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

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.

This study examined the effects of MSG-induced HPG axis disruption on orthodontic outcomes in neonatal rats.

Rats received either intraperitoneal MSG injections or saline (sham). After 56 days, hormone levels were measured. On the 57^th day a rat model for orthodontic tooth movement was established. On the 56^th and 84^th 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.

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.

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.