”The Essentials of Bonding”
– questions asked, questions answered
NIOM Scientist Frode Staxrud, DDS, was the presenter in a NIOM webinar held on October 24. He discussed the latest in dental adhesive techniques, as well as the do’s and don’t’s of dental bonding procedures.
His topics were:
- Why use bonding?
- How does it work?
- 1, 2 or 3-steps? What is best?
Insights from the Q&A:
Q: When using three-step bonding in bottles, e.g. Kerr Opti Bond FL, is there any loss of quality of the resin/bonding when there is only a little left in the bottles?
A: The product must be used prior to the expiry date. The problem is that solvent evaporates from the primer bottle, making it a little thicker than usual. It no longer flows and wets the surface well enough. It loses its functionality. As to the bonding/adhesive; polymerization may start in the bottles if they stay on the shelf too long, making them less reactive and thus lose bonding quality. The bottles should then be replaced and not used.
Q: As I understand you, the 3 steps are better than the 2 steps. Is it right?
A: Within the same group, for example, Etch & Rinse (ER) that is right, but 2-step Self-Etch may be equal to 3-step Etch & Rinse when you use selective enamel etch (making the SE system into a 3-step).
Q: Do you think we really need to remove solvent before light-curing step?
A: Yes, it is necessary because the solvents lead to accumulation of water and separation between resin and solvent (water/ethanol/acetone) so-called “phase-separation”. This phenomenon creates bubbles or voids in the material. These voids weaken the material and attract water which eventually leads to degradation of the matrix by hydrolysis.
Q: Do you recommend the use of “wetting agents” (such as Gluma desensitizer) prior to the primer when using the 3-step total-etch technique?
A: It is not necessary as long the dentine is not desiccated (over-dried). Not too dry, not too wet, just moist.
Q: What you mean by ”use selective enamel etch?”
A: Selective-etch means: Etching only the enamel with an etching gel, rinse with water thoroughly and gentle air blowing before applying the primer.
Q: On unprepared dentin, is it best to rub with diamond or just etch (using one bottle SE, Scotchbond Universal)?
A: To make the bonding agent adhere to unprepared dentine (i.e. exposed to oral fluids for a long time and therefore sclerotic); it is necessary to remove the outer 20 µm. This is difficult with etching only and should be performed by a superficial preparation with a diamond bur (grinding of the surface layer).
Q: Does the thickness of the bonding layer matter?
A: The bonding layer is the weak part, so yes, as little and thin bonding layer as possible.
Q: Are there any differences between the old ”golden standard” and the “new golden standard” when it comes to bonding strength, the speed of bonding strength, degradation and other important details?
A: Not really, they both perform well. There are no significant differences. The main idea is that the SE systems are gentler on and create stronger hybrid layers into dentine.
Q: Why is it not OK to dip instruments in bonding?
A: The adhesive resins dilute the composite. The manufacturers often call it contamination. This weakens the material, often the outer parts where we want the best physical properties. The resins may also be the cause of color disturbance as they are more easily degraded and not color stable to the same degree as the composite.
Q: Bonding to old composites, how to get the best results?
A: Check out our first webinar on restorations. Use bonding just as you would on dentin. In addition, use silane.
Q: Do you recommend liners in deep cavities?
A: No liners of any kind improve bonding; they are only for pulp protection, but this may be relevant in a lot of cases. If you consider it necessary to use pulp protection, I do not think it will affect (reduce) the retention of a restoration to any degree worth mentioning if you lose a few square mm of the dentine bonding.
Q: Do you recommend removing a smear layer, and if so what irrigation do you recommend?
A: Either you remove the smear layer with phosphoric acid when using the E&R systems, or the smear layer will be integrated into the resin/dentine hybrid layer by the use of acidified primers in the SE systems. There is therefore no need for other kinds of cleansing the cavity than water spray. As mentioned ethanol may have an impact on stopping degradation processes (chlorhexidine is more uncertain), but there are no other absolute recommendations than water spray.
Q: Are there any health/ecological aspects to be considered when choosing product or system?
A: Good question. Bonding materials may represent small occupational hazards, such as contact allergies etc.