Available online 18 November 2022

Author links open overlay panelRenan LuizLuftDDS, MScaLucas Saldanhada RosaDDS, MScbPablo SoaresMachadoDDS, MSccLuiz FelipeValandroDDS, MSc, PhDdRafaelSarkis-OnofreDDS, MSc, PhDeGabriel Kalil RochaPereiraDDS, MSc, PhDfAtaisBacchiDDS, MSc, PhDgPersonEnvelopeAbstractStatement of problem

Zirconia has been reported to be suitable for multiunit monolithic restorations. However, as the connector region is the weakest part of the system, studies are needed to determine the optimal connector geometry.

Purpose

The purpose of this in vitro study was to evaluate the load-bearing capacity under fatigue of implant-supported fixed partial prostheses made of monolithic zirconia with different connector cross-sectional geometries.

Material and methods

Three-unit monolithic fixed partial prostheses (from mandibular second premolar to the second molar) were fabricated in zirconia (Zenostar T) by computer-aided design and computer-aided manufacture (CAD-CAM). Different connector cross-sectional geometries, with an area of 9 mm2, were tested (n=10): round, square with rounded angles, or trapezoid with rounded angles. The prostheses were screwed over 2 implants and inserted into acrylic resin bases. The specimens were submitted to a mechanical fatigue test until failure, with load applied to the pontic using the stepwise stress methodology (initial load of 100 N for 5000 cycles, followed by an increase to 200 N for 20 000 cycles, with a subsequent increase of 50 N each step). For data analysis, fatigue failure load (FFL) and cycles for fatigue failure (CFF) were recorded. Failed structures were analyzed by fractography. The Kaplan-Meier test followed by a log-rank Mantel-Cox post hoc test was used to analyze FFL and CFF (α=.05). Weibull analysis was also performed.

Results

The round (1065 N) and trapezoid (1010 N) groups presented higher FFL values than the square one (870 N) (P≤.05). For CFF, the round connector (358 777) was better than the square (280 310) (P=.006), and the trapezoid (337 773) was statistically similar to both (P>.05). No difference among groups was observed in Weibull modulus either for CFF or FFL data. All failures were catastrophic, originating at the base of the connector and propagating toward the occlusal surface of the pontic (region under loading).

Conclusions

The connector cross-sectional geometry significantly influenced the mechanical fatigue performance of implant-supported fixed partial prostheses made of monolithic zirconia.

Section snippetsMaterial and methods

This study evaluated the fatigue performance of implant-supported fixed partial prosthesis made of monolithic zirconia with different connector cross-sectional geometries—round, square with rounded angles, or trapezoid with rounded angles, as seen in Figure 1. The specimens simulated a mandibular prosthesis from the second premolar to the second molar, supported by 2 implants, with the first molar as a pontic. Data were obtained for fatigue failure load, number of cycles until failure, and

Results

Data for fatigue failure load (FFL) and cycles to fatigue failure (CFF) are depicted in Table 1. The round and trapezoid groups presented higher FFL than did the square one (P≤.05) and differences were not statistically significant between them (P=.165). For CFF, the round connector was better than the square (P=.006), and the trapezoid one was statistically similar to both (P>.05). No statistically significant difference among groups was observed in Weibull modulus either for CFF or FFL.

The

Discussion

The null hypothesis was rejected as the monolithic zirconia 3-unit implant-supported fixed partial prostheses with round and trapezoid connectors had better fatigue performance in comparison with the prosthesis with the square connector. A previous laboratory study tested different triangular connector shapes, and the best strength was associated with taller triangles, surpassing the results of triangles with a wider base but with reduced height.18 These results were consistent with those of

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

1.

The connector cross-sectional geometry significantly influenced the mechanical fatigue performance of implant-supported fixed partial prostheses made of monolithic zirconia.

2.

The round and trapezoid connectors led to better fatigue performance than the square ones.

CRediT authorship contribution statement

Renan Luiz Luft: Conceptualization, Methodology, Validation, Formal analysis, Data curation, Writing – review & editing. Lucas Saldanha da Rosa: Validation, Formal analysis, Data curation, Writing – review & editing. Pablo Soares Machado: Validation, Formal analysis, Data curation, Writing – review & editing. Luiz Felipe Valandro: Conceptualization, Methodology, Writing – review & editing. Rafael Sarkis-Onofre: Conceptualization, Methodology, Writing – review & editing. Gabriel Kalil Rocha

Acknowledgments

The authors thank DSP biomedical - Brazil for donating the dental implants.

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© 2022 by the Editorial Council for The Journal of Prosthetic Dentistry.