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.

The Effect of Overexpression of Lrp5 on the Temporomandibular Joint.

OBJECTIVE: The temporomandibular joint (TMJ) is a unique fibrocartilaginous joint that adapts to mechanical loading through cell signaling pathways such as the Wnt pathway. Increased expression of low-density lipoprotein receptor-related protein 5 (Lrp5), a co-receptor of the Wnt pathway, is associated with a high bone mass (HBM) phenotype. The objective of this study was to analyze the effect of overexpression of Lrp5 on the subchondral bone and cartilage of the TMJ in mice exhibiting the HBM phenotype. DESIGN: Sixteen-week-old Lrp5 knock-in transgenic mice carrying either the A214V (EXP-A) or G171V (EXP-G) missense mutations, and wildtype controls (CTRL) were included in this study. Fluorescent bone labels, calcein, alizarin complexone, and demeclocycline were injected at 3.5, 7.5, and 11.5 weeks of age, respectively. The left mandibular condyle was used to compare the subchondral bone micro-computed tomography parameters and the right TMJ was used for histological analyses. Cartilage thickness, matrix proteoglycan accumulation, and immunohistochemical localization of Lrp5 and sclerostin were compared between the groups. RESULTS: Subchondral bone volume (BV) and percent bone volume (BV/TV) were significantly increased in both EXP-A and EXP-G compared with CTRL (P < 0.05) whereas trabecular spacing (Tb.Sp) was decreased. Cartilage thickness, extracellular matrix production, and expression of Lrp5 and Sost were all increased in the experimental groups. The separation between the fluorescent bone labels indicated increased endochondral maturation between 3.5 and 7.5 weeks. CONCLUSIONS: These data demonstrate that Lrp5 overexpression leads to adaptation changes in the mandibular condylar cartilage of the TMJ to prevent cartilage degradation.

Pyk2 deficiency enhances bone mass during midpalatal suture expansion.

OBJECTIVE: To determine if Pyk2 deficiency increases midpalatal suture bone mass and preserves sutural integrity after maxillary expansion. SETTING AND SAMPLE: Thirty-six male Pyk2 knockout (KO) and control (WT) mice at 6 weeks of age. MATERIALS AND METHODS: Mice received nickel-titanium spring expanders delivering 0 g (no intervention control), 10 or 20 g force for 14 days. High-resolution micro-CT was used to determine bone volume/tissue volume (BV/TV), sutural width and intermolar width. Effects on osteoclasts, chondrocytes and suture morphology were determined by histomorphometry. RESULTS: Pyk2-KO controls (0 g) had 7% higher BV/TV compared with WT controls. Expanded Pyk2-KO maxillae also exhibited 12% (10 g) and 18% (20 g) higher BV/TV than WT mice. Although bone loss following expansion occurred in both genotypes, BV/TV was decreased to a greater extent in WT maxillae (-10% at 10g; -22% at 20 g) compared with Pyk2-KO maxillae (-11% only at 20 g). Expanded WT maxillae also showed a greater increase in sutural width, intermolar width and fibrous connective tissue width compared with expanded Pyk2-KO maxillae. Moreover, osteoclast number was increased 77% (10 g) and 132% (20 g) in expanded WT maxillae, but remained unchanged in expanded Pyk2-KO, compared to their respective controls. Cartilage area and chondrocyte number were increased to the same extent in expanded WT and Pyk2-KO sutures. CONCLUSIONS: These findings suggest that midpalatal suture expansion increases osteoclast formation in WT but not Pyk2-KO mice, leading to higher BV/TV in expanded Pyk2-KO maxillae. These studies suggest Pyk2-targeted strategies may be beneficial to increase bone density and preserve sutural integrity during maxillary expansion.

Osteoblast differentiation during orthodontic tooth movement.

OBJECTIVES: To analyse the expression of osteoblast differentiation markers and osteoclast activity in the periodontal ligament (PDL) following 2, 4 and 7 days of orthodontic tooth movement (OTM) in an animal model. SETTING AND SAMPLE POPULATION: Eighteen C57BL/6 wild-type mice. MATERIAL AND METHODS: For the OTM model, orthodontic force was applied to the maxillary right first molar using a closed-coil NiTi spring activated between the molar and incisors. The left side served as the control. Following OTM, the dissected tissues were scanned for micro-computed tomography (micro-CT) analysis and processed for histology. Histological stains included tartrate-resistant acid phosphatase (TRAP) staining for osteoclasts and immunohistochemistry for osteoblast markers alpha-smooth muscle actin (α-SMA), osteopontin (OP) and osteocalcin (OC). RESULTS: Micro-CT analysis showed increasing OTM on days 2, 4 and 7 days as well as decrease in bone volume and per cent bone volume at 4 and 7 days. Statistically significant increases in osteoblast marker expression were seen in all groups when compared to the control. TRAP expression was highest at 4 and 7 days, α-SMA was highest at 2 days and OP/OC was highest at 4 days. CONCLUSION: During OTM, proliferation of pre-osteoblasts peaks at 2 days while mineralization of the osteoid peaks at 4 days. The osteoclast response is delayed.

