Adhesive Dentistry and Endodontics: Materials, Clinical Strategies and Procedures for Restoration of Access Cavities: A Review

Endodontic management of badly broken down teeth using the canal projection system: two case reports

AIM

Teeth that have been weakened by caries and require root canal treatment to maintain their functional integrity may present with minimal coronal tooth structure and are a challenge for isolation and restoration. The aim of this clinical report is to demonstrate the management of badly broken down teeth using the Projector Endodontic Instrument Guidance System (PEIGS).

SUMMARY

The PEIGS is an adjunct to root canal treatment designed to enhance the ease of treatment delivery. Use of this system facilitates projection of canal orifices from the floor of the pulp chamber to the cavosurface, providing direct visualization of and physical access to the projected canals. This report demonstrates the use of this novel device for the management of two badly broken down teeth.

KEY LEARNING POINTS

Use of the endodontic projection system has the following advantages: * 'Projects' the canal orifice from the floor of the pulp chamber to the cavosurface, thereby enhancing visualization and access to the canals. * The bonded coronal build up reduces the risk of interappointment crack initiation and coronal-radicular fracture of weakened tooth structure. * Permits individualization of canals especially when they lie in close proximity to each other on the chamber floor. * Isolation may be facilitated by ease of clamp retention, rendering many structurally debilitated teeth endodontically treatable.

The effect of sandblasting on adhesion of a dual-cured resin composite to methacrylic fiber posts: Microtensile bond strength and SEM evaluation

OBJECTIVES

To evaluate the influence of different surface treatments on the microtensile bond strength of a dual-cured resin composite to fiber posts.

METHODS

Thirty-two glass methacrylate-based fiber posts (GC Corp.) were used in the study. Posts were divided into two groups, according to the surface pretreatment performed. Group 1: sandblasting (Rocatec-Pre, 3M ESPE). Group 2: no pretreatment. In each of the two groups posts received three types of additional "chair-side" treatments. (1) Silane application (Monobond S, Ivoclar Vivadent); (2) adhesive application (Unifil Core self-etching bond, GC); (3) no treatment was performed. A dual-cured resin composite (Unifil Core, GC) was applied on the posts to produce cylindrical specimens. Specimens were cut to obtain microtensile sticks that were loaded in tension at a cross-head speed of 0.5mm/min until failure. The morphology of the post/composite interface and the post surface morphology were evaluated under SEM. Statistical analysis was performed with two-way ANOVA and Tukey test for post hoc comparisons (p<0.05).

RESULTS

Post surface pretreatment did not prove to be a significant factor in post-composite bond strength (p=0.08), whereas "chair-side" treatment modalities and the interaction between pretreatment and treatment showed a significant influence on bond strength (p<0.001). When no "chair-side" treatment was performed, bond strength was significantly higher on sandblasted posts. Additional adhesive application resulted in significantly lower bond strength on sandblasted posts. When no pretreatment was performed, silane application resulted in higher bond strength than adhesive application.

CONCLUSIONS

Sandblasting may give an increase in microtensile strength to methacrylate-based glass fiber posts, eliminating the need for additional "chair-side" treatments. Reducing the number of clinical steps could contribute to simplify the clinical procedures.

Improving the Performance of EndoRez Root Canal Sealer With a Dual-cured Two-Step Self-etch Adhesive. I. Adhesive Strength to Dentin

This study examined the hypotheses that the use of a self-etching-adhesive improves the adhesion of EndoRez to dentin, and that both techniques are unaffected by the prolonged use of NaOCl when EDTA is used as the final rinse. A tensile bond testing design was employed with composite cylinders bonded to dentin using: (a) 17% EDTA-2 min/EndoRez; (b) 6.15% NaOCl-1 h/EDTA-2min/EndoRez; (c) EDTA-2 min/Clearfil Liner Bond 2V/EndoRez; and (d) NaOCl-1 h/EDTA-2min/Clearfil Liner Bond 2V/EndoRez. Fractographic analyses of debonded specimens were performed using SEM. Two-way ANOVA and Tukey test revealed higher tensile bond strengths with the self-etching-adhesive-modified EndoRez technique (p < 0.001). Sealer tags pulled away from dentinal tubules when EndoRez was used alone, whereas mixed failures occurred within sealer tags, hybrid layers, adhesive, and sealer in the self-etching-adhesive-modified EndoRez technique. Both techniques were unaffected by the prolonged use of NaOCl (p > 0.05) when EDTA was employed as the final rinse.

