CAM restorations fabricated with Procera technology: an overview.

Q U I N T E S S E N C E I N T E R N AT I O N A L

RESTORATIVE DENTISTRY

Matthias Karl

In vitro studies on CAD/CAM restorations fabricated with Procera technology: An overview Matthias Karl, Priv-Doz, Dr med dent1 Objective: The number of available CAD/CAM systems has dramatically increased in recent years. Consequently, although clinical data for the newer systems are missing, in vitro studies are published frequently. The goal of this review was to provide an overview of in vitro studies conducted with the Procera system. Method and Materials: Repeated online searching in PubMed was done until June 2014 using the search terms Nobel, Procera, dental, implant. Papers reporting clinical studies, evaluating cementation procedures as well as investigations using norm-shaped test specimens were excluded from analysis. Data were then assigned to the following categories: material characterization, scanner technology, single crown and multi-unit restorations, passivity of fit of implant-support-

ed restorations, and implant abutments. Results: Relative comparisons within specific studies based on the control specimens used indicate that all Procera restorations meet clinical requirements. Absolute comparisons between studies are not possible due to great variations in study design and outcome measures. Conclusion: While the relevance of in vitro data is frequently questioned, practicing clinicians have to rely on such information when judging the applicability of a novel CAD/CAM system. Given that the Procera CAD/CAM system has proven its reliability both in vitro and in clinical use, existing in vitro data for this CAD/CAM system may serve as a useful reference providing benchmark values for future developments. (Quintessence Int 2015;46:561–574; doi: 10.3290/j.qi.a33937)

Key words: CAD/CAM, in vitro, Procera

The application of computer-aided design/computerassisted manufacture (CAD/CAM) techniques has dramatically increased over recent years, resulting in numerous CAD/CAM systems being available on the market.1 Major advantages of using CAD/CAM technology include the accuracy and precision of the manufactured pieces, cost and time efficiency, as well as the use of materials such as Zirconia, which can otherwise be difficult or even impossible to use in traditional laboratory-based workflows.1 While for most systems long1

Associate Professor, Department of Prosthodontics, University of ErlangenNuremberg, Erlangen, Germany.

Correspondence: PD Dr Matthias Karl, Department of Prosthodontics, University of Erlangen-Nuremberg, Glueckstrasse 11, 91054 Erlangen, Germany. Email: [email protected]

VOLUME 46 • NUMBER 7 • JULY/AUGUST 2015

term experience is not yet available, classic CAD/CAM systems such as Cerec (Sirona), Lava (3M Espe), and Procera (Nobel Biocare) are still available on the market and have been studied extensively, both in vitro and in vivo.2 After publishing developmental studies on a novel digitization and fabrication technique in the late 1980s, Procera was commercially launched in 1994.3 In its original version, the system could fabricate single- and multi-unit restorations following the digitization of conventional stone casts using a touch probe scanner with a sapphire ball.4 The data acquired then formed the basis for manufacturing a graphite electrode, which could subsequently be used to spark-erode the internal surface of copings from a titanium blank, while the external shape of the coping was created by a CNC mill-

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Q U I N T E S S E N C E I N T E R N AT I O N A L Karl

ing process.5 Alternatively, an oversized refractory die was generated and aluminum oxide powder was pressed over it.6 Sintering of the coping caused shrinkage to such an extent that the final restoration would fit on the original die. Multi-unit restorations could only be fabricated from titanium by manufacturing individual copings as described above and by connecting them through a laser-welding process.7 A proprietary kit of veneering ceramic was recommended for finishing Procera-based restorations in the dental laboratory. Subsequent versions of Procera added the use of zirconium oxide ceramics and ultimately resulted in a portfolio of prosthetic components ranging from single crown copings to multi-unit fixed dental prosthesis (FDP) frameworks on both natural teeth and dental implants. In 2009, a novel type of lab-based scanner based on the principle of conoscopic holography was introduced. The latest updates in scanner technology and proprietary software allow integrating data from cone beam computed tomography (CBCT) scans and classic model scans thereby approaching the goal of creating a fully virtual representation of a patient. Although they may be questioned with respect to their clinical relevance,8 data from in vitro studies are often used for an initial evaluation of novel treatment options and for comparing competing treatment modalities. This holds particularly true for CAD/CAM dentistry, where new materials as well as novel hard- and software options are frequently introduced. Therefore, it was the goal of this paper to present an overview on the published in vitro data for all types of available Procera restorations as well as for the scanner technology in order to provide benchmark values for future developments.

