Franklin R. Tay

Micro-tensile bond testing of resin cements to dentin and an indirect resin composite

OBJECTIVESnMicro-tensile bond strength (microTBS) evaluation and fractographic analysis were used to compare four resin cement systems (AC: All-Bond 2/Choice; RX: Single Bond/RelyX ARC; SB: Super-Bond C & B; and PF: Panavia F) in indirect composite/dentin adhesive joints.nnnMETHODSnFlat dentin surfaces were created on extracted human third molars. The resin cements were used according to the manufacturers instructions for bonding silanized composite overlays to deep coronal dentin. 0.9x0.9 composite-dentin beams prepared from the luted specimens were stressed to failure in tension. Dentin sides of all fractured specimens were examined by scanning electron microscopy (SEM) to examine the failure modes. In group PF, morphologic features that could not be resolved at the SEM level were further validated by transmission electron microscopy (TEM) examination of the SEM specimens.nnnRESULTSnStatistical analyses revealed significant difference (p<0.05) among microTBS and failure modes in the resin cement groups. The two groups (AC and RX) with highest microTBS failed predominantly along the composite overlay/cement interface. Cohesive failure in resin cement was primarily observed in group SB that exhibited intermediate microTBS values. In group PF with the lowest microTBS, failure occurred mostly along the dentin surface. Globular resin agglomerates seen by SEM on PF-treated dentin were distinguished from silica fillers by TEM.nnnSIGNIFICANCEnThe bond between the processed composite and the luting resin cement was the weak link in indirect composite restorations cemented with AC or RX. Super-Bond C&B exhibited intermediate tensile strength and Panavia F is less reliable when used in conjunction with a self-etching primer for bonding indirect restorations to dentin.

The overwet phenomenon in two-component acetone-based primers containing aryl amine and car☐ylic acid monomers

OBJECTIVESnThe overwet phenomenon was first reported when a moist bonding technique was used with an earlier commercial version of All-Bond 2 (Bisco) that contained BPDM in primer B. This study investigated whether ultrastructural features of the overwet phenomenon could also be detected in other commercially available two-component acetone-based primers containing BPDM, PMDM and PMGDM, as well as an experimental two-component primer containing DSDM.nnnMETHODSnThirty 1 mm dentin discs prepared from third molars were each conditioned with 10% H3PO4 for 20 s and rinsed for 20 s. They were randomly divided into 5 groups: Group I (Bond-It, Jeneric/Pentron:PMGDM); Group II (Wet Bond, Chameleon Dental Products:PMGDM); Group III (Tenure S, Den-Mat:PMDM); Group IV (present commercial version of All-Bond 2, Bisco:BPDM) and Group V (Experimental two-component primer system containing DSDM in primer B). Following a moist bonding technique using the respective system, discs from each group were further bonded together to form three disc pairs using a chemical-cured resin. Bonded disc pairs were demineralized in EDTA and processed for TEM examination. For this ultramicroscopical study, results such as the features of the overwet phenomenon were analyzed by visual inspection of the specimens in each group (n = 12).nnnRESULTSnIsolated blister-like spaces of variable dimensions were observed within the primer layer in all groups and possessed the following characteristics: 1) a layer of resin-impregnated dentin was always present along the base of the primary blister; 2) surface primer globules, sometimes containing secondary blisters, were identified within these primary blisters; 3) dentinal tubules within the blister-like spaces were not completely sealed; 4) primer globules were circumscribed by a halo of fine kinked strands of material.nnnSIGNIFICANCEnAlthough the technique of moist bonding is based on valid biological principles, incorporation of resin monomers that are immiscible with water rendered the application of current two-component, acetone-based primers very technique-sensitive in terms of tubular seal, when used on moist, acid-conditioned dentin. Further studies should be directed at elimination of this type of oil-in-water (O/W) macroemulsion formation through optimal micellar solubilization of these resin monomers in water.

Cervical Sclerotic Dentin: Resin Bonding

Many reports have indicated that resin bond strengths to noncarious sclerotic cervical dentin are lower than bonds made to normal dentin. This is thought to be due to tubule occlusion by acid-resistant mineral salts, preventing resin tag formation following acid etching. The purpose of this review was to critically examine what is known about the structure of this type of dentin. Recent transmission electron microscopy revealed that in addition to occlusion of the tubules by mineral crystals, many parts of wedge-shaped cervical lesions contain a hypermineralized surface that resists the etching action of both self-etching primers and phosphoric acid. This layer prevents hybridization of the underlying sclerotic dentin. In addition, bacteria are often detected on top of the hypermineralized layer. Sometimes the bacteria were embedded in a partially mineralized matrix. Acidic conditioners and resins penetrate variable distances into these multilayered structures. Examination of both sides of the failed bonds revealed a wide variation in fracture patterns that involved all of these structures. Microtensile bond strengths to the occlusal, gingival, and deepest portions of these wedge-shaped lesions are significantly lower than similar areas artificially prepared in normal teeth. When resin bonds to sclerotic dentin are extended to include peripheral sound dentin, their bond strengths are probably high enough to permit retention of class V restorations by adhesion, without additional retention.