Biomechanical Properties of First Maxillary Molars with Different Endodontic Cavities: A Finite Element Analysis.

Purpose To analyze stress distribution in premolars restored with inlays or onlays using various materials. Materials and methods Three-dimensional maxillary premolar models of abutments were designed to include the following: 1) inlay with O cavity (O group), 2) inlay with MO cavity (MO group), 3) inlay with MOD cavity (MOD group), and 4) onlay (ONLAY group). A restoration of each inlay or onlay cavity was simulated using gold alloy, e.max ceramic, or composite resin for restoration. To simulate masticatory forces, a total of 140 N static axial force was applied onto the tooth at the occlusal contact areas. A finite element analysis was performed to predict the magnitude and pattern of stresses generated by occlusal loading. Results Maximum von Mises stress values generated in the abutment teeth of the ONLAY group were ranged from 26.1 to 26.8 MPa, which were significantly lower than those of inlay groups (O group: 260.3-260.7 MPa; MO group: 252.1-262.4 MPa; MOD group: 281.4-298.8 MPa). Maximum von Mises stresses generated with ceramic, gold, and composite restorations were 280.1, 269.9, and 286.6 MPa, respectively, in the MOD group. They were 252.2, 248.0, 255.1 MPa, respectively, in the ONLAY group. Conclusion The onlay design (ONLAY group) protected tooth structures more effectively than inlay designs (O, MO, and MOD groups). However, stress magnitudes in restorations with various dental materials exhibited no significant difference among groups (O, MO, MOD, ONLAY).

Stress distribution in premolars restored with inlays or onlays: 3D finite element analysis.

Introduction Cavity preparations of posterior teeth have been frequently associated with decreased fracture strength of the teeth. Choosing the correct indirect restoration and the cavity design when restoring the posterior teeth i.e., premolars was difficult as it involves aesthetic, biomechanical and anatomical considerations. Aim To evaluate the fracture resistance and failure pattern of three different cavity designs restored with monolithic zirconia. Materials and methods Human maxillary premolars atraumatically extracted for orthodontic reasons were chosen. A total of 40 teeth were selected and divided into four groups (n=10). Group I-Sound teeth (control with no preparation). Group II-MOD Inlay, Group III-Partial Onlay, Group IV-Complete Onlay. Restorations were fabricated with monolithic partially sintered zirconia CAD (SAGEMAX- NexxZr). All the 30 samples were cemented using Multilink Automix (Ivoclar) and subjected to fracture resistance testing using Universal Testing Machine (UTM) (Instron) with a steel ball of 3.5 mm diameter at crosshead speed of 0.5 mm/minute. Stereomicroscope was used to evaluate the modes of failure of the fractured specimen. Fracture resistance was tested using parametric one way ANOVA test, unpaired t-test and Tukey test. Fracture patterns were assessed using non-parametric Chi-square test. Results Group IV (Complete Onlay) presented highest fracture resistance and showed statistical significant difference. Group II (MOD Inlay) and Group III (Partial Onlay) showed significantly lower values than the Group I (Sound teeth). However, Groups I, II and III presented no significant difference from each other. Coming to the modes of failure, Group II (MOD Inlay) and Group III (Partial Onlay) presented mixed type of failures; Group IV (Complete Onlay) demonstrated 70% Type I failures. Conclusion Of the three cavity designs evaluated, Complete Onlay had shown a significant increase in the fracture resistance than the Sound teeth.

The Effect of Cavity Design on Fracture Resistance and Failure Pattern in Monolithic Zirconia Partial Coverage Restorations - An In vitro Study.

The restoration of endodontically treated teeth remains a challenge. The success of the final restoration depends mostly on the structure of the remaining tooth. Although the materials and procedures available today result in successful restoration of root-filled teeth via direct (in situ) techniques, one should first consider the amount of the coronal tooth structure remaining as well as the functional requirements. Restoration using direct composite resin is a good treatment option, but polymerization shrinkage is one of the major limitations of this material. The application of various base materials under the composite resin is an effective method. Covering the cusps with the restorative material is another option to save the remaining tooth structure; however, some materials may be unsuitable in stress-bearing areas. Materials applied to the orifice of a root canal also have a major effect on tooth biomechanics. This article reviews the direct restoration of endodontically treated teeth and discusses the current materials and techniques used for this purpose.

