and abutments. There were no exclusively cohesive failures, no adhesive failures at the abutment/restoration interface, and no solely adhesive failures at the composite resin–metal abutment interface. These results confirm the reliability of the resinto-resin and resin-to-porcelain bonds. However, they contrast with data obtained with zirconia abutments by Magne et al,15 for which restorations presented a higher incidence of adhesive failure, leaving the abutment intact. Both studies used a bonding protocol that employed regular composite resin as an adhesive cement. Unlimited time to bond the restoration and to remove the excess materials, reducing considerably the need to finish/polish the restoration, is an advantage.49 Another significant finding was the absence of screw loosening/fracture, which may be explained in part by the reliability of the tapered abutment/implant internal connection. The weak link in the present study seems to be the interface between the composite resin mesostructure and the metal abutment, which was exposed in most
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Table 5 Comparison of Restorative/Abutment Material on Implant-Supported Restorations Abutment material
Anterior
Zirconia15
Composite resin Ceramic
P = .18
Composite resin25
Composite resin Ceramic
Ceramic, P < .02
Zirconia27
Composite resin Ceramic*
Composite resin, P = .0001
Composite resin (present study)
Composite resin Ceramic*
Composite resin, P < .027
Posterior
Restoration material
Restoration material comparison
Location
Abutment material comparison
P = .76
Zirconia, P = .0035
*Ceramic restoration bonded to zirconia and composite resin abutments presented similar performance (P = .43).
instances. Because it is possible to achieve a predictable resin bond to a titanium abutment by means of tribochemical silicoating and a silane,50 it is probable that the metal bonding itself was not the main reason for the abutment failure in this study. It can be hypothesized that the design of the metal component could have caused the problem, since it consisted of a relatively rigid solid abutment, which was not modified. Further work, including finite element analysis, would be needed to optimize the design of this titanium part to match the resilience of the overlying composite resin mesostructure and possibly relieve the stress on this interface. This hypothesis was confirmed by existing data on anterior teeth using modified temporary metal abutments (which are more flexible, like composite resin). When associated with composite resin mesostructures, those metal components demonstrated performance similar to that of zirconia abutments of the same design.25 The predominantly cohesive failure mode in the present study (10% to 25%) was similar to that of natural teeth with an oblique crack from the functional area to the buccocervical area51,52 and seemed to happen at earlier load steps than completely adhesive failures. Those cohesively failed specimens fractured with a single fragment (unlike completely adhesive failures), and all appeared to be repairable by rebonding the fragment. Because of advances in elemental chemistry, modern composite resins feature improved repairability53,54 and adhesion to tooth and metallic substrates.53,55 A pilot test confirmed that repair of failed metal–composite resin premolar implant abutments (by means of tribochemical coating and a silane) can yield high fatigue resistance. Additional computations obtained by pooling the data for the restorative material (onlays and crowns) revealed the superior survival probability of Paradigm MZ100 compared to Paradigm C (P = .027), with 18 composite resin restorations surviving the test (60%), compared to only 8 ceramic restorations (26.7%).
This result differs from the data obtained from same materials (Paradigm C and MZ100) when metal–composite resin premolar abutments were restored in the anterior dentition.25 The ability to deform under loading makes Paradigm MZ100 more likely to absorb the stress and avoid damage to the abutment itself. In the anterior dentition, restorations were subjected to low and oblique loads up to 280 N,25 while posterior restorations in this study were subjected to vertical loads up to 1,400 N. The damping effect expected from the composite abutments protecting the ceramic restorations in the posterior area was not observed under those high compressive loads. In addition, when pooled data from this study (ceramic restorations only) were compared to ceramic restorations bonded to zirconia abutments with identical design and testing conditions,27 no difference was observed (P = .43) (Table 5). In contrast, composite resin restorations bonded to zirconia premolar abutments yielded outstanding results (100% survival rate) and coincidentally, seemed to respond like natural teeth when considering their dynamic response to impact loading (measured energy absorption; Periometer, Periometrics LLC).28 When data from both studies in posterior implants27 and from the present study were combined, zirconia abutments performed significantly better than metal– composite resin premolar abutments (P < .0035) and their performance was further improved with composite resin restorations instead of ceramic restorations. The excellent performance of composite resin restorations milled from MZ100 blocks has already been demonstrated in other applications on teeth.21–24 Many professionals have been reluctant to use composite resin as a posterior restorative material because of its low wear resistance compared to ceramics. Wear of the restoration itself, however, should not be the only consideration in the selection of restorative material; the wear of opposing enamel, when appropriate (total wear, restoration, and enamel combined) should also be taken into account. Because it is less abrasive The International Journal of Oral & Maxillofacial Implants 371
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to enamel, Paradigm MZ100 demonstrates less total wear compared to ceramic restorative materials.20 This represents an important advantage of composite resin restorations over ceramic restorations for implants that will be subjected to parafunctional loading to preserve the volume and morphology of the opposing enamel. One may question the clinical implications of failure as defined in the present study. Failure of the restoration or abutment, when repairable, may also be perceived as a protective mechanism to limit the amount of stress on the implant itself and possibly to reduce the stress on the surrounding bone. Other significant clinical implications can be drawn from this study related to the restoration design and material. The concept of adhesively retained (nonretentive) restorations gives the surgeon, restorative dentist, and ceramist more freedom during the determination of optimal implant orientation (allowing for a more “bone-driven” placement when needed) and the design of secondary components compatible with severely reduced mesiodistal or occlusal clearances. The simulation of any crown-root angle and reduced subgingival margin placement, along with the improved optical properties and design of the abutment in this novel posterior restorative approach, simplifies delivery of the definitive restoration and enhances the esthetic outcome (eg, in case of thin labial peri-implant mucosa).7,8,49 There is also less risk that excess subgingival cement will remain. Based on the data from this study, it is difficult to conclude that polymer abutments are contraindicated for posterior teeth; however, further studies should be conducted to determine the optimum design of restorative components and to explore and develop the use of novel fiber-reinforced composite resin CAD/ CAM materials.
