M.K. Wu

The effects of canal preparation and filling on the incidence of dentinal defects

AIM To evaluate ex vivo the incidence of defects in root dentine before and after root canal preparation and filling. METHODOLOGY Eighty extracted mandibular premolars were divided equally in four groups. Group 1 was left unprepared. All other root canals were prepared using Gates Glidden drills and System GT files up to size-40, 0.06 taper at the working length. Group 2 was not filled while the canals of the other groups were filled with gutta-percha and AH26, either with a master cone and passive insertion of secondary gutta percha points (group 3) or lateral compaction (group 4). Roots were then sectioned horizontally 3, 6, and 9 mm from the apex and observed under a microscope. The presence of dentinal defects (fractures, craze lines or incomplete cracks) was noted and the differences between the groups were analysed with the Fishers exact test. RESULTS No defects were observed in the roots with unprepared canals. The overall difference between the groups was significant (P < 0.05). Canal preparation alone created significantly more defects than unprepared canals (P < 0.05). The total number of defects after lateral compaction was significantly larger than after noncompaction canal filling. CONCLUSION Root canal preparation and filling of extracted teeth created dentine defects such as fractures, craze lines and incomplete cracks.

Laser-activated irrigation within root canals: cleaning efficacy and flow visualization.

AIM To test ex vivo the efficiency of laser-activated irrigation in removing dentine debris from the apical part of the root canal and to visualize in vitro the fluid dynamics during the activation of the irrigant by laser, using high-speed imaging at a relevant timescale. METHODOLOGY Root canals with a standardized groove in one canal wall filled with dentine debris were irrigated with syringe irrigation, ultrasonically or laser-activated irrigation (LAI) using 2% sodium hypochlorite as irrigant. The quantity of dentine debris after irrigation was determined. Visualization of the fluid dynamics during activation was achieved using a high-speed camera and a glass model. RESULTS Laser-activated irrigation was significantly more effective in removing dentine debris from the apical part of the root canal than passive ultrasonic irrigation or hand irrigation when the irrigant was activated for 20 s. CONCLUSIONS The in vitro recordings suggest that streaming, caused by the collapse of the laser-induced bubble, is the main cleaning mechanism of LAI.

Incidence of dentinal defects after root canal filling procedures

AIM To compare the incidence of dentinal defects (cracks and craze lines) after root canal preparation, lateral compaction and continuous wave compaction of gutta-percha and AH26 sealer. METHODOLOGY Two hundred mandibular premolar teeth were divided into four groups with similar average canal diameters (n=50). One group was left untreated and served as the control. The other three groups were prepared with ProTaper rotary instruments up to size F4. After preparation, one group was left unfilled while two groups were filled with gutta-percha and AH26 using either lateral compaction or the continuous wave technique. Roots were then sectioned at 3, 6 and 9 mm from the apex and inspected under a microscope. The appearance of dentinal defects was noted as well as the minimum and mean remaining dentine thickness. Chi-square tests were performed to compare the incidence of dentinal defects between the groups (α=0.05), and Pearson correlation test was performed to check the correlation between defects and root level or remaining dentine thickness. RESULTS The unprepared control group had no dentinal defects. The other groups exhibited significantly more defects than the unprepared group (P<0.05). There was no difference in the incidence of defects between the two filling techniques. There was no correlation between the appearance of defects and level of the root or remaining dentine thickness. CONCLUSIONS In extracted teeth, dentinal defects were observed in roots filled with gutta-percha and AH26 using the lateral compaction and continuous wave techniques.

Glucose reactivity with filling materials as a limitation for using the glucose leakage model

AIM To evaluate the reactivity of different endodontic materials and sealers with glucose and to asses the reliability of the glucose leakage model in measuring penetration of glucose through these materials. METHODOLOGY Ten uniform discs (radius 5 mm, thickness 2 mm) were made of each of the following materials: Portland cement, MTA (grey and white), sealer 26, calcium sulphate, calcium hydroxide [Ca(OH)(2)], AH26,Epiphany, Resilon, gutta-percha and dentine. After storing the discs for 1 week at 37 degrees C and humid conditions, they were immersed in 0.2 mg mL(-1) glucose solution in a test tube. The concentration of glucose was evaluated using an enzymatic reaction after 1 week. Statistical analysis was performed with the anova and Dunnett tests at a significant level of P < 0.05. RESULTS Portland cement, MTA, Ca(OH)(2) and sealer 26 reduced the concentration in the test tube of glucose significantly after 1 week (P < 0.05). Calcium sulphate reduced the concentration of glucose, but the difference in concentrations was not significant (P = 0.054). CONCLUSIONS Portland cement, MTA, Ca(OH)(2) and sealer 26 react with a 0.2 mg mL(-1) glucose solution. Therefore, these materials should not be evaluated for sealing ability with the glucose leakage model.

