Early-stage periodontal ligament compression predicts orthodontically induced root resorption in rats.

OBJECTIVES: To determine the effect of orthodontic pressure on periodontal ligament (PDL) compression in rats and assess correlation between PDL compression and orthodontically induced root resorption (OIRR). MATERIALS AND METHODS: Eight female Wistar rats aged 10 weeks underwent surgery to place 2 mini-screws at the center of the palatal plate. 25 cN coil springs connecting the maxillary first molars and mini-screws were applied bilaterally to generate mesial force. Maxillary first molars were assigned to undergo either bodily or tipping movements. Micro-computed tomography (µCT) scans were taken on days 0, 3, 7, and 14, and histological sections were taken on day 14. OIRR was measured from histological sections, and the corresponding PDL compression ratio was quantified using µCT images. RESULTS: The PDL was compressed by approximately 76% in tipping movement and 55% in bodily movement after 3 days, and by approximately 47% in bodily and tipping movements after 7 days of orthodontic force application. The extent of OIRR in tipping movement was significantly greater than that in bodily movement. A strong positive correlation between OIRR and PDL compression ratio was observed on day 3; however, no correlation was observed on day 7. CONCLUSIONS: A strong correlation between PDL compression ratio and OIRR was observed at an early stage after the application of orthodontic force regardless of the tooth movement type (bodily or tipping), implying the importance of early stage PDL compression in the induction of OIRR.

Fixation of an orthodontic anchor screw using beta-tricalcium phosphate in a screw-loosening model in rats.

OBJECTIVES: To create an orthodontic anchor screw (OAS)-loosening model and to investigate whether filling the bone hole with beta-tricalcium phosphate (ß-TCP) can fix the OAS against orthodontic force. MATERIALS AND METHODS: Bone holes with different diameters (1.6, 2.1, or 2.5 mm) were drilled in the tibias of 11-week-old male Wistar rats, and an OAS (3.0 mm in length and 1.2 mm in diameter) was inserted. After a healing period of 2 or 4 weeks, orthodontic force was applied, and the diameter of the bone hole appropriate for the loosening model was determined. Subsequently, under the loosening model, the bone hole was filled with ß-TCP, orthodontic force was applied, and movement of the OAS and surrounding tissue changes were evaluated by micro-computed tomography images and histological specimen analysis. RESULTS: The bone hole of 1.6 mm in diameter was employed as the OAS-loosening model. When ß-TCP was inserted into the bone hole, the linear distance and mesial tipping angle of the OAS movement decreased markedly. Furthermore, the values of bone morphometry significantly increased with ß-TCP filling. CONCLUSIONS: An OAS-loosening model was established in rats and demonstrated that the loosening OAS was stabilized by ß-TCP filling through bone formation. ß-TCP may be useful for fixation of a loosening OAS.

Effect of masseter muscle mass on the rate of experimental tooth movement in rats.

BACKGROUND: Previous clinical observational studies have suggested that orthodontic tooth movement (OTM) is related, at least partly, to the mass and/or capabilities of the masticatory muscles. OBJECTIVES: Our study aimed to examine the influence of masticatory muscle mass on the OTM in an animal experimental model in which the masseter muscle was modulated by botulinum neurotoxin type A (BTX) injection. METHODS: Eighteen Wistar rats were equally divided into two groups: BTX injection and control. BTX was injected bilaterally into the masseter muscles. Three days after the injection, the maxillary left first molars were orthodontically moved for 14 days. At the end of the experiment, micro-computed tomography was performed to evaluate the rate of OTM and bone morphometry. The masseter muscles were weighed and prepared for histological analyses. RESULTS: The masseter muscle mass in the BTX group was less than that in the control group, and histological findings showed atrophy of muscle fibres. The rate of OTM was significantly higher in the BTX group than in the control group. Furthermore, a negative correlation was detected between masseter muscle mass and OTM in the BTX group. Bone morphometry showed no difference between the control and BTX groups. CONCLUSION: Decreased masseter muscle mass was found to be closely related to an increase in the rate of OTM in rats using BTX injection to modify the masseter muscle mass. Masseter muscle mass could be a predictive factor for OTM in rats injected with BTX.

