Figure 5: Alginate substitute (COUNTER-FIT) is injected into a Border- Lock ® (Clinician’s Choice) tray lined with a PVS (Affinity Tray Adhesive [Clinician’s Choice]) adhesive. Figure 6: Internal detail of a COUNTER-FIT impression that has been repoured four times. (An alginate should never be poured a second time.) Figure 7: Alginate-derived stone models on PVS bite registration material show an obvious open-bite relationship. Figure 8: Alginate-driven stone models on Affinity Quick Bite PVS bite registration material show inaccurate fit. Figure 9: Mounted case from Figure 8 shows mismounted open bite. Figure 10: COUNTER-FIT−driven stone model on Quick Bite PVS shows good interdigitation of the three components. Figure 11: Precise mounting of the opposing casts is obvious when using matching accuracies in the impression and bite registration materials. This creates clinical predictability. Alginate Substitutes: Rationale for Their Use59
One of the main driving forces of a change in direction from opposing models produced from alginate to opposing models derived from alginate substitutes in fixed prosthodontics is the severe mismatch of accuracy between modern bite registration materials and alginate-driven stone models. Boksman 26 looked at PVS bite registration materials and the need for extensive occlusal adjustments on crown & bridge prostheses, showing the severe open-bite mounting that can result when using a highly accurate PVS bite registration with a poorly detailed alginate-driven stone model (Fig. 7). Using PVS for the final impression, for the bite registration and for the opposing models eliminates the dimensional mismatch between materials, resulting in more accurate mounting of the case and less clinical necessity for occlusal adjustments (Fig. 8−11). The surface replication of the casts is also much smoother than models derived from alginate impressions. Even though the cost of the PVS alginate substitutes is higher than the irreversible hydrocolloid alginate materials, the impression is easier to take due to the thixotropic nature of these materials, the time and cost of pouring up the opposing model can be eliminated, the impression can be repoured if the model is broken or chipped, there is increased office efficiency, the opposing model is more accurate, the bite registration actually fits, and the time and frustration of adjusting the final prosthesis is minimized. These many benefits more than compensate for the extra cost. In addition, the clinician can now (in some cases) bill this as part of the laboratory procedure. CM References 1. Pace SL. Polyvinyl impression materials vs. alginate impression materials. Contemp <strong>Dental</strong> Assisting. Feb 2006:20−23. 2. Rubel BS. Impression materials: a comparative review of impression materials most commonly used in restorative dentistry. Dent Clin North Am. 2007:51:629−642. 3. Cohen BI, Pagnillo M, Deutsch AS, et al. Dimensional accuracy of three different alginate impression materials. J Prosthodont. 1995:4:195−199. 4. Perry R. Using polyvinyl impressions for study models: a case report. Dent Today. Oct 2004:23:106−107. 5. Chen SY, Liang WM, Chen FN. Factors affecting the accuracy of elastometric impression materials. J Dent. 2004:32:603−609. 6. Straw J, Iuorno F, Lindauer S. Dimensional stability of Kromopan, an irreversible hydrocolloid impression material. Presented at 32nd Annual Meeting and Exhibition of the ADR; March 12-15, 2003; San Antonio, TX. Abstract 0290. http://iadr.confex.com/iadr/2003SanAnton/techprogram/abstract_26049.htm. Accessed Feb 3, 2009. 7. Bayindir F, Yanikoglu N, Duymus Z. Thermal and pH changes, and dimensional stability in irreversible hydrocolloid impression material during setting. Dent Mater J. 2002:21:200−209. 8. Kanehira M, Finger WJ, Endo T. Volatization of components from and water absorption of polyether impressions. J Dent. 2006:34:134−138. 