Therapeutic changes in extraction versus non-extraction orthodontic treatment

Abstract

Pre- and post-treatment lateral cephalograms of two extraction groups (E4: extraction of the four first premolars; E5: extraction of the four second premolars) and one non-extraction group (NE) were evaluated in patients treated with Begg appliances. It was the intention to investigate the initial amount of crowding, the changes in the position of incisors and molars, the soft tissue profile changes, and the clinical outcome. Ten linear and eight angular measurements were analysed. In order to assess the initial amount of crowding, the Arch Length Discrepancy (ALD) was measured on dental casts taken before treatment. The clinical outcome was evaluated using the PAR Index. The mean pretreatment crowding was nearly twice as large in group E4 when compared with groups E5 and NE. This difference was the main reason for the higher mean PAR score (21.4) for E4 when compared with E5 (15.4) and NE (15.2). In addition, for the cephalometric pretreatment values, some significant differences between the three groups were found: the upper and lower incisors and the lower lip region relative to the pterygomaxillary vertical plane (PMV) were more protrusive in group E5; the inter-incisal angle in both extraction groups was smaller than in the non-extraction group. During treatment, the lower incisor position relative to PMV did not change significantly, and the upper incisors moved backward approximately 2 mm in both extraction groups. This was not reflected in a significant change in lip position. In the non-extraction group, tooth alignment was accompanied by a significant proclination of the incisors, and a comparable forward movement in the lip region when measured in relation to PMV. In the three types of cases, no unfavourable changes in the facial profile were seen. A mean enlargement of about 6 degrees normalized the inter-incisal angle in both extraction groups, while in the non-extraction group the inter-incisal angle became smaller than the norm value. In the three types of cases, upper and lower molars were moved mesially. This movement was higher in group E5 than E4, and lower in the NE cases. Mainly due to the case selection (Class I or very mild Class II or Class III malocclusions), the pretreatment PAR Index was not very high. The percentage reduction for the three groups was higher than 90 per cent. With post-treatment mean PAR scores less than 2, groups E4, E5, and NE can be regarded as having an almost ideal clinical outcome.