/pdf/direct-restoration-of-endodontically-treated-teeth-a-brief-3y7np8hjaw.pdf

Direct Restoration of Endodontically Treated Teeth: a Brief Summary of Materials and Techniques

This study was to compare the influence of glass fiber post placement and crown restoration on endodontically treated maxillary first premolars with severe NCCLs using three-dimensional finite element analysis and fracture resistance testing. G1, intact teeth. G2, teeth with artificial defect. G3, composite resin (CR). G4, CR and fiber post in buccal canal (FPB). G5, CR and fiber post in palatal canal (FPP). G6, CR and fiber posts in buccal and palatal canals (FPBP). G7, CR and crown (C). G8, CR, FPB, C. G9, CR, FPP, C. G10, CR, FPBP, C. Teeth in G2, G3, and G5 showed a similar stress concentration at the tip of the defect. The fracture resistance of G2 did not differ significantly from G3 and G5 (p>0.05) but differed significantly from that in other groups (p<0.05). The fractures in G4 were more favorable, and the difference of those in G1 from those in G7, G8, G9, and G10 was statistically significant (p<0.05). Restoration of root-filled maxillary premolars with severe NCCLs using fiber post in the buccal canal may be more efficacious than other restoration methods.

Fracture resistance and stress distribution of repairing endodontically treated maxillary first premolars with severe non-carious cervical lesions.

In the recent years, there has been an increasing interest in the research of biomechanical aspects of biomaterials and human tissues (1-3). Although studies conducted in vivo and in vitro have provided some of the answers in this field, dental and medical research is usually costly, and may be ethically questionable and time-consuming (4,5). Because of this, the use of numerical models and in vitro simulations became a valuable tool for saving time and money associated with laboratory and clinical research (6). Previous studies have reported different techniques for generating three-dimensional (3D) solid models of the teeth (7-9). Nowadays, technological development brings new possibilities for efficient generation of sophisticated 3D solid models. For example, using specialized software, these models can be generated based on computed-tomography (CT) scan data (5,10-12). In addition, the application of finite element analysis (FEA) allows calculation of stress and strain within tooth structure and biomaterials, which can hardly be measured in vivo (13).

Cavity design preparation has a great impact on stress values and fracture resistance of a tooth (7,14-16). It is a factor of a paramount importance, especially in cases of restoring maxillary premolars with extensive mesio-occlusal-distal (MOD) cavities (14,17,18). From the biomechanical point of view, different opinions have been reported on the most appropriate restorative procedure in such cases. Kuijs et al have found that ceramic, indirect resin composite and direct resin composite provide comparable fatigue resistance in a cusp replacing restorations (19). These findings were supported by clinical trials performed by van Dijken and Hickel et al (20,21). On the other hand, Soares et al found that MOD cavities restored with resin composite placed with direct technique attained better biomechanical performance than those restored with laboratory processed resin and ceramic restorations (15,16). Another study also confirmed that in comparison with ceramic restorations, resin composite restoration had higher fatigue resistance (17). As opposed to preparation for direct restoration, cavity preparation for indirect restorations requires removal of additional amount of tooth structure (22). The situation is the same with the cavity preparation for the amalgam (23). Since the quantity of the tooth structure removed while doing cavity preparation affects the biomechanical characteristics of the restored tooth, the use of adhesive direct restorations should be recommended for reinforcing the remaining dental structure (2,16).

When planning the design of MOD cavity preparation, cavity wall thickness and cusp reduction should be carefully considered. Usually, cusp reduction is recommended when cavity isthmus width is 2/3 of intercuspal width (7,24). Although this promotes more dental tissue reduction (25), it was shown that the reduction of cuspal height by 2.0 mm increases fracture resistance of a premolar when restored with direct resin composite (26,27). On the other hand, cavity wall thickness is not well defined. Macpherson et al found that 2.25 mm wall thickness is critical for restoring fracture resistance of tooth with MOD cavity (28), but another study, which investigated 1.0-3.0 mm wall thicknesses, reported that the thickness of remaining cavity walls was not relevant to fracture resistance (27).

The aim of this study was to investigate the effect of cavity design preparation on stress values in remaining tooth structures restored with resin composite. The null hypothesis was that stress values were not significantly influenced by the cavity wall thickness and cusp reduction.

/pdf/influence-of-cavity-design-preparation-on-stress-values-in-39ix2j1axs.pdf

Ivana Kantardzic

Papers

Influence of cavity design preparation on stress values in maxillary premolar: a finite element analysis.