Сraig. Dental Materials

382 Chapter 12 IMPRESSION MATERIALS

syringe with a low-consistency material (at the correct time after mixing under proper conditions) to cover the teeth and gum surfaces before placing the high-consistency material with the tray.

Problem 9

When a polysulfide impression was withdrawn from the mouth, the impression material was separated from the tray in some areas. What caused this separation, and how accurate are the dies obtained from such an impression?

Solution

The adhesion of an impression material to the custom-made tray is obtained by coating the tray with an adhesive. To get good adhesion to the tray, use enough coats of the adhesive. It is also necessary to wait until the volatile organic solvent evaporates and the adhesive is dry. When the tray is filled with the highconsistency material too soon after applying the adhesive, the retention fails and the impression material separates from the tray. In this instance, a distortion of the impression is always present and results in a distorted model and dies. It is better to remake the impression than to continue with the procedure. When the failure is caused by the adhesive itself, better mechanical retention for the impression material can be obtained by making perforations with a bur in the same type of custom-made tray. These mechanical interlocks retain the impression material in position, and the uniform thickness of impression material in the custom-made tray helps control the polymerization shrinkage of the material.

Problem 10

Preparation of a complete-arch fixed bridge was completed, a wash impression with a condensation silicone was taken, and a single cast was obtained as a master model. The metal frame of the bridge fit perfectly on the cast but did not fit well on all abutments. Is this

a problem of the impression material, and how can it be solved? What factors may have produced this problem?

Solution a

Polymerization shrinkage occurs with condensation silicone material. Dimensional change in these silicone materials increases with time up to 24 hours, although about half the change takes place in the first hour. The longer the impression is left on the bench before the cast is poured, the greater the shrinkage of the material. Usually, some castings fit individual abutments, but when such a cast is used as a master model to make the fixed prosthesis, the general accuracy is unsatisfactory.

Solution b

Distortion may be produced as a result of relaxation of stresses in the impression. If the impression is removed from the mouth when polymerization has not progressed sufficiently, stresses may be induced in the mass and a distorted impression is obtained. A distorted impression can result from excessive pressure on the Inaterial during setting, which produces residual stresses that can be relieved.

Solution c

Distortion can be produced when the impression is removed with slow movements. Like all elastic impression materials, condensation silicone impressions must be removed from the mouth with a sudden motion. A slow removal induces permanent deformation in the mass, and an inaccurate cast is obtained. If a fixed appliance is made on such a cast, it will not fit on all teeth preparations. Note that less permanent deformation occurs with silicone than with polysulfide impressions.

Solution d

Distortion may result when too much space is provided between the tray and teeth. The amount of silicone impression material between the tray and the abutments should be

small. A thin layer is better than a thick mass because less permanent deformation occurs during the removal of the impression and more-accurate dies and models will be obtained.

Problem 11

An impression of a dentulous quadrant was taken with a medium-consistency polyether impression material in a custom-made acrylic tray. The normal relief of 2 mm was provided between the tray and the oral structures. After removal of the impression, tearing was noted at several locations. What adjustments can be made so that the possibility of tearing will be minimized on retaking the impression?

Solution a

Polyethers adhere quite well to hard and soft tissues and the medium consistency is quite stiff when set (low strain in compression). The adhesion and stiffness, combined with moderate tear strength, increases the probability of tearing of the impression. Before removal, first break the seal of the impression to tissues by pulling the impression slightly in the vestibular area. Syringing water into the area can also help break the seal. Finally, increase the relief space between the tray and the tissues to at least 4 mm to allow greater flexibility of impression material, thereby improving the ease of removal.

Solution b

Use the new, softened, medium-consistency polyether impression material in the tray; it is less rigid and possesses reduced Shore A hardness in the set condition. Also, provide additional relief space between the tray and the tissues (at least 4 mm) to increase the effective flexibility of the elastomer.

Problem 12

The manufacturer of an addition-silicone impression specified that high-strength stone dies should not be poured until after 1 hour.

An epoxy die was desired, and therefore pouring was delayed for 1hour. On separation, the die was covered with negative bubbles. What caused the problem, and how can it be avoided?

Solution

Some brands of addition silicones release hydrogen after setting. Waiting 1 hour before pouring the fast-setting, high-strength stone allows the rate of hydrogen release to decrease sufficiently so bubble-free dies can be produced. However, many epoxy die materials set slowly compared with high-strength stone, and sufficient hydrogen is still being released at 1 hour to produce bubbles on the surface of the epoxy die. Even waiting 4 hours may not result in a bubble-free epoxy die. Allowing the impression to stand overnight before pouring the epoxy die solves the problem. Also, note that the accuracy of additionsilicone impressions is excellent at 24 hours, even with the evolution of hydrogen.

