Dr. Peter GehrkeBismarckstraße 27D - 67059 LudwigshafenE-mail: dr-gehrke@dr-dhom.de

Retentive Strength of Two-Piece CAD / CAM Zirconia Implant Abutments

Peter Gehrke 1, Jochen Alius 2, Carsten Fischer 3, Florian Tebbel 4, André Spanel 4

Crestal bone stability and a healthy mucosa are considered inevitable for the long-term success of implant-supported restorations. The soft tissue around dental implants serves as a protective barrier between the oral cavity and the underlying bone 1. These peri-implant tissues are recurrently challenged my numerous hazards that can have adverse effects on the implant longevity, such as plaque, load, and prosthetic interference. The implant abutment material seems to be of decisive importance for the quality of the attachment between the mucosa and the surface of the abutment 2. Different materials are available for the fabrication of implant abutments. Because of their dark color, metal abutments were reported to cause a grayish discoloration of the surrounding soft tissues, compromising the esthetic outcome in the esthetic zone 3. Ceramic abutments are of increasing interest, not only because of their tooth-like color but also for their possible biologic advantages. Although there is currently no mutual consent that ceramic abutments perform superior to titanium alloy abutments, the results of human histology studies indicate, that zirconium-dioxide may have a more favorable effect on the health of the peri-implant tissues 4. Today, zirconia abutments with various implant-abutment connection geometries exist for different implant types. Recent in-vitro studies demonstrated that the type of implant-abutment connection had a critical influence on the technical outcome of zirconia abutments 5. An internal connection of zirconia abutments can be obtained by means of a secondary metallic component (two-piece) or by the abutment itself (one-piece). Significantly higher values were achieved for CAD/ CAM zirconia abutments with internal connection via a secondary titanium insert (two-piece) than for the ones with external connection 6. Therefore, the use of a secondary titanium insert might have a beneficial influence on the stability of zirconia abutments and appears to be clinically useful for premolar and molar single-tooth replacement. Various bonding methods to zirconia ceramic and titanium have been reported. However, limited data is available on the retention of CAD/ CAM zirconia copings on secondary titanium inserts 7. The aim of the present study was to evaluate the retention of two-piece, CAD/ CAM zirconia abutments after aging under simulated oral conditions.

OBJECTIVE

Twenty-one identical two-piece, CAD/ CAM customized zirconia abutments with an internal implant abutment connection (Compartis/ XiVE®, DENTSPLY Friadent, Mannheim, Germany), were fabricated (Fig. 5-6). In that process CAD/ CAM generated zirconia copings, seven in each group, were bonded to a prefabricated secondary titanium implant insert, using three different types of resin-based luting agents: Group A: Panavia 21, Kuraray Co, Kurashiki, Japan; Group B: Multilink Implant, Ivoclar Vivadent, Schaan, Liechtenstein and Group C: SmartCem2, DENTSPLY DeTrey, Konstanz, Germany. For all groups, the bonding surfaces of the titanium inserts and the zirconia ceramic copings were air-abraded with 50 μm aluminum oxide particles at 2.0 bars pressure (0.25 MPa) for 20 seconds and were finally cleaned in alcohol. All specimens were stored in distilled water (37°C) for 60 days and subsequently thermal-cycled 15,000 times between 5°C and 55°C with a dwell time of 30 seconds to artificially age the bond interface. Following thermo-cycling, a bond strength test was conducted (Fig. 7-8). All samples were subject to a pullout test using an universal testing machine (Zwick, Ulm, Germany) at a crosshead speed of 2 mm/min. The type of failure mode and the load required to de-cement each two-piece zirconia abutment was recorded and mean values for each group were calculated. Means and standard deviations of retention at failure were analyzed.

