Reliability of Soft-tissue Measurement Applying a Three-dimensional Computer-aided Analysis

Objective: The growing emphasis on red-white aesthetics in prosthetic dentistry has created a demand for an objective assessment. The reliability of the three-dimensional computer-aided analysis developed for this purpose concerning soft-tissue measurements had to be verified.

Method: Saw-cut models of 20 probands were made from impressions taken after soft-tissue management on the palatal side of 24 and 25 or 14 and 15. The teeth in the contralateral quadrant served as control. After digitizing (digiSCAN, AmannGirrbach, Germany) baseline and follow-up models, data was orientated according to a constructed occlusal plane. Hard- and soft-tissue reference points were constructed (cuspit, mesial and distal marginal ridge, mesial and distal interdental papilla tip, mid-marginal gingiva) and the distance between corresponding reference points was calculated (geomagic studio and qualify 9.0, geomagic Inc., USA). As the distal interdental papilla of the first premolar is identical with the mesial interdental papilla of the second premolar, these values could be used for verifying the measurements’ reliability. Statistical analysis was performed with SPSS Statistics 17.0 (SPSS Inc., USA) at α=0.05.

Result: No significant difference was found between the measurements of the interdental papilla between first and second premolar (p=0.839). The mean value for 14/24 was 0.0164 (SE: 0.0287, 95% CI:0.0731-0.0404) and 0.0074 (SE:0.0333, 95% CI:0.0733-0.0585) for 15/25.

Conclusion: The developed method showed to be reliable for the assessment of the soft-tissue contour. Once constructed, the same hard-tissue reference points can be used for the calculation of differences to soft-tissue reference points recorded by impressions at any given time. The orientation according to the occlusal plane minimizes errors in the calculation of differences. Measurements can show changes in soft-tissue over time in a clinically relevant range.