Bilateral treatment: A strategy for enhancing the mechanical strength of machinable veneers

Abstract 

Objective

To investigate the potential application of bilateral treatment of glazing plus staining in machinable veneer mechanical strength improvement.

Methods

Standard laminate specimens (n=105) were sliced from machinable ceramic blocks and divided into seven batches for further treatments: (1) batch C, standard specimens; (2) batch P, one specimen surface polished; (3) batch F, fired in glaze-firing-program without glaze; (4) batch G, fired with glaze on one surface; (5) batch S, fired with stain on one surface; (6) batch GA, fired with glaze on one surface, then re-fired in stain-firing-program without stain, and (7) batch GS, fired with glaze on one surface then fired with stain on the other side. The flexural strength of all specimens was tested with a three-point-bending test and the results statistically evaluated. Scanning electron microscopy (SEM) was used to analyze fractographs of bilateral treatment specimens. X-ray diffraction (XRD) analysis was performed to evaluate the influence of thermal annealing effect on strength improvement in bilateral treatment.

Results

The flexural strength of bilateral treated GS (143.23±14.02MPa) was significantly higher (P<0.05) than unilateral treated G (125.92±14.01MPa) and P (114.48±8.45MPa) and other batches, including C (100.11±6.65MPa), F (99.48±8.61MPa), S (119.28±19.34MPa) and AG (126.65±9.83MPa). SEM imaging showed that no underlying separation between the glaze–matrix or stain–matrix could be found in the fractured GS specimen. No evidence of Bragg diffraction peak broadening could be seen in XRD spectra compared with specimens from batches C and AG.

Significance

To improve machinable laminate strength, a bilateral treatment comprising staining and glazing gave higher strength than unilateral glazing or polishing alone. It was the surface layer effect achieved by glazing and staining, not the thermal annealing effect achieved during glaze and stain sintering, which contributed to the laminate strength improvement.

Keywords: Dental veneers, Computer aided design and computer aided manufacturing, Materials testing, Scanning electron microscopy, X-ray diffraction, Heat, Stains, Dental polishing, Dental stress analysis, Surface properties