Effect of surface treatment on the retention of implant-supported zirconia restorations over short abutments Farahnaz Nejatidanesh, DDS, MS,a Omid Savabi, DDS, MS,b and Ehsan Jabbaric School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran Statement of problem. The retention of cement-retained implant-supported restorations can be affected by the height of the abutments. Purpose. The purpose of this study was to evaluate the effects of the surface treatment on the retention of implant-supported zirconia restorations over short abutments. Material and methods. Eighty solid abutments reduced to 3 mm in height and their corresponding fixture replicas were embedded vertically in autopolymerizing acrylic resin blocks. Eighty zirconia copings (Cercon) with an occlusal loop were fabricated and divided into 2 groups (n¼40). One group was airborne-particle abraded with 110 mm aluminium oxide and the other group was treated with silica coating (Rocatec System). Each group was then divided into 4 subgroups (n¼10). The subgroups received either no treatment (control) or were treated with silane (Clearfil Porcelain Bond ActivatorþSE Primer), acid etching followed by silane, or ceramic primer (Clearfil). All copings were luted with a self-adhesive luting agent (Clearfil SA). After 1 week of conditioning in artificial saliva and thermal cycling (5000 cycles, 5 C-55 C), the removal force of the copings were tested with a universal testing machine at a 5 mm/min crosshead speed. The dislodgment force and failure mode were recorded. Two-way ANOVA and the Tukey honestly significant difference and the Fisher exact tests were used for data analysis (a¼.05). Results. The highest retentive values were obtained for airborne-particle abrasion–ceramic primer (228.84 N) and silica coating–ceramic primer (230.37 N), which were not significantly different from silica coating alone (216.26 N; P¼.95) or a combination of airborne-particle abrasion followed by silanation (211.67 N; P¼.87). The failure mode was primarily adhesive and cement principally remained on the copings. Conclusions. Within the limitations of this study, ceramic primer that contains adhesive phosphate monomer significantly improved the retention of zirconia ceramic restorations. Silicoating as a mechanical treatment provided greater retention for zirconia copings than airborne-particle abrasion when a resin-luting agent was used. (J Prosthet Dent 2014;112:38-44)

Clinical Implications Results of this in vitro study suggest that silicoating and the chemical treatment of zirconia-based restorations with a ceramic primer that contains adhesive phosphate monomer can improve the retention of implant-supported restorations over short abutments luted with resin luting agents.

This study was supported by Isfahan University of Medical Sciences research grant 390086. Based on a thesis submitted to the postgraduate school of Isfahan University of Medical Sciences in partial fulfillment of the requirement for the Master of Science Degree. a

Professor, Dental Materials Research Center, Department of Prosthodontics. Professor, Torabinejad Dental Research Center, Department of Prosthodontics. c Postgraduate student, Dental Students’ Research Committee. b

The Journal of Prosthetic Dentistry

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July 2014 Cement-retained implant-supported prostheses offer several advantages over screw-retained prostheses. These include the axial loading of implants due to the development of optimal occlusal contact,1 simplicity in adjustment of the superstructure,2,3 elimination of screw loosening,4 and improved esthetics.5 However, residual cement is a major problem with cement-retained restorations.6,7 The cementation of customized zirconia abutments to titanium bases has recently been introduced.8,9 Zirconia is considered advantageous because of its strength, excellent mechanical properties, and biocompatibility, which results in its use in restorative dentistry as a core material for tooth and implant-supported restorations8,9 and also for implant abutments in the esthetic zone.10 As a result of its high fracture resistance, zirconia restorations can be luted with conventional cements, which provide retention primarily by their physical strength and micromechanical qualities.11,12 Adhesive resin luting agents can increase fracture strength and the lifetime of ceramic restorations.13,14 In addition, small cracks in the intaglio surface of ceramic restorations due to acid etching or airborne-particle abrasion (APA) can be sealed with resin cement, which significantly improves the strength of the ceramic. Ceramic-resin bonding is successfully achieved through chemical bond and micromechanical interlocking at the ceramic-resin interface.15 Pretreating silica-based ceramics with acid etching followed by silanization16-20 provides a rough surface, which improves wettability.15,21 Unlike glass ceramics, oxide ceramics such as aluminum oxide (Al2O3) or zirconium oxide have a high crystalline content and cannot be adequately treated with these techniques.22-25 APA with Al2O3 particles23,26-31 and a tribochemical coating process20,25,32 can increase the bond strength of these ceramics. APA in combination with modified bisphenol A-glycidyl methacrylate resin luting agents that contain an adhesive phosphate monomer (10-methacryloyloxydecyl dihydrogen phosphate [MDP])

