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.

Assessment of imatinib as first-line treatment of chronic myeloid leukemia: 10-year survival results of the randomized CML study IV and impact of non-CML determinants

Chronic myeloid leukemia (CML)-study IV was designed to explore whether treatment with imatinib (IM) at 400 mg/day (n=400) could be optimized by doubling the dose (n=420), adding interferon (IFN) (n=430) or cytarabine (n=158) or using IM after IFN-failure (n=128). From July 2002 to March 2012, 1551 newly diagnosed patients in chronic phase were randomized into a 5-arm study. The study was powered to detect a survival difference of 5% at 5 years. After a median observation time of 9.5 years, 10-year overall survival was 82%, 10-year progression-free survival was 80% and 10-year relative survival was 92%. Survival between IM400 mg and any experimental arm was not different. In a multivariate analysis, risk group, major-route chromosomal aberrations, comorbidities, smoking and treatment center (academic vs other) influenced survival significantly, but not any form of treatment optimization. Patients reaching the molecular response milestones at 3, 6 and 12 months had a significant survival advantage. For responders, monotherapy with IM400 mg provides a close to normal life expectancy independent of the time to response. Survival is more determined by patients' and disease factors than by initial treatment selection. Although improvements are also needed for refractory disease, more life-time can currently be gained by carefully addressing non-CML determinants of survival.