Lan Zhang

C-shaped root canal system in mandibular second molars in a Chinese population evaluated by cone-beam computed tomography

AIMnTo evaluate the anatomical features of C-shaped canal systems in Chinese mandibular second molars by cone-beam computed tomography (CBCT).nnnMETHODOLOGYnA total of 608 patients of Chinese descent with healthy, well-developed mandibular second molars were enrolled. These patients were referred to the West China Hospital of Stomatology and required radiographic examination by CBCT as part of their routine dental treatment. Of the 608 examined CBCT images, 528 showed unilateral intact molars and 80 showed bilateral intact molars. Bilateral molar data were only used to analyse the distribution of unilateral and bilateral occurrences of C-shaped canals. The following in vivo CBCT observations were made: (i) frequency and type of root; (ii) frequency of C-shaped canals by gender, age and tooth position (left versus right); (iii) the classification of cross-sectional canal images of C-shaped canals; and (iv) unilateral and bilateral occurrences of C-shaped canals.nnnRESULTSnFused roots were present in 39% of molars. A C-shaped canal system was present in 39% of the teeth. This prevalence did not differ with gender, age and tooth position. Most (81%) of the C-shaped canals in individuals with bilateral molars were symmetrical. Most of the canals with uninterrupted C-shapes appeared to divide into two or more canals towards the canal terminus.nnnCONCLUSIONnThere was high prevalence of C-shaped canals in the mandibular second molars of Chinese population. The canal systems varied considerably in their anatomical configuration.

Associations between Maxillary Sinus Mucosal Thickening and Apical Periodontitis Using Cone-Beam Computed Tomography Scanning: A Retrospective Study

INTRODUCTIONnThis study evaluated the pathologic and spatial associations between apical periodontitis of the maxillary premolars/molars and the maxillary sinus mucosal thickening using cone-beam computed tomography (CBCT) scanning.nnnMETHODSnCBCT images of 372 patients with 508 exposed maxillary sinuses were inspected retrospectively. Clinical features such as sex and age of the patients and pathologic findings of the maxillary sinus and adjacent teeth were recorded, graded, and analyzed.nnnRESULTSnMaxillary sinus mucosal thickening was found in 180 (48.4%) patients and 235 (46.2%) sinuses. The prevalence of maxillary sinus mucosal thickening increased dramatically as the severity of apical periodontitis increased (from 41.5% in those without periodontal disease to 100%). However, the nature of the spatial relationship between the maxillary sinus floor and the infected root tips or between the sinus floor and periapical lesions did not appear to have an effect on the prevalence of maxillary sinus mucosal thickening. Patients over 60 years of age had the highest prevalence of maxillary sinus mucosal thickening.nnnCONCLUSIONSnA retrospective inspection of CBCT images revealed that the prevalence and severity of maxillary sinus mucosal thickening were positively associated with the degree of apical periodontitis. CBCT imaging is applicable for the evaluation of the maxillary sinuses and adjacent teeth.

Expression of TRAF6 and pro-inflammatory cytokines through activation of TLR2, TLR4, NOD1, and NOD2 in human periodontal ligament fibroblasts

OBJECTIVEnHuman periodontal ligament fibroblasts (HPDLFs) play a crucial role in protecting against oral bacteria in periapical tissue. Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) are two major forms of innate immune sensors that recognize microbial pathogens and initiate pro-inflammatory signalling. Tumour necrosis factor receptor-associated factor 6 (TRAF6) is an adapter protein for TLR-mediated nuclear factor-κB (NF-κB) signalling pathway activation that induces the production of pro-inflammatory cytokines. The aim of this study was to investigate the expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. We also investigated the expression of TRAF6 and pro-inflammatory cytokines induced by the activation of TLRs and NODs.nnnMETHODSnThe expression of TLR2, TLR4, NOD1, and NOD2 was measured by reverse transcription-polymerase chain reaction (RT-PCR), flow cytometry, and immunostaining. HPDLFs were stimulated with TLR and NOD agonists. Then, the expression of TRAF6 was measured by real-time PCR and western blot. Concentrations of IL-1β, IL-6, and IL-8 in the culture supernatants were determined by enzyme-linked immunosorbent assay (ELISA). Finally, by using small interfering RNA (siRNA) for TRAF6, we analysed the production of IL-1β, IL-6, and IL-8 in HPDLFs upon stimulation with TLRs and NODs agonists.nnnRESULTSnWe found clear mRNA and protein expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. The expression levels of TRAF6 and pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) were markedly up-regulated upon the activation of TLRs and NODs. Furthermore, the co-activation of TLRs and NODs had synergistic effect on the production of TRAF6 and pro-inflammatory cytokines. We also found TRAF6 suppression resulted in reduced IL-1β, IL-6, and IL-8 expression upon TLR and NOD agonists challenge.nnnCONCLUSIONnThese findings indicated that TLR2, TLR4, NOD1, and NOD2 are functional receptors in HPDLFs during innate immune responses to invading bacteria, and a combination of signalling through TLRs and NODs leads to the synergistic enhancement of inflammatory reactions in HPDLFs. In addition, TLR and NOD signalling involving TRAF6 contribute to inflammatory responses in HPDLFs.

