Impression Materials PDF

1 Assoc. Prof. Dr. Özay ÖNÖRAL COURSE ID Code of Committee: CS-2 Name of Committee: Fixed Prosthetic Restorations Lecturer: Assoc. Prof. Dr. Özay Önöral Topic of the Course: Impression Materials in Fixed Prostheses Duration of the Course: 100 minutes After completion of this course, the st...

1 Assoc. Prof. Dr. Özay ÖNÖRAL COURSE ID Code of Committee: CS-2 Name of Committee: Fixed Prosthetic Restorations Lecturer: Assoc. Prof. Dr. Özay Önöral Topic of the Course: Impression Materials in Fixed Prostheses Duration of the Course: 100 minutes After completion of this course, the student will be able to: Use the terminology for the impression procedure Classify elastomeric impression materials, make case-specific choices and defend the selection. List the properties of polysulfite impression material, associate the dimensional stability with the by-product after the setting reaction. List the properties of C-type silicone impression material, define its existing forms, associate the dimensional stability with the by-product after the setting reaction. List the properties of A-type silicone impression material, explain the prominent features of the material in terms of dimensional stability and elastic recovery, and define its existing forms. List the properties of the polyether impression material, explain the prominent features of the material in terms of dimensional stability and elastic recovery, define in which situations it can be preferred depending on its rigidity and present its existing forms. Contemporary Fixed Prosthodontics, 6th Edition. Book by Junhei Fujimoto, Martin F. Land, and Stephen F. Rosenstiel. Published by Elsevier in 2022. McCabe JF, Walls AWG. Applied Dental Materials. 9th ed. Blackwell Publishing, 2008. Sakaguchi RL, Powers JM. Craig’s Restorative Dental Materials. 13th ed. Elsevier Mosby, 2012. Anusavice KJ, Shen C, Rawls HR. Phillips’ Science of Dental Materials. 12th ed. Elsevier Saunders, 2013. Powers JM, Wataha JC. Dental Materials Properties and Manipulation. 10th ed. Elsevier Mosby, 2013. Learning Objectives of the Course: Suggested References to Review: Near East University, Faculty of Dentistry 2 Assoc. Prof. Dr. Özay ÖNÖRAL ELASTOMERIC IMPRESSION MATERIALS CHARACTERISTICS OF IMPRESSION MATERIALS Elastic recovery: It is the ability to return the impression material to its original size without distortion during removal from the mouth. For the impression material not to be distorted, its minimum thickness should be 3-4 times the undercut depth. Dimensional accuracy: How closely the impression material reproduces the details of the patient’s mouth. Dimensional stability: It is the feature that the accuracy of the material does not change over time. It is the percentage of shrinkage or expansion of the material. Some materials have a longer time, with a poured cast remaining accurate up to two weeks, whereas others last just two hours or less. It is an essential consideration depending on how soon a cast will poured. Contact angle and wettability: The angle formed between the tangent line of the drop formed by the liquid on the solid surface and the solid surface is called the contact angle. Hydrophilic/hydrophobic character (Hydrophilicity/Hydrophobicity): If the material is hydrophilic in character, it shows fluidity in a humid environment and can be worked comfortably, thus giving an accurate measurement. While hydrophilic materials show a low contact angle, hydrophobic materials have a contact angle greater than 90º. Hydrophilic materials record the surface with high precision and create fewer air bubbles during gypsum model obtainment due to their wettability properties. Fluidity and thixotropic property: Wettability and fluidity allow the material to give fine details. Materials with low wetting angles have more fluidity, are less affected by oral fluids, and give a clearer impression. The thixotropic feature is that the material has low fluidity under gravity but high fluidity under pressure. Thixotropic materials remain stable when applied to the tooth surface with an injector, but when they come on materials with a dense consistency, they show fluidity towards the sulcus. Viscosity: The viscosity of a liquid is its resistance to fluidity. The low viscosity material gives good detail, but the material cannot support itself. Therefore, it is not recommended to be used alone, it should be used with a higher viscosity material. Flexibility: Ease of removal from the mouth after setting. If the material is stiff, it is considered less flexible. Ease of handling: The “how it works in my hands” characteristic inherent in how clinicians choose dental materials. Features that affect ease of handling include viscosity and the working time/set time ratio. Near East University, Faculty of Dentistry 3 Assoc. Prof. Dr. Özay ÖNÖRAL Tear strength: Likelihood of tearing when removed from the patient’s mouth. Materials with high tear strength are essential for an impression to capture a subgingival margin. ELASTOMERIC IMPRESSION MATERIALS Elastomeric impression materials are cross-linked polymers that show flexible properties when hardened. These materials stand out with their properties