Effect of a static magnetic field on orthodontic tooth movement in the rat.
(9/447)
Orthodontic tooth movement may be enhanced by the application of a magnetic field. Bone remodelling necessary for orthodontic tooth movement involves clastic cells, which are tartrate-resistant acid phosphatase (TRAP) positive and which may also be regulated by growth hormone (GH) via its receptor (GHR). The aim of this study was to determine the effect of a static magnetic field (SMF) on orthodontic tooth movement in the rat. Thirty-two male Wistar rats, 9 weeks old, were fitted with an orthodontic appliance directing a mesial force of 30 g on the left maxillary first molar. The appliance incorporated a weight (NM) or a magnet (M). The animals were killed at 1, 3, 7, or 14 days post-appliance insertion, and the maxillae processed to paraffin. Sagittal sections of the first molar were stained with haematoxylin and eosin (H&E), for TRAP activity or immunohistochemically for GHR. The percentage body weight loss/gain, magnetic flux density, tooth movement, width of the periodontal ligament (PDL), length of root resorption lacunae, and hyalinized zone were measured. TRAP and GHR-positive cells along the alveolar bone, root surface, and in the PDL space were counted. The incorporation of a SMF (100-170 Gauss) into an orthodontic appliance did not enhance tooth movement, nor greatly alter the histological appearance of the PDL during tooth movement. However significantly greater root resorption (P = 0.016), increased width of the PDL (P = 0.017) and greater TRAP activity (P = 0.001) were observed for group M at day 7 on the compression side. At day 14 no differences were observed between the appliance groups. (+info)
Root resorption after orthodontic treatment in high- and low-risk patients: analysis of allergy as a possible predisposing factor.
(10/447)
The development of excessive root resorption during orthodontic tooth movement is an adverse side-effect, which is of great concern. The aim of this investigation was to analyse factors that might be associated with orthodontically induced root resorption. After buccal movement of maxillary premolars in 96 adolescents, the experimental teeth were extracted and subjected to histological analysis and measurement of resorbed root area. Fifty individuals, 18 boys and 32 girls, mean age 13.4 years, were selected and divided into two equal groups: the high-risk group based on measurements of the most severe root resorptions, and the low-risk group on measurements of mild or no root resorptions. After a preliminary screening of possible risk factors regarding root resorption, i.e. root morphology, gingivitis, allergy, nail-biting, medication, etc., only those subjects with allergy showed an increased risk of root resorption, but this was not statistically significant. (+info)
A radiographic comparison of apical root resorption after orthodontic treatment with a standard edgewise and a straight-wire edgewise technique.
(11/447)
The purpose of this study was to compare the severity of apical root resorption occurring in patients treated with a standard edgewise and a straight-wire edgewise technique, and to assess the influence of known risk factors on root resorption incident to orthodontic treatment. The sample consisted of 80 patients with Angle Class II division 1 malocclusions, treated with extraction of at least two maxillary first premolars. Variables recorded for each patient included gender, age, ANB angle, overjet, overbite, trauma, habits, invagination, agenesis, tooth shedding, treatment duration, use of Class II elastics, body-build, general factors, impacted canines, and root form deviation. Forty patients were treated with a standard edgewise and 40 with a straight-wire edgewise technique, both with 0.018-inch slot brackets. Crown and root lengths of the maxillary incisors were measured on pre- and post-treatment periapical radiographs corrected for image distortion. Percentage of root shortening and root length loss in millimetres were then calculated. There was significantly more apical root resorption (P < 0.05) of both central incisors in the standard than in the straight-wire edgewise group. No significant difference was found for the lateral incisors. Root shortening of the lateral incisors was significantly associated with age, agenesis, duration of contraction period (distalization of incisors), and invagination, while root shortening of the central incisors was related to treatment group and trauma. (+info)
Influence of different elastic moduli of dowel and core on stress distribution in root.
(12/447)
This study was carried out to investigate the influences of elastic moduli of the dowel-core combination on the stress distribution in the root by the use of 2-dimensional finite element analysis. The peak stress at the dowel-cement interface was influenced strongly by a change of elastic modulus of the post (from 20,000 kg/mm2 as a hard prefabricated post to 8,000 kg/mm2 as a custom cast post) for both vertical and 45 degree oblique loading (rho > 90%). Peak dentinal stress adjacent to the luting cement layer depended only on the post material for vertical loading (rho [symbol: see text] 99%). In contrast, the post and core materials (from 8,000 kg/mm2 as cast core to 300 kg/mm2 as composite resin core) acted in cooperation on the stress magnitude for oblique loading, but the influence of the core material was stronger than that of the post (rho of core [symbol: see text] 41% and rho of post [symbol: see text] 26%). On the other hand, at the marginal region the effect of the core material contributed more than 86% to the peak stress value for both loadings, and the post material affected at most about 11% of the bending resistance. (+info)
Application of high resolution microfocus X-ray CT for the observation of human tooth.
