Damage tolerance of indirect restorative materials (including PICN) after simulated bur adjustments.

Esthetic high-strength lithium disilicate glass ceramics (LDGC) are used for monolithic crowns and bridges produced in dental CAD/CAM and oral adjusting processes, which machinability affects the restorative quality. A machinability study has been made in the simulated oral clinical machining of LDGC with a dental handpiece and diamond burs, regarding the diamond tool wear and chip control, machining forces and energy, surface finish and integrity. Machining forces, speeds and energy in in vitro dental adjusting of LDGC were measured by a high-speed data acquisition and force sensor system. Machined LDGC surfaces were assessed using three-dimensional non-contact chromatic confocal optical profilometry and scanning electron microscopy (SEM). Diamond bur morphology and LDGC chip shapes were also examined using SEM. Minimum tool wear but significant LDGC chip accumulations were found. Machining forces and energy significantly depended on machining conditions (p<0.05) and were significantly higher than other glass ceramics (p<0.05). Machining speeds dropped more rapidly with increased removal rates than other glass ceramics (p<0.05). Two material machinability indices associated with the hardness, Young’s modulus and fracture toughness were derived based on the normal force-removal rate relations, which ranked LDGC the most difficult to machine among glass ceramics. Surface roughness for machined LDGC was comparable for other glass ceramics. The removal mechanisms of LDGC were dominated by penetration-induced brittle fracture and shear-induced plastic deformation. Unlike most other glass ceramics, distinct intergranular and transgranular fractures of lithium disilicate crystals were found in LDGC. This research provides the fundamental data for dental clinicians on the machinability of LDGC in intraoral adjustments.

Machinability of lithium disilicate glass ceramic in in vitro dental diamond bur adjusting process.

Diamond grinding used in dental adjustment of high-strength zirconia-reinforced lithium silicate glass ceramic (ZLS) and lithium disilicate glass ceramic (LDGC) is challenging in restorative dentistry. This study aimed to compare the machinability of ZLS and LDGC in diamond grinding in terms of machining forces and energy, debris, surface and edge chipping damage. Grinding experiments in simulation of dental adjustment were conducted using a computer-assisted high-speed dental handpiece and coarse diamond burs. A piezoelectric force dynamometer and a high-speed data acquisition system were used for on-processing monitoring for assessment of grinding forces and energy. Grinding debris and grinding-induced surface and edge chipping damage were examined using scanning electron microscopy. The results show that grinding of ZLS required higher tangential and normal forces and energy than LDGC (p   0.05), continued efforts are required to explore new reinforcement technologies for optimized LDGC.

Machinability: Zirconia-reinforced lithium silicate glass ceramic versus lithium disilicate glass ceramic.

Modelling the strain rate sensitivity on the subsurface damages of scratched glass ceramics

A diamond sphere of radius 105 μm was used to slide on fused silica under ramping load from 5 mN to 5 N in order to investigate scratch-induced deformation and micro-cracking of brittle solids. Complete circular cracks were observed with elastic deformation playing the predominant role. Results show: initial cracking can be detected by acoustic emission; the valleys of horizontal mean contact pressure and the apparent friction coefficient together with the sudden rise of the ratio of vertical work over horizontal work indicate the beginning stage of circular cracks; micro-comminution is signified by the decrease in residual depth. Values of fracture toughness obtained by Vickers hardness techniques are larger than reasonable ones. Scratch-based approaches by linear elastic fracture mechanics and microscopic energetic size effect laws are found to be applicable to assess fracture toughness of brittle glass by scratch test with a spherical indenter under an appropriate range for curve fitting. Fracture toughness of fused silica measured by scratch test is 0.7 MPa• m1/2, which is compared favorably with the values obtained by conventional methods.

Sliding of a diamond sphere on fused silica under ramping load

A smart anti-corrosion coating based on triple functional fillers

Cutting characteristics of dental glass ceramics during in vitro dental abrasive adjusting using a high-speed electric handpiece

A novel polymer composite coating with high thermal conductivity and unique anti-corrosion performance

Dental cutting using handpieces has been the art of dentists in restorative dentistry. This paper reports on the scientific approach of dental cutting of two dental ceramics using a high-speed electric handpiece and coarse diamond burs in simulated clinical conditions. Cutting characteristics (forces, force ratios, specific removal energy, surface roughness, and morphology) of feldspar and leucite glass ceramics were investigated as functions of the specific material removal rate, Qw and the maximum undeformed chip thickness, hmax. The results show that up and down cutting remarkably affected cutting forces, force ratios, and specific cutting energy but did not affect surface roughness and morphology. Down cutting resulted in much lower tangential and normal forces, and specific cutting energy, but higher force ratios. The cutting forces increased with the Qw and hmax while the specific cutting energy decreased with the Qw and hmax. The force ratios and surface roughness showed no correlations with the Qw and hmax. Surface morphology indicates that the machined surfaces contained plastically flowed and brittle fracture regions at any Qw and hmax. Better surface quality was achieved at the lower Qw and the smaller hmax. These results provide fundamental data and a scientific understanding of ceramic cutting using electric dental handpieces in dental practice.

Jian-Hui Peng

Papers

A smart anti-corrosion coating based on triple functional fillers

Cutting characteristics of dental glass ceramics during in vitro dental abrasive adjusting using a high-speed electric handpiece

A novel polymer composite coating with high thermal conductivity and unique anti-corrosion performance

A Machining Science Approach to Dental Cutting of Glass Ceramics Using an Electric Handpiece and Diamond Burs

Endowing versatility and superamphiphobicity to composite coating via a bioinspired strategy