Peri-implant Stress Research Articles

Impact of implants number and attachment type on the peri-implant stresses and retention of palateless implant-retained overdenture.

To evaluate the impact of implants number and attachments type on the peri-implant stresses and retention of maxillary palateless implant-supported overdenture. Four edentulous maxillary educational acrylic resin models were used. According to the implants number and type of attachment used, four groups were compared: Group I, 2-locator attachments in the canine area; Group II, 2- OT equator attachments in the canine area; Group III, 4-locator attachments in the canine, second premolar area and Group IV, 4-OT equator attachments in the canine, second premolar area. Implants retained palateless overdenture was constructed on each model. Four self-protected linear strain gauges were cemented on each implant. A digital loading device was used to apply compressive loads to measure the resulting peri-implant stresses. Forcemeter and Universal testing machines were used to test the retention of palateless overdenture. A significant difference between the same implant number and distribution with different attachments was found (P = 0.003, P = 0.020), respectively. Least stresses amount was found around the 4-implant locator palateless overdenture, while the highest was found around the 2-implant OT equator palateless overdenture. Nevertheless; the result was that 2-implant locator palateless overdenture recorded insignificant higher retentive forces than the 4-implant OT equator one. It can be concluded that the implant-retained palateless overdenture with four locator attachments is considered a promising treatment option regarding stress distribution. Using locator attachments, for implant-retained palateless overdenture with either two or four implants considering their superior retentive properties, is advantageous when compared to OT equator attachments.

Stress distribution in the peri-implant area of pure titanium and titanium-zirconium small implants

Aim: In dental implant treatment, there is a demand for mechanically stronger implants. Despite the existence of several studies showing the clinical success of narrow diameter implants, most of them are based on pure titanium (cpTi) alloys. There is a few clinical evidences of the success rate of titanium-zirconium (TiZr) narrow diameter implants. The aim of this study was to evaluate the stress distribution in the peri-implant area of narrow diameter cpTi and TiZr implants under axial and oblique loads. Methods: Photoelastic models were produced using epoxy resin (PL2, Vishay Precision Group) from a master model. The implants (cpTi and TiZr; Straumann AG) had 3.3 mm in diameter and 12 mm in height. Loads of 100 N and 200 N were applied to the abutment at angles of 0° (axial), 10°, 20°, and 30° (oblique). A circular polariscope (Eikonal) was used under dark field white-light configuration. The isochromatic fringes were analyzed in the peri-implant region in 5 areas, using ASTM table with isochromatic fringes; cervical-mesial, cervical-distal, mid-mesial, mid-distal and apical. Results: In general, under axial and oblique loads, the stress in the TiZr implant was lower than in the cpTi implant. The load of 200 N produced the highest stress values in cpTi and TiZr implants. In both implants and loads, the fringes were located more in apical area at all angles evaluated. Conclusion: It can be concluded that for small implants, the load inclination and intensity change the pattern of stress distribution and the cpTi implant exhibited the highest peri-implant stress.

Influence of Implant Length and Associated Parameters Upon Biomechanical Forces in Finite Element Analyses: A Systematic Review.

The aim of this systematic review is to provide an overview of finite element analyses comparing standard and short dental implants concerning biomechanical properties and to detect the most relevant parameters affecting periimplant stress concentrations. After screening the literature and assessment of studies, 36 studies were included in this review. Eighty-three percent of the studies state that short dental implants have to bear higher stress concentrations compared with standard length implants. At the same time, 44% of articles note that implant diameter can be considered a more effective design parameter than implant length to reduce stress concentrations and to avoid an overload of periimplant bone. Regardless of implant dimension, in all studies, the highest stress concentrations are found in the cortical section around the upper part of the implant. Unaffected of bone quality, implant diameter is found to play a key role to minimize periimplant stress concentrations. Concerning stress reduction implant length gains increasing relevance with decreasing bone density. Furthermore, splinting of short implants constitute an appropriate tool to avoid crestal overloading.

