Key Properties and Types of Dental Materials

Acidity (pH)

Acidity refers to the pH level of a material and its effect on oral tissues.

Normal oral pH

Around neutral (pH 7.0).

Importance of Acidity

Dental materials must react appropriately to changing acidity levels in the mouth. Acidic materials can irritate gingival tissues or damage the pulp.

Example of Acidity

Zinc phosphate cement has an acidic liquid (phosphoric acid), which requires a protective base or liner to prevent pulp irritation.

Adhesion

The force of attraction that holds unlike substances together.

Types of Adhesion

Physical Adhesion: Common but weaker (e.g., dental plaque adhering to a tooth). Chemical Adhesion: Stronger and preferable (e.g., certain dental cements bond chemically to tooth structure).

Importance of Adhesion

Adhesion is critical for retaining restorations and preventing microleakage.

Biting Forces

The forces exerted on dental materials during mastication (chewing).

Types of Stress

Tensile Stress: Pulls and stretches a material (e.g., elongation of a material). Compressive Stress: Pushes or compresses a material (e.g., chewing forces). Shearing Stress: Slides one part of a material parallel to another (e.g., bruxism or teeth grinding).

Importance of Biting Forces

Dental materials must withstand these forces without failing.

Corrosion

Chemical or electrochemical attack on metals in the oral environment.

Causes of Corrosion

Reaction of metals with food or saliva, leading to pitting, roughness, or discoloration.

Example of Corrosion

Amalgam restorations can corrode over time, leading to tarnish or dullness.

Dimensional Change

Changes in the size or volume of a material due to setting, heat, or cold.

Importance of Dimensional Change

Dimensional changes can affect the fit of restorations.

Example of Dimensional Change

Impression materials must maintain accurate dimensions to ensure proper fitting of restorations.

Elasticity

The ability of a material to return to its original shape after being deformed by an applied force.

Elastic Modulus

Measures the stiffness of a material below its elastic limit.

Importance of Elasticity

Elastic materials are used in applications where flexibility is needed (e.g., impression materials).

Flow (Creep and Slump)

The continuing deformation of a solid under constant force.

Examples of Flow

Dental waxes and certain impression materials exhibit flow. Amalgam can flow under constant compressive forces.

Importance of Flow

Flow can affect the long-term stability of restorations.

Galvanism

The creation of small electrical shocks when two different metals are present in the mouth.

Cause of Galvanism

Oral fluids act as a conductor between the metals.

Example of Galvanism

A gold restoration in one arch contacting an amalgam restoration in the opposite arch can cause galvanism.

Importance of Galvanism

Galvanism can cause discomfort and should be avoided in restorative dentistry.

Hardness

The resistance of a material to scratching or indentation.

Importance of Hardness

Hard materials are more durable and resistant to wear.

Example of Hardness

Enamel is harder than dentin, and restorative materials should match the hardness of natural teeth.

Microleakage

The seepage of saliva and debris between the tooth structure and restorative materials.

Causes of Microleakage

Improper sealing of restorations.

Effects of Microleakage

Can lead to recurrent decay and tooth sensitivity.

Prevention of Microleakage

Proper cavity preparation and use of bonding agents or sealants.

Retention

The means by which materials are held in place.

Mechanical Retention

Achieved through undercuts, grooves, or roughening the tooth surface.

Chemical Retention

Achieved through chemical bonding between the tooth and material.

Retention

Ensures the longevity of restorations.

Bonding

The process by which materials adhere firmly to each other.

Bonding Agents

Used to bond restorative materials to enamel and dentin.

Bonding Importance

Bonding improves the retention and sealing of restorations.

Solubility

The ability of a material to dissolve in fluid.

Solubility Importance

Soluble materials are useful as bases or liners where they are not exposed to oral fluids.

Solubility Risk

If exposed to saliva, soluble materials can dissolve and expose tooth structure.

Thermal Conductivity

The ability of a material to transmit heat.

Thermal Conductivity Importance

Materials with low thermal conductivity protect the pulp from temperature changes.

Thermal Expansion

The expansion and contraction of materials with temperature changes.

Thermal Expansion Importance

Dental materials should expand and contract at a rate similar to tooth structure to prevent microleakage.

Viscosity

The ability of a material to flow.

Viscosity Importance

High viscosity materials are thicker and do not spread easily.

Viscosity Example

Cement that is too viscous may not flow adequately over the tooth surface, affecting retention.

Wettability

The ability of a material to flow over a surface.

Wettability Importance

Good wettability ensures proper coverage and adhesion of materials.

