A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Objectives. The purpose of this study was to determine the effect of pitch and thread depth of orthodontic miniscrew implants(MSI's) on stress generation. Methods. Quasi-three dimensional photoelastic models were created with MSI's embedded and then loaded with 60 and 104 grams respectively and evaluated under a full field reflection polariscope. The control MSI's (1.0mm pitch / 0.25mm thread depth) were compared to 3 experimental groups (n=10) which varied with only one design characteristic: Group 1 (0.75mm pitch), Group 2 (1.25mm pitch) and Group 3 (0.40 thread depth). The maximum shear stress (τmax) was calculated at 5 predetermined and standardized points. A two-way ANOVA was conducted to compare the means of τmax followed by a Tukey's post hoc (p<0.05). Results. No statistical differences were found for τmax between the control group and each of the 3 experimental groups except at point 4. At point 4, the control group was higher by an average of 5.05 and 7.1 MPa for the 60 and 104 gram loads respectively (p<0.05). No statistically significant differences were found for points 1, 2, and 5 for the 60 gram load and for points 1, 2, 3, and 5 for the 104 gram load. The mean τ max from highest to lowest was located at points 5<1< 2<4 <3 in both the 60 and 104 load steps. The variability in τmax at point 4 may have been due to its proximity to the neutral zone of the present loading conditions. Conclusions. As the orthodontic load was increased, maximum shear stress also increased for each of the four MSI designs used in this study. The results of this study suggest that, within limits, variation of pitch and thread depth of MSI's may not have a significant influence on the stress generation when loaded for orthodontic purposes. Photoelastic analysis has shown to be a viable option to evaluate mechanical properties of MSI'S.

The pillar screw is an important element of conventional dental implants. It is used to fix the pillar or intermediary to the implant set. In conventional dental implants, the torque level applied is near of 20 Ncm, however it knows that the pillar screw resists to bigger torque levels, and that a high pre-load could improve its setting. Many problems related to the breakings and reliefs of the screw are related in literature. The improvement of osseointegration conditions and the dental implantations project could provide to the application of high torque to the pillar screws, minimizing the relief problems. For this, the knowledge of the physical behavior of these elements about their stress and strain fields is important, when a certain torque level and pre-load level is applied. In this work, the stress gradient in the pillar screw was evaluated with an applied pre-load level. The technique of the bidimentional photoelasticity in a photoelastic model of a conventional dental implant of the Conexão Sistemas de Prótese Ltda company was used. For the attainment of the photoelastics parameters, a Matlab program was developed to acquire and to process the fringe images. A photoelastic prismatic bar submitted to a four points bending effort was used, installed in a transmission polariscope, adjusted for elliptical polarized light. The principal stresseses directions had been obtained through a non linear equation solution. To improve the precision of the principal stresseses directions values a disc under axial compression was used to calibrate values RGB of the acquired images. For the torque standard of 20 Ncm, the pre-load was of 111 N. It is possible estimate that torque values in the order of 40 to 50 Ncm could be applied in the pillar screw, if the osseointegration level allied to the project of the dental implant to support such torque levels. A bigger number of experiments must be carried through so that if it can conclude on the maximum values of torque of the daily pay-load. The program Fringes" revealed efficient in the determination of the models optics parameters until 4ª fringe order. / O parafuso pilar é um importante elemento constituinte de implantes dentários convencionais. Ele é utilizado para fixar o pilar ou intermediário ao implante. Em implantes dentários convencionais, o nível de torque aplicado é da ordem de 20 Ncm, porém sabe-se que o parafuso pilar resiste a maiores níveis de torque, e que uma maior pré-carga aplicada poderia melhorar sua fixação. Muitos problemas relacionados às fraturas e desapertos do parafuso são relacionados na literatura. A melhoria das condições de osseointegração e do projeto dos implantes dentários poderia proporcionar a aplicação de maiores torques aos parafusos pilar, minimizando os problemas de desaperto. Para isso, é importante o conhecimento do comportamento físico destes elementos quanto ao campo de tensão e deformação, quando um certo nível de torque e pré-carga são aplicados. Neste trabalho, o gradiente de tensões no parafuso de pilar foi estudado com um nível de pré-carga aplicado. Foi utilizada a técnica da fotoelasticidade de transmissão plana em um modelo fotoelástico de um implante dentário convencional da empresa Conexão Sistemas de Prótese Ltda. Um programa em ambiente Matlab foi desenvolvido para adquirir e processar as imagens das franjas, para a obtenção dos parâmetros fotoelásticos. Foi utilizada uma barra prismática fotoelástica submetida à flexão em quatro pontos, instalada em um polariscópio de transmissão, ajustado para luz polarizada elíptica para a obtenção das ordens de franja. As direções das tensões principais foram obtidas através da solução de uma equação não linear. Para melhorar a precisão dos valores das direções das tensões principais foi utilizado um disco sob compressão axial para calibrar os valores RGB das imagens adquiridas. Para o torque padrão de 20 Ncm, a pré-carga estimada foi de 111 N (GARCIA, 2006). Estima-se que valores de torque na ordem de 40 a 50 Ncm poderiam ser aplicados no parafuso de pilar, se o nível de osseointegração aliado ao projeto do implante dentário suportar tais níveis de torque. Um número maior de experimentos devem ser realizados para que se possa concluir sobre os máximos valores de torque da pré-carga. O programa computacional Fringes , mostrou-se eficiente na determinação dos parâmetros óticos em modelos solicitados até a 4ª ordem de franja. / Mestre em Engenharia Mecânica