‘No-bottle’ vs ‘multi-bottle’ dentin adhesives—a microtensile bond strength and morphological study

Purpose: To compare the adhesive capability of the new adhesive Prompt L-Pop (ESPE) with that of two total-etch adhesive systems—EBS Multi (ESPE) and Prime&Bond NT (Dentsply). Methods: Extracted human molars were bonded and prepared for microtensile dentin bond strength (μTBS) testing using Prompt L-Pop, EBS Multi, and Prime&Bond NT combined with Pertac II (composite) or Hytac Aplitip (compomer). Prompt L-Pop was applied using five different protocols: (1) as an ‘all-in-one’ self-conditioning adhesive, as per manufacturerʹs instructions (LP); (2) as a self-etching primer combined with a separate bonding resin (LP/self-etch 2-step); (3) as a classical primer used upon etching dentin with phosphoric acid, followed by a bonding resin (LP/total-etch 3-step); (4) as a multi-application ‘all-in-one‘ self-conditioning adhesive (LP/multi-coat) to leave a visibly glossy dentin surface; and (5) as a filled adhesive, upon adding quartz fillers to its composition (LP/filled). After 24 h of storage in water at 37°C the μTBS were measured in an Instron machine. Corresponding interfaces of the same specimens were micromorphologically analyzed using SEM and TEM. Results: When used with a composite resin, LP/filled and LP/multi-coat resulted in significantly higher μTBS than LP. The addition of an extra adhesive bonding resin (LP/self-etch 2-step) had no effect on bond strength. The use of Prompt L-Pop as a primer of a fourth-generation adhesive (LP/total-etch 3-step) replacing the EBS Multi primer, resulted in lower bond strengths than those of the original EBS Multi. LP/multi-coat showed similar μTBS to Prime&Bond NT (P&BNT). When used with a compomer, LP exhibited higher bond strengths than when used with the resin composite and was as effective as the experimental groups LP/filled and LP/multi-coat and the control group P&BNT. The SEM evaluation showed an inconsistent hybrid layer for the LP specimens, whereas in both the LP/filled and LP/multi-coat specimens a hybrid layer was clearly evident. Under the TEM all groups displayed dentin hybridization with dissolved smear plugs in the specimens that had been conditioned with Prompt L-Pop without a separate etching step. In many tubules of specimens conditioned with LP (as per manufacturerʹs instructions), fillers of the resin composite were present within the dentinal tubules. Conclusions: When combined with a resin composite, Prompt L-Pop resulted in statistically lower bond strengths when applied in one layer than when applied in multiple layers. Prompt L-Pop also resulted in higher bond strengths when used with a polyacid-modified composite resin than with a composite resin. When applied in multiple coats, Prompt L-Pop results in bond strengths that are not statistically different from those of Prime&Bond NT, a total-etch adhesive.