Comparison of the periimplant bone stress distribution on three fixed partial supported prosthesis designs under different loading. A 3D finite element analysis

ABSTRACTDespite high success and survival rates of implant-supported prosthesis therapy, biomechanical complications such as periimplant bone resorption continue to exist due to occlusal overloading. The purpose of this article is to analyse and compare the influence of bone density, direction and distribution of the occlusal load and the design of three-unit implant-supported prostheses. Three-dimensional finite element analysis study was developed to evaluate the influence on the periimplant bone stress distribution of three different designs of a 3-unit bridge supported by two implants (intermediate pontic, tilted implant, cantilever pontic), two different bone qualities (D3 and D4), and different loading directions (axial and non-axial) and distributions (uniform and non-uniform). Bridge configuration with intermediate pontic and parallel implants presents the lowest periimplant stress, whereas the highest stress was found on the tilted implant bridge. Bone D3 is biomechanically more favourable than D4. Non-axial and uniform loading conditions produce more periimplant stress. Distal cantilever and 45° convergent distal tilted implant are the second and third treatment options on a posterior three-unit rehabilitation. Lightening occlusal contacts on the pontic and avoiding non-axial loading, reduce periimplant bone stress. Bone D4 increases periimplant bone strain.

Fractures in patients with osteopetrosis, insights from a single institution.

Osteopetrosis is a hereditary skeletal disorder in which defective osteoclast function leads to abnormally hard and brittle bones. This study aims to describe the pattern of fractures occurring in this group of patients, possible complications, and strategies to avoid them. This is a case series of six osteopetrotic patients with a total of 12 fractures managed in our institution over a period of nineyears. Patient records were also reviewed for complications both intra- and post-operatively. The majority of the fractures involved the femur, with three of these being peri-implant in nature. Other bones involved include the tibia, humerus, patella, fifth metatarsal, and proximal phalanx of the toe. There was a high rate of complications while managing these patients: three patients had peri-implant stress fractures, three with retained broken screws, and one case each of delayed union, non-union, and surgical site infection. Osteopetrosis fractures present a unique challenge to the orthopedic surgeon. Careful pre-operative planning should be undertaken before proceeding with surgery in these cases.

Irregular Implant Design Decreases Periimplant Stress and Strain Under Oblique Loading.

To investigate whether a different implant geometry with the same potential contact surface area (PCSA) affects the principal stress and strains in bone. Three-dimensional finite-element models were created with a single endosseous implant embedded in bone. The irregular (IR) dental root-analog implant and regular (R) cylindrical implant with the same PCSA 350 mm were modeled, keeping the size of the thinnest implant wall 0.8 mm, and the thinnest bone wall 1 mm. The regular or irregular abutments were either 4.5 mm lower than the platform of the implants or 5 mm higher than the platform of the implants, both with the taper 1.44°. A 100 N vertical or 100 N vertical/50 N horizontal occlusal loading was applied. The biomechanical behaviors of periimplant bone were recorded. The IR implant design experienced lower periimplant stress and strain under oblique loading than that of R implant design. In the IR implant design, comparable stress in bone, implant, and abutment were found under 100 N vertical loading or 100 N vertical/50 N horizontal loading. In the R implant design, much higher stress in bone, implant, and abutment were found under 100 N vertical/50 N horizontal loading than that under 100 N vertical loading. Irregular dental root-analog implant is a biomechanically favorable design principle for decreasing periimplant stress and strain under oblique loading.

The effect of direct and indirect force transmission on peri-implant bone stress – a contact finite element analysis

In almost all finite element (FE) studies in dentistry, virtual forces are applied directly to dentures. The purpose of this study was to develop a FE model with non-linear contact simulation using an antagonist as force transmitter and to compare this with a similar model that uses direct force transmission. Furthermore, five contact situations were created in order to examine their influence on the peri-implant bone stresses, which are relevant to the survival rate of implants. It was found that the peri-implant bone stresses were strongly influenced by the kind of force transmission and contact number.

Effects of monocortical and bicortical mini-implant anchorage on bone-borne palatal expansion using finite element analysis.