Precision of the virtual occlusal record.

OBJECTIVES: To evaluate the precision of the virtual occlusal record using the Carestream CS3600 Intraoral Scanner (Carestream Dental, Atlanta, Ga). MATERIALS AND METHODS: A total of 20 participants were recruited for this prospective study using preestablished inclusion/exclusion criteria. A complete intraoral scan and two bite registrations were obtained. The participants were instructed to bite with normal pressure when bite registrations were acquired. Contact locations, size (circumference), and intensity were identified on the maxillary first molars and canines. Agreement between contact size and intensity was assessed with intraclass correlation coefficients. Kappa statistics evaluated agreement in contact locations. Statistical significance was set at P < .05. RESULTS: All participant data were included for statistical analysis. Between the two bite registrations, nonstatistically significant differences were observed in the proportion of locations with contacts (P = .7681). A nonstatistically significant difference (-0.25 mm, P = .8416) in mean contact circumference size was observed. A statistically significant difference in mean contact intensity was observed (P = .0448). When evaluating agreement between the bite registrations, a weak correlation for size (intraclass correlation coefficient = 0.35) and intensity (intraclass correlation coefficient = 0.32) was observed as well as a moderate agreement for contact location (κ coefficient = 0.67). CONCLUSIONS: The findings suggest that the Carestream intraoral scanner software possesses adequate precision when acquiring the location and size of the contacts in bite registrations. The scanner failed to demonstrate adequate precision when acquiring contact intensities in bite registrations. Additional research is warranted to further investigate the precision of virtual occlusal records with currently available software systems.

Dose analysis of photobiomodulation therapy on osteoblast, osteoclast, and osteocyte.

The objective of this study was to evaluate the effects of varying light doses on the viability and cellular activity of osteoblasts, osteocytes, and osteoclasts. A light application device was developed to apply 940-nm wavelength light from light-emitting diodes on three cultured cells, MC3T3-E1, MLO-A5, and RANKL-treated RAW264.7 cells. The doses (energy density) on cells were 0, 1, 5, and 7.5 J / cm2. The corresponding light power densities at the cell site were 0, 1.67, 8.33, and 12.5 mW / cm2, respectively, and the duration was 10 min. The results showed that the three cell types respond differently to light and their responses were dose dependent. Low-dose treatment (1 J / cm2) enhanced osteoblast proliferation, osteoclast differentiation, and osteoclastic bone resorption activity. Osteocyte proliferation was not affected by both low- and high-dose (5 J / cm2) treatments. While 1 J / cm2 did not affect viability of all three cell types, 5 J / cm2 significantly decreased viability of osteocytes and osteoclasts. Osteoblast viability was negatively impacted by the higher dose (7.5 J / cm2). The findings suggest that optimal doses exist for osteoblast and osteoclast, which can stimulate cell activities, and there is a safe dose range for each type of cell tested.

Low-Magnitude Forces for Bone Modeling and Remodeling in Dentofacial Orthopedics.

PURPOSE OF REVIEW: To examine the evidence in support of light continuous forces for enhancing bone adaptation (modeling and remodeling) in orthodontics and dentofacial orthopedics. RECENT FINDINGS: Clinical evidence suggests that light continuous orthodontic force can achieve physiologic expansion of the maxillary arch, but the long-term stability and the biological effects of the procedure are unclear. Compared to conventional orthodontic appliances that deliver heavy interrupted forces for tooth movement, the application of low-magnitude forces in animal models leads to anabolic modeling and remodeling of the alveolar bone in the path of orthodontic tooth movement. This results in dental translation and expansion of the alveolar process. Light continuous forces are preferable to heavy forces for more physiologic dentofacial orthopedics. The interaction of low-magnitude loads with soft tissue posture achieves therapeutic adaptation of the craniofacial skeleton. The increasing emphasis on genomic medicine and personalized treatment planning should focus on low-magnitude loads in orthodontics and dentofacial orthopedics.

Accuracy of three-dimensional dental resin models created by fused deposition modeling, stereolithography, and Polyjet prototype technologies: A comparative study.

