Angel Alvarez-Arenal

Non-linear numerical analysis of a double-threaded titanium alloy dental implant by FEM

The aim of this work is to study the performance of a double-threaded variable pitch titanium alloy dental implant in a maxillary molar tooth after an implantology treatment by the finite elements method (FEM). The study employed three-dimensional finite elements modelling in order to simulate typical occlusal loads. The three-dimensional basic design of the dental implant, consisting of a dental implant and a piece of jaw, was developed with a three-dimensional parametric design program. One of the major areas of non-linear analysis is the solution of problems where separate bodies or structures may come in contact with each other. The non-linearity due to the contact between the dental implant and the jaw has been taken into account here. In order to study the influence of the variable pitch in the biomechanical behaviour of the dental implant, several configurations of this screw were solved. The nominal occlusal load was applied in all of them. A total of 27 specimens were checked. The stresses and displacements of each are shown in different tables and figures. The optimum configuration was chosen according to these results. From an osseointegration point of view, the optimum dental implant configuration presents a major advantage over the other specimens considered: the bone-implant contact surface is greater than in the other ones and the maximum von Mises stress in the jaw remains close to minimum values. From the biomechanical point of view, one of the specimens was chosen as the best dental implant screw of those checked in the present article. Such selection was made taking into account the stresses produced in its checking and the total bone-implant contact surface. Finally, the stresses of the different elements of the dental implant, the configuration of the optimum dental implant screw as well as conclusions of this research are expounded.

La reestenosis en el stent depende del daño vascular inducido. ¿Son válidos los modelos experimentales actuales de análisis de los stents farmacoactivos?

INTRODUCTION AND OBJECTIVES Drug-eluting stents are useful for preventing restenosis, but the patho-physiological processes involved in the proliferative response after implantation are still not known in detail. The aim of this study is to compare the coronary vascular histomorphometry after implanting drug-eluting stents and bare metal stents in a swine model. METHODS Sixty stents were randomly implanted in 20 Large White female pigs with a ratio of baremetal/drug-eluting stents of 1:2. After 28 days, euthanasia and histomorphometry were performed. We defined the vessel injury score in accordance to whether the internal elastic lamina was intact or ruptured. RESULTS There were no differences between drug-eluting stents and bare metal stents in the intact internal elastic lamina group regarding neointimal area or % restenosis (1.3 [1.1-2.2]) vs 2.0 [1.3-2.5] mm²; P=.6; and 14.0 [12.1-20.8] vs 22.2 [14.1-23.3] %; P=.5). We assessed statistically significant differences for the ruptured internal elastic lamina group, (neointimal area 1.2 [0.8-2.0] vs 2.9 [2.3-3.7] mm²; P=.001 and % restenosis 16.63 [11.2-23.5] vs 30.4 [26.4-45.7] %; P=.001). CONCLUSIONS In our swine model, we did not find any differences between proliferative response of drug-eluting stents and bare metal stents when the internal elastic lamina is intact; differences are only found when vascular injury is deeper.

Stress distribution in the abutment and retention screw of a single implant supporting a prosthesis with platform switching.

PURPOSE Three-dimensional finite element analysis was conducted to evaluate and compare the stress distribution in the abutment and retention screw of implant-supported single crowns with platform switching and with a conventional platform under vertical and oblique loading. MATERIALS AND METHODS Two finite element models were created simulating an osseointegrated implant (4 × 10 mm, platform 4.1 mm) embedded in jawbone. One model simulated a 4-mm-diameter abutment connection (conventional model) and the other represented a 3.8-mm-diameter abutment connection (platform-switched model). A crown with a cobalt-chromium framework and feldspathic porcelain veneering was applied to the titanium abutment. Static vertical and oblique loads were applied to the crown, with a maximum load of 150 N. RESULTS In both models, the highest stress values occurred in the abutment during vertical and oblique loading. Nevertheless, the von Mises stresses in the abutment and the retention screw were lower in the platform-switched model than in the conventional model. During axial loading, the abutment and screw supported slightly less stress in the conventional model than in the platform-switched model. Increases in the angle of force application caused a progressive increase in stresses in the abutment and screw in both models. The maximum stress was distributed at the margin and transgingival area of the abutment and on two-thirds of the flat area and the first threads of the retention screw in both models. CONCLUSIONS Platform switching reduced the stress values on the abutment and retention screw of a single-unit prosthesis during oblique loading. Regardless of whether platform switching was employed, the stress on the abutment and screw gradually increased as the loading direction changed from vertical to 45 degrees oblique. The locations and distributions of stresses were similar in both models.

