Incisor Mandibular Plane Angle Research Articles

Accelerated decompensation of mandibular incisors in surgical skeletal Class III patients by using augmented corticotomy: A preliminary study

Our objectives were to evaluate the amount of decompensation of the mandibular incisors and the change of periodontal support around them after corticotomy with bone augmentation before orthognathic surgery. Before orthognathic surgery for 15 skeletal Class III patients, orthodontic treatment was combined with corticotomy and bone augmentation labially to the anterior mandibular roots. Lateral cephalograms were taken before orthodontic treatment and before surgery (completion of preoperative orthodontic treatment). The amounts of mandibular incisor proclination, alveolar bone thickness, and periodontal support (gingival margin levels and augmentation pattern) were evaluated. Significant proclination of the mandibular incisors was shown after decompensation (P <0.001; incisor mandibular plane angle, 10.45°; incisor symphyseal plane angle, 10.74°). The incisor edge moved labially by 3.47 mm. The alveolar bone thickness increased by 1.56 mm at the root apex and 1.98 mm at the level of B-point (P <0.001). There was no gingival recession irrespective of the degree of proclination of the mandibular incisiors. Two types of bone augmentation pattern were evident. One was characterized by alveolar bone proclination proportional to the labial tipping of the mandibular incisors. Buccal alveolar bone at the cervical area was well maintained (60%, 9 subjects). The other showed greater increases in alveolar thickness at B-point than at the cervical area (40%, 6 subjects). The augmented corticotomy provided effective decompensation of the mandibular incisors in skeletal Class III patients while maintaining labial bone thickness and with no periodontal side effects. This technique reduces or eliminates the risk of moving the roots through the labial plate during decompensation with the associated risk of gingival recession.

Treatment effects of the R-appliance and twin block in Class II division 1 malocclusion

The purpose of this study was to compare the effects of a differently designed functional appliance (the R-appliance) with a twin-block (TB)-treated group. Thirty patients (18 girls and 12 boys) with a mean age of 10.5±0.7 years were treated with the R-appliance for 16.2±0.3 months and 25 (11 boys and 14 girls) with a mean age of 11.2±1.3 years with a TB for 16.1±1.4 months (control). All had a Class II division 1 malocclusion due to mandibular deficiency. Lateral cephalograms obtained at the beginning (T1) and end (T2) of the study were analysed. Paired t-tests showed that SNB significantly increased in both groups. The incisor mandibular plane angle (IMPA) was reduced in the R-appliance group by 1.9±4.9 degrees (P<0.04) but increased by 0.5±5.1 degrees (P<0.6) in the TB group. SNA in the R-appliance group showed an increase of 0.2±1.8 degrees (P<0.5), while it was decreased by 0.2±1.3 degrees (P<0.3) in the TB group. Both treatment modalities were successful in moving the mandible forward. However, with the R-appliance, this was achieved without retroclination of the lower incisors.

Effects of Transmandibular Symphyseal Distraction on Teeth, Bone, and Temporomandibular Joint

The aim of this clinical study was to investigate the clinical effects and long-term results of the transmandibular symphyseal distraction technique for the correction of mandibular transverse deficiencies. This was achieved by assessing the dental, skeletal, and temporomandibular joint changes in the sagittal, vertical, and axial planes using cephalograms, dental casts, and computed tomography (CT). Seven patients with mandibular transverse deficiencies (3 females and 4 males), aged 14.3 to 22.5 years (mean 16.2), were treated with a bone-borne transmandibular distractor. Lateral and posteroanterior cephalometric films, CT scans of both temporomandibular joints, and dental casts were obtained preoperatively, at the end of the distraction period, and at the end of 3 years (clinical follow-up period). The clinical findings were assessed according to the morphologic and functional success criteria established by the Steering Group of European Collaboration on Cranial Facial Anomalies for patients with developmental dentofacial anomalies undergoing craniofacial distraction osteogenesis. The statistical analysis of cephalometric films and dental cast measurements was done using the paired t test. The mean postoperative examination period was 40 months (range 36 to 48). The desired amount of distraction was achieved in all patients (mean 6.48 mm). The intraoperative and postoperative complications encountered included damage to the central incisors during vertical osteotomy (1 patient), wound dehiscence after a latent period (3 patients), mild temporomandibular joint pain during the distraction period (3 patients), and chronic gingivitis around the activation rods (7 patients). The success criteria for craniofacial distraction osteogenesis were fulfilled at the end of the 3-year follow-up period. Model analysis showed that the maximal amount of expansion was achieved at the premolar region (first premolar 5.79 mm, second premolar 5.07 mm). Frontal (posteroanterior) cephalograms taken at the end of the distraction period revealed significant increases in the bicondylar (0.35 mm), bigonion (3.43 mm), biantegonion (2.29 mm), and intermolar (4.0 mm) widths, and the ramal angle had decreased significantly (-1.64 degrees). The increase in the transverse measurements was greater at the dentoalveolar level than at the base of the mandible. Lateral cephalograms showed that transmandibular symphyseal distraction produced significant increases in the incisor mandibular plane angle (2.79 degrees) and mandibular body length (1.72 mm). The effect of the procedure on the condyle was 2.5 degrees to 3 degrees of distolateral rotation as calculated using the CT scans. Dental crowding was resolved rapidly by the movement of the teeth into the distraction regenerate. The clinical and radiologic results of the present study have shown that a transmandibular distractor is a clinically effective bone-borne distractor for the correction of mandibular transverse deficiencies and anterior crowding. The follow-up cephalograms and CT scans showed the transverse skeletal stability of the distraction procedure and no permanent temporomandibular dysfunction. However, additional multicenter studies with more patients are necessary to precisely evaluate the long-term postdistraction changes on the skeleton, teeth, and temporomandibular joint.

