Indian Journal of Dental ResearchIndian Journal of Dental ResearchIndian Journal of Dental Research
HOME | ABOUT US | EDITORIAL BOARD | AHEAD OF PRINT | CURRENT ISSUE | ARCHIVES | INSTRUCTIONS | SUBSCRIBE | ADVERTISE | CONTACT
Indian Journal of Dental Research   Login   |  Users online: 3233

Home Bookmark this page Print this page Email this page Small font sizeDefault font size Increase font size         

 


 
Table of Contents   
ORIGINAL RESEARCH  
Year : 2011  |  Volume : 22  |  Issue : 2  |  Page : 200-204
Comparison of the linear dimensional accuracy of denture bases cured the by conventional method and by the new press technique


Department of Prosthodontics, Meenakshi Ammal Dental College, Chennai, India

Click here for correspondence address and email

Date of Submission15-Jun-2010
Date of Decision13-Aug-2010
Date of Acceptance11-Apr-2011
Date of Web Publication27-Aug-2011
 

   Abstract 

Aim: The purpose of this study was to investigate and compare the linear dimensional accuracy of denture bases processed with the conventional heat-polymerization technique and the Rafael and Saide (RS) tension system, taking a multidirectional approach.
Materials and Methods: Twenty standard edentulous maxillary casts were randomly assigned into two groups. A uniform denture base of 1.5 mm thickness was fabricated in wax and later processed by two methods: Group I acrylic resin flasked with the conventional technique and Group II acrylic resin flasked with the RS tension system. The dimensional accuracy was assessed using traveling microscope.
Results: The linear dimensional changes that occurred between the dentures produced with the new press method and the conventional method were statistically insignificant and ranged from 0.002 to 0.11. The dimensionally stable areas were the canines and the most unstable was the posterior palate.
Conclusions: The results of this study suggest that the maximum linear dimensional change occurs around the molars and palatal segment, with the most stable areas being the canines. There was no significant linear dimensional change of the dentures processed between the conventional and the new press technique.

Keywords: Dimensional accuracy, new press technique, Rafael and Saide plates

How to cite this article:
Abby A, Kumar R, Shibu J, Chakravarthy R. Comparison of the linear dimensional accuracy of denture bases cured the by conventional method and by the new press technique. Indian J Dent Res 2011;22:200-4

How to cite this URL:
Abby A, Kumar R, Shibu J, Chakravarthy R. Comparison of the linear dimensional accuracy of denture bases cured the by conventional method and by the new press technique. Indian J Dent Res [serial online] 2011 [cited 2019 Dec 6];22:200-4. Available from: http://www.ijdr.in/text.asp?2011/22/2/200/84282
Acrylic resins were introduced to dentistry in 1937, and to date are regarded as one of the best materials to be used as denture bases for removable prosthesis. [1] Denture bases are responsible for artificial tooth retention, stability, and distribution of masticatory forces over a large tissue-bearing area. [2] The lack of dimensional accuracy must be accepted as one of the disadvantages of acrylic resin base.

Retention of a maxillary denture requires close adaptation to the tissue surface, where the most important physical force for retention is the saliva film, the average thickness of which is reported as 17-25 μm. [2] When the acrylic resin flasking procedure is performed under routine laboratory conditions, the combination of polymerization shrinkage, thermal contraction during flask cooling, and strain accompanying stress release during de-flasking may cause diminished adaptation of the denture to the tissues. [2]

In spite of improvements in acrylic resin properties, the problem of undesirable dimensional shrinkage remains unresolved. [3] Several previous literature reports and reviews have shown that there always exists a gap between the base and the tissues when the denture base is processed by the conventional method. [2],[4],[5] Rafael and Saide [2] introduced an improved processing technique wherein the flask is held under constant pressure using two iron plates which proved to decrease the magnitude of this gap. Reduced dimensional changes seen in the denture base processed with the Rafael and Saide (RS) system suggested that the flask closure maintained acrylic resin dough under constant flask pressure because the flask halves remained in contact when the flask was removed from the press. This inhibited the pre-mature release of the residual internal stresses from the acrylic resin dough before polymerization.

Previous study [2] that was conducted to compare the dimensional stability of the denture base processed by the conventional method and by the RS system had shown that the RS system produced denture base with lesser discrepancies. The study conducted measured the adaptability of the base with the cast in the palatal region.

The purpose of this study was to investigate and compare the linear dimensional accuracy of denture bases processed with the conventional heat-polymerization technique and with the RS tension system, taking a multidirectional approach.


