Objective:
Endodontically treated teeth often suffers a lack of coronal tooth structure, so that adding a suitable core build-up material is required, before the abutment tooth preparation and crown reconstruction can be performed. The core build-up material is the fundamental part of the load bearing structure of the tooth. Therefore, it needs to possess adequate mechanical and physical properties and has to support and protect the residual tooth structure before the final restauration. The grindability behavior of the core materials is one of the important aspects for a successful crown placement, which was specifically tested under clinical conditions and analyzed in this study. Dentin is the natural core material found in the teeth, so the similarity of core build-up materials to dentin in terms of their mechanical characteristics is an important consideration.
The present study deals with the grindability characteristics of several different materials. Their similarity to dentin characteristics was then analyzed.
Methods:
The glass ionomer cement used in this study was Ketac Fil, and the resin composites were LuxaCore Smartmix Dual, Visalys Core Dual, Rebilda DC, MultiCore Flow, Core Paste XP and Core-Flo DC. Dentin specimens were used as control group. The study consists of two phases, namely, the rough-cutting phase and the polishing phase, all simulating clinical conditions. The rough-cutting phase was performed under three different press forces of 0.5 N, 0.85 N and 1.2 N, using medium-grit size (106-125 µm) diamond burs attached to dental handpiece with 200,000 min^-1 rotation speed under 50 ml/min water cooling. The generated material depths of each material were then measured and compared to those of dentin. The polishing phase was performed under 0.5 N press force using fine-grit size (46\,µm) diamond burs with rotational speed of 150,000 min^-1 under the same water cooling rate as the previous phase. The surface roughness of each material were then measured and compared to those of dentin. The statistical analysis of one-way ANOVA with Dunnett's post test was performed
Results:
Results showed statistically significant differences (p<0.05) of removal depths between Ketac Fil and dentin under 0.5 N, 0.85 N and 1.2 N press forces. Luxacore Smartmix also displayed significant differences (p<0.05) under 0.85 N and 1.2 N press forces, while Core-Flo DC exhibited significant differences only under 1.2 N press force.
Visalys Core, Rebilda DC, MultiCore Flow and Core Paste XP maintained their removal depth similarity to dentin by showing no significant differences on every adjusted press force.
The surface roughness between dentin specimens, Visalys Core and Luxacore Smartmix are pretty similar, and there was no significant difference, while Ketac Fil, Core Past XP and Core-Flo DC showed a statistically significant difference to dentin (p<0.05).
Conclusions:
Overall, Visalys Core and Rebilda DC exhibited the greatest similarity to dentin in terms of grindability behavior, whereby the polymer component and chemical bond between fillers and polymers could play a significant role. Visalys Core has better surface roughness and showed no inhomogeneous structure.