| Background:Genioplasty is one of the most commonly used methods in orthognathic surgery,including overgrowth,dysplasia and deflection of the chin.Since Hofer first proposed genioplasty via an extraoral approach in 1942,a variety of osteotomy designs have been developed to meet different clinical needs.Objective:In this study,we introduced a modified genioplasty and compared it with traditional genioplasty to determine whether it could reduce the risk of bone defects in the lower margin of the mandible.In addition,the effect of the modified procedure on airway function was evaluated by observing its effect on posterior airway space and hyoid bone position in patients with dentofacial deformities.Methods:In this study,the modified genioplasty was performed with the posterior edge of the osteotomy line designed according to the severity of the deformity and the distance of mental movement.The greater the mental movement distance,the osteotomy line can be extended posteriorly.Then take the chin front point as the center,rotate the chin bone block clockwise to ensure that both sides of the chin bone block contact with the mandible,so as to maintain the continuity of the lower edge of the mandible.1.From January 2018 to April 2020,16 patients with dentofacial deformities who received improved genioplasty（Group A）and 15 patients with dentofacial deformities who received conventional genioplasty（Group B）were enrolled in our department.The facial and imaging data of one week and one year after surgery were collected.The chin moving distance was measured on the midsagittal plane with Pro Plan software one week after surgery.Mimics software was used to reconstruct the volume of the mental bone block,and the volume change of the mental bone block from one week to one year after surgery was analyzed.The length and Angle of the bone defect at the lower margin of the upper and lower jaw were measured by 3d reconstruction one year after surgery.The mandibular model of the patient was imported into Geomagic Studio one week and one year after surgery to analyze the difference in bone resorption degree and location of the chin bone block.Finally,satisfaction was rated by likert scale one year after surgery.All measurement results were imported into SPSS software for statistical analysis.In addition,the relationship between questionnaire score and measurement results were analyzed using Spearman rank correlation analysis.2.A total of 14 patients with mandibular hypoplasia who received modified genioplasty in our department from January 2016 to July 2019 were included.The facial and imaging data of one week before and one year after surgery were collected.The facial convex Angle and facial proportion were analyzed by preoperative and postoperative facial images.The position of the hyoid bone and the width of the posterior airway space were analyzed by preoperative and postoperative cranial lateral radiographs.Dolphin Imaging software was used to reconstruct the preoperative and postoperative posterior airway space and measure its cross-sectional area and volume changes.P<0.05 indicated that the results were statistically significant.Results:1.Due to the large difference of bone defects on both sides of the mandible one year after surgery,the length and angle of bone defects on both sides of the mandibular inferior border lower were measured.The results showed that the bone defect length of group A was 7.14mm±3.92 mm,and that of group B was 8.43mm±2.65 mm（P=0.138）.The average bone defect angle was 159.11°±13.74°in group A and 131.80°±16.50°in group B（P=0.000）.2.Intergroup analysis showed that there was no statistical difference in bone volume one week and one year after surgery between the modified group and the traditional group.In group analysis,bone volume decreased in both the modified group and the traditional group after one year of bone resorption,with statistical difference.Meanwhile,there were statistically significant differences in bone resorption amount and bone resorption ratio between the two groups:the average bone resorption amount in the modified group was 183.13mm~3±71.73mm~3,and that in the traditional group was253.67mm~3±112.52mm~3（P=0.045）;The average bone resorption rate was 4.42%±1.34%in the modified group and 5.96%±1.07%in the conventional group（P=0.002）.The results showed that compared with the traditional group,the absorption degree of free bone in the chin was slighter in the modified group.3.Color-coded distance maps showed blue part at the edge of the osteotomy line of the chin segment clearly（blue part indicates bone absorption greater than 0.5mm）,indicating a certain degree of bone absorption.In addition,color-coded distance maps showed that bone resorption was particularly pronounced at the two sharp upper edges of the chin segment,suggesting that bone resorption occurred primarily here.4.Likert scale results showed that the average score of the modified group was4.75±0.45 and that of the traditional group was 3.87±0.83,indicating a statistically significant difference between the two groups（P=0.010）,indicating that patients in the modified group were more satisfied with the contour of their lower mandibular margin than those in the traditional group.5.Spearman correlation analysis showed that there was a moderate positive correlation between the questionnaire score and the right bone defect Angle（R=0.48,P=0.006）and the left bone defect Angle（R=0.52,P=0.003）,which meant that the larger the defect Angle was,the less obvious the notch was and the higher the patient satisfaction was.At the same time,the questionnaire score was negatively correlated with bone resorption rate（r=-0.47,P=0.008）in a moderate degree,indicating that the more bone resorption,the lower patient satisfaction.6.By analyzing the preoperative and postoperative facial images,we found that the patient’s facial morphology was successfully improved,with the facial convexity angle reduced from 22.7°±2.1°to 14.2°±1.5°（P=0.001）.Meanwhile,the percentage of bottom third to middle third increased from 88.1%±2.8%to 98.5%±1.4%（P=0.001）.7.Cephalometric results show that:The distance from hyoid bone point to Y base increased by 0.64mm±0.36mm（P=0.001）,the distance from hyoid bone point to X base decreased by 0.81mm±0.82mm（P=0.004）,and the distance from hyoid bone point to the anterior and lower point of the third cervical body increased by 0.54mm±0.66mm（P=0.016）.The distance from hyoid bone point to mandibular plane decreased by0.69mm±1.56mm,but it was not statistically significant（P=0.056）.Modified genioplasty can affect the position of the hyoid bone to a certain extent by pulling the lingual muscles of the chin to move the hyoid bone forward and downward.8.The posterior airway space width was significantly increased at the level of mandibular angle and hyoid bone,which were 0.90mm±1.11mm（p=0.001）and1.38mm±0.66mm（p=0.001）,respectively.In addition,the airway cross-sectional area at the tongue base and hyoid bone increased by 14.6mm~2±14.5mm~2（p=0.004）and32.4mm~2±14.3mm~2（p=0.001）,respectively.The minimum cross-sectional area of posterior airway space was automatically measured by software,and the results showed an increase from 150.7mm~2±58.9mm~2 preoperatively to 203.7mm~2±49.9mm~2postoperatively,with an average increase of 53.1mm~2±22.7mm~2（p=0.001）.The mean cross-sectional area,one of the most important indicators for evaluating airway function,also increased by 28.8mm~2±14.4mm~2（p=0.001）.The total airway volume increased by1528mm~3±638mm~3（p=0.001）.The spatial volume of hypopharynx increased by1161mm~3±643mm~3（p=0.001）.The oropharyngeal volume showed a certain increase of367mm3±535mm3,but the increase was not statistically significant（p=0.096）.These results suggest that modified genioplasty has a significant positive effect on the posterior airway space in patients with dentofacial deformity.Conclusion:Modified genioplasty can reduce the risk of bone defects in the mandibular inferior border effectively and maintain the continuity of the mandibular inferior border for a long time.In addition,it has a significant positive effect on the posterior airway space in patients with dentofacial malformation,which not only has airway safety but also contributes to the improvement of obstructive sleep apnea syndrome symptoms to some extent. |
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