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The bonding step for a direct resin-composite restoration (any cavity class, and non-carious cervical lesions) where a single-bottle universal adhesive is used on a mix of cut enamel and dentine and the field can be kept dry.
⚑ adhesion mandatory
Selective-etch is the default for a universal adhesive. Selectively etch the enamel margins only with 37% phosphoric acid (15–30 s, rinse, dry), keep the acid off freshly cut dentine, then apply the universal adhesive in self-etch mode over the whole prep: scrub it actively into enamel and dentine for the full IFU time, air-thin thoroughly to evaporate the solvent, and light-cure. This couples the best-performing enamel bond (acid-etched) with a mild self-etch on dentine, where phosphoric etching can reduce long-term bond durability. Prefer a 10-MDP–containing adhesive for a more hydrolytically stable dentine bond.
Selective enamel etch with 37% phosphoric acid, then a mild 10-MDP universal adhesive in self-etch mode over enamel and dentine — actively scrubbed for the full IFU time, solvent thoroughly air-thinned, and light-cured. Etch the enamel; 10-MDP gives the most stable dentine bond.
▢Rubber dam kit (preferred) or cotton rolls + high-volume suction
▢37% phosphoric acid etch gel + microbrushes / applicator tips
1Isolate and dry the field — rubber dam preferred; cotton rolls + high-volume suction are an acceptable alternative. The bond is moisture-sensitive, so control the field before you start and keep it dry through curing.
2Selectively etch the enamel only — apply 37% phosphoric acid to the cut enamel margins for 15–30 s, keeping it off freshly cut dentine. Rinse 15 s and dry the enamel; cut dentine is left unetched for the self-etch step.
TIP · Selectively etch the enamel even with a 'no-etch' universal adhesive. In-vitro meta-analyses agree the enamel bond strength of universal adhesives is improved by prior phosphoric-acid etching, while a mild universal on cut dentine bonds just as well without etching — and acid-etching dentine can hurt its long-term bond. Selective enamel etch captures the best of both: acid-etched enamel, self-etched dentine.
3Apply Scotchbond Universal Plus in self-etch mode over the whole prep — dispense fresh, then actively scrub it into enamel and dentine for the full IFU time (do not just paint it on). Active agitation drives the acidic monomer and 10-MDP into the smear layer and dentine surface.
TIP · Prefer a 10-MDP–containing universal. 10-MDP chemically bonds to the calcium of hydroxyapatite and self-assembles into a stable MDP–Ca nanolayer; in laboratory work, 10-MDP adhesives resisted thermocycling degradation whereas adhesives with other functional monomers lost bond strength. That chemical bond is what underpins durable dentine adhesion in self-etch mode.
TIP · Actively scrub the adhesive — don't just paint it on. Mechanical agitation for the full IFU time drives the acidic/10-MDP monomers into the smear layer and the dentine surface, improving infiltration and bond performance compared with passive application.
4Air-thin to evaporate the solvent — gently air-dry with a clean, oil- and moisture-free air stream for several seconds until the surface stops moving and looks glossy but no longer flows. Residual water/ethanol/acetone solvent left in the film weakens the bond.
TIP · Evaporate the solvent properly. Universal adhesives carry water plus ethanol or acetone; residual solvent trapped in the film leaves a poorly polymerised, water-rich layer that weakens the bond. Air-thin with a clean, oil-free stream for several seconds until the film stops flowing and looks evenly glossy before curing.
5Light-cure the adhesive per IFU before placing composite — check the curing-light output beforehand and cure for the full recommended time. Make sure light reaches deep or cervical margins (e.g. the gingival floor of a proximal box).
6Proceed to incremental or bulk-fill composite placement against the cured adhesive layer.
TIP · Mode is a trade-off, and selective-etch sits in the sweet spot. In NCCL randomised trials, selective-etch and etch-and-rinse give more predictable retention than pure self-etch over 1–2 years, while self-etch lowers the risk of postoperative sensitivity. With no dentine etching, a mild universal still performs reliably across modes — so selectively etching only the enamel keeps retention up without the sensitivity penalty of etching dentine.