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At least 217 records · Page 12Linked to original sources

Three-dimensional finite element analysis for stress in the periodontal tissue by orthodontic forces.

This study was designed to investigate the stress levels induced in the periodontal tissue by orthodontic forces using the three-dimensional finite element method. The three-dimensional finite element model of the lower first premolar was constructed on the basis of average anatomic morphology and consisted of 240 isoparametric elements. Principal stresses were determined at the root, alveolar bone, and periodontal ligament (PDL). In all loading cases for the buccolingually directed forces, three principal stresses in the PDL were very similar. At the surface of the root and the alveolar bone, large bending stresses acting almost in parallel to the root were generally observed. During tipping movement, stresses nonuniformly varied with a large difference from the cervix to the apex of the root. On the other hand, in case of movement approaching translation, the stresses induced were either tensile or compressive at all occlusogingival levels with some difference of the stress from the cervix to the apex. The pattern and magnitude of stresses in the periodontium from a given magnitude of force were markedly different, depending on the center of rotation of the tooth.

Alveolar Process↗

The clinical management of ectopically erupting first permanent molars.

The literature on ectopically erupting first permanent molars is reviewed. The progression of the ectopic condition is discussed along with factors that will affect the practitioner's decision on a mode of treatment. The optimal treatment approach depends on the clinical eruption status of /6/, the change in position of /6/, the amount of enamel ledge of /E/ entrapping /6/, the mobility of /E/, and the presence of pain or infection. A variety of treatment approaches together with diagnostic rationale and clinical guidelines are presented. Overall aspects of the malocclusion must be considered when planning the management of ectopically erupting first permanent molars.

Child↗

Labial root torque: effect on the maxilla and incisor root apex.

This study was designed to determine the effectiveness of labial root torque on anterior nasomaxillary development. Quantification was made of the angular and linear changes in Downs' point A (representing midsagittal basal bone) and incisor point A (representing the dentoalveolar bone) and any concomitant incisor root resorption. The study was divided into two parts: part 1--to determine the anatomic configuration of the premaxillary region by use of laminagraphy on skulls, and part 2--to use the morphologic landmarks found in part 1 to assess the development of the nasomaxillary complex in maxillary retrusive patients. The clinical study involved 17 maxillary retrusive patients, aged 8.0 to 15.7 years, who had been treated for a period between 0.31 and 3.70 years with edgewise advancing mechanics. Clinical results indicate that during the first phase of orthodontic treatment with labial root torque, encompassing a 0.63-year mean treatment period, a greater rate of advancement of Downs' point A was produced when compared with normal growth. The skeletal convexity increased, whereas normal growth straightened the profile. Incisor point A advanced at a greater rate than Downs' point A, suggesting that treatment caused a larger dentoalveolar effect than the effect on midsagittal basal bone. When treatment was extended to 1.57 years, similar changes were found but at a reduced rate. Overall apical root resorption was 12.7%/year. Sex and age were not found to have any correlation to the amount of apical root loss.

Cephalometry↗

Three biologic variables modifying faciolingual tooth angulation by straight-wire appliances.

The facial surface contours of 600 maxillary and mandibular teeth, including 50 of each type of tooth from central incisors to first molars, were measured. Facial contours present at the same location, facial contours from occlusal/incisal to gingival surfaces and the angle formed by the coronal and radicular long axes varied among teeth of the same type. The magnitude of the variation found was so great as to suggest that differences between patients or differences in height of bracket placement are greater than the differences between the standard torque prescriptions now used in orthodontics. No single point, including the coronal midpoint (LA point), was found to be constant among teeth of the same type. Variation in facial surface contour tended to be greater in the posterior teeth than in the anterior teeth. Future custom construction of brackets, adjusted to individual facial contour differences, will also require information regarding optimal tooth position in the head, including compensations necessary for variations in facial skeletal pattern.

Humans↗

Patterns of initial tooth displacements associated with various root lengths and alveolar bone heights.

