Photoelastic Analysis of Biomechanical Behavior of Single and Multiple Fixed Partial Prostheses With Different Prosthetic Connections

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The influence of bone quality on the biomechanical behavior of full-arch implant-supported fixed prostheses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

BIOMECHANICAL BEHAVIOR OF THE SYSTEM PROSTHESIS/DENTAL IMPLANT: ANALYSIS BY THE PHOTOELASTICITY METHOD

One of the main reasons for the failure in dental implant treatments is the overload, which can cause bone resorption and later, the osseointegration loss in the implant. Therefore, the aim of this study was to analyze the tension generated around dental implants in the rehabilitation of three mandible posterior teeth, varying the connection type, the disposal, and the quantity of implants. The photoelasticity method was used in order to accomplish it. Through photoelasticity, the quantity and localization of the tensions around the implants in the different studied groups were compared (three straight line implants, three offset placement implants, two implants with a mesial cantilever, and two implants with a pontic). The results showed that the tension quantity and disposition around the dental implants of the connection external hexagon and internal hexagon were similar in all groups. In the group where the cantilever was used, an increase of the tension around the implant, adjacent to the cantilever, was observed. From the results it is concluded that the type of connection used in this study did not influence the tension quantity and distribution around the implants; however, the prosthetic configuration with the cantilever use, led to an increase of the tension around the implant, adjacent to the cantilever.

Analysis of the biomechanical behavior of short implants: the photo-elasticity method

The aim of this study was to analyze the stress distribution of short implants supporting single unit or splinted crowns by the photo-elasticity method. Four photo-elastic models were produced: A (3.75×7mm); B (3.75×7mm, 3.75×7mm and 3.75×7mm); C (3.75×10mm, 3.75×7mm and 3.75×7mm); D (3.75×13mm, 3.75×7mm and 3.75×7mm). The prostheses were made with Ni-Cr alloy. A load of 100N in the axial and oblique directions was applied, totaling 380 applications, individually capturing their images in each model. The data were randomized and analyzed qualitatively and quantitatively by 2 examiners. The oblique loading was significantly more damaging. The increase in length was favorable for stress distribution (p<0.05). The splinting was beneficial for the transmission of stresses mainly (p<0.05). The splinting of the crowns, as well as increasing the length of the first implant and axial loading was most beneficial in the stress distribution. Short splinted implants behaved better than single unit implants. Increasing of the length of the first implant significantly improved the stress distribution in all analyzed situations.

Implant Platform Switching: Biomechanical Approach Using Two-Dimensional Finite Element Analysis

In implant therapy, a peri-implant bone resorption has been noticed mainly in the first year after prosthesis insertion. This bone remodeling can sometimes jeopardize the outcome of the treatment, especially in areas in which short implants are used and also in aesthetic cases. To avoid this occurrence, the use of platform switching (PS) has been used. This study aimed to evaluate the biomechanical concept of PS with relation to stress distribution using two-dimensional finite element analysis. A regular matching diameter connection of abutment-implant (regular platform group [RPG]) and a PS connection (PS group [PSG]) were simulated by 2 two-dimensional finite element models that reproduced a 2-piece implant system with peri-implant bone tissue. A regular implant (prosthetic platform of 4.1 mm) and a wide implant (prosthetic platform of 5.0 mm) were used to represent the RPG and PSG, respectively, in which a regular prosthetic component of 4.1 mm was connected to represent the crown. A load of 100 N was applied on the models using ANSYS software. The RPG spreads the stress over a wider area in the peri-implant bone tissue (159 MPa) and the implant (1610 MPa), whereas the PSG seems to diminish the stress distribution on bone tissue (34 MPa) and implant (649 MPa). Within the limitation of the study, the PS presented better biomechanical behavior in relation to stress distribution on the implant but especially in the bone tissue (80% less). However, in the crown and retention screw, an increase in stress concentration was observed.

Tilted and Short Implants Supporting Fixed Prosthesis in an Atrophic Maxilla: A 3D-FEA Biomechanical Evaluation

Purpose: This study compared the biomechanical behavior of tilted long implant and vertical short implants to support fixed prosthesis in an atrophic maxilla. Materials and Methods: The maxilla model was built based on a tomographic image of the patient. Implant models were based on micro-computer tomography imaging of implants. The different configurations considered were M4S, four vertical anterior implants; M4T, two mesial vertical implants and two distal tilted (45°) implants in the anterior region of the maxilla; and M6S, four vertical anterior implants and two vertical posterior implants. Numerical simulation was carried out under bilateral 150N loads applied in the cantilever region in axial (L1) and oblique (45°) (L2) direction. Bone was analyzed using the maximum and minimum principal stress (σmax and σmin), and von Mises stress (σvM) assessments. Implants were analyzed using the σvM. Results: The higher σmax was observed at: M4T, followed by M6S/L1, M6S/L2, M4S/L2, and M4S/L1 and the higher σvM: M4T/L1, M4T/L2 and M4S/L2, M6S/L2, M4S/L1, and M6S/L1. Conclusions: The presence of distal tilted (all-on-four) and distal short implants (all-on-six) resulted in higher stresses in both situations in the maxillary bone in comparison to the presence of vertical implants (all-on-four). © 2013 Wiley Periodicals, Inc.

