Malocclusion impairs cognitive behavior via AgRP signaling in adolescent mice.

Introduction: Occlusal disharmony induced by deteriorating oral health conditions, such as tooth loss and decreased masticatory muscle due to sarcopenia, is one of the causes of cognitive impairment. Chewing is an essential oral function for maintaining cognitive function not only in the elderly but also in young people. Malocclusion is an occlusal disharmony that commonly occurs in children. The connection between a decline in cognitive function and malocclusion in children has been shown with chronic mouth breathing, obstructive sleep apnea syndrome, and thumb/digit sucking habits. However, the mechanism of malocclusion-induced cognitive decline is not fully understood. We recently reported an association between feeding-related neuropeptides and cognitive decline in adolescent mice with activity-based anorexia. The aim of the present study was to assess the effects of malocclusion on cognitive behavior and clarify the connection between cognitive decline and hypothalamic feeding-related neuropeptides in adolescent mice with malocclusion. Methods: Four-week-old mice were randomly assigned to the sham-operated solid diet-fed (Sham/solid), sham-operated powder diet-fed (Sham/powder), or malocclusion-operated powder diet-fed (Malocclusion/powder) group. We applied composite resin to the mandibular anterior teeth to simulate malocclusion. We evaluated cognitive behavior using a novel object recognition (NOR) test, measured hypothalamic feeding-related neuropeptide mRNA expression levels, and enumerated c-Fos-positive cells in the hypothalamus 1 month after surgery. We also evaluated the effects of central antibody administration on cognitive behavior impairment in the NOR test. Results: The NOR indices were lower and the agouti-related peptide (AgRP) mRNA levels and number of c-Fos-positive cells were higher in the malocclusion/powder group than in the other groups. The c-Fos-positive cells were also AgRP-positive. We observed that the central administration of anti-AgRP antibody significantly increased the NOR indices. Discussion: The present study suggests that elevated cerebral AgRP signaling contributes to malocclusion-induced cognitive decline in adolescents, and the suppression of AgRP signaling can be a new therapeutic target against cognitive decline in occlusal disharmony.

Evaluation of maxillary central incisors on the noncleft and cleft sides in patients with unilateral cleft lip and palate-Part 1: Relationship between root length and orthodontic tooth movement.

OBJECTIVES: To measure the root lengths of maxillary central incisors (U1) and evaluate the relationship among U1 root length, tooth movement, and type of treatment appliance in patients with unilateral cleft lip and palate over a long-term follow-up period. MATERIALS AND METHODS: Occlusal radiographs of 30 patients with unilateral cleft lip and palate, acquired less than 6 months before secondary alveolar bone grafting (SBG, T1) and after edgewise treatment (T2), were measured for U1 root length (R1 and R2, root lengths at T1 and T2, respectively). Frontal and lateral cephalometric radiographs acquired at eruption of U1 (T0), T1, and T2 were evaluated to determine the inclination and position of U1. RESULTS: The average values of R1 and R2 on the cleft side were significantly lower than those on the noncleft side. Frontal cephalometric analysis revealed that the horizontal distance of the root apex from the median vertical line at T0 on the cleft side was significantly smaller than that on the noncleft side and was correlated with short U1 root length on the cleft side. On the other hand, R1 in patients treated with maxillary protraction appliances between T0 and T1 was significantly shorter than that in patients without maxillary protraction appliances. However, none of the changes in cephalometric measurements were correlated with root length. CONCLUSIONS: In patients with unilateral cleft lip and palate, the short root length of cleft-adjacent central incisors might be associated with the horizontal position of the root apex. In addition, orthodontic treatment with a maxillary protraction appliance before secondary alveolar bone grafting might be associated with short U1 root length.

Evaluation of maxillary central incisors on the noncleft and cleft sides in patients with unilateral cleft lip and palate-Part 2: Relationship between root resorption, horizontal tooth movement, and quantity of grafted autogenous bone.

OBJECTIVE: To evaluate the relationship between external apical root resorption (EARR) of the maxillary central incisors (U1), horizontal orthodontic tooth movement, and quantity of grafted bone in subjects with unilateral cleft lip and palate (UCLP) over an average duration of 8 years. MATERIALS AND METHODS: Thirty subjects with UCLP were evaluated for EARR of U1 after edgewise treatment (T2). The teeth were classified as having no EARR, moderate EARR (combined into "no/moderate" EARR), or severe EARR. Frontal cephalometric radiographs acquired at eruption of U1 (T0), less than 6 months before secondary alveolar bone grafting (T1), and T2 were evaluated to determine the horizontal inclination (U1-axis angle) and distance of the root apex from the median line (U1-root-VL distance). On the cleft side, the quantities of grafted bone at less than 12 months postsecondary bone grafting and at T2 were evaluated using the alveolar bone graft (ABG) scale. RESULTS: Cleft-adjacent teeth exhibited more severe EARR than did teeth on the noncleft side. The cleft side exhibited greater changes in U1-axis angle and U1-root-VL distance between T0 and T2 than did the noncleft side. On the cleft side, the ABG score at T2 in the severe EARR group was significantly lower than that in the no/moderate EARR group. These measurements were correlated with EARR grade. CONCLUSIONS: Cleft-adjacent U1 exhibited more severe EARR than did the U1 on the noncleft side, which might be associated with orthodontic treatment-induced changes in horizontal inclination and root apex movement. On the cleft side, severity of EARR may be correlated with the success of ABG.