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Resin modified glass ionomers (Glass ionomer containing restoratives)

Resin modified glass ionomers are glass ionomer cements and restoratives that contain a small amount of polymerizable resin component (in the region of 4.5% to 6%).  These  materials have most of the advantages of glass ionomer materials with the added advantage of water insolubility while setting. They are always dispensed as two-component systems and begin hardening only when both components are mixed together.  The resins included in some systems have dual curing capability, which means that they will cure chemically once the pastes are mixed, but the curing can be accelerated by the use of high intensity light.  The ability to light cure the excess material reduces chair time. 

Resin modified glass ionomers appear to have properties intermediate to conventional glass ionomer materials and resin composites.  They appear to have the advantages of both glass ionomers and resin based composites:

• Command set on application of visible light,
• Good adaptation and adhesion,
• Acceptable fluoride release,
• Aesthetics similar to those of composites,
• Superior strength characteristics when compared with standard glass ionomer restoratives, but inferior when compared with resin-glass restoratives.
• They will chemically adhere to enamel and dentin without the need for acid etching or bonding agents.
• They will chemically adhere to metal as well as to tooth structure.
• They are nearly as biocompatible as glass ionomer and often work well as pulp capping agents or sealants for minor root and furcation perforations during endodontics.

Resin modified glass ionomers have the following drawbacks

• Their setting shrinkage is not much less than that of resin-glass restoratives, which makes them inferior to regular glass ionomers when used as bases under composite or amalgam fillings.
• They have a limited depth of cure compared with resin-glass restoratives.
• They are not recommended for restoration in stress bearing areas of adult teeth since they wear much faster than resin-glass restorations.
• They are NOT recommended for the cementation of all-porcelain crowns or veneers.

• Resin modified glass ionomer cements
  • These are a real success story in dentistry.   They have become the standard material used to cement metal and ceramic based crowns and bridges onto prepared teeth.  Some resin modified glass ionomer cements have dual cure capability, meaning that they will set chemically under a restoration, but the set of  exposed material can be accelerated by the use of a curing light. 
  • They have many of the advantages of glass ionomer cements such as adhesion to tooth structure without bonding techniques, good esthetics, and fluoride release while also having resin's ability to rapidly harden using visible light. 
  • Resin modified glass ionomer cements reduce post operative sensitivity and utilize the resin's water resistance to reduce the likelihood of cement washout. 
  • They prefer to bond to slightly wet tooth structure.
  • They chemically bond to both the metal inside a PFM crown, as well as the calcium rich components of the tooth structure making them extremely effective crown and bridge cements. 
  • They exhibit somewhat less shrinkage on setting than resin based composites. 
  • They are also easy to use and simple to mix, unlike zinc phosphate cement which was the industry standard up until the introduction of these cements.
• Resin modified glass ionomer restoratives
  • Resin modified glass ionomer restoratives lack the ability to resist occlusal wear, but they have become the filling material of choice for deciduous teeth since they can be placed in a field that cannot be kept entirely dry, and without the rituals associated with bonding reagents.
  •  Since they will bond chemically to metal, they can be used to repair broken porcelain over a metal substructure.  They can even be used to place tooth colored veneers over full gold crowns. 
  • Resin modified glass ionomer is more biocompatible than composites and they are becoming popular as pulp capping agents. 
  • They also release fluoride into the tooth structure throughout their service life. 
    • They are especially useful for filling cavities around the gum line.  In this capacity they leach fluoride into the tooth throughout their service life thus reducing the likelihood of recurrent decay.
    • Because of their continual release of fluoride ions, they are also useful in geriatric dentistry, as fillings in patients prone to recurrent caries due to xerostomia.

The Compomers (polyacid-modified resin composites)

A compomer is really a modified composite resin.  These materials have two main constituents: A resin modified with dimethacrylate monomer(s) with two carboxylic groups present in their structure, and a filler that is similar to the Alumino-Fluoro-Silicate present in glass ionomer cements. The filler particles are only partially silanated to help the adhesion of the resin to the glass particles, while at the same time allowing some of the soluble fluoride in the glass to leach out into the tooth structure.  

When first marketed, it was claimed that the carboxylic groups in the resin would allow adhesion to tooth structure without the acid etch bonding technique, similar to glass ionomer cements.  This turned out to be a false assertion.  Even so, compomers are still popular with dentists for filling deciduous (baby) teeth, and, due to their high degree of translucency, they are highly esthetic when used for the repair of cervical (gum line) caries.  They confer a degree of fluoride release into the tooth, although less than that found in glass ionomer and resin modified glass ionomer restoratives.  Thus, at least in the short term, they prevent recurrent decay while allaying parents' concern about the presence of mercury in standard amalgam fillings. 

Compomers do not have the surface durability of standard composite resins, but will wear quite well for the life of a deciduous tooth.  Unlike glass ionomer and resin modified glass ionomer restorations, they do NOT adhere to tooth structure without an acid etch bonding technique.   They are esthetically pleasing and seem to resist recurrent decay for several months after placement when used to fill cavities near the gum line.

•  paste compomer restorative (filling) material; These materials are excellent tooth colored filling materials when used on front teeth in non stress bearing areas, such as for filling cavities at the gum line, or in larger restorations if they are fully supported by natural tooth structure and do not involve incisal or occlusal surfaces.  They are especially good on the buccal or labial (front) surfaces of teeth where esthetics is extra important.  They are often used to cover exposed, sensitive root structure on both anterior and posterior teeth.  

In spite of the fact that they are less wear resistant than regular composites, some dentists use light activated compomers to  fill deciduous (baby) teeth due to their extended fluoride release, and also to allay parents' fears about the mercury in amalgam fillings.  The deciduous teeth generally exfoliate (fall out) before the wear becomes a problem.  Compomers are also useful in geriatric dentistry since oral hygiene is often poor in elderly patients, and they frequently suffer xerostomia (dry mouth).  The combination of poor oral hygiene and dry mouth causes rampant decay in these patients, and the release of fluoride at the tooth/restorative junction can be helpful to prevent recurrent decay.  While once popular as a general restorative, they have fallen out of favor, and my own experience with them has shown them to have a limited shelf life. 

• Flowable compomers; These are like the paste compomer restorative, but they contain much more of the unfilled resin.  They are used in the same fashion as flowable composites, except they are rarely used in stress bearing areas such as the occlusal surfaces of adult teeth. 

Next page==>Achieving Radiopacity in restorative materials

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