Frankfort Mandibular Plane Angle Research Articles

Computed tomography evaluation of mandibular incisor bony support in untreated patients

In this study, we aimed to verify, via computed volumetric tomography, a correlation between the morphology of the mandibular symphysis and the various facial types. From a sample of 148 digital volumetric tomographs, the subjects were classified as either short face (25 subjects), normal face (27 subjects), or long face (28 subjects) according to the average values of their Frankfort-mandibular plane angle. The 80 healthy subjects were between 12 and 40 years of age. Tomography was carried out using NewTom 3G volume scanner (QRsr1, Verona, Italy). The following parameters were measured on the sections corresponding to the 4 mandibular incisors: height, thickness, and area of the entire symphysis; height, thickness, and area of the cancellous bone of the symphysis; distance of the vestibular and lingual cortices from the apices of the 4 incisors; and possible inclination of each mandibular incisor, expressed in degrees. The F test or analysis of variance (ANOVA) and the Tukey HSD Test were subsequently used. The total thickness of the symphysis was greater in the short-face subjects than in the long-face subjects. No statistically significant differences in the total and cancellous areas of the symphysis were found between the 3 facial types. In all 3 groups, the total and cancellous heights and areas were greater at the central incisors than at the lateral incisors. There is a statistically significant relationship between facial type and the total thickness of the mandibular symphysis.

Relationship between vertical skeletal pattern and success rate of orthodontic mini-implants

The objective of this research was to determine which clinical and skeletal factors are related to the success rate of orthodontic mini-implants in the maxillary and mandibular posterior buccal areas. A total of 778 orthodontic mini-implants (Dual-Top Anchor System, Jeil Medical, Seoul, Korea; 1.6 mm diameter, 8 mm length, cylinder shape, self-drilling type) in 306 patients were retrospectively examined. The success rate was calculated according to clinical variables (sex, age, soft-tissue management, placement position, sagittal skeletal classification, arch-length discrepancy, and side) and skeletal variables (articular angle, mandibular plane to palatal plane angle, Frankfort-mandibular plane angle, mandibular plane angle, gonial angle, upper gonial angle, and lower gonial angle). Analysis of variance (ANOVA), chi-square tests, and multiple logistic regression analysis were used for statistical analysis. The overall success rate was 79.0%. Almost 80% of the failures occurred within the first 4 months. The clinical variables sex, age, soft-tissue management, sagittal skeletal classification, arch-length discrepancy, and side did not show significant differences in the success rate. Although the success rates were significantly different according to placement position (P <0.01), there was no significant difference in the odds ratios among placement positions. In the skeletal variables, average upper gonial angle (84.2%) had a significantly higher success rate than low (75.7%) and high (71.2%) upper gonial angles (P <0.01). High Frankfort-mandibular plane angle (P <0.05) and low upper gonial angle groups (P <0.05) showed significant lower odds ratios than did the other types. Vertical skeletal pattern might be an important factor for the success of orthodontic mini-implants placed in posterior buccal areas.

The facial goniometer: an instrument for the direct measurement of the Frankfort-mandibular plane angle and the gonion angle.

The facial goniometer: an instrument for the direct measurement of the Frankfort-mandibular plane angle and the gonion angle.

Class II Division 1 malocclusion with a high mandibular plane angle corrected with 2-phase treatment

A 10-year-old girl with maxillary protrusion and crowding of the maxillary and mandibular anterior teeth was treated in 2 phases. In the first phase of treatment, maxillary anterior growth was restrained and mandibular anterior growth promoted for skeletal improvement. In the second phase, at age 13, 4 first premolars were extracted, and an edgewise appliance was used for alveolar improvement. Because the patient had a high mandibular plane angle with a large Frankfort-mandibular plane angle, special care was taken from the beginning to prevent mandibular clockwise rotation. The Frankfort-mandibular plane angle decreased 3.1 degrees at posttreatment. In addition to the skeletal changes, we obtained a favorable lateral profile. This was achieved by the alveolar changes from the lingual movement of the maxillary and mandibular anterior teeth, and the anterior growth of the nasal apex region. The occlusion was stable at the 38-month postretention follow-up.