such as good accuracy and dimensional stability, and record surface details very clearly compared to hydrocolloids. There are 4 types of silicone elastomers: polysulfide, condensation silicone, addition silicone, and polyether. Polysulfide is the first elastomeric impression material used in dentistry (1950). In the following years, condensation silicones (1955), polyether (1965), and polyvinyl siloxane (1975) entered the dental market. The most preferred materials today are polyvinyl siloxane and polyether. Silicon-polyether hybrid material (vinyl polyether silicone) (2009) which has been recently developed has not yet found widespread use. Elastomeric impression materials consist of base and catalyst pastes. They have different density options (extralow, low, medium, high, very high [putty]) with respect to the amount of filler they contain. Materials with different densities can be preferred according to their intended use. Low-density material gives a more detailed Near East University, Faculty of Dentistry 4 Assoc. Prof. Dr. Özay ÖNÖRAL and clear impression, but polymerization shrinkage during hardening is higher. Low and high-density materials can be used in combination. Polysulfide Composition: It is available in two paste forms, base and catalyst. The base paste contains poly-sulfide polymer, a filler (titanium dioxide) to increase resistance, a plasticizer to provide proper viscosity, and 0.5% sulfur as an accelerator. The catalyst paste contains lead dioxide, filler, a plasticizer, and oleic or stearic acid as retarders to control the setting reaction. The base paste is white, while the catalyst paste is brown, which is the characteristic color of the lead dioxide. The contrasting colors of the pastes help to understand that they are mixed homogeneously. Setting reaction: When the two pastes are mixed, the terminal groups of the polymer chain react with lead dioxide and cross-linking occurs by extending the chain. In each reaction step, a water molecule appears as a byproduct, which weakens the dimensional stability of the material. As the chain elongation continues, the viscosity increases. When the crosslinking reaches a certain level, the material begins to show elastic properties. Characteristics: • It is low-medium hydrophilic; can give the correct impression in the presence of saliva and blood. • Tear resistance is high. • Working (6 min) and setting (12 min) times are longer than other elastomers. • Dimensional stability is weak. There are two main reasons for this: (1) Cross-linking continues even after the curing reaction, resulting in increased shrinkage of the material. (2) In the hardening reaction, water is released as a by-product and causes mass loss of the material. • The elastic recovery feature is weak, prone to plastic deformation. • It requires the use of an individualized tray and tray adhesive should be used. • The model should be poured in a maximum of 1 hour after taking the impression. Near East University, Faculty of Dentistry 5 Assoc. Prof. Dr. Özay ÖNÖRAL • Its taste and smell disturb the patient. • It can dye clothes. • The cost is suitable. • It is the only impression material with the radiopaque feature. Condensation Silicone (C-type Silicone) Composition: Available forms are (i) two pastes; (ii) a base paste and a low-density catalyst liquid, or (iii) two putty systems (putty-wash technique). Putty can be used as a tray material; low-density silicon can be added to it. This method is called the “putty-wash impression technique”. The base paste contains polydimethylsiloxane with hydroxyl terminal group and filler such as silica. The filler controls the viscosity, ensures the integrity of the material, and modifies the physical properties. In the catalyst paste, there is an alkyl silicate, the cross-linking agent, and the tin compound acting as an activator. Setting reaction: Through the tin compound contained in the catalyst paste, cross-linking occurs between tetrafunctional alkyl silicates and polydimethylsiloxane, and a three-dimensional network structure is formed. As a result of this reaction, ethyl alcohol is released as a by-product, which results in excessive polymerization shrinkage of the material. The curing times of condensation silicones are shorter than polysulfide and elasticity starts earlier. Characteristics: • It is very hydrophobic. To the extent of saliva and moisture, air bubbles are formed. Near East University, Faculty of Dentistry 6 Assoc. Prof. Dr. Özay ÖNÖRAL • Although it is lower than polysulfide, it has sufficient tear resistance. • It shows polymerization shrinkage due to ethyl alcohol released during the hardening reaction. • The elastic recovery feature is good. • There is no need to make an individualized tray; it can be used with a fabricated tray. • Working and setting times are suitable. • The model should be obtained immediately after the impression is taken. • Its cost is suitable in comparison with other elastomeric impression materials. Addition Silicone (Polyvinyl siloxane, A-type Silicone) Composition: Available in two paste forms, base and catalyst. Base paste polymethyl-hydro siloxane and divinylpolysiloxane; the catalyst contains divinylpolysiloxane