[Advances in the application of the bony window technique in endodontic microsurgery].

The bony window technique refers to cutting the intact bone plate to form a bone window and a free bone block to get access to lesions under the bone. At the end of the surgery, the dislocated bony lid needs to be repositioned to its original position. In endodontic microsurgery, compared with conventional osteotomy, the bony window technique has the advantages of improving the view of surgery and operability, reducing postoperative bone defects, promoting bone healing, and maintaining the integrity of the jaw outline. Accurate positioning and preparation of the bony window are important prerequisites for subsequent operations during the surgery, but it's difficult in some situations, such as when the operative area is located posteriorly or the bone cortex on the lesion surface is thick and intact. What's more, whether the free bone block can be stabilized in situ after repositioning is closely related to the prognosis of the surgery. The complementary application of digital navigation technology and bone cavity filling materials may help to improve the bony window technique and provide more possibilities for the retention of affected teeth in difficult cases.

[Clinical application of direct composite resin in esthetic restoration].

The direct composite resin bonding is widely used in the esthetic restorations of anterior teeth. Due to the technique sensitive procedure, the esthetic effect and long-term clinical performance of direct composite resin restoration have long been the focus of dental clinicians. This article will analyze the influencing factors of esthetic effect of composite resin from three aspects, including materials, teeth and technology. Also, it will summarize the clinical performance of direct composite resin from the perspective of esthetic evaluation. Eventually, this article will provide guidance for the clinical application of esthetic restoration of direct composite resin bonding.

Observation of Monoenergetic Electrons from Two-Pulse Ionization Injection in Quasilinear Laser Wakefields.

The generation of low emittance electron beams from laser-driven wakefields is crucial for the development of compact x-ray sources. Here, we show new results for the injection and acceleration of quasimonoenergetic electron beams in low amplitude wakefields experimentally and using simulations. This is achieved by using two laser pulses decoupling the wakefield generation from the electron trapping via ionization injection. The injection duration, which affects the beam charge and energy spread, is found to be tunable by adjusting the relative pulse delay. By changing the polarization of the injector pulse, reducing the ionization volume, the electron spectra of the accelerated electron bunches are improved.

[Diagnosis and treatment strategy of permanent tooth developmental disturbances caused by primary tooth trauma].

The trauma to primary tooth may lead to developmental disturbances of permanent tooth. Because the traumatic events are often forgotten as accurred earlier, the timely diagnosis and intervention treatment are not conducted, resulting in aesthetic and functional disorders. This paper systematically elaborates the types of developmental disturbances in permanent tooth after traumatic injuries to the primary predecessor, and the etiology, mechanism, related factors as well as the treatment options, in order to provide references for the prevention of serious complications in inherited permanent tooth caused by primary tooth trauma.

[Causes, diagnosis and treatment strategies for dental pulp calcification].

Dental pulp calcification can lead to root canal stenosis or obliteration. It is usually difficult to negotiate the root canal if the affected tooth needs to be treated and intraoperative complications are easily brought about during the root canal treatment. The etiologies of dental pulp calcification are complicated and careful considerations should be given to the diagnosis and treatment. Only by weighing the advantages and disadvantages can appropriate treatment plan be chosen. Based on the literature and authors' clinical experiences, the present article summarizes the causes, pathogenesis, diagnosis and treatment strategies of dental pulp calcification, in order to provide some references in diagnosis and treatment for the dental clinicians.

[Strengthening the prevention and treatment of caries in patients receiving systemic therapy].

The development of dental caries is affected by various factors. Patient's general health status can affect the risk of caries. Some systemic diseases may improve caries incidence or cause dental caries by changing oral microenvironment, affecting salivary gland function and salivary composition, and destroying dental structure directly or indirectly. The clinical symptoms and signs of caries associated with systemic diseases are different from common caries and this type of caries has its special strategy of prevention and therapy. The present review article analyzes the causes and mechanisms of caries susceptibility in patients receiving systemic therapy and systematically introduce the modern concepts of caries prevention and management in systemic therapy.

