Impression materials for dental prosthesis

Impression materials for dental prosthesis

9

Payam Zarrintaj1,2,3, Sahba Rezaei4, Seyed Hassan Jafari4, Mohammad Reza Saeb2,3,5, Shadi Ghalami6, Mahsa Roshandel6, Brouki Milan Peiman7,8, Daghigh Ahmadi Ehsaneh9, Farshid Sefat10,11 and Masoud Mozafari7,8 1 Polymer Engineering Department, Faculty of Engineering, Urmia University, Urmia, Iran, 2 Color and Polymer Research Center (CPRC), Amirkabir University of Technology, Tehran, Iran, 3Advanced Materials Group, Iranian Color Society (ICS), Tehran, Iran, 4School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran, 5 Department of Resin and Additive, Institute for Color Science and Technology, Tehran, Iran, 6Department of Anatomy and Pathology, University of Siena, Siena, Italy, 7Cellular and Molecular Research Center, Iran University of Medical Sciences, Tehran, Iran, 8 Department of Tissue Engineering & Regenerative Medicine, Faculty of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran, Iran, 9Centre for Nanohealth, College of Engineering, Swansea University, Swansea, United Kingdom, 10 Biomedical and Electrical Engineering Department, School of Engineering, University of Bradford, Bradford, United Kingdom, 11Interdisciplinary Research Centre in Polymer Science & Technology (IRC Polymer), University of Bradford, Bradford, United Kingdom

Chapter Outline 9.1 Introduction 198 9.2 Elastic impression materials 9.2.1 9.2.2 9.2.3 9.2.4 9.2.5

9.3 Inelastic impression materials 9.3.1 9.3.2 9.3.3 9.3.4

200

Polyethers 200 Polysulfide 201 Alginate 201 Agar 202 Silicones 202

204

Impression wax 204 Impression compound 205 Impression plaster 205 Metallic oxide pastes (zinc oxide
eugenol impression paste) 206

Advanced Dental Biomaterials. DOI: https://doi.org/10.1016/B978-0-08-102476-8.00009-8 Copyright © 2019 Elsevier Ltd. All rights reserved.

198

Advanced Dental Biomaterials

9.4 Characteristics of impression materials 9.4.1 9.4.2 9.4.3 9.4.4 9.4.5

9.5 Conclusion and future perspective References 212

9.1

207

Dimensional accuracy/dimensional stability 207 Wettability 208 Elastic recovery/flexibility 208 Mechanical properties 209 Miscellaneous 209

212

Introduction

Biomedical scientists have endeavored to repair the organs, mainly with the aid of regeneration or implanting strategies (Chiu et al., 2017; Zarrintaj et al., 2017b; Bakhshandeh et al., 2017). Dental health issues are related to the esthetic features of people who naturally desire for being perfectly evaluated for their beauty; hence, a wide range of materials have been utilized in dentistry with miscellaneous features from both beauty and health-care views (Hafshejani et al., 2017; Zamanian et al., 2013; Zarrintaj et al., 2018a). Indeed the key imprints of such concerns are impression materials (IMs) that have been widely used in dentistry. IMs have been utilized in prosthodontics (e.g., denture), orthodontics, restoration, maxillofacial prosthetics, diagnosis/treatment planning, and dental implants. IMs have been known as negative imprints of the mouth tissues, which are utilized for the positive formation of the teeth and juxtaposing tissues model. Various materials exhibit the appropriate properties as candidates for IMs, these can be classified into elastic (nonrigid) and inelastic (rigid) materials. Common elastic materials, when examined clinically, are reversible hydrocolloids, such as agar, which work on the basis of phase change caused by temperature rise; irreversible hydrocolloids such as alginate salt; elastomeric materials such as silicones; and polyethers. Plasters, zinc oxide, and eugenol-based impression pastes are categorized as rigid/inelastic IMs. Such materials are used for the dental arches using dental impression trays (Ting-shu and Jian, 2015). Fig. 9.1 depicts the restoration the lost teeth using IMs (Bhakta et al., 2011). Typically, choosing the appropriate substance for a particular clinical usage/ application depends on either expense or precision. For designing more precise materials, when they are needed for a special purpose and not routinely, particular considerations are required. For cases where undercuts are not present among the recording surfaces, stiff substances are preferred. Rigid IMs can also be utilized in edentulous subjects, where soft tissue (compressible) undercuts are present (McCabe and Walls, 2013). The reason for using the impression tray is to prepare the supporting matrix for the IMs before simply inserting the impression into the mouth. In general, two types of trays are available: custom-made and stock trays (Marotti et al., 2014). Stock trays are supplied in various shapes and size in order to help the clinician to choose the tray that fits well to the patient’s mouth. Such trays are often either under- or overextended in relation to the extent of the oral soft and

Impression materials for dental prosthesis

199

Figure 9.1 Exposed fixture head after removal of the healing abutment (A); closed tray impression coping screwed in place (B); light-bodied IM syringed around impression coping (C); impression taken in a stock tray (D); impression with details of soft tissue around the implant and adjacent teeth (E); and impression coping repositioned into the impression (F) (Bhakta et al., 2011).

hard tissues, which need to be recorded for the clinical purposes so as to facilitate modification if needed (Pastoret et al., 2017). On the other hand, custom-made trays are constructed on the study casts of a patient’s mouth that have been obtained with IMs, thus having a greater accuracy when compared to the stock trays. For recording the oral soft tissues, such trays should be suitably extended in all orientations. Some methods are used to stick IMs to the trays including puncturing perforation in the tray, utilizing adhesives, and rim lock (McCabe and Walls, 2013; Tripathi et al., 2017). IMs can be applied in liquid state or solid-like state to form the shape of dentition and the surrounding structures of the oral cavity before being set. Materials used should possess the following acceptable features: they should have pleasant esthetic color/ taste/odor with no releasable toxic ingredients, should be biocompatible with no irritation to the tissue, have an appropriate shelf-life, be affordable, be dimensionally stable, and have sufficient mechanical strength. Techniques for taking impressions can be defined as mucostatic (normal resting position), mucocompressive (compression position), and selective pressure techniques (Oh and Morris, 2017). In order to construct a proper cast, IMs should be scrutinized; fulfilling this aim, in this overview, IMs and their properties are discussed. In the following sections, first, we focus on elastic IMs, followed by inelastic IMs, and finally their characteristics.

