2. Oral Environment and Patient Considerations

Oral Environment and Patient Considerations

Chapter Objectives

Upon completion of this chapter, the student will be able to:

1. List the qualities of the oral environment that make it challenging for long-term clinical performance of dental materials.

2. Describe the long-term clinical requirements of therapeutic and restorative materials.

3. List the three types of biting forces and the tooth structures most ideally suited to them.

4. Define stress, strain, and ultimate strength, and compare the ultimate strength of restorative materials during each type of stress to tooth structures.

5. Describe the effects of moisture and acidity on dental materials.

6. Describe the clinical significance of galvanism and how it can be prevented.

7. Define thermal conductivity and thermal expansion and contraction, and compare the values of thermal expansion and conductivity of restorative materials versus those of tooth structures.

8. Describe the process used to achieve mechanical, chemical, and bonding retention.

9. Describe the factors that determine successful adhesion, including wettability, viscosity, film thickness, and surface characteristics.

10. Describe microleakage and how the results of this process can lead to recurrent decay and postoperative sensitivity.

11. Define biocompatibility, and discuss why requirements for biocompatibility may fluctuate.

12. List the three visible light wavelengths that are sensed when color is recognized.

13. Describe tooth color in terms of hue, value, and chroma.

14. Discuss the importance of detection of restorations and methods for detection.

KEY TERMS defined within chapter

Therapeutic Agents   materials used to treat disease

Biocompatible   the property of a material that allows it to not impede or adversely affect living tissue

Restorative Agents   materials used to reconstruct tooth structure

Compressive Force   force applied to compress an object

Tensile Force   force applied in opposite directions to stretch an object

Shearing Force   force applied when two surfaces slide against each other or in a twisting or rotating motion

Stress   the internal force, which resists the applied force

Strain   distortion or deformation that occurs when an object cannot resist a stress

Flexural Stress   bending caused by a combination of tension and compression

Fatigue Failure   a fracture resulting from repeated stresses that produce microscopic flaws that grow

Retention   a material’s ability to maintain its position without displacement under stress

Solubility   susceptible to being dissolved

Water Sorption   the ability to absorb moisture

Corrosion   deterioration of a metal caused by a chemical attack or electrochemical reaction with dissimilar metals in the presence of a solution containing electrolytes (such as saliva)

Tarnish   discoloration resulting from oxidation of a thin layer of a metal at its surface. It is not as destructive as corrosion

Galvanism   an electrical current transmitted between two dissimilar metals

Dimensional Change   a change in the size of matter. For dental materials, this usually manifests as expansion caused by heating and contraction caused by cooling

Coefficient of Thermal Expansion   the measurement of change of volume or length in relationship to change in temperature

Percolation   movement of fluid in the microscopic gap of the restoration margin as a result of differences in the expansion and contraction rates of the tooth and the restoration with temperature changes associated with ingestion of cold or hot fluids or foods

Thermal Conductivity   the rate at which heat flows through a material

Insulators   materials having low thermal conductivity

Exothermic Reaction   the production of heat resulting from the reaction of the components of some materials when they are mixed

Adhesion   the act of sticking two things together. In dentistry, it is used to describe the bonding or the cementation process. Chemical adhesion occurs when atoms or molecules of dissimilar substances bond together and differs from cohesion in which attraction among atoms and molecules of like (similar) materials holds them together

Bonding   to connect or fasten; to bind (Webster’s New World Dictionary)

Wetting   the ability of a liquid to wet or intimately contact a solid surface. Water beading on a waxed car is an example of poor wetting

Viscosity   the ability of a liquid material to flow

Film Thickness   the minimum thickness obtainable by a layer of a material. It is particularly important to dental cements

Surface Energy   the electrical charge that attracts atoms to a surface

Interface   the space between the walls of the preparation and the restoration

Microleakage   leakage of fluid and bacteria caused by microscopic gaps that occur at the interface of the tooth and the restoration margins

Hue   the color of the tooth or restoration. It may include a mixture of colors, such as yellow-brown

