A preliminary three-dimensional finite element analysis of mandibular implant overdentures

Single implant retained overdentures: Evaluation of effect of implant length and diameter on stress distribution by finite element analysis

PURPOSE

Single implant retained mandibular overdenture treatment has been shown to be a minimally invasive, satisfactory, and cost-effective option for edentulous individuals. However, the impact of implant diameter and length on stress distribution at the implant, bone, and other components in this treatment approach remains unclear. The purpose of this 3D finite element analysis was to evaluate the effect of implant length and diameter on equivalent von Mises stress and strain distribution in single implant retained overdentures at bone, implant, and prosthetic components.

MATERIALS AND METHODS

Nine models were constructed according to implant lengths (L) (8, 10, 12 mm) and diameters (D) (3.3, 4.1, 4.8 mm). The implants were positioned axially, in the midline of the mandible. A 3D model of the edentulous mandible was created from a computed tomography image. A single implant, abutment with insert PEEK and a housing, acrylic denture, and Co-Cr framework were modeled separately. In the ANSYS software program, occlusal loads were applied as 150 N, bilaterally vertical direction, or unilaterally oblique direction to the first molar. Minimum principal stress values were evaluated for bone and equivalent von Mises stress and strain values were evaluated for implant and prosthetic components.

RESULTS

Von Mises stress values for vertical load increased at implant, housing, and insert PEEK for all groups when the length of the implant increased. When oblique load was applied, 3.3 mm diameter implant groups showed maximum von Mises stress values for implants, cortical bone, cancellous bone, and housing among all groups. A minimum stress level for implant was found in D4.1/L8 group. Regarding the insert PEEK, strain values were found to be higher as the diameter of the implant increased both for vertical and oblique loads. Cortical bone showed higher minimum principal stress values as compared to cancellous bone under both loading conditions.

CONCLUSIONS

The 3.3 mm diameter implant groups exhibited the highest von Mises stress and strain values for both loading conditions at the implant. The diameter of the implant had a greater impact on stress and strain levels at the implant site compared to length. For vertical loading, stress value increased at implant, housing, and PEEK when the length of the implant increased.

Radiographic determination of trabecular bone change in 2- and 4-implant-supported overdenture prostheses

OBJECTIVE

The aim of this study was to compare the fractal dimensions (FDs) of peri-implant trabecular bone around 2-implant-supported overdentures with the FDs around 4-implant-supported overdentures at the time of implant placement (T0) and 1 year after placement (T1).

STUDY DESIGN

Standardized regions of interest were chosen at sites mesial and distal to 60 mandibular implants: 20 in 2-implant-supported prostheses (group 1) and 40 in 4-implant-supported prostheses (group 2), for a total of 120 measurements. FD values were calculated by using ImageJ software with the box-counting method.

RESULTS

The mean FD values of peri-implant bone were significantly lower at T1 than at T0 in both groups (P ≤ .001). Differences between the groups in the decrease in FD between T0 and T1 were mostly insignificant.

CONCLUSIONS

Within the limitations of this study, 2-implant and 4-implant-supported overdentures exhibited the same degree of reduction in peri-implant FD over time, suggesting similar risk of failure because FD is related to implant stability. Depending on the patient's residual ridge status and other factors, the 2-implant-supported overdenture may be preferred because it requires less surgery and is less costly.

Effect of supporting implants inclination on stability of fixed partial denture: A finite element study

The aim of this finite element study was to analyze effect of supporting implants inclination on stress distribution in the bone for a four-unit fixed partial denture. A three-dimensional finite element model of mandibular molar section of the bone to receive implants was constructed. Three implant-supported fixed partial dentures, with null, moderate and wide tilting, of 0°, 15° and 30° implant inclinations, respectively, were modeled. A mechanical load of 10 MPa was applied in coronal–apical direction on bridge framework at the regions of crowns positions. The finite element analysis was performed, and von Mises stress levels were calculated. Peak stress concentration in the cortical bone was observed mostly around the implant necks, in inter-implants line. There was favorable stress distribution during loading, with peak stress being 90.04 MPa for 0°, which decreased to 54.33 MPa for 15° and 46.36 MPa for 30° inclination. The supporting implants inclination in fixed partial denture plays an important role in stress distribution and may be helpful in preventing bone loss and implant failure. This phenomenon is likely to be more pronounced in bones of poor quality. Within the limitation of this study, it seems that the inclination of implants in fixed partial denture has a favorable effect on stress distribution pattern values around the supporting implants.

