Method for enhancing retention in complete denture bases

Masahiko Kikuchi, DDS, PhD, a Fazal Ghani, BSc, BDS, MSc, PhD, b and Makoto Watanabe, DDS, PhD c Tohoku University School of Dentistry, Sendai, Japan

Sta tement o f problem. Physical retention of a denture depends on adhesion of a salivary film to its fit- ring surface and supporting tissues. Adhesion is influenced by many factors. Purpose. This study examined the effect of the texture of the fitting surface on denture retention. Material and methods . According to the method developed, mucosal-supported palatal bases were made for 10 dentate subjects who had no obvious oral disease, history of allergy to dental materials, or palatal mucosal undercuts. A specially designed strain gauge force transducer and a pen-chart recorder were used to record forces that were needed to dislodge the bases from the palate. Forces were recorded 30 times (10/day) for each subject. Similar forces were recorded after the fitting surface of each base was uniformly air-particle abraded under 4 kg/cm 2 of pressure for 1 minute with 50-p,m grit alumina dust. Data were ana- lyzed with a 2-sample Student t test and a paired t test. Results. Substantial variations for all measurements were observed both between and within subjects. Notwithstanding, these variations, the mean retention of the bases significantly (/'<.05) increased by more than 2-fold when the fitting surface was air-particle abraded. These force values were similar to those recorded previously for well-fitting mucosal-supported palatal bases in a separate group of dentate subjects. Conclusions. While reinforcing the importance of good adaptation of the denture to the tissues, these findings also suggest that an additional improvement in denture retention can be accomplished after the fit- ting surface is air-particle abraded. (J Prosthet Dent 1999;81:399-403.)

C L I N I C A L I M P L I C A T I O N S

Because air-particle abrading the fitting surface significantly improved the retention of the test bases, this method might be useful in patients who complain of a lack of reten- tion for dentures that are otherwise weU-fitting and accurate.

D e n t u r e retention denotes the force required to completely remove a denture from its basal seat. 1 Influ- ence o f adhesive and cohesive forces, surface tension, atmospheric pressure, viscosity and volume o f saliva, and gravity on denture retention has been demonstrat- ed. 2-7 Denture retention by air depression between the denture and the mucosa could not be long-lasting because constant elasticity is not the histophysiologic feature of the mucosa. 8

A sufficient layer of saliva is essential for retention as a result of physical effects. 9-11 Many models have been devised to determine the relative importance o f various physical factors that act through the salivary film at the denture-tissue interface.lO,12,13 Denture retention is understood to be a function of saliva surface tension, its viscosity, the thickness o f the salivary film, the contact surface, and the saliva denture c o n t a c t angle.9,14,15

Presented at the 75th general session of the International Association for Dental Research and Exhibition, Orlando, Fla., March 1997.

aLecturer, Department of Geriatric Dentistry. bVisiting Scientist, Department of Geriatric Dentistry; and Assistant

Professor and Head, Department of Prosthetic Dentistry, Khyber College of Dentistry.

cprofessor and Head, Department of Geriatric Dentistry.

Mathematical models have demonstrated that dis- placement o f the contact line of the liquid film on the denture under the application o f dislodging force plays a predominant role in denture retention.S, 16 Therefore a modification o f dentures by making the fitting surface more hydrophilic and wettable may affect denture retention. The purpose of this study was to examine the effect o f texture o f the fitting surface on the adhesion o f saliva and its consequent clinical effect on denture retention.

M A T E R I A L A N D M E T H O D S

Healthy dentate subjects from the staff at Tohoku University School o f Dentistry, who had no obvious oral disease, history o f allergy to dental materials, or palatal mucosal undercuts, were invited to participate in this study. There was no a t tempt to standardize palatal form in patient selection. Their ages ranged from 25 to 31 years (mean age 27.2 years). Complete sets of data were collected from 10 subjects (7 men and 3 women) by including fresh recruits as replacements for those who left the experiment for various reasons.

A maxillary cast using dental stone (New Plastone, GC Corp, Tokyo, Japan) was prepared for each subject

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THE JOURNAL OF PROSTHETIC DENTISTRY KIKUCHI, GHANI, AND WATANABE

Fig. 2. Strain gauge force transducer.

