title: Machinability of lithium disilicate glass ceramic in in vitro dental diamond bur adjusting process.
abstract: 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.
authors: Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, School of Mechanical Engineering, Tianjin University, Tianjin 300072, China. Electronic address: xiaofeisong@tju.edu.cn.
authors: Xiao-Fei
authors: XF
authors: Song
authors: Key Laboratory of Advanced Ceramics and Machining Technology of Ministry of Education, School of Mechanical Engineering, Tianjin University, Tianjin 300072, China.
authors: Hai-Tao
authors: HT
authors: Ren
authors: Matter & Materials, College of Science, Technology & Engineering, James Cook University, Townsville, QLD 4811,Australia. Electronic address: Ling.yin@jcu.edu.au.
authors: Ling
authors: L
authors: Yin
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003748:Dental Equipment; D003776:Dental Porcelain / Q000737:chemistry*; D018130:Diamond; D013499:Surface Properties; D013997:Time Factors
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain; D018130:Diamond; C023506:Glass ceramics
keywords: Dental adjusting; Forces; Lithium disilicate glass ceramic (LDGC); Machinability; Specific machining energy; Surface roughness and integrity