A finite element analysis of the maxillary first molar PDL with maxillary protraction in a mixed dentition Class III malocclusion.

OBJECTIVES: To analyze the stress distribution on the PDL of the maxillary first molar in a mixed dentition Class III malocclusion, using a Hyrax-type appliance and maxillary protraction. SETTING AND SAMPLE POPULATION: A Class III malocclusion in the mixed dentition was reconstructed based on CBCT images. MATERIAL AND METHODS: The 3D FEM comprised the maxilla, alveolar bone, right first permanent molar teeth, and PDL and consisted of 1 133 497 nodes and 573 726 elements. Maxillary protraction force was applied to a hook positioned close to the deciduous canines with 600 g and at 15°, 30°, and 45° downward angles to the maxillary occlusal plane. RESULTS: Analysis was carried out from the top and buccal view of the sagittal plane. The magnitude of the stresses at 15°, 30°, and 45° of protraction angulation resulted in the highest stress magnitude being in the region between the distobuccal and palatal roots, as well as on the distal surface of the mesial root. The vector direction in this area showed traction and mesial movement. With 30° and 45° protraction angulations, the stress was located only between the distobuccal and palatal roots, and the vector direction was more extrusive at 15°. CONCLUSIONS: The suggested orthodontic movement is in the mesial direction with a small amount of extrusion with 15° angulation and greater extrusion with 30° and 45°.

In vivo analysis of bone strain about the sagittal suture in macaca mulatta during masticatory movements.

In vivo strain gauge analysis demonstrated that tensile bone strain is transmitted along the cranial vault to the parasagittal region during isotonic temporalis contraction. This strain is sufficient to cause measurable separation of the sagittal suture, and thus could influence growth at the sutural margins.

A system for graphic representation during stereotaxic procedures.

A method is presented wherein the attachment of linear potentiometers to the electrode carrier of a standard stereotaxic headholder permits the use of a reference voltage and an X-Y recorder to generate rapid, accurate graphic representations of various neural structures within the field of the electrode. The method is described in application to studies in rat and cat.

Severe localized destruction of the periodontium secondary to subgingival displacement of an elastic band. Report of a case.

A seven-year-old male with localized severe periodontal destruction at the maxillary central incisior region presented for treatment. There was a history of acute trauma, but local factors were inconsistent with the clinical picture. Initial treatment consisting of palliative nonsurgical debridement coupled with systemic tetracycline resulted in a more chronic lesion with progressive bone loss. Surgical entry revealed an elastic band close to the apices of the central incisors. Removal of the etiologic agent has resulted in increased radiographic bone density and decreased probing depths. Periodontal lesions induced by elastic bands are difficult to diagnose but have several features in common that may aid in rapid diagnosis and treatment.

Extraction versus periodontal-orthodontic treatment: a case report.

This paper reports the management of a patient with severe localized periodontitis accompanied by drifting and extrusion of a central incisor. Although the traditional treatment approach to this condition often includes extraction and prosthetic replacement, the approach presented here provides an alternative to extraction by combining periodontal and orthodontic treatment.

Components of class III malocclusion in juveniles and adolescents.

A statistical comparison of cross-sectional cephalometric records of Class III malocclusion subjects from ages 5-15 with serial Class I controls, finding strong tendencies for early appearance of distinctive characteristics.

Sexual dimorphism in normal craniofacial growth.

The purpose of this investigation is to re-evaluate an existing sample of Caucasian individuals, of mostly Northern European ancestry and undefined ethnic origins, who have been characterized as having excellent occlusions and balanced facial proportions (from a subjective assessment). The focus is the emergence of sexual dimorphism in the skeletal and dental relationships. Serial lateral cephalograms of 51 subjects were obtained from the Bolton-Brush Study at ages 6, 9, 12, 14, 16 and 18 yrs. At each age, the records of 16 males and 16 females were selected. Cephalometric evaluation indicated that the length of the anterior cranial base was larger in males but the cranial base angle was similar for both sexes at all age intervals studied. The effective lengths of the maxilla and mandible were similar in both sexes up to 14 years; thereafter in females this length remained relatively constant while in males it increased. The direction of facial growth was similar for both sexes, with a tendency towards a more horizontal growth pattern in females.

The effect of orthodontic treatment on centric discrepancy.

