Atilim Eser

Biomechanical comparison of implant retained fixed partial dentures with fiber reinforced composite versus conventional metal frameworks: A 3D FEA study

Fiber reinforced composite (FRC) materials have been successfully used in a variety of commercial applications. These materials have also been widely used in dentistry. The use of fiber composite technology in implant prostheses has been previously presented, since they may solve many problems associated with metal alloy frameworks such as corrosion, complexity of fabrication and high cost. The hypothesis of this study was that an FRC framework with lower flexural modulus provides more even stress distribution throughout the implant retained fixed partial dentures (FPDs) than a metal framework does. A 3-dimensional finite element analysis was conducted to evaluate the stress distribution in bone, implant-abutment complex and prosthetic structures. Hence, two distinctly different models of implant retained 3-unit fixed partial dentures, composed of Cr-Co and porcelain (M-FPD model) or FRC and particulate composite (FRC-FPD model) were utilized. In separate load cases, 300 N vertical, 150 N oblique and 60 N horizontal forces were simulated. When the FRC-FPD and M-FPD models were compared, it was found that all investigated stress values in the M-FPD model were higher than the values in the FRC-FPD model except for the stress values in the implant-abutment complex. It can be concluded that the implant supported FRC-FPD could eliminate the excessive stresses in the bone-implant interface and maintain normal physiological loading of the surrounding bone, therefore minimizing the risk of peri-implant bone loss due to stress-shielding.

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.

Stability of locking and conventional 2.0-mm miniplate/screw systems after sagittal split ramus osteotomy: finite element analysis.

OBJECTIVE The aim of this study was to evaluate the mechanical stresses over the bone and hardware after sagittal split ramus osteotomy (SSRO) fixed with standard titanium or locking plate/screws using finite element analysis. STUDY DESIGN A 3-dimensional finite element model of the mandible was created, and SSRO and 5 mm advancement was simulated on a computer model. The model was fixed with either 2.0-mm titanium conventional miniplate/screw or 2.0-mm titanium locking miniplate/screw system, and oblique 200 N bite force was applied. RESULTS The values of von Mises stresses in the cortical layer of the distal segment using the locking plate system was higher. However, in the cortical layer of the proximal segment the stresses were higher at conventional plate system. In the spongiosa layers of both segments, stresses were higher with the conventional plate system. CONCLUSION The locking miniplate/screw system spreads the load over the plate and screws and diminishes the amount of force transfered to each unit.

Finite element analysis of stress distribution with splinted and nonsplinted maxillary anterior fixed prostheses supported by zirconia or titanium implants.

PURPOSE The aim of the present study was to evaluate the effect of splinting titanium (Ti) or zirconia (Zr) implants supporting maxillary anterior fixed prostheses on the stress levels and patterns in the implants, prostheses, and the surrounding bone; and to compare the effects of Zr and Ti implant materials on the stress distribution in splinted and nonsplinted designs via finite element modeling. MATERIALS AND METHODS Zr and Ti dental implants and the anterior maxilla were modeled. In the nonsplinted design (D1), implants were placed into the maxillary left central incisor and canine regions, and a three-unit zirconia fixed prosthesis was modeled. In the splinted design (D2), a symmetric model of D1 was generated and the two prostheses were splinted together to create a six-unit prosthesis. Loading was applied horizontally and obliquely. Von Mises, tensile, and compressive stresses were evaluated in the implants, prostheses, and surrounding bone. RESULTS Under both loading conditions, the stresses on the D2 implants were lower than those in the D1 implants. Stresses were concentrated on the neck of the implant and decreased through the apex. All of the stress values in cortical bone in D1 were slightly higher than in D2 for both implant materials under both loading conditions. CONCLUSION When the implants were splinted together, stresses were reduced in the supporting bone and implants in both loading conditions, but increased stress was observed in the prostheses under oblique loading. Intense stress concentrations were found in the connector of the splinted prosthesis and the cervical region of the nonsplinted prosthesis. Zr and Ti implants showed very similar stress distributions in all materials. Under oblique loading, lower stresses occurred in implants and the prosthesis core material when Ti implants were used.

Effects of different fixture geometries on the stress distribution in mandibular peri-implant structures: a 3-dimensional finite element analysis

OBJECTIVE The purpose of this study was to compare 3 different solid screw implant fixture designs of stepped cylindric tapered, straight cylindric nontapered, and cylindric with vertical groove tapered on stress distribution in the posterior mandible at a fixed interimplant distance of 1.0 cm. STUDY DESIGN Three-dimensional finite element analysis was used to compare stress distribution around the endosseous titanium implants using 3 different implant fixture geometries. Two identical dental implants of 3 commercially available fixture designs were embedded in each model with a fixed interimplant distance of 1.0 cm. Loads were applied to each of these fixtures: vertically 70 N, with an inclination of 60 degrees obliquely (buccolingually) 35 N, and horizontally (mesiodistally) 14 N. Tensile and compressive stresses on each simulated mandible were calculated using finite element analysis software. Finally, evaluation of the stress around 3 different implant fixtures was performed. RESULTS In the vertical and buccolingual directions, the highest tensile stresses (P(max)) and compression stresses (P(min)) mostly occurred around the cylindric with vertical groove tapered fixture design in both cortical and cancellous bone. In mesiodistal direction, the highest P(max) and P(min) values in cortical and cancellous bone mostly occurred around the straight cylindric nontapered fixture design. CONCLUSION On the basis of the knowledge of deterioration of osseointegration under undesirable stresses within the surrounding bone, the implant fixture design should be chosen carefully. The results of this study reveal that in a clinical situation of molar edentulism, 2 identical stepped cylindric fixture designs which were embedded at a fixed distance of 1.0 cm were the most desirable choice of stress distribution in the surrounding bone.

