Bart Van Meerbeek

Bonding effectiveness and sealing ability of fiber-post bonding

OBJECTIVES To evaluate the push-out bond strength and the sealing ability of five adhesive cements routinely used for fiber-post bonding. METHODS Fifty extracted single-rooted teeth were randomly divided in five groups and restored using Parapost FiberLux and the following luting agents: Panavia 21 (PAN), Clearfil Esthetic Cement (CLF), Variolink II (VAR), RelyX Unicem (UNI) and experimental GC self-adhesive cement (EGC). After 1 week of water storage at 37 degrees C, three sections (coronal, middle and apical) of 2mm thickness were prepared from each specimen. Sealing ability was quantified with a fluid-filtration system (Flodec) during 10 min, after which the push-out bond strength was immediately measured. Data were analyzed with ANOVA (push-out) and Kruskal-Wallis (sealing ability). RESULTS The push-out bond strength and sealing ability were not significantly different among the coronal, middle and apical sections for each luting agent. The highest push-out bond strength was measured for CLF (14.60+/-3.63 MPa), which was not significantly different from PAN (12.57+/-2.45 MPa), but significantly higher than VAR (11.09+/-4.09 MPa), UNI (11.29+/-4.31 MPa) and EGC (7.65+/-4.79 MPa). When evaluating the sealing ability, significant differences were not found among PAN, CLF and VAR, and between UNI and EGC. The latter luting agents scored significantly lower than the former ones. The push-out bond strength was correlated to the sealing ability (p<0.001). SIGNIFICANCE The self-etching MDP-based cements presented the highest push-out bond strength. Although the bonding effectiveness of self-adhesive cements appears promising, their interaction with root dentin might be too weak to minimize microleakage at the post-cement-dentin interface.

Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin

OBJECTIVES This study evaluated the effects of six phosphoric acid-etching agents on dentin, the independent variables being two acid concentrations (10% and 32%-37%) and three thickener conditions (no thickener, silica, and polymer). The tested hypothesis was that the use of different etchants with similar concentrations of phosphoric acid would result in similar depths of dentin demineralization. METHODS Thirty dentin disks were obtained from extracted human teeth by microtome sectioning. The dentin surfaces were etched with one of the etching agents, fixed, dehydrated and dried. The specimens were observed using a FE-SEM. The mean deepest demineralization of intertubular dentin was measured from fracture surfaces of the disks. These values were analyzed by ANOVA and Duncans Test. The morphological appearance of the dentin surfaces was compared using the following observation criteria: 1) Presence of a cuff of peritubular dentin; 2) Relative thickness of the layer containing residual collagen or smear layer particles; and 3) Formation of a submicron hiatus at the bottom of the exposed collagen network. The pH of each of the etching agents was measured. A correlation analysis was made of the pH vs. the depth of dentin demineralization. RESULTS Silica-thickened etchants did not demineralize dentin as deeply as did polymer-thickened etchants and unthickened etchants. High magnifications revealed three distinct zones within the demineralized dentin layer; an upper porous zone of residual smear layer or denatured collagen and residual silica particles (in groups etched with silica-thickened etchants), an intermediate area with randomly oriented collagen fibers, and a lower zone with submicron hiatus, few collagen fibers, and scattered hydroxyapatite inclusions. This hiatus was observable in all the specimens etched with the polymer-thickened etchants, in 90% of the specimens etched with the unthickened phosphoric acid liquids, and in 60% of the specimens etched with the silica-thickened gels. SIGNIFICANCE The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.

Nano-controlled molecular interaction at adhesive interfaces for hard tissue reconstruction

Although decayed/fractured teeth can be reconstructed minimally invasively and nearly invisibly using adhesive technology, the clinical longevity of dental composite restorations is still too short. Water sorption is thought to be the principal cause of destabilization of the biomaterial-tooth bond. However, the actual mechanisms of interfacial degradation are far from understood. Here we report how nano-controlled molecular interaction at the biomaterial-hard tissue interface can improve bond durability. The use of functional monomers with a strong chemical affinity for the calcium in hydroxyapatite is essential for long-term durability. Correlative X-ray diffraction and solid-state nuclear magnetic resonance disclosed a time-dependent molecular interaction at the interface with stable ionic bond formation of the monomer to hydroxyapatite competing in time with the deposition of less stable calcium phosphate salts. The advanced tooth-biomaterial interaction model gives not only an insight into the mechanisms of bond degradation, but also provides a basis to develop functional monomers for more durable tooth reconstruction.

