Methylphenidate-effects on orthodontic tooth movement, orthodontically induced and nonorthodontic root resorption? : A micro-computed tomography and immunohistochemical analysis.

Purpose: The aim of this study was to examine the effect of methylphenidate, prescribed for individuals with attention deficit hyperactivity disorder (ADHD), on orthodontic tooth movement (OTM) and root resorption.

Methods: In all, 30 rats were divided into (1) control (C), (2) constant (MCD), and (3) increasing dose of methylphenidate (MID) groups and 2 subgroups for each of them (nonorthodontic (30 days)/orthodontic (44 days)). After receiving saline or methylphenidate for 30 days, rats in the nonorthodontic groups were euthanized (n = 5/group). Subsequently, 50 g of orthodontic force was applied to the remaining rats' first molars for 14 days (orthodontic groups). Quantitative micro-computed tomography (micro-CT) and immunohistochemical analyses were conducted. For statistical analyses Kruskal-Wallis and Dunnet tests were applied with a significance set at p < 0.05.

Results: Micro-CT analysis demonstrated a statistically significant increase in tooth displacement with higher doses of methylphenidate compared to control and lower-dose groups, though no significant difference was detected between MID-44 and MCD-44 groups. Orthodontic force led to a significant increase in root resorption, peaking in the coronal region and diminishing toward the apex. The highest amount of resorption was observed in the MID groups, with a significant difference between nonorthodontic MID-30 and C‑30 groups. No significant changes in bone parameters were noted in the tension zone, but numerical reductions in trabecular thickness (Tb.Th), bone volume fraction (BV/TV), and bone mineral density (BMD) were observed. In nonorthodontic cohorts, VEGF and RANK levels were significantly elevated in the MID-30 group, along with increased TRAP expression, indicating bone resorption. Orthodontic cohorts exhibited a significant increase in RANK- and TRAP-positive cells with methylphenidate administration. Reductions in OPG and elevations in RANK, RANKL, VEGF, and TRAP were noted, primarily between orthodontic and nonorthodontic groups.

Conclusion: The present rat model suggests a weak potential for methylphenidate to increase root resorption. However, increased doses of methylphenidate accelerated OTM.