Identification of Aberrantly Expressed lncRNAs Involved in Orthodontic Force Using a Subpathway Strategy.

BACKGROUND: The aim of the study was to identify key long noncoding RNAs (lncRNA) and related subpathways in the periodontal ligament tissue following orthodontic force. METHODS: We adopt a novelty subpathway strategy to identify lncRNAs competitively regulated functions and the key competitive lncRNAs in periodontal ligament disorders after undergoing orthodontic force. To begin with, patients with orthodontics in our hospital were enrolled in our research. The relationship of lncRNA-mRNA was established through shared predicted miRNA by using the hypergeometric test, Jaccard coefficient standardization, and the Pearson coefficient to determine the valid interaction relationship. After embedding screened lncRNA interactions to pathways, the significant subpathways were recognized by lenient distance and Wallenius approximation methods to calculate the false discovery rate value of each subpathway. RESULTS: The lncRNA-mRNA intersections including 263 lncRNAs, 1,599 mRNAs, and 3,762 interacting pairs were obtained. The enriched mRNAs were further enriched into various candidate pathways such as the PI3K-Akt signaling pathway. Several subpathways were screened, including the PI3K-Akt signaling pathway, 04510_1 focal adhesion, and p53 signaling pathway, respectively. The network of pathway-lncRNA-mRNA was constructed. Several key lncRNAs including DNAJC3-AS1, WDFY3-AS2, LINC00482, and DLEU2 were screened. CONCLUSIONS: DNAJC3-AS1, WDFY3-AS2, LINC00482, and DLEU2 as aberrantly expressed lncRNAs involved in orthodontic force might play crucial roles in periodontal ligament disease pathogenesis.

Reduced Orthodontic Tooth Movement in Enpp1 Mutant Mice with Hypercementosis.

Previous studies revealed that cementum formation is tightly regulated by inorganic pyrophosphate (PPi), a mineralization inhibitor. Local PPi concentrations are determined by regulators, including ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which increases PPi concentrations by adenosine triphosphate hydrolysis. Orthodontic forces stimulate alveolar bone remodelling, leading to orthodontic tooth movement (OTM). To better understand how disturbed mineral metabolism and the resulting altered periodontal structures affect OTM, we employed Enpp1 mutant mice that feature reduced PPi and increased cervical cementum in a model of OTM induced by a stretched closed-coil spring ligated between the maxillary left first molar and maxillary incisors. We analyzed tooth movement, osteoclast/odontoclast response, and tooth root resorption by micro-computed tomography, histology, histomorphometry, and immunohistochemistry. Preoperatively, we noted an altered periodontium in Enpp1 mutant mice, with significantly increased periodontal ligament (PDL) volume and thickness, as well as increased PDL-bone/tooth root surface area, compared to wild-type (WT) controls. After 11 d of orthodontic treatment, Enpp1 mutant mice displayed 38% reduced tooth movement versus WT mice. Molar roots in Enpp1 mutant mice exhibited less change in PDL width in compression and tension zones compared to WT mice. Root resorption was noted in both groups with no difference in average depths, but resorption lacunae in Enpp1 mutant mice were almost entirely limited to cementum, with 150% increased cementum resorption and 92% decreased dentin resorption. Osteoclast/odontoclast cells were reduced by 64% in Enpp1 mutant mice, with a predominance of tartrate-resistant acid phosphatase (TRAP)-positive cells on root surfaces, compared to WT mice. Increased numbers of TRAP-positive cells on root surfaces were associated with robust immunolocalization of osteopontin (OPN) and receptor-activator of NF-κB ligand (RANKL). Collectively, reduced response to orthodontic forces, decreased tooth movement, and altered osteoclast/odontoclast distribution suggests Enpp1 loss of function has direct effects on clastic function/recruitment and/or indirect effects on periodontal remodeling via altered periodontal structure or tissue mineralization.

RUNX2 mutation impairs bone remodelling of dental follicle cells and periodontal ligament cells in patients with cleidocranial dysplasia.