CONCLUSIONS Within the limitations of the present study, it was possible to conclude that Paradigm MZ100 onlays/crowns bonded to metal–composite resin premolar implant abutments presented higher survival rates when compared to ceramic onlays/crowns. Zirconia abutments outperformed metal–composite resin premolar abutments in terms of fatigue resistance.
Acknowledgments The authors wish to express their gratitude to the CAPES Foundation Brazil (grants PDEE 1897-09-8 and PDEE 1909-09-6); Neodent Implant System (Curitiba, PR, Brazil) for the donation of dental implants and metal abutments; 3M/ESPE (St. Paul, MN) for Paradigm C, Paradigm MZ100 blocks, Filtek Z100 composite resin, and Cojet; Kerr (Orange, CA) for Optibond FL and
Occlubrush; Patterson (El Segundo, CA) for Cerec 3; Ultradent (South Jordan, UT) for Ultra-Etch, Porcelain Etch, and Silane; Heraeus Kulzer (Armonk, NY) for Palapress; Brasseler (Savannah, GA) for Dialite; and Komet (Rock Hill, SC) for the Q-Polishing System. The authors reported no conflicts of interest related to this study.
REFERENCES 1. Haas R, Mensdorff-Pouilly N, Mailath G, Watzek G. Brånemark single tooth implants: A preliminary report of 76 implants. J Prosthet Dent 1995;73:274–279. 2. Haas R, Polak C, Fürhauser R, Mailath-Pokorny G, Dörtbudak O, Watzek G. A long-term follow-up of 76 Brånemark single-tooth implants. Clin Oral Implants Res 2002;13:38–43. 3. Andersson B, Odman P, Carlsson L, Brånemark PI. A new Brånemark single tooth abutment: Handling and early clinical experiences. Int J Oral Maxillofac Implants 1992;7:105–111. 4. Searson L, Meredith N. The role of implants in restorative dentistry: Prosthesis design and aesthetic considerations. Dent Update 1997;24:388–390. 5. Park SE, Da Silva JD, Weber HP, Ishikawa-Nagai S. Optical phenomenon of peri-implant soft tissue. Part I. Spectrophotometric assessment of natural tooth gingiva and peri-implant mucosa. Clin Oral Implants Res 2007;18:569–574. 6. Ishikawa-Nagai S, Da Silva JD, Weber HP, Park SE. Optical phenomenon of peri-implant soft tissue. Part II. Preferred implant neck color to improve soft tissue esthetics. Clin Oral Implants Res 2007;18:575–580. 7. Sailer I, Sailer T, Stawarczyk B, Jung RE, Hämmerle CH. In vitro study of the influence of the type of connection on the fracture load of zirconia abutments with internal and external implant-abutment connections. Int J Oral Maxillofac Implants 2009;24:850–858. 8. Zembic A, Sailer I, Jung RE, Hämmerle CH. Randomized-controlled clinical trial of customized zirconia and titanium implant abutments for single-tooth implants in canine and posterior regions: 3-years result. Clin Oral Implants Res 2009;20:802–808. 9. Yildirim M, Fischer H, Marx R, Edelholff D. In-vivo fracture resistance of implant-supported all-ceramic restorations. J Prosthet Dent 2003;90:325–331. 10. Jung RE, Pjetursson BE, Glauser R, Zembic A, Zwahlen M, Lang NP. A systematic review of the 5-year survival and complication rates of implant-supported single crowns. Clin Oral Implants Res 2008;19:119–130. 11. De Boever AL, Keersmaekers K, Vanmaele G, Kerschbaum T, Theuniers G, De Boever JA. Prosthetic complications in fixed endosseous implant-bone reconstructions after an observations period of at least 40 months. J Oral Rehabil 2006;33:833–839. 12. Pjetursson BE, Bragger U, Lang NP, Zwahlen M. Comparison of survival and complication rates of tooth-supported fixed dental prostheses (FDPs) and implant supported FDPs and single crowns (SCs). Clin Oral Implants Res 2007;18:97–113. 13. Wolfart M, Lehmann F, Wolfart S, Kern M. Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods. Dent Mater 2007;23:45–50. 14. Phark JH, Duarte S Jr, Blatz M, Sadan A. An in vitro evaluation of the long-term resin bond to a new densely sintered high-purity zirconium-oxide ceramic surface. J Prosthet Dent 2009;101:29–38. 15. Magne P, Paranhos MP, Burnett LH Jr, Magne M, Belser UC. Fatigue resistance and failure mode of novel-design anterior single-tooth implant restorations – Influence of material selection for Type III veneers bonded to zirconia abutments. Clin Oral Implants Res 2011;22:195–200. 16. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater 1999;15:426–433. 17. Curtis AR, Wright AJ, Fleming GJ. The influence of surface modification techniques on the performance of a Y-TZP dental ceramic. J Dent 2006;34:195–206. 18. Wang H, Aboushelib MN, Felizer AJ. Strength influencing variables on CAD/CAM zirconia frameworks. Dent Mater 2008;24:633–638.