Antibacterial effect of bactericide immobilized in resin matrix

OBJECTIVE Biomaterials with anti-microbial properties are highly desirable in the oral cavity. Ideally, bactericidal molecules should be immobilized within the biomaterial to avoid unwanted side-effects against surrounding tissues. They may then however loose much of their antibacterial efficiency. The aim of this study was to investigate how much antibacterial effect an immobilized bactericidal molecule still has against oral bacteria. METHODS Experimental resins containing 0, 1 and 3% cetylpyridinium chloride (CPC) were polymerized, and the bacteriostatic and bactericidal effects against Streptococcus mutans were determined. Adherent S. mutans on HAp was quantitatively determined using FE-SEM and living cells of S. mutans were quantified using real-time RT-PCR. The amount of CPC released from the 0%-, 1%- and 3%-CPC resin sample into water was spectrometrically quantified using a UV-vis recording spectrophotometer. RESULTS UV spectrometry revealed that less than 0.11 ppm of CPC was released from the resin into water for all specimens, which is lower than the minimal concentration generally needed to inhibit biofilm formation. Growth of S. mutans was significantly inhibited on the surface of the 3%-CPC-containing resin coating, although no inhibitory effect was observed on bacteria that were not in contact with its surface. When immersed in water, the antibacterial capability of 3%-CPC resin lasted for 7 days, as compared to resin that did not contain CPC. SIGNIFICANCE These results demonstrated that the bactericidal molecule still possessed significant contact bacteriostatic activity when it was immobilized in the resin matrix.

Environmental Scanning Electron Microscopy Connected with Energy Dispersive X-ray Analysis and Raman Techniques to Study ProRoot Mineral Trioxide Aggregate and Calcium Silicate Cements in Wet Conditions and in Real Time

INTRODUCTION ProRoot mineral trioxide aggregate (MTA) and calcium silicate cements are able to set in a moist environment. The aim of the study was to examine the surface structure and composition of a cement paste under wet conditions and in real time during setting by environmental scanning electron microscopy connected with energy dispersive x-ray analysis (ESEM-EDX) and micro-Raman techniques. METHODS White ProRoot MTA and experimental white tetrasilicate cement (wTC) and wTC containing bismuth oxide (wTC-Bi) were studied. Cement disks were analyzed 10 minutes after powder-liquid mixing (freshly prepared samples) and after immersion in Dulbecco phosphate-buffered saline at 37 degrees C for 24 hours (24-hour-aged samples). RESULTS Freshly prepared wet cements at ESEM-EDX exposed an irregular surface (displaying calcium, silicon, aluminum, chlorine reflexes, and bismuth traces in MTA and wTC-Bi) with needle-like and cubic-hexagonal shaped crystals. Aggregates of spheroidal Ca-P-rich crystals (spherulites) appeared on the surface of 24-hour-aged samples. The starting unhydrated powders displayed the typical Raman bands of Portland cement components: alite, belite, and calcium sulfate (only as anhydrite in MTA and as both anhydrite and gypsum in wTC and wTC-Bi). MTA powder showed higher amount of calcium carbonate and lower quantities of anhydrite and higher crystallinity of the silicate component, leading to a slower hydration reaction. Products/markers of hydration reactions were present on fresh samples; ettringite formed on the surface of all the cements; calcium hydroxide (portlandite) was detected only on the surface of wTC, but no conclusion can be drawn on wTC-Bi and MTA because of the interference of bismuth oxide. Calcium phosphate and calcite/aragonite bands were detected on all 24-hour-aged cements; portlandite was no longer detected on wTC. CONCLUSIONS ESEM and micro-Raman are powerful and suitable techniques to investigate endodontic calcium silicate hydrated cements in real time and in their humid state without inducing artifacts by sample preparation. The formation of apatite spherulites on calcium silicate cements might have clinical relevance.