200

9.2

Advanced Dental Biomaterials

Elastic impression materials

9.2.1 Polyethers Among the elastomers, polyethers are the least hydrophilic; therefore they are preferably chosen for moisture condition uses to capture preparation margins adequately; moreover, their wetting feature facilitates the fabrication of a gypsum cast. It can be prepared by the monophase impression technique or syringe-andtray method (Fig. 9.2) (Rafael and Liebermann, 2017; Livaditis, 1998). Polyether has some advantages, such as highly hydrophilic, high-to-moderate stability, good accuracy, impressible in a monophase transition state, available in wide range of viscosity, appropriate tear resistance, high modulus, and proper elastic recovery. On the other hand, it suffers from being too stiff, susceptible to moisture absorption, and with potential for allergic reactions (Von Fraunhofer, 2013). Cationic ring-opening polymerization of ethylene imine controls the polyether setting behavior (Sakaguchi and Powers, 2012). New emerging polyethers exhibit proper flexibility that is essential for its facile removal from the mouth. Because of water absorption characteristics, polyethers should not be fully immersed in the water to prevent distortion (Powers and Wataha, 2017). It was observed that exposing polyether to immersion disinfection deteriorates its wettability potential. Sodium hypochlorite and phenol enhance its wettability, while iodophor has the inverse effect (Shetty et al., 2013).

Figure 9.2 Matrix filled with high-viscosity polyether impression material by the use of impression syringe to minimize entrapment of air (Livaditis, 1998).

Impression materials for dental prosthesis

201

9.2.2 Polysulfide Polysulfide, because of its nauseous taste, is not solely preferable for a dental prosthesis. It has been introduced as a paste to the two-component systems after mixing. Condensation polymerization helps the polysulfide setting process to yield a crosslinked rubbery polymer with high molecular weight, while together with polysulfide water forms as a by-product (Shoemaker et al., 2012; Guiraldo et al., 2017). Polysulfide enjoys the advantages of proper tear resistance, dimension stability, appropriate accuracy, and flexibility, whereas unpleasant taste, prolonged setting time, and mixing difficulties limit its capabilities (Levartovsky et al., 2011). Silica and TiO2 are being added as fillers to the base paste and have revealed promise in altering polysulfide viscosity. The set reaction consists of the oxidation of the
SH groups that cause cross-linking and chain extension to yield elastomeric properties, which can be easily removed from the mouth, comparably easier than that of polyether (Hamalian et al., 2011; Yang et al., 2016). Its prolonged reaction results in a long-term dimensional change, while its setting time takes a value around 10 minutes with setting shrinkage (Von Fraunhofer, 2013). Due to the hydrophobic nature of polysulfide, it has been desirable to be utilized in milieu therapy without saliva and blood (Hamalian et al., 2011).

9.2.3 Alginate Alginate is an irreversible hydrocolloid resulting from a sol
gel transition caused by chemical reaction (Serrano-Aroca et al., 2017). Alginate is a polysaccharide presenting excellent biocompatibility with tissues (Atoufi et al., 2017). When exposed to calcium ions (Ca21), alginate aqueous solution cross-links. Sodium phosphate can be used as a retarder for regulating the setting time that has been found to vary from 1 to 5 minutes with a mild rise in water temperature (Fokkinga et al., 2017). Alginate is normally utilized when the accuracy is not so important. Elastomeric materials can be used as a secondary layer over the alginate. Thanks to its low price, easy flow, swift setting time, and minimal displacement, alginate can play the role of an IM. On the other hand, low-dimensional stability, inappropriate tear strength, and bubbling during mixing place some questions on alginate usage. The fraction of powder regulates the properties of the final product, such as gel strength, setting reaction, flow, and stability (Al-Enazi and Naik, 2016). It was reported that the gelation time is governed by the secondary materials such as disinfection liquids. For instance, chlorhexidine increases gelation time increment, while sodium hypochlorite decreases the gelation time. Alginate gelation is related to ion availability so that a higher content of ions results in fast gelation; moreover, ion concentration affects the mechanical stability (de Azevedo Cubas et al., 2014). Chlorhexidine will consume the ions and reduce the cross-link density (CLD); hence, the mechanical stability of alginate plunges down. On the other hand, sodium hypochlorite generates ions leading to the amelioration of the CLD and mechanical stability enhancement (Amalan et al., 2013). Operational conditions,

202

Advanced Dental Biomaterials

such as temperature and humidity in storage and transport, manipulation of instructions, and ingredients ratio, govern the final product properties, such as distortion and stability (Kulkarni and Thombare, 2015).

9.2.4 Agar Agar is a kind of polysaccharide obtained from seaweed. It is a reversible hydrocolloids yielded via sol
gel transition under the influence of temperature, so that exhibits thermogelling behavior (Han et al., 2017; Zarrintaj et al., 2017a). Agar provides high accuracy that makes it effective for use in crowns and bridges (fixed prosthodontics); moreover, because of its thermoreversible behavior it can be used several times. Because of the hydrophilicity of agar, dental drying is not mandatory, and it can be used in the wet state. Agar formation necessitates the water bath and rim-lock trays with coiled edges, which can allow water to pass through to cool down the agar for the sake of setting (Iwasaki et al., 2016). Agar exhibits viscoelastic behavior, and its elastic recovery can be promoted by removing the impression quickly so that the material tolerates the stress for a concise time; furthermore, agar can be torn by applying a very low amount of stress because of poor mechanical properties. The dimensional stability of materials is not desirable due to high water uptake of gel (McCabe and Walls, 2013; Atoufi et al., 2017). Pouring the impression at several time intervals may bring about dimensional fluctuations. On this issue, sequential pouring of the IMs (alginate, agar, and polyvinyl siloxane) for several times on dimensional precision of the impressions was recommended. It was shown that when the materials were poured instantly, their dimensional exactness did not differ noticeably, while when the same materials were repoured after 30 minutes (the second pour), dimensional accuracy of alginate indicated the most alteration compared to the other aforementioned materials (Craig, 1988).