Bone-borne palatal expansion relies on mini-implant stability for successful orthopedic expansion. The large magnitude of applied force experienced by mini-implants during bone-borne expansion may lead to high failure rates. Use of bicortical mini-implant anchorage rather than monocortical anchorage may improve mini-implant stability. The aims of this study were to analyze and compare the effects of bicortical and monocortical anchorages on stress distribution and displacement during bone-borne palatal expansion using finite element analysis. Two skull models were constructed to represent expansion before and after midpalatal suture opening. Three clinical situations with varying mini-implant insertion depths were studied in each skull model: monocortical, 1-mm bicortical, and 2.5-mm bicortical. Finite element analysis simulations were performed for each clinical situation in both skull models. Von Mises stress distribution and transverse displacement were evaluated for all models. Peri-implant stress was greater in the monocortical anchorage model compared with both bicortical anchorage models. In addition, transverse displacement was greater and more parallel in the coronal plane for both bicortical models compared with the monocortical model. Minimal differences were observed between the 1-mm and the 2.5-mm bicortical models for both peri-implant stress and transverse displacement. Bicortical mini-implant anchorage results in improved mini-implant stability, decreased mini-implant deformation and fracture, more parallel expansion in the coronal plane, and increased expansion during bone-borne palatal expansion. However, the depth of bicortical mini-implant anchorage was not significant.

Effect of Buccal Implant Inclination on Stresses Around Two-Implant-Retained Overdentures with Resilient Stud Attachments.

This study aimed to evaluate the effect of buccal implant inclination on stresses around two-implant-retained overdentures with resilient stud attachments. Four acrylic models representing a mandibular edentulous ridge were constructed. For each model, two implants were placed at canine areas. Models were classified into four types according to the degree of buccal implant inclination: Group I (GI, 0 degrees), Group II (GII, 10 degrees), Group III (GIII, 20 degrees), and Group IV (GIV, 30 degrees). Overdentures were connected to the implants with Locator attachments. Regular light-retention inserts were used for all groups, and extended range inserts were also used for GIV (GIVext), making a fifth comparison group. Four strain gauges were bonded at the buccal, lingual, mesial, and distal surfaces of each implant to monitor the stresses during bilateral and unilateral load application. Tensile stresses were recorded at distal and lingual gauges, and compressive stresses were recorded at mesial and buccal gauges for all groups. GIV recorded the highest stresses, followed by GIII, GII, GIVext, and GI. Distal position recorded the highest stresses, followed by lingual, mesial, and buccal. Nonloading side was associated with significantly higher stresses than loading side. The peri-implant stresses increase as the buccal implant inclination increases when resilient stud attachments are used for implant overdentures. Therefore, it is recommended to insert the implants parallel to each other to decrease peri-implant stresses. However, when buccal inclination is inevitable due to anatomical limitations, it should be limited to 10 degrees for standard nylon inserts, or extended range inserts are recommended.

Effect of Implant Position and Edentulous Span Length on Stresses Around Implants Assisting Claspless Distal Extension Partial Overdentures: An In Vitro Study.

The aim of this in vitro study was to evaluate the effect of implant position and edentulous span length on stresses around implants assisting claspless distal extension partial overdentures. Four bilateral mandibular distal extension acrylic models were constructed. Two implants were inserted in the distal extension ridges parallel to each other and perpendicular to the ridges. Based on the implant position, models were categorized into two groups: Group I, mesial implants position and Group II, distal implant position. Each group was subdivided into 2 subgroups according to the length of edentulous span: Subgroup a, long span and Subgroup b, short span. Four claspless partial overdentures were fabricated on the models and retained to the implants with ball-and-socket attachments. Three strain gauges were cemented to the acrylic resin at buccal, lingual, and distal sides of each implant. Static unilateral vertical load of 60N was applied in the central fossae of the first molar, and peri-implant stresses were measured on loading and nonloading sides. Distal implant placements recorded significantly higher peri-implant stresses than did mesial implant placements. Long saddle recorded significantly higher stresses than did short saddle. The greatest peri-implant stresses were recorded with distal placement and long saddle at the loading side. At loading and nonloading sides, the mesial placement with a short saddle recorded the lowest strain. For mandibular distal extension partial overdentures, a mesially placed implant combined with short saddle may be preferable to a distally placed implant combined with long saddle, as the former was associated with reduced peri-implant stresses.

