| BackgroundSmooth and compact lower face is crucial to shaping the overall facial appearance.The manifestations of the aging of the lower face are the formation of jowl deformity on the lower cheeks outside the angulus oris,the redundant skin wrinkles forming in the labiomandibular sulcus,and the blurred jaw line[1-3]At present,there are multiple procedures like facelifting[4,5],deoxycholic acid injection[6],lipofilling[7,8]in lower facial rejuvenation treatment.treatment.However,those procedures could not provide satisfactory results.With the introduction of "volumetric restoration theory",fat restoration has been widely used in facial rejuvenation.However,the aging process of lower facial fat tissue is poorly understood.It is unclear whether the lower face gains or loses volume or if it changes its shape over time.These lead to insufficient or excessive filling.In the past,multiple cadaveric studies have demonstrated that facial fat is highly compartmentalized.[9-11]But these cadaveric studies have many limitations in describing the age-related changes in the facial fat compartments.First,the sample size was small.Second,the cadavers were deformed during the preservation process.Third,the research objects were elderly,which was difficult to explain the aging process of compartments.Fourth,the affects of weight and disease on fat tissue were not considered.In addition,the current research and application of facial fat tissue compartments mainly on fat filling in the midface,the lower facial fat compartments are rarely reported.Meanwhile,the important structures such as marginal mandibular nerve(MMN),facial artery and facial vein are located in the soft tissue of the lower face[12-15].Embolism events and MMN injury occur frequently due to undeserved injection process[16,17].Previous studies on facial artery and vein are mostly based on corpses,which cannot truly reflect the physiological function of blood vessels,but are affected by perfusion pressure and atrophy of corpses.Based on the above research background,this study aims at demonstrating the age-related changes in lower facial fat compartments using CT,with strict control of body mass index(BMI)and the underlying diseases.CT scanning imageswere used to measure the thickness changes of fat compartments in different regions of the lower face,the aging characteristics of adipose tissue in the lower face were revealed by the comparison of different age groups.The distribution and arrangement of facial blood vessels were also analyzed provide safety evidence for rejuvenation strategies based on facial volumetric theory.ObjectiveIn this study,CT scanning images were used to accurately describe the thickness of the lower facial fat compartments of different ages,to deeply understand the natural distribution and aging changes of the lower facial fat compartments,to enrich the quantitative study of the aging of the fat tissue in the lower part,and to provide new basis and ideas for the rebalancing technology of the fat in the lower face.MethodsThe CT scanning and enhancement images of 60 adult women in Zhujiang Hospital of Southern Medical University(Guangzhou,China)from January 2015 to September 2020 were retrospectively collected.Among them,20 cases were young group(18-39 years old),20 cases were middle-aged group(40-59 years old),and 20 cases were elderly group(60-79 years old).Image calibration The sella(S)-nasion(N)line was used as the cross-sectional position line.The coronal position line was perpendicular to the S-N line,and the sagittal position median line passed through the nasal septum.In order to realize the standardization of measurement,the S-N connection was used as the reference baseline for sagittal measurement.The position plane with complete display of the upper dentition was selected.The horizontal line was made at the posterior margin of the second molar(J1)and the midpoint of the mandibular ramus(J2),the vertical line was made at the middle suture of the maxillary incisor(C)and the lateral said of the maxillary canine(L&L’).The anterior part of the jowl fat compartment The coronal image at the posterior edge of the second molar was selected.The fat in this region was divided into deep and superficial layers by platysma.The distance from the buccal muscle on the upper edge of the mandible to the platysma represents the deep fat thickness;The superficial fat thickness was represented by the distance between the platysma and skin,and the superficial fat thickness was measured at the upper edge of the mandible,the attachment point of the platysma and the midpoint of the two points.The posterior part of the jowl fat compartment The coronal images of the middle point of the mandibular ramus were selected to measure the fat thickness of the superior,middle and inferior points of the posterior jowl fat compartment.The labiomandibular fat compartment The lateral sagittal image of mandibular canine was selected,which can clearly expose the depressor anguli oris muscle,and the thickness of the deep and superficial layers of labiomandibular fat compartment was measured with the muscle as a symbol.The chin fat compartment The sagittal image of the middle seam of the incisor was selected to clearly expose the mental muscle,which was used as a symbol to measure the thickness of the deep and superficial layers of the chin fat compartment.Analysis of the traveling characteristics of facial artery and facial vein:The lateral images of CT three-dimensional reconstruction of head and neck were selected to establish a two-dimensional coordinate system with the gonial angle as the origin and the lower mandibular border as the horizontal axis.The trajectory of facial artery and facial vein in the lower face was depicted in coordinate system.5mm×5mm as the cell probability analysis,the possibility of facial artery and facial vein traveling in different cells were calculate.And the distance between the facial artery and facial vein through the gonial was measured.Statistical analysisAll the data were measured three times,Statistical analysis was performed using the SPSS 20.0 software(IBM,Armonk,NY,USA).LSD-t test was used for multiple comparisons between the two groups.The mean,and standard deviation(SD)for the structures were calculated.A P value of less than 0.05 was considered statistical significant.ResultThe superficial and deep layer of the anterior jowl fat compartment showed a tread of thickness with aging.The thickening of the lower segment of the superficial fat compartment became quite obvious.There was no tread of changes with aging of the posterior jowl fat compartment.The superficial labiomandibular fat compartment showed a thickening trend with the increase of age,and the deep labiomandibular fat compartment showed a trend of thinning with age.The superficial and deep chin fat compartments showed a thickening trend with age.Facial artery and vein were all found deep to the platysma.The facial vein passes through the lower mandibular border at the anterior edge of the masseter muscle and moved upward approximately perpendicular to the lower mandibular border.The facial artery ran in front of the facial vein,and the high-risk area of the facial artery is approximately 45° to the lower mandibular border.ConclusionThe research demonstrated that different lower facial fat compartments were undergoing selective thickening or thinning trends with age,The characteristics of facial artery and facial vein in the mandibular region were different.The aging appearance of the lower face could be improved by selecting liposuction or lipofilling according to the aging changes of the fat compartments in the lower face.Familiar with the running characteristics of facial artery and facial vein can increase the safety of lower facial rejuvenation. |
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