Antibacterial and bioactive dental restorative materials: Do they really work?

PURPOSE: This proceedings reviews current antibacterial and bioactive dental materials and new agents in development. METHODS: Experts from across academia, industry and clinical practice were invited to present, discuss, and work together to develop solutions to the challenge of formulating and applying antibacterial dental materials in a symposium in Seoul, Korea in June, 2016.

Fracture resistance of simulated immature maxillary anterior teeth restored with fiber posts and composite to varying depths.

BACKGROUND: Traumatized immature teeth present a unique challenge during treatment, both endodontically as well as restoratively. Hence, the purpose of this study is to evaluate the type and depth of restoration that would be effective in simulated immature maxillary anterior teeth in terms of fracture resistance and mode of failure. MATERIALS AND METHODS: Seventy-five extracted human maxillary anterior teeth were used in this study that was standardized to a length of 13 mm. Instrumentation of the canals was performed after which a Peezo no. 6 was taken 1 mm past the apex to simulate an incompletely formed root. MTA apexification was simulated after which all the teeth were mounted and a 3-mm-diameter engineering twist drill extended the preparation 3 and 7 mm below the facial cemento-enamel junction (CEJ) to simulate Cvek's stage 3. These teeth were divided into seven different groups: Group 1: Negative control: intact teeth; Group 2: Positive control: 3 mm, no restoration; Group 3: Positive control: 7 mm, no restoration; Group 4: 3-mm composite; Group 5: 3-mm quartz fiber post; Group 6: 7-mm composite; Group 7: 7-mm quartz fiber post. Fracture resistance was performed at 130° to the long axis of the tooth with a chisel-shaped tip at the cingulum with a cross-head speed of 5 mm min(-1) , and the maximum load at which the fracture occurred was recorded. RESULTS: Group 1 that was the negative control showed the highest fracture resistance. Among the experimental groups, 4 and 5 showed the highest fracture resistance, which were significantly different from groups 6 and 7, respectively. CONCLUSIONS: Within the limitations of this in vitro study, it can be concluded that using either dual-cure composite or a quartz fiber post with composite resin to a depth of 3 mm would significantly strengthen the roots in immature teeth.

Influence of different types of mouthguards on strength and performance of collegiate athletes: a controlled-randomized trial.

BACKGROUND: Prevention of traumatic dental injuries relies on the identification of etiologic factors and the use of protective devices during contact sports. Mouthguards are considered to be an effective and cost-efficient device aimed at buffering the impacts or blows that might otherwise cause moderate to severe dental and maxillofacial injuries. Interestingly, besides their role in preventing injury, some authors claim that mouthguards can enhance athletic performance. Thus, the purpose of this controlled randomized trial was to evaluate and compare the effect of two different types of mouthguards on the athletic performance and strength of collegiate athletes. MATERIALS AND METHODS: Eighteen college athletes ranging from 19 to 23 years participated in this study. Devices tested in this study included an over-the-counter boil-and-bite mouthguard (O-Flow™ Max Under Armour®) (UA) and a custom-made mouthguard (CM). Physical tests were carefully selected by the head athletic trainer and aimed at evaluating the strength and performance. The following sequence was carried out on each test day: (i) 3-stroke maximum power ergometer test, (ii) 1-min ergometer test, and (iii) a 1600-m run. A random assignment was developed to test all three experimental groups on each test day. Following the tests, each athlete completed a brief anonymous survey aimed at evaluating the athletes' overall satisfaction with each type of mouthguard. RESULTS: Custom-made mouthguards had no detrimental effect on athletic strength and performance and were reported by the athletes as being comfortable and not causing difficulty in breathing. In contrast, boil-and-bite mouthguards did not perform as well and were reported as being uncomfortable and causing breathing difficulties. CONCLUSIONS: Based on the results of this study, the use of custom-made mouthguards should be encouraged in contact sports as a protective measure, without concern for any negative effect on the athletic performance of the athletes.

