Study Of The Different Mandibular Positions On Cephalometric Roentgenograph

mandibular position means relation between mandible and maxilla or cranium. The mandiblular movement may bring lots of positions, mai nly including the rest posi tion of mandible, the centric relation position, the intercuspal position, the largest open position and the edentulous position. In 1990, Dr. Liu Hongchen first advanced the concept of the edentulous position, i.e. the mandibular position when the maxillary-mandibular alveolar bone closes as possible as one can.No study has been reported on the relationship between Mandibular positions and cranium from the edentulous position to the largest open position, as well as on the occlusal reconstruction of the edentulous jaw by cephalometry, especially incorporating the edentulous position and the largest open position.Purposes: By measuring the angles and the line distancesin five positions of mendible (the edentulous position, the centric relation position, the 1/2 open position, the 3/4 open position and the largest open position), the paper is to discuss: (1) The changes of the distances from Co to S and from Pg to the centric point (determined by researcher)in the five positions. (2) The changes of the distances of the Co and Pg from the edentulous position to the centric relation position. (3) The changes of the mandibular protrusion. (4) Related angles and distance were measured in three positions (the edentulous position, the centric relation position and the largest open position) of the mandible. The characters of the centric relation position and the relationships between the distance of mandibular position from the edentulous position to the centric relation position and the distances of the mandibular position from the edentulous position to the largest open position are studied. Purposes: (1) To discuss the relationship between the di fferent mandi bular posi tions and cranium. (2) To help reconstruct occlusion.Materials and Methods: Cephalometric roentgenographs were made for 22 edentulous patients, 11 women and 11 men in five positions(the edentulous position, the centric relation position, the 1/2 open position, the 3/4 open position and the largest open position). N, S, Co, Pg, centric point, SNplane and Go-On plane were selected according to the requirements of cephalometry. S and N were connected as the X axis; on its extended line, a point 4cm ahead of S was selected as the original point. The Y axis was drawn perpendicularly to X axis through the original point. The distances from Co to S and from Pg to centric point, and the SNPg angle in five positions (10 patients were only measured the three of them, including the edentulous position, the centric relation position, and the largest open position) were measured. The changes of the distance of Co from the edentulous position to the centric relation position , Pg from the edentulous position to the centric relation position and the largest open position on the X and Y axis were measured. The values of the SNæ¡®n-Go , the SNPg and the NSPg angle in the centric relation position were measured.Results: (1) In the five positions, there were no marked difference in the distances from Co to S (P>0. 05) . (2) In the five positions, there were no marked changes from Pg to the centric point (determined by researcher) (P>0. 05) . (3) These two independent values (the values of the S\Pg angles) showed statistical difference(P=0.002) at 5% level of significance from the edentulous position to the centric relation position. These two independent values (the valuesof the SNPg angles) showed no statistical difference(P=0. 763) at 5% level of significance from the 3/4 open position to the largest open position. ( From the centric relation position to the 1/2 open position, and from the 1/2 open position to the 3/4 open position, compared the two angles, P equaled 0. 177 and 0. 097.) (4)Co moved 0. 25cm backward from the centric relation position to the edentulous position on the X-axis, and 0. 22cm on the Y-axis. The t-test of these two independent values showed statistical differ...