Frankfort Mandibular Plane Angle Research Articles

A study of occlusion as related to the Frankfort-mandibular plane angle

The relation of the Frankfort-mandibular plane angle (FMA) to naturally occurring occlusion groups was studied in 112 subjects. Occlusion types were categorized into four groups depending on the magnitude of first-molar contact on the working side. Percentage (frequency) of occurrence of occlusion groups were: disclusion, 17.9 per cent; delayed disclusion, 19.6 per cent; progressive disclusion, 8.9 per cent; and group function, 53.6 per cent. The mean FMA for the study sample was 25.68 degrees with a range of 13 to 40 degrees. Mean FMA's for the occlusion groups showed a progressive increase from disclusion (19.6 degrees) to group function (28.9 degrees). A statistical test, extension of the median, indicated a highly significant relation between occlusion groups and the FMA. Considering these results, an FMA determination provides a structure-function basis to consider in selecting a scheme for occlusal reconstruction and should be incorporated in the treatment planning procedure as a major adjunctive diagnostic tool. However, further research, focused upon the many variables that determine a type of occlusion, must precede the formulation of a set of “rules” for selection of occlusion.

Significance of the Frankfort-mandibular plane angle to prosthodontics

Cephalometric information, specifically, vertical facial types and the Frankfort-mandibular plane angle, pertinent to prosthodontics has been discussed. The Frankfort-mandibular plane angle (FMA) is formed by the intersection of the Frankfort horizontal plane and the mandibular plane. This angle can be traced and measured by means of a diagnostic overlay. An FMA of 25 ± 5 degrees is within normal range. A high-angle patient has an FMA of 30 degrees or more, and a low-angle patient has an FMA of 20 degrees or less. A high FMA is characterized by open-bite skeletal patterns, and a low FMA by closed-bite skeletal patterns. The clinical manifestations pertinent to prosthodontics in high- and low-angle (FMA) patients are shown in Table I. However, not all clinical characteristics are present in a given patient. The classification in Table I is a beginning. The authors consider the prosthodontic study of cephalometrics an unexploited research tool. Hopefully, in the future, it will help to bridge the gap of the biological-technical interplay that is such an integral part of prosthodontics.

Bony profile changes resulting from cervical traction compared with those resulting from intermaxillary elastics

Before- and after-treatment headfilms were measured according to certain angular and linear measurements on thirty-two cases treated with cervical anchorage and on thirty-eight cases treated with intermaxillary elastics in addition to cervical anchorage. The variations in the changes occurring in points A and B, pogonion, lower face height, and mandibular plane angle were recorded. According to the mean of the reduction in A-B difference, change in point A distally was responsible for any improvement in either type of treatment. Point B also moved distally in both types of treatment, but to a larger degree in those cases treated with cervical anchorage alone. Except in individual cases, the forward movement of the mandible was not responsible for improvement in A-B distance. The amount of increase in vertical height was similar in the two groups, but the Frankfort-mandibular plane angle opened more in the group handled with cervical anchorage, and point B moved farther distally. Seven patients from the cervical anchorage group and nine patients from the intermaxillary elastic group were chosen because of their excellent cooperation. The same measurements were compiled on them, and a comparison was made of the changes occurring in certain areas. The findings were similar to those in the larger groups, except that in several instances the variation of the treatment results found in the two types of treatment was considerably more emphatic.

The Frankfort-mandibular plane angle and the facial pattern

The Frankfort-mandibular plane angle has been shown to be a valuable diagnostic criterion in the analysis of the facial pattern in orthodontic patients. It is not an anatomical entity, however, and in this study 150 patients have been classified with respect to the Frankfort-mandibular plane angle. An analysis of mean values for different dimensions of the face shows that a definite progression of mean values may be observed in practically all of the dimensions under study when facial patterns are segregated into different classes based on the magnitude of the Frankfort-mandibular plane angle. These progressions of mean values indicate that the Frankfort-mandibular plane angle is affected by vertical development of the alveolar process in the anterior portion of the denture, by the absolute length of the mandibular ramus, and by the inferosuperior placement of the glenoid fossa in the skull. It is furthermore shown that, statistically speaking, there is a direct relationship between the size of the gonial angle and the size of the Frankfort-mandibular plane angle. Where the Frankfort-mandibular plane angle is relatively small (i.e., less than 25 °), a more or less separate and distinct facial type is encountered, which has special connotations in esthetics and in prognosis for orthodontic treatment.

The angulator—An instrument for measuring the Frankfort-mandibular plane angle

T HE angulator is a simple device for measuring, directly on the head of the patient, the Frankfort-mandibular plane angle for orthodontic diagnosis. It gives the measurements immediately-they can be read on the protractor which is part of the instrument,. It will also give the distance from the tragion to the point where the Frankfort and mandibular planes intercept each other somewhere behind the head. Dr. Tweed was the first to describe the importance of this angle in orthodontics. The Frankfort-mandibular plane angle is somewhere in back of the head, formed by the intersection of the Frankfort plane which is aligned from the orbitale to the tragion with a plane tangent to the lower border of the body of the mandible.

The frankfort-mandibular plane angle in orthodontic diagnosis, classification, treatment planning, and prognosis

The frankfort-mandibular plane angle in orthodontic diagnosis, classification, treatment planning, and prognosis