Preservation-based approaches to restore teeth with amalgam, resin or a combination of materials
PURPOSE: A systematic assessment of the status quo of dental amalgam, resin-based composites and glass ionomer restorations for carious lesions as it applies to new concepts. To identify an approach to managing carious lesions based upon selected advantages of dental amalgam, resin-based composite, and glass ionomer technology applied to what is termed ‘preservation-based’ approaches to restoring teeth.
MATERIALS & METHODS: This paper did not have any true materials or methods. It was basically a review of information collected from previous research. The author has divided each concept into individual topics. I will describe each one separately.
AMALGAM: It is still used by more than 90% of dentists in North America. It has a potential half-life of up to 25 years. Although it does not have any caries resistant properties in itself, it will corrode in the oral environment and the corrosion products will seal the margins against microleakage. However, the estimated longevity of amalgam restorations decreases, as the restoration size increases. For example, it is 13.5 years for a 1 surface, 9.7 years for a 2 or 3 surface and 6.1 years for a 4 or 5 surface restoration
Provides strengthening of teeth added retention for the restorations, better marginal adaptation, and reduced secondary caries. However, there are no long-term studies greater than 2 years available.
Resin used to seal amalgam restorations:
Application of pit and fissure sealants is an effective method for maintenance of the marginal integrity of amalgam restorations and preventing recurrent caries. Results demonstrate that conservative cavity preparation with sealing for prevention is a successful technique, which conserves valuable tooth structure. This concept makes it no longer necessary to remove all unsupported demineralized enamel around the cavity margin
Cusp / Tooth Fracture:
Main negative feature of amalgam has been an increased risk of cusp fracture. The width of the restoration has been the predominant factor. Laboratory data indicate that fracture tendency could be reduced by ‘bonding’ amalgam with resin or glass ionomer adhesives. This provides a more uniform distribution of forces.
Use for posterior teeth has been on the rise for the last 25 years. The smaller the composite restoration, the greater it’s longevity and serviceability. Isolated lesions should be treated individually and not connected. No attempt should be made to reduce the level of the gingival floor beyond the lesion. Stresses are highest in the area of the gingival floor. No isthmus cut is preferred. Occlusal beveling is not required due to the enamel rod direction. All internal line angles should be rounded. It is imperative to record preoperative occlusal contact areas in centric to ensure they are kept off the restorative material. A method to seal damaged enamel margins is to etch and reseal.
Packable (Condensable): (the term packable is preferred over condensable):
Better handling characteristics and higher physical properties than previous micro hybrid composites. Can be cured to a depth of 5mm with a conventional light cure unit. However, shear bond strength was much lower when polymerized in 5mm increments than in 2mm increments. Composites can be selected as an alternative to amalgam, but they are neither equal nor better than dental amalgam. For posterior composites, the price paid for improvements has included a significant increase in a fracture, especially bulk fractures of restorations. Studies show that the packable composites also could not seal the gingival floor adequately. The composites of today are being replaced at a rate of 1 of every 5 restorations due to fracture and new or recurrent caries.
COMPOSITE VS. DENTAL AMALGAM:
To date, there are still no tooth-colored materials that are as easy to use, available at the same cost, show proven biocompatibility, and have the same chemical durability as amalgam. The excellent mechanical properties, the fit and the coefficient of thermal expansion are the main reasons for the long-term durability of amalgam. The long-term bonding capability of composites is mostly unknown and caries susceptibility remains a problem. A recent Swedish study showed that the longevity of composites was about 6 years. The same study showed that amalgam restorations lasted 9 years. Failure was attributed to secondary caries, fracture, poor appearance and/or marginal discrepancies. Similar results have been reported in the U.K. The majority of class II composite failure is microleakage at the gingival margin. What is more, making a tight contact area has been a major problem. Also, wear of the posterior composites is observed at the proximal contact areas where stresses are the highest.
Indirect (Luted) Restorations:
A 3-year study showed that breakage rate was 3 times greater for indirect resins than for direct resins. Molar restorations performed worse than the premolar restorations.
