Perception of a modular 3D print model in undergraduate endodontic education.

AIM: To evaluate a modular 3D print training dental model with embedded human teeth and electronic working length determination for undergraduate endodontic education. METHODOLOGY: Cone-beam volume tomography data of a human skull were transferred into stereolithographic (STL) data, and a customizable modular 3D print model with individually removable sextants and teeth was generated for the use in commercially available phantom heads. Each of sixty-eight students performed a complete root canal treatment on an extracted human tooth. Working lengths were determined with electronic apex locators (EAL) and verified radiographically. Subsequently, an evaluation was carried out with regard to the difficulty of the working steps access cavity preparation, working length determination, root canal preparation/irrigation and canal filling, and these steps were compared to commonly used benchtop models. Additionally, the agreement of electronic and radiographic working length determination was assessed and analysed statistically with the chi-square test. RESULTS: A total of 68 teeth (20 incisors, 26 premolars and 22 molars) with 127 root canals were treated. In total, 87% of the students considered the modular 3D print model considerably more demanding than the conventional benchtop model. Overall, 96% felt better prepared for the clinical situation, 92% felt markedly reduced stress levels during endodontic practice in the subsequent clinical courses, and 93% of the students suggested the model should be used in future preclinical endodontic training. The preradiographic use of EAL resulted in 85% of the cases having radiographically acceptable working length determination within 0-2 mm from the radiographic apex. Readings more than 2 mm from the apex or beyond were significantly more common in molars than in premolars and incisors (P < 0.05). CONCLUSIONS: The vast majority of students rated the modular 3D print training model positively despite it being more demanding. They also recommended its use in preclinical teaching and training. The model allowed a more realistic simulation of the clinical situation with a simultaneous use of EALs and led to reduced stress levels in endodontic treatment in the subsequent clinical courses.

Physico-chemical investigation of endodontic sealers exposed to simulated intracanal heat application: epoxy resins and zinc oxide-eugenols.

AIM: To gain information in a laboratory setting about the effect of thermal treatment of epoxy resin-based and zinc oxide-eugenol-based sealers. METHODOLOGY: AH Plus and Pulp Canal Sealer (PCS) were exposed to thermal treatment at 37, 47, 57, 67, 77, 87 and 97 °C for 30 s. According to clinically relevant considerations, intracanal sealer temperature is likely not to exceed 60 °C during warm vertical root canal filling. Heat application is recommended for less than 30 s during continuous wave technique, but might exceed this threshold in complex cases. Furthermore, heat treatment at 97 °C was performed for 60 and 180 s to simulate inappropriate implementation of warm vertical filling techniques. Specimens were heated inside 2-mL plastic tubes in a thermo-controlled water bath until the temperatures were reached and kept at this temperature for the determined period of time. Afterwards, specimens were cooled to body temperature and physical properties (setting time, flow, film thickness according to ISO 6876) were assessed. Chemical properties (Fourier transformed infrared spectroscopy) were assessed after complete setting of the specimens in an incubator at 37 °C and 100% humidity. Statistical analysis of physical properties was performed using Kruskal-Wallis test (P = 0.05). RESULTS: The setting time of AH Plus and PCS decreased when temperature and duration of heat application increased. Whilst the setting time of AH Plus decreased from 622 min at 20 °C (for 30 s) to 381 min at 97 °C (for 180 s; P < 0.05), heat treatment of PCS at 97 °C for 180 s led to an immediate setting of the material. From 20 °C (for 30 s) to 97 °C (for 30 s), the setting time of PCS decreased from 80.1 to 41.0 h (P < 0.05). Film thickness and flow were not relevantly influenced by thermal treatment except for PCS at 97 °C for 180 s. FT-IR spectroscopy did not reveal any chemical changes of either sealer after thermal treatment. CONCLUSIONS: Thermal treatment simulating clinically relevant temperature levels and heating times did not lead to any substantial physical or chemical changes at all temperature levels when heating did not exceed 60 s. AH Plus and Pulp Canal Sealer can be considered suitable for warm root filling techniques.

A critical appraisal of studies on cyclic fatigue resistance of engine-driven endodontic instruments.

The endodontic literature contains a plethora of studies on static and dynamic cyclic fatigue resistance tests performed on a large array of rotary or reciprocating nickel-titanium endodontic instruments. It was the aim of this review to summarize the currently available evidence to point out the different outcomes from static versus dynamic tests and to assess whether cyclic fatigue tests provide useful data and information for clinical practice. An electronic literature research in the database PubMed was performed using appropriate search terms, and the titles and abstract were screened for relevance. Language was restricted to English. The review reveals marked differences between the results obtained in static and dynamic tests, and also, the results for the same instruments assessed either under static or dynamic experimental conditions are widely inconsistent. Between the lowest and the highest value for one and the same pathfinding instrument was a factor of about 123 when cyclic fatigue was assessed either under static or dynamic experimental conditions. Moreover, standard deviations of up to 30% have been reported. Environmental temperature has a 500% impact on the lifetime of instruments. In conclusion, fatigue resistance tests conducted under room temperature should be regarded as having little meaning and the scientific and clinical benefits of fatigue resistance tests are very limited. These data should be provided by the manufacturer of the instruments.

