Dental Materials (properties and prosthetic materials) by Eman Alsheikh

Dental Material Science Study Notes & Questions

Dr. Eman Alsheikh

Part (1)

Dental Material Sciences

Dr Eman Alsheikh

Dental ▪ DENTAL MATERIALS A science that deals with the study of materials used in dentistry, which includes chemical properties, physical properties, manipulation & their applications in dental practice. ▪ GOAL OF DENTISTRY Maintain or improve the quality of life of dental patients by: 1) 2) 3) 4) 5)

Preventing disease, Relieving pain, Improving mastication efficiency, Enhancing speech, Improving the general appearance of patients.

……. ➢ Dental materials play an integral role in dentistry. ➢ Besides use in the oral cavity many materials are also used in the laboratory to aid in the fabrication of appliances or prostheses. ➢ Dentistry over the years has evolved into a highly complex field & materials play a critical role in every aspect of treatment.

▪ OBJECTIVES OF THE DENTAL BIOMATERIAL SCIENCES ARE TO 1• Know the proper usage of dental materials 2• Know the physical & chemical properties of dental materials 3• Understand proper manipulation of materials in dental profession 4• Stimulate further research (improve the quality of the material). 5• Bridge the gap between knowledge from “chemistry, physics, etc.” with dental materials

Dental Material Sciences

Dr Eman Alsheikh

▪ Classifications of Dental Materials A. General Classification: In general, Dental Materials may be classified into: (1) Preventive materials (2) Restorative materials (3) Auxiliary materials

1) Preventive Materials • Preventive materials include pit & fissure sealants, liners, bases & other materials used to prevent the onset of dental diseases.

2) Restorative Materials • Restorative materials include materials used to repair or replace tooth structure. • This includes materials like amalgam, composites, ceramics, cast metal structures & denture materials.

3) Auxiliary Materials • Auxiliary materials are substances that aid in the fabrication process but do not actually become part of the restoration, appliance or prosthesis. • This includes materials like gypsum products, impression materials, casting investments, waxes, etching gels, custom tray materials, etc. Note: − Materials used to replace lost oral tissues are called restorative materials. Those that replace lost tooth structure & restore the function of the teeth must be strong & hard. − Some restorative materials simulate the appearance of the tissues that are being replaced.

− Tissues simulated by restorative materials include: 1) The enamel of teeth (fillings & crowns), 2) The mucosa of the periodontium (dentures), 3) The skin of the face (maxillofacial prostheses). − Materials that are tooth-colored are often called esthetic materials.

Dental Material Sciences

Dr Eman Alsheikh

B. Classification by Use: Dental materials may be classified by their use into: 1. Restorations

2. Crowns

3. Bridges

4. Complete & Partial Dentures

5. Impressions, Casts, & Models

6. Cements

7. Temporary Materials

8. Preventive Materials

9. Polishing Materials 10. Implants 11. Specialty Materials

Depending on the degree of destruction of a tooth, different restorations or fillings are used to replace lost tooth structure. Some restorations replace a small to moderate amount of tooth structure & are supported by the remaining tooth structure. Crowns are used to restore teeth when a substantial amount of tooth structure is missing. Crowns encircle & support the remaining tooth structure. Crowns are cemented in place. A dental bridge replaces a lost tooth or teeth. A typical dental bridge is much like a bridge over a river. At each end, the dental bridge is supported by an actual tooth called an abutment. Each abutment tooth is prepared & then restored with a crown called a retainer. The missing tooth is replaced with a false tooth called a pontic. A prosthesis is an artificial device that replaces a lost organ or tissues. A denture replaces missing teeth, bone, & gingiva after the teeth have been lost or extracted. A complete denture is supported by & precisely rests on the mucosal tissue covering the maxilla or mandible. A removable partial denture replaces few or many teeth placed & is removed by the patient in the same manner as a full denture, & it has several metal clasps that are designed to encircle several remaining teeth so that the prosthesis is stabilized. The dental impression (or negative copy) is then filled with a material that solidifies to form the replica. If a restoration is constructed on the replica, it is called a cast. If the resulting replica is used to study the size and position of the oral tissues, it is called a study model or diagnostic cast. (a) Luting agents: are frequently called dental cements. The cement holds the crown onto the prepared tooth & fills in the microscopic gaps between the tooth and the crown. (b) Bases & liners: materials used for luting crowns, bridges, or inlays may also serve other purposes. A liner would be a relatively thin layer of material painted on to protect the underlying dentin from chemical irritation. A base has greater bulk, which serves to restore part of the missing tooth structure and to provide thermal insulation. (a) Temporary crowns: is constructed & luted during the same appointment in which the crown preparation is performed. (b) Temporary restorations: A dentist may remove all or part of the decay from a tooth & then place a temporary restoration to give the pulp time to heal before determining the specific treatment that is needed. Several materials are used predominantly to prevent disease or trauma. These include: (a) Pit and fissure sealants, to prevent decay. (b) Mouthguards, to prevent injury during athletic activities. (c) Fluoride trays, custom and stock, which fit over the teeth to apply topical treatments. Custom fluoride trays look very much like custom mouthguards or bleaching trays. A tremendous amount of time in a dental practice is spent in polishing teeth, restorations, & appliances. Use of a rubber cup with an abrasive agent is termed polishing, but the predominant function is to remove stain, plaque, and debris from the tooth surface. Dental implants typically are screws or posts that are anchored into alveolar bone and that protrude through the gingiva into the oral cavity. Many specialties in dentistry have products & materials unique to that field. At times, these products overlap (e.g., sutures), whereas others are limited strictly to that specialty (e.g., “rubber bands” or elastics used in orthodontics).

Dental Material Sciences

Dr Eman Alsheikh

Restorations

Crowns

Bridges

Complete Dentures

Partial Dentures

Impressions, Casts, & Models

Dental Material Sciences

Dr Eman Alsheikh

Cements (base)

Temporary Materials

Preventive Materials

Polishing Materials

Implants

Specialty Materials

A mouthguard

Dental Material Sciences

Dr Eman Alsheikh

C. Classification by Location of Fabrication I. Direct Restorative Materials “Some restorations are constructed directly in the oral cavity and are called direct restorative, such as: Amalgam, composite, Glass ionomers & other cements” II. Indirect Restorative Materials “materials must be fabricated outside the mouth because the processing conditions of many materials would harm oral tissues, such as: Gold, Ceramic materials”

D. Classification by Longevity of Use 1. Permanent Restorations: Permanent restorations are those restorations that are not planned to be replaced in a particular time period. Although they are referred to as permanent, they are not. Fillings, crowns, bridges

2. Temporary Restorations “provisional restorations” Temporary restorations are restorations that are planned to be replaced in a short time (a week or a month).

3. Interim Restoration At times, dental treatment requires “long-term” temporary restorations or “interim” restorations.

Classification of Dental Caries & Restorations Dental caries is not evenly distributed throughout the mouth. Certain surfaces of the teeth are particularly susceptible to carious lesions; others are nearly immune. Dr. G.V. Black classified the most common sites for dental caries. His classification system adequately describes most simple carious lesions. In high-caries patients, a single tooth may have more than one lesion. These lesions may be of the same class or of different classes. At times, extensive lesions could be described as being a combination of two classes.