MATERIAL & METHODS

Water storage at a constant temperature and thermal cycling are commonly utilized to simulate aging of resin bonds. However, it has been shown that different luting systems are influenced differently by these two parameters 8. As both are considered clinically relevant, water storage was combined with thermal cycling to test the durability oft the retention of CAD/ CAM manufactured zirconia copings bonded to titanium inserts using three different resin-based luting agents. As the results of this study show, it is possible to achieve sufficient, stable retention between zirconia copings and titanium inserts when airborne particle abrasion is used as a pretreatment. These retention values are somehow different than that obtained when the same cements are used on natural teeth. The material and surface characteristics of the implant abutment are likely responsible for this difference. To estimate the clinical failure risk of two-piece zirconia abutments, their actual bending strength in various restorative concepts has to be taken in to account. The results of a recent in vitro study demonstrate all over bending moments between 380 and 430 N for zirconia abutments with an internal connection accomplished by a secondary metallic component 6. In the present study, the mean retentive strength of all investigated resin cements exceeded this limit of fracture resistance. However, a significant difference between the mean retention values of the tested bond materials could be shown (Fig. 4). Limited data is available on the long-term clinical behavior of air-abraded zirconia copings. The roughening of the bonding surface of the zirconia coping by airborne particle abrasion, leading to an increase of retention, may also influence the integrity of the material itself 9. Hence, it can only be assumed that resin luting material has the ability to seal the roughened surface and to prevent adverse effects of surface alteration.

DISCUSSION

Based on the results of this study, the use of resin-based luting agents in combination with air abrasion of the bonding surfaces of titanium inserts and zirconia copings lead to a sufficient and stable retention of two-piece CAD/ CAM abutments. The failure modes of all tested two-piece abutments were completely adhesive, leaving the detached zirconia chimney and titanium insert undamaged. The bonding stability of the investigated luting agents exceeded the general limits of fracture resistance of two-piece zirconia abutments. However, a significant difference between the mean retention values of the tested bond materials could be shown.

CONCLUSION

The mean retention values were 924.93 ± 363.31 N for Panavia 21; 878.05 ± 208 33 N for Multilink Implant and 650.77 ± 174.92 N for Smart Cem 2. The failure modes of all tested two-piece abutments were completely adhesive, leaving the detached zirconia chimney and titanium insert undamaged (Fig. 9). The individual retention values, means and standard deviations are summarized in Table 1-3.

RESULTS

3 MDT, Dental laboratory, Sirius Ceramics, Frankfurt, Germany4 Engineer, Mannheim, Germany

1 Dr. med. dent., Private practice, Ludwigshafen, Germany2 Dr. med. dent., Private practice, Nürnberg, Germany

15th DENTSPLY Friadent World SymposiumHamburg, March 16/17, 2012

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2. Abrahamsson I, Berglundh T, Glantz PO, Lindhe J. The mucosal attachment at different abutments. An experimental study in dogs. J Clin Periodontol. 1998 Sep;25(9):721-7.

3. Sailer I, Zembic A, Jung RE, Hämmerle CH, Mattiola A. Single-tooth implant reconstructions: esthetic factors influencing the decision between titanium and zirconia abutments in anterior regions. Eur J Esthet Dent. 2007 Autumn;2(3):296-310.

4. Degidi M, Artese L, Scarano A, Perrotti V, Gehrke P, Piattelli A. Inflammatory infiltrate, microvessel density, nitric oxide synthase expression, vascular endothelial growth factor expression, and proliferative activity in peri-implant soft tissues around titanium and zirconium oxide healing caps. J Periodontol. 2006 Jan;77(1):73-80.

5. Sailer I, Sailer T, Stawarczyk B, Jung RE, Hämmerle CH. In vitro study of the influence of the type of con-nection on the fracture load of zirconia abutments with internal and external implant-abutment connec-tions. Int J Oral Maxillofac Implants. 2009 Sep-Oct;24(5):850-8.

6. Truninger TC, Stawarczyk B, Leutert CR, Sailer TR, Hämmerle CH, Sailer I. Bending moments of zirconia and titanium abutments with internal and external implant-abutment connections after aging and chewing simulation. Clin Oral Implants Res. 2012 Jan;23(1):12-8.

7. Ebert A, Hedderich J, Kern M. Retention of zirconia ceramic copings bonded to titanium abutments. Int J Oral Maxillofac Implants. 2007 Nov-Dec;22(6):921-7.

8. Chang JC, Hart DA, Estey AW, Chan JT. Tensile bond strengths of five luting agents to two CAD-CAM restorative materials and enamel. J Prosthet Dent. 2003 Jul;90(1):18-23.

