13: Biomaterials

Biomaterials

Biomaterials, restorative materials, and tissue engineering are fundamental to the dental hygiene process of care and are used in a variety of dental hygiene roles and practices. This chapter reviews the general considerations of specific biomaterials as well as preventive and restorative materials, including applications, terminology, and classifications for each; the structures of materials in terms of the starting components, reactions involved in their use, and manipulation procedures; and the properties of materials, including physical, chemical, mechanical, and biologic characteristics.

Direct applications of these materials include dental amalgams; dental composites; pit-and-fissure sealants; infiltrants for lesions; bonding agents; cement liners, cement bases, and other cements; fluoride-releasing restorative materials, topical fluorides, and fluoride varnishes; dentifrices and prophylactic pastes; and bleaching agents. Indirect applications include impression materials, provisional materials, models, casts, dies, waxes, investment materials, casting alloys, dental solders, chromium alloys for partial dentures, porcelain-fused-to-metal (PFM) alloys, dental ceramics, crown-and-bridge cements, acrylic appliances, acrylic denture bases, denture teeth, denture liners, denture cleansers, mouth protectors, veneers, computer-assisted design and computer-assisted machining (CAD/CAM) and copy-milled restorations, and dental implants.

Introduction

Structure

Composition

Reaction during use

Manipulation

1. Proportioning variables

2. Mixing variables

3. Stages of manipulation

Properties

Physical properties—events that do not involve changes in composition or primary bonds

1. Descriptive properties

2. Thermal properties

a. Linear coefficient of thermal expansion (LCTE, α)

b. Thermal conductivity

3. Electrical properties—electrical conductivity

4. Surface properties

5. Color properties

a. Perception—physiologic response to physical stimulus by the eye, which can distinguish three parameters

b. Measurement

c. Definitions

Chemical properties

1. Primary chemical bonding types

2. Secondary chemical bonds

3. Corrosion

a. Chemical corrosion—chemical reaction at surface

b. Electrochemical corrosion—chemical reaction that requires an anode (e.g., dental amalgam), a cathode (e.g., gold crown), an electrolyte (e.g., saliva), and an electrical circuit (e.g., contact) for electron flow (Figure 13-2)

c. Corrosion potential

Mechanical properties

1. Resolution of forces (Figure 13-3)

image

FIGURE 13-3 Resolution of forces.

2. Normalization of forces and deformations

3. Stress-strain diagrams

a. Plot of stress (vertical) versus strain (horizontal)

b. Analysis of curves (see Figure 13-4)

(1) Elastic behavior

(a) Elastic strain—initial response to stress (elastic—when the stress is removed, the strain returns to zero and the material returns to its original length)

(b) Elastic modulus—slope of first part of curve; represents the stiffness of the material, or the resistance to deformation under force

(c) Elastic limit (proportional limit)—stress above which the material no longer behaves totally elastically

(d) Yield strength—stress that is an estimate of the elastic limit at 0.002 permanent strain

(e) Hardness—value on a relative scale that estimates the elastic limit in terms of a material’s resistance to indentation, for example, Knoop hardness scale, Diamond pyramid hardness scale, Brinnell hardness scale, Rockwell hardness scale, Barcol scale, Shore A hardness scale, and Mohs’ hardness scale (Table 13-1); hardness values are used to determine the ability of abrasives to alter the substrates they contact

(f) Resilience—area under the stress–strain curve up to the elastic limit; estimates the total elastic energy that can be absorbed before the onset of plastic deformation

(2) Elastic and plastic behavior

(3) Time-dependent behavior

4. Principles of cutting, polishing, and surface cleaning

a. Terminology

b. Surface mechanics for materials (Table 13-2)

TABLE 13-2

Hardness Values for Dental Substrates*

Hardness Value Number
CAD/CAM ceramic 6–7
Porcelain 6–7
Composite 5–7
Glass 5–6
Dental enamel 5–6
Dental amalgam 4–5
Dentin 3–4
Hard gold alloys 3–4
Pure gold 2–3
Acrylic 2–3
Cementum 2–3

*Based on Mohs’ scale: diamond = 10; talc = 1 (see Table 13-1).

c. Factors affecting cutting, polishing, and surface cleaning

d. Factors affecting air abrasion

e. Precautions

Biologic properties

1. Definitions of biohazards

2. Definitions of local tissue interactions with biomaterials

3. Classification of biologic materials—tissue interfaces

4. Clinical analysis of biocompatibility

5. Agencies that oversee materials, devices, and therapeutics

Direct Preventive and Restorative Materials

Dental Amalgam

General considerations

1. Applications

2. Terminology

3. Classification of dental amalgam by:

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 13: Biomaterials
Premium Wordpress Themes by UFO Themes