The sagittal soft-tissue changes of the lower lip and chin associated with surgical maxillary impaction and consequent mandibular autorotation

[摘要] This study assessed the sagittal soft-tissue changes of the lower lip and chin area in 22 patientssubsequent to mandibular autorotation following surgical vertical impaction of the maxilla. Asubgroup of six patients in addition had undergone advancement genioplasty procedures.Lateral cephalometric radiographs were taken immediately prior to surgery and on average 15months following surgery. Sixteen cephalometric landmarks were identified on eachradiograph and these were digitized using a Kontron Videoplan Image Analysis System toenable differences reflecting changes to be assessed.The comparison between those cases that had had maxillary elevation only and the six casesthat had received additional advancement genioplasty procedures revealed statisticallysignificant differences in relation to the proportional changes in the chin area. Therefore, whenstudying the soft-tissue chin changes following mandibular autorotation, these six patientswere excluded from the sample. It was found that there was no significant difference in thelower lip response between the two groups and therefore when studying the lower lip changes,the two groups could be pooled.The soft-tissue changes in the chin area showed statistically and clinically significantcorrelations. In the horizontal plane, a ratio of 0.9:1 was found for the changes between sulcusinferior and point B, between soft-tissue pogonion and hard-tissue pogonion, and betweensoft-tissue gnathion and hard-tissue gnathion. In the vertical dimension, soft-tissue gnathion followed hard-tissue gnathion in a ratio of 0.9:1, whereas soft-tissue menton followed hardtissuementon in a ratio of 1:1.In the study of the lower lip response, a significant correlation with a ratio of 1:1 existed forthe horizontal change in the lower lip as measured at labrale inferius relative to both lowerincisor tip and lower incisor anterius. In the vertical dimension, stomion inferius followedlower incisor anterius in a ratio of 1.3:1, while labrale inferius followed lower incisor anteriusin a ratio of 1.5:1.Multiple regression analyses revealed that presurgical tissue thickness exerted no influenceupon the strength of the correlations between changes expressed at corresponding soft- andhard-tissue landmarks located in the lower lip and soft-tissue chin area.Based on the findings of this study, it is suggested that the soft-tissue to hard-tissue ratios maybe applied to prediction tracings with enhanced confidence. As a result, the tracings willreflect a more accurate prediction of the lower lip and soft-tissue chin positions followingautorotation of the mandible.

[发布机构] University of the Witwatersrand