Reverse engineering of mandible and prosthetic framework: Effect of titanium implants in conjunction with titanium milled full arch bridge prostheses on the biomechanics of the mandible

This study aimed at investigating the effects of titanium implants and different configurations of full-arch prostheses on the biomechanics of edentulous mandibles. Reverse engineered, composite, anisotropic, edentulous mandibles made of a poly(methylmethacrylate) core and a glass fibre reinforced outer shell were rapid prototyped and instrumented with strain gauges. Brånemark implants RP platforms in conjunction with titanium Procera one-piece or two-piece bridges were used to simulate oral rehabilitations. A lateral load through the gonion regions was used to test the biomechanical effects of the rehabilitations. In addition, strains due to misfit of the one-piece titanium bridge were compared to those produced by one-piece cast gold bridges. Milled titanium bridges had a better fit than cast gold bridges. The stress distribution in mandibular bone rehabilitated with a one-piece bridge was more perturbed than that observed with a two-piece bridge. In particular the former induced a stress concentration and stress shielding in the molar and symphysis regions, while for the latter design these stresses were strongly reduced. In conclusion, prosthetic frameworks changed the biomechanics of the mandible as a result of both their design and manufacturing technology.     

Finite element investigation of implant-supported fixed partial prosthesis in the premaxilla in immediately loaded and osseointegrated states

The aim of this study was to gain insight into the behaviour of the stresses and strains at the bone–implant interface of an implant-supported fixed partial prosthesis (FPP) in the premaxilla under immediate loading and osseointegrated conditions. Finite element models of a four-unit FPP were generated. An extreme condition was simulated, using only two immediately loaded implants in order to derive recommendations for possible clinical application. Straight and 20°-angled abutments and bonded or sliding contact between the bridge and abutment were simulated. In addition, two models were generated with two completely osseointegrated implants. A 150 N load to the prosthesis at a 45° angle to the long axis of each implant was applied. Minor differences were observed in implant displacements, stress and strain distributions of the two abutment designs. However, bone loading exceeded the physiological limits, including a risk of bone atrophy. A considerable decrease in implant displacements and bone loading was observed in the osseointegrated cases. An FPP supported by only two implants cannot be recommended for immediate loading.     

Soft and hard tissue response to zirconium dioxide dental implants--a clinical study in man

Titanium dental implants have been used successfully in implantology for more than 40 years. Recent research, however, suggests that titanium might have more side effects than previously believed. Zirconia ceramics have been employed in orthopaedic surgery for approximately 30 years and were recently introduced into dentistry as a metal replacement for crown and bridge work as well as implant abutments. Zirconium dioxide has been shown in both in vitro and in vivo studies to have desirable osseointegrative properties. This clinical study shows that dental implants made from zirconia are a feasible alternative to titanium dental implants. In addition to excellent cosmetic results, zirconia implants allow a degree of osseointegration and soft tissue response that is superior to titanium dental implants.     

Finite element analysis of implant-supported prosthesis with pontic and cantilever in the posterior maxilla

The aim of this study was to evaluate the influence of pontic and cantilever designs (mesial and distal) on 3-unit implant-retained prosthesis at maxillary posterior region verifying stress and strain distributions on bone tissue (cortical and trabecular bones) and stress distribution in abutments, implants and fixation screws, under axial and oblique loadings, by 3D finite element analysis. Each model was composed of a bone block presenting right first premolar to the first molar, with three or two external hexagon implants (4.0 × 10 mm), supporting a 3-unit splinted dental fixed dental prosthesis with the variations: M1 – three implants supporting splinted crowns; M2 – two implants supporting prosthesis with central pontic; M3 – two implants supporting prosthesis with mesial cantilever; M4 – two implants supporting prosthesis with distal cantilever. The applied forces were 400 N axial and 200 N oblique. The von Mises criteria was used to evaluate abutments, implants and fixation screws and maximum principal stress and microstrain criteria were used to evaluate the bone tissue. The decrease of the number of implants caused an unfavorable biomechanical behavior for all structures (M2, M3, M4). For two implant-supported prostheses, the use of the central pontic (M2) showed stress and strain distributions more favorable in the analyzed structures. The use of cantilever showed unfavorable biomechanical behavior (M3 and M4), mainly for distal cantilever (M4). The use of three implants presented lower values of stress and strain on the analyzed structures. Among two implant-supported prostheses, prostheses with cantilever showed unfavorable biomechanical behavior in the analyzed structures, especially for distal cantilever.     

