Сraig. Dental Materials

General Reading

Cagle CV: Handbook of adhesive bonding, ed 1, New York, 1973, McGraw-Hill.

Bonding to Tooth Structure

Abdalla AI, Davidson CL: Bonding efficiency and interfacial morphology of one-bottle adhesives to contaminated dentin surfaces, Am J Dent 11:281, 1998.

Barakat MM, Powers JM: In vitro bond strength of cements to treated teeth, Aust Dent J 31:415, 1986.

Bayne SC, Fleming JE, Faison S: SEM-EDS analysis of macro and micro resin tags of laminates, J Dent Res 61A:304, 1982.

Bayne SC, Swift Jr EJ: Solvent analysis of three reduced-component dentin bonding systems, Trans Acad Dent Mater 1:156, 1997. Boghosian A: Clinical evaluation of a filled ad-

hesive system in Class 5 restorations, Compend Contin Educ Dent 17:750-752,

754, 1996.

Bouillaguet S, Wataha JC, Hanks CT et al: In vitro cytotoxicity and dentin permeability of HEMA, J Endodont 22:244, 1996.

Bouillaguet S, Wataha JC, Virgillito M et al: Effect of sub-lethal concentrations of HEMA (2-hydroxyethyl methacrylate) on THP-1 human monocyte-macrophages, in vitro, Dent Mater 16:213, 2000.

Bowen RL, Eick JD, Henderson DA et al: Smear layer: removal and bonding considerations, Oper Dent Suppl3:30, 1984.

Bozalis WG, Marshall Jr GW, Cooley RO: Mechanical pretreatments and etching of primary-tooth enamel, ASDC J Dent Child 46:43, 1979.

Buonocore MG: Simple method of increasing the adhesion of acrylic filling materials to enamel surfaces,J Dent Res 34:849, 1955. Choi KK, Condon JR, Ferracane JL: The effects of adhesive thickness on polymerization contraction stress of composite, J Dent Res

79:812, 2000.

Clemmensen S: Sensitizing potential of 2- hydroxyethylmethacrylate. Contact Dermatitis 12:203, 1985.

Costa CA, Teixeira HM, do Nascimento AB

et al: Biocompatibility of an adhesive system and 2-hydroxyethylmethacrylate, ASDC

J Dent Child 66537, 1999.

Davidson CL, Feilzer AJ: Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives, J Dent

25:435, 1997.

Drummond JL, Sakaguchi RL, Racean DC et al: Testing mode and surface treatment effects on dentin bonding, J Biomed Mater Res 32533, 1996.

Eick JD, Wilko RA, Anderson CH et al: Scanning electron microscopy of cut tooth surfaces and identification of debris by use of the electron microprobe, J Dent Res

49 (Suppl):1359, 1970.

Eick JD: Smear layer-materials surface, Proc Finn Dent Soc 88 (Suppl 1):225, 1992. el-Kalla IH, Garcia-Godoy F: Saliva contamination and bond strength of single-bottle

adhesives to enamel and dentin, A m J Dent 10:83, 1997.

Farah JW,Powers JM, editors: Bonding agents, Dent Advis l7(9): 1, 2000.

Fissore B, Nicholls JI, Yuodelis RA: Load fatigue of teeth restored by a dentin bonding agent and a posterior composite resin,

J Prosthet Dent 65:80, 1991. Frankenberger R, Kramer N, Petschelt A:

Fatigue behaviour of different dentin adhesives, Clin Oral Investig 3:11, 1999.

Fritz UB, Finger WJ, Stean H: Salivary contamination during bonding procedures with a one-bottle adhesive system, Quint Int 29:567, 1998.

Fusayama T: [Cavity preparation for a new adhesive restorative resin], Shikai Tenbo 57:1223, 1981.

Fusayama T: A simple pain-free adhesive restorative system by minimal reduction and total etching, Tokyo, 1993, Ishiyaku EuroAmerica, Inc.

Garberoglio R, Brannstrom M: Scanning electron microscopic investigation of human dentinal tubules, Arch Oral Biol21:355, 1976.

Hansen EK, Munksgaard EC: Saliva contamination vs. efficacy of dentin-bonding agents, Dent Mater 5:329, 1989.

