ENDO, 01/2017

Objective: To compare the fracture resistance of mandibular premolars restored with mesial-occlusal composites after access with traditional endodontic cavity (TEC) or contracted endodontic cavity (CEC) designs. Materials and Methods: Forty-five virgin single-rooted mandibular premolars were randomly divided into three groups and embedded in acrylic resin moulds. Group I (n = 15) remained untreated. Group II and III were prepared with mesial-occlusal cavities and accessed with TEC or CEC designs. Chambers were irrigated with 5.25% sodium hypochlorite/17% EDTA and dried. After etching and priming with Optibond, access cavities were restored with 3M Filtek. All samples were then fixed in a universal testing machine with the long axis of the roots positioned 45o to a load applied at a crosshead speed of 0.5 mm/min until failure. All specimens were visually assessed for failure modes. Fracture force data was statistically analysed by one-way ANOVA and Tukey post-hoc (P = 0.05). Results: The average fracture force for untreated teeth was 609.7 ± 279.1 N; 601.7 ± 307.9 N for mesial-occlusal cavities with TEC; and 600.9 ± 360.3N for teeth with CEC. There was no significant difference in fracture resistance between groups (F (2,42) = 3.299, P = 0.996). There was no significant difference in fracture resistance between traditional and modified groups (P = 0.994). All three groups had an equal number of "favourable" (repairable) and "unfavourable" failures (7:8), defined as irreparable failures or root fractures below the level of simulated bone. Conclusions: Modifying access outline to a contracted design did not improve fracture resistance of mandibular premolars restored with mesial-occlusal composites. Clinical Significance: A mandibular premolar with minimal caries that has been accessed endodontically with a CEC or TEC design may be restored provisionally with a class II composite with an equal measure of confidence with regard to fracture resistance. Keywords: Endodontic access cavity, fracture resistance, mandibular premolars

Aim: Large apical openings are encountered as a result of pulp necrosis in immature teeth, apical resorption, or over-enlargement of the apical foramen. Cleaning, shaping, obturation and apical seal of root canal systems are essential for the success of root canal treatment. There is scarce data comparing coronal leakage of teeth prepared to different apical sizes and obturated with Mineral Trioxide Aggregate (MTA). The aim of this study was to investigate the effect of apical preparation size on the leakage of MTA obturated root canals. Materials and Methods: A total of 125 extracted human teeth were divided into five groups each containing 25 samples and prepared to apical file sizes 30, 40, 50, 60 and 70. Twenty teeth served as positive and negative controls. Obturation was completed with grey MTA. Bacterial leakage was investigated after 120 days using Proteus vulgaris. Data was analysed using Independent-Samples Kruskal-Wallis test. Results: The average time for leakage of apical preparation sizes 30, 40, 50, 60 and 70 were 58.5, 70.2, 64.8, 59.0 and 55.2 days, respectively. No significant differences in leakage were observed between apical preparation sizes 30 to 70. Conclusions: Based on the present results, it appears leakage of MTA filled root canals is largely unaffected by varied apical size. MTA appears to seal well regardless of the apical size and is considered the material of choice for obturation of larger sized apices. Keywords: proteus vulgaris, root canal obturation, silicates

Objective: To investigate technical outcome and time efficiency, using ProTaper Universal (PTU) or ProTaper Next (PTN) rotary nickel titanium (NiTi) files, to prepare simulated canals, by undergraduate dental students. Methods: Sixty-six students were randomly assigned to two groups. Both groups prepared two endodontic blocks (n = 66) using PTU and PTN in crossover design. Preparation time was also recorded. The blocks were photographed under magnification and were assessed for procedural errors by two different observers. Data were recorded and analysed by descriptive statistics, generalised mixed model and analysis of variance (ANOVA) using SPSS. Results: The different file systems had a significant effect on the presence or absence of procedural errors, with a significance value of P 0.001. More successful preparation was achieved with PTN (89%) than PTU (37.5%). There were a total number of procedural errors of n = 58.The highest incidence of procedural errors by different file systems was transportation. The PTU showed 24 transportation errors out of a total of 51 errors and the PTN showed five transportation errors out of a total of seven. PTN demonstrated the quickest mean time of preparation with a P value of P 0.001. Conclusion: In the hands of novice operators, PTN showed a lower incidence of procedural errors and better time efficacy during instrumentation of simulated canals, compared with PTU. Keywords: procedural errors, ProTaper Universal, ProTaper Next, rotary

