Achint Utreja

Increased mandibular condylar growth in mice with estrogen receptor beta deficiency.

Temporomandibular joint (TMJ) disorders predominantly afflict women of childbearing age, suggesting a role for female hormones in the disease process. In long bones, estrogen acting via estrogen receptor beta (ERβ) inhibits axial skeletal growth in female mice. However, the role of ERβ in the mandibular condyle is largely unknown. We hypothesize that female ERβ‐deficient mice will have increased mandibular condylar growth compared to wild‐type (WT) female mice. This study examined female 7‐day‐old, 49‐day‐old, and 120‐day‐old WT and ERβ knockout (KO) mice. There was a significant increase in mandibular condylar cartilage thickness as a result of an increased number of cells, in the 49‐day‐old and 120‐day‐old female ERβ KO compared with WT controls. Analysis in 49‐day‐old female ERβ KO mice revealed a significant increase in collagen type X, parathyroid hormone–related protein (Pthrp), and osteoprotegerin gene expression and a significant decrease in receptor activator for nuclear factor κ B ligand (Rankl) and Indian hedgehog (Ihh) gene expression, compared with WT controls. Subchondral bone analysis revealed a significant increase in total condylar volume and a decrease in the number of osteoclasts in the 49‐day‐old ERβ KO compared with WT female mice. There was no difference in cell proliferation in condylar cartilage between the genotypes. However, there were differences in the expression of proteins that regulate the cell cycle; we found a decrease in the expression of Tieg1 and p57 in the mandibular condylar cartilage from ERβ KO mice compared with WT mice. Taken together, our results suggest that ERβ deficiency increases condylar growth in female mice by inhibiting the turnover of fibrocartilage.

Murine TMJ Loading Causes Increased Proliferation and Chondrocyte Maturation

The purpose of this study was to examine the effects of forced mouth opening on murine mandibular condylar head remodeling. We hypothesized that forced mouth opening would cause an anabolic response in the mandibular condylar cartilage. Six-week-old female C57BL/6 mice were divided into 3 groups: (1) control, (2) 0.25 N, and (3) 0.50 N of forced mouth opening. Gene expression, micro-CT, and proliferation were analyzed. 0.5 N of forced mouth opening caused a significant increase in mRNA expression of Pthrp, Sox9, and Collagen2a1, a significant increase in proliferation, and a significant increase in trabecular spacing in the subchondral bone, whereas 0.25 N of forced mouth opening did not cause any significant changes in any of the parameters examined. Forced mouth opening causes an increase in the expression of chondrocyte maturation markers and an increase in subchondral trabecular spacing.

Effect of cyclical forces on the periodontal ligament and alveolar bone remodeling during orthodontic tooth movement

OBJECTIVE To investigate the effect of externally applied cyclical (vibratory) forces on the rate of tooth movement, the structural integrity of the periodontal ligament, and alveolar bone remodeling. METHODS Twenty-six female Sprague-Dawley rats (7 weeks old) were divided into four groups: CTRL (unloaded), VBO (molars receiving a vibratory stimulus only), TMO (molars receiving an orthodontic spring only), and TMO+VB (molars receiving an orthodontic spring and the additional vibratory stimulus). In TMO and TMO+VB groups, the rat first molars were moved mesially for 2 weeks using Nickel-Titanium coil spring delivering 25 g of force. In VBO and TMO+VB groups, cyclical forces at 0.4 N and 30 Hz were applied occlusally twice a week for 10 minutes. Microfocus X-ray computed tomography analysis and tooth movement measurements were performed on the dissected rat maxillae. Tartrate-resistant acid phosphatase staining and collagen fiber assessment were performed on histological sections. RESULTS Cyclical forces significantly inhibited the amount of tooth movement. Histological analysis showed marked disorganization of the collagen fibril structure of the periodontal ligament during tooth movement. Tooth movement caused a significant increase in osteoclast parameters on the compression side of alveolar bone and a significant decrease in bone volume fraction in the molar region compared to controls. CONCLUSIONS Tooth movement was significantly inhibited by application of cyclical forces.

Effect of corticision and different force magnitudes on orthodontic tooth movement in a rat model

