The Comparative Dermal Stimulation Potential of Constant-Volume and Constant-Amount Diluted Calcium Hydroxylapatite Injections Versus the Concentrated Form

INTRODUCTION Biostimulation properties of diluted and hyperdiluted calcium hydroxylapatite (CaHA) injections have become increasingly popular. However, the existing data are insufficient to certify a particular dose–response pattern. OBJECTIVE To assess and compare the dermal stimulation potentials of different concentrations of CaHA injections. MATERIALS AND METHODS Two independent experiments (Experiment-1: constant injection volume vs Experiment-2: constant CaHA amount) included 4 study groups each, and these experimental groups were placed consecutively on the abdominal skin of a juvenile Yorkshire pig. Histopathological and immunohistochemical stainings were performed on punch biopsy materials collected 4 months after the injection day. RESULTS The fibroblast count significantly decreased upon dilution from 1:3 to 1:19 in experiment 1 ( p = .000) but still higher than the control group. In experiment 1, the collagen density of the concentrated form was more elevated than the 1:19 dilution and the negative control groups ( p = .034 and .000, respectively) but similar to the 1:3 dilution ( p = .123). No significant difference was observed between the groups regarding collagen density with a standard amount of CaHA (0.2 mL, 30%) ( p > .05). CONCLUSION Despite the efficacy being more pronounced till 1:3 dilution, hyperdiluted CaHA at any dilution ratio up to 1:19 can provide a higher fibroblast count than the negative control group.