A Comparative Analysis of the Curve of Spee (Lateral aspect) before and after Orthodontic Treatment

Abstract

The present study dealt with the curves of Spee, respective incisal cusp ridge distances and degrees of overbite before and after a dynamic treatment as well as after retention of a selected number of orthodontic patients.As a result, the following conclusions were arrived at : 1. On preoperative 1-6 o.p., the largest curves were observed with the maxillary right and left first premolars and with the mandibular right and left second premolars.On 1-7 o.p., the deepest curves were observed with the right and left second premolars, the pattern being similar to the maxilla and mandible. The deepest curve at the second premolars is in agreement with the reports of previous investigators.In some cases in whom the pronounced curves were formed, distal inclination of the maxillary first and second molars was noteworthy, being mesially positioned. Because of a pronounced mesial inclination of the mandibular together with premature loss of deciduous molars at the successional replacement period, enough space had not been provided for the second premolars which are much later in their eruption. For this reason, it is thought, the occlusal position tended to be lower.2. On postoperative 1-6 o.p., a slight reverse mode resembling almost at raight line was observed with the maxilla, while a shallow curve was observed with the mandible.On 1-7 o.p., on the other hand, a smooth and shallow curve was observed with the maxillary right and left first molars (disto-buccal cusps) and the mandibular right and left first molars (mesio-buccal cusps).Since there was confirmed a tendency that the occlusal plane would become deeper after an orthodontic treatment, the treatment policy was adopted to render it either even or reverse at the finish.3. On 1-6 o.p. after retention, a slight curve was observed similar to that of posttreatment cases with a somewhat noticeable trend, this fact being in common to the maxilla and mandible.On 1-7 o.p. after retention, the findings were similar to those of postoperative cases but, as compared with the maxilla, the curve became somewhat deeper in the mandible.It was not possible to establish definitely whether this deepening of curve in the mandible was due to relapse, natural result by reason of treatment or occlusal movement on the part of patients.4. When the curve of Spee in normal occlusal subjects was compared with those of orthodontic patients both after dynamic treatment and retention, the latter were found to be either reverse or straight line. In the former, the curve was smooth and slight. Except for the lateral incisal region, the curve of Spee in the mandible was similar to that of normal occlusal subjects but with a tendency of being somewhat flat or even.Similarly, on 1-7 o.p., the findings of postoperative and after retention curves were nearly the same, and this is particularly true of the mandible.5. The degrees of overbite were 59.2% preoperatively, 42.6% postoperatively and 41.4% after retention.As shown by these changes, a reducing tendency took place in proportion to an improved occlusion.6. The following values were measured regarding intervals or distances of the incisal cusp ridges. Preoperative Postoperative After retention Maxilla 131.8 mm 113.2 mm 111.1 mm Mandible 115.4 mm 199.2% 98.8 mmIt may be inferred that these changes were brought about by the extraction of first premolars and closure 'adjustment of the band space.