Hanatani et al.

Int Chin J Dent 2009; 9: 9-13.

Dimensional accuracy of autopolymerized resin applied using thebrush-on techniqueShigeru Hanatani, DMD, PhD, Naoyuki Shibuya, DMD, PhD, Ema Muraishi, DMD,
Daigo Hayashi, DMD, Tomoko Osada, DMD, PhD, Yohei Sato, DMD, PhD,
Chikahiro Ohkubo, DMD, PhD, and Toshio Hosoi, DDS, PhD
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine,
Yokohama, Japan
Purpose: The brush-on technique was developed to compensate for polymerization shrinkage. In this study, weassess the dimensional accuracy of autopolymerized resin applied using a brush-on technique.
Materials and Methods: Each of five autopolymerized resins, Unifast II (GC), Unifast Trad (GC), Provinice(Shofu), Metafast (Sun Medical), and Miky (Nissin), was applied three times inside a ceramic cylinder (10 mminternal diameter; 5 mm width) using a brush-on technique (horsehair resin brush, Seiundo). As controls, thefive resins were applied inside cylinders after the polymer and monomer were mixed at 0.5 mL/g for 10 s. Afterpolymerization, the cylinders were cut into 3-mm wide pieces using a precision cutting machine. The maximum
gaps between the ceramics and resins were measured using a scanning electron microscope at a magnification ofx500. The dimensional accuracy (n=5) was assessed as the shrinkage percentage (the gaps divided by theinternal diameter of the tubes). The data were analyzed by ANOVA/Tukey’s test (α=0.05).
Results: Excluding Metafast, the brush-on technique differed significantly from the controls (p<0.05). Using
the brush-on technique, Metafast had the greatest shrinkage, and Unifast had the lowest shrinkage. However,there was no significant difference among all the resins tested (p>0.05).
Conclusion: The dimensional accuracy of the autopolymerized resin using the brush-on technique was better
than that of the conventionally mixed polymer and monomer because the polymer and monomer ratio using thebrush-on technique was lower and polymerization shrinkage was minimized due to the brush-on technique.
(Int Chin J Dent 2009; 9: 9-13.)
Key Words: autopolymerized acrylic resin, brush-on technique, dimensional accuracy, polymerization
shrinkage.

Introduction
Autopolymerized acrylic resins are constantly used for the repair and adjustment of removable dentures orprovisional restorations.1-4 Generally, two methods for autopolymerized acrylic resin are used, namely, theconventional mixing technique and the brush-on technique.5 In the “mixing technique,” the polymer andmonomer are mixed in a rubber cup at their standard liquid/powder (L/P) ratio and then poured into a repair
portion or formed as resin dough. Another technique was developed half of a century ago.6 To compensate forpolymerization shrinkage, autopolymerized acrylic resins were used to fill a tooth cavity.5,6 An animal hairbrush is soaked in the monomer and then dipped into the polymer powder. A bead of slurry resin attached to theend of the brush is then placed into the cavity. These procedures are repeated at 10- to 15-second intervals.
Although autopolymerized acrylic resins are currently never used as filling materials, the brush-on technique isstill widely used in clinical and laboratory procedures, namely, for the repair of broken dentures, the extension ofdenture flanges, the additional repair of retainers or artificial teeth, and the adjustment of individual trays forabutment impressions.
Regarding the autopolymerized resins used in the clinic chair-side, the following characteristics are required:satisfactory handling efficiency, suitable fluidity and hardening time, greater hardness, stiffness, and adhesivestrength to acrylic resin, lower dimensional accuracy, and better color stability.5,7-11 In the case of the brush-ontechnique, Kamada et al.12 evaluated the fluidity and hardening time of autopolimerized acrylic resin. However,its dimensional accuracy was well known, even though the brush-on technique was developed to reduce the9Hanatani et al.

Int Chin J Dent 2009; 9: 9-13.

shrinkage of this resin. The purpose of this study was to assess the dimensional accuracy of autopolymerizedresin using the brush-on technique.

Materials and Methods
Specimen preparation
The five autopolymerized resins used in this study are listed in Table 1. A ceramic tube (10 mm internaldiameter; 5 mm width) was prepared for this study (Fig. 1). After the cylinder was placed on the glass plate,each of the five autopolymerized resin was applied three times inside the cylinder using the brush-on technique(horsehair resin brush; Seiundo, Japan) until the cylinder was full of resin. As controls, the five resin slurries(approximately 0.1 g) were applied inside the cylinders after the polymer and monomer had been mixed at 0.5
mL/g for 10 s (mixing technique). The cylinder was maintained at room temperature (23±1°C; humidity:50-60%), and polymerization was completed. After that, the ceramic cylinders were cut into 3 mm-wide pieces
using a precision cutting machine (Accutom-5, Struers, Ballerup, Denmark) (Fig. 2). A total of 25 specimens,
five of each type, were fabricated.
Table 1.

