An in vitro assessment of the strength of porcelain veneers dependent on tooth preparation

Effect of incisal preparation design on load-to-failure of ceramic veneers

OBJECTIVE

This in vitro study aims to evaluate load-to-failure of ceramic veneers with butt joint (BJ) and feathered edge (FE) incisal preparation designs, and to correlate these results to the failure mode of the restorations.

MATERIALS AND METHODS

One hundred and forty-eight typodont teeth (customized Nissin A25A-UL19B) were divided into two different preparation configurations BJ and FE and two different loading angulations, 0° and 20°. Lithium disilicate ceramic veneers (IPS e.max CAD, Ivoclar Vivadent) were milled using computer-aided-design-and-computer-aided-manufacturing (CAD/CAM) techniques. Veneers were bonded to typodont teeth with resin cement (IPS Variolink Esthetic, Ivoclar Vivadent). Each group was loaded at the incisal edge using an Instron Universal Testing Machine at a crosshead speed of 0.01 mm/s till failure.

RESULTS

Pairwise comparison showed veneers from the BJ groups had a significantly higher load-to-failure value compared to the FE groups. Veneers with a FE preparation design loaded at 20° angulation had the lowest load-to-failure value.

CONCLUSIONS

Within the limitations of the present study, both incisal preparation designs and loading angulations have significant effects on the load-to-failure values of ceramic veneers. BJ group exhibits a significantly higher load-to-failure value compared to the FE group.

CLINICAL SIGNIFICANCE

BJ incisal preparation is preferred over FE preparation design.

Influence of Preparation Depth and Design on Stress Distribution in Maxillary Central Incisors Restored with Ceramic Veneers: A 3D Finite Element Analysis

PURPOSE

To evaluate the influence of different preparation designs and depths on the stress field developed in maxillary central incisors restored with veneers made with different ceramic materials using finite element analysis (FEA).

MATERIALS AND METHODS

A linear static three-dimensional finite element analysis model was used with the aid of reverse engineering to develop digital models of maxillary central incisors restored with ceramic veneers, according to two different preparation depths (thin vs deep) and two different preparation designs (feather edge vs butt joint). Three ceramic systems were tested: (i) feldspathic porcelain, (ii) heat pressed glass ceramic IPS Empress 2 (Ivoclar Vivadent AG), and (iii) heat pressed glass ceramic IPS e.max-Press (Ivoclar Vivadent AG). Each model was subjected to a compressive force of 200N applied to the palatal surface 2 mm below the incisal edge. The longitudinal axis of the restored tooth formed an angle of 130^o with the direction of the force. The biomechanical behavior of the different models was examined according to the von Mises stress criterion. Statistical analysis was performed using nonparametric confidence interval estimation using bootstrapping.

RESULTS

The maximum observed stress values were calculated and found to be similar between prepared and intact teeth. The cervical margin of the veneers displayed the highest von Mises stress values. Irrespectively of the depth and preparation design, the biggest von Mises stress values were observed at the veneer structures with the following order: (i) IPS Empress 2, (ii) IPS e.max-Press, (iii) feldspathic (p = 0.001). Preparation depth resulted in statistically significant differences (p = 0.001) in the stress distribution in the majority of tested structures. As the preparation depth was increased, the stresses within the veneer structure and the tooth structures were decreased. No statistically significant differences were detected in the stresses among the different restored models, when the preparation design was considered.

CONCLUSIONS

This FEA study suggests that ceramic veneers could restore the biomechanical behavior of prepared central incisors and made it similar of that of an intact tooth. Regardless of the preparation depth and design and the ceramic system used, the cervical margin of ceramic veneers presents the highest von Mises stress values. When feldspathic porcelain was compared with lithium disilicate (IPS e.max Press), the latter displayed the lowest transfer of stresses to dental tissues. An increase in preparation depth resulted in a statistically significant stress decrease in both the veneer and the tooth.

Clinical performance of pressable glass-ceramic veneers after 5, 10, 15, and 20 years: A retrospective case series study

OBJECTIVES

To evaluate the long-term clinical performance and survival rate of pressable lithium-disilicate glass-ceramic veneers (LDSVs).

MATERIALS AND METHODS

A total of 413 LDSVs were bonded to anterior and posterior teeth by three experienced clinicians between 1998 and 2012. The LDSVs were examined for color/ esthetic match of the glass-ceramic surface (esthetic evaluation), fracture rate, marginal discoloration (staining of the luting cement), and marginal integrity (including caries, clinical evaluation). For clinical and esthetic evaluations, the modified United States Public Health Services (USPHS) score was used in this study. The success rate was determined with a Kaplan-Meier survival analysis.

RESULTS

The mean observation time was 11.33 ± 4.85 years. There was no loss to follow-up, all restorations were accounted for in the final analysis. The probability of survival of the 413 veneers was 98% after 5 years, 95% at 10 years, 91% at 15, and 87% at 20 years, indicating a very low clinical failure rate. Of the 413 restorations, complications were occurred in 15 (3.63%) of all restorations, and fractures and debonding in 6 (1.45%) and 9 (2.18%), respectively.

CONCLUSIONS

The LDSVs showed high survival rate and very good results for color match and anatomic form and marginal integrity in the long-term analysis.

CLINICAL SIGNIFICANCE

The long-term performance of LDSVs can be considered as highly favorable when carefully planned.