Lithium reduces orthodontically induced root resorption by suppressing cell death, hyalinization, and odontoclast formation in rats.

OBJECTIVES: To examine whether lithium suppresses orthodontically induced root resorption (OIRR) via two mechanisms (prevention of hyalinization in periodontal tissue and suppression of odontoclasts) and to investigate the changes in the periodontal tissue and alveolar bone, focusing on the appearance of cell death, hyalinization, and odontoclasts. MATERIALS AND METHODS: The maxillary first molars of 10-week-old male Wistar rats were moved mesially by a closed-coil spring for 14 days. Lithium chloride (LiCl; 0.64 mM/kg) or saline (control) was administered intraperitoneally daily. Tooth movements were measured using micro-computed tomography. Appearances of cell death, hyalinization, and odontoclasts were evaluated by histological analysis. RESULTS: OIRR observed on day 14 in the control group was suppressed strongly by LiCl administration. Apoptotic cells observed on day 1 in the compression area were gradually diminished on days 2 and 3 and transformed to hyalinization tissue in the control group. LiCl administration remarkably suppressed this cell death and subsequent hyalinization. Also, the appearance of odontoclasts in the compression area observed on day 7 was significantly suppressed by LiCl administration. Accordingly, these degenerative processes to OIRR were suppressed substantially by LiCl treatment. CONCLUSIONS: Lithium reduces OIRR through the suppression of periodontal ligament cell death, hyalinization, and odontoclast formation.

A case of periosteal fasciitis located in the mandible in a child.

Periosteal fasciitis (PF), a subtype of nodular fasciitis, is an uncommon benign soft-tissue mass that originates from the periosteum or tissues adjacent to bones. PF has rarely seen in children, especially involving in the mandible. This case report presents a rare case of PF originating from the periosteum of the mandible in an 11-year-old girl. She was referred to our hospital with fast-growing painless swelling in her left mandible. Computed tomography revealed an exophytic juxtacortical mass eroding the lower part of the left mandible and lower mandibular cortex with a periosteal reaction. The mass showed low signal intensity on T1-weighted magnetic resonance imaging (MRI) and high signal intensity on T2-weighted MRI. The apparent diffusion coefficient (ADC) of the lesion found to be moderate. Dynamic contrast-enhanced MRI revealed a gradual increment pattern in the central region of the mass. On 18F-fluorodeoxyglucose (FDG) positron-emission tomography/computed tomography (PET/CT), relatively high 18F-FDG uptake was observed on the early scan and the 18F-FDG uptake was declined on the delayed scan. The clinical and conventional radiological findings of the mass were suggestive of malignancy. However, the findings of ADC and dynamic MRI and dual-time-point FDG-PET/CT favored benign etiology over malignant etiology. Histological and immunohistochemical findings along with reactive ossification of the periosteum confirmed the diagnosis of PF. Currently, comprehensive examinations, such as clinical, imaging, and histopathological examinations, are recommended for the definitive diagnosis of PF, while MRI and dual-time-point FDG-PET/CT could have a potential usefulness to differentiate from malignancy.

A case of tophaceous pseudogout of the temporomandibular joint extending into the cranium.

A case of tophaceous pseudogout (i.e., calcium pyrophosphate dihydrate crystal deposition disease) in the temporomandibular joint (TMJ) extending into the cranium is reported. A 59-year-old woman was referred to hospital with swelling and pain in the left cheek, and with trismus. Computed tomography imaging revealed a large, granular, calcified mass surrounding the left condylar head, partly destroying the cortex of the condylar head, and extending into the cranium by destroying the glenoid fossa. Magnetic resonance imaging revealed that the soft-tissue mass was of low-signal intensity on T1- and T2-weighted images, and was enhanced after intravenous injection of gadolinium. The mass was clinically and radiographically suspected to be a neoplastic lesion or a synovial osteochodromatosis. However, histological analysis demonstrated that the mass contained granulomatous lesion due to multiple nodular deposits of numerous rod-shaped and rhomboid crystals, which verified the diagnosis of tophaceous pseudogout. The lesion was excised surgically using a preauricular approach. Neither radiographic nor clinical examination demonstrated any signs of mass recurrence in the long-term 8- and 14-year postoperative recall examinations. Tophaceous pseudogout is a rare benign arthropathy that presents with clinical and radiographic features mimicking neoplastic conditions of the TMJ. Therefore, it is recommended that tophaceous pseudogout is considered in the differential diagnosis when a calcified mass lesion of the TMJ is encountered.

