Suzuki et al.

Int Chin J Dent 2009; 9: 33-38.

Handling efficiency of autopolymerized resin applied using thebrush-on techniqueYasunori Suzuki, DMD, PhD, Hikari Chiba, DMD, PhD, Natsuko Kamada, DMD, PhD,Daisuke Kurihara, DMD, PhD, Yukari Kanki, DMD, PhD, Yoshiya Miyama, CDT,Toshio Hosoi, DDS, PhD, and Chikahiro Ohkubo, DMD, PhD
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine,
Yokohama, Japan
Purpose: The brush-on technique is frequently used for applying autopolymerized resin during chairside denture
repair and adjusting individual tooth trays. This study evaluated the handling efficiency of autopolymerizedresin applied using this technique.
Materials and Methods: Five autopolymerized resins, Unifast II (GC), Unifast Trad (GC), Provinice (Shofu),
Metafast (Sun Medical), and Miky (Nissin), were used in this study. Five operators (one dental technician, twodentists, and two dental students; ages 23-51) fabricated round resin pieces, approximately 6 mm in diameter,from the five autopolymerized resins on a pasteboard in one procedure. Four different brushes were tested; acalligraphy brush (cat hair, Naokatsu), two resin brushes (nylon fiber and horsehair, Seiundo), and a bristle brush(weasel hair, Shofu). After polymerization, the resin pieces were weighed on an electric balance. The handlingbehavior (n=5) was assessed by the coefficient of variation (%) of the weight and analyzed by ANOVA/Tukey’stest (α=0.05). After the test, all the operators completed a questionnaire about fabricating the resin pieces.
Results: Although significant differences were found among the operators (p<0.05), there were no significant
differences among all the resins and brushes tested (p>0.05). However, the horsehair resin brush tended to havegreater coefficients of variation. The results of the questionnaire indicated that Unifast II and the calligraphy
brush were preferred by the operators.
Conclusion: The handling efficiency of the autopolymerized resin using the brush-on technique depended on theskill of the operators rather than the resins and brushes. (Int Chin J Dent 2009; 9: 33-38.)
Key Words: autopolymerized acrylic resin, brush-on technique, coefficient of variation, handling efficiency.

Introduction
Various autopolymerized acrylic resins have been commonly used for chairside prosthetic treatment, such as
the fabrication of provisional restorations, repair of denture breakage, additional repair of retainers and artificial
teeth, and adjustment of individual tooth trays for abutment impressions.1-4

Due to the low degree ofpolymerization, the physical characteristics of hardness, bending strength, color stability, and absorption of
autopolymerized resins are worse than those of heat-polymerized resins.5-8 However, most clinicians haveaccepted these characteristics because the autopolymerized resins are conventional and indispensable materials
for chairside prosthetic treatment.
The brush-on technique for applying autopolymerized resins is frequently used in clinical and laboratory
procedures.9 In our previous study, the hardening time for the brush-on technique was reported to be shorter
than for the conventional mixing technique, and there were great differences in the hardening time among the
autopolymerized acrylic resins tested.10

Hanatani et al.11 reported that the dimensional accuracy of theautopolymerized resin applied using the brush-on technique was better than that of the conventionally mixed
polymer and monomer technique because the polymer and monomer ratio using the brush-on technique waslower and polymerization shrinkage was minimized due to this technique. However, the efficiency of thebrush-on technique is affected by many factors, such as the size of the polymer particles and their distribution,
the quality of the brush, and the skill of the operators.
The purpose of this study was to evaluate the handling efficiency of autopolymerized resins applied using thebrush-on technique. The evaluation was performed using the coefficients of variation of the sizes of the resin

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Int Chin J Dent 2009; 9: 33-38.

specimens and the responses to a questionnaire about the resins and brushes.

Materials and Methods
Fabrication of the resin pieces
Five pink autopolymerized acrylic resins, Unifast II (GC Dental Industrial Corp., Tokyo, Japan), Unifast Trad
(GC Dental Industrial Corp.), Provinice (Shofu Inc., Kyoto, Japan), Metafast (Sun Medical Co., Ltd., Moriyama,Japan), and Miky (Nissin, Kyoto, Japan) were used in this study. The colors, the powder/liquid ratios designatedby the manufacturers, and the lot numbers are listed in Table 1. Five operators (A, 51-year-old male dental
technician; B, 45-year-old male dentist, C, 28-year-old male dentist, D and E, 23-year-old dental students) withvarying amounts of clinical and laboratory experience were chosen to participate in this study. Four different
brushes were used; a calligraphy brush (cat hair, Naokatsu, Yokohama, Japan), two resin brushes (nylon fiberand horsehair, Seiundo, Osaka, Japan), and a bristle brush (weasel hair, Shofu Inc.). Each operator fabricatedround resin pieces (approximately 6 mm in diameter) in one procedure on a pasteboard from each of the fiveautopolymerized resins using each brush (Fig. 1). Five resin pieces were made for each kind of resin and brush.
A total of 500 resin pieces were fabricated.
Table 1.

Autopolymerized resins used in this study.