The present study was designed to investigate the nature of initial tooth displacements associated with varying root lengths and alveolar bone heights. A three-dimensional model of the upper central incisor was developed for the finite element analysis. Tooth displacements were determined at various levels of the tooth and the apicogingival levels of the center of resistance and centers of rotation were calculated. The results showed that moment-to-force values at the bracket level for translation of a tooth decreased with shorter root length and increased with lower alveolar bone height. In addition, apicogingival levels of the center of resistance shifted more gingivally to the cervix, or the alveolar crest with a shorter root. Alveolar bone loss also shifted the center of resistance toward the alveolar crest, whereas its position was more apical relative to the alveolar bone heights exhibited very slight changes in both cases. The centers of rotation from a single force varied substantially with a short root and alveolar bone loss. However, the relative distances of the centers of rotation from the alveolar crest in comparison with the alveolar bone heights were constant at 0.4 mm, with variations in the root length and alveolar bone height. Because this study showed that root length and alveolar bone height affect the patterns of initial tooth displacements both in the center of resistance and the centers of rotation and also in the amount of displacement, forces applied during orthodontic treatment should take into consideration the anatomic variations in the root length and alveolar bone height so as to produce optimal and desired tooth movement.

Alveolar Process↗

An attractive solution to unerupted teeth.

A user- and patient-friendly method of treating unerupted teeth is described. A neodymium iron boron magnet is attached to the unerupted tooth, and a second, larger magnet is incorporated in a removable appliance. The resulting forces provide a friction-free system, requiring little or no adjustment, which rapidly encourages the unerupted tooth into a position in which it may be bonded and thereby aligned by more conventional methods.

Adolescent↗

Long-term occlusal guidance of a severely intoxicated patient with yusho (PCB poisoning): a case report.

The peculiar dentoorofacial characteristics and 12 years of interdisciplinary management of a patient who was severely intoxicated with the man-made chemical polychlorinated biphenyls (PCBs) are described in this case report. Cephalometric measurements showed that the SNA and SNB angles were reduced but that the developments in height and skeletal maturity were in normal ranges. Gingival hyperpigmentation that was caused by high blood PCB concentration was extremely slow to fade. A cystic mass, diffused trabeculae, and irregular calcification, which were shown on the radiograph and which were caused by high blood levels of PCB, changed gradually. However, the patient had periodontal disease because of horizontal alveolar bone resorption and a deep periodontal pocket, despite good plaque control. After the PCB poisoning the tooth roots were hypoplastic and dilacerated. One root was extracted because of chronic periodontitis. Some teeth were impacted, malposed, or ankylosed.

Adolescent↗

Distal movement of mandibular molars in adult patients with the skeletal anchorage system.

The skeletal anchorage system (SAS) consists of titanium anchor plates and monocortical screws that are temporarily placed in either the maxilla or the mandible, or in both, as absolute orthodontic anchorage units. Distalization of the molars has been one of the most difficult biomechanical problems in traditional orthodontics, particularly in adults and in the mandible. However, it has now become possible to move molars distally with the SAS to correct anterior crossbites, maxillary dental protrusion, crowding, and dental asymmetries without having to extract premolars. This study evaluated the treatment and posttreatment changes during and after distalization of the mandibular molars. In 15 adult patients (12 women and 3 men), a total of 29 mandibular molars were successfully distalized with SAS. The amount of distalization and relapse and the type of tooth movement were analyzed with cephalometric radiographs and dental casts. The average amount of distalization of the mandibular first molars was 3.5 mm at the crown level and 1.8 mm at the root level. The average amount of relapse was 0.3 mm at both the crown and root apex levels. Of 29 mandibular molars, 9 were tipped back, and the others were translated distally in accordance with the established treatment goals. SAS is a viable modality to move mandibular molars for distally correcting anterior crossbites, malocclusions characterized by mandibular anterior crowding, and dental asymmetries.

Adult↗

Clinical conditions for eruption of maxillary canines and mandibular premolars associated with dentigerous cysts.

