How Material Choices and Technology Can Impact Your Crown and Bridge FitBy Jeff Lineberry on July 20, 2015 | comments
If you are like me, one of the more satisfying things when delivering an indirect restoration is not only that it looks good, but it’s a great day when the marginal fit is so good that your explorer passes seamlessly over the marginal interface. Over the past 15 years of dental practice, we have gone from a mainstay of gold and PFM for our indirect restorations and the occasional all porcelain restoration to now we are predominantly using all porcelain restorations of zirconia and lithium disilicate restorations. We went from where we took impressions that were poured up in models, master dies created, and the restoration was waxed up and cast and/or porcelain stacked on top of it by a lab technician to where they can be made using a digital scanner (no impression needed), and then fabricated in a lab or chairside with a CAD/CAM machines. It’s amazing how things have changed and how technology is a driving factor in everything we do, all the way down to how our restorations fit.
So, where are we today and what are some thoughts/considerations for today and going forward?
When it comes to the success of having an excellent final restoration, capturing the information that is needed to fabricate your patient’s final restoration is one of the most critical aspects of the dental restoration to fit properly. Impressions have been a mainstay in dentistry and have proven themselves well and a majority of dental practices still use it today, but digital scanners have definitely come on strong and are not only accurate, but they are getting smaller in size and faster to use.
In regards to your material of choice nowadays for fit and finish: zirconia vs. lithium disilicate; CAD/CAM/milled vs. Pressed/fabricated restorations, here are some thoughts to consider:
- Lithium disilicate restorations can be either milled or pressed using the lost wax technique (similar technique as the one that was used for gold restorations)
- Zirconia restorations can only be milled
- Either restoration can be monolithic (single material with no layers) or layered or have porcelain added to them to enhance the overall fit, or esthetics of the final restoration
So, which one fits the best? Lithium disilicate has the distinct advantage over zirconia restoration in that they can be waxed and pressed to the tooth preparations including all of the imperfections that are present. Zirconia can only fit as good as what can be milled, which often is limited to having smooth margins with little or no imperfections.
Well, no matter what technology you use, and what material choice you make, a lot of it still comes back to the basics: how good is the preparation of the tooth, including the overall smoothness of the preparation and marginal consistency and design (chamfer vs. shoulder vs. feather/knife edged), tissue management around the area in question, to the person fabricating the final restoration. (Studies show that experience of the CAD/CAM operator has a very positive influence on the fit and finish of the final restorations). In fact, with newer technology and “impression-less” dentistry, it may be more critical than ever to have excellent preparations that are easy for the machines to capture and read, thus leading to restorations that can meet or exceed dentistry of yester year. Technology is here to stay and is getting better all the time, but ultimately, your final restoration is as only as good as what you are giving your laboratory (or CAD/CAM machine) to make.
Jeff Lineberry, DDS, FAGD, FICOI Visiting Faculty, Spear Education www.cccdds.com