RUNX2 is an important osteo-specific factor with crucial functions in bone formation and remodelling as well as resorption of teeth. Heterozygous mutation of RUNX2 can cause cleidocranial dysplasia (CCD), a systemic disease with extensive skeletal dysplasia and abnormality of tooth growth. In our study, dental follicle cells (DFCs) and periodontal ligament cells (PDLCs) were isolated, cultured and identified from one patient with CCD and compared with normal controls. This CCD patient was confirmed to have a heterozygous frameshift mutation of RUNX2 (c.514delT, p.Ser172fs) in the previous study. The results showed that the proliferation abilities of DFCs and PDLCs were both disturbed by the RUNX2 mutation in the CCD patient compared with the normal control. A co-culture system of these cells with human peripheral blood mononuclear cells was then used to investigate the effect of RUNX2 mutation on osteoclastogenesis. We found that the RUNX2 mutation in CCD reduced the expression of osteoclast-related genes, such as RUNX2, CTR, CTSK, RANKL and OPG The ability of osteoclastogenesis in DFCs and PDLCs detected by tartrate-resistant acid phosphatase staining in the co-culture system was also reduced by the RUNX2 mutation compared with the normal control. These outcomes indicate that the RUNX2 mutation disturbs the modulatory effects of DFCs and PDLCs on the differentiation of osteoclasts and osteoblasts, thereby interfering with bone remodelling. These effects may contribute in part to the pathological manifestations of retention of primary teeth and delayed eruption of permanent teeth in patients with CCD.

Cryogenically salvaged teeth as a potential source for grafting dentoalveolar, periodontal or maxillofacial defects.

Bone grafting uses a wide range of materials derived mainly from exogenous sources. Autogenous teeth are often used fresh or fixed with alcohol for later use. Proposed here is a method of using cryogenically preserved autogenous extracted teeth, which could be macerated after thawing. This method avoids the possibility of tissue being denatured by alcohol and preserves intact all calcified structures for optimal bone grafting success.

Should deciduous teeth be preserved in adult patients? How about stem cells? Is it reasonable to preserve them?

Abstract When seeking orthodontic treatment, many adolescents and adult patients present with deciduous teeth. Naturally, deciduous teeth will inevitably undergo exfoliation at the expected time or at a later time. Apoptosis is the biological trigger of root resorption. In adult patients, deciduous teeth should not be preserved, as they promote: infraocclusion, traumatic occlusion, occlusal trauma, diastemata and size as well as morphology discrepancy malocclusion. Orthodontic movement speeds root resorption up, and so do restoring or recontouring deciduous teeth in order to establish esthetics and function. Deciduous teeth cells are dying as a result of apoptosis, and their regeneration potential, which allows them to act as stem cells, is limited. On the contrary, adult teeth cells have a greater proliferative potential. All kinds of stem cell therapies are laboratory investigative non authorized trials.

Resumo Muitos adolescentes e adultos, ao procurar pelo tratamento ortodôntico, apresentam dentes decíduos persistentes. Naturalmente, os dentes decíduos ou se esfoliam na época esperada ou mais tardiamente, de forma inevitável. A apoptose é o gatilho biológico da rizólise. Em adultos, os dentes decíduos não devem ser preservados, pois promovem: infraoclusão, oclusão traumática, trauma oclusal, além de diastemas e má oclusão por discrepância de tamanho e morfologia. O movimento ortodôntico acelera o processo de rizólise, assim como restaurar ou reanatomizar dentes decíduos para inseri-los em uma estética e função. As células dos dentes decíduos estão morrendo por apoptose e seu potencial regenerativo para atuarem como células-tronco tem limitações, ao contrário das células de dentes adultos, que têm maior potencial proliferativo. Todas as terapias com células-tronco ainda são laboratoriais e se enquadram como ensaios investigativos não autorizados.

Sequential Changes in Cortical Excitation during Orthodontic Treatment.