[Reconsideration of the diagnosis and treatment for dens invaginatus].

Dens invaginatus (DI) is a developmental dental anomaly with complicated anatomical features and a broad spectrum of morphologic variations posing challenges of diagnosis and treatment to dental clinicians. Cone-beam CT (CBCT) can provide a more detailed 3D view of the complex anatomical variations in DI and help dental clinicians to verify the classification of DI and to improve the accuracy of diagnosis. A number of treatment planning options may need to be considered based on DI types, peri-radicular pathology involved and apical orifice closure status. Applications of modern endodontic techniques and novel materials may induce successful treatments and favorable outcomes. The aim of the present article is to review the etiology, classification and treatment outcome of DI and to provide guidelines of diagnosis and management of DI cases for dental clinicians.

[Depletion of PRDM9 inhibited the osteogenic differentiation potential of periodontal ligament stem cells].

Objective: To investigate the effect of PR domain zinc finger protein 9 (PRDM9), one of the histone methylated transferases, on osteogenic differentiation ability of periodontal ligament mesenchymal stem cells (PDLSC). Methods: PDLSC with PRDM9 gene knocked down by PRDM9 shRNA using recombinant lentiviral vector were allocated into the PRDM9sh group, and the transfected shRNA was as the control group. The gene expression efficiency was evaluated by reverse transcription polymerase chain reaction (RT-PCR). Alkaline phosphatase activity (ALP), alizarin red staining, mineralization and osteocalcin, which belongs to osteogenic differentiation markers detected by RT-PCR and Western blotting to detect the osteogenic differentiation ability of stem cells from periodontal ligaments in vitro. In vivo, PRDM9sh and control group cells was transplanted into the dorsal dermal to explore the osteogenesis. The area percentage of new osteogenic tissue was calculated by image pro software and statistically analyzed. Results: RT-PCR results showed that the relative expression of PRDM9 gene in PRDM9sh (0.460±0.017) was significantly lower than that in control group (1.000±0.107) (P<0.05). The results of ALP activity determined at 5 days postinduction in a significant decrease in PRDM9sh cells (0.762±0.063) compared with control group (1.225±0.058) (P<0.01). Alizarin red staining induced by osteogenesis at 2 weeks and 3 weeks showed that the staining of PRDM9sh was significantly lighter than that in control group. Quantitative calcium analysis results showed that the calcium ion concentration induced by osteogenesis at 2 weeks and 3 weeks [(0.071±0.004), (0.075±0.001)] in PRDM9sh was significantly lower than that in control group at 2 weeks and 3 weeks [(0.282±0.006), (0.485+0.004)] (P<0.01). RT-PCR results showed that the relative expression of osteocalcin mRNA in PRDM9sh (1.059±0.148) was significantly lower than that in control group at 2 weeks (2.542±0.190) (P<0.01). Western blotting results showed that osteocalcin expression in PRDM9sh was significantly lower than that in control group at 1 and 2 weeks after osteogenesis induction. Animal transplantation experiments results indicated that PRDM9 significantly inhibited the osteogenesis of PDLSC in vivo, and the proportion of osteogenic area calculated showed that the osteogenic capacity of PRDM9sh [(3.8±2.41)%] was significantly lower than that in control group [(24.54±7.06)%](P<0.05). Conclusions: Depletion of PRDM9 repressed the osteogenic differentiation of stem cells from periodontal ligament in vitro and in vivo.

[Complications occurred in root canal mechanical preparation: the reason, prevention and management].

Root canal preparation is one of the important procedures in root canal treatment as well as one of the key factors to the success of root canal treatment. It consists root canal cleaning and shaping, and further provides a favourable condition for root canal obturation. Because of the complexity and irregularity of root canal system, complications may occur during the root canal mechanical preparation, such as root canal ledges, transportations, perforations, instruments separating and flare ups. Understanding the reason and management of root canal mechanical preparation complications is helpful to prevent its occurrence and to reduce the unfavourable prognosis as well. This article discusses and systematically analyzes the reason, prevention and management of the complications in root canal mechanical preparation, in order to enhance the awareness of clinicians on these complications.