Novel strategies to enhance survival and growth of pulp cells after dental restorations.

Using ex vivo human tooth, the authors demonstrated that dental pulp stromal cells that survive after placement of composite, mineral trioxide aggregate, and glass ionomer are weaker since they undergo synergistic cell death when exposed to 2-hydroxyethylmethacrylate. DPSCs extracted from teeth that were restored with the combination of composite or MTA or GI with N-acetyl cysteine were protectedfrom cell death. Therefore, application of NAC may protect the DPSCs from adverse effects after tooth restoration.

Immunomodulatory Effects of N-Acetyl Cysteine Treated SCAP.

INTRODUCTION: Stem cells of the apical papilla (SCAP) play an important role in regenerative endodontic procedures (REPs). Previous studies have shown that during REPs, bacteria can activate the innate immune system and cause indirect stem cell toxicity, leading to the lysis of SCAP. N-acetylcysteine (NAC)-treated cells are resistant to apoptosis and have increased differentiation capabilities. The immunomodulatory properties of NAC-treated SCAP are still unknown. Hence, the aim of this study is to evaluate the interactions of SCAP pretreated with and without NAC with the immune system. METHODS: Flow cytometric analysis was performed to assess the effects of NAC on SCAP viability. Human SCAP were then cultured and were either pretreated with NAC or non-treated and co-cultured with human peripheral blood mononuclear cells. A lactate dehydrogenase assay was performed to evaluate the levels of immune cell mediated apoptosis, followed by an enzyme-linked immunosorbent assay (ELISA) to measure levels of proinflammatory cytokines for these co-cultures. Data were analyzed using analysis of variance with post hoc Tukey test. RESULTS: Cells treated with NAC had similar levels of viability as the controls. SCAP pretreated with NAC had significantly lower immune cell-mediated cytotoxicity to nonactivated and activated peripheral blood mononuclear cells. The ELISA results showed that SCAP pretreated with NAC induced lower levels of proinflammatory cytokines. CONCLUSIONS: SCAP pretreated with NAC have a higher chance of surviving the activated immune system. This information may provide a better insight into the properties of these stem cells and may be the key to making REPs more predictable.

Odontoblast apoptosis and intratubular mineralization of sclerotic dentin with aging.

OBJECTIVES: The aims of the study were to evaluate the roles of odontoblast apoptosis in the progression of tubular sclerosis of teeth from donors at different ages and assess its correlation to chemical composition and mechanical properties. DESIGN: Healthy human teeth were obtained and divided into young (age ≤ 25, n = 12) and old (age ≥ 60, n = 12) groups. Odontoblasts were counted with standard hematoxylin and eosin staining. Odontoblast apoptosis within dentinal tubules was determined by cleaved caspase-3 immunostaining. Teeth in each group were evaluated by dynamic nanoindentation and energy-dispersive X-ray spectroscopy (EDS). RESULTS: The number of odontoblasts decreased significantly with age. The most prominent change occurred in the apical third of roots. Odontoblastic apoptosis was visualized within dentinal tubules. The apoptosis staining fraction was significantly higher in the outer and inner dentin of old teeth when compared with young teeth (p < 0.05). EDS showed increased calcium content in peritubular dentin but a decrease in the intertubular dentin with increasing age. Scanning based nanoindentation showed that the old intertubular dentin exhibited a significantly higher elastic modulus. CONCLUSIONS: Odontoblast apoptosis, starting at the cell extension in dentinal tubules and proceeding from outer to inner dentin, contributes to the stoichiometric Ca/P ratio in peritubular dentin, which is potentially responsible for intratubular mineralization due to an imbalance of calcium and phosphorous ions.

Phenotypic and Functional Alterations of Immune Effectors in Periodontitis; A Multifactorial and Complex Oral Disease.

