Representative Points of the Morphology of Mandibular Edentulous Alveolar Ridges

Objectives: Comprehensive objective evaluation of the three-dimensional morphology of edentulous alveolar ridges is difficult. The purpose of this study was to determine representative points sufficient to characterize the morphology of mandibular edentulous alveolar ridges and serve as efficient, objective criteria for evaluation.

Methods: Sixty-five pairs of mandibular edentulous casts and waxed complete dentures were used. Their shapes were digitized with a three-dimensional laser scanner following coordinate transformation so that the occlusal plane became level. We assumed cylindrical coordinates R and phi in the occlusal plane and Z extending perpendicularly upward. The central axis passed through the intersection between the midsagittal plane and the line connecting the posterior ends of both retromolar triangles. The extracted shape of the ridge was divided mesiodistally with a uniform interval of phi, then into equal-length portions buccolingually. Principal component (PC) analysis was performed using R and Z of the points on the grid as the variables. Multiple regression analysis with each PC score as a dependent variable was performed to confirm the validity of the representative points selected with reference to eigenvalues for each PC. The independent variables were the average coordinates of the selected points on both sides corresponding to each other and the differences between them.

Results: Over 80% of the coordinates of all points could be expressed by a search up to the seventh PCs. Multiple regression analysis indicated that at least 50% of the PC scores could be explained. The contribution rates of the first, second and third PCs exceeded 90%.

Conclusion: Approximate morphological characteristics of the mandibular edentulous alveolar ridges tested could be expressed with the coordinates of the selected points. These parameters may be efficient to evaluate the morphology of mandibular edentulous alveolar ridges.

Grant-in-Aid (No.18592107) for Scientific Research of Japan Society of the Promotion of Science.