Michel Degrange

Meta-analytical review of factors involved in dentin adherence.

Literature data on adherence tests of dentin-bonding systems (DBS) may differ widely, even for the same DBS. The problem of bond testing is that materials are seldom compared with a standard, and experimental conditions often vary. We sought to identify the parameters that influence this variability. Using inclusion and exclusion criteria, we conducted a meta-analytical review of 75 articles, published between 1992 and 1996 in SCI reviews, that give bond strength data for 15 dentin-bonding agents of the so-called third and fourth generations. Seventeen selected parameters were classified into four groups: Group A includes factors related to the dentin substrate (i.e., nature of teeth); group B, composite and bonding area (i.e., composite stiffness); group C, storage conditions of the bonded samples (i.e., thermocycling); and group D, test design (i.e., crosshead speed). For each report, the experimental features, the bond strength means and standard deviations, and the failure mode were extracted and tabulated. Statistical Analysis System software was used to perform Pearson correlation analysis and analysis of variance, with bond strength as the dependent variable and experimental conditions as the independent variables. The meta-analytical review highlighted the significant influence of various parameters in the different groups: origin of dentin, types of teeth, pulpal pressure, tooth storage temperature, maximum storage time of teeth, and dentin depth in group A; type and stiffness of composite and bonding area in group B; storage of bonded samples (medium, temperature, and time) in group C, and testing mode and crosshead speed in group D. A significant positive correlation was observed between the mean bond strength and the rate of cohesive failure. It can be concluded from this study that some of these parameters should be controlled by the use of a standardized protocol. Unfortunately, the substrate-related variables are more difficult to control, even though their influence is consistent.

Effects of surface treatment on the free surface energy of dentin

OBJECTIVESnThe purpose of this study was to evaluate the influence of six treatments on the dispersive, acid, and base components of the free surface energy of dentin.nnnMETHODSnOcclusal dentin surfaces were polished with 4000 grit abrasive paper, washed and air dried. Characteristics of the surface energy were calculated by measuring contact angles of the four following liquids:alpha-bromonaphtalene, glycerol, ethylene glycol, and water. The dentin was then treated with aqueous solutions containing: (1) oxalic acid and glycine (OX/GLY),(2) oxalic acid, glycine, and HEMA (OX/GLY/HEMA), (3) phosphoric acid (PA), (4) maleic acid (MA),(5) EDTA, or (6) NaCIO. After treatment, washing and air drying, the energy characteristics of the samples were evaluated again.nnnRESULTSnThree kinds of wetting behavior were observed: an increase (OX/GLY/HEMA), a stabilization (PA, NaCIO) or a decrease (OX/GLY, MA, EDTA) of the wettability of the dentin surface. The calculations demonstrated that dentin surfaces are basic.nnnSIGNIFICANCEnThis study of the evolution of the surface energy components gave information on adhesion mechanisms involving hydrophilic and hydrophobic interactions. The results may be helpful in the formulation of conditioners and primers.

Self-etching Increases Matrix Metalloproteinase Expression in the Dentin-Pulp Complex

In adhesive restorations, one major problem is hybrid layer degradation. At present, this deterioration is explained by the activation of the endogenous matrix metalloproteinases (MMPs) present in dentin due to the acidic property of adhesive systems. We hypothesized that self-etching adhesive should also stimulate the expression of MMPs in odontoblasts. In cultured tooth slices, we evaluated the changes in MMP-2 and proMMP-9 expression in the dentin-pulp complex after self-etching adhesive treatment on dentin cavities in immunochemistry and by zymography. The treatment resulted in increased MMP-2 expression in odontoblasts, as shown by immunohistochemistry. Zymography showed increased proMMP-9 and MMP-2 in dentin under self-etching treatment when pulp was present. These results showed that self-etching adhesive stimulates the secretion of MMPs from the dentin-pulp complex and, more precisely, by odontoblasts, suggesting that odontoblasts participate in hybrid layer degradation.

Influence of drying and HEMA treatment on dentin wettability

OBJECTIVESnThe aim of this study was to evaluate the effect of drying time and primer pre-application (35% HEMA in water) on water spreading/infiltration on dentin.nnnMETHODSnFreshly extracted molars were embedded in resin and sectioned on their coronal side. Flat occlusal dentin surfaces were prepared using wet SiC paper from nos. 80-4000. A computerized contact angle device complementing a special software (Wingoutt) was used to measure the contact angle (theta) kinetics of a reference liquid (pure H(2)O) in the ten groups each of ten dentin surfaces during 120 s: Gp1: etched (37% phosphoric acid for 15 s) and blot-dried; Gp2: 3 s dried; Gp3: 5 s air-dried; Gp4: 10 s air-dried; Gp5: 20 s air-dried; Gp6: 30 s air-dried; Gp7: 1 min dried with hair dryer; Gp8: 5 s air-dried and HEMA treated; Gp9: 30 s air-dried followed by HEMA treatment; Gp10: HEMA treated prior to 30 s air-drying. three drops were applied on each sample. 40 contact angles were recorded for each drop with a frequency of one measure every 3 s. A one-way ANOVA test was used for data analysis. A PLSD test was conducted to identify statistical differences between pairs of groups at a reliability level of 95%.nnnRESULTSnAt each measurement time, air-drying, whatever its duration, significantly decreased the wetting ability of the pure water on the etched dentin in comparison with the blot-dried group. The contact angle increases with drying time. No significant differences in water contact angle were obtained between 3, 5 and 10 s in spite of a slight decrease in the spreading/infiltration ability of water the longer the drying time. HEMA increases the spreading/infiltration ability of water on 5 or 30 s air-dried etched dentin surfaces; 30 s air-drying did not alter the spreading/infiltration ability of the water on etched and HEMA treated dentin.nnnSIGNIFICANCEnDentin hydrophobicity increases depending on air-drying time. HEMA-based primer allows to prevent collagen collapse, which may be created by air-drying and partly rewet the collapsed collagen network.