50

4O

A

"5 o .

2o

10 r ~ = 0.9999

0 1 2 3 4 5

Force(N)

Fig. 3. Force-output relationship of transducer.

Fig. 1. Nonfitting surface (A) and fitting surface (B) of test base.

from impressions made with a stock tray and irre- versible hydrocolloid impression material (Aroma Fine Mixer Type, GC Cow). Autopolymerizing acrylic resin (Tray Resin II, Shofu Inc, Kyoto, Japan) was used to fabricate a standardized design mucosal-supported palatal base on each subject's maxillary cast according to a previously developed method. 17 Adaptation of each base to its cast was subsequently perfected by relining its fitting surface with quick-setting autopoly- merizing acrylic resin (Unifast, GC Cow). Each of the mucosal-supported test prostheses extended to the junction of the hard and soft palates posteriorly, and to within 3 mm of the palatal gingival margins. With quick-setting autopolymerizing acrylic resin, a string was secured in the palate of each base to detach it from the subject's palate, and hence to record the amount of force required for dislodgment. Figure 1 illustrates var- ious aspects of the test bases.

A specially designed strain gauge force transducer (Fig. 2) was made to record the force required to dis- lodge the base from the subject's palate. Forces were traced with a pen-chart recorder. During calibration, the transducer showed a highly linear relationship between the applied force and voltage output (Fig. 3). The transducer was capable of recording forces much higher than those expected under the experimental conditions. The transducer was always calibrated before and after each test session, and no error of any kind was noted in the testing system. None of the subjects expe- rienced any discomfort from the level of forces needed to dislodge the test bases from their palates.

R e t e n t i o n force m e a s u r e m e n t

Each subject was asked to sit comfortably in a den- tal chair with their head on the headrest and the occlusal plane of the maxillary teeth parallel to the floor. The subjects were trained to manipulate the base in their mouth in a consistent manner with uniform digital pressure until it occupied a comfortable and accurate position (Fig. 4, A). One minute was then allowed for the base to reach a stable equilibrium posi- tion in relation to the palatal mucosa before it was detached from the palate (Fig. 4, B). For each subject,

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0.5

1.5 z =o o

1.0

l

2 0

Before air alDrasion

l / After air abrasion

Fig. 5. Mean retention forces (N) before and after air-particle abrasion (N = 10).

Fig. 4. Base in subject's mouth (A) and its detachment from palate and force recording (B).

on every occasion, the force required to dislodge the test prosthesis from the palate was recorded 10 times, and it was repeated on 3 days. Thirty force values were obtained for the test prosthesis for each subject. The same test regimen was repeated for each subject after the fitting surface o f the prosthesis was uniformly abraded under 4 kg / cm 2 of pressure for 1 minute with 50 ~tm grit alumina dust (Power Blast 50 N, Okamoto- Shiken, Shiga, Japan).

S ta t i s t ica l analysis

To compare the retention forces o f the test base before and after air-particle abrasion, a 2-sample Stu- dent t test for individual subjects and a paired t test for the whole group were used. Statistical significance was defined at a 5% level of significance.

R E S U L T S

The mean forces recorded before and after air-parti- cle abrading the fitting surface of the bases for individ- ual subjects are shown in Table I. Mean forces for the whole group in both conditions are depicted in Figure 5. There were substantial variations in forces both between and within subjects for all measurements.

Notwithstanding these variations, the mean forces increased after the fitting surface o f the bases was abraded, except for 1 subject. The forces required to dislodge the bases before air-particle abrading ranged from 0 to 2.41 N, whereas those required after air-par- ticle abrading were between 0 and 4.04 N. In 7 sub- jects, the retention forces of the air-particle abraded bases were significantly higher than those recorded before treatment, whereas a significant decrease after air-particle abrasion was seen in 1 subject.

Statistical analyses of the combined group data before and after t reatment showed that air-particle abraded bases required significantly greater forces (Table I). Retention after air-particle abrading the fit- ting surface of the bases was up to 5.49-fold greater than that recorded before air-particle abrading. On average, air-particle abrading increased retention by more than 2-fold (Fig. 5).

