The use of the stable isotope 44Ca in studies of calcium incorporation into dentin

The incorporation into rat incisor dentin of two calcium isotopes, the stable ⁴⁴Ca and the radioactive ⁴⁵Ca, was studied using secondary ion mass spectrometry (SIMS) stepscanning and imaging, and autoradiography, respectively. The results demonstrated a time-dependent incorporation of the calcium isotopes into the mineral phase of dentin. With the SIMS step-scanning, detecting ⁴⁴Ca, the ion yield was high in the odontoblasts 2 min after intravenous injection. After 10 min a marked increase in signal intensity was found at the dentin mineralization front. This result was consistent with those obtained by ⁴⁵Ca autoradiography; a peak of incorporation occurred 10 min after injection of the isotope. Likewise, localization of ⁴⁴Ca to the mineralization front could be demonstrated 10 min after injection by SIMS imaging. In images obtained at earlier intervals, no such increase in ion yield could be detected. The results show that the nonradioactive, stable isotope ⁴⁴Ca can be used as a marker for biomineralization in a similar way to radioactive ⁴⁵Ca.     

Alpha-hydroxy glycolic acid for root dentin etching: Morphological analysis and push out bond strength

The purpose of this study was investigated the use of α-hydroxy glycolic acid as a dentin etchant for adhesive procedures in the root canal. The etching pattern of glycolic acid and mineral content distribution of root canal dentin were assessed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The effect of glycolic acid surface etching on the push out bond strength of fiber post to root dentin was assessed using three adhesive systems: Single Bond Universal [SBU], Scotchbond Multipurpose [SBMP], and Ambar [AM]. The 37% phosphoric acid was used as a control group. The bond strength values were statistically compared using ANOVA/Fisher LSD tests (α = 0.05). SEM revealed similar etching patterns for phosphoric acid and glycolic acid. Both acids also shared similar interfacial morphology of the hybrid layer. EDS showed similar levels of Ca and Mg after treatment with glycolic acid when compared with phosphoric acid. When the P level was compared, it was observed that phosphoric acid caused greater removal of P. The push out bond strengths were statistically similar between glycolic acid and phosphoric acid in all groups (p > 0.05). Comparisons using post hoc Fisher LSD test showed that the bond strengths in the SBU and SBMP groups were not significantly different from each other (p > 0.05). The bond strength in the AM group was similar to that in the SBMP group (p > 0.05); however, it was significantly lower than that in the SBU group (p < 0.05). It can be concluded that the glycolic acid effectively etched root dentin surfaces, resulting in a surface pattern, hybrid layer, and push out bond strength similar to those produced by traditional phosphoric acid. Therefore, glycolic acid may be recommended as a suitable root dentin surface etchant for adhesive restorative procedures.     

The role of an interfacial interpenetrating polymer network formation on the adhesion of resin composite layers in immediate dentin sealing

The aim of this study was to evaluate the influence of chemical and physical processes at the resin-composite and composite-cement interface as a function of the resin composite's water exposure on the bond strength (BS) between these two components. The free-radical concentration was studied using electron paramagnetic resonance (EPR), while the chemical changes at the resin composite's surface were studied using attenuated total-reflection FTIR spectroscopy (ATR-FTIR). The free-radical concentration in the studied samples dropped to 10% in 24 h, indicating that prolonged BS values do not correlate with the free-radical concentration. An alternative bonding mechanism between the resin composite and the composite cement was proposed, based on the formation of an interpenetrating polymer network (IPN) layer at the interface. As proven using ATR-FTIR spectroscopy, changes occurred at the resin composite's surface as a consequence of water exposure, comprising the diffusion of water molecules into the resin composite. These changes reduced the diffusion rate of the composite cement's phosphorus-containing monomers into the resin composite, as shown by the linescan SEM-EDS analysis of phosphorus, thus reducing the thickness of the IPN layer at the interface and consequently reducing the BS between both components.This study reveals that the concentration of free radicals at the surface of the resin composite is only relevant immediately after the polymerisation to the bond strength between the resin composite and the composite cement. Therefore, an alternative explanation is given by applying the theory of the formation of a gradient IPN at the interface between the resin composite and the adhesive cement by changes in the rate of diffusion of the adhesive cement's monomers into the resin composite as a function of the resin composite's exposure to water.     

