Wear of anatomic 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.

M any improvements have been made in the func- tional and esthetic characteristics of acrylic resin teeth. Denture teeth are subject to wear/abrasion in use, but this subject is not addressed in the standard specification for acrylic resin teeth.’

A previous study* investigated the wear characteristics of nonanatomic (monoplane) teeth with a reciprocating abrader, and it was found that there were no significant differences in the abrasion of acrylic resin teeth produced by different manufacturers. The decision was made to extend the study to assess the abrasion characteristics of cusp (20-degree anatomic) teeth to determine whether the presence of a cusp affects wear.

MATERIAL AND METHODS

Blocks of four acrylic resin posterior teeth, two premolars, and two molars, were embedded in dental stone with the occlusal surfaces aligned in one plane. Four blocks were prepared with teeth from three differ- ent manufacturers: Dentsply (Dentsply International, York, Pa.), Myerson (Myerson Tooth Corp., Cam- bridge, Mass.), and Universal (Lactona Corp., Morris Plains, N.J.). A total of 12 blocks were prepared with 20-degree cusp teeth.

The experimental technique was the same as that used in the previous study* with tooth wear being expressed as percent loss in occlusal height:

II, - H, 100% we.,i‘ = - x - Ho 1

*AsGsunt Profeawr ,md Il~rcctor of Post Gratluare Prosthodontics. Ikpartment of Prosthotlontics.

**Associate Professor. Department of Prosthodontic~. ***Professor. Lkparlment of Krbtorative Lkntistry.

where H, is the initial height of the teeth and H,~ the height of the teeth after abrasion. This study differed from the previous study in that the teeth had cusps: two for the premolars and four for the molars. Consequently the height losses were determined for each cusp of each tooth, and the values cited for the different types of teeth for each manufacturer were the mean values obtained for all cusps of all four teeth within a given group.

RESULTS

The occlusal wear under the abrasion test regimen of the three brands of acrylic resin denture teeth are given in Table I. Comparison of the manufacturers’ mean values of abrasion by means of the Student t test, after ANOVA established that differences were present, is summarized in Table II. At 500 abrades there were no statistically significant differences between the Dentsply and Myerson teeth (is > .05) or between the Dentsply and Universal teeth (p > .05), but a significant differ- ence (p < .Ol) was found between the Myerson Andy Universal teeth. At 1000 abrades there was no statisti- cally significant difference between the Dentsply and Myerson teeth, but the Universal teeth were found to abrade less than both the Dentsply (or, < .05) and the Myerson ($ < .OOl) teeth.

Comparison of wear/abrasion rates of the teeth.of an individual manufacturer showed no statistically signifi- cant differences (p > .05) for the Myerson and Universal teeth at 500 and 1000 abrades. In the Dentsply teeth, however, the first molar teeth abraded less (p < ‘05) than the first premolar teeth, while the abrasion of the second molar was significantly less than that of the first and second premolar teeth @I < .05 and k, < .Ol, respec-

Table I. Height reduction (%) of acrylic resin teeth after abrasion (mean values _t standard deviations)

