Thermal-stress analysis of ceramic laminate veneer restorations with different incisal preparations using micro-computed tomography-based 3D finite element models

Highlights

• Transient thermal FE simulations were carried out.

• Butt joint design showed lower stresses than palatinal chamfer for each load type.

• Cold thermal load induced larger stresses than those of hot thermal load.

• Larger stresses were obtained on the buccal areas than palatinal areas.

• Insignificant stresses were obtained near pulp and root dentin regions.

Abstract

Main objective of this study is to investigate the thermal behavior of ceramic laminate veneer restorations of the maxillary central incisor with different incisal preparations such as butt joint and palatinal chamfer using finite element method. In addition, it is also aimed to understand the effect of different thermal loads which simulates hot and cold liquid imbibing in the mouth. Three-dimensional solid models of the sound tooth and prepared veneer restorations were obtained using micro-computed tomography images. Each ceramic veneer restoration was made up of ceramic, luting resin cement and adhesive layer which were generated based on the scanned images using computer-aided design software. Our solid model also included the remaining dental tissues such as periodontal ligament and surrounding cortical and spongy bones. Time-dependent linear thermal analyses were carried out to compare temperature changes and stress distributions of the sound and restored tooth models. The liquid is firstly in contact with the crown area where the maximum stresses were obtained. For the restorations, stresses on palatinal surfaces were found larger than buccal surfaces. Through interior tissues, the effect of thermal load diminished and smaller stress distributions were obtained near pulp and root-dentin regions. We found that the palatinal chamfer restoration presents comparatively larger stresses than the butt joint preparation. In addition, cold thermal loading showed larger temperature changes and stress distributions than those of hot thermal loading independent from the restoration technique.

Introduction

Development, testing and monitoring of biomedical devices on living organisms is an ethically problematic issue in medical studies as well as it is difficult and expensive to practice. Engineering tools such as finite element (FE) method has recently become an important multidisciplinary approach providing an alternative solution to these problems (Pałka et al., 2012). Although FE method has been using for a long time in engineering, it also has found a good application particularly in the biomechanical investigation of various dental related problems (Assunção et al., 2012).

Teeth are exposed to different mechanical loadings during the mastication process (Friedman, 1987; Matson et al., 2012) and thermal loadings during the hot and cold liquid/food intake (Lin et al., 2010b; Nawafleh et al., 2016). These daily thermal and mechanical loadings are highly prone to lead several defects on restorations such as fracture, microleakage and bond failure (Peumans et al., 2000). In addition, the balance among the biological components at oral cavity can be affected or even damaged due to the stresses caused by these loads. The variation of a tooth structure in microscopic and macroscopic level prevents to utilize a standard parameterization related to dental components, and hence desired experimental conditions usually cannot be achieved either in vivo or in vitro studies. Considering these troublesome in the experiments, FE approach enables the user to impose various environmental and material parameters in order to simulate the experimental conditions. The great majority of the FE based studies in literature focuses on the structural behavior of restorative treatments under mechanical loadings (Ausiello et al., 2001; Chang et al., 2015; Lazari et al., 2014; Rocha et al., 2011; Shinya et al., 2008; Sorrentino et al., 2007). However, there are much less number of FE based studies in literature examining the effects of thermal loadings (Cornacchia et al., 2010; Fenner et al., 1998; Magne et al., 1999b; Oskui et al., 2013; Pałka et al., 2012).

There is an increasing demand for non-metallic treatments in restorative dentistry that strongly encourage the development of ceramic based structures suitable for crowns, bridges or veneers (Sorrentino et al., 2009; Tinschert et al., 2000). Through improvement of innovative materials and minimally invasive techniques, ceramic laminate veneers have found an application in the restoration of fractured, deformed or unaesthetic teeth (Obradović-Đuričić et al., 2014). Ceramic veneer restoration is a commonly-used method to change the color, form, and position of an unaesthetic tooth by bonding a thin ceramic structure to the tooth using a proper luting resin cement and an adhesive layer (Peumans et al., 2000).

Many scientists recommend the ceramic laminate veneer restoration since it is a reliable and successful technique. While the veneer restoration preserves the maximum amount of healthy dental tissue during the restoration, it also provides a long-lasting survival rate. Aristidis and Dimitra (2002) and Peumans et al. (2004) reported respectively 98.4% and 92% success rates after five-years clinical trials. Moreover, Beier et al. (2012) investigated clinical quality and survival rate of anterior ceramic veneers, and estimated the survival rates as 94.4%, 93.5% and 82.93% after 5, 10 and 20 years period, respectively. In addition, a 93% success rate for 15 years of clinical trials was reported by Friedman (1998). While such high success of ceramic laminate veneer restoration in university-based clinical trials, it was also reported that multiple factors such as patient gender, age, geographical area, economic status and whether patient paid out-of-pocket significantly affects the survival of porcelain laminate veneers (Burke and Lucarotti, 2009). Considering these facts, frequent failures by fracture, fatigue or debonding were observed in porcelain laminate veneer restoration (Stappert et al., 2005). It was reported that the incisal margin and cervical areas particularly show a stronger tendency to yield to mechanical failures (Castelnuovo et al., 2000; Hahn et al., 2000). To improve mechanical resistance in associated areas, different preparation designs were considered in several studies (Friedman, 1987; Li et al., 2014). Therefore, comprehensive investigations are required to fully understand the effects of different preparation designs on the mechanical behavior of ceramic laminate veneers.

The main objective of this study is to investigate the biomechanical behavior of the ceramic laminate veneer restoration of a maxillary central incisor with different incisal preparations such as butt joint and palatinal chamfer designs under thermal loadings. To the best of our knowledge, there is no previous FE-based study in the literature focusing on this problem. Motivated by this fact, this study was initiated by a realistic micro-computed tomography (micro-CT) based modeling of complex dental tissues which provides more reliable and accurate predictions. Using micro-CT based models, transient thermal FE simulations were employed for different thermal loading conditions mimicking hot and cold liquid exposure. Variations in temperature and thermal stresses in different tissues were presented. In addition, results of sound tooth model under the same loading conditions were also presented in order to have a comparison on a solid ground.