Fracture resistance of titanium and zirconia abutments: An in vitro study

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Statement of problem

Little information comparing the fracture resistance of internal connection titanium and zirconia abutments exists to validate their use intraorally.

Purpose

The purpose of this study was to determine the fracture resistance of internal connection titanium and zirconia abutments by simulating cyclic masticatory loads in vitro.

Material and methods

Twenty-two specimens simulating implant-supported anterior single crowns were randomly divided into 2 equal test groups: Group T with titanium abutments and Group Z with zirconia abutments. Abutments were attached to dental implants mounted in acrylic resin, and computer-aided design/computer-aided manufacturing (CAD/CAM) crowns were fabricated. Masticatory function was simulated by using cyclic loading in a stepped fatigue loading protocol until failure. Failed specimens were then analyzed by using scanning electron microscopy (SEM) and fractographic analysis. The load (N) and the number of cycles at which fracture occurred were collected and statistically analyzed by using a 2-sample t test (α=.05).

Results

The titanium abutment group fractured at a mean (SD) load of 270 (56.7) N and a mean (SD) number of 81 935 (27 929) cycles. The zirconia abutment group fractured at a mean (SD) load of 140 (24.6) N and a mean (SD) number of 26 296 (9200) cycles. The differences between the groups were statistically significant for mean load and number of cycles (P<.001). For the titanium abutment specimens, multiple modes of failure occurred. The mode of failure of the zirconia abutments was fracture at the apical portion of the abutment without damage or plastic deformation of the abutment screw or implant.

Conclusions

Within the limitations of this in vitro study, 1-piece zirconia abutments exhibited a significantly lower fracture resistance than titanium abutments. The mode of failure is specific to the abutment material and design, with the zirconia abutment fracturing before the retentive abutment screw.

Section snippets

Specimen Preparation

Twenty-two specimens were prepared for 2 test groups of 11 specimens each, representing implant-supported anterior single crowns (Fig. 1). Group T consisted of specimens with identical stock titanium abutments (TiDesign, 3.5/4.0, 4.5 mm diameter, 1.5 mm height; AstraTech Dental AB, Mölndal, Sweden), and Group Z consisted of specimens with identical 1-piece stock zirconia abutments (ZirDesign 3.5/4.0, 4.5 mm diameter, 1.5 mm height; AstraTech Dental AB). Twenty-two identical dental implants

Results

The results of the study are shown in Table I. The titanium abutment group fractured at a mean (SD) load of 269.6 (56.7) N and a mean (SD) of 81 14;935 (27 14;929) cycles. The zirconia abutment group fractured at a mean (SD) load of 139.8 (24.6) N and a mean (SD) of 26 14;296 (9200) cycles. The difference was statistically significant for both mean load and mean number of cycles (P<.001). The survival rate of titanium abutments was significantly higher than that of zirconia abutments (P<.001).

Discussion

The null hypothesis was rejected as the zirconia abutments demonstrated a significantly lower fracture resistance than the titanium abutments. This study used a stepped fatigue loading protocol,39, 40, 41 in which a predetermined load was applied for a defined number of cycles, followed by incremental increases in load for a set number of cycles until failure of the specimen. The benefit of this type of test is that it provides a better simulation of clinical conditions than a static load test,

Conclusions

1-piece titanium and zirconia abutments were tested in a stepped fatigue loading protocol. Within the limitations of this in vitro study, the titanium abutment system was significantly more fracture resistant than the zirconia abutment system. The following conclusions can be made:

  • 1.

    The mean number of cycles until failure of the titanium abutment group was 3 times that of the zirconia abutment group.

  • 2.

    The average load before failure for the titanium abutment group was almost twice that of the

Acknowledgments

The authors thank Mr Clay Taylor, Mr Ilya Zalizniak, and Mr Ed Ormerod for assistance in specimen preparation; Dr Gerard Clausen and Dr Brian Fitzpatrick for assistance with the manuscript; Mr Chris Owen for the photography; Miss Sandy Clarke (Statistical Consulting Centre, University of Melbourne) for statistical expertise; Astra Tech Dental for the donation of implant materials; and The Melbourne Dental School, the University of Melbourne, the Australian Dental Research Fund, Bio 21

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