Written by Jose-Luis Ruiz, DDS Sunday, 28 February 2010 19:00
In this interview with our editor-in-chief, Dr. Damon Adams, Dr. Ruiz explains the importance of understanding and using new materials correctly. He will share important clinical tips, explaining the benefits of what he likes to call “supragingival dentistry,” specifically for indirect restorations like veneers, onlays, and all-ceramic crowns.
Advances in dental materials have truly changed the way we practice dentistry. New dental adhesives, restorative composites, cements, impression materials, porcelain systems, as well as digital impression and CAD/CAM technology are helping make amazing changes in the way that we practice. Some new materials may present certain challenges and require learning new techniques. Sometimes the changes can seem radical and a bit scary, especially if these new materials are used incorrectly and negative results occur. However, when used properly, most of these new materials and techniques are revolutionizing dentistry, resulting in many benefits to the patient and doctor alike.
Dr. Adams: You have previously stated that using nonmetal indirect restorations with supragingival techniques is easier and more predictable than doing traditional restorations such as PFMs with subgingival margins. Is that correct?
Dr. Ruiz: I am convinced that nonmetal supragingival dentistry is easier, more predictable, and healthier for our patients than traditional dentistry. Knowing that the statement is controversial, let’s look at the evidence. Dental laboratories report that gold onlays are rarely used; the reason is that they exhibit unnatural aesthetics and therefore patients refuse them. Let’s also think about the most used indirect restoration in dentistry, the PFM crown, which requires subgingival margins when traditionally designed. Every dental school and textbook teaches that a crucial step in the technique of these restorations is the placement of the restorative margins subgingivally. This is necessary to hide an unaesthetic margin. The increase in difficulty, potential complications, and unpredictability this routine procedure brings to the table is significant. It starts with a difficult preparation, with the need to place a preparation margin subgingivally, yet in an atraumatic style.
Dr. Adams: How does the concept of supragingival dentistry relate to the clinical realities around tissue control issues and the proper use of impression materials?
Dr. Ruiz: When done correctly, traditional subgingival preparations require that we first prepare an initial equagingival preparation margin. Then retraction cord is placed in order to expose subgingival tooth structure, and the margin is placed subgingivally. After this difficult procedure, a second, smaller cord must be placed in order to take a proper impression of the subgingival margin. This procedure, along with taking an excellent impression, is technically very challenging; in fact, it is one of the most difficult and unsuccessful procedures in dentistry, as dental technicians around the country can attest to. In his lectures, Dr. Christensen found that interviewed dental laboratory owners report that as many as 90% of the impressions received have less-than-adequate margin registration/definition.
Dr. Adams: So that brings us back to the supragingival alternative, doesn’t it?
Dr. Ruiz: Yes, in my opinion, the best solution is to implement the use of supragingival dentistry techniques whenever possible. Supragingival dentistry is a style of dentistry which uses modern materials and techniques such as enamel preservation and margin elevation. It also involves the proper use of the contact lens effect which employs an important characteristic of many ceramic systems (nonmetal restorations)─translucency. This allows us to intentionally keep restorative margins supragingival while still achieving excellent aesthetic results. This in turn helps to make dentistry truly easier, more predictable, aesthetic, and healthier for the patient.
Dr. Adams: Can you address the issue of translucency found in all-ceramics versus traditional metal-ceramics in a bit more detail?
Dr. Ruiz: Sure! Translucency allows for an easier blend of the restoration to the tooth because it allows some light to go through into the tooth and root. Teeth are like fiber-optic rods, in that when light hits the crown it goes down the root. We also know that some ceramic systems’ (nonmetal) restorative materials are more translucent than others by their very nature, based on the materials from which they are made and how they are manufactured.
Dr. Adams: You also said that modern ceramic restorative materials are available in various translucencies. Clinically speaking, how do you decide which material should be used in a particular case?
Dr. Ruiz: This a great question! As previously discussed, one of the most important characteristics of all nonmetal restorations is translucency. Translucency allows for an easier blend of the restoration margin to the tooth, because it allows some light to go through into the tooth. Translucency does vary dramatically depending on the porcelain system. Feldspathic porcelains, and pressed/ layered porcelains, tend to be very translucent. Layered and pressed feldspathic porcelain can be one of the most aesthetic options available, and for that reason it is an ideal material choice for porcelain veneers. Also, these materials have some great advantages when used for nonmetal onlays or inlay/onlays. Crowns using alumina and zirconia copings are always more opaque, yet can be made to be translucent using layering porcelains…just to a lower degree of translucency. And then you have lithium disilicate, a very promising material that has historically lain kind of in the middle. Recently, it has been further developed to include several different levels of translucency/ opacity. For example, it is now available in a high translucency (HT) version (e.max HT [Ivoclar Vivadent]), which can be used for very thin 0.3 mm veneers. It can also be used as a monolithic restoration, giving it strength and acceptable aesthetics. It is available as a pressable ingot option, or as block, for the E4D (D4D) and E4D LabWorks CAD/CAM system, which is the version I am currently using. It is also available for the CEREC (Sirona) CAD/CAM in-office and CEREC InLab systems. Lithium disilicate is a very promising material. We need to keep in mind that usually, the more translucent the material, the weaker it is, and vice versa; this is very important when choosing a cementation material and technique.
Dr. Adams: Knowing how critical that proper adhesion is to success with these nonmetal materials, please tell us how you decide which bonding system to use, and what’s new in regards to dental adhesives?