Apically extruded debris and irrigant with two Ni‐Ti systems and hand files when removing root fillings: a laboratory study

AIMnTo compare the amount of apically extruded debris and irrigant produced by two Ni-Ti instruments and hand files when removing root fillings, and to compare two experimental models.nnnMETHODOLOGYnSixty single straight root canals in human mandibular premolars were prepared with K-files and filled with gutta-percha and AH Plus sealer. The teeth were randomly divided into three groups of 20 for removal of the root filling material with Reciproc files (Group 1, RP), Mtwo retreatment files (Group 2, MR) or hand files (Group 3, H). Each group was then equally divided into experimental subgroups: A, with 1.5% agar gel model (AG); B, with empty tube model (ET). Apically extruded debris and irrigant was quantified by subtracting the initial weight of the test apparatus without a tooth from its weight after the root canal retreatment. Comparative analysis of the amount of apically extruded debris and irrigant for each of the instruments and the experimental models was performed. Time for gutta-percha removal was recorded. Data were statistically analysed using one-way analysis of variance.nnnRESULTSnRemoval of root fillings with two Ni-Ti instruments produced less apically extruded debris and irrigant than hand files in both experimental models (P < 0.05). More apically extruded debris and irrigant was produced with Reciproc files than Mtwo retreatment files using the 1.5% agar gel model (P > 0.05). Significantly more apically extruded debris and irrigant was produced with Reciproc files than Mtwo retreatment files using the empty tube model (P < 0.05). The time required to remove the root fillings followed Reciproc<Mtwo R<hand files (P < 0.05).nnnCONCLUSIONSnAll the instruments produced apically extruded debris and irrigant. The two Ni-Ti instruments produced less apically extruded debris and irrigant than hand files. A 1.5% agar gel can provide resistance to apically extruded debris and irrigant and may represent the clinical situation better than the empty tube model.

Spatial distribution of the human enamel fracture toughness with aging

A better understanding of the fracture toughness (KIC) of human enamel and the changes induced by aging is important for the clinical treatment of teeth cracks and fractures. We conducted microindentation tests and chemical content measurements on molar teeth from young (18 ≤ age ≤ 25) and old (55 ≤ age) patients. The KIC and the mineral contents (calcium and phosphorus) in the outer, the middle, and the inner enamel layers within the cuspal and the intercuspal regions of the crown were measured through the Vickers toughness test and Energy Dispersive X-Ray Spectroscopy (EDS), respectively. The elastic modulus used for the KIC calculation was measured through atomic force microscope (AFM)-based nanoindentation tests. In the outer enamel layer, two direction-specific values of the KIC were calculated separately (direction I, crack running parallel to the occlusal surface; direction II, perpendicular to direction I). The mean KIC of the outer enamel layer was lower than that of the internal layers (p<0.05). No other region-related differences in the mechanical properties were found in both groups. In the outer enamel layer, old enamel has a lower KIC, II and higher mineral contents than young enamel (p<0.05). The enamel surface becomes more prone to cracks with aging partly due to the reduction in the interprismatic organic matrix observed with the maturation of enamel.

Detection of vertical root fracture using cone beam computed tomography: report of two cases

Vertical root fractures (VRFs) often occur in endodontically treated teeth and in patients older than 40 years of age. However, VRFs in teeth without endodontic treatment are relatively uncommon. VRFs are difficult to diagnose as the symptoms are non-specific or often delayed. The most common radiographic findings are thickening of the periodontal ligament, deep, localized, vertical bone loss, and localized periradicular bone loss. The explicit feature for detecting VRFs is direct visualization of a radiolucent fracture line on radiographs. However, the fracture line can be difficult to directly visualize in conventional diagnostic methods such as periapical radiographs. If unrecognized, VRFs can lead to frustration and inappropriate endodontic treatment. The two cases reported here demonstrate that the use of cone beam computed tomography (CBCT) successfully diagnoses VRFs on teeth without representative clinical and periapical radiographic findings. The clear fracture line can be discerned from the images of CBCT. Thus, CBCT imaging is useful in rapid diagnosis of VRFs and designing of further treatment.

The effects of ageing on the biomechanical properties of root dentine and fracture.

OBJECTIVESnKnowledge of the mechanical behaviour of root dentine can facilitate better understanding of spontaneous vertical root fracture (VRF), an age-related disease initiated mainly at the root apex. We tested the hypothesis that the biomechanical properties of root dentine change with ageing.nnnMETHODSnSixteen human premolars were divided into old (17-30 years) and young (50-80 years) groups. The elastic modulus, nano-hardness, micro-hardness, elemental contents, tubular density/area of root dentine in cervical, middle and apical root regions were evaluated using atomic force microscopy-based nano-indentation, Knoop indentation, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively.nnnRESULTSnThe apical dentine showed a lower nano-hardness, a lower elastic modulus, a lower calcium content, a lower calcium-to-phosphorus ratio and a smaller tubular density/area than the cervical dentine in both age groups, whereas spatial differences in micro-hardness were observed only in old roots. Compared with young dentine, old dentine showed a greater hardness, a higher elastic modulus, a greater mineral content and a smaller tubular size in the cervical portion, whereas the age-induced changes in tubular density were insignificant. Finite element analysis revealed that due to its higher elastic modulus, old apical dentine has a higher stress level than young dentine.nnnCONCLUSIONSnThe intrinsic material properties of root dentine have spatial variations, and they are altered by ageing. The higher stress level in old apical dentine may be one reason, if not the most important one, why spontaneous VRFs are more likely to occur in the elderly population.