Problem 13

An impression, taken in a non-hydrophilized addition silicone, had been mixed by hand spatulation. The resulting high-strength stone die had enough positive and negative bubbles, especially along the internal line angles and finish lines of the preparation, so a retake of the impression was necessary. What could be done to reduce the number of bubbles?

Solution

Changing to an addition silicone supplied in automixing cartridges substantially reduces the number of bubbles in the mix, compared with one prepared by hand spatulation, and minimizes the number of positive bubbles. In addition, changing to hydrophilized, automixing addition silicone decreases the number of negative bubbles in the die because of the better wetting of the impression by the mix of high-strength stone.

384 Chapter 12 IMPRESSION MATERIALS

Review Articles-Impression Materials

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of the American Academy of Restorative Dentistry, J Prosthet Dent 82:50, 1999.

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24:171, 1996.

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25:193, 1997.

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Agar and Alginate Hydrocolloids

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Farah JW, Powers JM, editors: Impression materials for fixed prosthodontics, Dent Advis 14:4, 1997.

Farah JW, Powers JM, editors: Bite registration materials, Dent Advis 15:4, 1998.

Fish SF, Braden M: Characterization of the setting process in alginate impression materials, J Dent Res 43:107, 1964.

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Int J Prosthodont 7:424, 1994.

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Int J Prosthodont 9:223, 1996.

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Jarvis RG, Earnshaw R: The effect of alginate impressions on the surface of cast gypsum. 11. The role of sodium phosphate in incompatibility, Aust Dent J 26:12, 1781.

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Johnson GH, Craig RG: Accuracy and bond strength of combinations of agadalginate hydrocolloid impression materials, J Prosthet Dent 55:1, 1786.

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MacPherson GW, Craig RG, Peyton FA: Mechanical properties of hydrocolloid and elastomeric impression materials, J Dent Res 46:714, 1967.

Matyas J, Dao N, Caputo AS et al: Effects of disinfectants on dimensional accuracy of impression materials, J Prosthet Dent 64:25, 1990.

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Peutzfeldt A, Asmussen E: Effect of disinfecting solutions on surface texture of alginate and elastomeric impressions, Scand J Dent Res 98:74, 1990.

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Assoc 732306, 1976.

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J Prosthodont 7:418, 1994.

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J Prosthodont 7315, 1774.

Wanis TM, Combe EC, Grant AA: Measurement of the viscosity of irreversible hydrocolloids, J Oral Rehabil20:377, 1973.

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Duplicating Materials

Craig RG, Gehring PE, Peyton FA: Aging characteristics of elastic duplicating compounds, J Dent Res 41:176, 1962.

Craig RG, Peyton FA: Physical properties of elastic duplicating materials, J Dent Res 39:391, 1760.

Finger W: Accuracy of dental duplicating materials, Quint Dent Tech 10239, 1986.

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Peyton FA, Craig RG: Compatibility of duplicating compound and casting investments,

JProsthet Dent 12:1111, 1962.

Properties and Use of Elastomeric Impression Materials

Baumann MA: The influence of dental gloves on the setting of impression materials,

Br Dent J 179:130, 1995.

Bell JW, Davies EH, von Fraunhofer JA: The dimensional changes of elastomeric impression materials under various conditions

of humidity, J Dent 4:73, 1976.

Boening KW, Walter MH, Schuette U: Clinical significance of surface activation of silicone impression materials, J Dent 26:447, 1998.

Braden M: Characterization of the setting process in dental polysulfide rubbers, J Dent Res 45:1065, 1966.

386 Chapter I2 IMPRESSION MATERIALS

Braden M, Causton B, Clarke RL: A polyether impression rubber, J Dent Res 51:889, 1972.

Braden M, Inglis AT: Visco-elastic properties of dental elastomeric impression materials, Biomater 7:45, 1986.

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Issue B): 946 (Abstract 2517), 1998. Chai J, Pand IC: A study of the thixotropic

property of elastomeric impression materials,

Int J Prosthodont 7:155, 1994.

Chong YH, Soh G: Effectiveness of intraoral delivery tips in reducing voids in elastomeric impressions, Quint Int 22:897, 1991.

Cook WD: Permanent set and stress relaxation in elastomeric impression materials,

J Biomed Mater Res 15:44, 1981.

Cook WD: Rheological studies of the polymerization of elastomeric impression materials. I. Network structure of the set state,

J Biomed Mater Res 16:315, 1982.

Cook WD: Rheological studies of the polymerization of elastomeric impression materials. 11. Viscosity measurements, J Biomed

Mater Res 16:331, 1982.

Cook WD: Rheological studies of the polymerization of elastomeric impression materials. 111. Dynamic stress relaxation modulus,

J Biomed Mater Res 16345, 1982.

Cook WD, Liem F, Russo P et al: Tear and rupture of elastomeric dental impression materials, Biomater 5275, 1984.

