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Mapping the progression of non-carious cervical lesions

Grenness, MJ 2008 , 'Mapping the progression of non-carious cervical lesions', PhD thesis, University of Tasmania.

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'Non-carious cervical lesion’ (NCCL) is a term used to describe loss of hard
tissue in the cervical one-third of teeth. NCCLs are commonly encountered
in dental practice and frequently require clinical intervention. There are few
reports of high quality mapping and monitoring of NCCLs, and dental
practitioners currently have no reliable method for measuring and
monitoring their progress. Improved understanding of the underlying
causes and progression of NCCLs will rely on reliable and practical methods
of mapping their topography and monitoring their progress.
NCCLs on the facial surfaces of teeth can be easily imaged, either directly or
on cast replicas, and therefore may be well suited to mapping using a
photogrammetric approach. A preliminary investigation led to the
development of a casting material that incorporated optical texture so that
photogrammetric image-matching techniques could be utilized.
Three-dimensional coordinate data for tooth replicas was successfully
generated using the casting material, convergent stereoscopic photography
and commercial digital photogrammetric software. Imaging was performed
initially using a semi-metric 35 mm film camera, then a high-resolution
digital SLR camera, and finally a fixed-base digital SLR stereo camera. The
quality of the surface data and the capacity to align tooth surfaces was
investigated. Two specific examples of NCCLs were mapped and monitored
at baseline, 12 month and 24 month time periods.
For the film camera and the single digital camera, the photogrammetric solutions were not highly stable, with systematic height errors of up to 80 μm
attributed to unstable exterior orientation. However, for the fixed-base
stereo camera, model precision was shown to be in the order of 13 μm and
the accuracy of surfaces derived from automatic measurement was
approximately 3 μm. The error associated with aligning independent
measurements of tooth surfaces was approximately 17 μm. Change detection of the two NCCL surfaces was sensitive to 30 μm, with change ranging from
30 to 320 μm per annum for one surface and 30 to 70 μm per annum for the
second surface. Different rates of change were clearly evident in different
areas of the same surfaces. The replication, stereoimagery, photogrammetric
processing, and detection of changes to the surfaces were shown to be
reliable and convenient.
The results of this investigation show that stereo-photogrammetric
techniques can be applied to the mapping of NCCLs, and that the surfaces
can be mapped at sufficient accuracy to enable change to be monitored. The
two examples suggest that annual change detection studies will provide a
clearer picture of the rate of progression and the geometry of progression
and, in combination with other analytical techniques, a more detailed
explanation of the natural history of non carious cervical lesions.

Item Type: Thesis - PhD
Authors/Creators:Grenness, MJ
Keywords: Dental mapping; Tooth surface mapping; Dental photogrammetry; Stereo camera calibration; 3D superimposition; Non-carious cervical lesions
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