Shimpo et al.

Asian Pac J Dent 2019; 19: 65-69

Bonding of auto-polymerized poly(methyl methacrylate) resin topolyamide thermoplastic resin
Hidemasa Shimpo, DMD, PhD and Chikahiro Ohkubo, DMD, PhD
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine,
Yokohama, Japan
Purpose: Auto-polymerized poly(methyl methacrylate) (PMMA) resin cannot be bonded to polyamide
thermoplastic resin. This study evaluated the bonding strengths of auto-polymerized PMMA resin to nylon
denture bases using adhesive agents.
Materials and Methods: The surfaces of polyamide thermoplastic resin plates were polished using abrasive
paper and blasted with 50 µm alumina particles. An adhesive agent, 4-META/MMA-TBB resin (Super-Bond)was used on the surfaces under the following conditions: monomer + catalyst (4:1, Group 1), monomer +catalyst (8:1, Group 2), monomer + catalyst (4:1) + polymer (Group 3), monomer + catalyst (8:1) + polymer(Group 4), treatment with dichloromethane (Group 5), alumina-blasted (Group 6), without treatment (Group 7),and PMMA resin (Group 8). Auto-polymerized PMMA resin was poured into a Teflon ring and polymerizedaccording to the manufacturer’s instructions. After polymerization, the specimens were stored in 37˚C distilledwater for 24 hours. The specimens for each condition were thermo-cycled for 5,000 cycles. The tensile bondstrengths were measured on an autograph at a crosshead speed of 2.0 mm/min. The data obtained (n = 13) wereanalyzed using a two-way ANOVA and Tukey’s multiple comparisons test (α = 0.05).
Results: The bonding strengths of Groups 1 to 4 were significantly higher than for Groups 5 to 7. No significant
differences were found among Groups 1-4, although Group 3 had the highest bonding strengths.
Conclusion: Auto-polymerized PMMA resin will adhere to polyamide thermoplastic resin using 4-META/MMA-TBB after alumina-blasting.
(Asian Pac J Dent 2019; 19: 65-69.)
Key Words: bond strength, 4-META/MMA-TBB resin, polyamide, thermoplastic resin

Introduction
Several thermoplastic resins, such as polyamide, polyethylene terephthalate, polycarbonate, and acrylic resins,
have been developed and are commercially available for flexible denture construction [1-6]. In particular,
polyamide (nylon) thermoplastic resin has the highest elasticity for flexible resin clasps and is more commonlyused than the other thermoplastic resins [7-9]. However, there are several disadvantages of the clinical use ofnylon dentures, for instance, poor machinability, i.e., cutting and grinding, difficulty of polishing, poor
adjustability of the retentive force of the resin clasp, easy to roughen on the surface, and little bonding ability of
the auto-polymerized poly(methyl methacrylate) (PMMA) resin [2,4]. Therefore, it is difficult to achieve thechair-side repair of the flexible dentures using auto-polymerized PMMA resin due to denture breakage,detachment of the artificial teeth, difficulty of adding the artificial teeth if a tooth is missing, direct relining, andso on.
Using 4-META/MMA-TBB resin as the adhesive agent, chair-side relining or denture repair of polyamide
dentures with auto-polymerized PMMA resin can be developed. The aim of this study was to evaluate thebonding strengths of auto-polymerized PMMA resin to polyamide denture polymer using adhesive agents.