Autopolymerized resins used in this study.

Trade name

Manufacturer

Color

L (mL) / P (g)Lot number

Unifast IIGCTokyo, Japan#3 Pink

0.5

Powder 0503172
Liquid 0504261

Unifast Trad

GC

#3 Pink

0.5

Powder 0504261
Liquid 0503221

Provinice

Shofu
Kyoto, Japan

U30.5

Powder 020507
Liquid 030555

Meta Fast

Sun Medical
Moriyama, Japan#2 Pink

0.7

Powder 41101
Liquid 41103

Miky

NissinKyoto, Japan#20.5

Powder PEIL
Liquid LELG

Fig. 1.

Illustration of a ceramic cylinder.

Fig. 2.

Ceramic cylinders were cut into 3-mm wide pieces.

Measurements of dimensional accuracy
The cutting surfaces of the cylinders were observed using a scanning electron microscope (SEM; JSM
5600LV, JEOL, Akishima, Japan) at a magnification of x500. The maximum gaps between the internal surfaceof the ceramic tube and resins were measured using SEM images (Fig. 3). The dimensional accuracy wasassessed as the shrinkage percentage by dividing the gaps by the internal diameter (10.0 mm) of the cylinders.

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Int Chin J Dent 2009; 9: 9-13.

The data obtained were analyzed by one-way ANOVA and Tukey’s multiple comparison test at a significancelevel of α=0.05.

ResultsFig. 4 shows the polymerization shrinkage of autopolymerized resins using both the brush-on and mixing
techniques. Excluding Metafast, the brush-on technique indicated significantly lower shrinkage than the mixing
technique (p<0.05). Using the brush-on technique, the shrinkage percentages of all resins were approximately
0.5% or less. Metafast and Unifast II had the greatest shrinkage, and Unifast Trad had the lowest shrinkage.
However, there was no significant difference among all the resins tested (p>0.05). In contrast, the shrinkage
percentages of all resins were approximately 0.6% or more using the mixing technique. Although Miky showed
the greatest shrinkage and Metafast showed the lowest shrinkage, no significant difference was found in any of
the resins tested (p>0.05). Hence, the difference in shrinkage between the two techniques was the smallest withMetafast.

UNIFAST IIFig. 3.

UNIFAST Trad

PROVINICE

META FASTMIKY

The gaps between the internal surface of the ceramic cylinder and the resins were measured using SEM
images. Upper, Mixing technique; Lower, Brush-on technique.

Fig. 4.

Polymerization shrinkage of autopolymerized resins using both the brush-on and mixing techniques.

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Int Chin J Dent 2009; 9: 9-13.

Discussion
The L/P ratio of the brush-on technique is not constant and depends on the quality of the brush and the skill ofthe operators. Shirato5 reported the L/P ratio of both techniques for autopolymerized resins (brush-on technique:0.31-0.38 L/P, mixing technique: 0.5 L/P). As reported above, the brush-on technique was developed by Nealon
to compensate for the polymerization shrinkage by filling little by little, and its L/P ratio is lower than that forthe mixing technique. Therefore, the brush-on technique indicated significantly less dimensional accuracy thanthe mixing technique (p<0.05) excluding Metafast.
Generally, the autopolymerized resin had a positive correlation with the polymerization temperature anddimensional accuracy.13 Autopolymerized resins indicate the greatest shrinkage at the highest temperatures. In
our previous study,12 the polymerization temperatures of both the brush-on and mixing techniques were very
similar, whereas the hardening times differed. Therefore, the correlation between the dimensional accuracy andpolymerization temperature was not obvious in this study.
Usually, two colors of autopolymerized resins, namely, ivory for artificial teeth and pink for denture bases, areused for prosthetic treatment. There are few differences in the characteristics of each resin by the color pigments
they contain. Pink resins were used in this study on the assumption that dentures were being repaired. Thus, thestudy is limited to the results for denture repair.
Unifast Trad using the brush-on technique showed the least shrinkage (approximately 0.2%). However, theother properties, such as hardness, adhesive strength, color stability, and bending strength, are also importantfactors to consider when selecting resins.
Within the limitations of this study, the dimensional accuracy of the autopolymerized resin using the brush-on
technique was better than that of the conventionally mixed polymer using the monomer technique. This finding
is attributed primarily to the fact that the polymer and monomer ratio using the brush-on technique is lower andthat the polymerization shrinkage was minimized due to the brush-on technique.
Acknowledgment
This work was supported in part by research grant to improve the quality of dental products from the Japan Dental
Association.

References
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Int Chin J Dent 2009; 9: 9-13.

Correspondence to:
Dr. Chikahiro Ohkubo
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine
2-1-3, Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan
Fax: +81-45-573-9599 E-mail: okubo-c@tsurumi-u.ac.jp
Received March 3, 2009. Accepted March 21, 2009.
Copyright ©2009 by the International Chinese Journal of Dentistry.

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