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Implant Tribune Italian Edition No.1, 2016

11 Implant Tribune Italian Edition - Marzo 2016 Speciale Digital Dentistry Tab. 5 - 3-D analysis. Mean values, standard deviations (S.D.), medians, and 25th and 75th percentiles of the volume reduction of the alveolar process in absolute values in mm3 and in % at the test and control sites. < < pagina 10 Consequently, the software au- tomatically defined the limits of the volume loss. The region of interest (ROI) was manually delimited mesially and distally 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 chang- es were included in that region, as indicated by the mesh-to-mesh deviation (Δ; Fig. 5) performed with the Rhino Open Projects for Rhinoceros plug-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. Final- ly, the delimited areas were elab- orated by closing the holes and obtaining a solid that represent- ed the buccal and lingual/palatal volume changes (Fig. 6). The file containing the data on the solid was exported in STL format and imported into Rhinoceros for vol- umetric analysis. In order to obtain standardized data, the solid was further elab- orated using the Geo-magic soft- ware. Only the outer surfaces were maintained, while the rest of the solid was eliminated. The two outer surfaces were com- bined together with bridges and, after closing the gaps (between bridges), another solid was gen- erated that represented the glob- al volume of the alveolar process delimited into the ROI (V-ROI; Fig. 7) before volume changes (i.e., at T0). Similar procedures were ap- plied to the corresponding con- tralateral control site to obtain volume changes between T0 and T1. Volumetric analysis The average convergence distance represents the misfit between the two meshes. The differences in volume (Δ) between the meshes of the two periods at the extrac- tion sites were calculated as total amount (V-tot), as well as for the buccal (V-b) and lingual/palatal (V-l) aspects separately, and ex- pressed in mm3 . In order to reduce the variability associated with the use of abso- lute measurements in mm3 due to the dimensional variability of patients’ arches, the relative per- centage of loss was also calculat- ed in relation to the V-ROI at T0. Percentages of the total amount (V-tot%) and of the buccal (V-b%) and lingual/palatal (V-l%) aspects were obtained. At the control sites, the same methodology for measurements was applied for both absolute and relative (percentage) values, and the results were used to de- fine the global errors of the pro- cedure due to the Boolean meth- od, superimposition, impression taking, gypsum casting and 3-D scanning. Data analysis Mean values and standard de- VP3 VP2 VP1 VP0 VP-1 VP-2 VP-3 HP 0 -14.8 (7.1) -17.5 (4.6) -24.0 (24.0) -16.8 (17.8) -20.0 (15.9) -18.0 (10.5) -12.5 (5.7) HP -1 -12.7 (6.5) -15.7 (7.0) -17.6 (8.2) -15.9 (7.5) -15.7 (6.1) -12.5 (3.3) -9.5 (4.4) HP -2 -9.1 (5.6) -11.0 (5.8) -12.2 (5.1) -11.9 (4.1) -10.6 (3.4) -9.2 (3.8) -7.0 (3.6) HP -3 -6.7 (5.1) -8.1 (5.5) -8.8 (5.0) -8.9 (4.7) -8.3 (4.3) -6.7 (3.7) -5.0 (2.9) HP -4 -4.6 (4.7) -5.7 (5.3) -5.9 (5.0) -5.6 (4.4) -5.1 (3.7) -4.1 (2.9) -3.0 (2.3) HP -5 -2.6 (3.7) -3.3 (4.3) -3.6 (4.2) -3.4 (4.2) -3.1 (3.9) -2.6 (3.1) -2.0 (2.4) VP3 VP2 VP1 VP0 VP-1 VP-2 VP-3 HP 0 -9.4 (3.9) -14.7 (4.2) -19.9 (7.8) -24.1 (14.1) -20.9 (8.4) -19.7 (9.5) -17.9 (13.6) HP -1 -7.6 (5.6) -11.1 (5.6) -14.6 (9.2) -17.7 (12.7) -15.4 (10.1) -11.8 (6.6) -8.5 (4.6) HP -2 -4.1 (3.1) -6.0 (3.7) -7.6 (4.6) -8.7 (4.8) -8.1 (4.5) -6.8 (3.9) -5.2 (3.0) HP -3 -2.7 (2.0) -3.3 (2.3) -4.3 (2.8) -4.8 (2.7) -4.6 (2.4) -4.1 (2.1) -3.5 (2.0) HP -4 -1.7 (1.4) -2.0 (1.8) -2.7 (2.0) -2.9 (1.8) -2.9 (1.8) -2.8 (1.8) -2.7 (1.7) HP -5 -1.2 (1.3) -1.1 (1.4) -1.5 (1.7) -2.0 (1.9) -2.2 (1.6) -2.1 (1.5) -2.1 (1.5) VP3 VP2 VP1 VP0 VP-1 VP-2 VP-3 HP 0 -24.2 -32.2 -43.9 -40.9 -40.9 -37.8 -30.4 HP -1 -20.4 -26.8 -32.2 -33.6 -31.1 -24.3 -18.0 HP -2 -13.2 -17.0 -19.8 -20.6 -18.7 -15.9 -12.2 HP -3 -9.4 -11.3 -13.1 -13.7 -12.9 -10.8 -8.5 HP -4 -6.2 -7.6 -8.6 -8.5 -7.9 -6.9 -5.7 HP -5 -3.8 -4.4 -5.2 -5.4 -5.3 -4.7 -4.0 Vertical plane Buccal aspect Lingual/palatal aspect 3 -1.4 (0.6) -1.1 (0.5) 2 -1.2 (0.4) -1.2 (0.6) 1 -0.8 (0.5) -1.5 (0.6) 0 -0.5 (0.7) -1.3 (1.2) -1 -0.6 (0.9) -1.5 (0.8) -2 -0.9 (0.6) -1.1 (1.6) -3 -1.2 (1.0) -1.0 (1.6) Δ V-b mm3 Δ V-l mm3 Δ V-tot mm3 V-ROI mm3 Δ V-b% Δ V-l% Δ V-tot% Test implant site Mean (SD) 69.7 (39.1) 74.3 (29.8) 144.1 (61.2) 1202.9 (524.4) 5.9 (1.9) 6.8 (2.2) 12.7 (3.1) Median (25th ; 75th percentiles 63.8* (34.4; 105.4) 75.5* (49.6; 88.8) 134.3* (106.0; 174.5) 1288.5 (895.3; 1557.8) 6.4* (5.4; 7.1) 6.7* (5.6; 8.3) 12.9* (11.8; 13.4) Contralateral control site Mean (SD) 1.98 (1.74) 3.31 (4.04) 5.29 (5.24) 1202.9 (524.4) 0.18 (0.13) 0.39 (0.42) 0.57 (0.50) Median (25th ; 75th percentiles) 1.73* (0.60; 3.31) 2.67* (0.17; 3.61) 4.02* (2.23; 7.11) 1288.5 (895.3; 1557.8) 0.19* (0.11; 0.26) 0.20* (0.02; 0.77) 0.45* (0.18; 0.98) *A p-value of < 0.05 between the test and control sites. Tab. 1 - 2-D analysis. Mean values and standard