and platinum salt as an activator. There are fillers in both pastes and 4 different viscosity material options are available depending on the number of fillers. Different viscosity pastes can be used together or can be used as single-stage (mono-phase). By introducing the pastes in cartridge format and mixing them in a manual manner or automatic mixing device, both a homogeneous mixture is obtained and the amount of residual material is reduced. Also, some of the mixture is transferred to the injector and more accurate impressions can be obtained by injecting the material directly into the relevant region before placing the tray in the mouth. Setting reaction: When two pastes are mixed, the platinum acts as a catalyst, and the addition (addition type) reaction begins, crosslinking occurs between both siloxane prepolymers. The lack of by-products as a result of this reaction is one of the most important advantages of the material. Besides, the residual polymethyl hydroxy siloxane in the material reacts secondarily with moisture in the medium and produces hydrogen gas. This does not adversely affect the stability of the material; however, it causes small gaps to form on the plaster model surface. For this reason, some manufacturers suggest that plaster should not be poured into the impression immediately and that it is waited for at least 30 minutes. Characteristics: • It had a hydrophobic character, but with the addition of nonionic surfactants, a less hydrophobic material with improved wettability has been developed. • It records surface details clearly. To save the surface details more clearly and to eliminate the disadvantage due to the hydrophobic character of the material, it is recommended to cover hard and Near East University, Faculty of Dentistry 7 Assoc. Prof. Dr. Özay ÖNÖRAL soft tissue surfaces with a surface-active spray before the impression process. These sprays provide the plaster model with a smooth surface. • Its dimensional stability is very good. • In terms of elastic recovery, it is the best material among elastomeric impression materials. • It shows moderate rigidity after setting. • It has a wide viscosity option. • Impression can be taken with a prefabricated tray, but tray adhesive should be used. • It is contaminated with sulfur compounds and should not be contacted with latex and rubber-dam. • The impression can be stored for several weeks and poured again. • It is not toxic and irritant, its smell and taste do not disturb the patient. • This does not adversely affect the stability of the material; however, it causes small gaps to form on the plaster model surface. For this reason, some manufacturers recommend not to pour the plaster immediately and wait at least 30 minutes. Polyether Composition: Available in two pastes, one in the big tube and the other in the small tube. The large tube is a base and contains ethylene oxide copolymer and silica filler. The small tube is a catalyst and contains aromatic sulfonic acid ester, silica filler, oil, and plasticizer (phthalate) that all initiate crosslinking. Low and medium viscosity options are available, but there is no high viscosity and putty consistency material. It is a mono-phase impression material that generally uses a single viscosity material. Near East University, Faculty of Dentistry 8 Assoc. Prof. Dr. Özay ÖNÖRAL Setting reaction: When the pastes are mixed, cationic ring-opening polymerization occurs. The ionized form of the sulfonic acid ester is the starting source of the cations and the new cation is produced by opening the epimine ring at each stage of the reaction. The reaction continues as a chain elongation or crosslinking reaction. As the reaction progresses, the viscosity increase, resulting in rigid, cross-linked rubber. The reaction does not produce by-products. Characteristics: • It is the only elastomeric impression material that presents a hydrophilic character. • It has high accuracy and dimensional stability. • Elastic recovery is good. • When it sets, it has high rigidity and it is difficult to remove it, especially in the presence of an undercut. • It gives surface details very clearly. • There is no need to make an individualized tray; Impressions are taken with a non-perforated prefabricated tray, and spoon adhesive should be used. • Its cost is higher than other elastomeric materials. Summary of Characteristics of Elastomers Property Polysulfide Working time (min) Setting time (min) Tearing strength (N/m) Contraction percentage (After 24 hours) Contact angle (º) Elastic recovery Auto-mixing The need for a custom tray Unpleasant smell Possibility to obtain many models 4-7 7-10 2500-7000 0.40-0.45 Condensation Silicone 2.5-4 6-8 2300-2600 0.38-0.60 Polyvinyl Siloxane (Addition Silicone) 2-4 4-6.5 1500-4300 0.14-0.17 3 6 1800-4800 0.19-0.24 82 98 98/53* 49 Medium NO YES YES NO High NO NO NO NO Very High YES NO NO YES High YES NO NO YES 2 2 1 (2**) 2 4 3 Hardness 3 (1 indicates highest hardness) Distortion while removing from the 1 mouth (1 for maximum, 4 for minimum distortion potential) * Valid for less hydrophobic polyvinyl siloxane. ** It is valid for soft polyether. Near East University, Faculty of Dentistry Polyether