Chroma   the intensity or strength of a color (e.g., a bold yellow has more chroma than a pastel yellow)

Value   how light or dark a color is. A low value is darker and a high value is brighter

Transparent   light passing directly through an object

Opaque   optical property in which light is completely absorbed by an object

Translucency   varying degrees of light passing through and being absorbed by an object

Vitality   a life-like quality

In the selection, manipulation, and handling of dental materials, it is important that the student have an appreciation for the complexity and challenges of the oral environment. Materials placed and used within the oral cavity must be biocompatible, durable, nonreactive in acid or alkaline conditions, compatible with other materials, and esthetically acceptable. All of these factors must be considered within a very unique environment. The oral environment produces many limitations—limitations on what can and cannot be used safely, limitations in the type and long-term clinical needs of the treatment, and limitations in the conditions of the oral cavity. These limitations may vary somewhat from patient to patient or in specific circumstances.

Materials must be compatible in an environment of moisture and differing stresses, temperatures, and acid levels. The degree of compatibility may depend on how and how long the materials are expected to be used. Therapeutic agents, those used to treat disease, are generally used for short periods, whereas restorative agents, those used to reconstruct tooth structure, are expected to remain in contact with tissues for indefinite lengths of time. Consider the following cases. If a therapeutic agent is being used to treat a specific condition, such as a denture sore, it would have to be biocompatible with the tissues but would not require an extreme amount of longevity. If the material were being placed as a permanent restoration, such as a gold crown, biocompatibility and longevity would be of great concern.

Patient concerns, questions, and demands must also play a part in the decision process. The patient should be brought into the decision process very early. Tooth-colored materials are frequently requested by the patient but may have limited use under certain circumstances. The patient needs to be educated on the limitations of his or her particular situation and the appropriate restorative choices. The allied oral health care practitioner is frequently involved in this education.

Biocompatibility

Materials must be biocompatible, that is, they must not impede or adversely affect living tissue. However, all materials contain potentially irritating ingredients. Responses may include postoperative sensitivity, toxicity, and hypersensitivity. A material may be acceptable for use or fabrication on hard tissues (tooth structure), while it may not be acceptable for use on soft tissues. Some materials may be therapeutic in small quantities or if in contact with tissues for short periods of time but may be irritating or toxic with longer or larger doses. Topical fluoride is highly beneficial when used according to the manufacturer’s directions, but it can be irritating to soft tissues and can even excessively etch enamel if used improperly. Dentistry is not alone in its concern for the development of biocompatible materials; practitioners of orthopedics must consider biocompatibility in the placement of joint prostheses and cardiology in the placement of catheters and prosthetic heart valves. All must consider the short-term and long-term functional and biocompatible responses of any material.

Postoperative sensitivity is often associated with operative procedures. This may be due to the toxicity of the restorative, preventive, or therapeutic material or to bacterial invasion into or near the pulpal tissues.

Adverse responses may be caused by the material itself or by the breakdown of its components in the oral environment. Frequently, materials are used in combination to produce the restoration, as when a porcelain-fused-to-metal crown is cemented with glass ionomer cement. The use of multiple materials makes adverse responses more difficult to evaluate. It has been reported that significant percentages of people have skin allergies or hypersensitivity to some metals, in particular nickel and acrylics, and should avoid these materials. A complete health history and questioning of the patient can help to identify those individuals. In general, materials intended for permanent replacement of tooth structures should exhibit no adverse biological responses.

In subsequent chapters, the limitations and precautions for the use of each material will be clearly outlined.

Biomechanics

The success or failure of a restoration may be related to its performance in any given situation. The function of a material is dependent on the properties of that material and on what the material is expected to do. These design considerations define the biomechanics of the material, that is, the application of engineering principles to biological systems. Much as an engineer would do, a dentist must design a bridge while taking into consideration load, span, and supporting structures. Excessive wear of a material may be due to the forces of a stronger material against a weaker material, such as porcelain against enamel, and may be intensified with the addition of/>

Jan 1, 2015 | Posted by in Dental Materials | Comments Off on 2. Oral Environment and Patient Considerations
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