Lithium chloride reduces orthodontically induced root resorption and affects tooth root movement in rats.

OBJECTIVE: To investigate the influence of lithium chloride (LiCl) on orthodontic tooth movement (OTM), orthodontically induced root resorption (OIRR), and bone morphometry. MATERIALS AND METHODS: Ten-week-old female Sprague Dawley rats (n = 32) were divided into four groups based on the concentration of LiCl administered daily per kilogram body weight: 0 (control group), 0.32, 0.64, and 1.28 mM/kg body weight. The maxillary left first molars were moved mesially by a 10 cN coil spring for 14 days. Micro-computed tomography, scanning electron microscope, and scanning laser microscope images were taken to measure the amount of OTM, the volume of OIRR, and bone morphometry. RESULTS: OIRR clearly decreased depending on the amount of LiCl administered, although OTM moderately decreased. The tooth inclined mesially and the root apex moved distally in the control and 0.32 mM groups. On the other hand, the tooth inclination angle became smaller and the root apex moved mesially in the 0.64 and 1.28 mM groups. In bone morphometry, the cortical bone mineral content and bone volume increased because of LiCl administration, and the trabecular bone measurements decreased. OIRR negatively correlated to the cortical bone measurements, and the amount of OTM significantly correlated to the cortical bone morphometry. CONCLUSIONS: In rats, LiCl reduced OIRR, which induced mesial movement of the tooth root apex. OIRR positively correlated to cortical bone morphometry.

Types of tooth movement, bodily or tipping, do not affect the displacement of the tooth's center of resistance but do affect the alveolar bone resorption.

OBJECTIVE: To investigate how types of tooth movement, bodily or tipping, influence the displacement of the center of resistance in teeth and alveolar bone resorption. MATERIALS AND METHODS: Ten-week-old female Wistar rats were divided into eight groups of different factors, as follows: type of movement (bodily and tipping) and force magnitude (10, 25, 50, and 100 cN). The maxillary left first molars were moved mesially with nickel-titanium coil springs for 28 days. Micro-computed tomography (micro-CT) images were taken before and after tooth movement. The position of the center of resistance was determined by using finite element models constructed from the micro-CT image. The displacement of the center of resistance and the volume of alveolar bone resorption were measured. RESULTS: The displacement of the center of resistance showed no significant difference between the bodily and tipping groups. The displacements of the center of resistance were increased with force magnitude at 10 and 25 cN, whereas they were not further increased at 50 and 100 cN. On the other hand, cervical alveolar bone resorption was significantly greater in the tipping group than in the bodily group. CONCLUSIONS: Displacement of the center of resistance was not influenced by the types of tooth movement. However, volume of cervical alveolar bone resorption was greater in the tipping movement group than in the bodily movement group.

Increasing the amount of corticotomy does not affect orthodontic tooth movement or root resorption, but accelerates alveolar bone resorption in rats.

Objectives: The purpose of this study was to evaluate the relationships among the volume of bone cut during corticotomy, amount of tooth movement, volume of root resorption, and volume of the resultant alveolar bone resorption after tooth movement. Methods: Ten-week-old female Wistar rats were distributed into the corticotomy groups and a control group that underwent sham corticotomy. Two experiments employing two different orthodontic forces (10 or 25g) and experimental periods (14 or 21 days) were performed. The volumes of the bone cut by corticotomy were 0.1, 1.0, and 1.7mm3 in the 25g groups, and 1.0 and 1.7mm3 in the 10g groups. Nickel-titanium closed-coil springs were set on the maxillary left first molars to induce mesial movement. After orthodontic tooth movement, the amount of tooth movement, volume of root resorption, and volume of alveolar bone resorption were measured. Results: Despite differences in the volume of bone cut among the different corticotomy groups, there were not significant differences in the amount of tooth movement and volume of root resorption between the control group and any of the corticotomy groups. However, higher volume of bone cut during corticotomy was significantly related to the decreased alveolar bone volume-in particular, to the reduced height of the alveolar bone crest after tooth movement. Conclusions: The volume of the alveolar bone cut during corticotomy does not affect tooth movement or root resorption in 10-week-old female Wistar rats; however, it may increase alveolar bone loss after tooth movement.

Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats.

OBJECTIVE: To investigate differences in the amount of tooth movement and root resorption that occurred after tipping and bodily movement of the maxillary first molar in rats. MATERIALS AND METHODS: Ten-week-old female Wistar rats were divided into two groups according to type of tooth movement and subdivided into four subgroups according to the magnitude of applied force. Nickel-titanium closed-coil springs exerting forces of 10, 25, 50, or 100 g were applied to the maxillary left first molars to induce mesial tooth movement. We designed a novel orthodontic appliance for bodily tooth movement. Tooth movement distance and root resorption were measured using microcomputed tomography and scanning electron and scanning laser microscopy. RESULTS: The amount of tooth movement in the bodily tooth movement group was less than half that in the tipping tooth movement group. The greatest amount of tooth movement occurred in the 10-g tipping and 50-g bodily tooth movement subgroups, and the amount of tooth movement decreased with the application of an excessive magnitude of force. Conversely, root resorption increased when the heavier orthodontic force was applied in both groups. Root resorption in the tipping tooth movement group was approximately twice that in the bodily tooth movement group. CONCLUSIONS: Root resorption in the tipping tooth movement group was more pronounced than that in the bodily tooth movement group. Although the amount of tooth movement decreased when extremely heavy forces were applied, root resorption increased in both the tipping and bodily tooth movement groups in rats.

The effect of bone morphometric changes on orthodontic tooth movement in an osteoporotic animal model.

OBJECTIVE: To elucidate the effect of bone morphometric changes on orthodontic tooth movement (OTM) in zoledronic acid-treated ovariectomized rats. MATERIALS AND METHODS: Twenty-one 10-week-old female Wistar rats were divided into ovariectomy (OVX), OVX with zoledronic acid administration (OVX + ZOL), and sham operation (control) groups. Two weeks after OVX, ZOL administration was initiated. Twelve weeks after OVX, a nickel-titanium closed-coil spring of 25-g force was applied mesially to the maxillary left first molar. In vivo micro-computed tomography (CT) of the left proximal tibia was performed for bone morphometric analysis every 2 weeks after OVX. In addition, OTM was investigated using micro-CT at 0, 12, and 14 weeks after OVX. RESULTS: There were significant differences in the bone mineral content (BMC), bone volume (BV), BMC to tissue volume ratio (BMC/TV), and BV to TV ratio of trabecular bone between the control and OVX groups and also between the OVX + ZOL and OVX groups. In the OVX + ZOL group, increased BMC and BV in the cortical bone and increased bone mineral density (BMD) in the trabecular bone were observed. Interestingly, OTM in the OVX group was almost two times more than that in the control and OVX + ZOL groups. Moreover, OTM was correlated with BMD, BMC, BV, and BMC/TV in the trabecular bone. CONCLUSIONS: OVX accelerated OTM, while ZOL suppressed it. OTM demonstrated a significant negative relationship with trabecular bone mass.

Removable orthodontic appliance with nickel-titanium spring to reposition the upper incisors in an autistic patient.

A newly designed removable appliance with a shape-memory wire was used for the orthodontic treatment of the anterior teeth in an 11-year-old child who had autism and intellectual disability. The device was designed to reduce the lateral incisor crossbite and the central incisors' labial rotation. The child was treated for 1 year with this removable appliance. Tooth movement was analyzed using cephalograms and surface data were derived from study models. This device proved to be very durable. The lateral incisor crossbite was corrected, and the inclination of the upper central incisors and the interincisal angle were improved. This appliance exerts light and continuous orthodontic force, without requiring any adjustments of the spring wire. The appliance also facilitated orthodontic treatment in a child with intellectual disability in whom treatment with a standard orthodontic device would be unsuitable.

