Anterior Mandibular Rotation Research Articles

Skeletal stability of inter-molar mandibular distraction osteogenesis in growing patients

IntroductionThe aim of this retrospective study was to firstly assess the stability of surgical advancement using inter-molar mandibular distraction osteogenesis (IMDO) and secondly to assess the impact of the surgical intervention on subsequent mandibular growth in patients with residual growth.MethodsThe sample consisted of 17 (13F and 4M) consecutively treated patients who underwent IMDO and orthodontic treatment. Cephalometric analysis was performed at three time points: T0 prior to distraction; T1 post-distraction immediately prior to surgical removal of the distractors; and T2 following completion of orthodontic treatment when the final lateral cephalogram was taken (0.86–4.37 years after T1). Statistical comparison of lower facial height, mandibular length, growth, condylar position and anterior mandibular rotation was performed.ResultsNo association was found between changes in any of the cephalometric measurements and the length of the follow-up interval. The anterior mandibular segment underwent clockwise rotation during distraction and recovered to near its pre-distraction angulation during remodelling. An increase in the lower facial height of 1.88 ± 2.81mm also occurred during distraction (T0–T1) and was maintained during the follow-up period (T1–T2). Post-distraction (T1–T2) growth of lower facial height (p value 0.872) and mandibular length (p value 0.251) showed no association when compared to an untreated control group and an overall reduction in growth was reported.ConclusionsIMDO was highly stable within a follow-up period of 2.3 ± 0.9 years; however, growth appears to have been inhibited.

The effects of altered maxillary growth on patterns of mandibular rotation in a pig model

ObjectivesA thorough understanding of influence of maxillary growth on patterns of mandibular rotation during development is important with regard to the treatment of skeletal discrepancies. In the present study, we examined whether experimentally altered maxillary position has a significant influence on patterns of mandibular rotation in a pig model. DesignMaxillary growth was altered in a sample of n=10 domestic pigs via surgical fixation of the circummaxillary sutures. We compared the experimental group to control and surgical sham samples and assessed the effects of altered maxillary growth on mandibular form using geometric morphometric techniques. We tested for significant differences in mandibular shape between our samples and examined axes of morphological variation. Additionally, we examined whether altered mandibular shape resulting from altered maxillary position was predictably associated with morphological changes to the condylar region. ResultsThere was a statistically significant difference in mandibular shape between the experimental and control/sham groups. As a result of vertical displacement of the snout, mandibles in the experimental sample resulted in greater anterior rotation when compared to the control/sham pigs. Variation in rotation was correlated with morphological changes in the condyle including the shape of the articular surface and condylar orientation indicative of greater anterior mandibular rotation. ConclusionsVertical displacement of the maxilla had a significant effect on mandibular shape by encouraging anterior mandibular rotation. This result has important implications for understanding the effects of altered mandibular posture on condylar remodeling the treatment of skeletal discrepancies such as the correction of hyperdivegent mandibular growth.

Dental compensation for moderate Class III with vertical growth pattern by extraction of the lower second molars

Analysis of the effects and side effects of treatment of patients with moderate skeletal Class III and vertical growth pattern by means of extraction of the second molars in the lower jaw. A total of 20 patients with a mean age of 12.9 years were examined retrospectively. Inclusion criteria consisted of a Wits value of 0 to -5, a posterior growth pattern of the mandible (Hasund analysis), an overjet of -2 to 1 mm, and an overbite of 0 to -3 mm. Treatment was performed using a straight-wire appliance. As part of the treatment, the lower second molars were extracted and Class III elastics attached. Cephalograms and orthopantomograms taken before and after treatment were used for evaluation. Treatment resulted in a significant change in the mean overjet from 0.5 mm to 2.1 mm and the attainment of a positive mean overbite of -1.0 mm to 0.9 mm. The occlusal plane rotated anteriorly from 18.8° to 13.7°. The skeletal parameters showed a change in the Wits value from -3.3 mm to -1.4 mm and an anterior mandibular rotation (ML-NSL 35.5° vs. 32.0°). The soft tissues revealed an increase in the distance between the lower lip and the "esthetic line" to the posterior (-2.0 mm vs. -3.9 mm). Dental compensation of moderate skeletal Class III with a tendency to an anterior open bite with vertical growth pattern by extracting the lower second molars, combined with Class III elastics, resulted in an anterior rotation of the occlusal plane and mandible. Eighteen of 20 patients achieved a physiological overjet and positive overbite. A prerequisite for this therapy is the presence of lower wisdom teeth; a potential side effect is elongation of the upper second molars.

