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rev port estomatol med dent cir maxilofac . 2019;60(4):155-162 157

Cold was established as the minimal concentration effective (Panreac Applichem, Darmstadt, Germany) were weighted us-
against Candida albicans, without affecting mechanical properties, ing a precision balance (A&D FZ-200i Company, Limited, Tokyo,
both immediately after acrylic preparation and after thermal ag- Japan), to obtain a 2.5%powder weight (w/w) for Kooliner and
ing. 17,26-31 However, the effect of the chemical aging process on a 5% powder weight (w/w) for Ufi Gel Hard and Probase Cold.
the resin properties may also be relevant since, when in function They were then mixed with a mortar and a pestle until homog-
inside the oral cavity, reline acrylic resins may biodegrade faster enization was achieved. Two groups were set for each materi-
due to daily exposure to an acidic environment. 32-34 al: one control group without CHX, and one experimental
The surface free energy of a solid consists in the sum of group with CHX incorporation.
components arising from dispersive (apolar) and polar contri- For the surface free energy (γ) study, a metallic rectangular
butions. Changes in this property will impact the surface wet- mold was used to prepare 42 specimens (n=7) with standard-
tability of the material and, consequently, its interaction with ized dimensions (25x16x1 mm). After allowing the resin to
saliva molecules, microbial molecules and other materials. 13,35 polymerize under pressure, the specimens were polished with
Also, an adequate bonding between the denture base resin and a 600-grit silicon carbide paper (Carbimet Paper Discs, Buehler
the reline material is essential since a failure can harbor bac- Ltd., Lake Bluff, IL). They were then submitted to a chemical
teria, promote staining, decrease the strength of the denture aging process in a graduated falcon tube filled with artificial
and cause fractures. 11,16-39 saliva, with a ratio of 1 g / 5 mL, in an incubator (Memmert,
The objective of this study was to evaluate the impact of Schwabach, Germany) at 37 ± 2ºC with constant gentle shaking
incorporating CHX in reline acrylic resins subjected to oral pH (300 rpm). 40,41 The specimens were exposed to pH fluctuations
fluctuations on their surface free energy and their microtensile in cycles of 6 hours in saliva at pH=3 and 18 hours at pH=7, for
bond strength to the denture base resin. The following hypoth- 28 days. Between each cycle, specimens were washed with
eses were established: 1) no differences in surface free energy distilled water and dried with absorbent paper (Figure 1).
and bond strength are observed between the three resins; 2) The γ test was performed with a Tensiometer K12 (Kruss,
CHX incorporation does not influence the surface free energy; Hamburg, Germany), where the specimen was suspended and
and 3) incorporating CHX in the reline resins does not affect immersed 4 mm in water (Merck Millipore, Germany) and
their bond strength to the denture base. 1,2-propanediol (1-2 Propanediol R.822324-1L; Merck, Germa-
-1
ny) at a speed of 20 μms . The contact angles were measured
at 25 ± 0.1ºC using the Wilhelmy plate technique, and were
Materials and methods used to estimate total surface free energy (γ), as well as its
p
d
dispersive (γ ) and polar components (γ ), based on the har-
Three auto-polymerizing reline acrylic resins were selected: two monic mean method proposed by Wu. 42,43
direct reline resins mainly formed by poly(ethyl methacrylate) – For the microtensile bond strength (µTBS) study, 36 cubic
Kooliner and Ufi Gel Hard, and an indirect reline resin mainly (10×10×10 mm) specimens of the heat-polymerizing denture
composed by poly(methyl methacrylate) – Probase Cold. base acrylic resin Probase Hot (Ivoclar Vivadent AG, Liechten-
The acrylic resins were manipulated according to the man- stein) were produced by a conventional flasking technique.
ufacturer’s recommendations (Table 1). The liquid was mea- These specimens were submitted to 2500 thermal cycles, al-
sured using a graduated pipette. The powder of each reline ternating submersions of 20 seconds at 5ºC and 55ºC with a
acrylic resin and the chlorhexidine diacetate monohydrate duel time of 5 seconds, on a thermocycling machine (Refri

Table 1. Materials under evaluation in the investigation.

Composition Batch number
Material P/Li Ratio (G/Ml) Curing cycle Manufacturer
P | Li (Expiration date)
P
10 min GC America Inc., 1707271 (2020-07)
Kooliner PEMA IBMA 1.4/1
37ºC Alsip, IL., USA Li
1704191 (2020-04)
P
7 min 1816582 (2020-09)
Ufi Gel Hard PEMA 1,6-HDMA 1.77/1 Voco GmbH.,
37ºC Li
Cuxhaven, Germany
1804406 (2020-02)
P
15 min Ivoclar Vivadent AG., XT1222 (2022-10-24)
Probase Cold PMMA MMA 1.5/1 40ºC Liechtenstein Li
3 bar
X45991 (2022-10-11)
Chlorhexidine Panreac Applichem,
Chlorhexidine diacetate – – Darmstadt, 8F015944 (10/2023)
monohydrate Germany

P = Powder; Li = Liquid; PEMA = Poly(ethyl methacrylate); IBMA = Isobutyl methacrylate; 1,6-HDMA = 1,6-hexanodioldimethacrylate;
PMMA = Poly(methyl methacrylate); MMA = Methyl methacrylate.