Survival and function of immune subsets in the oral blood, peripheral blood and gingival tissues of patients with periodontal disease and healthy controls were assessed. NK and CD8 + T cells within the oral blood mononuclear cells (OBMCs) expressed significantly higher levels of CD69 in patients with periodontal disease compared to those from healthy controls. Similarly, TNF-α release was higher from oral blood of patients with periodontal disease when compared to healthy controls. Increased activation induced cell death of peripheral blood mononuclear cells (PBMCs) but not OBMCs from patients with periodontal disease was observed when compared to those from healthy individuals. Unlike those from healthy individuals, OBMC-derived supernatants from periodontitis patients exhibited decreased ability to induce secretion of IFN-γ by allogeneic healthy PBMCs treated with IL-2, while they triggered significant levels of TNF-α, IL-1ß and IL-6 by untreated PBMCs. Interaction of PBMCs, or NK cells with intact or NFκB knock down oral epithelial cells in the presence of a periodontal pathogen, F. nucleatum, significantly induced a number of pro-inflammatory cytokines including IFN-γ. These studies indicated that the relative numbers of immune subsets obtained from peripheral blood may not represent the composition of the immune cells in the oral environment, and that orally-derived immune effectors may differ in survival and function from those of peripheral blood.

Comparison of the sealing ability of various bioceramic materials for endodontic surgery.

OBJECTIVES: Endosequence Bioceramic Root Repair Material (BC-RRM) is used in endodontic microsurgery. It is available as a paste and a putty. However, no studies to date have examined the sealing ability of these forms alone or in combination as root-end filling materials. Hence, this study aimed to compare the sealing properties of these 2 forms of BC-RRM. MATERIALS AND METHODS: Forty-two extracted upper anterior teeth were divided into 3 experimental groups, a positive and negative control. After the root canal treatment, the root ends were resected, retroprepared and retrofilled with either putty, paste + putty or mineral trioxide aggregate (MTA). The teeth were mounted in tubes so the apical 3 mm was submerged in Brain Heart Infusion (BHI) broth. The coronal portions of the canals were inoculated with Enterococcus faecalis and BHI broth and incubated for 30 days. The broth in the tubes was analyzed for colony forming units to check for leakage of bacteria from the canal. The teeth from the groups were sectioned and analyzed using scanning electron microscopy (SEM). The Kruskal-Wallis test and analysis of variance were used to analyze the data with a significance level p < 0.05. RESULTS: The BC-RRM and MTA groups showed similar sealing ability. The positive control showed leakage in all samples. The SEM imaging showed the presence of bacteria in all experimental groups at the material-tooth interface. CONCLUSIONS: No significant differences were noted in the experimental groups, providing sufficient evidence that any combination could be effectively used during endodontic microsurgery.

Shrinkage Strains in the Dentin of Endodontically Treated Teeth with Water Loss.

INTRODUCTION: Dehydration has been considered as a potential contributor to vertical root fractures (VRFs) after root canal treatment (RCT). A loss of water could cause embrittlement of dentin and detrimental shrinkage strains. Senior patients have the highest risk of VRF. In this study, we characterized the spatial distribution in shrinkage of tooth roots with respect to donor age and prior RCT. METHODS: Single-rooted human teeth with and without prior RCT were collected from young (age <25 years) and old (age >60 years) adults. Transverse slices were sectioned from the apical, middle, and coronal thirds of the roots, and digital image correlation was used to evaluate shrinkage during free convection. Crack initiation and growth analysis was performed via optical microscopy, and bound water in dentin was characterized by Raman spectroscopy. RESULTS: The rate of shrinkage was significantly higher (p ≤ .05) in the apical third than in the middle and coronal thirds of all teeth regardless of donor age. The highest shrinkage strain occurred in the apical third of old donor teeth with prior RCT. In addition, the RCT-treated old teeth suffered the highest percentage of water loss with dehydration. Cracks initiated from the root surface and extended toward the canal with loss of water and shrinkage. CONCLUSIONS: The apical third undergoes significantly larger shrinkage strains with dehydration than the remainder of the root. Prior RCT exacerbates the extent of shrinkage, particularly in the teeth of seniors and after clinical function, which could increase the propensity for VRF.