Wettability Example

Pit and fissure sealants need good wettability to cover the grooves of the occlusal surface.

Zinc Phosphate Cement

High strength, reaching two-thirds of its strength in less than an hour.

Zinc Phosphate Cement Setting Time

Sets (hardens) in 5 to 9 minutes.

Zinc Phosphate Cement Mixing Time

Long mixing time (up to 2 minutes).

Zinc Phosphate Cement Bonding

Bonds to the tooth by mechanical interlocking.

Zinc Phosphate Cement Reaction

Exothermic reaction during mixing (releases heat).

Zinc Phosphate Cement pH

Acidic liquid, which can irritate the pulp, so a protective base or liner is required.

Zinc Phosphate Cement Viscosity

Viscosity is affected by mixing time and temperature.

Zinc-Oxide-Eugenol (ZOE) Cement

Sedative or soothing effect on the dental pulp.

ZOE Type I

Weaker and used for temporary restorations and cementation.

ZOE Type II

Reinforced and stronger, used for permanent cementation.

Intermediate Restorative Material (IRM)

A type of ZOE that lasts up to 1 year.

ZOE Solubility

Very soluble in the mouth.

ZOE pH

Neutral pH, so it does not require a protective base or liner.

ZOE Compatibility

Not compatible with composites or acrylic restorations due to eugenol, which retards the setting process.

Viscosity

Viscosity is affected by mixing time and temperature.

Type I ZOE Cement

Weaker and used for temporary restorations and cementation.

Type II ZOE Cement

Reinforced and stronger, used for permanent cementation.

ZOE Cement Solubility

Very soluble in the mouth.

ZOE Cement pH

Neutral pH, so it does not require a protective base or liner.

ZOE Cement Compatibility

Not compatible with composites or acrylic restorations due to eugenol, which retards the setting process.

Polycarboxylate Cement

Kind to the pulp and chemically bonds to the tooth structure.

Polycarboxylate Cement Setting Time

Sets in 3 to 5 minutes without exothermic heat.

Polycarboxylate Cement Strength

Strength similar to reinforced ZOE but less than zinc phosphate.

Glass Ionomer Cement

Strong enough to act as a supportive base, similar in strength to zinc phosphate.

Glass Ionomer Cement Bonding

Bonds mechanically and chemically to enamel, dentin, and metallic materials.

Glass Ionomer Cement Fluoride Release

Releases fluoride ions, which help prevent secondary decay.

Glass Ionomer Cement Solubility

Low solubility in the mouth.

Glass Ionomer Cement Setting Time

Complete setting reaction takes up to 24 hours.

Resin-Modified Glass Ionomer Cement

Modified to include a light-curing resin component.

Resin-Modified Glass Ionomer Cement Properties

Stronger, more water-insoluble, and more adhesive to tooth structures than conventional glass ionomer.

Calcium Hydroxide Cement

Used as a low-strength base or liner, particularly in pulp capping procedures.

Calcium Hydroxide Cement Properties

Therapeutic effect on the pulp, encouraging secondary dentin formation.

Composite Resin Cement

Used for permanent cementation of various restorations, including crowns, veneers, and orthodontic brackets.

Cavity Varnish

Used to seal dentin tubules exposed during cavity preparation.

Fluoride Varnish

Used to prevent dental decay and as a desensitizer.

Etchants

Typically 30-40% phosphoric acid solution used to enhance retention/bonding between the tooth surface and dental materials.

ADA Seal of Acceptance

Indicates that a dental product meets safety and efficacy standards.

Responsibilities of Dental Assistant

Prepare and mix dental materials, assist the dentist in placing materials in the oral cavity, understand material properties for proper preparation and patient education, and expanded-function dental assistants may place and finish materials.

Importance of Knowledge for Dental Assistants

Dental assistants must understand material properties to ensure proper use and patient safety.

Restorative Dentistry

The process of restoring teeth affected by decay, fracture, abrasion, or attrition.

Materials Used in Restorative Dentistry

Amalgam, composites, and other direct restorative materials.

Reasons for Restoring Teeth

Arrest the loss of tooth structure, prevent recurrence of decay, restore tooth contour and function, and improve esthetics.

Cavity Detection Methods

Radiographs, explorer, caries detection dye, and DIAGNOdent.

Radiographs

Detect decay not visible to the eye.

Explorer

Manual probing to detect soft areas in the tooth.

Caries Detection Dye

Distinguishes between healthy and decayed dentin.

DIAGNOdent

A laser device that measures fluorescence levels to quantify caries progression.