Class III occlusion with missing maxillary first molars and facial asymmetry treated with intraoral vertical ramus osteotomy: 7-year follow-up.

A 17-year-old girl with a Class III occlusion and facial asymmetry was treated with orthodontics and intraoral vertical ramus osteotomy (IVRO). She had a severe skeletal Class III relationship (Wits, -17 mm). Even though she had a prognathic mandible, she showed a straight rather than concave profile because of severe mandibular dental compensation. The patient also had severe mandibular deviation. After 17 months of presurgical orthodontic treatment, IVRO was performed. Total active treatment time was 26 months. Both occlusion and facial appearance were significantly improved by the surgical-orthodontic treatment. There were no functional problems during or after treatment. Posttreatment records after 7 years showed excellent results with good, stable occlusion; facial balance and harmony; and long-term stability.

Orthodontic tooth movement and root resorption in ovariectomized rats treated by systemic administration of zoledronic acid.

INTRODUCTION: The effect of zoledronic acid, a potent and novel bisphosphonate, on tooth movement and orthodontically induced root resorption in osteoporotic animals systemically treated with zoledronic acid as similarly used in postmenopausal patients has not been elucidated. Therefore, this study was undertaken. METHODS: Fifteen 10-week-old female Wistar rats were divided into 3 groups: ovariectomy, ovariectomy + zoledronic acid, and control. Only the ovariectomy and ovariectomy + zoledronic acid groups underwent ovariectomies. Two weeks after the ovariectomy, zoledronic acid was administered only to the ovariectomy + zoledronic acid group. Four weeks after the ovariectomy, 25-g nickel-titanium closed-coil springs were applied to observe tooth movement and orthodontically induced root resorption. RESULTS: There were significant differences in the amounts of tooth movement and orthodontically induced root resorption between the ovariectomy and the control groups, and also between the ovariectomy and the ovariectomy + zoledronic acid groups. There was no statistically significant difference in tooth movement and orthodontically induced root resorption between the ovariectomy + zoledronic acid and the control groups. Zoledronic acid inhibited significantly more tooth movement and significantly reduced the severity of orthodontically induced root resorption in the ovariectomized rats. The ovariectomy + zoledronic acid group showed almost the same results as did the control group in both tooth movement and orthodontically induced root resorption. CONCLUSIONS: Zoledronic acid inhibits excessive orthodontic tooth movement and also reduces the risk of severe orthodontically induced root resorption in ovariectomized rats.

High extracellular Ca2+ stimulates Ca2+-activated Cl- currents in frog parathyroid cells through the mediation of arachidonic acid cascade.

Elevation of extracellular Ca(2+) concentration induces intracellular Ca(2+) signaling in parathyroid cells. The response is due to stimulation of the phospholipase C/Ca(2+) pathways, but the direct mechanism responsible for the rise of intracellular Ca(2+) concentration has remained elusive. Here, we describe the electrophysiological property associated with intracellular Ca(2+) signaling in frog parathyroid cells and show that Ca(2+)-activated Cl(-) channels are activated by intracellular Ca(2+) increase through an inositol 1,4,5-trisphophate (IP(3))-independent pathway. High extracellular Ca(2+) induced an outwardly-rectifying conductance in a dose-dependent manner (EC(50) ∼6 mM). The conductance was composed of an instantaneous time-independent component and a slowly activating time-dependent component and displayed a deactivating inward tail current. Extracellular Ca(2+)-induced and Ca(2+) dialysis-induced currents reversed at the equilibrium potential of Cl(-) and were inhibited by niflumic acid (a specific blocker of Ca(2+)-activated Cl(-) channel). Gramicidin-perforated whole-cell recording displayed the shift of the reversal potential in extracellular Ca(2+)-induced current, suggesting the change of intracellular Cl(-) concentration in a few minutes. Extracellular Ca(2+)-induced currents displayed a moderate dependency on guanosine triphosphate (GTP). All blockers for phospholipase C, diacylglycerol (DAG) lipase, monoacylglycerol (MAG) lipase and lipoxygenase inhibited extracellular Ca(2+)-induced current. IP(3) dialysis failed to induce conductance increase, but 2-arachidonoylglycerol (2-AG), arachidonic acid and 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12(S)-HPETE) dialysis increased the conductance identical to extracellular Ca(2+)-induced conductance. These results indicate that high extracellular Ca(2+) raises intracellular Ca(2+) concentration through the DAG lipase/lipoxygenase pathway, resulting in the activation of Cl(-) conductance.