Preliminary studies on the optimum shape of dental bridges

Several pre-existing anterior and posterior dental bridge models using Finite elements and the new ceramic material In-Ceram have been developed. The mechanical behaviour of these models has been compared with optimised profiles obtained from a newly developed evolutionary algorithm known as Evolutionary Structural Optimisation (ESO). The results show that the mechanical behaviour of the bridges was mainly restricted by the properties of the porcelain veneer and the design of the bridges themselves. For the case of the anterior bridge, it was found that there existed a specific thickness of veneer that minimised the maximum principal stress. This was related to peak stresses that occurred at the bridge surface. Peak stresses also occurred in the material interface between the In-Ceram and the veneer. These extreme stresses were attributed to the notch size and shape. For the case of the posterior bridge, it was concluded that the shape of the bottom of the Pontic tooth is crucial in reducing the magnitude of the maximum principal tensile stress. The ESO process produced bridge designs which have uniformly stressed bridge surfaces, and which also have significantly lower maximum principal tensile stresses compared to the pre-existing designs (up to 44%).     

过盈植入对种植体-骨界面应力分布影响的三维有限元分析（英文）

目的：应用三维有限元分析法研究牙种植体过盈植入对种植体-骨界面接触压力的影响。方法：选择直径为3.3 mm的ITI种植体和成人离体下颌骨,模拟种植体植入下颌骨内,过盈量为0.5 mm,建立三维有限元模型,应用ANSYS软件分析种植体-骨界面的应力分布情况。结果：种植体周围骨最大应力为48.796 MPa,应力分布均匀。种植体所受应力主要集中于颈部,最大应力值为87.832 MPa。结论：过盈量为0.5 mm时,种植体-骨界面所产生的应力值在骨组织所能承受的最大应力值范围内,种植体所受到的应力值远远小于钛的屈服强度,从生物力学角度,周围骨所受应力在骨组织能够承受范围,种植体也不会断裂,过盈联结在临床种植时有其可行性。     

Preliminary Studies on the Optimum Shape of Dental Bridges

Several pre-existing anterior and posterior dental bridge models using Finite elements and the new ceramic material In-Ceram have been developed. The mechanical behaviour of these models has been compared with optimised profiles obtained from a newly developed evolutionary algorithm known as Evolutionary Structural Optimisation (ESO).

The results show that the mechanical behaviour of the bridges was mainly restricted by the properties of the porcelain veneer and the design of the bridges themselves. For the case of the anterior bridge, it was found that there existed a specific thickness of veneer that minimised the maximum principal stress. This was related to peak stresses that occurred at the bridge surface. Peak stresses also occurred in the material interface between the In-Ceram and the veneer. These extreme stresses were attributed to the notch size and shape. For the case of the posterior bridge, it was concluded that the shape of the bottom of the Pontic tooth is crucial in reducing the magnitude of the maximum principal tensile stress. The ESO process produced bridge designs which have uniformly stressed bridge surfaces, and which also have significantly lower maximum principal tensile stresses compared to the pre-existing designs (up to 44%).     

Bone Loss at Implant with Titanium Abutments Coated by Soda Lime Glass Containing Silver Nanoparticles: A Histological Study in the Dog

The aim of the present study was to evaluate bone loss at implants connected to abutments coated with a soda-lime glass containing silver nanoparticles, subjected to experimental peri-implantitis. Also the aging and erosion of the coating in mouth was studied. Five beagle dogs were used in the experiments. Three implants were placed in each mandible quadrant: in 2 of them, Glass/n-Ag coated abutments were connected to implant platform, 1 was covered with a Ti-mechanized abutment. Experimental peri-implantitis was induced in all implants after the submarginal placement of cotton ligatures, and three months after animals were euthanatized. Thickness and morphology of coating was studied in abutment cross-sections by SEM. Histology and histo-morphometric studies were carried on in undecalfied ground slides. After the induced peri-implantitis: 1.The abutment coating shown losing of thickness and cracking. 2. The histometry showed a significant less bone loss in the implants with glass/n-Ag coated abutments. A more symmetric cone of bone resorption was observed in the coated group. There were no significant differences in the peri-implantitis histological characteristics between both groups of implants. Within the limits of this in-vivo study, it could be affirmed that abutments coated with biocide soda-lime-glass-silver nanoparticles can reduce bone loss in experimental peri-implantitis. This achievement makes this coating a suggestive material to control peri-implantitis development and progression.     