Johnson ME, Burgess JO, Hermesch CB et al: Saliva contamination of dentin bonding agents, Oper Dent 19:205, 1994.

Katsuno K, Manabe A, Hasegawa T et al: Possibility of allergic reaction to dentin primerapplication on the skin of guinea pigs,

Dent MaterJ11:77, 1992.

LeGeros RZ: Calcium phosphates in oral biology and medicine, Monographs in Oral Science, Vol. 15, Basel, 1992, Karger.

Marshall GW Jr, Wu-Magidi IC, Watanabe LG et al: Effect of citric acid concentration on dentin demineralization, dehydration, and rehydration: atomic force microscopy study, J Bionzed Mater Res

42:500, 1998.

May KN Jr, Swift EJ Jr, Bayne SC: Bond strengths of a new dentin adhesive system, A m J Dent 10:195, 1997.

Mjor IA: Frequency of secondary caries at various anatomical locations, Oper Dent 10:88, 1985.

Munksgaard EC: Permeability of protective gloves to (dilmethacrylates in resinous dental materials, Scand J Dent Res 100:189, 1992.

Nakabayashi N, Ashizawa M, Nakamura M: Identification of a resin-dentin hybrid layer in vital human dentin created in vivo: durable bonding to vital dentin, Quint Int 23: 135, 1992.

Nakabayashi N, Nakamura M, Yasuda N: Hybrid layer as a dentin-bonding mechanism,

J Esthet Dent 3:133, 1991.

Nakabayashi N. Dentinal bonding mechanisms,

Quintessence Int 22:73, 1991. Nakabayashi N: The hybrid layer: a resin-

dentin composite, Proc Finn Dent Soc 88 (Suppl 1):321, 1992.

Pashley DH, Carvalho RM, Sano H et al: The microtensile bond test: a review, J Adhes Dent 1:299, 1999.

Pashley DH: Smear layer: overview of structure and function, Proc Finn Dent Soc 88

(Suppl 1):215, 1992.

Pashley DH: Smear layer: physiological considerations, Oper Dent Suppl3:13, 1984.

Pashley DH: Dentin: a dynamic substrate-a review, Scan Microsc 3:161, 1989.

PerdigHo J, Lambrechts P, van Meerbeek B et al: Morphological field emission-SEM study of the effect of six phosphoric acid

etching agents on human dentin, Dent Mater 12:262, 1996.

Powers JM, Finger WJ, Xie, J: Bonding of composite resin to contaminated human enamel and dentin, J Prosthodont 4:28, 1995.

Roeder LB, Berry I11 EA, You C et al: Bond strength of composite to air-abraded enamel and dentin, Oper Dent 20:186, 1995.

Rose EE, Joginder L, Williams NB et al: The screening of materials for adhesion to human tooth structure, J Dent Res 34577, 1955.

Sano H, Ciucchi B, Matthews WG et al: Tensile properties of mineralized and demineralized human and bovine dentin, J Dent Res 73:1205, 1994.

Sano H, Takatsu T, Ciucchi B et al: Nanoleakage: leakage within the hybrid layer, Oper Dent 20:18, 1995.

Sano H, Yoshiyama M, Ebisu S et al: Comparative SEM and TEM observations of nanoleakage within the hybrid layer, Oper Dent 20:160, 1995.

Silverstone LM, Saxton CA, Dogon IL et al: Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy, Caries Res

9:373, 1975.

Swift EJ, Perdiggo J, Heymann HO et al: Clinical evaluation of a filled and unfilled dentin adhesive, J Dent, in press, 2001.

Tate WH, You C, Powers JM: Bond strength of compomers to dentin using acidic primers, Am JDent 12:235, 1999.

284 Chapter 10 BONDING TO DENTAL SUBSTRATES

Tate WH, You C, Powers JM: Bond strength of compomers to human enamel, Oper Dent 25:283, 2000.

van Meerbeek B, Dhem A, Goret-Nicaise M et al: Comparative SEM and TEM examination of the ultrastructure of the resindentin interdiffusion zone, J Dent Res 72:495, 1993.

Xie J, Flaitz CM, Hicks MJ et al: In-vitro bond strength of composite to sound dentin and artificial carious lesions in dentin, Am J Dent 9:31, 1996.

