Influence of cavity design on the biomechanics of direct composite resin restorations in Class IV preparations

Abstract

This study evaluated the effect of cavity design on stress distribution and fracture resistance of direct composite resin restorations in Class IV preparations. A finite element analysis (FEA) model of the maxillary central incisor with a Class IV cavity was established. Five model variations were studied: (i) a 1-mm bevel (ii) a 2-mm bevel, (iii) a plain chamfer, (iv) a stair-step chamfer, and (v) butt joints (a control configuration). All FEA variations modeled a tooth restored with composite resin loaded under 100 N at an angle of 45° to the longitudinal axis. The interfacial von Mises stress was evaluated. The FEA was complemented with an in vitro assessment. Fracture resistance of direct composite resin restorations was tested with a universal testing machine and fracture patterns were observed. Finite element analysis showed that stress in chamfer and stair-step chamfer models was more homogenously distributed, while stress in bevel models was relatively concentrated at lingual regions. Fracture resistance of a 1-mm bevel preparation was lower than for the 2-mm bevel, plain chamfer, and stair-step chamfer preparations, but was higher than for butt joints. The stair-step chamfer group presented the most favorable failure pattern. Considering biomechanics and esthetics, the present study indicates that the stair-step chamfer and 2-mm bevel should be recommended for clinical restoration.

Effect of the lingual margin configuration on the fracture strength of class IV resin based composite restorations under static loading

“…This type of combined in vitro mechanical test was also proposed by Coehlo et al 2008and Xu et al(2012) for Class IV resin based composite restorations bonded to human extracted teeth. Considering the integration of these two in vitro tests, this experiment design allows the investigator to evaluate the physical response and some properties of the tooth-restoration complex under critical conditions such as temperature fluctuations and controlled static forces.…”

“…Fracture strength and thermocycling are two complementary in vitro experiments to challenge teeth or materials, as reported in the literature (Coelho-de-Souza et al, 2008;Gandhi & Nandlal, 2006;Stellini et al, 2008;Xu H, 2012).…”

“…Finally, bevels can increase adhesion of a restoration when the bevel configuration can expose the enamel prism to the surface in a cross section, therefore increasing the surface adhesion area (Swanson, Feigal, Tantbirojn, & Hodges, 2008). Literature claims that bevels configuration for Class IV restorations can also withstand biomechanical forces during function on the lingual surfaces (Coelho-de-Souza et al, 2008) (Stellini et al, 2008) (Xu H, 2012).…”

“…Fracture and chipping of the restoration under stress on the incisal edge is reported in previous studies. In contrast to van Dijken and Pallesen (2010), other authors state that one of the possible reasons for chipping is the lack of mechanical support on the restoration (Xu H, 2012) (Coelho-de-Souza et al, 2008). Since Class IV restoration requires macro and micro mechanical support, factors have to be considered when designing the preparation, including: occlusion pattern of the patient, tooth substrate, adhesive protocol, adhesive system, and retentive design.…”

“…In-vitro studies by Coelho-de-Souza et al (2008), Stellini et all (2008) and Xu et al (2012) have been conducted to evaluate the fracture strength and stress distribution on specific margin preparations including facial chamfer, butt joint and different facial bevel designs. Coelho-de-Souza et al (2008), Xu et al (2012) all agree that beveling preparations on facial can improve the fracture strength of anterior resin based composites. However no previous studies in the literature have compared specifically lingual bevels and their effect on the fracture strength of resin based composites on human incisors when they support interincisal loads.…”