Gregory J. King

Anteroposterior skeletal and dental changes after early Class II treatment with bionators and headgear.

In this study we examined anteroposterior cephalometric changes in children enrolled in a randomized controlled trial of early treatment for Class II malocclusion. Children, aged 9.6 +/- 0.8 years at the start of study, were randomly assigned to control (n = 81), bionator (n = 78), and headgear/biteplane (n = 90) treatments. Cephalograms were obtained initially, after Class I molars were obtained or 2 years had elapsed, after an additional 6 months during which treated subjects were randomized to retention or no retention and after a final 6 months without appliances. Calibrated examiners, blinded to group, used Johnstons analysis to measure anteroposterior cephalometric changes. Statistical analysis was used to determine annual skeletal and dental changes during treatment, retention, and follow-up, and overall. Our data reveal that both bionator and head-gear treatments corrected Class II molar relationships, reduced overjets and apical base discrepancies, and caused posterior maxillary tooth movement. The skeletal changes, largely attributable to enhanced mandibular growth in both headgear and bionator subjects, were stable a year after the end of treatment, but dental movements relapsed.

Measuring dental drift and orthodontic tooth movement in response to various initial forces in adult rats

A method for the quantification of orthodontic tooth movement in the rat is presented. Reliability, sensitivity, and validity were assessed and tooth movement kinetics were determined for initial forces of 20, 40, and 60 gm. The appliance consisted of a 9 mm length of closed coil spring suspended between a cleat and bonded to the occlusal surface of the maxillary first molars and the maxillary incisors. Initial tipping forces were placed by suspending known weights from the anterior end of these coils before fixation to the incisors. Tooth movement was quantified from enlarged cephalograms by measuring the position of a reproducible landmark on the molar cleat with respect to either zygomatic amalgam implants or a barbed broach placed submucosally on the palate. All measurements were made along the molar-incisor vector by projecting at 90 degrees to this line. Validity and sensitivity were assessed by quantifying molar distal drift and comparing these results with reports of bone turnover rates adjacent to distally drifting adult rat molars. Reliability was obtained by estimating the error of a single measurement in a longitudinal study of 12 adult male Sprague-Dawley rats (180 to 200 days) receiving both amalgam and broach implants and a cross-sectional study of 72 animals divided equally into six groups to be killed at 1, 3, 5, 7, 10, and 14 days. No orthodontic forces were used in this portion of the study. Implant stability within the craniofacial complex was assessed by measuring bilateral broaches as a function of time with respect to each other. There were no systematic errors between replicate films for either the amalgam or the broach method. The 95% confidence limit for a single determination of molar position was 62 microns using the amalgams and 47 microns for the broach (p less than 0.001). The latter could be reduced to 23 microns when the average of four independent determinations was used. Homologous implants did not differ with respect to each other in the sagittal plane but did in the transverse plane (p less than 0.01), migrating laterally 9 microns/day. Linear regression analysis of molar distal movement over time predicted 7.7 microns/day distal drift (p less than 0.01), which compared favorably with reports of 6.7 microns/day of alveolar bone turnover during this drifting process. Characteristic three-part cumulative tooth movement kinetics were obtained for the 40 and 60 gm initial force groups. No individual time point at 60 gm differed from its counterpart at 40 gm.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on the efficacy of implants as orthodontic anchorage

The abilities of two types of small cylindrical endosseous implant to resist movement when loaded with constant forces of orthodontic magnitudes were tested. Pairs of Bioglass-coated implants and pairs of Vitallium implants of the same size were implanted into the femurs of twelve rabbits. After a 28-day healing period, these implants were loaded with forces of 60 grams, 120 grams, and 180 grams. Analysis of implant movement after 28 days revealed that no statistically significant movement occurred at any of the three force levels for either type of implant. Histologic evaluation revealed a connective tissue encapsulation with the Vitallium implant and an implant-bone bond with the Bioglass implant. No histologic evidence of implant movement was observed for either implant type at any force level.