9.2.5 Silicones 9.2.5.1 Polysiloxanes Polysiloxane (PVS), usually called addition silicone, has been utilized widely in advanced restorative dentistry. Its grades are classified based on the filler content that controls its properties, such as thickness and flowability (Wang, 2016). The most well-known forms are extra light-bodied (low filler content), light-bodied, universal or medium-bodied, heavy-bodied, and putty (high filler content). A paste-topaste system and additional polymerization (without by-product) have been used for synthesizing such silicone leading to a stable production. However, the hydrophobicity of such material necessitates accurate moisture control in applying time (Goodall et al., 2015). Monophase polyvinyl siloxane and polyether elastomeric IMs have been widely studied. It was revealed that impregum, Penta, and aquasil acted better under the dry state; also, impregum acted better than the aquasil in both situations (Vadapalli et al., 2016). New hydrophilic elastomeric IMs have been recommended for diminishing the voids and distortion in the impressions. Soft

Impression materials for dental prosthesis

203

Figure 9.3 Polysiloxane (PVS) impression in a custom tray for fixed prosthodontics (Punj et al., 2017).

polyether exhibited higher strain and lower tensile strength in comparison with addition silicones. Moreover, the tear and tensile strength of heavy-bodied materials were higher than those of light-bodies (Lu et al., 2004). Cole et al. synthesized thiol- and allyl-functionalized siloxane oligomers using radical-mediated polymerizations to gain swift set elastomeric dental IMs. Thiol-ene siloxane was crosslinked through the redox-initiated reaction. Properties of such dental impression were adjusted with plasticizer and kaolin filler; moreover, it exhibited a high accuracy (Cole et al., 2014). PVS should be cast in appropriate trays to use as an IM (Fig. 9.3) (Punj et al., 2017).

9.2.5.2 Condensation silicone The main materials of condensation silicones are dimethyl siloxane with CaCO3 or silica as a filler. Stannous octoate and alkyl silicate act as catalysts. Ethyl alcohol is the polymerization by-product that leads to high shrinkage during setting. Such silicones set quickly down on the tooth and are considered to get rigid to some extent (Von Fraunhofer, 2013). The condensation silicones are available in putty, paste, or light-bodied forms to be formed accurately. Hydrophobicity, shrinkage, and releasing their by-products, however, are disadvantages of condensation silicones to be taken into account before choosing them for dental treatments. Disinfectant within the silicone-based impression should be carefully controlled because it was reported that the dimensional stability of such products varies formulation to formulation. It is noteworthy that disinfectants containing benzalkonium chloride and glutaraldehyde are not deteriorative to the dimensional consistency of the aforementioned elastomeric materials (Sinobad et al., 2014).

204

Advanced Dental Biomaterials

9.2.5.3 Vinyl polyether siloxane This substrate is a novel IM receiving attention because of the simplicity of removal of additional silicone and the hydrophilicity of polyether simultaneously. Based on such specifications, it is a useful material for certain cases, such as narrow, deep gingival crevices (Punj et al., 2017). It was reported that VPS exhibited the appropriate dimensional stability (Nassar et al., 2013). Vinyl polyether silicone (VPES) and vinylpolysiloxane (VPS) were comparable regarding dimensional stability and surface detail reproduction after the disinfection process and long-time storage (Din et al., 2017). Investigations demonstrated that these materials are stable after 2-week storage; however, VPES showed less dimensional alteration compared to the VPS. Also, the disinfected species of both substrates were more consistent than the pristine ones. In vitro setting revealed that the VPES had enough dimensional stability and surface accuracy (Nassar and Chow, 2015).

9.3

Inelastic impression materials

9.3.1 Impression wax Varieties of natural waxes and resins have been utilized in dentistry for defined applications. Waxes refer to thermoplastic materials solidifying at ambient temperature and being molten without decomposition, which consist of two or more ingredients for the construction of nonmetallic denture bases (Powers and Craig, 1978). Dental waxes have a large thermal expansion coefficient. They can be expanded upon temperature rise and vice versa. The mechanical features of waxes depend inversely with temperature, but overall, their compressive strength and elastic modulus are poor. Waxes can be derived from natural sources, such as mineral (paraffin, microcrystalline, and montan), plant (carnauba, cocoa butter), insect (beeswax), animals (spermaceti), or from synthetic materials such as polyethylene, polyoxyethylene glycol, halogenated hydrocarbon, and hydrogenated (Tinto et al., 2017). Waxes, based on their usage, can be categorized into three groups in dentistry including pattern wax (inlay wax, casting wax, and base plate wax), processing wax (boxing wax, utility wax, and sticky wax), and impression wax (corrective wax and bite plate wax). The greatest disadvantage of wax is its distortion (Tinto et al., 2017). Conventional waxes consist of a paraffin wax with a low melting point and beeswax in a ratio of 3:1. This proportion assures that at mouth temperature, an appropriate flow is expectable. This kind of IM is not common in recording thorough impressions; in fact, they are used for the modification of small defects in other impressions, especially the zinc oxide
eugenol impressions (Von Fraunhofer, 2013). Waxes belong to the thermoplastic substances that are able to flow at mouth temperature. These waxes can fill the sections of the impressions not receiving adequate material or imperfections caused by the air blow with the aid of brushing. Prior to utilizing the wax in defective

Impression materials for dental prosthesis

205

parts of the impressions or impression trays, it should be melted. It is necessary to give the material enough time when it is in the mouth to reach the oral temperature as it should undergo plastic flow to record the denture bearing area more precisely (McCabe and Walls, 2013).