Xie J, Powers JM, McGuckin RS: In vitro bond strength of two adhesives to enamel and dentin under normal and contaminated conditions, Dent Mater 9:295, 1993.

Yoshii E: Cytotoxic effects of acrylates and methacrylates: relationships of monomer structures and cytotoxicity, J Biomed Mater Res 37:517, 1997.

Bonding to Other Substrates

Crumpler DC, Bayne SC, Sockwell S et al: Bonding to re-surfaced posterior composites, Dent Mater 5:417, 1989.

DeSchepper EJ, Cailletea, JG, Roeder L et al: In vitro tensile bond strengths of amalgam to treated dentin, J Esthet Dent 3117, 1991.

Hansson 0, Moberg LE: Evaluation of three silicoating methods for resin-bonded prostheses, Scand J Dent Res 101:243, 1993.

Hero H, Ruyter IE, Waarli ML et al: Adhesion of resins to Ag-Pd alloys by means of the silicoating technique, J Dent Res 66:1380, 1987.

Hummel SK, Pace LL, Marker VA: A comparison of two silicoating techniques, J Prosthodont 3:108, 1994.

Masil R, Tiller HJ: The adhesion of dental resin to metal surfaces: the Kulzer Silicoater technique, Wehrbeim: Kulzer and Co., Gmbh, 1st ed, 9, 1984.

Mazurat RD, Pesun S: Resin-metal bonding systems: a review of the Silicoating

and Kevloc systems, J Can Dent Assoc 64:503, 1998.

Miller BH, Nakajima H, Powers JM et al: Bond strength between cements and metals used for endodontic posts, Dent Mater

14:312, 1998.

Mukai M, Fukui H, Hasegawa J: Relationship between sandblasting and composite resinalloy bond strength by a silica coating,

J Prosthet Dent 74:151, 1995. NaBadalung DP, Powers, JM, Connelly ME:

Comparison of bond strengths of three denture base resins to treated nickel-chromium- beryllium alloy, J Prosthet Dent 80:354, 1998.

O'Keefe KL, Miller BH, Powers JM: In vitro tensile bond strength of adhesive cements to new post materials, Int J Prosthodont

13:47, 2000.

Pesun S, Mazurat RD: Bond strength of acrylic resin to cobalt-chromium alloy treated with the Silicoater MD and Kevloc systems, J Can Dent Assoc 64:798, 1998.

Ramos JC, Perdiggo J: Shear bond strengths and SEM morphology of dentin-amalgam adhesives, Am J Dent 10:152, 1997.

Roulet JF, Soderholm KJ, Longmate J: Effects of treatment and storage conditions on ceramic/composite bond strength, J Dent Res 74:381, 1995.

Schneider W, Powers JM, Pierpont HP: Bond strength of composites to etched and silicacoated porcelain fusing alloys, Dent Mater 8:211, 1992.

Shahverdi S, Canay S, Sahin E et al: Effects of different surface treatment methods on the bond strength of composite resin to porcelain, J Oral Rehabil25:699, 1998.

Stokes AN, Tay WM, Pereira BP: Shear bond of resin cement to post-cured hybrid composites, Dent Mater 9:370, 1993.

Sturdevant JR, Swift Jr EJ, Bayne SC: Cement bond strength to millable composite for CAD/CAM restorations, J Dent Res 79:453, 2000.

Suliman AH, Swift EJ Jr, Perdiggo J: Effects of surface treatment and bonding agents on bond strength of composite resin to porcelain, J Prosthet Dent 70:118, 1993.

Tate WH, Friedl K-H, Powers JM: Bond strength of composites to hybrid ionomers, Oper Dent 21:147, 1996.

Thompson VP, Del Castillo E, Livaditis GJ: Resin-bonded retainers. Part I: resin bond to electrolytically etched nonprecious alloys,

J Prosthet Dent 50:771, 1983.

Watanabe I, Kurtz KS, Kabcenell JL et al: Effect of sandblasting and silicoating on bond strength of polymer-glass composite to cast titanium, J Prosthet Dent 82:462, 1999.

Wolf DM, Powers JM, O'Keefe KL: Bond strength of composite to etched and sandblasted porcelain, Am J Dent 6:155, 1993.