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19. Rusin RP. Properties and applications of a new composite block for CAD/CAM. Compend Contin Educ Dent 2001;22:35–41. 20. Kunzelmann KH, Jelen B, Mehl A, Hickel R. Wear evaluation of MZ100 compared to ceramic CAD/CAM materials. Int J Comput Dent 2001;4:171–184. 21. Magne P, Knezevic A. Influence of overlay restorative materials and load cusps on the fatigue resistance of endodontically treated molars. Quintessence Int 2009;40:729–737. 22. Magne P, Knezevic A. Simulated fatigue resistance of composite resin versus porcelain CAD/CAM overlay restorations on endodontically treated molars. Quintessence Int 2009;40:125-133. 23. Magne P, Knezevic A. Thickness of CAD-CAM composite resin overlays influences fatigue resistance of endodontically treated premolars. Dent Mater 2009;25:1264–1268. 24. Magne P, Paranhos MP, Burnett LH Jr. New zirconia primer improves bond strength of resin-based cements. Dent Mater 2010;26:345–352. 25. Magne P, Oderich E, Boff LL, Cardoso AC, Belser UC. Fatigue resistance and failure mode of CAD/CAM composite resin implant abutment restored with type III composite resin and porcelain veneers. Clin Oral Implants Res 2011;22:1275–1281. 26. Magne P, Boff LL, Oderich E, Cardoso AC. CAD/CAM adhesive restoration of molars with a cracked compromised cusp: Effect of fiber-reinforced immediate dentin sealing and cusp overlap on the fatigue strength onlays. J Esthet Restorative Dent 2012;24:135–146. 27. Oderich E, Boff LL, Cardoso AC, Magne P. Fatigue resistance and failure mode of adhesively restored custom implant zirconia abutment. Clin Oral Implants Res 2012;23:1360–1368. 28. Magne P, Silva M, Oderich E, Boff LL, Enciso R. Dynamic load response of novel-design implant-supported restorations. Clin Oral Implants Res 2013;24:143–148. 29. Gracis SE, Nicholls JI, Chalupnik JD, Yuodelis RA. Shock-absorbing behavior of five restorative materials used on implants. Int J Prosthodont 1991;4:282–291. 30. Cibirka RM, Razzoog ME, Lang BR, Stohler CS. Determining the force absorption quotient for restorative materials used in implant occlusal surfaces. J Prosthet Dent 1992;67:361–364. 31. Papavasiliou G, Kamposiora P, Bayne SC, Felton DA. Three-dimensional finite element analysis of stress-distribution around single tooth implants as a function of bony support, prosthesis type, and loading during function. J Prosthet Dent 1996;76:633–640. 32. Sertgöz A. Finite element analysis study of the effect of superstructure material on stress distribution in an implant-supported fixed prosthesis. Int J Prosthodont 1997;10:19–27. 33. Stegaroiu R, Kusakari H, Nishiyama S, Miyakawa O. Influence of prosthesis material on stress distribution in bone and implant: A 3-dimensional finite element analysis. Int J Oral Maxillofac Implants 1998;13:781–790. 34. Stegaroiu R, Khraisat A, Nomura S, Miyakawa O. Influence of superstructure materials on strain around an implant under 2 loading conditions: A technical investigation. Int J Oral Maxillofac Implants 2004;19:735–742. 35. Soumeire J, Dejou J. Shock absorbability of various restorative materials used on implants. J Oral Rehabil 1999;26:394–401. 36. Ciftçi Y, Canay S. The effect of veneering materials on stress distribution in implant-supported fixed prosthetic restorations. Int J Oral Maxillofac Implants 2000;15:571–582.
37. Geng JP, Tan KB, Liu GR. Application of finite element analysis in implant dentistry: A review of the literature. J Prosthet Dent 2001;85:585–598. 38. Wang TM, Leu LJ, Wang J, Lin LD. Effects of prosthesis materials and prosthesis splinting on peri-implant bone stress around implants in poor-quality bone: A numeric analysis. Int J Oral Maxillofac Implants 2002;1:231–237. 39. Juodzbalys G, Kubilius R, Eidukynas V, Raustia AM. Stress distribution in bone: Single-unit implant prostheses veneered with porcelain or a new composite material. Implant Dent 2005;14:166–175. 40. Rubo JH, Souza EA. Finite element analysis of stress in bone adjacent to dental implants. J Oral Implantol 2008;34:248–255. 41. Kim HK, Heo SJ, Koak JY, Kim SK. In vivo comparison of force development with various materials of implant-supported prostheses. J Oral Rehabil 2009;36:616–625. 42. Magne P, Magne M, Jovanovic SA. An esthetic solution for singleimplant restorations—Type III porcelain veneer bonded to a screw-retained custom abutment: A clinical report. J Prosthet Dent 2008;99:2–7. 43. Sterzenbach G, Kalberiah S, Beuer F, Frankenberger R, Naumann M. In-vitro simulation of tooth mobility for static and dynamic load tests: A pilot study. Acta Odontol Scand 2011;69:316–318. 44. Fennis WMM, Kuijs RH, Kreulen CM, Verdonschot N, Creugers NH. Fatigue resistance of teeth restored with cuspal-coverage composite restorations. Int J Prosthodont 2004;17:313–317. 45. Kuijs RH, Fennis WM, Kreulen CM, Roeters FJ, Verdonschot N, Creugers NH. A comparison of fatigue resistance of three materials for cusp-replacing adhesive restorations. J Dent 2006;34:19–25. 46. De Boever JA, McCall WD Jr, Holden S, Ash MM Jr. Functional occlusal forces: An investigation by telemetry. J Prosthet Dent 1978;40:326–333. 47. Ferrario VF, Sforza C, Serrao G, Dellavia C, Tartaglia GM. Single tooth bite forces in healthy young adults. J Oral Rehabil 2004;31:18–22. 48. Kelly JR. Clinically relevant approach to failure testing of all-ceramic restorations. J Prosthet Dent 1999;81:652–661. 49. Magne P, Schlichting LH, Maia HP, Baratieri LN. An in vitro fatigue resistance of CAD/CAM composite resin and ceramic posterior occlusal veneers. J Prosthet Dent 2010;104:149–157. 50. Watanabe I, Kurtz KS, Kabcenell JL, Okabe T. Effect of sandblasting and silicoating on bond strength of polymer-glass composite to cast titanium. J Prosthet Dent 1999;82:462–467. 51. Baratieri LN, Araujo EM, Monteiro S Jr. Composite Restorations in Anterior Teeth: Fundamentals and Possibilities. Chicago: Quintessence, 2005:55–65. 52. Magne P, Belser UC. Bonded Porcelain Restorations in the Anterior Dentition: A Biomimetic Approach. Chicago: Quintessence, 2002:117–128. 53. Rosentritt M, Behr M, Kolbeck C, Lang R, Handel G. In vitro repair of all-ceramic and fibre-reinforced composite crowns. Eur J Prosthodont Restorative Dent 2000;8:107–112. 54. Andriani WJ, Suzuki M, Bonfante EA, Carvalho RM, Silva NR, Coelho PG. Mechanical testing of indirect composite materials directly applied on implant abutments. J Adhes Dent 2010;12:1–7. 55. Behr M, Rosentritt M, Lang R, Handel G. Glass fiber-reinforced abutments for dental implants. A pilot study. Clin Oral Implants Res 2001;12:174–178.