Three-dimensional finite element analysis of the effects of implant diameter and photofunctionalization on peri-implant stress.

Previous finite element analyses of peri-implant stress assumed a bone-implant contact (BIC) ratio of 100%, even though the BIC ratio is known to be approximately 50% or less. However, the recent development of ultraviolet treatment of titanium immediately before use, known as photofunctionalization, significantly increased the BIC ratio, to 98.2%. We used a unique finite element analysis model that enabled us to examine the effects of different BIC ratios on peri-implant stress. A three-dimensional model was constructed under conditions of vertical or oblique loading, an implant diameter of 3.3, 3.75, or 5.0 mm, and a BIC ratio of 53.0% or 98.2%. Photofunctionalization and larger implant diameters were associated with reduced stress on surrounding tissues. Under vertical loading, photofunctionalization had a greater effect than increased implant diameter on stress reduction. Under oblique loading, increased implant diameter had a greater effect than photofunctionalization on stress reduction.

Stiffness and strength tailoring of cobalt chromium graded cellular structures for stress-shielding reduction

The use of cobalt chromium (CoCr) in orthopaedic joint replacement shields the peri-implant bone stress, contributing to a premature loosening of the implants. In order to reduce the need for revision surgeries, light weight implants with tailored functionalities need to be developed. In this study, the compressive mechanical properties of laser-melted CoCr cellular structures with a pillar octahedral architecture [0°±45°] were investigated. Four types of graded cellular structures, based on grading orientations along radial and longitudinal planes, were manufactured using selective laser melting techniques. The cellular structures in this study have the mechanical properties (E=2.3–3.1GPa, σ=113–523MPa) compatible with bone structures. Grading a porosity of the CoCr cellular structures provides a greater stress transfer to the proximal peri-implant area. The axially graded cellular structures demonstrated significant reduction of the peri-implant stress shielding. Incorporation of CoCr graded cellular structures into a structure like femoral stems is expected to have the potential to reduce the revision surgeries.

Peri-implant Stresses Around Mesially Inclined Implants Used to Retain mandibular over dentures With Locator Attachments. An Invitro Strain Gauge Analysis

Peri-implant Stresses Around Mesially Inclined Implants Used to Retain mandibular over dentures With Locator Attachments. An Invitro Strain Gauge Analysis

A comparison of the peri-implant bone stress generated by the preload with screw tightening between ‘bonded’ and ‘contact’ model

A number of finite element analyses (FEAs) for the dental implant were performed without regard for preload and with all interfaces ‘fixed-bonded’. The purpose of this study was comparing the stress distributions between the conventional FEA model with all contacting interfaces ‘fixed-bonded’ (bonded model) and the model with the interfaces of the components in ‘contact’ with friction simulated as a preloaded implant (contact model). We further verified the accuracy of the result of the FEA using model experiment. In the contact model, the stress was more widely distributed than in the bonded model. From the model study, the preload induced by screw tightening generated strain at the peri-implant bone, even before the application of external force. As a result, the bonded model could not reproduce the mechanical phenomena, whereas the contact model is considered to be appropriate for analysing mechanical problems.

Biomechanical effects of offset placement of dental implants in the edentulous posterior mandible.

