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Biomedical subjects

W R Proffit

Publications and source records attributed to W R Proffit.

At least 37 records · Page 2Linked to original sources
PubMed1988

Exposure reduction in cephalometric radiology: a comprehensive approach.

Various methods have been proposed and investigated for the purpose of reducing radiation exposures in cephalometric radiography. The purpose of this investigation was to use various dose-reducing methods from four major categories--(1) rare-earth intensifying screens, (2) rare-earth filtration, (3) prepatient soft-tissue enhancement methods, and (4) films varying in speed and latitude--to determine optimal combinations on the basis of exposure reduction and image quality achieved. In laboratory tests and clinical trials, radiation doses were compared along with various tests of image quality for the standard system currently used at this institution and for experimental systems. Image quality was assessed by standard panel-of-expert methods and more quantitative methods involving optical densitometry, contrast indices, and landmark envelopes of error. Results demonstrated that significant exposure reductions were achievable, often with improved image quality. The degree of exposure reduction was dependent largely upon the type of intensifying screen and to a lesser extent on beam filtration or film types. The greatest reduction in exposures were achieved with techniques using rare-earth beam filtration. Image quality was highest with a new wide-latitude type film. Because such significant reduction in radiation exposure for cephalometrics is possible with new techniques, we conclude that a change from the previous standard should occur. In establishing a new technique, orthodontists should consider adopting rare-earth screens and beam filters, flat-grained films, prepatient soft-tissue enhancement methods, and the elimination of grids.

Calcium Compounds↗
PubMed1988

Simultaneous superior repositioning of the maxilla and mandibular advancement. A report on stability.

Fifty-three patients who underwent simultaneous surgical superior repositioning of the maxilla and mandibular advancement were studied cephalometrically and clinically for at least 1 year after surgery (mean 2.4 years). The pattern of change for the maxilla and the percentage of patients who had 2 mm or more movement of landmarks were consistent with that observed following isolated superior repositioning of the maxilla. Although changes similar to those observed with isolated mandibular movement occurred, because the changes in the maxilla also affected the mandible, a greater percentage of patients experienced postsurgical movement of the mandible in this group than in those undergoing mandibular advancement alone. Clinically, satisfactory or better results were observed in 42 (79%) patients at their longest follow-up examination. The only significant variable associated with clinical outcome was the presence (presurgically) of an open bite (p less than 0.04) in 10 of 11 patients with poor clinical results. There was no statistically significant relationship between cephalometric stability and clinical outcome in this series of patients.

Adolescent↗
PubMed1988

Adaptations in lip posture and pressure following orthognathic surgery.

Lip pressures before and after orthognathic surgery were studied to evaluate the relationship between posttreatment soft-tissue adaptation and incisor stability. After all surgical procedures, physiologic adaptation resulted in the maintenance of pressures during speech and swallowing. When the maxilla was advanced by LeFort I osteotomy, a significant decrease in resting pressure of the upper lip was observed instead of the expected increase and incisor stability did not seem related to soft-tissue influences. When the mandible was advanced by sagittal split osteotomy, resting pressure did not increase as expected, but there was a tendency for incisors to become more upright after fixation release, perhaps as a rebound from labial tipping in fixation. When soft tissues were relaxed as the mandible rotated forward following superior repositioning of the maxilla, resting pressures decreased and lower incisors tended to be positioned forward as predicted by equilibrium theory.

Adaptation, Physiological↗
PubMed1987

Stability following superior repositioning of the maxilla by LeFort I osteotomy.

Cephalometric data from 61 patients who had undergone superior repositioning of the maxilla via LeFort I osteotomy by means of the downfracture technique were analyzed to evaluate stability of skeletal and dental landmarks at various time intervals up to 1 year. None of these patients had concurrent mandibular ramus or body osteotomy except genioplasty and all had at least 2 mm intrusion at the maxillary incisor or molar. In approximately 20% of the patients, there was 2 mm (critical value) or more postsurgical movement of skeletal or dental landmarks. During the first 6 weeks postoperatively, the maxilla showed a strong tendency to move farther upward in the patients in whom it was not stable. The posterior maxilla was vertically stable in 90% of the patients, the anterior maxilla in 80%. Horizontally, skeletal landmarks were stable in 80%, but when changes occurred, there was a tendency for the anterior maxilla to move back when it had been advanced. After the first 6 weeks, the posterior maxilla was stable vertically in all patients, but in 20% anterior maxillary landmarks moved downward, opposite to the direction of movement during fixation. In 11 of the 15 patients who demonstrated vertical changes postsurgery, the movement from fixation release to 1 year follow-up was opposite and approximately equal to the initial change, so that the net movement after 1 year was less than 2 mm. Only 6.5% (four patients) demonstrated 2 mm or greater net vertical movement for any of the variables studied 1 year after surgical treatment. There was no indication that the amount of presurgical orthodontic movement of incisors, the presence of multiple segments at surgery, the age of the patient, the presence or absence of genioplasty, or the presence or absence of suspension wires was a risk factor for instability.

Adolescent↗
PubMed1986

The effect of intermittent forces on eruption of the rabbit incisor.

Rabbits were prepared so that a variable capacitance displacement transducer (VCDT) could be used to monitor the eruptive movements of a previously-amputated lower incisor, and a strain gauge transducer mounted on a relay-controlled plate was used to place precisely controlled intermittent forces opposing the erupting tooth. Forces of one or three g were applied under time conditions of one second on, nine seconds off (1:9); one second on, three seconds off (1:3); and one second on, one second off (1:1). The data indicate that with force present for 10% of the time (1:9), there was little or no effect on eruption rate. In contrast, 50% time (1:1) produced essentially the same intrusive effect as continuous force, and 25% time (1:3) gave an intermediate response. The data are consistent with the hypothesis that force duration is more important than force magnitude for the vertical equilibrium, as is the case for facio-lingual equilibrium.