The International Journal of Oral & Maxillofacial Implants 373 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
1Visiting
Scholar, Department of Restorative Sciences, Herman Ostrow School of Dentistry, University of Southern California, USA; Assistant Professor and Researcher, Department of Dentistry, Federal University of Santa Catarina, Florianópolis, SC, Brazil. 2 Titular Professor, Science of Health Center, University of Santa Catarina, Florianópolis, SC, Brazil. 3 Tenured Associate Professor and Don and Sybil Harrington Foundation Professor of Esthetic Dentistry, Division of Restorative Sciences, The Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, California, USA. Correspondence to: Dr Pascal Magne, University of Southern California, Division of Restorative Sciences, The Herman Ostrow School of Dentistry, 925 W. 34th Street, Los Angeles, CA 90089-7792, USA. Fax: +213-821-5324. Email: [email protected] ©2014 by Quintessence Publishing Co Inc.
R
estorations for posterior implants require a strong and reliable material to withstand normal masticatory function. Titanium abutments and metal-ceramic crowns are traditionally used because of their mechanical properties.1–4 With an increasing trend for esthetic materials, zirconia abutments and all-ceramic restorations have been used as a substitute for metal, even in posterior areas of the arches. These new materials are not associated with the grayish appearance of the cervical soft tissue encountered around metal abutments and have been increasingly recommended to fabricate custom abutments.5–8 Zirconia (yttria-stabilized tetragonal zirconia polycrystal) appears to fulfill the requirements of strength and biocompatibility needed for implant abutments.9 However, reliable performance of the abutment itself does not guarantee the strength of the restoration. For single crowns sup-
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Boff et al
Fig 1 Correlation Mode in CEREC3. (Left) Impression of solid metal abutment. (Center) Correlation of metal abutment with final design from zirconia abutment from previous study.27 (Right) Final mesostructure to be milled (onlay design).
ported by implants, systematic reviews have revealed a slightly inferior 5-year survival rate for all-ceramic systems (91.2%) compared to metal-ceramic systems (95.4%).10 Survival rates can be expected to decline when bruxism is present because parafunctional habits play a significant role in the frequency of complications.11 The stiffness of ceramic in the absence of a periodontal ligament (PDL) results in a nonresilient monobloc structure. In contrast to natural tooth abutments, the inherent rigidity of the bone-implant-restoration assembly has been associated with a higher incidence of mechanical complications, including fracture of the veneering material, abutment or screw loosening, and loss of retention.12 Other drawbacks of zirconia are the difficulty of bonding to it13–15 and the risk of propagating microfractures while trimming prefabricated abutments.16–18 A decade ago, composite resin blocks (Paradigm MZ100, 3M/ESPE) were introduced for use with computer-aided design/computer-assisted manufacture (CAD/CAM) systems as an alternative to machinable ceramics.19,20 The blocks were manufactured from the original Filtek Z100 restorative material (3M/ESPE); this contains patented spheroidal zirconia-silica fillers (85% by weight) that provide restorations with excellent behavior under dynamic loading21–26 while maintaining a relatively low elastic modulus. This unique combination of strength and resilience has been incorporated into a new implant abutment/restoration concept in an attempt to mimic the behavior of natural teeth (the “biomimetic principle”).25 In this concept, the resilient component (to simulate the PDL) is integrated into the restoration. This concept was successfully applied to restore zirconium abutments in the anterior dentition15 and yielded outstanding results in the posterior dentition (100% survival of abutments and restorations).27 Interestingly, when considering the dynamic response to impact loading (measured energy absorption; Periometer, Perimetrics
LL), composite resin restorations bonded to zirconia abutments seemed to respond in a similar fashion to natural teeth with a simulated PDL.28 In the past, however, the use of resilient crowns over rigid abutments did not prove to provide significant stress relief to the bone.29–41 Therefore, a more efficient shockabsorption effect might be obtained with a larger volume of resilient material, for example, if the abutment itself were made of it. Hence, it has been proposed to fabricate anterior single-unit implant-supported restorations using Paradigm MZ100 composite resin abutments25 associated with adhesively retained nonretentive veneers.15,42 In the anterior dentition, the results demonstrated that survival of composite resin abutments did not differ from that of zirconia abutments. There are no data available for such an approach to restoring implants in the posterior dentition. A significant effect of the abutment and restorative material is expected, given the increased volume of those elements in the posterior dentition. It is also not known whether a posterior CAD/CAM composite resin custom abutment will withstand repeated mechanical loading in a moist environment and prevent early restoration failure. The aim of the present study was to assess in vitro the fatigue resistance and failure mode of onlays and crowns bonded to CAD/CAM metal–composite resin premolar implant abutments. The influence of the restoration material (ceramic vs composite resin) was also evaluated. The null hypothesis considered was that the abutment-restoration adhesive interface would not fail before the abutment itself failed and that the restorative material (ceramic vs composite resin) would influence the fatigue resistance and failure mode of the assembly. Previously published data using zirconia custom premolar abutments with the same design,27 generated randomly and simultaneously under strictly identical laboratory and testing conditions, were included for comparison. The International Journal of Oral & Maxillofacial Implants 365
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Fig 2 Restoration designs and dimensions for (left) an onlay and (right) a crown.
Fig 3 CAD/CAM (left) composite resin crown and (right) onlay designs, with the accompanying custom composite resin mesostructures and solid metal abutments.
