André Poitevin

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

OBJECTIVESnTo evaluate the effect of bulk-filling high C-factor posterior cavities on adhesion to cavity-bottom dentin.nnnMETHODSnA 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.nnnRESULTSnHighly 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.nnnSIGNIFICANCEnThe 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.

Bonding of low-shrinking composites in high C-factor cavities

OBJECTIVESnPolymerization shrinkage causes stress at the tooth-restoration interface. The magnitude of the stress depends upon several factors, such as the configuration factor (C-factor) of the cavity, the polymerization-conversion rate and filling technique. The aim of this study was to investigate the effect of curing time and filling method when high C-factor cavities were filled with low-shrinking composites.nnnMETHODSnThree low-shrinking (Filtek Silorane, 3M ESPE: FS; NDurance, Septodont: ND; Kalore, GC: Ka) and one conventional composite (Z100, 3M ESPE) were bonded into standardized occlusal Class-I cavities using either a two-step self-etch adhesive (Silorane System Adhesive, 3M ESPE: SSA) or a one-step self-etch adhesive (G-Bond, GC: GB). Five experimental groups were formed according to the employed adhesive/composite combination (SSA/FS, SSA/Z100, GB/ND, GB/Ka, GB/Z100), and further divided into three subgroups conforming to curing time and filling technique (20 s/bulk; 80 s/bulk; 80 s/layered). For each subgroup, non-trimmed 1 mm×1 mm sticks were prepared from five teeth to measure the micro-tensile bond strength (μTBS) to cavity-bottom dentine.nnnRESULTSnThe two-step self-etch adhesive SSA generated higher bond strengths than the one-step self-etch adhesive GB, irrespective of the filling method. When GB was used, bulk filling with a low-shrinking composite revealed the highest bond strengths. For all composites, the layering method provided the highest bond strengths.nnnSIGNIFICANCEnThe two-step self-etch adhesive Silorane System Adhesive (3M ESPE) performed better than the one-step self-etch adhesive G-Bond (GC), regardless of the composite used. When the latter all-in-one adhesive was used, effects of shrinkage stress became more apparent.

Bonding effectiveness of self-adhesive composites to dentin and enamel

UNLABELLEDnSelf-adhesive composites (SACs) are claimed to bond to tooth substrate without a separate adhesive. Bonding effectiveness data are however still limited.nnnOBJECTIVESnIn SubProject 1, the hypothesis was tested that the micro-tensile bond strength (μTBS) to dentin of two flowable SACs was alike that of a one-step self-etch adhesive (1-SEa) combined with a flowable composite (flowC). In SubProject 2, the hypothesis was tested that the nature of the smear layer did not affect the μTBS of the SACs to dentin/enamel.nnnMETHODSnSubProject 1: The μTBS to bur-cut dentin of two SACs (Fusio Liquid Dentin, Pentron; Vertise Flow, Kerr) was measured and compared to that of four 1-SEa/flowC combinations (AdheSe One/Tetric EvoFlow, Ivoclar Vivadent; Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE; iBond/Venus flow, Heraeus Kulzer; Xeno V/X-flow, Dentsply) and of one 3-step etch-and-rinse adhesive (3-E&Ra: OptiBond FL, Kerr) combined with Premise Flowable (Kerr). The effect of pre-etching dentin with phosphoric acid on the μTBS of the SAC Vertise Flow (Kerr) was measured as well. SubProject 2: The μTBS of the two SACs and one 1-SEa/flowC combination (Adper Prompt L-Pop/Filtek Supreme XT Flowable, 3M ESPE) to either bur-cut or SiC-paper ground dentin/enamel was measured. The effect of pre-etching enamel with phosphoric acid on the μTBS of the SAC Vertise Flow (Kerr) was also measured.nnnRESULTSnSubProject 1: The μTBS to dentin of both SACs was significantly lower than that of the 1-SEa/flowC and the 3-E&Ra/flowC combinations, of which the latter performed best. The SAC Fusio Liquid Dentin (Pentron) bonded significantly better to dentin than Vertise Flow (Kerr), except when dentin had additionally been pre-etched with phosphoric acid. SubProject 2: Surface smear did not interfere with bonding of the SACs to dentin/enamel, while their μTBS remained significantly lower than that of the 1-SEa/flowC combination. Prior phosphoric-acid etching of dentin/enamel significantly ameliorated the bonding effectiveness of Vertise Flow (Kerr).nnnSIGNIFICANCEnThe bonding effectiveness of flowable SACs underscores that of 1-SEas and one gold-standard 3-E&Ra when combined with their proprietary flowable composite. Consequently, routine clinical application of SACs should be carefully considered.