Influence of transmucosal height in abutments of single and multiple implant-supported prostheses: a non-linear three-dimensional finite element analysis

The aim of this study was to analyze the influence of three different transmucosal heights of the abutments in single and multiple implant-supported prostheses through the finite element method. External hexagon implants, MicroUnit, and EsthetiCone abutments were scanned and placed in an edentulous maxillary model obtained from a tomography database. The simulations were divided into two groups: (1) one implant with 3.75 × 10 mm placed in the upper central incisor, simulating a single implant-supported fixed prosthesis with an EsthetiCone abutment; and (2) two implants with 3.75 × 10 mm placed in the upper lateral incisors with MicroUnit abutments, simulating a multiple implant-supported prosthesis. Subsequently, each group was subdivided into three models according to the transmucosal height (1, 2, and 3 mm). A static oblique load at an angle of 45 degrees to the long axis of the implant in palatal-buccal direction of 150 and 75 N was applied for multiple and single implant-supported prosthesis, respectively. The implants and abutments were assessed according to the equivalent Von Mises stress analyses while the bone and ceramics were analyzed through maximum and minimum principal stresses. The total deformation values increased in all models, while the transmucosal height was augmented. The transmucosal height of the abutments influences the stress values at the bone, ceramics, implants, and abutments of both the single and multiple implant-supported prostheses, with the transmucosal height of 1 mm showing the lowest stress values.     

Radiologic Evaluation of Bone Loss at Implants with Biocide Coated Titanium Abutments: A Study in the Dog

The objective of the present study is to evaluate bone loss at implant abutments coated with a soda-lime glass containing silver nanoparticles subjected to experimental peri-implantitis. Five beagle dogs were used in the experiments, 3 implants were installed in each quadrant of the mandibles. Glass/n-Ag coted abutments were connected to implant platform. Cotton floss ligatures were placed in a submarginal position around the abutment necks and the animals were subject to a diet which allowed plaque accumulation, and after 15 weeks the dogs were sacrificed. Radiographs of all implant sites were obtained at the beginning and at the end of the experimentally induced peri-implantitis. The radiographic examination indicated that significant amounts of additional bone loss occurred in implants without biocide coating, considering both absolute and relative values of bone loss. Percentages of additional bone loss observed in implants dressed with a biocide coated abutment were about 3 times lower (p<0.006 distal aspect; and p<0.031 at mesial aspect) than the control ones. Within the limits of the present study it seems promising the use of soda-lime glass/nAg coatings on abutments to prevent peri-implant diseases.     

Evaluation in a Dog Model of Three Antimicrobial Glassy Coatings: Prevention of Bone Loss around Implants and Microbial Assessments

ObjectivesThe aim of the present study is to evaluate, in a ligature-induced peri-implantitis model, the efficacy of three antimicrobial glassy coatings in the prevention of biofilm formation, intrasulcular bacterial growth and the resulting peri-implant bone loss.MethodsMandibular premolars were bilaterally extracted from five beagle dogs. Four dental implants were inserted on each hemiarch. Eight weeks after, one control zirconia abutment and three with different bactericidal coatings (G1n-Ag, ZnO35, G3) were connected. After a plaque control period, bacterial accumulation was allowed and biofilm formation on abutments was observed by Scanning Electron Microscopy (SEM). Peri-implantitis was induced by cotton ligatures. Microbial samples and peri-implant crestal bone levels of all implant sites were obtained before, during and after the breakdown period.ResultsDuring experimental induce peri-implantitis: colony forming units counts from intrasulcular microbial samples at implants with G1n-Ag coated abutment remained close to the basal inoculum; G3 and ZnO35 coatings showed similar low counts; and anaerobic bacterias counts at control abutments exhibited a logarithmic increase by more than 2. Bone loss during passive breakdown period was no statistically significant. Additional bone loss occurred during ligature-induce breakdown: 0.71 (SD 0.48) at G3 coating, 0.57 (SD 0.36) at ZnO35 coating, 0.74 (SD 0.47) at G1n-Ag coating, and 1.29 (SD 0.45) at control abutments; and statistically significant differences (p<0.001) were found. The lowest bone loss at the end of the experiment was exhibited by implants dressing G3 coated abutments (mean 2.1; SD 0.42).SignificanceAntimicrobial glassy coatings could be a useful tool to ward off, diminish or delay peri-implantitis progression.     