OBJECTIVES: The aim of this study was to assess the dimensional accuracy of fused deposition modeling (FDM)-, Polyjet-, and stereolithography (SLA)-produced models by comparing them to traditional plaster casts. MATERIALS AND METHODS: A total of 12 maxillary and mandibular posttreatment orthodontic plaster casts were selected from the archives of the Orthodontic Department at the Indiana University School of Dentistry. Plaster models were scanned, saved as stereolithography files, and printed as physical models using three different three-dimensional (3D) printers: Makerbot Replicator (FDM), 3D Systems SLA 6000 (SLA), and Objet Eden500V (Polyjet). A digital caliper was used to obtain measurements on the original plaster models as well as on the printed resin models. RESULTS: Comparison between the 3D printed models and the plaster casts showed no statistically significant differences in most of the parameters. However, FDM was significantly higher on average than were plaster casts in maxillary left mixed plane (MxL-MP) and mandibular intermolar width (Md-IMW). Polyjet was significantly higher on average than were plaster casts in maxillary intercanine width (Mx-ICW), mandibular intercanine width (Md-ICW), and mandibular left mixed plane (MdL-MP). Polyjet was significantly lower on average than were plaster casts in maxillary right vertical plane (MxR-vertical), maxillary left vertical plane (MxL-vertical), mandibular right anteroposterior plane (MdR-AP), mandibular right vertical plane (MdR-vertical), and mandibular left vertical plane (MdL-vertical). SLA was significantly higher on average than were plaster casts in MxL-MP, Md-ICW, and overbite. SLA was significantly lower on average than were plaster casts in MdR-vertical and MdL-vertical. CONCLUSIONS: Dental models reconstructed by FDM technology had the fewest dimensional measurement differences compared to plaster models.

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.

Two-dimensional vs 3-dimensional comparison of alveolar bone over maxillary incisors with A-point as a reference.

INTRODUCTION: Our objectives were to compare, relative to A-point, (1) bone thickness over the most forward maxillary incisor (MFMI) in 2 dimensions vs 3 dimensions, and (2) bone thickness and inclination of each maxillary incisor in 3 dimensions. METHODS: Thirty-four cone-beam computed tomography (CBCT) images were coded, and 2-dimensional (2D) cephalograms were derived from each image using Dolphin software (Dolphin Imaging and Management Solutions, Chatsworth, Calif). A-point and the MFMI crown were located. After reliability tests, alveolar bone buccal to 3 points on the MFMI root, bone to reference line Frankfort horizontal (FH)-A-point, and incisor inclination were measured. This procedure was repeated on the 3-dimensional (3D) CBCT images comparing MFMI with all maxillary incisors. The 2D and 3D measurements were compared using paired t tests, and 3D measurements were compared with analysis of variance. A 5% significance level was used for all tests. RESULTS: The MFMI's buccal bone thickness at the root apices and the distance between buccal bone and FH-A-point line at 2 root points were significantly greater in 2 dimensions than in 3 dimensions. In 3 dimensions, bone thickness at MFMI's root apex and the distance from FH-A-point line at all root points were significantly greater than those of the lateral incisors. Bone buccal to MFMI was significantly smaller than at the lateral incisors 3 mm from the cementoenamel junction. CONCLUSIONS: Evaluation of 2D CBCT derivations can result in overestimation of alveolar bone buccal to the maxillary incisor root apices compared with 3D evaluations. The anterior nasal spine obscures bone measurements over the maxillary incisors in 2 dimensions.

Three-dimensional evaluation of molar buccolingual inclinations after orthodontic treatment using edgewise mechanics.

OBJECTIVES: The purpose of this study was to measure changes in buccolingual inclination and in thickness of maxillary and mandibular buccal and lingual bone of maxillary and mandibular molars following orthodontic treatment using edgewise mechanics. MATERIALS AND METHODS: Cone-beam computed tomography scans of 48 patients taken before and after completion of comprehensive orthodontic treatment were collected for this retrospective study. Buccolingual molar inclinations were reported as angular measurements using the long axis of the teeth and inferior border of the nasal floor and inferior border of the mandible, respectively. Distances between the buccal and lingual cusps of maxillary and mandibular molars, respectively, were measured to the occlusal plane to assess the change in buccolingual inclination after orthodontic treatment. The amount of buccal and lingual bone at the level of the root apex of each molar was also evaluated before and after orthodontic treatment. RESULTS AND CONCLUSION: Orthodontic edgewise mechanics caused significant increases in mandibular first molars' inclination angle, lingual bone, and mandibular second molars' buccal bone and inclination angle. Significant decreases were noted in mandibular first molars' buccal bone, inclination distance and mandibular second molars' lingual bone and inclination distance. Maxillary teeth had fewer significant changes than the mandibular teeth. Significant decreases were found for maxillary first molars' buccal bone, inclination distance, and maxillary second molar buccal bone.