Mechanical behavior of dental implants in different positions in the rehabilitation of the anterior maxilla

Statement of problem. In dental rehabilitations that involve implants, the number of implants is sometimes smaller than the number of lost teeth. This fact can affect the biomechanical behavior and success of the implants.Purpose. The purpose of this study was to investigate the mechanical behavior of different implant positions in the rehabilitation of the anterior maxilla.Material and methods. Three-dimensional models of the maxilla were created based on computed tomography images for 3 different anterior prosthetic rehabilitations. In group IL, the implants were placed in the lateral incisor positions with pontics in the central incisor positions; in group IC, the implants were in the central incisor positions with cantilevers in the lateral incisor positions; and, in group ILIC, one implant was in a lateral incisor position and one was in a central incisor position, with a pontic and a cantilever in the remaining positions. A 150 N load was distributed and applied at the center of the palatal surface of each tooth at a 45-degree angle to the long axis of the tooth. The resulting stress-strain distribution was analyzed for each group.Results. The lowest displacement of the prosthetic structure was observed in group IC, although the same group exhibited the largest displacement of the bone tissue. In the bone tissue, the von Mises stress was mainly observed in the cortical bone in all groups. The maximum value of the von Mises stress shown in the cortical tissue was 35 MPa in the implant that neighbors the cantilever in group ILIC. The maximum von Mises stress in the trabecular bone was 3.5 MPa.Conclusion. The prosthetic configuration of group IC limited the displacement of the prosthetic structure but led to greater displacement of the bone structure. The use of a cantilever increased the stress concentration in the implant and in the bone structure adjacent to the cantilever under the conditions studied here.

Assessment of corneal dynamics with high-speed swept source optical coherence tomography combined with an air puff system

We present a novel method and instrument for in vivo imaging and measurement of the human corneal dynamics during an air puff. The instrument is based on high-speed swept source optical coherence tomography (ssOCT) combined with a custom adapted air puff chamber from a non-contact tonometer, which uses an air stream to deform the cornea in a non-invasive manner. During the short period of time that the deformation takes place, the ssOCT acquires multiple A-scans in time (M-scan) at the center of the air puff, allowing observation of the dynamics of the anterior and posterior corneal surfaces as well as the anterior lens surface. The dynamics of the measurement are driven by the biomechanical properties of the human eye as well as its intraocular pressure. Thus, the analysis of the M-scan may provide useful information about the biomechanical behavior of the anterior segment during the applanation caused by the air puff. An initial set of controlled clinical experiments are shown to comprehend the performance of the instrument and its potential applicability to further understand the eye biomechanics and intraocular pressure measurements. Limitations and possibilities of the new apparatus are discussed.

Desenvolvimento de um método in vivo para melhor compreender a pele do obeso

O impacto da obesidade na fisiopatologia da pele humana parece relacionar-se com diversas dermatoses, resultado da alteração da sua fisiologia normal, incluindo alterações na função barreira e na função de “envelope”. Contudo, a informação disponível é ainda escassa devido às diversas complexidades do tema. Este trabalho pretende contribuir para a definição de uma metodologia de abordagem experimental para estudar, de forma objectiva, as alterações funcionais que caracterizam a pele obesa. O presente estudo, transversal, incluiu 28 voluntárias, do sexo feminino, saudáveis, com idade média 23±5 anos de idade, após consentimento informado. Foi realizada uma única medição de caracterização das diversas funções cutâneas obtidas por meios não invasivos em condições controladas. As variáveis consideradas relevantes foram, a hidratação (superficial e profunda) a função de barreira e o comportamento biomecânico, medidos em 4 áreas anatómicas distintas. Através do SPSS (v 20.0) realizámos uma análise estatística univariada com cálculo de medidas de tendência central e de dispersão. Recorremos aos testes de Pearson e de Spearman, para as variáveis que seguiam, ou não, uma distribuição normal, respectivamente, adoptando um grau de confiança de 95% . Os resultados permitem propor uma metodologia para o estudo da pele, aplicável ao doente obeso, incluindo a escolha das áreas anatómicas e das variáveis adequadas ao objetivo pretendido.

Evaluation of Stress Patterns Produced by Implant-Retained Overdentures and Implant-Retained Fixed Partial Denture

The purposes of this study were to photoelastically measure the biomechanical behavior of 4 implants retaining different cantilevered bar mandibular overdenture designs and to compare a fixed partial denture (FPD). A photoelastic model of a human edentulous mandible was fabricated, which contained 4 screw-type implants (3.75 x 10 mm) embedded in the parasymphyseal area. An FPD and 3 overdenture designs with the following attachments were evaluated: 3 plastic Hader clips, 1 Hader clip with 2 posterior resilient cap attachments, and 3 ball/O-ring attachments. Vertical occlusal forces of 100 N were applied between the central incisor and unilaterally to the right and left second premolars and second molars. Stresses that developed in the supporting structure were monitored photoelastically and recorded photographically. The results showed that the anterior loading, the overdenture with 3 plastic Hader clips, displayed the largest stress concentration at the medium implant. With premolar loading, the FPD and overdenture with 3 plastic Hader clips displayed the highest stresses to the ipsilateral terminal implant. With molar loading, the overdenture with 3 ball/O-ring attachments displayed the most uniform stress distribution in the posterior edentulous ridge, with less overloading in the terminal implant. It was concluded that vertical forces applied to the bar-clip overdenture and FPD created immediate stress patterns of greater magnitude and concentration on the ipsilateral implants, whereas the ball/O-ring attachments transferred minimal stress to the implants. The increased cantilever in the FPD caused the highest stresses to the terminal implant.