Teeth/abrasion

Dentsply 500 abrades

1000 abrades Myerson

500 abrades 1000 abrades

Universal 500 abrades

1000 abrades

First Second premolar premolar

5.42 t 2.10 5.39 rt 1.59 8.70 k 1.53 8.16 i 1.26

5.55 zk 1.74 5.20 ? 1.27 7.78 t 2.33 7.29 + 1.54

3.21 i 2.97 3.89 + 1.84 6.45 i 2.06 6.29 + 1.51

First molar

3.67 +- 1.60 6.70 zt 1.71

4.57 ? 0.73 7.38 + 1.68

3.95 t 1.04 5.69 i 1.53

Second molar

3.09 i 1.57 5.28 f 1.34

4.33 i 1.08 7.54 2 1.98

3.68 i_ 0.98 6.13 i 1.73

Overall mean

4.22 i I.tlb 6.91 f 1.94

4.98 f 1.74 7.39 -t’ I.37

3.76 3. 1.57 6.07 f~ 1 66

550 APRIL 1985 VOLUME 53 NUMBER 4

WEAR OF ANATOMIC ACRYLIC RESIN TEETH

tively) at 500 abrades. There were no differences between the two premolars or between the two molar teeth. At 1000 abrades, there were no differences between the premolar teeth, but the abrasion of the first molars was significantly less (p < .05) than that of the premolars; and the abrasion of the second molars was significantly less than that of the premolars at the 0.1% level. The difference in abrasion of the first and second molars was significant at the 5% level.

Comparison of the individual teeth of different manu- facturers are summarized in Table III. It can be seen that only one statistically significant difference (at the 5% level) occurred at 500 abrades, which was that between the second molars of Dentsply and Myerson teeth. At 1000 abrades significant differences (p < .Ol) were found between the second molars of Dentsply and Myerson teeth and between the first molars of Myerson and Universal teeth. Differences at the 5% level were found between the first and second premolars of Dent- sply and Universal teeth and between the Myerson and Universal second molar teeth.

The increase in detected abrasion between 500 and 1000 abrades was 63.7% for Dentsply, 48.4% for Myerson, and 61.4% for Universal teeth.

Comparison of the mean abrasion values of the cusp teeth evaluated in the present study and the previous findings for monoplane teeth2 showed no statistically significant QJ > .05) differences for the Dentsply or Universal teeth. In the Myerson teeth, however, the abrasion found at both 500 and 1000 abrades was

Table II. Statistical comparison of manufacturers’ overall mean values

Abrasion/teeth Dentsply Myerson Universal

500 Abrades Dentsplv - NS NS Myerson NS - S Universal NS S -

1000 Abrades Dentsply - NS PS Myerson NS - HS Universal PS HS -

NS = Not significant (1) > .05); I’S = probably significant (p < .05); S = significant (p < .Ol); and HS = highly significant (fj < .OOl).

significantly greater (p < .OOl) for the cusp (20-degree anatomic) teeth than for the monoplane teeth.

DISCUSSION

The findings indicate that there are differences in the overall abrasion of acrylic resin cusp teeth produced by different manufacturers, although the differences are small. Myerson teeth abrade slightly more than Dent- sply and Universal teeth, and there is a marginal difference between Universal and Dentsply teeth at longer abrasion times (1000 abrades). These differences are due to variations in the abrasion determined for individual teeth, notably the molars. However, the observed differences are relatively small, and in clinical situations it might not be significant over long periods.

Comparisons of the abrasion of the different teeth of a single manufacturer indicate that, in general, there is little difference in the wear rates of different teeth. This suggests that in the clinical situation, no problems should arise from uneven wear under normal function.

The slightly greater abrasion of the cusp Myerson teeth compared with the monoplane teeth was statistical- ly significant, but in long-term clinical use such differ- ences might not be a problem.

CONCLUSION

Overall, it appears that there are small but clinically insignificant differences in the abrasion characteristics of anatomic acrylic resin denture teeth produced by differ- ent manufacturers. Selection of teeth for dentures should therefore be based on personal preference and esthetic considerations rather than on assumed differences in wear rates.

REFERENCES

Table III. Statistical comparison of wear of individual teeth of different manufacturers (by number of abrades)

Comparison

First Second First Second premolar premolar molar molar

500 1000 500 1000 500 1000 500 1000

Dentsply vs. Myerson NS NS NS NS NS NS PS S Dentsply vs. Universal NS PS NS PS NS NS NS NS Myerson vs. Universal NS NS NS NS NS S NS I3

NS = Not significant (fi > .OS); PS = probably significant (p < .05); S = significant (1, < ,011.

THE JOURNAL OF PROSTHETIC DENTISTRY 551