Simulated Occlusal Loading Research Articles

Evaluation of Reliability and Validity of Different Thicknesses of Occlusal Contact Registration Strips Vs Conventionally used Articulating Papers – An Invitro Study

Aim: To compare and evaluate the reliability and validity of different thicknesses of Occlusal Contact Registration Strips (OCRS) under simulated occlusal load.  Settings and Design: In-Vitro Comparative Study  Materials and Methods: Articulated epoxy resin dental models obtained from completely dentulous patients were interposed with occlusal contact registration strip of various thicknesses and subjected to constant axial compressive load using universal testing machine. The photographs of consistent registration marks were subjectively assessed using a computer software.  Statistical Analysis Used: Analysis of Variance (ANOVA) and post hoc mean multiple comparison using Dunnett T3 test.  Results: The thinnest occlusal registration strip used in this study registered the highest average number of markings with a borderline statistically significant difference (P=0.06). The highest average area of markings was registered by the thickest strip, which had a near marginal significance (P=0.09), whereas the lowest average area was produced by the thinnest strip which was statistically significant (P=0.03).  Conclusion: There exists a relationship between the thickness of an occlusal contact registration strip, the number and the area of the marks registered. The average number of marks registered was inversely proportional to the thickness of the occlusal indicator. Hence, the thinner the occlusal contact registration strip, the more reliable is the occlusal contact registration. The average area of occlusal contact registration mark varies proportionately to its thickness. Hence, the thickest occlusal contact registration strips were more valid for marking occlusal contacts.

Comparative evaluation of stress generation in primary teeth restored with zirconia and BioFlx crowns: A finite element analysis

Background: Maintaining the functional integrity of primary teeth is important, as these teeth are integral in vital functions such as mastication, speech development, and space maintenance for permanent teeth; hence, premature loss of primary teeth can affect a child’s quality of life. Various restorative materials are available to restore the function of grossly decayed teeth. Stainless steel crowns and zirconia crowns are widely used in pediatric dentistry; however, there are certain disadvantages associated with these materials. Recently introduced BioFlx crowns provide acceptable esthetics with a conservative approach. Nevertheless, there is a lack of evidence regarding their strength and clinical acceptability. Finite element analysis measures the physical response of teeth and assesses the stress generation, which is important to estimate the integrity of the restorations and crowns. Purpose: The aim of this in vitro study was to evaluate and compare stress generation in primary teeth restored with zirconia and BioFlx crowns using finite element analysis. Methods: Models of extracted teeth restored with zirconia and BioFlx crowns were used for the study. The finite element analysis of these models was carried out through Analysis of Systems (ANSYS) software. The models were subjected to a simulated occlusal loading force of 245 N. Results: Von Mises stress generated in BioFlx crowns along with underlying dentin was much less compared to that which was generated in zirconia crowns. Conclusion: Restoring the functional integrity of carious teeth is essential. BioFlx crowns can be used as full coverage restorations and can be a suitable alternative to zirconia crowns and traditional stainless steel crowns.

Validation of a shape-optimized 2-unit cantilevered inlay-retained fiber-reinforced resin-bonded dental prosthesis