[Impact of fractured file removal from the middle third root canal on vertical root fracture resistance: three-dimensional finite element analysis].

Objective: To analyze effect of fractured file removal from the middle third root canal on root fracture resistance using finite element analysis, which provides a theoretical basis for clinical prognosis evaluation. Methods: Two finite-element models were established, the fractured file removal model (fractured file located in the middle third of root canals, followed by ultrasonic file removal and root canal preparation) and the control model (root canal preparation only), and compressive displacement dependencies on compressive force was computed and compared with experimental data for validation. The validated finite-element models were used to analyze the stress distribution differences during the initiation, propagation and completion of the crack between fractured file removal specimen and control one. Results: The critical breaking force of the fractured file removal specimen was 406 N, and the finite element simulation result was 396 N. The critical breaking force of the control specimen was 502 N, and the finite element simulation result was 483 N. The position of crack initiation in the finite element simulation was basically consistent with that in the experiment. The experimental data of compressive test and the results of finite-element computation were in agreement, thus validating the finite-element model. In the process of continuous pressure, the stress distribution of the control root is relatively uniform, and the location of crack initiation and the direction of propagation have a certain unpredictability. Compared with the control root, the stress concentration on the root with fracture file removal was obvious, especially on edges, and the number of cracks are much more. Because of the thinner radicular wall, the crack propagation rate is faster too. Therefore, the overall root fracture resistant is decreased obviously. Conclusions: During the fractured file removal procedure, amount of dentine removed should be minimized, and the edges and corners which caused by fractured file removal should be shaped to smooth in order to reduce the stress concentration and prevent the root from fracture.

[Effect of autoclave on surface microstructure and cyclic fatigue resistance of R-phase rotary instruments].

OBJECTIVE: To compare the effects of autoclave on surface microstructure and cyclic fatigue resistance of K3XF and K3. METHODS: Forty-eight size 25, 0.06 taper 25 mm-long K3XF or K3 were randomly divided into 4 groups (n=12). The instruments from group 1 were not autoclaved, and the groups 2 to 4 underwent autoclave for 10 cycles, 20 cycles, and 30 cycles, respectively. The surface microstructure of two instruments randomly selected from each group was observed using scanning electron microscope (SEM). The remaining 10 instruments were submitted to the cyclic fatigue test by using a simulated metal root canal with curvature of 60° and radius 3.5 mm. The time till fracture was recorded, the number of cyclic fatigue (NCF) calculated, the fragment length evaluated, and the topographic features were analyzed using SEM. The data were analyzed using the two-way ANOVA analysis by SAS 9.3 software at a significance level of P<0.05. RESULTS: SEM observation identified rough features on the surface of K3XF with micropores existing evenly. K3 was characterized by machining grooves, which located specifically in the flute, leaving a smooth cutting edge. After autoclave, SEM observation indicated that the micropores in the surface of K3XF became larger and more, whereas the machining grooves in the surface of K3 were squeezed, out of shape and flaking. As far as the NCF was concerned, new K3XF was 210±59, and no significant difference was found after 10, 20, and 30 cycles of autoclave for K3XF, values being 178±37, 208±48, and 227±43, respectively (P>0.05). For K3, the new one was 145±38, and no significant difference in NCF was demonstrated after 10 and 20 cycles of autoclave, with the values of 128±43 and 124±46, respectively (P>0.05). However, after 30 cycles of autoclave of K3, significant increase to 216±38 was identified (P<0.05). Topographic features demonstrated typical cyclic fatigue for all the groups. CONCLUSION: The surface roughness of K3XF was increased after autoclave, while the cyclic resistance remained stable after up to 30 cycles.