Dental Material Sciences

Dr Eman Alsheikh

❑ Properties of materials can be divided into three categories: 1. Physical >> Mechanical 2. Chemical 3. Biologic Physical properties: ❑ Physical properties determine how materials respond to changes in their environment. ❑ They are based on the laws of physics that describe mass, energy, force, light, heat, electricity, & other. ❑ Hue, value chroma & translucency – based on laws of optics. ❑ Color, density, & thermal conductivity are examples of physical properties. Mechanical properties: ❑ Are a subgroup of physical properties. ❑ They describe a material’s ability to resist forces. ❑ The Mechanical properties dependent on the amount of material & on the size & shape of the object. ❑ Examples are strength & stiffness. Chemical properties: ❑ Describe the setting reactions as well as the decay or degradation of materials. ❑ For example, gypsum products (used to make study models) set by a precipitation process, whereas dental composites polymerize. Biologic properties The biological properties of materials are the effects the materials have on living tissue. For example, a crown should not irritate the gingiva, tongue, or buccal mucosa. ❑ Materials use in oral cavity known as BIOMATERIALS.A biomaterial can be defined as any substance other than a drug that can be used for any period of time as a part of system that treats, augments or replaces any tissue, organ or function of the body. ❑ All materials have physical properties like color, weight, solubility, thermal conductivity & others, also mechanical properties like hardness or softness, strength or weakness.

Dental Material Sciences

Dr Eman Alsheikh

❑ There is no material till now which has ideal physical & mechanical properties. ❑ Most materials have some good & bad properties & sometime a property that is bad in one material may be good or acceptable in another.

Physical Properties 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12)

Density Boiling & melting points Thermal conductivity Heat capacity Heat of fusion & vaporization Electrical conductivity Viscosity Hardness Abrasion resistance Solubility Water sorption Color

Density: ❑ Is the mass per unit volume. Lightness is always an advantage in restorative materials, but sometimes TIN or LEAD is used inside full lower denture to make it heavy to control its mobility. ❑ Gold= 14 gm/ cm3 ❑ Acrylic= 1.2 gm/cm3 ❑ Chromium/ cobalt= 8.3 gm/cm3 ❑ Water= 1 gm/cm3 Boiling & Melting point: ❑ Some dental metals melt at very high temperatures & are very difficult to work with. ❑ Other materials do not boil or melt; instead, they decompose if heated sufficiently. ❑ Dental waxes are an example. Thermal Conductivity: ❑ Defined as the ability of a material to transmit heat or cold. ❑ A low thermal conductivity is desired in restorative materials used on the tooth. ❑ High thermal conductivity is desirable where the material covers soft tissue.

Dental Material Sciences

Dr Eman Alsheikh

Very Important NOTE: ◼ Generally, metals are better heat conductors than non-metals. ◼ Melting filling material like AMALGAM, sometimes cause pulp pain by transmitting heat or cold more than natural tooth especially in deep cavities thus they require heat insulting layer between the filling & the pulp.

Heat Capacity: ❑ The heat capacity of a material is a measure of the amount of thermal energy that a material can store. ❑ Some materials require more energy than others to heat. ❑ The specific heat capacity of a material is the amount of energy needed to raise the temperature of one unit of mass of that material by 1°C. ❑ Specific heat capacity is measured as Cal/g · deg. ❑ The heat capacity of water is 1 Cal/g · deg

Heat of Fusion & Vaporization: o The heat of fusion is the amount of energy required to melt a material. o On the other hand, the heat of vaporization is the amount of energy required to boil a material. o Both are typically large in relation to the heat capacity.

Electrical conductivity ❑ Metals are good electrical conductors. ❑ Polymers & ceramics are poor conductors and are termed insulators. Hardness ❑ It is the resistance of the material to deformation caused by penetrating or starching the surface. ❑ The Knoop hardness number (KHN) of enamel is 350, whereas the KHN of dentin is 70. ❑ Some dental materials are harder than enamel. - Porcelain has a KHN of 400 to 500. ❑ Other materials are not as hard as enamel. -

For example, acrylic denture teeth have a KHN of 20.

Dental Material Sciences

Dr Eman Alsheikh

Abrasion Resistance {wear resistance} ❑ In dentistry, we are interested in the abrasion resistance of dental restorations to food, opposing teeth, & other dental materials such as ceramic crowns or porcelain denture teeth. ❑ We are also interested in the wear of natural teeth opposing dental restorations. If a restorative material is too hard, it will wear the opposing teeth at an unacceptably accelerated pace. ❑ Restorative materials should not dissolve in the mouth, & if it is dissolves, it should not release toxic substance. ❑ Solubility of silicate = 0.7 -1.6% ❑ Solubility of composite = 0.01 %

Color ❑ Dimensions of Color: 1. HUE: Refers to the basic color of an object, e.g., whether it is red, green or blue. 2. VALUE: Colors can be separated into ‘light’ and ‘dark’ shades. Value represents the amount of lightness or darkness in the color. This lightness which can be measured independently of the hue is called value. 3. CHROMA: A particular color may be dull or more ‘vivid’, this difference in color intensity or strength is called chroma. Chroma represents the degree of saturation of a particular hue (color).

◼ Red can vary from scarlet to pink. ◼ Scarlet is more intense, having higher chroma; Pink is dull & has low saturation, so comparatively dull color.

Many dental restorative materials have to look like natural teeth & should not stain or change color by time. The anterior filling & artificial tooth material should be translucent. Translucence is the optical property that allows the light to go short way in the material before being reflected out again. Also, should looks like natural tooth substance at different Light conditions, such as day light & artificial light, ex, an artificial tooth may be acceptable in ordinary light but may be discovered by the relative darkness of the material in fluorescent light. For denture the material should have the same appearance of natural gum acrylic material can be made with various shades of pink to look as natural gum

Dental Material Sciences

Dr Eman Alsheikh

Solubility: ❑ Materials placed in the oral cavity are exposed to various aqueous fluids. The solubility of materials in water is an important consideration. ❑ Solubility is the amount of a material that dissolves in a liquid, such as water. ❑ To measure solubility, a test sample is immersed in water. The weight of the material dissolved into the water is the solubility of that material. Excessive solubility leads to loss of material & increases the risk of recurrent decay.

Water Sorption: ❑ Some materials absorb water. This property is termed water sorption. Water sorption is measured much like solubility. ❑ A test sample is immersed in water, and the weight that is gained by that sample is the water sorption.

Viscosity ❑ The viscosity of a material is its ability to flow. ❑ Thick or viscous liquids flow poorly, whereas thin liquids flow easily. ❑ Viscosity is a temperature-dependent property. For example, pancake syrup pours much more easily when it is warmed. ❑ A low viscosity & the ability to wet a surface are important in the use of many dental materials. ❑ Wetting a surface with an adhesive material, such as a sealant, brings the material into intimate association with the surface so that chemical & micromechanical bonding can occur.

