A Novel Rat Model of Orthodontic Tooth Movement Using Temporary Skeletal Anchorage Devices: 3D Finite Element Analysis and In Vivo

The aim of this animal study was to develop a model of orthodontic tooth movement using a microimplant as a TSAD in rodents. A finite element model of the TSAD in alveolar bone was built using μCT images of rat maxilla to determine the von Mises stresses and displacement in the alveolar bone surrounding the TSAD. For in vivo validation of the FE model, Sprague-Dawley rats (n=25) were used and a Stryker 1.2 × 3 mm microimplant was inserted in the right maxilla and used to protract the right first permanent molar using a NiTi closed coil spring. Tooth movement measurements were taken at baseline, 4 and 8 weeks. At 8 weeks, animals were euthanized and tissues were analyzed by histology and EPMA. FE modeling showed maximum von Mises stress of 45 Mpa near the apex of TSAD but the average von Mises stress was under 25 Mpa. Appreciable tooth movement of 0.62 ± 0.04 mm at 4 weeks and 1.99 ± 0.14 mm at 8 weeks was obtained. Histological and EPMA results demonstrated no active bone remodeling around the TSAD at 8 weeks depicting good secondary stability. This study provided evidence that protracted tooth movement is achieved in small animals using TSADs

Computer-assisted detection of cemento-enamel junction in intraoral ultrasonographs

The cemento-enamel junction (CEJ) is an important reference point for various clinical measurements in oral health assessment. Identifying CEJ in ultrasound images is a challenging task for dentists. In this study, a computer-assisted detection method is proposed to identify the CEJ in ultrasound images, based on the curvature change of the junction outlining the upper edge of the enamel and cementum at the cementum–enamel intersection. The technique consists of image preprocessing steps for image enhancement, segmentation, and edge detection to locate the boundary of the enamel and cementum. The effects of the image preprocessing and the sizes of the bounding boxes enclosing the CEJ were studied. For validation, the algorithm was applied to 120 images acquired from human volunteers. The mean difference of the best performance between the proposed method and the two raters’ measurements was an average of 0.25 mm with reliability ≥ 0.98. The proposed method has the potential to assist dental professionals in CEJ identification on ultrasonographs to provide better patient care

"Inhibition of mineralization in bones and teeth following ectopic expression of matrix Gla protein"

Matrix Gla Protein (MGP) inhibits mineralization of arteries and cartilage. To determine its mineral-inhibiting potential in hard tissues, MGP was ectopically expressed in bones and teeth of mice using an osteoblast/odontoblast-specific 2.3kb proximal promoter for type 1 collagen. Mandibles and long bones of Col1a1-Mgp mice and wild-type littermates were analyzed by Faxitron(TM) radiography, PIXImus(TM) dual-energy x-ray absorptiometry (DEXA) and micro-computed tomography (mu-CT). In addition, light microscopy (LM) and transmission electron microscopy (TEM) were performed. While bone and tooth extracellular matrices (ECMs) appeared normally established in Col1a1-Mgp mice, examination of the mineral phase by radiography, DEXA and mu-CT, together with histological mineral localization by LM after von Kossa staining of undecalcified tissue sections, and by TEM, revealed massive hypomineralization of bone and tooth ECMs. In the skeleton of Col1a1-Mgp mice, alveolar bone of the mandible was most heavily affected (compared to long bones), showing a 50% increase in the unmineralized osteoid volume compared to wild-type littermates. For teeth, mineralization was virtually absent in root dentin of both incisors and molars, and absent in molar cellular cementum, whereas crown dentin showed localized "breakthrough" areas of mineralization. Acellular cementum formation and mineralization was absent in the Col1a1-Mgp mice. Immunohistochemical staining of bone and tooth ECM proteins in Col1a1-Mgp mice showed variations in staining relative to wild-type tissues, with immunostaining generally restricted to areas of mineralization. In conclusion, these results confirm in vivo that ECM proteins can act as inhibitors of bone and tooth mineralization

Comparison of ultrasound imaging and cone-beam computed tomography for examination of the alveolar bone level: A systematic review.

BACKGROUND AND OBJECTIVE:The current methods to image alveolar bone in humans include intraoral 2D radiography and cone-beam computed tomography (CBCT). However, these methods expose the subject to ionizing radiation. Therefore, ultrasound imaging has been investigated as an alternative technique, as it is both non-invasive and free from ionizing radiation. In order to assess the validity and reliability of ultrasonography in visualizing alveolar bone, a systematic review was conducted comparing ultrasound imaging to CBCT for examination of the alveolar bone level. STUDY DESIGN:Seven databases were searched. Studies addressing examination of alveolar bone level via CBCT and ultrasound were selected. Risk of bias under Cochrane guidelines was used as a methodological quality assessment tool. RESULTS:All the four included studies were ex vivo studies that used porcine or human cadaver samples. The alveolar bone level was measured by the distance from the alveolar bone crest to certain landmarks such as cemento-enamel junction or gingival margin. The risk of bias was found as low. The mean difference between ultrasound and CBCT measurements ranged from 0.07 mm to 0.68 mm, equivalent to 1.6% - 8.8%. CONCLUSIONS:There is currently preliminary evidence to support the use of ultrasonography as compared to CBCT for the examination of alveolar bone level. Further studies comparing ultrasound to gold standard methods would be necessary to help validate the accuracy of ultrasonography as a diagnostic technique in periodontal imaging