Luting of ceramic inlays in vitro: marginal quality of self-etch and etch-and-rinse adhesives versus self-etch cements.

OBJECTIVES: To evaluate marginal integrity of IPS Empress inlays luted with different adhesives and cements before and after thermo-mechanical loading (TML). METHODS: MOD cavities with one proximal box beneath the cementoenamel junction were prepared in 72 extracted human third molars. IPS Empress inlays were luted with nine combinations of adhesive and luting composite or self-etch cement alone (n=8): Prime&Bond NT Dual-Cure+Calibra (PC), XP BOND/SCA+Calibra (XC), XP BOND/SCA light-cured+Calibra (XL), Syntac+Variolink II (SV), Multilink Primer+Multilink (ML), AdhesSE DC+Variolink II (AV), ED Primer+Panavia F 2.0 (EP), RelyX Unicem (RU), and Maxcem (MC). Marginal quality was analyzed under an SEM using epoxy resin replicas before and after thermo-mechanical loading (100,000x50N and 2500 thermocylces between +5 and +55 degrees C). RESULTS: All systems involving the etch-and-rinse approach resulted in significantly higher percentages of gap-free margins in enamel than all other luting systems (p<0.05). ML and AV achieved higher percentages of gap-free margins in enamel than EP and RU (p<0.05), with EP and RU being significantly above MC (p<0.05). For dentine margins, XP Bond resulted in significantly higher percentages of gap-free margins than Prime&Bond NT, independent of a separate light-curing step (p<0.05). Between the luting systems XC, XL, SV, ML, AV, ED, EP, and RU, no significant differences were computed (p>0.05). MC ranged at the end of the statistical subsets with 62% gap-free margins (p<0.05; Mann-Whitney U-test). SIGNIFICANCES: Etch-and-rinse adhesives combined with conventional luting resin composites reveal still the best prognosis for adhesive luting of glass ceramic inlays.

Resin tags do not contribute to dentin adhesion in self-etching adhesives.

PURPOSE: Self-etching adhesives partly remove or dissolve the dentin smear layer, causing incomplete resin tag formation or low resin tag density. The quantitative contribution of properly formed resin tags to dentin adhesion was evaluated. MATERIALS AND METHODS: We assessed how the presence or absence of resin tags affects tubules of human deep-coronal dentin. G-Bond was used to bond Gradia resin composite. To ensure deep tubule penetration, we used a vacuum exsiccator. For eliminating tag formation, dentin tubules were presealed with adhesive and reverse bonded after finishing. Microtensile bond strength (muTBS) was measured on flat specimens and on Class I cavity floors. Thermocyclic loading was used to estimate the influence of resin tags on long-term behavior. Confocal laser scanning microscopy was used to evaluate adhesive interface dimensions. RESULTS: Hybrid layer thickness, tag length, and tag diameter increased under vacuum treatment. Presealing dentin tubules led to a residual tag area of 3.1% with a tag length of 10.8 microm. Under vacuum, 24.7% of the total dentin surface was covered with tags of 87.8 microm. Low C-factor preparations produced superior muTBS (71.8 to 92.7 MPa) compared with high C-factor Class I cavities (47.0 to 67.6 MPa). Thermocyclic fatigue differed from low to high C-factor situations. In Class I cavities, muTBS significantly decreased after thermocycling. On flat specimens, vacuum infiltration led to reduced muTBS after thermocyclic loading. CONCLUSION: Initially, resin tag formation did not influence the muTBS in either type of C-factor preparation. After thermocyclic loading, muTBS decreased with or without resin tags. Adhesive fracture patterns occurred at the hybrid layer/dentin interface.

The effect of different air-polishing powders on dentin bonding.

PURPOSE: Air-polishing is routinely used for professional tooth cleaning. Therefore, the aim of this in vitro study was to evaluate the influence of different air-polishing powders on dentin bonding. MATERIALS AND METHODS: Dentin bond strengths of a resin composite (Clearfil AP-X) bonded with different classes of adhesives (4-step etch-and-rinse: Syntac; 3-step etch-and-rinse: OptiBond FL; 2-step etch-and-rinse: Single Bond Plus; 2-step self-etching: AdheSE, Clearfil SE Bond, Clearfil Protect Bond, One Coat Self-Etch Bond; all-in-one/mix: Xeno III; all-in-one/no mix: Clearfil S3 Bond, G-Bond) were measured on flattened dentin surfaces. In test groups, specimens were air polished with Prophypearls (calcium carbonate) or ClinPro Prophypowder (glycine) prior to bonding. Microtensile bond strengths were evaluated after 24 h of storage at 37 degrees C in water. Surfaces and resin-dentin interfaces were observed by SEM, TEM, and CLSM. RESULTS: Mean bond strengths varied from 18 to 73 MPa in control groups. Calcium carbonate air polishing generally caused significantly reduced dentin bond strengths (p < 0.05). TEM exhibited severe nanoleakage after calcium carbonate air polishing. Glycine did not affect dentin bonding performance of the adhesives under investigation. CONCLUSION: Calcium carbonate air polishing should be avoided when dentin-bonded restorations are applied. Glycine powder is an alternative.

Adhesive luting revisited: influence of adhesive, temporary cement, cavity cleaning, and curing mode on internal dentin bond strength.