METHOD AND MATERIALS Repeated online searching in PubMed was conducted until June 2014 using the following combinations of search terms: Nobel and Procera, Procera and dental, Procera and implant. Papers were excluded if they were reporting in vivo data, evaluating cementation procedures, and if Procera technology was only used to generate norm-shaped test specimens such as disks or bars

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(exception: biocompatibility and wear of antagonist testing). The analyzed papers were categorized as follows: material characterization, scanner technology, single crown and multi-unit restorations, passivity of fit of implant-supported restorations, and implant abutments.

RESULTS Material characterization A total of 29 publications were identified dealing with the description of basic material characteristics for alumina, zirconia, and titanium used with the Procera technology. The vast majority of papers evaluated fracture loads of different restoration types (Table 1). Due to the differences in experimental design and restoration type used, considerable variations in fracture load values could be observed. Kokubo and colleagues tested fracture load of various designs of Procera zirconia single crown copings after veneering and cementation. Using two experimental setups, applying vertical or oblique loading, the authors showed that the design of the coping had an effect on fracture load.22 While in most studies simple fracture tests8 were employed for characterizing and comparing various restoration types, in some studies more elaborate investigative techniques were used. As such, in addition to comparing fracture loads of Procera-based single crowns before and after creating access holes for endodontic treatment, Wood and colleagues also calculated Weibull moduli for the restorations studied.19 For intact Procera alumina-based single crowns a value of 12.8 was reported, while a higher value of 13.4 was reported for Procera zirconia-based restorations. In both cases, the creation of an access hole and subsequent repair with composite resin caused a decrease in Weibull modulus of more than 50%.19 Similarly, Baldassarri and colleagues determined the static failure load of three-unit implant supported FDPs based on Procera zirconia frameworks reaching mean values beyond 1,680 N.23 The authors also postulated greater reliability of hand-veneered restorations as compared to over-pressed restorations. Hosseini et al24 compared the numbers of load cycles needed to



Table 1

Mean fracture load values (standard deviations) reported for different Procera restorations

Publication

Specimen

Product

Kokubo et al9

3-unit FDP veneered

Procera Zirconia

Att et al10

3-unit FDP veneered

Att et al11

3-unit FDP veneered

Larsson et al12

4-unit FDP frameworks, thermotreated (simulated veneering process)

Potiket et al13

Single crowns – ceramic veneered

Persson and Bergman14


Snyder and Hogg15


Harrington et al16

Single crown coping 0.6 mm thick and axial veneer 0.4 mm thick

Procera Zirconia Control Procera Zirconia Control

Procera Zirconia

Procera Alumina Procera Zirconia Control


476 (174) 381 (166) 405 (130)

Thermomechanical loading

2897(789.83) 4122 (808.56) 2614 (1008.31) – 3152 (1114.91) 419 (79) 702 (61) 1142 (57) 1297 (210) 732 (69)

Control

Procera Alumina

Procera Zirconia

Single crowns – ceramic veneered Procera Zirconia


447 (123)

Coping thickness: 0.6 mm Coping thickness: 0.6 mm Coping thickness: 0.4 mm


Procera Alumina Procera Zirconia

Procera Alumina

Wood et al19

Coping thickness: 0.4 mm


767 (67.4)

Control

Vult von Steyern et al18

Thermomechanical loading Thermomechanical loading; connector size: 2.0 mm Thermomechanical loading; connector size: 2.5 mm Thermomechanical loading; connector size: 3.0 mm Thermomechanical loading; connector size: 3.5 mm Thermomechanical loading; connector size: 4.0 mm

Fracture load, N 1292.0 (123.9) 1397.8 (328.5) 1039.8 (510.3) 1496 (260) 1297 (242) 1659 (245) - 1713 (142) 1580 (197) - 1593 (174) 1730 (203) 1396 (206) 1771 (258) - 2071 (223) 1630 (141) - 1823 (278) 300 (0) 300 (0) 428 (28) 602 (79) 897 (113)