Animals↗
PubMed1986

Variables affecting measurements of vertical occlusal force.

Previous studies of occlusal force have provided conflicting results. The purpose of these studies was to determine whether the extent of vertical opening, contralateral occlusal support, or head posture influenced vertical occlusal forces during swallowing, simulated chewing, and maximum biting effort. Three samples of subjects with normal vertical facial proportions--one each of children, adolescents, and young adults--were evaluated to determine the effects of changes in small (2.5 vs. 6.0 mm) vertical separation of the first molars. A sample of young adults was used to evaluate changes in large (10-40 mm) vertical openings, and a sample of adolescents was used to investigate the effect of contralateral support and head posture. All between-group comparisons were evaluated using non-parametric statistics. For the small vertical openings, there was significantly more vertical occlusal force at 6.0 than 2.5 mm in children during swallowing and chewing but not during maximum biting effort. In adults, there was significantly more force during swallowing at 6.0 than at 2.5 mm separation, but no differences in chewing or maximum biting. Increasingly large vertical openings resulted in a progressive increase in maximum bite force to a maximum at about 20 mm, followed by a decrease and then a second increase to near-maximum force at about 40 mm for young adults. There were no significant differences in vertical force with or without contralateral support or between flexed, normal, and extended head postures at either of the small openings.

Adolescent↗
PubMed1985

The pattern and control of eruptive tooth movements.

Assumptions about eruptive tooth movements based on experience with adolescents may not be applicable to all ages. The eruptive process can be subdivided into six phases--three profunctional stages of individual tooth eruption (follicular growth, pre-emergent eruptive spurt, and postemergent eruptive spurt) and three postfunctional stages of the eruption of the entire dentition (juvenile occlusal equilibrium, circumpubertal occlusal eruptive spurt, and adult occlusal equilibrium). Differences in tooth-eruption rates in each of these phases result from variations in systemic and local factors. A series of working hypotheses which incorporate recent research into a theoretical explanation of the control of eruption during each stage is presented. Prior to emergence, the force of eruption may influence the rate of bone resorption and later of gingival remodeling, but the resorptive processes occur independently and are the rate-limiting factors in pre-emergent eruption. After emergence, intermittent occlusal loading disrupts the generative or adaptive mechanisms of the periodontal ligament so that eruption slows. The light continuous forces from resting tongue pressure also are significant influences on tooth eruption during periods of rapid facial growth. Cellular adaptation of the alveolar bone and gingiva plays an important role in the control of tooth eruption in the adult.

Adolescent↗
PubMed1985

Bone scanning with 99mtechnetium phosphate to assess condylar hyperplasia. Report of two cases.

Condylar hyperplasia poses a problem in planning treatment because it is a self-limiting process for some but not all patients. Continued growth creates a progressive deformity that requires condylectomy, whereas an enlarged condyle can be left in place after hyperplastic growth ceases, even if ramus surgery is needed to correct asymmetry. Bone scan with 99mtechnetium phosphate can be used to assist in making the differential diagnosis. In the two patients reported here, abnormal metabolic activity revealed by bone scans supported clinical and historical evidence that the condylar hyperplasia was active and required surgical correction, including condylectomy. The two cases demonstrate different approaches to postsurgical orthodontic treatment, depending on the amount of normal growth expected.

Adolescent↗
PubMed1985

Orthodontic care for medically compromised patients: possibilities and limitations.

Medically compromised children and adults are increasingly likely to seek orthodontic care as improved medical management creates more long-term survivors. For the majority, treatment of orthodontic problems is feasible, but special precautions usually are required. These include medical consultation to establish the patient's prognosis, maintaining a current knowledge of drug therapy, and modifications in office procedures. Patients with a history of multiple transfusions should be presumed to be hepatitis carriers until proved not to be, and special precautions to protect office staff members and other patients should be taken. Decreased resistance to infection is a common complicating factor in medically compromised patients. Dentists must therefore avoid mucosal irritation and carefully monitor periodontal health. The practitioner should be alert to side effects of drug treatment such as xerostomia and depressed immune response, and be aware of the particular features of the underlying disease. Bleeding disorders, which can be managed by replacement of missing clotting factors, do not contraindicate orthognathic surgery. The major contraindication is poor anesthetic risk, which almost always is true for patients having sickle cell anemia because of poor blood oxygen saturation. Because orthodontic treatment can provide positive benefits, it should not be withheld solely because of the presence of a serious medical problem. With appropriate management, successful orthodontic treatment can be done for most patients.

Adolescent↗
PubMed1978

Equilibrium theory revisited: factors influencing position of the teeth.

The major primary factors in the dental equilibrium appear to be resting pressures of tongue and lips, and forces created within the periodontal membrane, analogous to the forces of eruption. Forces from occlusion probably also play a role in the vertical position of teeth by affecting eruption. Respiratory needs influence head, jaw and tongue posture and thereby alter the equilibrium. "Deviate swallowing" is more likely to be an adaptation than a cause of tooth changes. Patients with failure of eruption have been recognized and alterations in the eruption mechanism may be more important clinically than has been recognized previously.

Dental Occlusion↗
PubMed1977

Tongue pressures and tooth stability after anterior maxillary osteotomy.

Tongue pressures against the maxillary dentition during swallowing were measured in a series of ten patients who underwent anterior maxillary osteotomy for correction of protrusion. In these patients, tongue pressures were low initially, especially pressures by the sides of the tongue in the molar region. After surgical retraction of the incisors, tongue pressures increased, but the increases brought pressures up to normal levels from the previous abnormally low values. The data are consistent with the view that function (swallowing) adapts to oral form, rather than the other way around.

Deglutition↗