Force Values and Rate of Distal Movement of the Mandibular First Permanent Molar

Abstract

A method is described for the distal replacement of mesially tipped mandibular first permanent molars in children nine to thirteen years of age. The study was designed to determine the rate of movement and pain response of this tooth when relatively light specified forces were applied for distal movement. This study was undertaken in the light of recent evidence which suggests that forces many times lighter than those currently employed may enhance rate of movement, diminish the amount of root and periodontal damage, and practically eliminate pain usually associated with tooth movement.

The sample was composed of children who had prematively lost deciduous mandibular second molars with resultant mesial tipping of the first permanent molar. There were eighteen cases in the sample of fifteen children, three of the children exhibiting bilateral loss.

The method of movement employed a sine loop helical torsion spring attached to a soldered lingual appliance to effect distal molar movement. This appliance was so fabricated to utilize all of the teeth anterior to the primary second molar space as anchorage.

Extensive records were taken before treatment began, during active treatment, and at the time of retention. These included models, lateral headplates, periapical radiographs, oriented occlusal radiographs, and direct divider measurement in the mouth. The children were routinely examined every four to ten days and appropriate records and measurements taken at these appointments.

It was found in those cases in which under 80 grams had been applied to the teeth there was one pattern of movement while in those above 100 grams another general type was observed. In the below 80 gram group there was a relatively large (0.69 mm.) initial increment of space opening in the first week followed by a one – two week latent period of non-movement. Movement then continued at an average of 0.22 mm/week. The 100 gram group exhibited a very small initial movement (0.27 mm) followed by a two-three week latent period. Movement then continued at a rather rapid rate, (0.39 mm/week).

Flaring of the anchorage united was noted in all but one case. The amount ranged between 1 and 2 mm. in four to six weeks. The cases above 100 grams appeared to show the largest amount of flaring.

Pain usually associated with tooth movement was non-existent in the patients where below 70 grams of force was applied. The intensity of the pain response in the cases above 70 grams (70 – 194) appeared generally to coincide with the magnitude of force application.

The many difficulties and variables associated with distal mandibular molar movement are discussed in detail. These include tooth inclination, occlusion and interlocking, relationship of the second permanent molar, and root configuration.

Based on the results of this study, it is suggested that threshold forces for tooth movement may be non-existent and that any force if allowed to remain on a given tooth for a sufficient length of time will elicit tooth movement.

The evidence shown both in this study and by other investigators point to the possibility of an optimal range of force for tooth movement.