Adhesion of bulk-fill resin composites as core and intraradicular post materials only versus the use of glass-fiber posts in different regions of root dentin

This study assessed adhesion of bulk-fill resin-composites as core and post materials only versus the use of fiber resin composite (FRC) posts. Human teeth (N?=?84) were cut at the CEJ and endodontically treated and randomly divided into seven groups: TP: Titanium post (Flat Head T); SFRC: S2-glass FRC (Pinpost); EFRC1: E-glass FRC (GC Everstick) directly bonded; GFRC: E-glass FRC (Glassix Nordin); EFRC2: E-glass FRC (Everstick); BF1: Bulk-fill resin (Surefill SDR); BF2: Bulk-fill resin (SonicFill). Groups TP, SFRC, EFRC and GFRC were cemented (Panavia 21), while other groups were bonded directly to the intraradicular dentin. The core parts were constructed using a resin composite (G-aenial) except for Groups BF1 and BF2. The core-cervical dentin interface was loaded under shear forces. Push-out tests were performed in a Universal Testing Machine (1?mm/min). Data (MPa) were analyzed using two-way ANOVA and Tukey`s tests (α?=?0.05). Not the root level (p?>?0.05) but the type of core and post material significantly affected shear and push-out bond results (p?<?0.001). BF1 (9.2?±?2.1) and BF2 (9.3?±?3.1) showed significantly lower bond strength to the cervical dentin (p?<?0.05) compared to other groups (11.6?±?2.5–19?±?6.8). FRC post types did not show significant difference being higher than those of TP, BF1 and BF2 (0.57?±?0.37–2.34?±?1.98) (p?>?0.05). Partial cohesive core fracture was more common while BF1 and BF2 showed exclusively adhesive failures. Cohesive failure in the cement was frequent in Group TP (53%) compared to other groups (3–24%). BF1 and BF2 presented exclusively complete adhesive failure of the bulk-fill material.     

Influence of chlorhexidine in cavities prepared with ultrasonic or diamond tips on microtensile bond strength

This study evaluated the effect of chlorhexidine (CLX) in cavities prepared with either ultrasound-mounted CVDentUS diamond tips or conventional diamond burs on dentin bond strength after 24 h and 180 days. Forty-eight dentin surfaces from sound third molars were flattened and divided into four groups (n = 12), according to the type of cavity preparation (CVDentUS ultrasound tip or conventional diamond) and with or without 2% CLX (Consepsis) treatment. After application of the adhesive system (Clearfil SE Bond), microhybrid composite resin blocks (Charisma) were made on the dentin surface in increments. After 24 h, the specimens were sectioned into stick-shaped samples with an adhesive interface of approximately 1 mm². From each tooth, half of the sticks were evaluated after 24 h of storage in distilled water and the other half after 180 days, using a universal testing machine. Three-way analysis of variance showed no significant triple interactions (p = 0.722) or double interactions between factors. Higher bond strength values were observed with the use of ultrasonic tips (p = 0.019), irrespective of whether or not CLX was applied in either time period. No difference in bond strength values was observed in terms of CLX application (p = 0.581). No significant difference in bond strength values was shown after storage for 24 h or 180 days (p = 0.302). In conclusion, the ultrasonic tips promoted greater bond strength to dentin, irrespective of whether or not CLX was applied, and storage time.     