A jaw model for the study of the mandibular flexure taking into account the anisotropy of the bone

Knowledge of the complex biomechanical behaviour of the human mandible is of great importance in various clinical situations. The biomechanical and physical behaviour of mandibles have been investigated by different approaches. Some research have been done to evaluate the functional character of mandibles. Methods such as indirect measurement of deformations performed by intraoral appliances and by holographic interferometry have being employed. Other studies evaluated the mechanical properties and material parameters of small cubes of mandibles. One disadvantage of the experiments using strain gauges or holographic interferometry is the inability to determine strains at defined positions within the specimen. Additionally, research in biomechanics by these methods is limited to surface deformations and neither stresses nor dislocations can be measured. In the course of this study, we have investigated the mandibular flexure under mechanical loads using the results of a Finite Element Analysis (FEA). In order to obtain more accurate and realistic results, the bone anisotropy has being taken into account for the mathematical modelling of the jaw. The objective of this study was to establish a non-invasive procedure to predict precisely the complex biomechanical reactions of mandibles under mechanical loading. In order to achieve this aim, a comparison of the numerical data obtained with the experimental values of previous studies was performed. It showed a good correlation between in vitro measurements and mathematical modelling. Then the Finite Elements (FE) model was used to evaluate some mandibular movements (corporal approximation, dorsoventral shear, and corporal rotation in edentulous subjects). It is concluded that the applied procedure of generating the FE model is a valid and accurate non-invasive method to predict different parameters of the complex biomechanical behaviour of human mandibles.

The selection criteria of temporary or permanent luting agents in implant-supported prostheses: in vitro study

PURPOSE The use of temporary or permanent cements in fixed implant-supported prostheses is under discussion. The objective was to compare the retentiveness of one temporary and two permanent cements after cyclic compressive loading. MATERIALS AND METHODS The working model was five solid abutments screwed to five implant analogs. Thirty Cr-Ni alloy copings were randomized and cemented to the abutments with one temporary (resin urethane-based) or two permanent (resin-modified glass ionomer, resin-composite) cements. The retention strength was measured twice: once after the copings were cemented and again after a compressive cyclic loading of 100 N at 0.72 Hz (100,000 cycles). RESULTS Before loading, the retention strength of resin composite was 75% higher than the resin-modified glass ionomer and 2.5 times higher than resin urethanebased cement. After loading, the retentiveness of the three cements decreased in a non-uniform manner. The greatest percentage of retention loss was shown by the temporary cement and the lowest by the permanent resin composite. However, the two permanent cements consistently show high retention values. CONCLUSION The higher the initial retention of each cement, the lower the percentage of retention loss after compressive cyclic loading. After loading, the resin urethane-based cement was the most favourable cement for retrieving the crowns and resin composite was the most favourable cement to keep them in place.

Fracture Resistance of Monolithic High Translucency Zirconia Implant-Supported Crowns.

Aim:To evaluate the resistance to axial forces of screw-retained monolithic high translucency zirconia (mHTZr) crowns compared with high translucency zirconia + feldspathic ceramic (HTZrC) crowns, low translucency zirconia + feldspathic ceramic (LTZrC) crowns, and metal-ceramic (MC) crowns, and also to observe the different fracture patterns between all groups. Methods:Twenty-four crowns were fabricated (6 of each group) and loaded until failure, using a testing machine with a 5.0-kN load cell. Results:Mean fracture results varied between 1092.7 N (LTZrC group) and 3439.7 N (mHTZr group). No statistically significant differences were found between the HTZrC, LTZrC, and MC groups. However, statistically significant differences (P < 0.05) were found between mHTZr and the other 3 groups. In the MC group, only chipping of the ceramic veneering occurred. In the mHTZr group, when fracturing occurred, it was of the whole structure. Finally, the LTZrC and HTZrC groups suffered both chipping and core fractures. Conclusion:High translucency monolithic zirconia implant–supported crowns proved to be the toughest group studied when an axial force was applied. Fracture patterns varied between different materials, chipping being the most common occurrence.

Relationship Between Insertion Torque and Resonance Frequency Measurements, Performed by Resonance Frequency Analysis, in Micromobility of Dental Implants: An In Vitro Study.