Nejatidanesh et al

39 provide a long-lasting bond between the resin and zirconia ceramics,23,24,30,31,33-36 with no decrease in bond strength after water storage and thermal cycling.28,31,37 In addition, the use of an MDPcontaining luting agent without a silane or a bonding agent for bonding to oxide ceramics has been suggested.23,24,28-31,38 These luting agents in combination with APA also provide a reliable bonding to pure titanium.39 The retention of cement-retained restorations depends on the geometry of the abutment, surface roughness, and luting agent.40,41 Abutment height is an essential factor, which affects the surface area, and using the short abutments in limited interarch space can jeopardize the retention and resistance of restorations.1,42 Sadig and Al Harbi43 showed that abutment height, roughness and treatment of the surface, and the type of luting agents can affect the retention of titanium castings on implant abutments. In comprehensive reviews, Kern44 and Thompson et al45 describe current approved procedures for resin bonding to zirconia, including cleaning, grinding with a diamond rotary instrument, airborne-particle abrasion with pure alumina or silica-coated alumina particles, and chemical activation by phosphate monomers or silanes. The retention of zirconia-base restorations milled by computer-aided manufacturing is minimal, and a luting agent with higher retentive strength is needed.46

Furthermore, zirconia is relatively inert, which results in a low reactive surface.47 A few studies can be found on the retention of cemented zirconia copings over titanium abutments.46,48,49 The purpose of this study was to evaluate the effect of different surfacetreatment methods on the removal force of implant-supported zirconium oxide copings on short abutments. The null hypothesis was that the different surface treatment methods do not affect the retention of implantsupported zirconium oxide copings over short abutments.

MATERIAL AND METHODS Eighty solid abutments 5.5 mm in height with a 6-degree taper (048.541, ITI Dental Implant System; Straumann AG) were attached to the implant analogs (048.124, ITI Dental Implant) and to a torque of 35 Ncm. The abutment-analog complex was mounted vertically in an autopolymerized T-shaped acrylic resin block with a dental surveyor for precise placement in the universal testing machine (Fig. 1). The height of the abutments was reduced to 3 mm by using a diamond rotary cutting instrument secured in a milling machine (HarnischþReith; Winterbach) and copious water irrigation to ensure the same preparation for each abutment. One of the abutment-analog complexes was scanned (Cercon Eye;

1 Shortened abutment in T-shaped acrylic resin block.

40

Volume 112 Issue 1 Degudent), and 80 zirconia copings with an occlusal loop were made in white zirconia (Cercon Base; Degudent) by CAM machine (Cercon Brain; Degudent) with a 30-mm space for the luting agent. The copings were sintered at 1350 C for 7 hours (Cercon Heat; Degudent). Silicone disclosing medium (Fit Checker; GC Co) was used to evaluate the fit of the copings on the abutments, and the marginal fit was evaluated at 4 magnification. Copings with improper fit were excluded. The copings were assigned to 2 groups (n¼40). The first group was treated with airborne-particle abrasion (Rocatec; 3M ESPE) with 110-

mm Al2O3 particles (Rocatec-Pre; 3M ESPE) at 300 kPa pressure perpendicular to each surface from a distance of 10 mm for 10 seconds. The second group was airborne-particle abraded with 110-mm Al2O3 particles and then treated with 30-mm silicamodified Al2O3 particles (Rocatec Soft; 3M ESPE) under the same conditions as the first group. After mechanical surface treatment, the copings were cleaned with 96% isopropyl alcohol in an ultrasonic cleaner (Sonorex; Bandelin Electronic) for 5 minutes. Each of the mechanically treated groups was divided into 4 subgroups

Zirconium oxide copings (n=80)

30 µm silica-modified airborne-particle abrasion (n=40)

110 µm airborne-particle abrasion (n=40)

Control (n=10)

Control (n=10)

Acid etching / silane (n=10)

Acid etching / silane (n=10)

Silane (n=10)

Silane (n=10)

Ceramic primer (n=10)

Ceramic primer (n=10)

2 Studied groups.

Table I.

Chemical composition of adhesives and luting agent

Materials

Lot No.