Bond Durability of Composite Luting Agents to Ceramic When Exposed to Long-term Thermocycling

PURPOSEnThis study evaluated the effect of thermocycling on the microtensile bond strength of four adhesive luting agents to GN-I CAD-CAM ceramic. The hypothesis tested was that thermocycling did not affect bonding effectiveness, irrespective of the luting agents used.nnnMATERIALS AND METHODSnCeramic specimens of two different sizes (6x8x3 mm; 13x8x4 nm) were fabricated from GN-I CAD-CAM ceramic blocks (GC) using a low-speed diamond saw. Two different sized porcelain discs were bonded with one of the four composite luting agents (Linkmax [LM], Panavia [PN], RelyX Unicem [UN] and Variolink II [VL]) according to the manufacturers instructions. The specimens were stored for 24 hours in distilled water at 37 degrees C and subjected to 0; 10,000; 20,000 and 40,000 thermocycles prior to microTBS testing. Two-way analysis of variance was used to test the influence of luting cement, thermocycling and interaction between both (p < 0.05). The Tukey HSD test determined statistical differences in microTBS for each luting composite between the different thermocycling conditions (p < 0.05). The mode of failure was determined at a magnification of 50x using a stereomicroscope (Wild M5A).nnnRESULTSnTwo-way ANOVA revealed that microtensile bond strength was affected by the luting cement, thermocycling and a combination of both. No difference in bond strength between Linkmax, Panavia F and Variolink II was noticed after 24 hours of water storage (LM: 47.6 MPa; PN: 41 MPa; VL: 36 MPa). RelyX Unicem scored significantly lower than Linkmax and Panavia F (UN: 24.2 MPa). The influence of thermocycling on bond strength was different for the four luting cements. Using Variolink II, the bond strength remained stable after 40,000 thermocycles (43.6 MPa). Linkmax showed a significant decrease in bond strength after 10,000 (26 MPa) and 40,000 thermocycles (14.8 MPa). Panavia F and RelyX Unicem were the most negatively influenced, as all specimens failed prior to testing (pre-testing failures) when the specimens were thermocycled 10,000 and 20,000 times or longer, respectively. Regarding the failure mode, there was a correlation between bond strength and type of failure. Initially, a combination of adhesive and mixed adhesive-cohesive failures was noticed. The percentage of adhesive failures increased, together with a decrease in bond strength.nnnCONCLUSIONnIt was concluded that there were significant differences among the four resin composite cements in terms of their bonding effectiveness to CAD-CAM ceramic after thermocycling. The varying degrees of bonding effectiveness of these adhesive luting agents highlight the need for material specifications.

Fracture toughness versus micro-tensile bond strength testing of adhesive-dentin interfaces

