Douglas C. Bowman

Variations in bracket placement in the preadjusted orthodontic appliance

This study was conducted to determine the accuracy of bracket placement with the direct bonded technique. Ten orthodontic faculty members bonded a preadjusted orthodontic appliance on models of five cases of malocclusion in a simulated clinical situation (mannequin). A total of 50 sets of models served as the population of the study. Photographs of the models were measured to determine vertical and angular discrepancies in position between adjacent bracket pairs from a constructed reference line. Variations are evaluated with respect to the classification of malocclusion, specific tooth type, and intra/inter operator differences. A mean of 0.34 mm for the vertical discrepancies and a mean of 5.54 degrees for the angular discrepancies are found in placement of the orthodontic brackets.

A cephalometric study of of Korean adults

A cephalometric study of 18-year-old Korean subjects with acceptable profile and occlusion was carried out by means of the Downs, Steiner, Ricketts, and vertical analyses. The subjects in the study sample consisted of 35 men and 45 women. Means and standard deviations of the Korean subjects were established. Statistical analyses were performed to compare Koreans to Caucasians.

Functional and Histologic Assessment of the Sensory Innervation of the Periodontal Ligament of the Cat

Activity along the inferior alveolar nerve in response to force application to canine teeth yielded two responses, one associated with light forces and the other with heavy forces. The two types of nerve endings found were naked terminals, which occurred throughout, and specialized receptors, innervated by large fibers, which were confined to the apical third of the root.

The influence of extraction and nonextraction orthodontic treatment on brachyfacial and dolichofacial growth patterns

The effects of extraction and nonextraction orthodontic treatment mechanics on patients with dolichofacial and brachyfacial growth patterns between one and two standard deviations were studied. Groups underwent treatment of either nonextraction or extraction of four premolars with the appropriate mechanics for the facial type. Changes in the facial axis and correlation between maxillary molar movement and facial axis change were measured. A positive correlation was found between the amount of anteroposterior movement of the upper molar and change in the facial axis in brachyfacial and dolichofacial patients undergoing nonextraction treatment. A weak correlation was found in the extraction treatment groups. No statistically significant difference was found in the facial axis change among any of the groups studied, regardless of facial type or plan of treatment. There were indications of a more severe opening of the facial axis (Ba-Na plane to constructed gnathion) with greater degrees of maxillary molar distal movement in both facial patterns studied.

Evaluation of the Human Subject's Ability to Differentiate Intensity of Forces Applied to the Maxillary Central Incisors

Minimal detectable differences between two centered forces applied to maxillary central incisors were determined for 50 subjects. The forces involved were 10, 50, 100, 200, 500, and 1,000 gm; most accurate subjective discrimination was between the 50- and 500-gm centered forces. Incisally and labially directed forces yielded nearly identical results.

Bond strength of three orthodontic adhesives

A method was devised to study the bond strength of direct-bonding orthodontic adhesives. A shear load was applied parallel to the tooth-adhesive-bracket interface by means of an Instron Universal Testing Machine. The bond strength was found to increase for some products after 27 days. However, no significant differences could be detected 1 day after placement. The interface was studied to determine the mode of failure. In all cases bond failure occurred as mixed adhesive-cohesive phenomena.

Ability of Human Subjects To Discriminate Forces Applied to Certain Teeth

Subjective ability to discriminate differences in intensity of forces applied to maxillary canines, and to mandibular incisors, canines, and first premolars was evaluated. Least relative differences in force could be discriminated through the maxillary canines (8.6 to 9.5%). Individuals showed nearly the same discriminatory ability for all mandibular teeth tested.

Hyoid positioning during deglutition following forced positioning of the tongue

Many investigators believe that improper tongue positioning during swallowing will lead to adverse positioning of the teeth. The tongue has been described as having a regulatory activity, even during the teething process, on both tooth position and jaw shape.l Carline? described normal swallowing as being characterized by negative intraoral pressure and by placement of the tongue tip against the ridge of the hard palate with lips closed and teeth together. The abnormal swallow was depicted as the opposite pattern. The tip of the tongue is thrust forward or laterally, the lips and teeth are apart, and the swallow is completed by positive rather than negative pressure. It has been pointed out that the swallowing reflex repeats itself approximately twice a minute while one is awake and once a minute when one is asleep. The pressure from this swallowing builds up a total force of from 6,000 to 12,000 pounds in a 24-hour period.3 One can imagine the results if this force is improperly directed. Maximum perioral and tongue forces on incisor teeth have been evaluated, and it has been reported that the maximum tongue thrust ranged from 600 to 2,500 grams.4 The hyoid bone serves as a scaffold largely responsible for mouth opening and swallowing. The hyoid bone is nonarticulating and suspended entirely by ligaments and tendons. Hyoid musculature is divided into those

Occlusal force discrimination by denture patients

A study was conducted on subjects with conventional dentures and with overlay dentures to compare their abilities to discriminate between occlusal forces. Perpendicular forces were applied to the dynamic center of the occlusal table of the mandibular denture. Each subjects ability to distinguish differences in values of force was observed and recorded. All subjects with dentures showed sensory threshold values close to those reported for natural teeth. A graphic plotting showed that the responses of subjects with overlay-type dentures were more closely correlated with the psychophysical law as expressed by Stevens as a power function. Since this phenomenon holds true for natural teeth, the overlay denture more closely resembles natural teeth in this type of sensory function than does the conventional denture. In addition to recognized advantages, such as preservation of the ridge and improved retention and stability, the overlay denture provides more typical sensory function than is provided by the conventional denture. This advantage should further motivate dentists and patients to consider the retention and utilization of at least two suitable teeth in an overlay-type denture service.

Effects of methyl methacrylate monomer vapors on respiration and circulation in unanesthetized rats

A study was conducted in which two groups of female rats were exposed to vaporized MMA-m for a period of 20 minutes daily for 21 and 42 days, respectively. Systolic blood pressure, heart rate, respiration, and ECG were monitored for 5 minutes prior to MMA-m exposure and then during a 20-minute exposure to MMA-m. On the twenty-first and forty-second day, respectively, the aforementioned vectors were monitored again. During the first exposure 63% of the experimental animals displayed marked changes in respiration ranging from a modified Cheyne-Stokes type to periods of very shallow breathing followed by deep breathing. Thirty-eight percent showed ECG changes ranging from premature ventricular contractions and altered QRS complexes to markedly depressed T waves. Continued exposure resulted in an initial decrease followed by an increased systolic blood pressure with an increased respiratory and heart rate. At the final testing period all animals showed abnormal respiratory patterns and ECG changes and demonstrated a heart block pattern. In all animals systolic blood pressure increased the longer they were exposed to MMA-m.