Сraig. Dental Materials

SELECTED PROBLEMS

Problem 1

In selecting a composite for placing a large Class 4 restoration, what are several advantages of a light-cured composite?

Solution

Contour can be more adequately achieved through incremental addition; fewer air voids should be incorporated, because mixing of two pastes is not necessary; shade development can more readily be accomplished through the increments of different-colored composites; and less excess material should exist after insertion and curing of the restoration, thus finishing should be facilitated.

Problem 2

An extensive posterior core buildup is required on a lower molar. Why is a selfcured, core composite is the material of choice?

Solution

Uniform curing takes place under a crown form, lower-viscosity resin adapts better to pins or posts, and opaque, colored composites can be used to differentiate core from tooth structure during crown preparation.

Problem 3

When small air voids appear on the surface of a self-cured composite restoration during finishing, what are the causative manipulative factors?

Solution

The problem may be caused by exposing the dispensed composite to operatory light before incremental insertion; extended working of each increment to the point that voids are incorporated between layers; mixing of increments of two different shades of pastes on a pad before insertion; or excessive use

of alcohol as a lubricant on the insertion instrument.

Problem 4

Is there reason to expect that the color of a large Class 4 restoration will be more stable when a light-cured composite is used instead of a self-cured composite? Why?

Solution

Yes. A self-cured composite contains an aromatic amine accelerator that is more susceptible to breakdown by oxidation than the aliphatic amine in a light-cured system.

Problem 5

When a thin composite anterior veneer is being placed to modify tooth color, what are the advantages of a microfilled composite?

Solution

The advantages are the following: greater translucency improves vitality in the final shade; smoother surface texture provides a glossy surface with light-reflective patterns similar to enamel; in a thin layer supported by the bond to enamel, high physical and mechanical properties are not as important as in a free-standing Class 4 restoration.

Problem 6

In polymerizing a large, light-cured, resin composite restoration, what manipulativevariables can be controlled to improve the depth of cure?

Solution

The following variables can be controlled: the exposure time of the light can be increased for darker shades and thicker increments (beyond 2 mm); the light source can be maintained within 1 mm of the resin surface; the light tip can be drawn across the composite surface in

steps, with multiple exposures ensuring uniformity of cure.

Problem 7

In selecting a composite for a large, Class 4 anterior restoration with significant incisal function, what are the enhanced properties of microhybrid composite that make it the material of choice?

Solution

The beneficial properties are greater strength and elastic modulus, lower polymerization shrinkage, lower thermal coefficient of expansion, lower water sorption, and greater wear resistance.

Problem 8

In the clinical evaluation of a 2-year-old composite restoration, penetrating marginal discoloration is noted. What factors contribute to this bond failure?

Solution

Contributing factors are residual stress from polymerization shrinkage; fatigue stresses on the bond from thermal cycling; contamination at the bond site during material insertion; deflection stress at the restoration margins caused by intermittent functional loading of the restoration; and hydrolytic breakdown of the bond at the tooth interface (particularly if it is dentin).

Problem 9

When repairing an anterior veneer restoration with a small area of severe marginal leakage, the discolored composite is removed and the deficient area is rebonded with new material. What is the character of the bond between old cured composite and new?

Solution

The bond is primarily micromechanical and is formed against the roughened surface of the original composite. A weak chemical bond may be formed between exposed unreacted bonds in the old material and the new bond-

ing agent/composite. The repaired composite has less cohesive strength than the original composite and is more durable if an adjacent fresh enamel area can also be prepared by acid etching.

Problem 10

In assessing the use of composites in posterior teeth, what are the factors that contribute to early wear and failure?

Solution

These factors are the loss of substance as a result of deterioration of the silane coupling agent that bonds the filler particles to the matrix; excessive polymerization shrinkage from the relatively large volume of such restorations; stress-crack propagation across filler-polymer interfaces; and the low abrasion resistance of a relatively large volume of polymer matrix.

Composites

Asmussen E: Clinical relevance of physical, chemical, and bonding properties of composite resins, Oper Dent 10:61, 1985.

Bailey SJ, Swift EJ Jr: Effects of home bleaching products on composite resins, Quint

Int 23:489, 1992.

Bayne SC, Thompson JY, Swift EJ Jr et al:

A characterization of first-generation flowable composites, J Am Dent Assoc 129567, 1998.