Distribution of the mandibular incisor-mandibular plane angle in Nubian shoolchildren.

Distribution of the mandibular incisor-mandibular plane angle in Nubian shoolchildren.

Incisor uprighting: Mechanism for late secondary crowding in the anterior segments of the dental arches

T he orthodontic literature abounds with speculation on the etiology of incisor crowding as a late (postpubertal) growth phenomenon. Lombardil cites most of the prominently considered factors in his survey of the literature: tooth discrepancies, arch size, interference of canines in lateral excursive movements, overbite, overjet, tooth removal, incisor-mandibular plane angle, type of original occlusion, third molars, and muscular forces. In their growth studies Bj6rk,2 Subtelny and Sakuda,3 and van der Linden4 report or present data revealing lingual uprighting of the incisor segments during late growth. Weinstein,5 citing Bjijrk’s study, speculated on the possible etiologic role of this uprighting in incisor-segment crowding during the typical postorthodontic-treatment growth period. LundstrijmG mentions the possible role of net lingual crown movement of the anterior teeth in decreases in arch circumference. The present study is a mathematical investigation of incisor uprighting, conducted in two parts. In the first part a mathematical method is derived to serve as a vehicle for the interpretation of and correlation between the data available from two growth studies, those of Sillman’ and Bj6rk.2 The method is used to predict the anterior crowding to be expected from the changes in mean anterior arch dimension reported by Sillman during a postpubertal growth period. The changes in mean incisor axial inclination during late growth reported by Bjiirk arc then related to the changes in mean anterior arch dimension of Sillman to determine the possible contribution of the former to the latter. The above investigation is based on mean dimensions and can therefore provide only a typical indication of the actual events. Therefore, the second part of the

A statistical roentgenographic cephalometric appraisal of the vertical changes in orthodontic patients with hypodivergent dento-facial growth patterns treated with the begg technique

relapse would lead one to follow the principle of overtreatment in this area. 3. There was no significant change in the incisor-mandibular plane angle between posttreatment and postretention. 4. There was no significant extrusion or intrusion of the maxillary central incisor during treatment or in the postretention period. 5. There was no significant change in the interincisal angle between the posttreatment and postretention periods.

Distribution of the mandibular incisor-mandibular plane angle in "normal" individuals.

W. B. Downs (Amer J Orthodont 34:812, 1948) presented findings from a study to determine the range of variation for certain variables that represented components of the dentofacial complex. He studied the distribution of these variables in 20 individuals with clinically excellent occlusions, who ranged in age from 12 to 17 years and who were about equally divided with respect to sex. Among the components of craniofacial morphology studied by Downs was the mandibular incisor-mandibular plane angle. Earlier investigators include Margolis (Amer J Orthodont 29:571, 1943), Noyes, Rushing, and Sims (Angle Orthodant 13:60, 1943), and Speidel and Stoner (Amer J Orthodont 35:536, 1944), who agreed closely on ranges and on a mean value of 900. Downs' group yielded a mean of 91.40; the measurements ranged from 81.5 to 97°. These figures have been accepted generally as representative of variation despite the fact that they are based on small samples from a special population. We are reporting the findings of a larger study of the distribution of this angle and we note that variation is considerably different from that reported by Downs. This investigation is based on cephalometric data from radiographs of children with normal dental occlusion. They were part of a survey of normal growth conducted at the Philadelphia Center for Research in Child Growth between 1948 and 1968 and were selected from a group of 2,500 white elementary and secondary school children. The project director,

The maxillator: A new instrument for measuring the frankfort-mandibular base angle, the incisor mandibular base angle, and other component parts of the face and jaws

A new instrument is presented by means of which various face and jaw measurements can be obtained directly on the subject or patient without the use of time-consuming methods and costly apparatus. Among the measurements that can be obtained by using this instrument are the Frankfort-mandibular base angle, the importance of which in orthodontics had been described by Tweed; the incisor-mandibular plane angle described by Margolis; and other angles, lines, and relationships of value in orthodontics, prosthetics, and fields which require the measurements of facial landmarks, lines, and angles.