Statement of problemCurrent designs of fiber-reinforced composite (FRC) resin-bonded fixed dental prostheses (RBFDPs) have a limited lifespan, failing mainly through veneer-fiber delamination, debonding, and fracture. PurposeThe purpose of this in vitro study was to validate a new inlay-retained 2-unit cantilevered RBFDP with an optimized cavity and fiber layout proposed in a previous study by using simulated occlusal loading. Material and methodsTwo groups of specimens (n=20), 1 with and 1 without glass fibers, were used to test the influence of the cavity design and that of the fiber layout on their load capacity, respectively. The specimens without fibers were directly cut from a resin-ceramic block by using a computer-aided manufacturing system, while those with fibers were manually fabricated with unidirectional glass fibers and composite resin in a silicone mold. The specimens with and without fibers were attached to abutments made of the same resin-ceramic with a cyanoacrylate-based adhesive and a resin-based dental cement, respectively. An increasing compressive load was applied on the mesial fossa of the premolar pontic until failure. Cracking in the specimens during loading was monitored with a 2-channel acoustic emission (AE) system. ResultsAll the specimens without fiber reinforcement debonded from the abutments. Those using the optimized shovel-shaped cavity design had a mean ±standard deviation failure load (50.0 ±17.3 N) that was 193% higher than that of those with the conventional step-box design (17.1 ±6.2 N; P<.001). No significant difference was found between the groups for the mean number of AE events per specimen (step-box: 49 ±34 versus shovel-shaped: 63 ±34; P=.427), the mean amplitude of each event (58.4 ±1.3 dB versus 59.5 ±2.4 dB; P=.299), or the mean time to failure (283.2 ±122.3 seconds versus 297.5 ±66.7 seconds; P=.798). Between the groups of specimens with reinforcing fibers, the mean failure load of the conventional design was approximately half that of the optimized one. Again, no significant difference was found for the mean number of AE events per specimen (conventional: 28 ±18 versus optimized: 52 ±53; P=.248) or the mean amplitude for each AE event (64.9 ±4.2 dB versus 61.7 ±5.2 dB; P=.187). The connectors of 8 fiber-reinforced specimens with the conventional design fractured; the other 2 debonded from the abutments. Half of the shape-optimized fiber-reinforced specimens had fractured abutments, but the cantilevers remained intact, 4 specimens fractured at the connector, and only 1 debonded from its abutment. ConclusionsThe shape-optimized 2-unit cantilevered FRC RBFDP had a higher load capacity than the conventional design.

In vitro Effect of Occlusal Loading on Cervical Wall Lesion Development in a Class II Composite Restoration

The aim of this study was to determine the effect of simulated occlusal loading on wall lesion development in cervical gaps of class II composite restorations in vitro. Sixty-four extracted human molars received standardized (4.0 × 4.2 × 3.0 mm) box preparations. The teeth were randomly assigned to one of two restoration groups: restoration with a normal or a low E-modulus composite material (CLEARFIL AP-X: E-modulus 16.8 GPa or CLEARFIL MAJESTY ES Flow: E-modulus 6.6 GPa). A metal matrix was placed at the bottom of the box for each restoration, creating a cervical gap of about 100 μm wide. Samples were exposed to simulated caries lesion development in a lactic acid solution (pH 4.8) for 8 weeks in a Rub&Roll device. Half of the samples were subjected to 90 N cyclic loading. After demineralization, the teeth were sectioned. Wall lesion development was measured using microradiography (transversal wavelength-independent microradiography) in two different locations (location 1: 1,000 μm and location 2: 1,600 μm from the gap entrance) and recorded in lesion depth (LD) (μm) and mineral loss (μm × vol%). Linear regression modeling was used to estimate the effect of loading and material on wall lesion development. Mean wall LD in location 1 across all groups was 150.83 μm with a standard deviation (SD) of 61.83 μm. In location 2, mean overall wall LD was 102.98 μm with an SD of 64.92 μm. Linear regression showed no significant effect of either loading or material on wall lesion development. Occlusal loading had no significant effect on secondary caries lesion development in composite class II restoration in this in vitro study.

What does 'toughness' look like? An examination of the breakdown of young and mature leaves under cyclical loading.

The material property of leaf toughness is considered the crucial mechanical challenge facing folivorous primates. Mature leaves have higher recorded toughness values than young leaves on average, leading to many assumptions about the patterning of food breakdown that follow a tough/not-tough dichotomy. We tested three hypotheses about how leaves break down under repetitive loading cycles, predicting that mature leaves (i) experience more force during simulated occlusal loads, (ii) more effectively resist fragmentation into small pieces, and (iii) show a more gradual decline in resistance over consecutive cycles than young leaves. Under displacement control using a mechanical testing system, we subjected young and mature leaves to 20 cycles of axial loading using interlocking steel wedges, then collected and quantified the size of the leaf fragments. While we found that mature leaves experienced more overall force than young leaves (p < 0.001), they also shattered into smaller pieces (p = 0.004) and showed a steeper decline in their resistance to the cycles over the course of a test (p < 0.01). These results suggest that putatively 'tougher' foods (i.e. mature versus young leaves) do not necessarily resist fragmentation as commonly assumed. The current tough/not-tough paradigm of primate foods may not accurately reflect how leaves break down during masticatory behaviour.