[Metallurgic behavior and mechanical property of nickel-titanium endodontic files made by 3 heat treatment techniques].

Objective: To compare the phase transformation behavior, bending property and cyclic fatigue resistance of CM-wire, R-phase and M-wire nickel-titanium endodontic files treated by 3 heat treatment techniques. Methods: Hyflex CM (25 mm, 25#/0.06) made from CM wire, TF (25 mm, 25#/0.06) made from R-phase heat treatment, ProTaper Next X2 (25 mm, tip size 25#/0.06) made from M-wire, Mtwo (25 mm, 25#/0.06) and ProTaper F2 (25 mm, tip size 25#/0.08) made from conventional nickel-titanium wire were chosen. Five of each files were chosen for differential scanning calorimetric (DSC) evaluation (n=5). The specimens were prepared from adjacent portions of the shaft. The weight and length were typically (20±1) mg and 2-3 mm. Another eight of the 5 nickel-titanium files were undergone cantilever-bending test, respectively (n=8). Further ten of the 5 instruments were submitted to the cyclic fatigue test by using a simulated metal root canal (n=10). The data of M(s), M(f), A(s), A(f), ΔH, bending load, number of cyclic fatigue (NCF), fragment length were analyzed using one-way analysis of variance at a significance level of P<0.05. Results: The A(f) of Hyflex CM [(60.27±0.94) ℃] and ProTaper Next [(51.40±0.32) ℃] were higher than body temperature of 37 ℃. The bending load values at 3.0 mm deflection of Hyflex CM [(0.867±0.074) N], TF [(1.275±0.146) N], Mtwo [(2.281±0.426) N], ProTaper Next [(3.104±0.252) N] and ProTaper [(4.227±0.483) N] increased gradually and significantly. The NCF of Hyflex CM (582±99), TF (427±85), ProTaper Next (158±22), Mtwo (129±32) and ProTaper (65±20) decreased gradually. Conclusions: The 3 heat treatment techniques exert tremendous influence on the phase transformation behavior and mechanical characteristics of the files, which demonstrate improved bending property and cyclic fatigue resistance than the conventional ones.

The regulation of DLTA gene in bacterial growth and biofilm formation by Parvimonas micra.

OBJECTIVE: To evaluate the effect of dltA-deficient mutant on the bacterial growth and biofilm formation by P. micra ATCC 33270. Parvimonas micra contributes to many human polymicrobial infections, and is common in dental plaque biofilms of patients with periodontal and endodontic conditions. Lipoteichoic acid (LTA) performs several functions in gram-positive bacteria, including maintenance of cationic homeostasis and modulation of autolytic activities. The activation of dltA gene expression protects LTA expressing gram-positive bacteria from innate immune anti-microbial defense. MATERIALS AND METHODS: Deficient mutant of the dltA gene was created from P. micra ATCC 33270 by homologous recombination. Colony-forming units (CFUs) and turbidity helped estimate the growth of P. micra. Crystal violet staining, Confocal Scanning Laser Microscopy (CSLM) and Scanning Electron Microscopy (SEM) evaluated biofilm mass and structure. RESULTS: P. micra ATCC 33270 with dltA-deficient mutant was successfully established. CFUs of the wild-type strains were significantly higher than that of the dltA-deficient mutant strains after 24 h, 48 h, 72 h and 7 d culture (all p < 0.05). The growth rate of dltA-deficient mutant strains was significantly lower than their wild-type counterparts. Furthermore, crystal violet staining showed that the dltA mutant formed significantly less biofilm as compared to wild-type strains. The dltA-deficient mutant synthesized a thin and incomplete biofilm after incubation for 48 h. With increasing incubation time, all biofilm units were seen to shrink, and this structure almost disappeared after 7 days of culture as observed by CSLM and SEM. CONCLUSIONS: The dltA gene is associated with bacterial growth and biofilm formation by P. micra ATCC 33270.