BackgroundProper implant placement is very important for long-term implant stability. Recently, numerous biomechanical studies have been conducted to clarify the relationship between implant placement and peri-implant stress. The placement of multiple implants in the edentulous posterior mandible has been studied by geometric analysis, three-dimensional finite element analysis (FEA), model experimentation, etc. Offset placement is a technique that reduces peri-implant load. However, few studies have used multiple analyses to clarify the value of the offset placement under identical conditions.The present study aimed to clarify the biomechanical effects of offset placement on the peri-implant bone in edentulous posterior mandibles by comparative investigation using FEA and model experimentation with strain gauges.MethodsThree implants were embedded in an artificial mandible in the parts corresponding to the first premolar, the second premolar, and the first molar. A titanium superstructure was mounted to prepare models (experimental models). Three load points (buccal, central, and lingual) were established on the part of the superstructure corresponding to the first molar. Three types of experimental models, each with a different implant placement, were prepared. In one model, the implants were placed in a straight line; in the other two, the implants in the parts corresponding to the second premolar and the first molar were offset each by a 1-mm increment to the buccal or lingual side. Four strain gauges were applied to the peri-implant bone corresponding to the first molar.The experimental models were imaged by micro-computed tomography (CT), and FEA models were constructed from the CT data. A vertical load of 100 N was applied on the three load points in the experimental models and in the FEA models. The extent of compressed displacement and the strain in the peri-implant bone were compared between the experimental models and the FEA models.ResultsBoth experimental and FEA models suffered the least compressed displacement during central loading in all placements. The greatest stress and compressive strain was on the load side in all types of placements.ConclusionsOffset placement may not necessarily be more biomechanically effective than straight placement in edentulous posterior mandibles.

Anterior augmentation plating of aseptic humeral shaft nonunions after intramedullary nailing.

Humeral shaft nonunion after intramedullary nailing is a rare but serious complication. Treatment options include implant removal, open plating, exchange nailing and external fixation. The objective of this retrospective study was to determine whether augmentation plating without nail removal is feasible for treating a humeral shaft nonunion. Between 2002 and 2014, 37 patients (mean age 51, range 20-84years) with aseptic humeral shaft nonunions prior to intramedullary nailing were treated with augmentation plating. The initial fractures had been fixed with retrograde nails (10 cases) or anterograde nails (27 cases). There were 34 atrophic nonunions and 3 hypertrophic nonunions. Nonunion treatment of all patients consisted of local debridement through an anterior approach to the humerus and anterior placement of the augmentation plates. Supplemental bone grafting was performed in all atrophic nonunion cases. All patients were followed until union was radiologically confirmed. Union was achieved in 36 patients (97%) after a mean of 6months (range 3-24months). There was one case of iatrogenic median nerve palsy that showed complete spontaneous recovery 6weeks postoperatively. One patient sustained a peri-implant stress fracture that was treated successfully by exchanging the augmentation plate to bridge the nonunion and the fracture. No infections or wound healing complications developed. At a mean follow-up of 14months, all patients showed free shoulder and elbow motion and no restrictions in daily or working life. The results indicate that augmentation plating using an anterior approach is a safe and reliable option for humeral shaft nonunions after failed nailing, and the treatment has no substantial complications. Because the healing rates are similar to the standard technique of nail removal and fixation by compression or locking plates, we consider this technique to be an alternative choice for treatment.

The effect of implant and abutment diameter on peri-implant bone stress: A three-dimensional finite element analysis

Introduction: Load transfer mechanisms from the implant to surrounding bone and failure of osseointegrated implants are affected by implant geometry and mechanical properties of the site of placement as well as crestal bone resorption. Estimation of such effects allows for a correct design of implant geometry to minimize crestal bone loss and implant failure. Objectives: To evaluate the effect of implant and abutment diameter on stress distribution in the peri-implant area. Materials and Methods: Three-dimensional finite element models created to replicate completely osseointegrated endosseous titanium implants and were used for the purpose of stress analysis. Two study groups that consisting of a regular platform (RP) group and narrow platform (NP) group were used with a standard bone density and loaded using the ANSYS Workbench software to calculate the von Mises and Principal (maximum tensile and minimum compressive) stress. Results: The von Mises, compressive, and tensile stresses in the peri-implant bone were lower in the RP model compared to the NP model. Conclusion: RP model yielded a positive result with regard to lowering of peri-implant bone stress levels, in healthy as well as compromised bone qualities when compared to NP designs.

