How Restorations Are Chosen

 

           The types of restorations and materials used to restore missing teeth and those with decay, fractures or defective older restorations are chosen based on the teeth to be restored or replaced and the tooth surfaces involved. There are two kinds of restorations: direct and indirect. An example of a direct restoration would be what is commonly called a "filling". Materials used for direct restorations include; silver amalgam, composite resin and gold foil. Examples of indirect restorations are; crowns (sometimes called caps), bridgework, inlays, onlays and veneers. Cast metals (including gold), porcelain and glass polymer (Cristobal for example) are materials used for indirect restorations. Each type of restoration and material has specific indications for use.

DIRECT RESTORATIONS
           The two most commonly used filling materials are silver amalgam and composite resin. Silver amalgam is a metal alloy (compound) that contains small amounts of several other elements in addition to silver that help give the material its unique properties. Composite resin materials (often called bonding) are essentially made of plastic. Exhaustive studies by both the Centers for Disease Control and the National Institute of Health have found neither substance to be at all deleterious to humans except in the minuscule number of allergic reactions reported to one of the ingredients in either material. For example, in over one hundred years of silver amalgam use in this country, less than fifty cases of allergy have been reported. Gold foil is used much more sparingly than the previously mentioned substances even though it is safe and effective because its cost and difficulty to remove in the instance of recurrent (new around the filling) decay make it less practical.

           When a direct restoration is placed, the choice of material used is based on the type and surface of tooth being filled. Teeth are classified as either anterior (front) or posterior (back). In the example of eating an apple, the front teeth are used to incise (cut into) the apple and then the piece removed is masticated (ground up) by the back teeth. This is because front teeth are narrower and sharper than back teeth which are wider and blunter. As is obvious from this example, posterior teeth do much more of the work in chewing and endure much more stress than anterior teeth do. The occlusal (chewing) surfaces of back teeth bear this heavy stress, which is known as a compressive force.

 

                

     Rampant decay of the lower front teeth is restored... ...with bonded fillings which are most appropriate for front teeth.



           In general, silver amalgam is harder than composite resin. For this reason, composite resin wears notably more under compressive forces. Those composite resins that are as hard as or harder than silver amalgam tend to wear away the surfaces of the opposing natural teeth that they meet in the bite. No other material either lasts longer, is kinder to opposing teeth, is more forgiving of the conditions under which it is placed, is more cost effective or is easier to place for direct restorations than silver amalgam. Composite resin also shrinks somewhat (2% - 4%) at the margins when it is placed. Because the compressive forces of mastication can pack food particles into the voids left by this shrinkage, recurrent decay around composite resin fillings on the chewing surfaces of back teeth is often much more aggressive. For these reasons and the example noted, silver amalgam is the best material for the direct restoration of the chewing surfaces of permanent back teeth.  Should you request a composite resin filling for the chewing surface of one of your back teeth, Dr. McArdle will do this for you, but with no guarantees. The chewing surfaces of primary (baby) back teeth may be directly restored with composite resin as their life span is limited and the longevity of restorations in primary teeth is not critical. The force that direct restorations sustain when they are not on the chewing surfaces of back teeth (when on the sides of teeth or at the gumline) is called a shear stress. Studies (see at the bottom of this page) have shown that composite resins hold up better against this type of force. Composite resin is the best material for filling the non-chewing, at the gumline surfaces of posterior teeth (known as Class V fillings). For esthetic reasons, bonding is used to directly restore front teeth because it is tooth colored. Direct restorations are used when sufficient tooth structure remains to support them. Fillings depend on teeth to hold them in, so things go wrong when a tooth is more filling than tooth. When this situation arises, or when missing teeth need to be replaced, an indirect restoration is called for.

 

This molar tooth broke less than 2 years after being directly restored with bonding, despite claims that such bonding prevents tooth fractures. Dark spots at the filling's margins, away from the fracture, are areas of recurrent decay where the bonding shrunk on placement and subsequently food particles were trapped.