Tooth movement and root resorption; the effect of ovariectomy on orthodontic force application in rats.

OBJECTIVE: To quantify the amount of tooth movement and orthodontically induced root resorption (OIRR) in ovariectomized rats. MATERIALS AND METHODS: Five 10-week-old female Wistar rats undergoing ovariectomy (OVX) were investigated as the experimental group, and the other five without ovariectomy served as the control group. Four weeks after ovariectomy, 25-g nickel-titanium closed-coil springs were applied mesially to the maxillary left first molars. Micro-computed tomography was taken at day 0, 1, 3, 7, 14, 21, and 28. At day 28, the molars were extracted. The surface area of root resorption craters, depth, and volume were measured using electron and laser scanning microscopes. RESULTS: Tooth movement gradually increased with time throughout 28 days. There was a significant difference in the amount of tooth movement between the control group and the OVX group. For OIRR, the OVX group showed wide and shallow root resorption craters scattered on the mesial root. The deep resorption craters were observed on the distal roots distributed in the cervical, middle, and apical thirds of the roots. Statistically significant differences were found between the control and the OVX groups in the depth and the volume of root resorption craters in the distal roots and the total volume of root resorption craters in all three roots. CONCLUSION: Ovariectomy affected not only tooth movement but also OIRR. Tooth movement in the OVX group was more rapid than the control group. Furthermore, the amount of OIRR in the OVX group was more severe than the control group.

Effects of fluoride intake on orthodontic tooth movement and orthodontically induced root resorption.

INTRODUCTION: Even though the beneficial effects of fluoride on enamel and root caries have been well documented, limited data are available concerning the effect of fluoride on orthodontically induced root resorption and tooth movement. Our objective was to investigate the effect of systemic fluoride administered from birth to 12 weeks on orthodontically induced root resorption and tooth movement in rat molars. METHODS: Fifty male Wistar rats were randomly divided into 5 groups. The negative control group received no sodium fluoride and had no tooth movement. The positive control group received no sodium fluoride but had tooth movement. Three experimental groups received sodium fluoride at 45 ppm from birth to 2, 4, and 12 weeks, respectively. At week 10, a 50-g nickel-titanium coil spring was applied to the maxillary left first molar for 2 weeks. The rats were killed at 12 weeks of age. Movement of the maxillary first molars was measured in relation to the maxillary second molar on digitized cephalometric radiographs. Mesial and distal roots were examined by using scanning electron and 3-dimensional laser microscopes. RESULTS: Fluoride reduced the depth, volume, and roughness of the resorption craters in the experimental groups. However, the area was similar to that in the positive control group. Regarding the duration of fluoride intake, the longer fluoride was administered via drinking water, the smaller the amount of tooth movement observed. CONCLUSIONS: Fluoride in drinking water from birth reduced the severity of orthodontically induced root resorption, but the amount of tooth movement was also decreased.

Using superimposition of 3-dimensional cone-beam computed tomography images with surface-based registration in growing patients.

OBJECTIVE: The purpose of this research was to evaluate a new method of superimposing detailed cone-beam computed tomography (CBCT) images. MATERIALS AND METHODS: This study used 5 different software programs to transform the digital imaging and communication in medicine (DICOM) data from CBCT image into polygon data. The data conversion errors from different software programs were verified by the poly-acetal ball test and the dry skull test. The iterative closest point (ICP) method was used for precise superimposition. To evaluate changes related to growth, three different domains were superimposed in order to investigate appropriate areas for evaluation by the ICP method. RESULTS: The ICP method in the cranial base (excluding the peripheral zone) was indicated as the most reliable surface in this research. There were no measurement errors in converting the image data between software programs. CONCLUSION: The ICP method in the cranial base (excluding the peripheral zone) is one of the most accurate methods for superimposition when the mandibular rotation or displacement has not occurred during growth or treatment. This 3-dimensional (3D) superimposition technique can be used for a valid and reproducible assessment of treatment outcomes for growing subjects. This method is considered to be of clinical value because of the manageability and 3D accuracy of the data comparison with multi planar reconstruction (MPR) images.

