A novel anatomical ceramic root canal simulator for endodontic training.

INTRODUCTION: Endodontic therapy is often complicated and technically demanding. The aim of this study was to develop a reproducible biomimetic root canal model for pre-clinical and postgraduate endodontic training. MATERIAL AND METHODS: A specific ceramic shaping technique (3D printing and slip casting of a root canal mould) was developed to reproduce canal systems with the desired shape and complexity using a microporous hydroxyapatite (HAp)-based matrix. The microstructural morphology, pore size and porosity, as well as the Vickers microhardness of the ceramic simulators (CS) were assessed and were compared with natural dentin and commercial resin blocks. The reproducibility of the root canal shapes was assessed using the Dice-Sørensen similarity index. Endodontic treatments, from refitting the access cavity to obturation, were performed on the CS. Each step was controlled by radiography. RESULTS: Many properties of the CS were similar to those of natural dental roots, including the mineral component (HAp), porosity (20%, porous CS), pore size (3.4 ± 2.6 µm) and hardness (120.3 ± 18.4 HV). DISCUSSION: We showed that it is possible to reproduce the radio-opacity of a tooth and variations in root canal morphology. The endodontic treatments confirmed that the CS provided good tactile sensation during instrumentation and displayed suitable radiological behaviour. CONCLUSIONS: This novel anatomic root canal simulator is well suited for training undergraduate and postgraduate students in endodontic procedures.

Three-dimensional Micro-culture System for Tooth Tissue Engineering.

The arrangement of cells within a tissue plays an essential role in organogenesis, including tooth development. Progress is being made to regenerate teeth by reassociating dissociated embryonic dental cells and implanting them in vivo. In the present study, we tested the hanging drop method to study mixed epithelial-mesenchymal cell reorganization in a liquid instead of semisolid medium to see whether it could lead to tooth histogenesis and organogenesis. This method allowed the control of the proportion and number of cells to be used, and the forming microtissues showed homogeneous size. The liquid environment favored cell migrations as compared with collagen gels. Three protocols were compared. The one that sequentially combined the hanging drop and semisolid medium cultures prior to in vivo implantation gave the best results. Indeed, after implantation, teeth developed, showing a well-formed crown, mineralization of dentin and enamel, and the initiation of root formation. Vascularization and the cellular heterogeneity in the mesenchyme were similar to what was observed in developing molars. Finally, after coimplantation with a trigeminal ganglion, the dental mesenchyme, including the odontoblast layer, became innervated. The real advantage of this technique is the small number of cells required to make a tooth. This experimental model can be employed to study the development, physiology, metabolism, or toxicology in forming teeth and test other cell sources.

Representations of the dental surgery profession and the motivations given by second-year French students for applying for dental surgery.

AIM: The aim of the present study was to evaluate the representations odontology students had of their career path. Second-year odontology students were questioned about their own motivations and the motivations they attributed to dentists in choosing this profession. METHODS: The students were asked to complete a questionnaire during the first course and again after 5 months. It was thus possible to study the evolution of their motivations after 5 months of interactions with their fellow students and professors. RESULTS: Whether or not students were able to choose their career path following the selection examination at the end of the first year of the medical programme was an important variable in determining individual motivations and the motivations they attributed to dentists in choosing the dental profession. For example, students who were unable to choose their career path reported that they would like to work in the public health system, while those who were able to choose said they chose odontology as a vocation. The closing of the gap between the two groups during the period between the two questionnaires highlighted the increasing cohesion of the group. CONCLUSION: Beyond the differences between the motivations provided, this study showed that students who had not planned to become dentists before the selection examination needed some time to familiarise themselves with the situation and accept the change in their career path.

Five methods of calcium hydroxide intracanal placement: an in vitro evaluation.

OBJECTIVE: The purpose of this study was to evaluate root canal dressing with calcium hydroxide paste using 5 techniques of placement. STUDY DESIGN: After endodontic preparation, each of 50 single-rooted premolars was filled with calcium hydroxide paste through use of one of the following techniques: Gutta-Condensor, MecaShaper, K-type ultrasonic file, Lentulo, and Pastinject. Radiographs of all 3 third root zones were made after cleaning and shaping and obturation. Density measurements (in pixels) were registered by means of an image analyzer and then compared through use of analysis of variance and Newman-Keuls multiple means tests. RESULTS: With respect to average filling density, the techniques ranked as follows, in ascending order: Gutta-Condensor, MecaShaper, K-type ultrasonic file, Lentulo, and Pastinject. There was a significant difference (P <.0009) between the Gutta-Condensor and Pastinject techniques, between the MecaShaper and Pastinject techniques, and between the ultrasonic file and Pastinject techniques; all favored the Pastinject. There were no significant differences between the Gutta-Condensor, MecaShaper, ultrasonic file, and Lentulo techniques or between the Lentulo and Pastinject techniques. CONCLUSIONS: The use of a specially designed paste carrier (the Pastinject) improved calcium hydroxide placement in root canals.