Effects of repetitive insertion/removal cycles and simulated occlusal loads on retention of denture retainers.

The purpose of this study was to investigate the effects of repetitive insertion/removal cycle tests on denture retainers with simulated occlusal loads on the retentive force and deformation of clasp. Abutment teeth in the form of mandibular secondary premolars and clasp in the form of Akers clasps were prepared. The retentive force of the clasp on the abutment teeth were evaluated before and after undergoing repetitive insertion/removal cycle tests with or without cyclic loading. Changes in the clasp shape were monitored using a 3D scanner and scanning electron microscope. The initial retentive force was approximately 10 N and this value later decreased due to deformation of the clasp tips. In contrast to the non-load group, the load group exhibited a reduction in retentive force during earlier stages. Therefore, cyclic loading was related to a decrease in retentive forces, specifically in the early stages of repetitive insertion/removal cycles.

Experimental validation of finite element simulation of a new custom-designed fixation plate to treat mandibular angle fracture

BackgroundThe objective of the study was to validate biomechanical characteristics of a 3D-printed, novel-designated fixation plate for treating mandibular angle fracture, and compare it with two commonly used fixation plates by finite element (FE) simulations and experimental testing.MethodsA 3D virtual mandible was created from a patient’s CT images as the master model. A custom-designed plate and two commonly used fixation plates were reconstructed onto the master model for FE simulations. Modeling of angle fracture, simulation of muscles of mastication, and defining of boundary conditions were integrated into the theoretical model. Strain levels during different loading conditions were analyzed using a finite element method (FEM). For mechanical test design, samples of the virtual mandible with angle fracture and the custom-designed fixation plates were printed using selective laser sintering (SLS) and selective laser melting (SLM) printing methods. Experimental data were collected from a testing platform with attached strain gauges to the mandible and the plates at different 10 locations during mechanical tests. Simulation of muscle forces and temporomandibular joint conditions were built into the physical models to improve the accuracy of clinical conditions. The experimental vs the theoretical data collected at the 10 locations were compared, and the correlation coefficient was calculated.ResultsThe results show that use of the novel-designated fixation plate has significant mechanical advantages compared to the two commonly used fixation plates. The results of measured strains at each location show a very high correlation between the physical model and the virtual mandible of their biomechanical behaviors under simulated occlusal loading conditions when treating angle fracture of the mandible.ConclusionsBased on the results from our study, we validate the accuracy of our computational model which allows us to use it for future clinical applications under more sophisticated biomechanical simulations and testing.

Modelling of stress distribution and fracture in dental occlusal fissures

The aim of this study was to investigate the fracture behaviour of fissural dental enamel under simulated occlusal load in relation to various interacting factors including fissure morphology, cuspal angle and the underlying material properties of enamel. Extended finite element method (XFEM) was adopted here to analyse the fracture load and crack length in tooth models with different cusp angles (ranging from 50° to 70° in 2.5° intervals), fissural morphologies (namely U shape, V shape, IK shape, I shape and Inverted-Y shape) and enamel material properties (constant versus graded). The analysis results showed that fissures with larger curved morphology, such as U shape and IK shape, exhibit higher resistance to fracture under simulated occlusal load irrespective of cusp angle and enamel properties. Increased cusp angle (i.e. lower cusp steepness), also significantly enhanced the fracture resistance of fissural enamel, particularly for the IK and Inverted-Y shape fissures. Overall, the outcomes of this study explain how the interplay of compositional and structural features of enamel in the fissural area contribute to the resistance of the human tooth against masticatory forces. These findings may provide significant indicators for clinicians and technicians in designing/fabricating extra-coronal dental restorations and correcting the cuspal inclinations and contacts during clinical occlusal adjustment.

A three-dimensional finite element analysis to evaluate stress distribution tooth in tooth implant-supported prosthesis with variations in non-rigid connector design and location.