Preliminary cone-beam computed tomography study evaluating dental and skeletal changes after treatment with a mandibular Schwarz appliance.

INTRODUCTION: The purpose of this study was to evaluate the efficacy of the Schwarz appliance with a new method of superimposing detailed cone-beam computed tomography (CBCT) images. METHODS: The subjects were 28 patients with Angle Class I molar relationships and crowding; they were randomly divided into 2 groups: 14 expanded and 14 nonexpanded patients. Three-dimensional Rugle CBCT software (Medic Engineering, Kyoto, Japan) was used to measure 10 reference points before treatment (T0) and during the retention period of approximately 9 months after 6 to 12 months of expansion (T1). Cephalometric and cast measurements were used to evaluate the treatments in both groups. Also, the mandibular widths of both groups were measured along an axial plane at 2 levels below the cementoenamel junction from a CBCT scan. Differences between the 2 groups at T0 and T1 were analyzed by using the Mann-Whitney U test. RESULTS: The dental arch (including tooth root apices) had expanded; however, alveolar bone expansion was only up to 2 mm below the cementoenamel junction. There was a statistically significant (P <0.05) difference between the groups in terms of crown, cementoenamel junction, root, and upper alveolar process. However, no significant (P >0.05) differences were observed in the interwidths of the mandibular body, zygomatic bones, condylar heads, or mandibular antegonial notches. In the mandibular cast measurements, arch crowding and arch perimeter showed statistically significant changes in the expanded group. The buccal mandibular width and lingual mandibular width values had significant changes as measured from a point 2 mm below the cementoenamel junction. CONCLUSIONS: The findings suggest that the Schwarz appliance primarily affected the dentoalveolar complex, but it had little effect on either the mandibular body or any associated structures. In addition, the molar center of rotation was observed to be below the root apex.

Repair of root resorption 2 to 16 weeks after the application of continuous forces on maxillary first molars in rats: a 2- and 3-dimensional quantitative evaluation.

INTRODUCTION: Root resorption is a side effect of orthodontic treatment that occurs with the removal of hyalinized tissue. Studies have shown that a reparative process in the periodontium begins when the applied orthodontic force is discontinued or reduced below a certain level. However, quantitative 3-dimensional evaluation of root resorption repair has not been done. The aim of this study was to quantitatively assess the 2- and 3-dimensional changes of root resorption craters after 2 weeks of continuous mesially applied orthodontic forces of 50 g on rat molars and 2- to 16-week retention periods. METHODS: We used 60 male Wistar rats (10 weeks old). Nickel-titanium closed-coil springs were used to apply 50-g mesial forces for 2 weeks to move the maxillary left first molars. The rats were randomly allocated to 6 groups. Those in the zero-week retention group were killed after force application. In the remaining 5 groups, the interdental spaces between the maxillary first and second molars were filled with resin to retain the molars. The molars were extracted after periods of retention from 2 and 16 weeks. The maxillary right molars were used as the controls. Mesial and distal roots (distobuccal and distopalatal) were examined by using scanning electron and 3-dimensional scanning laser microscopes. The surface area, depth, volume, and roughness of the root resorption craters were measured. RESULTS: The area, depth, and volume of the craters decreased gradually and showed similar trends over the retention time, approaching a plateau at the 12th week. After 16 weeks of retention, the volumes of the resorption craters of the distobuccal and distopalatal roots reached recovery peaks of 69.5% and 66.7%, respectively. Small pits on the mesial roots showed recovery of 62.5% at the 12th week. The healing patterns in distal roots with severe resorption and mesial roots with shallow resorption had no significant differences. CONCLUSIONS: The resorption and repair processes during the early stages of retention are balanced, and most of the reparative process occurs after 4 weeks of passive retention after the application of orthodontic force. Frequent orthodontic reactivations should be avoided to allow recovery and repair of root surface damage.