deviations of the horizontal reduction of the buccal aspect of the alveolar pro- cess at the 42 intersection points in %. HP = Horizontal plane; VP = Vertical plane. Tab. 2 - 2-D analysis. Mean values and standard deviations of the horizontal reduction of the lingual/palatal aspect of the alveo- lar process at the 42 intersection points in %. HP = Horizontal plane; VP = Vertical plane. Tab. 3 - 2-D analysis. Global horizontal reduction of the alveolar process in % represented by the sum of the mean values of the buccal and lingual/palatal reduction at the 42 intersection points. HP = Horizontal plane; VP = Vertical plane. Tab. 4 - 2-D analysis. Mean values and standard deviations of the vertical reduction of the buccal and lingual/palatal aspects of the alveolar process at the most coro- nal of the seven intersection points in mm. viations were calculated for the 2-D data, while mean values and standard deviations, as well as the 25th , 50th (median) and 75th percentiles, were calculated for the 3-D data. Differences in the volumetric variation (Δ) between the implant and the contralateral sites were analyzed using the Wil- coxon signed-rank test. The level of significance was set at a = 0.05. In case of normal distribution, a t-test was also performed. Results 2-D analysis At the buccal aspect (Table 1), a tendency to higher horizontal re- sorption of the alveolar process was seen in the central regions where tooth extraction was per- formed compared with the mesi- al and distal regions. Moreover, the resorption had a tendency to be higher at the coronal aspects com- pared with the apical. The horizontal resorption varied be- tween 3% and 25%, depending on the interception point from which it was analyzed, the highest variation being in the central/cor- onal regions, and the lowest being at the mesiodistal/apical regions. Similar results were observed at the lingual/palatal aspect (Table 2) and in the global horizontal variation (Table 3). The vertical resorption of the alve- olar process analyzed on the seven vertical cutting planes was higher in the mesial and distal regions compared with the central regions at the buccal aspect. A tendency to higher resorption was seen in the central regions at the lingual/pal- atal aspect (Table 4). 3-D analysis When the absolute values were taken into account (Table 5), it was observed that the larger the ROI, the higher the volume loss, with a positive linear correlation between the two variables (R2 = 0.9346; y = 0.126x). The volume loss was 69.7 ± 39.1 mm3 and 74.3 ± 29.8 mm3 at the buccal and lin- gual/palatal aspects, respective- ly, and a global volume loss of 144.1 ± 61.2 mm3 was observed. The global volume loss in per- centage was 12.7 ± 3.1%, showing a lower variability of the results between sites compared with the absolute values (Table 5).The loss was 5.9 ± 1.9% at the buccal and 6.8 ± 2.2% at the lingual/palatal aspects, the difference not being statistically significant. Small variations in volume at the con- trol sites were also observed that represented the errors included in the 3-D analysis. Discussion 2-D analysis The 2-D analysis demonstrated a reduction of the dimensions at both the buccal and lingual/pala- tal aspects. However, the analysis of each intersection point and the comparison of all of the patients were very demanding. Moreover, the variability per intersection point was very large, making drawing conclusions using this method difficult. It is, of course, possible to select just one inter- section point and compare it with the lingual/palatal aspect or with that of other patients. However, to perform a complete analysis of the phenomenon, 42 intersection points (such as those that com- posed the grid) were analyzed. 2-D analysis offers advantages for investigation of defect shape and for analysis of local defects. How- ever, limits to consider include the use of 2-D numbers to express 3-D aspects, the lack of informa- tion about the size of the area af- fected by the resorption, and the huge amount of data that must be recorded and that require a great deal of time to analyze. Moreover, great variability in resorption exists, depending on where the volume loss is inves- tigated. In the present study, a horizontal mean global volume loss of 3.8–43.9% in the analyzed area made it impossible to sum- marize the phenomenon with a unique number that expresses the volume loss. For the vertical loss in the 2-D analysis, the re- sults have to be reported in milli- metres, since it does not seem to be appropriate to report data in percentages because of the lack of a reference dimension. 3-D analysis The 3-D analysis showed that shrinkage of the volume of the alveolar process occurred at both the buccal and lingual/palatal as- pects after tooth extraction and immediate placement of an im- plant in the extraction socket. A global volume loss of 12.7% was observed, being 5.9% at the buc- cal and 6.8% at the lingual/pal- atal aspects. The difference was not statistically significant. > > pagina 12

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