The physiologically mobile natural tooth and rigidly fixed dental implant causes different distribution of stress when connected in prosthesis and nonrigid connector compensates this. Understanding of biomechanical behavior is necessary for an adequate choice and construction of this type of rehabilitation. However, there has been insufficient research focusing on different location and type of the nonrigid connector related with the prognosis of both implant and the tooth. The purpose of this finite element (FE) analysis was to evaluate the stress distribution around bone, implant, and tooth in tooth implant fixed prosthesis under static load with variations in design and location of nonrigid connectors under simulated functional loads. Three, 3-dimensional FE models connecting tooth and implant were constructed with different location and type of nonrigid connector. Simulated occlusal load was applied on the restorations and stresses developed in the supporting structures were monitored. The highest stresses were found around the implant in model with nonrigid connector placed between the tooth and implant and model with modified nonrigid connector. On the other hand, less stress was noted around the implant where nonrigid connector was placed between the implant and pontic. It is advisable to place the nonrigid connector between the implant and the pontic to protect the implant from torque effects in a tooth implant fixed prosthesis.

Interfacial degradation of adhesive composite restorations mediated by oral biofilms and mechanical challenge in an extracted tooth model of secondary caries

ObjectiveTo study the combined effect of simulated occlusal loading and plaque-derived biofilm on the interfacial integrity of dental composite restorations, and to explore whether the effects are modulated by the incorporation of sucrose. MethodsMOD-class-II restorations were prepared in third molars. Half of the specimens (n=27) were subjected to 200,000 cycles of mechanical loading using an artificial oral environment (ART). Then, both groups of specimens (fatigued and non-fatigued) were divided into three subgroups for testing in CDC-reactors under the following conditions: no biofilm (Control), biofilm with no sucrose (BNS) and biofilm pulsed with sucrose (BWS). BNS and BWS reactors were incubated with a multispecies inoculum from a single plaque donor whereas the control reactor was not. The BWS reactor was pulsed with sucrose five times a day. The biofilm challenges were repeated sequentially for 12 weeks. pH was recorded for each run. Specimens were examined for demineralization with micro-CT and load capacity by fast fracture test. ResultsDemineralization next to the restorations was only detectable in BWS teeth. Fracture loads were significantly reduced by the concomitant presence of biofilm and sucrose, regardless of whether cyclic mechanical loading was applied. Cyclic loading reduced fracture loads under all reactor conditions, but the reduction was not statistically significant. ConclusionsSucrose pulsing was required to induce biofilm-mediated degradation of the adhesive interface.We have presented a comprehensive and clinically relevant model to study the effects of mechanical loading and microbial challenge on the interfacial integrity of dental restorations.

Finite element analysis on tooth and periodontal stress under simulated occlusal loads.

The tooth stress elicited by occluding contact represents critical biomechanical information about dental health during chewing. Effects of occlusal contact on tooth stress remain obscure. In this study, a mandibular first molar finite element model was built from CT images. The effects of area size, location and direction of occlusal loading on both tooth and periodontal stresses were analysed. Results showed tooth and periodontal stress had drastically different patterns. Tooth stress value was much higher than periodontal stress value under the same task. Tooth stress concentration area and its value decreased from outside to inside. The Maximum Tooth Stress (MTS) always occurred at the loading site and a larger loading area elicited a smaller MTS value. The variation of MTS was larger when the fossa bottoms were inclined loaded than when the cusp tips were inclined loaded, larger when lingually loaded than when buccally loaded and larger when mesially loaded than when distally loaded. Distal loadings generally induced smaller Maximum Periodontal Stress (MPS) variations than the mesial loadings. These findings indicated exposure of the rational site(s) to occlusal contact should be helpful to achieve proper tooth and periodontal stress, thus to diminish loading associated structure problems.

