Resorption kinetics of eggshell: An in vivo study

Eggshell has been recently introduced as a bone substitute candidate in rec onstructive surgery. The aim of this experimental study study was to determ ine its degradation rate in both a skeletal and extraskeletal site. In expe riment 1, eggshell particles with four different sizes (50, 75, 150, and 30 0 mum in diameter) were implanted in subcutaneous pouches of 30 rats. In ex periment 2 a fragment of ostrich eggshell was implanted on the nasal dorsum of 10 rats. Animals were sacrificed at 1(N = 10), 2 (N = 10), and 4 months (N = 10) during the first stage of the study, and at 1 year during the sec ond stage of the study. The results were assessed by X-ray examination and routine histological techniques. In experiment I, all animals healed uneven tfully. At 1 month, only 50-mum particles had undergone resorption. At 2 mo nths, both 50- and 75-mum particles had undergone resorption. At 4 months, the 150- and 300-mum particles were resorbed incompletely. Histologically, the eggshell elicited a mild inflammatory reaction at 1 month that decrease d progressively at further stages. In experiment 2, all animals except one healed uneventfully. Radiologically, the eggshell implant displayed a notic eable stability. Histologically, seven of nine implants were encapsulated, but two of them were surrounded by a bony rim. In conclusion, eggshell is a resorbable implant, but the degradation kinetic is size dependent. Large o strich grafts are also suitable as onlay graft, but a complementary osteosy nthesis is recommended to enhance osteointegration.