Resin materials for root canal obturation

Experimental Resin-Based Monoblock Endodontic Obturation System

Objective. The aim of the present study was to characterize a novel resin-based monoblock endodontic obturation system consisting of a polymeric cone and a resin-based endodontic sealer. Methods. The preliminary tests performed for the experimental cone were as follows: cohesive strength, dimensional stability, standardization of the diameter and taper, calcium ion release, and radiopacity, for the characterization of the experimental sealer, film thickness and flow tests were performed. Tests were performed according to the American National Standards Institute/American Dental Association (ANSI/ADA) Standards Nos. 57 and 78. The experimental cone was compared to gutta-percha, whereas the experimental sealer was compared to AH Plus. Data were analyzed by Student’s t-test (α = 0.05). Results. The experimental cone had superior values for cohesive strength and dimensional stability compared to gutta-percha. Regarding calcium ion release, the experimental system continued to release calcium ions after 30 days. Film thickness was similar for both endodontic sealers; conversely, the experimental resin-based sealer achieved higher values for flow compared to AH Plus. Conclusion. The experimental resin-based monoblock obturation system fully met the requirements of the ANSI/ADA Standard No. 78 and the ANSI/ADA Standard No. 57, except for radiopacity. Considering this, further studies are still needed to evaluate other radiopacifiers and the effect of their incorporation on the physicochemical properties of this novel resin-based monoblock endodontic obturation system.

Discoloration Potential of Endodontic Sealers: A Brief Review

Tooth discoloration induced by endodontic sealers, is a common finding that impairs aesthetic outcome of endodontic treatment. The aim of the present mini literature review, was to summarize the existing data on discoloration potential of different endodontic sealers. The research covered the article published in PubMed and Google Scholar from 2000 to 2015. The searched keywords included ‘tooth discoloration AND endodontic’, ‘tooth discoloration AND sealer, ‘tooth discoloration AND zinc-oxide eugenol sealer’, ‘tooth discoloration AND Calcium Hydroxide Sealer’, ‘tooth discoloration AND Glass Ionomer Sealer’, ‘tooth discoloration AND epoxy-resin Sealer’, ‘tooth discoloration AND Silicon Based Sealer’, ‘tooth discoloration AND Bioceramic Sealer’ and ‘Spectrophotometry’.

Evaluation of the apical sealing ability and adaptation to the dentin of two resin-based Sealers: An in vitro study

AIM

To quantitatively evaluate the apical sealing ability and adaptation of two resin-based sealers to dentin.

MATERIALS AND METHODS

Fifty freshly extracted mandibular first premolars were taken and sectioned at the cemento-enamel junction. Thirty teeth were subjected to a leakage study by the resin infiltration method with two groups of 10 teeth each. Group I teeth were obturated with methacrylate resin-based sealer (EnoRez) and Group II teeth were obturated with epoxy resin-based sealer (AH Plus). The remaining 10 teeth were used as controls (positive and negative of five teeth each). Twenty teeth were divided into two groups and obturated as in the leakage study and subjected to a scanning electronic microscopy (SEM) analysis for adaptation and resin depth penetration.

RESULTS

Both the sealers produced apical leakage to a certain extent. The adaptation and resin sealer penetration in the coronal and middle thirds was better than in the apical third of the root canal under SEM observation. The hybridized resin sealer tags in the coronal and middle thirds of Group I were much longer than that shown by Group II.

CONCLUSION

We conclude that the physical integrity of the sealer matrix may also be important in providing resistance to leakage.

Effect of time of extraction on the biocompatibility of endodontic sealers with primary human fibroblasts

The aim of this work was to evaluate the effects of different times of extraction on the cytotoxicity of six representatives of different root canal sealer groups-Real Seal SE, AH Plus, GuttaFlow, Sealapex, Roth 801, and ThermaSeal Plus-with human gingival fibroblasts. The materials were prepared according to manufacturers' specifications, and were incubated in culture medium (DMEM) at 37ºC for 1, 7, 14, 21, and 28 days, with daily washing, to simulate periodontal ligament clearance. Human fibroblasts were exposed to the final extracts at 24 hours, and cell viability was determined by MTT assay, with exposure to unconditioned DMEM as a negative control. Statistical analysis comparing cytotoxicities at each exposure time was performed by ANOVA with Scheffé adjustment for multiple comparisons at a 95% confidence level. Results indicated that GuttaFlow was significantly less cytotoxic than all other sealers (p < 0.05) at 1 day of extraction. After 7 days of extraction, cell viability for GuttaFlow was significantly increased as compared with that of all groups except sealer AH Plus. At day 14, cytotoxicity of Sealapex was significantly higher than that of all other sealers (p < 0.05). At days 21 and 28, there were no significant differences in cytotoxicity among sealer groups. All materials presented some level of cytotoxicity to fibroblasts, while GuttaFlow was the least cytotoxic sealer tested. However, the cytotoxicity of all materials seemed to decrease similarly in a time-dependent manner.

