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ePaper created 2015-11-17, 15:11:47 | version 1.38.0
Vertically: Seven vertical planes located at +3, +2,+1,0,-1,-2and-3 mmfromthemesial(+3)to thedistalaspect(-3); Horizontally:Sixhorizontalplanesat0(vestibu- lar marginal gingiva), -1, -2, -3, -4 and -5 mm fromthemostcoronal(0)tothemostapical(-5). The occlusal plane, the cutting procedure and the distanceanalysiswereperformedwithautomated Python scripts for Rhinoceros software (Robert McNeel & Associates, Seattle, Wash., U.S.) to re- ducehumanerrorduringelaboration.Atotalof42 points for horizontal variation for each side was tested: 42 at the buccal aspect and 42 at the lin- gual/palatal aspect. The vertical variation was measuredatsevenpointsatthebuccalaspectand seven points at the lingual/palatal aspect. Using the measures of the alveolar process at T0 and at T1, the dimensionalvariations (Δ) were expressed inabsolute(Fig.3)andrelative(Fig.4)values(inre- spectofthetotalalveolarwidth). 3-D d igita l a n a lys is The 3-D analysis was performed by subtracting the volume of the second mesh (T1) from that of the first mesh (T0), generating a resulting vol- ume that represented the difference between the two meshes (Boolean difference). Conse- quently, the software automatically defined the limits of the volume loss. The region of interest (ROI) was manually delimited mesially and dis- tally using as limits a plane crossing through the middle of the crown of the two adjacent teeth. The limits of the ROI were decided on because the main volume changes were included in that region,asindicatedbythemesh-to-meshdevia- tion (Δ; Fig. 5) performed with the Rhino Open ProjectsforRhinocerosplug-in. Using the Geomagic software, the two meshes (T0 and T1) were further cleaned of the teeth and of apical imperfections derived from the technical procedures applied to obtain the casts. Finally, the delimited areas were elabo- rated by closing the holes and obtaining a solid that represented the buccal and lingual/palatal volume changes (Fig. 6). The file containing the data onthe solidwas exported in STLformat and importedintoRhinocerosforvolumetricanalysis. In order to obtain standardized data, the solid was further elaborated using the Geo- magic software. Only the outer surfaces were maintained, while the rest of the solid was eliminated. The two outer surfaces were combined to- gether with bridges and, after closing the gaps (between bridges), another solid was gener- ated that represented the global volume of the alveolar process delimited into the ROI (V-ROI; Fig. 7) before volume changes (i.e., at T0). Sim- ilar procedures were applied to the correspon- ding contralateral control site to obtainvolume changes between T0 and T1. Vo lu me tr i c analysi s The average convergence distance represents the misfit between the two meshes. The differ- ences in volume (Δ) between the meshes of the two periods at the extraction sites were calcu- lated as total amount (V-tot), as well as for the buccal (V-b) and lingual/palatal (V-l) aspects separately,andexpressedinmm3 . In order to reduce the variability associated with the use of absolute measurements in mm3 due to the dimensional variability of patients’ arches, the relative percentage of loss was also calculatedinrelationtotheV-ROIatT0.Percent- agesofthetotalamount(V-tot%)andofthebuc- cal (V-b%) and lingual/palatal (V-l%) aspects wereobtained. At the control sites, the same methodology formeasurementswasappliedforbothabsolute and relative (percentage) values, and the results Volume 1 | Issue 1/2015 65Journal of Oral Science & Rehabilitation Vo lu me tr i c 3- D di gi tal analysi s Fig. 5 The mesh-to-mesh deviation utility in Rhino Open Projects. The red area represents the volume loss. The area most affected by resorption corresponds to about the vertical middle line of the two adjacent teeth. Fig. 6 Palatal and buccal volumes, isolated from the rest of the model during 3-D elaboration. They represent the volume loss in the ROI and can be measured as absolute values in mm3 . Fig. 7 ROI volume of the first mesh, which represents the volume of the alveolar process at T0, expressed in mm3 . Fig. 5 Fig. 6 Fig. 7