Adhesion Gregory

properties red denture L. Polyzois,

School of Dentistry,

DDS,

University

of resilient resins DrDent,

lining

materials

bonded t

MScDa

of Athens, Athens, Greece

This study compared the adhesive strength of three resilient denture lining materials with different chemical compositions when bonded to visible light-cured (VLC) denture base resin. Shear adhesive strength was evaluated using a simple overlap-joint model. Three different bonding agents were used and the effect of water on the bonding stren.gth was evaluated by a series of samples tested after storage for 4 months. The findings showed that all of the lining materials were acceptable for clinical use but that water storage reduced their bond strength to VLC resin. (J PROSTHET DENT 1992;68:854-8.)

esilient

lining

materials

for removable

dentures

have provided a topic for discussion, research, and controversy for many decades. Resilient lining materials for dentures are products that are applied to the intaglio surface of dentures for the purpose of achieving a more equal distribution of the load and a reduction of local point pressures.i-3 The potential clinical value of using resilient lining materials in removable dentures for reducing the loading of edentulous ridges and improving load distribution is considerable. This is reflected from clinical surveys4a5 that have reported a strong patient preference for resilient linings as opposed to hard denture base. However, the use of resilient linings is often discouraged because of reported inadequate physical properties.6 Continued development of these materials has improved these properties and it is reported that an acceptable clinical life of several years can now be expected.* The desirable properties of resilient denture linings are widely recognized and many studies have been conducted over the years. The properties of interest are7,s: compatibility with oral tissues, dimensional stability, inhibition of fungal growth, wettability, rupture properties, friction characteristics, and adhesion to the denture base. The most common reason for failures of resilient linings in removable dentures is the separation of these linings from the denture base. Therefore poor adhesive properties are one of the serious defects of these materials in clinical practice.6a 9 In the last 10 years, a large number of experimental or commercially available resilient lining materials have been developed.10-13 New developments in polymer chemistry as applied to the dental profession led to the manufacture of new resilient lining materials or to modifications of existing formulas to improve their properties. The development and increasingly wider acceptance and use of visible lightaAssistant Professor, Department Removable Prosthodontics. 10/I/39548

854

of Prosthodontics,

Division of

Table I. Resilient resin investigated

lining materials and denture base

Product

Soft liner Novus

Flexor

PERform

Soft

TYW

Manufacturer

Polyphosphazine fluoroelastomer (heat-cured) Polydimethylsiloxaneperfluoralkanoldimethacrylate (heat-cured) Urethane acrylates Ethyl methacrylates (visible light-cured)

Hygenic Corp., Akron, Ohio

Denture base resin Triad Urethane dimethacrylate (visible light-cured)

Weil-Dental GmbH, Rosbach, Germany Whaledent GmbH, Friedberg, Germany Dentsply International Inc., York, Pa.

cured (VLC) denture base resins was also a major breakthrough that occurred in the last few years.14 This study investigate the adhesion characteristics of three recently introduced resilient denture lining materials to a VLC denture base resin material. MATERIAL

AND

METHODS

The resilient denture lining materials and VLC denture base resin investigated in this study are shown in Table I. The resilient lining materials were selected to include the products having new chemical compositions and processing methods. To study the bonding strength of these materials to VLC denture base resin, the shear test using a simple overlapjoint model was used. For the two heat-cured resilient liners, dental stone molds in denture flasks were prepared by investing patterns of the overlap-joint model. The patterns were made

NOVEMBER1992

VOLUME68

NUMBER5

ADHESION

OF RESILIENT

LINING

MATERlALS

RES\LIENT

LINING

MATERIAL

TRIAD DENTURE D A-IS-

. 13 nm

CZDZS

Fig.

