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

Abstract

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-designand-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. K E Y W O R D S butt joint, feathered edge, load-to-failure, preparation design, veneer preparation 1 | INTRODUCTION Ceramic veneers have become a popular treatment modality due to their conservative and esthetic nature and clinical performance. 1-3Compared to resin composite veneers, ceramic veneers are stronger and more durable, as they are less susceptible to wear, marginal fracture, discoloration, staining, and plaque accumulation. 4-6 A recent systematic review and meta-analysis of the clinical outcome of ceramic veneers showed that both feldspathic porcelain and glass-ceramic laminate veneers have high survival rates. 7 Glass-ceramic laminate veneers show a slightly higher survival rate than feldspathic porcelain veneers, 94% vs 87%, respectively. The complications reported were fracture/chipping (4%), debonding (2%), severe marginal discoloration (2%), endodontic problems (2%), and secondary caries (1%). 7 A recent retrospective clinical study conducted in a university setting by two academic staff with a follow-up of 20 years indicated that ceramic fracture was the main reason for failure of ceramic veneers. 1 This finding is also supported by numerous earlier clinical studies. 3,8-16

Stress distribution within the ceramic veneer‐tooth system with butt joint and feathered edge incisal preparation designs

“…The FE veneer preparation design incorporated a buccal reduction of 0.5‐mm thickness which does not extend past the proximal contact zone. The BJ typodont tooth has an additional 1.5 mm incisal reduction similar to previous in‐vitro study 24 (Figure 1).…”

“…Three typodont teeth representing maxillary left central incisors, of which one with no veneer preparation (control), one with FE veneer preparation design (A252A‐UL 19B), and the other had a BJ veneer preparation design (modified A252A‐UL 19B), were obtained from Nissin Dental Products Inc. (Kyoto, Japan) 24 . The FE veneer preparation design incorporated a buccal reduction of 0.5‐mm thickness which does not extend past the proximal contact zone.…”

“…The typodont teeth with FE and BJ veneer preparations were scanned using Ceramill Map 400+ (Amann Girrbach AG, Koblach, Austria). The FE and BJ incisal preparation designs were then designed using the Ceramill Mind CAD design software (Amann Girrbach AG) 24 . Each design has a designated cement gap of 50 μm.…”

“…The surface was then primed using Monobond Plus (Ivoclar Vivadent) and allowed to react for 60 seconds before air dispersion 26 . After lightly sandblasting the cementation surface of photoelastic model with 50 μm aluminum oxide particles at 0.2 MPa (2 bar) pressure for 10 seconds, the ceramic veneers were cemented onto the photoelastic models using a dual‐cure cement to ensure consistency with the methodology to the previous in‐vitro study (Variolink‐Esthetic DC, Ivoclar Vivadent) 24,26 . The veneers were seated on the photoelastic models by one operator using sustained finger pressure and any excess cement was removed 27 .…”

“…The purpose of this investigation was to study the stress distribution within the veneer‐tooth system with FE and BJ incisal preparation designs at two loading angulations using a photoelastic stress analysis technique, and to correlate these results to our previous published load‐to‐failure study of these restorations 24 …”