Full coverage crowns for rehabilitation of MIH affected molars: 24 month randomized clinical trial

BACKGROUND

Teeth affected with severe molar incisor hypomineralization (MIH) require extensive restorations, which do not last for a long time and often require treatment in the form of onlays or full coverage restorations.

AIM

To evaluate and compare the clinical performance of zirconia, lithium disilicate, and cast metal crowns as full-coverage restorations on MIH-affected first permanent molars (FPMs).

METHODS

60 MIH affected FPMs requiring full-coverage crowns were identified in children aged 8-15 years and were randomly allocated to the three treatment groups according to the type of full coverage restoration received using block randomization technique. After an adequate removal of the MIH defect and restoration with composite resin, the tooth preparation was done followed by fabrication of crown and its cementation using resin cement. The intergroup comparison was done on the basis of USPHS criteria, gingival, plaque scores, patient and parents acceptance through a visual analog scale to decipher their clinical performance at 6, 12, 24 months.

RESULTS

After 24 months, the crowns showed similar clinical success in terms of the criterias used to compare their clinical performance. The retention, marginal adaptation, relief from hypersensitivity, proximal contact, gingival health with no statistically significant difference among the three groups.

CONCLUSION

Based on the observations, Lithium disilicate, Zirconia and full cast metal crowns showed similar clinical success in rehabilitation of First permanent molars with severe MIH over 24 months of evaluation. The clinical success is not influenced by the material of the restoration. However, prospective studies with a longer follow-up are required to reach a more definitive conclusion.

Edge chipping and flexural resistance of monolithic ceramics

OBJECTIVE

Test the hypothesis that monolithic ceramics can be developed with combined esthetics and superior fracture resistance to circumvent processing and performance drawbacks of traditional all-ceramic crowns and fixed-dental-prostheses consisting of a hard and strong core with an esthetic porcelain veneer. Specifically, to demonstrate that monolithic prostheses can be produced with a much reduced susceptibility to fracture.

METHODS

Protocols were applied for quantifying resistance to chipping as well as resistance to flexural failure in two classes of dental ceramic, microstructurally-modified zirconias and lithium disilicate glass-ceramics. A sharp indenter was used to induce chips near the edges of flat-layer specimens, and the results compared with predictions from a critical load equation. The critical loads required to produce cementation surface failure in monolithic specimens bonded to dentin were computed from established flexural strength relations and the predictions validated with experimental data.

RESULTS

Monolithic zirconias have superior chipping and flexural fracture resistance relative to their veneered counterparts. While they have superior esthetics, glass-ceramics exhibit lower strength but higher chip fracture resistance relative to porcelain-veneered zirconias.

SIGNIFICANCE

The study suggests a promising future for new and improved monolithic ceramic restorations, with combined durability and acceptable esthetics.

Effect of polishing and glazing on the color and spectral distribution of monolithic zirconia

PURPOSE

The aim of this study was to evaluate the effect of polishing and glazing on the color and spectral distribution of monolithic zirconia.

MATERIALS AND METHODS

Forty-five monolithic zirconia specimens (16.3 mm × 16.4 mm × 2.0 mm) were fabricated and divided into 5 groups according to the number of A2-coloring liquid applications (Group I to V). Each group was divided into 3 subgroups according to the method of surface treatments (n=3): N: no treatment; P: polishing; G: glazing. Color and spectral distribution of five different areas of each specimen were measured according to CIELAB color space in the reflectance mode relative to the standard illuminant D65 on a reflection spectrophotometer. Data were analyzed using one-way ANOVA followed by Tukey's HSD test, Pearson correlation and regression analysis (α=.05).

RESULTS

There was a significant difference in CIE L^* between Subgroup N and P, and in CIE b^* between Subgroup P and G in each group. Spectral reflectance generally decreased in Subgroup P and G in comparison with Subgroup N. Color differences between Subgroup P and G were within the perceptibility threshold (ΔE^*_ab< 3.7) in most groups. Highly significant correlation was found between CIE b^*and each subgroups as the number of coloring liquid applications increased (R²>0.88, P<.001).

CONCLUSION

A perceptible color difference can be detected after polishing of monolithic zirconia. Polishing decreases the lightness, and glazing also decreases the lightness, but increases the yellowness of monolithic zirconia.