An orthodontic/orthopedic correction of the Class III malocclusion in young patients with a modified RPE appliance and a facemask.

Orthopedic appliances such as palatal expanders and facemasks have been successfully used for young patients with Class III malocclusions. A modified rapid palatal expansion (RPE) appliance in conjunction with a facemask can be used for correction of transverse and sagittal discrepancies in the initial phase of treatment for these patients.

Orthodontic treatment changes of chin position in Class II Division 1 patients.

INTRODUCTION: Because most patients with skeletal Class II malocclusions also have mandibular deficiencies, treatment plans should include improvement in chin projection. On that basis, the purposes of this study were to (1) determine how Class II treatment affects anteroposterior (AP) chin position in growing subjects and (2) ascertain the most important determinants of AP chin position. METHODS: Pretreatment and posttreatment lateral cephalograms of 67 treated patients (25 extraction headgear and Class II elastics, 23 nonextraction headgear, and 19 Herbst) were collected, traced, and digitized. The average pretreatment age was 12.2 years (range, 9-14 years), and the average treatment duration was 30.2 months (range, 17-65 months). Cephalometric changes were compared with 29 matched untreated Class II controls. Mandibular superimpositions were used to evaluate condylar growth and true mandibular rotation. RESULTS: All 3 treatment methods produced normal dental relationships and restricted or inhibited AP maxillary growth, with no significant improvement of AP chin position. Differences between changes in vertical position of the maxilla, maxillary and mandibular molars, and condylar growth could not reliably predict changes in chin position. Analyses demonstrated that true mandibular rotation was the primary determinant of AP chin position. Stepwise multiple regression showed that, combined with true mandibular rotation, condylar growth and movements of the glenoid fossa accounted for 81% of the variation in AP changes of pogonion. CONCLUSIONS: Contemporary treatments do not adequately address mandibular deficiencies. Future treatments must incorporate true mandibular rotation into Class II skeletal correction.

Long-term stability of combined rapid palatal expansion-lip bumper therapy followed by full fixed appliances.

INTRODUCTION: The purpose of this study was to evaluate the long-term postretention stability of rapid palatal expansion-lip bumper therapy followed by full fixed appliances. METHODS: The sample included 20 treated patients (11 women and 9 men) who were recalled to obtain postretention records. The subjects were out of retention for a minimum of 4 years and an average of 7.9 years. They had begun treatment in the late mixed dentition at a mean age of 11.1 with considerable incisor crowding but, on average, no tooth size-arch length discrepancies. Pretreatment, posttreatment (mean age, 13.6 years), and postretention (mean age, 24.3 years) models were digitized, and the computed measurements were compared with untreated reference data. RESULTS: The majority of treatment increases in maxillary and mandibular arch dimensions were statistically significant (P < .05) and greater than expected for untreated controls. Although many measurements decreased postretention, net gains were maintained for 21 of the 30 measurements evaluated. The notable exception was arch perimeter, which decreased to less than pretreatment values. Postretention incisor irregularity increased 0.5 +/- 1.2 mm in the maxillary arch and 1.1 +/- 1.5 mm in the mandibular arch. CONCLUSIONS: Based on the good long-term stability observed in this study, we concluded that use of rapid palatal expansion-lip bumper expansion therapy in the late mixed dentition followed by full fixed appliances is an effective form of treatment for patients with up to moderate tooth size-arch length discrepancies.

Challenges of assuring crew safety in space shuttle missions with international cargoes.

The top priority in America's manned space flight program is the assurance of crew and vehicle safety. This priority gained greater focus during and after the Space Shuttle return-to-flight mission (STS-26). One of the interesting challenges has been to assure crew safety and adequate protection of the Space Shuttle, as a national resource, from increasingly diverse cargoes and operations. The control of hazards associated with the deployment of complex payloads and cargoes has involved many international participants. These challenges are examined in some detail along with examples of how crew safety has evolved in the manned space program and how the international partners have addressed various scenarios involving control and mitigation of potential hazards to crew and vehicle safety.

Three-dimensional diagnosis and management of Class II malocclusion in the mixed dentition.

