Incidence and contributing factors of non-root canal treated teeth with chronic fatigue root fracture: A cross-sectional study.

BACKGROUND/PURPOSE: Chronic fatigue root fracture describes a root fracture in a non-root canal treated (non-RCT) tooth. This study aimed to report the incidence and contributing factors of non-RCT teeth with chronic fatigue root fracture in a Taiwanese population. METHODS: This cross-sectional study included teeth extracted at Taipei Veterans General Hospital in Taiwan between 2018 and 2019. The reasons for extractions were recorded and included vertical and horizontal root fractures (VRF and HRF). Comparisons of clinical factors between teeth with fatigue VRF and teeth with fatigue HRF were performed by chi-square or Fisher exact test, where appropriate. RESULTS: Of the 4207 extracted teeth examined, 263 (6.25%) had tooth fracture. Thirty-two non-RCT teeth had chronic fatigue root fracture, including 16 with VRF and 16 with HRF. The incidence was 0.76% (32/4207). The occurrence of chronic fatigue root fracture was higher in males (83.9%). The mean age of the 31 patients with chronic fatigue root fracture was 71.7 ± 13.1 years. More than half of these teeth had intact crowns with severe attrition. The fatigue VRF occurred more frequently in molars (P = 0.003), in roots with a long oval cross-section (P = 0.037), and in terminal teeth (P = 0.013) than the fatigue HRF. CONCLUSION: The incidence of chronic fatigue root fracture is 0.76%. Both VRF and HRF occur mainly in aged males, in posterior teeth with attrition, and in teeth without restoration. Tooth position, cross-section root morphology, and terminal tooth are contributing factors related to chronic fatigue root fracture.

A retrospective cohort study on outcome and interactions among prognostic factors of endodontic microsurgery.

BACKGROUND/PURPOSE: Endodontic microsurgery (EMS) is a reliable treatment for teeth with non-healing apical periodontitis. This study evaluated the outcome of EMS with mineral trioxide aggregate as the retrograde filling material and identified potential prognostic factors associated with the EMS outcome. METHODS: Consecutive clinical and radiographic records of EMS performed in a teaching hospital from 2013 to 2017 were reviewed. Cases of root fracture, cemental tear, re-surgery, and incomplete records were excluded. After selection, 268 EMS-treated teeth with the follow-up period more than one year were included. Surgical outcome as success or failure was evaluated according to Molven's criteria. For analysis of potential prognostic factors, multivariate logistic regression was performed followed by bivariate chi-square tests. Stratified analysis was performed to understand the interactions between two prognostic factors. RESULTS: The overall EMS success rate was 89.9% in this study. Tooth type (anteriors vs. molars, odds ratio (OR) = 6.83, P = 0.001, anteriors vs. premolars, OR = 4.27, P = 0.010) and endodontic-periodontal (endo-perio) communicating defects (with vs. without, OR = 4.92, P = 0.005) both had a significant influence on the EMS outcome. The negative impact of endo-perio communicating defects was closely associated with tooth type. Premolars with endo-perio communicating defects had significantly higher rates of failure. CONCLUSION: The EMS outcome is significantly affected by the tooth type and endo-perio communicating defect. The presence of endo-perio communicating defects has a greater negative influence on the success rate for premolars than for anteriors and molars.

Evaluation of students' self-assessment performance in preclinical endodontic training by means of rubrics and a 3D printed model.

BACKGROUND/PURPOSE: Effective evaluation of students' self-assessment ability is crucial. This study was to develop a standardized 3D printed teaching model accompanied by structured scoring rubrics for preclinical endodontic training, to appraise students' self-assessment ability, and to evaluate their perceptions of the training system. METHODS: The 3D printing model was designed to house a standardized central incisor. Forty-four undergraduate dental students were enrolled and their endodontic performance was self-assessed and also rated by a teaching assistant and a tutor using 3 structured rubrics including access cavity, mechanical preparation, and obturation assessments. In total, 21 rubric evaluation items of preclinical tasks were assessed, and the assessment results from the student, teaching assistant, and tutor were compared. Furthermore, questionnaires were used to evaluate students' experiences with the new system. RESULTS: The tutor, teaching assistant, and students all had similar scorings and high intraclass correlation coefficients (ICC) for mechanical preparation and obturation rubrics, while the students had underestimated scores on the access cavity rubric with a rather low ICC of 0.387, which also lead to the underestimated overall scoring (P < 0.05). Among the 21 evaluation criteria, 9 items were rated statistically different (P < 0.05), which denoted the major deficiencies of students' self-assessments. More than 80% of students rated satisfied for most of the questions regarding the new training system, except the tactile sensation, hardness, and radiopacity. CONCLUSION: The proposed standardized 3D printed model and structured scoring rubrics is feasible for preclinical endodontic training, and standardized evaluation of students' self-assessment ability.