Bulk-filling of high C-factor posterior cavities: Effect on adhesion to cavity-bottom dentin

OBJECTIVES To evaluate the effect of bulk-filling high C-factor posterior cavities on adhesion to cavity-bottom dentin. METHODS A universal flowable composite (G-ænial Universal Flo, GC), a bulk-fill flowable base composite (SDR Posterior Bulk Fill Flowable Base, Dentsply) and a conventional paste-like composite (Z100, 3M ESPE) were bonded (G-ænial Bond, GC) into standardized cavities with different cavity configurations (C-factors), namely C=3.86 (Class-I cavity of 2.5mm deep, bulk-filled), C=5.57 (Class-I cavity of 4mm deep, bulk-filled), C=1.95 (Class-I cavity of 2.5mm deep, filled in three equal layers) and C=0.26 (flat surface). After one-week water storage, the restorations were sectioned in 4 rectangular micro-specimens and subjected to a micro-tensile bond strength (μTBS) test. RESULTS Highly significant differences were found between pairs of means of the experimental groups (Kruskal-Wallis, p<0.0001). Using the bulk-fill flowable base composite SDR (Dentsply), no significant differences in μTBS were measured among all cavity configurations (p>0.05). Using the universal flowable composite G-ænial Universal Flo (GC) and the conventional paste-like composite Z100 (3M ESPE), the μTBS to cavity-bottom dentin was not significantly different from that of SDR (Dentsply) when the cavities were layer-filled or the flat surface was build up in layers; it was however significantly lower when the Class-I cavities were filled in bulk, irrespective of cavity depth. SIGNIFICANCE The filling technique and composite type may have a great impact on the adhesion of the composite, in particular in high C-factor cavities. While the bulk-fill flowable base composite provided satisfactory bond strengths regardless of filling technique and cavity depth, adhesion failed when conventional composites were used in bulk.

Effect of remaining dentin thickness and the use of conditioner on micro-tensile bond strength of a glass-ionomer adhesive

OBJECTIVES The purpose of this study is to investigate the effect of remaining dentin thickness and the use of a 20% polyalkenoic acid conditioner on the micro-tensile bond strength of a glass-ionomer adhesive to dentin. METHODS Resin composite was bonded to flat dentin surfaces from 14 extracted human teeth using Fuji BOND LC (GC) with or without a polyalkenoic acid conditioner, then sectioned to thin slabs, trimmed into an hourglass shape with the area of the interface being approximately 1mm(2), and subjected to micro-tensile testing at a cross-head speed of 1mm/min. Micro-tensile bond strengths were determined at three depth levels with a remaining dentin thickness of more than 3mm, between 2 and 3mm, and less than 2mm. Failure modes of the broken interfaces were determined using field-emission scanning electron microscopy. RESULTS The micro-tensile bond strength to dentin significantly improved when the remaining dentin thickness increased and the conditioner was used. When the conditioner was used (irrespective of remaining dentin thickness), failures mainly occurred adhesively at the interface between the adhesive and resin composite. When no conditioner was used, no adhesive failures between the adhesive and resin composite occurred, but failures occurred mainly adhesively between dentin and the adhesive, or mixed adhesive-cohesively. SIGNIFICANCE The bonding effectiveness of the glass-ionomer adhesive tested was affected by the area of intertubular dentin available for micro-mechanical retention through hybrid-layer formation. Removal of the smear layer improved the bond strength of the adhesive to dentin.