Procera Titanium

Control

Alhasanyah et al17

Special feature Bar shaped pontic Occlusally curved pontic Cervically curved pontic

Procera Alumina Procera Zirconia

Att et al20

Single implant crowns – ceramic veneered

Procera Alumina

Att et al21

Single implant crowns – ceramic veneered

Procera Zirconia


Occlusal veneer thickness: 0.0 mm Occlusal veneer thickness: 0.4 mm Occlusal veneer thickness: 0.9 mm Occlusal veneer thickness: 1.4 mm Occlusal veneer thickness: 0.4 mm Coping thickness: 0.6 mm; occlusal veneer thickness: 1.8 mm; mechanical loading Occlusal coping thickness: 1.7 mm; non- occlusal coping thickness: 1.2 mm; occlusal veneer thickness: 0.7 mm; mechanical loading Coping thickness: 1.2 mm; occlusal veneer thickness: 1.2 mm; mechanical loading Mechanical loading Water storage Mechanical loading Thermocycling Water storage Mechanical loading Thermocycling Endo Access & Repair Endo Access & Repair Titanium stock abutment; thermomechanical loading Zirconia stock abutment; thermomechanical loading Alumina stock abutment; thermomechanical loading Titanium stock abutment; thermomechanical loading Zirconia stock abutment; thermomechanical loading Alumina stock abutment; thermomechanical loading

1653.94 (391.45) 1841.59 (372.60) 1586.74 (418.71) 2118.99 (144.46) 905 (104) 904 (91) 917 (179) 975 (223) 1108 (190) 910 (215) 1410 (111) 1436 (223) 2432 (181) 2075 (348) 1344.2 (402.0) 470.1 (151.8) 428.8 (77.0) 1310 (218) 593 (252) 283 (136)

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fatigue-fracture implant-supported single crowns. While initial fracture of Procera zirconia-based crowns occurred earlier as compared to different control groups, final fracture required at least as many loading cycles as for the control groups.24 Finally, Menini et al25 demonstrated that greater percentages of occlusal load are transferred to the supporting structures when Procera zirconia restorations are used, a result in agreement with high level of stiffness of oxide ceramics compared to alternative restorative materials. Esthetic properties of restorative materials are frequently evaluated by means of contrast ratio measurements and translucency assessments. With contrast ratios of 0.74 for Procera zirconia and 0.62 for Procera alumina26 as well as a mean translucency of 2.878 × 103 Lux for Procera zirconia,27 the esthetic properties of these materials lie within the range of comparable oxide ceramics. In terms of radiopacity, Martinez-Rus and colleagues found that Procera zirconia showed greater values as compared to alternative zirconia-based products.28 Porcelain veneering of substructures made from oxide ceramics has been described as being problematic for a variety of material-related parameters.29-31 Consequently, Al-Dohan et al32 found lower strength values for veneered Procera zirconia and alumina crowns as compared to metal-ceramic crowns. Also, while cohesive veneer failures were predominant in metal-ceramic samples, adhesive failures occurred most frequently in allceramic specimens. In this context, Baldassarri and colleagues showed that in addition to compressive stresses within the veneering ceramic (40 to 50 MPa), a considerable amount of tensile stress is also present (9 to 11 MPa), which may be considered relevant for the occurrence of chipping fractures.33 The amount of wear, both of the restoration and of the antagonist, is of further interest when considering veneering materials. One study using diskshaped specimens indicated that porcelain veneered Procera alumina causes less enamel wear of the antagonist as compared to conventional feldspathic porcelain.34 Unfortunately, no in vitro studies assessing this topic using finished Procera products could be found. Biocompatibility of restorative materials with respect to biofilm formation and cell adhesion is of

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particular interest in implant prosthodontics where abutments penetrate soft tissues.35 Considering experimental limitations of in vitro biocompatibility tests, only two studies using disk-shaped specimens were found. The authors reported that the numbers of bacteria adhering to Procera zirconia are comparable to titanium and hydroxyapatite,36 while the adhesion and activity of human gingival fibroblasts are greater on milled zirconia and milled alumina as compared to polished and veneered structures.37

