Three-dimensional analysis of endosseous palatal implants and bones after vertical, horizontal, and diagonal force application.
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The effects of bite and orthodontic forces exerted on endosseous palatal implants are not completely understood. This applies especially to the biomechanical properties inherent in the different implant geometries and resulting bone remodelling reactions on the one hand, and to the influence on the direction and magnitude of the applied forces on the other. The results of this study should help in the selection of implants for clinical use. Three types of endosseous implants (all 9 mm in length and 3.3 mm in diameter, made of titanium) were used for this investigation. Type 1 was a simple, cylinder-shaped implant; type 2 a cylinder-shaped implant with a superperiosteal step; and type 3 a cylinder-shaped implant, subperiosteally threaded, with a superperiosteal step. The load on the implant was investigated under three conditions of bite and orthodontic forces from 0.01 to 100 N (vertically, horizontally, and diagonally). The study results were calculated by means of a finite element (FE) method. Vertical loading caused bone deformation of more than 600 microeps at the simple implant. The largest deformations at this load were found in the trabecular bone with all three implant geometries. However, trabecular bone deformation was reduced by a superperiosteal step. Horizontal loading of the implants shifted the deformation from the trabecular to the cortical bone. Furthermore, a large deformation was measured at the transition from cortical to trabecular bone. The smallest deformations (less than 300 microeps) were found for implants with a superperiosteal step and diagonal loading (type 2). The use of threads provided no improvement in loading capacity. All implant types investigated showed good biomechanical properties. However, endosseous implants with a superperiosteal step had the best biomechanical properties under low loads. Thus, the trend should be to optimize the design of implants by producing small implants with additional anchorage on the bone surface. (+info)
Restoration of mechanical strength and morphological features of the periodontal ligament following orthodontic retention in the rat mandibular first molar.
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Biomechanical properties and morphological features of the periodontal ligament (PDL) in the rat mandibular molars were examined during orthodontic retention. Seventy-three male rats of the Wistar strain, 8 weeks of age, were used for biomechanical analysis and six rats for morphological analysis. An elastic band was inserted between the mandibular first and second molars for 4 days; after removal of the elastic band the interdental space was filled with resin for 4 and 8 days. The maximum shear stress, tangent modulus, and failure strain energy density of the PDL of the first molar in the experimental animals decreased markedly following application of an orthodontic force. They increased rapidly and were restored completely to the control levels by the 8th day after retention. Light microscopy showed severe compression and extension of the PDL in the experimental animals on the 8th day after retention. Birefringent collagen fibre bundles running across the compressed and expanded PDL were observed, although they appeared to be thinner with less insertions into the alveolar bone or cementum in the experimental animals than in the controls. This suggests that the periodontal collagen fibres were partially reorganized and rearranged during retention. The reorganization and rearrangement of periodontal collagen fibres seemed to be partly related to the restoration of mechanical strength of the rat molar PDL during the 8 days of retention. (+info)
Social inequality and discontinuation of orthodontic treatment: is there a link?
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The aims of this study were to investigate the effects of social inequality on the likelihood of patients discontinuing orthodontic treatment, and to determine which, if any, indicators of social inequality are of greater relevance. In this retrospective study of English and Welsh General Dental Services (GDS) cases, consecutive 'discontinued' cases collected at the Dental Practice Board (DPB) during 1990-91, were compared for age, treatment modality, and measures of social inequality, with a 2 per cent sample of cases contemporaneously submitted as 'complete'. Three deprivation indices, and occupation-based social class spectra of neighbourhoods, were compared between the groups. A model was sought to predict discontinuation/completion using logistic regression analysis. The discontinued sample represented lower social stratum spectra for home and practice areas under all indicators tested, and the subjects were a little older at the start of treatment. Fewer were treated by orthodontically qualified practitioners or with fixed appliances, but more with extra-oral traction. Occupation-based classification (patient's home) and the Carstairs Index (practice area) were selected by the analysis as explaining more of the variation than other measures of social inequality, but the model failed to predict the discontinued cases. Lower social class may be a risk factor for discontinuation of orthodontic treament, but is not a predictor for it. Patients should be considered for, and counselled about, orthodontic treatment on an individual basis. Occupation-based social classifications and the Carstairs Index may be a little more sensitive to orthodontic applications than other indicators of social inequality. (+info)
Rapid palatal expansion in the young adult: time for a paradigm shift?