Creep: ❑ Time dependent plastic deformation or change of shape that occurs when a metal is subjected to a constant load near its melting point is known as creep. ❑ Creep may be static or dynamic in nature: A. Static creep is a time dependent deformation produced in a completely set solid subjected to a constant stress. B. Dynamic creep produced when the applied stress is fluctuating, such as in fatigue type test.

Dental Material Sciences

Dr Eman Alsheikh

Flow: ❑ It is somewhat similar to creep. ❑ In dentistry, the term flow is used instead of creep to describe rheology of amorphous substances, e.g., waxes. ❑ Although creep or flow may be measured under any type of stress, compression is usually employed for testing of dental materials.

Mechanical Properties ❑ One of the most important properties of dental materials is the ability to withstand the various mechanical forces placed on them during use as restoration, impression, models, appliances & tools.

❑ Mechanical properties are subset of physical properties that are based on the laws of mechanics that is the physical science that deals with energy and forces and their effects on the bodies. These properties are expressed most often in units of stress and strain.

❑ The basic mechanical properties: 1. 2. 3. 4.

Stress Strain Strength Elasticity

Stress ❑ When an external force is applied to acts a body, an internal force, equal in magnitude and opposite in direction to the applied force is set up in the body. ❑ This internal resistance to the external force is called “STRESS”. ❑ Stress defined as: the force per unit area induced in a body in response to some externally applied force. ❑ It is force\area measured in kg\cm2 or pound\inch2 or Pascal.

Types of Stress: ❑ Every stress is accompanied by a strain of the same type. ❑ There are different types of stresses according to the direction of the applied force.

Dental Material Sciences

Dr Eman Alsheikh

A- Tensile stress: ▪

It is the amount of force that can be used to stretch or elongate the material.

▪

Tensile stress is usually accompanied by tensile strain.

B- Compressive stress: ▪

It is the force per unit area induced in the material in response to externally applied force which tends to compress or shorten the material; it is usually accompanied by compressive strain. Investment materials, restorative materials & models should have high compressive strength

Dental Material Sciences

Dr Eman Alsheikh

C- Shear stress: ▪

It is the force per unit area induced in the material in response to externally applied force, one part of the force is in one direction while the other is in the opposite direction.

▪

Shear force is the force which cause tearing a paper or card. If one part of the crown is in occlusion while the rest is not, shear stress will develop. It is accompanied by shear strain

❑ Usually, three types of stress occur at the same time, if a piece of metal is being bend it will exhibit tensile stress on the outer surface, compressive on the inner & shear in the middle.

Dental Material Sciences

Dr Eman Alsheikh

Strain ❑ Is the change in dimension per unit dimension caused by externally applied forces. It is a unit less quantity. ❑ Strain

Final length Original length

❑ The stain may be recoverable, that is the material will return to its original length after removal of the applied force (elastic strain), or the material may remain deformed, in which case the strain is non-recoverable (plastic strain). A third possibility is that the strain may be partially recoverable (visco-elasticity).

Strength: ❑ It is the maximal stress required to fracture a structure. ❑ The three basic types of strength are: 1. Tensile strength 2. Compressive strength 3. Shear strength

Elasticity: ❑ Phenomenon of change in shape when apply force and when the force is removed the material returns to the original shape. ❑ The object returns to its original shape because the atoms return to their original position.

Dental Material Sciences

Dr Eman Alsheikh

Biological considerations of dental materials ❑ The importance of learning the biological properties of dental materials is to assess the biocompatibility of the material in use. ❑ Biocompatibility is defined as ability of biomaterial to perform its desired function without eliciting any undesirable local or systemic effects in the recipient & beneficiary of that therapy, but generating the most appropriate beneficial cellular or tissue response, thus optimizing the clinical relevance of that therapy. {Williams, 2008}

Biological requirements of dental materials ❑ A dental material should: 1. Be non-toxic to the body 2. Be non-irritant to the oral or other tissues 3. Not produce allergic reactions 4. Not be mutagenic or carcinogenic

Classification of materials from a biological perspective A. Those which contact the soft tissues within the mouth B. Those which could affect the health of the dental pulp C. Those which could affect the periapical areas of the tooth such as root-canal medicaments, filling materials, etc. D. Those which affect the hard tissues of the teeth E. Those used in the dental laboratory for fabricating dental appliances, which when handled may be accidentally ingested or inhaled

Examples of HAZARDS from chemicals in dental materials 1. Some dental cements are acidic and may cause pulp irritation. 2. Polymer based filling materials may contain irritating chemicals such as unreacted monomers, which can irritate the pulp. 3. Phosphoric acid is used as an etchant for enamel. 4. Mercury is used in dental amalgam; mercury vapor is toxic.

Dental Material Sciences

Dr Eman Alsheikh

Classification of adverse reactions from dental materials ❑ A number of biological responses are possible from materials. However, they may be broadly grouped into: 1. Toxic 2. Inflammatory 3. Allergic 4. Mutagenic

❑ Fortunately, most materials are screened very early on for toxicity & mutagenicity, therefore most of the possible responses if any to dental materials usually fall in the inflammatory or allergic category.

❑ Adverse effects may also be classified as: 1. Local 2. Systemic

❑ A local effect is a result of the direct contact of the material to the regions immediately adjacent to the material. Example of a local reaction is the allergic response of the oral mucosa to the denture seen in some individuals.

❑ A systemic reaction is caused by the absorption of the material into the body through local absorption, ingestion or inhalation.

Dental Material Sciences

Dr Eman Alsheikh

Chemical Properties TARNISH ➢ Tarnish is a surface discoloration on a metal or even a slight loss or alteration of the surface finish or luster. ➢ Tarnish generally occurs in the oral cavity due to: 1. Formation of hard & soft deposits on the surface of the restoration, e.g., calculus, mucin & plaque. 2. Pigment producing bacteria, produce stains. 3. Formation of thin films of oxides, sulfides or chlorides.

CORROSION ❑ It is not a surface discoloration but actual deterioration of a metal by reaction with the environment. ❑ Water, oxygen, chloride ions, sulfides like hydrogen sulfide or ammonium sulfide contribute to corrosion attack in the oral cavity. Various acids such as phosphoric, acetic and lactic are also present.

Classification of corrosion 1) Chemical or dry corrosion The metal reacts to form oxides and sulfides in the absence of electrolytes. Example — Formation of Ag2S in dental alloys containing silver. — Oxidation of alloy particles in dental amalgam.

2) Electrolytic or electrochemical or wet corrosion This requires the presence of water or other fluid electrolytes.

Dental Material Sciences

Dr Eman Alsheikh

What are impression materials? ❑ A dental impression is a negative record of the tissues of the mouth. It is used to reproduce the form of the teeth & surrounding tissues. ❑ The negative reproduction of the tissues given by the impression material is filled up with dental stone or other model materials to get a positive cast. ❑ The positive reproduction of a single tooth is described as a ‘die’, & when several teeth or a whole arch is reproduced, it is called a ‘cast’ or ‘model’.

❑ Impression materials are used to make replicas of oral structures. ❑ All impression materials must be in a plastic or fluid state while the replica is being made.

