Three-dimensional Reconstruction And Measurement Of The Edentulous Adult's Mandible

Objectives:To describe the course of the inferior alveolar canal(IAC),and collect the data related mandibular anatomy,as a reference in the implant surgery at the position of posterior mandibular teeth,using spiral computer tomography(CT) and threedimensional reconstruction.Materials and Methods:20 edentulous adults were chosen from JiaXing first people hospital.The mandible was divided into five regions:(1) the first premolar region(A region);(2) the second premolar region(B region);(3) the first molar region(C region);(4) the second molar region(D region);(5) the third molar region(E region).All the mandibles were scanned by the spiral CT,and three-dimensional reconstructed.All the data collected were analyzed statistically.The measurements included:(1) the distance between the superior border of IAC and the alveolar crest(D1);(2) the distance between the inferior border of IAC and the inferior border of mandible(D2);(3) the distance between the lateral border of IAC and the buccal cortex of the mandible(D3);(4) the distance between the interior border of IAC and the lingual cortex of the mandible(D4);(5) the longitudinal and lateral dimension of IAC in each region;(6) the distance between the inferior border of mental foramen and the superior border of IAC;(7) the horizontal distance between the anterior border of mental foramen and the anterior border of IAC;(8) the transverse cross section of mandible in each region were divided in three parts,superior(I ), middle(II),and inferior section(III),and software efilm was used to measure the relative bone mineral density.According to the variation of the CT value(Hounsfield Units),the variation of the relative bone mineral density in the regions or sections of mandible could be studied.Results:the IAC located in the cancellous bone of the mandible,starting from the mandibular foramen,and stretched in the mental canal.The course of IAC in the mandible is regular.In the B,C,D,and E region,the distance between the lateral border of IAC and the buccal border of the mandible were 4.18±1.05mm,5.73±1.31mm, 7.18±1.18mm,and 8.37±1.08mm.The distance between the interior border of IAC and the lingual cortex of the mandible were 4.97±1.21mm,3.68±1.16mm,2.69±0.79mm, and 2.31±0.56mm.So the IAC lies in the lingular side of the main mandibular body and more buccally in the posterior mandibular body.In the D and E region,the cortex of the IAC was connecting the lingular cortex of mandibular.In the B,C,D,and E region, the distance D1 were 16.04±2.49mm,16.74±2.43mm,17.74±2.77mm,and 19.64±3.87mm,and the distance D2 were 10.93±1.77mm,10.48±1.65mm,10.55±2.28mm,and 11.63±2.58mm.There are significant differences between the distance D1 and D2(p<0.05).So the IAC lies more closely to the inferior border of mandible.The transverse cross section of IAC is close to elliptic shape.The longitudinal dimension of IAC in the B,C,D,and E region were 3.54±0.99mm,3.51±1.22mm,3.83±1.04mm,and 3.60±1.05mm.The lateral dimension of IAC in the B,C,D,and E region were 2.85±0.77mm,2.64±0.66mm,2.86±0.64mm,and 2.44±0.63mm.There are significant differences between the longitudinal and lateral dimension of IAC(p<0.05).The longitudinal dimension of IAC was longer than the lateral dimension.The cortex of the IAC is compact bone,and more thick when close to mandibular foramen.The radio-opaque border of the IAC was becoming thinning when going through the mandible from the distal to the mesial.The radio-opaque border of the IAC became disrupted in molar region and absent radiographically in the anterior part of mandible. In this study,the IAC rises to the mental canal and the incisive branches in the premolar region,so there was no IAC in the A region.The mental foramen has three positions:(1) below the second premolar,61.11%;(2) between the first and second premolar,22.22%; (3) between the second premolar and the first molar,16.67%.In the mental foramen area, there was a rectangular turning from the lingular side to the buccal side.The vertical distance between the inferior border of mental foramen and the IAC was 3.44±0.53mm, and the horizontal distance between the anterior border of the mental foramen and the anterior end of IAC was 4.25±0.50mm(mean).The result of the relative bone mineral density:(1) in the anterior mandibular tooth area,the relative bone mineral density of the I,II,and III section were 984.51±309.73HU,778.94±289.42HU,and 673.97±458.68HU.There was no significant difference in the I section between the anterior mandibular tooth area and the posterior manddibular tooth area.The anterior mandibular tooth area was higher than the posterior manddibular tooth area in II and III section.(2)there was no significant difference in the A,B,C,D,and E region.Conclusion:1,The IAC lies in the lingular side of the main mandibular body and more buccally in the posterior mandibular body.,the IAC lies more closely to the inferior border of mandible.2,The longitudinal dimension of IAC was longer than the lateral dimension.3,The anterior mandibular tooth area was higher than the posterior manddibular tooth area,there was no significant difference in the A,B,C,D,and E region.4,The front of mental foramen over 5mm and the below of mental foramen in 4mm is safe.