OBJECTIVEnTo assess interfacial fracture toughness of different adhesive approaches and compare to a standard micro-tensile bond-strength (μTBS) test.nnnMETHODSnChevron-notched beam fracture toughness (CNB) was measured following a modified ISO 24370 standard. Composite bars with dimensions of 3.0×4.0×25 mm were prepared, with the adhesive-dentin interface in the middle. At the adhesive-dentin interface, a chevron notch was prepared using a 0.15 mm thin diamond blade mounted in a water-cooled diamond saw. Each specimen was loaded until failure in a 4-point bend test setup and the fracture toughness was calculated according to the ISO specifications. Similarly, adhesive-dentin micro-specimens (1.0×1.0×8-10 mm) were stressed in tensile until failure to determine the μTBS.nnnRESULTSnA positive correlation (r(2)=0.64) was observed between CNB and μTBS, which however was only nearly statistically significant, mainly due to the dissimilar outcome of Scotchbond Universal (3M ESPE). While few μTBS specimens failed at the adhesive-dentin interface, almost all CNB specimens failed interfacially at the notch tip. Weibull moduli for interfacial fracture toughness were much higher than for μTBS (3.8-11.5 versus 2.7-4.8, respectively), especially relevant with regard to early failures.nnnSIGNIFICANCEnAlthough the ranking of the adhesives on their bonding effectiveness tested using CNB and μTBS corresponded well, the outcome of CNB appeared more reliable and less variable. Fracture toughness measurement is however more laborious and requires specific equipment. The μTBS nevertheless appeared to remain a valid method to assess bonding effectiveness in a versatile way.

Influence of joint component mechanical properties and adhesive layer thickness on stress distribution in micro-tensile bond strength specimens

OBJECTIVESnDifferences in mechanical properties between adherents and adhesive result in stress singularity at the free edge for tensile test specimens. Beyond causing premature failures, these also trigger fracture initiation at the bond edge, where the use of the maximum stress at failure as a measure of strength is not a reliable parameter for obtaining bond strength. The aim of this study is to describe the pattern of stress concentration along the interface for micro-tensile bond strength (microTBS) specimens. Also, possible sources of variation in stress concentration (adhesive layer thickness and mechanical properties) were evaluated using the finite element method.nnnMETHODSnOne-fourth models of typical microTBS specimens were created using axisymmetric elements. A 15MPa load was applied at the outer edge and finite element calculations were performed within the elastic deformation range. In the first set of runs, the adhesive thickness was varied and in the second set, different nu/E ratios between the adhesive and the adherent were assigned.nnnRESULTSnWhen adhesive thickness increased, a significant increase in stress concentration at the free edge and in the length of the stress-affected area was observed. Increasing the nu/E ratio between adhesive and adherent lead to an increase in stress concentration at the free edge area without change in length of the stress-affected area.nnnSIGNIFICANCEnIf mechanical properties and adhesive thickness expected for a specific composite-dentin bond combination in microTBS specimens are known, stress concentration at the interface can be predicted. The adhesive thickness should remain constant when comparing different joints, as it facilitates the interpretation of nominal strength values.

Bonding effectiveness to different chemically pre-treated dental zirconia

ObjectiveThe objective of this study was to evaluate the effect of different chemical pre-treatments on the bond durability to dental zirconia.MethodsFully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were subjected to tribochemical silica sandblasting (CoJet, 3M ESPE). The zirconia samples were additionally pre-treated using one of four zirconia primers/adhesives (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent; Scotchbond Universal, 3M ESPE; Z-PRIME Plus, Bisco). Finally, two identically pre-treated zirconia blocks were bonded together using composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass and stored in distilled water (7xa0days, 37xa0°C), after which they were randomly tested as is or subjected to mechanical ageing involving cyclic tensile stress (10xa0N, 10xa0Hz, 10,000xa0cycles). Subsequently, the micro-tensile bond strength was determined, and SEM fractographic analysis performed.ResultsWeibull analysis revealed the highest Weibull scale and shape parameters for the ‘Clearfil Ceramic Primer/mechanical ageing’ combination. Chemical pre-treatment of CoJet (3M ESPE) sandblasted zirconia using Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) revealed a significantly higher bond strength than when Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco) were used. After ageing, Clearfil Ceramic Primer (Kuraray Noritake) revealed the most stable bond durability.ConclusionCombined mechanical/chemical pre-treatment, the latter with either Clearfil Ceramic Primer (Kuraray Noritake) or Monobond Plus (Ivoclar Vivadent), resulted in the most durable bond to zirconia.Clinical relevanceAs a standard procedure to durably bond zirconia to tooth tissue, the application of a combined 10-methacryloyloxydecyl dihydrogen phosphate/silane ceramic primer to zirconia is clinically highly recommended.

