Finite Element Stress Analysis of Diastema Closure with Ceramic Laminate Veneers

The Effect of Abutment Angulation and Crown Material Compositions on Stress Distribution in 3-Unit Fixed Implant-Supported Prostheses: A Finite Element Analysis

Objective

The aim of this study was to evaluate influence of abutment angulation and restoration material compositions on the stress pattern in dental implants and their surrounding bone.

Materials and Methods

In this finite element study, the six different solid 3D models of “mandibular 3-unit fixed implant-supported prostheses” were analyzed. In all of these models, a straight abutment was used for anterior implants at the second premolar site, and in order to posterior implant at the second molar site, abutments with three different angles (straight, 15, and 20°) were used. Also, two different restoration material compositions (porcelain fused to base metal (PFBM) and porcelain fused to noble metal (PFNM)) were considered for fixed implant supported restorations. A 450 N static force was exerted in a straight manner along the longitudinal axis of the anterior implant in a tripod, and the stress distribution was measured based on the restoration materials and abutment angulations of the models in the 3 sites of cortical, cancellous bone, and fixtures. The simulation was performed with ABAQUS 6.13 Software.

Results

In all models, stress values in surrounding cortical bone were more than in spongy bone. Maximum stress levels in an anterior abutment-implant complex were seen in models with angled implants. In models with parallel implants, the stress level of a molar straight abutment-implant complex was less than that of premolar straight ones. In an angled posterior abutment-implant complex, less stress level was detected compared to straight ones. In all PFNB models, stress values were slightly more and distributed in a wider area of premolar straight abutments.

Conclusion

Increasing an abutment angle, increases stress in surrounding bone and straight implant-abutment combination. It seems that the crown material composition affects stress distribution of the implant-abutment combination but does not affect stress distribution of surrounding bone.

Influence of post-core material and cement peculiarities on stress of post-cores under ultrasonic vibration: a three-dimensional finite element analysis

AIM

To analyse the effect of post-core, and cement materials and thickness of the cement lute on the stress in post-core systems under ultrasonic vibration at different frequencies and amplitudes using three-dimensional finite element analysis.

METHODOLOGY

Eight three-dimensional finite element models of a maxillary central incisor with post-cores were established. Two post-core materials (Au and Ni-Cr alloys), two cements (glass ionomer (GI) and zinc phosphate (ZP)) and two cement layer thicknesses (50 and 150 μm) were considered. Vibration loads were applied near the neck on the buccal side of the core at frequencies of 10-40 kHz and amplitudes of 10-50 μm. The maximum shear stress of the cement layer and maximum principal stress of the roots and their distributions were investigated.

RESULTS

The stresses on cements and roots increased with an increase in the frequency and amplitude of the vibration load and elastic modulus of the cements, and decreased with increasing thickness of the cement layer and elastic modulus of the post-core. Maximum cement stress was observed on the contralateral upper part of the loading side, whereas the maximum root stress was found on the ferrule where the load was applied.

CONCLUSIONS

In this simulated model, the frequency and amplitude of ultrasound needed to remove a post-core were positively related to the elastic modulus of the post-core and thickness of the cement layer and negatively related to the elastic modulus of the cements.

Evaluation of Stress Distribution in Tooth-Supported Fixed Dental Prostheses Made of Translucent Zirconia with Variations in Framework Designs: A Three-Dimensional Finite Element Analysis

PURPOSE

To evaluate the influence of the framework designs on the stress distribution within tooth-supported partially veneered fixed dental prostheses (FDPs) made of translucent zirconia under simulated loads using a three-dimensional finite element analysis (3D-FEA).

MATERIAL AND METHODS

For a linear 3D-FEA, simplified 3D solid models of prepared abutment teeth (first premolar and first molar) with different 3-unit FDPs were created. The models with different FDP designs-monolithic zirconia (control); semi-monolithic zirconia with 0.3 mm veneer thickness (SM0.3); semi-monolithic zirconia with 0.5 mm veneer thickness (SM0.5); semi-monolithic zirconia with 0.5 mm veneer thickness supported with cap design (SMC), and semi-monolithic zirconia with 0.5 mm veneer thickness supported with wave design (SMW)-were analyzed using 3D-FEA. The elastic properties of the components (bone, dentine, cement, translucent zirconia, and veneering porcelain) were obtained from the published data for FEA. Simulated static loading forces (300 N) were applied at 10° oblique direction over six points in the occlusal surfaces of the FDPs. Maximum principal stress, shear stress, and safety factor were calculated and analyzed among the different models.