DISCUSSION

In our study, the effect o f air-particle abrasion on retention forces of the test bases was evaluated and the air-particle abraded bases demonstrated significantly higher retention than those before treatment. The mucosal-supported palatal test bases were used in a previous study to record retention due purely to phys- ical forces with no contribution from any mechanical undercuts or muscular interference. 17 These bases were designed to simulate a conventional complete denture base. However, in clinical situations, the retent ion forces o f well-fitting maxillary complete dentures may be even higher than the values recorded for the bases used in our study. The force transducer was capable and reliable for measuring the forces required to dislodge the bases from the palates of the subjects in our study. The force-output relationship was highly linear (Fig. 3).

There were substantial variations both between and within subjects for all of the measurements of retention

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Table I. Mean retention forces, ranges (N), standard deviations, and ratios of the retention forces before and after air-particle abrading the fir ing surface of the test bases

Before air-particle abrasion After air-particle abrasion

Subject Mean Range (SD) Mean Range (SD) Ratio

1 0.17 0.01-0.71 (0.18) 0.93 0.30-2.25 (0.45) ** 5,49

2 1.00 0.14-2.41 (0.61) 2.35 1.01 -4.04 (0.75) ** 2.35

3 0.21 0.01-0.91 (0.25) 0.22 0.01-0.71 (0.20) NS 1.02

4 0.09 0.00-0.45 (0.09) 0.26 0.00-1,06 (0.23) ** 2.76

5 0.20 0.01-0.64 (0.16) 0.14 0.01-0.36 (0.11) NS 0,71

6 0.52 0.05-1.85 (0.48) 1.19 0.27-2.70 (0.64) ** 2.78

7 0.19 0.00-0.90 (0.23) 0.02 0.00-0.21 (0.05) ** 0.13

8 0.27 0.01-0,76 (0.20) 0.66 0.01-1.70 (0.45) ** 2.45

9 0.49 0.01-1.16 (0.28) 0.66 0.31-1.34 (0.27) * 1.35

10 0.28 0.01-0.79 (0.23) 0.59 0.27-1.16 (0.24) ** 2.12

Total 0.34 0.00-2.41 (0.27) 0.70 0.00-4.04 (0,69) * 2.05

For each subject, (I0 subjects). *P<.05; **P<.01;

the mean values are based on 30 measurements (10/day), and the mean values for the whole group in each condition are based on 10 forces

NS = not significant.

forces in this study as evidenced in the high standard deviations. This may be due to variations in the seating force applied by the subjects and its consequent effect on retention of the base, as noted by Ow and Beam. 18 There was a decrease in force noted for 1 subject after air-particle abrasion in our study. The variation of the seating force by this subject may have greatly influ- enced the result because the retention of the base for this subject was rather smaU from the start. Variations in palatal dimensions and structure, such as surface area, length, depth, and angulation of the palates, can also influence the ultimate retention of a test base in situ. It is worth noting that variations of this extent have been reported in clinical studies that involve the measurement of oral forces) 9 Retention forces of bases used in our study were within the range recorded by others,17,18 and our results could even be compared with those values recorded by Tallgren 2~ for maxillary complete dentures, which were in the order of 3.9 to 4.7 N for the first year of denture use.

The limit of effectiveness of the salivary film in retaining the denture base might depend on the nature of its adhesion to the fitting surface of the base. It was hypothesized that an altered fitting surface may give better results than a conventional fitting surfacc of the base made after routine processing procedures. As a result, air-particle abrasion produced a uniform increase in roughness and a consequent increase in the surface area of the test base and improved the adhesion of saliva to the surface.

Our findings are in agreement with those of Mon- sencgo et al,]6 who showed that acrylic resin disks with air-particle abraded surfaces exhibited greater contact-angle hysteresis, namely, a greater difference between the advancing contact angle (0A) and the receding contact angle (OR) than untreated acrylic

resin disks. In explaining the mechanism of this increase in contact-angle hysteresis, they noted that air-particle abrasion made the surface porous, and thereby encouraged saliva droplets to be entrapped in these pores, which rendered the resin surface more hydrophilic and wettable. Consequently, more resis- tance would be offered by the meniscus to recede at the denture-tissue interface.