9.3.2 Impression compound Impression compounds (ICs) are categorized as thermoplastic substances available in sheet or stick form. Such compounds have been produced by combining waxes, thermoplastic resins, fillers, and coloring agents. Some additives, such as shellac, stearic acid, and gutta-percha, can be added to the compound for plasticity enhancement. ICs softening takes a long time to complete because of low thermal conductivity of the ICs. It was observed that the shrinkage occurs after removal due to the high thermal expansion coefficient of ICs. Low thermal conductivity and high thermal expansion coefficient lead to the creation of internal stresses during the temperature fall form softening to the ambient degree resulting in distortion (Mete et al., 2017). Low-fusing substances have been used as IMs to aid flow at temperatures above 45 C and are available in sheet or stick form. In order to record the impressions of edentulous ridges, the sheet form is preferable, while the stick form is suitable for recording the impressions of single crowns. The method for softening the stick form is using a flame, whereas to soften the sheet a water bath is used. It is important to notice that during softening the stick material’s direct exposure to flame should be avoided to avoid ignition or boiling. Regarding the sheet forms, the softening time in water bath should be controlled, since if the submerged time is long, some important components, such as stearic acid, may be leached out. Higher fusing ICs can be applied for fabricating impression trays (McCabe and Walls, 2013; Von Fraunhofer, 2013; Anusavice et al., 2013).

9.3.3 Impression plaster Impression plasters (IPs) have conventionally been utilized as casting materials and IMs for edentate patients. The components of the IP are calcined, β-calcium sulfate hemihydrate that is mixed with water to trigger a reaction resulting in the formation of calcium sulfate dehydrate (Oppedisano, 2013). The ratio of water/powder affects mixture constancy and setting time. Controlling the behavior of IPs is an important factor; hence, some additives have been added to the compound. In order to decrease the setting expansion of the plasters, antiexpansion agents, such as potassium sulfate (K2SO4), have been utilized. It is reported that such agents speed up the setting reaction. Borax is also combined as a retarder to provide the dentist with an opportunity to control the setting features. Pigments, such as alizarin, can be utilized to make a difference between the impression and the mold (Dai et al., 2014). Conventional plaster casting materials, due to the adhesion to the mold, necessitate the use of releasing agents, but newly blended plaster is fabricated from acrylic resin or shellac to allow

206

Advanced Dental Biomaterials

easy separation. The disinfection process of IPs involves immersion in sodium hypochlorite. These materials are fragile, and whenever the pressure or tensile force is applied, they fracture; thus, they cannot be used in undercut conditions. IPs have been used for recording impressions of highly mobile soft tissues overlying the residual alveolar bone. Moreover, IPs should be preserved in the dry state, as water absorbed from the humid state causes setting time extension (Von Fraunhofer, 2013).

9.3.4 Metallic oxide pastes (zinc oxide
eugenol impression paste) Impression paste has been utilized to take the secondary impressions for a complete denture and consists of base part (zinc oxide) and catalyst paste (eugenol), which are mixed with a stainless steel spatula for about 1 minute. Zinc oxide is accompanied with vegetable or mineral oil, used for plasticizing, and also helps to neutralize the irritation caused by eugenol. Eugenol is usually available with rosin leading to smooth and homogeneous materials and also facilitating the reaction pace. The color of the zinc oxide paste is white, while eugenol paste is reddish brown. The color contrast helps in determining the perfect mixing, since in this state, the mixture should show a homogenous color (Manappallil, 2015). These substrates are divided into two main groups: hard paste (Type 1) for which the terminal set comes to pass within 10 minutes and soft paste (Type 2) that indicates a final set occurrence within 15 minutes. After the final set the impression can be removed from the mouth. The setting reaction is ionic in nature. Hence, ion concentration is an important factor in the reaction proceeding that can be affected by temperature and humidity, and ionizable salt also affects the reaction rate. Initially, ZnO hydrolyzes and reacts with eugenol to achieve zinc eugenolate salt (2C10H12O2 1 ZnO!Zn(C10H11O2)2 1 H2O) (Luengo et al., 2017). It was reported that an allergic response to the irritation can occur in some patients, as the eugenol leaches out and reaches the soft tissue. In such cases, ZOE-like materials, that is, eugenol-free zinc oxide impression pastes, are useful. ZOE-like materials are the products of the reaction between zinc oxide and different carboxylic acids, such as orthoethoxybenzoic acid. These acids are utilized instead of eugenol. In order to diminish the tissue burning sensation, oil of cloves (including 70%
85% eugenol) can be used instead of pure eugenol in the first tube. Regarding disinfection, a 2% alkaline glutaraldehyde is utilized through the steps as previously stated for ICs. In the case of dimensional accuracy the impression pastes are reliable materials as less than 0.1% shrinkage happens during setting. The impression pastes can be maintained without any change in shape arising from the relaxation or another motive of the distortion. This state can be assured if the material used in the tray structure shows dimensional stability (Anusavice et al., 2013). All the mentioned materials should be used with the appropriate tray to exhibit the functional performance. 3Dprinted trays showed better properties, such as uniform thickness distribution of IMs, than conventional ones (Fig. 9.4) (Sun et al., 2017).

Impression materials for dental prosthesis

207

Figure 9.4 Design process of the digital 3D-printed tray [(A
D) maxilla and (E
H) mandible]. (A and E) The scanned data of the primary impression. (B) and (F) The impression is trimmed to the appropriate range. (C and G) The main part of the tray and the tissue stop. (D and H) A handle is added to the tray. The finished trays [(Ai
Di) manual tray and (Ei
Hi) digital tray]. (Ai and Ei) A maxillary tray with a tissue stop. (Bi and Fi) A mandibular tray with a tissue stop. (Ci and Gi) A maxillary tray without a tissue stop. (Di and Hi) A mandibular tray without a tissue stop (Sun et al., 2017).