In Vivo Comparison of Conventional and Cone Beam CT Synthesized Cephalograms

To compare measurements from synthesized cone-beam computed tomography (CBCT) lateral cephalograms using orthogonal and perspective projections with those from conventional cephalometric radiographs. Thirty-one patients were imaged using CBCT and conventional cephalometry. CBCT volume data were imported in Dolphin 3D. Orthogonal and perspective lateral cephalometric radiographs were created from three-dimensional (3D) virtual models. Twelve linear and five angular measurements were made on synthesized and conventional cephalograms in a randomized fashion. Conventional image measurements were corrected for known magnification. Linear and angular measurements were compared between image modalities using repeated measures analysis of variance. Statistical significance was defined as an alpha level of .01. With the exception of the Frankfort-mandibular plane angle (P < .0001), angular measurements were not statistically different for any modality (P > .01). Linear measurements, whether based on soft or hard tissue landmarks, were not statistically different (P > .01). Measurements from in vivo CBCT synthesized cephalograms are similar to those based on conventional radiographic images. Thus, additional conventional imaging may generally be avoided when CBCT scans are acquired for orthodontic diagnosis.

Influence of Craniofacial Morphology on Hyoid Movement: A Preliminary Correlational Study

There has been little attention given to the relationship between variations in normal craniofacial morphology and swallowing physiology. This preliminary investigation evaluated the relationship between the Frankfort-mandibular plane angle (FMA) and hyoid displacement during swallowing. Hyoid movement was evaluated during 12-ml and 24-ml swallows of liquid barium in 12 healthy subjects (age = 20-29 years, median = 23 years). Lateral projection videofluorography was utilized. Positions of the hyoid at maximum forward displacement, maximum upward displacement, starting position, and ending position were determined using image analysis software. The mean FMA was 28.92 degrees +/- 4.08 degrees (mean +/- SD, range = 20 degrees -34 degrees ). A Pearson correlation (<or=0.05) demonstrated that hyoid forward displacement was significantly inversely correlated with the FMA [R = -0.68, p = 0.015 (12 ml) and R = -0.72, p = 0.009 (24 ml)]; thus, the greater the FMA, the smaller the hyoid forward displacement. Upward displacement of the hyoid was not significantly correlated with FMA for 12-ml (R = -0.41, p = 0.55) or 24-ml swallows (R = 0.21, p = 0.512). In addition, there was no significant correlation between hyoid starting or ending positions. In conclusion, the results of this preliminary study suggest that normal variations in morphology, as measured by the FMA, may influence hyoid movement and therefore affect swallowing physiology.

The relationship between vertical craniofacial morphology and the sagittal path of mandibular movements

The aim was to investigate the relationship between the vertical craniofacial morphology and the sagittal path of mandibular movements. The study was carried out in 40 subjects who were free of temporo-mandibular disorders. Mandibular movements and maximal jaw opening (MO) were recorded by means of a jaw tracking device. The opening-closing angle (OCA) was defined as the angle between the horizontal plane and the opening-closing path of movements. Vertical craniofacial morphology was assessed on prophile cephalograms by means of the Frankfort Mandibular Plane Angle (MP). The OCA did not differ between males and females (P>0.05). OCA and MP were negatively correlated (r=-0.62; P<0.001). MO was significantly greater in males that in females (P<0.05). MO was negatively correlated to MP (-0.44<r<-0.49; P<0.05). The findings suggest that the low-angle subjects exhibit a more vertical path of the mandibular movements than that of high-angle subjects. Differences in the sagittal path of jaw movements may be partly ascribed to anatomical factors.

