Restorative and Laboratory Materials in Dental Science

Restorative and Laboratory Materials

Make up 6% of the round one written exam and cover the main ideas from the textbook resources.

Dental Cements

Used to retain crowns, bridges, inlays, and onlays; can be permanent or temporary.

Bases

Used to protect the pulp when the cavity is deep and when the pulp may be sensitive.

Liners

Low-strength materials that are placed under the restoration.

Bonding Agents

Used to improve the retention between the tooth and the restoration.

ADA

American Dental Association, which regulates dental materials.

FDA

Food and Drug Administration, which regulates dental materials.

Role of the Dental Assistant

Involves preparing and mixing materials, while the dentist places them in the oral cavity.

Properties of Dental Materials

Include acidity, adhesion, biting force, corrosion, dimensional change, elasticity, flow, galvanism, hardness, microleakage, retention, bonding, solubility, thermal conductivity, viscosity, and wettability.

Acidity

Effect on materials and tissues in the mouth; normal pH of the oral cavity is about neutral (pH 7.0).

pH Scale

Used to measure the acidity in the oral cavity.

Adhesion

The force of attraction that holds unlike substances together, involving physical or chemical forces.

Chemical Adhesion

A strong form of adhesion that is preferable.

Physical Adhesion

More common form of adhesion, such as dental plaque adhering to a tooth.

Expanded-function Dental Assistants

Must understand and be competent with placing and finishing dental materials.

Cavity Preparation Terminology

Terms used to describe the steps and processes involved in preparing a cavity.

Cavity Preparation Steps

The specific procedures followed to prepare a cavity for restoration.

Restorative Dentistry

Involves various materials and techniques for restoring teeth.

Cavity Detection

Techniques used to identify cavities in teeth.

Cavity Cleaners

Materials used to clean cavities before restoration.

Disinfectants

Used to eliminate bacteria and pathogens in the oral cavity.

Desensitizers

Materials used to reduce sensitivity in teeth.

Chemical Adhesion

Certain dental cements function on the basis of a chemical reaction, which results in chemical adhesion.

Biting Forces

Dental materials are subject to various types of biting forces.

Natural Dentition

Natural dentition can withstand much more force than prostheses, such as dentures and bridges.

Force

A force is defined as any push or pull on an object.

Resistance

The result of force on an object is resistance.

Stress

Stress is defined as the force per unit area of a material.

Strain

This change, or deformation, is known as strain.

Tensile Stress

Tensile pulls and stretches a material. Under tensile stress and strain, the structure tends to be elongated.

Ductility

The ability of a material to withstand forces of tensile stress without failing is known as ductility.

Compressive Stress

Compressive pushes, or compresses, a material.

Malleability

The ability of a material to withstand compressive stresses without fracturing is known as malleability.

Shearing Stress

Shearing slides one part of a material parallel to another part in a back-and-forth motion.

Bruxism

An example of shearing stress and strain is bruxism, or grinding of the teeth.

Corrosion

Corrosion is the result of chemical or electrochemical attacks by the oral environment on pure metal, such as gold, or on an alloy, such as amalgam.

Tarnish

Sometimes the metals become dull and discolored. This effect is referred to as tarnish.

Dimensional Change

Dimensional change in a material can occur from a variety of causes, such as the setting process of a material, or exposure to heat or cold.

Elasticity

Elasticity is the ability of a material to return to its original shape, after being distorted or deformed by an applied force, once that force is removed.

Elastic Modulus

The elastic modulus, or modulus of elasticity, is a measure of the stiffness of a material below the elastic limit.

Flow

A flow, or creep and slump, is a continuing deformation of a solid.

Galvanism

When two different metals are present in the mouth, there is a potential for the creation of small electrical shocks. This is known as galvanism.

Hardness

The resistance of a material to scratching or indentation is known as the material's hardness.

Microleakage

When saliva and debris from the oral cavity seep between the tooth structure and restorative materials, this is known as microleakage.

Retention

In dentistry, retention is the means by which materials are held in place.

Retention Methods

Different types of retention methods are used with the various types of restorative materials.

Direct Restorative Materials

Materials placed directly into the cavity preparation, such as amalgam and composites, are retained in place by mechanical means.

Mechanical Retention

A mechanical retention includes preparing the walls of the cavity preparation to be convergent, roughening the tooth surface with etchant, or placing retentive grooves into the cavity walls.

Indirect Restorations

Retention for indirect restorations, such as gold inlays or crowns, is accomplished with bonding agents and cements.

Cements and Bonding Agents

Cements and bonding agents may be retained to the tooth surface by mechanical or chemical means.

Chemical Retention

A chemical retention involves a chemical reaction between the tooth surface and the material.

Bonding

Bonding is the process by which materials adhere firmly or hold together.