Mandibular Implant-supported Overdentures: Prosthetic Overview

Implant-supported overdentures are becoming the treatment of choice for the completely edentulous mandible. They significantly improve the quality of life in edentulous patients. For this review article, the literature was searched to identify pertinent studies. No meta-analysis was conducted because of high heterogeneity within the literature. Accordingly, in this review article, the author provides an update on implant-supported mandible overdentures with regard to the number of implants, type of loading, stress-strain distribution, mode of implant-to-denture attachment, occlusal considerations and complications.

Stress analysis of irradiated human tooth enamel using finite element methods

The objectives of this project were to use finite element methods to determine how changes in the elastic modulus due to oral cancer therapeutic radiation alter the distribution of mechanical stresses in teeth and to determine if observed failures in irradiated teeth correlate with changes in mechanical stresses. A thin slice section finite element (FE) model was constructed from micro CT sections of a molar tooth using MIMICS and 3-Matic software. This model divides the tooth into three enamel regions, the dentin-enamel junction (DEJ) and dentin. The enamel elastic modulus was determined in each region using nano indentation for three experimental groups namely - control (non-radiated), in vitro irradiated (simulated radiotherapy following tooth extraction) and in vivo irradiated (extracted subsequent to oral cancer patient radiotherapy) teeth. Physiological loads were applied to the tooth models at the buccal and lingual cusp regions for all three groups (control, in vitro and in vivo). The principal tensile stress and the maximum shear stress were used to compare the results from different groups since it has been observed in previous studies that delamination of enamel from the underlying dentin was one of the major reasons for the failure of teeth following therapeutic radiation. From the FE data, we observed an increase in the principal tensile stress within the inner enamel region of in vivo irradiated teeth (9.97 ± 1.32 MPa) as compared to control/non-irradiated teeth (8.44 ± 1.57 MPa). Our model predicts that failure occurs at the inner enamel/DEJ interface due to extremely high tensile and maximum shear stresses in in vivo irradiated teeth which could be a cause of enamel delamination due to radiotherapy.

Effect of implant- and occlusal load location on stress distribution in Locator attachments of mandibular overdenture. A finite element study

PURPOSE

The aim of this study is to evaluate and compare the stress distribution in Locator attachments in mandibular two-implant overdentures according to implant locations and different loading conditions.

MATERIALS AND METHODS

Four three-dimensional finite element models were created, simulating two osseointegrated implants in the mandible to support two Locator attachments and an overdenture. The models simulated an overdenture with implants located in the position of the level of lateral incisors, canines, second premolars, and crossed implant. A 150 N vertical unilateral and bilateral load was applied at different locations and 40 N was also applied when combined with anterior load at the midline. Data for von Mises stresses in the abutment (matrix) of the attachment and the plastic insert (patrix) of the attachment were produced numerically, color-coded, and compared between the models for attachments and loading conditions.

RESULTS

Regardless of the load, the greatest stress values were recorded in the overdenture attachments with implants at lateral incisor locations. In all models and load conditions, the attachment abutment (matrix) withstood a much greater stress than the insert plastic (patrix). Regardless of the model, when a unilateral load was applied, the load side Locator attachments recorded a much higher stress compared to the contralateral side. However, with load bilateral posterior alone or combined at midline load, the stress distribution was more symmetrical. The stress is distributed primarily in the occlusal and lateral surface of the insert plastic patrix and threadless area of the abutment (matrix).

CONCLUSION

The overdenture model with lateral incisor level implants is the worst design in terms of biomechanical environment for the attachment components. The bilateral load in general favors a more uniform stress distribution in both attachments compared to a much greater stress registered with unilateral load in the load side attachments. Regardless of the implant positions and the occlusal load application site, the stress transferred to the insert plastic is much lower than that registered in the abutment.

