Total etch vs self etch
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total etch self etch adhesive bond strength comparison
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"self-etch" AND "total-etch" AND dental adhesive
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total etch vs self etch adhesive dentistry comparison clinical
Here is a thorough comparison of total etch vs self etch adhesive systems:
Total Etch vs Self Etch Adhesive Systems
Classification by Generation
| Generation | System | Etching Step |
|---|---|---|
| 4th gen | Total etch (3-step: acid + primer + adhesive) | Phosphoric acid, separate |
| 5th gen | Total etch (2-step: acid + primer/adhesive combined) | Phosphoric acid, separate |
| 6th gen (Type I & II) | Self etch (2-step: self-etch primer + adhesive) | Built-in acidic monomers |
| 7th gen | Self etch (1-step, all-in-one bottle) | Built-in acidic monomers |
| 8th gen | Universal (can be used either way) | User's choice |
Mechanism of Action
Total Etch (Etch-and-Rinse)
- 30-40% phosphoric acid is applied to both enamel and dentin for 15-30 seconds, then rinsed
- On enamel: dissolves surface and subsurface hydroxyapatite, creating deep, irregular microporosities - resin tags penetrate 25-50 µm
- On dentin: removes the smear layer completely, opens dentinal tubules, and exposes a ~5-8 µm collagen network (demineralized zone)
- Primer is then applied to wet the exposed collagen, followed by adhesive resin
- Bond depends on formation of a thick resin-collagen hybrid layer
Self Etch
- Acidic monomers (e.g., 10-MDP, phenyl-P, HEMA) simultaneously etch and infiltrate the substrate without a rinse step
- Smear layer is incorporated into the bond (not removed)
- Creates a thinner hybrid layer (0.5-5 µm vs. 5-8 µm for total etch)
- Partial dissolution of hydroxyapatite - residual mineral remains within the hybrid layer, which may actually improve long-term stability
Bond Strength Comparison
| Substrate | Total Etch | Self Etch |
|---|---|---|
| Enamel | Superior - deep microporosities, strong micromechanical bond | Weaker on uncut/unprepared enamel; better on cut enamel |
| Dentin | Good, but technique-sensitive (risk of over-drying) | Comparable or superior - residual mineral reinforces hybrid layer |
| Overall | Higher peak bond strength | More consistent, less variable bond |
- After aging in acidic conditions (pH 2.3, 180 days), total-etch systems maintain ~13.75 MPa vs ~7.09 MPa for 2-step self etch - suggesting greater long-term durability under chemical stress
- The hybrid layer with total etch is thicker but paradoxically more prone to hydrolytic degradation because collagen is fully exposed without mineral protection
Clinical Steps
Total Etch Technique:
- Apply 35-37% phosphoric acid to enamel (15 sec), then dentin (15 sec)
- Rinse thoroughly (10-15 sec)
- Blot dry dentin - leave slightly moist ("wet bonding") - critical step
- Apply primer (if separate) then adhesive
- Light cure
Self Etch Technique:
- Apply self-etching primer directly to dentin and enamel
- Agitate for recommended time (10-20 sec)
- Apply adhesive
- Light cure (no rinsing needed)
Key Clinical Differences
| Parameter | Total Etch | Self Etch |
|---|---|---|
| Steps | More (3+ steps) | Fewer (1-2 steps) |
| Technique sensitivity | High - over-drying = collapse of collagen | Low |
| Enamel bond | Better | Weaker on intact enamel (selective etch enamel recommended) |
| Dentin bond | Good but variable | Consistent |
| Postoperative sensitivity | Higher risk (smear layer removed, tubules open) | Lower risk (smear layer incorporated) |
| Smear layer | Completely removed | Incorporated/modified |
| Hybrid layer thickness | 5-8 µm (thicker) | 0.5-5 µm (thinner) |
| Marginal discoloration | Less (better seal) | Slightly more (due to incomplete enamel etching) |
| Time | Longer | Shorter |
| Clinical indications | Anterior esthetics, enamel-heavy cavities | Posterior restorations, deep cavities, difficult isolation |
Selective Etch Strategy
Many clinicians use a selective etch approach - applying phosphoric acid only to enamel margins (for superior enamel bonding), then using a self etch system on dentin. This combines the best of both:
- Strong enamel bond from acid etching
- Reduced sensitivity from self etch on dentin
- A 2023 microleakage study (PMID 37929222) found selective etch performed comparably to or better than both pure total etch and self etch for Class II composites.
Postoperative Sensitivity
- Total etch: ~16% sensitivity at 18 months (open tubules, over-drying risk)
- Self etch: ~12% sensitivity at 18 months (smear layer plugs tubules)
- However, well-controlled clinical studies show no statistically significant difference in sensitivity between systems when technique is optimal
Clinical Performance Overall
An 18-month clinical trial on non-carious cervical lesions (NCCLs) concluded: "The clinical performance of total-etch and self-etch adhesive systems in NCCLs did not differ significantly with regard to retention, marginal integrity, and postoperative sensitivity" - as long as both met ADA's 90% retention threshold.
When to Use Which
Choose total etch when:
- Anterior restorations where enamel marginal integrity is critical
- Large enamel surface area (mostly enamel preparations)
- Indirect restorations (inlays, onlays, veneers with significant enamel)
- Resin-bonded fixed partial dentures
Choose self etch when:
- Posterior Class I/II/V restorations
- Deep dentin exposures (proximity to pulp)
- Patients prone to sensitivity
- Poor moisture control situations
- High-volume, efficiency-focused practice
Universal adhesives (8th gen) now let you switch between both strategies with a single bottle - when used in total etch mode, 10-MDP-containing universals show enhanced dentin bond strength across short-term, thermocycled, and extended immersion conditions.
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