A possible drawback of this procedure is that microbes may adhere to a fitting surface that has been roughened by air-particle abrasion. In a laboratory study, Yamauchi et al21 examined the effect of various resin denture bases with different surface textures on the adherence of microorganisms. They found that Candida albicans adhered most strongly to bases with a roughened surface. Although clinical trials are need- ed to confirm the in vitro findings, it is always advisable to strongly emphasize the importance of oral and den- ture hygiene in patients who wear such prostheses.

CONCLUSIONS

The results of this study indicated that air-particle abrading the intaglio at bases significantly improved the base retention (P<.01 to .05) in 7 of 10 subjects.

REFERENCES

1. Lindstrom RE, Pawelchak J, Heyd A, Tarbet WJ. Physical-chemical aspects of denture retention and stability: a review of the literature. J Prosthet Dent 1979;42:371-5.

2. Bril[ N. Factors in the mechanism of full denture retention--a discussion of selected papers. Dent Pract Dent Rec 1967;18:9-19.

3. Mack AO. Full dentures. Bristol: John Wright & Sons, Ltd.; 1971. p. 94. 4. Murray MD, Darvell BW. The evolution of the complete denture base.

Theories of complete denture retention--a review. Part 1. Aust Dent J 1993;38:216-9.

5. Murray MD, Darvell BW. The evolution of the complete denture base. Theories of complete denture retention--a review. Part 2. Aust Dent J 1993;38:299-305.

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6. Murray ME), Darrell BW. The evolution of the complete denture base. Theories of complete denture retention--a review. Part 3. Aust Dent J 1993;38:389-93.

7. Murray MD, Darrell BW. The evolution of the complete denture base. Theories of complete denture retention--a review. Part 4. Aust Dent J 1993;38:450-5.

8. Monsenego P, Proust J. Complete denture retention. Part I: physical analy- sis of the mechanism. Hysteresis of the solid-liquid contact angle. J Pros- thet Dent 1989;62:189-96.

9. Ostlund SG, Saliva and denture retention. J Prosthet Dent 1960;10:658- 63.

10, Craig RG, Berry GC, Peyton FA. Physical factors related to denture reten- tion. J Prosthet Dent 1960;10:459-67.

1 I. Kawazoe Y, Hamada T. The role of saliva in retention of maxillary com- plete dentures. J Prosthet Dent 1978;40:131-6.

12, Tyson ION. Physical factors in retention of complete upper dentures. J Prosthet Dent 1967;I 8:90-7.

13. O'Brien WJ, Base retention. Dent Olin North Am 1980;24:123-30. 14. Stanitz JD. An analysis of the part played by the fluid film in denture reten-

tion. ] Am Dent Assoc 1948;37:168-72. I S. Blahova Z, Neuman M. Physical factors in retention of complete dentures.

J Prosthet Dent 1971;25:230-5. 16. Monsenego P, Baszkin A, Costa ML, Lejoyeux J. Complete denture reten-

tion. Part lh wettability studies on various acrylic resin denture base mate- rials. J Prosthet Dent 1989;62:308-12,

17. Ghani F, Picton DC, Likeman PR. Some factors affecting retention forces with the use of denture fixatives in vivo. Br Dent ] 1991;171:15-21.

18. Ow RK, Beam EM. A method of studying the effect of adhesives on den- ture retention. J Prosthet Dent 1983;50:332-7.

19. Likeman PR. Some investigations on lingual responses to a dental pros- thetic appliance. [PhD Thesis.] London: University of London; 1985.

20. Tallgren A. Longitudinal studies on denture retention. Odont Tskr 1959; 67:314-35.

21. Yamauchi M, Yamamoto K, Wakabayashi M, Kawano J. In vitro adherence of microorganisms to denture base resin with different surface texture. Dent Mater J 1990;9:19-24.

Reprint requests to: DR M~AHIKO ~IKUCHL DEPARTMENT OF GERIATRIC DENTISTRY TOHOKU UNIVERSITY SCHOOL OF DENTISTRY 4-1, SEIRYO-MACHI, AOBA-KU SENDAl 980-8575 JAPAN FAX: 81-22-717-8399 E-MAiL:kikuchi@mandib[e.dent.tohoku.ac.jp

Copyright �9 1999 by The Editorial Council of The Journal of Prosthetic Dentistry.

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