Association between pain, anxiety, and pain relief in patients receiving emergent endodontic treatment.

OBJECTIVES: The experience of pain relief is closely associated with the affective-cognitive processing of hedonic value. Higher pain relief plays a key role in patients' satisfaction with treatment and higher motivation to receive treatment. Previous studies focused on pain and anxiety of endodontic treatment. However, the association between pain relief, pain, and anxiety has not been investigated. MATERIALS AND METHODS: We investigated 35 patients (20 females and 15 males, with mean age 46.3 years old) with symptomatic irreversible pulpitis receiving emergent endodontic treatment. Pain-related experience, including pain relief, pain, and anxiety, was assessed before and after treatment, based on an 11-point numerical scale. RESULTS: We found that before treatment, the expected pain relief (median score = 8) that one anticipated was positively correlated with the degree of pain reduction perceived after treatment (two-tailed rho = 0.51, p = 0.002). Expected pain relief was also positively correlated with the post-treatment relief (two-tailed rho = 0.76, p < 0.001) and the relief recalled after 6 weeks (two-tailed rho = 0.69, p < 0.001). Moreover, logistic regression models revealed that expected pain relief was a significant predictor of the subgroups of low vs. moderate scores of post-treatment pain (B = - 1.06, p = 0.017) and anxiety (B = - 1.60, p = 0.009), controlled for the condition of pre-treatment medication. CONCLUSIONS: The current findings highlight that for patients with symptomatic irreversible pulpitis who received emergent endodontic treatment, their expected pain relief before treatment is a critical factor associated with pain reduction and post-treatment pain/anxiety. CLINICAL RELEVANCE: Assessment of expected pain relief may be integrated into pre-treatment assessment for painful dental patients.

The role of fibroblasts in the modulation of dental pulp inflammation.

BACKGROUND/PURPOSE: Dental pulp fibroblasts can protect dental pulp from microbial invasion. However, little is known about the interaction between pulp fibroblasts and the immune cells. In this study, the production of proinflammatory cytokines related to inflammatory cell recruitment was evaluated in tumor necrosis factor (TNF)-α-stimulated human dental pulp fibroblasts (HDPFs). The role of TNF-α-stimulated HDPFs in the cell fusion under inflammatory process was determined with the cell co-culture with peripheral blood mononuclear cells (PBMCs). METHODS: HDPFs were stimulated with various concentrations of TNF-α, and the secretion of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1 was analyzed by the enzyme-linked immunosorbent assay. The mRNA expression levels of intercellular adhesion molecule-1 (ICAM-1), macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) were determined by real-time quantitative polymerase chain reaction. TNF-α-treated HDPFs were co-cultured with PBMCs for 21 days, and characteristics of cell differentiation were assessed. RESULTS: TNF-α induced IL-6, IL-8 and MCP-1 production in HDPFs. Moreover, mRNA expression levels of ICAM-1, M-CSF and OPG were significantly increased in TNF-α-treated HDPFs. Co-culture of TNF-α-treated HDPFs and PBMCs stimulated formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, and the F-actin rings were observed in these multinucleated cells. CONCLUSION: Our results indicate that under the stimulation of TNF-α, HDPFs may amplify inflammatory response by cytokines production, which in turn can modulate the differentiation of immune cells.

Magnification of fear and intention of avoidance in non-experienced versus experienced dental treatment in adults.

