A study was undertaken to determine the maximum shear strength of brackets bonded to anterior and posterior teeth. Brackets were bonded to two groups comprising 12 incisor and 12 molar teeth. After storage in water at 37 degrees C for 10 days, each bracket was tested to failure in a shear mode in a Instron machine. The mean value for the incisors was 164.3 +/- 35.1 kg/cm2 (16.1 +/- 3.4 MPa) and 115.7 +/- 41.1 kg/cm2 (11 +/- 4.0 MPa) for molars. These values, analyzed in a two-tailed test, were statistically different at the 0.01 level of confidence. It was concluded that differences in etching patterns do not necessarily affect shear bond strength and that the predominantly weak link in the bonding chain was at the bracket/resin interface. The lower values for molar teeth may relate to adaptation of the bracket and nonuniform resin thickness.

This article investigates the relationship of skeletal facial pattern and soft-tissue nasal form. The case sample comprises 123 white female subjects, aged 11.0 to 20.6 years, with no histories of pathology, trauma, surgical intervention, or orthodontic treatment. Measurements were made from cephalometric radiographs, posteroanterior radiographs, and the physioprint photographs. Skeletal classifications were based on the relationship of the maxilla to the mandible; the three classifications were straight profile, retrusive chin profile, and prognathic profile. Pearson product--moment correlation coefficients were used to test intercorrelations of all quantitative variables (including age) with each other. Correlations were highly significant for age, the three profile measurements, and two of the frontal measurements. Hence, noses and skeletal structures showed, as expected, increases with age. Also, profile measurements were highly significantly correlated; larger noses were larger in all profile dimensions. A stepwise discriminant analysis was used to study nonquantitative categories of nasal shape (straight, convex, and concave). This analysis indicated that more than 86% of patients in the sample of 123 demonstrated a correlation of nasal shapes with specific skeletal groupings. Patients with straight profiles tended to have straight noses; convex profiles accompanied convex nasal shapes; and concave profiles were found with concave nasal shapes. The clinical significance of this research is to emphasize the importance of total facial harmony (especially nasal shape) during orthodontic diagnosis and treatment planning.

The purpose of this paper was to compare retrospectively the effect on the soft tissues of two contrasting forms of treatment for Class II, Division 1 malocclusion. The first group of 30 persons exhibited uncrowded dentitions and were treated without extractions by means of the Andresen activator. No other appliance was used. The second group was also composed of 30 persons. These subjects were treated with the Begg appliance in its classical form. All of the Begg subjects showed varying amounts of crowding and were treated by extraction of four first premolars. It was believed that the Andresen appliance would maintain the incisors in the most labial position possible, while the Begg group with premolar extractions would involve the maximum lingual incisal movement. These groups were compared with a third group of 22 untreated persons who also exhibited Class II, Division 1 malocclusions. The overjets in the treated groups were successfully reduced in both cases by retraction of the upper incisors; in the Begg group only, retraction of lower incisors was also performed. The upper incisors were retracted substantially more in the Begg group than in the Andresen group, but there was only a slight difference within the two groups in the final position of the upper lip relative to a vertical reference line through sella. There was also a slight difference in the lengths of upper and lower lips within the two treated groups. The lower lip followed the lower incisors more closely in the Begg group. Both upper and lower lips "uncurled" in the treated groups and this probably allowed them to be held together with little strain. There was a wide variation in individual response in all three groups.

Although there has been considerable interest in the effects of nasal airway impairment on facial growth, the relationship is still unclear. This study examined the effect of nasal airway size on upper airway pressures during breathing. Three phases of data collection were involved. The first phase used a model to describe pressures during simulated normal and impaired respirations. The second phase involved subjects with normal airways, and the third used persons who were judged by an otolaryngologist to be nasally impaired. Aerodynamic assessment techniques were used to measure airway pressures during breathing and to assess nasal airway size. Results of the modeling study suggest that when nasal cross-sectional area is greater than 0.1 cm2, pressures associated with breathing are not excessive. These findings also suggest that slight lip opening (2 to 3 mm) would significantly reduce airway pressures. In addition, pressure magnitudes of the normal and nasally impaired groups were similar to the modeling data, and no significant difference in pressures was observed between the two groups. Accordingly, the assumptions that nasally impaired persons generate abnormal breathing pressures and that these pressures directly influence facial growth are questionable.