Fusobacterium nucleatum outer membrane proteins Fap2 and RadD induce cell death in human lymphocytes.

Bacterially induced cell death in human lymphocytes is an important virulence factor for pathogenic bacteria. Previously discovered mechanisms of bacterially induced cell death are predominantly based on the transfer of bacterial proteins to the target host cell, such as the toxins secreted through type I, II, and VI secretion systems or effector proteins injected through type III, IV, and Vb secretion systems. Here, we report a mechanism employed by the Gram-negative oral pathogen Fusobacterium nucleatum for cell death induction of human lymphocytes via two outer membrane proteins (OMPs), Fap2 and RadD, which share regions homologous to autotransporter secretion systems (type Va secretion systems). Genetic and physiological studies established that inactivation of the two OMPs led to significantly reduced ability to trigger cell death in Jurkat cells, while the corresponding double mutant was almost completely attenuated. Additional biochemical and molecular analyses demonstrated that cell-free F. nucleatum membranes are sufficient to induce cell death in Jurkat cells, suggesting that no active process or effector protein transfer was necessary to induce eukaryotic cell death.

Locating the MB2 canal in relation to MB1 in Maxillary First Molars using CBCT imaging.

The aim of this study is to determine the location of MB2 in maxillary first molars in relation to the MB1 using the cone-beam computed tomography (CBCT) imaging. In this retrospective study, electronic health records' system was utilised to identify patients who acquired CBCT for the maxillary first molar as an imaging adjunct to their endodontic treatment. Data were evaluated, and statistical analysis was performed. For the initial treatment cases, the distance from MB1 to MB2 was 2.06 ± 0.52 mm. This did not change significantly for cases that were being retreated. Statistically significant differences were observed between the distances from MB1 to MB2 in males vs. female teeth with males demonstrating longer distances as compared to females. Variations in anatomy exist between patients but this study established some guidelines for clinicians to locate the MB2 canal orifices. This could potentially help with treating these teeth with minimal failure rates.

In Vivo Evaluation of Effect of Preoperative Ibuprofen on Proinflammatory Mediators in Irreversible Pulpitis Cases.

INTRODUCTION: Preoperative administration of nonsteroidal anti-inflammatory drugs has been suggested as a method for increasing the efficacy of local anesthetics and decreasing postoperative pain in symptomatic irreversible pulpitis cases. However, the effects of ibuprofen at the molecular level are still unknown. Hence, the purpose of this study was to compare the levels of proinflammatory mediators in the dental pulp of teeth with irreversible pulpitis in patients who medicated with preoperative ibuprofen versus those who did not. METHODS: Thirty-four patients undergoing conventional endodontic therapy for teeth with irreversible pulpitis were selected and randomly assigned into either the ibuprofen or nonibuprofen group. Four patients undergoing endodontic therapy for prosthodontic reasons served as controls. Patients in the ibuprofen group were instructed to take 600 mg ibuprofen 1 hour before treatment, whereas patients in the nonibuprofen and control groups were asked to avoid analgesics before treatment. Blood samples obtained from the pulp upon access were tested for levels of prostaglandin E2, tumor necrosis efactor alpha, interleukin (IL)-6, IL-1ß, and interferon gamma using high-sensitivity enzyme-linked immunosorbent assay. Postoperative pain levels were recorded for the groups. Data for the cytokine levels and postoperative pain were analyzed using statistical analysis. RESULTS: There was a significant decrease in the levels of prostaglandin E2, tumor necrosis factor alpha, IL-6, and interferon gamma in the ibuprofen group compared with the nonibuprofen group. No significant differences were noted in the postoperative pain levels between these groups. CONCLUSIONS: The data showed that preoperative ibuprofen significantly decreased the levels of most proinflammatory cytokines in the dental pulp, which could possibly help with anesthesia in irreversible cases.

