Fresh-frozen vs. embalmed bone: is it possible to use formalin-fixed human bone for biomechanical experiments on implants?

Purpose: As formalin is an extremely reactive electrophilic chemical that reacts with tissues, the purpose of this study was to explore whether formalin fixation could potentially alter the mechanical properties of bone tissue and have an effect on the primary stability measurements of implants. Material and methods: empty set 3.3 x 8 mm, empty set 4.1 x 8 mm, and empty set 4.8 x 8 mm implants were placed on sockets prepared into the anterior surface of the radius of two fresh-frozen human cadavers. The insertion torque of each implant was quantified using a strain-gauged torque-wrench connected to a data acquisition system at a sample rate of 10 KHz, and resonance frequency analysis measurements were also undertaken for each implant. The cadavers were then subjected to embalment with 10% formalin for 3 months, and the same experiments were undertaken on the contra lateral radius of the cadavers. Results: The insertion torques before and after chemical fixation were similar for empty set 3.3 mm (P > 0.05), and higher values were obtained for empty set 4.1 mm and empty set 4.8 mm implants after chemical fixation (P < 0.05). The resonance frequency analysis values before and after chemical fixation were similar for all implants (P < 0.05). Conclusions: Implants have higher insertion torque values in formalin-fixed bone than fresh-frozen human bone, but similar implant stability quotients in both cases. The insertion torque technique can detect the difference between formalin-fixed and fresh-frozen human bone, but resonance frequency analysis cannot.