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New Technology
BV DR. RALPH W. PHILLIPS
O t s critics not withstanding, den tal amalgam today remains the restorative material of choice in the United States. The most recent ADA research shows that amalgam is used to fill roughly 80 percent of dental caries. It’s cost effective, easy to work with and has a proven track record dating to the early days of American dentistry. But there are times when it is not entirely successful. A chief reason for restorative failure with amal gam, when it occurs, is secondary or recurring caries. Partly because of this problem, increasing numbers of dentists are complementing the tra ditional advantages of amalgam with those of a newer material: a light-cured glass ionomer liner/base. In the early 1970s, silicate cements failed as restorative materi als because of their high solubility and pulpal toxicity. Nevertheless, dentists recognized one major advan tage silicates had over conventional cem ents-they allowed little or no secondary caries formation under neath. Since the ‘70s a class of materials that evolved from the silicate cements—glass ionomers—has pre served the cariostatic advantage of the silicates while dodging their pit
falls and adding certain other bene fits. These added benefits include: — good adhesion and clinical retention; -> biocompatibility; — radiopacity; — light curability, available in certain products. This light curability, which gives the newer glass ionomers a demand set and makes them more userfriendly, happens through a second setting reaction, independent of the ionic crosslinking mechanism char acteristic of all glass ionomers. 3M’s Vitrabond light cure glass ionomer liner/base was the first commercial product of this type to hit the market, followed by Kerr’s XR-Ionomer cavity liner system. Other manufacturers were consid ering similar products at press time. In a traditional amalgam restoration, calcium hydroxide has long been used-often with over coatings of copal varnish—as the base for the preparation. Calcium hydroxide’s main advantage is its capacity for stimu lating the growth of secondary or reparative dentin. Some researchers suggest this can hap-
159
pen when cal cium hydroxide is applied to a thin layer of remaining dentin, yet oth ers believe that Dr. Phillips is a secondary research professor emeritus of dental dentin forms materials from the only when there Indiana University dental school. He is pulpal expo has received such sure. honors for his work as the Gold Medal A disadvan Award of the Pierre tage of calcium Fauchard Academy; hydroxide is the the William J. Gies Award from the chance it will American College of crack when sub Dentists; and the William Souder jected to the Award from the crushing forces international Associ that occur ation for Dental Research, of which under the amal he is past president. gam restoration Dr. Phillips is cur rently a member of or while amal the U.S. Food and gam is being Drug Administra packed into tion’s dental prod ucts panel. preparation. Calcium hydroxide has rela tively low compressive strength (on the order of 1,500 to 4,400 pounds per square inch). Moreover, its high solubility can lead to washout before corrosion of the amalgam potentially reduces leakage. These factors can combine to spur an ingress of oral fluids that, in turn, foster secondary decay. Though calcium hydroxide remains the standard in cases of pulpal exposure, more and more dentists are turning to a glass ionomer liner-base—both as a seal ing layer over the calcium hydrox ide placed over pulpal exposures or used alone when there is at least a thin layer of remaining dentin.
mrt.
^ ^ ep en d in g on the glass ionomer’s powder-to-liquid ratio, the material can be applied as a liner; that is, relatively “wet,” using a ball-ended instrument to flood the
160
floor of the cavity. It also can be applied as a base; that is, as a thicker, more viscous layer that is tamped into place. Glass ionomer liners and bases have low solubility and are not subject to washout. They bond well to dentin and help seal it from microleakage, which helps prevent post-operative sensitivity. The sus tained fluoride release further reduces recurrent decay along with protecting the underlying pulp. Unlike calcium hydroxide, lightcured glass ionomer liner/bases are rigid and crack resistant—and their compressive strength exceeds the demands of placement under amalgam. For example, the com pressive strength of 3M’s Vitrabond liner-base is said to be 11,000 to 17,000 PSI. ^ ^ n addition, various tech niques—from the use of radiopaque glass to the insertion of metallic particles—can be used to make glass ionomers radiopaque. Dentists reluctant to incorporate glass ionomer materials into their practices often cite a lack of famil iarity or inadequate training in their use. Still others cite a lack of curing light in their operatory as the main reason for not using a glass ionomer liner-base under amalgam. The emphasis on light curing is understandable, given the reputa tion glass ionomers have gained for being “technique sensitive.” It’s a reputation that still holds true for applications where esthetic con cerns are paramount. The working time for non-light-cure glass ionomers can be as short as one minute. And before glass ionomers set completely, they are vulnerable to both moisture and dehydration. Either of these conditions can com promise the physical characteris
tics of the restoration—not to men tion spoiling the esthetics. But don’t despair. Products that incorporate a light cure setting reaction have taken a technological leap toward making glass ionomers easier to handle and use. These new products provide longer working times on the front end, while also allowing for a speedy “demand set” once the material is in place. ^ ^ h e procedure for applying a light cure glass ionomer as a liner/ base under amalgam is as follows: —prepare the cavity for amalgam restoration; «• isolate it and place matrix band and wedge; —mix the liner base and apply this to cover all exposed dentin and to block out undercuts from caries removal; —light cure and place retentive grooves; —use an adhesive or copal varnish at this point (optional); •» place, condense and finish the amalgam in the conventional manner. Through advances such as light curing, the new generation glass ionomer materials promise to han dle better, exhibit less sensitivity to both moisture contamination and desiccation and save clinicians’ valuable chair time.