mm

by using two 46 x 13 x 3 mm blocks of acrylic (Perspex, ICI Ltd., Welwyn Garden City, England) fastened together as shown in Fig. 1. Processing of VLC resilient lining material necessitated modification of the molding procedure. Therefore the upper half of a small crown and bridge flask was replaced by a transparent matrix to facilitate light polymerization of the liner. The overlap-joint pattern invested in dental stone on the lower part of the flask was placed in a vacuum-forming unit (Biostar, Sheu-Dental, lserlohn, Germany) and a 2 mm thick clear plastic sheet (Biocryl, Sheu-Dental) was vacuum-formed onto the lower part of the flask.i”s i6 The heae-cured resilient liners were packed and processed against precured as processed Triad resin specimens (Dentsply International Inc., York, Pa.). The rectangular VLC specimens were prepared in the stone molds in denture flasks and were cured in the Triad II unit (Dentsply International) for 6 minutes on one side, removed, turned 180 degrees, and cured for an additional 5 minutes-a total of 11 minutes. The application of bonding agents to the bonding area of the VLC resin specimens was made according to the manufacturer’s instructions. Novus and Flexor liners were processed in a water bath for 8 hours at 74O C (165.2’ F) and for 2 hours at 100’ C (212“ F), respectively. For the light-cured lining material (PERform Soft) and the Triad VLC bonding agent, the liner was processed against precured as processed VLC specimens in the crown and bridge flask. The application of a granulated adhesive (DS-ADP2) (Whaledent GmbH) first required the polymerization of the light-cured lining material in the crown and bridge flask followed by curing of the VLC resin against it. The light-cured lining material was processed in a Triad II curing unit for 1.7 minutes (Fig. 2). Ten test specimens were made for each resilient liner/ adhesive combination-a total of 50 specimens. After removal from the flasks, the excess material was trimmed and ~5 of the specimens were tested immediately. The

THE

JOURNitk

OF I’ROSTHETIC

DENTISTRY

F=Ci=46mm

1. Diagram of overlap-joint

Ez23

lv LC) RESIN

mm

model.

Fig. 2. Overlap-joint sample of VLC resilient lining material and VLC denture resin.

other 25 specimens were placed in distilled water at 37 f lo C for a period of 4 months before being tested. The samples were tested for shear tension on a Monsanto testing machine (Model T10, Monsanto Ltd., Swindon, England) at a constant rate of 50 mm/min until the lining material separated from the VLC resin specimens.

RESULTS Bonding strength measurements of the three resilient liners (not immersed and immersed) in water are shown in Table II and are presented graphically in Fig. 3. The type of bond failure is also presented in Table III. A two-factor analysis of variance and Tukey’s HSD test for multiple comparisons were used to analyze the results. Statistical analysis is summarized in Table IV.

DISCUSSION The most common dentures is the failure liner and the denture son the effect of water

reason for failure of resilient-lined of adhesion between the resilient base in clinical use.6,g For this reaon the adhesive properties of the re-

855

POLYZOH

Shear adhealveatrenath NPal 0.6

F-FB

F-TB

P-TB

P-PB

N-TB

F’ig. 3. Strength of bond of resilient liners to Triad denture base material. Bar chart shows mean adhesive strength before and after immersion in water for 4 months. F-TB, Flexor + Triad VLC bonding agent; F-FB, Flexor + Flexor bonding agent; P-TB, PERform Soft + Triad VLC bonding agent; P-PB, PERform Soft + PERform granulated adhesive (DS-ADPZ); N-TB, Novus + Triad VLC bonding agent.

Table II. Bonding strength (MPa) of resilient materials to VLC denture resin F-TB

Not immersed

(n = 25) Immersed (n = 25)

F-FB

P-TB

P-PB

lining

III.

Data on the type of bond failure F-TB

F-FB

P-TB

P-PB

N-TB

N-TB

0.222" 0.294 0.254 0.234 0.418 (0.035) (0.036) (0.028) (0.032) (0.020) 0.216 0.256 0.226 0.146 0.370 (0.048) (0.015) (0.032) (0.055) (0.010)

*Mean values in megapascals. Numbers in parentheses are SD. F-T& Flexor f Triad VLC bonding agent; F-F& Flexor + Flexor bonding agent: P-T& PERform Soft + Triad VLC bonding agent; P-P& PERform Soft + PERform granulated adhesive (DS-ADPZ); N-73, Novus + Triad VLC bonding agent.