   Materials and Methods Top


A standard edentulous maxillary mold was used. Twenty casts were poured in type III dental stone with a ratio of 30 ml of water to 100 g of powder. The stone cast was randomly assigned to two groups: Group I for acrylic resin flasking with the conventional technique and Group II for acrylic resin flasking with the RS tension system. A uniform denture base was made on the stone cast with wax of 1.5 mm thickness. Copper wires, 2 mm in diameter, were cut to lengths of approximately 3 mm. One end of the wire was polished and a fine dot was placed. A jig was used to mark seven spots on the wax base plates [Figure 1]. The seven spots were the incisal papilla (A), the canine region on either side (B, C), the molar area on either side (E, G), and two spots on the mid palatine area, one in the anterior region between the line joining the two canines (D) and the other one posteriorly between the two molar areas (F) [Figure 2]. The copper points were placed on all the wax base plates [Figure 3] and the inter distances were measured using a traveling microscope with a magnification of 10Χ (RAC; RAC Exports, Ambala, India). A total of 12 readings were obtained from each sample.
Figure 1: Reference points with the distances to be measured

Click here to view
Figure 2: Reference points being marked on wax base plate using surveyor

Click here to view
Figure 3: Wax base plate with attached copper wires on reference points

Click here to view


Each of the Group I (conventional) samples was processed as follows. The cast with wax pattern was flasked in the lower part of the traditional flask with type II dental plaster. The flasking was finished by pouring type III dental stone in the upper part after application of two coats of separating medium on the plaster in the lower flask. After 1 hour, the flask was placed in boiling water for 7 minutes to soften the base plate wax. The flask was then opened, the wax was removed, and the mold surfaces were cleaned with fresh boiling water and liquid detergent. After allowing the molds to cool for 1 hour, two coats of separating medium were applied. Poly(methyl- methacrylate) dough was packed with a monomer:polymer ratio of 1:3 by volume. After final pressing in a bench press for 5 minutes, the flask was kept in a traditional clamp for 1 hour bench curing. The flask was then immersed in water and cured at 74°C for 9 hours using a thermo-polymerizing unit (Acrylizer C 73; Confident Company, Bangalore, India). After the polymerization cycle, the flask was removed and allowed to bench cool for 3 hours before it was de-flasked. After de-flasking, all the samples were trimmed and placed on their respective casts [Figure 4].
Figure 4: Polymerized denture base

Click here to view
Figure 5: Trial closure with RS plate

Click here to view


Fabrication of the Rafael and Saide plates [2]

The assembly consisted of two iron plates, each measuring 150Χ40Χ8 mm, and a bolt of 9 mm diameter was soldered into each end of the lower plates; two corresponding holes with a cross-section diameter of 10 mm were present in the upper plates. During the definitive closure, the screws of the lower plates were fitted into the holes of the upper plates and, after hydraulic flask pressure, the screw nuts were strongly tightened to the screws. This procedure maintains constant metal to metal contact on the flask halves [Figure 5].{Figure 5}

Processing the denture base by the new press technique

For Group II (new press) samples, the flasking, dewaxing and packing of heat-cured polymethylmethacrylate were done in the same way as that for Group I, except that the flasks were placed between the RS plates and the entire assembly was placed in the bench press. On complete tightening with metal to metal contact of the flask halves achieved by the bench press, the bolts of the plates were tightened so as to maintain the same pressure [Figure 5]. The flasks clamped by the RS plates were removed from the bench press after 5 minutes and were allowed to bench cure for 1 hour, which was followed by curing at 74°C for 9 hours in a thermo-polymerizing unit (Acrylizer C 73; Confident Company). After curing, the flasks were removed and allowed to bench cool for 3 hours before they were de-flasked. The samples were then trimmed and placed on their respective casts [Figure 3].

The dimensional accuracy of the denture bases was assessed by measuring the distances among the seven reference points (12 readings in total for each sample) between waxed-up state and processed state. The distances among the reference points for all samples in Group I and Group II were measured with a traveling microscope by a single operator and the readings obtained before and after processing the denture bases were tabulated and compared [Figure 6] and [Figure 7].
Figure 6: Measurements with the new press technique

Click here to view
Figure 7: Measurements with the conventional method

Click here to view



   Results Top


The mean and standard deviation were estimated for the samples from each study group separately, for wax and acrylic. Student's paired "t" test was used to compare the mean values between wax and acrylic within each group. The Student's independent "t" test was used to compare the mean changes between the conventional method and the new press method. In this study, P<0.05 was considered as the level of significance.