Boyer DB, Chan KC, Reinhardt JW: Build-up and repair of light-cured composites: bond strength,J Dent Res 631241, 1984.

Braem M, Davidson CL, Lambrechts P et al: In vitro flexural fatigue limits of dental composites, J Biomed Mater Res

28:1397, 1994.

Braem M, Finger W, Van Doren VE et al: Mechanical properties and filler fraction of dental composites, Dent Mater 5:346, 1989.

254 Chapter 9 COMPOSITE RESTORATIVE MATERIALS

Chantler PM, Hu X, Boyd NM: An extension of a phenomenological model for dental composites, Dent Mater 15144, 1777.

Choi KK, Condon JR, Ferracane JL: The effects of adhesive thickness on polymerization contraction stress of composite, J Dent Res 795312, 2000.

Condon JR. Ferracane JL: Factors effecting dental composite wear in vitro, J Biomed Mater Res 38:303, 1777.

Condon JR. Ferracane JL: In vitro wear of composite with varied cure, filler level, and filler treatment, J Dent Res 7631405, 1997.

Condon JR, Ferracane JL: Reduction of composite contraction stress through non-bonded microfiller particles, Dent Mater

l4:256, 1998.

Cook WD: Spectral distributions of dental photopolymerization sources, J Dent Res 61:1436, 1982.

Council on Scientific Affairs: Posterior resinbased composites, J A m Dent Assoc 129:1627, 1798.

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77:818, 2000.

Dennison JB, Powers JM, Koran A: Color of dental restorative resins, J Dent Res 57:557, 1778.

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66:727, 1787.

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El Hejazi AA, Watts DC: Creep and visco-elastic recovery of cured and secondary-cured composites and resin-modified glassionomers, Dent Mater 15:138, 1997.

Eldiwany M, Fried1 K-H, Powers JM: Color stability of light-cured and post-cured composites, A m J Dent 8:177, 1995.

Eldiway M, Powers JM, George LA: Mechanical properties of direct and post-cured composites, A m J Dent 6:222, 1993.

Fan PL, Edahl A, Leung RL et al: Alternative interpretations of water sorption values of composite resins, J Dent Res 64:74, 1785.

Farah JW, Powers JM, editors: Laboratory composites, Dent Advis 16:1, 1777.

Farah JW, Powers JM, editors: Core materials, Dent Advis 16:1, 1777.

Farah JW, Powers JM, editors: Packable composites, Dent Advis 16:1, 1979.

Farah JW, Powers JM, editors: Provisional materials, Dent Advis 17:1, 2000.

Farah JW, Powers JM, editors: Microhybrid composites, Dent Advis 17:1, 2000.

Farah JW, Powers JM, editors: Flowable composites, Dent Advis 17:4, 2000.

Farah JW, Powers JM, editors: PAC lights, Dent Advis 18:5, 2001.

Fay R-M, Servos T, Powers JM: Color of restorative materials after staining and bleaching, Oper Dent 24:272, 1777.

Feilzer AJ, de Gee AJ, Davidson CL: Setting stress in composite resin in relation to configuration of the restoratives, J Dent Res 66:1636, 1987.

Feilzer AJ, de Gee AJ, Davidson CL: Quantitative determination of stress reduction by flow in composite restorations, Dent Mater 6:167, 1970.

Ferracane JL: Elution of leachable components from composites, J Oral Rehabil

21:441, 1994.

Ferracane JL: Current trends in dental composites, Crit Rev Oral Biol Med 6:302, 1775.

Ferracane JL, Mitchem JC, Condon JR et al: Wear and marginal breakdown of composites with various degrees of cure, J Dent Res 76:1508, 1777.

Ferracane JL, Moser JB, Greener EH: Rheology of composite restoratives, J Dent Res 60:1678, 1981.

Gerzina TM, Hume WR: Effect of dentine on release of TEGDMA from resin composite i n vitro, J Oral Rehabil21 :463, 1994.

Geurtsen W: Biocompatibility of resin-modified filling materials, Crit Reu Oral Biol Med

11:333, 2000.

Hanks CT, Craig RG, Diehl ML et al: Cytotoxicity of dental composites and other dental materials in a new i n vitro device, J Oral Path 17:396, 1988.

Hanks CT, Strawn SE, Wataha JC et al: Cytotoxic effects of composite resin components on cultured mammalian fibroblasts, J Dent Res 70:1450, 1991.

