Clinical results of the measurement of occlusal wear of complete dentures Alan Harrison, B.D.S., F.D.S., R.C.S.* The Welsh National School of Medicine, Dental School, Cardif, Wales, Great Britain T 1 n testing the clinical wear of materials, it is important that laboratory results correlate with the clinical situation. For example, it is possible under artificial wear conditions to show that porcelain abrades faster than acrylic resin, although clinically this is not true. Few clinical trials have been reported on the use of resin and porcelain teeth. BealP attempted to assess wear of resin teeth on complete dentures by making differ- ential measurements of stone replicas. He concluded that wear occurred at an appre- ciable rate. Sear? and Myerson reported on combinations of porcelain-to-resin tooth materials after clinical wear. They claimed the results were highly satisfactory and this combination was more resistant to abrasion than were resin-to-resin artificial teeth. Franks4 studied the wear of resin teeth on dentures which had been worn for four to five years and recorded perceptible change in cusp form in 52 per cent. He did not measure rate of wear. A similar survey by Thomson5 noted perceptible tooth wear in 62 per cent. Parameters of the masticatory cycle were specified,6 and a dental abrasion testing machine was designed to incorporate the basic principles.7 To establish conditions of wear (e.g., abrasiveness and time), it is necessary to know the amount of wear with time of acrylic resin and porcelain so that these materials can be studied on the machine. Thus a clinical trial was initiated to measure rate of wear on occlusal surfaces of artificial teeth. CLINICAL METHOD The objective of this trial was to establish differential rates of wear for acrylic resin and porcelain teeth. No attempt was made to separate rates of wear of teeth produced by different manufacturers. Also, no attempt was made to compile dietary histories, since it was anticipated that most patients would eat a wide range of foods *Lecturer, Department of Restorative Dentistry. 504
Transcript
Clinical results of the measurement of occlusal wear
of complete dentures
Alan Harrison, B.D.S., F.D.S., R.C.S.* The Welsh National School of Medicine, Dental School, Cardif, Wales, Great Britain
T 1 n testing the clinical wear of materials, it is important that laboratory results correlate with the clinical situation. For example, it is possible under artificial wear conditions to show that porcelain abrades faster than acrylic resin, although clinically this is not true.
Few clinical trials have been reported on the use of resin and porcelain teeth. BealP attempted to assess wear of resin teeth on complete dentures by making differ- ential measurements of stone replicas. He concluded that wear occurred at an appre- ciable rate. Sear? and Myerson reported on combinations of porcelain-to-resin tooth materials after clinical wear. They claimed the results were highly satisfactory and this combination was more resistant to abrasion than were resin-to-resin artificial teeth. Franks4 studied the wear of resin teeth on dentures which had been worn for four to five years and recorded perceptible change in cusp form in 52 per cent. He did not measure rate of wear. A similar survey by Thomson5 noted perceptible tooth wear in 62 per cent.
Parameters of the masticatory cycle were specified,6 and a dental abrasion testing machine was designed to incorporate the basic principles.7 To establish conditions of wear (e.g., abrasiveness and time), it is necessary to know the amount of wear with time of acrylic resin and porcelain so that these materials can be studied on the machine.
Thus a clinical trial was initiated to measure rate of wear on occlusal surfaces of artificial teeth.
CLINICAL METHOD
The objective of this trial was to establish differential rates of wear for acrylic resin and porcelain teeth. No attempt was made to separate rates of wear of teeth produced by different manufacturers. Also, no attempt was made to compile dietary histories, since it was anticipated that most patients would eat a wide range of foods
*Lecturer, Department of Restorative Dentistry.
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Measuring occlusal wear of complete dentures 505
Table I. Subjects included in clinical trial
Subject Sex
A.D.R. M N. O’D. F W. D. M D.G.M. M N. B. F F. S. M S. R. L. M D. R. F V. B. F P. G. M G. O’D. F P. H. F S. E. R. F T. 0. M M. R. F T. T. M
during the extended study. Patients were asked: “DO you wear dentures all day?” and “DO you wear dentures to eat ?” All subjects, except two, wore dentures all day and for eating. These two left the lower denture out occasionally and sometimes when eating.
Upper and lower complete dentures with acrylic resin teeth were made for nine persons. Teeth from four manufacturers were used, but each person’s dentures con- tained only one make. Several patients had worn their dentures for some time before the trial began. It was anticipated that the initial wear rate with acrylic resin teeth might be excessive while high spots were worn away, resulting in a false high annual wear rate. A true annual rate could be calculated perhaps by including these dentures in the trial.
