The length and eruption rates of incisor teeth in rats after one or more of them had been unimpeded.
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The eruption rate and length of all four incisor teeth in rats were measured under ether anaesthesia by recording the position of marks on their labial surfaces at 2-day intervals, using calibrated graticules in microscope eyepieces. The rats were divided into four groups and either a lower, an upper, both a lower and an upper, or no incisors were unimpeded. This paper describes the changes when the unimpeded incisors returned to the occlusion. Neither the unimpeded nor the impeded incisors simply returned to control values immediately the period of unimpeded eruption ended, but showed transient changes in their lengths and eruption rates. The results confirm that eruption rates are determined by the sum of the lengths of the lower and upper incisors, rather than by their own lengths, with longer teeth erupting more slowly. Specifically, restoring the bevel to the incisors did not slow their eruption below normal impeded rates. The slowing of the eruption of the longer of two adjacent incisors was related to the length differences of the incisors in the same jaw, not to the sum of the differences in both jaws. Contact with the contralateral incisor in the opposite jaw slowed the eruption of an incisor more than contact with the ipsilateral incisor. (+info)
Motivation for and satisfaction with orthodontic-surgical treatment: a retrospective study of 28 patients.
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Motivation for starting treatment and satisfaction with treatment results were evaluated on the basis of replies to a 14-item questionnaire and clinical examination of 28 orthognathic patients from 6 months to 2 years after treatment. The most common reasons for seeking professional help were problems in biting and chewing (68 per cent). Another major reason was dissatisfaction with facial appearance (36 per cent). Many patients also complained of temporomandibular joint symptoms (32 per cent) and headache (32 per cent). Women (8/19) were more often dissatisfied with their facial appearance than men (2/9), but the difference was not statistically significant. In agreement with earlier studies, the results of orthognathic treatment fulfilled the expectations of almost every patient. Nearly 100 per cent of the patients (27/28) were satisfied with treatment results, although 40 per cent experienced some degree of numbness in the lips and/or jaw 1 year post-operatively. The most satisfied patients were those who stated temporomandibular disorders as the main reason for seeking treatment and whose PAR-index had improved greatly. The majority of the patients experienced the orthodontic treatment as painful and as the most unpleasant part of the whole treatment, but all the patients were satisfied with the pre-treatment information they were given on orthodontics. Orthodontic-surgical therapy should be of a high professional standard technically, but the psychological aspects are equally important in the treatment protocol. The professionals should make efforts to understand the patient's motivations for and expectations of treatment. Patients should be well prepared for surgery and supported for a long time after to help them to adjust to post-surgical changes. (+info)
The functional shift of the mandible in unilateral posterior crossbite and the adaptation of the temporomandibular joints: a pilot study.
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Changes in the functional shift of the mandibular midline and the condyles were studied during treatment of unilateral posterior crossbite in six children, aged 7-11 years. An expansion plate with covered occlusal surfaces was used as a reflex-releasing stabilizing splint during an initial diagnostic phase (I) in order to determine the structural (i.e. non-guided) position of the mandible. The same plate was used for expansion and retention (phase II), followed by a post-retention phase (III) without the appliance. Before and after each phase, the functional shift was determined kinesiographically and on transcranial radiographs by concurrent recordings with and without the splint. Transverse mandibular position was also recorded on cephalometric radiographs. Prior to phase I, the mandibular midline deviated more than 2 mm and, in occlusion (ICP), the condyles showed normally centred positions in the sagittal plane. With the splint, the condyle on the crossbite side was displaced 2.4 mm (P < 0.05) forwards compared with the ICP, while the position of the condyle on the non-crossbite side was unaltered. After phase III, the deviation of the midline had been eliminated. Sagittal condylar positions in the ICP still did not deviate from the normal, and the splint position was now obtained by symmetrical forward movement of both condyles (1.3 and 1.4 mm). These findings suggest that the TMJs adapted to displacements of the mandible by condylar growth or surface modelling of the fossa. The rest position remained directly caudal to the ICP during treatment. Thus, the splint position, rather than the rest position should be used to determine the therapeutic position of the mandible. (+info)
An appraisal of the Peer Assessment Rating (PAR) Index and a suggested new weighting system.
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The PAR Index was developed to measure treatment outcome in orthodontics. Validity was improved by weighting the scores of some components to reflect their relative importance. However, the index still has limitations, principally due to the high weight assigned to overjet. Difficulties also arise from the application of one weighting system to all malocclusions, since occlusal features vary in importance in different classes of malocclusion. The present study examined PAR Index validity using orthodontic consultant assessments as the 'Gold standard' and clinical ranking of occlusal features and statistical modelling to derive a new weighting system, separate for each malocclusion class. Discriminant and regression analyses were used to derive new criteria for measuring treatment outcome. As a result a new and more sensitive method of assessment is suggested which utilizes a combination of point and percentage reductions in PAR scores. This was found to have better correlations with the 'Gold standard' than the PAR nomogram. (+info)
The heritability of malocclusion: part 2. The influence of genetics in malocclusion.