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A 19-year-old man presented for correction of a malocclusion that included a transverse maxillary deficiency. The patient was informed that he required orthognathic surgery to expand his upper jaw and correct his malocclusion, but he refused surgical expansion. Recent evidence indicates that rapid palatal expansion can be used without surgery in young adults; the decision was therefore made to treat the patient nonsurgically. Rapid palatal expansion of the maxillary arch was accomplished by means of a Hyrax appliance, with post-treatment radiographs revealing an opening of the midpalatal suture. The belief still persists among some clinicians that young adult patients require orthognathic surgery for palatal expansion, despite recent evidence supporting a nonsurgical approach after closure of the midpalatal suture. (+info)
The in vitro detection of early enamel de- and re-mineralization adjacent to bonded orthodontic cleats using quantitative light-induced fluorescence.
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The purpose of this study was to determine whether quantitative light-induced fluorescence (QLF) could detect very early demineralization and remineralization longitudinally adjacent to orthodontic components in an in vitro model. Extracted human premolars (n = 13) were sectioned sagittally to produce two equal halves and an orthodontic cleat was bonded to the buccal surface of each tooth. Transparent nail varnish was placed over the remaining surface, leaving exposed enamel windows adjacent to the cleat on the coronal and gingival aspects. Each half-tooth was placed into the lid of an Eppendorf tube and randomly assigned to either control (distilled water) or experimental (lactic acid demineralizing buffer, pH 4.5) regimes. Digital photographs and QLF baseline images were taken. The tubes were mounted into a rotating holder and left for 24 hours. QLF and digital photographs were taken, the solutions refreshed and the teeth returned. This was continued every 48 hours for 288 hours. At this time the lactic acid buffer was replaced with a remineralizing solution (artificial saliva, fluoride, calcium) and the experiment continued with weekly examinations. QLF images were analysed and deltaQ at the 5 per cent threshold recorded. Analysis of the QLF images showed that both demineralization and remineralization were identified and monitored. Statistical differences between each of the timed examinations were found (P < 0.05). Analysis of the photographs demonstrated that QLF detected subclinical lesions. This initial pilot study has demonstrated the potential for QLF to longitudinally monitor de- and re-mineralization of enamel adjacent to orthodontic cleats in vitro. (+info)
Forestadent Young Specialist Prize (1999).
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This paper describes the clinical orthodontic treatment of the three cases that were awarded the 1999 Forestadent Young Specialist Prize. There are two Class II division 1 cases treated by different treatment modalities and a Class II division 2 case complicated by a palatally ectopic maxillary canine. These case reports demonstrate the three main treatment modalities available to the orthodontist for treating skeletally-based malocclusions, i.e. growth modification, orthodontic camouflage, and a combined surgical-orthodontic approach. (+info)
The validity of computerized orthognathic predictions.
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OBJECTIVE: utilizing OPAL cephalometric prediction software. DESIGN: A retrospective investigation involving the random selection of Class II orthognathic patients from surgical records. SUBJECTS: These 25 cases had undergone treatment aimed at producing Class I incisors. This involved fixed orthodontic appliances and a mandibular advancement osteotomy with rigid internal fixation. METHODS: Lateral cephalographs from three key stages were digitized and processed using the OPAL software. Pre-treatment predictions were generated and compared with the actual clinical changes. RESULTS: Prediction of some of the principal OPAL variables (SNA, ANB, LAFH%, OJ, OB) was reasonably accurate in terms of mean values. However, there were large individual variations for most measurements, and prediction of Wits, MxP/MnP, LAFH, and LPFH was prone to systematic error. In particular, there was a tendency towards over-prediction of the surgically-induced backward mandibular rotation. CONCLUSION: In lieu of further validation caution should be exercised with the interpretation of individual OPAL predictions, especially vertical skeletal changes, and an explanation given to patients that orthognathic predictions are based on generalizations. (+info)
Nickel allergy and orthodontics.
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Nickel is the most common metal to cause contact dermatitis in orthodontics. Nickel-containing metal alloys, such as nickel-titanium and stainless steel, are widely used in orthodontic appliances. Nickel-titanium alloys may have nickel content in excess of 50 per cent and can thus potentially release enough nickel in the oral environment to elicit manifestations of an allergic reaction. Stainless steel has a lower nickel content (8 per cent). However, because the nickel is bound in a crystal lattice it is not available to react. Stainless steel orthodontic components are therefore very unlikely to cause nickel hypersensitivity. This article discusses the diagnosis of nickel allergy in orthodontics and describes alternative products that are nickel free or have a very low nickel content, which would be appropriate to use in patients diagnosed with a nickel allergy. (+info)