Maxillary second molar with two palatal roots.

A case report is presented describing the endodontic treatment of a maxillary second molar with two palatal roots.

Bacterial microleakage of Cavit, IRM, TERM, and Fermit: a 21-day in vitro study.

The aim of our study was to evaluate the leakage of four cements (Cavit, IRM, TERM, and Fermit) using a two-compartment model system and Streptococcus sanguis as bacterial marker. Access cavities in premolars were filled with cement and the teeth immersed in culture medium in the model system. Half of the teeth were thermocycled on day 2. Bacterial percolation into the upper compartment was measured at regular intervals (days 2, 7, 14, and 21). Cement thickness was measured at the end of the study. In the nonthermocycled group, Cavit was more leakproof than the other cements at day 2 (p = 0.011), than TERM and IRM at day 7 (p = 0.043). Fermit was more leakproof than IRM at day 7 (p = 0.043). In the thermocycled group, Cavit was more leakproof than the other cements at day 7 (p = 0.041). Thermocycling did not significantly affect leakage. Cement thickness averaged 4.1 mm and did not significantly affect leakage. These results should be considered when using cements as temporary fillings.

Dimensional stability of seven elastomeric impression materials immersed in disinfectants.

Dental impressions can increase the transmission of microorganisms and infections. The purpose of this study was to assess the influence of three disinfectant solutions on the dimensional accuracy of seven elastomeric impression materials. Impressions of a test block were either left untreated (controls) or treated by immersion in a disinfectant solution. Measurements were taken on die stone replicas of the impressions. Comparisons were made between (1) the measurements for the variations in the nontreated impressions and those for the treated impressions and (2) measurements for the treated impressions and the test block. Results indicated that the aminoamphoteric agent or glutaraldehyde derivative-based solutions created little change in relation to the initial dimensional accuracy of the impression products. However, the sodium hypochlorite solution often leads to expansion by comparison with controls. By comparison to the test block, this expansion then makes it possible in most cases to obtain better dimensional accuracy than initially. Within the limits of this study this expansion could lead to an improvement in clinical fixed prosthodontic procedures.

Bacterial microleakage of Cavit, IRM, and TERM.

In this in vitro study, a model system was developed and tested to evaluate the sealing ability of temporary restorative materials used in endodontic access preparations. The materials studied, Cavit, IRM, and TERM, were tested on 40 premolars against a known bacterial species, Streptococcus sanguis. The leakage of bacterial cells was checked 4 and 8 days after initial immersion in the culture. Thermocycling was introduced on the fourth day. After 8 days the cement thicknesses were measured after the teeth had been longitudinally sectioned. Before and after thermocycling, IRM was less leakproof than Cavit (p < 0.05) and TERM (p < 0.05). Thermocycling aggravated percolation in the case of IRM, and decreased the tightness of Cavit, whereas TERM remained leakproof. The thicknesses were as follows: Cavit, 3.73 mm; IRM, 3.45 mm; and TERM, 5.49 mm. There was no statistically significant relationship between thickness and tightness.

Survival of Prevotella intermedia (Bacteroides intermedius) in transport media.

Five transport media were selected for testing, in vitro, the survival of a pure strain of Prevotella intermedia (Bacteroides intermedius) for 6, 24, and 72 hours. Two were non-nutrient transport media (RTF and VMG IV). The three others (TG, PY, PYG) were nutrient media. An increase in the transport time, and manipulations in an aerobic atmosphere compromised the survival of the bacteria. PY ensured good survival of the bacteria. RTF seems to be the best medium for the transport of P. intermedia, when quantitative analysis is required.

In vitro survival of Bacteroides intermedius in five transport media, alone or in the presence of Streptococcus sanguis.

The survival rate of Bacteroides intermedius was first tested in monoculture, and Streptococcus sanguis was then added in 5 different transport media; 2 nonnutritious media, the viability-preserving medium of the University of Göteborg No. IV (VMG IV), reduced transport fluid (RTF), and 3 nutritious media, thioglycolate medium (TG), peptone yeast extract medium (PY) and PY medium with 1% glucose (PYG). All manipulations were carried out in an anaerobic chamber. After a given transport time (6 or 24 h) aliquots were spread on plates containing solid PY medium by means of an automated spiral system device, thus permitting counts after incubation. The slight variations in the counts of B. intermedius in monoculture, not exceeding 0.5 log10 in the 5 media tested, indicated its good survival capability, i.e. at least 24 h. By contrast, when S. sanguis was added, it was only possible to use nutritious media such as PY or TG for 6 h. In the glocose-containing media (PYG, TG), the multiplication of rapidly glucose-fermenting microorganisms such as streptococci influenced the B. intermedius survival rate. Therefore, the transport time for oral microbiological samples needs to be reduced as much as possible. The use of excessively rich media (particularly media containing a high level of glucose) should be avoided.