[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.

[Immune responses of pulpodentinal complex during caries progression].

Caries is an infectious disease in which the invasion of pathogens and their metabolites can activate the recognition and defense system of the pulpodentinal complex. In-depth understanding of the immune responses mediated by the pulpodentinal complex will help to estimate the real state of the dental pulp during the progression of caries and to take reasonable clinical treatment strategies, which can be more targeted and less invasive. Based on the physiology of the pulpodentinal complex, the present article introduce its immunocompetence and mechanism, reactive changes, clinical intervention and its significance during the caries progression, as to improve diagnostics as well as treatment strategies for caries.

[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.

[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.

[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.

[Role of the operating microscope in diagnosis and treatment of endodontic diseases].

The excellent magnification and illumination of the operating microscope not only helps to improve the quality of conventional root canal therapy, but also plays an important role in the diagnosis and treatment of the difficult cases of endodontic diseases. It has an irreplaceable position over other equipment especially for the treatment of root canal therapy complications and the apical surgery. The structure and operation of the operating microscope are relatively complicated. The proficiency of the dentist may influence the evaluation of its clinical application effect. Based on the review of literature and author's clinical experience, this paper evaluates the role of operating microscope in the diagnosis and treatment of endodontic diseases.

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.

[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.

[Study on the incidence of lateral canals and sealing quality in the apical third roots of permanent teeth with failed endodontic treatments].

Objective: To investigate the association between the frequency and filling rate of lateral canals and the sealing quality in the apical third roots of the permanent teeth with failed endodontic treatments, so as to explore the failure factors of root canal therapy. Methods: Clinical records of the permanent teeth with failed endodontic treatments were collected from the Department of Endodontics, Capital Medical University School of Stomatology during a period of 2 years. The teeth were diagnosed as chronic apical periodontitis and then undergone endodontic microsurgery. The sealing quality of the apical root canal was observed by means of periapical radiographs. The surgical treatments were performed and the resected root apices were collected. The samples were scanned by micro-computed tomography and the 3D volume rendered images of the resected root apices were reconstructed. Moreover, the frequency and the filling rate of lateral canals in the apical third roots were calculated. The potential relationship between tooth position and the presence of lateral canals was evaluated. Results: Totally 89 teeth with 89 root apices met the inclusion criteria and were included in the present study. The rate of correct-filling, underfilling and overfilling was 40% (36/89), 32% (28/89), and 28% (25/89), respectively, examined by periapical radiographs. Amongst all of the 89 samples, lateral canals were found in 44 samples. The incidence of apices with lateral canals was 49% (44/89). Furthermore, 3 out of 44 samples were fully filled with material in the lateral canals, and the rest 41 samples showed no filling materials. The filling rate of the lateral canals was 7% (3/44). However, no significant difference was detected between the tooth position and the presence of lateral canals (P>0.05). Conclusions: The sealing quality of the apical third roots in permanent teeth with failed endodontic treatments was not good enough. The incidence of apices with lateral canals was high, but the filling rate of the canals was low. Further studies are needed to explore the relationship between lateral canals and the failure of endodontic treatment.

[Analysis of the key points in the micro-endodontic treatment].

Micro-endodontic treatment refers to the microscope-assisted endodontic treatment techniques. The microscope offers a stereoscopic, enlarged image under great magnification and illumination at a comfortable working position. It will greatly promote the precision and improve the outcomes of endodontic treatment through enhancing the ability to detect the complexity of the root canal system of teeth that probably cannot be seen by the naked eyes, remove the infectious substances in root canal more efficiently, provide a tight root canal obturation and carry out effective retreatment procedures. The requirements of micro-endodontic treatment are different from the conventional root canal therapy carried out without microscope due to the complicated structure of the microscope. In order to make the use of microscope easier, it is of great importance to learn how to adjust the position of the operator and the patient, preset the angle of objective lens and the eyepiece, select the proper magnification and instruments, practice eye-hand cooperation under the microscope, etc. The purpose of this article was to analyze the key points in the applications of the microscope in endodontic treatment by reviewing the literature together with the author's clinical experience.

[Analysis of virulence factors of Porphyromonas endodontalis based on comparative proteomics technique].

Objective: To analyze the protein expression profile and the potential virulence factors of Porphyromonas endodontalis (Pe) via comparison with that of two strains of Porphyromonas gingivalis (Pg) with high and low virulences, respectively. Methods: Whole cell comparative proteomics of Pe ATCC35406 was examined and compared with that of high virulent strain Pg W83 andlow virulent strain Pg ATCC33277, respectively. Isobaric tags for relative and absolute quantitation (iTRAQ) combined with nano liquid chromatography-tandem mass spectrometry (Nano-LC-MS/MS) were adopted to identify and quantitate the proteins of Pe and two strains of Pg with various virulences by using the methods of isotopically labeled peptides, mass spectrometric detection and bioinformatics analysis. The biological functions of similar proteins expressed by Pe ATCC35406 and two strains of Pg were quantified and analyzed. Results: Totally 1 210 proteins were identified while Pe compared with Pg W83. There were 130 proteins (10.74% of the total proteins) expressed similarly, including 89 known functional proteins and 41 proteins of unknown functions. Totally 1 223 proteins were identified when Pe compared with Pg ATCC33277. There were 110 proteins (8.99% of the total proteins) expressed similarly, including 72 known functional proteins and 38 proteins of unknown functions. The similarly expressed proteins in Pe and Pg strains with various virulences mainly focused on catalytic activity and binding function, including recombination activation gene (RagA), lipoprotein, chaperonin Dnak, Clp family proteins (ClpC and ClpX) and various iron-binding proteins. They were involved in metabolism and cellular processes. In addition, the type and number of similar virulence proteins between Pe and high virulence Pg were higher than those between Pe and low virulence Pg. Conclusions: Lipoprotein, oxygen resistance protein, iron binding protein were probably the potential virulence factors of Pe ATCC35406. It was speculated that pathogenicity of Pe was more similar to high virulence Pg than that to low virulence strain.