Hong et al.

Asian Pac J Dent 2011; 11: 45-50.

The initial viscosity and adhesive strength of denture adhesives
and oral moisturizers
Guang Hong, DDS, PhD,a Hiroki Tsuka, DDS, PhD,b Maimaitisawuti Dilinuer, DDS,c
Wei-Qi Wang, DT,c and Keiichi Sasaki, DDS, PhDcab

Liaison Center for Innovative Dentistry, Graduate School of Dentistry, Tohoku University, Departmentof Advanced Prosthodontics, Graduate School of Biomedical Sciences, Hiroshima University,c
Hiroshima, and Division of Advanced Prosthetic Dentistry, Graduate School of Dentistry, Tohoku
University, Sendai, Japan
Purpose: The purpose of this study was to determine the initial viscosity and adhesive strength of commercial
denture adhesives and oral moisturizers.
Materials and Methods: Four cream-type denture adhesives, one gel-type denture adhesive and three gel-typeoral moisturizers were used in the study. The initial viscosity was measured using a controlled-stress CarriMed
CSL500 rheometer. The adhesive strength was measured according to the ISO-10873 recommended procedures
using a constant load compression testing machine and a materials testing machine.
Results: Significant differences in initial viscosity were found among the materials (p<0.05). Similar viscosity
values were recorded in all materials except Tafugrip Gel and Corect Cream. The adhesive strength of dentureadhesives increased significantly with time, but the adhesive strength of oral moisturizers decreased significantlywith time.
Conclusion: Cream-type denture adhesives and gel-type oral moisturizers exhibit similar initial viscosity, anddenture adhesives and oral moisturizers function with different adhesion behaviors.
(Asian Pac J Dent 2011; 11: 45-50.)
Key Words: adhesive strength, denture adhesive, oral moisturizers, viscosity

Introduction
Denture adhesives have been widely used by denture wearers with well-fitting and ill-fitting dentures as ameans to enhance denture retention, stability and function.1-5 The American Dental Association first reported theuse of a denture adhesive in 1935.6 Clinical opinion about denture adhesives has often been negative,7-10 anddentists have been slow to accept these products. Reported reasons for trying denture adhesives include to
improve fit, comfort, chewing ability, and also to improve patient confidence in wearing dentures.5,11 In the US
in 1980, 15% of denture wearers used denture adhesives.12,13 Wilson et al.14 reported in 1990 that 30% of
denture wearers used, or had used, denture adhesives. However, Coates15 reported that a significant number ofsubjects in his study did not know that denture adhesives existed. However, denture adhesives still hold alegitimate and indispensable place in prosthetic dental treatment.
Dry mouth, or xerostomia, is a common symptom of the elderly population. In recent years, the number ofedentulous patients with dry mouth has increased, resulting in more patients suffering from poor denture
retention and reduced quality of life.
function.

16-18

Dry mouth may compromise oral health and interfere with oral

Dry mouth is caused by a number of factors, including Sjögren’s syndrome, the administration of

medicine, age, diabetes, and radiotherapy of the head and neck during cancer treatment.18-22 Österberg et al.23
reported that 16% of men and 25% of women complained of oral dryness. Several investigators have reported
that the prevalence of dry mouth among the aged population varies between 12% and 39%, and the prevalence
increases with age and the number of medications being taken.24-27 Yet no effective treatment for dry mouth has
been available except for symptomatic therapies such as taking frequent sips of water, the use of saliva
substitutes (oral moisturizers), artificial saliva, glycerin, troches and sugar-free gum, salivary gland hormones,
and herbal medicine.18 Oral moisturizers are available as gels, mouth rinses and sprays,28,29 and are currently the45

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Asian Pac J Dent 2011; 11: 45-50.

most commonly used treatment for dry mouth.
The mechanical properties and cytotoxicity of denture adhesives have been widely investigated using a variety
of testing methods.30-32 However, few studies have examined the initial viscosity and adhesive strength ofdenture adhesives.

Furthermore, almost no research has investigated the mechanical properties of oral

moisturizers. Information about these characteristics may be important for the clinical use of these materials.
Patients would benefit greatly from a dental professional’s guidance regarding the use of denture adhesives andoral moisturizers. However, in clinical situations, patients and dentists fail to select the most appropriate
product.
The purpose of this study was to examine the initial viscosity and adhesive strength of commercial dentureadhesives and oral moisturizers.