BACKGROUND: Dental fear is associated with the experience of prior dental treatment and avoidance of dental visits. It remains unclear if individuals show an intention of avoidance (IA) towards treatments that they have not received (i.e., non-experienced dental treatment). The study aims to investigated (a) if individuals showed an increased fear and IA to non-experienced, compared to experienced dental treatment, and (b) if fear and IA to non-experienced treatment is associated with dental anxiety. METHODS: Fear/IA of 12 common conditions of dental treatment of 402 adults were investigated. If subjects have experienced the condition, fear and IA were assessed based on subjects' prior experience (i.e., ExpFear/ExpIA). If they have not experienced the condition, fear and IA were assessed based on their anticipation (i.e., NExpFear/NExpIA). Trait dental anxiety was assessed using the Index of Dental Anxiety and Fear (IDAF-4C+). RESULTS: (A) NExpFear and NExpIA were significantly higher than ExpFear and ExpIA, respectively. (B) The IDAF-4C+ scores are positively correlated with NExpFear/NExpIA and negatively correlated with the magnification of fear (i.e., the discrepancy in the fear/IA of non-experienced vs. experienced conditions). (C) The condition 'extraction of a wisdom tooth' and 'root canal treatment' showed the highest ratings on NExpFear. CONCLUSIONS: Individuals may develop a high degree of fear and IA of the treatment they have not received. Trait dental anxiety plays a key role in the fear of non-experienced treatment.

Inhibitory effects of tea catechin epigallocatechin-3-gallate against biofilms formed from Streptococcus mutans and a probiotic lactobacillus strain.

OBJECTIVE: Effects of tea catechin epigallocatechin-3-gallate (EGCG) against biofilm formation by Streptococcus mutans and probiotic Lactobacillus casei in Yakult® (LcY) were examined. DESIGN: Biofilms were formed by S. mutans alone (Sm) and co-culture of S. mutans and LcY (Sm + LcY) in the absence or presence of EGCG. The biomass of biofilms, which were sonicated or not, was measured by the crystal violet assay. Biofilm morphology was observed by scanning electron microscopy. Bacterial viability and extracellular polysaccharides were determined by SYTO9/propidium iodide and dextran-conjugated fluorescein staining, respectively, and confocal microscopy. Gene expression of glucosyltransferase was determined by quantitative polymerase chain reaction. RESULTS: While 250 µg/ml EGCG significantly decreased the biomass and acid production of Sm biofilms, 500 µg/ml EGCG was required to inhibit Sm + LcY biofilm formation and acid production. EGCG decreased the amount of live bacteria present in both Sm and Sm + LcY biofilms. The level of dead bacteria in Sm + LcY biofilms was higher than in Sm biofilms when formed in the presence of 250 µg/ml EGCG. EGCG decreased levels of extracellular polysaccharides in Sm and Sm + LcY biofilms. The extent of biofilm removal by sonication was not different between Sm and Sm+LcY biofilms formed in the absence or presence of 62.5 or 125 µg/ml EGCG. The level of Sm gtfB and gtfD expression in Sm + LcY biofilms was higher than those in the Sm biofilms when formed in the presence of EGCG at 250 µg/ml. CONCLUSION: The results indicated that LcY might interfere the inhibitory effects of EGCG against biofilm formation by S. mutans.

A cone-beam computed tomography study of C-shaped root canal systems in mandibular second premolars in a Taiwan Chinese subpopulation.

BACKGROUND/PURPOSE: The purpose of this study is to investigate the prevalence and the morphologic characteristics of the radicular groove and root canal system in human mandibular second premolars with C-shaped root in a Taiwan Chinese subpopulation using cone-beam computed tomographic (CBCT) imaging. METHODS: CBCT images of 580 mandibular second premolars were collected from 317 patients. All of the mandibular second premolars were examined in serial axial sections to identify the presence of any C-shaped root and C-shaped canal systems. The morphologic characteristics of mandibular second premolars with C-shaped roots were studied by performing measurements of serial axial sections. RESULTS: The prevalence rate of mandibular second premolars with a C-shaped root was 3.45% (20/580 teeth) and the rate of those with a C-shaped canal system was 2.24% (13/580 teeth). It was found that 69% of the radicular grooves were located on the lingual half of the root (9/13 teeth) in mandibular second premolars with a C-shaped canal system. In those teeth with a lingual radicular groove, the main canal was toward the buccal side. Frequently, the first C-shaped canal image was found at the mid-root level. The deepest part of the radicular groove was located at about 2.5 mm apical to the first C-shaped canal image. CONCLUSION: There was a 2-3% morphologic variation of the mandibular second premolar with a C-shaped root canal system among the Taiwan Chinese subpopulation investigated in this study. Detailed knowledge of the morphological characteristics of teeth may be valuable when choosing clinical treatments.

The best radiographic method for determining root canal morphology in mandibular first premolars: A study of Chinese descendants in Taiwan.