Influence of different abutment diameter of implants on the peri-implant stress in the crestal bone: A three-dimensional finite element analysis--In vitro study.

The study was designed to evaluate and compare stress distribution in transcortical section of bone with normal abutment and platform switched abutment under vertical and oblique forces in posterior mandible region. A three-dimensional finite element model was designed using ANSYS 13.0 software. The type of bone selection for the model was made of type II mandibular bone, having cortical bone thickness ranging from 0.595 mm to 1.515 mm with the crestal region measuring 1.5 mm surrounding dense trabecular bone. The implant will be modulated at 5 mm restorative platform and tapering down to 4.5 mm wide at the threads, 13 mm long with an abutment 3 mm in height. The models will be designed for two situations: (1) An implant with a 5 mm diameter abutment representing a standard platform in the posterior mandible region. (2) An implant with a 4.5 mm diameter abutment representing platform switching in the posterior mandible region. Force application was performed in both oblique and vertical conditions using 100 N as a representative masticatory force. For oblique loading, a force of 100 N was applied at 15° from the vertical axis. von Mises stress analysis was evaluated. The results of the study showed cortical stress in the conventional and platform switching model under oblique forces were 59.329 MPa and 39.952 MPa, respectively. Cortical stress in the conventional and platform switching model under vertical forces was 13.914 MPa and 12.793 MPa, respectively. Results from this study showed the platform switched abutment led to relative decrease in von Mises stress in transcortical section of bone compared to normal abutment under vertical and oblique forces in posterior mandible region.

Influence of Trabecular Bone on Peri-Implant Stress and Strain Based on Micro-CT Finite Element Modeling of Beagle Dog.

The objective of this investigation is to analyze the influence of trabecular microstructure modeling on the biomechanical distribution of the implant-bone interface. Two three-dimensional finite element mandible models, one with trabecular microstructure (a refined model) and one with macrostructure (a simplified model), were built. The values of equivalent stress at the implant-bone interface in the refined model increased compared with those of the simplified model and strain on the contrary. The distributions of stress and strain were more uniform in the refined model of trabecular microstructure, in which stress and strain were mainly concentrated in trabecular bone. It was concluded that simulation of trabecular bone microstructure had a significant effect on the distribution of stress and strain at the implant-bone interface. These results suggest that trabecular structures could disperse stress and strain and serve as load buffers.

FEA of Peri-Implant Stresses in Fixed Partial Denture Prostheses with Cantilevers.

To compare stresses in the peri-implant bone produced by fixed partial prostheses with mesial and distal cantilevers, when cemented or screwed onto implants. The experimental design consisted of four 3D models obtained by volumetric computerized tomography and analyzed using finite element analysis (FEA). Stresses were simulated in two stages. Stage 1 consisted of application of the preload. A 288 N load was applied to pillar screws of the cemented prosthesis, resulting in 389 MPa peak; 257 N was applied to the intermediate screw (multi-unit) resulting in 390 MPa peak; and 111 N was applied to the prosthesis infrastructure screw in the screwed prostheses, resulting in 390 MPa peak. In stage 2, the axial and oblique loads were applied. The axial load consisted of 50 N for molar implants and 30 N for premolar implants. The oblique load (on the buccal slope of the buccal cusp of each crown) consisted of 30 N for premolar implants and 50 N for molar implants, with a buccolingual vector at a 45° angle with the occlusal plane. The response variables were the axial and oblique stresses on the peri-implant bone, according to the following groups: group 1-models of fixed partial prostheses cemented onto implants with mesial or distal cantilevers; group 2-models of fixed partial denture screwed onto implants with mesial or distal cantilevers.Data were recorded, evaluated, and compared. Oblique loads produced higher peak values than axial loads, and were located at the bone crest of the implant closest to the cantilever, regardless of the prosthesis type. In the cemented prosthesis models, oblique loads produced the highest peaks in the primary implant region when compared with the screwed prosthesis models. The screwed fixed prostheses caused less stress on peri-implant bone regardless of whether the cantilever was located mesially or distally.