Cephalometric norms of Nigerian children

The purpose of this study was to develop cephalometric standards for Nigerian children. The average values of 7 dentoskeletal angles were determined from standardized lateral head radiographs of 100 schoolchildren (aged 11 to 13 years; mean, 12.6 years) in Enugu, a city in southeastern Nigeria. The children, born to Nigerian parents of Igbo ancestry (Igbo is 1 of the 3 major ethnic groups in Nigeria), were selected on the basis of a well-balanced face and acceptable profile, Class I occlusion with normal overjet and overbite, minor or no crowding or spacing, and no history of orthodontic treatment. There were no statistically significant differences in cephalometric measurements between boys and girls; thus, the data were combined for analysis. The mean values and standard deviations obtained for the measured variables were: SNA, 85.5 degrees (+/- 4.3 degrees); SNB, 81.2 degrees (+/- 4.0 degrees); ANB, 4.3 degrees (+/- 2.5 degrees); UI-FP, 122.8 degrees (+/- 7.5 degrees); Ll-MP, 98.8 degrees (+/- 5.8 degrees); Ul-LI, 109.1 degrees (+/- 8.0 degrees); and FMA, 26.1 degrees (+/- 5.0 degrees). Compared with the norms for other ethnic groups, Igbo children have a prognathic relationship of the maxilla and the mandible to the anterior cranial base with a tendency toward a protrusive skeletal pattern. The children also exhibited prominent bimaxillary proclination with procumbent and protrusive maxillary and mandibular incisors and a steep Frankfort-mandibular plane angle. The findings emphasize the need for group-specific norms for orthodontic diagnosis and treatment planning, and provide cephalometric standards for Igbo children.

Significance of the Frankfort mandibular plane angle in prosthetic management of partially or completely edentulous patients with Class II malocclusions

Complete or partially edentulous patients with a skeletal class II skeletal jaw relationship due to a skeletal etiology comprise approximately 15% of the population with the two largest sub-categories being high and low FMA groups. Occlusal relationships in skeletal class II patients are often challenging because of arch size discrepancies which limits the potential occlusal contact area, steep guidance factors which can introduce occlusal interferences, and excessive range of motion which can complicate centric relation records. FMA determination provides a structure-function basis in selecting a scheme for occlusal reconstruction and should be incorporated in the treatment planning procedure as a major adjunctive diagnostic tool. The following treatise provides background information and treatment guidelines to facilitate improved prosthetic treatment for partially and completely edentulous skeletal class II patients.

Changes in the curve of Spee with treatment and at 2 years posttreatment

The purposes of this study were to determine pretreatment skeletal and dental patterns related to curve of Spee depth, evaluate changes in the curve of Spee with treatment and the effects on dentofacial structures, and determine factors associated with the stability of the curve of Spee after treatment. Lateral cephalograms and dental casts were evaluated for 24 white male and 26 white female patients at pretreatment, posttreatment, and at least 2 years postretention. All patients had mandibular permanent second molars and premolars erupted and in occlusion. The following variables were correlated with increased pretreatment curve of Spee depth: low Frankfort-mandibular plane angle, deep overbite, increased overjet, and Class II molar malocclusion. No significant differences were found in pretreatment curve depth between male and female patients or between right and left sides. Leveling the curve of Spee was accomplished by uprighting the molars, extruding the premolars, and intruding or flaring the incisors. Extraction and nonextraction cases demonstrated no significant differences in the amount of curve relapse. Increased curve relapse was correlated with postretention increases in overbite, irregularity index, and patients given removable retainers. Overall, the curve of Spee was relatively stable after treatment, with only a 16% relapse of the leveled curve.

Skeletodental patterns in patients with multiple congenitally missing teeth

Congenitally missing teeth (CMT) are a relatively frequent phenomenon. In severe cases of multiple CMT, the skeletodental pattern can be unique. However, the characteristics of this pattern are still controversial. Thus, it was our aim to evaluate the skeletodental patterns of patients with multiple CMT and compare them with norms. Lateral cephalograms of 115 subjects with at least 3 CMT, of at least 2 different tooth groups (excluding third molars), were analyzed. The measurements were compared with classical and Israeli norms. Differentiation between anterior and posterior lack of teeth was also evaluated. In the CMT patients, the maxillary and mandibular basal bones were more retruded than in normal populations, but the intermaxillary relationship was normal. The profile was flatter than in the normal Israeli population but more convex than the classical norms. In the vertical dimension, the study group exhibited a reduced Frankfort mandibular plane angle when compared with Israeli norms. The dental pattern was characterized by upright incisors. When differentiation between anterior and posterior lack of teeth was undertaken, the above features were exacerbated in the patients with anterior tooth absence. It was concluded that patients with multiple CMT demonstrate a characteristic skeletodental pattern, especially those with missing incisors.