PURPOSE: To evaluate microtensile bond strength to Class I cavity floor dentin beneath adhesive inlays that were luted with different adhesives, temporary cements, cleaning methods, and curing modes. MATERIALS AND METHODS: Occlusal cavities (4 x 4 mm, depth 3 mm) were prepared in 96 extracted human third molars. One part of the cavities was temporized with different temporary cements, which were removed after one week using three techniques (scaler or air polishing with Prophypearls or ClinPro powder). Direct resin composite inlays (Clearfil AP-X) were then placed with the luting composite Calibra using three adhesives (XP BOND/SCA, Syntac, OptiBond FL). Teeth were cut into beams and after 24 h of water storage at 37 degrees C, the sticks were subjected to microtensile bond strength evaluation. Samples were subjected to SEM fractographic analysis of failed interfaces. RESULTS: Contamination with temporary cement reduced dentin bond strengths (p < 0.05). Removing remnants of cements with Prophypearls air polishing resulted in the lowest bond strengths (p < 0.05). Separate light curing of the adhesives did not produce higher dentin bond strengths (p > 0.05). Syntac still worked when Heliobond was omitted (p > 0.05). Immediate dentin sealing prior to temporizing increased internal bond strength (p < 0.05). CONCLUSION: The dual-cured adhesive provided higher internal bond strengths between adhesive inlays and dentin. Contamination of dentin with temporary cements is a hazard for excellent dentin adhesion of adhesive inlays. Therefore, immediate dentin sealing and resin coating is promising.

Marginal integrity: is the clinical performance of bonded restorations predictable in vitro?

PURPOSE: In vitro testing of dental materials is daily routine for the preclinical investigation of restoratives. Although clinical trials remain the ultimate instrument, preclinical screenings are still important. However, it is still not fully understood whether clinical performance is predictable in the lab. The aim of this paper is to combine known facts and recent results to answer the question concerning in vitro predictability of clinical marginal integrity and related outcome. MATERIALS AND METHODS: (a) The literature in the field from 1990-2005 was analyzed regarding marginal integrity in vitro and in vivo, especially in frequently cited papers. (b) Five different adhesives, a 4-step etch-and-rinse adhesive (Syntac), a 3-step etch-and-rinse adhesive (OptiBond FL), a 2-step etch-and-rinse adhesive (Single Bond), a 2-step self-etching adhesive (Clearfil SE Bond), and a 1-step self-etching adhesive (Xeno III) were used for bonding of a resin composite (Tetric Ceram) in Class I cavities (n = 8 in vitro and n = 8 in vivo). In vitro, the restorations were thermomechanically loaded (TML; 100,000 with 50 N and 2500 cycles of 5 degrees C/55 degrees C) according to a previously published protocol. Replicas of restorations were analyzed initially and after TML (in vitro) and two years of clinical service (respectively). RESULTS: (a) Marginal integrity is reliably predictable in laboratory in vitro studies by simulating clinical circumstances. However, marginal analyses of direct restorations in vitro still suffer from not being able to determine a lower boderline, ie, actually worse in vitro results may still result in acceptable restorations in vivo. (b) The in vitro-in vivo comparison revealed significantly better marginal adaptation in (enamel) margins when etch-and-rinse adhesives were used for bonding. After 2 years of clinical service, restorations bonded with self-etching adhesives did not clinically fail but exhibited significantly more marginal gaps. CONCLUSION: Clinical behavior of restoration margins is predictable. However, marginal adaptation is only one among several important aspects in restorative dentistry, ie, clinical outcome is not predictable from marginal integrity alone.

Influence of c-factor and layering technique on microtensile bond strength to dentin.

OBJECTIVE: Due to polymerisation shrinkage of resin-based composites, a high configuration factor in deep Class I cavities leads to a certain amount of stress when the material is bonded. The aim of this in vitro study was to evaluate the influence of c-factor and different layering approaches on bonding to dentin with three different adhesive systems. MATERIALS AND METHODS: Dentin bond strengths of Z250 bonded with OptiBond FL, Single Bond, and One Up Bond F were measured on flattened dentin surfaces without cavity walls and on the cavity floor of Class I cavities (10 layering concepts). The resin composite increments were applied horizontally, vertically and obliquely, both with and without a flowable liner. The tests were carried out in a microtensile apparatus at a crosshead speed of 1 mm/min after 24 h of storage at 37 degrees C in water. Mean bond strengths were analysed using the Wilcoxon test and multiple comparisons according to the Mann-Whitney U-test. Specimens having failed prior to the bond strength test were included as 0 MPa. RESULTS: The groups bonded on flat surfaces exhibited significantly higher bond strengths than specimens cut from filled cavities. Within the cavity groups, OptiBond FL and Single Bond exhibited no significant differences, however, being above One Up Bond F. Within the groups of each adhesive, major differences between the layering concepts were detectable. Bulk technique led to low dentin adhesion at the cavity floor, above all for Single Bond and One Up Bond F. Horizontal layers resulted in significantly higher bond strengths than did vertical or oblique. Lining with a flowable composite did not promote bond strength for OptiBond FL. For the other adhesives, a lining improved adhesion when vertical or oblique layers were applied, for horizontal increments no effect was evident. CONCLUSIONS: The c-factor is an influencing factor for dentin adhesion. However, using an appropriate layering technique, high bond strengths to deep cavity floors can be achieved.