The effect of corticotomy on the compensatory remodeling of alveolar bone during orthodontic treatment.

BACKGROUND: This study aimed to explore whether compensatory remodeling of the alveolar bone surface occurred during the buccal palatal movement of orthodontic teeth. We preliminarily explored whether corticotomy could activate or accelerate osteogenesis in the alveolar bone surface by measuring the expression of TGF-ß1 (transforming growth factor-ß1), which can facilitate the proliferation and differentiation of osteoblasts and regulate the maturity and formation of bone. METHODS: Sixty 10-week-old male Wistar rats were selected. In the orthodontic group, 20 rats were implanted with a constriction device between the maxillary first molars under general anesthesia. In the corticotomy group, 20 rats were implanted with a constriction device, and a palatal incision was made to penetrate the cortical bone. In the control group, 20 rats underwent no experimental operation except general anesthesia. After 1, 3, 5 and 7 days, the maxillary first molars and the surrounding alveolar bone were harvested, and coronal sections containing the apical mesial buccal root were prepared and observed using tetracycline fluorescence, HE staining and immunohistochemical staining for TGF-ß1. Image-Pro Plus software was used to assess the immunohistochemical results, and SPSS 22.0 statistical software was used to analyze variance and perform the LSD test. RESULTS: The tetracycline fluorescence results showed that in the periosteum near the apical region, an obvious fluorescence signal was observed in the orthodontic group and the corticotomy group compared with the control group. In the orthodontic group and corticotomy group, HE staining showed that the morphology was similar to cube-shaped. The immunohistochemical results showed that TGF-ß1 was significantly increased in the periosteum near the apical region in the orthodontic group and corticotomy group, and there were significant differences among the three groups. In addition, the expression of TGF-ß1 in the periosteum in the orthodontic group and the corticotomy group gradually increased over time, reaching a peak on day 5 and slightly decreasing on day 7. CONCLUSION: Osteogenesis occurred on the alveolar bone surface during the buccal palatal movement of orthodontic teeth, and corticotomy had a positive effect, and TGF-ß1 was involved in this process.

The Effect of Functional Mandibular Shift on the Muscle Spindle Systems in Head-Neck Muscles and the Related Neurotransmitter Histamine.

The aim of this study is to explore the effects of abnormal occlusion and functional recovery caused by functional mandible deviation on the head and neck muscles and muscle spindle sensory-motor system by electrophysiological response and endogenous monoamine neurotransmitters' distribution in the nucleus of the spinal tract. Seven-week-old male Wistar rats were randomly divided into 7 groups: normal control group, 2W experimental control group, 2W functional mandible deviation group, 2W functional mandible deviation recovery group, 4W experimental control group, 4W functional mandible deviation group, 4W functional mandible deviation recovery group. Chewing muscles, digastric muscle, splenius, and trapezius muscle spindles electrophysiological response activities at the opening and closing state were recorded. And then the chewing muscles, digastric, splenius, trapezius, and neck trigeminal nucleus were taken for histidine decarboxylase (HDC) detection by high performance liquid chromatography (HPLC), immunofluorescence, and reverse-transcription polymerase chain reaction (RT-PCR). Histamine receptor proteins in the neck nucleus of the spinal tract were also examined by immunofluorescence and RT-PCR. Electromyography activity of chewing muscles, digastric, and splenius muscle was significantly asymmetric; the abnormal muscle electromyography activity was mainly detected at the ipsilateral side. After functional mandibular deviation, muscle sensitivity on the ipsilateral sides of the chewing muscle and splenius decreased, muscle excitement weakened, modulation depth decreased, and the muscle spindle afferent impulses of excitation transmission speed slowed down. Changes for digastric muscle electrical activity were contrary. The functions recovered at different extents after removing the deflector. However, trapezius in all the experimental groups and recovery groups exhibited bilateral symmetry electrophysiological responses, and no significant difference compared with the control group. After functional mandibular deviation, HDC protein and messenger ribonucleic acid (mRNA) levels on the ipsilateral sides of the chewing muscle and splenius increased significantly. HDC level changes for digastric muscle were contrary. After the removal of the mandibular position deflector, HDC protein and mRNA levels decreased on the ipsilateral sides of the chewing muscle and splenius while they increased in the digastric muscle. The difference of histamine decarboxylase content in the bilateral trapezius in each experimental group was small. After functional mandibular deviation, the temporomandibular joint mechanical receptors not only caused the fusimotor fiber hypoallergenic fatigue slow response on the ipsilateral sides of splenius, but also increased the injury neurotransmitter histamine release. The authors' results further support the opinion that the temporomandibular joint receptors may be involved in the mechanical theory of the head and neck muscles nervous system regulation.