INTRODUCTION The aims of this study were to evaluate the effect of 2 distinct magnitudes of applied force with and without corticision (flapless corticotomy) on the rate of tooth movement and to examine the alveolar response in a rat model. METHODS A total of 44 male rats (6 weeks old) were equally divided into 4 experimental groups based on force level and surgical intervention: light force, light force with corticision, heavy force, and heavy force with corticision. The forces were delivered from the maxillary left first molar to the maxillary incisors using prefabricated 10-g (light force) or 100-g (heavy force) nickel-titanium springs. The corticision procedure was performed at appliance placement and repeated 1 week later on the mesiopalatal aspect of the maxillary left first molars, with the right sides serving as the untreated controls. Microcomputed tomography was used to evaluate tooth movement between the maxillary first and second molars, and the alveolar response in the region of the maxillary first molar on day 14. Osteoclasts and odontoclasts were quantified, and the expression of receptor activator of nuclear factor kappa ß ligand was examined. RESULTS Intragroup comparisons of bone volume fraction (BVF) and tissue density were found to be significantly less on the loaded sides, with the exception of BVF in the light force group. Intergroup comparisons evaluating magnitude of tooth movement, BVF, apparent density, and tissue density showed no significant differences. Histomorphometric analysis indicated that BVF was decreased in the light force group. No significant differences in the total numbers of osteoclasts and odontoclasts and the expression of receptor activator of nuclear factor kappa ß ligand were found between the groups. CONCLUSIONS No differences in tooth movement or alveolar response were observed with microcomputed tomography based on force level or corticision procedure. A flapless surgical insult in the mesiopalatal aspect of the first molar with a single-site corticision was unable to induce clinical or histologic changes after 2 weeks of orthodontic tooth movement regardless of the force magnitude. Histologic analysis of the furcation area showed that light force significantly decreased BVF.

Orthodontic tooth movement causes decreased promoter expression of collagen type 1, bone sialoprotein and alpha-smooth muscle actin in the periodontal ligament.

OBJECTIVE To evaluate the effects of orthodontic tooth movement on the promoter expression of collagen type 1 (3.6Col1), bone sialoprotein (BSP) and alpha-smooth muscle actin (αSMA) in the periodontal ligament (PDL) using transgenic mice containing transgenes of these promoters fused to green fluorescent proteins (GFP). MATERIALS AND METHODS The maxillary first molars of 10-12 week-old transgenic mice were loaded with 10-12 g of force for 12, 48 h, or 7 days. Mice were transgenic for one of the following GFP-tagged bone markers of osteoblast lineage cells: 3.6-kb fragment of the rat collagen type 1 promoter (3.6Col1), BSP or α-smooth muscle actin (αSMA). Loaded molars under compression and tension were compared with contra-lateral unloaded controls. RESULTS On the compression side of the PDL, orthodontic tooth movement caused a significant decrease in GFP expression of all the promoters at each time point. On the tension side, there was a significant increase in BSP-GFP expression, 12 h following loading compared to the contralateral unloaded controls. CONCLUSIONS An in vivo tooth movement model using transgenic mice with promoter-GFP constructs provides an efficient and effective way of investigating the cellular events underlying orthodontic tooth movement. PDL cells may undergo decreased differentiation in response to the compressive force.

Marfan Syndrome—An Orthodontic Perspective

Marfan syndrome is a heritable disorder of connective tissue that can affect the heart, blood vessels, lungs, eyes, bones, and ligaments. It is characterized by tall stature, elongated extremities, scoliosis, and a protruded or caved-in breastbone. Patients typically have a long, narrow face. A high-arched palate produced by a narrow maxilla and skeletal Class II malocclusion due to mandibular retrognathia are other common features. For a patient with no family history of the disorder, at least three body systems must be affected before a diagnosis can be made. Individuals affected by the syndrome routinely seek orthodontic treatment to correct the orofacial manifestations. In this report, the authors present the records of three patients with Marfan syndrome who were treated at a dental school. Two patients had severe periodontal disease in the absence of significant contributing local factors. The presentation of systemic symptoms and typical physical characteristics varied. The syndrome thus went unnoticed in one patient for many years. We discuss here the observed intraoral findings and the progress of orthodontic treatment to provide a brief overview of the challenges involved in treating such patients.

A prospective comparative study between differential moments and miniscrews in anchorage control

The purpose of this study was to measure the efficacy of anchorage control between differential moments mechanics and temporary anchorage devices in a clinical trial. Forty-six patients requiring extraction of maxillary first premolars were allocated into 2 treatment groups. The differential moments group (G1) received a nickel titanium (NiTi) intrusion arch and a 150g NiTi closing coil spring for separate canine retraction, followed by a continuous mushroom loop archwire for the retraction of the incisors. The TAD group (G2) received one miniscrew placed between maxillary second premolars and first molars with a 150 g NiTi closing coil spring connecting the miniscrew to a hook placed in the archwire between the lateral incisor and canine. Lateral cephalograms were taken before (T1) and after incisor retraction (T2). The ratio of molar protraction to incisor retraction was calculated and intragroup and intergroup changes in upper lip, maxillary incisor and molar position were analyzed by paired and independent t-tests. Twenty-eight patients were analyzed after 18 patients did not receive the intervention, were lost to follow-up, or discontinued treatment. The ratio of molar protraction to incisor retraction in G1 was 0.44 and in G2 was -0.11, which was significantly different. There was a statistically significant change in upper lip from T1 to T2 but no difference between the two groups. Moreover, there was a significant distal molar tipping and lingual incisor tipping in G2. There is a significant difference in the amount of anchorage control using differential moments mechanics compared to TADs. Although statistically significant retraction of upper lip was observed in both groups, there was no significant difference between the two groups.