Kinetic coefficients of friction for stainless steel, beta-titanium, nickel-titanium, and cobalt-chromium arch wires were measured on a smooth stainless steel or Teflon surface. A universal materials testing instrument was used to pull 0.017 X 0.025-inch rectangular arch wires through a pneumatically controlled binding surface. Classical friction relationships were evaluated by varying applied normal force--similar to ligature tie force--via this pneumatic control. Coefficients of friction were determined under dry and wet (artificial saliva) conditions. Frictional force values, and thus coefficients of friction, were found to increase with increasing normal force for all materials. Beta-titanium and stainless steel wires sliding against stainless steel, and stainless steel wire on Teflon consistently exhibited the lowest dry friction values. Artificial saliva increased friction for stainless steel, beta-titanium, and nickel-titanium wires sliding against stainless steel. Artificial saliva did not increase friction for cobalt chromium, stainless steel sliding against stainless steel, or stainless steel wire on Teflon compared to the dry condition. Stainless steel and beta-titanium wires sliding against stainless steel and stainless steel wire on Teflon showed the lowest friction values for the wet condition.

The role of nasal respiratory function in oral and facial development remains unclear in spite of the long-standing interest of clinicians. Much of the current controversy stems from our inability to define mouth breathing in objective terms and evaluate nasal airway impairment quantitatively. Recent advances in respiratory monitoring technology provide new opportunities to assess upper airway breathing more objectively. The purpose of this study was to describe a new approach for measuring oral and nasal respiration and to test its reliability. The technique involves inductive plethysmography and the data provide an assessment of respiratory mode without the need to enclose the subject's head in an airtight box. The data were compared to pneumotachography and the results demonstrate the reliability of the technique.

Intrusion has been regarded as a very controversial topic in the orthodontic literature. Although it seems a logical way to handle deep overbite in adult patients who have elongated teeth, reports on iatrogenic damage have led to the suggestion of alternative methods. Considering the disadvantages of these alternatives, it seems reasonable, however, to improve our knowledge of tissue reaction as related to intrusion. Three Macaca fascicularis monkeys were used for the experiment. By means of a segmented arch approach, the upper incisors and the four first premolars were submitted to forced eruption for 8 weeks followed by 12 weeks of intrusion. A split-mouth technique was used to study the influence of oral hygiene on the tissue reaction. On the right side of the mouth, the teeth were brushed with chlorhexidine three times per week. On the left side, no oral hygiene was performed. After intrusion of the teeth, a 1-to-14 day retention period with passive appliance preceded the killing of the monkeys. A buccolingual hematoxylin- and eosin-stained serial section was produced, and soft- and hard-tissue reactions described. It appeared that the hygiene program could limit but not prevent gingival inflammation. There was, however, a marked difference in the histologic picture of the marginal bone on the two sides. On the hygiene side, clear signs of bone deposited during forced eruption were still present. This was not the case on the nonhygiene side. The extension of bone resorption was also different on the two sides.(ABSTRACT TRUNCATED AT 250 WORDS)

The behavior and role of blood vessels and blood-borne cells in the process of the remodeling of the periodontal ligament (PDL) incident to experimental tooth movement was studied in rats. Particular interest was focused on areas of tension and of pressure with frontal bone resorption but without overt hyalinization. An increase of vascular activity occurred in the above mentioned situations. Extensive breakdown of collagen was observed in pressure areas with frontal resorption and in areas of tension concomitant with vascular invasion. Two patterns of fiber and bone remodeling were seen in areas of tension: intense vascular activity within the periodontal membrane and intense vascular activity inside the alveolar bone. Macrophages occurred consistently near blood vessels both in areas of tension and in areas of resorption. These are multipotent cells that obviously influence the remodeling process.

In this exhaustive review, a number of parameters related to maxillary and mandibular second molar extractions are discussed. The parameters reviewed include the timing of extractions and the effect of extractions on third molar eruption, posterior interdigitation, and incisor imbrication. The advantages and limitations of this procedure are outlined. The available information strongly suggests that the extraction of second molars relieves crowding in the posterior part of the arch, causes faster eruption of third molars, and diminishes the number of unerupted and/or impacted third molars. Consideration of the decrease in the number of impacted third molars after second molar extraction should be balanced with the fact that the extracted teeth are usually sound and are unimpacted. In addition, the third molars that do erupt frequently are poorly angulated and/or in poor contact with the first molars. This will necessitate an additional "late" period of fixed-appliance therapy to bring these teeth into good occlusion.

This article describes the Active Vertical Corrector (AVC), which is a simple removable or fixed orthodontic appliance that intrudes the posterior teeth in both the maxilla and mandible by reciprocal forces. By the use of effective posterior intrusion of teeth, the mandible is allowed to rotate in upward and forward directions. The uniqueness of this appliance is that it allows the clinician to correct anterior open bite problems by actually reducing anterior facial height. This treatment approaches the problem at its cause (overeruption of posterior teeth) and provides better facial balance and esthetics than most conventional orthodontic treatment procedures. Problems formerly thought to require orthognathic surgery can now be treated successfully with the AVC.