Wear of nonanatomic (monoplane) acrylic resin denture teeth

Zafrulla Khan, D.D.S.,* Jack C. Morris, D.M.D., M.Sc.,** and J. A. von Fraunhofer, M.Sc., Ph.D.*** University of Louisville, School of Dentistry, Louisville, Ky.

A crylic resin teeth are widely used in complete and removable partial dentures, and over the years the functional and esthetic characteristics of denture teeth have been improved. They do, however, undergo wear/abrasion in use; and although there is a standard specification for acrylic resin teeth,’ the problem of wear and abrasion is not addressed.

The factors involved in wear include the pressure between the abrading surfaces, the relative speed of movement between the surfaces, the characteristics of the surfaces, and the composition of the materials in contact. Tooth wear in vivo is related to the chewing pattern of the patient, the masticatory forces exerted, the daily period of use, the dietary habits, and various other factors.2-4

Wear and abrasion studies have been made typically on denture teeth with reciprocating wear devices.4 Investigators tend to relate wear resistance to surface hardness, and a wide variety of hardness tests are used to assess surface characteristics.5s 6

In this study, the use of a commercially available abrasion test device to evaluate the wear characteristics of three brands of monoplane teeth is reported.

MATERIAL AND METHODS

Four posterior denture teeth were embedded in dental stone with the occlusal surfaces aligned in one plane. Four blocks were prepared with teeth from three different manufacturers (Dentsply International Corp., Inc., York, Pa.; Myerson Tooth Corp., Cam- bridge, Mass.; and Universal, Lactona Corp., Morris Plains, N. J.) for a total of 12 blocks. Only monoplane (nonanatomic) teeth were used.

After the dental stone blocks had dried to constant

*Assistant Professor, Department of Prosthodontics. **Associate Professor, Department of Prosthodontics. ***Professor, Department of Restorative Dentistry.

Fig. 1. Mitutoyo dial caliper and denture teeth in dental stone test block.

weight, the height of the occlusal surface of each tooth above the dental stone surface was measured with a dial caliper (Mitutoyo Mfg. Co., Tokyo, Japan) (Fig. 1). The dial caliper could be read within 0.01 cm. Thereafter, each block was mounted in the arm of the abrader (R. E. L. Hampton Hill, Middlesex, U.K.) (Figs. 2 and 3) and subjected to 500 abrades across water-lubricated 600 grit (17 pm) silicon carbide abrasive paper. After remeasurement of the occlusal heights, the blocks were subjected to a further 500 abrades and the loss of occlusal height was measured again.

The wear of the teeth expressed as percent loss in occlusal height was determined with the formula:

wear=HO~H,~ Ho 1 0

where Ho is the original height of the occlusal surface, and H, is the height after abrasion of the teeth.

RESULTS

The occlusal wear of the three brands of denture teeth is given in Table I. Comparison of the mean

172 AUGUST 1984 VOLUME 52 NUMBER 2

NONANATOMIC TOOTH WEAR

Fig. 2. R. E. L. Hampton Hill single arm abrader. Fig. 3. Test block mounted on abrading table.

Table I. Height reduction (%) of acrylic resin teeth after abrasion (mean ? standard deviation) ______

First premolar Second premolar First molar Second molar Overall mean

Dentsply 500 abmdes 6.08 + 2.32 5.72 f 1.53 4.38 i 1.49 4.03 _+ 0.92 5.08 _+ 1.77

1000 abasdes 9.43 k 2.70 8.53 +- 1.53 6.50 2 1.44 5.62 + 1.25 7.52 -r- 2.31 Myerson

500 abrades 4.07 + 1.40 2.98 + 0.94 2.80 f 0.71 4.20 f 2.05 3.51 + 1.43 1000 abrades 5.85 + 1.35 5.17 * 1.22 5.07 2 1.42 5.92 + 2.17 5.50 rt 1.53

Universal 500 abrades 4.37 ?I 1.94 3.78 + 1.77 3.78 2 1.10 3.32 f 0.79 3.81 rt 1.43 1000 abrades 7.47 f 1.35 6.73 f 1.84 6.32 + 1.84 5.98 + 1.11 6.63 + 1.57

_____

values of abrasion by means of the Student t test, after ANOVA established that differences were present, is summarized in Table II. It can be seen in this table that there was no difference in overall abrasion between the Myerson and Universal teeth at 500 abrades, while the Dentsply teeth showed significantly (p < .Ol) more abrasion than the other two products. At 1000 abrades, there was no significant difference in abrasion between the Myerson and Universal teeth (is, > .05) or between the Universal and Dentsply teeth (p > .05), but the difference in abrasion of the Dentsply and Myerson teeth was highly significant (ia < .OOl).

