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Tooth-coloured restorations – choice of materials, procedures and longevity

Scientists from the Nordic Institute of Dental Materials (NIOM) were invited to the national dental conventions in Sweden and Norway this autumn. Head of laboratory Hilde M. Kopperud, researcher Simen E. Kopperud and guest-researcher Frode Staxrud from NIOM interacted in the two-hour lecture which presented data from both clinical and laboratory studies, and was entitled:

Tooth-coloured restorations – choice of materials, procedures and longevity

Longevity of dental restorations is affected by factors related to the material, the procedure, the patient and the dentist. A questionnaire study has revealed that while Norwegian dentists chose actively among the different categories of direct restorative materials in 1995, composite resin is by far the most used restorative material for posterior Class II direct restorations today (95%). Composites are basically a mixture of resin and filler particles. The resin is an organic matrix of different monomers. Large, stiff and hydrophobic monomers (e.g. Bis-GMA) give the material strength and reduce polymerization shrinkage and water uptake. Smaller, less viscous monomers (e.g. TEGDMA) are necessary to improve the consistency of the material, and will also increase the degree of conversion. More hydrophilic monomers (e.g. HEMA) are used where a good contact with the tooth structure is necessary. A large variation in size distribution and chemical composition of the filler particles is now used to optimize the material properties.

1Clinical studies performed in the 1990’s showed significantly better performance of amalgam restorations compared to composites. However, studies published later show comparable longevity of both materials, with annual failure rates (AFR) ranging from 1% to 7%. Reasons for failure of composite resins are mainly secondary caries and fractures. Saucer-shaped preparations in a Norwegian study have shown significantly higher failure rates than traditional Class II restorations. This indicates that some mechanical retention in small Class II preparations could improve the longevity of approximal restorations. Unpublished data from the same study also show that tooth surfaces in contact with newly placed composite restorations have significantly higher risk of developing caries.


Mild self-etching primer, followed by bonding materials is considered the new golden standard for bonding restorations to tooth substance. Enamel should be separately etched prior to applying primer.

Composites are bonded to the tooth. A new golden standard for bonding of restorations to tooth substance is recently introduced in dentistry. While a three-step etch & rinse procedure was recommended previously, is it now claimed that it is better for the dentine if a mild self-etching primer is used, followed by bonding materials. Enamel should be separately etched prior to applying primer. The bond strength is affected by water, since some chemical bonds will be broken by hydrolysis. Therefore hydrophilic residues from the primer should be evaporated before applying the bonding material. Some manufacturers add MDP or silane to achieve better bonding to old restorations. Metal primers are recommended when repairing metal containing restorations. Studies performed at NIOM show that – when repairing old composite resin restorations – bonding is significantly improved if a silane is applied to the old composite prior to bonding and placing the new restoration.

As materials with larger layer thicknesses are introduced, as well as high-intensity curing devices advocating short curing times, an awareness of proper curing is important. A longer curing time will produce a larger curing depth. We recommend increasing the curing time, rather than using high-intensity curing lamps, which may cause thermal damage to soft tissues and may present blue-light hazards to the eye.

3Longevity of restorations is strongly related to patient and dentist related factors. Restorations placed in caries active patients have a much higher failure rate compared with low-risk patients. Likewise, restorations in molars have 2-3 times as high risk of failure compared with restorations in premolars. Although little evidence is available, the dentist is considered one of the most important factors for longevity of restorations in clinical studies, since the dentist both decides which lesions that need to be filled, chooses the restorative material, prepares the cavity, places the restoration, follows up the patient postoperatively and finally decides when the restoration should be replaced.






  1. Paul November 28, 2014

    Yes it is me again, the 60-year-old dentist, who some months ago replied to a question posted on Oasis, regarding how to best attain contacts with composite resin for Class II restorations. My comment was, and remains, it is consistently difficult. Even if you do obtain a contact, it does not hold up over the years given the poor wear characteristics of the material. My suggestion was to use amalgam. The picture shown in this post is most ironic. There you can see the second bicuspid failure which is typical, and I will bet that there is recurrent decay contributing to this. A radiograph would have been beneficial. But take a look at the amalgam in the first molar. I will go on to wager that this restoration is 10 to 15 years old and has another 10 years left in it. Yes it is silver and not a pollster-child of “Cosmetic Dentistry”, which is a term best stricken from our professional vocabulary. A beautiful restoration, regardless of its colour, is one that maintains form and function for decades, not six or seven years. Given the weak remaining cusps on the bicuspid, a crown should have been placed as on the first bicuspid.
    Yes, I appreciate market pressures and the deceitful misinformation of “Mercury Poisoning”. My comment here is not an attempt to dissuade endontists of the error of their ways. That task would be doomed to fail.
    This comment is meant for those of us that know what methods and materials can stand the test of time. We do not need the reassurance of blogs. We are bolstered by the success of restorations that are decades old. I find it ironic that the author of the article uses the quote “a new golden standard” for bonding. This phrase should be exclusive to the use of gold, because that is what really lasts.