Scanner technology Digitizing dental structures such as prepared teeth or implants is one of the most critical steps, determining the precision of fit of a CAD/CAM fabricated restoration. For the Procera system, two types of laboratory-based scanners have been introduced. While a touch probe scanner has initially been used for digitizing stone casts, the newer scanner generation (Fig 1) has been based on the principle of conoscopic holography, allowing for faster processing times while being less critical in digitizing free-form objects such as prepared teeth. Although relative comparisons between different dental scanners and scan modes have shown reasonable levels of reproducibility and accuracy,38,39 only a few studies describe the absolute accuracy and precision of these scanners using external references such as industrial scanners and coordinate measuring machines. In one such study, Holst and colleagues showed that when digitizing a mandibular cast with five implants and implant position locators, the deviations caused by either Procera scanner type were in the range of 11 μm and repeated scanning led to deviations in the range of 4 μm.40 These results are in line with another study showing that the precision of the touch probe scanner would be in the range of 7 to 16 μm for digitizing dies of prepared teeth.41 Another assessment of scanner accuracy comes from vertical gap measurements between implant shoulders and FDP frameworks reported by Katsoulis and colleagues.42 Comparing samples made from zirconia using both types of Procera scanners, smaller mean gap values were described in those restorations made



Fig 1 Current version of the NobelProcera scanner based on conoscopic holography (reproduced with permission; © Nobel Biocare Services AG, 2015).

Fig 2 NobelProcera zirconia coping for single crown restorations (reproduced with permission; © Nobel Biocare Services AG, 2015).

Table 2a Mean marginal fit (standard deviations) of single crown copings Publication

Product

Rahme et al43

Procera Alumina

Marginal gap, μm Fit checker 33.60 (23.61) Cement 31.90 (25.91)

Procera Zirconia

8.67 (3.96)

Control groups

12.24 (3.08) – 29.98 (3.97)

Procera Alumina (different finish lines and different cement types)

Precementation 22 (15) – 28 (10)

Procera Alumina (different finish lines and different cement types)

Postcementation 38 (22) – 53 (20)

Control groups

Precementation 31 (20) – 85 (28)

Control groups

Postcementation 68 (39) – 191 (64)

Procera Zirconia

50.29 (5.19)

Control groups

43.02 (4.00) – 47.51 (12.79)

Procera Alumina (different cement types)

29.30 – 53.37

Procera Zirconia

51 (50)

Control groups

81 (66)

Procera Zirconia

56.9 (36.8)

Procera Titanium

Postcementation 52 (31)

Control group


Martinez-Rus et al51

Quintas et al52

Korkut et al44 Pilathadka et al53 Grenade et al45 Kokubo et al46 Valderrama et al47

on the basis of tactile scans, while the smallest mean gap sizes within this study were found in Procera titanium frameworks fabricated using conoscopic holography scans. However, one needs to keep in mind that by measuring gap sizes of restorations, unknown fabrication inaccuracies are to be taken into account in addition to scanning inaccuracies.


Single crown and multi-unit restorations Twenty-four publications evaluated the fit of single crown copings (Fig 2), single crowns, and multi-unit restorations fabricated with the Procera technology (Table 2) showing a general tendency towards greater gap sizes on axial walls and occlusal surfaces as compared to marginal areas.43-50

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Table 2b Marginal fit (standard deviations) of single crowns Publication

Product

Marginal gap, μm

Procera Titanium veneered Jesus Suarez et al54

Leong et al Karlsson49


Procera Titanium veneered

54 (65)

Control groups

34 (52) – 66 (41)


Sulaiman et al56

Stone die 58 (36) – 61 (37) Tooth 70 (39) – 73 (42)

Procera Alumina veneered

82.88 (41.45)

Control groups

62.77 (37.32) – 160.66 (45.98)

Procera Zirconia veneered Martinez-Rus et al57

Precementation 9.94 (4.18) Postcementation 14.71 (3.17) – 39.01 (3.19) Precementation 13.04 (3.23) – 31.45 (4.47)

Control groups

Postcementation 24.87 (4.23) – 93.12 (6.77)

Procera Alumina veneered 58

Kohal et al

Before loading 90.9 After loading 98.7 Before loading 54.3 – 79.1

Control groups Valderrama et al47

Postcementation 28 (6) Precementation 55 (16)

Control groups 55

Precementation 14 (6)

After loading 53 – 84.6



Control group


Table 2c Marginal fit (standard deviations) of multi-unit restorations Publication