Materials and Methods
Four cream-type denture adhesives (Poligrip S, Liodent Cream, Corect Cream, Tafugrip Cream; PGS, LDC,
COC, TGC), one gel-type denture adhesive (Tafugrip Gel; TGG) and three gel-type oral moisturizers (Fit Angel
Gel, Biotene Oral Balance, Bio Xtra Aqua Mouth Gel; FAG, BOB, BMG) were used in the study (Table 1). The
initial viscosity of the materials was measured using a controlled-stress CarriMed CSL500 rheometer (TAInstruments Ltd., New Castle, DE, USA) in dynamic oscillation mode with a cone-and-plate configuration. The
radius of the upper cone was 10 mm with a 2° cone angle and the gap between the plates was 54 µm (Fig. 1).
The instrument was used in a constant strain mode with an angular velocity of 10 rad/s at 37°C.
Table 1.
Code
FAG
BOB
BMG
TGG
PGS
LDC
COC
TGC

Used commercial materials

Materials
Fit Angel Gel
Biotene Oral Balance
Bio Xtra Aqua Mouth Gel
Tafugrip Gel
Poligrip S
Liodent Cream
Corect Cream
Tafugrip Cream

Manufacturers
Panasonic Dental Co., Ltd., Osaka, Japan
Lacleden Inc., Rancho Dominguez, USA
Weltec Co., Osaka, Japan
Kobayashi Pharmaceutical Co., Ltd., Osaka, Japan
Glaxo Smith Kline K.K., Tokyo, Japan
Lion Co., Tokyo, Japan
Shionogi & Co., Ltd., Osaka, Japan
Kobayashi Pharmaceutical Co., Ltd.

Type
Oral moisturizer
Gel-type denture adhesive
Cream-type denture adhesive

The adhesive strength was measured according to the ISO-10873 recommended procedures.33 The hole of thesample holder (Fig. 2) was filled with denture adhesive, and the surface was flattened. The sample holder wasthen immersed in water at 37°C for 0, 1, and 10 minutes. The holder was removed and shaken once to remove
water from the sample surface. The sample holder was fixed on the sample stand, and a load of 9.8±0.2 N was
applied to the sample using a constant load compression testing machine (A-001, Japan Mecc Co. Ltd., Tokyo,
Japan) at a pressurizing velocity of 5 mm/minute using a 20±0.5 mm pressure sensitive knob, and maintained for
30 s. The sample was then pulled in the reverse direction with tensile velocity using a materials testing machine(Model 5565, Instron Co., Canton, MA, USA) at a crosshead speed of 5 mm/minute. The maximum force on thepressure sensitive knob was measured at that time and the force per unit area was set as the adhesive strength.
The sample holder and pressure sensitive knob were prepared using denture base acrylic resin (Acron, Lot No.
Powder-030471, Liquid-0112203; P/L:10/4.3 g; GC Corp., Tokyo, Japan), and were polymerized according to
the manufacturer’s instructions. The surfaces were abraded with 400 grit waterproof abrasive paper, scrubbed

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Asian Pac J Dent 2011; 11: 45-50.

with tap water for 15 s, and allowed to air dry for at least 5 minutes.
All the data were analyzed independently by one-way analysis of variance (ANOVA) and two-way ANOVA
combined with a Student-Newman-Keuls (SNK) multiple comparison test at a 5% level of significance. Allanalyses were computed with PASW Statistics for Windows (PASW Statistics 18, SPSS Japan Inc., Tokyo,
Japan).

Fig. 1. Cone plate for viscosity test

Fig. 2. Sample holder for the adhesive strength test

Results
Figure 3 shows the initial viscosity of materials tested. Significant differences were found between the
different materials (p<0.05, one-way ANOVA). TGG had significantly higher viscosity than the other materials(p<0.05, SNK test), and COC had significantly lower viscosity (p<0.05, SNK test). The remaining materials
recorded similar viscosity values.

Fig. 3. Mean initial viscosity with standard deviation (left). Identical letters indicate no significant differences (p>0.05, SNK-test).
Fig. 4. Mean adhesive strength with standard deviation before and after immersion in distilled water (right).
Identical letters indicate no significant differences (p>0.05, SNK-test).

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Figure 4 shows the variations in adhesive strength of the different materials according to immersion time. The
ANOVA results indicated significant differences among the materials and revealed significant effects ofimmersion time on adhesive strength (p<0.05). Before immersion, the oral moisturizers tended to exhibit higher
adhesive strength than the denture adhesives. However, after immersion, this tendency was reversed. The
adhesive strength of denture adhesives increased significantly (p<0.05, ANOVA) with immersion time except
for the gel-type denture adhesive (TGG). The adhesive strength of TGG increased significantly up until 1 minafter immersion, and then decreased significantly up until 10 minutes. The adhesive strength of the oral
moisturizers decreased significantly with immersion time (p<0.05, ANOVA).