Impact of genioplasty on mandibular growth during puberty

Genioplasty has been validated for the correction of mandibular vertical excess and is generally performed at the end of the growth period, either alone or in association with other forms of osteotomy. Our aim was to assess whether genioplasty performed at an earlier age can impact mandibular growth. This comparative prospective study included 25 high-angle, mouth-breathing adolescents following orthodontic and ENT treatment. Subjects were divided into two groups according to their stage of puberty, either early (group 1: Tanner's stage 3, n=12) or late stage (group 2: Tanner stage 4-5, n=13). Genioplasty was performed in both groups. Cephalometric comparison was made on the overall population and for each group, before and after genioplasty (at 1, 6, 12 and 18months). In the immediate postoperative period, significant variation of all the cephalometric measures was observed within each group showing reduction of the vertical dimension and sagittal augmentation. Eighteen months post-surgery, only group 1 exhibited a significant increase in SNPog. Augmentation of the SNB and anterior mandibular rotation were also significantly greater in group 1. The difference in the direction of growth of the mandible before genioplasty (18months of orthodontics) and postgenioplasty (18months of postoperative monitoring) was also significant. Early genioplasty permits redirection of mandibular growth conducive to orthopedic correction of high angle Class II.

Is postadolescent mandibular anterior growth rotation a risk factor for relapse of incisor alignment in males?

The purpose of this study was to test the hypotheses that (1) pronounced postadolescent anterior mandibular rotation is associated with relapse of mandibular incisor alignment and (2) mandibular anterior rotation is conducive to more severe relapse. Based on the amount of mandibular anterior rotation posttreatment, 2 groups of orthodontically treated males were selected: 1 with pronounced anterior rotation (Max AR group; n = 27), defined as maximal decrease of sella-nasion/gonion-menton angle (SN/GoMe), and 1 with minimal anterior rotation (Min AR group; n = 29). Cephalograms and study models made before treatment, after treatment (T2), and at a minimum of 10 years postretention (T3) were evaluated, and SN/GoMe, the irregularity index (II), and intercanine width were measured. The incisor II increased in both groups from T2 to T3, but independent t tests failed to detect an intergroup difference (P = 0.969). Moderate crowding (II >or=3.5 and <or=5.5 mm) was 3 times higher in the Min AR than in the Max AR group (P = 0.03). However, when subjects with mild (II < 3.5 mm) and moderate crowding were pooled in each group, chi-square tests failed to demonstrate an intergroup difference. Mandibular anterior rotation does not contribute to relapse of incisor alignment in males. Pronounced anterior rotation is not conducive to more severe relapse in males.

Technique de Tweed-Merrifield et dimension verticale dans les classes II hyperdivergentes

The cases presented in this paper share a common skeletal characteristic, hyperdivergence, a common therapeutic strategy, similar diagnostic elements, and a common choice of non-symmetrical extractions. Interceptive treatment is especially useful for this type of malocclusion to prevent deep over-bites, atypical habits, and severe malocclusion. In the Tweed-Merrifeld technique, orthodontists use careful dental, occlusal, cephalometric, and esthetic evaluations to establish an appropriate treatment plan and therapeutic strategy whose goal will be: to eliminate unhealthy compensations, re-position, if necessary, alveolar structures on basal bone, reduce anterior-posterior and vertical discrepancies, favor anterior mandibular rotation, improve facial esthetics, restore functional occlusion, and assure stability of results. Because of its consistent capability of achieving predictable resolution of the most varied and complex orthodontic disorders, the author has chosen this technique for routine use in his daily orthodontic practice.

Skeletal and dental effects during observation and treatment with a magnetic device.