9.4

Characteristics of impression materials

9.4.1 Dimensional accuracy/dimensional stability Viscosity has a crucial role in determining the accuracy of the detail reproduction. In fact, a low viscosity or degree of pseudoplasticity helps to record the surface segments precisely (Hamalian et al., 2011). When fixing the IM into the patient’s mouth, it should be in the fluid state. The capability of the IMs to preserve the material accuracy over time indicates their dimensional stability; however, by the phrase dimensional accuracy, the absence of dimensional change for a short time after removing from the mouth and during setting is considered (Anusavice et al., 2013). The dimensional accuracy of some materials is time dependent, reported for the case of elastomeric IMs, including polyvinyl siloxane, polyether, and polysulfide. In other words the highest level of dimensional accuracy corresponds to the product collected right after the polymerization is completed, while it diminishes during the storage of IMs over a prolonged period (Rubel, 2007). Materials with low shrinkage have been chosen to be utilized as dental impressions (Hamalian

208

Advanced Dental Biomaterials

et al., 2011). For instance, polyvinyl siloxane and polyether can keep their dimensional accuracy for about 1
2 weeks after making the impression (Rubel, 2007). PVS can be infinitesimally poured into the mold during the operation period, whereas since polyether can absorb humidity from the environment and swell, it is better for polyether to be poured within 1 hour after ejection from the mouth. Regarding polysulfide and condensation silicone, as by-products accompany their polymerization during the setting reaction, water and volatile ethyl alcohol should be poured within 30 minutes after ejection from the mouth because such byproducts volatilize from the set impression and cause distortion. All of the elastomeric IMs shrink during polymerization; moreover, because of the generation of by-products during the setting, they show more constriction. Overall, the greatest dimensional change during setting refers to the polysulfide and polyvinyl silicone, and the smallest one pertains to the PVS (Hamalian et al., 2011).

9.4.2 Wettability A hydrophilic nature is one of the essential characteristics an actual IM needs, as this substance is in continuity with the wet tissue. Affinity toward spreading on hydrophilic substances results in flow capability into tiny areas or splitting and recording partial details. IMs with low contact angle flow easily into small gaps and make impressions with fewer voids. Hence, such materials are reliable for utilization in fixed prosthodontics (Hamalian et al., 2011). The sort of IMs that can flow into partial segments in the scale of 20
70 μm have been required in the field of fixed partial dentures; on the other hand, IMs that can reproduce details in the scale of 100
150 μm are useful in the fields of removable prosthodontics (Rubel, 2007). Hydrophilic IMs enable dental stone to flow smoothly. Accordingly, the casts without bubbles can be obtained. In order to produce more precise casts when the IMs have high contact angle, both the particular pouring technique and attention should be considered. Hydrophobic materials necessitate the surfactant utilization to reduce the contact angle prior to pouring casts; on the contrary, polyether, polysulfide, and hydrocolloids are hydrophilic IMs with low contact angle (Rubel, 2007).

9.4.3 Elastic recovery/flexibility It is of paramount importance for IMs to have an elastic recovery property, allowing it to return to its main dimensions without noticeable distortion upon removal from the mouth (Re et al., 2015). It was indicated that PVS exhibited foremost elastic behavior (with over 99% elastic recovery), followed by polyether and then polysulfide. Instantly after mixing, PVS, because of swift elasticity development, should be applied promptly, particularly at high temperatures. Conversely, polyether kept the plasticity for the more extended duration after mixing. Also, the ultimate stiffness of the polyether is greater than that of PVS and may affect the ease of removing the material from the mouth (Mehta et al., 2014). The flexibility of the impressions can facilitate the removal of the materials from the mouth. Polyether is

Impression materials for dental prosthesis

209

the stiffest IM. Polyvinyl siloxane is moderately rigid, and the rigidity relies on the viscosity of the material (Hamalian et al., 2011). Alginate is evaluated as the most flexible IM (Rubel, 2007). The investigations demonstrated that the viscosity is an important factor in fabricating impressions and die with the least bubbles and maximal details. The increase in the amount of deformation and the time spent for removal of the impression from the mouth have an influence on the accuracy of the impression (Hamalian et al., 2011).

9.4.4 Mechanical properties The main three relevant mechanical features of IMs in clinical terms having a functional impact on dental impression applications are yield strength, strain at yield point, and tear energy. The yield strength is attributed to the point in which the material can tolerate the stress without permanent deformation. The strain at yield illustrates the quantity of undercut that an impression can defeat without permanent deformation (Re et al., 2015). The tear energy determines and shows the degree to which a material maintains resistance against tearing after setting. The material should provide some properties such as appropriate and sufficient elastic recovery and consumption of much energy to commence and spread tearing. Polysulfides are incredibly resistant to tearing but show permanent deformation and do not indicate complete elastic recovery after a critical point of permanent deformation (Al-Enazi and Naik, 2016). Hydrocolloids show low tear strength. Both PVS and polyether have the greatest tear strength, and they tear before they reach their perennial deformation point. Hence, they are more appropriate for clinical use (Hamalian et al., 2011). Since producers have their exclusive formulations, various viscosities and flow features exist. As different producers produce the materials, they also are at various working times available according to standard-set versus quick-set IMs (Rubel, 2007).

9.4.5 Miscellaneous In addition to all the general properties that have been mentioned in previous sections, some other criteria are essential, including evaluating whether the materials are tolerable for the patients, gaining the best consequences for low costs, and utilizing the disinfectants that cause the least dimensional changes. Disinfection of some materials, for example, hydrocolloids, polyethers, and methacrylates, need particular protocols to prevent distortion taking place after setting (Rubel, 2007; Zarrintaj et al., 2018b). Various antibacterials and disinfectants can be used for dental impressions (Hafshejani et al., 2017; Maller et al., 2012). Diluted sodium hypochlorite is a disinfectant but not a sterilizer, accepted by the American Dental Association for all materials except zinc oxide
eugenol paste. Disinfection of zinc oxide
eugenol impression paste is done using glutaraldehyde (Rubel, 2007). In Table 9.1 the properties of IMs are described.