Contribution of Root Canal Treatment to the Fracture Resistance of Dentin.

INTRODUCTION: Although the strength and toughness of dentin decrease with age, no study has explored if restorative treatments are a contributing factor. METHODS: Multiple extracted teeth were obtained from randomly selected donors and categorized according to donor age and prior root canal treatment. The microstructure and chemical composition of radicular dentin were evaluated using scanning electron microscopy and Raman spectroscopy, respectively, and the strength was evaluated in 4-point flexure to failure. Data were compared using the Student t test. RESULTS: Dentin from the root canal-restored teeth exhibited significantly lower strength (P < .05) than tissue from age- and donor-matched unrestored tooth pairs. Although there was no significant difference in the mineral-to-collagen ratio between the 2 groups, dentin obtained from the root canal-treated teeth exhibited more extensive collagen cross-linking and lower tubule occlusion ratios than the unrestored tooth pairs. CONCLUSIONS: There is a decrease in the strength of radicular dentin with aging, but prior root canal treatment increases the extent of degradation.

Regulation of IGFBP6 gene and protein is mediated by the inverse expression and function of c-jun N-terminal kinase (JNK) and NFkappaB in a model of oral tumor cells.

The aim of this study is to identify potential gene and protein targets when nuclear factor kappa B (NFkappaB) and c-jun N-terminal kinase (JNK) were inversely expressed in oral tumors. To determine which genes were regulated synergistically by the inverse expression of NFkappaB and JNK, a pathway specific microarray analysis was performed. While either inhibition of NFkappaB or activation of JNK alone was unable to affect the IGFBP6 gene expression in microarray analysis, concomitant increase in JNK activation in the presence of NFkappaB inhibition increased the expression of this gene significantly. Synergistic increase in IGFBP6 gene expression was also confirmed by RT-PCR and Northern blot analysis of transfected cells. Accordingly, the levels of IGFBP6 protein secretion rose synergistically when JNK was over-expressed in NFkappaB knock down cells. In addition, increased expression of JNK in the absence of NFkappaB resulted in a significant induction of cell death in oral tumors when either left untreated or treated with TNF-alpha and TPA. Moreover, when JNK was inhibited by dominant negative JNK (APF), a significant decrease in cell death could be observed in TNF-alpha and TPA treated NFkappaB knock down oral tumors. Therefore, increased induction of IGFBP6 gene or protein expression in oral tumors could be regarded as a potential predictive marker of tumor sensitivity and could be used for prognostic purposes, since a significant correlation could be observed between increased induction of apoptotic cell death and elevated levels of IGFBP6 in these tumors.

Efficacy of different carriers for the triple antibiotic powder during regenerative endodontic procedures.

Chemical debridement during Regenerative Endodontic procedures is important. Previous research studies have evaluated various antibiotics and their concentrations but none have addressed the concern of delivering these materials. Hence, the purpose of this study was to determine what carrier could be used effectively in a clinical setting. Sixty caries-free maxillary incisors were used and inoculated with Enterococcus faecalis and divided into positive and irrigation controls and experimental groups that had triple antibiotic powder (1:1:1 ciprofloxacin:metronidazole:minocycline) delivered using various carriers: saline, cotton, sponge and methylcellulose. Current AAE regenerative protocols were followed. S2 sampling was performed and tested for bacterial presence via culturing and SEM. The results demonstrated that saline was the most effective carrier for the triple antibiotic powder while cotton and sponge were most ineffective. Saline and methylcellulose both reduced bacterial counts to a significant level. Overall, this study demonstrated that saline as a carrier was most effective and should be routinely used.

The Incidence of Second Mesiobuccal Canals Located in Maxillary Molars with the Aid of Cone-beam Computed Tomography.