    Old Guy

  2. Bob December 9, 2014

    I concur with the good doctor above. The problem with all longevity studies is that they aren’t. I have published in the restorative literature and when leafing through the journals I note follow-up times of 1 to 2 years. When I got my restorations in my teeth, or I bought a vehicle, or acquired a wife (one so far) I got them to last somewhat longer than this. People who are wet-fingered dentists, and not practicing “conscience-free dentistry” know that amalgam restorations are both more forgiving, and longer lasting. The problem with composite resins are, – they are economically more remunerative and they are easy to “market.” Everyone should take one step back and ask themselves: If I was being paid 40% more to do mercury-amalgam restorations would I be likely to place composites – knowing that the latter contain bisphenols?

  3. Ross Anderson December 9, 2014

    With regards to statements of longevity of restorations in the article/blog it would be helpful to see references rather than just quotes.

    In posterior primary teeth the same cannot be said about longevity of composites as stated in this article/blog. This has been pointed out by the Bellinger (New England) and DeRouen (Portugal) studies. The serindipitous finding of these two well designed longitudinal randomized prospective studies was that composite restorations were replaced twice as often as amalgam restorations in children and follow up studies were done. If I am trying to minimize the number of potentially unpleasant experiences a child will have I really only want to do a restoration once if at all possible. I also want to use dental materials to assist in therapeutic management of a disease if I can and resin bares none of these properties.

    JAMA. 2006 Apr 19;295(15):1775-83.
    Neuropsychological and renal effects of dental amalgam in children: a randomized clinical trial.Bellinger et al

    The longevity of amalgam versus
    compomer/composite restorations in
    posterior primary and permanent teeth
    Findings From the New England Children’s Amalgam Trial

    JAMA. 2006 Apr 19;295(15):1784-92.
    Neurobehavioral effects of dental amalgam in children: a randomized clinical trial. DeRouen et al

    J Am Dent Assoc. 2007 Jun;138(6):775-83.
    Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. Bernardo et al.

    A recent masters thesis at the UoT by Bourbia entitled “Biodegradation of Dental Resin Composites and Adhesives by
    Streptococcus mutans: An in vitro Study” concluded that S Mutans produce esterases similar to those contained in human saliva that cause biodegradation (of composite resin). This could compromise the resin-dentin interface and reduce the longevity of the restoration.


    I note as well the weakest area for bonding of a composite is the gingival seat for a Class II and in primary teeth the surface area of enamel in the gingival seat is very minimal. Given the technique sensitivity of composite resins that are often challenged in a fidgity child this is considered with the parent too.

    Microleakage and thermal coefficient of expansion are other areas that help me choose materials.

    With regards to toxicity parents on an informed consent basis will need to choose between low levels of BPA and its potential (though minimal) estrogenic effects or the purported toxic effects of Hg. All literature would suggest that neither is of great concern in the amounts that are released and removal of restoratations containing either is not warranted nor should this be a major consideration in material selection in either case.

    I find it relatively easy in the informed consent process to explain the concept of minimizing poked and prodded syndrome for the child and of trying to place a restoration that will last the life span of the tooth when parents request white fillings in posterior primary teeth. Generally common sense prevails as parents want to minimize the number of experiences a child may have at the dentist. However, if they are insistent and want to pay more for something that will likely, based on science, not last as long they do so on an informed consent basis. I am very frank in letting parents know that as competent as I am I do not have a magic wand.

    With reference to my colleagues post I too can attain seniors discounts though I hope science and patient need influence my choices with parents! And by the way like gold in permanent posterior molars, steel lasts even longer when indicated in primary posterior teeth.


  4. Mike Christensen December 10, 2014

    Interesting comments. You know, all composite is not created equal. There are literally dozens of composites. They are not the same at all. As for proximal contacts, there are several products that can help achieve tight proximal contacts (iccluding things like Compositight and Greater Taper Bands and other things). Wear which we know in composite to actually be dissolution on products like Heliomolar for instance are quite impressive. It is useful to have occlusion that is not ridiculously low. Composite on a large “filling” which is actually a buildup (I am talking about 4 and 5 surface “fillings”) is advantageous because the bond is reliable and also because the occlusion can be made initially high and then be carved to the precise height wanted after the restoration is placed. This keeps the opposing teeth from super erupting into the way too low surface of amalgam 4 and 5 surface fillings that were made way too low to avoid fracture with the first bite after the band is removed and the occlusion is checked. Then of course, there is smoothness. Amalgam is rough unless it is polished and that has become taboo these days because of supposed release of mercury when they are polished. However, if composite is used–again, the brand has to be chosen carefully–the surface can be highly polished and it will actually become smoother over time. The Amalgam vs Composite debate is so done. Our patients decided it long ago. It’s best to do your homework about specific composite products and make the best choice for the clinical situation that presents itself. The writing is already on the wall. Patients don’t want amalgam. Being upset over that fact is like crying over spilled milk. Best to move on and make the best choice available. Yes, composite is technique sensitive. Choose your composite brand and specific type very carefully. Learn how to use it and maximize its characteristics. We have little other choice.

  5. Greg December 13, 2014

    The previous post says “Patients don’t want amalgam”. The fact is if you have a good relationship with your patients, and they trust you, and you engage them in a proper informed consent discussion, many will select amalgam. This is especially true in the posteriors where aesthetics are not critical. I present the facts and advise patients where I think composite will work well and where it won’t work so well. Many cases involve placement of both composites and amalgam, along with other materials such as glass ionomers or resin modified glass ionomers.


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