Discussion
In recent years, increasing numbers of patients have been complaining of dry mouth in line with the aging ofsociety.16,18 Dry mouth leads to difficulty in chewing food, speaking, swallowing, and considerable discomfort,
and results in reduced quality of life.17 Currently, there is no effective treatment for dry mouth except for
symptomatic therapies,18 with gel-type oral moisturizers being the most commonly used treatment.
Denture adhesives can be classified as cushion type, cream type, powder type and seal type.3 In this study,
cream-type denture adhesive and gel-type denture adhesives were used. Several cases have been reported ofdeformation of the mandibular alveolar ridge caused by home reliners (cushion-type denture adhesives),
confirming that there is a risk of alveolar bone resorption caused by inappropriate use of home reliners.7,8 Chew4
reported that cream-type denture adhesives were significantly more effective in improving the retention between
an acrylic disc and rat skin than powder and seat-type denture adhesives. Dental professionals are most likely torecommend a cream-type denture adhesive. A gel-type denture adhesive has been developed that is easier toremove from the oral mucosa than existing commercially available denture adhesives,34 and whose main
components differ from existing cream-type denture adhesives.
The initial viscosity of denture adhesives and oral moisturizers may affect their effectiveness, and isdependent on the composition of the material. Denture adhesives consist of a base and a thickening agent. In
cream-type denture adhesives, vaseline is mainly used for the base, and water-soluble polymers, such as sodium
carboxymethyl cellulose (CMC) and methoxy ethylene maleic anhydride copolymer (PVM-MA), are usuallyused for the thickening agent.3,30,34 These cream-type denture adhesives first exhibit low viscosity. When theadhesive is placed in the mouth, they become viscous and sticky due to water absorption by the water-soluble
polymer.34 However, since PGG uses distilled water as the base,34 the water-soluble polymer (CMC) of PGG isalready saturated with water. This may explain why the initial viscosity of PGG is higher than the othercream-type denture adhesives. Other differences between the initial viscosity of cream-type denture adhesives
may be due to variations in the type and content of thickening agent used. Unlike denture adhesives, gel-typeoral moisturizers consist of a base (mainly water) and a moisturing component such as glycerin, sorbitol, orhydrolyzed hydrogenated starch. Thickening agents such as CMC are present in small amounts,28,29 which may
explain why the initial viscosity of oral moisturizers is low.
The main reasons for using denture adhesives are to improve fit, comfort, chewing ability, and also to improve
patient confidence in wearing dentures.5,11 Therefore, the adhesive strength of the denture adhesive is the mostimportant factor for clinical use of these materials. According to the ISO standards,33 the adhesion strength mustbe 5 kPa or more. The adhesive strength of all denture adhesives used in our experiment was higher than 5 kPa,

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thus meeting the ISO standard. Therefore, all denture adhesives used in this study were acceptable for clinicaluse. The adhesive strength of the gel-type oral moisturizers decreased with immersion time; and the adhesivestrength of the cream-type denture adhesives increased with immersion time. According to several reports,
cream-type denture adhesives showed higher adhesive strength after application,2,4,10 due to water absorption by
the water-soluble polymer.34 These materials form water-soluble macromolecules which absorb water over timeand increase in viscosity, thus increasing the retention of the denture. According to Chew,4 denture adhesives
are most effective one hour after application. Therefore, if our study had continued measurements over a longer
time interval, the adhesive strength of the cream-type denture adhesives may have increased even more. The
major component of gel-type oral moisturizers is water, glycerin and sorbitol.28,29 These components are soluble
in water and hygroscopic by nature. This could explain why the adhesive strength of the oral moisturizers
decreased with immersion time. Since PGG has water as a base, it is thought that it is initially more soluble inwater than cream-type denture adhesives which use a grease component for the base. This may be the reason
why the adhesive strength of TGG increased until 1 minute after immersion, then decreased over the next 10
minutes.
The results of this study indicate that cream-type denture adhesives and oral moisturizers exhibit similar initialviscosity, but they possess different adhesion behaviors. Our study did not completely simulate clinical behavior
because the specimens were tested for viscosity in a dry state, and all adhesive strength tests were conducted
after immersion in distilled water. It is unknown whether these results can be generalized to other samples. To
overcome the limitations of the in vitro tests, artificial saliva should be used as an immersion solution. For a
more complete understanding of the differences in adhesion behavior between denture adhesives and oral
moisturizers, a study should be conducted to assess the influence of denture adhesives and oral moisturizers on
the measurement of bite force until denture dislodgement in complete denture wearers.
Our findings indicate that oral moisturizers provide the best properties for denture retention, stability andfunction. The adhesive strength of gel-type denture adhesive (TGG) was observed to decrease from its initialadhesive strength over the first 10 minutes. Dentists should understand the differences in the properties ofdenture adhesives and oral moisturizers, and should be careful to choose the most appropriate materials forclinical use.
Acknowledgment
This research was supported in part by a Grant-in-Aid (No. 21791899) for Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.

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Correspondence to:
Dr. Guang Hong
Liaison Center for Innovative Dentistry, Graduate School of Dentistry, Tohoku University
4-1 Seiryo-machi, Aoba-ku, Sendai, 980-8575, Japan
Fax: +81-22-717-8345 E-mail: hong@m.tohoku.ac.jp
Accepted August 24, 2011.
Copyright ©2011 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

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