Enzymatic degradation of adhesive-dentin interfaces produced by mild self-etch adhesives

Endogenous matrix metalloproteinases (MMPs) released by adhesive procedures may degrade collagen in the hybrid layer and so compromise the bonding effectiveness of etch-and-rinse adhesives. In this study, endogenous enzymatic degradation was evaluated for several simplified self-etch adhesives. In addition, primers were modified by adding two MMP inhibitors: chlorhexidine, a commonly used disinfectant, but also a non-specific MMP inhibitor; and SB-3CT, a specific inhibitor of MMP-2 and MMP-9. Gelatin zymography of fresh human dentin powder was used to identify the enzymes released by the adhesives. Micro-tensile bond strength (μTBS) testing was used to assess the mechanical properties of resin-dentin interfaces over time. In none of the experimental groups treated with the mild self-etch adhesives was MMP-2 and/or MMP-9 identified. Also, no difference in the μTBS was measured for the inhibitor-modified and the control inhibitor-free adhesives after 6 months of water storage. It is concluded that in contrast to etch-and-rinse adhesives, the involvement of endogenous MMP-2 and MMP-9 in the bond-degradation process is minimal for mild self-etch adhesives.

Bond strength of self-etch adhesives to dentin prepared with three different diamond burs

OBJECTIVES To evaluate the micro-tensile bond strength (mu TBS) of a control etch-and-rinse and three self-etch (strong, mild, ultra-mild) adhesive systems to dentin prepared with three different grit size of diamond burs. METHODS Dentin surfaces were created from mid-coronal sound dentin in extracted, human third molars. The teeth were ground with high-speed medium grit (100 microm), fine grit (30 microm), or extra-fine grit (15 microm) diamond bur. Resin composite (Z100) was bonded to the surfaces using Optibond FL, Adper Prompt L-Pop, Clearfil SE Bond, or Clearfil S3 Bond. Rectangular micro-specimens were prepared using the slow-speed diamond saw and tested in tensile to determine the mu TBS. Failure analysis was performed using a stereo-microscope and Fe-SEM. Data were analyzed by two-way analysis of variance and Tukeys HSD test (p<0.05). RESULTS The etch-and-rinse adhesive yielded high micro-tensile values (58-69 MPa), irrespective of the diamond burs used. The bond strength values were comparable for Adper Prompt L-Pop and Clearfil SE Bond irrespective of the burs used. The mu TBS values were significantly higher as the particle size of diamond burs is smaller for Clearfil S3 Bond. Most failures were recorded as interfacial failure when the fine and extra-fine diamond burs were used. SIGNIFICANCE Overall, different grit-sized diamond burs did not affect the mechanical properties of the interface, except for the ultra-mild one step self-etch adhesive. This adhesive performed significantly better when a smaller grit size was used to prepare dentin surface.

Effect of air-drying and solvent evaporation on the strength of HEMA-rich versus HEMA-free one-step adhesives

OBJECTIVES The objectives of this study were (1) to clarify the relationship between the duration of air-drying of one-step self-etch adhesives (1-SEAs) and the evaporation degree (ED) of solvents, and (2) to evaluate the effect of ED on the ultimate micro-tensile strength (microTS) of the adhesives. METHODS The ED of one HEMA-rich 1-SEA, Clearfil S3 Bond (Kuraray), and two HEMA-free 1-SEAs, iBond (Heraeus-Kulzer) and G-Bond (GC), was determined without air-drying and after, respectively, 5- and 10-s air-drying using a gravimetric method. Next, the microTS of the adhesives at ED equivalent to 0-, 5- and 10-s air-drying was measured. RESULTS The ED increased with extension of air-drying time. Among the adhesives tested, iBond showed the largest ED, followed by G-Bond and Clearfil S3 Bond in this order. A longer air-drying time for 10-s resulted in a statistically significantly higher microTS for the HEMA-rich Clearfil S3 Bond. The microTS of the latter was higher than that of the other two HEMA-free adhesives for each air-drying time. SIGNIFICANCE Air-drying of 1-SEAs had a significant effect on the degree of solvent evaporation (ED) and also on the mechanical properties (microTS) of the 1-SEAs upon setting. It is therefore beneficial to remove solvents of the 1-SEAs as much as possible by thorough, strong air-drying in order to achieve a strong adhesive layer at the interface.