Therapeutic Potential of Chlorhexidine-Loaded Calcium Hydroxide-Based Intracanal Medications in Endo-Periodontal Lesions: An Ex Vivo and In Vitro Study.

Endo-periodontal lesions are challenging clinical situations where both the supporting tissues and the root canal of the same tooth are infected. In the present study, chlorhexidine (CHX)-loaded calcium hydroxide (CH) pastes were used as intracanal medications (ICMs). They were prepared and tested on pathogens found in both the root canal and the periodontal pocket. Exposure to 0.5% and 1% CHX-loaded ICMs decreased the growth of Porphyromonas gingivalis and was effective in eradicating or inhibiting an Enterococcus faecalis biofilm. CH was injected into the root canal of extracted human teeth immersed in deionized water. CHX-loaded ICMs resulted in the transradicular diffusion of active components outside the tooth through the apex and the lateral dentinal tubules, as shown by the release of CHX (from 3.99 µg/mL to 51.28 µg/mL) and changes in pH (from 6.63 to 8.18) and calcium concentrations (from 2.42 ppm to 14.67 ppm) after 7 days. The 0.5% CHX-loaded ICM was non-toxic and reduced the release of IL-6 by periodontal cells stimulated by P. gingivalis lipopolysaccharides. Results indicate that the root canal may serve as a reservoir for periodontal drug delivery and that CHX-based ICMs can be an adjuvant for the control of infections and inflammation in endo-periodontal lesions.

Shaping Ability of F6 SkyTaper®, Hyflex® EDM One File, and One Curve®: A Micro-computed Tomographic Evaluation in Curved Root Canals.

OBJECTIVE: The present study aimed to compare the shaping ability of the F6 SkyTaper® (F6S), HyFlex® EDM OneFile (HEDM), and One Curve® (OC) nickel-titanium single-file instruments using micro-computed tomography. METHODS: Fifty-two mesiobuccal roots of maxillary first molars, with a degree of curvature between 20° and 42°, were randomised into three experimental groups (n=15 per group): F6S, HEDM, and OC, and a non-instrumented control group (n=7). All specimens were scanned by micro-computed tomography before and after instrumentation. The following parameters were evaluated: preparation time, volume of dentine removed, cutting efficiency, unshaped surfaces, and canal transportation. Cutting efficiency was analysed using an ANOVA parametric test and Tukey's multiple comparison post hoc test. Other parameters were analysed using a non-parametric Kruskall-Wallis test followed by Dunn's multiple comparison post hoc test. RESULTS: No instrument separation occurred during instrumentation. No significant differences were found between the instrument groups with respect to all the parameters (p>0.05). All the instruments induced morphological changes in the root canal dentine (p<0.05) and tended to increase canal transportation toward the coronal portion of the root canals (p>0.05). CONCLUSION: All instruments were able to shape curved canals and preserve their original anatomy. Single-file endodontic procedures with these instruments can be used with comparable changes in the root canal shape with minimal transportation. (EEJ-2022-01-06).

Effect of dimensional variations on the manufacturing process and the 3D shrinkage ratio of stereolithographic dental alumina ceramics.

The purpose of the present study was to evaluate the influence of height and length variations of alumina ceramics manufactured by stereolithography on deformations caused by the manufacturing process and on the 3D shrinkage ratio to control the final dimensions and improve the adaptation of stereolithographic ceramic dental prostheses. Two different U-shaped models were designed with variable heights or lengths. The specimens were manufactured by stereolithography and were scanned using a microtomographic device before and after the heat treatment. Dimensional variations were measured using inspection software. The number and surface of layers of alumina ceramic influenced the reliability of the stereolithography manufacturing but did not influence the 3D shrinkage ratio. The larger the layer surface, the larger the deformation of the ceramic. Dental ceramics manufactured by stereolithography with smallest layer surface are the most reliable. This helps in the selection of the build orientation.

How Adding Chlorhexidine or Metallic Nanoparticles Affects the Antimicrobial Performance of Calcium Hydroxide Paste as an Intracanal Medication: An In Vitro Study.

The aim of our study was to explore the potential value of metallic (Ag, Cu, and Zn) salts, polymer/metallic nanoparticles, and chlorhexidine (CHX) for improving the antimicrobial activity of calcium hydroxide (CH) against E. faecalis and C. albicans, associated with persistent endodontic infections. A first screening was performed by determining minimum inhibitory/bactericidal concentrations (MIC/MBC). Antimicrobial activity of the CH paste mixed with metallic salts, chitosan or cyclodextrin polymer metallic nanoparticles was compared to the antimicrobial activity of CH paste alone and CH + CHX using a time-kill kinetics assay. The effect of the antimicrobials on the rheological and the key mechanical properties were also examined. Copper and zinc were discarded because of their MIC/MBC values and silver because of its kill time curve profile. Except for a slower setting time after 24 h and a higher weight loss after 1 week of incubation, the mechanical behavior of the CH paste was unaffected by the addition of CHX. Polymeric/metallic nanoparticles failed to potentiate the antimicrobial effect of CH. By contrast, CHX increased this effect and thus could help eradicate E. faecalis associated with persistent root canal infections without altering the desired key physical properties of the CH paste.

