MS16-P22 How heating and surface finishing affects the crystalline and mechanical properties of CAD-CAM dental lithium disilicate glass-ceramic Javier García-Mira (Department of Geology. University of Oviedo, Oviedo, Spain) Giordana P. Furini ( Faculdade de Odontologia. Universidade de Passo Fundo, Passo Fundo , Brazil) Paula Benetti ( Faculdade de Odontologia. Universidade de Passo Fundo, Passo Fundo , Brazil) Pedro Álvarez-Lloret (Department of Geology. University of Oviedo, Oviedo, Spain) Oscar E. Pecho ( Faculdade de Odontologia. Universidade de Passo Fundo, Passo Fundo , Brazil)email: uo252650@uniovi.es

The crystalline characteristics of a dental lithium disilicate glass-ceramic (LDGC) determine the esthetics, strength, and applicability of this material in clinical procedures. The computer-aided design and computer-aided manufacturing (CAD-CAM) technique and heat treatments (temperature, pressure and time) precisely controls the material properties of a LDGC during the manufacturing of dental restorations. During clinical manipulation, finishing and polishing procedures have to be performed on dental restorations. These procedures may affect the topography and modify the microstructural properties of dental ceramics. In the present study, the effect of final crystallization and different finishing and polishing procedures on crystalline and mechanical properties of LDGC were analyzed. For this purpose, the crystalline properties of the LDGC (IPS e.max CAD, Ivoclar Vivadent) were evaluated using 1D and 2D X-ray diffraction (XRD) analyses. The 1D-XRD analyses were performed with an X’Pert Pro (PANalytical) powder diffractometer while 2D-XRD patterns were obtained using an X-ray single crystal diffractometer (Bruker D8 VENTURE) equipped with an area detector (PHOTON100). The crystallization mechanism after heat treatment resulted in a conducted transformation process of the material microstructure. Thus, lithium metasilicate (LM) crystals are transformed into lithium disilicate (LD) crystals. The crystallite size, representing the average coherent crystal diffraction domains, were determined as a crystallinity index for LM and LD crystals after final crystallization. This parameter can be also influenced by the chemical composition of the material aimed for specific clinical purposes. The degree of crystallinity (i.e. crystalline to amorphous) was also obtained by 1D-RXD analyses using the ratio of the intensity of the crystalline peaks to the total intensity in the diffraction pattern, including the signal corresponding to the glass component from the ceramic. The 2DXRD patterns showed a randomly orientation of crystals in both pre and post crystallization during heating. These XRD analyses were also complementary with the results obtained by SEM observations. The increment on the crystallite size and crystal orientation during heat treatment could allow the lower presence and size of voids (densification of the material) that could be acted as potential locations for cracks or affect the optical properties of the material surface. Furthermore, finishing and polishing protocols of ceramic dental restorations differently affect the texture of the material surface, resulting in changes on the flexural strength of the restoration. Overall, translucency and mechanical properties of the lithium disilicate glass-ceramic may be influenced by the crystalline properties of the glass-ceramic during final crystallization and finishing and polishing procedures.

References:

Keywords: dental ceramics, x-ray diffraction, silicate crystals