An in vitro comparison of photogrammetric and conventional complete-arch implant impression techniques

Abstract

Statement of problem: Conventional impression techniques for recording the location and orientation of implant-supported, complete-arch prostheses are time consuming and prone to error. The direct optical recording of the location and orientation of implants, without the need for intermediate transfer steps, could reduce or eliminate those disadvantages.

Purpose: The objective of this study was to assess the feasibility of using a photogrammetric technique to record the location and orientation of multiple implants and to compare the results with those of a conventional complete-arch impression technique.

Material and methods: A stone cast of an edentulous mandibular arch containing 5 implant analogs was fabricated to create a master model. The 3-dimensional (3D) spatial orientations of implant analogs on the master model were measured with a coordinate measuring machine (CMM) (control). Five definitive casts were made from the master model with a splinted impression technique. The positions of the implant analogs on the 5 casts were measured with a NobelProcera scanner (conventional method). Prototype optical targets were attached to the master model implant analogs, and 5 sets of images were recorded with a digital camera and a standardized image capture protocol. Dimensional data were imported into commercially available photogrammetry software (photogrammetric method). The precision and accuracy of the 2 methods were compared with a 2-sample t test (α=.05) and a 95% confidence interval.

Results: The location precision (standard error of measurement) for CMM was 3.9 µm (95% CI 2.7 to 7.1), for photogrammetry, 5.6 µm (95% CI 3.4 to 16.1), and for the conventional method, 17.2 µm (95% CI 10.3 to 49.4). The average measurement error was 26.2 µm (95% CI 15.9 to 36.6) for the conventional method and 28.8 µm (95% CI 24.8 to 32.9) for the photogrammetric method. The overall measurement accuracy was not significantly different when comparing the conventional to the photogrammetric method (mean difference = -2.6 µm, 95% CI -12.8 to 7.6).

Conclusions: The precision of the photogrammetric method was similar to CMM, but lower for the conventional method as compared to CMM and the photogrammetric method. However, the overall measurement accuracy of the photogrammetric and conventional methods was similar.