Effect of filling technique and root canal area on the percentage of gutta‐percha in laterally compacted root fillings

AIM To determine the influence of filling technique and root canal area on the percentage of gutta-percha (PGP) in laterally compacted root fillings. METHODOLOGY Sixty extracted canine teeth were accessed and the root canals instrumented to the same size. They were then divided in three groups and filled with laterally compacted gutta-percha cones and AH Plus using different techniques. A variation of cold lateral compaction using a sequence of spreaders prior to accessory cone placement was compared to two commonly-used techniques. Twenty additional canines with prepared root canals were used as negative controls in which gutta-percha was introduced into the canals but no compaction applied. The roots were sectioned horizontally at 3 and 6 mm from the apex and micro-photographs taken. Using software, the area of the canals and gutta-percha at each level were measured and PGP calculated. A Multivariate analysis was used to determine the variables influencing PGP. A linear regression test was used to verify the variation in PGP explained by canal area. RESULTS At each level the largest canal was two to three times wider than the smallest. Canal area significantly influenced the PGP at both levels (P < 0.05), however, the variation in PGP was only partially explained by canal area (r(2) = 0.154, 6 mm; r(2) = 0.119, 3 mm). The PGP at the 3 mm level was lower than at 6 mm (P = 0.003). The spreader-sequence technique achieved a higher PGP than the other two techniques (P = 0.00002). The control group had the lowest area of GP. CONCLUSIONS Variations in root canal filling technique and canal area influenced the percentage of gutta-percha of laterally compacted root fillings. The percentage of gutta-percha was lower at the 3 mm level compared to the 6 mm level.

New terms for categorizing the outcome of root canal treatment

Dear Editor Various terms have been used to categorize the outcomes of root canal treatment. ‘Success’ and ‘failure’ are the most popular terms that are used, but ‘healing’ and ‘healed’ have been suggested (Friedman & Mor 2004). ‘Success’ means ‘the accomplishment of an aim or purpose’ (Oxford Dictionary). According to most endodontic textbooks, the purpose of root canal treatment is to prevent and eliminate apical periodontitis (AP) (Ørstavik & Pitt Ford 1998). Because the outcome of treatment is evaluated using the history provided by the patient at recall along with a thorough clinical examination and with radiographs, ‘success’ has been defined as the prevention and elimination of a periapical radiolucency and symptoms, with ‘failure’ being the development or persistence of AP and/or symptoms (European Society of Endodontology 2006). It has been demonstrated that bacteria cannot be removed completely from the canal system using current techniques in both primary root canal treatment and retreatments (Nair et al. 2005, Haapasalo et al. 2011). To conform to these limitations, the aim of root canal treatment should be restated as – ‘the minimization of the burden of root canal infection and the severity of AP’. It is well known that several years may be required for complete resolution of periapical radiolucencies (Ørstavik 1996), and thus a long follow-up time period is required, which reduces the recall rate. With a low recall rate, the reported success rates could be overor under-estimated (Ørstavik et al. 2004, Marquis et al. 2006, Wu et al. 2009). Sixty-three clinical studies (1922–2002) were selected in a review by Ng et al. (2007), the median recall rate was 52.7% and the lowest recall rate was 11% (Selden 1974). In the Toronto studies phases I, II and III, data of only 27% of the treated teeth were included in the final analysis in spite of several and various attempts to stimulate the participants to return for recall (Marquis et al. 2006). The problems of conducting clinical trials in mobile populations are well documented (Ng et al. 2007). In comparison with ‘success’ and ‘failure’, ‘effective’ and ‘ineffective’ are reasonable terms that should be considered. ‘Effective’ treatment is defined as the absence of symptoms and complete or partial resolution of the preoperatively existing periapical radiolucency 1 year following treatment. In cases where no preoperative lesion was present, ‘effective’ would mean that no lesion or signs/symptoms will develop after 1 year. ‘Ineffective’ treatment is defined as the development or enlargement of a radiolucency and/or the persistence/ emergence of symptoms and signs 1 year following treatment, and a timely retreatment should be suggested to the patient (Wu & Wesselink 2005). Asymptomatic teeth, where the size of the radiolucency does not noticeably change 1 year following treatment, should be placed into an uncertain category and monitored for a further period of one more year. Friedman & Mor (2004) suggested the use of ‘healed/ healing/ disease’ in place of ‘success’ and ‘failure’. The newly suggested term ‘effective’ would include the categories ‘healed’ and ‘healing’ and will not result in further treatment, whilst the term ‘ineffective’ at 1 year would mean the emergence or enlargement of the periapical radiolucency and/or symptoms and signs that will require intervention. A 1-year follow-up period is too short to judge a tooth as ‘diseased’ (Haapasalo et al. 2011) and this is why this term is not included in the present suggestion. The advantages of using ‘effective’ and ‘ineffective’ over previous terms to describe the outcome are the following: 1. shorten the follow-up period from 4 year to 1 year and thereby increase the recall rate and reduce the number of appointments and radiographs; 2. reduce the number of unnecessary retreatments indicated by adhering to previous definitions (Figdor 2002); and 3. the terms ‘effective’ and ‘ineffective’ relate directly to an indication for treatment and make clinical decisions easier and reproducible. We wish to initiate an open discussion on the issue of terms used to categorize the outcome of root canal treatment, beginning with this letter.

Optical Coherence Tomography for Endodontic Imaging

In root canal therapy, complications frequently arise as a result of root fracture or imperfect cleaning of fins and invaginations. To date, there is no imaging method for nondestructive in vivo evaluation of the condition of the root canal, during or after treatment. There is a clinical need for a technique to detect defects before they give rise to complications. In this study we evaluate the ability of optical coherence tomography (OCT) to image root canal walls, and its capacity to identify complicating factors in root canal treatment. While the potential of OCT to identify caries has been explored before, endodontic imaging has not been reported. We imaged extracted lower front teeth after endodontic preparation and correlated these images to histological sections. A 3D OCT pullback scan was made with an endoscopic rotating optical fiber probe inside the root canal. All oval canals, uncleaned fins, risk zones, and one perforation that were detected by histology were also imaged by OCT. As an example of an area where OCT has clinical potential, we present a study of vertical root fracture identification with OCT.