| Objective The distance between inferior alveolar nerve and the inner,outer,lower edge of mandible,as well as the cortical thickness of external mandibular plate is measured and analyzed based on different patients' thin-layer CT and three-dimensional reconstruction image of computer,which provides anatomical basis for routine operation of prominent mandibular angle and sets safe operation range and depth of intervention for navigation system of mandibular angle area.Method The data of 30 patients,including 15 females and 15 males,who performed multi-slice spiral CT in maxillofacial region in the past two years is collected and imported into Mimics software to reconstruct complete three-dimensional mandibular model in DICOM format,which helps label the route of bilateral inferior alveolar nerve.A straight line parallel to the leading edge of the mandibular ramus in lateral view of mandibular three-dimensional model is made.this line intersects projection of inferior alveolar nerve on external bone plate to point B and move it back and forth in parallel.The line through the midpoint of the second molar intersects projection of inferior alveolar nerve on external bone plate to point C.The line through the midpoint of the first molar intersects projection of inferior alveolar nerve on external bone plate to point D.The line through the midpoint of the second premolar intersects projection of inferior alveolar nerve on external bone plate to point E.The foramen of the mandible is point A.The distance between inferior alveolar nerve and the inner,outer,lower edge of mandible at these five points are measured separately.A straight line parallel to the lower alveolar is made.This line is moved to the middle position of lateral plate of mandible and intersects with four straight lines passing through A,B,C and D points,which divides the external plate of mandible into eight regions,namely,F?F';G?G';H?H';I?I'.The cortical thickness in each region is measured.All the data are analyzed in both sides,sex,different sections and different areas by Spss 22.0 software.Results 1.The average distance from the inferior alveolar nerve to the ou-ter edge of mandible at five measuring points are point A 6.60±1.39(mm),poin-t B 8.27±1.57(mm),point C 9.50±1.03(mm),point D 7.55±0.49(mm),point E 5.94±0.51(mm).Distance between two sides at the same point has no significant di-fference(P>0.05).Distance between the sexes at points A,B,C and E has signi-ficant difference(P<0.05)but there is no significant difference at point D(P>0.05).The difference between five segments is significant(P<0.05)but there is no significant difference between A,D;A,E and B,D(P>0.05).2.The average distance from the inferior alveolar nerve to the inner edge of mandible at five measuring points are point A 0(mm),point B 2.31±0.35(m m),point C 2.99±0.44(mm),point D 3.51±0.28(mm),point E 5.94±0.51(mm).Distance between two sides at the same point has no significant difference(P>0.05).Distance between the sexes at all five points has no significant difference(P>0.05).The difference between five segments is significant(P<0.05).3.The average distance from the inferior alveolar nerve to the lower edge of mandible at five measuring points are point A 27.01±4.69(mm),point B 13.77±3.23(mm),point C 9.80±3.31(mm),point D 8.85±1.82(mm),point E 10.19±2.29(mm).Distance between two sides at the same point has no significant differenc-e(P>0.05).Distance between the sexes at points A,C,D and E has significant difference(P<0.05)but there is no significant difference at point B(P>0.05).The difference between back and front end is significant(P<0.05).Distance bet-ween A and B has significant difference(P<0.05)but not for C,D and E(P>0.05).4.The average cortical thickness of external mandibular plate in eight diffe-rent areas are F 2.46±0.21(mm),F' 2.73±0,22(mm),G 3.13±0.18(mm),G' 3.63±0.34(mm),H 4.16±0.13(mm),H' 3.95±0.30(mm),I 3.47±0.24(mm),I' 3.29±0.23(mm).Thickness between two sides at the same area has no significant difference(P>0.05).thickness between the sexes in area H' has significant difference(P<0.05)but there is no significant difference for the rest of the areas(P>0.05).Th-e difference between H and H' in longitudinal comparison of cortical thickness is significant(P<0.05).The difference between F,G,H and I as well as F',G',H' and I' in horizontal comparison of cortical thickness is significant(P<0.05).Conclusion 1.This experiment verifies the feasibility of accurately measur-ing the distance of multiple sections of the inferior alveolar nerve and the cor-tical thickness of the external mandibular plate based on thin-layer CT and thr-ee dimensional reconstruction.2.This experiment describes the three-dimensional route of the inferior alve-olar nerve in the mandible based on the numerical measurement,which provide-s anatomic basis for mandibular angle osteotomy.3.This experiment analyzes the changes of cortical thickness of external m-andibular plate in different regions based on the numerical measurement,which provides anatomic basis for mandibular angle splitting ostectomy.4.This experiment provide reference to the safe operation range and depth of intervention for normal mandibular angle operation and navigation system of mandibular angle area.The vertical safe distance between the first molar and t-he front plane should be within 7mm.The interventional depth of external man-dibular plate should be within 5mm. |
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