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Dental Materials (1)

Introduction of Dental Materials

Dr. Hiba Al-Helou

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Introduction of dental materials

The science of dental materials involves a study of the composition and

properties of materials and the way in which they interact with the

environment in which they are placed.

Many dental materials are fixed permanently into the patient’s mouth or are

removed only intermittently for cleaning. Such materials have to withstand

the effects of a most hazardous environment. Temperature variations, wide

variations in acidity or alkalinity and high stresses all have an effect on the

durability of materials.

Normal temperature variations in the oral cavity lie between 32°C and 37°C

depending on whether the mouth is open or closed. The ingestion of hot

or cold food or drink however, extends this temperature range from 0°C up to

70°C. The acidity or alkalinity of fluids in the oral cavity as measured by pH

varies from around pH 4 to pH 8.5, whilst the intake of acid fruit juices or

alkaline medicaments can extend this range from pH 2 to pH 11.

The load on 1 mm2 of tooth or restorative material can reach levels as high as

many kilograms indicating the demanding mechanical property requirements

of some materials.

First , the loss of tooth structure, which requires restoration of a portion of an

anterior tooth, may be caused either by injury or by caries . Resin composite

materials usually are chosen for these restorations. These materials are shaded

to match the teeth in appearance. Their strength is a secondary factor because

the anterior teeth are usually not subject to high biting forces. Although resin

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composite materials are weaker than metals, their excellent appearance and

acceptable durability are the main reasons for their choice.

A metallic restoration may be preferable to a resin composite material for the

restoration of the portion of a posterior tooth subject to greater biting forces

because of strength and wear resistance considerations.

Dental silver amalgam restorations and gold inlays are used most often for this

type of posterior restoration.

The cavity preparation for the gold alloy inlay is tapered so that the base is

slightly smaller than the occlusal surface. This design is required because the

solid cast gold alloy or ceramic restoration must be able to be inserted and

cemented to the cavity preparation.

When the inlay involves the occlusal and proximal surface or surfaces and

covers all the cusps it is called an onlays.

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If a deep restoration is required, a cement base is placed below the metallic

restoration. Such a base insulates the pulp of the tooth from the irritation of

thermal sensations transmitted through metallic restorations. A number of

cements are available for this application.

A crown is a restoration of part or the entire coronal portion of a tooth. The

cast metallic crown is suitable for the posterior portion in the mouth, where

strength is needed and appearance is secondary.

A crown made from a ceramic can be used because this material combines

strength with excellent esthetic properties. Different types of ceramics are

available. A ceramic-fused-to-metal crown, which combines the esthetics of

a ceramic veneer and the strength and fit of a cast metal crown may be used.

On occasion, the pulp of the tooth becomes infected and must be removed.

Drilling through the crown allows access to remove the pulp and to clean out

the root canal. Once the infection is controlled the root canal is filled-

frequently with gutta-percha rubber- a restoration is placed in the access

opening. If the crown of the tooth is degraded severely, a metal post and core

can be fabricated and cemented into the root canal. A ceramic or other

restoration can be made and cemented to the core.

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Esthetic veneers may be used to cover unsightly areas of anterior teeth that

are severely discolored, malformed, or eroded. The veneer can be made from

a resin composite that can be placed directly or indirectly (cemented) or can

be a cemented ceramic veneer.

The fixed partial denture (bridge) is used to replace a missing tooth or teeth.

The two teeth adjacent to the space must be prepared with abutment

restorations to support the artificial tooth (pontic) or teeth. Gold or nickel-

chromium alloys are used for fixed partial dentures Because of

Their strength

Tarnish resistance

Ease of casting (fabrication).

If a number of teeth are missing, a more complex prosthetic appliance

known as a removable partial denture may be used. The artificial teeth are

mounted on a metal framework. Clasps are used to attach the partial denture

to the remaining abutment teeth. Silver-colored metals composed of mainly

nickel, cobalt, and chromium is strong and highly resistant to corrosion.

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Acrylic resin materials that possess excellent esthetic qualities are used to

fabricated artificial teeth on the removable partial denture.

If all the natural teeth in an arch are lost, a full denture or complete denture

is required. The denture consists of a base with artificial teeth. Most denture

bases are made from acrylic resins that are pigmented to match the pink shades

of the oral tissues. The teeth are made from acrylic resin or porcelain

Dental Implant has been used to replace the root of extracted teeth by insertion

it in bone, after that it support and stabilize the prosthesis. Manufactures

use titanium or a titanium alloy to construct the implant, and ceramic implants

have been used. The surface may be plasma-sprayed with Titanium or coated

with hydroxyapatite (similar to the mineral portion of human enamel).

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