FRACTURE RESISTANCE OF ENDODONTICALLY TREATED TEETH RESTORED WITH FOUR DIFFERENT RESTORATIVE TECHNOLOGIES

This study was conducted to evaluate both the effect of different cavity designs and different ceramic, composite CAD/CAM blocks and regular direct resin composite on the fracture resistance of endodontically treated teeth. Materials and methods: A total of 80, non-carious, crack-free freshly extracted human maxillary premolars were used in this study. The teeth received a standardized endodontic treatment and then were divided in to two groups (40 each) according to the cavity design Design1 (MOD cavities) and Design2 (MOD with buccal and lingual cusp reduction), the two groups were further subdivided into sub groups (10 each) according to the type of restorative material used, either IPS e max CAD, Lava Ultimate, Vita Enamic, or Filtek Z 350 XT. Teeth were mounted in a universal testing machine, compressed with crosshead speed of 1mm/min, for testing their fracture resistance.Results: One-way ANOVA was used to test each main effect separately. One-way ANOVA for the effect of cavity design showed statistical significant difference between both designs (P= 0.003). The post-hoc test revealed that Design 2 has the significantly higher mean fracture resistance (P= 0.001) than did Design 1. Meanwhile, One-way ANOVA for the effect of type of restorative material used showed statistical significance for types of restorative material used (P= 0.001). The post-hoc test revealed that IPS e max CAD has significantly the highest mean fracture resistance (P= 0.001). Moreover, Lava Ultimate and Vita Enamic had significantly higher mean fracture resistance than that of Filtek Z 350 XT (P= 0.001). Conclusions: Within the limitations of the study, it can be concluded that Endodontically treated maxillary premolars prepared with an extensive loss of tooth structure and restored with chair-side indirect esthetic restorations had a resistance to fracture under simulated occlusal load significantly higher than that of direct resin composite restorations.Chair-side CAD/CAM ceramic restorations are superior over hybrid ceramics.Allowing a cusp coverage of approximately 2.5 mm in bulk would enhanced fracture resistance of dentin-bonded onlays over inlay preparations with no cusp coverage in vitro.

Stress and strain analyses of removable partial denture abutment tooth in relation to the position of the minor connector

Introduction/Objective For optimum loading distribution, the angle formed by the occlusal rest and the vertical minor connector from which it originates should be less than 90?. The objective of the article was to visualize the optimum angle between the occlusal rest and the minor connector in terms of intensity and distribution of occlusal loads using finite element analysis. It was the intention, concerning biomechanical behavior, to document that the optimum angle between the occlusal rest and the minor connector should be less than 90?. Methods Three different virtual models of partial edentulous Kennedy III class were created using the CATIA design computer program with different angles between the occlusal rest and the minor connector. Stress distribution after simulated occlusal loading was analyzed using the finite element method. Results Comparing the results obtained for three models, the highest stress values were seen in model 3 (the angle between the occlusal rest and the small connector is greater than 90?) whether the load is applied in the middle or at the end of the saddle. Conclusion Within limitations and on the basis of the study results, the minimum compressive stress was seen in model 1, where the angle between the occlusal rest and the minor connector was less than 90? whether the load is applied in the middle or at the end of the saddle. It is recommended that obtuse angle between the rest and the minor connector should be avoided due to potential hazardous stress concentration on abutment teeth.

Influence of Implant Design (Cylindrical and Conical) in the Load Transfer Surrounding Long (13mm) and Short (7mm) Length Implants: A Photoelastic Analysis.

Purpose:This study compared the influence of implant design (cylindrical and conical) in the load transfer on bone surrounding 13mm and 7mm length implants under simulated occlusal loading, using photoelastic analysis.Method:Dental implants of 4mm diameter were divided into four groups, which varied in length and design: Group 1- standard (13 mm) cylindrical implant; Group 2 - standard conical implant; Group 3 – short (7 mm) cylindrical implant, and Group 4 - short conical implant. After the inclusion of the implant models in a photoelastic resin, they were subjected to a static load of 100 N. The lengths of the fringes that were generated were measured in three portions since the implants body: crestal, central and apical portion, parallel to the implant long axis. Furthermore, the entire extension area of dissipation of force was measured. Data were analyzed by one-way ANOVA (α = 0.05).Results:Lower stress was observed at the crestal bone in groups 2 and 4, while the stress levels in groups 1 and 3 were higher with significant differences compared to the other groups (p<0.05).Conclusion:The total amount of stress transmitted to the bone was not affected by implant length under axial loading condition, but changed in relation to the implant design with respect to the concentration of the fringes, which corresponded to the load distribution, with even more dissipation by conical implants.

