A COMPARATIVE STUDY OF IMPRESSION TAKING PROCEDURES IN DENTISTRY 
A. Detreksi®, M. Kaän“®, K. Fekete‘®, P. Fejerdy®, Gy. Szabö®, Z. T6th”, B. Kaän“ 
* Department of Prosthodontics 
Semmelweiss University 
H-1088 Budapest, Mikszáth-tér 5. 
? Department of Photogrammetry and Geoinformatics 
Budapest University of Technology and Economics, 
H-1111 Budapest, Müegyetem rkp. 3. 
Hungary 
Commission V, WG V/3 
KEY WORDS: Close-range photogrammetry, Medical photogrammerty 
ABSTRACT: In dental practice, making crownwork is a well-established and often employed method for saving teeth. An 
indispensable phase of that procedure is taking an impression of the prepared die. In this paper, we report on a series of experiments 
conducted for the assessment of various dental impression taking technologies, using a photogrammetric method. 
1. INTRODUCTION 
The practising dentist often uses crownwork in order to save 
teeth that are in bad condition, as well as for fastening stable 
prostheses. An indispensable phase of making crownwork 
consists in abrading the tooth and taking an impression of the 
abraded die. The dental technician then prepares the crownwork 
itself on the basis of that impression. In the traditional method, 
the dentist puts a thick pliant material into the impression taking 
spoon and presses it against the original die in the patient's 
mouth to make a basic impression (step 1). In step 2, then, that 
basic impression takes over the role of the impression taking 
spoon: a thinner, lower-viscosity material is put into it and 
pressed against the original die in order to correct any 
inaccuracies that may have occurred in step 1. Using this 
method, the plaster dies finally produced will necessarily be 
smaller than the original dies in the patient's mouth, basically 
because the outflow of surplus modelling material is not taken 
care of (Kaán, 2002.). Typical distortions of samples made by 
the above procedure are shown in Fig. 1. 
  
Figure 1. Typical distortions of the traditional procedure 
Various solutions have been proposed in order to eliminate or at 
least diminish the generally known deficiencies of that 
procedure, technically known as the two-time two-phase 
impression taking method. One such proposal involves various 
overflow grooves to be cut into the basic impression, whereas 
another group of authors suggests that some place-holding 
material should be applied to the basic impression in order to 
make room for the correction material (Kaán, 2002.). In this 
paper, we report on a series of experiments in which we 
compared four different impression taking technologies 
(without either place-holding or grooves; with grooves; using 
Plicafol place-keeping foil; and using Fuji impression- 
separating pellicle). Each technology was tested both for single 
dies and for sets of adjacent dies, as well as with both 
*shoulder' and *knife-edge' abrasion types (Fig. 2). That is, a 
total of 16 different types of impressions have been compared. 
  
  
Figure 2. Shoulder and knife-edge abrasion 
In the evaluation of the results obtained we assumed that the 
strength and durability of crowns were crucially influenced by 
their geometrical accuracy, that is, how well they fit the dies. 
Therefore, we investigated the geometrical precision with 
which the various procedures of impression taking reflected the 
shape and size of the original dies. The results of photogram- 
metric measurements were subsequently subjected to 
mathematical statistical evaluation. 
  
   
   
  
   
  
    
  
   
  
  
   
  
  
  
  
  
  
  
  
   
  
   
   
   
   
    
    
  
  
   
   
   
   
  
  
  
  
  
   
  
  
   
  
  
    
  
    
    
   
   
  
   
  
    
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