Purpose:To evaluate the micromobility of dental implants under occlusal loading in relation to stability measurements of resonance frequency analysis and insertion torque. Materials and Methods:The sample comprised of 24 implants inserted in 12 fresh cow ribs. Insertion torque and Osstell implant stability quotient (ISQ) measurements were recorded. An “ad hoc” acrylic premolar was made on a temporary abutment and screwed to each implant, and a force of 100 N was subsequently applied at an angle of 6 degrees. Implant micromotion was measured using a Questar microscope with a resolution of 2 &mgr;m and an image analysis program. Results:Data show a statistically significant inverse correlation between the ISQ values and implant micromotion under a load of 100 N (R2 = 0.86, P < 0.0001). The same relationship is found between insertion torque and implant micromotion, although the relationship is linear up to 34 N·cm and becomes exponential for higher values (R2 = 0.78, P < 0.0001). A direct correlation is established between insertion torque and ISQ values. Conclusion:There is an inverse relationship between both ISQ and insertion torque values and implant micromotion under a load of 100 N.

Effect of implant- and occlusal load location on stress distribution in Locator attachments of mandibular overdenture. A finite element study

PURPOSE The aim of this study is to evaluate and compare the stress distribution in Locator attachments in mandibular two-implant overdentures according to implant locations and different loading conditions. MATERIALS AND METHODS Four three-dimensional finite element models were created, simulating two osseointegrated implants in the mandible to support two Locator attachments and an overdenture. The models simulated an overdenture with implants located in the position of the level of lateral incisors, canines, second premolars, and crossed implant. A 150 N vertical unilateral and bilateral load was applied at different locations and 40 N was also applied when combined with anterior load at the midline. Data for von Mises stresses in the abutment (matrix) of the attachment and the plastic insert (patrix) of the attachment were produced numerically, color-coded, and compared between the models for attachments and loading conditions. RESULTS Regardless of the load, the greatest stress values were recorded in the overdenture attachments with implants at lateral incisor locations. In all models and load conditions, the attachment abutment (matrix) withstood a much greater stress than the insert plastic (patrix). Regardless of the model, when a unilateral load was applied, the load side Locator attachments recorded a much higher stress compared to the contralateral side. However, with load bilateral posterior alone or combined at midline load, the stress distribution was more symmetrical. The stress is distributed primarily in the occlusal and lateral surface of the insert plastic patrix and threadless area of the abutment (matrix). CONCLUSION The overdenture model with lateral incisor level implants is the worst design in terms of biomechanical environment for the attachment components. The bilateral load in general favors a more uniform stress distribution in both attachments compared to a much greater stress registered with unilateral load in the load side attachments. Regardless of the implant positions and the occlusal load application site, the stress transferred to the insert plastic is much lower than that registered in the abutment.

Temporomandibular disorder or not? A case report

Objectives: The purpose of this case study is to show the need for a good differential diagnosis of suspected temporomandibular disorder (TMD) with otologic symptoms. Methods/Results: This study is a clinical case referring to a patient seeking treatment for pain in the right maxilla. The usual Medical History for diagnosis of a TMD was applied. Anamnesis revealed the patient had had a right maxillary pain for one month, a slight hearing loss and dizziness for the past five to six months, and two implants placed in the upper jaw two years previously. Clinical examination showed right temporomandibular joint (TMJ) clicking and tenderness in the lateral pterygoid muscles and in the right masseter muscle. Temporomandibular disorder and orofacial pain were diagnosed, and the appropriate treatment was initiated. In addition, a cranial magnetic resonance imaging (MRI) evaluation was requested and revealed acoustic neuroma. Conclusion: The coexistence of TMD with otovestibular symptoms suggests the need for a cranial MRI evaluation, especially if the dental or TMD treatment has not been positive.

An artificial neural network model for the prediction of bruxism by means of occlusal variables

Patients suspected of bruxism represent a very heterogeneous group. Some require immediate treatment while others, with only minor disorders, may not need treatment at all. In this work, artificial neural network ensembles models were trained on with data from 325 bruxist patients examined at the Department of Prosthodontics and Occlusion (Craniomandibular Dysfunction Unit) of Oviedo University. The information retrieved from each patient included some occlusal variables and other information such as their gender and age. The aim of the model is to classify individuals suffering from bruxism in clenching and grinding patients. The models were analyzed using receiver operating characteristics curve analysis, calibration assessments, inter- and intra-method variations. Effective odds ratios for the artificial neural network ensembles were compared. The model resulted in an area under the receiver operation characteristics curve of 86%. At 95% sensitivity, the specificity was 84.1%, for the existence of 43.5% of bruxists clenching patients in the population of this study. This population corresponds to a grinding patients’ best predictive value of 97.2% and a clenching patients’ best predictive value of 89.5% both using the bagging method. The artificial neural network model obtained can distinguish between clenching and grinding patients requiring the analysis of a few variables and with a high rate of success.