Influence of coloring techniques on the surface characteristics and color stability of a monolithic zirconia ceramic.

STATEMENT OF PROBLEM: The color of monolithic zirconia restorations is obtained by presintering or postsintering coloring techniques. However, studies on the differences in surface characteristics and their influence on color stability are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the influence of shading and staining techniques for a zirconia ceramic on the surface characteristics and colorimetric parameters (color difference, translucency, and whiteness index) after exposure to coffee or red wine and then polishing. MATERIAL AND METHODS: Ceramic disks (N=30; Ø10×1mm) were allocated into 3 groups: preshaded-shaded by the manufacturer (IPS e.max ZirCAD MT, shade A2); manually shaded-unshaded zirconia (IPS e.max ZirCAD MT, bleaching shade-BL) colored by the brushing technique, before sintering; stained-unshaded zirconia (IPS e.max ZirCAD MT BL) colored by the staining technique, after sintering. Spectrophotometric color assessments ensured the same initial perceived color (Vita Classical A2) for specimens included in the study (∆E00<1.77 acceptability threshold). Surface characteristics were assessed by scanning electron microscopy and atomic force microscopy. The specimens were immersed in coffee (n=5) or red wine (n=5) for 12 and 24 days and subsequently polished. The data were statistically and descriptively analyzed for color differences (∆E00), translucency parameters (TP00), and whiteness indexes for dentistry (WID), considering acceptability and perceptibility thresholds. RESULTS: The shaded groups found an irregular ceramic surface with uniformly sized zirconia crystals. The stained group found a glass-covered smoother surface. Significant alterations in color parameters (∆E00, TP00, WID) were observed with immersion in pigmenting beverages (P<.001) both after 12 days, and after 24 days. The shaded specimens had greater color alterations after immersion but benefited from the polishing procedure, which reduced color differences below an acceptable threshold in comparison with the baseline. Stained specimens had lower color alterations after immersion, but the polishing protocol was detrimental as it whitened the ceramic by subsurface exposure. CONCLUSIONS: The coloring technique influences the surface characteristics of zirconia ceramic and also the color parameters after exposure to colored beverages and polishing.

Fit and fatigue behavior of CAD-CAM lithium disilicate crowns.

STATEMENT OF PROBLEM: New computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate glass-ceramics have been marketed. However, information concerning their biomechanical behavior is lacking. PURPOSE: The purpose of this in vitro study was to compare the fit and fatigue behavior of two recently introduced CAD-CAM lithium disilicate materials with the standard IPS e.max CAD ceramic and to investigate the effect of the thermal treatment for crystallization on crown fit. MATERIAL AND METHODS: Monolithic crowns (n=15) were milled from 3 CAD-CAM lithium disilicates: IPS e.max CAD (Ivoclar AG), Rosetta SM (Hass), and T-lithium (Shenzhen Upcera Dental Technology). Marginal and internal fit were evaluated using the replica technique before and after crystallization, and the fatigue behavior of the luted crowns was evaluated by the step-stress method. One-way ANOVA and the Tukey test were used to compare fit among the materials. Fatigue failure load was evaluated by the Kaplan-Meier and Mantel-Cox tests. The effect of crystallization on fit was evaluated with the paired t test (α=.05). RESULTS: Marginal fit was different between IPS e.max CAD (74 µm) and Rosetta SM (63 µm) (P=.02). T-lithium was similar to the other ceramics (68 µm) (P>.05). Occlusal internal space was similar among all materials (P=.69). Fatigue failure loads of Rosetta SM (1160 N) and T-lithium (1063 N) were similar to IPS e.max CAD (1082 N) (P>.05). The fatigue failure load of Rosetta SM was higher than that of T-lithium (P=.04). Crystallization reduced the axial internal space of all materials (P<.05) without significantly affecting marginal fit (P>.05). CONCLUSIONS: The fit and fatigue behavior of Rosetta SM and T-lithium were similar to that of IPS e.max CAD. Crystallization reduced the internal space of the crowns.

Efficacy of fluoride gel in arresting active non-cavitated caries lesions: a randomized clinical trial.

This study evaluated the efficacy of fluoride gel in arresting active non-cavitated caries lesions in permanent teeth. This randomized, triple-blind, placebo-controlled clinical trial randomized 100 schoolchildren aged 10.7 ± 2.2 years to test treatment (1.23% acidulated phosphate fluoride [APF] gel) or control treatment (placebo gel) for 4-6 applications at weekly intervals. Data collection included the visible plaque index, gingival bleeding index, visible plaque accumulation on the occlusal surfaces, eruption stage, and dental caries. The association between group and lesion arrestment was assessed using logistic regression, and estimates were adjusted for plaque accumulation over the lesion at baseline, surface type, and tooth type. Models were fitted using generalized estimating equations for accounting for the clustering of data (i.e., the same individual contributed > 1 lesion). Ninety-eight children completed the study (48 fluoride and 50 placebo). When all dental surfaces were analyzed, the likelihood of lesion arrestment was similar between both groups (p > 0.05). A secondary analysis including only the occlusal lesions in molars showed that for teeth under eruption, lesions receiving the 1.23% APF gel were about 3-fold more likely to become arrested than lesions receiving the placebo gel (OR = 2.85; 95%CI = 1.23-6.61; p = 0.01). No significant difference was detected for molars with complete eruption (p > 0.05). The benefit of fluoride gel for arresting non-cavitated caries lesions could not be identified by clinical assessment in this short-term trial. Notwithstanding, when the cariogenic challenge was greater (as on the occlusal surfaces of erupting molars), 1.23% APF gel treatment was an important tool for caries control.

Efficacy of fluoride gel in arresting active non-cavitated caries lesions: a randomized clinical trial

Abstract: This study evaluated the efficacy of fluoride gel in arresting active non-cavitated caries lesions in permanent teeth. This randomized, triple-blind, placebo-controlled clinical trial randomized 100 schoolchildren aged 10.7 ± 2.2 years to test treatment (1.23% acidulated phosphate fluoride [APF] gel) or control treatment (placebo gel) for 4-6 applications at weekly intervals. Data collection included the visible plaque index, gingival bleeding index, visible plaque accumulation on the occlusal surfaces, eruption stage, and dental caries. The association between group and lesion arrestment was assessed using logistic regression, and estimates were adjusted for plaque accumulation over the lesion at baseline, surface type, and tooth type. Models were fitted using generalized estimating equations for accounting for the clustering of data (i.e., the same individual contributed > 1 lesion). Ninety-eight children completed the study (48 fluoride and 50 placebo). When all dental surfaces were analyzed, the likelihood of lesion arrestment was similar between both groups (p > 0.05). A secondary analysis including only the occlusal lesions in molars showed that for teeth under eruption, lesions receiving the 1.23% APF gel were about 3-fold more likely to become arrested than lesions receiving the placebo gel (OR = 2.85; 95%CI = 1.23-6.61; p = 0.01). No significant difference was detected for molars with complete eruption (p > 0.05). The benefit of fluoride gel for arresting non-cavitated caries lesions could not be identified by clinical assessment in this short-term trial. Notwithstanding, when the cariogenic challenge was greater (as on the occlusal surfaces of erupting molars), 1.23% APF gel treatment was an important tool for caries control.