Minimally Destructive Biomechanical Test Coupled With Histological Evaluation of Osseointegration

Objectives: The aim of this study was to develop a novel minimally destructive biomechanical test that would allow further histological processing/analysis of the same sample.
Methods: The study was a randomized, split mouth design with six implants (4.1x 6mm) placed on each side of 3 lab-bred mongrel hound dog mandibles. Prior to implant placement, premolars and first molars were extracted and a healing period of 19 weeks was selected. Two implant groups were used: (1) commercially pure (c.p.) Titanium (Ti) and (2) Ti alloy, all implants were blasted with Al2O3 and acid etched with HCl/H2SO4. The dogs were euthanized at 8 weeks following implant placement. Each bone-implant block was placed in an empty container and later filled with low melting point metal alloy to ensure a perfect alignment between the implant and the extractor. Removal turnout torque was applied using a new custom designed extractor at a rotation rate of 0.1 degrees per second. The stress-strain curve was recorded and the maximum value reported. Later the samples were processed for histological analysis and sections 20 µm thick were stained with toluidine-blue. The histomorphometric evaluations comprised measurements of the bone-in-contact (%) (BIC) and bone area (%) (BA). Statistical analysis was performed using linear mixed model that included the fixed effects (group and location) and random effect (canine).
Results: The pre-clinical model developed by our group indicated higher torque values (p<0.0001) for c.p. Ti (115.0 ± 25.0 Ncm) compared to Ti alloy implants (73.9 ± 17.9 Ncm). In agreement with the biomechanical test, enhanced BIC (p<0.05) was calculated for c.p. Ti (24.4±8.6) compared to Group 2 (20.4±9.9). Bone area values were not statistically different.
Conclusions: The results demonstrated that a minimally destructive biomechanical test will allow further histological analysis of the same sample. The histological analysis of an implant submitted to both biomechanical and histomorphometric tests demonstrated, for the first time, that bone-in-contact values are in agreement with the strength of osseointegration as measured with turnout torque.