Restoration type

Product Procera Zirconia

Gonzalo et al59

3-unit FDPs - veneered Control groups

Marginal gap, μm Precementation 9 (10) Postcementation 12 (9) Precementation 40 (19) – 67 (42) Postcementation 48 (15) – 76 (29) Framework 82

Procera Zirconia Att et al60

Veneered 89 Postcementation 89 After loading 88

3-unit FDPs – veneered

Framework 64 – 86 Control groups

Veneered 67 – 86 Postcementation 76 – 86 After loading 78 – 84

Gonzalo et al

61

3-unit FDPs - veneered

Beuer et al50

3-unit FDP frameworks

Procera Zirconia


Control group


Procera Zirconia


Control group


Procera Zirconia Gonzalo et al

62

3-unit FDPs - veneered Control groups

Postcementation - microscope measurement 12 (9) Postcementation - SEM measurement 26 (19) Postcementation - microscope measurement 71 (45) – 76 (29) Postcementation - SEM measurement 65 (26) – 76 (37) Framework 61.08

Procera Zirconia Vigolo and Fonzi

63

Veneered 62.46 Glazed 63.46

4-unit FDPs - veneered

Framework 46.30 – 63.37 Control groups

Veneered 46.79 – 65.34 Glazed 47.28 – 65.49

566



Lin et al64 evaluated the fit of Procera titanium copings including modification of several parameters such as finish line, occlusal reduction, and additional retentive features. The authors concluded that the finish line design affected marginal opening and recommended to avoid feather edge preparations. Neither the occlusal reduction form nor the extent of occlusocervical undulation was found to affect marginal adaptation. Adding auxiliary retentive features had a negative effect on the fit of the copings. To avoid the replica technique for fit assessment, Holst et al65 used a virtual approach following digitization of both copings and dies to report that the cement gap of Procera titanium copings lies in the range of 0.049 mm to 0.090 mm. Two other studies demonstrated a trend towards larger gaps when restorations were assessed on definitive abutment teeth as compared to stone dies.48,49 This finding may be explained by inaccuracies resulting from impression making and master cast fabrication, and constitutes a general issue in all conventional fabrication techniques as well as in all laboratory-based CAD/CAM fabrication techniques. Potentially, intraoral scanning and scanning of conventional impressions may provide a solution to this problem.39 While veneering caused an increase in marginal gap size of single tooth restorations,47,48 it had only a minor effect on marginal fit in multi-unit FDPs.60,63 Importantly, although a wide variety of gap sizes were reported, all authors unanimously stated that the gaps observed would be clinically acceptable.

Passivity of fit of implant-supported multiunit restorations Due to the ankylotic fixation of dental implants in alveolar bone, misfit between multi-unit restorations (Fig 3) and the supporting implants may cause potentially detrimental static loads. Consequently, a passive fit of implant superstructures has been considered a prerequisite for long-term implant success, although the term has never been defined biomechanically and there is no standard method for fit assessment.66,67 A total of 13 papers addressed the issue of passive fit of Procera superstructures, with the majority applying gap


Fig 3 Implant-supported screw-retained Procera framework for a full-arch fixed restoration.

measurements between implants and restorations (Table 3). Although gap size does not always correlate with the amount of static load evoked in the peri-implant area,66 strain measurements in the areas adjacent to the supporting implants clearly indicated that three-unit FDP titanium Procera frameworks show greater passivity of fit as compared to conventionally cast restorations.67 Furthermore, Abduo et al76 were able to positively correlate vertical misfit and resulting strain development for both three-unit FDPs made from zirconia and titanium. As indirect indicators for the degree of fit, torque angle signatures68 as well as preload of retention screws69 have been measured and found comparable for restorations fabricated with the Procera system vs conventionally cast restorations. A number of studies used virtual fit assessment approaches for determining the level of precision of multi-unit Procera restorations made from titanium. Independent of the variable measured or the measuring technique used, Procera technology was shown to achieve a precise fit.70-73

Implant abutments Given that a precise fit and a stable connection between the implant and the abutment is of paramount importance in restorative implant dentistry in order to avoid technical complications such as screw

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Table 3

Passivity of fit of implant-supported multi-unit restorations

Publication

Product

Marginal gap, μm

Procera Zirconia FDP frameworks on 6 implants – conoscopic holography

32.7 (39.3)