Aim: The aim of this study was to compare the dislodgement resistance of Biodentine (BD) and mineral trioxide aggregate (MTA), when used as coronal barriers during revascularisation procedures, on exposure to a bleaching agent in a simulated "walking bleach" technique. Materials and Methods: The study used 100 human, maxillary central incisors. Root canals were enlarged up to size 6 Peeso drills. After coronal-barrier placement, either BD or MTA, specimens of each material were randomly divided into five subgroups (n=10) according to time and setting environment: For subgroups A, B and C, specimens were placed in contact with a saline-moistened cotton pellet in a pulp chamber for 1 day, 1 week or 2 weeks respectively. Subgroup D specimens were placed in contact with a saline-moistened cotton pellet for 1 day, then in contact with the bleaching agent for 1 week. For subgroup E the specimens were prepared as subgroup D, followed by a change of bleaching agent for the second week. Push-out bond strength was measured. ANOVA was used to compare means, followed by the Tukey post hoc test for pair-wise comparisons. The significance level was set at P = 0.05. Results: BD recorded higher dislodgement resistance than MTA after 1 day, 1 and 2 weeks of setting (P 0.05); BD retained its higher dislodgement resistance than MTA after bleaching for 1 week (P 0.05). After 2 weeks of bleaching, however, there was no significant difference between BD and MTA (P > 0.05). There was no significant difference in dislodgement resistance of BD with or without bleaching after 1 or 2 weeks and of MTA with and without bleaching after 1 week (P > 0.05). After 2 weeks, however, MTA showed higher dislodgement resistance with bleaching than without (P 0.05). Conclusions: BD seems to have better retention qualities than MTA as a coronal barrier for revascularising teeth providing a suitable alternative. The walking bleach technique can be safe to use in discoloured, immature teeth undergoing revascularisation, retention-wise. Keywords: Biodentine, bond strength, sodium perborate

Background: This study aimed to evaluate Biodentine as a retrograde filling in terms of solubility, bond strength to the root canal dentine, and sealing ability. Biodentine was compared with mineral trioxide aggregate (MTA) as a control material. Materials and methods: For the solubility test, samples of 10 mm diameter and 1.5 mm thickness were prepared in Teflon moulds. After setting, specimens were weighed and placed in distilled water and then reweighed after one and three weeks. For bond strength and sealing ability, a total of 32 trimmed roots of 16 mm length from single rooted teeth were used. Roots were prepared with ProTaper Universal instruments. They were obturated using System B and Obtura. Apical 3 mm roots were cut off and retrograde cavities were prepared (3 mm depth and 0.8 mm diameter) and filled with either Biodentine or MTA. Samples were embedded in acrylic blocks and a horizontal section of 2 mm thickness was cut off. Bond strength of each material was measured immediately, and after one and three weeks while placed in saline solution. For sealing ability, fluid filtration test was used. The coronal parts of the roots were embedded in glass ionomer cement except for their apical 3 mm. Results: After 3 weeks' immersion, the solubility of Biodentine was significantly higher compared with MTA. For bond strength, Biodentine showed higher immediate bond strength than MTA; however, after three weeks, the difference was significant in favour of MTA. For sealing ability, Biodentine showed better leakage resistance at zero time, however the difference was statistically insignificant after one and three weeks. Conclusion: Based on the assessment of different physioco-chemical properties Biodentine seems to be an alternative to MTA when used as root end filling material. Keywords: Biodentine, bond strength, fluid filtration, leakage, MTA, push-out, solubility

Aim: The aim of the present study was to evaluate the influence of the surface roughness on the torsional resistance of polished and unpolished nickel-titanium BR4C endodontic instruments. Materials and Methods: Ten instruments of each type (electropolished and unpolished) were evaluated with a profilometer to quantify the surface roughness on the working part of the instruments and then subjected to torsional stress to evaluate the maximum torque and angular deflection at failure. Torsion was applied using a custom-made device attached to the crosshead of a universal testing machine (Emic DL 10.000, São José dos Pinhais, PR, Brazil). Data obtained from the maximum torque, angular deflection and from the roughness of the polished and unpolished instruments were statistically analysed by Student t-test. Results: The profilometer analysis showed that the surface grooves on the unpolished instruments were deeper compared with their electropolished counterparts. Significant differences in roughness (peak and valley) (P 0.05) were observed between the polished and unpolished specimens. In the torsion tests, the maximum torque and angular deflection were not significantly different (P > 0.05). Conclusion: This study showed that the depth of the surface grooves resulting from machining during the manufacturing process did not affect the maximum torque and angular deflection of the instruments tested. Keywords: roughness, surface finish, torsional fracture

Curved root canals are within the complex anatomic range of the root canal system and a possible reason for failure in the preparation of the root canals during root canal treatment. The introduction of NiTi files was a milestone for accessing difficult root canal anatomy. Lately, manufacturers have focused on the development of single file NiTi systems. The comparison of these rotary single file systems to the established full sequence NiTi systems, particularly with regard to their performance in curved canals, is being researched thoroughly. The main objective of this case report is to show the clinical performance of the rotary NiTi single file system F6 SkyTaper (Komet, Lemgo, Germany) in severely curved root canals. Keywords: curved root canal, F6 SkyTaper, NiTi, single file systems