Table 9.1 Comparison of various types of dental impression properties. Impression materials

Type

Advantage

Polyether

Elastic

G

G

G

G

G

G

G

Polysulfide

Elastic

G

G

G

G

Hydrophilic elastomeric Dimensionally stable Minimal shrinkage Proper accuracy Monophase impression Good tear resistance Low shrinkage Good tear resistance Stable dimensional Proper accuracy Most flexible elastomer

Disadvantage G

G

G

G

G

G

G

G

Agar

Elastic

G

G

G

Alginate

Elastic

G

G

G

G

G

Addition silicone

Elastic

G

G

G

G

G

High accuracy Hydrophilic Reusable Easy flow Cheap Reproduction of adequate detail Fast setting time Minimal tissue displacement in the mouth

G

Good detail reproduction Excellent dimensional stability No shrinkage on set High patient acceptance More than one model can be poured from one cast

G

G

G

G

G

G

G

G

G

G

G

Ref.

Too stiff Short working time

Guiraldo et al. (2017)

Low patient satisfaction Unpleasant taste and odor Long setting time Requires excellent moisture control Difficult to mix Some shrinkage on set with the release of by-product Complex procedural steps Significant start-up cost of the hardware

Punj et al. (2017)

Poor dimensional stability Poor tear strength Unsupported Distortion Easy to include air during mixing A minimum thickness of 3 mm is required, which is hard to achieve in thin areas in between the teeth Hydrophobic Too accurate Poor tear resistance Expensive

Khalid et al. (2015)

Iwasaki et al. (2016)

Punj et al. (2017)

(Continued)

Table 9.1 (Continued) Impression materials

Type

Advantage

Condensation silicone

Elastic

G

G

Accurate High patient acceptance

Disadvantage G

G

G

G

G

Plaster

Inelastic

G

G

G

G

G

Impression compound

Inelastic

G

G

G

G

Zinc oxide
eugenol plaster

Inelastic

G

G

G

G

Hydrophilic Good detail reproduction Excellent dimensional stability (contraction on setting) Good patient tolerance 2
3 min working time Primary impressions of complete dentures Border molding of trays Extension of trays Achieving mucocompression in the postdam area when working impressions are taken for complete dentures Thermoplastic Can be heated to aid removal from the casting material Good detail reproduction Excellent dimensional stability (0.15% shrinkage on setting)

G

G

G

Hydrophobic Requires excellent moisture control Unreliable dimensional stability Difficult to accurately proportion components leading to variable results Marked shrinkage on setting with the release of byproduct Brittle No recovery from deformation. Therefore if an undercut is present, the material will have to be broken off the impression and then glued back together before casting Excess salivation by the patient could have an adverse effect on detail reproduction

Ref. Punj et al. (2017)

Von Fraunhofer (2013)

Von Fraunhofer (2013)

G

G

Rigid Presence of undercuts can distort the final material or cause the section engaged to separate from the resultant impression

Luengo et al. (2017)

212

9.5

Advanced Dental Biomaterials

Conclusion and future perspective

Dental IMs have been utilized for developing the numerous dental and orthodontic applications. They are the first stage in the chain of a dental prosthesis or the initial level of placing a crown or bridge. Due to such aims, various materials have been examined for dental prostheses purposes ranging from elastic to rigid materials. To preventing contamination, various disinfection materials have been added to the IMs to reach a desired product. The maintenance of properties, such as dimensional stability, is found to be among the major properties needed for the suitable functioning of IM. Various properties, such as setting time, accuracy, wettability, and recovery, should be considered in IM usage. IMs preparation necessitates the tray involved in IM casting. Recently, a digital technique has been utilized for the preparation of IMs and to optimize the process by shortening the process time, enhancing the accuracy, and facilitating the setting procedure. To reach the best dental impression, however, the material should be designed so as to meet several requirements simultaneously including low shrinkage, high accuracy, high stability, and proper hydrophilicity, and it must be applied with modern techniques to achieve the appropriate product. In this regard the current chapter gives some insights into the status of IMs used for dental prostheses. In the near future, digital dentistry will cover all aspects of this. The new emerging digital devices are starting to be used in the IM field, and they will become more user friendly, more precise, and smaller in size of wand/equipment. Tomography is used for capturing the basic graph to construct proper restorative implants. Hence, the digital methods in IMs preparation should be evaluated in more detail in future studies to design a road map for IMs selection for the next generation of restorative materials.

References Al-Enazi, T.A., Naik, A.V., 2016. Disinfection of alginate and addition silicon rubber-based impression materials. Int. J. Stomatol. Occlusion Med. 8 (1), 44
48. Amalan, A., Ginjupalli, K., Upadhya, N., 2013. Evaluation of properties of irreversible hydrocolloid impression materials mixed with disinfectant liquids. Dent. Res. J. 10 (1), 65. Anusavice, K.J., Shen, C., Rawls, H.R., 2013. Phillips’ Science of Dental Materials. Elsevier Health Sciences. Atoufi, Z., Zarrintaj, P., Motlagh, G.H., Amiri, A., Bagher, Z., Kamrava, S.K., 2017. A novel bio electro active alginate-aniline tetramer/agarose scaffold for tissue engineering: synthesis, characterization, drug release and cell culture study. J. Biomater. Sci., Polym. Ed. 1
43. just accepted. Bakhshandeh, B., Zarrintaj, P., Oftadeh, M.O., Keramati, F., Fouladiha, H., Sohrabi-jahromi, S., et al., 2017. Tissue engineering; strategies, tissues, and biomaterials. Biotechnol. Genet. Eng. Rev. 33 (2), 144
172. Bhakta, S., Vere, J., Calder, I., Patel, R., 2011. Impressions in implant dentistry. Br. Dent. J. 211 (8), 361
367.