Classification of impression materials

Dental Material Sciences

Dr Eman Alsheikh

There are several ways of classifying impression materials 1. According to mode of setting & elasticity 2. According to their uses in dentistry

According to their uses in dentistry: 1. Impression Materials used for Complete Denture Prosthesis ➢ Impression plaster, impression compound & impression paste set to a hard rigid mass & hence cannot be removed from undercuts without the impression being fractured or distorted. Therefore, these materials are best suited for edentulous mouth.

2. Impression Materials used for Dentulous Mouths ➢ On the other hand, alginates & rubber base impressions are sufficiently elastic to be withdrawn from undercut areas. Such elastic impression materials are suitable for impressions for fabrication of removable & fixed partial denture prostheses, where the impressions of the ridge & teeth are required. The rigid impression materials 1. Impression plaster 2. Impression compound 3. Zinc oxide eugenol impression paste 4 Impression waxes

Types of elastic impression materials Two systems are used: 1. Hydrocolloids 2. Elastomeric materials

Dental Material Sciences

Dr Eman Alsheikh

Impression Trays Use of Impression Trays − Impression trays are used to: 1.Carry the impression material into the mouth, & the handle of the tray is used to remove the impression. 2.Support a weak material impression & improve accuracy. − Trays are supplied in a variety of shapes & sizes and are made from several materials. Plastic disposable trays are very popular & work well with current infection control practices. Plastic trays are inexpensive & convenient, but they do not support the impression as well as metal trays do. Metal trays are more expensive but reusable. In addition, metal trays are stiffer &, thus, are less likely to distort when removed from the mouth. Cleaning & sterilizing metal trays adds to the cost of their use.

Dental Material Sciences Stock Trays

Dr Eman Alsheikh Custom Trays

Stock trays are “off-the-shelf” items that The most accurate impressions are made with come in a variety of materials, shapes, & custom trays. Custom trays are made on a model sizes. of the patient’s arch with acrylic or other resin. Two impressions are necessary when a custom The different-shaped trays are designed to tray is used. take impressions of different oral conditions: A preliminary impression is taken with a stock tray and an inexpensive material. − Edentulous mouths, A gypsum product is poured into the − Partially edentulous mouths, & − Mouths with a full complement of impression & the resulting model is used to construct the custom tray. The custom tray is teeth. then used to take a final impression. Custom Stock trays also come in a range of sizes, trays are used to take final impressions for full from very small trays for pediatric patients dentures, inlays, crowns, bridges, & some to very large trays for large adult mouths. removable partial dentures. Custom trays use less impression material than stock trays because they fit around the teeth better than a Stock trays can be metal or plastic. stock tray does. Some say that custom trays are cost-effective because they use less material. Others say that custom trays are cost-effective because they make the impressions easier to take and accurate impressions result more frequently than with stock trays. Two techniques for the fabrication of custom trays for crown and bridge impressions. It is important to note that proper mixing and handling of the impression material are the factors most critical for success.

Special-Use Trays A variety of special-use trays have been developed. Bite registration trays, record the occlusal surfaces of both arches. Bite registrations are used to relate the upper and lower casts in the dental laboratory in precisely the same manner as they come together in the patient’s mouth. The use of a bite registration without a tray. Another popular impression tray is the triple tray, which is used with the dual-arch or closed-mouth impression technique. The triple tray is a quadrant tray with a “J” shape that curls around the posterior of the most distal molars. With the dual-arch technique, the loaded tray (on both sides) is seated on the arch with the prepared tooth. The patient then closes the mouth to his or her normal bite & the tray records an impression of the prepared tooth, an impression of the opposing teeth, & a bite registration, all at the same time.

Dental Material Sciences

Dr Eman Alsheikh

Different types of impression trays are shown & listed below with their distinguishing characteristics. Adhesives may be indicated with the use of some trays to aid in the retention of the impression materials.

1. Edentulous metal perforated impression trays • For use with edentulous patients • Autoclavable • Available in different sizes • Not easily adapted • Available in perforated and non-perforated trays • May be used in conjunction with an adhesive

2. Edentulous plastic perforated impression trays • For use with edentulous patients • Single use • Available in different sizes • Easily adapted using a heat source and/or impression compound • Available in perforated and non-perforated trays • May be used in conjunction with an adhesive • May have a separate metal handle that is autoclavable

3. Dentate metal perforated impression trays • For use with dentate patients • Autoclavable • Available in different sizes (the size is usually engraved on the handle of the tray) • Not easily adapted • Available in perforated and non-perforated trays • May be used in conjunction with an adhesive

Dental Material Sciences

Dr Eman Alsheikh

4. Dentate plastic perforated impression trays • For use with dentate patients • Single use • Available in different sizes (usually denoted by colours) • Easily adapted using a heat source and/or impression compound • Available in perforated and non-perforated trays • May be used in conjunction with an adhesive

5. Universal sectional impression tray • For use with dentate patients • Used for impressions of a specific areas of the mouth • Easily adapted as it is fabricated from flexible metal • Available in perforated and non-perforated trays • May be used in conjunction with an adhesive

6. Custom/ special tray • Fabricated from a plaster model of the patient’s dentate or edentulous arch • Fabricated from an acrylic material • Single use • May be used in conjunction with an adhesive

Dental Material Sciences

Dr Eman Alsheikh

7. Triple tray • Used to take an impression of both arches simultaneously • Fabricated from a combination of plastic and flexible webbing material • Different sizes available • Single use • May be used in conjunction with an adhesive

Dental Material Sciences

Dr Eman Alsheikh

RIGID IMPRESSION MATERIALS — Impression Compound (Compo) Impression compound is one of the oldest of the dental impression materials. It can be described as a rigid, reversible impression material which sets by physical change. On applying heat, it softens & on cooling it hardens. It is mainly used for making impressions of edentulous ridges. Impression compound is a thermoplastic material used to record a preliminary impression of an edentulous ridge to fabricate a special tray. A more viscous variety of compound (tray compound) is used to form a tray in which a second more fluid material is placed to make a more detailed impression compound. Synonyms Modeling compound or modeling plastic. Classification Type I - Impression compound Type II- Tray compound Tray compound is used to prepare a tray for making an impression. A second material is then carried in it in order to make an impression of oral tissues. Since reproduction of the fine details is not essential, it is generally stiffer & has less flow than regular impression compound.

Dental Material Sciences

Dr Eman Alsheikh

Supplied as Supplied as sheets, sticks, cakes and cones in a variety of colors.

Applications 1. 2. 3. 4. 5.

For making a preliminary impression in an edentulous (mouth without teeth) mouth For individual tooth impression Type I Peripheral tracing or border moulding To check undercuts in inlay preparation To make a special tray Type II

Single Tooth Impression In conservative dentistry, an impression is made of a single tooth in which a cavity is prepared. The compound is softened and carried in a copper band. The filled band is pressed over the tooth & the compound flows into the prepared cavity. It is referred to as a tube impression. Tube impressions were also used to make electroformed dies. Complete Denture Impressions In complete denture fabrication, it is common to make two sets of impressions —the preliminary and the final impression. The preliminary impression is made in a stock tray. A study cast made from this is used to construct a custom tray or special tray. The custom tray is used to make the final impression. The technique of making a preliminary and final impression greatly improves the accuracy of the complete denture.