9. Nichols PV. An investigation of the dimensional stability of dental alginates. Sydney, Australia: Faculty of Dentistry, University of Sydney; 2006. http://hdl.handle net/2123/1270. Accessed Feb 23, 2009. 10. Taylor RL, Wright PS, Maryan C. Disinfection procedures: their effect on the dimensional accuracy and surface quality of irreversible hydrocolloid impression materials and gypsum casts. <strong>Dental</strong> Mater. 2002:18:103−110. 11. Jagger DC, Al Jabra O, Harrison A, et al. The effect of a range of disinfectants on the dimensional accuracy of some impressionmaterials. Eur J Prosthodont Restor Dent. 2004;12:154−160. 12. Machado C, Johnston W, Coste A, et al. Simulated clinical compatibility of disinfectant solutions with alginate impression materials. Presented at: IADR General Session & Exhibition; June 28-July 1, 2006; Brisbane, Australia. Abstract 2467. http://iadr.confex.com/iadr/2006Brisb/techprogram/ abstract_82984.htm. Accessed Feb 23, 2009. 13. Muller-Bolla M, Lupi-Pegurier L, Velly AM, et al. A survey of disinfection of irreversible hydrocolloid and silicone impressions in European Union dental schools: epidemiologic study. Int J Prosthodont. 2004:17:165−171. 14. Lu JX, Zhang FM, Chen YM, et al. The effect of disinfection on dimension stability of impressions [in Chinese]. Shanghai Kou Qiang Yi Xue. 2004:13:290−292. 15. Phoenix RD, Cagna DR, DeFreest CE. Stewart’s Clinical Removable Partial Prosthodontics. 3rd ed. Chicago, IL: Quintessence Publishing; 2003:162−167. 16. Frey G, Lu H, Powers J. Effect of mixing methods on mechanical properties of alginate impression materials. J Prosthodont. 2005:14:221−225. 17. Mendez AJ. The influence of impression trays on the accuracy of stone casts poured from irreversible hydrocolloid impressions. J Prosthet Dent. 1985:54:383−388. 18. Gordon GE, Johnson GH, Drennon DG. The effect of tray selection on the accuracy of elastomeric impression materials. J Prosthet Dent. 1990:63:12−15. 19. Leung KC, Chow TW, Woo EC, et al. Effect of adhesive drying time on the bond strength of irreversible hydrocolloid to stainless steel. J Prosthet Dent. 1999:81:586−590. 20. Smith SJ, McCord JF, Macfarlane TV. Factors that affect the adhesion of two irreversible hydrocolloid materials to two custom tray materials. J Prosthet Dent. 2002:88:423−430. 21. Craig RG. Review of dental impression materials. Adv Dent Res. 1988:2:51−64. 22. Christensen GJ. Ask Dr. Christensen. Dent Econ. March 2008:98:66. 23. Karthikeyan K, Annapurni H. Comparative evaluation of dimensional stability of three types of interocclusal recording materials: an in vitro study. J Indian Prosthodont Soc. 2007:7:24−27. 24. Boksman L. Eliminating variables in impression-taking. Ontario Dentist. Dec 2005:22−25. 25. Waranowicz MT, O’Keefe KL. Alginates and alginate substitutes. The <strong>Dental</strong> Advisor. 2007:24:1−7. 26. Boksman L. Point of care: how do I minimize the amount of occlusal adjustment necessary for a crown? J Can Dent Assoc. 2005:71:494−495. Dr. Len Boksman is adjunct clinical professor at the Schulich School of Medicine and Dentistry and maintains a private practice in London, Ontario, Canada. He is also a paid part-time consultant to Clinical Research <strong>Dental</strong> Inc. and Clinician’s Choice. Contact him at lboksman@clinicalresearchdental.com or 519-641-3066, ext. 292. Gregg Tousignant, CDT, is technical support manager for Clinical Research <strong>Dental</strong> Inc. E-mail him at gtousignant@clinicalresearchdental.com. Reprinted by permission of Dentistry Today, ©2009 Dentistry Today. “DOCTOR-TECHNICIAN PERSPECTIVES: Alginate Substitutes: Rationale for Their Use,” by Leendert Boksman, DDS, and Gregg Tousignant, CDT: Dentistry Today, Vol. 28, No. 4, 04/09, pp 104−105. 60 chairsidemagazine.com
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