Impression materials for dental prosthesis

213

Craig, R.G., 1988. Review of dental impression materials. Adv. Dent. Res. 2 (1), 51
64. Chiu, L.L.Y., Chu, Z., Radisic, M., Mozafari, M., 2017. Tissue engineering. Reference Module in Materials Science and Materials Engineering. Elsevier. Cole, M.A., Jankousky, K.C., Bowman, C.N., 2014. Thiol-ene functionalized siloxanes for use as elastomeric dental impression materials. Dent. Mater. 30 (4), 449
455. Dai, J., Cheng, N., Miron, R.J., Shi, B., Cheng, X., Zhang, Y., 2014. Effect of decreased implant healing time on bone (re)modeling adjacent to plateaued implants under functional loading in a dog model. Clin. Oral. Invest. 18 (1), 77
86. de Azevedo Cubas, G.B., Valentini, F., Camacho, G.B., Leite, F.R.M., Cenci, M.S., PereiraCenci, T., 2014. Antibacterial efficacy and effect of chlorhexidine mixed with irreversible hydrocolloid for dental impressions: a randomized controlled trial. Int. J. Prosthodont. 27 (4), 363
365. Din, S.U., Parker, S., Braden, M., Tomlins, P., Patel, M., 2017. Experimental hydrophilic vinyl polysiloxane (VPS) impression materials incorporating a novel surfactant compared with commercial VPS. Dent. Mater. 33, e301
e309. Fokkinga, W.A., Witter, D.J., Bronkhorst, E.M., Creugers, N.H., 2017. Clinical fit of partial removable dental prostheses based on alginate or polyvinyl siloxane impressions. Int. J. Prosthodont. 30 (1), 33
37. Goodall, R.H., Darras, L.P., Purnell, M.A., 2015. Accuracy and precision of silicon based impression media for quantitative areal texture analysis, Sci. Rep., 5. p. 10800. Guiraldo, R.D., Berger, S.B., Siqueira, R.M., Grandi, V.H., Lopes, M.B., Gonini-Ju´nior, A., et al., 2017. Surface detail reproduction and dimensional accuracy of molds: influence of disinfectant solutions and elastomeric impression materials. Acta Odontol. Latinoam. 30 (1), 13
18. Hafshejani, T.M., Zamanian, A., Venugopal, J.R., Rezvani, Z., Sefat, F., Saeb, M.R., et al., 2017. Antibacterial glass-ionomer cement restorative materials: a critical review on the current status of extended release formulations. J. Control. Release 262, 317
328. Hamalian, T.A., Nasr, E., Chidiac, J.J., 2011. Impression materials in fixed prosthodontics: influence of choice on clinical procedure. J. Prosthodont. 20 (2), 153
160. Han, M., Li, Q.-L., Cao, Y., Fang, H., Xia, R., Zhang, Z.-H., 2017. In vivo remineralization of dentin using an agarose hydrogel biomimetic mineralization system. Sci. Rep. 7, 41955. Iwasaki, Y., Hiraguchi, H., Iwasaki, E., Yoneyama, T., 2016. Effects of immersion disinfection of agar-alginate combined impressions on the surface properties of stone casts. Dent. Mater. J. 35 (1), 45
50. Khalid, M., Shah, S.N., Chughtai, M.A., 2015. Comparison of mean dimensional measurement of alginate impression using sodium hypochlorite versus gluteraldehyde and benzalkonium chloride for disinfection. Cell 321, 9001101. Kulkarni, M.M., Thombare, R.U., 2015. Dimensional changes of alginate dental impression materials—an in vitro study. J. Clin. Diagn. Res.: JCDR. 9 (8), ZC98
ZC102. Levartovsky, S., Folkman, M., Alter, E., Pilo, R., 2011. Elastomeric impression materials. Refu’at ha-peh veha-shinayim (1993) 28 (2), 54
64. Livaditis, G.J., 1998. Comparison of the new matrix system with traditional fixed prosthodontic impression procedures. J. Prosthet. Dent. 79 (2), 200
207. Lu, H., Nguyen, B., Powers, J.M., 2004. Mechanical properties of 3 hydrophilic addition silicone and polyether elastomeric impression materials. J. Prosthet. Dent. 92 (2), 151
154. Luengo, J., Reyes, H., Toscano, I., Garcia, Y., Anaya, M., 2017. Clinical and radiographic evaluation of CTZ (chloramphenicol-tetracycline-zinc eugenol oxide) antibiotic paste in pulp treatment of primary molars. J. Dent. Health Oral Disord. Ther. 8 (1), 00272.