Comparison of peer assessment ratings (PAR) from 1-phase and 2-phase treatment protocols for class II malocclusions

The purpose of this study was to compare the dentoalveolar outcomes after 1-phase and 2-phase orthodontic treatment of Class II malocclusions. Class II subjects (n = 208) were randomized to 1-phase or 2-phase treatment with either bionator or headgear/biteplate. The peer assessment rating (PAR) was calculated from pretreatment, prephase 2, and final study models. Chi-square, Kruskal-Wallis, and Wilcoxon rank sum tests were used to evaluate the differences among treatment groups, sexes, races, pretreatment, mandibular plane angle, severity, and compliance. Spearman rank correlation coefficients were used to examine relationships between PAR at different times. The dropout rate of 24.6% did not adversely affect the ability to detect differences of clinical importance or impact treatment groups disproportionately. There were no significant differences with respect to initial PAR or final PAR among the 3 treatment protocols. The 2 early treatment groups had lower PAR scores than the 1-phase group before phase 2 (P =.0001). Lower PAR scores were achieved at both the beginning and end of phase 2 in girls (P =.03; P =.02, respectively). There were differences in the pre-phase-2 and post-phase-2 PAR scores based on initial severity (P =.0006; P =.02, respectively), with greater improvement in the patients whose malocclusions were less severe initially. Mandibular plane angle had no effect on pre-phase-2 or post-phase-2 PAR scores. These results do not support the hypothesis that different dentoalveolar outcomes are obtained between 2-phase and 1-phase treatment of Class II malocclusions.

Risk factors associated with temporomandibular joint sounds in children 6 to 12 years of age.

The relationship between temporomandibular joint (TMJ) sounds and a persons dental and skeletal characteristics is poorly understood. In this study, data were obtained from 3428 grade schoolchildren (mean age = 9.0 years, SD = 0.8, range 6 to 12 years), without a history of orthodontic treatment. Each child had been examined independently by one of six orthodontists to assess: TMJ sounds (none, click, crepitus), gender, age, race (white/black), skeletal relationships (convexity, maxillary, and mandibular positions), malocclusion (molar class, overjet, overbite, anterior crowding, posterior crossbite), maximum opening, chin trauma (none, cut, scar), and history of lower facial trauma. Temporomandibular joint sounds were present in 344 children (10.0% of the sample); 276 (8.1%) had an isolated unilateral sound, 254 (7.4%) had unilateral clicking, 50 (1.5%) had bilateral clicking, 22 (0.6%) had unilateral crepitus, and 11 (0.3%) had bilateral crepitus. Univariate analyses compared children with and without sounds for each variable; logistic regression analyses examined the relationship between groups of variables and TMJ sounds. The prevalence of TMJ sounds was associated with examiner (chi 2 = 23.4, df = 5, p < 0.001); increased prevalence of TMJ sounds occurred in children with maxillary anterior crowding (t = 2.8, p < 0.006), mandibular anterior crowding (t = 3.0, p < 0.002), and increased maximum opening (t = 4.7, p < 0.001). In contrast to other reports on children, the prevalence of joint sounds was not associated with age, race, gender, or molar class.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of bracket placement and bond strength when comparing direct bonding to indirect bonding techniques

A clinical evaluation was made to determine the advantages and disadvantages of two currently used techniques for bonding brackets to teeth of orthodontic patients. The two techniques were compared with respect to (1) bracket placement, (2) bond strength, (3) rate of failure, and (4) clinical and laboratory time involved in the two procedures. Vertical bracket placement showed no statistically significant differences. The only exceptions were the maxillary canines, where the indirect technique yielded better results (P less than 0.05), and the mandibular second premolars where the direct-bonded brackets were placed closer to ideal (P less than 0.01). Angular bracket placement showed statistically significant differences on the maxillary (P less than 0.01) and mandibular (P less than 0.05) canines, with the indirect bonds being more accurate. The bond strength results indicated great variability from one patient to another. The bracket failures, recorded 3 months after appliance placement, were 4.5 percent for the indirect technique and 5.3 percent for the direct technique. Average time needed for completion of the direct bonding technique was 42.18 minutes. The indirect technique and laboratory procedures required 53.73 minutes, of which 23.91 minutes represented actual clinical time.

Histomorphometric study of dental pulp during orthodontic tooth movement

Orthodontic tooth movement has been implicated in secondary changes to the dental pulp. The purpose of this study was to correlate the effects of orthodontic tooth movement on the dental pulp by histomorphometric parameters. Four groups, each consisting of 36 male adult Sprague-Dawley strain rats, were studied with differing force magnitudes. These included a sham group in addition to groups with bilaterally placed appliances activated to 20, 40, and 60 g of initial force designed to mesially tip the maxillary first molars. Six rats were killed at 1, 3, 5, 7, 10, and 14 days. Specimens were fixed, embedded, and stained with tetrachrome. Pulpal measurements were made with an image analyzer and included changes in predentin and vascularity. Findings indicated a significant increase (p < or = 0.05) relative to time and force magnitude in capillary number. An initial pulpal hyperemia was observed following activation of orthodontic force which was unrelated to force magnitude. A force-dependent increase in predentin width was measured at the peak of the tooth movement cycle.