Sealing ability of three materials in the orifice of root canal systems obturated with gutta-percha

There were 130 single roots randomly assigned to one of 12 experimental or two control groups. Forty specimens each were sealed with 1, 2, 3, or 4 mm of Cavit, ProRoot MTA, or Tetric. After creation of a uniform orifice diameter, the smear layer was removed and the canal systems obturated using warm lateral compaction of gutta-percha (GP). GP was removed to the experimental depth, experimental materials placed in the orifice, and roots submerged in India ink in a vacuum flask. Specimens were demineralized and leakage measured using a 10x stereomicroscope and graded for depth of leakage by one calibrated, blinded rater. There was no significant interaction (p > 0.05) between test materials and orifice depths, nor main effect of orifice depth (p > 0.05). However, there was a statistically significant main effect of test materials with Tetric demonstrating a significantly better seal than Pro Root or Cavit (p < 0.0001) irrespective of orifice depth.

Effect of Hygroscopic Expansion on the Push-Out Resistance of Glass Ionomer-Based Cements Used for the Luting of Glass Fiber Posts

This study examined the contribution of hygroscopic expansion of glass-ionomer (GIC) and resin modified glass-ionomer (RMGIC) luting cements to the push-out resistance of fiber posts. Glass fiber posts were luted to post spaces using different cements. Experimental specimens were stored in water, while control specimens were desiccated and stored in mineral oil to eliminate water from intraradicular dentinal tubules and/or the external environment that could have contributed to hygroscopic expansion of the cements. Thin slice push-out tests revealed no difference in retention strengths of resin composite cements that were stored in water or oil. Conversely, GIC and RMGIC cements exhibited increased retention strengths after water sorption. As unfavorable cavity geometry is taxing to dentin bond integrity in root canals, a strategy that relies on increasing the frictional resistance to post dislodgement via delayed hygroscopic expansion of glass-ionomer based materials may be a more pragmatic approach to fiber post retention.

Effect of Orifice Plugs on Periapical Inflammation in Dogs

Gutta-percha (G) and sealer do not resist coronal leakage. In this study, the effect of orifice plugs using dentin-bonding/composite resin(C) or IRM on coronal leakage was evaluated in vivo. Sixty-one premolar roots in three beagle dogs were instrumented and filled with G and AH 26(S), or G alone. The coronal 2 mm was replaced with C or IRM, or left untreated. The access cavities were kept open for 8 months, the dogs were killed and the periapical regions of the roots were histologically examined. Periapical inflammation was observed in 89% of the group without plugs, but in those with plugs, the occurrence was decreased to 39% (C + G + S), 38% (IRM + G + S) and 58% (C + G), respectively. Furthermore, severe inflammation was observed in 50% of the former group but only 0 to 17% of the latter. The substantial reduction in apical periodontitis by the use of coronal plug underscores the clinical importance of providing an additional barrier to coronal leakage in comparison to that provided by gutta-percha and sealer alone.

Is An Oxygen Inhibited Layer Required for Bonding of Resin-Coated Gutta-Percha to a Methacrylate-Based Root Canal Sealer?

Removal of the oxygen inhibition layer from the surface of resin-coated gutta-percha cones during packaging has been hypothesized for their weak adhesion to a methacrylate-based root canal sealer, resulting in their frequent delamination from the sealer after root canal obturation. This study examined the feasibility of creating oxygen inhibition layers on resin-coated gutta-percha cones via the adjunctive application of a dual-cured dentin adhesive just before bonding. Composite cylinders were bonded with EndoREZ to flat, resin-coated gutta-percha disks and similar disks that were post-treated with Prime&Bond NT Dual Cure adhesive and stressed to failure using a modified microshear testing design. Although shear strengths for both groups were relatively low, a 5-fold increase in shear strength was observed after adhesive application, with complex interfacial failures instead of complete sealer delamination from the resin-coating. In-situ dentin adhesive application appears to have merits in enhancing the coupling of resin-coated gutta-percha to methacrylate sealers.