Cook WD, Thomasz F: Rubber gloves and addition silicone materials, Aust Dent J 31:140, 1986.

Council on Dental Materials and Devices: Status report on polyether impression materials, J Am Dent Assoc 95:126, 1977.

Craig RG: Composition, characteristics and clinical and tissue reactions of impression materials. In Smith DC, Williams DF, editors:

Biocompatibility of dental materials, vol 3, Biocompatibility of dental restorative materials, Boca Raton, Fla, 1982, CRC Press.

Craig RG: Evaluation of an automatic mixing system for an addition silicone impression material, J Am Dent Assoc 1lO:2l3, 1985.

Craig RG: Properties of 12 addition silicones compared with other rubber impression materials, Phillip'sJ Rest Zahnmed

3244, 1986.

Craig RG, Sun Z: Trends in elastomeric impression materials, Oper Dent 19:138, 1994.

Craig RG, Urquiola NJ, Liu CC: Comparison of commercial elastomeric impression materials, Oper Dent 1594, 1990.

Goldberg AJ: Viscoelastic properties of silicone, polysulfide, and polyether impression materials, JDent Res 531033, 1974.

Gordon GE, Johnson GH, Drennon DG: The effect of tray selection on the accuracy of elastomeric impression materials, J Prosthet Dent 63:12, 1990.

Herfort TW,Gerberich WW, Macosko CW et al: Viscosity of elastomeric impression materials, J Prosthet Dent 38:396, 1977.

Herfort TW,Gerberich WW, Macosko CW et al: Tear strength of elastomeric impression materials, J Prosthet Dent 3959, 1978.

Hondrum S: Tear and energy properties of three impression materials, Int J Prosthodont 7:155, 1994.

Idris B, Houston F, Claffey N: Comparison of the dimensional accuracy of one-step techniques with the use of putty/wash addition silicone impression materials, J Prosthet Dent 74535, 1995.

Inoue K, Wilson HJ: Viscoelastic properties of elastomeric impression materials. 11. Variation of rheological properties with time, temperature and mixing proportions, J Oral Rehabil5:261, 1978.

Johansson EG, Erhardson S, Wictorin L: Influence of stone mixing agents, impression materials and lubricants on surface hardness and dimensions of a dental stone die niaterial, Acta Odontol Scand 33:17, 1775.

Johnson GH, Craig RG: Accuracy of four types of rubber impression materials compared with time of pour and a repeat pour of models, J Prosthet Dent 53:484, 1785.

Johnson GH, Craig RG: Accuracy of addition silicones as a function of technique, J Prosthet Dent 55:177, 1786.

Johnson GH, Lepe X, Aw TC: Detail reproduction for single versus dual viscosity impression techniques. J Dent Res 78 (Spec

Issue B):140 (Abstract 2731, 1999.

Kim KN, Craig RG, Koran A 111: Viscosity of monophase addition silicones as a function of shear rate, J Prosthet Dent 67:774, 1772.

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Assoc 75:75, 1777.

Laufer BZ, Baharav H, Ganor Y et al: The effect of marginal thickness on the distortion of different impression materials, J Prosthet Dent 76:466, 1776.

Lee IK, Delong R, Pintado MR et al: Evaluation of factors affecting the accuracy of impressions using quantitative surface analysis, Oper Dent 20:246, 1775.

Lepe X, Johnson GH, Berg JC et al: Effect of mixing technique on surface characteristics of impression materials, J Prosthet Dent 793475, 1778.

Lorren RA, Salter DJ, Fairhurst CW: The contact angles of die stone on impression materials, J Prosthet Dent 36:176, 1776.

Mansfield MA, Wilson HJ: Elastomeric impression materials: a comparison of methods for determining working and setting times, Br Dent J 132:106, 1772.

McCabe JF, Arikawa H: Rheological properties of elastomeric impression materials before and during setting, J Dent Res 77:1874, 1778.

McCabe JF, Bowman AJ: The rheological properties of dental impression materials, Br Dent J l j l : l 7 7 , 1781.

McCabe JF, Storer R: Elastomeric impression materials. The measurement of some properties relevant to clinical practice, Br Dent J 147:73, 1780.

Neissen LC, Strassler H, Levinson I'D et al: Effect of latex gloves on setting time of polyvinylsiloxane putty in~pressionmaterial,

J Prosthet Dent 55:128, 1786.

Norling BK, Reisbick MH: The effect of nonionic surfactants on bubble entrapment in elastomeric impression materials, J Prosthet Dent 42342, 1777.

Ohsawa M, Jorgensen KD: Curing contraction of addition-type silicone impression materials, Scand J Dent Res 71:51, 1783.

Pang IC, Chai J. The effect of a shear load on the viscosities of ten vinyl polysiloxane impression materials, J Prosthet Dent

71:177, 1774.