The measurement of acid and alkaline phosphatase in gingival crevicular fluid during orthodontic tooth movement.

This study examines acid and alkaline phosphatase activities in gingival crevicular fluid (GCF) to learn whether bone turnover dynamics can be monitored in human subjects during orthodontic tooth movement. Three female subjects were observed longitudinally to assess tooth movement, plaque, and inflammation. For each subject, one randomly selected premolar served as the control and was not treated, and another was moved buccally with 100 gm of force. The GCF was collected weekly and assayed for phosphatases. Alkaline phosphatase peaked between the first and third weeks, followed by an increase in acid phosphatase between the third and sixth weeks. After the first week, tooth movement averaged 0.9 mm. Additional 0.9 mm of movement occurred during the next 3 weeks, followed by 1.4 mm during weeks 4 to 6. Thirty additional patients, randomly divided into headgear/biteplate, bionator, and control groups, were also sampled cross-sectionally at the maxillary first molars. The GCF phosphatase activities were assessed as functions of location on the tooth, treatment modality, duration of treatment, gingival inflammation, and plaque accumulation. The plaque index did not show a relationship to either acid or alkaline phosphatase activity on the mesial or distal in the treated groups. However, alkaline phosphatase increased with inflammation on the distal in treated groups and acid phosphatase was consistently higher on the mesial than on the distal in the treatment groups. Alternating peaks of acid and alkaline phosphatase were found in the GCF of treated teeth as functions of treatment duration. The sequence of these changes is similar to that reported for alveolar bone turnover in a rodent orthodontic tooth movement model. We conclude that phosphatase activities in GCF may be a useful means for monitoring tissue responses to orthodontic treatment.

Risk factors associated with incisor injury in elementary school children

This study examined risk factors associated with incisor injury in 3396 third and fourth grade school children in Alachua County, Florida. One of six orthodontists completed a standardized examination form for each child to assess severity of incisor injury, gender, age, race, skeletal relationships, morphologic malocclusion, incisor exposure, interlabial gap, TMJ sounds, chin trauma, and history of lower facial trauma. One in five (19.2%) exhibited some degree of incisor injury. This was limited to a single tooth in 73.1% of those with injury, while enamel injury predominated (89.4%). The majority of the injuries (75.4%) were localized in the maxillary arch, with central incisors the most frequently traumatized. Chi-square tests of association indicated that gender, race, school, orthodontist, history of lower facial trauma, chin trauma, profile, and maxillary and mandibular horizontal positions were associated with incisor injury (P < 0.05). Wilcoxon rank sum tests identified differences in age, overjet, time of screening, and interlabial gap between those with and without injury (P < 0.05). Results of logistic regression analyses indicated risk of incisor injury was greater for children who had a prognathic maxilla, a history of trauma, were older, were male, and had greater overjet and mandibular anterior spacing.

Serum and alveolar bone phosphatase changes reflect bone turnover during orthodontic tooth movement

Acid and alkaline phosphatase changes have been demonstrated histochemically and biochemically during the early stages of an orthodontic tooth movement cycle. However, quantitative data on neither alveolar bone nor serum phosphatase changes over an entire tooth movement cycle have been reported. This study examined acid, tartrate-resistant acid (TRAP), and alkaline phosphatase changes in serum and alveolar bone during an orthodontic tooth movement cycle in 288 adult male Sprague-Dawley strain rats. The effect of differing initial force magnitudes on phosphatase changes was also examined. Data were obtained from four groups: sham control and three treatment groups (20, 40, and 60 gm activations). Each group (n = 72) was subdivided equally into six sacrifice subgroups (1,3,5,7,10, and 14 days). Treated animals received a precisely loaded orthodontic tipping force to the maxillary molars. Phosphatase measures were obtained by colorimetric assays. Analysis of variance (ANOVA) procedures were performed to examine for differences within groups across time and among groups at each time point. Data from treated animals were combined, adjusted for control values, and examined across time to permit comparisons with previously described histomorphometric changes. Analysis of variance indicated no differences occurred in the control group across time. Significant differences in serum values occurred across time within the force groups (p < 0.01), and among force and control groups at various times in both sera and bone (p < 0.05). In the pooled treatment data, a peak in serum acid phosphatase occurred at day 1 and in bone at day 3 (the later mirroring histomorphometric findings) (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)