Dentin-smear remains at self-etch adhesive interface

OBJECTIVEnThe bonding potential of mild self-etch adhesives may be compromised due to smear interference, as they may not dissolve/penetrate the smear layer effectively due to their relatively low acidity. We observed that the thickness of the dentin smear layer differed depending on the surface-preparation methodology used.nnnMETHODSnThe interaction of an (ultra-)mild self-etch adhesive (Clearfil S3 Bond, Kuraray Noritake) with human dentin, prepared either using a medium-grit diamond bur (thick, clinically relevant smear layer) or 600-grit SiC-paper (thin smear layer), or just fractured (smear-free), was evaluated using high-resolution transmission electron microscopy (TEM). Non-demineralized/demineralized 30-100nm interfacial cross-sections were prepared following common TEM-specimen processing and diamond-knife ultra-microtomy.nnnRESULTSnThe adhesive did not dissolve the bur-cut, nor the SiC-ground smear layer, but impregnated it. Within this resin-smear complex, hydroxyapatite was abundantly present. At fractured dentin, this complex was not present, while the actual layer of interaction of the adhesive was limited to about 100nm. Non-demineralized ultra-thin (30-50nm) sections confirmed the interfacial ultra-structure to differ for the three surface-preparation methods. An electron dense band was consistently disclosed at the adhesive interface, most likely representing the documented chemical interaction of the functional monomer 10-MDP with Ca.nnnSIGNIFICANCEnThe dentin surface-preparation method significantly affects the nature of the smear layer and the interaction with the ultra-mild self-etch adhesive.

Interfacial fracture toughness of aged adhesive-dentin interfaces.

OBJECTIVEnTo assess interfacial fracture toughness of different adhesive approaches and compare to a standard micro-tensile bond-strength (μTBS) test after 6 months water storage.nnnMETHODSnChevron-notched beam fracture toughness (CNB) was determined using a modified ISO 24370:2005 standard. Adhesive-dentin micro-specimens (1.0 mm × 1.0 mm × 8-10 mm) were stressed in tensile until failure to determine the micro-tensile bond strength (μTBS).nnnRESULTSnThe highest mean μTBS and interfacial fracture toughness were measured for the multi-step adhesives Clearfil SE Bond (Kuraray Noritake) and OptiBond FL (Kerr). While large differences were observed in the bond strength values (from 7.4 to 27.2 MPa) of the one-step self-etch adhesives tested, interfacial fracture toughness was less different (from 0.7 to 1.0 MPam(1/2)). The adhesive with the lowest mean toughness (All-bond Universal, Bisco) had however the highest Weibull reliability, which might be a better parameter in regard to more consistent clinical performance. The self-adhesive composite Vertise Flow (Kerr) scored significantly lower at all levels.nnnSIGNIFICANCEnAlthough the ranking of the adhesives tested using CNB and μTBS corresponded well, the outcome of CNB appeared more reliable and less variable.

Hydrolytic stability of three-step etch-and-rinse adhesives in occlusal class-I cavities

ObjectivesA dental adhesive without small and hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) would be beneficial in order to avoid contact allergies. However, these monomers are important to increase infiltration and polymerization of the adhesive. Therefore, the purpose of this study was to evaluate the bonding effectiveness and bond durability of a more hydrophobic and biocompatible adhesive as compared to a conventional three-step etch-and-rinse adhesive.MethodsSixteen non-carious human third molars were used to determine the micro-tensile bond strength testing (μTBS) and interfacial ultrastructure by transmission electron microscopy (TEM) of the more hydrophobic cmf adhesive system (Saremco) adhesive as compared to the control OptiBond FL (Kerr).ResultsThe more hydrophobic and biocompatible three-step etch-and-rinse adhesive was able to produce a reasonable short-time bonding effectiveness. In the long term, the collagen fibrils in the hybrid layer were not effectively protected and were prone to hydrolytic degradation. As a result, long-term bonding effectiveness of this novel adhesive was very low.ConclusionsApplication of a more hydrophobic adhesive without altering the application procedure considerably results in a reduced durability of the created bondClinical relevanceOmitting small and hydrophilic components from the adhesive formulation may impair the durability of your composite restoration.