An analysis of the development of complete denture impression techniques.

Abstract Sixty-eight textbooks published in English since 1845 have contained references to impression making. References in these volumes to biologic, psychologic, behavioral and material science, and to clinical procedures were recorded. These notations were then tabulated into four eras for statistical analysis. There were a total of 9, 005 references in the various categories. For each classification an index of frequency was calculated (Figs. 1 to 9). The index of frequency is the number of times an item was recorded in an era divided by the number of books in that era. For example, under the category of pressure phenomena (Fig. 3), a reference to “equalization of pressure” in the 1900 to 1929 era was recorded 33 times. There were a total of 22 books published in this era. Therefore the index of frequency for this item in the second era is 33 ÷ 22 or 1.5 (Fig. 3). The index of frequency gives a measure of the interest in impression making (Table I). An increase in the index of frequency for compressive impressions, border molding, and denture extension was recorded over four eras. References to closed mouth impressions showed a smaller increase. No increase in references to displaceable ridges and facial contours was seen over the four eras, and a decrease was noted in the index of frequency for rebase impressions (Fig. 1). The index of frequency increased greatly in various categories of oral muscle and tissue movements over the four eras as authors became more sophisticated in the biologic concepts of impression making (Fig. 2). Similarly there were large increases in the index of frequency for many subcategories of physical phenomena—surface area coverage, retention, denture extension, and soft tissue displacement (Fig. 3). On the other hand, references to atmospheric pressure, peripheral seal, posterior palatal displacement, and border tissue adaptation showed little or no trends over the four periods of time. Index of frequency for references to anatomic areas remained fairly constant for nonspecific sites but showed an increase in references to specific bones, muscles, and oral spaces (Figs. 4 to 6). References to modeling compound and plaster showed large increases, especially in the later era, despite the introduction of new materials such as zinc oxide-eugenol paste, alginates, reversible hydrocolloids, thiokol rubbers, and silicones (Fig. 7). There were very few references to pathology, histology, and behavioral aspects of impression making and no trend was observed over the four eras (Figs. 8 and 9). The history of impression making shows that most of the significant advances occurred before 1930. Basic principles of pressure, maximum extension of the denture base over the denture-bearing area, and equal distribution of pressure were first introduced in the era 1845 to 1899. The most significant advances in the art were developed in the second era, 1900 to 1929. Advances in the accuracy of impression techniques and an increase in the methods of border molding and obtaining a posterior palatal seal were among the major innovations in this era. The era from 1930 to 1949 saw great advances in the knowledge of the anatomy of the oral and perioral tissues as they affect impression making. The use of immediate denture techniques and the introduction of several new materials such as zinc oxide-eugenol paste and the hydrocolloids were also noted. The fourth era saw progress in the biologic aspects of denture impression making. There was an appreciation of the rationale for border molding and an awareness of the muscles and how they relate to complete denture impression techniques. The importance of an in-depth review of impression making lies in the assessment of the historical value of all factors. The categorization for these factors into their respective physical, biologic, and behavioral areas can show their relativity to the time in which they were discussed and taught as well as to their assigned importance.