Journal of Dental Medicine

Statement of Problem: In the treatment of edentulous patients with implant supported fixed partial dentures several factors such as implant numbers, implant position, superstructure pattern and cantilever length must be considered. Mandibular flexture in function exerts forces in peri-implant bone, however this phenomenon has received little attention.

Purpose: The goal of this finite element analysis (FEA) study was to evaluate the effect of mandibular dimensional changes on peri-implant bone stress in different prosthesis and implant treatment plans.

Materials and Methods: In this experimental study, three dimensional finite element computer model of mandible was simulated according to data from CT-Scan in 0.5 mm sections. The model of 4.110 mm ITI implant, measured by profile projector, was simulated in solid works 2003 software. Implant models were inserted, in two different patterns, on mandible and three different superstructures were placed on implants. Two clenching tasks were modeled (incisal clench and right molar clench).

Results: Analysis of Von Misses stress for peri-implant bone revealed the lowest stress values in three-piece superstructure.

Conclusion: According to this study, additional placement of implants in order to fabricate independent prostheses and to achieve the freedom of mandibular flexture are recommended.

Background and Aim: Due to the complications associated with fixation by Titanium screws and plates in Bilateral Sagittal Split Ramus Osteotomy (BSSRO) surgery, the use of resorbable polymers has been increasingly recommended. Since there are not enough studies on this issue, this study aimed to assess the most appropriate stress distribution in fixation with resorbable screws after BSSRO surgery by Fnite Element Analysis (FEA).
Materials and Methods: This experimental study was performed on simulated human mandible using Ansys and Catia softwares. The osteotomy line was applied to the simulated model and experimental loads of 75, 135 and 600 N were respectively exerted according to the natural direction of occlusal force. The distribution pattern of stress was assessed and compared for fixation with one resorbable screw, two resorbable screws in vertical pattern, two resorbable screws in horizontal pattern, three resorbable screws in L pattern and three resorbable screws in inverted backward L pattern using Ansys software.
Results: Among the four simulated fixations, L pattern showed the highest primary stability. Two screws in vertical pattern were also associated with sufficient primary stability and less trauma and cost for patients. One screw did not provide enough stability under 600 N.
Conclusion: Polymer-based resorbable screws (polyglycolic acid and D, L polylactide acid) provided satisfactory primary stability in BSSRO surgery.

Background and Aims: The All-on-4 design with its significant advantages is an appropriate model in reconstruction of edentulous mandible. Evaluation of stress and strain distribution in this model is necessary for better judgment. The purpose of this FEA study was to measure stress and strain distribution on peri-implant bone in All-on-4 design in edentulous mandible.

Materials and Methods: Three dimensional finite element model of human mandible was simulated according to data from CT-Scan of a cadaver. The model of 4×13.5 mm Nobel Biocare implant was simulated. Posterior implants were inserted in 452 inclination and anterior implants were parallel and vertical. Implants were splinted with a titanium bar and an acrylic superstructure was then simulated around the bar. Vertical loads of 178 N and 300 N were applied at incisor and left first molar positions, respectively. After meshing, defining boundary conditions and materials properties, analysis was performed with the aid of ABAQUS.

Results: Maximum Von-Mises stress of 38.9 MPa during anterior loading was located in peri-implant bone of anterior implants but maximum strain was observed in peri-implant bone of posterior implants. In posterior loading, maximum stress (77.3 MPa) was in peri-implant bone of posterior implant which was next to the place of load insertion. Maximum strain was found in the same area.

Conclusion: During posterior loading, significant amount of strain was observed in peri-implant bone of posterior angulated implant. As a result, there was a possibility of resorption in this area. During anterior loading, detected stress and strain was absolutely favorable.

Background and Aims: Freestanding fixed partial prosthesis is considered the first choice whenever possible. However, anatomical limitations for implants and other reasons may create situation in which it would be preferable to connect the implants to teeth. A biomechanical dilemma in a tooth/implant-supported system comes from dissimilar mobility. This disparity cause the bridge to function as a cantilever and a series of potential problems such as osseointegration loss, screw loosening arise. The aim of this study was to analyze the tooth-implant supported bridges in rigid/non-rigid connectors in cemented prostheses using finite element stress analysis.

Materials and Methods: In this study four three-dimensional models were simulated by use of Solid works software. These models are: 1-RCCP: rigid connector between tooth and implant, 2-NRC CP1: non-rigid connector at mesial side of implant, 3-NRC CP2: non-rigid connector at distal side of second premolar, 4-NRC CP3: non-rigid connector at the middle of pontic, The stress values of four models loaded with vertical forces (150 N) were analyzed.

Results: The maximum stress concentration was located at the crestal bone around implant and stress distribution was more balanced around the teeth except in the model of NRCCP2. Stress distribution was imbalanced in non-rigid connection especially in the NRCCP1 model. The presence of non-rigid connector in bridge increases the stress values in suprastructure and transfers to the adjacent structures. Conclusion: The tooth-implant supported prosthesis should be considered as a valuable prosthetic option. It could be suggested that if tooth and implant abutments are to be used together as fixed prostheses supports, rigid connector is the choice because the prosthesis and implant possess the inherent flexibility to accommodate dissimilar mobility characteristics.

Background and Aims: Relative displacement of the implant with respect to bone and quality of bone-implant contact play critical roles in the dental implant stability. The goal of this study was to investigate the dental implant stability using non-linear finite elements method. Therefore, bone-implant relative displacement due to applied force to the implant was calculated, and then an appropriate factor for defining quality of bone-implant contact was presented.
Materials and Methods: In order to develop a three dimensional model and compare the results with clinical studies, computed tomography (CT) scan data of a rabbit tibia was considered as a base. The model was exported to ABAQUS 6.9-1 to be analyzed using nonlinear finite elements method. Dynamic analysis was done on the model using the proper boundary condition and dynamic loads.
Results: Force-displacement curves in bone-implant interface were nonlinear. Friction coefficient, which is a criterion for implant stability and relative displacement, approximately became doubled as the vertical contact force was halved. However, the friction coefficient decreased with reduction of coulomb frictional coefficient.
Conclusion: Friction coefficient, which is calculated upon force-displacement curves, could be considered as a criterion to evaluate the dental implant stability. Decrease of the vertical contact force and also using rough surfaces improved the quality of bone-implant contact and stability of dental implant.

  Background and Aims: Dental implants have been studied for replacement of missing teeth for many years. Productivity of implants is extremely related to the stability and resistance under applied loads and the minimum stress in jaw bone. The purpose of this study was to study numerically the 3D model of implant under thermal loads.

  Materials and Methods: Bone and the ITI implant were modeled in “Solidworks” software. To obtain the exact model, the bone was assumed as a linear orthotropic material. The implant system, including implant, abutment, framework and crown were modeled and located in the bone. After importing the model in Abaqus software, the material properties and boundary conditions and loads were applied and after meshing, the model was analyzed. In this analysis, the loads were applied in two steps. In the first step, the mechanical load was applied as tightening torque to the abutment and the abutment was tightened in the implant with 35 N.cm torque. In the second step, the thermal load originated from drinking cold and hot water was applied as thermal flux on the ceramic crown surface in this model.

  Results: Thermal analysis results showed that the thermal gradient in the bone was about 5.5 and 4.9 degrees of centigrade in the case of drinking cold and hot water respectively , although the maximum gradient of the whole system was reduced to 14 degrees, which occurred, in the crown by drinking cold water.

  Conclusion Thermal stresses were so small and it was because of the low thermal gradient. Maximum stresses occurred in the abutment were due to the tension preloads which were originated from the tightening torque.