Materials and Methods
Rectangular polyamide thermoplastic resin plates (Bioplast, Denken-Highdental, Kyoto, Japan; Lot, 1303217)(10.0 × 10.0 × 2.0 mm) were fabricated using the injection molding technique (injection pressure 1.5 MPa)
according to the manufacturer’s instructions (MIS-II, i-CAST, Kyoto, Japan). After deflasking, all the surfaces

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of the resin plates were finished and polished using abrasive paper (600 grit) and blasted with 50 µm alumina
particles (0.48 MPa). As an adhesive agent, 4-META/MMA-TBB resin (Super-Bond, Sun Medical, Moriyama,Japan) was applied on the bonding surfaces using following four mixing conditions: monomer + catalyst (4:1,Group 1), monomer + catalyst (8:1, Group 2), monomer + catalyst (4:1) + polymer (Group 3), and monomer +catalyst (8:1) + polymer (Group 4). Groups 1-4 were alumina-blasted before application of adhesive agent(Table 1). Following three surface treatment conditions were added to compare their use with
4-META/MMA-TBB resin: treatment with dichloromethane (Meta base M resin primer, Sun Medical; Group 5),
alumina-blasted (50 µm Al2O3; Group 6), without surface treatment (Group 7), and PMMA resin without surface
treatment (Group 8). As a control, heat-polymerized PMMA plates (Acron, GC, Tokyo, Japan) were also
prepared for comparison between the conventional dentures and the nylon dentures. After application of theadhesive agent, auto-polymerized PMMA resin (Meta base M, Sun Medical) was poured into a Teflon ring (3.0mm diameter, 1.0 mm height) on the bonding surface using the brush-on technique and polymerized according
to the manufacturer’s instructions (Fig. 1). After polymerization, all the specimens were stored in distilled waterat 37˚C for 24 hours before tensile testing. Thermo-cycled (5,000 cycles; 5˚C, 1 min-55˚C, 1 min) specimens(TC5000) were also prepared for each condition.
Table 1 Surface treatments
Group
12
3
4
5
6
7
8

Surface treatment
Super-Bond Monomer + Catalyst (4:1)
Super-Bond Monomer + Catalyst (8:1)
Super-Bond Monomer + Catalyst (4:1) + Polymer (1/2 cup)Super-Bond Monomer + Catalyst (8:1) + Polymer (1/2 cup)
DichloromethaneAlumina blasting
Without surface treatment
Without surface treatment (control)

Fig. 1 Bonded specimen

Adherend
Polyamide
Polyamide
Polyamide
Polyamide
Polyamide
Polyamide
Polyamide
PMMAFig. 2 Assembly for tensile bond strength testing

Each specimen was mounted on a screw-driven mechanical testing machine (AG-IS, Shimadzu, Kyoto,Japan). The bond strengths were measured at a crosshead speed of 2.0 mm/min (Fig. 2). The data obtained (n =5) were analyzed by two-way ANOVA and Tukey’s multiple comparisons test at α = 0.05.
The abraded and sandblasted surfaces of the thermoplastic resin were observed with a scanning electron
microscope (SEM, ×500 magnification, JSM 6300, JEOL, Akishima, Japan) with an accelerating voltage of 15kV.

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Results
Bond strengths
The tensile bond strengths of all conditions are indicated in Fig. 3. The specimens in Groups 1 to 4 showedsignificantly higher bonding strengths than Groups 5 to 7 (p < 0.05) and were comparable to heat-polymerized
PMMA at TC0. Of the 4-META/MMA-TBB resin, Group 3 had the highest bonding strengths (p > 0.05)
followed by Groups 2, 4, and 1. After thermo-cycling, the bonding strengths of all the specimens significantlydecreased (p < 0.05). In particular, all the Group 6 and 7 specimens failed before testing. Comparing
heat-polymerized PMMA, Groups 1 to 4 decreased approximately one second of bonding durability.

Fig. 3 Bond strengths of PMMA resin to polyamide thermoplastic resin
Identical letters indicate that the values are not statistically different (p > 0.05).

Fig. 4 Scanning electron micrographs of polyamide: left, alumina-blasted and polished; right, polishedSEM observation
Electron micrographs of the abraded and alumina-blasted surfaces of the polyamide plates are shown in Fig. 4.
The surfaces abraded using abrasive paper (#600) were rougher and had many sharp edges. Although thealumina-blasted surfaces were rougher than the abraded surfaces, few sharp-edged surfaces were observed.

