Quantitative measurement of volume changes induced by oral plastic surgery: validation of an optical method using...

The purpose of this research was to study the validity and variability of a projection Moiré system, measuring volume differences of geometrically different formed specimens mimicking localized alveolar ridge defects. Nine pairs of specimens were fabricated, each of which simulated a preoperative ridge defect and a corresponding surgically-corrected postoperative ridge defect. All specimen pairs had a mathematically defined form which allowed the accurate assessment of their volume differences by a mechanical 3-D coordinate measuring machine or by a software-controlled milling machine. Measurements achieved with these methods were used as the references for comparison. Six specimen pairs, A1 to A6, possessed a simple rectangular geometrical form which facilitated their fabrication. Three specimen pairs, B1 to B3, were milled and consisted of geometrically more complex 3-D sculptured surfaces, which came closest to a true imitation of a localized ridge defect. An optical measurement system in the form of the projection Moiré was utilized, applying a 4-phase shift technique, and results obtained with this device were regarded as test volumes. The absolute variability of the test volume measurements differed between 0.397 mm3 to 15.872 mm3, corresponding to a relative variability of 0.83% to 2.83%. The mean of the relative variability was within 1.68% for the "A" specimens and 2.15% for the "B" specimens. However, the difference was not significant, probably due to the limited number of "B" specimens. The systematic error of the Moiré measurements in relation to the reference methods was surprisingly low, ranging from -0.12 mm3 to 7.67 mm3. The relative systematic error, expressed as a percentage of reference volume, ranged between 0.06% and -2.23%. The mean of the relative error for the more complex "B" specimens was 1.37%, which was less accurate in comparison to the more simply formed "A" specimens with a relative systematic error of 0.35%. Therefore, in this in vitro model it was possible to measure volume differences of geometrically different formed specimens, mimicking localized alveolar ridge defects, with a validity within 2.2% and with a variability of less than 2.8%.