Monosodium L-glutamate affects orthodontic outcomes by inhibiting hypothalamic-pituitary-gonadal axis function

Background: Orthodontic treatment involves complex bone remodeling, with the Osteoprotegerin (OPG)/Receptor Activator of nuclear factor Kappa-B Ligand (RANKL)/Receptor activator of nuclear factor Kappa-B (RANK) (OPG/RANKL/RANK) signaling pathway regulating osteoclast activity. Monosodium L-glutamate (MSG) disrupts the hypothalamic-pituitary-gonadal (HPG) axis and may influence bone metabolism. Objectives: This study examined the effects of MSG-induced HPG axis disruption on orthodontic outcomes in neonatal rats. Methods: Rats received either intraperitoneal MSG injections or saline (sham). After 56 days, hormone levels were measured. On the 57th day a rat model for orthodontic tooth movement was established. On the 56th and 84th days, hormone levels and inflammatory cytokine expression, including interleukin-6, interleukin-1beta and tumor necrosis factor alpha, was assessed. The OPG/RANKL ratio, osteoclast counts and bone structure were also measured. Results: MSG significantly reduced sex hormone levels (GnRH, FSH, LH, estradiol and testosterone), increased osteoclast numbers, elevated cytokine expression decreased the OPG/RANKL ratio, indicating enhanced bone resorption. Micro-CT revealed increased periodontal space, reduced bone volume fraction, greater inter-molar distance in MSG-treated rats, reflecting accelerated orthodontic tooth movement. Conclusion: These results suggest that MSG-induced disruption of the HPG axis alters bone metabolism and orthodontic tooth movement, indicating that hormonal imbalance plays an important role in bone metabolism and tooth movement during orthodontic treatment.