Cortical excitation responding to periodontal ligament (PDL) stimulation is observed in the rat primary somatosensory (S1), secondary somatosensory, and insular oral region of the cortex (S2/IOR), which are considered to process somatosensation, including nociception. Our previous studies have demonstrated that excitatory propagation induced by PDL stimulation is facilitated in S1 and S2/IOR 1 d after experimental tooth movement (ETM), and tetanic stimulation of IOR induces long-term potentiation of cortical excitatory propagation consistently. These findings raise the possibility that ETM induces neuroplastic changes, and as a result, facilitation of cortical excitation would be sustained for weeks. However, no information is available about the temporal profiles of the facilitated cortical responses. We estimated PDL stimulation-induced cortical excitatory propagation in S1 and S2/IOR of rats by optical imaging 1 to 7 d after ETM of the maxillary first molar. ETM models showed facilitated cortical excitatory propagation in comparison with controls and sham groups 1 d after ETM, but the facilitation gradually recovered to the control level 3 to 7 d after ETM. Sham groups that received wire fixation without orthodontic force tended to enhance cortical responses, although the differences between controls and sham groups were almost insignificant. We also examined the relationship between cortical responses and expression of inflammatory cytokines, interleukin (IL)-1ß and tumor necrosis factor (TNF)-α, in PDL of the first molar. The peak amplitude of optical signals responding to PDL stimulation tended to be increased in parallel to the number of IL-1ß and TNF-α immunopositive cells, suggesting that, at least in part, the enhancement of cortical responses is induced by PDL inflammation. These findings suggest that ETM-induced facilitation of cortical excitatory propagation responding to PDL stimulation 1 d after ETM recovers to the control level within a week. The time course of the facilitated cortical responses is comparable to that of pain and discomfort induced by clinical orthodontic treatments.

Cementum and Periodontal Ligament Regeneration.

The unique anatomy and composition of the periodontium make periodontal tissue healing and regeneration a complex process. Periodontal regeneration aims to recapitulate the crucial stages of wound healing associated with periodontal development in order to restore lost tissues to their original form and function and for regeneration to occur, healing events must progress in an ordered and programmed sequence both temporally and spatially, replicating key developmental events. A number of procedures have been employed to promote true and predictable regeneration of the periodontium. Principally, the approaches are based on the use of graft materials to compensate for the bone loss incurred as a result of periodontal disease, use of barrier membranes for guided tissue regeneration and use of bioactive molecules. More recently, the concept of tissue engineering has been integrated into research and applications of regenerative dentistry, including periodontics, to aim to manage damaged and lost oral tissues, through reconstruction and regeneration of the periodontium and alleviate the shortcomings of more conventional therapeutic options. The essential components for generating effective cellular based therapeutic strategies include a population of multi-potential progenitor cells, presence of signalling molecules/inductive morphogenic signals and a conductive extracellular matrix scaffold or appropriate delivery system. Mesenchymal stem cells are considered suitable candidates for cell-based tissue engineering strategies owing to their extensive expansion rate and potential to differentiate into cells of multiple organs and systems. Mesenchymal stem cells derived from multiple tissue sources have been investigated in pre-clinical animal studies and clinical settings for the treatment and regeneration of the periodontium.

Cytological Kinetics of Periodontal Ligament in an Experimental Occlusal Trauma Model.

Using a model of experimental occlusal trauma in mice, we investigated cytological kinetics of periodontal ligament by means of histopathological, immunohistochemical, and photographical analysis methods. Periodontal ligament cells at furcation areas of molar teeth in the experimental group on day 4 showed a proliferation tendency of periodontal ligament cells. The cells with a round-shaped nucleus deeply stained the hematoxylin and increased within the day 4 specimens. Ki67 positive nuclei showed a prominent increase in the group on days 4 and 7. Green Fluorescent Protein (GFP) positivity also revealed cell movement but was slightly slow compared to Ki67. It indicated that restoration of mechanism seemed conspicuous by osteoclasts and macrophages from bone-marrow-derived cells for the periodontal ligament at the furcation area. It was suggested that the remodeling of periodontal ligament with cell acceleration was evoked from the experiment for the group on day 4 and after day 7. Periodontal ligament at the furcation area of the molar teeth in this experimental model recovered using the cells in situ and the bone-marrow-derived cells.

Effects of occlusal hypofunction and its recovery on PDL structure and expression of VEGF and bFGF in rats.

