Visibility of alveolar bone thicknesses on CBCT images-a study on minimum bone requirements using various reconstruction techniques, viewing modes, and resolutions.

Objectives: To evaluate at which thickness marginal bone becomes visible to the observer on cone-beam computed tomography (CBCT) images and how reconstruction technique and viewing mode affect assessment.

Materials and methods: Fourteen anterior teeth from six human mandibles were examined with two CBCT resolution protocols: standard- and high-resolution. Distance from the cementoenamel junction to the visible marginal bone level (MBL) was measured in three groups of reconstructed CBCT images: multiplanar reformation (MPR) with grey scale, MPR with inverted grey scale, and 3D rendering. These measurements were used to identify the bone level where marginal bone width should be measured on histological photographs of sliced teeth. Gold standards comprised measurements of bone thickness at the superior MBL on histological photographs.

Results: MPR grey scale images exposed at high-resolution settings yielded highest validity: bone widths of 0.173 mm (buccal) and 0.356 mm (lingual) were necessary for visibility on a CBCT image. 3D-rendered lingual surfaces exposed with high-resolution settings had lowest validity. Intra-observer agreement for all CBCT and histological measurements was high.

Conclusion: The best CBCT resolution protocol, reconstruction technique, and viewing mode for analyzing buccal and lingual surfaces of the alveolar bone margin are images exposed with a high-resolution protocol, reconstructed using MPR, and viewed in grey scale. Bone thickness required to be visualized was twice lingually compared to buccally.

Clinical relevance: The visualization of bone thickness in CBCT requires a greater thickness on the lingual side compared to the buccal side. 3D-rendered reconstructions should be avoided when evaluating thin bony structures.