(13/447)
The calcification degree of extracted human teeth was observed by using high resolution microfocus X-ray CT. As samples, upper and lower first premolars extracted from a 21-year-old female were used. The computed tomograms were produced by high resolution microfocus X-ray CT with a open vacuum X-ray source, rotating sample stage, and image sensor. The distinction between enamel and dentin was very clear, and the shape of the pulp cavity was also clearly identified. The secondary dentin was visible in the circumpulpal dentin. The color map displays showed the heterogeneity of the calcification degree not only in the dentin but also in the enamel. The enamel was divided into three layers according to the calcification degree. High resolution microfocus X-ray CT was very useful for the observation of the internal structure of human teeth without destroying the samples. (+info)
Relationships among facial type, buccolingual molar inclination, and cortical bone thickness of the mandible.
(14/447)
The purpose of this study was to evaluate the relationships between different facial types, and both the buccolingual molar inclination and cortical bone thickness of the mandible. The material consisted of 31 dry skulls of modern Japanese males from the Museum of the University of Tokyo. They all demonstrated normal occlusion with minimal dental discrepancy, and without crossbite or facial asymmetry. The buccolingual inclination of the second molar (M2) in the long-faced subjects was significantly smaller than the same dimension in the average- and short-faced subjects. It was found that the teeth of long-faced subjects were more lingually inclined than those of the short-faced subjects. The cortical bone thickness of the first molar (M1) and M2 sections was thicker in short-faced subjects than in average- and long-faced subjects. The results of this study provide evidence that a significant, but complex relationship exists between structures of the mandibular body and facial types. The morphological features that relate to masticatory function and facial types are associated with the cortical bone thickness of the mandibular body, and the buccolingual inclination of the first and second molars. (+info)
Factors predictive of difficulty of mandibular third molar surgery.
(15/447)
AIM: Historically the difficulty of third molar surgery has been judged using radiologically assessed dental factors specifically tooth morphology and position. This study investigated additional factors that have a bearing on the difficulty of extraction. STUDY DESIGN: A prospective study undertaken by three clinical assistant grade surgeons who removed 354 single mandibular third molar teeth under day case anaesthesia over the 4-year period (1994-1998). METHOD: Data relating to patient, dental and surgical variables were collected contemporaneously as the patients were treated. The difficulty of extraction was estimated by the surgeons pre-operatively using dental radiographic features and compared by the same surgeon within the actual surgical difficulty encountered at surgery. Operation time strongly related to both pre and post treatment assessments of difficulty and proved to be the best measure of surgical difficulty. RESULTS: Univariate analysis identified increased patient age, ethnic background, male gender, increased weight, bone impaction, horizontal angulation, depth of application, unfavourable root formation, proximity to inferior alveolar canal and surgeon as factors increasing operative time. Multivariate analysis showed that increasing age (P = 0.014), patient weight (P = 0.024), ethnicity (P = 0.019), application depth (P = 0.001), bone impaction (p=0.008) and unfavourable root formation (P = 0.009) were independent predictors for difficulty of extraction. CONCLUSIONS: Half of the six independent factors that predicted surgical difficulty of third molar extraction were patient variables. (+info)
The formation of apical delta of the permanent teeth in dogs.
(16/447)
To determine the process of formation of apical delta, a histological study on the permanent teeth was carried out in dogs. A litter of 7 clinically healthy beagle dogs and 33 adult dogs (4- to 15- year-old) of 12 breeds with periodontal disease were used for the experiments. Teeth extracted from 6-,7-,8- and 9-month-old beagles were sectioned and stained with HE solution. Tooth roots obtained from adult dogs with periodontal disease were ground. Each tooth was classified into the following root types under a light microscope: Type I (no apical delta = no apical closure), II (few apical delta), IIIA (low apical delta) and IIIB (high apical delta). In the 6-month-old beagles, more than half the tooth roots were classified as type I. In the 7-month-old beagles, type IIIB apical delta was the most predominant and types I, II and IIIA apical delta were occassionally seen. Apical closure and delta were observed in all beagles at 8 months of age histologically. In the 8- and 9-month-old beagles, all root apexes observed were type IIIB. Most of the 314 tooth roots extracted from 33 adult dogs were type IIIB, but a few were type IIIA. (+info)