Koizumi et al.

Asian Pac J Dent 2011; 11: 15-18.

Characteristics of light-polymerizable adhesives for bonding
retentive beads to cut-back wax surfaces
Hiroyasu Koizumi, DDS, PhD,a,b Mamiko Kochi, DDS,c Kazuhiro Honda, DDS,cMichiya Ayano, DDS,a Kiyoshi Nagano, PhD,d and Hideo Matsumura, DDS, PhDa,bab

Department of Fixed Prosthodontics, Division of Advanced Dental Treatment, Dental Research
cCenter, Nihon University School of Dentistry, Division of Applied Oral Sciences, Nihon UniversitydGraduate School of Dentistry, Tokyo, and Nagasaki University Hospital, Nagasaki, Japan
Purpose: The purpose of the current study was to evaluate characteristics of chemical ingredients to be used forretentive beads adhesives.
Materials and Methods: An ultraviolet light-polymerizable adhesive (Particle Bond) and 12 UV and visible
light-polymerizable compositions were assessed. Undercuts created on the surface of castings were evaluatedusing two retentive beads adhesives; Particle Bond and Retention Beads II Adhesive. The cross section of castspecimens was observed with a confocal scanning laser microscope.
Results: In addition to the composition of Particle Bond, a dual-polymerizable material consisting of 93.5%
neopentylglycol diacrylate and 6.5% light initiators polymerized satisfactorily. In evaluation of the undercut ofretentive devices, the ratio of diameter of bonded area and retentive bead at an identical cross section was 0.65
for Particle Bond and 0.49 for Retention Beads II Adhesive (p<0.05).
Conclusion: Although wetting ability and polymerization performance of the Particle Bond adhesive wereexcellent, there was room for improvement in reproduction of undercuts. A dual-polymerizable composition
was proposed for the development of a new adhesive. (Asian Pac J Dent 2011; 11: 15-18.)
Key Words: adhesive, bead, cut-back, retentive device, spherical retention

Introduction
The application of highly loaded composite materials for veneering anterior and posterior restorations as wellas pontics has increased substantially. This trend is attributed to the improvement in the properties of composite
veneering materials. Mechanical retention, chemical retention, and a combination of both have been used forbonding between facing composites and framework alloys.
Among them, spherical retentive devices are widely accepted in dental laboratory procedures. Tanaka et al.1
reported that bond strength between a heat-polymerized cross-linked resin and cast silver-palladium alloy wasmaximal when the diameter of retentive device was 0.18 mm. Lee et al.2 used three materials for retaining alight-polymerized composite to cast nickel-chromium alloy with 0.35 mm retentive beads. The result was thatcyanoacrylate adhesive exhibited greater retentive strength than a veneering resin and shellac.

After the3,4However,development of chemical bonding systems, retentive devices appeared to be eliminated in part.

laboratory and clinical experiences demonstrate that deterioration against physical or chemical attack of bonded
veneers is smaller for mechano-chemically bonded systems than for mechanically or chemically bonded systems.
Although several papers reported data on retentive strength of mechanical bonding systems, only limited
information is available about the characteristics of retentive beads adhesives.5

This study evaluatedpolymerization performance of light-polymerizable retentive beads adhesives.

Materials and Methods
Polymerization characteristics
An ultraviolet (UV) light-polymerizable adhesive (Particle Bond; Toho Dental Products, Saitama, Japan) and12 UV and visible light (VL) polymerizable compositions (UV-VL) were evaluated as retentive beads adhesives

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Asian Pac J Dent 2011; 11: 15-18.