The purpose of this study is to investigate the effects of orthodontic treatment on centric discrepancy. Thirty-six orthodontic patients who had been treated with an edgewise appliance were selected for this study while 30 persons who had no history of orthodontic treatment were used as a control group. After recording centric relation using a leaf gauge, centric prematurity, and centric slide were compared using a SAM2 articulator and mandibular position indicator. Results indicated that the number of subjects with one prematurity was significantly greater in the control group (86.7%); however, the number of subjects with two or more prematurities was greater in the orthodontic treatment group (41.6%). The orthodontic treatment group showed more bilateral prematurities. There were no differences between the two groups with regard to the teeth involved in centric prematurities. Just considering the anatomic portion of teeth, centric prematurities were significantly associated with the buccal incline of the maxillary palatal cusp. There were no significant differences in the amount or direction of centric slide between the orthodontic and control groups. This study indicates that orthodontic treatment does not generally result in an increase in centric discrepancy.

The demographic outlook for orthodontists in Texas at the start of the next millennium.

Like all health care professionals, orthodontists are concerned about the need and demand for their services. Orthodontists should experience an increase in demand for their services as a result of an increasing population and an aging orthodontist population. How many additional orthodontic graduates do we need per year in Texas? Based on many factors, Texas dental schools could graduate additional students per year to be consistent with those factors. In conclusion, it appears that Texas can easily support three graduate orthodontic residency programs. As we enter the next millennium, the future of orthodontics has never looked better.

Facial divergence and mandibular crowding in treated subjects.

OBJECTIVE: To understand the relationships between facial divergence, vertical growth, and postretention mandibular crowding. MATERIALS AND METHODS: Seventy-five white extraction patients were evaluated immediately posttreatment (15.4 years) and again 16.6 years later. Hyperdivergent subjects, subjects with open bite or severe deep bites were not evaluated. Changes in incisor irregularity and tooth-size arch-length discrepancies (TSALD) were evaluated and correlated with measures of divergence and skeletal growth. RESULTS: Incisor irregularity increased 0.9 mm and TSALD increased 0.7 mm after treatment; 68% of the subjects had less than 3.5 mm incisor irregularity at postretention. Male patients showed significantly more growth than female patients did. Female patients, who were significantly more hyperdivergent than male patients, showed weak to moderately weak associations between posttreatment facial divergence and crowding. Female posttreatment changes in anterior face height, lower incisor eruption, and changes in arch depth were also related to crowding; male patients showed moderate relationships between posttreatment changes in arch width and crowding. CONCLUSIONS: Greater vertical growth, incisor eruption, and especially facial divergence are related to greater posttreatment mandibular crowding.

Education, research, and personnel needs in orthodontics.

Because of changing patterns of dental care delivery, the nature of orthodontic education, research, and personnel needs has changed markedly in recent times. Changes have occurred in the university environment, dental education, and undergraduate and graduate orthodontic education. Orthodontic research is shifting to more clinically oriented topics. Orthodontic personnel needs are being addressed by changing levels of specialist and general practitioner involvement.

The premaxillary-maxillary suture and orthodontic mechanotherapy.

Even though there has been debate over whether a separate premaxilla exists in the human being, it has been suggested that the premaxillary-maxillary suture remains patent into adolescence and provides an explanation for the action of certain orthodontic and orthopedic appliances. To assess whether this suture is pertinent to an understanding of appliance effects, the skulls of 50 subadult subjects were scrutinized to determine patency with regard to age. Remnants of a premaxillary-maxillary suture may be present on the surface of the palate at all ages studied, and often this suture extends deep to the surface. However, in no case was the suture continuous so as to distinguish a distinct premaxilla. These findings disprove the claim that the premaxillary-maxillary suture system provides an explanation for any form of orthodontic or orthopedic therapy.

Normal length changes in hand bones during adulthood: exploratory study of ray two.

A longitudinal analysis was made of total length changes of the four epiphyseal bones of ray two, the index finger, during adulthood. Matched pairs of standardized hand-wrist radiographs on 37 individuals between earlier (means = 22 years) and later (means = 54 years) adult age-grades show that the distal and middle phalanges continue to increase in overall length; the proximal phalange exhibits no change; and the metacarpal significantly decreases in size. The changes in these normal adults are also discernible in cross-sectional data but are not obvious statistically. Causes of the specific increases and decreases remain speculative.

The intrinsic stability of Class I molar relationship: a longitudinal study of untreated cases.

Attainment of a Class I molar relationship (Angle) is often a prime treatment objective. In addition to considerations of improved function and skeletodental harmonies, a Class I relationship often is deemed the "correct" and stable situation. This study assessed the relative stability of the sagittal molar relationship in orthodontically untreated persons with full dentitions who were followed longitudinally from young (approximately 20 years) to older (approximately 55 years) adulthood. The Class I relationship is indeed most stable; none of 69 cases (sides) starting in a Class I cusp-in-groove relationship moved from that condition. In contrast, Class II relationships naturally became significantly "more" Class II (that is, greater distoclusion), and Class III cases shifted significantly to greater mesioclusion.