Measurement And Analysis Of Cancellous Bone Density And Cortical Bone Thickness In Edentulous Areas

Objective:With the development of oral implant technology and the improvement of people’s economic level,implant denture has become the preferred repair method for dentition defects and missing dentition because of its good comfort,aesthetics,and advantages of not hurting adjacent teeth and high success rate.Osseointegration is the theoretical basis of dental implants.Many researches have confirmed that the initial stability is the key factor affecting the osseointegration.Without good initial stability,the implants must be surrounded by fibrous connective tissue and fail to get good osseointegration,and even become detached with infection and fall off.Among the many factors that affect the initial stability of implants,the bone condition in the area to be implanted is of crucial importance.There is a certain degree of bone resorption during alveolar bone healing process after teeth loss.The bone condition（cancellous bone density,cortical bone thickness,etc.）in the area to be implanted affects not only the choice of implant plan,the choice of implant system specifications,and the surgery Surgical procedures,etc.,but also affect the late osseointegration,repair weight-loading time,and even affect the success rate of implants.In this study,90 cone-beam computed tomography（CBCT）images were obtained from adults with single non-dissociated maxillary/mandibular missing teeth.To correct the CBCT gray value,the theory of quantitative computed tomography（QCT）was applied to CBCT.This experiment measures changes of cancellous bone density and cortical bone thickness in edentulous regions after tooth loss,as well as explores whether there are differences in cancellous bone mineral density（BMD）and cortical bone thickness in different genders,different age stages,and different regions of maxillary and mandibular alveolar bone,providing reference for clinical implantation.Methods:K₂HPO₄ was chosen as the equivalent bone phantom in this experiment,and a series of standard K₂HPO₄solutions with a concentration gradient of 0,50,150,250,350,450,550,650,750,850 mg/cm³ was prepared.After each concentration of K₂HPO₄solution was scanned by the CBCT machine,three-dimensional reconstruction was performed using Ez3D plus software.Through analyzing the correlation of the CBCT value of the K₂HP₄ solution and its concentration,a linear regression model was established,so as to clarify the specific relationship between the CBCT value and the solution concentration.Totally 90 cases of CBCT images with 41 from female and49 from male are selected from April 2014 to October 2016 at the Affiliated Stomatological Hospital of Southwest Medical University.All the cases had the feature that there was only one missing tooth as well as non-dissociated in maxillary or mandibular bone,the corresponding tooth with the same name in the same jaw on the opposite side was healthy,and the tooth had been lost for three to six months.We collected 90 adult patients’（41 females and 49 males）preoperative CBCT images and used Ez3D plus software to reconstruct three-dimensional images.The CBCT values of cancellous bone and cortical bone thickness were measured in 90 patients,and then the CBCT values of cancellous bone were converted to BMD,using the relationship formula between the CBCT value and the solution concentration obtained from the phantom.SPSS 17.0 software was used to compare the differences of cancellous BMD and cortical bone thickness in edentulous area and the control area,different genders,different age stages,and different regions of maxilla and mandibula.Results:1.There is a linear relationship between the liquid concentration and the CBCT value（t=1.953,P=0.028<0.05）,and the linear regression equation is y=91.233+1.953x.2.The density of cancellous bone:⑴There was a significant difference in the density of cancellous bone between the edentulous area and the control area（P<0.001）,so we can consider that the density of the cancellous bone decreases after the tooth loss.⑵In different genders,there was no significant cancellous bone density difference in edentulous area,the control area,and their difference（control area-edentulous area）（P>0.05）.⑶In different ages,there were no significant cancellous bone mineral density differences in edentulous areas and the difference（control area-edentulous area）（P all greater than 0.05）,but the difference in control area was significant（P=0.020<0.05）.The comparisons were performed separately（P all less than 0.05）.The BMD of the control group in the≤40-year-old group was the largest,followed by the40-60-year-old group,and the smallest was the over 60-year-old group.⑷The maxillary and mandible BMD were compared:There were significant differences in edentulous areas and control areas（all P<0.05）.So the maxillary BMD was considered to be lower than that of the mandible.The difference in bone mineral density（control area-edentulous areas）was not statistically significant（P=0.054>0.05）.⑸The maxillary anterior region,the maxillary posterior region,the mandibular anterior region,and the mandibular posterior region were compared separately:there was no significant difference in the edentulous areas and BMD difference（control area-edentulous areas）（P are all greater than 0.05）,but the difference in the control area was significant（P all less than 0.05）:mandibular anterior region>maxillary anterior region>mandibular posterior region>maxillary posterior region.3.The analysis of cortical bone thickness:⑴There was no significant difference in cortical bone thickness between edentulous areas and control areas（P=0.056>0.05）.⑵There was no significant difference in cortical bone thickness between different genders（P=0.068>0.05）.⑶There was no significant difference in cortical bone thickness between different ages（P=0.210>0.05）.⑷The difference of maxillary and mandible cortical bone thickness was statistically significant（P<0.001）.It can be considered that the thickness of cortical bone in mandibular edentulous region is greater than that in maxilla.Conclusion:1.There is a clear linear relationship between CBCT values and BMD.2.The BMD of cancellous bone in the edentulous region decreases after tooth loss.The reduction is not related to age and gender.3.BMD of cancellous bone in edentulous region is not related to age and sex,while BMD of cancellous bone in normal dentition area decreases with age,but is not related to gender.4.Comparison of cancellous bone BMD in different regions:Anterior mandibular region>Anterior maxillary region>Mandibular posterior region>Maxillary posterior region.5.There are no significant changes in cortical bone thickness after teeth loss.There is no significant correlation between cortical bone thickness in edentulous area and age,gender.The cortical bone thickness of the mandibular area to be implanted is greater than that of the maxilla.