(Table 1). Two laboratory light polymerization units were used for polymerizing the adhesives; a UV lightpolymerization unit (Twinkle Q, Toho Dental Products) and a xenon flash polymerization unit (Dentacolor XS;Heraeus Kulzer & Co., GmbH, Wehrheim, Germany). Thin layer of each adhesive was applied by brush to thesurface of a piece of paraffin wax (GC Corp., Tokyo, Japan) and immediately light-exposed with one of thepolymerization units for 10-30 s. The plate was manually bent after light exposure. More than four out of fivespecimens that showed crack propagation after light exposure were judged as polymerized group. The results ofthe UV-polymerizable composition were quoted from the previous work.5
Comparison of undercut of retentive beads
Undercuts created on the surface of castings were next evaluated. Rectangular specimens (5x5x2 mm) were
fabricated with a wax material (Inlay Wax M; GC Corp.). One of the two retentive beads adhesives (ParticleBond; Toho Dental Products: Retention Beads II Adhesive; GC Corp.) was applied with a proprietary brush.
Solvent of the Retention Beads II Adhesive was naturally evaporated. Retentive beads 200 µm in average
diameter (Retention Beads II; GC Corp.) was next sprinkled on the adhesive layers. The Particle Bond adhesive
was polymerized with the Twinkle Q unit for 20 s. The wax patterns with retentive beads were invested in acristobalite mold material (Cristobalite Micro; GC Corp.) and Ag-Pd-Cu-Au alloy (Castwell M.C. 12; GC Corp.)
was cast in the mold with a centrifugal casting apparatus. The castings were cut with a low-speed cutting saw
with water coolant. The cut surfaces were observed with a confocal scanning laser microscope (1LM21W,Lasertec Corp., Yokohama, Japan) equipped with a He-Ne (Wavelength: 633 nm) laser light source. The
diameter of bonded area divided by diameter of retentive bead within an identical cross section of the retentive
bead was measured with a measuring system (LM eye, Lasertec Corp.). A diagram of the determination of theundercut is shown in Fig. 1.
Laboratory procedure
Fabrication of a typical framework of composite veneered restoration using the Particle Bond adhesive wasplanned. A technique for placement of retentive beads with proper undercut was proposed.
Table 1.

Composition and polymerization characteristics of retentive beads adhesives
Composition (wt%)

101
102
201
202
203
204
205
206
207
208
209
210
211
212

TMPTA
80
79.5
NPGDA
97
95
96.5
94.5
9896
94
97.5
95.5
93.5
99
98.5

EHA1515BME3535135135BME
55CQPolymerization unit and exposure time period (s)Twinkle QDentacolor XS
102030102030+++++++++++102030102030+++++++++++++++++++DMABA
0.5DMABA

0.50.5111111110.5
0.5
0.50.5TMPTA, trimethylol propane triacrylate; EHA, 2-ethylhexyl acrylate; BME, benzoin methyl ether; DMABA; N,N-dimethylaminobenzaldehyde; NPGDA, neopentylglycol diacrylate; CQ, dl-camphorquinone; (-), unpolymerized; (+), polymerized

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Asian Pac J Dent 2011; 11: 15-18.

Results
Table 1 shows a comparison between polymerization characteristics of UV- and UV-VL-polymerized
adhesive compositions. The composition 102 (Particle Bond) could be polymerized either with Twinkle Q orwith Dentacolor XS after 10-s light exposure. Characteristics of The UV-VL-polymerizable compositions varied
considerably.

The results showed that incorporation of 6.5% of initiation system is necessary for thepolymerization of UV-VL system based on neopentylglycol diacrylate (NPGDA).
Table 2.

Comparison of undercuts generated with the use of two retentive beads adhesives

Retentive beads adhesive
Bonded area D/Retentive bead D

Particle Bond (Composition #102)
Median IQRMean (SD)
0.65
0.17
0.63 (0.08)

GC Retention Beads II Adhesive
Median IQRMean (SD)
0.49
0.08
0.49 (0.06)

D, diameter; Mean, n=20; Significant difference was found between the two systems (t-test, F=3.935, p<0.05).

Fig. 1.
Fig. 2.

