TBU: #043 How To Bond An Onlay Following Biomimetic ProtocolsMar 18, 2023
New Issue of The Biomimetic Uprising
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Onlays are an important part of biomimetic dentistry. This treatment choice is used instead of traditional crowns. You've probably heard me say it before, but I've never prepped a tooth for a crown that didn't already have one. So for any of these larger defects where traditional dentistry would do a crown, I'd do a an onlay.
I'd save say that onlays are typically more technique sensitive compared to crowns. Forming the bio base takes considerable steps and attention to details. Cementing the onlay requires the same focus.
Biomimetic protocols for bonding an onlay involve a series of steps to mimic the natural structure and function of the tooth. Here are the general steps involved in bonding an onlay with biomimetic protocols:
- Preparation of the tooth: The tooth is prepared by removing any decay or old filling material. The preparation should be minimal to preserve the natural structure of the tooth. A compression dome technique is often used. However, I often find these to be too aggressive and can remove important tooth structure in the cusps.
- Air abrasion: Air abraid the bio base and tooth to "activate" the compost resin and to open up the double chains so that we can bond to them. If you don have air abrasion, you can use a red stripe polishing diamond bur to gently do the same. Typically only a few seconds is needed.
Etching: The tooth and bio base are etched with phosphoric acid solution to create a rough surface that will help the bonding agent adhere to the tooth and base. Etch for 30 seconds then rinse until clean. Dry for another 10 seconds
Bonding agent application: A bonding agent is applied to the tooth surface. The bonding agent is usually a resin that is light-cured to create a strong bond between the tooth and the onlay. I typically use SE Protect or OptiBond FL. Remember, the primer is not needed. Primer is used to infiltrate the dentin to help create resin tags for the adhesive. We are only needing 'bottle 2' of these bonding systems. In other words, just use the adhesive bottle. I also place this on the intaglio surface of the onlay after the porcelain primer is ready.
Onlay treatment: The onlay is typically acid etch treated when coming back from the lab. Depending on your lab settings, an additional acid etch step or steps may be needed with either porcelain etch and an addition phosphoric etch.
- Onlay treatment: Use porcelain primer. I use ceramic primer plus from Clearfil. Heat dry is preferred. If not possible, let it sit for 5 min in the ambient room temperature before cementing.
Onlay placement: The onlay is carefully placed on the prepared tooth and bonded to the tooth using the bonding agent and a cement or heated composite. The onlay is then cured with a special light to harden the resin. I'll typically use heated composite as it adapts will to the surfaces, better bond strengths, and better wear properties compared to cements. However, Panavia is my 'go-to' whenever it's needed.
Finishing and polishing: The onlay is finished and polished to ensure a smooth surface that matches the natural surface of the tooth. Make sure to adapt the only to the tooth a few times to ensure the onlay is seated all the way and that there isn't excess cement being used. Here's an extra tip I did for removing excess cement when seating an onlay.
Once again, our biomimetic protocols aim to preserve the natural structure and function of the tooth, so the onlay should be designed to fit the tooth precisely and restore its natural shape and function. This may require using advanced imaging techniques, like digital scanners, and computer-aided design to create a customized onlay that fits perfectly.
If you're new to biomimetics, dont be afraid to try out some basic only preps. I let the decay and damaged areas dictate my prep designs. From there you can easily add in an onlay or inlay.
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