214

Advanced Dental Biomaterials

Maller, S.V., Karthik, K., Maller, U.S., Abraham, M.C., Kumar, R.N., Manikandan, R., 2012. Drug and dental impression materials. J. Pharm. Bioallied Sci. 4 (Suppl 2), S316. Manappallil, J.J., 2015. Basic Dental Materials. JP Medical Ltd. Marotti, J., Tortamano, P., Castilho, T.R., Steagall, W., Wolfart, S., Haselhuhn, K., 2014. Accuracy of a self-perforating impression tray for dental implants. J. Prosthet. Dent. 112 (4), 843
848. McCabe, J.F., Walls, A.W., 2013. Applied Dental Materials. John Wiley & Sons. Mehta, R., Dahiya, A., Mahesh, G., Kumar, A., Wadhwa, S., Duggal, N., et al., 2014. Influence of delayed pours of addition silicone impressions on the dimensional accuracy of casts. J. Oral Health Commun. Dent. 8, 3. Mete, J.J., Rajguru, V.L., Dange, S.P., 2017. Aluminum barrier laminate or plastic tube as a dispenser for modeling plastic impression compound for border molding. J. Prosthet. Dent. 119, 676
677. Nassar, U., Chow, A.K., 2015. Surface detail reproduction and effect of disinfectant and long-term storage on the dimensional stability of a novel vinyl polyether silicone impression material. J. Prosthodont. 24 (6), 494
498. Nassar, U., Oko, A., Adeeb, S., El-Rich, M., Flores-Mir, C., 2013. An in vitro study on the dimensional stability of a vinyl polyether silicone impression material over a prolonged storage period. J. Prosthet. Dent. 109 (3), 172
178. Oh, W., Morris, H., 2017. The principles of functional and mucostatic impressions for complete denture bases: a review. Compend. Continuing Educ. Dent. (Jamesburg, NJ: 1995) 38 (10), 664. Oppedisano, M., 2013. Delayed Linear Expansion of Two Ultra-low Expansion Dental Stones (Doctoral dissertation). Pastoret, M.-H., Krastl, G., Bu¨hler, J., Weiger, R., Zitzmann, N.U., 2017. Accuracy of a separating foil impression using a novel polyolefin foil compared to a custom tray and a stock tray technique. J. Adv. Prosthodont. 9 (4), 287
293. Powers, J.M., Craig, R.G., 1978. Thermal analysis of dental impression waxes. J. Dent. Res. 57 (1), 37
41. Powers, J.M., Wataha, J.C., 2017. Dental Materials: Foundations and Applications. Elsevier. Punj, A., Bompolaki, D., Garaicoa, J., 2017. Dental impression materials and techniques. Dent. Clin. North Am. 61 (4), 779
796. Rafael, C.F., Liebermann, A., 2017. Clinical characteristics of an allergic reaction to a polyether dental impression material. J. Prosthet. Dent. 117 (4), 470
472. Re, D., De Angelis, F., Augusti, G., Augusti, D., Caputi, S., D’Amario, M., et al., 2015. Mechanical properties of elastomeric impression materials: an in vitro comparison. Int. J. Dent. 2015, 428286. Rubel, B.S., 2007. Impression materials: a comparative review of impression materials most commonly used in restorative dentistry. Dent. Clin. North Am. 51 (3), 629
642. Sakaguchi, R.L., Powers, J.M., 2012. Craig’s Restorative Dental Materials-E-Book. Elsevier Health Sciences. ´ ., Ruiz-Pividal, J.-F., Llorens-Ga´mez, M., 2017. Enhancement of water difSerrano-Aroca, A fusion and compression performance of crosslinked alginate films with a minuscule amount of graphene oxide. Sci. Rep. 7 (1), 11684. Shetty, S., Kamat, G., Shetty, R., 2013. Wettability changes in polyether impression materials subjected to immersion disinfection. Dent. Res. J. 10 (4), 539. Shoemaker, D.P., Chung, D.Y., Mitchell, J., Bray, T.H., Soderholm, L., Chupas, P.J., et al., 2012. Understanding fluxes as media for directed synthesis: in situ local structure of molten potassium polysulfides. J. Am. Chem. Soc. 134 (22), 9456
9463.

Impression materials for dental prosthesis

215

Sinobad, T., Obradovi´c-Ðuriˇci´c, K., Nikoli´c, Z., Dodi´c, S., Lazi´c, V., Sinobad, V., et al., 2014. The effect of disinfectants on dimensional stability of addition and condensation silicone impressions. Vojnosanit. Pregl. 71 (3), 251
258. Sun, Y., Chen, H., Li, H., Deng, K., Zhao, T., Wang, Y., et al., 2017. Clinical evaluation of final impressions from three-dimensional printed custom trays. Sci. Rep. 7 (1), 14958. Ting-shu, S., Jian, S., 2015. Intraoral digital impression technique: a review. J. Prosthodont. 24 (4), 313
321. Tinto, W., Elufioye, T., Waxes, R.J., 2017. Pharmacognosy. Elsevier, pp. 443
455. Tripathi,, A., Singh,, S.V., Aggarwal,, H., Gupta,, A., Arya,, D., 2017. A technique to preserve spacer thickness during custom tray fabrication with autopolymerizing polymethylmethacrylate. Int. J. Dent. Res. 2 (1), 1
2. Vadapalli, S.B., Atluri, K., Putcha, M.S., Kondreddi, S., Kumar, N.S., Tadi, D.P., 2016. Evaluation of surface detail reproduction, dimensional stability and gypsum compatibility of monophase polyvinyl-siloxane and polyether elastomeric impression materials under dry and moist conditions. J. Int. Soc. Prev. Commun. Dent. 6 (4), 302. Von Fraunhofer, J.A., 2013. Dental Materials at a Glance. John Wiley & Sons. Wang, Z., 2016. Comparison of dimensional accuracies using two elastomeric impression materials in casting three-dimensional tool marks. J. Forensic. Sci. 61 (3), 792
797. Yang, Z.-Z., Wang, H.-Y., Lu, L., Wang, C., Zhong, X.-B., Wang, J.-G., et al., 2016. Hierarchical TiO2 spheres as highly efficient polysulfide host for lithium-sulfur batteries. Sci. Rep. 6, 22990. Zamanian, A., Yasaei, M., Ghaffari, M., Mozafari, M., 2013. Calcium hydroxide-modified zinc polycarboxylate dental cements. Ceram. Int. 39 (8), 9525
9532. Zarrintaj, P., Bakhshandeh, B., Rezaeian, I., Heshmatian, B., Ganjali, M.R., 2017a. A novel electroactive agarose-aniline pentamer platform as a potential candidate for neural tissue engineering. Sci. Rep. 7, 17187. Zarrintaj, P., Moghaddam, A.S., Manouchehri, S., Atoufi, Z., Amiri, A., Amirkhani, M.A., et al., 2017b. Can regenerative medicine and nanotechnology combine to heal wounds? The search for the ideal wound dressing. Nanomedicine 12 (19), 2403
2422. Zarrintaj, P., Manouchehri, S., Ahmadi, Z., Saeb, M.R., Urbanska, A.M., Kaplan, D.L., et al., 2018a. Agarose-based biomaterials for tissue engineering. Carbohydr. Polym. 187, 66
84. Zarrintaj, P., Urbanska, A., Gholizadeh, S.S., Goodarzi, V., Saeb, M.R., Mozafari, M., 2018b. A facile route to the synthesis of anilinic electroactive colloidal hydrogels for neural tissue engineering applications. J. Colloid Interface Sci. 516, 57
66.