RESULTS

Semi-monolithic with cap design showed the smallest maximum principal stress levels in the veneering porcelain compared to all other models (SM0.3, SM0.5, SMW). The SM0.3 had lower maximum principal stress levels in the veneering porcelain compared to SM0.5. Regarding stresses in the zirconia framework, all models had comparable results in maximum principal tensile stresses, except SMW had a lower value. Maximum principal stress levels were located in the veneer component of SM0.3, SM0.5, and SMW, whereas, such levels were observed in the cervical areas of the zirconia frameworks of SMC and control. The SM0.3 had the highest maximum shear stress levels at the zirconia-veneer interface, while SMW had the lowest shear values. The 3D-FEA models with different FDP designs showed different minimum safety factor levels.

CONCLUSIONS

Framework and veneer designs play a significant role in the stress distribution of the partially veneered zirconia FDPs under loading. The FDPs with zirconia frameworks with cap design minimize the maximum principal tensile stress in the veneering porcelain. The FDPs with 0.3-mm-veneering porcelain show low maximum principal tensile stress in the veneering porcelain, but highest maximum shear stress at the zirconia-veneer interface. The FDPs with wave design of zirconia frameworks minimize the maximum shear stress considerably.

Validation of in-vitro tests of zirconia-ceramic inlay-retained fixed partial dentures: A finite element analysis

OBJECTIVE

In the past, discrepancies between laboratory results and clinical behavior have been observed for all-ceramic restorations. This analysis of fracture resistance of zirconia-based inlay-retained fixed partial dentures (IRFPDs) aimed at identifying correlations between an in-vitro test setup and the clinical situation. The effects of tooth material, tooth mobility, restoration design, load direction, and different cements were taken into account.

METHODS

The in-vitro test model and IRFPD were reverse engineered (Geomagic DesignX) and meshed predominantly with hexahedral elements (approx. 230,000 elements). Homogenous, linear-elastic behavior was assumed for all materials. On the basis of the calculated stresses (ANSYS 18.2) and already known strength distributions for the restorative materials fracture resistance of the complete restoration and force at initial damage (fracture within the veneer) was estimated on the basis of the principal stress hypothesis. Differences depending on the assumed clinical situation and effects of different variables on fracture resistance were evaluated.

RESULTS

All variables tested in the finite element analysis affected the calculated fracture resistance of the IRFPD. Use of resin teeth led to an underestimation of fracture resistance by up to -57%, whereas fracture resistance of IRFPDs on metal abutment teeth was close to the clinical reference (-6% to +15%). Good correlation between the clinical scenario and that using metal teeth could only be achieved when the natural resilience of the abutment teeth was simulated.

SIGNIFICANCE

When testing fracture resistance of zirconia-based IRFPDs, metal abutment teeth in combination with simulated tooth resilience can reflect the clinical situation accurately.

Effects of differing thickness and mechanical properties of cement on the stress levels and distributions in a three-unit zirconia fixed prosthesis by FEA

PURPOSE

This study analyzed the impact of cement layer thickness (CLT) and Young's modulus of the cement on the stress distribution in a three-unit zirconia fixed dental prosthesis (FDP) and in the bonding interfaces by means of finite element method.

MATERIALS AND METHODS

A 3D finite element model was created from a stylized three-unit FDP-cement-tooth/socket system. The pulp and the periodontal ligament were not modeled. Two CLTs (50 and 150 μm) and two values of Young's modulus of the cement (4.9 for simulation of resin cement, 20.1 GPa for glass ionomer cement) were evaluated. A 500 N static vertical load was applied at the central fossa of the pontic to calculate maximum displacement in the framework and maximum principal stresses in both framework and bonding interfaces.

RESULTS

The simulated results showed that the Young's modulus affected stress occurrence only in the cement interface. Lower moduli were associated with less stress. The thickness of the cement layer influenced the maximum principal stress in both the FDP and in the cement layer itself. Thicker cement layers led to higher stresses in the framework but lower stresses in the cement layer. Maximum displacement was less dependent of the investigated variables. During all trials, the location of the maximum principal stress did not change. Maximum stress concentrations were observed at the lower embrasures of the connector areas and in the bonding layer at the cervical margin of the preparation.

CONCLUSIONS

Choosing cements with a preferably low Young's modulus in combination with a CLT as small as possible might increase the clinical survival rate.