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In order to investigate growth modifications of the temporomandibular joint (TMJ) during dentofacial orthopaedic treatment, various functional appliances have been used to prompt the mandible into a protrusive position in various animal experimental models. The general purpose of this project was (i) to test the effectiveness of a functional appliance specially designed for sheep; (ii) to clarify whether or not forward mandibular displacement in sheep is associated with faster and/or redirected condylar growth; (iii) to evaluate the sheep as a model for dentofacial orthopaedic research by comparing the similarities of mandibular condylar growth in sheep and humans; (iv) to detail the position of the mandible during forward mandibular posturing and the effects of mandibular forward displacement on modelling and remodelling of the mandibular condyle. The specific purpose of this project was to reveal whether functional appliance treatment increases the quantity of bone formed during the treatment, or changes the distribution of the bone, or both. Eight, 4-month old, castrated male Merino sheep were randomly assigned to experimental or control groups with 4 in each group. Cast functional appliances were fabricated for the animals in the experimental group. The treatment period was 15 weeks. Calcein (day 1) tetracycline (13 weeks) and alizarin red S (3 days before sacrifice) fluorochromes were administered to all animals. Dental casts, endosseous implant markers and cephalograms were used to analyse the 3-D displacement of the mandible. Undecalcified mid-sagittal sections of TMJ were used to evaluate the tissue responses induced by the appliances. Dynamic parameters of bone formation, static indices of bone-forming and resorbing activity as well as structural indices of trabecular bone were estimated using histomorphometry. The trabecular bone was sampled from two regions: (i) a subchondral region; (determined by 2nd and 3rd labels), believed to comprise bone newly-formed during the experimental period; and (ii) a central region (labelled by all the three fluorochromes), believed to comprise bone which existed before the experiment. The cortical bone was divided into anterior and posterior regions for analysis. The weight of the animals was measured monthly to monitor their growth. Metacarpus growth was also evaluated. During the experimental period, the animals were found to maintain their weight within the normal range and grew normally. The appliance was found to displace the mandible to a downward and forward position with a net condylar displacement of 2.4 mm. The observed adaptive responses in the TMJ induced by the appliances included; the condylar process was less tapered and rounder in the experimental group than in the controls, and anteriorly thickened condylar cartilage and a thickened compact bone layer along the anterior surface of the posterior wall of the glenoid fossa. The mandibular condylar growth vector in sheep was found to be in a postero-superior direction. Condylar growth in the control sheep during the experimental period varied from 8.8 to 11.9 mm, with the mean being 10.6 mm, which is quantitatively similar to two years of condylar growth in human adolescents. In the experimental sheep, the condylar growth varied from 8.5 to 13.3 mm, with the mean being 11.4 mm. When metacarpal growth and weight gain were taken into consideration using multivariant analysis, the coefficients for growth in the postero-superior and posterior direction were found to be high, with adjusted r2 as 0.84 and 0.82 respectively. The induced condylar growth was estimated to be largest in the posterior direction (2.3 mm), which is also similar to previous reports in humans. Regional differences in adaptive response within the mandibular condyle were found in this study. In the experimental group, bone volume fraction (BV/TV) of the subchondral regions decreased, although the specific bone surface and bone formation rates increased. This low BV/TV was associated with decreased trabecular thickness and increased trabecular separation. In the central region of the experimental group's condyle, BV/TV was unchanged. However, an increased osteoid surface (OS/BS) was defined when the eroded surface (ES/BS) was taken into consideration. The sheep were found to cope well with the experimental procedures and the appliance used in this study has been effective in inducing adaptive responses in the TMJ. Consequently, it is believed that the sheep is an appropriate animal model for quantitative histological analysis of the responses to functional appliance treatment. The first null hypothesis, that functional appliance treatment has no effect on bone matrix mineralisation was rejected. The second null hypothesis, functional appliance treatment has no effect on the mineralisation lag time, was rejected. The results indicated that the treatment effects of functional appliances involve reorganisation of the TMJ through bone modelling and remodelling. An important mechanism of functional appliance treatment is, therefore, suggested to be a change in the distribution of bone rather than an increase in the quantity of bone. Posterior rotation of the principle tensile strain angle (Et) suggested an posteriorly altered direction of the condylar growth. Increased new bone formation in the glenoid fossa suggested an anterior re-positioning of the temporomandibular joint. / Thesis (Ph.D.)--Dental School, 2002.

