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.

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.

A computerized analysis of the shape and stability of mandibular arch form

To determine whether a particular ideal orthodontic arch form could be identified, the mandibular dental casts of 30 untreated normal cases, 30 Class I nonextraction cases, and 30 Class II nonextraction cases were examined. Following computerized digitizing and the use of a mathematic function called polynomial of the fourth degree, arch forms were generated for each sample and then compared to 17 commercially produced arch forms. Results showed that no particular arch form predominated in any of the three samples. A shape representing a combination of the "Par" and "Vari-Simplex" arch forms approximated to only 50% of the cases in the three samples. The remaining 50% of the cases displayed a wide variety of arch forms. Cases that had changes in arch form during nonextraction treatment frequently were not stable; almost 70% showed significant long-term posttreatment changes. Customizing arch forms appears to be necessary in many cases to obtain optimum long-term stability because of the great individual variability in arch form found in this study.

Nonextraction orthodontic therapy: posttreatment dental and skeletal stability

To assess the long-term stability of nonextraction orthodontic treatment, the dental cast and cephalometric records of 28 cases were evaluated. Thirty cephalometric and seven cast parameters were examined before treatment, posttreatment, and an average of almost 8 years postretention. Results showed overall long-term stability to be relatively good. Relapse patterns seen were similar in nature, but intermediate in extent, between untreated normals and four first premolar extraction cases. Significant decreases were seen in arch length and intercanine width during the postretention period despite minimal changes during treatment. Incisor irregularly increased slightly postretention; intermolar width, overjet, and overbite displayed considerable long-term stability. Mandibular incisor mesiodistal and faciolingual dimensions were not associated with either pretreatment or posttreatment incisor crowding. Class II malocclusions with large ANB values and shorter mandibular lengths showed increased incisor irregularity, shorter arch lengths, and deeper overbites at the postretention stage, suggesting that the amount and direction of facial growth may have been partially responsible for maturational changes seen during the postretention period.

Differential diagnosis and treatment planning for the adult nonsurgical orthodontic patient

Increasing numbers of adult patients are seeking orthodontic care and some, despite significant skeletal malocclusions, elect not to have combined orthodontic-surgical treatment. The purpose of this article is to outline some of the diagnostic and therapeutic principles that can be used in the adult nonsurgical orthodontic patient. The importance of realistic goal setting in the face of compromised occlusions is emphasized. Diagnosis should include evaluation of all three dimensions and recognize the limitations of therapy in each dimension for the nongrowing patient. Periodontal considerations, extraction decisions, and retention regimens are of vital importance to the achievement and maintenance of an optimum result. Clinical records will demonstrate four commonly seen problems and their resolution.

Droplet sorting of large particles

The systematics of droplet formation conditions for orifices with diameters up to 200 micron are described. Sorting recovery experiments indicate that particles up to 44 micron in diameter can be recovered by charged droplet deflection of two drops with at least 75% recovery. By reducing the jet velocity, a deflection of greater than 1 cm was obtained for all droplet sizes.

The accuracy of computerized growth prediction in Class II high-angle cases

This study was conducted to test the accuracy of a commercially available forecasting system in predicting the effects of growth and orthodontic treatment. The pretreatment cephalograms and wax bites of mandibular casts of thirty-three consecutively treated Class II patients with high mandibular plane angles, along with twenty-six criteria related to treatment preference, were submitted for analysis. All patients had already been treated on a nonextraction basis by a single practitioner using high-pull face-bow headgear. The computer-generated posttreatment predictions or visual treatment objectives (VTO's) were compared to the actual posttreatment cephalograms, using twenty-one linear and nine angular measurements. Fifteen of the thirty parameters evaluated showed statistically significant (P less than 0.01) differences between the actual posttreatment result and the computer prediction. The computer was found to be accurate in predicting the effects of growth and treatment on maxillary position and rotation, mandibular length, upper face height, and incisor positions. It was found to be inaccurate in predicting the effects of growth and treatment on maxillary length, mandibular rotation, lower anterior and posterior face heights, the horizontal and vertical positions of the molars, and over 50% of the soft-tissue parameters.

Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis

The dental casts and cephalometric records of forty-three patients exhibiting bilateral congenital absence of maxillary lateral incisors were evaluated to determine the nature and extent of any concurrent craniofacial and dental anomalies. The effects of bilateral orthodontic space closure were evaluated on a subsample of twenty-two cases. The data revealed normal dental arch length, arch width, overjet, and overbite, while significant tooth size discrepancies were found in several anterior and posterior teeth. Craniofacial deviations from normal included smaller maxillary length, smaller mandibular length, smaller anterior cranial base, and nasal bone. Vertical facial dimensions, both anterior and posterior, were significantly less, as was the mandibular plane angle. Soft-tissue examination revealed a 10 degrees greater nasiolabial angle, which was increased a further 5 degrees as a result of a mean incisor retraction of 1.5 mm during space closure. The craniofacial anomalies noted in the present sample were similar to those seen in persons with clefts and may reflect a common etiology related to a developmental disturbance during fusion of the facial processes in utero. In the treatment of patients with bilateral congenital absence of maxillary incisors, mechanotherapy designed to open the mandibular plane, increase the vertical dimension, and move the maxillary posterior teeth forward is recommended in order to prevent worsening the Class III tendency and to minimize maxillary incisor and upper lip retraction. Most cases will require significant mesiodistal reduction in tooth size in order to achieve an optimal occlusion.