Microleakage evaluation of intraorifice sealing materials in endodontically treated teeth

OBJECTIVE

Evaluate intraorifice sealing materials Cavit, Vitremer, and Flow-It for the prevention of coronal microleakage in root-canal treatment.

STUDY DESIGN

Root-canal treatment was performed on 80 extracted human molars. Three millimeters of coronal gutta-percha was removed from the coronal aspect of the root canal and replaced with one of the 3 filling materials. After thermocycling (5 degrees C to 55 degrees C) and 5 days of immersion in dye, the teeth were cleared for stereomicroscope evaluation for evidence of dye penetration into the sealing material and along canal walls.

RESULTS

All groups showed dye penetration into the root canal. Cavit sealed significantly better than the other groups (P < .01), preventing the coronal leakage in 90% of the specimens. Flow-It exhibited the highest leakage (65% of specimens) and did not differ significantly from the Vitremer group, which showed dye penetration in 55% of specimens.

CONCLUSION

Cavit sealed significantly better than Vitremer and Flow-It when used as intraorifice filling materials.

Shear bond strength of Resilon to a methacrylate-based root canal sealer

AIM

To evaluate the adhesive strength of Resilon to Next root canal sealant (Heraeus-Kulzer), a methacrylate-based root canal sealer, using a modified microshear bond testing design.

METHODOLOGY

Flat Resilon surfaces of different roughnesses (smooth surface and surface roughness equivalent to 320-grit and 180-grit) were prepared by compression moulding for bonding to the sealer and compared with a composite control. The shear strength data were statistically analysed using Kruskal-Wallis one-way anova on ranks and Dunn's multiple comparison tests (alpha = 0.05). After shear testing, fractured specimens were examined using a field emission-scanning electron microscope for detailed analysis of the failure modes.

RESULTS

The composite control exhibited significantly higher mean shear strength (7.62 MPa) that was 4.4-4.7 times those of the Resilon groups (1.64-1.74 MPa; P < 0.001). Increasing the surface roughness of the Resilon surface did not contribute to further improvement in shear bond strength for this methacrylate-based sealer (P > 0.05). Failure modes in the composite control were cohesive and mixed failures, while those in the Resilon groups were predominantly adhesive failures, with a small percentage of mixed failures. Ultrastructural evidence of phase separation of polymeric components could be identified in Resilon. Both intact, non deformed and plastically deformed Resilon surfaces could be observed in specimens that exhibited adhesive failures.

CONCLUSION

The low shear strength of Resilon to a methacrylate-based sealer compared with a composite control suggests that the amount of dimethacrylate incorporated in this filled, polycaprolactone-based thermoplastic composite may not yet be optimized for effective chemical coupling to methacrylate resins.

Effectiveness of Resin-Coated Gutta-Percha Cones and a Dual-Cured, Hydrophilic Methacrylate Resin-Based Sealer in Obturating Root Canals

The introduction of a polybutadiene-diisocyanate-methacylate resin-coating of gutta-percha enables the polyisoprene to be chemically coupled to methacrylate-based resin root canal sealers. This study examined the effectiveness of using passively fitting cones of this type of gutta-percha with a dual-cured version of EndoREZ sealer in obturating cleaned and shaped root canals. The hydrophilic nature of the sealer enabled the creation of an extensive network of 800 to 1200 mum long sealer resin tags after removal of the endodontic smear layer. Although no adhesive was employed, thin hybrid layers in root dentin were observed when EDTA was used as the final rinse. Nevertheless, interfacial gaps and silver leakage could be observed along the sealer-dentin interfaces that might be attributed predominantly to polymerization shrinkage of the sealer. Gaps and silver leakage were also identified between the gutta-percha resin-coating and the sealer.