Oral Environment and Patient Considerations
Chapter Objectives
Upon completion of this chapter, the student will be able to:
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.
5. Describe the effects of moisture and acidity on dental materials.
6. Describe the clinical significance of galvanism and how it can be prevented.
8. Describe the process used to achieve mechanical, chemical, and bonding retention.
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
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
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
Bonding to connect or fasten; to bind (Webster’s New World Dictionary)
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
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/>
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