Class II malocclusion is a commonly observed problem, occurring in about one third of the United States population. The numerous treatment approaches that have been advocated to treat this malocclusion presumably produce differing treatment effects within the skeletal, dentoalveolar, and soft tissue components of the face. In the first section of this article, the three-dimensional components of Class II malocclusion are described, with transverse maxillary discrepancy, mandibular skeletal retrusion, and increased lower anterior facial height observed as common findings in a mixed dentition sample of Class II subjects. Second, the literature concerning two seemingly diverse treatment methods (extraoral traction and functional jaw orthopedics) is reviewed in detail. Last, cephalometric data are presented from a retrospective clinical study and is used to evaluate the treatment effects produced by cervical traction and the FR-2 appliance of Fränkel in comparison with an untreated sample of mixed dentition Class II patients. The results of this study indicated that although both skeletal and dentoalveolar components of Class II, Division 1 malocclusion were altered in the Class I direction by either a facebow or a Fränkel appliance, these two appliance systems accomplished the correction in dramatically differing ways. Cervical traction affected the skeletal and dentoalveolar components of the maxilla and mandible, whereas the FR-2 appliance had less of an effect on maxillary and dentoalveolar components and a greater effect on mandibular length. Thus, these two treatment modalities produce decidedly different treatment effects in patients with Class II malocclusions.

Long-term stability of Class II, Division 1, nonextraction cervical face-bow therapy: II. Cephalometric analysis.

The long-term stability of Class II, Division 1 nonextraction therapy, using cervical face-bows with full fixed orthodontic appliances was evaluated for 42 randomly selected patients. Part 1, a study model analysis, was published in the March 1996 issue of the JOURNAL. Each patient was treated by the same practitioner, with the same techniques, and the treatment goals had been attained for all patients. Pretreatment records were taken at a mean age of 11.5 years; the posttreatment and postretention records were taken 3.0 and 11.6 years later, respectively. The results showed that the ANB angle decreased 2 degrees during treatment, most of which was due to the 1.6 degree decrease of the SNA angle. The mandibular plane angle was not changed significantly during treatment. Although upper incisor inclination was maintained during treatment, the lower incisor was proclined 2.3 degrees and the lower molar was tipped back 4 degrees. Of the 22 cephalometric measures evaluated, only four indicated relapse related with the treatment change. Three of the four measures pertain to lower incisor retroclination subsequent to excessive proclination. The ratio of treatment proclination of incisors to posttreatment retroclination is approximately 5:1. Similarly, for every 3 degrees of molar tip back, there was approximately 1 degree of relapse. It is concluded that nonextraction therapy for Class II malocclusion can be largely stable when the orthodontist ensures proper patient selection and compliance and attains treatment objectives.

Long-term stability of Class II, Division 1, nonextraction cervical face-bow therapy: I. Model analysis.

The long-term stability of Class II, Division 1 nonextraction therapy remains poorly described. This study evaluates the face-bow therapy, in conjunction with full-fixed appliance therapy, of 42 patients (34 females and 8 males) who were treated by the same practitioner. Treatment goals had been attained for all patients. The pretreatment, posttreatment, and postretention records were taken at 11.5, 14.5, and 23.1 years, respectively. The results showed that mandibular and maxillary arch widths were increased significantly during treatment. Mandibular intercanine width decreased 0.3 mm during the postretention period; the remaining width measures increased or remained stable. Arch length, which did not change during treatment, decreased 1.0 mm after treatment. Overjet and overbite decreased 4.4 mm and 2.5 mm, respectively, during treatment. Both overjet (0.5 mm) and overbite (0.4 mm) showed small increases after retention. Mandibular incisor irregularity was decreased 2.7 mm during treatment and increased only 0.4 mm after treatment. Within the limits of this study, it is concluded that, when the described techniques are used, nonextraction therapy for patients with Class II malocclusion is largely stable.

Differences in dental arch morphology among adult females with untreated Class I and Class II malocclusion.

