Influence of preparation design and ceramic thicknesses on fracture resistance and failure modes of premolar partial coverage restorations

Guess, Petra C. Dr Med Dent, PhD
Schultheis, Stefan Dr Med Dent
Wolkewitz, Martin Dr Sc hum, PhD
Zhang, Yu PhD
Strub, Joerg R. Prof Dr Med Dent Dr hc

^aAssociate Professor, Department of Prosthodontics, School of Dentistry, Albert-Ludwigs-University Freiburg, Germany
^bAssistant Professor, Department of Prosthodontics, School of Dentistry, Albert-Ludwigs-University Freiburg, Germany
^cStatistician, Institute of Medical Biometry and Medical Informatics, Albert-Ludwigs-University Freiburg, Germany
^dAssociate Professor, Department of Biomaterials and Biomimetics, New York University, New York
^eProfessor and Chairman, Department of Prosthodontics, School of Dentistry, Albert-Ludwigs-University Freiburg, Germany

^*Corresponding author: Dr Petra C. Guess, Department of Prosthodontics, School of Dentistry, Albert-Ludwigs-University Freiburg, Hugstetter Strasse 55, 79106 Freiburg, GERMANY

This project was supported by Ivoclar Vivadent, the United States National Institute of Dental and Craniofacial Research (Grant 2R01 DE017925), and the National Science Foundation (Grant CMMI-0758530) for financial support.

Presented at the Academy of Prosthodontics Meeting, May 12, 2012.

The Journal of Prosthetic Dentistry 110(4):p 264-273, October 2013. | DOI: 10.1016/S0022-3913(13)60374-1

Statement of problem.

Preparation designs and ceramic thicknesses are key factors for the long-term success of minimally invasive premolar partial coverage restorations. However, only limited information is presently available on this topic.

Purpose.

The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of ceramic premolar partial coverage restorations with different preparation designs and ceramic thicknesses.

Material and methods.

Caries-free human premolars (n=144) were divided into 9 groups. Palatal onlay preparation comprised reduction of the palatal cusp by 2 mm (Palatal Onlay Standard), 1 mm (Palatal-Onlay-Thin), or 0.5 mm (Palatal Onlay Ultrathin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal Onlay Standard; Occlusal Onlay Thin; Occlusal Onlay Ultrathin). Labial surface preparations with chamfer reductions of 0.8 mm (Complete-Veneer-Standard), 0.6 mm (Complete-Veneer-Thin), and 0.4 mm (Complete Veneer Ultrathin) were implemented for complete veneer restorations. Restorations were fabricated from a pressable lithium disilicate ceramic (IPS-e.max-Press) and cemented adhesively (Syntac-Classic/Variolink-II). All specimens were subjected to cyclic mechanical loading (F=49 N, 1.2 million cycles) and simultaneous thermocycling (5°C to 55°C) in a mouth-motion simulator. After fatigue, restorations were exposed to single-load-to-failure. Two-way ANOVA was used to identify statistical differences. Pair-wise differences were calculated and P-values were adjusted by the Tukey-Kramer method (α=.05).

Results.

All specimens survived fatigue. Mean (SD) load to failure values (N) were as follows: 837 (320/Palatal-Onlay-Standard), 1055 (369/Palatal-Onlay-Thin), 1192 (342/Palatal-Onlay-Ultrathin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultrathin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete-Veneer-Ultrathin). Palatal-onlay restorations revealed a significantly higher fracture resistance with ultrathin thicknesses than with standard thicknesses (P=.015). Onlay restorations were not affected by thickness variations. Fracture loads of standard complete veneers were significantly higher than thin (P=.03) and ultrathin (P<.001) restorations.

Conclusions.

In this in vitro study, the reduction of preparation depth to 1.00 and 0.5 mm did not impair fracture resistance of pressable lithium-disilicate ceramic onlay restorations but resulted in lower failure loads in complete veneer restorations on premolars.