OBJECTIVES: The purpose of this study was to clarify whether occlusal hypofunction and its recovery affect the structure of the periodontal ligament (PDL) and expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in rats. MATERIALS AND METHODS: Forty-eight Wistar rats aged 5 weeks were used and randomly divided into three groups: the hypofunctional group (HG), recovery group (RG), and control group (CG). In HG and RG, appliances were attached to the maxillary and mandibular incisors. In HG, appliances were set for 11 weeks. In RG, appliances were set for 7 weeks. Appliances were then removed at 0, 1, 3, 7, 14, and 28 days. Untreated rats served as CG. Histological sections were prepared and immunohistochemically stained for VEGF and bFGF. Three groups were evaluated for PDL area and the number of VEGF and bFGF immunopositive cells in PDL. RESULTS: The number of immunopositive cells and PDL area in CG and RG were significantly larger when compared with HG, and PDL area in RG was similar to that in CG. In the recovery process, PDL area and number of VEGF-positive cells in PDL increased from days 0 to 7 and decreased from days 7 to 28. Conversely, the number of bFGF-positive cells in PDL increased significantly after day 1 and peaked at 28 days. CONCLUSIONS: This study suggests that occlusal stimuli regulate PDL area through expression of VEGF and bFGF in rat PDL. CLINICAL RELEVANCE: Occlusal stimuli are able to regulate the expression of VEGF and bFGF in PDL cells, and these growth factors may lead to alveolar bone remodeling in PDL.

Effect of a tunnel-structured ß-tricalcium phosphate graft material on periodontal regeneration: a pilot study in a canine one-wall intrabony defect model.

BACKGROUND AND OBJECTIVE: Tissue regeneration is affected by the porosity, chemical properties and geometric structure of graft materials. Regeneration of severe periodontal defects, such as one-wall intrabony defects, is difficult because of reduced tissue support, and bone grafts are commonly used in such cases. In the present study, a tunnel-structured ß-tricalcium phosphate (tunnel ß-TCP) graft material designed to stimulate bone formation was fabricated. The objective of this pilot study was to evaluate the effect of this graft material on periodontal regeneration in one-wall intrabony defects in dogs. MATERIAL AND METHODS: Six male beagle dogs were used in this study. First, the mandibular second and third incisors were extracted. Experimental surgery was performed 12 wk after tooth extraction. Bilateral 4 × 8 mm (width × depth) one-wall intrabony defects were created in the mesial side of the mandibular canines. At the experimental sites, the defects were filled with tunnel ß-TCP, whereas the control defects were left empty. Twelve weeks after surgery, qualitative and quantitative histological analyses were performed. RESULTS: There were no signs of clinical inflammation 12 wk after surgery. Coronal extension indicative of new bone formation was higher at the experimental sites than at the control sites, although the differences between both the sites in the newly formed cementum and connective tissue attachment were not significant. Newly formed periodontal ligament and cementum-like tissue were evident along the root surface at the experimental sites. The inner surface of the tunnels was partially resorbed and replaced with new bone. New blood vessels were observed inside the lumens of tunnel ß-TCP. CONCLUSION: Tunnel ß-TCP serves as a scaffold for new bone formation in one-wall intrabony defects.

Biomechanical adaptation of the bone-periodontal ligament (PDL)-tooth fibrous joint as a consequence of disease.

In this study, an in vivo ligature-induced periodontitis rat model was used to investigate temporal changes to the solid and fluid phases of the joint by correlating shifts in joint biomechanics to adaptive changes in soft and hard tissue morphology and functional space. After 6 and 12 weeks of ligation, coronal regions showed a significant decrease in alveolar crest height, increased expression of TNF-α, and degradation of attachment fibers as indicated by decreased collagen birefringence. Cyclical compression to peak loads of 5-15N at speeds of 0.2-2.0mm/min followed by load relaxation tests showed decreased stiffness and reactionary load rate values, load relaxation, and load recoverability, of ligated joints. Shifts in joint stiffness and reactionary load rate increased with time while shifts in joint relaxation and recoverability decreased between control and ligated groups, complementing measurements of increased tooth displacement as evaluated through digital image correlation. Shifts in functional space between control and ligated joints were significantly increased at the interradicular (Δ10-25µm) and distal coronal (Δ20-45µm) regions. Histology revealed time-dependent increases in nuclei elongation within PDL cells and collagen fiber alignment, uncrimping, and directionality, in 12-week ligated joints compared to random orientation in 6-week ligated joints and to controls. We propose that altered strains from tooth hypermobility could cause varying degrees of solid-to-fluid compaction, alter dampening characteristics of the joint, and potentiate increased adaptation at the risk of joint failure.

Hypoxia regulates the proliferation and osteogenic differentiation of human periodontal ligament cells under cyclic tensile stress via mitogen-activated protein kinase pathways.