Three-dimensional evaluation of root dimensions and alveolar ridge width of maxillary lateral incisors in patients with unilateral agenesis.

BACKGROUND: The objective of this retrospective case-control study was to measure the maxillary lateral incisor root dimensions and quantify the labial and palatal bone in patients with unilateral maxillary lateral incisor agenesis (MLIA) after orthodontic treatment and compare them to non-agenesis controls using cone beam computed tomography. METHODS: The labiopalatal and mesiodistal root dimensions, mesiodistal coronal dimensions, and labiopalatal bone and alveolar ridge widths of the maxillary lateral incisor were assessed on posttreatment cone beam computed tomography scans of 15 patients (mean age 16.5 ± 3.4 years, 9 females and 6 males) with maxillary lateral incisor agenesis and 15 gender-matched patients (mean age 16.08 ± 3.23 years) with no dental agenesis or anterior Bolton discrepancy. The Mann-Whitney test was used to distinguish any differences in root width, crown width, or changes in labial or palatal bone width between the two groups. RESULTS: The median labiopalatal root width was narrower in the MLIA group at the level of the cementoenamel junction (CEJ) to 8 mm apical of the CEJ compared to controls (p ≤ 0.009). The mesiodistal root width was significantly reduced in the MLIA group at the CEJ and at 4 mm apical to the CEJ. The labiopalatal alveolar ridge width was significantly decreased at 2 mm apical to the CEJ in MLIA group. The mesiodistal crown width was significantly smaller in the MLIA group at both the incisal edge and at the crown midpoint. The bone thickness was similar in both groups. CONCLUSIONS: Coronal and root dimensions in patients with MLIA were reduced compared to controls. Alveolar ridge width was also reduced in patients with MLIA, although bone thickness was not different than controls.

The Effect of Altered Loading on Mandibular Condylar Cartilage.

OBJECTIVE: The purpose of this study was to delineate the cellular, mechanical and morphometric effects of altered loading on the mandibular condylar cartilage (MCC) and subchondral bone. We hypothesized that altered loading will induce differentiation of cells by accelerating the lineage progression of the MCC. MATERIALS AND METHODS: Four-week-old male Dkk3 XCol2A1XCol10A1 mice were randomly divided into two groups: (1) Loaded-Altered loading of MCC was induced by forced mouth opening using a custom-made spring; (2) Control-served as an unloaded group. Mice were euthanized and flow cytometery based cell analysis, micro-CT, gene expression analysis, histology and morphometric measurements were done to assess the response. RESULTS: Our flow cytometery data showed that altered loading resulted in a significant increase in a number of Col2a1-positive (blue) and Col10a1-positive (red) expressing cells. The gene expression analysis showed significant increase in expression of BMP2, Col10a1 and Sox 9 in the altered loading group. There was a significant increase in the bone volume fraction and trabecular thickness, but a decrease in the trabecular spacing of the subchondral bone with the altered loading. Morphometric measurements revealed increased mandibular length, increased condylar length and increased cartilage width with altered loading. Our histology showed increased mineralization/calcification of the MCC with 5 days of loading. An unexpected observation was an increase in expression of tartrate resistant acid phosphatase activity in the fibrocartilaginous region with loading. CONCLUSION: Altered loading leads to mineralization of fibrocartilage and drives the lineage towards differentiation/maturation.

The effect of corticision on root resorption with heavy and light forces.

OBJECTIVE: To investigate the association between corticision and different force magnitudes with the amount of root resorption. METHODS: Forty-four male Wistar rats (7 week old) were evaluated after an orthodontic spring delivering either 10 or 100 g was placed on the left maxillary first molars to move molars mesially. Experimental rats were divided into four groups, with 11 animals in each group: (1) LF, no corticision and 10 g of orthodontic force; (2) LFC, corticision and 10 g of force; (3) HF, no corticision and 100 g of force; and (4) HFC, corticision and 100 g of force. Contralateral sides were used as unloaded controls. The total duration of the experimental period was 14 days. Two-dimensional (histomorphometric) and three-dimensional (volumetric, micro-focus X-ray computed tomography [microCT]) analysis of root craters were performed on maxillary first molars. RESULTS: Histomorphometric and microCT analysis revealed a significant amount of resorptive areas in the experimental groups when compared to unloaded controls. However, no significant difference was detected in the amount of resorption among the four experimental groups. CONCLUSIONS: At day 14, neither the amount of force nor the cortical incision caused significant effect on root resorption that was registered by histomorphometric or microCT analysis.

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.

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.

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.

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.