Cognitive and neurochemical alterations in hyperhomocysteinemic rat.

Accumulating data have shown that the level of serum homocysteine in patients with mild cognitive impairment, vascular dementia and Alzheimer's disease is higher than normal while the underlying mechanism is not fully understood. Here, a hyperhomocysteinemic rat model was made by maintaining rats on a diet high in methionine. The cognitive behavior, level of monoamine neurotransmitters in brain homogenates and brain-derived neurotrophic factor (BDNF) in cerebral spinal fluid (CSF) were compared between high-methionine diet and control group. The high-methionine diet group presented longer mean latency of escape and lesser time in target quadrant in morris maze test, lower level of serotonin and dopamine in cortex homogenates and lower level of BDNF in CSF. Together, our findings provide evidence that hyperhomocysteinemia could cause alterations of monoamine and neurotrophic factor, which might be further pathogenetic mechanisms underlying the cognitive deterioration.

Dehiscence and fenestration in anterior teeth : Comparison before and after orthodontic treatment.

BACKGROUND: Previous studies have reported incidence rates of dehiscence (DEH) and fenestration (FEN) as high as 36.51 and 51.09%, respectively. Only a few studies comparing DEH and FEN before and after orthodontic treatment (OT) are available in the literature. PURPOSE: The aim of this study was to evaluate the occurrence of DEH and FEN in anterior teeth, before and after OT, using cone-beam computed tomography (CBCT). In addition, findings may provide a clinical basis for avoiding DEH and FEN during therapeutic tooth alignment. PATIENTS AND METHODS: CBCT images of 21 patients near the end of their peak growth and development were included. DEH and FEN in the anterior teeth and thicknesses of the alveolar bone at the palatal (TP) and labiolingual (LL) sides of each anterior tooth were measured before and after OT. RESULTS: After OT, the incidence rates of mandibular anterior labial DEH, maxillary anterior TP-bone defect, and mandibular anterior lingual bone defect were increased by 20, 19, and 30%, respectively. Assessment of CT images prior to treatment showed that the teeth developing bone defects were significantly different regarding the apical alveolar bone thicknesses compared to the teeth that did not develop bone defects after OT, i.e., the incidence of DEH and FEN after OT was lower if the thickness of the apex to labiolingual alveolar bone before OT was as follows: the apex to labial alveolar bone thickness of the maxillary central incisor and maxillary lateral incisor was >4 mm, the apex to palatal alveolar bone thickness of the maxillary lateral incisor was >3 mm; the apex to labiolingual alveolar bone thickness of the lower incisor was >5 mm. CONCLUSION: The incidence of post-OT DEH at the maxillary anterior and mandibular anterior lingual surfaces were increased significantly compared to before treatment. In general, the smaller the apex to labiolingual alveolar bone thickness, the greater the likelihood of bone defects occurring after OT. Evaluation of the apical position of anterior teeth in alveolar bone can help minimize the occurrence of bone defects after OT.

[Comparison of root resorption between self-ligating and conventional brackets using cone-beam CT].