Procera Zirconia FDP frameworks on 6 implants – tactile scan

22.2 (14.7)

Procera Titanium FDP frameworks on 6 implants – conoscopic holography

15.2 (12.9)

Control group FDP frameworks on 6 implants

239.3 (113.0)

Procera Titanium Bars on 6 implants – conoscopic holography

24.6 (16.5)

Control groups Bars on 6 implants

18.6 (13.8) – 49.7 (38.7)

Procera FDP frameworks (full arch; partial arch)

26.9 (9.3)

Control group FDP frameworks (full arch; partial arch)

46.8 (8.8)

Katsoulis et al42

Katsoulis et al74

Takahashi and Gunne75 Single screw test 13.6 (10.1) Procera Titanium 3-unit FDP frameworks Two screw test 3.6 (0.9) Abduo et al76 Single screw test 5.5 (2.1) Procera Zirconia 3-unit FDP frameworks Two screw test 3.7 (1.1) Best fit – Fixed 3.73 (2.812) Procera Titanium FDP frameworks on 6 implants Best fit – Unfixed 2.44 (1.462) Sierraalta et al77 Best fit – Fixed 21.00 (9.306) Control group FDP frameworks on 6 implants Best fit – Unfixed 13.44 (5.221)

loosening and biologic complications such as bone loss,78 a total of 27 publications were identified dealing with these aspects. The majority of the studies focused on fracture load / bending moments (Table 4a) and measurements of marginal gap sizes at the implantabutment interface (Table 4b). Zirconia abutments showed greater strength when they contained a metallic insert,79 and abutments made of titanium (Fig 4a) performed better than zirconia abutments (Fig 4b) in strength assessments.80,81 In addition to testing unmodified products, Att and colleagues described that post-fabrication modifications of zirconia abutments would not affect fracture load,82 which is in contrast to a more recent publication claiming a marked reduction in fracture load of manually modified zirconia implant abutments.83 Trying to simulate clinical conditions, Nguyen and colleagues fatigue tested Procera zirconia abutments on different Nobel Biocare implants using Biomet-3i implant-abutment combinations as control groups.84 While the authors described no significant differences between the implant systems evaluated, the diameter of the implants did have an

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effect on fatigue performance, with small diameter implants showing a tendency towards earlier failure. Similarly, Delben et al85 calculated the Weibull modulus as a measure of reliability for Procera zirconia abutments on external hex implants as being 13.1, which was much greater than the control groups consisting of Biomet-3i Osseotite and Ankylos implants combined with zirconia abutments with a maximum Weibull modulus of 5.8. By contrast, Kerstein and colleagues estimated the probability of failure of Procera zirconia abutments on Brånemark implants to be much higher when compared to Atlantis zirconia abutments on the same implants.86 Rotational freedom between implant and abutment was assessed by various studies. Depending on the abutment material used, Vigolo and colleagues found values for rotational play of Procera abutments on Brånemark implants ranging from 2.01 degrees to 2.06 degrees,87 which is consistent with a previous report by Lang et al,88 who found similar values for Nobel Biocare stock abutments and Procera abutments when a counter torque device was used during tightening of the



Table 4a Bending moments and fracture loads of Procera abutments Publication

Implant

Abutment

Aging

Nobel Biocare Replace

Bending moments, Ncm 429.7 (62.8)

Procera Zirconia Nobel Biocare Branemark

285.8 (64.4)

Truninger et al80

Thermomechanical loading Control groups Zirconia

331.7 (57.8) – 379.9 (59.1)

Control group Titanium

714.1 (184.9)

Nobel Biocare Branemark

Procera Zirconia

276.5 (47.6)


Procera Zirconia plus crown

291.5 (31.7)


Procera Zirconia



351.5 (58.0)

Control groups Zirconia

182.5 (136.5) – 371.5 (142.3)

Control groups

434.9 (124.8)

Sailer et al79

No

Control groups Control groups Zirconia plus crown

184.3 (77.7) – 283.3 (44.8)



581.8 (172.8)



Mühlemann et al81

556.7 (128.4) Thermomechanical loading

Control groups Zirconia plus crown

216.4 (90.0) – 605.4 (54.7)