Influence of Different Abutment Designs on the Biomechanical Behavior of One-Piece Zirconia Dental Implants and Their Surrounding Bone: A 3D-FEA

BackgroundIn a dental implant/bone system, the design factors affect the value and distributions of stress and deformations that plays a pivotal role on the stability, durability and lifespan of the implant/bone system.ObjectiveThe aim of this study was to compare the influence of different abutment designs on the biomechanical behavior of one-piece zirconia dental implants and their surrounding bone tissues using three-dimensional finite element analysis.MethodsA three-dimensional geometrical model of a zirconia dental implant and its surrounding bone tissue were created. The occlusal loading force applied to the prosthetic abutments was a combination of 114.6 N in the axial direction, 17.1 N in the lingual direction and 23.4 N toward the mesial direction where these components represent masticatory force of 118.2 N in the angle of approximately 75° to the occlusal plane.ResultsThe system included implant abutment Model 01 showed a decrease of 9.58%, 9.92% and 3.62% at least in the average value of maximum von Mises stress compared to Model 02, Model 03 and Model 04 respectively. The results also showed that the system included implant abutment Model 01 decreases the average value of maximum deformation of 16.96%, 7.17% and 9.47% at least compared to Model 02, Model 03 and Model 04 respectively.ConclusionThe one-piece zirconia dental implant abutment Model 01 presents a better biomechanical behavior in the peri-implant bone than others. It can efficiently distribute the applied load and present more homogeneous behavior of stress distribution and has less deformation than others, which will enhance the stability of implant/bone system and prolong its lifespan.     

Finite element and experimental analyses of polymer-based dental bridges reinforced by ceramic bars

Dental bridges made of polymer materials reveal only low loading capacity. This paper analyzes possible improvements of the loading capacity of polymer-based dental bridges reinforced by incorporated ceramic bars. Finite element (FE) analyses were performed to study the stress distribution caused by the mastication process in the bridge material. In the experimental part of the study, the fracture load of dental bridges with and without ceramic bar reinforcement was evaluated. Critical stresses occur in the connector area between abutment and pontic of bridges without bar reinforcement. A suitably shaped ceramic bar incorporated into the polymer-based bridge can significantly reduce these critical stresses. The fracture load of the bridge was increased from 515 to 1603N by the bar reinforcement. We conclude from our study that a ceramic bar can significantly improve the loading capacity of a polymer-based dental bridge. The FE and the experimental analyses revealed that the detailed design of the ceramic bar is of decisive importance for the effectiveness of the suggested ceramic reinforcement.     

Stress transfer properties of different commercial dental implants: a finite element study

Dental implantology has high success rates, and a suitable estimation of how stresses are transferred to the surrounding bone sheds insight into the correct design of implant features. In this study, we estimate stress transfer properties of four commercial implants (GMI, Lifecore, Intri and Avinent) that differ significantly in macroscopic geometry. Detailed three-dimensional finite element models were adopted to analyse the behaviour of the bone-implant system depending on the geometry of the implant (two different diameters) and the bone-implant interface condition. Occlusal static forces were applied and their effects on the bone, implant and bone-implant interface were evaluated. Large diameters avoided overload-induced bone resorption. Higher stresses were obtained with a debonded bone-implant interface. Relative micromotions at the bone-implant interface were within the limits required to achieve a good osseointegration. We anticipate that the methodology proposed may be a useful tool for a quantitative and qualitative comparison between different commercial dental implants.     

An in vitro study of implant--tooth-supported connections using a robot test system.

Many unsolved problems in dental implant research concern the interfacial stress distributions between the implant components, as well as between the implant surface and contacting bone. To obtain a mechanical understanding of how vertical and horizontal occlusal forces are distributed in this context, it is crucial to develop in vitro testing systems to measure the force transmission between dental implants and attached prostheses. A new approach to such testing, involving a robotic system, is described in this investigation. The system has been designed to produce simulated mandibular movements and occlusal contact forces so that various implant designs and procedures can be thoroughly tested and evaluated before animal testing or human clinical trials. Two commonly used fixed prosthesis designs used to connect an implant and a tooth, a rigid connection and a nonrigid connection, were fabricated and used for experimental verification. The displacement and force distributions generated during simulated chewing activities were measured in vitro. Force levels, potentially harmful to human bone surrounding the connected dental implant and tooth, were analyzed. These results are useful in the design of prostheses and connecting components that will reduce failures and limit stress transfer to the implant/bone interface.     

Numerical investigation of bone remodelling around immediately loaded dental implants using sika deer (Cervus nippon) antlers as implant bed

This study combines finite element method and animal studies, aiming to investigate tissue remodelling processes around dental implants inserted into sika deer antler and to develop an alternative animal consuming model for studying bone remodelling around implants. Implants were inserted in the antlers and loaded immediately via a self-developed loading device. After 3, 4, 5 and 6 weeks, implants and surrounding tissue were taken out. Specimens were scanned by μCT scanner and finite element models were generated. Immediate loading and osseointegration conditions were simulated at the implant-tissue interface. A vertical force of 10 N was applied on the implant. During the healing time, density and Young’s modulus of antler tissue around the implant increased significantly. For each time point, the values of displacement, stresses and strains in the osseointegration model were lower than those of the immediate loading model. As the healing time increased, the displacement of implants was reduced. The 3-week immediate loading model (9878 ± 1965 μstrain) illustrated the highest strains in the antler tissue. Antler tissue showed similar biomechanical properties as human bone in investigating the bone remodelling around implants, therefore the use of sika deer antler model is a promising alternative in implant biomechanical studies.     

