Histomorphometry and micro-computed tomography of bone augmentation under a titanium membrane

Bone augmentation underneath an occlusive titanium membrane is evaluated in most cases by means of serial histological sections and histomorphometry. Micro-computed tomography (micro-CT) is a less invasive and dynamic technique to measure bone volume in animals of a size that fits into the gantry. The aim of the present study was to evaluate whether the latter approach could match histomorphometry to assess bone augmentation under a titanium membrane.

Pre-formed titanium cups were placed on the skull of 16 rabbits. Bone formation underneath the cups was allowed to occur for 12 weeks. The amount of bone volume assessed by micro-CT was expressed as a numerical unit. One unit volume corresponds to 0.043 mm3. The measurements reveal the volume of bone-like tissue under the membrane, with the same density as that of the original rabbit skull bone. Histological sections were cut along the same plane as the one used for the micro-CT images. The total bone surface was assessed by a digital image system in double-stained undecalcified histological sections and related to the maximum available surface of the titanium cups, which was on average 1366 mm2.

The amount of total bone surface found under the titanium membrane varied between 40 and 163 mm2. Measured by micro-CT, the bone detected ranged from 3.7 to 396 numerical units. A highly significant (P<0.001) correlation was found between the total bone volume measured in conventional serial histological sections and by the micro-CT technique (r2=0.72).

The total bone volume measured underneath a membrane using the micro-CT when compared with histological sections remained within a 16% error. This is because of the scattering effect of the metallic membrane and the impossibility to distinguish newly formed bone from the original skull bone on the micro-CT images.