A.P. Manso

Durability of bonds and clinical success of adhesive restorations

Resin-dentin bond strength durability testing has been extensively used to evaluate the effectiveness of adhesive systems and the applicability of new strategies to improve that property. Clinical effectiveness is determined by the survival rates of restorations placed in non-carious cervical lesions (NCCL). While there is evidence that the bond strength data generated in laboratory studies somehow correlates with the clinical outcome of NCCL restorations, it is questionable whether the knowledge of bonding mechanisms obtained from laboratory testing can be used to justify clinical performance of resin-dentin bonds. There are significant morphological and structural differences between the bonding substrate used in in vitro testing versus the substrate encountered in NCCL. These differences qualify NCCL as a hostile substrate for bonding, yielding bond strengths that are usually lower than those obtained in normal dentin. However, clinical survival time of NCCL restorations often surpass the durability of normal dentin tested in the laboratory. Likewise, clinical reports on the long-term survival rates of posterior composite restorations defy the relatively rapid rate of degradation of adhesive interfaces reported in laboratory studies. This article critically analyzes how the effectiveness of adhesive systems is currently measured, to identify gaps in knowledge where new research could be encouraged. The morphological and chemical analysis of bonded interfaces of resin composite restorations in teeth that had been in clinical service for many years, but were extracted for periodontal reasons, could be a useful tool to observe the ultrastructural characteristics of restorations that are regarded as clinically acceptable. This could help determine how much degradation is acceptable for clinical success.

Micropush‐out dentine bond strength of a new gutta‐percha and niobium phosphate glass composite

AIM To characterize an experimental gutta-percha and niobium phosphate glass composite (GNB) applied with a thermoplastic technique to the root canals without sealer in a moist environment and to evaluate its micropush-out bond strength to root canal wall dentine. METHODOLOGY The root canals of sixty human mandibular pre-molars were prepared using rotary NiTi instruments and irrigation with sodium hypochlorite and EDTA. The teeth were then randomly divided into three groups according to the root filling material used: AH plus sealer and gutta-percha (AH), EndoSequence BC gutta-percha without sealer (GBC), and GNB without sealer. The root canals were filled with a single cone using warm vertical condensation. Push-out bond strengths associated with the filling materials in slices from middle root thirds was determined 30 days after root filling. The failure mode was analyzed with SEM. Analysis using EDX and SEM-EDS was carried out to verify the composition and distribution of the particles of the tested materials. Data were statistically analyzed by one-way anova and Tukeys test (P < 0.05). RESULTS AH and GNB groups had bond strengths of 2.83 ± 0.64 MPa and 2.68 ± 0.84 MPa, respectively, with no significant difference between them (P > 0.05). The GBC group had the lowest mean bond strength (1.34 ± 0.42 MPa), which was significantly different compared with the other groups (P < 0.05). Cohesive failures prevailed in the AH group, whereas failures were mixed in the GBC and GNB groups. The SEM-EDS analysis on the surface and in the bulk of GBC revealed only a superficial coating of bioceramic particles. Glass particles were detected both on the surface and in the bulk of GNB. CONCLUSIONS The experimental root filling composite (GNB) had an ability to adhere to root canal wall dentine equal to the current gold standard root filling with gutta-percha and sealer (AH Plus).

Flexural properties of experimental nanofiber reinforced composite are affected by resin composition and nanofiber/resin ratio

OBJECTIVES To evaluate the influence of different resin blends concentrations and nanofibers mass ratio on flexural properties of experimental Poliacrylonitrile (PAN) nanofibers reinforced composites. MATERIALS AND METHODS Poliacrylonitrile (PAN) nanofibers mats were produced by electrospinning and characterized by tensile testing and scanning electron microscopy (SEM). Experimental resin-fiber composite beams were manufactured by infiltrating PAN nanofiber mats with varied concentrations of BisGMA-TEGDMA resin blends (BisGMA/TEGDMA: 30/70, 50/50 and 70/30weight%). The mass ratio of fiber to resin varied from 0% to 8%. Beams were cured and stored in water at 37°C. Flexural strength (FS), flexural modulus (FM) and work of fracture (WF) were evaluated by three-point bending test after 24h storage. RESULTS The tensile properties of the PAN nanofibers indicated an anisotropic behavior being always higher when tested in a direction perpendicular to the rotation of the collector drum. Except for WF, the other flexural properties (FS and FM) were always higher as the ratio of BisGMA to TEGDMA increased in the neat resin beams. The addition of different ratios of PAN fibers did not affect FS and FM of the composite beams as compared to neat resin beams (p>0.05). However, the addition of fibers significantly increased the WF of the composite beams, and this was more evident for the blends with higher TEGDMA ratios (p<0.05). SIGNIFICANCE The inclusion of PAN nanofibers into resin blends did not negatively affect the properties of the composite and resulted in an increase in toughness that is a desirable property for a candidate material for prosthodontics application.

Can 1% chlorhexidine diacetate and ethanol stabilize resin-dentin bonds?

OBJECTIVES To examine the effects of the combined use of chlorhexidine and ethanol on the durability of resin-dentin bonds. METHODS Forty-eight flat dentin surfaces were etched (32% phosphoric acid), rinsed (15 s) and kept wet until bonding procedures. Dentin surfaces were blot-dried with absorbent paper and re-wetted with water (water, control), 1% chlorhexidine diacetate in water (CHD/water), 100% ethanol (ethanol), or 1% chlorhexidine diacetate in ethanol (CHD/ethanol) solutions for 30 s. They were then bonded with All Bond 3 (AB3, Bisco) or Excite (EX, Ivoclar-Vivadent) using a smooth, continuous rubbing application (10 s), followed by 15 s gentle air stream to evaporate solvents. The adhesives were light-cured (20 s) and resin composite build-ups constructed for the microtensile method. Bonded beams were obtained and tested after 24-h, 6-months and 15-months of water storage at 37°C. Storage water was changed every month. Effects of treatment and testing periods were analyzed (ANOVA, Holm-Sidak, p<0.05) for each adhesive. RESULTS There were no interactions between factors for both etch-and-rinse adhesives. AB3 was significantly affected only by storage (p=0.003). Excite was significantly affected only by treatments (p=0.048). AB3 treated either with ethanol or CHD/ethanol resulted in reduced bond strengths after 15 months. The use of CHD/ethanol resulted in higher bond strengths values for Excite. CONCLUSIONS Combined use of ethanol/1% chlorhexidine diacetate did not stabilize bond strengths after 15 months.

Biodegradation of Resin-Dentin Bonds: a Clinical Problem?

Biodegradation of the resin-dentin interfaces has been a focus of research over the last decade. Most studies show that degradation of both the collagen and the adhesive take place within short periods of time after bonding, and claim that such loss of structure at the interface opens opportunity for secondary caries initiation and progression thus leading to failure of the restoration. Open margins are further compromised by thermo-mechanical loading and enzymes produced by local bacteria. While marginal gaps appear to be unavoidable, it is remarkable that resin composite restorations can deliver successful clinical service for many years provided preventive and conservative measures to reduce the caries-risk of the patient are applied along with the restorative treatment. This review will look into the evidence from laboratory studies that investigated degradation of bonds and the consequences leading to clinical failure and balance that against the results of clinical trials that evidence the factors associated with the durability and clinical success of resin composite restorations.