2003 Volume 23 Issue 2 Pages 119-128
The first objective of the present study was to compare the changes in occlusal force (OcFr) during retention in patients with various types of malocclusion using pressure-sensitive occlusal sheets (Dental Prescale). The second objective was to calculate the irregularity index before and after orthodontic treatment.
The final objective was to evaluate the correlation between the increase in OcFr during retention and the relapse rate in the lower incisors calculated by the study models at pre-and post-treatment.
The male subjects treated in Showa University Dental Hospital were selected according to the following criteria : 1) clinically normal function of the oral and maxillofacial region, 2) less than 4 mm deviation between the maxillary and mandibular midlines, 3) no congenital craniofacial anomaly such as cleft lip and/or palate and 4) first and second molars were all present and functioning without extensive defects. The subjects were divided into four types : Class I, II, III and surgical class III (S-Cl.III). All subjects completed active treatment with or without extraction of premolars. OcFr was recorded using Dental Prescale at both early and late retention stages. The irregularity index, defined by Dr. Little, was calculated using study models at pre-treatment and late retention stages.All subjects showed a positive correlation between the increase in OcFr during retention and the relapse rate in lower incisors. In particular, the positive correlation was statistically significant in Cl.I and Cl.III. OcFr at early retention stages among the four types of malocclusion ranked in the following order : Cl.III>Cl.I>Cl.II. The order changed to S-Cl.III>Cl.I>Cl.III>CUT in the late retention stage. Therefore, the increase in the rate of OcFr during retention ranked as follows : Cl.I>Cl.II= S-Cl.III>Cl.III.
The irregularity index during both pre-treatment and late retention stages, and the relapse rate of the lower incisors among the four types of malocclusion all ranked in the following order : Cl.II>Cl.I>Cl.III>These results suggest that Cl.I patients as well as S-Cl.III patients experienced an increase in OcFr during retention since S-Cl.III patients had diminished skeletal disharmony as the results of mandibular setback surgery. The relapse rate of the lower incisors in Cl.III patients tended to be greater than that in either Cl.III patients or S-Cl.III patients. The I.I. at the beginning of active treatment in Cl.II patients is relatively large due to undergrowth of the mandible. On the other hand, the I.I. at the beginning of active treatment in either WIT patients or S-Cl.III patients is relatively small due to sufficient mandible size.
