Effect of soft tissue thickness on the morphology of lip in orthodontic treatment / Efecto del grosor del tejido blando en la morfología del labio en el tratamiento de ortodoncia

The aim of this study was to evaluate the effect of soft tissue thickness of upper lip on lip retraction in orthodonticaltreated females and identify the ratio of maxillary incisor retraction to upper lip retraction. Pre- and post-treatment lateral cephalograms of 100 adults were examined to measure the lip thickness in upper lip and establish the classification standard. All subjects were treated with 4 first premolar extractions followed by upper central incisors retraction. Pre- and post-treatment lateral cephalograms of 19 patients were reviewed to determine the changes of the upper lip and incisor positions through landmarks displacement. An independent-samples t test and one-way analysis of variance were performed. The correlations between maxillary incisor retraction and upper lip retraction were explored by the Pearson correlation method. P-values<0.05 were considered statistically significant. The lip thickness of adult male patients was greater than that of adult female patients. The average ratio of maxillary incisor retraction to upper lip repositioning was 1.6:1,1.9:1 and 2.2:1 in the thin lips group, normal lips group and thick lips group, respectively. Gender differences exist in the thickness of upper lip. Horizontal changes of the maxillary incisor showed a significant correlation to horizontal changes of the upper lip (P<0.001).There were negative correlations between the thickness of upper lip and the ratio between change in maxillary incisor protrusion and change in upper lip protrusion.

El objetivo de este estudio fue evaluar el efecto del grosor de los tejidos blandos del labio superior, sobre la retracción del labio en mujeres tratadas con ortodoncia e identificar la proporción de retracción del diente incisivo maxilar con respecto a la retracción del labio superior. Se examinaron cefalogramas laterales, previos y posteriores al tratamiento de 100 adultos, para medir el grosor del labio superior y establecer un estándar de clasificación. Todos los sujetos fueron tratados con 4 extracciones de los primeros premolares seguidas de retracción de los incisivos centrales superiores. Se revisaron los cefalogramas laterales, previos y posteriores al tratamiento de 19 pacientes, para determinar los cambios del labio superior y las posiciones de los incisivos a través del desplazamiento de los puntos de referencia. Se realizó una prueba t de muestras independientes y un análisis de varianza de una vía. Las correlaciones entre la retracción del incisivo maxilar y la retracción del labio superior se exploraron mediante el método de correlación de Pearson. Los valores de p<0,05 fueron considerados estadísticamente significativos. El grosor de los labios de los pacientes adultos masculinos fue mayor que el de las pacientes adultas. La relación promedio de la retracción del incisivo maxilar al reposicionamiento del labio superior fue de 1,6:1,1; 9:1 y 2,2:1 en el grupo de labios delgados, grupo de labios normales y grupo de labios gruesos, respectivamente. Existen diferencias de sexo en el grosor del labio superior. Los cambios horizontales del incisivo maxilar mostraron una correlación significativa con los cambios horizontales del labio superior (P<0,001). Hubo correlaciones negativas entre el grosor del labio superior y la relación entre el cambio en la protuberancia del incisivo maxilar y el cambio en la protrusión del labio superior.

Changes in root and alveolar bone before and after treatment by retracting the upper incisors / 华西口腔医学杂志

OBJECTIVE@#Using cone beam computed tomography (CBCT) in image measurement on the patients with maxillary protrusion, the study aims to identify the changes in root and alveolar bone before and after treatment by upper incisor retraction.@*METHODS@#The study was conducted on 37 patients who have received orthodontic treatment from January 2014 to December 2015. The sample comprised 17 males and 20 females, with an average age of 14.5 years. The patients underwent extraction of bimaxillary premolars and given maximum anchorage to retract the upper incisors. The adducent angle, adducent amount, and the amount of elongation of the upper incisor teeth were measured by cephalograms. The patients were scanned by NewTom VGi to obtain CBCT data before and after treatment with upper incisor retraction. Using the NewTom NNT tool, we obtained the multiple planar reconstruction and then adjusted the coronal, axial, and sagittal axis. The sagittal section of the long axis of the maxillary central incisor through the incisal edge and root apex was selected to measure the changes in the root and alveolar bone before and after incisional treatment.@*RESULTS@#Before and after retracting the upper incisors, the adducent angle of central incisor measured 12.92°±6.43°. Adducent amount of the incisors reached (5.54±2.21) mm. Incisor extension amount totaled (0.60±0.95) mm. Root absorption length was (0.81±0.46) mm. Root absorption rate was 6.80%±3.60%. Statistical differences were observed in the changes in root length before and after incisor retraction (P<0.05). After upper incisor retraction, increasing distance from the labial side alveolar ridge to the cemento-enamel junction reached (0.20±0.22) mm. After treatment, we observed that the height of the labial-side alveolar bones decreased and showed statistical difference with the height of labialside alveolar bones before treatment (P<0.05). The results show the correlation between root absorption and horizontal displacement of maxillary center incisor and the distance from the upper incisor apex to labial cortical bone. A correlation also exists between the variable quantity of the labial-side alveolar bones and adducent angle of the upper incisor, with a correlation coefficient of 0.354. The results also show significant difference (P<0.05).@*CONCLUSIONS@#After compensatory treatment of patients with maxillary protrusion, the root length of upper incisor was absorbed remarkably. The height of the labial-side alveolar bones was reduced. A greater tooth movement or beyond the anatomical limitations and alteration limits of the alveolar bone can easily lead to root resorption. A negative correlation exists between the variable quantity of the labialside alveolar bones and adducent angle of the upper incisor.