Active Chemical Composition

Clearfil ceramic primer

00019C

MDP, 3-methacryloxypropyl trimethoxysilane

Clearfil porcelain bond activator

00265A

3-methacryloxypropyl trimethoxysilane

Clearfil SE primer

01061A

MDP, 2-hydroxyethyl methacrylate, dl-camphorquinone

Clearfil SA cement

038ABA

MDP, bisphenol A diglycidylmethacrylate, triethyleneglycol dimethacrylate, dl-camphorquinone, benzoyl peroxide

MDP, 10-methacryloyloxydecyl dihydrogen phosphate.

The Journal of Prosthetic Dentistry

(n¼10) for chemical treatment. No chemical treatments were used for the first 2 subgroups with APA and silica coating (SC). Subgroups 3 and 4 were etched with 9% hydrofluoric acid (Porcelain Etch; Ultradent) for 60 seconds, silanated (Clearfil Porcelain Bond Activator and SE primer; Kuraray), and then air-dried. Subgroups 5 and 6 were conditioned with a silane coupling agent (Clearfil Porcelain Bond Activator and SE primer; Kuraray). Subgroups 7 and 8 were conditioned with ceramic primer (Clearfil Ceramic primer; Kuraray). A flow chart of the groups is presented in Figure 2. The active chemical compositions of the materials used are presented in Table I. No power analysis was performed because sample size was determined in a previous study,46 which showed that a minimum of 8 per group was needed (a¼.05 and power¼.80). The zirconia copings were luted with a dual-polymerizing, self- adhesive resin cement (Clearfil SA; Kuraray) according to the manufacturer’s instructions. The specimens were gently seated on the abutments with hand pressure and then placed under 49 N force for 10 minutes. The restorations were light polymerized for 10 seconds with a lightpolymerization unit (blue phase C8; Ivoclar Vivadent AG). After removing excess cement, the copings were light polymerized for 30 seconds on each side. After incubation at 37 C for 24 hours, the specimens were conditioned in artificial saliva for the next 7 days. The specimens were then subjected to 5000 thermal cycles, 5 C to 55 C with 30 seconds of dwell time. The copings of all groups were dislodged along the long axis of the abutment-implant analog with a universal testing machine (Model 4302; Instron) at a crosshead speed of 5 mm/min. The dislodgment force and the failure mode were recorded. One specimen from the SC subgroup and 1 specimen from the SC plus the ceramic primer subgroup failed during the test because the occlusal loops fractured. The failure modes were as follows50: more than 75% of the luting agent remained on the intaglio surface of the coping, between 25% and 75% of the

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July 2014

Table II.

41 Mean (SD) of dislodging force (N)

Mechanical Treatment APA

95% Confidence Interval of Mean

Chemical Treatment

Mean (SD)

Lower Bound

Control

160.11 41.86

130.16

190.06

bc

Silane

211.67 50.90

175.26

248.08

ab

Upper Bound

Tukey Groups

145.71 53.05

107.76

183.66

c

Ceramic primer

228.84 52.65

191.17

266.51

a

Control

216.26 42.09

183.90

248.61

AB

Etch-silane

SC

Silane

157.81 38.06

130.58

185.04

B

Etch-silane

157.19 77.66

101.64

212.74

B

Ceramic primer

230.37 60.33

183.99

276.74

A

SD, standard deviation; APA, airborne-particle abrasion; SC, silica coating. Significant difference between means are characterized by different letters. Lower case, APA; upper case, SC.

3 Mean dislodging force of studied groups (N). Values are plotted with 95% confidence interval error bars. Significant difference between means are characterized by different letters. Lower case, APA; upper case, SC. luting agent remained on the intaglio surface of the coping, and more than 75% of the luting agent remained on the abutment surface. The dislodging forces were statistically analyzed with 2-way ANOVA, and the Tukey honestly significant difference post hoc test. The failure mode was analyzed with the Fisher exact test (a¼.05).

RESULTS The mean retention and standard deviation of the studied groups are presented in Table II. The ceramic primer combined with SC and APA

Nejatidanesh et al

resulted in the highest removal force (Fig. 3). Two-way ANOVA showed a significant difference among the groups with respect to the chemical surface treatment (F¼6.935; P

Effect of surface treatment on the retention of implant-supported zirconia restorations over short abutments.

The retention of cement-retained implant-supported restorations can be affected by the height of the abutments...
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