Evaluation of Electrophysiological and Histopathological Effects of Hydroxyapatite and Glass Ionomer Bone Cement on Facial Nerve: An Animal Study.

OBJECTIVE

To investigate whether otologic bone cements-hydroxyapatite (HAC) and glass ionomer cement (GIC)-cause facial nerve damage by evaluating their electrophysiological and histopathological effects in a rat model.

MATERIALS AND

METHODS

All rats, except those in the control group, underwent surgical exposure of the facial nerve. Bone cement was applied in the intervention groups. Rats were randomly assigned to 6 groups (n = 10 each): (1) control; (2) sham; (3) HAC; (4) HAC with soft tissue graft; (5) GIC; and (6) GIC with soft tissue graft. In Groups 3 and 5, bone cement was applied directly onto the facial nerve trunk near the stylomastoid foramen. In Groups 4 and 6, the nerve trunk was first covered with a soft tissue graft to prevent direct contact. Facial nerve function was assessed using evoked electromyography (EMG) and video-based whisker movement analysis. Tissue samples from the facial nerve and surrounding structures were collected for histopathological evaluation.

RESULTS

The HAC and GIC groups showed significant histopathological changes compared to the control group in all parameters assessed-including foreign body reaction, granulation tissue, perineurium thinning, disorganized nerve fiber structure, axon-myelin swelling, and Schwann cell nuclear enlargement-except for necrosis. However, there were no statistically significant differences among groups in terms of EMG or whisker movement outcomes.

CONCLUSION

This study underscores the need for caution when using bone cement near neural structures. Although HAC and GIC did not impair facial nerve function, their histopathological effects highlight the importance of avoiding direct neural contact. Future research should explore improved surgical techniques and neurotoxin-sparing alternatives.