|Year : 2018 | Volume
| Issue : 3 | Page : 21-23
Dental impression materials in prosthodontics: An overview for the general dentist
Musab Abu Arqoub1, Tarek Rabi2, Naji Ziad Arandi3
1 Assistant Professor, Department of Conservative Dentistry and Prosthodontics, Al-Quds University, Jerusalem, Israel
2 Lecturer, Department of Conservative Dentistry and Prosthodontics, Al-Quds University, Jerusalem, Israel
3 Assistant Professor, Department of Conservative Dentistry and Prosthodontics, The Arab American University, Jenin, Palestine, Israel
|Date of Web Publication||30-Jan-2019|
Dr. Tarek Rabi
Department of Conservative Dentistry and Prosthodontics, Faculty of Dentistry, Al-Quds University, PO Box. 89, Abu Dis, Jerusalem, Palestine
Source of Support: None, Conflict of Interest: None
Dental impression creation is the procedure of formulating a negative replica of the teeth and oral tissues, into which different die materials can be processed to create working analogs. Impression making is a routine procedure carried out at the start of any prosthodontic procedure. The accuracy and dimensional stability of impression materials are of paramount importance to the accuracy of fit of the resultant prosthesis. Hence, in the present review, we aim to highlight some of the important aspects of dental impression materials used in prosthodontics.
Keywords: Alginate, impression material, prosthodontics
|How to cite this article:|
Arqoub MA, Rabi T, Arandi NZ. Dental impression materials in prosthodontics: An overview for the general dentist. Int J Prev Clin Dent Res 2018;5:21-3
|How to cite this URL:|
Arqoub MA, Rabi T, Arandi NZ. Dental impression materials in prosthodontics: An overview for the general dentist. Int J Prev Clin Dent Res [serial online] 2018 [cited 2019 Feb 23];5:21-3. Available from: http://www.ijpcdr.org/text.asp?2018/5/3/21/251053
| Introduction|| |
In today's modern field of dentistry, numerous impression materials are available. Both physical and chemical properties of all the impression materials are different from each other. Along with this, all these materials have different indications and contraindications for use. A systematic knowledge of these concepts is essential if the clinicians are to produce accurate reproductions of oral structures.
| Classification of Dental Impression Material|| |
Impression materials can be categorized on the basis of their composition, setting reaction, and setting properties, but a commonly used system is based on the properties after the material has set. Hence, conventional impression materials are of two subtypes: elastic and inelastic. Elastic impression materials include the following: reversible hydrocolloid, irreversible hydrocolloid, polysulfide, polyether, addition silicone (polyvinyl siloxane [PVS]), condensation silicone, and vinyl polyether siloxane. Inelastic impression materials include impression waxes, impression compound, impression plaster, and metallic oxide pastes.
Reversible hydrocolloid (agar)
Agar-agar is an organic colloid obtained from the cell wall of red seaweed. It is fundamentally a hydrophilic, emulsoid polysaccharide. Agar was first introduced into dentistry for recording crown impressions in 1937 by Sears and was the first elastic impression material available. All impression materials with agar-agar component have a jelly-like substance which becomes soft when heated and hardens when cooled. The use of agar-agar was not convenient as it required special equipment such as heaters, syringes, and water-cooled rim-lock trays. Agar-agar impression materials are no longer used in clinics because of the inconvenience of manipulation, whereas alginates are still popularly advocated. Alginates remain as an economical option and easily manipulated impression material.,,
Irreversible hydrocolloid (alginate)
Irreversible hydrocolloid can be used in preliminary impressions, provisional crown-and-bridge impressions, study models, and opposing dentition impressions. Alginate is an elastic, irreversible hydrocolloid impression material. Irreversible hydrocolloid impressions form an inseparable part of indirect restorations. Alginate is one of the most frequently used impression materials, and it is simple, cost-effective, and an indispensable part of dental practice. Yet very few people can make alginate impressions just right the first time; therefore, it becomes mandatory to understand the material and follow certain fundamental guidelines for flawless, predictable impressions, and hence avoid repeat impression/restorations. Alginates are used for impressions in orthodontic models, sports mouth guards, bleaching trays, and more.