288 Chapter 11 AMALGAM

A n amalgam is an alloy of mercury and one or more other metals. Dental amalgam is produced by mixing liquid mercury with solid particles of an alloy of silver, tin, copper, and sometimes zinc, palladium, indium, and selenium. This combination of solid metals is known as the amalgam alloy. It is important to differentiate between dental amalgam and the amalgam alloy that is commercially produced and marketed as small filings, spheroid particles, or a combination of these, suitable for mixing with liquid mercury to produce the dental amalgam. Once the amalgam is freshly mixed with liquid mercury, it has the plasticity that permits it to be conveniently packed or condensed into a prepared tooth cavity. After condensing, the dental amalgam is carved to generate the required anatomical features. Amalgam is used most commonly for direct, permanent, posterior restorations and for large foundation restorations, or cores, which are precursors to placing crowns. Dental amalgam restorations are reasonably easy to insert, are not overly technique sensitive, maintain anatomical form, have reasonably adequate resistance to fracture, prevent marginal leakage after a period of time in the mouth, can be used in stress bearing areas, and have a relatively long

service life.

The principal disadvantage of dental amalgam is that the silver color does not match tooth structure. In addition, they are somewhat brittle; are subject to corrosion and galvanic action; may demonstrate a degree of marginal breakdown; and do not help retain weakened tooth structure.

Finally, there are regulatory concerns ahout amalgam being disposed in the wastewater. In summary, dental amalgam is a highly successful material clinically and is very cost effective, but alternatives such as cast gold and esthetic restorative materials are now very competitive in terms of frequency of use. Many argue, however, that the use of amalgam must be strongly supported given its large public health benefit in the United States and many other countries.

In this chapter, the composition and morphology of the different dental amalgams are presented, followed by a discussion of lowand high-copper amalgams, the chemical reactions occurring during amalgamation, and the resultant microstructures. Various physical and mechanical properties are covered in the next section, as well as the factors related to the manipulation of amalgam. Finally, biological effects of amalgam and mercury are presented.

DENTAL AMALGAM ALLOS , " ,;

COMPOSITION AND MORPHOLOGY

ANSVADA Specification No. 1 for amalgam alloy (IS0 1559) includes a requirement for composition. This specification does not state precisely what the composition of alloys shall be; rather, it permits some variation in composition. The chemical composition must consist essentially of silver and tin. Copper, zinc, gold, palladium, indium, selenium, or mercury may be included in lesser amounts. Metals such as palladium, gold,

and indium in smaller quantities and copper in larger quantities have been included to alter the corrosion resistance and certain mechanical properties of the finished amalgam mass. These and other elements may be included, provided the manufacturer submits the alloy's composition and adequate clinical and biological data to the ADA's Council on Scientific Affairs to show that the alloy is safe to use as directed.

Alloys with more than 0.01% zinc are classified as zinc containing, and those with less than 0.01% as non-zinc alloys. Zinc has been included in amalgam alloys as an aid in manufacturing by helping to produce clean, sound castings of the ingots. However, improved manufacturing pro-

cedures have resulted in the elimination of zinc in most alloys. Recent studies have shown, however, that small amounts of zinc in high-copper dental amalgams improve clinical performance, presumably by reducing brittleness.

The approximate composition of commercial amalgam alloys is shown in Table 11-1, along with the shape of the particles. The alloys are broadly classified as low-copper (5% or less copper) and high-copper alloys (13% to 30% copper). I'articles are irregularly shaped; microspheres of various sizes; or a combination of the two. Scanning electron micrographs of the particles are presented in Fig. 11-1. The low-copper alloys are either irregular or spherical. Both mor-

phologies contain silver and tin in a ratio approximating the intermetallic compound Ag,Sn. Highcopper alloys contain either all spherical particles of the same composition (unicompositional) or a mixture of irregular and spherical particles of different or the same composition (admixed).

When the particles have different compositions, the admixed alloys are made by mixing particles of silver and tin with particles of silver and copper. The silver-tin particle is usually irregular, whereas the silver-copper particle is usually spherical in shape. The composition of the silver-tin particles in most commercial alloys is the same as that of the low-copper alloys. Different manufacturers, however, have somewhat different compositions for the silver-copper particle. The compositional ranges of the spherical silver-copper particles are shown in Table 11-1. The admixed regular alloy contains 33% to 60% spherical particles that have a composition close to the eutectic composition of Ag,Cu, (see Fig. 6-9); the balance are irregular particles.