Dental Material Sciences

Dr Eman Alsheikh

Requirements of ideal impression compound It should: 1. Harden at or little above mouth temperature. 2. Be plastic at a temperature not injurious or harmful to oral tissues. 3. Not contain irritating or toxic ingredients. 4. Harden uniformly when cooled without distortion. 5. Have a consistency when softened which will allow it to reproduce fine details. 6. Be cohesive but not adhesive. 7. Not undergo permanent deformation or fracture while withdrawing the impression from the mouth. 8. Be dimensionally stable after removal from the mouth and during storage. 9. Exhibit a smooth glossy surface after flaming. 10. Withstand trimming with sharp knife without flaking or chipping after hardening. 11. Should not boil and lose volatile components on flaming. 12. Should remain stable without losing soluble plasticizers when immersed in water for long periods.

− Because the thermal conductivity of impression compound is low, time & patience are required to soften the material properly. − The heated, softened, & moldable material is placed in an impression tray, resoftened, & then seated in the mouth. − When the material has cooled to mouth temperature, it returns to a rigid state & is removed. − Impression compound is a stiff, thermoplastic material & is used by many dentists to make preliminary impressions for complete dentures. Other impression materials that record fine details are better suited for final impressions.

COMPOSITION In general impression compound is: 1. A mixture of waxes, 2. Thermoplastic resins, 3. Organic acids, 4. Fillers & 5. Coloring agents.

Dental Material Sciences

Dr Eman Alsheikh

Disinfection→ The recommended disinfectant is 2% glutaraldehyde. Pouring the cast & cast separation The cast should be poured without delay. The cast is separated from the impression by immersing it in warm water until it is soft enough. Excessively hot water is avoided as it can make the material sticky and difficult to remove from the cast. Properties • May be used in conjunction with a wash of zinc oxide eugenol paste to record detail • Reversible physical reaction Indications • To take a preliminary impression of an edentulous arch in order to fabricate a special tray Contraindications • Where there are undercuts are present Advantages 1. The material can be reused a number of times (for the same patient only) in case of errors. 2. Inaccurate portions can be remade without having to remake the entire impression. 3. Accuracy can be improved by flaming the surface. 4. The material has sufficient body to support itself especially in the peripheral portions. It does not collapse completely if unsupported by the tray.

Dental Material Sciences

Dr Eman Alsheikh

Disadvantages 1. Records less detail because of its high viscosity. 2. Compresses soft tissues during impression. 3. Distortion due to its poor dimensional stability. 4. Difficult to remove if there are severe undercuts. 5. There is always the possibility of overextension especially in the peripheries.

Zinc Oxide Eugenol Impression Paste Zinc oxide & eugenol-based products are widely used in dentistry: 1. Cementing & insulating medium. 2. Temporary filling material. 3. Root canal filling material. 4. Surgical pack in periodontal surgical procedures. 5. Bite registration paste. 6. Temporary relining material for dentures. 7. Impressions for edentulous patients. In dentistry, zinc oxide eugenol is popular as an impression material for making impressions of edentulous arches for the construction of complete dentures. It is classified as a rigid, irreversible impression material. It cannot be used for recording impressions of dentate arches & in areas of severe undercuts.

Classification ADA specification No. 16. 1. Type I “Hard” 2. Type II “Soft”

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Dr Eman Alsheikh

Composition:

Available as In paste form in two tubes A. Base paste (white in color). B. Accelerator or reactor or catalyst paste (red in color).

Setting reaction The setting reaction is a typical acid-base reaction to form a chelate. This reaction is also known as chelation & the product is called zinc eugenolate.

Working Time There should be sufficient time for: 1. Mixing, 2. Loading onto the tray & 3. Seating the impression into the mouth.

Mechanical mixer

Dental Material Sciences

Dr Eman Alsheikh

Setting Time Once the material is in place, it should set fast. Why should an impression material set quickly in the mouth? ____________________ Any material which takes a long time to set in the mouth Would: 1. Obviously be uncomfortable to the patient. 2. Movement is bound to occur, resulting in stresses & errors in the impression. 3. Result in a wastage of time for the dentist. In a busy practice, this is unacceptable.

Initial setting time is the period from the beginning of the mixing until the material ceases to pull away or string out when its surface is touched with a metal rod of specified dimensions. The impressions should be seated in the mouth before the initial set. The final set occurs when a needle of specified dimension fails to penetrate the surface of the specimen more than 0.2 mm under a load of 50 gm.

Factors Controlling Setting Time 1. Particle size of zinc oxide powder: If the particle size is small and if it is acid coated, the setting time is less. 2. By varying the lengths of the two pastes (not recommended). 3. Setting time can be decreased by adding zinc acetate or a drop of water or acetic acid (acetic acid is a more effective than water. It increases speed of formation of the zinc hydroxide). 4. Longer the mixing time, shorter is the setting time. 5. High atmospheric temperature & humidity accelerate setting. 6. Setting can be delayed by cooling the mixing slab, spatula or adding small amounts of retarder or oils or waxes.

Dental Material Sciences

Dr Eman Alsheikh

Advantages 1. It has sufficient body so as to make-up for any minor under extensions in the tray itself during impression making. 2. It has enough working time to complete border moulding. 3. It can be checked in the mouth repeatedly without deforming. 4. It registers accurate surface details. 5. It is dimensionally stable. 6. Does not require separating media since it does not stick to the cast material. 7. Minor defects can be corrected locally without discarding a good impression.

Disadvantages 1. It requires a special tray for impression making. 2. It is sticky in nature and adheres to tissues. 3. Eugenol can cause burning sensation and tissue irritation. 4. It cannot be used for making impression of teeth and undercut areas as it is inelastic in nature.

Other zinc oxide pastes: Surgical pastes (periodontal packs)

Non-eugenol impression & surgical pastes

Bite registration pastes

Available as a 2-paste system.

After certain periodontal surgeries (e.g., gingivectomy, i.e., surgical removal of diseased gingival tissues) where sutures cannot be placed, a zinc oxide based surgical paste, may be placed over the wound to aid in the retention of the medicament, to protect the wound & to promote healing.

The paste is mixed & formed into a rope that is packed over the gingival wounds (using wet fingers) & into the interproximal spaces to provide retention. The final product after setting should be sufficiently strong so that it is not readily displaced during mastication.

1. Shorter setting time to prevent distortion. 2. More plasticizers to prevent it from sticking to the teeth or occlusion rims.

Dental Material Sciences

Dr Eman Alsheikh

ELASTIC IMPRESSION MATERIALS — Reversible Hydrocolloids—Agar Agar hydrocolloid was the first successful elastic impression material to be used in dentistry. It is an organic hydrophilic colloid (polysaccharide) extracted from a type of seaweed (Gelidium, Gracilaria, etc). China and South America are major sources of farmed seaweed.

Agar is a sulfuric ester of a linear polymer of galactose. Although it is an excellent impression material & yields accurate impressions, currently it has been largely replaced by alginate hydrocolloid & rubber impression materials.

