New Posterior Composite Materials Improving Placement Efficiency
Compendium features peer-reviewed articles and continued education opportunities on restorative techniques, clinical insights, and dental innovations, offering essential knowledge for dental professionals.
April 1, 2012
Volume 33, Issue 4, April 2012
Page(s): pp 292-293
In 1990, 94% of dentists in the United States chose amalgam as their primary intracoronal posterior restorative material.1 By 2010, composite resin restorations had exceeded amalgam by a ratio of 2:1.2 In fact, it is estimated that one-third of U.S. dentists no longer use amalgam, and those that do report a steady decline. This is not an indictment of amalgam, a material that has served dentistry well for more than 100 years. There are many reasons for this relatively rapid and significant change in restorative dentistry. In this author’s opinion, the primary reasons include the following:
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Predictability seems to center on two main issues. The first is postoperative sensitivity to chewing and/or cold. Some dentists believe postoperative sensitivity to chewing is caused by the composite material. When properly placed, however, this is very unlikely with today’s highly filled, low-shrink composite resins. If the patient states that the pain on chewing is sharp and occurs only when hitting a specific spot, the problem is almost always the result of an adhesive error, as opposed to a high restoration, which would hurt every time the patient chews on it. Thus, an intermittent type of postoperative sensitivity is, for the most part, iatrogenic.6 It should be noted that this problem, once erroneously ascribed to the use of the etch-and-rinse technique, has declined significantly in recent years.6 The majority of dentists now respect the precise nature of this particular adhesive process and have learned how to execute the technique properly. Additionally, there has been an increase in the use of self-etch adhesives, with or without selective enamel etch, which avoids some of the potential errors of the etch-and-rinse technique. It is anticipated that the continued development of advanced adhesives will further reduce the incidence of this particular cause of postoperative sensitivity.
Sensitivity to cold following restoration placement is multifactorial and occurs with all kinds of operative procedures and materials. Because teeth restored with composite resin are always sealed with an adhesive, the incidence and duration of this problem should be less with bonded restorations.
The second major concern regarding predictability is the lack of achieving a proper contact. Again, this is not a fault of the composite material but entirely a matricing factor. Fortunately, newly designed sectional matrix systems, introduced in the past few years, as well as newly introduced circumferential and specialty matrices, used with or without a contact former, have virtually eliminated this problem.
Even with the predictability issue resolved, dentists still have to endure the time and effort needed for the actual placement of the composite resin. Current composite resins now yield high physical properties of hardness, flexural strength, and fracture toughness, as well as low shrinkage and low wear. However, these highly filled, highly viscous materials can make it more difficult to achieve intimate adaptation to cavity walls and, because of low depth of cure, require multiple, separately cured layers.
Manufacturers have begun to address this concern by introducing new composite resins and technologies specifically for posterior use, which enable dentists to place restorations faster and easier. In short, these new products reduce the need for multiple layers when placing posterior composite restorations. In addition, some of these new materials and systems allow even better adaptation to cavity walls when compared to previous materials and techniques. These advances have prompted changes and/or additions in the resin chemistry to address depth of cure and shrinkage. These “smart” composites have also necessitated a re-examination of the science of light curing, polymerization kinetics, and shrinkage stress, especially considering the higher output of today’s curing lights.
In 1996 Versluis first questioned whether the incremental filling technique actually reduced overall polymerization shrinkage stress.7 Indeed, his conclusion was that it increased it. Since then, there have been many published papers concluding that placing composite resins in posterior preparations using incremental layers does not appear to be clinically significant with regards to the overall outcome of the restoration.8-13 A recent article examining cuspal deflection published in the Journal of the American Dental Association also confirmed this premise.14 In addition, this paper further validated the trans-tooth illumination technique to improve depth of cure, espoused by Belvedere in 2001.15
It is important to understand that there are two methods used to measure depth of cure. One method, ISO standard No. 4049, cures a column of composite from the top surface. The soft, uncured composite is scraped away from the bottom surface until reaching hard cured material. The depth of cure is then defined by dividing by two the remaining length of cured composite. In this author’s opinion, the ISO standard seems arbitrary and not specifically clinically relevant. A second method, used by many investigators, seems to be more clinically relevant. It defines the depth of cure as the distance from the top of a cured column of composite to a point where the ratio of bottom microhardness to top microhardness is at least 80%. This has been shown to correlate to the carbon conversion ratio, which relates to overall polymerization and is clinically significant.16 It should be noted that some of the newest materials rely on this second method of measurement in reporting depth of cure rather than the ISO 4049 method.
The main objective of these new posterior composite resin materials is to reduce the cured layers of composite the dentist has to place, thereby increasing efficiency. The materials rely on high depth of cure (at least 4 mm or, more recently, 5 mm) along with low shrinkage and controlled stress to allow most preparations to be rapidly filled in just two increments. With at least one material, only one bulk-fill increment is necessary. These features, along with improved, non-slumping, non-sticky sculptability, speed up placement time and simplify the amount of effort required, similar to the use of amalgam. This is something dentists have asked for ever since composite resins were first introduced for posterior restorations.
All of these materials are too new to have long-term clinical trial data; however, they are proving popular with dentists and they continue to grow in the marketplace. Given the number of posterior composites dentists place in practice, this growth would seem unlikely if these new posterior composite materials and technologies were not performing successfully.
Ronald D. Jackson, DDS
Private Practice
Middleburg, Virginia
Related content:
For more information, read Posterior Composite Resin Restorations at dentalaegis.com/go/cced102
Related content:
Go to dentalaegis.com/go/cced110. The page features video commentary on composites from Dr. Louis Rose, editor-in-chief. You'll also find an online archive of Special Reports on a range of topics.