Predicting bone remodeling around tissue- and bone-level dental implants used in reduced bone width

The objective of this study was to predict time-dependent bone remodeling around tissue- and bone-level dental implants used in patients with reduced bone width. The remodeling of bone around titanium tissue-level, and titanium and titanium-zirconium alloy bone-level implants was studied under 100 N oblique load for one month by implementing the Stanford theory into three-dimensional finite element models. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x- and y- axes of the implant were evaluated. Maximum and minimum principal stresses around tissue-level implant were higher than bone-level implants and both bone-level implants experienced comparable stresses. Total strain energy density in bone around titanium implants slightly decreased during the first two weeks of loading followed by a recovery, and the titanium-zirconium implant showed minor changes in the axial plane. Total strain energy density changes in the loading and contralateral sides were higher in tissue-level implant than other implants in the cortical bone at the horizontal plane. The displacement values of the implants were almost constant over time. Tissue-level implants were associated with higher stresses than bone-level implants. The time-dependent biomechanical outcome of titanium-zirconium alloy bone-level implant was comparable to the titanium implant.

Biomechanical comparison of two different collar structured implants supporting 3-unit fixed partial denture: A 3-D FEM study

Abstract Objective. The purpose of the study was to compare the effects of two distinct collar geometries of implants on stress distribution in the bone as well as in the fixture-abutment complex, in the framework and in the veneering material of 3-unit fixed partial denture (FPD). Material and methods. The 3-dimensional finite element analysis method was selected to evaluate the stress distribution in the system composed of 3-unit FPD supported by two different dental implant systems with two distinct collar geometries; microthread collar structure (MCS) and non-microthread collar structure (NMCS). In separate load cases, 300 N vertical, 150 N oblique and 60 N horizontal, forces were utilized to simulate the multidirectional chewing forces. Tensile and compressive stress values in the cortical and cancellous bone and von Mises stresses in the fixture-abutment complex, in the framework and veneering material, were simulated as a body and investigated separately. Results. In the cortical bone lower stress values were found in the MCS model, when compared with NMCS. In the cancellous bone, lower stress values were observed in the NMCS model when compared with MCS. In the implant-abutment complex, highest von Mises stress values were noted in the NMCS model; however, in the framework and veneering material, highest stress values were calculated in MCS model. Conclusions. MCS implants when compared with NMCS implants supporting 3-unit FPDs decrease the stress values in the cortical bone and implant-abutment complex. The results of the present study will be evaluated as a base for our ongoing FEA studies focused on stress distribution around the microthread and non-microthread collar geometries with various prosthesis design.

Numerical simulation of the effect of time-to-loading on peri-implant bone.

PURPOSE To evaluate the effect of time-to-loading on trabecular bone around single-tooth dental implants using numerical solutions based on computer models. MATERIALS AND METHODS A global model with a coarse mesh carrying a Straumann dental implant (043.033S; Institut Straumann, Basel, Switzerland) was created. A region of interest in trabecular bone was defined to study a localized part of the global model with a refined mesh. Time-to-loading submodels to simulate 2h, 4 days, 1, 4, 6 and 12 wks of trabecular bone-healing status were designed and created. Bone types were considered in the simulation by different elastic bone properties. A 100-N oblique static load was applied. Maximum and minimum principal stresses were calculated and visualized. RESULTS Bone types with higher elastic moduli experienced higher stress levels. Changes in the quality and quantity of bone at the bone-implant interface did not affect the overall stress distribution. Peri-implant bone with a higher elastic modulus preserved the stress increase at the implant-bone interface. DISCUSSION Reduced bone contact may not have a prevailing effect over bone quality and quantity on stress generation at the peri-implant bone. CONCLUSION Time-to-loading of single-tooth implants may not differ in terms of load distributions in neighboring peri-implant bone.

Biomechanical effects of two different collar implant structures on stress distribution under cantilever fixed partial dentures

Abstract Objective. The purpose of the study was to compare the effects of two distinct collar geometries of implants on stress distribution in the bone around the implants supporting cantilever fixed partial dentures (CFPDs) as well as in the implant-abutment complex and superstructures. Materials and methods. The three-dimensional finite element method was selected to evaluate the stress distribution. CFPDs which was supported by microthread collar structured (MCS) and non-microthread collar structured (NMCS) implants was modeled; 300 N vertical, 150 N oblique and 60 N horizontal forces were applied to the models separately. The stress values in the bone, implant-abutment complex and superstructures were calculated. Results. In the MCS model, higher stresses were located in the cortical bone and implant-abutment complex in the case of vertical load while decreased stresses in cortical bone and implant-abutment complex were noted within horizontal and oblique loading. In the case of vertical load, decreased stresses have been noted in cancellous bone and framework. Upon horizontal and oblique loading, a MCS model had higher stress in cancellous bone and framework than the NMCS model. Higher von Mises stresses have been noted in veneering material for NMCS models. Conclusion. It has been concluded that stress distribution in implant-supported CFPDs correlated with the macro design of the implant collar and the direction of applied force.