BACKGROUND/PURPOSE: There is large variation in root canal morphology and undetected canals and incomplete instrumentation are reasons for root canal treatment failure. The purpose of this study was to determine the best radiographic method for determining root canal morphology in mandibular first premolars in Chinese descendants in Taiwan. MATERIALS AND METHODS: Mandibular first premolars extracted due to caries, periodontal diseases, trauma, or for orthodontic reasons were used. Four indices were examined: (1) root canal bifurcation observed in the buccolingual view; (2) root canal continuity in the buccolingual view; (3) double root outline in the buccolingual view; and (4) Vertucci canal classification in the mesiodistal view. RESULTS: A total of 82 left and right mandibular first premolars were included, a complicated root canal was confirmed in 38 (46.3%) by cross-sectional imaging and a single root canal was found in 44 (53.7%). Bifurcation identified on the mesiodistal view exhibited the highest sensitivity (94.7%) and second highest specificity (88.6%) for identifying a complicated root canal; however, this view is not possible to obtain clinically. Canal bifurcation on the buccolingual view was the most specific (93.2%), but had the lowest sensitivity (73.7%). Canal continuity on the buccolingual view had a sensitivity of 94.7%, and specificity of 70.5%. CONCLUSION: Combined X-ray analyses, such as performing the buccolingual view for identification of canal bifurcation and canal continuity, may increase the accuracy of identifying complex root canal morphology.

Porphyromonas gingivalis GroEL induces osteoclastogenesis of periodontal ligament cells and enhances alveolar bone resorption in rats.

Porphyromonas gingivalis is a major periodontal pathogen that contains a variety of virulence factors. The antibody titer to P. gingivalis GroEL, a homologue of HSP60, is significantly higher in periodontitis patients than in healthy control subjects, suggesting that P. gingivalis GroEL is a potential stimulator of periodontal disease. However, the specific role of GroEL in periodontal disease remains unclear. Here, we investigated the effect of P. gingivalis GroEL on human periodontal ligament (PDL) cells in vitro, as well as its effect on alveolar bone resorption in rats in vivo. First, we found that stimulation of PDL cells with recombinant GroEL increased the secretion of the bone resorption-associated cytokines interleukin (IL)-6 and IL-8, potentially via NF-κB activation. Furthermore, GroEL could effectively stimulate PDL cell migration, possibly through activation of integrin α1 and α2 mRNA expression as well as cytoskeletal reorganization. Additionally, GroEL may be involved in osteoclastogenesis via receptor activator of nuclear factor κ-B ligand (RANKL) activation and alkaline phosphatase (ALP) mRNA inhibition in PDL cells. Finally, we inoculated GroEL into rat gingiva, and the results of microcomputed tomography (micro-CT) and histomorphometric assays indicated that the administration of GroEL significantly increased inflammation and bone loss. In conclusion, P. gingivalis GroEL may act as a potent virulence factor, contributing to osteoclastogenesis of PDL cells and resulting in periodontal disease with alveolar bone resorption.

Esthetic periodontal surgery for impacted dilacerated maxillary central incisors.

Clinicians do not frequently see impacted dilacerated maxillary incisors in their patients. When they do, there are several diagnostic and management challenges for correcting root dilacerations. An unfavorable esthetic outcome might occur as a result of soft-tissue complications during surgical eruption procedures. We present 2 patients with an impacted and dilacerated maxillary central incisor. Computed tomography scans with 3-dimensional reformation were used to accurately assess the positions of the dilacerated teeth, the degree of dilaceration, and the stage of root formation. The therapy primarily involved 2-stage crown exposure surgery combined with orthodontic traction. An apicoectomy was performed on 1 dilacerated tooth; the other exhibited pulp vitality. This article highlights the periodontal surgical strategies for the esthetic management of inverted crowns. Through periodontal plastic surgery and interdisciplinary cooperation, the impacted dilacerated central incisors were properly aligned, and successful esthetic results were achieved.

Up-regulation of nucleotide-binding oligomerization domain 1 in inflamed human dental pulp.