Alginate materials possess the qualities of good surface detail and faster reaction at higher temperatures. They are elastic enough to be drawn over the undercuts, but tear over deep undercuts and are not dimensionally stable on storing due to evaporation. Alginates are nontoxic and nonirritant. Alginate powder is unstable on storage in the presence of moisture or in warm temperatures. Alginate impression materials are hydrophilic in nature, and this property facilitates making of accurate impressions in the presence of saliva or blood. It has a low wetting angle and hence full-arch impressions are easily captured. Impressions made with irreversible hydrocolloids are easier to remove than those with elastomeric materials. As their tear strength is low, they can reproduce subgingival contours and anatomy but tear upon removal. They are good for only one pour per impression.,
Alginate impression materials are easy to use yet with a quick setting time. The setting time can be controlled with the temperature of water used. They are mildly flavored. Their disadvantages include less accurate reproduction of details as compared with elastomeric impression materials, poor dimensional stability, and that they are messy to work with.,
Polyether, polysulphide, and silicones
Polyethers were introduced in the late 1960s. The setting reaction for these materials is via cationic polymerization by opening of the reactive ethylene imine terminal rings to unite molecules with no by-product formation. These materials are hydrophilic, allowing them to be used in a moist environment. Their good wetting properties also allow gypsum casts to be made more easily. Newer polyether impression materials are slightly more flexible than the older products, making them easier to remove from the mouth. PVS impression material is one of the most favored impression materials in dentistry because of excellent properties and availability in different viscosities ranging from extralight body to putty. Impressions made from this material produce great detail reproduction and can be poured multiple times because of their high tear strength and high elastic recovery. A new impression material that combines the properties of polyether and PVS, vinyl siloxanether, or vinyl polyether siloxane was introduced in the dental market in 2009 (Identium, Kettenbach Co, Eschenburg, Germany). This material has been reported to combine the ease of removal of PVS with the hydrophilicity (wetting properties) of polyether, making it a promising material for difficult situations in which moisture control issues are present, such as narrow, deep gingival crevices.
The hydrophilicity of the impression materials is critically crucial to wet the hard and soft tissues in the mouth and to create accurate impressions and casts. During making the impression, the material needs to flow and adhere to the tooth structure and periodontal tissues that may be wetted by blood, saliva, and water. Only when the impression material is hydrophilic, can water be displaced and can the material ideally adhere on these surfaces. Considering the impact of hydrophilicity on accurate die casting, inadequate wetting results in gypsum casts and dies producing pits and voids located in critical areas such as margins, pin holes, and retentive grooves.
Polyether > polysulphide > silicones – These impression materials are placed according to the descending order of hydrophilicity. Since the introduction of polyether in 1969, it has helped clinicians to obtain accurate and dimensionally stable impressions. Polyether impression materials are composed of moderately low-molecular-weight polyether, a silica filler and plasticizer and have excellent wettability.,
Wettability is determined by measuring the magnitude of the contact angle that is formed between the drop of liquid and the surface in question. The contact angle is usually calculated using the Young–Dupré equation. Complete wetting occurs at a contact angle of 0°, and no wetting occurs at an angle of 180°. Therefore, a contact angle of 90° is arbitrarily selected to distinguish wetting from a nonwetting phenomenon. A material exhibiting contact angle of >90° is an indication of poor wetting, which means that the material exhibits hydrophobicity and a material exhibiting contact angle of <90° is an indication of better wetting, which means that it exhibits hydrophilicity.,
| Conclusion|| |
One of the important aspects of the dental procedure, which is usually overlooked, is the impression making and impression materials. The high demand of improved quality impression materials as a result of the development of combination technique should level off and continue at a modest level. With the selection of a suitable impression material and impression technique, impression taking is consistent and reproducible, with reliable successful results.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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