INDIRECT RESTORATIONS
           There are several reasons for placing indirect restorations. Most often indirect restorations are used when a large volume of a tooth's original structure is lost due to being extensively filled, decayed or fractured as when one of a back tooth's cusps (support pillars) is lost. The presence of obvious cracks in conjunction with considerable filling materials in a tooth is also indicative of the need for crown placement. Fillings depend on teeth to hold them in whereas crowns hold teeth together. Another reason involves esthetics. Severely discolored or misshapen front teeth may have their appearance improved with indirect restorations that can be shaded and shaped as desired. Tooth colored inlays made of Cristobal may be placed on the chewing surfaces of back teeth instead of silver amalgam. Glass polymer displays many of the advantages of silver amalgam. An additional benefit of Cristobal is that it is bonded in place. This adhesive placement binds the inlayed tooth together to make it more resistant to fracture. Silver amalgam is retained mechanically by contrast. To replace missing teeth, bridges are used when the remaining anchor teeth are extensively restored. When anchor teeth are minimally restored, precarious or bridgework would be long span, implants supporting crowns are used. Veneers and 3/4 crowns are much like crowns on front and back teeth respectively in that they replace more than half of a tooth's original structure, however their design leaves much natural tooth above the gumline. This makes for both more margin and more marginal exposure (above the gumline) with these than with a crown. The more margin a restoration has and the more exposed that margin is increases its chances of sustaining recurrent decay. Because of this, Dr. McArdle does not place veneers or 3/4 crowns.

 

3 years after being placed, this indirect glass polymer restoration is still

supporting an intact tooth and has no signs of any recurrent decay.



           Materials used for indirect restorations are chosen for functional, tissue compatibilty and esthetic reasons. Because of the heavier chewing loads that they undergo, posterior teeth need the added strength of metal based crowns and bridges. These types of restorations may be covered in porcelain for esthetics. Dr. McArdle uses porcelain fused to metal crowns made of Captek, a material that produces the most beautiful results from this type of indirect restoration and is also kindest to the gums. If the patient exhibits tooth wear indicative of bruxism (grinding or clenching of the teeth), crowns or bridges with all metal chewing surfaces should be used because bruxers often fracture porcelain. Front teeth that have not been endodontically treated (root canalled) can have all porcelain crowns placed. Porcelain alone is not quite as strong as metal covered in porcelain, but it can be the most life-like material available. Root canaled teeth require metal posts for support that show through belleGlass. Anterior short span bridgework may be made of all porcelain, but longer bridges and those placed for bruxers should be of the metal based type. Inlays can be of either metal (usually gold) or belleGlass, but the latter is more cost effective and strengthens teeth as noted above.

 

 

The huge, older fillings in this patient's back teeth were deteriorating badly and a fracture had occurred. The teeth were crowned to protect them against fracture and restore their original estehtics.

 

        

These old crowns looked lifeless and caused receding and irritated gums. When replaced with Captek, they looked beautiful with healthy gums one year later.


Neme AL, Evans DB, Maxson BB. Evaluation of dental adhesive systems with amalgam and resin composite restorations: comparison of microleakage and bond strength results. Oper Dent. 2000 Nov-Dec;25(6):512-9.


University of Detroit Mercy School of Dentistry, Department of Restorative Dentistry, 8200 West Outer Drive, PO Box 19900, Detroit, MI 48219-0900, USA.

           A variety of laboratory tests have been developed to assist in predicting the clinical performance of dental restorative materials. Additionally, more than one methodology is in use for many types of tests performed in vitro. This project assessed and compared results derived from two specific laboratory testing methods, one for bond strength and one for microleakage. Seven multi-purpose dental adhesives were tested with the two methodologies in both amalgam and resin composite restorations. Bond strength was determined with a punch-out method in sections of human molar dentin. Microleakage was analyzed with a digital imaging system (Image-Pro Plus, Version 1.3) to determine the extent of dye penetration in Class V (at the gumline) preparations centered at the CEJ on both the buccal and lingual surfaces of human molar teeth. There were 32 treatment groups (n = 10); seven experimental (dental adhesives) and one control (copal varnish, 37% phosphoric acid) followed by restoration with either amalgam or resin composite (aka bonding). Specimens were thermocycled 500 times in 5 degrees and 55 degrees C water with a one-minute dwell time. Bond strength and microleakage values were determined for each group. ANOVA and Student-Newman-Keuls tests demonstrated an interaction between restorative material and adhesive system with a significant difference among adhesives (p < 0.05). Using a multi-purpose adhesive system resulted in both a statistically significant increase in bond strength and a statistically significant decrease in extent of microleakage (p < 0.05). The effect of the adhesive upon both microleakage and bond strength was greater in the resin composite restorations than in the amalgam restorations. Bond strength testing was more discriminating than microleakage evaluation in identifying differences among materials.

 




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Dr. Barry F. McArdle, D.M.D. ~ 118 Maplewood Avenue, The Captain Moses House, Suite B-7, Portsmouth, NH 03801

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