| Objective: Mandibular laterognathism can be treated by orthognathic surgery.However,in clinical practice,many doctors found that after correcting the jaw deviation by orthognathic surgery,the eye plane canting of these patients was also corrected to some extent.Some scholars have suggested that these were caused by the frontal natural head position(f-NHP)changes after surgery.The purpose of this study is to determine whether the change of eye plane canting is caused by f-NHP tilt and to figure out the relationship between the mandibular deviations and changes of f-NHP.Methods: In this retrospective study,twenty-six patients with mandibular laterognathism corrected by orthognathic surgery were selected.All the cases were treated in Hospital of Stomatology,China Medical University from February 2018 to February 2019.We collected the maxillofacial CBCT data of these patients which scanned in natural head position before surgery and 1 year after surgery,and the data was imported into Proplan CMF 3.0 software to create 3D models of soft and hard tissue.The digital skull models were overlapped in order to analyze and compare the post-operative with pre-operative coincidence in orbital region.We set points on the models and measure related indicators.The angle between the bilateral inner canthus line and the true horizontal plane(THP)represents the canting of the eye plane,and the angle between the bilateral infraorbital point and the THP represents the f-NHP tilt.The distance between the menton and median sagittal plane represents the degree of mandibular deviation.IBM SPSS Statistics 25 software was used for statistical analysis.The statistical method of paired sample t-test was used to evaluate the differences between preoperative and postoperative measurements,as well as the differences between eye plane and f-NHP tilt.The statistical method of bivariate regression analysis was used to evaluate the relationship between the mandibular deviation and the change of f-NHP tilt.Results: Compared with pre-operation,there was a significant change in the horizontal angle of the inner canthus line and the horizontal angle of the suborbital line after surgery in all the patients.The average horizontal angle of the inner canthus line decreased from 3.43±0.67° to 1.67±0.54°,and the average horizontal angle of the suborbital line decreased from 3.12±0.47° to 1.36±0.32°.Paired sample t-test results showed that the difference between the corresponding measured values before and after surgery was statistically significant(P<0.01).The results of superimposed skull model comparison showed that the soft and hard tissues in the orbital region overlapped highly before and after surgery in all patients included in the study.The mean horizontal angle of the inner canthus line decreased by 1.76±0.14°,and the horizontal angle of the suborbital line decreased by 1.76±0.16° on average.There was no significant difference between these index(P> 0.05).The change of f-NHP tilt(Y)gradually increased with the increase of mandibular deviation(X).The two variables showed a linear regression relationship.The calculated linear correlation equation is ? = 1.084 + 0.076 X Conclusion: The significant corrections on the eye plane canting in patients with mandibular laterognathism were caused by changes of f-NHP after orthognathic surgery.Changes in eye plane are equivalent to changes in f-NHP.The f-NHP angle changes have a linear regression relationship with the preoperative mandibular deviation.It can be predicted according to the preoperative mandibular deviation.For patients with mandibular laterognathism combined with developmental orbitozygomatic asymmetry,the change of f-NHP should be estimated in advance when planning the surgery,and then the reference plane should be based on THP after f-NHP decompensation. |
PDF Full Text Request