The purpose of the study was to evaluate differences in dental arch morphology among an orthodontic sample of 386 untreated adult females between 17 and 68 years of age, categorized by age group (17-25 years, 26-35 years, or 35+ years) and malocclusion (Class I, Class II division 1, or Class II division 2). The results show that both maxillary and mandibular dental arch size were significantly larger for the younger age group. Arch shape was relatively shorter and wider for the oldest age group. Palatal height was greatest for the youngest age group and least for the oldest group. Subjects with Class II malocclusion had significantly smaller arches, greater maxillary incisor irregularity, and less mandibular incisor irregularity than patients with Class I malocclusion. Subjects with Class II division 1 malocclusion had greater palatal heights and relatively longer/narrower maxillary dental arches than subjects with Class II division 2 malocclusion.

Physiologic drift of the mandibular dentition following first premolar extractions.

A retrospective study of two groups of patients was conducted to evaluate the physiologic drift, or "driftodontics", of the mandibular teeth following the extraction of four first premolars. Group 1 included 32 patients who underwent early extraction in the mixed dentition stage at a mean age of 10.4 years; they were followed for approximately 2.5 years postextraction. Group 2 included 20 patients whose premolars were extracted after the permanent dentition had fully erupted. Their mean age at the time of extraction was 14.2 years, followed by a 0.8 year observation period. Except for the extractions, no other mandibular therapy was rendered. The results show no differences in rates of molar movements between groups. The molar apex moved mesially approximately 0.6 mm/yr; the molar cusp moved mesially approximately 1.2 mm/yr. In contrast, there were marked group differences in movements of the mandibular incisors and canines; rates of change were significantly greater in Group 2 than in Group 1. The canines drifted laterally and distally into the extraction sites while the incisors became more upright over basal bone and less crowded. Incisor irregularity decreased 1.3 mm/yr in Group 1 and 5.5 mm/yr in Group 2. The group differences in amounts of tooth movement were accounted for by changes in incisor crowding.

Lip bumper therapy for gaining arch length.

With the use of pretreatment and posttreatment lateral cephalograms and study models, lip bumper therapy for two groups of 20 patients was evaluated. One group was treated with lip bumpers fabricated from stainless steel round wire covered with shrink tubing and activated every 2 to 3 months. The second group was treated with larger prefabricated lip bumpers covered with acrylic shields from canine to canine and activated every 4 to 5 weeks. Yearly rates of treatment change indicate that the type of lip bumper used and the method of clinical manipulation have no effect on mandibular incisor position. Both groups showed similar rates of controlled incisal tipping with the center of rotation at the apex. Dental movements of the posterior segment were significantly different between groups. The second group displayed significantly more molar tipping than the first group. The second group also showed significantly greater transverse expansion of the canines, first premolars, and first molars.

Reversible accumulation of plant suspension cell cultures in g(1) phase and subsequent synchronous traverse of the cell cycle.

The induction of DNA synthesis in Datura innoxia Mill. cell cultures was determined by flow cytometry. A large fraction of the total population of cells traversed the cell cycle in synchrony when exposed to fresh medium. One hour after transfer to fresh medium, 37% of the cells were found in the process of DNA synthesis. After 24 hours of culture, 66% of the cells had accumulated in G(2) phase, and underwent cell division simultaneously. Only 10% of the cells remained in G(0) or G(1). Transfer of cells into a medium, 80% (v/v) of which was conditioned by a sister culture for 2 days, was adequate to inhibit this simultaneous traverse of the cell cycle. A large proportion of dividing cells could be arrested at the G(0) + G(1)/S boundary by exposure to 10 millimolar hydroxyurea (HU) for 12 to 24 hours. Inhibition of DNA synthesis by HU was reversible, and when resuspended into fresh culture medium synchronized cells resumed the cell cycle. Consequently, a large fraction of the cell population could be obtained in the G(2) phase. However, reversal of G(1) arrested cells was not complete and a fraction of cells did not initiate DNA synthesis. Seventy-four percent of the cells simultaneously reached 4C DNA content whereas the frequency of cells which remained in G(0) + G(1) phase was approximately 17%. Incorporation of radioactive precursors into DNA and proteins identified a population of nondividing cells which represents the fraction of cells in G(0). The frequency of cells entering G(0) was 11% at each generation. Our results indicate that almost 100% of the population of dividing cells synchronously traversed the cell cycle following suspension in fresh medium.