Bialveolar protrusion in a Zimbabwean sample

This study was undertaken to assess dentoalveolar relationships in a well-balanced sample of adult black Zimbabweans. Lateral cephalograms of 25 men and 25 women 18 to 38 years of age with Class I occlusions were obtained from the University of Zimbabwe. Twelve angular and 6 linear measurements were analyzed, and men and women were compared with the Student t test. No statistically significant difference was noted between the 2 sexes. The Zimbabwean sample had a low Frankfort-mandibular plane angle (19.6° ± 5.5°) with a receding chin as shown by the negative Pog-NB measurement (−0.7 ± 1.5 mm). Both the maxilla (SNA = 88.5° ± 4.7°) and the mandible (SNB = 83.3° ± 4.4°) were prognathic, and the ANB difference was large (5.3° ± 2.7°). The maxillary incisors were more upright compared with those of white people as measured by the angle of the maxillary incisor to NA line (20.6° ± 7.7°), while the mandibular incisors were severely proclined (IMPA = 105.8° ± 6.0°, L1-Apog = 6.9° ± 2.7°, L1-NB = 37.6° ± 4.9°), and this proclination was considered to be compensatory to the prognathic maxilla. (Am J Orthod Dentofacial Orthop 2003;123:133-7)

Evaluation of the vertical holding appliance in treatment of high-angle patients

Controlling the vertical dimension of high-angle patients without the benefit of compliance can be a challenging aspect of orthodontic treatment. This retrospective study examines the skeletal and dental effects of a modified transpalatal bar, dubbed the vertical holding appliance (VHA), which was used in an attempt to control the vertical dimension of high-angle patients. Two cephalometrically similar groups of high-angle patients (16 patients each) were compared to determine advantages from using the VHA. Group I (n = 16, pretreatment age 13.4 ± 1.6 years) was treated with 4 premolar extractions in conjunction with the VHA cemented in place for 17.4 ± 6.1 months. Group II (n = 16, pretreatment age 13.4 ± 1.9 years), which was matched for age and pretreatment skeletal pattern, was treated with the Tweed technique and 4 premolar extractions. Lateral cephalometric radiographs were taken before the placement of the VHA, as well as at the end of treatment. The results showed that although y-axis increased significantly in group II ( P < .05), it remained the same in group I. Within group I, the Frankfort mandibular plane angle and gonion gnathion/sella nasion angle decreased, whereas both of these values increased in group II. However, these changes were statistically insignificant. Lower anterior face height increased more in group II than in group I ( P < .05). The percentage of lower anterior face height to total anterior face height decreased in group I, whereas it increased in group II. The difference between the 2 groups was determined to be significant ( P < .01). Eruption of the maxillary first molar within group I was less than in group II. No significant differences were found between groups I and II for changes in overbite. (Am J Orthod Dentofacial Orthop 2000;117:700-5)

Mandibular rest position and electrical activity of the masticatory muscles

Statement of problem. The determination of a correct vertical dimension of occlusion is a critical procedure in clinical dentistry. Purpose. The objectives of this study were to analyze the relation between mandibular rest position and electrical activity of masticatory muscles and to compare clinical and electromyographic rest position in subjects with different vertical facial morphologic features. Material and methods. Clinical rest position and electromyographic rest position were investigated in 40 subjects. Electromyographic rest position ranged from 0.4 to 12.7 mm (average 7.7 ± 2.7 mm). Clinical rest position ranged from 0.1 to 4.4 mm (average 1.4 ± 1.1 mm). The average difference between electromyographic rest position and clinical rest position was 6.3 ± 2.5 mm (range 0.3 to 10.3 mm). Sixteen subjects were selected according to the Frankfort mandibular plane angle and separated in two groups with the first group (eight subjects) having a mandibular plane angle ≤20 degrees and the second group having a mandibular plane angle ≥28 degrees. Results. Rest position was significantly greater ( p < 0.05) in the low-angle group (2 ± 1.3 mm) than in the high-angle group (0.8 ± 0.8 mm). Electromyographic rest position did not differ between subjects with different facial morphologic features (8.1 ± 1.7 mm low-angle group; 7.6 ± 4.1 mm high-angle group). By varying the vertical dimension millimeter by millimeter, masseter and anterior temporal electromyographic activity demonstrated a considerable decrease over an interocclusal distance of 3 to 4 mm. Further mandibular opening up to 18 mm corresponded to small changes in postural activity. Conclusion. This study suggests that a jaw posture with a few millimeters of interocclusal distance involves a great reduction of masticatory muscle activity. (J Prosthet Dent 1997;78:48-53.)

