[Mechanics of the mesial movement of teeth in the posterior mandibular segment for treating class II by extraction of l4-24 and 35-45 in Tweed's technic].
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Open bite treatment with microscrew implant anchorage is discussed in relation to vertical control of the posterior dentoalvelar dimension. Maxillary microscrew implants provided anchorage for intruding the posterior teeth and retracting the anterior teeth; mandibular microscrew implants were used to apply intrusion force distal to the mandibular first molars to prevent mesial tipping of the posterior teeth during space closure. Closing the mandibular plane after intruding the maxillary posterior teeth and bodily mesial movement of the mandibular posterior teeth contributed to facial profile improvement. The efficacy and potency of microscrew implants in open bite treatment are discussed.
A clinical study was designed to disclose the effects of activator treatment in the correction of Class II malocclusions. The rationale for the use of the activator appliance was based on the premise that correction of distocclusion can be achieved by inhibition of forward growth of the maxilla, inhibition of mesial migration of maxillary teeth, inhibition of maxillary alveolar height increase and extrusion of mandibular molars, increased growth of the mandible, anterior relocation of the glenoid fossa, mesial movement of mandibular teeth, and combinations of these effects. The appliance, as designed for this study, could potentially have an effect on all of these factors. Measurements were obtained from cephalometric head films obtained at 6-month intervals. Matched-pairs analyses of control versus treatment change after 6 months and after 1 year of treatment were done on 36 and 29 pairs, respectively. Pretreatment versus treatment changes were analyzed on 33 subjects by means of the spline regression analysis; posttreatment versus treatment changes were analyzed on 18 subjects by means of the Student Newman-Keuls multiple comparison test. The matched-pairs analyses of mean values demonstrated significant reduction in forward growth of the maxilla, uprighting of the maxillary incisors, reduced overjet, leveling of the mandibular occlusal plane, improved molar relationship, downward and forward relocation of the glenoid fossae, increased advancement of all mandibular structures, increased face profile angle, and increased lower face height. The two longitudinal analyses yielded similar findings, but some differences were noted. Because rather severe dental malocclusions were corrected, the slight average inhibition of maxillary growth and the anterior relocation of glenoid fossae alone could not account for the correction of the Class II dental arch relationship. It was therefore concluded that, in addition to the statistically significant changes, smaller changes occurred in several areas without being consistent enough or of a large enough magnitude to become statistically significant in the analyses of mean values. Comparison of group averages may mask treatment effects that significantly contribute to the correction of malocclusions in individual cases.
Microscopic observations were made of wear on the proximal surfaces of tooth crowns of Australian Aboriginals and whites. Typical wear facets displayed well-defined borders within which vertical or near vertical furrows, ranging from about 0.1 to 0.5 mm in width, were noted. Furrows on the interproximal surface of one tooth seemed to "interdigitate" with those on the proximal surface of the adjacent tooth. These observations are not consistent with the commonly-held view that interproximal tooth wear results from a buccolingual movement of adjacent teeth that maintain contact through mesial migration. Vertical or near vertical movement of teeth, possibly including a tipping action, must be an important factor, although the precise nature of the movement requires further investigation.
BACKGROUND: Distraction osteogenesis (DO) has become a mainstream surgical technique for patients with jaw deformities. In cases of maxillary hypoplasia, DO with a rigid external distraction (RED) system has been used for maxillary advancement; however, DO with internal devices is currently popular. MATERIALS: This article describes DO with an internal device and a RED system in 2 patients with maxillary hypoplasia with oligodontia. The first patient, a young girl, had a concave profile due to maxillary hypoplasia and 9 congenitally missing permanent teeth. At age 11 years 11 months, she received DO with an internal device. The second patient, a boy aged 11 years 7 months, was treated with DO with a RED system. RESULTS: In the girl, the maxilla was advanced 5.0 mm without any dentoalveolar compensation. In the boy, the maxilla was advanced 7.0 mm, but undesirable mesial movement of posterior teeth was observed. CONCLUSIONS: DO with internal devices is simpler and more useful than the RED system for maxillary hypoplasia with oligodontia.
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Both the hard substances and the soft tissues of the teeth and their attachment apparatus are subject to constant change. This begins immediately after eruption and continues throughout life. An exact dividing line between changes which are physiological and pathological cannot always be drawn. Enamel undergoes attrition, and in addition its mechanical characteristics alter, owing probably to changes in diffusion conditions. The age-induced changes occurring in dentine are much more obvious, the biological properties of this hard substance being fundamentally altered. The dentine of older people is characterized by the continuous narrowing of the lumen of the dentinal tubule, increasing calcification, reduction in the amount of peritubular fluid and reduced sensitivity. In this process, dentine becomes able to assume the function of enamel as it wears. With age cementum undergoes continuous deposition, mainly functionally induced. It is evident, even macroscopically, that the volume of the pulp declines owing to the deposition of secondary dentine or of amorphous dentine with age. Histologically, young pulp differs fundamentally from that of the pulp of an older person. Regressive processes commence immediately after tooth eruption. The number, nature, properties and capabilities of the cells change, but the pulp does not suffer any appreciable loss of vitality. Circulation in the pulp is affected by deposition of hard substance in the apical part of the root canal. These processes are important in endodontics, and because of them different treatment methods have to be used for patients of different ages. The tooth supporting tissues are also subject to constant rearrangements, the physiological occlusal and mesial movements of the teeth being relevant here. All these structural and biological differences must be allowed for when therapy is being considered. They have not hitherto been taken sufficiently into account.
