The effect of overexpression of Lrp5 on orthodontic tooth movement.

OBJECTIVE: To analyse the effect of gain-of-function mutations in the low-density lipoprotein receptor-related protein 5 (Lrp5) on orthodontic tooth movement (OTM). SETTING AND SAMPLE POPULATION: A split-mouth study design was utilized. Thirty-two male Lrp5-high bone mass (HBM) knock-in mice including A214V and G171V mutants (n = 16/group) and sixteen C57BL/6 wild-type (WT) mice were included in the study. MATERIALS AND METHODS: A mouse model of OTM was used for mesial movement of the maxillary first molar using a closed-coil nickel titanium (NiTi) spring attached between the molar and the incisors. After 21 days, the dissected maxillae were scanned for micro-computed tomography (micro-CT) analyses and embedded in methyl methacrylate and paraffin for histological staining and imaging. Histological analyses included immunohistochemistry for sclerostin (Sost), tartrate-resistant acid phosphatase (TRAP) staining for osteoclasts and fluorescent imaging. RESULTS: OTM in the A214V and G171V groups was significantly less than the WT group. Bone volume (BV), per cent bone volume (BV/TV) and trabecular thickness (Tb.Th) were significantly increased in both A241V and G171V animals compared to the WT animals. On the compression side, decreased osteoclast activity was seen in both A214V and G171V groups compared to the WT group. Fluorescent labelling demonstrated that the pattern of bone deposition in the A214V animals was periosteal whereas the G171V animals added bone endocortically. CONCLUSION: Gain-of-function mutations of Lrp5 decrease orthodontic tooth movement by increasing alveolar bone mass and reducing osteoclast-mediated bone resorption.

Maxillary expansion in an animal model with light, continuous force.

OBJECTIVES: Maxillary constriction is routinely addressed with rapid maxillary expansion (RME). However, the heavy forces delivered by most RME appliances to expand the palate may lead to deleterious effects on the teeth and supporting tissues. The objective of this study was to explore a more physiologic maxillary expansion with light continuous force. MATERIALS AND METHODS: Twenty 6-week-old Sprague-Dawley rats were equally divided into experimental (EXPT) and control (CTRL) groups. A custom-fabricated archwire expansion appliance made from 0.014-inch copper-nickel-titanium wire was activated 5 mm and bonded to the maxillary molar segments of animals in the EXPT group for 21 days. The force applied to each maxillary segment was 5 cN. Microfocus x-ray computed tomography and histological analyses were used to compare the tooth movement and bone morphology in the midpalatal suture and buccal aspect of the alveolar process between the EXPT and CTRL groups. Descriptive statistics (mean ± standard error of the mean) and nonparametric statistical tests were used to compare the outcomes across groups. RESULTS: Compared to the CTRL group, there was a statistically significant increase in buccal tooth movement and expansion of the midpalatal suture in the EXPT group. There was no difference in the bone morphologic parameters between groups. The mineral apposition rate was increased on the buccal surface of the alveolar process in the EXPT group. CONCLUSIONS: Application of light, continuous force resulted in maxillary osseous expansion due to bilateral sutural apposition and buccal drift of the alveolar processes. This animal experiment provides a more physiologic basis for maxillary expansion.