Evaluation of an intraoral maxillary molar distalization technique

The purpose of this study was to determine the effects of the pendulum appliance on distalization of maxillary molars and the reciprocal effects on the anchor premolars and maxillary incisors. Initial and follow-up cephalometric radiographs were obtained on 41 subjects (26 girls and 15 boys) who were treated with the pendulum appliance for bilateral distalization of the maxillary first molar teeth, for correction of the Class II molar relationship or for gaining space in the maxillary arch. Dental casts were available on 31 patients. Dental, skeletal, and soft tissue changes were determined. The mean maxillary first molar distalization was 3.37 mm, with a distal tipping of 8.36 degrees. The mean reciprocal mesial movement of the first premolar was 2.55 mm, with a mesial tipping of 1.29 degrees. The maxillary first molar position intruded 0.1 mm, whereas the first premolar extruded 1.7 mm. The transverse width between the mesiobuccal cusps of the first molars increased 1.40 mm. The maxillary second molars were also distalized 2.27 mm, tipped distally 11.99 degrees, and moved buccally 2.33 mm. The effect of distalization on the maxillary third molars was extremely variable. The eruption of maxillary second molars had minimal effect on distalization of first molars. The lower anterior face height increased by 2.79 mm. This increase was greater in patients with higher Frankfort-mandibular plane angle measurements. The pendulum appliance is an effective and reliable method for distalizing maxillary molars, provided the anchor unit is adequately reinforced. Its major advantages are minimal dependence on patient compliance, ease of fabrication, one-time activation, adjustment of the springs if necessary to correct minor transverse and vertical molar positions, and patient-acceptance.

The Probability Index

The clinical study of the treatment of a sample of Class II malocclusions was made. This information from both successful and unsuccessful Class II malocclusion correction was recorded. The objective of the study was to determine whether there are predictive characteristics of Class II cases that could give, with reasonable accuracy, an indication of those Class II malocclusions that would more readily respond to treatment and those that would have less chance of conventional treatment being successful. This information could give the orthodontist differential diagnostic guidance before starting treatment to determine whether alternative treatment strategy should be considered. The study used five very important cranial and dental cephalometric measurements that individually had significance, but no predictive value. However, these measurements, when combined, and given a weighted value that reflected a relative importance of each criteria, were found to collectively give a predictive capability in determining whether the case was favorable for Class II correction. The five angles selected were (1) the Frankfort mandibular plane angle (FMA); (2) the point A nasion point B, (ANB) angle; (3) the occlusal plane, Frankfort plane angle; (4) the Frankfort-mandibular incisor (FMIA) angle; (5) the sella-nasion-point B, (SNB) angle. The Probability Index is the sum of the weighted values of the five cranial, and dental angles and seems to have significant predictive value in the differential diagnosis and treatment planning of the Class II malocclusion. (A M J O RTHOD D ENTOFAC O RTHOP 1995;107:165-71.)

A cephalometric evaluation of nonextraction cervical headgear treatment in Class II malocclusions.

The effects of orthodontic treatment with the use of the cervical pull facebow headgear in patients with Class II malocclusions were evaluated with special reference to the dentition, the maxillary complex, the mandible, and the facial profile. The records of 85 patients, with a mean age of 11.3 +/- 1.7 years, were selected from a sample of 125 patient records requested from the office of John S. Kloehn in Appleton, Wisconsin. Dr. Kloehn has used traditional cervical pull facebow therapy in his practice. Over 100 linear and angular cephalometric measurements were made from the pretreatment and posttreatment records. These measurements were used to evaluate growth and/or treatment changes. The treatment sample was divided by size of the pretreatment FMA, sex, and the age range in which treatment was started, i.e., prepubertal, circumpubertal, and postpubertal. Overall, the results showed that the changes were very close to what would occur as a result of normal growth in Class I individuals. The maxillary permanent first molars continued to progress forward, the maxilla continued to grow forward, and the cranial base showed very little change, if any. The mandibular plane angle did not increase appreciably with treatment, regardless of the size of the pretreatment mandibular plane angle. Very few significant differences were found between sexes, pretreatment age groups, or between groups based on pretreatment Frankfort mandibular plane angle.

