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

Abstract

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 aim 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-Ultra-Thin). Complete-coverage onlay preparation additionally included the buccal cusp (Occlusal-Onlay-Standard; Occlusal-Onlay-Thin; Occlusal-Onlay-Ultra-Thin). 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-Ultra-Thin) 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-Ultra-Thin), 963 (405/Occlusal-Onlay-Standard), 1108 (340/Occlusal-Onlay-Thin), 997 (331/Occlusal-Onlay-Ultra-Thin), 1361 (333/Complete-Veneer-Standard), 1087 (251/Complete-Veneer-Thin), 883 (311/Complete-Veneer-Ultra-Thin). Palatal-onlay restorations revealed a significantly higher fracture resistance with ultra-thin 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 ultra-thin (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.

Comparative fracture behavior of monolithic and veneered zirconia posterior fixed dental prostheses

“…This reproduction of the in vivo condition was designed to observe changes representative of the expected clinical in vivo changes, which might result in the undesired phenomenon of low temperature degradation (LTD) 20) . In the study, a load application in the range of physiologic occlusal forces of 50 N was selected according to previous studies 17,29) . All FDPs survived the artificial aging in the chewing simulator, indictating this result a stable performance of the zirconia ceramics analyzed in the presence of mechanical and thermal stress like in the oral environment, as previously reported 17,20,29) .…”

“…In the study, a load application in the range of physiologic occlusal forces of 50 N was selected according to previous studies 17,29) . All FDPs survived the artificial aging in the chewing simulator, indictating this result a stable performance of the zirconia ceramics analyzed in the presence of mechanical and thermal stress like in the oral environment, as previously reported 17,20,29) . In the study 3-point flexure test until fracture was used as previously reported 4,18) .…”

Influence of material thickness on fractural strength of CAD/CAM fabricated ceramic crowns

“…There are several factors influencing the fracture resistance of ceramic restorations 5,[8][9][10] . The fracture resistance of all-ceramic restorations can be increased by an ideal combination of these factors.…”

“…The material characteristics of ceramics have been shown to significantly depend on prior thermal and mechanical fatigue loading 4) . Four factors have been identified to mainly influence the fracture resistance of all-ceramic restorations: restoration design, tooth preparation, cementation and material thickness [5][6][7][8][9] . The fracture resistance can be increased by an ideal combination of these four factors, however, the factors restoration material and material thickness have been reported to be of primary importance 10) .…”

Marginal quality of ceramic inlays after three different instrumental cavity preparation methods of the proximal boxes

“…The restoration geometry, design considerations, preparation methods, and loading conditions are key factors for the long-term success of dental restorations [2][3][4][5][6][7][8]. For tooth-colored ceramic inlays in esthetic dentistry, the long-term success is an actual problem [7].…”