Y.-L. Ng’s research while affiliated with UCL Eastman Dental Institute and other places

Objectives The aims of this study were to (1) investigate the relative time-dependent disruption and bactericidal effects of detergent-type surfactants on single- or dual-species biofilms of root canal isolates and (2) to examine the utility of polygonal graphs for depiction of biofilm disruption and cell killing. Materials and methods Single-species biofilms of Streptococcus sanguinis, Enterococcus faecalis, Fusobacterium nucleatum and Porphyromonas gingivalis were grown on nitro-cellulose membranes for 72 h and immersed in Tween®80, cetyltrimethylammoniumbromide (CTAB), and sodium dodecyl sulphate (SDS) for 1-, 5- or 10-min (n = 3 per test). The number of viable and non-viable bacteria “disrupted” from the biofilm and those “remaining-attached” was determined using a viability stain in conjunction with fluorescence microscopy. The data were analysed using non-parametric Kruskal-Wallis test with 5% significance level. Results Gram-negative obligate anaerobes were more susceptible to cell removal than gram-positive facultative anaerobes. The majority of cells were disrupted after 1-min of exposure; however, the extent varied according to the agent and species. CTAB and SDS were more effective than Tween 80™ at disrupting biofilms and killing cells but all agents failed to achieve 100% disruption/kill. Conclusions Biofilm disruption and cell viability were influenced by the species, the test agent and the duration of exposure. CTAB and SDS were more effective in biofilm disruption than Tween 80™. Graphical depiction of biofilm disruption- and viability-outcomes provides an alternative means of simultaneously visualising and analysing relative efficacy in different domains. Clinical relevance Surfactants were not as effective at biofilm disruption as NaOCl but may be added to other non-disruptive antibacterial agents to enhance this property.

Aim: To refine FTIR protocol for detection of NaOCl-induced dentinal collagen changes using an ex vivo irrigation model, and to apply it to determine the collagen change within 0.5mm of canal or root surfaces, with or without mature roots or periodontal involvement. Methodology: Extracted human roots were irrigated with control saline (n=3) or 5% NaOCl (n=3) and sectioned into transverse discs for FTIR analyses, 0.5mm from both the canal lumen and root surface, before and after surface-treatment with 17% EDTA. Amide I/phosphate and amide II/phosphate absorbance ratios were compared using the Wilcoxon sign rank test. Mature roots without periodontal involvement were irrigated with: saline (n=7), 5% NaOCl (n=7), or 5% NaOCl+17% EDTA (n=7); those with periodontal involvement (n=7) or immature roots (n=7) were irrigated with 5% NaOCl. Dentine discs were then prepared for FTIR analyses. The effects of irrigant/root-maturity/periodontal involvement were analysed using linear mixed models. Results: FTIR analyses of the irrigated samples revealed significant (P < 0.05) reduction in collagen bands near the canal lumen after NaOCl irrigation using surface-EDTA treated samples. Irrigation with test solutions resulted in significant (P < 0.0001) dentinal collagen changes in the mature roots, whilst those in the immature roots were significantly (P < 0.05) greater compared with the mature roots with or without periodontal involvement; but there were no difference between the latter groups. Conclusion: EDTA surface-treatment of polished dentine surfaces enhanced FTIR detection of NaOCl-induced collagen changes. Both root maturity and irrigation protocol influenced the ability of NaOCl to alter dentinal collagen up to 0.5mm from the canal lumen. This article is protected by copyright. All rights reserved.

Aims To investigate the prevalence, pain catastrophizing and other predictive factors, and clinical course of persistent pain/discomfort associated with teeth displaying periapical healing following non‐surgical root canal treatment (NSRCT). Methodology One‐hundred‐ninety‐eight patients (264 teeth) who had NSRCT were reviewed at 5‐14 months, post‐operatively. Teeth with persistent post‐treatment pain or discomfort, plus evidence of periapical healing were further monitored 0.5, 4 & 10 years later. Pain Catastrophizing Scale (PCS) and Short Form of the McGill Pain Questionnaire (SF‐MPQ) were completed. Predictive factors were investigated using logistic regression models. Results Twenty‐four per cent (60/249) of teeth displaying periapical healing at first review, were associated with persistent pain or discomfort. Fifty‐five teeth monitored 6‐7 months later, were associated with reduction in pain (17/30) or discomfort (7/25). CBCT of eight teeth with persistent symptoms and complete periapical healing (by conventional radiographs) revealed distinct, small apical radiolucencies (n = 3) or root‐apex fenestration through the buccal plate (n = 2). History of chronic pain (headache, temporo‐mandibular joint, masticatory muscle, neck, shoulder, or back pain) (P = 0.005), pre‐operative pain (P = 0.04), responsive pulp (P = 0.009), tooth‐crack (P = 0.05) and small periapical radiolucency (P = 0.005) were significant predictive factors. The PCS revealed 16 patients (22 teeth) were catastrophizers (PCS ≥30) but this had no influence on post‐treatment symptoms (P = 0.5). Conclusions Persistent pain or discomfort associated with teeth showing periapical healing at the first review after NSRCT, decreased in intensity in most cases over the following 6‐months. Longer‐term follow‐up revealed spontaneous improvement or symptom resolution in the majority of those with confirmed radiographic absence of periapical disease. Five predictive factors (history of chronic pain, teeth with responsive pulps, association with pain, diagnosis of tooth‐crack before treatment, and diameter of pre‐operative radiolucency) were identified. This article is protected by copyright. All rights reserved.