Isolation and characterization of murine mandibular condylar cartilage cell populations.

Objectives: The mandibular condylar cartilage is a heterogeneous tissue containing cells at various stages of chondrocyte maturation organized into 4 zones: superficial, polymorphic, flattened, and hypertrophic. The goal of this study was to use transgenic mice containing chondrocyte maturation markers fused to fluorescent protein transgenes to isolate and characterize homogenous cell populations of the mandibular condylar cartilage. Methods: Fluorescent reporter expression in the mandibular condylar cartilage of transgenic mice containing the 3.6-kb fragment of the rat collagen type 1 promoter fused to a topaz-fluorescent protein (Col3.6-tpz), collagen type 2 promoter fused to a cyan-fluorescent protein (Col2-cyan), and/or collagen type 10 promoter fused to cherry-fluorescent protein (Col10-cherry) was examined. Mandibular condylar cartilage cells were analyzed by fluorescence-activated cell sorting (FACS) and either used for gene expression analysis or plated in cell cultures and exposed to adipogenic, osteogenic, or chondrogenic conditions. To determine cell fate, transgenic mice containing the Col3.6-cre recombinase were bred with cre reporter mice. Results: Localization and analysis of gene expression revealed that Col3.6-tpz-positive cells corresponded to the polymorphic/flattened zones and Col2-cyan-positive cells corresponded to the flattened/hypertrophic zones of the mandibular condylar cartilage. Mandibular condylar cartilage FACS-sorted Col3.6-tpz-positive cells have the potential to differentiate into bone, cartilage, and fat. Cell fate mapping revealed that Col3.6 cells are precursors of some of the hypertrophic chondrocytes in the mandibular condylar cartilage. Conclusion: Col3.6-tpz cells represent an earlier stage of the mandibular condylar cartilage maturation pathway.

Osteocyte death during orthodontic tooth movement in mice

OBJECTIVE To investigate the time course of osteocyte death in a mouse model of orthodontic tooth movement (OTM) and its association to the caspase-3 activation pathway and osteoclast formation. MATERIALS AND METHODS Twenty-five male wild type CD-1 mice (8-12 weeks old) were loaded with an orthodontic appliance. A spring delivering 10-12 g of force was placed between the right first molar and the incisor to displace the first molar mesially. The contralateral unloaded sides served as the control. The animals were equally divided into five different time points: 6, 12, 24, and 72 hours and 7 days of orthodontic loading. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, caspase-3 immunostaining, and tartrate-resistant acid phosphatase (TRAP) staining was performed on histologic sections of the first molars. The labeling was quantified in osteocytes on the compression side of the alveolar bone at each time point. RESULTS TUNEL labeling significantly increased at 12, 24, and 72 hours after orthodontic loading; the peak was observed at 24 hours. Elevated caspase-3 labeling was noted at 12, 24, and 72 hours and 7 days after loading, although the increase was not significant. Significant osteoclast formation was initially evident after 72 hours and progressively increased up to 7 days. CONCLUSIONS Osteocyte death during OTM peaks at 24 hours, earlier than initial osteoclast activation. However, only a slight trend for increased caspase-3 activity suggests that other mechanisms might be involved in osteocyte death during OTM.

Dental Anomalies Associated with Craniometaphyseal Dysplasia

Craniometaphyseal dysplasia (CMD) is a rare genetic disorder encompassing hyperostosis of craniofacial bones and metaphyseal widening of tubular bones. Dental abnormalities are features of CMD that have been little discussed in the literature. We performed dentofacial examination of patients with CMD and evaluated consequences of orthodontic movement in a mouse model carrying a CMD knock-in (KI) mutation (Phe377del) in the Ank gene. All patients have a history of delayed eruption of permanent teeth. Analysis of data obtained by cone-beam computed tomography showed significant bucco-lingual expansion of jawbones, more pronounced in mandibles than in maxillae. There was no measurable increase in bone density compared with that in unaffected individuals. Orthodontic cephalometric analysis showed that patients with CMD tend to have a short anterior cranial base, short upper facial height, and short maxillary length. Microcomputed tomography (micro-CT) analysis in homozygous AnkKI/KI mice, a model for CMD, showed that molars can be moved by orthodontic force without ankylosis, however, at a slower rate compared with those in wild-type Ank+/+ mice (p < .05). Histological analysis of molars in AnkKI/KI mice revealed decreased numbers of TRAP+ osteoclasts on the bone surface of pressure sides. Based on these findings, recommendations for the dental treatment of patients with CMD are provided.