Stop Agonising Over the Etch: Surface Treatment for Glass Ionomer Sandwich Bases
A 2025 systematic review and meta-analysis by Ismail, Ali, and Garcia-Godoy finds that for fresh resin-modified glass ionomer treated before composite overlay, phosphoric acid and Er,Cr:YSGG laser produce statistically equivalent bond strengths — making one of restorative dentistry's more agonised technique decisions a non-variable.
Acid and laser: equivalent
Source Paper
Effect of surface treatment on glass ionomers in sandwich restorations: a systematic review and meta-analysis of laboratory studies
Some clinical decisions consume disproportionate energy relative to their importance. Clinicians debate them at conferences, quietly second-guess their own protocol, spend more on a laser system than the evidence justifies. The surface treatment step before bonding composite over a glass ionomer base in a sandwich restoration is exactly this: phosphoric acid or an erbium, chromium:yttrium, scandium, gallium, garnet (Er,Cr:YSGG) laser?
A 2025 systematic review and meta-analysis in Restorative Dentistry and Endodontics supplies the answer: it does not matter. The paper, “Effect of surface treatment on glass ionomers in sandwich restorations: a systematic review and meta-analysis of laboratory studies” by Ismail, Ali, and Garcia-Godoy (Mansoura University and the University of Tennessee Health Science Center), reviewed 29 laboratory studies and found that for fresh resin-modified glass ionomer (RMGI) prepared with either method before an etch-and-rinse adhesive, bond strength to resin composite is statistically identical.
The Data Anchor
The review screened 11,007 articles across MEDLINE/PubMed, Scopus, and ScienceDirect, yielding 29 laboratory studies. The meta-analysis was narrow: only three studies met criteria for pooled analysis, all comparing shear bond strength (SBS) for Fuji II LC (GC Corporation) treated with either phosphoric acid or Er,Cr:YSGG laser before an etch-and-rinse adhesive, with n = 40 per arm.
Using a random-effects model (I² = 90.83%, p < 0.001), the overall mean difference was 1.555 MPa (95% CI –2.857 to 5.968, P = 0.490). The individual studies disagreed: Ghubaryi et al. favoured acid by 2.19 MPa; Navimipour et al. favoured laser by 5.37 MPa; Zakavi et al. favoured laser by 2.02 MPa. The pooled result lands in no-man’s-land.
The mechanistic explanation is neat. Er,Cr:YSGG laser (2780 nm, high hydroxyl group affinity) produces micro-irregularities and porosity in the RMGI surface. Phosphoric acid achieves a similar outcome by different chemistry. If the surface modification is functionally equivalent, the bond strength follows.
Key Findings
- No statistically significant difference between phosphoric acid and Er,Cr:YSGG laser for fresh RMGI before etch-and-rinse adhesive (mean difference 1.555 MPa, 95% CI –2.857 to 5.968, P = 0.490). Permission to stop optimising on this dimension is hereby granted.
- Surface treatment remains non-negotiable. Seven studies found significant differences between no treatment and chemically treated surfaces; the untreated option is not clinically neutral.
- RMGI outperforms conventional glass ionomer cement (GIC) regardless of surface treatment (seven studies confirm this); the advantage is intrinsic to RMGI’s polymerisable functional groups.
- For aged glass ionomer repair, the calculus changes. Mechanical roughening before adhesive application is supported; bur or silicon carbide sanding exposes unreacted glass particles and methacrylate monomers that a fresh surface provides naturally.
- Adhesive acidity matters more than adhesive category. Mild self-etch adhesives (pH ≥ 2) outperformed strong systems (pH < 1); stronger acids neutralise calcium cations and form weaker bonding structures.
- Limitation: Three studies, all using Fuji II LC, I² = 90.83%, and possible publication bias (Egger’s test P = 0.043). Generalisability beyond this specific protocol is unestablished.
Three studies that individually disagreed producing a pooled null result is not the same as three studies agreeing there is no difference.
💡 The Clinical Bottom Line
For the fresh RMGI base in your next sandwich restoration, the surface treatment decision between phosphoric acid and Er,Cr:YSGG laser has no evidence-based winner. Use what your practice has.
The choice that matters is to use surface treatment at all. For aged glass ionomer repairs, add mechanical roughening to the protocol; that is where the evidence for combined treatment genuinely sits.
Restorative dentistry’s investment in optimising the etch step may occasionally be energy spent on a variable that was never the one that mattered.
Dr Samuel Rosehill is a general dentist with a prosthodontic focus, practising at Ethical Dental in Coffs Harbour, NSW. He holds a BDSc (Hons) from the University of Queensland, an MBA, an MMktg, and an MClinDent in Fixed & Removable Prosthodontics (Distinction) from King’s College London.
Clinical Relevance
For clinicians using a fresh resin-modified glass ionomer (RMGI) base in a sandwich restoration and applying an etch-and-rinse adhesive, this meta-analysis of three studies finds no significant bond strength difference between phosphoric acid etching and Er,Cr:YSGG laser treatment (overall mean difference 1.555 MPa, 95% CI –2.857 to 5.968, P = 0.490). Surface treatment of any kind remains necessary; the specific choice between these two methods, at least for this scenario, does not appear to matter.
Disclosure: The author has no financial conflicts of interest related to the products or topics discussed in this review. This is an independent summary prepared for educational purposes.
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