Determination of undercut (left)
Cross section of alloy castings prepared with Particle Bond (center) and Retention Beads II Adhesive (right)

Table 2 compares the undercuts generated with the use of two retentive beads adhesives. Ratio of diameter ofbonded area and retentive bead at an identical cross section was 0.65 for the Particle Bond and 0.49 for the GC
Adhesive. Figure 2 shows the cross sections of Ag-Pd-Au-Cu alloy castings. Difference in undercuts between
the two systems can be observed.

Fig. 3.

Cut-back wax patternFig. 4.

Application of Particle Bond

Fig. 5.

Retentive beads (200 µm)

Fig. 6.

Light-exposure for 20 s

Fig. 7.

Polymerized adhesiveFig. 8.

Cast framework

Figures 3-8 show fabrication of Ag-Pd-Au-Cu alloy frameworks of resin veneered restorations using theParticle Bond adhesive. The reproduction of spherical retentive device appeared to be satisfactorily.

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Asian Pac J Dent 2011; 11: 15-18.

Discussion
This study evaluated the characteristics of light-polymerizable retentive beads adhesives.

A UV light-5

polymerizable composition #102 was found to be effective in the previous study, and the composition wasreleased as the Particle Bond adhesive. The advantages of Particle Bond are; 1) low viscosity, 2) low thicknessof oxygen inhibited layer, which is derived from a UV initiation system, and 3) adequate wetting ability to wax
material. However, if the viscosity of the composition is too low, undercuts between retentive beads and wax
surface are reduced by capillary phenomenon (Fig. 2 and Table 2). To alleviate this problem, application of abi-functional aliphatic acrylate was proposed (Table 1).

Also, considering the spread of intermediatevisible-light sources designed for dental laboratories, a visible-light initiation system was adopted. It was foundthat composition #210 exhibited favorable polymerization performance.

By application of more viscouscomposition, the capillary phenomenon, as observed in the Fig. 7, should be prevented.
The size of retentive beads, type of adhesive, mold material, casting alloy, casting technique, and alumina
air-abrasion are key factors affecting mechanical retention between opaque resin materials and cast metalframeworks. Further investigation into these factors is necessary.
Acknowledgments
This work is supported in part by Grants-in-Aid for Scientific Research (C 20592283, C 21592474) from the Japan Society for thePromotion of Science (JSPS), Grant from Dental Research Center, and Sato Fund, Nihon University School of Dentistry (2009, 2010).

References
1. Tanaka T, Atsuta M, Uchiyama Y, Nakabayashi N, Masuhara E. Spherical powder for retaining thermosetting acrylic resin
veneers. J Prosthet Dent 1978; 39: 295-303.
2. Lee CF, Pierpont HP, Strickler ER. The effect of bead attachment systems on casting patterns and resultant tensile bondstrength of composite resin veneer cast restorations. J Prosthet Dent 1991; 66: 623-30.
3. Barzilay I, Myers ML, Cooper LB, Graser GN. Mechanical and chemical retention of laboratory cured composite to metal
surfaces. J Prosthet Dent 1988; 59: 131-7.
4. Jones RM, Moore BK, Goodacre CJ, Munoz-Viveros CA. Microleakage and shear bond strength of resin and porcelain
veneers bonded to cast alloys. J Prosthet Dent 1991; 65: 221-8.
5. Matsumura H, Tanaka T, Atsuta M. A light-cured acrylic adhesive for fixing resin retention devices to the wax pattern. J JpnProsthodont Soc 1990; 34: 364-71.

Correspondence to:Dr. Hiroyasu Koizumi
Department of Fixed Prosthodontics, Nihon University School of Dentistry
1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
Fax: +81-3-3219-8351 E-mail: koizumi@dent.nihon-u.ac.jp
Copyright ©2011 by the Asian Pacific Journal of Dentistry.

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Accepted December 27, 2010.
Online ISSN 2185-3487, Print ISSN 2185-3479