From the results of the conventional method, it is seen that the dimensional change that occurred at various positions across the denture base was statistically insignificant and the maximum distortion occurred around the slope of the anterior and posterior segments of the denture. From the values that were obtained by the new press technique, it is observed that the dimensional change was statistically significant in only three areas and the maximum change occurred in the slope of the anterior and posterior segment.

However, comparing the conventional and the new press methods, it can be observed that the difference was statistically insignificant. The difference in values between the two methods ranged from 0.002 to 0.11, with the maximum difference in the posterior segment (FG).


   Discussion Top


Consani et al. [2] reported in their study that the range of discrepancy between the maxillary denture bases and the casts was only 0.129-0.286. The greatest mean dimensional change was recorded in the posterior palatal zone processed with the conventional packing technique. Dimensional change values associated with the RS tension system were significantly lower than those associated with traditional acrylic resin packing. [2] Dimensional change values were analyzed in relation to only three sections established for measurement. The worst adaptation was demonstrated in the posterior palatal zone and the best at the distal of the canines. [2]

The study took into consideration only the changes that would occur along the slopes of the palate. The mean of the changes occurring in five different areas has been taken into consideration. This will not give the exact nature of the distortion as shrinkage varies at different areas. Areas of shrinkage, if it occurred between the canines and the molars, and also the change in direction along the anterior segments have not been taken into consideration. Again, it must be remembered that the shrinkage can occur in any direction around a given point and also that the same would occur maximum at the weakest or thinnest portion of the denture base.

Another study conducted by the same author verified the influence of flask closure methods on tooth displacement in maxillary dentures. [6] The study concluded that the teeth displacement was smaller when the dentures were processed with the RS flask closure system when compared with the conventional system. Metallic pins were fixed at the incisal border of the central incisors, buccal cusp of the first premolars, and mesio-buccal cusp of the second molars, and the linear dimensional displacement of teeth was measured.

In this study, all directions of possible shrinkage were taken into consideration. A total of seven reference points had been used and 12 distances were recorded. From the results of the conventional method, it can be found that the dimensional change that occurred at various positions across the denture base was statistically insignificant and the maximum dimensional change occurred around the posterior segment of the denture.

From [Figure 6], it can be seen that greater change occurred on the right side when compared to the opposite side. This could be because of the anatomy of the ridge and there were variations in the distances of placement of the reference points. Least variations were recorded along the ridges (AB, AC, BE, CG) and the greatest change along the slopes of the palate (DB, DC, DG, DE). These changes were found both in the anterior segment, between the incisive papilla (A) and the mid palate (D), and also the posterior slope, between the posterior palate (F) and the molar (G). These variations could be as a result of change in angulations or plane and also because they are the thinnest areas of the denture. [6]

From the values that were obtained by the new press technique, it was found that the dimensional change was statistically significant in only three areas. It can also be seen that the maximum change occurred only in the slopes of the posterior segment and the slopes of the anterior segment. The reasons for these variations can be attributed again to the change in plane and shrinkage occurring in the thinnest areas. [6] It was seen that even though the areas of maximum shrinkage occurred along the posterior segment, there were variations within each segment in both conventional and new press methods. For example, in the new press method, the shrinkage occurred greater in the area between the molar (G) and the mid palate (D).

By a comparative study done between the conventional and the new press method, it can be observed that the difference was statistically insignificant. The difference in values between the two methods ranged from 0.002 to 0.11, with the maximum difference in the posterior segment of FG. In previous studies, [2],[4],[5],[6],[7] it was found that the most dimensionally stable areas during processing were the canines and the incisal region, while the most unstable region was the posteriors between the molars and the palate. [2],[6]

The numeric values of the present study do not support the same, as it can be seen from the result that in both the techniques the larger values were found in the anterior slope of the palate (AD) and the posterior slopes of the palate (DG, FG), when compared to the remaining segments. The possible explanation for this could be the change in plane and that they are the thinnest areas. In simpler words, maximum adaptation occurs on a flat plane rather than a curve.

Clinical significance

The factors affecting denture success are

  • adhesion,
  • cohesion and
  • capillarity, which together produce interfacial surface tension, and
  • atmospheric pressure, which comes into play on the application of masticatory load. [8],[9],[10]


To achieve all the physical factors, it is essential to produce dentures that are dimensionally stable and have a close adaptability to the surrounding tissues. The results from this study show that the dimensional changes between the dentures produced with the new press method and the conventional method were statistically and clinically insignificant. Dimensional changes in the denture base occurred along the slopes of the base irrespective of the segments, but the least dimensional change occurred on a flat surface. This would clinically mean that flatter the arch, better would be the retention with saliva, acting as the intermediate surface. But in reality, this is however not the case.

