Yoneyama et al.

Int Chin J Dent 2010; 10: 17-21.

Pressure distribution of mandibular complete denture using soft
lining materials
Yoshikazu Yoneyama, DMD, PhD, Toshiaki Tojyo, DMD, PhD, Chikahiro Ohkubo,DMD, PhD, and Toshio Hosoi, DDS, PhD
Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine,
Yokohama, Japan
Purpose: This study evaluated the effectiveness of pressure distribution under dentures using two types of soft
lining materials to improve denture stability and comfort.
Materials and Methods: Two experimental dentures were duplicated from an existing complete mandibulardenture. Denture base resin was shaved from the basal surface of each denture to allow for 1- and 2-mm thickacrylic (COE-Soft) or silicone (Soft Relining) lining materials to be affixed. Four microminiaturized pressure
sensors were fixed to the intaglio surface of the denture bases to monitor bite pressure at four locations, namely,
the bilateral first molars and first premolars. Each degree of bite pressure was measured five times under 49, 98,
147, and 196 N loads for 5 s. All data were statistically analyzed using ANOVA/Tukey’s test at α=0.05.
Results: As the loads increased, the total pressure at the four locations proportionally increased for boththicknesses. The 2 mm-thick silicone lining showed a significantly lower pressure burden than the 1 mm-thicksilicone lining (p<0.05). However, there was no difference in the pressure burden between the 1- and 2-mm
acrylic lining materials (p>0.05).
Conclusion: Acrylic lining materials should be used for difficult cases of mandibular edentulous patients whensufficient lining space is not available. (Int Chin J Dent 2010; 10: 17-21.)
Key Words: complete denture, pressure distribution, soft lining material

Introduction
The number of elderly people in Japan has increased over the years, and this circumstance has led to anincreasing number of severely edentulous patients. In these patients, the alveolar ridge bone height tends todecrease with the thinning of the mucosa. Because such conditions are likely to cause pain, the masticatory
pressure must be dispersed and/or decreased. For this purpose, clinical countermeasures, namely, increasing thesize of the denture base, decreasing the vertical dimension, and using lingualized occlusion, have been applied.1
However, there are some patients whose pain does not diminish even if normal clinical procedures are carriedout.
Soft lining materials are often affixed to denture base intaglio surfaces in order to distribute the occlusal force
more evenly during mastication and to reduce the overall pain. Silicone and acrylic soft lining materials are
currently available for long-term use. The use of soft lining materials is not a new concept, and various studies
focusing on bacteriology2-4 and physical science5-8 have been reported.

However, there is little detailed

information regarding the use of soft lining materials and the effectiveness of pressure distribution under various
loads of biting force.9,10 The purpose of this study was to evaluate the effectiveness of pressure distribution
using two different thicknesses of two types of materials. Four pressure sensors were placed on a complete
mandibular denture, and the pressure was measured under several loads of biting force using a simulation model.

Materials and Methods
Experimental denture constructionUsing Copy Flask H.T. (Towa Giken, Tokyo, Japan), two experimental dentures were duplicated from anexisting denture that the selected patient had been wearing for five years.

Following the manufacturer’s

instructions, an autopolymerized resin (PalaXpress, Heraeus Kulzer, Hanaeus, Germany) was poured and cured

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Int Chin J Dent 2010; 10: 17-21.

at 55˚C at an atmospheric pressure of 0.27 kPa for 30 minutes. The two duplicate dentures were mounted on anarticulator (EM Relining Articulator, YDM Corp., Tokyo, Japan). An imaginary occlusal plane for experimental
dentures was created parallel to the articulator’s basal surface. The duplicate dentures were removed from thearticulator after their proper positions were recorded, and 1 mm of basal resin was then removed from theintaglio surface of one denture and 2 mm was removed from the intaglio surface of the other denture. Fourminiature pressure sensors (PS-10KA, Kyowa Electronic Instruments Co., Ltd., Tokyo, Japan) were positioned
in four locations: left molar (LM), left premolar (LP), right premolar (RP), and right molar (RM), as shown in
Fig. 1.

Fig. 1.
Fig. 2.

1
2
Experimental denture. Pressure sensors were placed in four locations:left molar (LM), left premolar (LP), right premolar (RP), and right molar (RM).
Loads were applied to the experimental dentures using a digital force gauge.

Two soft lining materials were used in this study (Table 1). Autopolymerized lining materials were used dueto the ease of sensor installment at lower temperatures. The soft lining materials were applied to the target areas
and mounted on the articulator again so that the 1- and 2-mm thick lining materials were uniformly attached tothe intaglio surface. All lining materials, i.e., the 1- and 2-mm-thick acrylic and silicone, were polymerized at35˚C.
Table 1.

