QUANTITATIVE MEASUREMENT OF VOLUME CHANGES INDUCED BY ORAL PLASTIC-SURGERY - VALIDATION OF AN OPTICAL METHOD USING DIFFERENT GEOMETRICALLY-FORMED SPECIMENS

THE PURPOSE OF THIS RESEARCH was to study the validity and variability of a projection Moire system, measuring volume differences of geometr ically different formed specimens mimicking localized alveolar ridge d efects. Nine pairs of specimens were fabricated, each of which simulat ed a preoperative ridge defect and a corresponding surgically-correcte d postoperative ridge defect, All specimen pairs had a mathematically defined form which allowed the accurate assessment of their volume dif ferences by a mechanical 3-D coordinate measuring machine or by a soft ware-controlled milling machine, Measurements achieved with these meth ods were used as the references for comparison. Six specimen pairs, A1 to A6, possessed a simple rectangular geometrical form which facilita ted their fabrication. Three specimen pairs, B1 to B3, were milled and consisted of geometrically more complex 3-D sculptured surfaces, whic h came closest to a true imitation of a localized ridge defect. An opt ical measurement system in the form of the projection Moire was utiliz ed, 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 mm(3) to 15.872 mm(3) , 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 a nd 2.15% for the ''B'' specimens. However, the difference was not sign ificant, probably due to the Limited number of ''B'' specimens. The sy stematic error of the Moire measurements in relation to the reference methods was surprising ly low, ranging from -0.12 mm(3) to 7.67 mm(3). The relative systematic error, expressed as a percentage of reference volume, ranged between 0.06% and -2.23%. The mean of the relative err or for the more complex ''B'' specimens was 1.37%, which was less accu rate in comparison to the more simply formed ''A'' specimens with a re lative 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%.