Hanks CT, Wataha JC, Parsell RR et al: Permeability of biological and synthetic molecules through dentine, J Oral Rehabil

21:475, 1994.

Hirasawa T, Hirano S, Hirabayashi S et al: Initial dimensional change of composites in dry and wet conditions, J Dent Res

62:28, 1983.

Hu X, Harrington E, Marquis PM et al: The influence of cyclic loading on the wear of a dental composite, Biomater 20:907, 1999.

Hu X, Marquis PM, Shortall AC: Two-body in vitro wear study of some current dental composites and amalgams, J Prosthet Dent 82:214, 1999.

Inohoshi S, Willems G, Van Meerbeek B et al: Dual-cure luting composites, Part I filler particle distribution, J Oral Rehabil

20:133, 1993.

Johnson GH, Bales DJ, Gordon GE et al: Clinical performance of posterior composite resin restorations, Quint Int 23:705, 1992.

Johnson GH, Gordon GE, Bales DJ: Postoperative sensitivity associated with posterior composite and amalgam restorations,

Oper Dent 13:66, 1988.

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Kalachandra S: Influence of fillers on the water sorption of composites, Dent Mater

5:283, 1989.

Kim K-H, Park J-H, Imai Y et al: Fracture toughness and acoustic emission behavior of dental composite resins, Engin Fract Mech 40:8ll, 1991.

Labella R, Lambrechts P, Van Meerbeek B et al: Polymerization shrinkage and elasticity

of flowable composites and filled adhesives, Dent Mater 15:128, 1999.

Lee Y-K, El Zawahry M, Noaman KM et al: Effect of mouthwash and accelerated aging on the color stability of esthetic restorative materials, Am J Dent 131159, 2000.

Leinfelder KF: Posterior composite resins: the materials and their clinical performance,

J Am Dent Assoc 126:663, 1995.

Letzel H: Survival rates and reasons for failure of posterior composite restorations in multicentre clinical trial, J Dent 17:S10, 1989.

Leung RL, Fan PL, Johnston WM: Postirradiation polymerization of visible lightactivated con~positeresin, J Dent Res 62:363, 1983.

Manhart J, Kunzelmann K-H, Chen HY et al: Mechanical properties and wear behavior of light-cured packable composite resins, Dent Mater 16:33, 2000.

Mitchem JC, Gronas DG: The continued in vivo evaluation of the wear of restorative resins, J Anz Dent Assoc 111:961, 1985.

Neo JC, Denehy GE, Boyer DB: Effects of polymerization techniques on uniformity of cure of large-diameter, photo-initiated composite resin restorations, J Am Dent

Assoc 113:905, 1986.

Oysaed H, R~iyterIE: Water sorption and filler characteristics of composites for use in posterior teeth, J Dent Res 65:1315, 1986.

Pallav P, DeGee AJ, Davidson CL et al: The influence of admixing microfiller to smallparticle composite resin on wear, tensile strength, hardness, and surface roughness, J Dent Res 68:489, 1989.

Park Y-J, Chae K-H, Rawls HR: Development of a new photoinitiation system for dental light-cure composite resins, Dent Mater 15:120, 1999.

256 Chapter 9 COMPOSITE RESTORATIVE MATERIALS

Perry R, Kugel G, Kunzelmann K-H, et al: Composite restoration wear analysis: conventional methods vs. three-dimensional laser digitizer, J A m Dent Assoc

131:1472, 2000.

Powers JM: Lifetime prediction of dental materials: an engineering approach, J Oral Rehabil22:491, 1995.

Powers JM, Burgess JO: Performance standards for competitive dental restorative materials,

Trans Acad Dent Mater 9:68, 1996.

Powers JM, Dennison JB, Koran A: Color stability of restorative resins under accelerated aging, J Dent Res 57964, 1978.

Powers JM, Dennison JB, Lepeak PJ: Parameters that affect the color of direct restorative resins, J Dent Res 57:876. 1978.

Powers JM, Hostetler RW, Dennison JB: Thermal expansion of composite resins and sealants, J Dent Res 58:584, 1979.

Powers JM, Smith LT, Eldiwany M et al: Effects of post-curing on mechanical properties of a composite, A m J Dent 6:232, 1993.

Pratten DH, Johnson GH: An evaluation of finishing instruments for an anterior and a posterior composite, J Prosthet Dent 60:154, 1988.

