15: Dental Biomaterials

CHAPTER 15 Dental Biomaterials

CHARACTERISTICS OF DENTAL MATERIALS

Understanding of mechanical, physical, electrical, surface, biological properties of dental materials enables clinician to determine proper use and care of dental materials.

Mechanical Properties

Mechanical properties include reactions of materials to application of external forces, such as the magnitude of biting forces.

Table 15-1 Hardness of restorative materials

Dental material KHN
Acrylic 20
Dentin 70
Calculus on teeth 86
Enamel 350
Porcelain 400-500

KHN, Knoop hardness number.

CLINICAL STUDY

Age 59 YRS SCENARIO
Sex image Male image Female The patient is in the dental office because of a fractured tooth. Visual examination of tooth #18 reveals a fracture of the ML cusp. The remainder of the tooth holds a large MOD (mesio-occlusal-distal) amalgam restoration. After the dentist removes all of the old amalgam, some caries is discovered that will result in a near pulpal exposure. Patient also has amalgam restorations in teeth #2, #14, #19, and #31, and full gold crowns on teeth #3 and #30.
Chief Complaint “I bit down on a popcorn kernel and my tooth broke.”
Medical History

Current Medications None Social History

Physical Properties

Physical properties depend primarily on the type of atoms and bonding that is present in a material. Allows clinician to understand how given material will withstand oral environment (i.e., temperature fluctuations, biting forces, moisture).

Table 15-2 Expansion of tooth and dental materials: linear thermal coefficients of expansion

Material Coefficient (×10-6/°C)
Tooth 11.4
Amalgam 25.0
Acrylic resin 81.0
Composite resin 35.0
Silicone impression material 210.0

Surface Properties

Surface properties are associated with surface of dental materials and include surface tension and absorbability.

C. Attaching solid structures to each other: by mechanical bonding, cohesion, adhesion.

3. Adhesion: force of attraction between unlike atoms and molecules on two different surfaces when brought into contact.

Biological Properties

Biological properties refer to the biological response of the human body to various materials and the continued examination of the host–foreign body response. Response of both patients and clinicians can involve allergy, microleakage, and toxicity factors.

See Chapter 8, Microbiology and Immunology: allergic reactions, including rubber latex allergy.

IMPRESSION MATERIALS

Function of impression and replication materials is to accurately record hard and soft tissues in the oral cavity. Impressions produce negative reproduction, which then can be used by clinician for construction of restorations to replace missing tooth structure and for fabrication of preventive devices. Vary in accuracy and ease of use, especially in removal from the mouth, such as around tooth undercuts, portion of tooth that lies between its height of contour and attached gingiva. Replication materials to preserve the impressions are discussed in next section.

C. Characteristics, properties, manipulation of each:

3. Irreversible hydrocolloid (alginate):

Table 15-3 Composition of irreversible hydrocolloid alginate impression material

Ingredient Percentage (%) Function
Diatomaceous earth 60 Filler
Calcium sulfate 16 Reacts with potassium alginate to create gelation
Potassium alginate 15 Reacts with calcium sulfate to create gelation
Zinc oxide 4 Filler
Potassium titanium fluoride 3 Accelerates setting of gypsum
Trisodium phosphate 2 Retardant

Table 15-4 Composition of reversible hydrocolloid

Ingredient Percentage (%) Function
Agar-agar 8-15 Substance is extracted from a type of seaweed whose fibrils form a colloid that results in a partially rigid but elastic gel
Water 80-85 Main component that occupies the spaces between the agar-agar fibrils
Borax Trace amounts Increases the strength of the gel (also can retard the setting of gypsum; requires the addition of an accelerator)
Potassium sulfate 2 Accelerates the setting of gypsum

Replication Materials

Impression plaster and stone are examples of replication materials that are used to produce positive reproduction of impressions. Standard precautions for lab discussed later.

D. Types and uses of gypsum:

E. Procedure for use:

Table 15-5 Water/powder (W/P) ratios of gypsum materials

Gypsum Water (mL/100 g powder)
Model plaster (type II) 37-50
Dental stone (type III) 28-32
High-strength dental stone (type IV-V) 19-24

Recommended W/P ratios vary among products and manufacturers.

DIRECT RESTORATIVE MATERIALS

Direct restorative materials can be placed directly in or on a prepared tooth. Advantageous because of immediate results and timesaving benefits. Can be either temporary or permanent restorations.

See Chapter 11, Clinical Treatment: enamel (pit and fissure) sealants.

Esthetic Restorations

Esthetic (tooth-colored) restorations include ceramics, porcelains, composites.

C. Composites: used in ALL classes of restorations, as veneers to cover teeth stained by drugs and chemicals such as fluoride or tetracyclines, to fill spaces between teeth (diastemas), to enhance contour of misshapen teeth.

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 15: Dental Biomaterials
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