MATERIALS AND METHODS Sixty implants with an internal tapered abutment interface (Titamax CM, 4.0 mm diameter, 11 mm length, Neodent) were embedded in a standard position in autopolymerizing acrylic resin (Palapress, Heraeus Kulzer), which is considered a suitable material for bone simulation because of its similar elastic modulus.43 The Cerec 3 system (version 3.60, Sirona Dental Systems) was used in Correlation Mode (Fig 1) to design two CAD/CAM custom abutments by combining the optical impressions of two different custom zirconia premolar abutments (onlay and crown designs) from a previous study27 and that of a solid metal abutment (CM Universal Post, 4.5 mm diameter, 4.5 mm height, 2.5 mm neck, Neodent). Both abutments followed the natural emergence profile of a maxillary second premolar and included clearance for either a crown or an onlay restoration. The metal abutment was used as an interface with the implant platform to connect the CAD/CAM composite resin mesostructure to the implant. Thirty identical CAD/CAM composite resin pre-
molar abutments (Paradigm MZ100, 3M/ESPE) were milled for each preparation design. Following the same methodology, 30 identical crowns and 30 identical onlays were fabricated. Thirty restorations (15 crowns and 15 onlays) were milled in composite resin (Paradigm MZ100, 3M/ESPE), and in a similar fashion 30 of the same restorations were milled in glass-ceramic (Paradigm C, 3M/ESPE) (Fig 2). All mesostructures and restorations (Fig 3) were milled with the sprue located at the palatal surface. The porcelain restorations were initially polished using the intraoral Dialite porcelain adjustment polishing kit (Brasseler), and the composite resin restorations were polished using the Q-Polishing System (Kit ref. 4477, Komet) and silicon carbide–impregnated polishing brushes (Occlubrush, Kerr-Hawe). With a coarse round diamond bur (801-023, Brasseler), a circular hole (future access for screw tightening) was created in the occlusal surface of the CAD/CAM composite resin mesostructure. The fitting surfaces of the metal solid abutment and the composite resin mesostructure were subjected to the same surface treatment, ie, airborne-particle abrasion with 27-µm silica-modified aluminum oxide (Cojet, 3M/ESPE) at 0.2 MPa for 10 seconds at a distance of 10 mm, application of a silane (Ultradent) for 20 seconds, and drying at 100°C for 1 minute using a standard oven (ERC Dental Burn Out Oven, Model 500S, Dental Tech). For convenience and to ensure precise positioning during the assembly, the metal abutment was set into an implant analog and the screw-access channel was filled with expanded polytetrafluoroethylene tape. The two parts were luted together with adhesive resin (Optibond FL, Bottle 2, Kerr) and composite resin (Filtek Z100, 3M/ ESPE; preheated for 5 minutes in Calset, Addent). After removal of the excess composite resin, all surfaces were light polymerized for 60 seconds at 1,000 mW/ cm2 (Valo, Ultradent). Surface treatment of porcelain restorations (crowns and onlays) included airborne-particle abrasion with 50-µm aluminum oxide at 0.2 MPa, followed by etching with 9% hydrofluoric acid (Porcelain Etch, Ultradent)
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for 45 seconds and rinsing with water for 20 seconds. Postetching cleaning was done with 35% phosphoric acid (Ultra-Etch, Ultradent) with a gentle brushing motion for 1 minute, followed by rinsing with water for 20 seconds. After final cleaning by immersion in distilled water in an ultrasonic bath for 2.5 minutes and oil-free air drying, intaglio surfaces were silanated (Silane, Ultradent) and heat dried at 100°C for 1 minute. The same surface treatment was applied to the fitting surfaces of the composite resin abutments and composite resin restorations (crowns and onlays) without hydrofluoric acid treatment. Each metal–composite resin abutment was inserted into an implant, and 15 N/cm of torque was applied to the abutment screw. Expanded polytetrafluoroethylene tape was used to cover the abutment screw and fill part of the access channel. Each restoration was bonded individually to its abutment using adhesive resin (Optibond FL, Bottle 2, Kerr) and composite resin (Filtek Z100, 3M/ESPE; preheated for 5 minutes in Calset, Addent). After all excess composite resin was removed, each surface was light polymerized for 60 seconds at 1,000 mW/cm2 (Valo, Ultradent). All margins were covered with an air-blocking barrier (K-Y Jelly, Personal Products Company) and were light polymerized for an additional 10 seconds per surface. Unlimited time to bond the restoration reduced considerably the time needed to remove excess adhesive resin, which was carefully eliminated with hand instruments (scaler, blade); specimens were stored in distilled water for 24 hours before testing. An artificial chewing device actuated by closedloop servo hydraulics (Mini Bionix II, MTS Systems) was used to simulate masticatory forces (Fig 4). The chewing cycle was replicated by an isometric contraction (with load control), which was applied through a 7-mm-diameter cylindric composite resin antagonist (Filtek Z100, 3M/ESPE) to reproduce in every specimen two equidistant contact points (standard position). A new antagonist was fabricated for each specimen. The load chamber was filled with distilled water to submerge the sample during testing. Cyclic loading was applied at a frequency of 5 Hz. A loading protocol was used; this began with a “warm-up” at 50 N for 5,000 cycles and was followed by stages of 200, 400, 600, 800, 1,000, 1,200, and 1,400 N for a maximum of 25,000 cycles each. Samples were loaded until fracture or to a maximum of 180,000 cycles. The fatigue machine was set and calibrated to stop automatically when any movement greater than 0.3 mm was detected inside the load chamber. The number of endured cycles and the failure mode of each specimen were recorded. After the testing, each sample was evaluated by transillumination (Microlux, Addent) with the aid of an optical microscope
Fig 4 Close-up view of specimen and cylindric composite resin antagonist before testing.
(Leica MZ 125, Leica Mycrosystems) at 10:1 magnification (two-examiner agreement). Failure mode analyses were repeated by each examiner with an interval of 7 days, and the data presented were mean values. In the case of a disagreement, a third calibrated examiner was prepared to collaborate in this study. To prevent visual fatigue, the examiners stopped for an interval after every 10 specimens analyzed. A visual distinction was made between cohesive fractures of the abutment, screw, or implant, as well as cohesive fracture of the restorations and/or adhesive failure of the restoration/mesostructure/abutment interfaces. The fatigue resistance of the four groups was compared using the Kaplan-Meier survival analysis (MedCalc Software, version 12.3.0). At each time interval (defined by each load step), the number of specimens that started the interval intact and the number of specimens that fractured during the interval were counted to allow the calculation of survival probability at each interval. The influences of the restoration materials (composite or ceramic) and the different restoration designs (crown or onlay) on the fracture strength of the metal–composite resin premolar abutments were analyzed with the log-rank test at a significance level of .05. Additional computations were carried out to compare the findings of this study with simultaneously generated data using zirconia premolar abutments of the same design that had been tested in identical laboratory/testing conditions.