INTRODUCTION: Many endodontic treatment failures in maxillary molars result from missed second mesiobuccal (MB2) canals. An MB2 canal orifice is present in as many as 95% of maxillary molars, but these canals are not always located during endodontic procedures. Additional tools, such as cone-beam computed tomographic (CBCT) imaging, may be needed to locate these canals in maxillary molars. Hence, the aims of this study were to investigate the frequency of use of CBCT imaging during the treatment of maxillary molars and to evaluate the influence of its use on the detection of MB2 canals. METHODS: Endodontic treatment records, digital intraoral radiographs (when present), and CBCT images from all maxillary first and second molars treated at the University of Washington, Seattle, WA, between 2010 and 2014 (N = 886) were reviewed. Statistical analysis was performed to assess differences between the groups. RESULTS: Overall, an MB2 canal was found in 55.8% of the maxillary molars studied, and CBCT imaging assisted in detecting 11.7% of these canals. CBCT imaging was used in 16.5% of the cases treated and was used significantly more for retreatment cases. CBCT imaging was used preoperatively in 5.6% of cases, and the data show that significantly more MB2 canals were located when a preoperative CBCT image was available. More MB2 canals were located in first molars without full-coverage crowns. CONCLUSIONS: The data show that CBCT imaging is a valuable tool in locating MB2 canals. Based on the results of his study, the use of CBCT imaging could be warranted when treating maxillary molars.

Characterization of the Cellular Responses of Dental Mesenchymal Stem Cells to the Immune System.

INTRODUCTION: Dental stem cells have gained importance recently and are being used for various purposes in regenerative medicine and dentistry. Although much research has been done to show the various properties of these dental stem cells, the immunomodulatory properties of some of these stem cells are still unknown. This is important considering these cells are being used routinely. Therefore, the aim of this study was to investigate the interactions between the activated immune cells and 3 types of dental-derived mesenchymal stem cells: dental pulp stem cells, stem cells from human exfoliated deciduous teeth, and stem cells of the apical papilla (SCAP). METHODS: SCAP, dental pulp stem cells, stem cells from human exfoliated deciduous teeth, and periodontal ligament fibroblasts were cultured, and various assays were performed including a proliferation assay, flow cytometric analysis, lactate dehydrogenase and chromium-51 cytotoxicity assays, and an enzyme-linked immunosorbent assay to evaluate the interactions of these dental stem cells when cocultured with either peripheral blood mononuclear cells or natural killer cells. RESULTS: SCAP were less resistant to immune cell-mediated cytotoxicity as seen from the results obtained from the LDH and chromium-51 cytotoxicity assays. The flow cytometric analysis showed a lower resilience of SCAP to cytotoxic compounds. The enzyme-linked immunosorbent assay results demonstrated that the SCAP induced high levels of proinflammatory cytokine secretion compared with the other dental stem cells. CONCLUSIONS: SCAP did not perform as well as the other dental stem cells. This could in turn affect their survival and differentiation abilities as well as their functionality. This may be an important aspect to consider when selecting dental stem cells for various regenerative procedures.

N-acetylcysteine protects dental pulp stromal cells from HEMA-induced apoptosis by inducing differentiation of the cells.

Resin-based materials are now widely used in dental restorations. Although the use of these materials is aesthetically appealing to patients, it carries the risk of local and systemic adverse effects. The potential risks are direct damage to the cells and induction of immune-based hypersensitivity reactions. Dental pulp stromal cells (DPSCs) and oral keratinocytes are the major cell types which may come in contact with dental resins such as 2-hydroxyethyl methacrylate (HEMA) after dental restorations. Here we show that N-acetylcysteine (NAC) inhibits HEMA-induced apoptotic cell death and restores the function of DPSCs and oral epithelial cells. NAC inhibits HEMA-mediated toxicity through induction of differentiation in DPSCs, because the genes for dentin sialoprotein, osteopontin (OPN), osteocalcin, and alkaline phosphatase, which are induced during differentiation, are also induced by NAC. Unlike NAC, vitamins E and C, which are known antioxidant compounds, failed to prevent either HEMA-mediated cell death or the decrease in VEGF secretion by human DPSCs. More importantly, when added either alone or in combination with HEMA, vitamin E and vitamin C did not increase the gene expression for OPN, and in addition vitamin E inhibited the protective effect of NAC on DPSCs. NAC inhibited the HEMA-mediated decrease in NF-kappaB activity, thus providing a survival mechanism for the cells. Overall, the studies reported in this paper indicate that undifferentiated DPSCs have exquisite sensitivity to HEMA-induced cell death, and their differentiation in response to NAC resulted in an increased NF-kappaB activity, which might have provided the basis for their increased protection from HEMA-mediated functional loss and cell death.

