Richard F. Ceen

Transverse dentoalveolar changes after slow maxillary expansion

INTRODUCTION In this study, we evaluated the transverse dentoalveolar changes in the maxillary first molar region after early treatment with the quad-helix appliance. METHODS Seventy-three consecutive patients (39 boys, 34 girls) who had phase 1 quad-helix treatment were evaluated with cone-beam computed tomography scans taken before phase 1 (mean age, 9.2 years) and phase 2 (mean age, 11.9 years) treatments. Buccal bone thickness, buccal cortical plate thickness, lingual bone thickness, alveolar width, palatal width, and intermolar width were measured by using standardized orientations. RESULTS Slow palatal expansion with the quad-helix decreased buccal bone thickness (1.6 mm ± 0.8), and increased lingual bone thickness (1.6 mm ± 1.3) and alveolar width (0.5 mm ± 1.0). Intermolar widths and palatal widths increased 6.5 mm ± 2.9 and 3.9 mm ± 1.8, respectively. At the beginning of phase 2, approximately one third of the patients showed little or no buccal cortical plate on at least 1 side. Patients retained with the Hawley demonstrated some relapse tendencies; patients without retention had the greatest relapse tendencies. CONCLUSIONS Early treatment with the quad-helix appliance proved to be highly effective in increasing intermolar, palatal, and alveolar widths. The teeth moved through the alveolus, leading to substantial decreases in buccal bone thickness and increases in lingual bone thickness.

Orthodontic bonding with varying curing time and light power using an argon laser

OBJECTIVE To test the effects of curing time and light intensity on the shear bond strength of adhesive composites for stainless-steel orthodontic brackets. MATERIALS AND METHODS An argon laser at four different power settings (100, 150, 200, and 250 mW) and four different exposure times (5, 10, 15, and 20 seconds) was used to bond adhesive-precoated (APC) stainless-steel incisor brackets to the facial surfaces of 154 bovine incisors. The shear bond strength of each specimen in 16 randomly divided groups was randomly tested to failure using an Instron universal testing machine. Each mode of failure was described using the adhesive remnant index (ARI). RESULTS The ARI scoring system showed that the location of bond failure did not differ significantly in relation to exposure time (P = .40). However, the location of bond failure was significantly different in relation to light power (P = .03). CONCLUSIONS A short exposure time and a low power setting produce shear bond strengths equivalent to those produced by longer exposure times and higher power settings.

Timing effects of growth hormone supplementation on rat craniofacial growth

Growth hormone (GH) supplementation has become a popular treatment approach for GH normal children with short stature. To investigate how the timing of GH supplementation affects the growth of the craniofacial region, three groups of GH-normal, 28-day-old female Wistar rats were examined over 4 weeks: the early group (n = 10) received two daily injections of rhGH (2 mg/kg/day) from days 1 to 28, the late group (n = 10) received two daily saline injections from days 1 to 14 (Phase I) followed by two daily injections of rhGH from days 14 to 28 (Phase II), and the control group (n = 12) received two daily saline injections from days 1 to 28. Lateral cephalometric, forelimb and hindlimb radiographs obtained weekly were scanned, standardized points digitized, and distances were measured using the Viewbox software. Growth curves between groups were compared using multilevel iterative generalized least squares curve fitting procedures. Supplementation during Phase I in the early group produced significant treatment effects in cranial and cranial base, midface, posterior corpus, and limb lengths which varied inversely with relative maturity (percentage growth completed at the start of the study). During Phase II, GH supplementation in the early and late groups showed treatment effects as above and additional viscerocranial and mandibular measurements, but these effects were unrelated to the relative maturity of the variables. These latter results are at variance with earlier findings in GH-deficient rats, raising the possibility that that GH-normal rats may not respond to GH supplementation in a similar fashion to GH-deficient rats.

Demographic characteristics of orthodontic practice sites in the United States

Few studies have addressed the demographic characteristics of dental-practice sites, including orthodontic practice sites. In this study, we investigated the demographic characteristics of orthodontic practice sites in the United States. Demographic data and orthodontic practices were organized by zip codes and analyzed with discriminant analysis. The demographic characteristics associated with zip codes that contained an orthodontic practice were determined vs those without an orthodontic practice. The resulting model correctly classified 90.3% of the 30,134 zip code areas, based on the presence or absence of an orthodontic practice. The variables most closely associated with a zip code containing an orthodontic practice included number of dental practices (general practice) and population size. Several variables related to the socioeconomic status of the area were also positively related to zip codes with an orthodontic practice. Further analysis indicated a positive relationship between the models output and its ability to predict single vs several orthodontic practices in a zip code area. A practical method for assessing the relative merits of alternate site locations is also provided.