Quantitative analysis of remodeling activity was done using microradiographs of horizontal ground sections of human alveolar bone obtained from autopsies. The results demonstrated no significant age- or sex-dependent variations. The local distribution of remodeling activity in younger individuals pointed to a tipping mesial movement of the teeth. In older individuals this distribution showed a more random pattern.
The outcome of orthodontic treatment involving early extraction of 4 second molars was evaluated in 52 patients (29 girls, 23 boys). Computer-assisted analysis of cephalograms, casts and panoramic X-rays was performed at the start (T1, mean age 11.5 years) and at the end (T2, mean age 14.4 years) of treatment. Following treatment, mesial migration of upper and lower first molars was counteracted; however, treatment only moderately influenced normal development of the position of the incisors and the profile. At the end of treatment, the third molars had erupted in only 3 patients. Nevertheless, on average a significant mesial movement of these teeth was observed. In addition, there was a significant improvement in the axial inclination of the third molars, especially in the upper arch. This improvement was correlated with the original position of the teeth. All patients needed a longer follow-up period and it seems reasonable that some of them might require a second treatment phase to adjust the position of the third molars.
The natural mechanisms of eruption, mesial migration, soft tissue pressure and occlusal forces can be used by the dentist to treat malocclusion in the growing child. The author describes how planned extractions of deciduous and permanent teeth can be employed to resolve crowding, promote spontaneous alignment, and avoid centreline displacement.
A capacitance transducer was used to measure the changes in the distance between pairs of adjacent teeth following the removal of tooth contact. Ten pairs of incisors and cheek teeth were studied over periods of several hours in three adult monkeys. Compared with minor changes in control tooth pairs, there was a sustained approximation of the capacitance plates for periods up to 2 h. Removal of tooth contacts with the teeth adjacent to the test pairs of teeth caused separation of the plates. It is proposed that removal of approximal tooth contact allows the transseptal fibre system to contract and produce approximation of the adjacent teeth.
OBJECTIVE: Delayed eruption of the first permanent molar (M1) is a relatively rare finding. This report describes the occurrence of delayed development and eruption of a single M1 in Japanese child patients. DESIGN: Cases were identified by surveying 353 orthopantomograms taken of child patients attending a Dental Hospital. Dental age, crown morphology and the presence of third permanent molars (M3) were determined from radiographs and clinical examination. SETTING: Osaka University Dental Hospital in Japan. RESULTS: Nine cases were identified from radiographs. The occlusal morphology of the affected molars showed a reduction of the distolingual cusp. Dental ages correlated more closely to chronological ages when the affected teeth were assumed to be second permanent molars (M2) than they did when the teeth were assumed to be M1. M3 proximate to the affected molar was congenitally absent in the orthopantomograms of all affected subjects. CONCLUSIONS: It is suggested that in the cases seen here the affected teeth were likely to have been second permanent molars that had migrated mesially in association with the congenital absence of M1, although congenital absence of M1 has been reported to be extremely rare.
The influence of bone metabolism on both the rate and the type of orthodontic tooth movement was investigated. A rat model in which high (n = 16) and low (n = 17) bone turnover was pharmacologically induced was used. A non-pharmacologically treated group (n = 19) served as the control. A mesially directed constant single force of 25 cN was applied to the upper left first molar for a period of 3 weeks. The study was performed as a split-mouth design, the contralateral side of each animal serving as its control. The displacement of the molar crown was measured with an electronic calliper, while changes in inclination of the teeth were measured from micro-CT scans of the excised maxillae. The bone turnover significantly affected the rate of tooth movement. In the case of high turnover, the rate of tooth movement was increased while it was reduced in the case of low turnover. A controlled mesial tipping in all three groups was observed, but the actual location of the centre of rotation seemed to be influenced by the metabolic state of the bone. Based on the results it can be concluded that deviations in bone turnover influence the response to orthodontic forces, and should be taken into consideration when planning orthodontic treatment in patients with metabolic bone disease or those on chronic medication influencing bone metabolism.
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The angulation of lower third molars on opposite sides of the jaw was compared on 50 orthopantographic radiographs of children who had mesial migration of lower first permanent molars on one side only following unilateral extraction of lower second deciduous molars. On 36 films the lower third molar was less tilted on the extraction side. Applying a paired t-test this difference is significant (p less than 0.001). The distance of mesial migration was estimated, and the findings are discussed in relation to the hypothesis that early mesial migration of posterior teeth reduces the tilt of lower third molars.
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