Comparison of the abrasion of the individual teeth at 500 abrades showed no statistically significant differ- ence between any two of the Myerson and Universal teeth, but a probable significant difference @ < .05) was found between the abrasion of the second premolar and second molar of the Dentsply teeth. Comparison at 500 abrades showed that the Dentsply second premolar abraded more than that of Myerson (p < .Ol), and there was a probable significant difference (la < .05) in the abrasion of the Dentsply and the Myerson first molars. No other differences in the abrasion of an

individual manufacturer’s teeth or between the same teeth from different manufacturers were found.

At 1000 abrades, no significant differences were found between the premolar or the molar teeth for any given manufacturer. There was no difference in the abrasion found with the premolar and molar teeth for Myerson and Universal. In contrast, the Dentsply first and second premolar teeth showed significantly (p < .Ol) greater abrasion than the second molar teeth and probable significantly greater 0, < .05) abrasion than the first molars. Comparisons of the same teeth of different manufacturers showed that the Dentsply first and second premolar teeth abraded significantly (p < .Ol) more than the corresponding Myerson teeth. No other differences in abrasion were detected.

The increase in detected abrasion between 500 and 1000 abrades was 48% for Dentsply teeth, 57% for Myerson teeth, and 74% for the Universal teeth.

DISCUSSION

Overall, the findings indicate that there are differ- ences in the abrasion of nonanatomic (monoplane) acrylic resin teeth produced by different manufactur-

THE JOURNAL OF PROSTHETIC DENTISTRY 173

KHAN, MORRIS, AND VON FRAUNHOFER

Table II. Statistical analyses (Student t test)

Dentsply Myerson Universal

500 abrades Dentsply Myerson Universal

1000 abrades Dentsply Myers-on Universal

-

S

S

-

hs ns

S

-

ns

hs -

ns

S

IIS

-

ns ns -

Significance levels: ns = p > .05; s = p < .Ol; hs = p < .qOl.

em. In particular, Dentsply teeth showed greater abrasion than those of Myerson and Universal at 500 abrades, and greater abrasion than the Myerson teeth at 1000 abrades. No differences were detected between Universal and Myerson teeth. The differences in abrasion are due to differences in the individual teeth of different manufacturers, as indicated previously. The study shows, however, that even under severely abra- sive conditions the performance of modern acrylic resin denture teeth appears to be satisfactory.

The abrasion test used in this study is probably more severe than that found in clinical practice, but it appears to be rapid and reproducible, and as such it represents a convenient method of comparing the abrasion resistance of different manufacturers’ prod- ucts.

The relatively greater increase in wear for the Myerson and Universal teeth between 500 and 1000 abrades compared with the increase for the Dentsply teeth suggests that over long periods of use, the wear rates of the three brands of teeth would become comparable.

Further studies are being done in comparing the abrasion characteristics of cusp (anatomic) teeth.

REFERENCES

1.

2.

3.

4.

5.

6.

American Dental Association: American Dental Association Specification No. 15 for acrylic resin teeth. Am Dent Assoc 56~53, 1964. Franks, A. S. T.: A clinical appraisal of acrylic tooth wear. Dent Practit 12~149, 1962. El-Said, M., Khamis Abdel Razek, M., and Shaaban, S. A.: Wear of acrylic teeth. Egypt Dent J 18~423, 1972. Thomson, J. C.: Attrition of acrylic teeth. Dent Practit 15~233, 1965. Phillips, R. W.: Skinner’s Science of Dental Materials, ed 8. Philadelphia, 1982, W. B. Saunders Co. Craig, R. G.: Restorative Dental Materials, ed 6. St. Louis, 1980, The C. V. Mosby Co.

Reprint requests to: DR. ZAFRULLA KHAN

UNIVERSITY OF LOUISVILLE

SCHOOL OF DENTISTRY

LOUISVILLE, KY 40292

174 AUGUST 1984 VOLUME 52 NUMBER 2