Rathbun MA, Craig RG, Hanks CT et al: Cytotoxicity of a BIS-GMA dental composite before and after leaching in organic solvents, J Biomed Mater Res 25:443, 1991. Sakaguchi RL, Berge HX: Reduced light energy

density decreases post-gel contraction while maintaining degree of conversion in composites, J Dent 26:695, 1998.

Sakaguchi RL, Peters MCRB, Nelson SR, Douglas WH: Effects of polymerization contraction in composite restorations, J Dent 20:178, 1992.

Soderholm K-JM: Leaking of fillers in dental composites, J Dent Res 62:126, 1983.

Soderholm K-J, Zigan M, Ragan M et al: Hydrolytic degradation of dental composites,

J Dent Res 63:1248, 1984.

Stanford CM, Fan PL, Schoenfeld CM et al: Radiopacity of light-cured posterior composite resins, J A m Dent Assoc 115:722, 1987.

Suh BI, Ferber C, Baez R: Optimization of hybrid composite properties, J Esthetic Dent 2:44, 1990.

Tate WH, Fried1 K-H, Powers JM: Bond strength of composites to hybrid ionoiners, Oper Dent 21:147, 1996.

Tate WH, Powers JM: Surface roughness of composites and hybrid ionomers, Oper Dent 21:53, 1996.

Tirtha R, Fan PL, Dennison JB et al: In vitro depth of cure of photo-activated composites, J Dent Res 61:1184, 1982.

Van Dijken JWV: A clinical evaluation of anterior conventional, microfiller, and hybrid composite resin fillings: a 6-year follow-up study, Acta Odontol Scand 44:357, 1986.

Van Dijken JWV, Ruyter IE, Holland RI: Porosity in posterior composite resins, Scand

J Dent Res 94:471, 1986.

Van Dijken JWV,Sjostrotn S, Wing K: The effect of different types of composite resin fillings on marginal gingiva, J Clin Periodont 14:185, 1987.

Wataha JC, Hanks CT, Strawn SE et al: Cytotoxicity of components of resin and other dental restorative materials, J Oral Rehabil 21:453, 1994.

Watts DC, Haywood CM, Smith R: Thermal diffusion through composite restorative materials, Br Dent J 154:101, 1983.

Wendt SL Jr: The effect of heat used as a secondary cure upon the physical properties of three composite resins. I. Diametral tensile strength, compressive strength, and a marginal dimensional stability, Quint Int 18:265, 1987.

Wendt SL Jr: Microleakage and cusp fracture resistance of heat-treated composite resin inlays, Am J Dent 4:10, 1991.

Wendt SL Jr, Leinfilder KF: The clinical evaluation of heat-treated composite resin inlays, J A m Dent Assoc 120:177, 1990.

Xu HHK: Whisker-reinforced heat-cured dental resin composites: effects of filler level and heat-cure temperature and time, J Dent

Res 79:1392, 2000.

Compomers

Cattani-Lorente MA, Dupuis V, Moya F et al: Comparative study of the physical properties of a polyacid-modified composite resin and a resin-modified glass ionomer cement, Dent Mater 15:21, 1999.

Farah JW, Powers JM, editors: Compomers, Dent Advis 15:1, 1998.

Light-CuringUnits

Albers HF: Resin polymerization, Adept Report 6:1, 2000.

Fan PL, Wozniak WT, Reyes WD et al: Irradiance of visible light-curing units and voltage variation effects, J Am Dent Assoc 115:442, 1987.

Farah JW, Powers JM, editors: Light-curing units, Dent Advis 16:1, 1999.

Harrington E, Wilson HJ: Determination of radiation energy emitted by light activation,

J Oral Rehabil22:377, 1995.

Jandt KD, Mills RW, Blackwell GB et al: Depth of cure and compressive strength of dental composites cured with blue light emitting diodes (LEDs), Dent Mater l6:4l, 2000.

Mills RW, Jandt KD, Ashworth SH: Dental composite depth of cure with halogen and blue light emitting diode technology, Br Dent J 186338, 1999.

Peutzfeldt A, Sahafi A, Asmussen E: Characterization of resin composites polymerized with plasma arc curing units, Dent Mater

16330, 2000.

Sakaguchi RL, Berge HX: Reduced light energy density decreases postgel contraction while maintaining degree of conversion in composites, J Dent 26:695, 1998.

Satrom KD, Morris MA, Crigger LP: Potential retinal hazards of visible light photopolymerization units, J Dent Res

66:731, 1987.