Photopolymerized microfeatures for directed spiral ganglion neurite and Schwann cell growth

Cochlear implants (CIs) provide auditory perception to individuals with severe hearing impairment. However, their ability to encode complex auditory stimuli is limited due, in part, to poor spatial resolution caused by electrical current spread in the inner ear. Directing nerve cell processes towards target electrodes may reduce the problematic current spread and improve stimulatory specificity. In this work, photopolymerization was used to fabricate micro- and nano-patterned methacrylate polymers to probe the extent of spiral ganglion neuron (SGN) neurite and Schwann cell (SGSC) contact guidance based on variations in substrate topographical cues. Micropatterned substrates are formed in a rapid, single-step reaction by selectively blocking light with photomasks which have parallel line-space gratings with periodicities of 10-100 μm. Channel amplitudes of 250 nm-10 μm are generated by modulating UV exposure time, light intensity, and photoinitiator concentration. Gradual transitions are observed between ridges and grooves using scanning electron and atomic force microscopy. The transitions stand in contrast to vertical features generated via etching lithographic techniques. Alignment of neural elements increases significantly with increasing feature amplitude and constant periodicity, as well as with decreasing periodicity and constant amplitude. SGN neurite alignment strongly correlates (r = 0.93) with maximum feature slope. Multiple neuronal and glial types orient to the patterns with varying degrees of alignment. This work presents a method to fabricate gradually-sloping micropatterns for cellular contact guidance studies and demonstrates spatial control of inner ear neural elements in response to micro- and nano-scale surface topography.

Evaluation of the sealing ability of resin cement used as a root canal sealer: An in vitro study

AIM

This study was designed to evaluate the apical seal of root canals obturated with resin cement as a root canal sealer and compare with that of the glass ionomer and zinc oxide eugenol sealers using a cold lateral condensation gutta-percha technique.

BACKGROUND

Successful root canal treatment requires three-dimensional obturation of the root canal system with nonirritating biomaterials. None of the available materials are capable of providing a fluid tight seal.

MATERIALS AND METHODS

The prepared teeth were randomly divided into three groups of 15 each to be obturated using three different sealers. Group I: zinc oxide eugenol (Tubliseal), Group II: Glass ionomer (Ketac Endo), and Group III: resin cement (C & B Superbond). All the specimens were stored in 100% relative humidity at 37° for 24 h. The specimens were placed in 2% methylene blue dye for 48 h and sectioned. The dye penetration was evaluated under a stereomicroscope.

RESULTS

The "Kruskal" Wallis test was carried out to test the equality of mean. All the specimens showed dye leakage, and there was a statistically significant difference (P < 0.0001) among the groups. The specimens in Group III showed a minimal leakage and the specimens in Group I showed a maximum leakage.

CONCLUSION

Resin cement sealed the root canals significantly better when compared with zinc oxide eugenol and glass ionomer sealers.

Clinical and radiographic evaluation of a resin-based root canal sealer: 10-year recall data

Objectives. This retrospective clinical and radiographical study evaluated the 10-year outcome of one-visit endodontic treatment with gutta-percha and a methacrylate resin-based sealer. Methods. From an initial sample size of 180 patients, 89 patients with 175 root canals responded to a recall. Treatment outcome was based on predetermined clinical and radiographic criteria. Results. Root canals had been adequately filled to the working length in 80 teeth (89.88%), short in 6 instances (6.74%), while 3 (3.37%) with extrusion immediate postoperatively, showed no sealer in periradicular tissues. The difference in the outcomes of treatments with respect to age, gender, preoperative pulp or periapical status, the size of periapical lesions and the type of permanent restorations were not statistically significantly different (P > 0.05). Overall, 7 (7.86%) cases were considered clinically and radiographically a failure. A life table analysis showed a cumulative probability of success of 92.13% after 10 years with a 95% confidence interval of 83.0 to 94.0. Conclusions. The results of this retrospective clinical and radiographical study suggest that the tested methacrylate-resin based sealer used with gutta-percha performed similarly to other root canal sealers over a period 10 years. Clinical Implications. Considering the success rate after 10 years of this methacrylate resin-based sealer can be recommended as an alternative to other commonly used root canal sealers.

Micropatterned methacrylate polymers direct spiral ganglion neurite and Schwann cell growth

Significant advances in the functional outcomes achieved with cochlear implantation will likely require tissue-engineering approaches to improve the neural prosthesis interface. One strategy is to direct spiral ganglion neuron (SGN) axon growth in a highly organized fashion to approximate or contact stimulating electrodes. Here we assessed the ability of micropatterns induced by photopolymerization in methacrylate (MA) polymer systems to direct cultured neonatal rat SGN neurite growth and alignment of SG Schwann cells (SGSCs). SGN survival and neurite length were comparable among various polymer compositions. Remarkably, there was no significant difference in SGN survival or neurite length between laminin and non-laminin coated MA polymer substrates, suggesting high biocompatibility with SG tissue. Micropatterning with photopolymerization generated microchannels with a ridge periodicity of 50 μm and channel depths of 0.6-1.0 μm. SGN neurites grew within the grooves of the microchannels. These topographies strongly induced alignment of dissociated SGN neurites and SGSCs to parallel the pattern. By contrast, fibroblasts failed to align with the micropattern suggesting cell specific responses to topographical cues. SGN neurites extending from explants turned to parallel the pattern as they encountered the microchannels. The extent of turning was significantly correlated with angle at which the neurite initially encountered the pattern. These results indicate that SGN neurites respond to microtopographical features and that these features can be used to direct neurite growth in a highly organized fashion.