BACKGROUND: Previous studies have shown that periodontal ligament exists in a hypoxic microenvironment, especially under the condition of periodontitis or physical stress. The present study is designed to investigate the effects and mechanisms of hypoxia on regulating the proliferation and osteogenic differentiation of human periodontal ligament cells (hPDLCs) under cyclic tensile stress (CTS). METHODS: hPDLCs were cultured in 2% O2 (hypoxia) or 20% O2 (normoxia) and then subjected to a cyclic in-plane tensile deformation of 10% at 0.5 Hz. The following parameters were measured: 1) cell proliferation by flow cytometry; 2) cell ultrastructure by transmission electron microscopy; 3) expression of hypoxia-inducible factor-1α (HIF-1α) and osteogenic relative factors (i.e., secreted phosphoprotein 1 [SPP1; also known as bone sialoprotein I/osteopontin], runt-related transcription factor 2 [RUNX2], and transcription factor Sp7 [SP7]) by real-time polymerase chain reaction and Western blot; and 4) involvement of mitogen-activated protein kinase (MAPK) signaling pathways by Western blot with specific inhibitor. RESULTS: Proliferation index in the hypoxia with CTS group was significantly higher than in other groups. Significant increases in HIF-1α, SPP1, RUNX2, and SP7 occurred in the presence of hypoxia for 24 hours. In addition, MAPK inhibitor (PD 98,059) significantly attenuated hypoxia and CTS-induced phosphor-ERK1/2 (extracellular regulated kinase 1/2), phosphor-JNK (c-jun N-terminal kinase), and phosphor-P38 expression. CONCLUSIONS: Hypoxia regulates CTS-responsive changes in proliferation and osteogenic differentiation of hPDLCs via MAPK pathways. Hypoxia-treated hPDLCs may serve as an in vitro model to explore the molecular mechanisms of periodontitis.

Tissue resistance to soft tissue emphysema during minimally invasive periodontal surgery.

AIM: The aim of this study was to determine the pressure where oral soft tissue resistance will be overcome resulting in soft tissue emphysema and to measure the safety of an antifouling device for a videoscope used during minimally invasive periodontal surgery. MATERIALS AND METHODS: Resistance was measured in vitro in porcine tissue. One study arm measured palatal tissue resistance to air applied through a needle. Another arm measured resistance in a surgical access for minimally invasive periodontal surgery (MIS). India ink was placed on the tissue,pressure at 0,3,10,15,20, and 25 pounds/square inch (psi)applied, and penetration of India ink into the tissue was measured. Three trials in three sites were performed at each pressure in both arms of the study. RESULTS: Pressure applied to palatal tissue through a needle showed no significant penetration of India ink until 15 psi (0.90 ± 0.24 mm, p = 0.008). Penetration considered clinically significant was noted at 20 and 25 psi (4 to 6 mm, p ≤ 0.0001). No significant penetration was noted in minimally invasive incisions. CONCLUSION: Within the test system, pressures of 15 psi or less seem unlikely to cause soft tissue emphysema. No evidence of tissue emphysema was noted with the video scope antifouling device. CLINICAL SIGNIFICANCE: The use of pressures greater than 15 pounds per square inch should be avoided during surgical procedures. The antifouling device for a videoscope appears safe for use during minimally invasive periodontal surgery.

Hyperocclusion stimulates osteoclastogenesis via CCL2 expression.

Excessive mechanical stress (MS) during hyperocclusion is known to result in disappearance of the alveolar hard line, enlargement of the periodontal ligament (PDL) space, and destruction of alveolar bone, leading to occlusal traumatism. We hypothesized that MS induces expression of osteoclastogenesis-associated chemokines in PDL tissue, resulting in chemotaxis and osteoclastogenesis during occlusal traumatism. We examined the effect of MS on relationships between chemokine expression and osteoclastogenesis using in vivo and in vitro hyperocclusion models. In an in vitro model, intermittent stretching-induced MS was shown to up-regulate the expression of CC chemokine ligand (CCL)2, CCL3, and CCL5 in PDL cells. The expression levels of CCL2 in PDL tissues, its receptor CCR2 in pre-osteoclasts, and tartrate-resistant acid-phosphatase-positive cells in alveolar bone were significantly up-regulated 4-7 days after excessive MS during hyperocclusion in in vivo rodent models. Hyperocclusion predominantly induced CCL2 expression in PDL tissues and promoted chemotaxis and osteoclastogenesis, leading to MS-dependent alveolar bone destruction during occlusal traumatism.

Mechanical stress enhances production of cytokines in human periodontal ligament cells induced by Porphyromonas gingivalis.

