[A simplified technique for the clinical measurement of the Frankfort-mandibular plane angle]

The FMA is an angle formed by the intersection of the Frankfort horizontal plane and the mandibular plane. The significance of the FMA to prosthodontic diagnosis, treatment planning and prognosis has been well documented. The objective of this study was to determine the reliability of an instrument designed for the clinical measurement of the FMA. 10 dried skulls (dentate dentulous or partially edentulous) were used in this preliminary study. To ensure the firm position of the mandibles during measurements all mandibles were firmly attached to the upper members of the skulls by a combination of compound and adhesive tape. The FMA was measured on both sides (right-left) of each skull a total of two times by two examiners. The average of the four readings was taken as the final clinical measurement. Lateral cephalometric roentgenograms were obtained for all skulls using standard Radiological techniques. Tracings were made on acetate from all the radiographs and the deviation between the two planes (Frankfort-Mandibular) was measured. The data were statistically analyzed using the student's paired t-test. The results of this preliminary study indicate that the instrument is reliable. Further clinical application however and research is needed to confirm our results and make the instrument a valuable tool to the hands of the clinician.