Stress and strain distribution in demineralized enamel: A micro-CT based finite element study.

Physiological oral mechanical forces may play a role on the progression of enamel carious lesions to cavitation. Thus, the aim of this study was to describe, by 3D finite element analysis, stress, and strain patterns in sound and carious enamel after a simulated occlusal load. Micro-CT based models were created and meshed with tetrahedral elements (based on an extracted third molar), namely: a sound (ST) and a carious tooth (CT). For the CT, enamel material properties were assigned according to the micro-CT gray values. Below the threshold corresponding to the enamel lesion (2.5 g/cm(3) ) lower and isotropic elastic modulus was assigned (E = 18 GPa against E1 = 80 GPa, E2 = E3 = 20 GPa for sound enamel). Both models were imported into a FE solver where boundary conditions were assigned and a pressure load (500 MPa) was applied at the occlusal surface. A linear static analysis was performed, considering anisotropy in sound enamel. ST showed a more efficient transfer of maximum principal stress from enamel to the dentin layer, while for the CT, enamel layer was subjected to higher and concentrated loads. Maximum principal strain distributions were seen at the carious enamel surface, especially at the central fossa, correlating to the enamel cavity seen at the original micro-CT model. It is possible to conclude that demineralized enamel compromises appropriate stress transfer from enamel to dentin, contributing to the odds of fracture and cavitation. Enamel fracture over a dentin lesion may happen as one of the normal pathways to caries progression and may act as a confounding factor during clinical diagnostic decisions.

PREMAKSİLLA İLE TEK TARAFLI MAKSİLLER DEFEKTLİ REZEKSİYON OBTURATÖRLERİNİN ÜÇ BOYUTLU SONLU ELEMANLAR STRES ANALİZ YÖNTEMİYLE DEĞERLENDİRİLMESİ

Purpose: The objective of this study is to analyze comperatively the properties of functional load and stres distribution by using Aramany Class IV obturator protheses with/without zygomatic implants. Material and Methods: A 3-D solid model of an Aramany Class IV maxillary resection case and it’s prosthesis was constructed. 150 N vertical force was loaded by first molar teeth. Simulated occlusal loading was applied on three different points. First loading was applied to the defected side, second was applied to the contralateral side and third one was applied to both. Qualitative analysis was based on the scale of maximum and minimum principle stress in the bone were investigated in Algor(Fempro, USA) programme Results: Maximum and minimum principal stresses in bone under different loading were illustrated with figures and color scales. Obtained numerical datas was represented in graphics. Conclusion: Placing a zygomatic implant to the defected area decreased the stresses occured in the bone. Zygomatic implant is an alternative treatment option for Aramany class IV obturator protheses

Platform switching on wide-diameter external hex implants: a finite element analysis.

Objectives: The objective of this work was to use finite element analysis to compare the effect of forces coming to bear on abutments 4.1 or 5.0 mm in diameter connected to a 5.0 mm implant (i.e. with or without platform switching). Study design: A 3D CAD model of a 5 x 11.5 mm external hex implant was developed, complete with a connection screw and either of two abutments, one 4.1 and the other 5 mm in diameter, to assess the influence of two loading conditions, i.e. 200 N loaded either axially or off center on the top of the abutment. Results and conclusions: In the symmetrically loaded models, greater stresses were transmitted to the bone in the area below the neck of the implant in the case of the wider-diameter abutment. When the narrower abutment was considered, the stress lines remained confined to the metal and were transferred to the bone in a more distal position. When the stresses in the bone where compared under non-symmetrical loading of the larger- and smaller-diameter abutments, the stresses reached lower values in the latter case. These findings indicate that platform switching (i.e. coupling a 4.1 mm abutment with a 5 mm implant) achieves a better, more even distribution of the peri-implant stresses deriving from simulated occlusal loads on the bone margins. Key words:Platform switching, finite element analysis, implant.