O t s critics not withstanding, den tal amalgam today remains the restorative material of choice in the United States. The most recent ADA research shows that amalgam is used to fill roughly 80 percent of dental caries. It’s cost effective, easy to work with and has a proven track record dating to the early days of American dentistry. But there are times when it is not entirely successful. A chief reason for restorative failure with amal gam, when it occurs, is secondary or recurring caries. Partly because of this problem, increasing numbers of dentists are complementing the tra ditional advantages of amalgam with those of a newer material: a light-cured glass ionomer liner/base. In the early 1970s, silicate cements failed as restorative materi als because of their high solubility and pulpal toxicity. Nevertheless, dentists recognized one major advan tage silicates had over conventional cem ents-they allowed little or no secondary caries formation under neath. Since the ‘70s a class of materials that evolved from the silicate cements—glass ionomers—has pre served the cariostatic advantage of the silicates while dodging their pit
falls and adding certain other bene fits. These added benefits include: — good adhesion and clinical retention; -> biocompatibility; — radiopacity; — light curability, available in certain products. This light curability, which gives the newer glass ionomers a demand set and makes them more userfriendly, happens through a second setting reaction, independent of the ionic crosslinking mechanism char acteristic of all glass ionomers. 3M’s Vitrabond light cure glass ionomer liner/base was the first commercial product of this type to hit the market, followed by Kerr’s XR-Ionomer cavity liner system. Other manufacturers were consid ering similar products at press time. In a traditional amalgam restoration, calcium hydroxide has long been used-often with over coatings of copal varnish—as the base for the preparation. Calcium hydroxide’s main advantage is its capacity for stimu lating the growth of secondary or reparative dentin. Some researchers suggest this can hap-
159
pen when cal cium hydroxide is applied to a thin layer of remaining dentin, yet oth ers believe that Dr. Phillips is a secondary research professor emeritus of dental dentin forms materials from the only when there Indiana University dental school. He is pulpal expo has received such sure. honors for his work as the Gold Medal A disadvan Award of the Pierre tage of calcium Fauchard Academy; hydroxide is the the William J. Gies Award from the chance it will American College of crack when sub Dentists; and the William Souder jected to the Award from the crushing forces international Associ that occur ation for Dental Research, of which under the amal he is past president. gam restoration Dr. Phillips is cur rently a member of or while amal the U.S. Food and gam is being Drug Administra packed into tion’s dental prod ucts panel. preparation. Calcium hydroxide has rela tively low compressive strength (on the order of 1,500 to 4,400 pounds per square inch). Moreover, its high solubility can lead to washout before corrosion of the amalgam potentially reduces leakage. These factors can combine to spur an ingress of oral fluids that, in turn, foster secondary decay. Though calcium hydroxide remains the standard in cases of pulpal exposure, more and more dentists are turning to a glass ionomer liner-base—both as a seal ing layer over the calcium hydrox ide placed over pulpal exposures or used alone when there is at least a thin layer of remaining dentin.
mrt.
^ ^ ep en d in g on the glass ionomer’s powder-to-liquid ratio, the material can be applied as a liner; that is, relatively “wet,” using a ball-ended instrument to flood the
160
floor of the cavity. It also can be applied as a base; that is, as a thicker, more viscous layer that is tamped into place. Glass ionomer liners and bases have low solubility and are not subject to washout. They bond well to dentin and help seal it from microleakage, which helps prevent post-operative sensitivity. The sus tained fluoride release further reduces recurrent decay along with protecting the underlying pulp. Unlike calcium hydroxide, lightcured glass ionomer liner/bases are rigid and crack resistant—and their compressive strength exceeds the demands of placement under amalgam. For example, the com pressive strength of 3M’s Vitrabond liner-base is said to be 11,000 to 17,000 PSI. ^ ^ n addition, various tech niques—from the use of radiopaque glass to the insertion of metallic particles—can be used to make glass ionomers radiopaque. Dentists reluctant to incorporate glass ionomer materials into their practices often cite a lack of famil iarity or inadequate training in their use. Still others cite a lack of curing light in their operatory as the main reason for not using a glass ionomer liner-base under amalgam. The emphasis on light curing is understandable, given the reputa tion glass ionomers have gained for being “technique sensitive.” It’s a reputation that still holds true for applications where esthetic con cerns are paramount. The working time for non-light-cure glass ionomers can be as short as one minute. And before glass ionomers set completely, they are vulnerable to both moisture and dehydration. Either of these conditions can com promise the physical characteris
tics of the restoration—not to men tion spoiling the esthetics. But don’t despair. Products that incorporate a light cure setting reaction have taken a technological leap toward making glass ionomers easier to handle and use. These new products provide longer working times on the front end, while also allowing for a speedy “demand set” once the material is in place. ^ ^ h e procedure for applying a light cure glass ionomer as a liner/ base under amalgam is as follows: —prepare the cavity for amalgam restoration; «• isolate it and place matrix band and wedge; —mix the liner base and apply this to cover all exposed dentin and to block out undercuts from caries removal; —light cure and place retentive grooves; —use an adhesive or copal varnish at this point (optional); •» place, condense and finish the amalgam in the conventional manner. Through advances such as light curing, the new generation glass ionomer materials promise to han dle better, exhibit less sensitivity to both moisture contamination and desiccation and save clinicians’ valuable chair time.