Improving the retention of complete dentures

Improving Sheldon Michael

the retention

Winkler, D.D.S.,* 1. Ryczek, B.S.***

of complete

Harold

R. Ortman,

dentures D.D.S.,**

and

State University of New York at Buflalo, School of Dentistry, Bufalo, N. Y.

1

he adhesive action of a thin film of saliva between the oral mucosa and the inner (basal) surface of a complete denture is recognized as one of the principle sources of denture retention. The retaining force due to capillarity (capillary attraction) is directly proportional to the surface tension of the fluid film, the area of solid surfaces, and the receding contact angle of the liquid to the solid, and it is inversely proportional to the thickness of the fluid film. Therefore, retention increases as the surface tension of the saliva increases, as the denture becomes more wettable, and as the area of contact increases. As the space between the denture and the oral mucosa increases, the retention decreases. The resistance of acrylic resin to surface wetti.ng, due to its low surface energy, has been realized since its introduction as a denture base material. In an effort to increase its wettability and hence its retention, various fillers and surface treatments have been proposed. This study was done to separate supposition from fact concerning (1) a new denture base material that is supposedly completely hydrophilic,+ (2) depositing an ultrathin layer of silicon dioxide on the denture base,$ and (3) sandblasting the denture base with various substances for different periods of time. All of these methods seem to offer promise of improving retention. CONTACT-ANGLE

MEASUREMENT

If a small amount of liquid is placed on a solid surface and if it does not spread, a drop is formed. The angle of intersection of a line tangent to the liquid and the This investigation Western New York. *Associate **Chairman ***Senior

Professor,

was supported, Department

and Professor, dental

in part,

by a grant

of Removable

Department

from

the United

Health

Foundation

of

Prosthodontics.

of Removable

Prosthodontics.

student.

j’Hydrocry1,

Hydron

$Durabond,

J. F. Jelenko

Dental

Products, & Company,

Inc., Inc.,

New New

Brunswick,

N. J.

Rochelle,

N. Y.

11

12

Winkler,

Ortman,

Fig.

1. The

J. Prortlwt. Dent. July. 1975

and Ryczek

contact

Fig. 2. A telemicroscope determinations.

with

angle

(arrows)

a protractor

of a liquid

eyepiece

and

drop

on a solid

assembly

surface.

is used

for

contact-angle

surface of the solid that it contacts is the contact angle (Fig. 1) . This angle is characteristic of the substances in the system due to the surface tension of the liquid and the surface energy of the solid, modified by certain properties such as roughness. Stated another way, a low contact angle indicates good wettability while a high contact angle results in poor wettability. As the contact angle increases, the wetting decreases. Hence, the wetting properties of saliva and distilled water can be evaluated by contact-angle measurements. A number of specimen discs 2f/4 inches in diameter were prepared under identical conditions in a Carver laboratory press * from an ADA-certified acrylic denture base resin and from Hydrocryl. The surfaces were flat, highly polished, and free of scratches. One disc of each material was used as a control, and another was treated with Durabond. Durabond is a transparent (1 ,U thick) and supposedly hydrophilic coating of silicon dioxide that increases the capillary attraction between dentures and tissues and, thereby, significantly improves retention. *Fred

S. Carver,

Inc.,

Summit,

N. J,

VOlUrnf! 34 Number 1

Improving

Table I. Contact

angles of distilled

Material Methyl

methacrylate

Hydrocryl

water

Surface

retention

of

complete

13

at 72 + 2” F.

treatment

Advancing contact angle

Receding contact angle 28 f 15 f 9% 6f2 105 14*4 8&2 18f2 15% 9f2 4%2

None Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Durabond

15 seconds 30 seconds 60 seconds 15 seconds 30 seconds 60 seconds 15 seconds 30 seconds 60 seconds

with with with with with with with with with

quartz quartz quartz Jet Brite Jet Brite Jet Brite shell shell shell

II f 655 56i 56 f 63 f 67 & 65 zt 68 * 66 f 55 f 19 *

None Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Durabond

I5 30 60 15 30 60 15 30 60

with with with with with with with with with

quartz quartz quartz Jet Brite Jet Brite Jet Brite shell shell shell

78 62 55 60 62 65 65 66 62 62 65

seconds seconds seconds seconds seconds seconds seconds seconds seconds

dentures

3 I 2 3 3 2 2 3 3 2 4

f 2 It 3 f 2 f 2 f 3 f 3 31 3 f 2 f 3 f 2 zt 3

4 2 I 2

3

24 f 2 7f2 5f 1 5fl 8&2 l2f 3 9f I l3f2 IOf 2 91t2 II Zt2

The remaining discs of each material were sandblasted for 15 seconds, 30 seconds, and 60 seconds with quartz, Jet Brite” (silicone-coated glass beads), and ground walnut shells. The discs were held 3 inches from the outlet of the sandblasting machine with a line pressure of 40 pounds. The fluids used to test the wettability of the 22 discs were distilled water and saliva. The discs were placed on a horizontal plane during the measurements. Contact angles were measured by use of a telemicroscope equipped with a protractor eyepiece (Fig. 2). Twenty readings were made for each determination.