RESULTS The fatigue resistance and survival rates of composite resin and porcelain onlays and crowns bonded to custom metal–composite resin premolar implant abutments are presented in Tables 1 to 3 and Fig 5. The Paradigm C (ceramic) onlays and crowns fractured at The International Journal of Oral & Maxillofacial Implants 367
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Boff et al
Table 1 Fatigue Resistance of Composite Resin and Ceramic Onlays Bonded to CAD/CAM Composite Resin Abutments
Table 2 Fatigue Resistance of Composite Resin and Ceramic Crowns Bonded to CAD/CAM Composite Resin Abutments
Veneer material/ specimen
Veneer material/ specimen
Maximum load (N)
Cycles
Failure mode
Ceramic (Paradigm C)
Maximum load (N)
Cycles
Failure mode
Ceramic (Paradigm C)
CO_01
1,400
180,000
No failure
CC_01
1,400
157,926
Mostly adhesive
CO_02
1,000
109,183
Mostly cohesive
CC_02
1,400
170,246
Mostly adhesive
CO_03
1,400
158,577
Mostly adhesive
CC_03
1,400
180,000
No failure
CO_04
1,200
143,396
Mostly adhesive
CC_04
1,400
155,243
Mostly adhesive
CO_05
1,200
150,722
Mostly adhesive
CC_05
1,200
136,158
Mostly adhesive
CO_06
1,000
106,447
Mostly adhesive
CC_06
1,400
166,367
Mostly adhesive
CO_07
1,200
135,275
Mostly adhesive
CC_07
1,400
158,048
Mostly adhesive
CO_08
1,400
180,000
No failure
CC_08
1,400
180,000
No failure
CO_09
1,200
130,297
Mostly adhesive
CC_09
1,200
151,453
Mostly cohesive
CO_10
1,400
180,000
No failure
CC_10
1,200
130,549
Mostly adhesive
CO_11
1,000
125,149
Mostly adhesive
CC_11
1,000
105,013
Mostly cohesive
CO_12
1,400
180,000
No failure
CC_12
1,000
110,676
Mostly adhesive
CO_13
1,400
162,597
Mostly adhesive
CC_13
1,400
180,000
No failure
CO_14
1,400
180,000
No failure
CC_14
1,000
126,426
Mostly adhesive
CO_15
1,200
151,482
Mostly adhesive
CC_15
800
85,217
Mostly cohesive
Average
1,253
Average
Composite resin (Paradigm MZ100)
1,240
Composite resin (Paradigm MZ100)
CRO_01
1,400
180,000
No failure
CRC_01
1,400
180,000
No failure
CRO_02
1,400
180,000
No failure
CRC_02
1,400
180,000
No failure
CRO_03
1,400
180,000
No failure
CRC_03
1,400
180,000
No failure
CRO_04
1,000
113,010
Mostly adhesive
CRC_04
1,400
180,000
No failure
CRO_05
1,000
118,410
Mostly adhesive
CRC_05
1,400
180,000
No failure
CRO_06
1,400
180,000
No failure
CRC_06
1,400
155,890
Mostly adhesive
CRO_07
1,400
180,000
No failure
CRC_07
1,400
156,273
Mostly adhesive
CRO_08
1,400
180,000
No failure
CRC_08
1,000
105,595
Mostly adhesive
CRO_09
1,000
105,129
Mostly adhesive
CRC_09
1,200
151,989
Mostly adhesive
CRO_10
1,400
180,000
No failure
CRC_10
1,400
171,737
Mostly adhesive
CRO_11
1,200
134,274
Mostly adhesive
CRC_11
800
83,691
Mostly cohesive
CRO_12
1,400
180,000
No failure
CRC_12
1,400
180,000
No failure
CRO_13
1,000
105,196
Mostly adhesive
CRC_13
1,400
180,000
No failure
CRO_14
800
88,894
Mostly cohesive
CRC_14
1,400
180,000
No failure
CRO_15
1,400
180,000
No failure
CRC_15
1,400
180,000
No failure
Average
1,240
Average
1,320
Table 3 Survival Rates of Ceramic and Composite Resin Implant-Supported Restorations
Table 4 Failure Modes of Composite and Ceramic Onlays and Crowns Bonded to CAD/CAM Composite Abutments
Material
Onlays
Restoration and material
Crowns
Total failure
Partial failure
Paradigm C
20%
33.3%
Paradigm C onlays
90%
10%
Paradigm MZ100
60%
60%
Paradigm MZ100 onlays
83.3%
17.7%
Paradigm C crowns
75%
25%
Paradigm MZ100 crowns
75%
25%
368 Volume 29, Number 2, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Survival probability (%)
Fig 5a Life table survival analysis of CAD/CAM composite resin implant abutments restored with adhesive restorations: composite resin (Paradigm MZ100) onlays (CRO) and crowns (CRC) and ceramic (Paradigm C) onlays (CO) and crowns (CC).
Crowns Onlays
100 75 50 25 0
50
200
400
Survival probability (%)
CC CO CRO CRC
600 800 1,000 1,200 1,400 Load (N)
Paradigm C Paradigm MZ100
100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Fig 5b Life table survival analysis of onlays vs crowns (MZ100 = composite resin; C = ceramic) bonded to CAD/CAM composite resin implant abutment (pooled data).
Survival probability (%)
Survival probability (%)
Boff et al
Zir abutments CR abutments
100 75 50 25 0
50
200
400
600 800 1,000 1,200 1,400 Load (N)
Fig 5c Life table survival analysis of CAD/CAM composite resin implant abutments restored with Paradigm MZ100 and Paradigm C adhesive restorations (pooled data).
