Reduced Orthodontic Tooth Movement in Enpp1 Mutant Mice with Hypercementosis

Abstract

Previous studies revealed that cementum formation is tightly regulated by inorganic pyrophosphate (PP), a mineralization inhibitor. Local PP concentrations are determined by regulators, including ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which increases PP concentrations by adenosine triphosphate hydrolysis. Orthodontic forces stimulate alveolar bone remodelling, leading to orthodontic tooth movement (OTM). To better understand how disturbed mineral metabolism and the resulting altered periodontal structures affect OTM, we employed Enpp1 mutant mice that feature reduced PP and increased cervical cementum in a model of OTM induced by a stretched closed-coil spring ligated between the maxillary left first molar and maxillary incisors. We analyzed tooth movement, osteoclast/odontoclast response, and tooth root resorption by micro-computed tomography, histology, histomorphometry, and immunohistochemistry. Preoperatively, we noted an altered periodontium in Enpp1 mutant mice, with significantly increased periodontal ligament (PDL) volume and thickness, as well as increased PDL-bone/tooth root surface area, compared to wild-type (WT) controls. After 11 d of orthodontic treatment, Enpp1 mutant mice displayed 38% reduced tooth movement versus WT mice. Molar roots in Enpp1 mutant mice exhibited less change in PDL width in compression and tension zones compared to WT mice. Root resorption was noted in both groups with no difference in average depths, but resorption lacunae in Enpp1 mutant mice were almost entirely limited to cementum, with 150% increased cementum resorption and 92% decreased dentin resorption. Osteoclast/odontoclast cells were reduced by 64% in Enpp1 mutant mice, with a predominance of tartrate-resistant acid phosphatase (TRAP)-positive cells on root surfaces, compared to WT mice. Increased numbers of TRAP-positive cells on root surfaces were associated with robust immunolocalization of osteopontin (OPN) and receptor-activator of NF-κB ligand (RANKL). Collectively, reduced response to orthodontic forces, decreased tooth movement, and altered osteoclast/odontoclast distribution suggests Enpp1 loss of function has direct effects on clastic function/recruitment and/or indirect effects on periodontal remodeling via altered periodontal structure or tissue mineralization.

Automated tooth segmentation as an innovative tool to assess 3D-tooth movement and root resorption in rodents

“…For the application part, i.e. aim (iii), μCT scans from a previously described and published animal experiment analyzing the effect of orthodontic tooth movement in mice were used [ 24 ]. For that purpose, a nickel titanium spring was attached between the left upper first molar and the incisor, and molar protraction was conducted at 0.5 N for 11 days (Fig.…”

Current Trends in In Vitro Modeling to Mimic Cellular Crosstalk in Periodontal Tissue

“…[39][40][41][42] Periodontal ligament fibroblasts (PDLFs), PDLSCs, and cementoblasts have been investigated in in vitro and in vivo models focusing on the secretion of cytokines and growth factors turnover during remodeling and regeneration. [10,43] All of these modifications inevitably activate mechanotransduction signals that advance the internal signal propagation cascades and gene transcription. In fact, the periodontium is a highly mechanoresponsive tissue, with canonical Wnt pathway as a main actor of the process.…”

Guidelines for Micro–Computed Tomography Analysis of Rodent Dentoalveolar Tissues

“…These also have their own capabilities and limitations that dictate to some degree the ease and efficiency of analysis. All analyses and images included in this report were accomplished using Scanco proprietary software for scan reconstructions (default settings) and AnalyzePro 1.0 medical imaging software (Analyze Direct, Overland Park, KS), a software system used in our studies (23,(44)(45)(46)(47)(48)(49).…”

“…With this separation, Enpp1 -/mice exhibited a 500% increase in acellular cementum volume, whereas cellular cementum increased ~50%, compared to controls. We further evaluated the PDL space for alterations as a result of cementum expansion (47). PDL was segmented using a combination of semi-automated and manual functions (see Fig.…”