BACKGROUND:With the development and progress in the field of stomatology,oral implant technology has gradually become the mainstream alternative to traditional dentures.In recent years,the maturity of various bone increment techniques and the continuous development of the oral digital field have expanded the indications of dental implantation,and the success rate of implantation surgery is also increasing.However,it has become a difficult problem for some clinicians to use cone-beam computed tomography(CBCT)to accurately measure the residual alveolar ridge bone mass before implantation and to make a suitable implantation plan. OBJECTIVE:To measure the residual alveolar ridge bone mass in the proposed implant area of the mandibular first molar using the CBCT. METHODS:In a retrospective study design,the CBCT images of 205 patients with mandibular first molar loss were included to measure the height and width of the residual alveolar ridge in the proposed implant area of the mandibular first molar.The residual alveolar ridges were divided into four categories:Ⅰ,Ⅱ,Ⅲ and Ⅳ(Class Ⅱ,Ⅲ,and Ⅳ residual alveolar ridge defined as insufficient bone).Statistical analyses were conducted in terms of frequency distribution of residual alveolar ridge height,width,and morphology of the mandibular first molar,differences in residual alveolar ridge height and alveolar ridge crest width of the mandibular first molar in patients of different sexes,correlation of the residual alveolar ridge height with the crest width and bottom width of the residual alveolar ridge,as well as correlation of age with the width and height of the residual alveolar ridge crest. RESULTS AND CONCLUSION:(1)The average height of the residual alveolar ridge in the proposed implant area of the mandibular first molar was(12.14±2.96)mm,of which 43.41％(89/205)were less than 12 mm.The average width of the residual alveolar ridge in the proposed implant area of the mandibular first molar was(6.80±1.65)mm,of which 26.34％(54/205)were less than 6 mm.(2)The height of the residual alveolar ridge of the mandibular first molar was higher in males than in females,with no significant difference(P>0.05),and the width of the residual alveolar ridge of the mandibular first molar was significantly wider in males than in females(P<0.01).(3)The height of the residual alveolar ridge was negatively correlated with the top and bottom width of the residual alveolar ridge(P<0.01).Age showed a positive correlation with the residual alveolar ridge width(P<0.05)and no significant correlation with the residual alveolar ridge height(P>0.05).(4)The residual alveolar ridge of class Ⅰ accounted for 58.05％(119/205),class Ⅱ accounted for 9.27％(19/205),class Ⅲ accounted for 20.49％(42/205),and class Ⅳ accounted for 12.19％(25/205),most of which were class Ⅲ with insufficient remaining alveolar ridge bone mass.Clinicians need to individualize and design the optimal implantation plan based on the type of residual alveolar ridge.