Made available in DSpace on 2016-06-02T20:18:11Z (GMT). No. of bitstreams: 1 2456.pdf: 6548607 bytes, checksum: 486173aee7443e35a2910af043a12256 (MD5) Previous issue date: 2009-04-03 / Universidade Federal de Sao Carlos / Bioactive materials have the ability to bond and to integrate with bone tissue by forming a biologically active bonelike apatite layer, which has chemical and structural properties equivalent to the mineral phase of living bone. This process is determined by chemical reactions, whose products also influence the attachment, the proliferation, the differentiation and the mineralizing capacity of bone cells. Cellular responses contribute to the bioactive behavior, which is known for being higher in glass materials. However, as low mechanical properties are also inherent characteristics of glasses, researchers from Federal University of Sao Carlos were stimulated to develop nucleation and growth thermal treatments for the obtainment of the Biosilicate®, a fully-crystallized bioactive glassceramic of the quaternary system P2O5-Na2O-CaO-SiO2. Although a high in vitro osteogenic potential of this novel glass-ceramic has been previously demonstrated, its in vivo effects have not been investigated yet. To contribute to this knowledge, two studies were developed. The first one aimed to investigate the in vivo biological performance of Biosilicate® in bone defects of rat tibias, by means of hystomorphometric and biomechanical analyses 20 days after the surgical procedure. This study revealed that the fully-crystallized Biosilicate® has good bone-forming and bone-bonding properties. Hence, the second study aimed to compare the kinetics of the bone reactions to two different granulometric distributions of this novel glass-ceramic. Although they were both efficient for bone formation, smaller-sized particles of Biosilicate® showed partial reabsortion, which was accompanied by a more pronounced osteogenic activity within the period of time studied. Since positive results were obtained, the search for scaffolds that could serve as supports for the guided bone regeneration had started. A third study preliminarily evaluated cell culture and cocultures in porous structures made of Biosilicate® and of other chemical compositions that were specifically developed for this purpose. The findings suggest that, when in adjusted conditions, the scaffolds can create favorable cellular responses for bone tissue engineering purposes. Taken togheter, these studies point to a promising potential and provide directives for the use of Biosilicate® in bone regenerative processes. / Materiais bioativos possuem a capacidade de se ligar ao tecido ósseo por meio da formação de uma interface apatítica que apresenta similaridade química e estrutural com a fase mineral dos ossos. Esse processo ocorre devido a uma série de reações químicas, cujos produtos também influenciam a adesão, a proliferação, a diferenciação e a capacidade de mineralização da matriz pelas células ósseas. As respostas celulares contribuem para o comportamento bioativo, que é conhecido por ter maiores índices em materiais vítreos. No entanto, como baixas propriedades mecânicas também são características inerentes aos vidros, pesquisadores da Universidade Federal de São Carlos foram estimulados a empregarem nucleação e tratamentos térmicos especiais para o desenvolvimento do Biosilicato®, uma vitrocerâmica biotiva, totalmente cristalina, pertencente ao sistema quaternário P2O5-Na2O-CaO-SiO2. Embora um elevado potencial osteogênico in vitro tenha sido demonstrado para esta vitrocerâmica, seus efeitos in vivo ainda não são conhecidos. Para auxiliar este entendimento, foram desenvolvidos dois estudos. O primeiro teve como objetivo investigar o desempenho biológico in vivo do Biosilicato® particulado em defeitos ósseos em tíbias de ratos, por meio de análises histomorfométricas e biomecânicas 20 dias após o procedimento cirúrgico. Este estudo evidenciou que o Biosilicato® parece favorecer a formação óssea in vivo e o estabelecimento de fortes ligações com o tecido neoformado. Com isso, o objetivo do segundo estudo foi comparar a cinética das reações ósseas frente a duas diferentes distribuições granulométricas desta nova vitrocerâmica. Embora ambas tenham sido eficientes para a formação óssea, as partículas de Biosilicato® com menores diâmetros demonstraram reabsorção parcial no período estudado, que foi acompanhada de uma maior atividade osteogênica. Com os resultados positivos obtidos nestas investigações, iniciou-se uma busca para o desenvolvimento de matrizes porosas que pudessem servir de suporte para a regeneração guiada do tecido ósseo. Um terceiro estudo preliminarmente avaliou monoculturas e coculturas celulares em matrizes porosas de Biosilicato® e de outras novas composições químicas desenvolvidas especificamente para este propósito. Os achados sugerem que, quando em condições adequadas, as matrizes avaliadas podem produzir respostas celulares favoráveis ao seu emprego na engenharia do tecido ósseo. Estes estudos, de maneira conjunta, apontam para um potencial promissor e fornecem diretrizes para o emprego do Biosilicato® no favorecimento de processos regenerativos ósseos.

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