Control group Titanium plus crown

1042.0 (86.8)

Control groups Procera Zirconia plus crown Kim et al99


480.01 (174.46) No

Control group Metal plus crown

901.67 (102.05)

Procera Zirconia plus crown Kim et al100


484.6 (56.6) Thermocycling

Control group Zirconia plus crown

503.9 (46.3) – 729.2 (35.9) No

519 (85)

Procera Titanium plus crown Att et al82


484 (144)

No

473 (68) – 493 (73)


478 (102) – 481 (66)

Nobel Biocare Replace Procera Zirconia plus crown Control group Metal plus crown

Protopapadaki et al101


Alqahtani and Flinton83


525.89 (143.55) Thermomechanical loading


413.70 (35.52)

Procera Zirconia

567.3 (35.4) Mechanical loading

Procera Zirconia modified

430.5 (39.4) – 445.4 (41.0)


Procera Zirconia veneered

Control groups

Control groups Zirconia veneered

429.6 (29.9) – 464.4 (119.1)


Procera Titanium

555 (25)

Delben et al94

646.1 (77.8) No

Gigandet et al89 Control groups Kerstein et al86

Control groups Titanium

508 (43) – 700 (32)

Procera Zirconia veneered

740 (96)

Control group Zirconia

831 (69)


abutments. In a more recent study, Gigandet et al89 found rotational play of Procera titanium abutments on Nobel Biocare Replace implants in the range of 3.50 degrees, a value greater than for other implant-abutment combinations evaluated in this investigation. Similarly, rotation of Procera abutments as well as Nobel Biocare stock abutments ranging from 3.92 to


4.13 degrees were described by Garine et al,90 which was also greater than for the control groups used. Three identified publications used detorque values of implant-abutment assemblies as an indicator for screw-joint stability. Detorque values increased when abutments were tightened under moist conditions91 as well as when the distance between the implant’s exter-

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Table 4b Microgaps between Procera abutments and supporting implants Publication

Implant

Abutment

Microgap, μm

Procera Zirconia

0.083

Procera Alumina

0.06

Control groups

Control groups

0.03 – 0.075


Procera Zirconia

5.7 (0.39)

Control groups

Procera Zirconia

9.53 (0.52) – 10.62 (2.16)


Procera Zirconia

1.83 (3.21)

Control groups


0.38 (0.28) – 0.90 (0.59)

Nobel Biocare Branemark Garine et al90

de Morais Alves da Cunha et al96

Baixe et al102 Procera Titanium

0.94 (0.05)


0.61 (0.27)


Hamilton et al103

Procera Titanium

1.38 (0.25)


1.37 (0.24)

Nobel Biocare Replace Procera Titanium

0.78 (0.24) – 2.28 (0.53)

Control groups

0.41 (0.05) – 2.08 (0.95)

Procera Zirconia

8.4 (5.6)


5.7 (1.9) – 11.8 (2.6)


1.6 (0.5)


2.52 (0.48)

Procera Alumina plus crown

3.15 (0.67)

Procera Titanium plus crown

3.19 (0.59)

Procera Zirconia – 20 Ncm torque

14.3 (4.4)

Procera Zirconia – 35 Ncm torque

10.5 (1.4)

Control group Titanium – 20 Ncm torque

5.3 (1.9)

Control group Titanium – 35 Ncm torque

5.2 (2.2)

Control groups Nobel Biocare Replace 104

Baldassarri et al

Control groups

Yuzugullu and Avci105

Smith and Turkyilmaz98



nal surface and the abutment’s internal surface were increased.92 Comparing UCLA gold and titanium abutments with Procera zirconia abutments on Biomet-3i implants, Delben and colleagues showed a tendency of smaller detorque values for the Procera abutments.93,94 One possible explanation that could account for these results is the issue of combining implants and abutments from different manufacturers. As demonstrated in two independent papers, Procera abutments and retention screws fit a variety of implant brands while not all implant manufacturers’ retention screws fit Procera abutments.86,95 These findings are further supported by a recent study on vertical misfit of Procera zirconia abutments on proprietary and clone implant systems showing that greater gap sizes occur when non-original off-label components are being used.96

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In an investigation of implant-abutment interface, Sumi and colleagues used SEM and optical microscopy to evaluate Astra and Nobel Biocare Replace implants assembled with Atlantis and Procera abutments, respectively.97 Due to substantial design differences between these two implant systems, the data presented seemed to be inappropriate for quantitative comparisons, with the exception of SEM analysis, which showed a complete seal for the Astra implant-abutment assemblies while Nobel Biocare implant-abutment assemblies showed gaps in the range of 30 to 100 μm. Smith and Turkyilmaz98 investigated the influence of different abutment materials and increasing torque values on bacterial leakage from implant-abutment assemblies. The results of this study showed that abut-



Fig 4a Procera titanium abutment fitting an external hexagon Brånemark implant.