OBJECTIVE: We have previously reported that human periodontal ligament (hPDL) cells produced many kinds of cytokines as a result of bacterial stimulation, including stimulation with Porphyromonas gingivalis (P. gingivalis). However, the effects of mechanical stress on cytokine production in hPDL cells stimulated by periodontopathogenic bacteria are not clearly understood. In this study, we investigated the effects of mechanical stress on the production of inflammatory cytokines in hPDL cells induced by stimulation with P. gingivalis. METHODS: The hPDL cells were exposed to various levels of mechanical stress (1, 6, 10 and 50MPa) and costimulated with mechanical stress and P. gingivalis for 24h. Cytokine mRNA expressions were determined by RT-PCR. Cytokines in the culture supernatant were assessed by ELISA, and morphologic changes in hPDL cells were observed. RESULTS: The expressions of interleukin (IL)-6, IL-8 and tumor necrosis factor-α mRNA were observed in hPDL cells after exposure to mechanical stress. Moreover, the production of IL-6 and IL-8 increased significantly after exposure to mechanical stress ranging from 1 to 10MPa. The amount of IL-8 in the culture supernatants of hPDL cells costimulated with P. gingivalis and mechanical stress was significantly higher than the expected additive amount. The morphology of hPDL cells did not change after exposure to 6MPa, but these cells were partly detached from the Petri dish after exposure to 50MPa. CONCLUSIONS: These results suggest that local inflammation of the periodontal ligament may be induced mainly by periodontal bacteria, and mechanical stress may promote local inflammation.

Periapical bone regeneration after endodontic microsurgery with three different root-end filling materials: amalgam, SuperEBA, and mineral trioxide aggregate.

INTRODUCTION: The purpose of this study was to determine the bone regeneration potential to different root-end filling materials by evaluating the distance between the materials and newly regenerated bone after root-end surgery. MATERIAL AND METHODS: Periapical lesions were induced in premolars and molars of five female beagle dogs. The teeth were treated endodontically after the development of the lesions. After 1 week, the teeth underwent root-end surgery using modern microsurgical techniques. Three different root-end filing materials were used: amalgam (Tytin; Kerr Mfg Co, Romulus, MI), SuperEBA (Bosworth, Skokie, IL), and mineral trioxide aggregates (MTA; Dentsply, York, PA). After 4 months, the dogs were sacrificed, and the jaws were prepared for histological sectioning. The distances from the root-end filling materials to the regenerated bone were determined by the evaluation of microradiographic images of the sections with imaging software (Sigma Scan/Image; Jandel Scientific Software, San Rafael, CA). The results were statistically analyzed with analysis of variance using Sigma Stat software (Jandel Scientific Software, San Rafael, CA). RESULTS: The mean distances from the newly regenerated bone were 0.397 +/- 0.278 mm in the MTA group, 0.756 +/- 0.581 mm in the SuperEBA group, and 1.290 +/- 0.386 mm in the amalgam group. There was a statistically significant difference between the amalgam and MTA groups (p < 0.05). No significant differences existed for amalgam versus SuperEBA and SuperEBA versus MTA. CONCLUSION: MTA showed the most favorable periapical tissue response. The distance from MTA to the regenerated bone was similar to the normal average periodontal ligament thickness in dogs.

The role of periodontal ligament cells in delayed tooth eruption in patients with cleidocranial dysostosis.

OBJECTIVE: The clinical appearance of patients with cleidocranial dysplasia (CCD), which is caused by mutations in the RUNX2 gene, is characterized by anomalies of the clavicles, thorax, spine, pelvis and extremities and by disturbances of the skull and tooth development. Of orthodontic relevance are multiple supernumerary teeth associated with delayed tooth eruption. The present investigation is based on the hypothesis that an altered phenotypic expression of periodontal ligament (PDL) cells from CCD patients and a reduced ability of those cells to support the differentiation of bone-resorbing osteoclasts might contribute to delayed tooth eruption. MATERIALS AND METHODS: To test this hypothesis, PDL cells from healthy donors and from two patients with clinically and molecular biologically diagnosed CCD were characterized for the basal and induced mRNA expression of osteoblast marker genes. The physiological relevance of the findings for the differentiation of osteoclasts was examined in an osteoclast assay, as well as in a co-culture model of PDL cells and osteoclast precursors. RESULTS: Both CCD patients displayed missense mutations of the RUNX2 gene. The in vitro experiments revealed an unaltered expression of RUNX2 mRNA, however especially in CCD patient 2 there was a reduced basal expression of mRNA for the key regulatory gene for bone remodeling RANKL. Furthermore, compared to the control cells from healthy donors, these factors were less inducible by stimulation of the cultures with 1alpha,25(OH)(2)D(3). In the osteoclast assays as well as in the co-culture experiments, PDL cells from the CCD patients showed a reduced capacity to induce the differentiation of active osteoclasts. CONCLUSIONS: These data indicate that PDL cells from CCD patients express a less distinctive osteoblastic phenotype resulting in an impaired ability to support osteoclastogenesis which might, in part, account for the delayed tooth eruption that can be observed clinically.