Fig 5d Life table survival analysis (pooled data) of CAD/CAM composite resin (CR) vs zirconia (Zir) abutments (120 samples).
average loads of 1,253 N and 1,240 N, respectively. Five ceramic onlays and three ceramic crowns withstood all 180,000 loading cycles without damage (33.3% and 20% survival rates, respectively); for MZ100 (composite resin) onlays and crowns, specimens fractured at average loads of 1,240 N and 1,320 N, respectively. Nine composite resin onlays and nine crowns survived the testing (60% survival rate for each). There was no significant difference in the survival of the four groups (P = .24). Pooled data for the restoration design (porcelain and composite resin combined) did not demonstrate a significant difference between onlays and crowns (P = .9). However, pooled data for the restoration material (onlays and crowns combined) revealed superior survival probability for Paradigm MZ100 compared to Paradigm C (P = .027). All data from the present study were pooled for comparison with existing data from a previous study,27 which presented an identical experimental design (same operators, implant brand, and model) using zirconia abutments instead of metal–composite resin (60 specimens, 30 of which were restored with ceramic onlays and crowns and 30 of which were restored with composite resin onlays and crowns). A significant differ-
ence in survival probability was found when comparing abutments (zirconia was superior to metal–composite resin, P = .0035) and restoration material (Paradigm MZ100 was superior to Paradigm C, P = .0001). The four groups demonstrated similar failure modes (Table 4), with 100% of the failures involving the restoration and the abutment. There were no exclusively cohesive failures—solely adhesive failures or screw loosening/fractures. The fractures were predominantly adhesive at the metal-resin interface (75% to 90% of the fractured specimens), with complete metal abutment exposure (when more than 75% of the metal abutment surface was exposed, it was classified as totally adhesive) (Fig 6a). The partially adhesive fractures (less than 75% of the metal abutment surface was exposed) were observed only in 10% to 25% of the failures and were associated with a lower failure load (800 to 1,200 N) (Fig 6b).
DISCUSSION The present study evaluated in vitro the fatigue resistance and failure modes of onlays and crowns bonded The International Journal of Oral & Maxillofacial Implants 369
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Boff et al
Fig 6 (a) Composite resin onlay presenting predominantly adhesive failure and (b) composite crown presenting partially cohesive failure type.
a
b
to CAD/CAM metal–composite resin premolar implant abutments and the influence of veneer material selection on fatigue resistance. The null hypothesis was accepted, as the abutment/restoration adhesive interface did not fail before the abutment itself, and the restorative material (ceramic vs composite resin) showed a significant influence on the fatigue resistance of the assembly. Furthermore, identical zirconia abutments from a previous study (data pooled for ceramic and composite onlays and crowns) presented a superior survival rate compared to metal–composite resin premolar abutments in this study. During their life cycle, teeth are subjected to many cycles of relatively low forces and may eventually undergo a sudden high-force impact, eg, trauma. In vitro tests mimicking clinical fatigue are relevant but time-consuming. They contrast with load-to-failure tests, which yield quick results but are also less clinically relevant. The loading protocol used in this study represents a good balance between the traditional fatigue tests and load-to-failure experiments. Originally introduced by Fennis et al44 and later used in numerous other studies,21–23,45 the approach can be considered an “accelerated fatigue test” that covers a wide range of clinically relevant situations (normal and high loads). The first part of the test fell within the range of normal bite forces in the posterior region, namely, up to 600 N.46,47 The second part comprised a range of loads that may be encountered in bruxism, trauma (high extrinsic loads), or masticatory accidents (under chewing loads but delivered to a small area as the result of a hard foreign body such as a stone or seed, for example). Another modification applied in this study was the replacement of the traditional stainless steel antagonist with a composite resin cylinder, as has been suggested in similar fatigue studies.22,26,27 Compared to metal as an antagonist, composite resin prevents localized intense point loads and unrealistic surface damage to specimens.48 Confounding variables were avoided by the
fabrication of both abutments and restorations with CAD/CAM technology. Composite resin and ceramic restorations performed well, considering that all samples survived the normal range of forces in the first half of this test (up to 600 N). Paradigm C and MZ100 specimens fractured at average loads of 1,133 to 1,266 N. Based on these data, it is difficult to conclude that adhesively restored polymer implant abutments are contraindicated on posterior teeth. These results are similar to those of a previous study, in which metal–composite resin abutments restored with Paradigm C and MZ100 easily survived normal bite forces in the anterior region (100 N).25 A further confirmation is the similar performance of ceramic restorations bonded either to zirconia27 or to metal–composite resin premolar abutments on posterior implants (33.3% vs 26.7% survival rates, respectively). The four groups in this study showed similar failure modes, with 100% of the failures involving restorations and abutments. There were no exclusively cohesive failures, no adhesive failures at the abutment/restoration interface, and no solely adhesive failures at the composite resin–metal abutment interface. These results confirm the reliability of the resinto-resin and resin-to-porcelain bonds. However, they contrast with data obtained with zirconia abutments by Magne et al,15 for which restorations presented a higher incidence of adhesive failure, leaving the abutment intact. Both studies used a bonding protocol that employed regular composite resin as an adhesive cement. Unlimited time to bond the restoration and to remove the excess materials, reducing considerably the need to finish/polish the restoration, is an advantage.49 Another significant finding was the absence of screw loosening/fracture, which may be explained in part by the reliability of the tapered abutment/implant internal connection. The weak link in the present study seems to be the interface between the composite resin mesostructure and the metal abutment, which was exposed in most
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Table 5 Comparison of Restorative/Abutment Material on Implant-Supported Restorations Abutment material
Anterior
Zirconia15
Composite resin Ceramic
P = .18
Composite resin25
Composite resin Ceramic
Ceramic, P < .02
Zirconia27
Composite resin Ceramic*
Composite resin, P = .0001
Composite resin (present study)
Composite resin Ceramic*
Composite resin, P < .027
Posterior
Restoration material
Restoration material comparison
Location
Abutment material comparison
P = .76
Zirconia, P = .0035
*Ceramic restoration bonded to zirconia and composite resin abutments presented similar performance (P = .43).