Four subjects with complete dentures with porcelain teeth and four persons with one denture with acrylic resin teeth and an opposing complete denture with porcelain teeth were included. Ages of subjects, ages of their dentures, and types of teeth are shown in Table I. Combinations of acrylic resin and porcelain teeth were of particu- lar interest, since there has been little evidence to indicate that this combination reduces over-all rate of wear.3
Dentures of each subject were measured at the start of the trial, and this measure- ment was used as a base line from which rate of wear over the following months could be calculated. Each patient was to be recalled six months after original mea- surements for a repeat procedure and at six-month intervals thereafter.
LABORATORY METHOD
Since no reference could be found in the literature to relocate and measure dentures precisely, a new method and technique were evolved. The dentures, with
506 Harrison J. Prosthet. Dent. May, 1976
Fig. 1. Points measured on occlusal surfaces of teeth.
Fig. 4. Wear of porcelain teeth opposing porcelain teeth.
steel balls positioned distal to the last molars as datum points, were mounted using a jig on mounting plates with a mix of plaster of Paris. The mounted denture was placed on the measuring machine’s worktable, and heights of several points on the occlusal surfaces of the teeth were recorded. When readings were complete, the steel balls were covered with a thin layer of wax, self-curing acrylic resin was spread over t:he area contoured to the original denture’s shape, and the denture was returned to the patient. Subsequent measurements were made using the original plaster of Paris casts for accurate positioning. The technique is fully described in a previous article.8
508 Harrison J. Prosthet. Dent. May, 1976
Fig. 5. Wear of acrylic resin teeth opposing porcelain teeth.
RESULTS
Occlusal surfaces of the teeth were measured at the start of the trial and at approximate six-month intervals for up to two years. On each occasion, mean wear for each quadrant and mean wear for each upper and lower complete denture were mathematically determined,
Initially, all denture teeth were measured, but later, only those teeth which contacted, or very nearly contacted, when chewing were included since these ap- proximated the situation to be copied with the laboratory experiments. Incisors and canines were not included, since in several dentures, they were not in occlusion. The mathematical analysis, therefore, only included points A to J (Fig. 1) of the occlusal surfaces of the molars and premolars.
The point measured on a tooth rarely increased in height from one occasion to the next. It never increased where a facet was visible, and the amount was almost always small enough to be within the range of accuracy of the technique (kO.015 mm. or +0.0006 inch). All positive increases were included in the mathematical analysis.
Wear was plotted against time, and the first two graphs show acrylic resin teeth vs. acrylic resin teeth (Figs. 2 and 3). There was a wide range of rate of wear, but the rates of upper and lower dentures were fairly similar for the same individual except Subject G who admitted to leaving the lower denture out quite regularly. Subject H was an elderly, somewhat frail lady with a poor appetite which may ex- plain the low wear rate of her dentures.
Fig. 4, drawn on the same scale as Figs. 2 and 3, plots the wear of the group
of dentures all having only porcelain teeth. The wear rate is considerably less than that of acrylic resin teeth. Subjects 0 and Q showed an increase in mean height of one of their dentures on one measurement occasion. In both instances, this amount falls within the range of accuracy of the measuring technique and is exaggerated on this graph because of the low wear rates illustrated. It is unlikely that this is an increase in height of the teeth, but it indicates no wear since the previous measure- ment.
Fig. 5 illustrates rates of wear of acrylic resin opposing porcelain teeth and the marked difference in the rates of the two materials. The rates of wear of the dentures with porcelain teeth all fall within the range shown on Fig. 4 illustrating porcelain teeth only, whereas opposing complete dentures with acrylic resin teeth show a high rate of wear compared to the dentures with only acrylic resin teeth (Figs. 2 and 3). The picture is distorted by Subject J who was a bruxer and who worked in a heavily dust-laden atmosphere which partly explains the severe wear patterns seen on his dentures. The trend indicates that acrylic resin teeth opposing porcelain have an increased wear rate as compared to acrylic resin teeth which oppose acrylic resin. The total mean wear rate of the acrylic resin teeth opposing porcelain teeth was slightly greater than that for acrylic resin opposing acrylic resin teeth.
The mean annual wear rate of all the dentures in the different groups was esti- mated from the graphs, and the results are shown in the form of a block diagram (Fig. 6).