PURPOSE: To analyze the differences of root resorption between passive self-ligating and conventional brackets, and to determine the relationship between passive self-ligating brackets and root resorption. METHODS: Fifty patients were randomly divided into 2 groups using passive self-ligating brackets or conventional straight wire brackets (0.022 system), respectively. Cone-beam CT was taken before and after treatment. The amount of external apical root resorption of maxillary incisors was measured on CBCT images. Student's t test was performed to analyze the differences of root apical resorption between the 2 groups with SPSS17.0 software package. RESULTS: No significant difference(P> 0.05) in root resorption of maxillary incisors was found between passive self-ligating brackets and conventional brackets. CONCLUSIONS: Passive self-ligating brackets and conventional brackets can cause root resorption, but the difference was not significant. Passive self-ligating brackets do not induce more root resorption.

Integrated three-dimensional digital assessment of accuracy of anterior tooth movement using clear aligners.

OBJECTIVE: To assess the accuracy of anterior tooth movement using clear aligners in integrated three-dimensional digital models. METHODS: Cone-beam computed tomography was performed before and after treatment with clear aligners in 32 patients. Plaster casts were laser-scanned for virtual setup and aligner fabrication. Differences in predicted and achieved root and crown positions of anterior teeth were compared on superimposed maxillofacial digital images and virtual models and analyzed by Student's t-test. RESULTS: The mean discrepancies in maxillary and mandibular crown positions were 0.376 ± 0.041 mm and 0.398 ± 0.037 mm, respectively. Maxillary and mandibular root positions differed by 2.062 ± 0.128 mm and 1.941 ± 0.154 mm, respectively. CONCLUSIONS: Crowns but not roots of anterior teeth can be moved to designated positions using clear aligners, because these appliances cause tooth movement by tilting motion.

[Bond strengths of customized titanium brackets manufactured by selective laser melting].

OBJECTIVE: To investigate the bond strengths of customized titanium bracket manufactured by selective laser melting. METHODS: Eighty human premolars which had been extracted for orthodontic purpose were collected and divided randomly (by random table) into two groups (customized bracket group and 3M bracket group, 40 molars in each group). The 35% phosphoric acid was used for etching and the brackets were bonded with 3M Unitek bonding adhesive. All bonded specimens were placed in saline for 24 hours at room temperature and were tested on DWD3050 electronic testing machine to determine the shear bond strength and tensile bond strength. After debonding, the adhesive remnant indexes (ARI) were recorded. RESULTS: The shear bond strengths of customized brackets was 6.80 (6.20, 8.32) MPa, which was significantly lower than that of the 3M brackets [10.46 (9.72, 11.48) MPa] (Z = -3.463, P < 0.05). And the tensile bond strengths of customized brackets was (6.93 ± 1.21) MPa, which was significantly higher than that of the 3M brackets [(5.88 ± 1.23) MPa] (t = 2.81, P < 0.05). No significant difference was found in the ARI between two different kinds of the brackets. CONCLUSIONS: The shear bond strength and tensile bond strength of both kinds of brackets were enough for clinic application.

[Application of integrated digital maxillodental model in computer aided design of individualized lingual brackets].

OBJECTIVE: To create an integrated digital maxillodental model and to apply it in computer aided design (CAD) of individualized lingual brackets in order to align both crowns and roots without fenestration and dehiscence. METHODS: Cone-beam computerized tomography (CBCT)-based maxillodental model and laser-scanned dental model were integrated by auto registration in 10 patients with malocclusions. The registration error was calculated automatically. Three observers tested the method independently. The inter-observer difference was investigated. An integrated model was selected randomly and the setup was created with roots and jaws in good relationship without fenestration and dehiscence. The individualized lingual brackets were designed by CAD on the setup. RESULTS: No significant difference was found in inter observers (P > 0.05). The registration errors of maxilla and mandible were (0.144 ± 0.020) mm and (0.141 ± 0.022) mm, respectively. The digital individualized lingual brackets based on the virtual treatment in integrated digital maxillodental model were produced. CONCLUSIONS: An integrated digital maxillodental model was created in good accuracy. By applying the integrated model, individualized lingual brackets were designed.