instances. Because it is possible to achieve a predictable resin bond to a titanium abutment by means of tribochemical silicoating and a silane,50 it is probable that the metal bonding itself was not the main reason for the abutment failure in this study. It can be hypothesized that the design of the metal component could have caused the problem, since it consisted of a relatively rigid solid abutment, which was not modified. Further work, including finite element analysis, would be needed to optimize the design of this titanium part to match the resilience of the overlying composite resin mesostructure and possibly relieve the stress on this interface. This hypothesis was confirmed by existing data on anterior teeth using modified temporary metal abutments (which are more flexible, like composite resin). When associated with composite resin mesostructures, those metal components demonstrated performance similar to that of zirconia abutments of the same design.25 The predominantly cohesive failure mode in the present study (10% to 25%) was similar to that of natural teeth with an oblique crack from the functional area to the buccocervical area51,52 and seemed to happen at earlier load steps than completely adhesive failures. Those cohesively failed specimens fractured with a single fragment (unlike completely adhesive failures), and all appeared to be repairable by rebonding the fragment. Because of advances in elemental chemistry, modern composite resins feature improved repairability53,54 and adhesion to tooth and metallic substrates.53,55 A pilot test confirmed that repair of failed metal–composite resin premolar implant abutments (by means of tribochemical coating and a silane) can yield high fatigue resistance. Additional computations obtained by pooling the data for the restorative material (onlays and crowns) revealed the superior survival probability of Paradigm MZ100 compared to Paradigm C (P = .027), with 18 composite resin restorations surviving the test (60%), compared to only 8 ceramic restorations (26.7%).
This result differs from the data obtained from same materials (Paradigm C and MZ100) when metal–composite resin premolar abutments were restored in the anterior dentition.25 The ability to deform under loading makes Paradigm MZ100 more likely to absorb the stress and avoid damage to the abutment itself. In the anterior dentition, restorations were subjected to low and oblique loads up to 280 N,25 while posterior restorations in this study were subjected to vertical loads up to 1,400 N. The damping effect expected from the composite abutments protecting the ceramic restorations in the posterior area was not observed under those high compressive loads. In addition, when pooled data from this study (ceramic restorations only) were compared to ceramic restorations bonded to zirconia abutments with identical design and testing conditions,27 no difference was observed (P = .43) (Table 5). In contrast, composite resin restorations bonded to zirconia premolar abutments yielded outstanding results (100% survival rate) and coincidentally, seemed to respond like natural teeth when considering their dynamic response to impact loading (measured energy absorption; Periometer, Periometrics LLC).28 When data from both studies in posterior implants27 and from the present study were combined, zirconia abutments performed significantly better than metal– composite resin premolar abutments (P < .0035) and their performance was further improved with composite resin restorations instead of ceramic restorations. The excellent performance of composite resin restorations milled from MZ100 blocks has already been demonstrated in other applications on teeth.21–24 Many professionals have been reluctant to use composite resin as a posterior restorative material because of its low wear resistance compared to ceramics. Wear of the restoration itself, however, should not be the only consideration in the selection of restorative material; the wear of opposing enamel, when appropriate (total wear, restoration, and enamel combined) should also be taken into account. Because it is less abrasive The International Journal of Oral & Maxillofacial Implants 371
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Boff et al
to enamel, Paradigm MZ100 demonstrates less total wear compared to ceramic restorative materials.20 This represents an important advantage of composite resin restorations over ceramic restorations for implants that will be subjected to parafunctional loading to preserve the volume and morphology of the opposing enamel. One may question the clinical implications of failure as defined in the present study. Failure of the restoration or abutment, when repairable, may also be perceived as a protective mechanism to limit the amount of stress on the implant itself and possibly to reduce the stress on the surrounding bone. Other significant clinical implications can be drawn from this study related to the restoration design and material. The concept of adhesively retained (nonretentive) restorations gives the surgeon, restorative dentist, and ceramist more freedom during the determination of optimal implant orientation (allowing for a more “bone-driven” placement when needed) and the design of secondary components compatible with severely reduced mesiodistal or occlusal clearances. The simulation of any crown-root angle and reduced subgingival margin placement, along with the improved optical properties and design of the abutment in this novel posterior restorative approach, simplifies delivery of the definitive restoration and enhances the esthetic outcome (eg, in case of thin labial peri-implant mucosa).7,8,49 There is also less risk that excess subgingival cement will remain. Based on the data from this study, it is difficult to conclude that polymer abutments are contraindicated for posterior teeth; however, further studies should be conducted to determine the optimum design of restorative components and to explore and develop the use of novel fiber-reinforced composite resin CAD/ CAM materials.
CONCLUSIONS Within the limitations of the present study, it was possible to conclude that Paradigm MZ100 onlays/crowns bonded to metal–composite resin premolar implant abutments presented higher survival rates when compared to ceramic onlays/crowns. Zirconia abutments outperformed metal–composite resin premolar abutments in terms of fatigue resistance.
Acknowledgments The authors wish to express their gratitude to the CAPES Foundation Brazil (grants PDEE 1897-09-8 and PDEE 1909-09-6); Neodent Implant System (Curitiba, PR, Brazil) for the donation of dental implants and metal abutments; 3M/ESPE (St. Paul, MN) for Paradigm C, Paradigm MZ100 blocks, Filtek Z100 composite resin, and Cojet; Kerr (Orange, CA) for Optibond FL and
Occlubrush; Patterson (El Segundo, CA) for Cerec 3; Ultradent (South Jordan, UT) for Ultra-Etch, Porcelain Etch, and Silane; Heraeus Kulzer (Armonk, NY) for Palapress; Brasseler (Savannah, GA) for Dialite; and Komet (Rock Hill, SC) for the Q-Polishing System. The authors reported no conflicts of interest related to this study.
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