Bonding Agent

In dentistry, a bonding agent is used to bond the dentin and enamel with restorative materials.

Solubility

When a material is soluble, it dissolves in fluid.

Solubility in Dental Materials

The solubility of a dental material is one factor used to determine its success in the oral cavity.

Use of Soluble Materials

A material that is soluble may be useful as a base or liner where it is not exposed to oral fluids.

Effect of Saliva on Soluble Materials

If the material is exposed to saliva, it dissolves and exposes the tooth structure.

Thermal Conductivity

Thermal conductivity is the ability of a material to transmit heat.

Thermal Conductivity Variability

With some materials heat transmits rapidly, while with others the process is very slow.

Thermal Conductivity and Dental Pulp

The thermal conductivity of a material is a consideration when it is placed near the dental pulp.

Protection from Thermal Changes

A material that has a low rate of thermal conductivity offers more protection.

Thermal Expansion

With temperature changes, materials expand and contract.

Dimensional Changes

Dimensional changes that occur from thermal expansion and contraction can lead to microleakage and sensitive teeth.

Viscosity

The viscosity of a material is related to its ability to flow.

Effect of Viscosity on Flow

The thicker the material, the less it flows; therefore, it is said to be more viscous than a thin material that flows easily.

Wettability

The ability of a material to flow over a surface is wettability.

Demonstrating Wettability

Wettability can be demonstrated by observing the shape of a drop on a solid material.

Types of Restorative Dental Materials

The ADA and the International Standards Organization (ISO) have classified restorative materials into three types according to their use and properties.

Type I Materials

Type I materials include cements or luting agents, which may be permanent or temporary materials.

Type II Materials

Type II materials include amalgam, composite, and glass ionomer, which may be permanent or temporary restorative materials.

Type III Materials

Type III materials include liners, bases, and bonding agents, which are placed in the cavity preparation.

Responsibility of Dental Assistant

It is the dental assistant's responsibility to maintain the materials and the mixing equipment.

Dental cements

Materials used in dentistry that can be set or cured by self-curing, light curing, or dual curing.

Self-curing

A method of setting dental cements through a chemical reaction between two materials.

Light curing

A method of setting dental cements using a curing light.

Dual curing

A method that combines self-curing properties with light-curing techniques.

Luting

The process of bonding or cementing together, often used for inlays and bridges.

Permanent luting cement

A long-term cementing agent used in dental procedures.

Temporary luting cement

A short-term cementing agent used in dental procedures.

Intermediate luting cement

A material that lasts six months to a year.

Liner

A material placed in a thin layer on the walls and floor of the cavity preparation to protect the pulp.

Base

Applied in a putty or thick layer between the tooth and restoration to protect the pulp from irritation.

Sedative or palliative effect

A soothing effect that a material may have on a tooth.

Varnish

A thin layer of material placed to seal the walls and floor of the cavity preparation.

Zinc phosphate cement

One of the oldest types of dental cements, used as a permanent luting and base cement.

Composition of zinc phosphate cement

Primarily zinc oxide with a small amount of magnesium oxide and pigments.

Liquid of zinc phosphate cement

A solution of phosphoric acid in water buffered to slow down the setting reaction.

Exothermic reaction

A chemical reaction that releases heat when zinc phosphate powder and liquid are mixed.

Strength of zinc phosphate cement

Reaches two-thirds of its strength in less than an hour.

Setting time of zinc phosphate cement

Sets (hardens) in 5 to 9 minutes with a mixing time of up to 2 minutes.

Viscosity of zinc phosphate cement

Affected by mixing time and temperature.

Mechanical interlocking

The method by which zinc phosphate bonds to the tooth.

Manipulation considerations of zinc phosphate cement

Includes mixing on a cool glass slab and using a cool stainless steel spatula.

Zinc Phosphate Cement

A type of cement that requires careful mixing to dissipate heat from the exothermic reaction, allowing for stronger cement.

Mixing Techniques for Zinc Phosphate Cement

Techniques include cooling the glass slab, mixing the first increment of powder into the liquid for 10 to 15 seconds, spatulating slowly, and mixing over a large area.

Zinc-Oxide-Eugenol Cement (ZOE)

A dental cement known for its sedative effect on dental pulp, used for various applications due to its diverse functions.

Type I ZOE

A weaker form of zinc-oxide-eugenol cement used for temporary restorations and cementation.

Type II ZOE

A reinforced and stronger form of zinc-oxide-eugenol cement used for permanent cementation.

Intermediate Restorative Material (IRM)

A type II zinc-oxide-eugenol cement that lasts up to 1 year when placed in a patient's mouth.

Forms of ZOE

ZOE is available in powder/liquid, two-paste systems, capsules, and syringes.