Temperature rise on the surface of NiTi and stainless steel fractured instruments during ultrasonic removal.

AIM: To investigate the temperature rise induced by ultrasonic tips when activated against two types of fragments at two power-settings. METHODOLOGY: Twenty-four F2-ProTaper Universal rotary files and 36 stainless steel K-files, size 50, were sectioned at a point 5.5 mm from their tips. At specific power-settings, ET40D ultrasonic tips were activated against the peripheral surface of the fragment coronal part (1 mm) for 30 s with/without Air-Active function according to each group; (i) without Air-Active function at power-setting 1.5 against NiTi fragments, (ii) without Air-Active function at power-setting 1.5 against SS fragments, (iii) without Air-Active function at power-setting 3 against SS fragments, (iv) with Air-Active function at power-setting 3 against SS fragments, and (v) with Air-Active at power-setting 3 against NiTi fragments. Temperature rises were inspected at 15 and 30 s using the thermocouples. RESULTS: With no Air-Active function and power-setting 1.5, the temperature rises induced on NiTi fragments at 15 and 30 s (36.33 and 55.44 °C, respectively) were significantly greater than those induced on SS fragments at 15 and 30 s (26.08 and 35.27 °C, respectively) (P = 0.001 and <0.001, respectively). When ultrasonic tips were activated against SS fragments without Air-Active, the temperature rises induced by power-setting 3 at 15 and 30 s (35.25 and 45.32 °C, respectively) were significantly greater than those induced by power-setting 1.5 at the same intervals (26.08 and 35.27 °C, respectively) (P = 0.006 and 0.012, respectively). At 30 s, the overall temperature rise induced with Air-Active (25.56 °C) was significantly lower than that induced without Air-Active (45.34 °C) (P < 0.001). CONCLUSIONS: Lower power-settings and shorter application times are recommended when using ultrasonics for removal of NiTi fragments compared with SS ones. Air-Active function, as a coolant, is recommended when dealing with both types of fragments.

Temperature rise on the external root surface during removal of endodontic fractured instruments.

OBJECTIVES: To investigate the temperature rise (TR) on the external root surface while preparing a staging platform, for removing intra-canal fractured instruments, using Gates Glidden (GG) drills. MATERIALS AND METHODS: Thirty extracted mandibular incisors were decoronated and 3-3.5 mm of F3 ProTaper files were fractured 3 mm from the most coronal end of the root. Roots were divided into three groups. GG drills were used in a size-2 to size-5 sequence to prepare the staging platform coronal to the fractured segment. They were rotated at three speeds according to the study groups: group A for 2,000 revolutions per minute (rpm); group B for 4,000 rpm; and group C for 8,000 rpm. Temperature changes were recorded at the proximal and buccal or lingual external root surfaces while preparing the staging platform. Data were analyzed using the paired sample T, one- and two-ways ANOVA tests at p ≤ 0.05. RESULTS: Overall, TR at the proximal root surface (5.44 °C) was significantly higher than that at the buccal or lingual surface (3.25 °C) (p < 0.001). Generally, TR increased significantly as the size of GG drills or the revolution speed increased (p < 0.05). GG5 drills rotated at 8,000 rpm produced the highest TR (10.85 °C). There was no interaction effect of the GG drill size and the revolution speed on TR (p = 0.272). CONCLUSION: The highest TR on the external root surface, associated with preparation of a staging platform and produced by using GG drills size-5 rotating at up to 8,000 rpm, was lower than the damaging threshold. CLINICAL RELEVANCE: A staging platform can be performed by modified GG drills (no 2 to 5) rotating at 8,000 rpm without generating a hazardous TR.

The impact of fractured endodontic file removal on vertical root fracture resistance: three-dimensional finite element analysis.

This study investigated by means of finite element analysis the influence of fractured file removal on root fracture resistance in an endodontically-treated canine. A 4mm fragment of an endodontic file was deliberately fractured in the apical third of an upper canine root and removed by ultrasonic tips. Micro-computed tomography scans were carried out before and after fractured file removal on the same tooth. Two 3D-FE models (before and after file removal) were subjected to 100N loading. Results indicate that the fractured file removal increased von Mises stresses by 55%. Peak stresses were located around the root filling/dentine interface prior to file removal. Following file removal, peak stresses were concentrated at the buccal root surface/bone interface that might initiate vertical root fracture buccolingually.

Effect of retained fractured instruments on tooth resistance to vertical fracture with or without attempt at removal.

AIMS: To investigate the effect of retained fractured endodontic instruments on root strength and to evaluate the effectiveness of several root filling materials in reinforcing roots that had undergone unsuccessful attempt at removal of fractured instruments. METHODOLOGY: Seventy five mandibular premolar roots were divided into five groups. In group A (control), canals were prepared to a size F5-ProTaper instrument and filled with gutta-percha and TubliSeal sealer fragments. In the experimental groups (B, C, D and E), 4 mm of F5-ProTaper instruments were fractured in the apical one-third of the canal and then treated as follows: in group B, the fragments were left in situ without attempt at removal, and canals were filled with gutta-percha and TubliSeal sealer (GP No Removal). In groups C, D and E, an attempt at removal of the fragment was simulated by preparing a staging platform coronal to the fragment using modified Gates Glidden burs (No 2-5). Canals in group C were filled with gutta-percha and TubliSeal sealer (GP Removal), group D filled with Resilon (Resilon Removal) and group E with mineral trioxide aggregate (MTA Removal). Roots then underwent vertical fracture. Data were analysed using the one-way anova at P<0.05. RESULTS: Roots in the GP Removal group had significantly lower values for mean force for fracture (404.9 N). There was no significant difference between the control group and GP No Removal (765.2 and 707.8, respectively). Resilon Removal and MTA Removal groups (577.3 and 566.6 N) were not significantly different from the GP No Removal group. CONCLUSIONS: Leaving fractured instruments in the apical one-third of the canal does not appear to affect the resistance of the root to vertical fracture; Resilon and MTA appear to compensate for root dentine loss that occurred as a consequence of attempts at retrieval of fractured instruments when used as canal filling materials.