Influence of Occlusal Forces on Stress Distribution on Preloaded Dental Implant Abutment Screws: A Finite Element Analysis Study

Purpose: The aim of the study is to determine stress distribution on preloaded implant-abutment screws in three different implant systems under simulated occlusal loads. Materials and methods: Three abutments to implant internal hex joint systems were simulated by using the 3-dimensional finite element analysis; (1) Nobel Biocare replace tapered (2) Uniti (3) Lifecare self-threaded tapered cement retained abutments. Thermal load and contact analysis were used to simulate preload resulting from the torque in implant screw joint assemblies. The simulated preload implants were then loaded with three static occlusal loads (10N horizontal; 35N vertical; 70N oblique) onto the crown into the implant complex. Results: Under preload and static occlusal forces, maximum Von-Mises stresses were concentrated at the lower portion of abutment for all systems. Maximum stresses were concentrated at lower threaded portion of abutment screw in Nobel Biocare, Uniti but in Lifecare system, stresses were concentrated at the middle threaded portion. Maximum stresses were concentrated at middle threaded portion of implant in Nobel Biocare, Uniti but at the upper threaded portion in Lifecare. Stresses increased under static occlusal forces in abutment screw in Nobel Biocare and Uniti but were more under oblique forces. In Lifecare stresses decreased under horizontal forces and increased in vertical and oblique forces. Conclusion: Although, an increase or decrease was demonstrated for the maximum calculated stress values in preloaded screws. After occlusal loads, these maximum stress values were well below the yield stress of abutment screw systems tested.

Study of Deflections in Maxillary Major Connectors: A Finite Element Analysis

The Major connector is the major component of the cast partial denture to which all other parts are directly or indirectly attached. It also provides cross arch stability to help resist displacement by functional stresses. The major connector should be rigid. A flexible major connector causes an unequal distribution of forces with changes in their intensity and may cause damage to the supporting structures. Thus rigidity is of paramount to resist flexing and torquing forces. The commonly used major connectors for the maxillary arch are Anteroposterior strap, palatal strap and complete palatal plate. Application of load on the prosthesis will result in deflection. The magnitude and direction of the deflection that the prosthesis undergoes depends on the rigidity of the major connector. (1) To determine the deflection seen in maxillary removable partial denture frameworks under simulated occlusal load. (2) To compare the rigidity and deflection characteristics of different maxillary major connectors used in maxillary Kennedy's class I, class II, class III and class IV situations. A CT scan of human edentulous maxilla was taken and each section from the incisive foramen to the hamular notch was projected on the graph paper and three dimensional volumes were created from the connected successive profiles to define the final solid geometry of bone. Six framework models with different Maxillary major connectors such as Anteroposterior straps and complete palatal plate for Kennedy's class I, class II, class III and class IV situations were created. Three Dimensional Finite Element Models corresponding to the geometric model were created using ANSYS 9.0 version. The model was assigned the material properties. A vertical biting force of 20N was applied. The results showed maximum displacements were observed at the posterior edge of the saddle for all the frameworks. Anteroposterior palatal strap in class III and class IV situation showed the least deflection when compared to class I and class II (distal extension situation) Anteroposterior palatal strap is more rigid connector than the full palatal plate, single palatal strap, and U-shaped palatal strap and can be used in all situations.

Angled abutments result in increased or decreased stress on surrounding bone of single-unit dental implants: A finite element analysis

The influence of angled abutments on stress is a matter of debate. It is widely accepted that increased stress on implants and bone has been associated with the use of angled abutments.However, comparisons of clinical success rates of implants restored with angled and straight abutments indicate no significant differences. The aim of the present study was to determine whether angled abutments could result in decreased stress on surrounding bone of single-unit dental implants. By means of finite element analysis (FEA), four simplified models were designed to simulate clinical scenarios in which that implants were placed in an ideal axial position or at an angled position. Each implant was paired with a straight or angled abutment. A simulated occlusal load of 100N was applied along the vertical axis of the jawbone. The von Mises stress and strain were recorded for each model. The numerical results showed that angled abutments resulted in decreased stresses when implants were not placed in ideal axial position. The present study identified by means of FEA that angled abutments could result in decreased stress on the supporting bone of implant system and may provide some clues to resolve the debate regarding the influence of angled abutments.