Trade name

Manufacturer

Color

Lot number

Unifast IIGCTokyo, Japan#3 Pink

Powder 0503172
Liquid 0504261

Unifast Trad

GC

#3 Pink

Powder 0504261
Liquid 0503221

Provinice

Shofu
Kyoto, Japan

U3

Powder 020507
Liquid 030555

Metafast

Sun Medical
Moriyama, Japan#2 Pink

Powder 41101
Liquid 41103

MikyNissinKyoto, Japan#2Powder PEIL
Liquid ELG

Assessment of handling behavior
After polymerization, the resin pieces were removed from the pasteboard and weighed on an electric balance(Libor AEG-45SM, Shimadzu Corp., Kyoto, Japan). The handling behavior (n=5) was assessed by thecoefficient of variation (%) of the weight of each resin piece. All the data were analyzed by an ANOVA andTukey’s multiple comparisons test at a significance level of α=0.05.
SEM observations
The specimens were examined using a scanning electron microscope (SEM JSM5600LV, JEOL, Tokyo,Japan) at magnifications of x300 and x500. Polymer particles of the autopolymerized resins and the used andunused hairs of the brushes were observed on the specimens.
Questionnaire about handlingAfter the test, all the operators completed a questionnaire about the handling efficiency of theautopolymerized resins and brushes. Their personal opinions were categorized according to a 5-point scale(minimum: 1 point, maximum: 5 points) based on three resin factors (picking up the resin pieces, filling the mold,34Suzuki et al.

Int Chin J Dent 2009; 9: 33-38.

and mixing of the polymer and monomer) and on four brush factors (picking up, filling, mixing, and handlingafter repetitive use).

Results
Figures 2a-2c show the handling efficiency of the operators, the autopolymerized resins, and the brushes,respectively. The weight of the resin pieces ranged from 24 to 39 mg (Fig. 2a). The coefficients of variation(CV) of the resin pieces fabricated by the dental technician (age 51) were the smallest, and significant
differences were found among the operators (p<0.05). As shown in Fig. 2b, there were no significant differencesin the CV among all the resins tested (p>0.05). The Metafast resin pieces were lighter than the other resin pieces.
Although the horsehair resin indicated a greater CV among the brushes tested (Fig. 2c), there were no significant
differences in CV (p>0.05).

Fig. 1.

Round resin pieces 6.0 mm in diameter on a pasteboard made using brush-on technique (left).

Fig. 2a. Weight of resin pieces and their coefficient of variation (CV). Operators (right).

Fig. 2b. Weight of resin pieces and their coefficient of variation (CV). Autopolymerized resin (left).
Fig. 2c. Weight of resin pieces and their coefficient of variation (CV). Brushes (right).

The SEM observations showed that the Metafast polymer tended to be a uniform size compared to the otherresins (Fig. 3). In the unused bristles, the hair cuticle was clearly observed on the surface of the three types ofanimal hairs (Fig. 4). However, the polymer particles were attached, and resin coated the bristles of the usedbrushes. The low-magnification views showed that the bristles on the nylon brush were of uniform thickness,whereas the bristles on the other brushes were not. The thickness and length of the hairs in the horsehair brushin particular tended to be irregular. The results of the questionnaire indicated that the operators preferred Unifast
II and the calligraphy brush (Fig. 5). In contrast, Metafast and the weasel hair brush had a lower score. Therewere few differences in handling between the used and unused brushes.

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Fig. 3.

SEM observations of the polymers of the autopolymerized resins.

Fig. 4.

Fig. 5.

SEM observations of the used and unused brushes.

Results of the questionnaire about handling. Autopolymerized resin (left) and Brushes (right).

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Discussion
The handling efficiency of the autopolymerized resins using the brush-on technique depended on the skill of
the operators rather than the kinds of resins and brushes. In this technique, the brush is soaked in resin monomer
and then dipped in the polymer. Although it is easy to repeatedly form the finely-shaped slurry resin, it isdifficult to form a similar size of the resin. Thus, the handling depends on each operator’s skill. The shrinkageof the autopolymerized resin using the injection method, brush-on technique, and injection-press-method has
been compared in vitro.12 Although the shrinkage using the injection-press method was the lowest, the brush-on
technique used by dental technicians in one study was comparable to the injection-press method.12

Thisphenomenon confirms that the accuracy of the brush-on technique depended on the skill of the operators.
There were no significant differences among the resins tested although the resin pieces of Metafast werelighter than those of the other resins. The weights of the resin pieces were affected by the size of polymer
particles and the standard liquid-powder (L/P) ratio. Since the Metafast polymers tended to be of uniform size
compared to the others, fewer polymers were attached to the tip of the brushes. In addition, the standard L/Pratio of Metafast (0.67) is greater than for the other resins (0.50). In the case of greater L/P ratio, the mixed resin
pieces would be smaller.
There were no significant differences in the CV among the brushes tested but the horsehair brush tended tomake the resin pieces larger. In this study, three brushes were made of animal hair and one was nylon fiber.
However, the thickness and length of the hairs on the horsehair brush were not uniform. Therefore, the horsehairbrush produced a greater CV of the resin pieces.
The results of the questionnaire indicated that Unifast II and the calligraphy brush were preferred by theoperators. However, there was no correlation between the CV and the preferred tendency. The reason why theoperators selected Unifast II and the calligraphy brush was probably because they have generally been using
Unifast and this particular brush in their practice. In the laboratory and in clinical practice, not only theoperator’s characteristics but also their familiarity with the materials and equipment may affect the handlingefficiency during any type of procedure.
The handling efficiency of the autopolymerized resins using the brush-on technique depended on the skill of
the operators rather than the kinds of resins and brushes. Although the effect of the autopolymerized resins on
the handling apparently could not be found, the calligraphy brush indicated superior handling efficiency.
Acknowledgment
This work was supported in part by research grant to improve the quality of dental products from the Japan DentalAssociation.

References
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Correspondence to:
Dr. Yasunori Suzuki
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: suzuki-ys@tsurumi-u.ac.jp
Accepted August 25, 2009.

Copyright ©2009 by the International Chinese Journal of Dentistry.

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