Materials used in this study.

Material

CodeType

Manufacturer

CuringType

Batch No.

Batch No.
(Primer)

COE-SoftCS

Acrylic

GC America, USA

Self cured

802211
70320-Soft Relining

SR

Silicone:ad.

Tokuyama, Tokyo,
Japan

Self cured

77268

76868

Measurement of pressure distribution
A brass plate (2 mm thick) was fixed to the experimental denture parallel to the occlusal plane. Using a
digital force gauge (DFG-50, Imada Co., Ltd., Toyohashi, Japan), loads simulating various biting forces wereapplied at the intersection of the midline and the line of the bilateral first molars on the plate (Fig. 2).	 	 Each load
was measured under each weight phase in 49 N increments of 49, 98, 147, and 196 N for 5 s. Each measurement
was performed five times, and the sensor results were monitored using a personal computer (9153C, Hewlett

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Int Chin J Dent 2010; 10: 17-21.

Packard, Palo Alto, CA, USA). All the data were analyzed using a two-way analysis of variance and Tukey’s
multiple comparisons test at a significance level of α=0.05.

Results
The pressure distribution at all loading phases of the 1-mm-thick CS acrylic and SR materials is shown in Fig.
3. Similarly, comparisons of the 2-mm-thick lining materials are depicted in Fig. 4. Figure 5 shows the meanpressure of the four sensors at all loading phases of the 1- and 2-mm-thick CS and SR silicone lining materials.
Regarding the pressure distribution of the 1-mm-thick materials, the silicone showed remarkable differencesin the highest and lowest reading for each sensor, whereas the 1-mm acrylic material demonstrated only smalldifferences. The tendency for the pressure distribution for the 2-mm-thick silicone and acrylic lining materials
was similar to that of the 1-mm lining materials.
The overall pressure burden for both the 1- and 2-mm soft lining materials proportionally increased as the load
weight increased (Fig. 5). The total pressure of the SR silicone lining was significantly greater than that of CS at
all loads (p<0.05). The two-mm-thick SR showed significantly less mean pressure than the 1-mm-thick SR(p<0.05). Little variance in pressure burden was found using the acrylic material after analyzing both the 1- and2-mm lining materials (p>0.05) (Fig. 5).

Fig. 3.

Comparison of pressure distribution for 1-mm-thick CS and SR materials.
Left: CS acrylic, Right: SR silicone.

Fig. 4.

Comparison of pressure distribution for 2-mm-thick CS and SR materials.
Left: CS acrylic, Right: SR silicone.

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Fig. 5.

Int Chin J Dent 2010; 10: 17-21.

Total pressure of the four sensors at all loading phases of the 1- and 2-mm-thick
CS and SR lining materials.

Discussion
For fully or partially edentulous patients who have thin mucosa and height loss of the alveolar ridge bone,
both relief from pain and denture stability have resulted from the use of soft lining materials.9,10 If patients havea low pain threshold, attaching soft lining materials with different thicknesses would provide even more pressure
distribution and pain reduction. In particular, the viscoelasticity of the soft lining material would contribute toimproving the pressure distribution and pain reduction.9,10 The soft lining materials used in this experiment havegeneral viscoelasticity for long-term use and are commercially available. The occlusal force of the averagedenture wearer is approximately 294 N;11 however, the load pressure used in this study was set at a 196 N
max-load pressure because edentulous patients have a lower pain threshold.
In this study, the four miniature pressure sensors were placed on the intaglio surface of the experimental
dentures, and the soft lining materials were then attached using an articulator. This laboratory procedure canaccurately reproduce the alveolar ridge shape and provide a uniform lining. A patient with a flat alveolar ridge
was specifically selected because the flat shape allowed the sensors to be easily installed. Furthermore, the flatridge also helped make it easy to compare the pressure distribution of both lining materials. The angle of thesensor positioning on dentures, either flat or at a slight angle, caused variations in the overall sensor pressure
value. As for the data recorded using the 1-mm-thick silicone material, the pressure distribution was notsufficient. The 2-mm silicone material might have given adequate comfort, but not as much comfort or pressure
distribution compared to both the 1- and 2-mm acrylic linings. The acrylic material generally provided a higher
level of support for both comfort and pain reduction. Both the 1- and 2-mm acrylic linings showed nearly thesame pressure distribution, producing similar levels of comfort.

Moreover, for patients who don’t havesufficient denture space, using even a 1-mm thick acrylic lining can make a big difference in overall denture
comfort.

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Correspondence to:
Dr. Yoshikazu Yoneyama
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: yoneyama-y@tsurumi-u.ac.jp
Accepted February 22, 2010.

Copyright ©2010 by the International Chinese Journal of Dentistry.

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