The effectiveness of glass ionomer cement as a fiber post cementation system in endodontically treated teeth

This study compared the performance of a glass ionomer (GC Gold Label 1, GIC) as a fiber post cementation system for glass fiber posts with a self‐adhesive resin cement (Relyx U200, RUC) and a conventional resin cement system (Scotchbond Muli‐Purpose and Relyx ARC, RAC). Thirty endodontically treated canines were randomly divided in three groups (n = 10), according to the fiber post cementation system: (RAC)—Scotchbond Multi‐Purpose and Relyx X ARC; (RUC)—Relyx U200 and (GIC)—GC Gold Label 1 Luting & Lining. Rhodamine was incorporated into the cementation system prior to the fiber post cementation. After glass fiber post cementation, roots were incubated in artificial saliva for 6 months. After that, specimens from the cervical, middle, and apical thirds of the post space were prepared and analyzed using a push‐out bond strength test and confocal laser microscopy. ANOVA one way and Tukey tests showed that GIC and RUC demonstrated similar push‐out bond strength values, independently of the post space third (p > .05); however, values were greater than those shown by RAC (p < .05). For dentin penetrability, GIC and RUC also had similar results (p > 0.05) and lower than RAC (p < 0.05). Inside the root canal, the cementation system using glass ionomer cement (GC Gold Label 1 Luting & Lining) has similar push‐out bond strength to the self‐adhesive resin cement (Relyx U200) and these were higher than the conventional resin (Relyx ARC), despite its higher dentin penetrability.     

The effect varied scanning electron microscopy desiccation techniques has on demineralized dentin

The study objective was to assess (a) the effect of a rubbing‐application of ethylenediaminetetraacetic acid (EDTA) or citric acid (CA) has on the ultrastructure of surface dentin and (b) the effect of two scanning electron microscopy (SEM) desiccation preparation techniques have on the collagen surface produced. Treatment regions on proximal root surfaces of extracted human teeth were root planned to expose dentin. Cotton pellets soaked in either 30% CA or 24% EDTA solution were rubbed on the treatment region then processed for SEM using one of two desiccation techniques, that is, (a) critically point dried from liquid CO₂ (control) or (b) air‐dried from tetramethylsilane (experimental). Specimens were coated with gold/palladium and viewed/photographed with an SEM. Specimens of the control groups displayed tufted fibrils (CA > EDTA) with many dentin tubules being partially obscured by overhanging fibrils. Air‐dried specimens of both treatment groups displayed a flat intact monolayer devoid of a matted meshwork of fibrous collagen. Discrete fibril “sprigs,” emanating from the surface monolayer, were characteristic of the EDTA group only. The rubbing‐application of EDTA on dentin produces a tufted fibril surface somewhat similar to that produced by CA. Air‐drying desiccation of both resulted in marked distortion with fibril collapse/coalescence of the tufted collagen matrix.     

Bonding of resin adhesives to caries-affected dentin – A systematic review

Minimal invasive dentistry aims at preserving the firm, discolored caries affected dentin (CAD), which is remineralizable. Research studies on resin adhesives are usually performed on sound dentin (SD), though CAD is the substrate routinely encountered for bonding in clinical practice. The aim of this paper was to systematically analyze the published literature on resin-dentin bonding to CAD substrate, in order to answer the question: “Does resin adhesive bonding to CAD produce lower bond strength when compared to SD?”. Three electronic databases (Pubmed, Scopus and ISI web of Science) were searched to identify original laboratory studies that evaluated the bond achieved between resin adhesive and natural CAD by measuring their bond strength. Only articles that met the specific inclusion criteria were included in the review. Among the 29 studies included for this review, majority of the studies had tested the simplified etch-and-rinse or self-etch adhesives. 85% of them showed higher bond strength to SD compared to CAD and the remaining 15% of them showed no difference between these two substrates. Among the studies that used 3-step etch-and-rinse adhesives, 40% showed higher and 60% showed no difference, when bond strength was compared between SD and CAD. Resin adhesives produce lower bond strength to caries-affected dentin than sound dentin. Research studies that reported bond strength of resin adhesives to dentin from sound extracted teeth alone cannot be blindly extrapolated to clinically relevant CAD. Hence, the results from such studies should be dealt with caution.