Aim To establish a method using Fourier Transform Infra‐Red spectroscopy (FTIR) to characterise the nature and depth of changes in dentinal collagen following exposure to sodium hypochlorite (NaOCl) during root canal irrigation in an ex‐vivo model. Methodology FTIR was used to assess the changes in dentinal collagen when the root canal was exposed to NaOCl. The changes in dentinal collagen caused by NaOCl irrigation of root canals in transverse sections of roots, at 0.5 mm from the canal wall and 0.5 mm from the external root surface were assessed by FTIR. The data were analysed using paired t‐test with 5% significance level. Results FTIR confirmed that NaOCl exposure caused alterations in the chemistry and structure of collagen in dentine. FTIR spectra obtained from dentine surfaces and dentine adjacent to root canals exposed to NaOCl, all consistently showed degradation and conformational change of the collagen structure. FTIR data from the ex‐vivo model showed that the depth of effect of NaOCl extended to at least 0.5 mm from the canal wall. Conclusion NaOCl caused changes in dentinal collagen that are measurable by FTIR. In an ex‐vivo model, the depth of effect into dentine extended at least 0.5 mm from the canal wall. This article is protected by copyright. All rights reserved.

Aim: To evaluate the efficacy of sonic irrigation (EndoActivator(®) ) using various polymer tips and power-settings in a stained collagen ex-vivo model. Methodology: Fifty human, straight single-rooted extracted teeth were prepared to size 40,.08 taper. The roots were split longitudinally; stained collagen applied to the canal surfaces, photographed and re-assembled. The canals were subjected to syringe without supplementary (Group 1, n = 10), or with supplementary sonic (groups 2-5, n = 10) irrigation. EndoActivator(®) tip sizes (size 15, .02 taper for groups 2 & 3, size 35,.04 taper for groups 4 & 5) and power-settings (Low for groups 2 & 4, high for groups 3 & 5) were tested. After irrigation, the canals were re-photographed and the area of residual stained-collagen was quantified using the UTHSCA Image Tool program (Version 3.0). The data were analysed using Wilcoxon signed rank test and General Linear Mixed Models. Results: Supplementary sonic irrigation using EndoActivator(®) resulted in significantly (P < 0.0001) less residual collagen compared with syringe irrigation only. Agitation of irrigant using the large EndoActivator(®) tip with high-power resulted in significantly less (22.4% - 29.5%) residual collagen compared to other combinations (large-tip/low-power P = 0.001; small-tip/low-power P = 0.01; small-tip/high-power P = 0.04). There was no significant difference amongst the latter three groups (P > 0.5). Conclusions: Supplementary sonic irrigation using the EndoActivator(®) system was significantly more effective in removing stained collagen from the canal surface than syringe irrigation alone. EndoActivator(®) used with large-tip (size 35, .04 taper) and high power-setting in size 40,.08 taper canals was more effective than other combinations. This article is protected by copyright. All rights reserved.

Aim: To characterize chemical degradation of the principal constituents of dentine after exposure to NaOCl and EDTA using Infrared Spectroscopy (ATR-FTIR). Methodology: Ground dentine particles, from extracted permanent human molars, were passed through sieves of 38 to 1 000 μm to provide six size ranges. Portions (250 mg) of each size range were reacted with 5 mL of 2.5% NaOCl for 2-10 min; or 17% EDTA for 5-1440 min. Powders larger than 75 μm were also sequentially exposed to NaOCl/EDTA/NaOCl each for 10 min. All experiments were repeated five times. Reacted and unreacted powders were washed and dried. Particles larger than 75 μm were then reground. FTIR spectra of unground and reground reacted particles enabled assessment of particle surface versus bulk chemistry, respectively, plus estimation of reaction depth. Changes in the ratio of the 1 640 cm(-1) collagen: 1 010 cm(-1) phosphate peak height or its inverse were obtained. These were used to estimate surface and bulk fraction reacted and thus depth to which collagen or phosphate was reduced following immersion in NaOCl or EDTA, respectively. The data were analysed descriptively. Results: Surface collagen fraction declined by ~40% within 2 min of NaOCl exposure, and plateaued at ~60% between 6-10 min. Bulk spectra showed average depth of collagen loss at 10 min was 16 ± 13 μm. Ten minute EDTA exposure caused ~60% loss of surface phosphate. Average depth of phosphate loss was 19 ± 12 μm and 89 ± 43 μm after 10 and 1 440 min EDTA immersion, respectively. Sequential NaOCl/EDTA immersion yielded a 62 ± 28 μm thick phosphate-depleted surface. Sequential NaOCl/EDTA/NaOCl treatment resulted in approximately 85 μm of collagen loss. Conclusions: Data revealed the sequential depletion of collagen by NaOCl and apatite by EDTA in dentine, simultaneously exposing the other moieties. Alternate exposure to NaOCl and EDTA therefore enhances the depth of erosion.