It can be concluded that irrespective of the material or method used for processing the denture base, it is the anatomic and physiological duplication of the edentulous ridge, which is absolutely essential. It is the peripheral border seal achieved by the impression that is essential for the factors to act as a unit. Shrinkage of acrylic denture base is inevitable, and distortion of the denture base depends on several factors such as

  • morphology of the edentulous arch,
  • the depth of the palate,
  • the size of the arch and
  • thickness of the denture base.


It is the tissue resiliency and like effects which will compensate for these processing errors in achieving clinical success. [11]th


   Conclusions Top


Within the limitations of the study, the following conclusions were drawn:

  • The dimensional changes between the dentures produced with the new press method and the conventional method were statistically insignificant.
  • The dimensional change occurred at various positions across the denture base and maximum distortion occurred along the slopes of the anterior segment of the palate and the slopes in the posterior segment between the molar and mid palate.
  • The difference in dimensional change values between the two methods ranged from 0.002 to 0.11.
  • The dimensionally stable areas during processing were the canines and the unstable area was the posterior palate.



   Acknowledgment Top


The authors sincerely thank Dr. TV Padmanabhan, Dr. Vijay Vaikunth and Dr. Vinaya Bhat for their constant guidance and support toward this research.

 
   References Top

1.Wong DM, Cheng LY, Chow TW, Clark RK. Effect of processing method on dimensional accuracy and water sorption of acrylic resin denture. J Prosthet Dent 1999;81:300-4.  Back to cited text no. 1
[PUBMED]  [FULLTEXT]  
2.Consani RL, Domitti SS, Consani S. Effect of a new tension system, used in acrylic resin flasking, on the dimensional stability of denture bases. J Prosthet Dent 2002;88:285-9.  Back to cited text no. 2
[PUBMED]  [FULLTEXT]  
3.Firtell DN, Green AJ, Elahi JM. Posterior peripheral seal distortion related to processing temperature. J Prosthet Dent 1981;45:598-601.  Back to cited text no. 3
[PUBMED]  [FULLTEXT]  
4.Polyzois GL, Karkazis HC, Zissis AJ, Demetriou PP. Dimensional stability of dentures processed in boilable acrylic resins: A comparative study. J Prosthet Dent 1987;57:639-47.  Back to cited text no. 4
[PUBMED]  [FULLTEXT]  
5.Vig RG. Method of reducing shifting of teeth in denture processing. J Prosthet Dent 1975;33:80-4.  Back to cited text no. 5
    
6.Negreiros WA, Consani RL, Mesquita MF, Sinhoreti MA, Faria IR. Effect of Flask closure method and post-pressing time on the displacement of maxillary denture teeth. Open Dent J2009;3:21-5.  Back to cited text no. 6
[PUBMED]  [FULLTEXT]  
7.Abuzar MA, Jamani K, Abuzar M. Tooth movement during processing of complete dentures and its relation to palatal form. J Prosthet Dent 1995;73:445-9.  Back to cited text no. 7
[PUBMED]    
8.Rudd KD. Processing complete dentures. Dent Clin North Am 1996;40:121-49.  Back to cited text no. 8
[PUBMED]    
9.Jacobson TE, Krol AJ. A Contemporary review of the factors involved in complete denture retention, stability, support. Part I-Retention. J Prosthet Dent 1983;49:5-15.  Back to cited text no. 9
[PUBMED]    
10.Shay K. The retention of complete denture. In: Zarb, Bolender, Carlson, editors. Boucher's prosthodontic treatment for edentulous patient. 11 th ed. Missouri: Mosby; 1997. p. 400-14.  Back to cited text no. 10
    
11.Anthony DH, Peyton FA. Evaluating dimensional accuracy of denture bases with a modified comparator. J Prosthet Dent 1959;9:683-92.  Back to cited text no. 11
    

Top
Correspondence Address:
Abraham Abby
Department of Prosthodontics, Meenakshi Ammal Dental College, Chennai
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.84282

Rights and Permissions


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]



 

Top
 
 
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *
* Registration required (free)  
 


    Abstract
    Materials and Me...
   Results
   Discussion
   Conclusions
   Acknowledgment
    References
    Article Figures

 Article Access Statistics
    Viewed3484    
    Printed105    
    Emailed8    
    PDF Downloaded192    
    Comments [Add]    

Recommend this journal