silient lining materials to denture base materials is of utmost importance in their final clinical success. The results revealed a statistically significant (p = 0.000089) effect of water storage on the bond strength (Table IV). After storage in water for 4 months, all the materials showed a significant reduction in bond strength (Table II and Fig. 3). This finding agrees with the conclusions of earlier reports by Amin and Ritchie,i7 Amin et al.,ls and Wright.19 The reduction in bond strength is the result of swelling and stress buildup at the bond interface or of changing the viscoelastic propierties of the resilient lining material, rendering the material stiffer and thus transmitting the external loads to the bond site.18sz0 Analysis of variance and Tukey’s test showed that the strongest bond (p < 0.05) was between the Novus lining

856

Table

Not 100%AdlOO% AdlOO% CohlOO%Coh 60% Coh immersed 40% Ad Immersed 100%AdlOO% AdlOO% Coh 100%Ad 100% Coh Ad, Adhesive failure; Coh, cohesive failure; other abbreviations II.

as in Table

material and the Triad base material when a Triad bonding agent (N-TB; see Table II for letter codes) was used. The superiority of Novus lining material was also indicated by the bond failure’s being mainly cohesive in nature (Table III) before and after immersion in water. The light-cured lining material PERform showed greater (p < 0.05) bonding strength to Triad resin when the Triad bonding agent was used (P-TB) instead of the manufacturer’s granulate bonding agent (P-PB). In both cases the bond failure was of a cohesive type, with the exception of immersed granulate bonding agent samples, which failed adhesively (Table III). These samples also showed the lowest bond strength (Table II and Fig. 3). The granulate type bonding agent (mechanical bond) seems to be more sensitive to water storage compared with other agents used in the study. Flexor resilient soft lining material exhibited similar bond strengths to the PERform resilient soft lining material, whereas it failed adhesively at all times (Tables III and IV). It seems that the rupture properties of Flexor were superior to those of PERform lining materials.

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1992

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ADHESION

Table

OF RESILIENT

LINING

MATERIALS

IV. Analysis of variance (ANOVA) Source

ss

Resilient liner/adhesive Water storage Interaction Error Total

0.251 0.022 0.0091

Tukey’s

HSD

summary and Tukey’s test results df

MS

4 1

0.063 0.022

4 40 49

0.046 0.0327

0.00228 0.00114

F

55.038 18.975 2.006

p Value

0.0000 0.000089 0.1121

NS

test N-TB

F-FB

P-TB

F-TB

P-PB

(HSD = 0.040)

Groups joined by horizontal lines are not significantly different at the 95% confidence level. SS, Sum of squares; MS, mean square; other abbreviations as in Table II.

In 1989 Khan et al.sO conducted a study using a pure tension test with cylindrical specimens of Triad denture base material and three resilient lining materials (TruSoft, Esscheem, Molloplast-B). They used only the Triad VLC bonding agent and reported that all the materials tested bonded sufficiently to Triad denture base material so as to be considered clinically acceptable. A range of separation forces from 21.4 to 193.5 lb (95.2 to 860.7 N) was reported in their study. In this study, the range of separation forces was from 29.5 to 128.4 N. A direct comparison of the two studies cannot be made because of the different mechanical tests and research protocols used. However, it has been reported by Craig and Gibbonszl that an adhesive value of 10 psi is satisfactory for the clinical use of the resilient lining materials. In this study, all the materials tested showed adhesion values greater than 0.07 MPa, a value equivalent to that reported by Craig and Gibbons.

CLINICAL IMPLICATIONS CONCLUSIONS

AND

The analysis of the adhesive properties of the resilient lining materials to a VLC denture resin showed that they had differing adhesive characteristics depending on the chemistry, physical properties, mode of polymerization, and the bonding agent used. The results of this investigation showed that the bond strength values were reduced after storage in water for 4 months. Considering the criterion of bonding strength only, all the liners used are acceptable for clinical use. Novus, a polyphosphazine fluoroelastomer lining material, showed the highest values for bonding strength and had mainly cohesive failures. Both Flexor and PERform resilient lining materials exhibited quite similar bond strengths, whereas the first failed adhesively and the second failed cohesively, indicating a weak resistance of PERform to external loads. The bonding agents used in this study seem to be acceptable with the exception of the granulated type supplied with the VLC resilient lining material, which was af-

THE

JOURNAL

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DENTISTRY

fected most by prolonged water storage. It must be pointed out that although laboratory studies simulating clinical conditions showed good bonding characteristics, a clinical study may prove disappointing where bond failures are concerned. Resilient lining materials can only be realistically tested in the mouth. We thank Dr. P. Lagouvardos for statistical consultation and analysis.