Fig 4b Procera zirconia abutment fitting an external hexagon Brånemark implant.

ments should be tightened to recommended torque levels for minimizing gaps at the prosthetic interface, and that zirconia abutments were associated with larger microgaps when compared to titanium abutments. However, there was no significant difference in bacterial leakage between the different experimental groups.98 A novel study design allowing for direct assessment of relative motion between implant and abutment tested various combinations of Procera zirconia and Procera titanium abutments on both proprietary and competitor implants using stock and CAD/CAM abutments as controls. While the absolute amount of micromotion was affected by the implant shoulder geometry, Procera abutments performed at least as well as the control abutments.78

patients, which can surpass 400 N in bruxism patients.106 Based on reports of fracture loads for nonuniform dental restorations with specific shapes, however, it seems to be impossible to directly derive information on material strength. Furthermore, the values reported by different authors show considerable standard deviations. In addition, static overloading of restorations is less frequently seen as reason for fracture as compared to cyclic thermomechanical loading.8 CAD/CAM methods affect numerous steps in the fabrication of a restoration, from data acquisition, matching of data sets, virtual design, to milling and sintering processes, and they are much more sophisticated than conventional techniques. Given the proprietary features of the CAD/CAM systems as well as an occasionally limited educational background of clinicians, the amount of error introduced by each single step of CAD/CAM cannot easily be separated from one another. Traditional approaches assessing the fit of a final product onto the corresponding die using the replica technique (fit checker disclosing medium)107 seem to be insufficient and should be replaced by highresolution virtual analysis.65 Optimal marginal adaptation of tooth-supported restorations has been described as a prerequisite for its longevity. Considering that marginal gap size of up to 200 μm has been reported as clinically acceptable,48 all CAD/CAM restorations meet this requirement. However, many studies report on mean values, which may obscure clinically unacceptable fit in a particular area.65

DISCUSSION The vast majority of publications reported on studies using gap sizes and fracture loads as outcome measures, and both have been given limited clinical relevance.8 Only a few papers reported on more complex studies such as fatigue testing. In addition, the sample size used in most of the studies was limited, which in part may be due to the costs involved in testing commercially available products. Classic testing of dental materials involves fracture load measurements, taking into account that restorations have to withstand masticatory forces in human


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In addition, the measurement technique employed for determining marginal gaps62 as well as the definition of what constitutes a gap differ from study to study and thus have to be taken into account. For multi-unit implant supported restorations, there is an even greater demand for perfect fit in order to avoid misfit stresses causing technical and biologic complications.67 Many investigations in this field are based on marginal gap measurements,42 although they seem insufficient due to lack of information on threedimensional deformations inherent to a specific restoration and may not provide all the data necessary to calculate strains and stresses experienced by the superstructure or the supporting implant system.66 From a functional perspective, implant and abutments should have a perfect fit in order to limit micromotion and bacterial leakage,98 and should withstand loads of clinically relevant magnitudes. While these aspects have repeatedly been tested in various setups, a “zero gap” fit of an abutment on an implant seems to be technically impossible.78

CONCLUSION Based on the data presented, and independent of the study design or the measured variable, Procera restorations perform at least as well as conventionally fabricated prostheses or CAD/CAM restorations fabricated with alternative systems. While clear links between in vitro and clinical performance remain missing,108 existing in vivo data on Procera restorations show good long-term outcomes.109,110 As such, the findings presented may serve as useful reference for practicing clinicians when evaluating new CAD/CAM restorative options.

ACKNOWLEDGMENT The author thanks Dr Alexandra Rieben, Head of External Studies, Department of Clinical Research at Nobel Biocare, for assistance with the search strategy.

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