Classification (ISO 1564: 2001) − Type I – High consistency (for use as tray material) − Type II – Medium consistency (for use as tray or syringe material) − Type III – Low consistency (for syringe use only)

Uses 1. 2. 3. 4.

Widely used at present for cast duplication (during the fabrication of cast metal removable partial dentures, etc.). For full mouth impressions without deep undercuts. It was used extensively for FPD impressions prior to elastomers. As a tissue conditioner.

Supplied as 1. Gel in collapsible tubes (for impressions). 2. As cartridges or gel sticks (syringe material). 3. In bulk containers (for duplication).

Dental Material Sciences

Dr Eman Alsheikh

Commercial names: 1. Syringe materials include—Herculloid, Cartriloids (Van R), etc. 2. Duplicating materials include Wirogel (Bego), Dubliform (Dentaurum).

Composition

Functions of the ingredients Ingredients

Functions Basic constituent 13-17% for tray material 6-8% for syringe material

1. Agar

Improves the strength of the gel, (it also retards the setting of plaster or stone cast when

2. Borates

poured into the finished impression - a disadvantage).

3. Potassium sulphate 4. Hard Wax 5. Thixotropic materials

It counters retarding effect of borates, thereby ensures proper setting of the cast or die. It acts as a filler. Fillers affect the strength, viscosity & rigidity of the gel. Other fillers are zinc oxide, diatomaceous earth, silica, rubber, etc. It acts as plasticizer. Examples are: Glycerine, & Thymol. Thymol acts as bactericide also.

6. Alkylbenzoates

It acts as preservative.

7. Coloring & flavoring

For patient comfort and acceptance.

8. Water

It acts as the dispersion medium.

Manipulation The equipment & material required for an agar impression are: 1. 2. 3. 4. 5. 6.

Hydrocolloid conditioner. Water cooled rim lock trays Impression syringes Connecting water hose Agar tray material in tubes Agar syringe material

Dental Material Sciences

Dr Eman Alsheikh

IMPRESSION TRAYS Rim lock trays with water circulating devices are used. The rim lock is a beading on the inside edge of the tray which helps to retain the material (as agar does not adhere to the tray). It also has an inlet and outlet for connecting the water tubes. The tray should allow a space of 3 mm occlusally and laterally and extend distally to cover all teeth. Working and setting time The working time ranges between 7-15 minutes and the setting time is about 5 minutes. Both can be controlled by regulating the flow of water through the cooling tubes. Since the cooling tubes are on the periphery, the material sets from the periphery towards the teeth surfaces. LAMINATE TECHNIQUE (agar-alginate combination technique) After injecting the syringe agar on to the area to be recorded, an impression tray containing a mix of chilled alginate that will bond with the agar is positioned over it. The alginate gels by a chemical reaction, whereas the agar gels through contact with the cool alginate rather than the water circulating through the tray. Advantages 1. The syringe agar gives better details than alginate. 2. Less air bubbles. 3. Water cooled trays are not required and therefore more convenient. 4. It sets faster than the regular agar technique

Dental Material Sciences

Dr Eman Alsheikh

Advantages & Disadvantages of Agar Hydrocolloid Advantages 1. Accurate dies can be prepared, if the material is properly handled. 2. Good elastic properties help reproduce most undercut areas. 3. It has good recovery from distortion. 4. Hydrophilic, moist mouth not a problem. It also gives a good model surface. 5. It is palatable and well tolerated by the patient. 6. It is economical when compared to synthetic elastic materials. 7. It can be reused when used as a duplicating material (reuse is not recommended when used as impression material). 8. Low cost because it can be reused.

Disadvantages 1. Does not flow well when compared to newly available materials. 2. It cannot be electroplated. 3. During insertion or gelation the patient may experience thermal discomfort. 4. Tears relatively easily. Greater gingival retraction is required for providing adequate thickness of the material. 5. Only one model can be poured. 6. Has to be poured immediately. Cannot be stored for too long. 7. Requires special and expensive equipment. 8. A soft surface of the gypsum cast results unless a plaster hardener is used. 9. Although it can be reused, it is impossible to sterilize this material. Also, with repeated use there may be contamination of the materials and a deterioration in its properties.

Dental Material Sciences

Dr Eman Alsheikh

IRREVERSIBLE HYDROCOLLOID—ALGINATE The word alginate comes from ‘alginic acid’ (anhydro-β-d-mannuronic acid) which is a mucous extract yielded by species of brown seaweed (Phaeophyceae). Alginic acid is a naturally occurring hydrophilic colloidal polysaccharide. Alginate was developed as a substitute for agar when it became scarce due to World War II (Japan was a prime source of agar). Currently alginate is more popular than agar for dental impressions, because it is simpler to use. Alginate is perhaps the most widely used impression material in the world.

Types Type I — Fast setting. Type II — Normal setting.

Supplied as A powder that is packed: A. Commonly in bulk packing (tins, bins or sachets). B. In preweighed packets for individual impression.

A plastic scoop is supplied for dispensing the bulk powder A plastic cylinder is supplied for measuring the water.

Dental Material Sciences

Dr Eman Alsheikh

Modified Alginates In the form of a sol, containing the water. A reactor of plaster of Paris is supplied separately. As a two-paste system One contains the alginate sol, while the 2nd contains the calcium reactor. These materials are said to contain silicone & have superior resistance to tearing when compared to unmodified alginates. They may be supplied in both tray & syringe viscosity. One product is supplied in low density for use with syringe.

Dust free alginates Concern over the inhalation of alginate dust have prompted manufacturers to introduce (dust free alginates). Chromatic alginates Alginates which change color on setting.

Commercial Names Zelgan (DPI), Jeltrate (Dentsply), Hydrogum (Zhermack), etc.

APPLICATIONS 1. It is used for impression making — When there are undercuts. — In mouths with excessive flow of saliva. — For partial dentures with clasps. 2. For making preliminary impressions for complete dentures. 3. For impressions to make study models and working casts. 4. For duplicating models.

Dental Material Sciences

Dr Eman Alsheikh

Composition

Manipulation Fluff or aerate the powder by inverting the can several times. This ensures uniform distribution of the filler before mixing. The top of the can should be taken off carefully to prevent the very fine silica particles from being inhaled. Mixing equipment includes: — A clean flexible plastic bowl and — A clean wide bladed, reasonably stiff metal spatula Note: It is better to use separate bowls for plaster and alginate as plaster contamination can accelerate setting.

1. The proper W/P ratio as specified by the manufacturer should be used (usually one measure water with two level scoops of powder. 2. The water measure & scoop are supplied by the manufacturer). 3. The water is taken first. 4. The powder is sprinkled in to the water in the rubber mixing bowl & the lid of the metal can is replaced immediately. 5. The mixing is started with a stirring motion to wet the powder with water. 6. Once the powder has been moistened, rapid spatulation by swiping or stropping against the side of the bowl is done. 7. A vigorous figure - eight motion can also be used

Dental Material Sciences

Dr Eman Alsheikh

Mixing time For fast set alginate - 45 seconds. For normal set alginate - 60 seconds.

Over Mixing Results In — Reduction in final strength as the gel fibrils are destroyed. — Reduction in working time.

