A comparative analysis of soft tissue volumetric alterations utilizing root mean square and positive and negative...

Clinicians and researchers analyze standard tessellation language (STL) files to assess soft tissue volumetric changes over time. Various software programs are available for this purpose. This study aimed to compare the root mean square (RMS), the average of positive deviations (AVG(+)), and the average of negative deviations (AVG(-)) obtained from metrology-grade and nonmetrology-grade software at the shortest and normalized distances when conducting a 3D comparison of a region of interest using multiple scans of the same patient over time.

Forty-five intraoral scans from 11 patients who underwent soft tissue augmentation procedures were used to evaluate RMS, AVG(+), and AVG(-) at both the shortest and normalized distances using metrology-grade (Geomagic Control X, 3D Systems) and nonmetrology-grade (Medit Design, Medit Link) software programs. All scans of each patient were first aligned and combined into a single STL file using proprietary dental software. The region of interest, where the soft tissue procedure was performed, was then isolated, and the combined file was separated into individual scans for further comparison. Each aligned and cut scan was then compared with the others to assess RMS, AVG(+) and AVG(-) at the shortest and normalized distances using Geomagic Control X and Medit Design. A total of 344 previously aligned and cut scans were compared, resulting in 86 deviation measurements for each software and measurement mode. After assessing normality and homoscedasticity using the Shapiro-Wilk and Levene's tests, respectively, a two-way analysis of variance was performed to determine significant differences in RMS, AVG(+), and AVG(-), considering the software (Geomagic Control X and Medit Design) and measurement mode (shortest and normalized). Pearson correlation and R-squared values were also calculated for each software's RMS, AVG(+), and AVG(-). Statistical significance was set at 0.05.

The RMS and AVG(+) measurements calculated using Medit Design were statistically greater than those obtained with Geomagic Control X at both the shortest and normalized distances (p < 0.001). No statistically significant differences were observed when comparing AVG(-) (p > 0.05). A significant correlation was observed between the RMS (R = 0.804; p < 0.001), AVG(+) (R = 0.833; p < 0.001), and AVG(-) obtained (R = 0.613; p < 0.001), obtained with Geomagic Control X and Medit Design.

Significant differences were observed when comparing deviations of different scans of the same patient over time, using RMS and AVG(+) at both shortest and normalized distances with metrology-grade (Geomagic Control X) and non-metrology-grade software (Medit Design). No statistically significant differences were found in AVG(-).RMS and AVG(+) demonstrated a very strong correlation between Medit Design and Geomagic Control X, along with a strong correlation in AVG(-).

The RMS, AVG(+), and AVG(-) deviations obtained from Geomagic Control X and Medit Design cannot be directly compared, as each software employs its own algorithm. Caution is necessary when interpreting RMS, AVG(+), and AVG(-) measurements reported in the dental literature.