Effect of build orientation on the manufacturing process and the properties of stereolithographic dental ceramics for crown frameworks.

STATEMENT OF PROBLEM: Stereolithography (SLA) ceramic crown frameworks are suitable for clinical use, but the impact of SLA build orientation has not been identified. PURPOSE: The purpose of this in vitro study was to investigate the effect of 3 build orientations on the physical and mechanical properties and the microstructure of SLA alumina dental ceramics. MATERIAL AND METHODS: The physical and mechanical properties and microstructures of 3 different oriented SLA alumina ceramics (ZX, ZY, and XY) were evaluated by visual observation, hydrostatic weighing (n=10/group), Weibull analyses (n=30/group), scanning electron microscopy, 3-point flexural strength (n=30/group), fracture toughness (indentation, single-edge-V-notched-beam) (n=4/group), and Vickers hardness (n=15/group) testing. The hydrostatic weighing, 3-point flexural strength, fracture toughness, and Vickers hardness testing data were statistically analyzed (α=.05). RESULTS: The minimum resting period of slurries between the polymerization of 2 layers was shorter for the ZY- and ZX-oriented specimens and increased with the layer surface. The density and Vickers hardness of the SLA-manufactured specimens were similar for all groups (P>.05). The 95% confidence intervals of the Weibull moduli of the ZX- and ZY-oriented specimens were higher than that of the XY-oriented specimens, with no overlap fraction. The ZY-oriented specimens displayed significantly higher 3-point flexural strength (P<.05) and fracture toughness as evaluated by the single-edge-V-notched-beam method than the ZX-oriented specimens (P<.05). They also displayed significantly higher 3-point flexural strength than the XY-oriented specimens (P<.05). The microstructural analysis showed that the texturing was heterogeneous and that the major axis of the large grains of alumina ran parallel to the orientation of the layers. CONCLUSIONS: The ZY orientation produced a reliable dental ceramic by SLA, with the shortest general manufacturing time and the highest mechanical strength when the layers were perpendicular to the test load surface.

Are the evaluation criteria used in preclinical endodontic training courses relevant? A preliminary study.

This study aimed to evaluate the relevance of a conventional evaluation protocol (CEP) for preclinical endodontic training. Seven dental students performed root canal treatments on an extracted human molar which was then evaluated by CEP (clinical and radiographic observations, including preparing the access cavities, preparing and filling the root canal, and detecting iatrogenic errors). A reference evaluation protocol (REP) based on micro-computed tomographic images analysis was used as a control. The evaluation scores obtained by CEP and REP were compared using a non-parametric Wilcoxon's test. CEP was relevant for access cavity, irrigation, working length and ledge detection training but was no more effective than the REP for evaluating the apical diameter and taper of the root canals, the quality of the fillings, and the presence of perforations and fractured instruments using retro-alveolar radiographs. The conventional evaluation criteria used in preclinical endodontics should be used with care to detect 'unsafe' students.

Optimization and Preclinical Perception of an Artificial Simulator for Endodontic Training: A Preliminary Study.

The aim of this study was to evaluate the performance of ceramic, hybrid ceramic, and commercial plastic bloc root canal simulator (RCS) as preclinical training aids in the learning phase of endodontic treatments. A previously developed hydroxyapatite ceramic RCS was improved by adding epoxy resin to the ceramic matrix to more closely mimic the organic phase of dentin and to simulate the clinical situation as realistically as possible. The sintered hydroxyapatite ceramic RCS was vacuum infiltrated with epoxy resin, and the degree of infiltration was evaluated by methylene blue staining. The suitability of the resin-infiltrated ceramic simulator (CR) for preclinical endodontic training was compared to that of a non-infiltrated ceramic simulator (C) and a commercial epoxy bloc (P) using a cohort of 30 dental students at one dental school in France. The study was conducted in 2016. The students' perceptions following the required exercises using the CR, C, and P were scored using a questionnaire. The learning outcomes were also assessed by examining the canal preparations that the students performed on extracted teeth using a master cone try-in test. The vacuum process resulted in a good degree of resin infiltration into the ceramic. The questionnaire showed that the C and CR groups generally reported greater satisfaction, especially for radiographic visualizations, than the P group. The CR group had a higher score than the P group for tactile sensation. There was no significant difference among the three groups with respect to the canal preparations using extracted teeth. Resin infiltration improved the performance of the ceramic RCS, especially with respect to perception during root canal instrumentation. A larger scale student training investigation and an assessment by experienced endodontists are required to validate the model.

Stereolithography: A new method for processing dental ceramics by additive computer-aided manufacturing.