Fracture strength of flared bovine roots restored with different intraradicular posts

OBJECTIVE: The aim of this study was to evaluate the fracture strength and failure mode of flared bovine roots restored with different intraradicular posts. MATERIAL AND METHODS: Fifty bovine incisors with similar dimensions were selected and their roots were flared until 1.0 mm of dentin wall remained. Next, the roots were allocated into five groups (n=10): GI- cast metal post-and-core; GII- fiber posts plus accessory fiber posts; GIII- direct anatomic post; GIV- indirect anatomic post and GV- control (specimens without intraradicular post). A polyether impression material was used to simulate the periodontal ligament. After periodontal ligament simulation, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min in a servo-hydraulic testing machine (MTS 810) applied at 135¨¬ to the long axis of the tooth until failure. The data (N) were subjected to ANOVA and Tukey's post-hoc test (¥á=0.05). RESULTS: GI and GIV presented higher fracture strength (p<0.05) than GII. GIII presented intermediate values without statistically significant differences (p>0.05) from GI, GII and GIV. Control specimens (GV) produced the lowest fracture strength mean values (p<0.05). Despite obtaining the highest mean value, GI presented 100 percent of unfavorable failures. GII presented 20 percent of unfavorable failures. GIII, GIV and GV presented only favorable failures. CONCLUSIONS: Although further in vitro and in vivo studies are necessary, the results of this study showed that the use of direct and indirect anatomic posts in flared roots could be an alternative to cast metal post-and-core.

Biologic response of rapid tooth movement with periodontal ligament distraction.

INTRODUCTION: Length of treatment is a complaint of many orthodontic patients. The purpose of this study was to evaluate the security and feasibility of rapid tooth movement with periodontal ligament distraction. METHODS: Eight male beagles, aged 13 to 16 months, were used in this study. Extraction of the mandibular second premolar and alveolar surgery to reduce the osteal resistance on the mesial side of the extraction socket were performed on the experimental side. Then a device was placed to distract the first premolars distally on the experimental side; on the control side, the first premolars were distalized with nickel-titanium coil springs. The beagles were killed in the first, second, fourth, and eighth weeks after orthodontic force application. RESULTS: The first premolar on the experimental side moved more rapidly than that on the control side (P <0.05). Histologic data indicated that more new bone was deposited on tension area of the experimental side than on the control side. Active and extensive bone resorption in the compressive area and bone deposition in the tension area were observed on the experimental side. CONCLUSIONS: These results suggest that the periodontal ligament can be rapidly distracted without complications. The rapid orthodontic tooth movement by distracting the periodontal ligament cannot be emulated by current conventional orthodontic concepts and methods.

Compressive force induces VEGF production in periodontal tissues.

During orthodontic tooth movement, the activation of the vascular system in the compressed periodontal ligament (PDL) is an indispensable process in tissue remodeling. We hypothesized that compressive force would induce angiogenesis of PDL through the production of vascular endothelial growth factor (VEGF). We examined the localization of VEGF in rat periodontal tissues during experimental tooth movement in vivo, and the effects of continuous compressive force on VEGF production and angiogenic activity in human PDL cells in vitro. PDL cells adjacent to hyalinized tissue and alveolar bone on the compressive side showed marked VEGF immunoreactivity. VEGF mRNA expression and production in PDL cells increased, and conditioned medium stimulated tube formation. These results indicate that continuous compressive force enhances VEGF production and angiogenic activity in PDL cells, which may contribute to periodontal remodeling, including angiogenesis, during orthodontic tooth movement.