Canal cleanliness using different irrigation activation systems: a SEM evaluation.

OBJECTIVES: The purpose of this study was to assess the efficacy of different final irrigation activation methods in removing debris and smear layer in the apical, middle, and coronal portion of straight root canals. MATERIAL AND METHODS: Straight root canals of 58 freshly extracted mandibular premolars were used. Root canals were prepared to size 40.06. Irrigation was performed using 3% sodium hypochlorite. Samples were divided into four equal groups (n = 12) according to the irrigation activation techniques: (A) manual irrigation (MI), (B) EndoActivator (EA) (Dentsply Maillefer, Ballaigues, Switzerland), (C) sonic activation EDDY (EDDY; VDW, Munich, Germany), and (D) passive ultrasonic irrigation (PUI). Ten teeth served as negative controls. Roots were split longitudinally, and the canal walls were subjected to scanning electron microscopy. The presence of debris and smear layer at coronal, middle, and apical levels were evaluated using a 5-point scoring system and statistically analyzed using Kruskal-Wallis and chi-square tests. RESULTS: Canal cleanliness decreased from coronal to apical (P = 0.035). Significantly more debris was removed with EA, EDDY, and PUI compared to MI (P < 0.001; total values), but no differences were observed in the different portions of the root canals (P > 0.05). Smear layer removal with PUI, EA, and EDDY was not significantly different (P > 0.05), but only EDDY and PUI were superior to MI (P < 0.01). CONCLUSION: All activation methods created nearly debris-free canal walls and were superior compared to manual irrigation (P < 0.001). EDDY and PUI also showed significantly better smear layer scores compared to manual irrigation. CLINICAL RELEVANCE: The sonic activation system EDDY performed equally as well as PUI, and both methods were significantly superior compared with manual irrigation in straight root canals with regard to debris and smear layer removal.

A comparison of ankle taping methods.

Four different types of ankle tapings were applied to a model of the human ankle joint. The model was constructed so that it contained a hinge to represent the ankle joint and had an external shape identical to a real ankle and foot. A mechanical testing machine was used to apply moments to the model at a controlled loading rate. From these tests, the deflection and torque to failure and the tangent stiffness were determined. Loadings of an ankle joint in vivo revealed that the angular deflection to initiate pain was approximately 8 degrees. Only the figure eight and full tapings could withstand 8 degrees of angular displacement on the ankle model prior to failure. Analysis of athletic trauma revealed that torques of 420 Nm could be applied to the ankle joint. Only the figure eight taping with three or more wraps has adequate strength to withstand this moment, and thus this taping is recommended. In practice, tapings failed by shearing away from the surface of the foot of shrinking rather than by rupture of the tape.

Transcutaneous muscle stimulation to retard disuse atrophy after open meniscectomy.

Immobilization of an extremity inevitably results in disuse muscle atrophy. The effectiveness of transcutaneous muscle stimulation by a portable device in preventing atrophy has been determined. Ten patients treated by open meniscectomy and given the usual isometric training were matched with ten patients in whom electrostimulation, consisting of a strong, tetanizing, five-second sustained muscular contraction about 400 times/day, was used for two weeks. Muscular strength and leg circumference were measured before surgery and four weeks after surgery. The electrically stimulated group had a significantly smaller loss of muscle volume and muscle strength, were able to walk earlier without crutches, had a greater range of knee motion, had much less postoperative knee swelling, and used significantly less pain medication. Transcutaneous electrical stimulation may prevent muscle atrophy due to immobilization, thereby shortening rehabilitation time.

Transcutaneous muscle stimulation as a method to retard disuse atrophy.

Thirty healthy, young adults (18 to 25 years of age), were volunteers in a three-group study to determine the efficacy of transcutaneous electrostimulation as a means of preventing atrophy of normal musculature on wearing a long-leg cast. Each group of ten subjects (five males and five females) were chosen by lot: Group I, nonisometric, Group II, isometric, Group III, TMS electrostimulated thigh and calf muscles. There was little difference in the findings in Groups I and II, and each lost an appreciable amount of muscle mass and power after just two weeks of immobilization. However, in the electrostimulated group muscle atrophy was one-half that of the other groups in the thigh area and one-fifth that of the others in the calf area. In addition, the calf musculature retained its bulk and power with actual increase in a few of the less athletic individuals. Trancutaneous muscle stimulation offers great promise for surgically treated or impaired extremities, enabling early return to activity with optimal function.