| Objective:Hemifacial microsomia(HFM)is a common congenital craniofacial deformity.At present,individuals mainly focus on the correction of the mandibular asymmetric deformity and the reconstruction of external ear defect or other soft tissue dysplasia,regardless of the underlying stomatognathic dysfunction,which is still a lack of systematic research.We designed a new kind of clinical bite force test system was designed for children with hemifacial microsomia.Patients with hemifacial microsomia and their counterparts(without hemifacial microsomia)were tested with the bite force test system.Also,we use the Mimics software to analysis their CT data.Measure outcomes were recorded and went through the statistical analysis for the evaluation of hemifacial microsomia children’s biting function.This experiment is to study of the biting force distribution characteristics,its change after the mandibular distraction osteogenesis(DO)and the anatomic characteristics of hemifacial microsomia children related with the biting function.And to reflect the influence of mandibular asymmetry development in HFM children and the influence of DO to the stomatognathic system.It can also be seen as a foundation and pilot research of stomatognathic system function in hemifacial microsomia deformity.Methods:A.The design and development of a measuring instrument for biting force:According to the occlusal characteristics of children with HFM,the bite force measuring system was designed and manufactured.It includes a sensing unit converting bite force signal into electric signal,an amplifier circuit and the AVR single-chip microcomputer for data transfer.The measured bite force values can be read directly by the liquid crystal display terminal.It has been proved a simple,convenient,effective and clinical practical system.B.The measurement and analysis of bite force in children with HFM:PART ONE:74 children aged from 6-10 years-old,with or without hemifacial microsomia,were randomly selected from Plastic Surgery Hospital,Chinese Academy of Medical Science(CAMS)and Peking Union Medical College(PUMC)between 2014 May to 2018 February.According to the inclusion criteria,we collected the bite force data from 74 subjects,37 normal children and 37 HFM ones.The maximum bite force value was measured in the first molar region.Each child was tested three times on each side and the highest value of the three were recorded as the maximum bite force on the particular side.Age,gender,chewing habits and other factors like Pruzansky-Kaban classification of hemifacial microsomia were all recorded at the same time.Based on the data listed above,the statistical analysis was performed in accordance with grouping and gender.PART TWO:22 children aged from 6-8 years-old,with hemifacial microsomia,were randomly selected from Plastic Surgery Hospital,Chinese Academy of Medical Science(CAMS)and Peking Union Medical College(PUMC)between 2014 May to 2015 November.They underwent the operation of mandibular distraction osteogenesis and their biting force data were collected.The maximum bite forces in incisor area,bilateral premolar area and molar area were measured before surgery and 1 year after surgery.C.The measurement of the anatomic characteristics related with the biting force:20 children aged from 6-8 years-old,with hemifacial microsomia,were randomly selected from Plastic Surgery Hospital,Chinese Academy of Medical Science(CAMS)and Peking Union Medical College(PUMC)between 2014 May to 2015 November.They were arranged for masseter,temporalis,and medial pterygoid muscles volume measurement by Mimics software.Mandibular angles areas and the max cross-sectional area of muscles were measured before surgery and after surgery.Results:In the study of 74 children aged from 6-10 years-old,we found that HFM children showed no significant difference(p>0.05 in each group)compared with the average maximum bite force of the NORMAL children on the unaffected side.By the contrast,the affected side showed multivariately significant difference(p<0.01 in each group)in average maximum bite force comparison with NORMAL children of the same age.In HFM children group,bite force distribution was observed unbalanced in the same patient,with a statistical significant differences(p<0.05).In the study of 22 HFM children aged from 6-8 years-old,we found that most patients had uneven distribution of bite force between the affected side and unaffected side before surgery.And the bite force in the molar area of the affected side was significantly improved by the surgery(P<0.05).Regression analysis showed that the postoperative bite force distribution had a tendency to become more symmetrical in hemifacial microsomia patients.In the study of 20 HFM children aged from 6-8 years-old,we found that the volume of bilateral masseter muscle,temporal muscle and pterygoid muscle were significantly different(P<0.001).After distraction distraction osteogenesis,the masseter muscle,temporal muscle and pterygoid muscle volume of the affected side were increased to varying degrees compared with the preoperative self control(P<0.05).Postoperative masseter muscle cross-sectional area decreased(P<0.05),length increased(P<0.05)after operation.The cross-sectional area of temporal muscle increased(P<0.05)and the length was unchanged(P>0.05)after operation.The cross-sectional area of the pterygoid muscle increased(P<0.05)and the length increased(P<0.05)after operation.There was no significant change in the area of mandibular angle in the unaffected side(P＝0.15)after operation,and the area of the mandibular angle area on the affected side was significantly reduced(P<0.001)after operation.Conclusion:This study uses the biting force to reflect the stomatognathic function in HFM children.We found that the unilateral temporo-mandibular joint and mandible deformities in HFM children is not an obvious influencial factor of the occlusion on the unaffected side,but plays a crucial role in the occlusal development on the affected side.The bite force distribution was observed unbalanced in the most HFM patients.After DO,the bite force distribution of the HFM patients was re-adjusted(the bite force of the affected molar area increased),enhancing the balance of masticatory long-term postoperatively.CT data analysis showed that the effects of DO on different masticatory muscles on the affected side varied:the pterygoid muscle was thickened and extended,the masseter muscle was prolonged and thinner,and the temporal muscle was only thicker.We also observed the obvious absorption of the mandibular angle bone after DO,suggesting that the changes in the masticatory muscle group after DO were combined with the physical extension and the physiological occlusal adjustment.Here,we put forward a hypothesis:the growth of the lateral masseter,pterygoid and temporal muscles in children with HFM were changed differently after DO,making the distribution of the masticatory stress changed,establishing a new balance,and in general improved the bilateral unbalance of the bite force in HFM.Therefore,we put forward the hypothesis of physiological"Adaptive Rebalance" after DO.We think that the DO therapy of HFM can be regarded as a whole of morphology and function.We should not only consider the functional effects of the mandibular deformation,but also prevent the recurrence of skeletal deformity caused by the functional factors.So that we can retain the prolongation effect of DO to the greatest extent and make it more suitable for the regulation and reconstruction of physiological function. |