REFERENCES 1. Mack PJ. Denture soft lining: materials available. Aust Dent J 1989;34:517-21. 2. Demetriou PP, Polyzois GL, Andreopoulos AG. The compressive creep of soft liners. Clin Mater 1988;3:163-70. 3. Brown D. Resilient soft liners and tissue conditioners. Br Dent J 198&X4:357-60. 4. Schmidt WF, Smith DE. A six-year retrospective study of MolloplastB-lined dentures. Part II. Liner serviceability. J PROSTHET DENT 1983;50:459-65. 5. Makilti E, Honka 0. Clinical study of a heat-cured silicone soft lining material. J Oral Rehabil 1979;6:199-204. 6. Wright PS. The success and failure of denture soft-lining materials in clinical use. J Dent 1984;12:319-27. 7. Wright PS. Composition and properties of soft lining materials for acrylic dentures. J Dent 1981;9:210-23. 8. Suchatlampong C, Davies E, van Fraunhofer JA. Frictional characteristics of resilient lining materials. Dent Mater 1986;2:135-8. 9. Wright PS. A three-year longitudinal study of denture soft lining materials in clinical use. Clin Mater 1986;1:281-9. 10. Hayakawa I, Kawae M, Tsuji Y, Masuhara E. Soft denture liner of fluoroethylene copolymer and its clinical evaluation. J PROSTHET DENT 1984;51:310-13. 11. Parker S, Braden M. New soft lining materials. J Dent 1982;10:149-53. 12. Farris CL, Gettlemen L, Rawls HR. Improvement of bonding and strength of polyphosphasine elastomer for denture liner [Abstract]. J Dent Res 1982;61:285. 13. Casper RA, Dunn RL, Lewis DH. Characterization of new biomedical polymers as soft denture liners [Abstract]. J Dent Res 1982;61:285. 14. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthodontics. J PROSTHET DENT 1986; 56:497-506. 15. Tan HK, Brudvik JS, Nicholls JJ, Smith DE. Adaptation of a visible light-cured denture base material. J PROSTHET DENT 1989;61:326-31. 16. Triad VLC System technique manual. York, Pa.: Dentsply International, York Division, 1986. 17. Amin WM, Ritchie GM. The effect of water on the bonding properties of soft lining materials to acrylic bases. Proc Eur Prosthodont Assoc 1981;4:144-49.

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POLYZOIS

18. Amin WM, Fletcher AM, Ritchie GM. The nature of the interface between polymethylmethacrylate denture base materials and soft lining materials. J Dent 1981;9:336-46. 19. Wright PS. Characterization of the adhesion of soft lining materials to poly(methy1 methacrylate). J Dent Res 1982;61:1002-5. 20. Khan Z, Martin J, Collard S. Adhesion characteristics of visible lightcured denture base material bonded to resilient lining materials. J

Reprint requests to: DR. GREGORY POLYZOIS DEPARTMENT OF PROSTHODONTICS,SCHOOL OF DENTISTRY UNIVERFJTY OF ATHENS 2 THIVON STREET 11527 ATHENS, GREECE

PROSTHETDENT1989;62:196-200. 21. Craig RG, Gibbons P. Properties of resilient denture liners. J Am Dent Assoc 1961;63:382-90.

NOVEMBER

1992

VOLUME 68 NUMBER 5

Adhesion properties of resilient lining materials bonded to light-cured denture resins.

This study compared the adhesive strength of three resilient denture lining materials with different chemical compositions when bonded to visible ligh...
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