Preparation time and surface roughness of core foundation resins and dentin.

STATEMENT OF PROBLEM: It is unclear if the preparation of core foundation resins is similar to that of dentin. PURPOSE: The purpose of this in vitro study was to compare the preparation time and resulting roughness of 5 core foundation resins and dentin. MATERIAL AND METHODS: Standardized preparations (10 mm length, 5 mm height) were made of 5 specimens of 5 core materials with a device-mounted dental handpiece (150 000 rpm, water-cooling) with weight-controlled contact pressure (50 g). To assess the cutting time of 100 µm grit cylindrical diamond rotary cutting instruments, 2 mm and 4 mm depths were cut 3 times (n=15). Afterwards surface roughness Ra and Rz were measured. Blocks of dentin were used as a control. Both preparation time and surface roughness data were statistically analyzed (1-way ANOVA, Scheffé correction, α=.05). RESULTS: The average preparation times for dentin were 7 seconds for a 2 mm preparation depth and 22 seconds for a 4 mm depth with an average Ra of 5.4 µm or Rz of 30 µm. For a 4 mm depth, preparation times for Build-It, Rebilda LC, and Ti-Core ranged from 24 to 27 seconds. The preparation times of these 3 core foundation materials did not differ significantly from dentin for a 4 mm depth. The results of Core Paste and Luxacore were significantly lower (10 and 11 seconds, P<.001). For a 2 mm cutting depth, Core Paste and Luxacore showed similar preparation times compared to dentin (7 seconds, P>.05). Build-It (12 seconds) and Rebilda LC (10 seconds) showed greater preparation times compared to dentin, whereas Ti-Core preparation (5 seconds) was less. ANOVA revealed significantly lower Ra (5.0 µm) and Rz values (23-26 µm) after preparation of Core Paste, Luxacore, and Ti-Core than those of dentin (P<.05). CONCLUSIONS: The preparation times of only some core foundation materials were comparable to dentin. Regarding the cutting depths, different materials provided a dentin-like preparation ability. The surface roughness values of core resins were comparable with or significantly lower than those of dentin.

Wear and hardness of different core build-up materials.

Before crown preparation, teeth with extensive coronal destructions are built up with core materials. Sometimes, these build ups are exposed to the oral environment without the protection of crowns. Therefore, this in vitro investigation was aimed at evaluating the wear, surface roughness, Vickers hardness, and surface structure of 10 core composites, two glass ionomer cements (GICs), and four posterior restoration composites. The three-body wear was tested after water storage and 2,00,000 cycles. We measured both surface roughness and Vickers hardness (DIN 50133) and evaluated the surface structures by scanning electron microscopy. Results were statistically analyzed by use of the Mann-Whitney U test (alpha = 0.05). Lowest wear was found for the restorative composites (20 microm Grandio; others about 40 microm). A comparison of the composites Build-It, Chroma Core, Rebilda LC, and Rebilda DC to Quixfil showed similar wear values for each material (43-50 microm). Wear values of GICs and all others core composites ranged between 58 and 75 microm. Only Ti-Core showed significantly higher wear than all other materials (p < 0.05). All core materials except Ti-Core (35 HV) showed Vickers hardness values between 42 and 61 HV. Most core composites, particularly Build-It, Multicore Flow, Rebilda LC, Ecusit, and Tetric Evo Ceram, showed more homogenous surface structures compared to GICs and restorative composites. Therefore, wear values of core build-up materials not only differed widely but were higher than those of conventional restorative materials; yet, core build-up materials showed advantageous surface structures.