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International Poster Journal of Dentistry and Oral Medicine



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Int Poster J Dent Oral Med 12 (2010), No. 1     15. Mar. 2010

Int Poster J Dent Oral Med 2010, Vol 12 No 1, Poster 476

Factors in polymerization influencing the accuracy of PMMA denture bases

Language: English

Andreas Peters, Christin Arnold, Jürgen M. Setz, Arne F. Boeckler,
Department of Prosthodontics, Centre for Dentistry and Oral Medicine, Martin-Luther-University Halle-Wittenberg

April 1st-4th, 2009
87th General Session & Exhibition of the IADR


Different technologies are available for the manufacturing of denture-base-resins with different types of polymerization. Although there have been permanent advancements in the range of denture-base-resins(1) polymerization shrinkage is still an important problem which leads to dorsal and lateral gaps and therefore decreasing functional fit. Comparing the different types of polymerization, especially heat-polymerized resins suffer under considerably larger dorsal gaps (2).
A further problem is the allergic property of different ingredients in PMMA denture bases such as residual monomer or BPO (3). Although there are some disadvantages regarding the dimensional accuracy, heat-polymerized PMMA resins are considered to have advantages in terms of allergic potential as there was less residual monomer left after denture processing (4). Recently, special hypo-allergic denture base resins were developed. According to the respective manufacturers these hypo-allergic resins have a significantly reduced allergic potential.
To meet clinical requirements, polymerization shrinkage of PMMA denture bases should be reduced to a minimum. Different processing technologies such as several types of injection-moulding or conventional flasking were developed in respect of reducing polymerization shrinkage (5).


The aim of this in-vitro study was to investigate the dimensional accuracy of conventional and modern denture-base-resins after polymerization depending on the type of polymerization and the manufacturing technology.

Material and Methods

Ten standardized denture bases from 7 PMMA resins (Tab. 1) were fabricated on identical casts. All 70 casts were made from stone as a duplicate of a brass-master-model. Depending on product and manufacturers instructions 4 different manufacturing technologies were applied (Tab. 1). The dorsal gap between resin base and master cast represents a measure of fit and accuracy of a polymerized denture. The dorsal gap was measured at 5 points (palatal centre, bilateral vertical/horizontal border) engraved on the brass-master-model. To investigate the dimensional behaviour over a certain period, measurements took place at 4 particular times: immediately after embedding, after one hour, after one day and after one week. Between the measurements specimens were stored under constant humidity and temperature (22°C) in a hygrophore. A light-microscope with automatic video measuring technology (x 560, VMZM, TV-tubus 1,6x - objective 2,0x - screenlevel 4,0 x, Metrona Software, 4H JENA engineering, Jena, Germany) was used for the measurements.
The data were recorded and analyzed (Metrona- 4H Version 4.0, 4H JENA engineering). At different times for each product the average dorsal gap was calculated and analyzed for statistical differences and correlations (ANOVA, Bonferroni P<0,05).

Type of Polymerization Product Process Manufacturer
Heat-polymerizing Fururacryl 2000 Manual injection Schütz Dental, Rosbach, Germany
Heat-polymerizing Paladon 65 Conventional-flask-technique Heraeus Kulzer, Hanau, Germany
Heat-polymerizing SR-Ivocap Pneumatic injection Ivoclar Vivadent, Ellwangen, Germany
Auto-polymerizing Futura Gen Manual injection Schütz Dental, Rosbach, Germany
Auto-polymerizing PalaXpress Pneumatic injection Heraeus Kulzer, Hanau, Germany
Auto-polymerizing Probase Conventional-flask-technique Ivoclar Vivadent, Ellwangen, Germany
Melting Polyan Injection-moulding Polyapress, Altkirchen, Germany
Tab 1: Tested PMMA denture base resins
Fig. 1: Overview of Total gaps Fig. 2: Total gap in subject to type of polymerization
Fig. 3: Total gap in subject to type of technology  
Fig. 4: Conventional-flask-technique Fig. 5: Manual injection (Unipress) Fig. 6: Pneumatic injection (SR-Ivocap)
Fig. 7: Pneumatic injection (Palajet) Fig. 8: Injection-moulding (Polyapress) Fig. 9: Measuring points and dorsal gap measurement at point 3


After embedding all products showed different dorsal gaps (Fig. 2). The tested auto-polymerizing PMMAs showed the smallest average dorsal gaps (196(±46µm) to 256(±83)µm), the heat-polymerizing PMMAs the highest measured values (317(±57) to 369(±88)µm). The industrially pre-polymerized hypo-allergic PMMA presented a dorsal gap in between (301(±116)µm). After one week the dorsal gap of both auto-polymerizing and heat-polymerizing PMMAs except SR-Ivocap increased significantly about 53(±75) to 71(±57)µm. There was no significant change detectable in dorsal gap for the industrially pre-polymerized PMMA Polyan. 71% of the products had a significant increase of dorsal gaps after one week. In this respect, PalaXpress showed the best, Paladon65 the worst results. Considering all measuring times, statistical analysis (descriptive statistics/cross-chart) revealed a significantly higher correlation of dorsal gap to the type of polymerization (eta=0.513) than to the applied manufacturing technology (eta=0.145).


Dimensional behaviour of PMMA during and after polymerization is decisively responsible for the quality of dentures in terms of clinical fit.
At different measuring times dorsal gaps of the auto-polymerizing denture base resin were smaller than the dorsal gaps of industrially pre-polymerized denture base resin which were followed by the significantly larger dorsal gaps of heat-polymerizing denture base resins.
Compared to the manufacturing process the type of polymerization had a greater effect on the dimensional accuracy of the tested denture-base-resins.


  1. Körholz K: Is there a chance for new developments in denture base resins? Quintessenz Zahntech (2007) 33:296-306.
  2. Keenan PL et al.: Dimensional change in complete dentures fabricated by injection molding and microwave processing. J Prosthet Dent (2003) 89(1):37-44.
  3. Boeckler AF et al.: Release of dibenzoyl peroxide from polymethyl methacrylate denture base resins: an in vitro evaluation. Dent Mater (2008) 24(12): 1602-7.
  4. Zissis A et al.: A long term study on residual monomer release from denture materials. Eur J Prosthodont Restor Dent (2008) 16(2):81-4.
  5. Nogueira SS et al.: Comparison of accuracy between compression- and injection-molded complete dentures. J Prosthet Dent (1999) 82(3):291-300.

This Poster was submitted by Andreas Peters.

Correspondence address:
Arne F. Boeckler
Martin-Luther-University Halle-Wittenberg
Department of Prosthodontics, Centre for Dentistry and Oral Medicine
Poliklinik für Prothetik
Grosse Steinstrasse 19
06108 Halle /Saale