Gold, Ceramic and Composite: A Restorative Dental Material DiscussionBy Gary DeWood on October 12, 2016 | comments
In selecting an appropriate restorative material, the "gold standard" was, and perhaps still is, gold.
Of course that depends on the parameters within which one is making the selection. Today one of those parameters is usually the similarity in appearance of the restorative material to a natural tooth. That being said, a high percentage of dental professionals have gold restorations in their mouths despite its failure to match the color of natural teeth. They have witnessed the long service life and tremendous adaptability of gold in the mouths of the patients they see, and they are drawn to gold for their own posterior restorations.
This preference for gold does not extend to the public served by the dental profession. The general public, having no such history of experience to draw on as they make choices, do the natural thing and ask for materials that look like teeth. The dental industry has worked diligently over the past century to meet their demand.
In 1976, when I began having these conversations with patients, there were not a lot of options for restorative materials period, let alone ones that mimiced the color of a natural tooth. By far the most utilized restorative material was amalgam. Amalgam is silver at placement and frequently black after a time of service due to the oxidation of the silver present in it. It is hardly an esthetic restoration.
Amalgam's history is a long one, with the ealiest documentation of it in a medical text published in 659, and documented use of it as a dental restorative in Germany in 1528. By 1850 it was the most widely used material to “restore” tooth structure. As a material for filling teeth, it worked. It still works, and there are still situations in which its merits outweigh the risks. As a long-time amalgam user and supporter, I nonetheless agree that there is no doubt that it increases the mercury exposed to and present in at least one population: dental personnel. Additionally, its use causes an increase in mercury in waste water, and for these reasons alone its use should be limited or eliminated. I have yet to be convinced that it caused or causes patients without an allergy to the material substantial risks.
For the purposes of our discussion, however, amalgam has already been de-selected as a preference due to its non-similarity to tooth appearance, so we are left to ponder whether or not its risks could be acceptably managed since few patients on the planet would request it given alternatives.
My best tool back then for a natural looking "tooth-colored" restorative was a porcelain-jacket crown or a porcelain-fused-to-metal crown with porcelain-shoulder margins all the way around. While I did have two composite materials available for my use, truth was they would not qualify today as adequate. Although bonding had been pioneered, its use with composites and ceramics was in the very early stages and not part of regular use in practice, so it was not part of my dental school education. We did have one material that permitted a tooth-colored material to be "bonded" to enamel: Nuva-Fil. Ultraviolet-light polymerized, it was the best we had, and although the colors available were very limited and quickly changed their color once placed in the oral cavity, it was used used for several years as the best alternative to full coverage with a porcelain material. But a revolution was on the way.
Dentin Bonding and Composite materials hit the dental world like a tsunami. From the late 1970s through today, they represent the majority of the change that is fundamental to modern dentistry. When bonding became a viable and reliable technique, it became possible to build, mill, and eventually press composites and ceramics into shapes that could readily replace amalgam or gold. Millions of these were and are placed as anterior and posterior restorative solutions.
Composites are by far the majority of direct dental restorations placed today in the United States. A 2010 a study in the United Kingdom of UK and Irish dental schools showed that while posterior composite restorations were taught as the preferred choice, a majority of practioners at that time were still preferentially placing amalgam in posterior teeth. Amalgam is still more widely used than composite in some countries for posterior direct restorations despite the fact that in the dental schools composite is taught as a better alternative. Given that new dentists are being taught this, the trend away from amlagam will continue. In the future it might cease to be an option, and although I have long championed its benefits, advances in materials and techniques have convinced me its benefits are not worth the risks.
Dental composite materials are composed of a resin matrix based on BISGMA (bisphenol A-glycidyl methacrylate), UDMA (urethane dimethacrylate) or PEX (semi-crystalline poly ceram). One of these has been cited as containing a component material that may be of concern: BPA (bisphenol A), a component of the BISGMA resin. As in all controversies, there is data suggesting both sides of this discussion have an argument.
BPA can be present in dental materials (composites and sealants) for one or both of two reasons. It can be present as a by-product of other ingredients in the materials that have degraded, and it can be present as a trace material left-over from the manufacture of other ingredients used in the materials. BPA is not used as a formula ingredient in any dental materials according to the manufacturers, a fact that American Dental Association research has confirmed.
A 2008 report from the National Toxicology Program at the department of Health and Human Services states, "Dental sealant exposure to bisphenol A occurs primarily following the use of dental sealants that contain bisphenol A dimethacrylate. This exposure is considered an acute and infrequent event with little relevance to general population exposures; food and beverage consumption accounts for the majority of human exposure to BPA.”
While BPA has potential effects on the brain, behavior, and prostate glands of fetuses, infants and children, the research into how those effects apply to exposure from dental materials does not seem to apply to the exposures from food and beverages. Sealant placement is a transient event, and the BPA from such exposure is not detectable following placement. Data also suggests that regardless of the exposure source, BPA is excreted and not detectable after a short period of time. One recent study looked for BPA in urine at one day, 14 days and six months after placement of a dental composite and recorded an initial increase at one day, but no detectable presence of BPA at 14 days and no detectable presence at six months.
The future of dental restorations
We have come a long way in what we are able to offer our patients in the time that I have been involved in dentistry. As most of you know, my daughter, Dr. Kathryn DeWood (Katie), is a 2014 dental school graduate. Her practice does not include amalgam, and it has included the ability to create ceramic restorations at time of preparation, two things that are so far outside of the 1976 box her mother and I lived in that I could not have imagined them back then. I’m betting the speed of change and innovation will only pick up, and that Katie’s daughter will undoubtedly wonder how her mother could possibly practice with the stuff she has available in 2016.
This is why dentistry is so much fun. Everything I know gets re-written and the excitement of the ride doesn't end! Ain't it a great time to be alive!
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Gary DeWood, D.D.S., M.S., Spear Faculty and Contributing Author