The aim of this study was to investigate the eruption of teeth associated with dentigerous cysts in the mandibular premolar and maxillary canine regions in preadolescents. Fifty-eight cyst-associated teeth, including 47 mandibular premolars and 11 maxillary canines, were examined retrospectively by using normalized panoramic radiographs and histological materials. The subjects were divided into 2 groups: the erupted group, in which the teeth had erupted successfully after marsupialization, and the nonerupted group, in which the teeth had undergone orthodontic traction or cystectomy with removal of the cyst-associated tooth. Eighty-one percent of the mandibular premolars and 36% of the maxillary canines in the cysts erupted successfully about 100 days after marsupialization without traction. The eruption of a mandibular premolar was significantly related to a shallow position in the alveolar bone, shallow angulation of the tooth, and young age of the patient but not to cyst size and dental space for the eruption. The eruption of the maxillary canine was significantly related to the small size of the cyst and the patient's age. The cyst walls of the erupted group showed severe inflammatory cellular infiltration. These findings present a treatment guideline for dentigerous cysts associated with mandibular premolars and maxillary canines in preadolescents.

Age Factors↗

Controlled slicing in the management of congenitally missing second premolars.

This report describes a simple method of allowing permanent first molars to drift mesially in patients with congenitally missing second premolars, thus facilitating future orthodontic treatment. Controlled slicing of the deciduous second molar between the ages of 8 and 9 years produced a bodily controlled mesial movement of the permanent first molar in less than 1 year with no or minor rotations or inclination. These results are compared with controlled slicing in 10- to 11-year-olds and with treatment involving extraction alone.

Anodontia↗

Emergency orthodontic treatment after the traumatic intrusive luxation of maxillary incisors.

Treatment of traumatically intruded teeth is based largely on empirical clinical experience rather than on scientific data. The aim of this qualitative meta-analysis was to provide an evidence base to evaluate the orthodontic repositioning approach. In a MEDLINE search of the literature in English, 14 reported patients involving 22 teeth were found to have been treated by this modality. Additionally, 3 new patients, involving 9 intruded teeth and presented herein, were combined to form a total study sample of 17 subjects (7 girls, 10 boys, aged 8.9 +/- 1.2 years). Orthodontic extrusive forces were applied in the immediate posttrauma period (up to 3 months), with a variety of orthodontic appliances. Repositioning was achieved for 90.3% of the affected teeth but failed in 9.7% because of inflammatory resorption (2 teeth) or a misdiagnosis of root fracture (1 tooth). Early complications included loss of pulp vitality and external root resorption. All intruded teeth with closed root apices lost their vitality regardless of the degree of intrusion, whereas among those with incomplete apices, 45.5% that had been moderately intruded remained vital. External resorption was encountered in 54.8% of the teeth. Loss of marginal bone support was rarely encountered. Late complications included inflammatory root resorption in teeth with closed apices, in which endodontic treatment was not initially performed, and obliteration of the pulp tissue in teeth that remained vital. The results show that this method is superior to other treatment alternatives.

Child↗

Focal hyalinization during experimental tooth movement in beagle dogs.

The aim was to study morphological differences between the periodontal structures of beagle dogs showing different rates of tooth movement under identical experimental conditions. An orthodontic appliance was placed on the mandibular second premolar and the first molar to exert a continuous and constant reciprocal force of 25 cN. Tooth movement was recorded weekly. The dogs were killed after 1, 4, 20, 40, and 80 days for histological evaluation. Haematoxylin and eosin staining was used for tissue survey, alkaline phosphatase staining was used as a marker for active osteoblasts, and tartrate resistant acid phosphatase staining was used for osteoclasts. After 24 hours, osteoclastic and osteoblastic activity had already increased at the pressure and tension sides, respectively, and, in some samples, hyalinization was found. In case of fast-moving teeth, areas of direct bone resorption at the pressure side and deposition of trabecular bone at the tension side were found throughout the experimental period. In the periodontal ligaments of teeth showing little movement, small patches of hyalinization were found at the pressure side, mostly located buccally or lingually of the mesiodistal plane. These phenomena were found in both molars and premolars and at all time points. It is concluded that small focal hyalinizations might be a factor that could explain individual differences in the rate of tooth movement.

Acid Phosphatase↗