The aim of this study was to investigate the biomechanical interactions between cuspal preparation designs and cement thickness in a cusp-replacing ceramic premolar restoration. The cavity was designed in a typical MODP (mesial-occlusal-distal- palatal) restoration failure shape when the palatal cusp has been lost. Twelve 3D finite element (FE) models with four cavity preparations (without coverage and with buccal cuspal coverage in 1.0, 1.5 and 2.0 mm reducing in cuspal height) and three cement thicknesses (50, 100 and 150 microm) were constructed to perform the simulations. The results indicated that enamel and cement stresses in designs with no buccal cusp replacement or a 1.0 mm thick buccal cusp replacement were higher than the designs with 1.5 and 2.0 mm thick replacement. No apparent differences were found in the dentin, enamel, and cement stresses based on cement thicknesses of 50, 100, or 150 microm. This study concluded that when cusp replacement is indicated, reduction of the buccal cusp by 1.5 mm at least could reduce stress.

Background/purpose: The aims of this investigation were to describe the effect of different ceramic and remaining dentin thicknesses on substrate temperature during photocuring, and investigate whether the temperature increased by >5.5 C for different dentin/ ceramic combinations. Materials and methods: Three groups of dentin thicknesses of 1.0 (D1.0), 1.5 (D1.5), and 2.0 mm (D2.0), and three groups of ceramic thicknesses of 1.5 (C1.5), 2.5 (C2.5), and 3.5 mm (C3.5) were examined. Temperature changes and the maximum temperature were observed under a high-intensity halogen light (QTH-Atralis 10 ECS program at 1200 mW/cm 2 for 30 seconds, Ivoclar Vivadent AG, Schaan, Liechtenstein). Four groups, D1.0eC1.5 (þ11 C), D1.5 eC1.5 (þ7.2 C), D1.0eC2.5 (þ6.7 C), and D2e0C1.5 (þ5.8 C), demonstrated temperature changes of >5.5 C. Results and Conclusions: A statistical analysis showed that separate individual thicknesses and combinations of dentin and ceramic had significant effects on temperature changes (P < 0.01). It was observed that the ceramic exhibited a smaller temperature shielding effect than dentin. Clinically, it would be optimal to preserve the dentin to avoid damaging pulp tissues. Where there is insufficient overall thickness ( 3.5 mm), continuous high-energy output photocuring should be avoided to protect pulp tissues from thermal injury.

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