OBJECTIVES: The aim of this study was to compare the physical and mechanical properties of stereolithography (SLA)- manufactured alumina ceramics of different composition to those of subtractive- manufactured ceramics and to produce suitable dental crown frameworks. METHODS: The physical and mechanical properties of a control and six experimental SLA ceramics prepared from slurries with small (S) and large (L) particles (0.46±0.03 and 1.56±0.04µm, respectively) and three dry matter contents (70%, 75%, 80%) were evaluated by dynamic rheometry, hydrostatic weighing, three3-point flexural strength measurements, and Weibull analyses, and by the micrometrics measurement of shrinkage ratio before and after the heat treatments. RESULTS: S75 was the only small particle slurry with a significantly higher viscosity than L70. The viscosity of the S80 slurry made it impossible to take rheological measurements. The viscosities of the S75 and S80 slurries caused deformations in the printed layers during SLA manufacturing and were excluded from further consideration. SLA samples with low dry matter content had significantly lower and densityflexural strengths. Only SLA samples with a large particle size and high dry matter content (L75 and L80) were similar in density and flexural strength to the subtractive- manufactured samples. The 95% confidence intervals of the Weibull modulus of the L80 ceramic were higher (no overlap fraction) than those of the L75 ceramic and were similar to the control (overlap fraction). The Weibull characteristics of L80 ceramic were higher than those of L75 ceramic and the control. SLA can be used to process suitable crown frameworks but shows results in anisotropic shrinkage. SIGNIFICANCE: The hH High particle size and dry matter content of the L80 slurry allowed made it possible to produce a reliable ceramic by SLA manufacturing with an anisotropic shrinkage, and a density, and flexural strength similar to those of a subtractive-manufactured ceramic. SLA allowed made it possible to build up a dense 3D alumina crown framework with controlled shape. Further studies on the marginal adaptation and shrinkage model of alumina crown frameworks will be required to optimize the process.

Well-organized spheroids as a new platform to examine cell interaction and behaviour during organ development.

We present an experimental method allowing the production of three-dimensional organ-like structures, namely microtissues (MTs), in vitro without the need for exogenous extracellular matrix (ECM) or growth factors. Submandibular salivary glands (embryonic day ED14), kidneys (ED13) and lungs (ED13) were harvested from mouse embryos and dissociated into single cells by enzyme treatment. Single cells were seeded into special hanging drop culture plates (InSphero) and cultured for up to 14 days to obtain MTs. This strategy permitted full control of the quantity of seeded cells. The development of the MTs into organs was followed histologically and immunohistochemically. Well-organized epithelial structures surrounded by a basal lamina were formed, as confirmed by transmission electron microscopy. Expression of E-cadherin, vimentin, fibronectin and α-SMA was compared in organs and corresponding MTs by real-time quantitative polymerase chain reaction. Branching morphogenesis was induced in MTs (as shown by histology and immunostaining for fibronectin and perlecan) and was conserved even after 14 days of culture. MTs continued their development and their epithelial structures were comparable with those of the physiological organ at postnatal day 2 (PN2). Expression of aquaporins was investigated to obtain better support for the functional differentiation of epithelial cells. Histogenesis proceeded and led to the start of organogenesis. This experimental model might improve our knowledge of epithelial-mesenchymal histogenesis and can be employed to study development or cellular organization during the embryonic formation of organs.

Influence of heat and ultrasonic treatments on the setting and maturation of a glass-ionomer cement.

PURPOSE: To compare the effect of different treatments (heat capsule, ultrasound, and dual treatments) on the setting kinetics and maturation properties of a conventional GIC (EQUIA, GC) to that of standard setting. METHODS: The optimal durations of the heat and ultrasonic treatments were determined by monitoring changes in the COO-/COOH ratio, surface hardness, and temperature within the samples. The influence of optimal treatments on the maturation properties of the GIC (microhardness, and 3-point flexural strength) were assessed using GIC samples incubated in artificial saliva for 24 hours, 1 month, and 3 months. RESULTS: The optimal durations of the heat and ultrasonic treatments for accelerating setting were 5 minutes and 35 seconds, respectively. The dual treatment using the optimal conditions of the individual treatments further enhanced the setting kinetics. A temperature peak (49°C) within the GIC was detected during setting. Only the dual treatment increased the mechanical properties of the GIC after 24 hours compared to the control, while no significant difference was observed after 1 and 3 months.

Nanofibers implant functionalized by neural growth factor as a strategy to innervate a bioengineered tooth.

Current strategies for jaw reconstruction require multiple procedures, to repair the bone defect, to offer sufficient support, and to place the tooth implant. The entire procedure can be painful and time-consuming, and the desired functional repair can be achieved only when both steps are successful. The ability to engineer combined tooth and bone constructs, which would grow in a coordinated fashion with the surrounding tissues, could potentially improve the clinical outcomes and also reduce patient suffering. A unique nanofibrous and active implant for bone-tooth unit regeneration and also the innervation of this bioengineered tooth are demonstrated. A nanofibrous polycaprolactone membrane is functionalized with neural growth factor, along with dental germ, and tooth innervation follows. Such innervation allows complete functionality and tissue homeostasis of the tooth, such as dentinal sensitivity, odontoblast function, masticatory forces, and blood flow.