Influence of Implant Positions and Occlusal Forces on Peri-Implant Bone Stress in Mandibular Two-Implant Overdentures: A 3-Dimensional Finite Element Analysis

The aim of this study was to evaluate and compare the bone stress around implants in mandibular 2-implant overdentures depending on the implant location and different loading conditions. Four 3-dimensional finite element models simulating a mandibular 2-implant overdenture and a Locator attachment system were designed. The implants were located at the lateral incisor, canine, second premolar, and crossed-implant levels. A 150 N unilateral and bilateral vertical load of different location was applied, as was 40 N when combined with midline load. Data for von Mises stress were produced numerically, color coded, and compared between the models for peri-implant bone and loading conditions. With unilateral loading, in all 4 models much higher peri-implant bone stress values were recorded on the load side compared with the no-load side, while with bilateral occlusal loading, the stress distribution was similar on both sides. In all models, the posterior unilateral load showed the highest stress, which decreased as the load was applied more mesially. In general, the best biomechanical environment in the peri-implant bone was found in the model with implants at premolar level. In the crossed-implant model, the load side greatly altered the biomechanical environment. Overall, the overdenture with implants at second premolar level should be the chosen design, regardless of where the load is applied. The occlusal loading application site influences the bone stress around the implant. Bilateral occlusal loading distributes the peri-implant bone stress symmetrically, while unilateral loading increases it greatly on the load side, no matter where the implants are located.

Effect of two designs of implant-supported overdentures on peri-implant and posterior mandibular bone resorptions: a 5-year prospective radiographic study

OBJECTIVES

The aim of this study was to evaluate and compare the effect of two designs of implant-supported overdentures on peri-implant and posterior mandibular bone resorptions after 5 years of follow-up.

MATERIALS AND METHODS

Twenty edentulous patients were randomly assigned into two equal groups: Group I (GI), patients received overdentures supported and retained by cantilevered bars on two canine implants and Group II (GII), patients received overdentures retained by straight bars on two canine implants and supported by two-first molar implants. Peri-implant vertical (VBL) and horizontal (HBLO) bone losses were assessed on periapical radiographs at the time of overdenture insertion (T0), 6 months (T6 m), 1 year (T1), 3 years (T3), and 5 years (T5) after insertion. Posterior mandibular bone resorption was evaluated using proportional measurements (posterior area index, PAI) made on panoramic radiographs at T0 and T5.

RESULTS

Group I recorded significant higher VBL than GII. VBL increased significantly with advance of time in both groups. Posterior implant recorded significant higher VBL than anterior implants in GII. HBLO did not differ significantly between groups or between observation times. Group I recorded significant higher PAI than GII at T5. Group, age, and initial height of the mandibular ridge were significantly correlated with PAI.

CONCLUSION

Within the limitations of this study, regarding the small sample size, it could be concluded that overdentures retained by straight bars on two canine implants and supported by two-first molar implants present a clinical advantage in terms of peri-implant and posterior mandibular bone preservation compared to overdentures supported and retained by cantilevered bars on two canine implants after 5 years.

Stress distribution patterns of implant supported overdentures-analog versus finite element analysis: A comparative in-vitro study

Aims and Objectives:

The aim of this study was to asses & compare the load transfer characteristics of Ball/O-ring and Bar/Clip attachment systems in implant supported overdentures using analog and finite element analysis models.

Methodology:

For the analog part of the study, castable bar was used for the bar and clip attachment and a metallic housing with a rubber O-ring component was used for the ball/O-ring attachment. The stress on the implant surface was measured using the strain-gauge technique. For the finite element analysis, the model were fabricated and load applications were done in a similar manner as in analog study.

Results:

The difference between both the attachment systems was found to be statistically significant (P<0.001).

Conclusion:

Ball/O-ring attachment system transmitted lesser amount of stresses to the implants on the non-loading side, as compared to the Bar-Clip attachment system. When overall stress distribution is compared, the Bar-Clip attachment seems to perform better than the Ball/O-ring attachment, because the force was distributed better.