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Discussion
Clinically, fractures of nylon dentures have been rarely observed because of their mechanical characteristics.
However, polyamide is noted fatal problem, namely, it cannot be bonded to PMMA for denture repair or reline.
Thus, it must develop the adhesion method of polyamide and PMMA in chair side repair.
Because polyamide is chemically remarkable stable, dichloromethane as denture primer for showedsignificantly lower bonding strengths than the other treatment [10]. The 4-META/MMA-TBB resin has foundsound evidence that adhesion between dentin to metal prosthesis as a resin cement [11]. In this study,
4-META/MMA-TBB was applied as adhesive agent of the bonding of polyamide thermoplastic resin andPMMA. Specimens with only 4-META/MMA-TBB monomer + catalyst as surface treatment showed lower
bonding strength compared with monomer + catalyst with slight polymer. Condition of monomer + catalyst withslight polymer indicated similar bonding strength to acrylic denture base resin (control) without thermo-cycling.
Thus, mixing polymer is absolutely necessary for adhesion between 4-META/MMA-TBB resin andauto-polymerized acrylic resin.
This bonding mechanism would be occurred as minute mechanical binding occurred by sandblastingtreatment. It must be difficult that invaded to the molecular gap of polyamide because the molecular weight of
mixed 4-META/MMA-TBB resin was 239×103. The surface property greatly affects to adhesive strengths[12-15]. Minami et al. [16] examined the bonding strength of the acrylic denture base resin for repair. MMA
monomer can invade by dissolving the acrylic resin surface using dichloromethane. Ohkubo et al. [17] described
the minute mechanical surface treatment using the alumina-blast was needed to make adhere of acrylic resin
minute to framework alloy which MMA could not invade. Polyamide resin has a chemical superior homeostasis,the surface cannot be dissolved with menstruum by an MMA monomer or the dichloromethane similar to metal.
Therefore, the minute mechanical bond is also necessary to obtain high bonding strengths of PMMA tothermoplastic resin. Many sharp scratches were observed on the surface of polyamide by abrasive paper (#600)
from the SEM image (Fig. 3). However, the mechanical retention for higher adhesion was occurred by countlessunevenness on the polyamide treated by blasting in this study.
Although many studies were reported on the bonding of auto-polymerizing resin to conventional denture baseresins, there were few researches on the polyamide denture polymers. Katsumata et al. [10] reported that theshear bond strengths to another polyamide polymer (Lucitone FRS, Dentsply) were significantly greater using
the Rocatec System. This procedure applied the silane coupling treatment after silicate coating on the bonding
surface. However, an easier procedure without any special equipment is desirable for chair-side repair.
Nevertheless the bonding durability was only half that of conventional PMMA denture base resin, the repair orreline for polyamide denture could be easily accomplished at chair-side using 4-META/MMA-TBB resin.
Another reason why, as a result, the abrasion from margin of bonding materials is occurred, increased quantities
of PMMA as bonding material make curing shrinkage is increase [18] even if PMMA and polyamide
thermoplastic resin cannot adhere chemically. Therefore, the use of slight 4META-MMA/TBB as adhesive agent,
not only it is hard to exfoliate from polyamide thermoplastic resin as adherend by curing shrinkage is decrease
but also it can be adhered to PMMA.
After thermo-cycling (5,000 cycles), the bonding strengths of all conditions were showed significantly
decreased except the control. This result also suggested that the long-term stability of the bond might be slightly
prevented by mixing polymer to monomer + catalyst. This study could not elucidate the adhesion mechanism

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between polyamide and 4-META/MMA-TBB. Further study is necessary to examine the effect of the ingredientof 4-META/MMA-TBB gives to the surface of the polyamide.
Conflicts of Interest
There are no conflicts of interest.

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Correspondence to:Dr. Hidemasa Shimpo
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: shinpo-hidemasa@tsurumi-u.ac.jp
Accepted September 23, 2019.
Copyright ©2019 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

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