Dr. Ruiz: There is no doubt that predictable clinical success with bonding systems is indispensable for the overall success of nonmetal restorations. There is a tremendous amount of controversy and passion about this subject. Many academics and educators have stated that the fourth generation, total-etch bonding systems like OptiBond FL (Kerr) and Scotchbond Multi-Purpose (3M ESPE) are state-of-the-art, due to their long track records, very high bond strengths, and excellent marginal sealing abilities. All of the above are very important characteristics, and undoubtedly these bonding systems are excellent, when used by experienced clinicians who are good at using them. The problem is that sometimes these advocates of total-etch techniques forget the very real problem of postoperative sensitivity and technique complexity, which can be a problem with these bonding systems. There is no more frustrating problem in dentistry than when we perform a beautiful direct or indirect tooth color bonded restoration, and weeks later, the patient continues to complain of postoperative sensitivity. Clinical experience has shown that although total-etch bonding systems can be predictable, if used meticulously, they are more technique-sensitive than the self-etch systems.
Dr. Adams: Everyone seems so concerned about bond strengths; however, there is more to adhesive success than just that, right?
Dr. Ruiz: Yes, many clinicians incorrectly look at bond strength as the primary quality of a bonding system. However, from a clinician’s perspective, a good bonding system must have 4 important characteristics: (1) it must provide excellent adhesion and seal, (2) it must be durable, (3) it must be associated with low postoperative sensitivity, and (4) it must be easy to use. Some self-etch bonding systems fulfill all of these requirements, especially the 2-bottle sixth-generation types like Clearfil SE Bond, Clearfil SE Protect (both from Kuraray). All-in-one bottle self-etch seventh-generation systems are rapidly improving; Futurabond (VOCO) is a great example. Self-etch bonding systems have proven themselves to be an excellent choice. There is plenty of literature evidence showing that bond strength to dentin is equally as high with self-etch, and there is also evidence that the bond durability to dentin may even be better for self-etch versus total etch.
Dr. Adams: Jose-Luis, could you remind us what the advantages are in keeping restoration margins supragingival as related to cementation, and what is your take on newer cement materials and techniques?
Dr. Ruiz: Yes, Damon, it is a good idea to remember that the cementation protocol varies widely from one material to the other. It depends on the strength of the restorative material, the location of the gingival cavo-margin and the aesthetic needs. Feldspathic porcelain, layered and pressed, must be cemented with resin cement because this material is intrinsically weak.
Dr. Adams: You have made the point that keeping the margins supragingival is advantageous, but sometimes caries/fractures/ old restorations extend subgingivally. How do you suggest that these situations be handled?
Dr. Ruiz: You are totally right. Sometimes we have to deal with subgingival margins, and to me there are 2 ways to handle them. One, if the margin is subgingival all around, either because the subgingival caries are almost all around the tooth, which is rare, or when replacing a PFM crown with already subgingival margins; then I will choose to place an all-ceramic crown, most likely a zirconia. This will allow me to cement the crown with an RMGI cement like FujiCem, which is much more forgiving with moisture or contamination, as previously explained. The most common situation that I face clinically is a mesial or distal margin which is below the gingiva due to caries, an old amalgam, or other restoration. In these situations, using a toffelmire matrix band, I will elevate the margin to be 1.0 mm above the gingiva with either RMGI restorative materials like Fiji Filling LC (GC America) or Ketac Nano (3M ESPE); or I will elevate the margin similar to doing a Class II composite using a bonding system like Futurabond (VOCO), then a small layer of the highly-filled (80%) Grandio Flow (VOCO) and then a layer of Grandio (VOCO). After elevating the margin, I will refine and finish my onlay preparation which will now have all supragingival margins. Of course, impression and cementation of this restoration will be a cinch (Figures 6 to 9). There is strong evidence in the literature pointing out that subgingival margins perform better with RMGI restorative material due to the release of fluoride, thereby decreasing the chance of secondary caries.
Dr. Adams: Can you please comment briefly with regard to the life expectancy and failures with nonmetal restorations?
Dr. Ruiz: That sure is an important question. For the past 10 years, I have been doing nonmetal indirect restorations almost exclusively. In addition with regard to direct restorations, I haven’t done an amalgam in more than 15 years, including in second molars. These days, I rarely prepare a full crown of any type, and quite honestly, I can count with my fingers how many people have requested gold restorations of any type. So, what is the longevity of these restorations in my practice? My personal experience has been as a clinician practicing in the same place for almost 18 years. This has allowed me to witness my own successes and failures over quite some time. When I compare the problems and failures I had with traditional mechanically retained, subgingival dentistry, to the past 10 years with nonmetal supragingival dentistry, my life is easier with less complications and fewer failures. And although I have published a retrospective review of my cases with the assistance of Dr. Gordon Christensen and other clinicians, showing overwhelming success, it is of greater importance to look at what the literature shows. In the anterior area of the mouth, the profession is quite comfortable with all-ceramic restorations, and the literature is replete with success with these restorations. In the posterior area of the mouth, the results are less positive and conflicting; nevertheless, there is ample literature showing excellent long-term success with porcelain onlays at 8-plus years, when done correctly. How long do PFM crowns last? Some people have PFM crowns that have lasted 20 years or more, but looking at things from the realistic standpoint, PFM crowns in the United Span have an average lifespan of about 8 years, based on some insurance surveys. All-ceramic indirect restorations in the posterior area of the mouth should last as long, or longer, than PFM crowns, when we take in to consideration that they are also more repairable.
Dr. Adams: Jose-Luis, I want to sincerely thank you for taking the time to share your opinions, experiences, and knowledge with our readers. Your dedication to, and leadership within, the dental profession is commendable.
Disclosure: Dr. Ruiz reports no conflicts of interest.
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