DISCUSSION
Mahalick and associates,g in a laboratory study of occlusal wear in prosthodontics, found that porcelain/acrylic resin combinations caused a significant loss to the acrylic
5 10 Harrison J. Prosthet. Dent. May, 1976
Figs. 7 and 8. Wear facets on acrylic resin teeth opposing porcelain teeth.
resin sample. They also showed that acrylic resin/acrylic resin combinations appeared to be more wear-resistant than porcelain/acrylic resin combinations.
Although the author’s results do not support the original hypothesis of Myersor.? regarding total rate of wear of acrylic resin opposing porcelain teeth, use of this combination may be beneficial when considering displacement of complete dentures. NormanlO stated that the success of some dentures which utilize acrylic resin opposite porcelain teeth may result from a decrease in frictional resistance. He showed that porcelain opposing-porcelain contacts required nearly twice the displacement force as porcelain vs. acrylic resin.
Clinical experience has shown that porcelain teeth retain surface characteristics longer than do acrylic resin teeth.
Photographs of dentures of the subjects in this trial show the type of wear pattern which is commonly seen and also confirm the differential wear rate of acrylic resin and porcelain.
Fig. 7 shows an upper denture with porcelain teeth and the opposing lower denture with acrylic resin teeth. There are no obvious facets on the upper denture, but facets are immediately visible on the lower denture. This is illustrated again in Fig. 8.
CONCLUSIONS
This study supports the clinical impression that acrylic resin teeth wear down faster than porcelain teeth but does not support Myerson’? view that the total wear of acrylic resin opposing porcelain teeth is less than that of acrylic resin opposing acrylic resin teeth.
There was a wide range of rate of wear in acrylic resin teeth opposing acrylic resin teeth. Dentures of the four subjects in the porcelain-only group showed con- siderably less wear. The dentures with acrylic resin teeth opposing porcelain teeth showed the same general trend, i.e., a high rate of wear for the acrylic resin teeth with very little for the porcelain teeth.
Conclusive proof is given for the differing wear rates of acrylic resin and porcelain teeth when opposing like materials.
I thank Mr. R. Huggett for his technical assistance, Professor J. F. Bates for his advice and ‘encouragement, and Mr. B. Jones and his staff for the illustrations.
References
1. Beall, J. R.: Wear of Acrylic Resin Teeth, J. Am. Dent. Assoc. 30: 252-256, 1943. 2. Sears, V. H.: Occlusal Pivots, J. PROSTHET. DENT. 6: 332-338, 1956. 3. Myerson, R. L.: The Use of Porcelain and Plastic Teeth in Opposing Complete Dentures,
J. PROSTHET. DENT. 7: 625-633, 1957. 4. Franks, A. S. T.: Clinical Appraisal of Acrylic Tooth Wear, Dent. Pratt. Dent. Rec. 12:
149-153, 1962. 5. Thomson, J. Cl.: Non-functional Muscle Activity in Prosthetic Cases, Br. Dent. J. 114:
326-328, 1963. 6. Bates, J. F., Stafford, G. D., and Harrison, A.: Masticatory Function-A Review of the
Literature. 1. The Form of the Masticatory Cycle, J. Oral Rehab. 2: 281-301, 1975; Part 2, 2: 349-361, 1975. (Part 3 in press.)
7. Harrison, A., and Lewis, T. T.: The Development of an Abrasion Testing Machine for Dental Materials, J. Biomed. Mater. Res. 9: 341-353, 1975.
8. Harrison, A., and Huggett, R.: Measuring the Rate of Wear of Artificial Teeth in Com- plete Dentures, J. PROSTHET. DENT. 33: 615-619, 1975.
9. Mahalick, J. A., Knap, F. J., and Weiter, E. J.: Occlusal Wear in Prosthodontics, J. Am. Dent. Assoc. 82: 154-159, 1971.
10. Norman, R. L.: Frictional Resistance and Dental Prosthetics, J. PROSTHET. DENT. 14: 45-51, 1964.
THE WELSH NATIONAL SCHOOL OF MEDICINE DENTAL SCHOOL CARDIFF CF4 4XY WALES, GREAT BRITAIN
ARTICLES TO APPEAR IN FUTURE ISSUES
In-service teacher training in removable prosthodontics Gerald C. Brundo, D.D.S., M.A.
Microstructure of amalgam surfaces Kai Chiu Chan, D.D.S., M.S., John W. Edie, M.Sc., Ph.D., and Daniel B. Boyer, D.D.S., Ph.D.
Treatment planning for fixed and removable partial dentures: A periodontal view Nigel G. Clarke, B.D.S., Ph.D.
Dental casts made with natural teeth Hamil M. Cupero, D.D.S.