Under Mixing Results In — Inadequate wetting, lack of homogeneity and reduced strength. — The mix being grainy and poor recording of detail.

Working time Fast set alginate — 1¼ minutes. Normal set alginate: — 2 minutes.

Gelation time (setting time) Type I (fast set) — 1.5-2.0 mins. Type II (normal) — 3-4.5 mins.

Dental Material Sciences

Dr Eman Alsheikh

Tray selection Since alginate has poor adhesion, tray selection is very important. Alginate can be retained by: 1. Mechanical locking features in the tray — A rim lock (a beading round the edges of the tray — Perforations (holes or slits) in the tray 2. Applying adhesive (available as liquid or sprays) 3. A combination of the above. The tray should cover the entire impression area and provide a space of at least 3 mm on all sides.

After removal from the mouth, the impression should be:

 Washed with cold water to remove saliva.  Disinfected by immersion in a suitable disinfectant.  Covered with a damp napkin to prevent drying.  Cast should be poured as soon as possible, preferably within 15 minutes after making the impression.

Dental Material Sciences

Dr Eman Alsheikh

Properties • Available in regular and fast-set forms • Dust-free powder • Working and setting times may be adjusted by increasing or decreasing the temperature of the water (increasing temperature, decreases working and setting times & decreasing temperature increases working & setting times) • Optimal water temperature is 21◦C • Some materials are available that change color as they change state; this aids in ensuring that materials are completely set prior to removal from the mouth.

Dental Material Sciences

Dr Eman Alsheikh

Manipulation Wearing personal protective equipment, then: Step 1 • The patient’s oral cavity should be free of debris prior to taking alginate impressions Step 2 • Pass the operator the impression tray (maxillary or mandibular) for try-in (if needed, add impression compound to alter or extend the impression tray) Step 3 • Ensuring to not cross-contaminate the bottle, use a disposable applicator brush to apply tray adhesive to the impression tray if indicated (it is best practice to dispense some adhesive and then use a disposable brush to apply over the impression tray to avoid contamination) • Ensure that tray adhesive is painted on the rim area of the impression tray as well as the body.

Step 4 • Fluff the alginate in the jar & dispense the alginate powder using the measuring scoop provided by the manufacturer (overfill the scoop from jar & level using a disposable tongue depressor or a sterilized fish tailed spatula) • The size of the selected impression tray will dictate the amount of material to be dispensed

Dental Material Sciences

Dr Eman Alsheikh

Step 5 • Using the water measure supplied by the manufacturer, measure out the water needed (this corresponds to the amount of powder dispensed) • The ideal temperature for the water is 21◦C

Step 6 • Communicate with the dentist when the mixing should commence & add the powder & water • Mix the powder & water with a stirring motion, using the tip of the spatula • Turn the bowl on its side in the palm of your hand and rotate the bowl, continuing to mix the material with the wide part of the spatula blade until a homogenous mixture is achieved

Step 7 • Gather the alginate in the bowl & using the blade of the spatula, pick up the material to load the impression tray.

Dental Material Sciences

Dr Eman Alsheikh

Step 8 • Load the impression tray using the spatula • The mandibular tray is loaded from the lingual using an overlapping technique to ensure the tray is completely filled • The maxillary tray is filled from the posterior region and material is continuously added with pressure until the tray is full • Extra impression material may be required for the operator to manually insert in the event that a patient has a high palate • Leave some excess material on the back of your gloved hand – this is used to check if the material is set after placement in the oral cavity

Step 9 • Once the impression tray is filled, hand the tray to the operator extending the tray handle first Step 10 • Remove excess material from spatula and flexible mixing bowl & dispose of in the contaminated waste bin. Disinfect the flexible mixing bowl and fish-tailed spatula.

Dental Material Sciences

Dr Eman Alsheikh ADVANTAGES & DISADVANTAGES OF ALGINATE

Advantages 1. It is easy to mix and manipulate. 2. Minimum requirement of equipment. 3. Flexibility of the set impression. 4. Accuracy if properly handled. 5. Low cost. 6. Comfortable to the patient. 7. It is hygienic, as fresh material must be used for each impression. 8. It gives a good surface detail even in presence of saliva.

Disadvantages 1. Cannot be electroplated so metal dies are not possible. 2. It cannot be corrected. 3. Distortion may occur without it being obvious if the material is not held steady while it is setting. 4. Poor dimensional stability—it cannot be stored for long time. 5. Poor tear strength. 6. Because of these drawbacks and the availability of better materials, it is not recommended where a higher degree of accuracy is required, e.g., cast RPD, crowns & FPDs, etc.

Dental Material Sciences

Dr Eman Alsheikh

ELASTOMERIC IMPRESSION MATERIALS Types: ACCORDING TO CHEMISTRY Chemically, there are four kinds of elastomers: 1. Polysulfide 2. Condensation polymerizing silicones 3. Addition polymerizing silicones 4. Polyether ACCORDING TO VISCOSITY Each type may be further divided into four viscosity classes: 1. Light body or syringe consistency 2. Medium or regular body 3. Heavy body or tray consistency 4. Very heavy or putty consistency

ADA/ ISO 4823 CLASSIFICATION Based on selected elastic properties and dimensional change of the set materials, they are divided into three types—Type I, Type II and Type III ACCORDING TO WETTABILITY Impression materials are also classified as 1. hydrophilic, if their contact angle is from 80 to 105° 2. hydrophobic, if their contact angle is from 40 to 70° Uses of elastomeric impression materials 1. 2. 3. 4. 5. 6.

In fixed partial dentures for impressions of prepared teeth. Impressions of dentulous mouths for removable partial dentures. Impressions of edentulous mouths for complete dentures. Polyether is used for border molding of edentulous custom trays. For bite registration. Silicone duplicating material is used for making refractory casts during cast partial denture construction.

Dental Material Sciences

Dr Eman Alsheikh

Polysulphides Impression Materials (Polysulfides) (Rubber Base) Material constituents/composition • Supplied in a two-paste system • Available in low, medium and high viscosity

Properties • The working and setting times are altered with heat and humidity ◦ Higher the temperature and humidity, the shorter the working & setting time ◦ Lower the temperature and humidity, the longer the working & setting time • Hydrophilic • Useful when a long working time is needed

Advantages • High accuracy • Long working time • Good tear strength • Low cost

Disadvantages • Material will stain clothes • Very unpleasant odor • Must be used in conjunction with a custom/special tray

Dental Material Sciences

Dr Eman Alsheikh

Runny consistency • Long setting time • Cast must be poured within an hour • Polysulphides contract upon storage Indications • Fixed partial denture impressions • Crown and bridge impressions • Implant impressions Contraindications • Patients with a strong gag reflex

• • •

Mixing time → 45–60 seconds Working time → 5–7 minutes Setting time → 8–12 minutes

Dental Material Sciences

Dr Eman Alsheikh

SILICONE RUBBER IMPRESSION MATERIALS There are two types of silicone impression materials available: condensation & addition or vinyl silicones. They are categorized in relation to the type of reaction responsible for their setting.

