To test the shear bond strength (SBS) of the experimental composites to dentin through an adhesive system, the occlusal surfaces of extracted, caries-free, human molars were removed and their roots embedded in polycarbonate holders with chemical curing poly(methyl methacrylate) tray resin (Bosworth Fastray Powder and Liquid, Bosworth Company, Skokie, IL, USA). The exposed dentin surfaces were ground flat perpendicular to the longitudinal axis of the teeth with 320 grit silicon carbide paper (Fig. 1a). The bonding protocol included the following steps. Ground dentin surfaces were first dried, then etched for 15 s with phosphoric acid gel (mass fraction H3PO4 38 %; Etch-Rite®, Pulpdent Corporation, Watertown, MA, USA). The acid was rinsed away with distilled water for 10 s, and a moistened paper towel (Kimwipes®; Kimberly-Clark Global Sales, Inc., Roswell, GA, USA) was used to blot the surface to a near-dry condition. Two protocols were used to prime the moist dentin surfaces. In the ACP base-lining composite series, dentin surfaces were sequentially primed first with N-phenylglycine (NPG; mass fraction 5 %) solution in acetone for 30 s, and then with five consecutive coats of pyromellitic glycerol dimethacrylate (PMGDMA; mass fraction 20 %) in acetone solution and camphorquinone (CQ; mass fraction 0.028 %) as photo-activator. In the ACP orthodontic composite series, only one coating of PMGDMA-acetone primer (DenTASTIC UNO, Pulpdent Corporation, Watertown, MA, USA) was applied. Following the application of NPG and PMGDMA, or PMGDMA alone, the surfaces were air-dried for 10 s to remove acetone and visible-light cured for 10 s (Spectrum Curing Light, Dentsply Caulk Limited, Milford, DE USA). A poly(tetrafluoroethylene) (PTFE)-coated iris (4 mm in diameter and 1.5 mm thick) that defined the bonding area was positioned on the tooth surface, filled by the experimental composite and light-cured for 20 s for the experimental base-liner composites and 60 s for the orthodontic composites. ACP base-liner specimens were completed by applying a commercial resin-based composite (TPH, Dentsply Caulk, Milford, DE, USA), which was cured for an additional 60 s. The assemblies were then exposed to air for 5 min to allow further dry-curing at room temperature, after which they were immersed at 37 °C in either distilled water (ACP base-liner series) or a saliva-like solution [10 ] (orthodontic ACP series) for up to 6 months.