A comparative analysis based on different strength criteria for evaluation of risk factor for dental implants

A numerical analysis is developed to study the interaction phenomena between endousseus titanium dental implants and surrounding jawbone tissue. The interest is focused on the most appropriate evaluation of the stress state arising in the tissue because of the implant under physiological loading. The problem is considered with regard to linear elastic response of the one and to short time effect. Different configurations of bone-implant system are described, using axial-symmetrical and three-dimensional models, by means of finite and geometric element method. The investigation attains to the stress states induced in bone that lead to a limit condition near the effective failure surface. The parameter commonly adopted in literature, such as the Von Mises stress, represents an excessive simplification of problem formulation, leading to an incorrect evaluation of the real failure risk for the implant, due to the assumption of the isotropic and deviatoric nature of the adopted stress measure. More suitable criterion can be assumed, such as the Tsai-Wu criterion, to take into account the anisotropy that characterises the response of bone, as well as the influence of a hydrostatic stress state. The analysis developed offers a comparison of results by using different criteria, leading to an evaluation of reliability of the procedure to be followed and addressing also to an evaluation of a risk factor for the implant investigated.     

Finite element analysis of different loading conditions for implant-supported overdentures supported by conventional or mini implants

The effect of implants’ number on overdenture stability and stress distribution in edentulous mandible, implants and overdenture was numerically investigated for implant-supported overdentures. Three models were constructed. Overdentures were connected to implants by means of ball head abutments and rubber ring. In model 1, the overdenture was retained by two conventional implants; in model 2, by four conventional implants; and in model 3, by five mini implants. The overdenture was subjected to a symmetrical load at an angle of 20 degrees to the overdenture at the canine regions and vertically at the first molars. Four different loading conditions with two total forces (120, 300 N) were considered for the numerical analysis. The overdenture displacement was about 2.2 times higher when five mini implants were used rather than four conventional implants. The lowest stress in bone bed was observed with four conventional implants. Stresses in bone were reduced by 61% in model 2 and by 6% in model 3 in comparison to model 1. The highest stress was observed with five mini implants. Stresses in implants were reduced by 76% in model 2 and 89% increased in model 3 compared to model 1. The highest implant displacement was observed with five mini implants. Implant displacements were reduced by 29% in model 2, and increased by 273% in model 3 compared to model 1. Conventional implants proved better stability for overdenture than mini implants. Regardless the type and number of implants, the stress within the bone and implants are below the critical limits.     

The influence of implant number and abutment design on the biomechanical behaviour of bone for an implant-supported fixed prosthesis: a finite element study in the upper anterior region

It is always recommended to use more implants for supporting a prosthesis in the immediate loading condition than in the classical two-stage treatment procedure. By means of the finite element (FE) method, the influence of the number of implants used in immediately loaded fixed partial prosthesis (FPP) on the load distribution was investigated, considering the abutment geometry. Two 3D FE models were studied employing four implants to support a FPP in the premaxilla. One model was designed with straight abutments and the other with 20°-angled abutments. The results concerning implant displacements, stresses and strains were compared with those of two implant-supported FPPs, obtained in a previous study. A noticeable reduction in the determined biomechanical bone loading was observed with the use of more implants in supporting an immediately loaded prosthesis. This study confirms that the use of additional numbers of implants in an immediately loaded prosthesis is highly recommended.     

The influence of implant number and abutment design on the biomechanical behaviour of bone for an implant-supported fixed prosthesis: a finite element study in the upper anterior region

It is always recommended to use more implants for supporting a prosthesis in the immediate loading condition than in the classical two-stage treatment procedure. By means of the finite element (FE) method, the influence of the number of implants used in immediately loaded fixed partial prosthesis (FPP) on the load distribution was investigated, considering the abutment geometry. Two 3D FE models were studied employing four implants to support a FPP in the premaxilla. One model was designed with straight abutments and the other with 20°-angled abutments. The results concerning implant displacements, stresses and strains were compared with those of two implant-supported FPPs, obtained in a previous study. A noticeable reduction in the determined biomechanical bone loading was observed with the use of more implants in supporting an immediately loaded prosthesis. This study confirms that the use of additional numbers of implants in an immediately loaded prosthesis is highly recommended.