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The relative influence of genetics and environmental factors in the aetiology of malocclusion has been a matter for discussion, debate and controversy in the orthodontic literature. This paper reviews the literature and summarises the evidence for the influence of genetics in dental anomalies and malocclusion. Among the conclusions are that, while phenotype is inevitably the result of both genetic and environmental factors, there is irrefutable evidence for a significant genetic influence in many dental and occlusal variables. The influence of genetics however varies according to the trait under consideration and in general remains poorly understood. More precise research tools and methods are required to improve knowledge and understanding, which in turn is a prerequisite to the appreciation of the potential for genetic and/or environmental manipulation in orthodontic therapy. (+info)
Longitudinal post-eruptive mandibular tooth movements of males and females.
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Unbiased estimates of post-eruptive eruption and migration of the mandibular teeth for large representative samples are presently unavailable. The purpose of this study was to evaluate pure tooth movements of untreated children and adolescents longitudinally. Lateral cephalograms of 214 French-Canadians, followed bi-annually between 8 and 15 years of age, were traced, and the positions of the mandibular permanent central incisors and first molars were digitized. Temporal changes in tooth position were evaluated relative to naturally stable mandibular reference structures, using the mandibular reference line for orientation. The statistical analyses included t-tests to assess gender differences and Pearson product-moment correlations to evaluate associations. The results showed that the incisors proclined significantly more for males (6 degrees) than females (3 degrees). The incisor tips displayed early mesial movements that were countered by later distal movements. The incisor apex showed a consistent pattern of distal migration between 8 and 15 years. Mandibular arch length decreased over the 7-year observation period. Rates of mesial molar migration accelerated until 11 years of age and then decelerated. There was no significant change in the mandibular occlusal plane angle between 8 and 15 years of age. Incisor eruption showed the greatest rates during adolescence, attaining peaks at approximately 12 years for females and 14 years for males. The molars erupted approximately 5 mm between 8 and 15 years of age. The greatest gender differences occurred at the older ages, with males showing greater eruption potential than females. It was concluded that the mandibular teeth show significant migration and eruption during childhood and adolescence, with gender differences in the amount, direction, and timing of movement. (+info)
Residual need in orthodontically untreated 16-20-year-olds from areas with different treatment rates.
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Knowledge concerning residual orthodontic need among individuals who have passed the age at which orthodontic treatment is normally provided, is important in the discussion of guidelines for the provision of care. The purpose of the present study was to examine and compare orthodontic need (objective and subjective) in cohorts of orthodontically untreated individuals from areas with various treatment rates. A total of 250 individuals, aged 16-20 years, comprised four samples representing cohorts from areas in Norway with low, medium, and high treatment rates. The occlusion was assessed according to a treatment need index (NOTI) from clinical and radiographic records, and dental cast measurements. Attitudes were assessed from questionnaires addressing satisfaction with dental arrangement, desire for treatment, and value placed upon well-aligned teeth. A significant decrease in occurrence of normative need (P < 0.001) and reported dissatisfaction (P < 0.05) was observed in samples representing increasing treatment rates. Dissatisfaction was completely eliminated among individuals from the high treatment rate area. Although a significant association between severity of malocclusion and desire for treatment existed within samples, this was not reflected in a corresponding trend for a decrease in desire across the samples. Well-aligned teeth seemed to be taken for granted among individuals from the area with a high treatment rate. From the present observations, a 'correct' level of treatment provision could not be identified. (+info)
Skeletal muscle function and fibre types: the relationship between occlusal function and the phenotype of jaw-closing muscles in human.
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Mammalian skeletal muscle cells are composed of repeated sarcomeric units containing thick and thin filaments of myosin and actin, respectively. Excitation of the myosin ATPase enzyme is possible only with presence of Mg-ATP and Ca(2+). Skeletal muscle fibres may be classified into several types according to the isoform of myosin they contain. Nine isoforms of myosin heavy chain are known to exist in mammalian skeletal muscle including type I, IIA, IIB, IIX, IIM, alpha, neonatal, embryonic, and extra-ocular. Healthy adult human limb skeletal muscle contains type I, IIA, IIB, and IIX myosin heavy chains. The jaw-closing muscles of most carnivores and primates have tissue-specific expression of the type IIM or 'type II masticatory' myosin heavy chain. Adult human jaw-closing muscles, however, do not contain IIM myosin. Rather, they express type I, IIA, IIX (as in human limb muscle), and myosins typically expressed in developing or cardiac muscle. The morphology of human jaw-closing muscle fibres is also unusual in that the type II fibres are of smaller diameter that type I fibres, except in cases of increased function and hypertrophy. This paper describes the relationship of fibre types and motor unit function to changes in human occlusion and masticatory activity. Refereed Scientific Paper (+info)