9. Wegner SM, Kern M. Long-term resin bond strength to zirconia ceramic. J Adhes Dent. 2000 ;2(2):139-47.

LITERATURE

Retention values

Individual retention values of two-piece CAD/ CAM zirconia ceramic copings to titanium inserts (n = 7) utilizing Panavia 21 as luting material

Fig. 1: Illustration of retention values per path length at pull-out testing for Panavia 21 samples Table 1a: Individual retention values Table 1b: Mean and standard deviation

Table 2a: Individual retention values Table 2b: Mean and standard deviation

Table 3a: Individual retention values Table 3b: Mean and standard deviation

Fig. 2: Illustration of retention values per path length at pull-out testing for Multilink samples

Fig. 3: Illustration of retention values per path length at pull-out testing for SmartCem2 samples

Fig. 5: Bonded CAD/ CAM two-piece zirconia abutment with internal implant abutment connection (ZrO2 coping/ Compartis, Degudent Hanau, Frankfurt and Ti-Base XiVE®, DENTSPLY Friadent, Mannheim), modified for the test setup

Fig. 6: Two-piece zirconia abutments connected to implants (XiVE® D 3.8, DENTSPLY Friadent, Mannheim). Zirconia copings have been modified for test setup.

Fig. 10: Impression coping in place (XiVE® D 3.8) Fig. 11: Impression taking of prepared right central incisor and adjacent implant

Fig. 13: Soft-tissue emergence profile of peri-implant mucosa after wearing temporary restorationFig. 12: Clinical and laboratory sequence of CAD/ CAM two-piece zirconia abutment with internal implant abutment connection Fig. 14: Try-in of CAD/ CAM two-piece zirconia abutment

Fig. 15: Final full-ceramic restoration on maxillary right central incisor and implant in the region of left central incisor

Fig. 16: Close-up of anterior restoration and lip line

Fig. 4: Summary of bond strength for all tested samples (n = 21) including means and standard deviations of retention at failure

Panavia 21Serial graphic

Panavia 21

Multi LinkSerial graphic

SmartCem2Serial graphic

Mean (x) and standard deviation (s) of retention strength for Panavia 21 group

Individual retention values of two-piece CAD/ CAM zirconia ceramic copings to titanium inserts (n = 7) utilizing Multi Link as luting material

Mean (x) and standard deviation (s) of retention strength for Multi Link group

Individual retention values of two-piece CAD/ CAM zirconia ceramic copings to titanium inserts (n = 7) utilizing SmartCem2 as luting material

Mean (x) and standard deviation (s) of retention strength for SmartCem2 group

Statistics

Retention values

Multi LinkStatistics

Retention values

SmartCem2

Retention of zirconia copings bonded to titanium inserts (n = 21) using different resin-based luting agents

Statistics

1.11.21.31.41.51.61.7

898.481261.081312.92474.76

1290.69658.75577.86

Sample No.

Retention NCaption

Sample No.

Retention NCaption

3.13.23.33.43.53.63.7

545.021059.14831.49

1176.82965.14792.85775.89

Sample No.

Retention NCaption

2.12.22.32.42.52.62.7

403.42522.60777.30481.30833.93771.06765.77

0.0 0.2 0.4 0.6 0.8 1.0 1.20

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Path length in mm

Ret

entio

n va

lues

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0.0 0.5 1.0 1.5 2.00

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Panavian = 7

RetentionN

xs

924.93363.31

Multilink Implantn = 7

RetentionN

xs

878.05208.33

Smart Cem 2n = 7

RetentionN

xs

650.77174.92

ete t o o co a cop gs bo ded to t ta u se ts ( )using different resin-based luting agents

Fig. 7: Abutments have been thermal-cycled 15,000 times between 5°C and 55°C with a dwell time of 30 seconds to artificially age the bond interface

Fig. 8: Bond strength testing with universal testing ma-chine at a crosshead speed of 2 mm/min (Zwick, Ulm)

Fig. 9: Failure mode of all tested specimens were completely adhesive, leaving the detached zirconia coping and titanium insert undamaged