Residual Filling Material in Dentinal Tubules after Gutta-percha Removal Observed with Scanning Electron Microscopy

INTRODUCTIONnIn cases of failed root canal treatment, endodontic retreatment of the root canal system isxa0necessary. The present study aimed to assess variation in the incidence and depth of residual filling material in dentinal tubules after gutta-percha removal with H-files, the ProTaper Universal System (Dentsply Maillefer, Ballaigues, Switzerland), and the SybronEndo K3 System (SybronEndo Corporation, Orange, CA).nnnMETHODSnForty human mandibular premolars with single straight root canals were prepared with K-files (up to size 40) using the step-back technique and filled by cold lateral condensation with gutta-percha and AH Plus sealers (Dentsply DeTrey, Konstanz, Germany). After 1 year, the 40 teeth were divided into one control group and 3 retreatment groups (n = 10 each). Gutta-percha was removed using H-files, the ProTaper Universal System, or the SybronEndo K3 System. The teeth were sectioned, and the incidence and depth of residual filling material in the dentinal tubules were measured under scanning electron microscopy.nnnRESULTSnThe depth of filling material in the dentinal tubules did not differ significantly among groups (P > .05). Residual filling material was present in significantly more dentinal tubules in the ProTaper (P = .043) and K3 groups (Pxa0= .001) than in the H-file and control groups.nnnCONCLUSIONSnThe ProTaper Universal System and the SybronEndo K3 System left filling material in a greater proportion of dentinal tubules than did H-files.

Effect of heat stress on the expression levels of receptor activator of NF‐κB ligand and osteoprotegerin in human periodontal ligament cells

AIMnu2002 To investigate the expression levels of the receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) in human periodontal ligament fibroblasts (PDLs) when stimulated with heat.nnnMETHODOLOGYnu2002 Periodontal ligament fibroblasts were subjected to various temperature increases for 5u2003min and then maintained at 37u2003°C. After that, cell viability was determined using an MTT assay. The expression levels of RANKL and OPG were investigated using real-time RT-PCR and ELISA. As a control, the cells were cultured at 37u2003°C. Data were analysed using one-way anova at a significant level of Pu2003=u20030.05. Resultsu2002 Cell viability was reduced significantly in the heated groups (Pu2003<u20030.05). Heat stress downregulated the mRNA expression levels of RANKL and OPG (Pu2003<u20030.05). When the cells were heated at 39u2003°C, the protein release of OPG was increased (Pu2003<u20030.05). There were no significant differences between the heated groups and the control in the release of soluble RANKL (Pu2003>u20030.05). The relative RANKL/OPG expression ratios were decreased at 39, 43 and 50u2003°C (Pu2003<u20030.05), but increased at 47u2003°C (Pu2003<u20030.05).nnnCONCLUSIONSnu2002 Heat influenced the balance between RANKL and OPG in PDLs. Low heat downregulated their relative ratio, whilst high heat upregulated it.

Comparison of Mineral Trioxide Aggregate and iRoot BP Plus Root Repair Material as Root-end Filling Materials in Endodontic Microsurgery: A Prospective Randomized Controlled Study

Introduction: This prospective randomized controlled study evaluated the clinical and radiographic outcome of endodontic microsurgery when using iRoot BP Plus Root Repair Material (BP‐RRM; Innovative BioCeramix Inc, Vancouver, BC, Canada) or mineral trioxide aggregate (MTA) as the retrograde filling material and analyzed the relationship between some potential prognostic factors and the outcome of the surgery. Methods: By using strict inclusion and exclusion criteria, 240 teeth were successfully enrolled and randomly and equally allocated to either the MTA or BP‐RRM treatment group. A standardized surgical procedure was performed by a single operator. The patients were followed up at 1 week, 3 months, 6 months, and 12 months; follow‐up included clinical and radiographic examination. Clinical and radiographic evaluations acquired at the 12‐month follow‐up were taken as the primary outcome. For the identification of prognostic factors, the dichotomous outcome (success vs failure) was taken as the dependent variable. Results: A total of 158 teeth were analyzed at the 12‐month follow‐up, including 87 teeth in the MTA group and 71 teeth in the BP‐RRM group. The success rate in the MTA and BP‐RRM groups was 93.1% (81/87 teeth) and 94.4% (67/71 teeth), respectively (P > .05). Three significant outcome predictors were identified: quality of root filling (P < .05), tooth type (P < .05), and size of the lesion (P < .05) Conclusions: These results suggest that BP‐RRM is comparable with MTA in clinical outcome when used as root‐end filling materials in endodontic microsurgery.