The aim of this study was to evaluate the effects of a magnetic appliance, MAD IV, on the treatment of anterior open bites in growing patients. The study material included the lateral cephalograms and hand-wrist radiographs of 16 patients who had an anterior open bite malocclusion. The radiographs were taken at the beginning (T1) and at the end of observation period (T2) and at the end of MAD IV application (T3). At the beginning of the study, the mean age of the subjects was 11 years two months. To define the direction of facial growth, the patients were first observed for nine months without any orthodontic or orthopedic approach. At the end of the observation period, patients who had shown a vertical growth direction, resulting in an increase in open bite, were given an MAD IV appliance and were instructed to wear the appliance 18 hours a day for 7.5 months. Thirty-two different parameters were evaluated from the lateral cephalograms. Paired t-tests were used for statistical evaluation of differences that occurred during the periods and between the periods. During the observation period, the patients continued their mandibular posterior rotation resulting in an increase in lower facial height (P < .001) and an open bite (P < .01). During the treatment period, the patients showed an anterior mandibular rotation with statistically important decreases in lower facial height and open bite (P < .001). In the treatment of anterior open bite with the MAD IV appliance, skeletal changes played a role along with dental and dentoalveolar effects.

Comparison of the effects of passive posterior bite-blocks with different construction bites on the craniofacial and dentoalveolar structures

Posterior bite-blocks that are used in the early treatment of skeletal open bite, produce a forward and upward mandibular rotation by transmitting the masticatory muscle forces to the buccal dentoalveolar regions and preventing their vertical growth. Increasing the vertical dimension of the face artificially causes skeletal adaptations to occur not only in the dentoalveolar region but also in the other regions of the craniofacial complex. The effects of passive posterior bite-blocks, constructed in two different heights, were investigated for two treatment groups, in comparison to an untreated control group. Two treatment groups comprised of 25 growing patients, who had skeletal open bite and skeletal/dental Class I or Class II malocclusions, and one control group consisting of 14 growing patients were used. These groups were matched concerning their age, sex, and vertical and sagittal skeletal cephalometric and dental characteristics. Passive posterior bite-blocks of 5 and 10 mm heights were applied to the subjects of the treatment groups respectively for 18 hours per day. Untreated control subjects were observed for 7 to 9 months. The findings of this study revealed that the downward and backward mandibular rotation continued in the control group, increasing the lower facial height significantly, whereas in the treatment groups, the skeletal open bite was treated and the mandible rotated upward and forward. The increase of the height of the posterior bite-blocks had a significant effect on the anterior mandibular rotation and in the increase of the gonial angle.

A pilot study of the effect of masticatory muscle training on facial growth in long-face children.

Daily chewing of a tough chewing material consisting of resin from a pine tree (Mastix from the island of Chios, Greece) was instituted in 13 children (aged 7–12 years) with long-face morphology. The chewing exercise therapy was maintained for one year and aimed at revealing the possibility of strengthening the masticatory muscles and influencing facial growth. Masticatory muscle strength was monitored by measurement of bite force and electromyo-graphic recording of the activity of the anterior temporal and masseter muscles during biting and chewing. The facial morphology was recorded with profile cephalograms and dental casts. During the one-year experimental period, there was a significant increase in bite force and muscle activity during maximal bite. The change was already evident at the first control recording 3 months after the start of the chewing exercise therapy. The muscle activity during chewing of apple and peanuts did not change significantly. The facial growth was characterized by anterior mandibular rotation in 9 of 12 cases while a posterior rotation occurred in 2 cases. The anterior rotation was, on average, 2.5 degrees and thus considerably greater than would be expected during normal growth. There were no signs of reduced vertical growth of the maxilla, a reduced rate of molar eruption or increased growth of the mandible.

Mechanics, growth, and Class II corrections

Growth of the orofacial region is quantitatively described by locating the center of mandibular rotation relative to the cranial base. The center of mandibular rotation is positioned by the ratio of vertical facial growth (AFH/PFH) and the direction of condylar growth. Appliance therapy is associated with changes in the means of both of these parameters. These changes reduce or stop favorable anterior mandibular rotation and redirect the mean condylar growth vector more posteriorly. When appliance therapy is stopped, these parameters return toward their resting values. The mean direction of the condylar growth vector became even more anteriorly directed after treatment than the pretreatment mean value. These data support the hypothesis that orthodontic appliances significantly alter the facial growth pattern and when they are stopped, the growth pattern tends to rebound to or beyond the pretreatment values.