Stahl F, Ashworth SH, Jandt KD et al: Light emitting diodes (LED) polymerisation of dental composites: flexural properties and polymerisation potential, Biomater 21:1379, 2000.

Watts DC, A1 Hindi A: Intrinsic 'soft-start' polymerisation shrinkage-kinetics in an acrylicbased resin-composite, Dent Mater

15:39, 1999.

Every dental restoration requires retention by some system of connection or attachment.

Dentures are held in place by the combination of tissue irregularities, saliva, and adhesives. Crowns are held in place by luting cement that mates with minor irregularities along the crown and dentin surfaces. Partial dentures are held in place by clasps. Undercut regions in the cavity preparation retain dental amalgam. All of these methods of retention rely predominantly on macroscopic mechanisms. Even so, there has always been a strong desire to develop a dental adhesive that could provide a bonded and sealed interface. The scientific beginnings of dental adhesion originated in the early 1950s with studies of bonding to enamel and dentin. Now, 50 years later, bonding agents are used routinely in restorative and preventive dentistry. This chapter focuses on the science, systems, and success of bonding systems for dental substrates with emphasis on bonding resin composites to tooth structure.

ADHESIVE JOINTS

Adhesion or bonding is the process of forming an adhesive joint. The initial substrate is called the adherend, whereas the material producing the interface is generally called the adhesive.If two substrates are being joined, the adhesive produces two interfaces as part of the adhesive joint, as illustrated in Fig. 10-1.In dentistry, most adhesive joints involve two interfaces. A dental sealant attached to enamel is a simple adhesive joint with one interface. A bonded composite restoration is a more complex joint. In dentistry, there may be several steps in creating the adhesive layer, and these stages may involve separate components. These components are called a bonding agent.

ADHESION VERSUS BOND STRENGTH

Dentistry is interested in the process of forming a joint and the resistance of the joint to failure. The

science of adhesion studies the formation of an adhesive joint. There is a specific energy of adhesion determined by the chemical, physical, and mechanical attributes of the substrate and adhesive. Once formed, the joint's resistance to failure depends on the extent of defects along the interface that allow cracks to form, grow, and rupture the joint. Failure processes depend on the bulk properties of the adherend and adhesive, the environment of the bond, and time. Strengths of the bonded system are measured by bond tests.

INTERFACE FORMATION FOR ADHESION

Formation of an optimally bonded interface requires that (1) the surface of the substrate be clean; (2) the adhesive wet the substrate well, have a low contact angle, and spread onto the surface; (3) adaptation to the substrate produce intimate approximation of the materials without entrapped air or other intervening materials;

(4) the interface include the sufficient physical, chemical and/or mechanical strength to resist intraoral forces of debonding; and ( 5 ) the adhesive be well cured under the conditions recommended for use. These events are schematically summarized in Fig. 10-2.

Cleaning the surface of the substrate and then keeping it clean until the adhesive is applied are technical problems within a patient's mouth. Dental surfaces exposed to the oral environment contain a pellicle of adsorbed materials from saliva. The pellicle may be contaminated by the formation of plaque or the deposition of components of food, such as stains. This material must be removed before bonding. Once a surface is cleaned, its surface energy is higher, and it is more likely to adsorb material from the surrounding air, such as moisture or saliva droplets, to decrease its energy. Therefore the surface must be protected and the next step in a bonding procedure should proceed promptly.

Enamel and dentin prepared with rotary instruments contain a debris layer that is smeared onto their surfaces, called the smear layer. This

layer is usually a few micrometers thick and adheres weakly to the substrate. Thus it is essential to either remove this layer or penetrate it with adhesives. The most common approach to removing a smear layer is to chemically dissolve part or all of it.

When adhesive is applied to a substrate, it must wet the surface well. Good wetting is evidenced by a small contact angle and spreading of the adhesive onto the substrate (see Chapter 2). Clean dentin is hydrophilic and will be wet best by an adhesive that is also hydrophilic. In addition, the adhesive must flow in a practical time. Adding solvent to the adhesive promotes lower viscosity and good flow. However, it is not always possible to apply adhesive materials carefully in poorly accessible areas and in thin films.

Fig. 10-2 Examples of the microscopic steps involved in the formation of an adhesive joint. 1, Good adherend; 2, good wetting; 3, intimate adaptation; 4, bonding; 5, good curing.