Pratten DH, Craig RG: Wettability of a hydrophilic addition silicone impression material,

J Prosthet Dent 61:177, 1787. Reusch B, Weber B: In precision

impressions-a guide for theory and practice, theoretical section, Seefeld, Germany, 1777, ESPE Dental AG.

Rueda LJ, Sy-Munoz JT, Naylor WP et al: The effect of using custom or stock trays on the accuracy of gypsum casts, Int J Prosthodont 7:367, 1976.

Salem NS, Combe EC, Watts DC: Mechanical properties of elastomeric impression materials, J Oral Rehabil 15:125, 1788.

Sandrik JL, Vacco JL: Tensile and bond strength of putty-wash elastomeric impression materials, J Prosthet Dent 50:358, 1783.

Schelb E, Cavazos E Jr, Troendle KB et al: Surface detail reproduction of Type IV dental stones with selected polyvinyl siloxane impression materials, Quint Int 22:51, 1771.

Sneed WD, Miller R, Olean J: Tear strength of ten elastomeric impression materials, J Prosthet Dent 49:511, 1783.

Stackhouse JA Jr: The accuracy of stone dies made from rubber impression materials, J Prosthet Dent 24:377, 1970.

Stackhouse JA Jr: Relationship of syringe-tip diameter to voids in elastomeric impressions, J Prosthet Dent 53312, 1985.

Tolley LG, Craig RG: Viscoelastic properties of elastomeric impression materials, J Oral Rehabil5:121, 1978.

Vermilyea SG, Huget EF, de Simon LB: Apparent viscosities of setting elastomers, J Dent Res 591149, 1980.

Williams JR, Craig RG: Physical properties of addition silicones as a function of composition, J Oral Rehabil15:639, 1988.

Disinfection of Elastomeric Impression Materials

Bergman M, Olsson S, Bergman B: Elastomeric impression materials: dimensional stability and surface sharpness following treatment with disinfection solutions, Swed Dent J 4:161, 1980.

Drennon DG, Johnson GH: The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction

of improved gypsum casts, J Prosthet Dent 63:233, 1990.

Drennon DG, Johnson GH, Powell GL: The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions,

J Prosthet Dent 62:468, 1989.

Johnson GH, Drennon DG, Powell GL: Accuracy of elastomeric impressions disinfected by immersion, J Am Dent Assoc

116:525, 1988.

Lepe X, Johnson GH: Accuracy of polyether and addition silicone after long-term immersion disinfection, J Prosthet Dent 78245, 1997.

Lepe X, Johnson GH, Berg JC: Surface characteristics of polyether and addition silicone impression materials after long term disinfection, J Prosthet Dent 74: 181, 1995.

Rios MdP, Morgano SM, Stein RS et al: Effects of chemical disinfectant solutions on the stability and accuracy of the dental impression complex, J Prosthet Dent 76:356, 1996.

Storer R, McCabe JF: An investigation of methods available for sterilising impressions,

Br Dent J 151:217, 1981.

Thouati A, Deveraux E, Lost A et al: Dimensional stability of seven elastomeric impression materials immersed in disinfectants, J Prosthet Dent 76:8, 1996.

Zinc Oxide-Eugenol Pastes

Brauer GM, White EE, Moshonas MG: Reaction of metal oxides with o-ethoxy benzoic acid and other chelating agents, J Dent Res 37:547, 1958.

Copeland HI, Brauer GM, Sweeney WT et al: Setting reaction of zinc oxide and eugenol, J Res Nat Bur Stand 55:133, 1955.

Harvey W, Petch NJ: Acceleration of the setting of zinc oxide cements, Br Dent J 8O:l, 1946; 80:35, 1946.

Kelly EB: Dental impression paste, US Patent No 2,077,418, April 20, 1937.

Myers GE, Peyton FA: Physical properties of the zinc oxide-eugenol impression pastes, J Dent Res 40:39, 1961.

Olsson S, Bergman B, Bergman M: Zinc oxide-eugenol impression materials: dimensional stability and surface detail sharpness following treatment with disinfection solutions, Swed Dent J 6:177, 1982.

Smith DC: The setting of zinc oxide-eugenol mixtures, Br Dent J 105:313, 1958.

Tyas MJ, Wilson HJ: Properties of zinc oxide/ eugenol impression pastes, Br Dent J 129:461, 1970.

Ullmann's Encyclopedia of Industrial Chemistry, ed 6, (electronic release), ring opening polymerization, 2000.

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Impression Plaster

Jorgensen KD: Study on the setting of plaster of paris, Odont Tskr 6 ~ 3 0 51953,.

Sodeau WH, Gibson CS: The use of plaster of paris as an impression material, Br Dent J 48:1089, 1927.