In-vivo microbiologic evaluation of polytetrafluoroethylene and cotton as endodontic spacer materials.

OBJECTIVE: Spacers are commonly placed between the canal orifice and the temporary material between endodontic treatment appointments. This prevents the temporary restoration material from obstructing the canal orifices and allows for easy removal. Various endodontic spacers are currently used, including polytetrafluoroethylene (PTFE) tape. Previous in-vitro studies have demonstrated the advantages of using PTFE over using cotton; however, no in-vivo studies have demonstrated this. Hence, the purpose of this study was to evaluate which spacer showed less bacterial leakage between endodontic treatments. METHOD AND MATERIALS: Fifty patients participated in the study and were randomly assigned to either the cotton or the PTFE group. Root canal treatments were completed in two appointments. Cotton and PTFE spacers were collected after a 2- to 4- week time interval between the first and second appointments. Samples were incubated on agar plates for 48 hours and then evaluated for presence of microbial growth. Colony forming units (CFUs) were counted for each of the samples. The results were analyzed using nonparametric statistical tests. RESULTS: Fifteen of the 24 cotton spacers and two of the 24 PTFE spacers were positive for bacterial growth. CONCLUSION: Cotton fibers exposed to the oral environment could potentially wick contaminants into the pulp chamber. The tendency of cotton to distort under masticatory forces may allow disruption of the temporary material's marginal seal. Based on the results of this study, the use of PTFE is strongly recommended over cotton as an endodontic spacer material. PTFE performed better than cotton in this in-vivo microbial study.

Analysis of Surface Characteristics of ProTaper Universal and ProTaper Next Instruments by Scanning Electron Microscopy.

BACKGROUND: Many new rotary files systems have been introduced, however, limited research has been conducted related to the surface irregularities of these files and if these have any effects on the files themselves. Hence, the aim of the present study was to analyze surface irregularities of the ProTaper® Universal rotary files (PTU) and the ProTaper Next™ rotary files (PTN) before and after instrumentation in curved canals. The main objective was to investigate the nature of these irregularities and how they might influence the use and fracture of rotary files during root-canal treatments. MATERIAL AND METHODS: The files were examined pre-operatively using a stereomicroscope and scanning electron microscopy(SEM) to analyze surface imperfections and the presence of particles. Mesial roots of forty extracted mandibular molars were selected. Each instrument was used to prepare one of the mesial canals. The files were then rinsed with alcohol, and autoclaved and analyzed again. RESULTS: Of the 80 files used in this study, five files fractured, five files unwound and seven files were curved or bent and they all belonged to the PTU group. Irregularities and debris could be visualized with the SEM on both unused PTU and PTN files. Most of the debris was found associated with deeper milling grooves and defects on the surface of the metal. Surface analysis of the files that were used and sterilized were performed and the SEM images demonstrated organic debris, metal flash, and crack formation and initiation of fractures for both file types. All files showed machining grooves, metal flash, debris, and defects on cutting edges. CONCLUSIONS: These irregularities appear to be critical in the accumulation of debris and initiation of fatigue and crack propagation within the NiTi alloy. The accumulation of debris could be a concern due to the potential exchange of organic debris between patients. Key words:ProTaper® Universal, ProTaper Next™, surface characteristics, SEM.