Shear Bond Strengths of Self-Adhesive Luting Resins Fixing Dentine to Different Restorative Materials

The purpose of this study was to assess the bond strengths of three self-adhesive resin cements (Rely X Unicem, Maxcem and Multilink Sprint) fixing dentine to four different restorative substrates (Ni–Cr alloy, E-Max glass–ceramic, Y-TZP Zirconia and Adoro micro-filled composite) and to compare their performances with those of two conventional dual-cured luting cements (Variolink II + Total-etch Excite DSC and Multilink Automix + Self-etching Primer A + B). Cylindric specimens (5 × 5 mm) were prepared with the four restorative materials for bonding to human dentine. Three surface treatments were performed depending on the restorative material: (i) Al2O3 50 μm sandblasting (Ni–Cr, Adoro), (ii) #800 SiC polishing (Zirconia, E-Max), (iii) hydrofluoric acid (HF)-etching (E-Max). Twenty-five groups (n = 10) were designed according to luting cements, restorative materials and surface pre-treatments. In some experimental groups, Variolink II and Multilink Automix were coupled with, respectively, a silane primer (Monobond S) and an alloy/zirconia primer (Multilink A/Z primer). Specimens were stored in distilled water at 37°C for 24 h and then loaded in shear until failure. Variolink II and Multilink Automix showed the highest bond strengths, regardless of the restorative substrate, when used with dentine bonding systems and primers, while the weakest bonds were with Maxcem. The bond strength recorded with the two other self-adhesive cements depended on the nature of the restorative substrate. Increasing retention at the interfaces (i.e., HF ceramic etching) and using specific primers significantly improves the bond strength of luted restorative materials to dentine.

Factors Affecting the Adherence Energy of Experimental Resin Cements Bonded to a Nickel-Chromium Alloy

Reliable adherence of resin-based cements is of prime importance for the longevity of cemented restorations. The present study investigated whether a relationship exists between adherence energy to a metal substrate and the degree of cross-linking and wetting characteristics of resin-based luting agents. The adherence energies between a sand-blasted metal surface and a series of experimental resin cements were measured by means of the wedge test. The degree of cross-linking was calculated from the monomer composition of the resin cements. The measured wetting characteristics were work of adhesion and surface tension, and their dispersive and polar components. Adherence energy varied between 22 and 81 J/m2 and was influenced by the nature of the resin cements: Those with a low degree of cross-linking resulted in high adherence values. Furthermore, resin cements whose monomers were relatively polar gave rise to high adherence values. Although other metals may not behave in exactly the same way, these results may help in the formulation of new, more retentive resin cements.

Adherence of resin-based luting agents assessed by the energy of fracture

The present study assessed the adherence of nine commercial resin cements by means of the wedge test. The beams of the test were made of a Ni-Cr-Be alloy, and the adhering surfaces were sandblasted with 250 microns Al2O3. The energy of fracture of the investigated cements varied from less than 10 J/m2 to 121 J/m2. The fracture energies were not influenced by 1) the thickness of the joint, 2) the width of the beams, 3) the use of an intermediary noncomposite resin, or 4) storage in water beyond 24 h. In spite of a rather high variability within groups, it is concluded that the wedge test may give relevant data on the performance of adhesive joints.

Adhesion of a quartz fibre post to a composite resin core : influence of bonding agents and their curing mode

Fibre-reinforced composite posts are currently used to restore endodontically-treated teeth. Push-out tests were carried out to evaluate the performance of several bonding agents on the retention of an endodontic quartz fibre post to a composite resin core. Five bonding agents were investigated in both self-cure and light-cure modes. Ten experimental groups of 10 posts each were constituted as a function of curing mode and bonding agent. Specimens were mounted in a dedicated Teflon mould. This experimental set-up allowed the determination of true shear strength. One-way ANOVA and Student–Newman–Keuls tests were used for statistical analysis. The bonding strengths ranged from 23.4 MPa to 35.3 MPa. The best results were obtained with a light-cure self-etch bonding agent; in all cases photo-polymerisation led to statistically higher bonding strengths compared to chemical auto-polymerisation. Shear bond strength at the post–adhesive interface was also found to be significantly dependant on the nature of the bonding agent. AdheSe self-etch bonding agent was more effective than etch-and-rinse single-component bonding agents.