RESULTS Contact angles for distilled water and saliva on methyl methacrylate and Hydrocry1 are listed in Tables I and II. Advancing contact angles for both water and saliva on the untreated specimen discs were high. The receding contact angles were low with water and zero with saliva on the untreated discs. Sandblasting reduced all contact angles. Contact-angle determinations for methyl methacrylate and Hydrocryl were similar with no significant advantage of one material over the other. Generally, lower angles were observed as the time of sandblasting was increased. The quartz abrasive *J.

F. Jelenko

& Company,

Inc.,

New

Rochelle,

N.

Y.

14

Winkler,

Ortman,

Table II. Contact

Material

Methyl methacrylate

Hydrocryl

J. Proathet. Dent.

and Ryczek

July,

1975

angles of saliva at 72 f 2O F.

Surface

Advancing contact angle

treatment

Receding contact angle

None Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Durabond

15 seconds with 30 seconds with 60 seconds with 15 seconds with 30 seconds with 60 seconds with 15 seconds with 30 seconds with 60 seconds with

quartz quartz quartz Jet Brite Jet Brite Jet Brite shell shell shell

72 f 2 60 f 3 52 f 3 54 f 3 65 iz 2 62 f 2 61 f2 64 f 3 61 f 2 61 f2 39 f 4

0 0 0 0 0 0 0 0 0 0 0

None Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Sandblasted Durabond

15 seconds with 30 seconds with 60 seconds with 15 seconds with 30 seconds with 60 seconds with 15 seconds with 30 seconds with 60 seconds with

quartz quartz quartz Jet Brite Jet Brite Jet Brite shell shell shell

67 i 2 50 f 2 50f 2 47f 3 67 f 2 63 zk 2 54 f 2 63 f 2 57 f 2 58 zt 2 43 f 2

0 0 0 0 0 0 0 0 0 0 0

appeared to be the best of the sandblasting mediums, although the differences among the three were slight. Treating methyl methacrylate and Hydrocryl with Durabond significantly reduced the contact angles.

CONCLUSION From the standpoint of physics and surface chemistry, the receding contact angle is the most important retentive factor. The fluid film between the denture base and the oral mucosa recedes over these two surfaces during the dislodgment of a denture. If the receding contact angle is zero, the retention of a denture cannot be the advancing contact angle is improved upon by material variations. 1 However, important to the ease of wettability when the denture is seated. Hydrocryl was not found to be completely hydrophilic and offers no significant advantage over methyl methacrylate as to wettability when used as a denture base material. Sandblasting of methyl methacrylate and Hydrocryl noticeably increased their wettability by decreasing the advancing contact angles. It also reduced the receding contact angles of distilled water. The quartz abrasive appeared to be the best of the sandblasting mediums. The length of time a denture base material is sandblasted appears to affect the resultant contact angles. Thirty seconds to one minute seems to be adequate.

ypnn:‘, “1’ ” -

Improving

retention

of complete

dentures

15

As wettability of a denture base can be markedly improved by sandblasting, periodic sandblasting of the basal surface, regardless of the denture base resin used, is advantageous. Denture bases should not be processed against a separating medium which would give them a smooth, highly polished tissue surface. While the Durabond treatment significantly reduced the contact angles of both distilled water and saliva on methyl methacrylate and Hydrocryl, the length of time the coating lasts is important. Conditions of use, such as cleaning procedures, play an important role. Studies at the State University of New York at Buffalo indicate that the coating lasts a very limited time. Thus, the extra expense of this procedure for most patients can be questioned. Reference 1. Ortman, H. R., Winkler, S., and Morris, Ceramic-Filled Acrylic Resin Compound, STATE UNIVERSITY OF NEW SCIIOOL OF DENTISTRY CAPEN HALL BUFFALO, N. Y. 14214

YORK

H. F.: Clinical J. PROSTHET.

and Laboratory Investigation DENT. 24: 253-267, 1970.

of a