The development and testing of glaze materials for application to the fit surface of dental ceramic restorations

ObjectivesThe aims of the study were to develop and test overglaze materials for application to the fit surface of dental ceramic restorations, which could be etched and adhesively bonded and increase the flexural strength of the ceramic substrate.MethodsThree glaze materials were developed using commercial glass powders (P25 and P54, Pemco, Canada). P25 (90 wt%) was mixed with P54 (10 wt%) to produce (P25/P54). P54 (90 wt%) was mixed with P25 (10 wt%) to produce (P54/P25). P25 (90 wt%) was mixed with 10 wt% of an experimental glass powder (P25/frit). Eighty-two disc specimens (14 mm × 2 mm) were produced by heat pressing a leucite glass–ceramic and were sandblasted with 50 μm glass beads. Group 1 control specimens (10) were sandblasted. Groups 2–4 (10 per group) were coated using P25/frit (Group 2), P25/P54 (Group 3) and P54/P25 (Group 4) overglazes before sintering. Groups 1–4 were etched for 2 min using 9.5% HF (Gresco, USA). Composite cylinders (Marathon^® v, Den-Mat) were light cured and bonded to the glazed and prepared disc surfaces and groups water stored for 8 days. Groups were tested using shear bond strength (SBS) testing at 0.5 mm/min. Disc specimens (42) were tested using the biaxial flexural strength (BFS) test at a crosshead speed of 0.15 mm/min. Group 1 was tested as sandblasted (21) and Group 2 (21) after coating the tensile surface with P25/frit. Xrd, Eds and Sem analyzes were carried out.ResultsMean SBS (MPa ± S.D.) were: Group 1: 10.7 ± 2.1; Group 2: 9.8 ± 1.9; Group 3: 1.8 ± 1.0 and Group 4: 2.6 ± 1.7. Groups 1 and 2 were statistically different to Groups 3 and 4 (p < 0.001), but there was no difference between Groups 1 and 2 and 3 and 4 (p > 0.05). The mean BFS (MPa ± S.D.) of the overglazed Group 2 (200.2 ± 22.9) was statistically different (p < 0.001) to Group 1 (150.4 ± 14.3).SignificanceThe P25/frit overglaze significantly (p < 0.001) increased the biaxial flexural strength of the leucite glass–ceramic substrate and produced comparable shear bond strengths to an etched and bonded control. The application of etched overglaze materials to dental glass–ceramic and ceramic substrates may be useful in adhesive dentistry.     

Crystallization and flexural strength optimization of fine-grained leucite glass-ceramics for dentistry

Objectives

Leucite glass-ceramics with fine-grained leucite crystals promote improved mechanical strength and increased translucency. The objectives of the study were to optimize the microstructure of a fine-grained leucite glass-ceramic in order to increase its flexural strength and reliability as measured by its Weibull modulus.

Methods

Glass was prepared by a melt-derived method and ground into a powder (M1A). The glass crystallization kinetics were investigated using high temperature XRD and DSC. A series of two-step heat treatments with different nucleation/crystal growth temperatures and holds were carried out to establish the optimized crystallization heat treatment. Glass-ceramics were characterized using XRD, SEM and dilatometry. The glass-ceramic heat treated at the optimized crystallization parameters (M1A_opt) was both sintered (SM1A_opt) and heat extruded (EM1A_opt) into discs and tested using the biaxial flexural strength (BFS) test.

Results

High temperature XRD suggested leucite and sanidine crystallization at different temperatures. Optimized crystallization resulted in an even distribution of fine leucite crystals (0.15 (0.09) μm²) in the glassy matrix, with no signs of microcracking. Glass-ceramic M1A_opt showed BFS values of [mean (SD), MPa]: SM1A_opt = 252.4 (38.7); and EM1A_opt = 245.0 (24.3). Weibull results were: SM1A_opt; m = 8.7 (C.I. = 7.5-10.1) and EM1A_opt; m = 11.9 (C.I. = 9.3-15.1). Both experimental groups had a significantly higher BFS and characteristic strength than the IPS Empress Esthetic glass-ceramic, with a higher m value for the EM1A_opt material (p < 0.05).

Significance

A processable fine-grained leucite glass-ceramic with high flexural strength and improved reliability was the outcome of this study.