Two and Three Viscosity Composites:
Utilizing composites of 2 or 3 different viscosities have been proven effective in increasing strength and adaptation. Flowable, or light body composites, easily flow into and adapt to the line angles of class II preparations. The microfil, hybrid, and micro hybrid universal resins are considered medium body. The new packable composites can be termed heavy body. Placement technique involves applying a 0.5 to 1.0mm layer of a flowable light body in the proximal box at the gingival margin and across the entire pulpal floor. The entire dentin is then replaced with use of the heavy body. The enamel is then replaced with a single unit of translucent medium body. However, if a single increment connects opposing walls in a class I or II posterior restoration, the resulting high C-factor ratio (the ratio of the bonded to unbonded walls in a restoration) can further increase shrinkage stress. Also, there is no benefit one way or the other for the use of autocured and light cured composites other than technique advantage. Both materials still will shrink towards the fixed boundaries.
AMALGAM / COMPOSITE COMBINATION:
Such restorations consist of placing amalgam in the bottom of the proximal box where no gingival enamel remained and filling the remaining cavity with a direct or luted esthetic restoration. It was also demonstrated that light curing a dual cure adhesive for 10 seconds before placing the amalgam has resulted in the highest amalgam to dentin shear bond strengths (10 MPa)
Sandwich (Lamination) technique with Glass Ionomer:
Glass Ionomer is the material of choice for tunnel and sandwich restorations. It provides conservative treatment and assists in remineralization while maintaining the esthetic appeal. The most significant characteristic is its ability to bond chemically to dentin and enamel, its long-term fluoride release without high solubility and its ability to reabsorb fluoride ions and therefore act as a fluoride reservoir. The principle negative feature is its susceptibility to brittle fracture. It is unable to withstand undue occlusal loading.
Tunnel (Internal Occlusal Fossa) Restorations:
The most conservative approach for a lesion that is at least 2.5mm apical to the crest of the marginal ridge utilizes this approach. It is through the occlusal fossa, so removal of enamel is minimal. The material of choice is either glass ionomer or resin-modified glass ionomer cement. Indications are limited and restrictive for class II lesions. No comprehensive study is available at this time.
The combination of the 2 materials, where the composite is laminated over glass ionomer, is useful in situations where the occlusal load is heavy and there is a lack of enamel to provide adhesion to composite. Simply place a glass ionomer base in the gingival half of the proximal box and laminate over that with either composite or amalgam. The result will be a release of fluoride and a resistance to plaque formation. Having a stronger material laminated over it will compensate the physical limitations of the glass ionomer. It was also found that the combination of glass ionomer and composite allowed significantly less leakage than the glass ionomer or composite alone. Rein modified glass ionomer introduced in the early 1990’s, are less technique sensitive and show equal fluoride release and improved mechanical and physical properties compared with conventional glass ionomer.
CHOOSING BETWEEN RESTORATION MODALITIES:
Amalgam, composite resin and glass ionomer cement are the most widely used materials in a general dentistry practice. However, there is still no adequate, economic alternative for dental amalgam as a restorative material for moderately sized lesions in a high load bearing area. Glass ionomer is the only material currently available capable of true diffusion-based chemical adhesion to tooth enamel and dentin through an ionic exchange. The main limitation is its low fracture resistance. As a result, glass ionomer cannot be used alone to withstand undue occlusal load. The concept of using 2 or more materials to form a final restoration enables us to make the most of the physical and esthetic properties of each material, with maximum preservation.
DISCUSSION: Neither ‘wait and watch’ nor ‘extension for prevention’ is acceptable nowadays. Caries needs to be treated as an infectious disease. In preservation-based dentistry, restorations cannot be considered as a cure for caries. Such interventions include fluorides, sealents, enameloplasty and conservative restoration techniques. Modern conservative cavity designs should be universal. The 2 basic principles of outline form are: 1)all undermined enamel should be removed and 2)all margins should be placed in areas of least caries susceptibility. The principle of maximum tissue preservation must be respected.
SUMMARY/COMMENTS: ‘Extension for prevention” as proposed by G.V. Black is no longer accepted. It has been replaced by the standard of ‘prevention of extension of decay.’ The restoration is made to fit the requirements of the tooth, instead of the tooth being made to fit the requirements of the restoration. I felt that this was a well-written article. The information provided was very applicable to what we practice today and very concise as well. I would recommend this article for anyone who would like a quick reference guide to the more common dental materials we use and their usefulness along with their strengths and weakness.
Originally published at alfredkhallouf.com on June 1, 2016.