INTRODUCTION: The innate immune response is activated by recognition of microbial components through specific pattern recognition receptors including nucleotide-binding oligomerization domain (NOD)-like receptors. However, the regulation of NOD-1 in inflamed human dental pulp remains poorly understood. This study aimed to evaluate the expression of NOD-1 in healthy and inflamed human dental pulps. In addition, the secretion of chemokines induced by NOD-1 and the related signaling pathways were studied. METHODS: Samples of human dental pulp tissues were obtained from freshly extracted wisdom teeth. The protein localization of NOD-1 in the pulp tissues was detected by immunohistochemistry. In addition, human dental pulp fibroblasts were stimulated with NOD-1 agonist γ-D-glutamylmeso-diaminopimelic acid. Production of interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) was determined by an enzyme-linked immunosorbent assay. The involvement of mitogen-activated protein kinase (MAPK) signaling pathways was examined by Western blot analysis, and the association of MAPK signaling with chemokine production was determined. RESULTS: The results demonstrated the expression of NOD-1 in normal dental pulp, and up-regulated NOD-1 expression was observed in inflamed dental pulp. On stimulation with NOD-1 agonist, production of IL-8 and MCP-1 was induced in a dose-dependent manner. Moreover, phosphorylation of p38 MAPK and Jun N-terminal kinase (JNK) was enhanced by stimulation of NOD-1. With the treatment of p38 MAPK and JNK inhibitors, the NOD-1-induced IL-8 production was suppressed. CONCLUSIONS: In response to microbial invasion, the expression of NOD-1 can be regulated in a ligand-inducible manner. NOD-1 might participate in pulp inflammation through chemokine production via MAPK signaling pathways.

Use of rubber dams during root canal treatment in Taiwan.

BACKGROUND/PURPOSE: Isolation of teeth with rubber dams is an important procedure for infection control in dentistry, especially in endodontic treatment. This study surveyed the prevalence of rubber dam usage in nonsurgical root canal treatment (RCT) by dentists under the National Health Insurance system in Taiwan. METHODS: A total of 1,332 completed RCT cases were randomly selected from a large database from the Bureau of National Health Insurance in Taiwan in 2004. The radiographs and dental charts of the selected cases were evaluated for the prevalence of rubber dam usage in RCT. The frequencies of rubber dam usage for RCT by dentists were compared between hospitals and private dental clinics and among six different regions in Taiwan. RESULTS: The overall prevalence of rubber dam usage for RCT by dentists under the National Health Insurance system in Taiwan was 16.5%. The frequency of rubber dam usage for RCT by dentists in hospitals (32.8%) was significantly higher than that (10.3%) in private dental clinics (p < 0.0001). However, there was no significant difference in the frequency of rubber dam usage for RCT by dentists among six different geographic regions in Taiwan. CONCLUSION: The prevalence of rubber dam usage for RCT by dentists in Taiwan is relatively low. Because rubber dam isolation of an endodontically-treated tooth can provide better infection control, increase patient protection, and improve treatment efficiency, there is an urgent need to advise dentists in Taiwan to use rubber dams for every RCT case.

Effects of light attenuation by fibre posts on polymerization of a dual-cured resin cement and microleakage of post-restored teeth.

OBJECTIVES: The influence of light transmitting ability of different fibre posts on the polymerization of a dual-cured resin cement, and the further microleakage of the post-restored endodontically treated teeth were examined. METHODS: An LED curing light was used as light source and the measurements of 470 nm irradiances were made at 1mm intervals along the posts (P-Lux, P-White, and P-Steel). The polymerization of a dual-cured resin cement surrounding the posts at five depths (0, 2, 5, 8, and 10mm) from the top was evaluated using micro-Raman spectra after 40s light-curing. Meanwhile, 36 human single-rooted endodontically treated teeth were randomly divided into three groups and restored with these posts and the cement according to the manufacturers' instructions. Microleakages of the post-restored teeth were compared using an electrochemical measurement system on three consecutive days, and statistically analysed using nonparametric tests. RESULTS: Light transmission through fibre posts was exponentially reduced as the depth increased (p<0.05, R(2)>0.95), and the polymerization of the resin cement beyond the depth of 5mm significantly declined for all specimens (p<0.05). Fibre posts displayed higher value of light transmission, exhibited a higher polymerization rate of surrounding resin cement, and also demonstrated less microleakage; whilst P-Steel posts had the lowest polymerization rate and produced higher microleakage (p<0.017). CONCLUSIONS: The effective radiance along the post was diminished exponentially, which features the insufficient polymerization of a dual-cured resin cement surrounding the posts at apical region and might therefore influence the microleakage of post-restored teeth.

