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Clinical guide03 Jan 2026 · Updated 13 Sep 2026 · 7 min read
For most direct restorations, a universal adhesive used in selective-etch mode is the safest single-bottle choice: phosphoric acid on enamel only, then the adhesive on enamel and dentine. The marketing generations count bottles and steps, not bond quality. Two-step etch-and-rinse systems remain a sound, lower-cost option where enamel dominates the preparation.
Every dentist has seen it: a composite that debonds at the enamel margin after a year, a Class V that falls out, or a cold-sensitive tooth after a routine filling. The bonding step is the least visible part of a restoration and the one most often blamed. Meanwhile the shelf offers products called fifth, seventh and eighth generation, single bottle, two bottle, self-etch, total-etch and universal, and the numbers suggest a ranking that does not exist.
This guide explains what the generations actually describe, how modern adhesives bond to enamel and dentine, what the clinical evidence says about etching modes, and which adhesives in our catalogue fit which kind of work. The product choices at the end are ours; the clinical statements are labelled evidence, manufacturer, or practice so you can weigh them.
The generation numbers are a marketing history of how the chemistry was packaged. They tell you how many bottles you open and whether etching is a separate step. They do not tell you how strong or how durable the bond is.
| Generation | What it is | Steps | Etching |
|---|---|---|---|
| 4th | Separate etchant, primer and adhesive | 3 | Etch-and-rinse |
| 5th | Separate etchant; primer and adhesive combined in one bottle | 2 | Etch-and-rinse |
| 6th | Self-etching primer plus a separate adhesive, or two liquids mixed | 2 | Self-etch |
| 7th | Everything in one bottle, self-etching | 1 | Self-etch |
| 8th, universal | One bottle usable in etch-and-rinse, selective-etch or self-etch mode, often with primers for indirect substrates | 1 or 2 | Any |
Two things follow. First, a "5th generation" product is not older technology in a bad sense: many two-step etch-and-rinse adhesives have long clinical track records and remain a good choice for enamel-rich anterior work. Second, "7th" and "8th" describe convenience, not superiority, and the single-bottle products are the ones where technique errors, particularly solvent left in the film, cost the most.
Enamel and dentine bond differently. Enamel is highly mineralised; phosphoric acid creates micro-porosities that resin flows into and locks onto, a purely micromechanical bond that is strong and predictable. Dentine is wet, tubular and largely collagen. Etching or self-etching removes or dissolves the smear layer and exposes collagen; the primer and adhesive infiltrate that collagen to form a hybrid layer. If the collagen collapses because the dentine was over-dried, or if the etch went so deep that the resin cannot reach the bottom of the demineralised zone, the hybrid layer is weak and porous.
Universal adhesives add a chemical component. Most contain 10-MDP, a functional monomer that forms stable bonds with calcium in hydroxyapatite and with metal oxides, which is why the same bottle can prime zirconia. That chemistry is what lets them work in self-etch mode at all; it does not replace the need for a good enamel etch.
There are three ways to use a universal adhesive: etch-and-rinse on enamel and dentine, selective etching of enamel only, or self-etch everywhere. The clinical evidence comes mostly from non-carious cervical lesions, because they are the standard model for adhesive retention.
The practical reading: keep an etchant syringe next to every universal adhesive. Skipping the enamel etch to save 20 seconds trades a measurable amount of retention.
We stock three classes of adhesive. The table describes them by mode and indication; the manufacturers' instructions describe the exact times.
| Class | Stocked examples | Modes | Best fit |
|---|---|---|---|
| Universal, single bottle | 3M Scotchbond Universal Plus, 3M Single Bond Universal, Dentsply Prime & Bond Active, GC G-Premio Bond, HanBond 7th Generation | Etch-and-rinse, selective-etch, self-etch | One bottle for direct composites, core build-ups, repairs and, with the matching cement, indirect work |
| Two-step etch-and-rinse (5th generation) | Meta P & Bond, HanBond 5th Generation, Prime-Dent Light Cure One-Step | Etch-and-rinse only | Enamel-rich preparations, anterior aesthetics, clinics that want a lower-cost workhorse |
| Self-etch, single bottle (7th generation) | Prime-Dent Self Etch | Self-etch | Dentine-dominated cavities and situations where rinsing is impractical; add a selective enamel etch where enamel margins exist |
Alongside the adhesive you need an etchant (CharmEtch 37%, Ultra-Etch 35%, HanEtch 37%), disposable micro applicators, and, for indirect work on zirconia or metal, a primer such as GC G-Multi Primer when the adhesive does not already cover that substrate.
| Situation | Choose | Why |
|---|---|---|
| Everyday posterior and anterior composites, one bottle for the whole clinic | Universal adhesive in selective-etch mode | Best-supported mode for retention; one product for direct and indirect work |
| Deep dentine, sensitive patient, no enamel margin | Universal adhesive in self-etch mode | Avoids over-etching dentine, the most common cause of post-operative sensitivity |
| Anterior veneering in composite, enamel-rich preparation | Two-step etch-and-rinse | Long track record on enamel; separate hydrophilic primer wets dentine well |
| Bonding to zirconia, metal or an old composite during a repair | Universal adhesive containing MDP, with silane or a multi-primer for glass ceramics | Chemical bonding to metal oxides; glass ceramics still need hydrofluoric acid and silane |
| Core build-up under a crown with a dual-cure material | Universal adhesive plus its dual-cure activator, or a self-cure compatible adhesive | Acidic single-bottle adhesives can inhibit self-cure chemistry unless the activator is used |
Universal adhesives, from the two most widely used systems to a lower-cost kit:
Two-step etch-and-rinse and self-etch options, and the etchant and applicators every adhesive needs:
For indirect work on zirconia and metal, add a multi-primer:
If you are standardising the clinic on one adhesive, compare Scotchbond Universal Plus, Prime & Bond Active and G-Premio Bond on bottle size and price per drop, then add an etchant syringe and a box of micro applicators. If you already use a two-step system and your results are good, there is no evidence-based reason to change it; add a universal adhesive for repairs and indirect work instead.
No. The generation number describes how the chemistry is packaged: how many bottles, whether etching is separate, and whether primer and adhesive are combined. Clinical performance depends on the specific product and on technique, above all on isolation, etching mode and solvent evaporation.
You can skip it on dentine, but etching enamel with phosphoric acid before the adhesive gives a more reliable enamel bond and better retention in clinical studies. That combination is called selective enamel etching and is the mode most manufacturers recommend for direct restorations.
Universal adhesives are designed for both direct and indirect work, and most are compatible with dual-cure resin cements from the same manufacturer, sometimes with a separate activator. Check the cement's instructions for the adhesive it was tested with before relying on it for indirect work.
Total-etch, also called etch-and-rinse, uses phosphoric acid on enamel and dentine, then rinses before priming and bonding. Self-etch adhesives carry acidic monomers that condition the tooth without a rinse. Universal adhesives can be used either way, which is why they are often described as multi-mode.
Usually the solvent was not fully evaporated, or moisture from the field contaminated the film. Air-thin gently until the surface stops rippling, keep the field isolated, and cure for the full time in the instructions.