An analysis of the relationship between mandibular alveolar bone loss and a low Frankfort-mandibular plane angle

A group of complete denture patients was studied to determine the effect of a low Frankfort-mandibular plane angle on the loss of residual ridge height in the mandible. Measurements were made from tracings of cephalometric films. The low-FMA group did not experience statistically greater amounts of alveolar ridge loss when compared with the group with an FMA larger than 20 degrees. The loss of residual ridge height for both groups followed a linear relationship from year 5 to year 20. There was some indication that the residual ridge height was smaller initially in the low-FMA group. The relative effect of the loss of residual ridge height, combined with smaller residual ridge height originally, indicates that the low-FMA patients are more likely to have anatomic deficiencies and problems with complete dentures associated with this lack of mandibular residual ridge height.

Factors influencing the anterior component of occlusal force

We hypothesized that the anterior component of occlusal force (ACF) generated by mandibular molars was a function of molar inclination, height of the transverse condylar axis above the occlusal plane, steepness of the occlusal plane, gape, molar root dimensions, interproximal tooth contact force when not biting, and bite force. Our research aim was to identify those biomechanical factors which determine ACF. Mandibular second molars were axially loaded with a 90 N force (10 mm second molar gape) in 15 subjects, and the resulting ACF was measured at the mandibular first molar-second premolar contact using a recording technique based on interproximal frictional forces. Morphologic measurements were obtained from lateral cephalometric radiographs of each subject and included: Frankfort mandibular plane angle, occlusal plane angle, angles formed by the longitudinal axis of the second molar and the occlusal and mandibular planes, perpendicular distance from the top of the condyle to the occlusal plane, and second molar root width and root length. For ten subjects, ACF resulting from axial loads of 50, 100, 150, and 200 N was measured. For ten subjects, ACF resulting from an axial load of 50 N and second molar gapes of 10 mm, 14 mm, 18 mm, and 22 mm were measured. ACF increased with increasing gape and increased proportionally to increasing bite force. Correlation and stepwise regression analyses revealed that ACF varies with interproximal tooth contact force when not biting (contact ‘tightness’) and molar root width (model R 2 = 0.71, p < 0.01). The hypothesis that ACF is a function of bite force, gape, molar root width, and interproximal contact tightness has been supported, and the hypothesis that ACF is a function of molar inclination, occlusal plane steepness, condylar axis height, and root length was rejected.

Facial growth following pharyngeal flap surgery: Skeletal assessment on serial lateral cephalometric radiographs

The purpose of this study was to evaluate the effect of pharyngeal flap surgery on subsequent facial growth in patients with cleft lip and/or palate. Pharyngeal flap surgery is used in such patients to partially obliterate the velopharyngeal port, reducing hypernasal speech. Thirty-four patients (18 with cleft palate only, 16 with unilateral cleft lip and palate) were selected from the longitudinal growth study of the H. K. Cooper Clinic. Seventeen of these (9 with cleft palate only, 8 with unilateral cleft lip and palate) underwent pharyngeal flap surgery between the ages of 5 and 7 years. The other seventeen patients did not undergo pharyngeal flap surgery and served as a control group for this study. Serial lateral cephalometric radiographs were traced and digitized (ages 3 to 5, preflap; ages 7–10, postflap). Fourteen skeletodental measurements (six angular, six linear, two derived) were taken to determine whether pharyngeal flap surgery may be related to subsequent facial growth changes. The data from the 17 flap patients were compared with control data taken from the other seventeen patients. The groups were matched for sex, cleft type, and similarity of presurgical mandibular growth direction (facial axis angle). Results obtained demonstrate several significant areas of change following flap surgery, including a decrease in facial axis angle, an increase in Frankfort-mandibular plane angle, an increase in incremental gains in lower anterior face height, and increased retroclination of upper and lower incisors in the flap group as compared to their matched controls.