Like the admixed alloy, the unicompositional alloys have higher copper contents than the conventional lathe-cut or spherical low-copper alloys, but all the particles are spherical, as seen in Fig. 11-1. The silver content of the unicompositional alloys varies from 40% to 60%, copper content from 13% to 30%, and tin content varies only slightly.

A high-copper admixed alloy is also available, in which both spherical and irregular particles have the same composition and the copper content is between 29% and 30%. High-copper alloys are less commonly supplied as unicompositional, irregular particles. The lathe-cut, high-copper alloys contain more than 23% copper.

Interest has increased in admixed amalgams containing 10% to 15% indium (In) in the mercury. The addition of In to Hg decreases the amount of Hg needed, decreases the Hg vapor during and after setting, and increases the wetting. These amalgams have low creep and lower early-compressive strengths, but higher final strengths than comparable amalgams without indium. It is proposed that the lower levels of Hg vapor are due to oxides of In formed at the surface or the lower amount of Hg used in the mix.

It is estimated that more than 90% of the dental amalgams currently placed are high-copper alloys. Of the high-copper alloys, admixed are used more often than spherical types, and fewer irregularly shaped or lathe-cut types are selected. A high-copper alloy is selected to obtain a restoration with high early strength, low creep, good corrosion resistance, and good resistance to marginal fracture.

In general, alloy composition; particle size, shape, and distribution; and heat treatment control the characteristic properties of the amalgam.

PRODUCTION

Irregular Particles To produce lathe-cut alloys, the metal ingredients are heated and protected from oxidation until melted, then poured into a mold to form an ingot. The ingot is cooled relatively slowly, leading to the formation of mainly Ag,Sn (?I) and some Cu$n ( E ) , Cu6Sn5(q') and Ag,Sn (P). After the ingot is completely cooled, it is heated for various periods of time (often 6 to 8 hours) at 400" C to produce a more homogeneous distribution of Ag,Sn. The ingot is then reduced to filings by being cut on a lathe and ball milled. The particles are passed through a fine sieve and then ball milled to form the proper particle size. The particles are typically 60 to 120 pm in length, 10 to 70 pm in width, and 10 to 35 pm in thickness. Most products are labeled as fine-cut. The particle size and shape of lathe-cut amalgam alloys are shown in Fig. 11-1, A.

In general, freshly cut alloys amalgamate and set more promptly than aged particles, and some aging of the alloy is desirable to improve the shelf life of the product. The aging is related to relief of stress in the particles produced during the cutting of the ingot. The alloy particles are aged by subjecting them to a controlled temperature of 60" to 100" C for 1 to 6 hours. Irregularly shaped high-copper particles are made by spraying the molten alloy into water under high pressure.

Spherical Particles Spherical particles of lowor high-copper alloys are produced when all the desired elements are melted together. In

the molten stage the metallic ingredients form the desired alloy. The liquid alloy is then sprayed, under high pressure of an inert gas, through a fine crack in a crucible into a large chamber. Depending on the difference in surface energy of the molten alloy and the gas used in the spraying process, the shape of the sprayed particles may be spherical or somewhat irregular, as shown in Fig. 11-1,B. The size of the spheres varies from 2 to 43 pm.

SILVER-TIN ALLOY

Because two of the principal ingredients in the amalgam alloy are silver and tin, it is appropriate to consider the binary system and the equilibrium phase diagram for these two metals, as shown in Fig. 11-2.

The most important feature in this diagram concerning the silver-tin alloy is that, when an alloy containing approximately 27% tin is slowly cooled below a temperature of 480" C, an intermetallic compound (Ag,Sn) known also as the gamma (y) phase is produced. This Ag,Sn compound is an important ingredient in the silver amalgam alloy and combines with mercury to produce a dental amalgam of desired mechanical properties and handling. This silver-tin compound is formed only over a narrow composition range. The silver content for such an alloy would be approximately 73%.Practically, the tin content is held between 26% and 30%, and the remainder of the alloy consists of silver, copper, and zinc. If the concentration of tin is less than 26%, the beta one (PI) phase, which is a solid solution of silver and mercury, fornis. In one product, 5%