CONDENSATION SILICONE IMPRESSION MATERIALS Material constituents/composition • Available in two-paste or liquid/paste systems • Available in light, medium and heavy viscosities as well as a putty • May be difficult to achieve a uniform mix as base and catalyst pastes are not of the same consistency

Properties • Moderate shelf-life • Moderate tear strength

Advantages • Accurate • Easily manipulated • Fast setting time • Non-toxic and non-irritant • Very elastic

Disadvantages • Setting may be affected by changes in temperature and humidity • Hydrophobic • Prone to shrinkage on storage – condensation impressions must be poured up within an hour

Dental Material Sciences

Dr Eman Alsheikh

Indications • Fixed partial denture impressions • Inlay and onlay impressions • Crown and bridge impressions • Implants

Contraindications • May cause irritation with some patients

• Mixing time → 45–60 seconds • Working time → 3 minutes • Setting time → 6–8 minutes

Dental Material Sciences

Dr Eman Alsheikh

ADDITION (VINYL) SILICONE IMPRESSION MATERIALS Material constituents/composition • Supplied in a two-paste system and auto mix cartridge system (dispensing gun) • Available in light, medium and heavy viscosities as well as a putty • Base and catalyst pastes are the same consistency, which makes manipulation easy • May be referred to as vinyl polysiloxane impression materials

Properties • Accurate • Good shelf-life • Dimensionally stable • Non-toxic and non-irritant • Moderate tear strength

Advantages • Accurate • Easily manipulated • Range of viscosities • Fast setting time • Dimensionally stable – they are not prone to shrinkage on storage – addition silicones can be poured up multiple times. They are more expensive than condensation silicones

Dental Material Sciences

Dr Eman Alsheikh

Disadvantages • Setting may be affected by changes in temperature and humidity • Hydrophobic • Powdered latex gloves may retard the setting properties in the putty form of addition silicone impression materials

Indications • Fixed partial denture impressions • Inlay and onlay impressions • Crown and bridge impressions • Implants

Contraindications • Using powdered latex gloves during the manipulation of the putty form of material will affect the material properties adversely

• Mixing time → 45–60 seconds • Working time → 2–4 minutes • Setting time → 3–7 minutes

Dental Material Sciences

Dr Eman Alsheikh

Manipulation of silicon: • Prior to the commencement of mixing the impression material the operator will try in the custom/special tray to ensure adequate fit • Paint the custom/special tray with tray adhesive & allow it to dry as per the manufacturer’s instructions • Ensure that tray adhesive is painted on the rim area of the impression tray as well as the body • Ensuring to not cross contaminate the bottle, use a disposable applicator brush to apply tray adhesive to the impression tray if indicated (it is best practice to dispense some adhesive and then use a disposable brush to apply the adhesive over the impression tray to avoid contamination).

Dental Material Sciences

Dr Eman Alsheikh

Putty technique (Page105) • Powdered latex gloves may retard the setting properties in the putty form of addition silicone impression materials Step 1 • Using the color-coded scoops supplied, dispense one scoop (equal amounts) of both the base & the catalyst • Place on a waxed paper pad, ensuring they do not touch until ready to use Step 2 • With clean hands (no gloves) the dental nurse kneads the base & catalyst putties together until a homogenous color is achieved & loads it into the pre-prepared impression tray. • Kneading the putty together should not take more than 30 seconds

Mixing a two-pastes(Page106) Step 1 • Extrude equal lengths of the two pastes onto a paper mixing pad or glass slab (or if supplied as a liquid and base dispense one drop to one inch of base material) • The pastes are of different colors, do not let the pastes touch until mixing commences Step 2 • Using a stiff wooden-handled, stainless steel spatula, spatulate the two pastes together in a circular motion until a uniform color has been achieved Step 3 • Using the edge of the firm spatula, bring all of the material to the middle of the paper mixing pad or glass slab • Fill syringe or load impression tray Step 4 • Clean excess materials from the spatula and syringe Step 5 • Dispose of paper mixing pad in the contaminated waste bin

Dental Material Sciences

Dr Eman Alsheikh

Dental Material Sciences

Dr Eman Alsheikh

Dental Material Sciences

Dr Eman Alsheikh

Polyether Impression Materials Polyether impression materials are very rigid (stiff) impression materials. They have superior mechanical properties to polysulfides & less dimensional change than silicones. Material constituents/composition • Available in a two-paste system, single-mix and an electric mechanical mixer

Properties • Very accurate • Heat and humidity speed up working and setting times • Hydrophilic • Non-toxic • Good elasticity • Good dimensional stability • Low tear strength • Low setting contraction Advantages • Accurate • Easily manipulated Disadvantages • Low tear strength • Short working time • Rigid (stiff) material • May be hard to remove from the mouth due to stiffness

Dental Material Sciences

Dr Eman Alsheikh

Indications • Crown and bridge impressions • Partial denture impressions • Implants Contraindications • Due to the rigidity of the material it may be hard to remove from a patient’s mouth with mobile teeth

• Mixing time → 30–45 seconds • Working time → 2.5 minutes • Setting time → 4.5 minutes

Dental Material Sciences

Dr Eman Alsheikh

Manipulation Wearing personal protective equipment: Using ImpregumTM PentamixTM:

Step 1 • Load impression bag into the cartridge

Step 2 • Insert cartridge into the PentamixTM machine securely

Step 3 • Place tip onto impression bag

Step 4 • Close lever over impression cartridge

Step 5 • Close cover and push button to dispense material

Dental Material Sciences

Dr Eman Alsheikh

Dental waxes Waxes have a variety of uses within dentistry and are manufactured from various materials, including plants, minerals, animals and synthetic waxes. They can be used both intra- and extra-orally. Waxes can be divided into three categories: 1. Pattern waxes: are used to pattern moulds of various restorations and dental prosthesis. They all burn out without leaving a residue, create smooth surfaces and carve easily. 2. Processing waxes: have an auxiliary function in the fabrication of impressions and casts. 3. Impression waxes: are used intra-orally for taking impressions They are thermoplastic materials that present as solids at room temperature; they can be softened with heat and hardened with cooling. Waxes are often used in conjunction with dies and models to facilitate construction of various restorations, appliances and prostheses.

Instruments and materials used in set-up • Choice of wax • Choice of heat source • Wax knife • Le Cron carver • Flat plastic instrument • Bowl of cool water

Dental Material Sciences

Dr Eman Alsheikh

Dental Material Sciences

Dr Eman Alsheikh

Dental Material Sciences

Dr Eman Alsheikh

Dental Material Sciences

Dr Eman Alsheikh

Name the following:

____________________________

Impressions are sufficiently elastic to be withdrawn from undercut areas. ____________________________

____________________________

A negative record of the tissues of the mouth. It is used to reproduce the form of the teeth & surrounding tissues.

____________________________

Dental Material Sciences

Dr Eman Alsheikh

Matching table: (A) Dental waxes (B) Viscosity (C) KHN (D) Metals (E) Hue (F) Tin/ Lead 1. Used inside full lower dentures to make it heavy, & to control mobility. 2. An example of mixture with melting range 3. Good electrical conductors. 4. Hardness 5. Material’s ability to flow. 6. Basic color of an object.