Biomechanics Studies in Dentistry: Bioengineering Applied in Oral Implantology

The application of engineering knowledge in dentistry has helped the understanding of biomechanics aspects related to osseointegrated implants. Several techniques have been used to evaluate the biomechanical load oil implants comprising the use of photoelastic stress analysis, finite element stress analysis, and strain-gauge analysis. Therefore, the purpose of this Study was to describe engineering methods used in dentistry to evaluate the biomechanical behavior of osseointegrated implants. Photoelasticity provides good qualitative information oil the overall location and concentration of stresses but produces limited quantitative information. The method serves as ail important tool for determining the critical stress points in a material and is often used for determining stress concentration factors in irregular geometries. The application of strain-gauge method oil dental implants is based oil the use of electrical resistance strain gauges and its associated equipment and provides both in vitro and vivo measurements strains under static and dynamic loads. However, strain-gauge method provides only the data regarding strain at the gauge. Finite element analysis can Simulate stress using a computer-created model to calculate stress, strain, and displacement. Such analysis has the advantage of allowing several conditions to be changed easily and allows measurement of stress distribution around implants at optional points that are difficult to examine clinically All the 3 methodologies call be useful to evaluate biomechanical implant behavior close to the clinical condition but the researcher should have enough knowledge in model fabrication (experimental delineation) and results analysis.

Evaluation of Different Retention Systems on a Distal Extension Removable Partial Denture Associated With an Osseointegrated Implant

The aim of this study was to evaluate the biomechanical behavior of a mandibular distal extension removable partial denture (DERPD) associated with an implant and different retention system, by bidimensional finite element method. Five hemimandible models with a canine and external hexagon implant at second molar region associated with DERPD were simulated: model A, hemimandible with a canine and a DERPD; model B, hemimandible with a canine and implant with a healing abutment associated to a DERPD; model C, hemimandible with a canine and implant with an ERA attachment associated to a DERPD; model D, hemimandible with a canine and implant with an O'ring attachment associated to a DERPD; and model E, hemimandible with a canine and implant-supported prosthesis associated to a DERPD. Cusp tips were loaded with 50 N of axial or oblique force (45 degrees). Finite element analysis was performed in ANSYS 9.0. model E showed the higher displacement and overload in the supporting tissues; the patterns of stress distribution around the dental apex of models B, C, and D were similar. The association between a DERPD and an osseointegrated implant using the ERA or O'ring systems shows lower stress values. Oblique forces showed higher stress values and displacement. Oblique forces increased the displacement and stress levels in all models; model C displayed the best stress distribution in the supporting structures; healing abutment, ERA, and O'ring systems were viable with RPD, but DERPD association with a single implant-supported prosthesis was nonviable.

Influence of a preventive training program on lower limb kinematics and vertical jump height of male volleyball athletes

Objective: To examine the influence of a preventative training program (PTP) on sagittal plane kinematics during different landing tasks and vertical jump height (VJH) in males. Design: Six weeks prospective exercise intervention. Participants: Fifteen male volleyball athletes (13 ± 0.7 years, 1.70 ± 0.12 m, 60 ± 12 kg). Interventions: PTP consisting of plyometric, balance and core stability exercises three times per week for six weeks. Bilateral vertical jumps with double leg (DL) and single leg (SL) landings were performed to measure the effects of training. Main outcome measurements: Kinematics of the knee and hip before and after training and VJH attained during both tasks after training. The hypothesis was that the PTP would produce improvements in VJH, but would not generate great changes in biomechanical behavior. Results: The only change identified for the SL was the longest duration of landing, which represents the time spent from initial ground contact to maximum knee flexion, after training, while increased angular displacement of the knee was observed during DL. The training did not significantly alter the VJH in either the SL (difference: 2.7 cm) or the DL conditions (difference: 3.5 cm). Conclusions: Despite the PTP's effectiveness in inducing some changes in kinematics, the changes were specific for each task, which highlights the importance of the specificity and individuality in selecting prevention injury exercises. Despite the absence of significant increases in the VJH, the absolute differences after training showed increases corroborating with the findings of statistically powerful studies that compared the results with control groups. The results suggest that short-term PTPs in low risk young male volleyball athletes may enhance performance and induce changes in some kinematic parameters. © 2012 Elsevier Ltd.

Influência da espessura da camada de cimento e da variação da temperatura no comportamento mecânico de fragmentos cerâmicos utilizados em restaurações estéticas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)