Vertical fracture resistance of roots after ultrasonic removal of fractured instruments.

AIMS: To investigate ex vivo root resistance to vertical fracture after fractured instruments were ultrasonically removed from different locations in the root canal. MATERIALS AND METHODS: Fifty-three canine roots were weighed and divided into four groups. Eight roots served as a control group in which canals were instrumented to a size F5-ProTaper instrument. In the experimental groups, F5-ProTaper fragments were fractured in the coronal, middle and apical one-thirds, and then removed ultrasonically. The time required for removal was recorded. Roots were reweighed, and canals were shaped to a size F5-ProTaper and filled with GuttaFlow. After incubation, roots underwent a vertical fracture test in which the force at fracture was recorded. The difference in root mass before and after treatment (fractured file removal or canal preparation) was calculated. Data were analysed using the Kruskal-Wallis, Mann-Whitney post-hoc and regression tests at P < 0.05. RESULTS: The highest root-mass loss was recorded when fragments were removed from the apical one-third (46.04 mg) followed by the middle and coronal (27.7 and 13.5 mg, respectively); these differences were significant (P < 0.05). There were significant differences in the force required for vertical fracture amongst the experimental groups (P < 0.05) with the lowest mean force recorded in the apical-third group (107.1 N) followed by the middle and coronal (152.6 and 283.3 N, respectively). The highest mean force was recorded in the control group (301.5 N) which was not significantly different from that in the coronal group (P = 1.00). A negative exponential correlation (r = 0.669) existed between the root-mass loss and the force required to fracture the roots. CONCLUSION: Whilst removal of fractured instruments from the coronal one-third of the root canal can be considered as a safe procedure, removal from deeper locations renders the root less resistant to vertical fracture.

Endodontists experience using ultrasonics for removal of intra-canal fractured instruments.

AIM: To investigate the experience of UK endodontists with aspects of ultrasonic use for removal of intra-canal fractured instruments. METHODOLOGY: A questionnaire form comprising both close-ended and partially close-ended questions with a covering letter explaining the aims of the study and indicating that all information would remain confidential and anonymous were sent to 180 endodontists working in the UK. Non respondents received a reminder with a differently worded covering letter. After collecting the responses, data were entered into SPSS software through which frequencies were determined and the chi-square test at the 0.05 level of significance, when required, was applied. RESULTS: Overall, 97% of endodontists reported the use of ultrasonics for removal of fractured instruments. The majority of them (78%) used ultrasonics with a coolant at least some of the time. Forty-seven per cent of users activated tips at medium to maximum power settings. The greatest proportion (53%) activated the tips for approximately 10 s. CONCLUSIONS: Endodontists reported different techniques when using ultrasonics for removal of fractured instruments.

Opinions and attitudes of endodontists and general dental practitioners in the UK towards the intracanal fracture of endodontic instruments: part 1.

AIM: To investigate the attitudes and opinions of general dental practitioners (GDPs) and endodontists in the UK towards fracture of endodontic instruments. It was hypothesized that there would be no significant difference between GDPs and endodontists regarding their experience of fracture of endodontic instruments. METHODOLOGY: A pilot questionnaire was carried out on 20 postgraduate dental students to ensure that the questions were easily understood. This was followed by a further pilot survey on a group of GDPs and endodontists (50) to facilitate sample size calculation. The sample size comprised 330 systematically selected GDPs, and all endodontic specialists working in the UK (170). The questionnaire comprised both close-ended and partially close-ended questions in four categories: demographics; pattern of practice and experience of instrument fracture; management of fractured instruments; and unsuccessful management of fractured instruments. Nonrespondents were sent another two mailings (first and second reminders). After collecting the responses, data were analysed using chi-square and Linear-by-Linear Association tests at the 0.05 level of significance. RESULTS: The overall response rate was 75% (82.82% for endodontists and 70.92% for GDPs). Overall, 88.8% of respondents had experienced fractured instruments with a significantly higher proportion of endodontists (94.8%) compared with that of GDPs (85.1%). CONCLUSION: Both endodontists and GDPs were aware of most factors contributing to endodontic instrument fracture. With experience and knowledge, fracture of endodontic instruments was associated with the number of root canal treatments performed.

Factors contributing to the separation of endodontic files.

Cleaning and shaping of the root canal system is essential for successful endodontic treatment. However, despite improvements in file design and metal alloy, intracanal file separation is still a problematic incident and can occur without any visible signs or permanent deformation. Only a few studies have reported high success rates of fractured file removal using contemporary techniques. Conflicting results have been reported regarding the clinical significance of retaining separated files within root canals. An understanding of the mechanisms of, factors contributing to, file fracture is necessary to reduce the incidence of file separation within root canals. This article reviews the factors that are of utmost importance and in light of these, preventive procedures and measures are suggested.

Opinions and attitudes of endodontists and general dental practitioners in the UK towards the intra-canal fracture of endodontic instruments. Part 2.

AIM: To investigate the attitudes of general dental practitioners (GDPs) and endodontists in the UK towards management of fractured endodontic instruments. METHODOLOGY: A questionnaire was sent to 330 systemically selected GDPs and all endodontists working in the UK (170). It was accompanied by a covering letter explaining the aims of the study and indicating that all the information given would remain confidential. Those who did not respond to the first mailing were sent another two mailings. Data were analysed using chi-square test at P