The morphologic characteristics of the distolingual roots of mandibular first molars in a Taiwanese population.

INTRODUCTION: The prevalence of extra distolingual (DL) roots in mandibular first molars in Chinese population is about 20%. The purpose of this study was to evaluate the difference of root length and root curvatures between distobuccal (DB) and DL roots of three-rooted mandibular first molars in a Taiwanese (Chinese) population. METHODS: Of the 293 extracted mandibular first molars, DL roots were present in 29 (9.9%) teeth. Excluding teeth with fractured DB or DL roots, 21 mandibular first molars were further investigated. DB and DL root lengths were measured from the lower level of furcation at the distal surface to the root apex. The curvature of the DL root was measured on mesial-distal and buccal-lingual radiographs by Schneider's technique. RESULTS: The DL roots were significantly (p < 0.001) shorter than the DB roots with an average of 1.48 +/- 0.81 mm. Most DL roots had a greater curvature in a buccal-lingual orientation (36.35 degrees +/- 9.38 degrees ) than a mesial-distal orientation (9.24 degrees +/- 6.10 degrees ) and 28.57% of the curved DL roots had the curvature at the apical one third (p < 0.001). CONCLUSION: The results of this study verified the characteristics of shorter root length and severe buccal-lingual inclination of DL roots in three-rooted mandibular first molars.

Eugenol modulates cyclooxygenase-2 expression through the activation of nuclear factor kappa B in human osteoblasts.

Because eugenol is a major component of root canal sealers and retrograde filling materials, its effects on periapical bone healing are therefore of concern. In this study, the effects of eugenol on the activation of nuclear factor kappa B (NF-kappaB) and the expression of cyclooxygenase-2 (COX-2) in human osteoblasts were investigated. The results showed that eugenol activated the nuclear translocation of NF-kappaB. In addition, COX-2 protein expression in osteoblasts was induced by eugenol in a dose-dependent manner. Furthermore, the eugenol-modulated COX-2 expression was inhibited by an NF-kappaB inhibitor, N-acetylcysteine. Taken together, eugenol might induce COX-2 expression through the activation of NF-kappaB in human osteoblasts. These results suggest that eugenol might be involved in periapical healing by impairing the functions of osteoblasts.

Eugenol suppressed the expression of lipopolysaccharide-induced proinflammatory mediators in human macrophages.

Eugenol is commonly used as an analgesic agent during acute pulpitis and is a major component of root canal sealers. Despite the frequent applications of eugenol in the practice of dentistry, little is known about the role of eugenol under the status of inflammation. This study was aimed to investigate the influence of eugenol on human macrophages (U937) under the stimulation of lipopolysaccharide (LPS). Eugenol was shown to block the release of the bone resorbing mediators, including interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and prostaglandin E2 from LPS-stimulated macrophages. In contrast, eugenol alone did not alter the expression levels of these proinflammatory mediators in macrophages. Consistent with downregulation of bone-resorbing mediators, eugenol suppressed the messenger RNA expression of LPS-induced IL-1beta, TNF-alpha, and cyclooxygenase-2 in macrophages. The results suggest a potential anti-inflammatory effect of eugenol in the acute inflamed pulps and apical periodontitis.

Complicated root canal morphology of mandibular first premolar in a Chinese population using the cross section method.

The purpose of this study was to assess the canal anatomy and morphology of mandibular first premolars in a Chinese population. Eighty-two extracted mandibular first premolars with intact roots were collected and stored in a glutaraldehyde solution. The teeth were embedded in clear resin and the root length was measured. The roots were resected perpendicular to the long axis at 3, 6, 9, and 12 mm from the apex. The resected root surfaces were polished, rinsed, dried, and stained with methylene blue. Digital photographs of the cross-sectional root surfaces were made at 24X. The incidence of multiple canals and varied morphology was determined by two independent examiners. The results indicated that 54% of the mandibular first premolars demonstrated a single canal. Twenty-two percent contained two canals and 18% percent had C-shaped configuration. The C-shaped root canal occurred predominantly in the 3 and 6 mm sections with one or two canals coronally. A unique finding was the circumferential canal (apical delta), which was characterized by a single canal splitting into 3 or 4 canals. The incidence of circumferential canal was 6% and occurred only in the apical 3 mm cross-sections. Identification of this unique apical canal configuration and the high incidence of multiple canals in mandibular first premolars may explain endodontic treatment failure in this tooth group.