Machinability of IPS Empress� 2 framework ceramic

Abstract

Using ceramic materials for an automatic production of ceramic dentures by CAD/CAM is a challenge, because many technological, medical, and optical demands must be considered. The IPS Empress 2 framework ceramic meets most of them. This study shows the possibilities for machining this ceramic with economical parameters. The long life-time requirement for ceramic dentures requires a ductile machined surface to avoid the well-known subsurface damages of brittle materials caused by machining. Slow and rapid damage propagation begins at break outs and cracks, and limits life-time significantly. Therefore, ductile machined surfaces are an important demand for machine dental ceramics. The machining tests were performed with various parameters such as tool grain size and feed speed. Denture ceramics were machined by jig grinding on a 5-axis CNC milling machine (Maho HGF 500) with a high-speed spindle up to 120,000 rpm. The results of the wear test indicate low tool wear. With one tool, you can machine eight occlusal surfaces including roughing and finishing. One occlusal surface takes about 60 min machining time. Recommended parameters for roughing are middle diamond grain size (D107), cutting speed v(c) = 4.7 m/s, feed speed v(ft) = 1000 mm/min, depth of cut a(e) = 0.06 mm, width of contact a(p) = 0.8 mm, and for finishing ultra fine diamond grain size (D46), cutting speed v(c) = 4.7 m/s, feed speed v(ft) = 100 mm/min, depth of cut a(e) = 0.02 mm, width of contact a(p) = 0.8 mm. The results of the machining tests give a reference for using IPS Empress(R) 2 framework ceramic in CAD/CAM systems.

An overview of in vitro abrasive finishing & CAD/CAM of bioceramics in restorative dentistry

“…Thus, improved mechanical properties have been obtained while maintaining machinability [9] in the machinable glass-ceramic with improved fracture toughness and strength. The second one is the application of the ductile-regime machining technology in dental CAD/CAM for bioceramic prostheses to avoid the subsurface damage of brittle materials [101] and to obtain the occlusive surfaces with high quality [29]. This requires the development of new computer-controlled milling systems with the demands for ductile machining, including feed control, high loop stiffness and highly accurate toolpath control.…”

“…This is because the mechanical properties of dental bioceramics depend greatly on their microstructures [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Furthermore, their machining responses in CAD/CAM processes and clinical dental handpiece finishing rely on their mechanical properties [54][55][56][57].…”

“…1. This includes the fabrication of bioceramics and studies of their mechanical/physical behaviors [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], the performance evaluation of the prosthetic services [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], the CAD/CAM technology for rapid profile generation for crowns/inlays/onlays/bridges [14,[50][51][52][53], and the intraorally dental handpiece finishing for final fitting [54][55][56][57][58][59][60][61][62][63]…”

“…Extensive research has been conducted towards the roles of microstructures on damage and strength degradation of bioceramics [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], ceramic multi-layered structures [66][67][68][69][70] and ceramic whisker-reinforced composites [71][72][73][74][75][76][77]. A number of studies have also been reported with regard to the wear and fatigue of dental bioceramics using various test techniques and test conditions [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49].…”

Nano-mechanical behaviour of lithium metasilicate glass–ceramic

“…In abrasive machining, the plastically deformed material removal can produce damage-free surfaces when machining normal forces can be progressively diminished to milliNewtons per diamond grit (Bifano et al, 1991;Ma et al, 2003;Schmidt and Weigl, 2000;. For brittle materials to be machined in the ductile or plastic regime, their plastic deformation behaviour becomes very important, which can be studied using nanoindentation technique which also probes the contact hardness, H c , and the Young's modulus, E Pharr, 1992, 2004).…”