Enamel wear caused by three different restorative materials

Enamel wear caused by three different restorative materials

Enamel wear caused by three different restorative materials James D. Hudson, DMD, a Gary R. Goldstein, DDS, b and Maria Georgescu, MS c College o...

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Enamel wear caused by three different restorative materials James

D. Hudson,

DMD, a Gary R. Goldstein,

DDS, b and Maria Georgescu,

MS c

College of Dentistry, New York University, New York, N. Y. The ideal restorative material should cause minimal wear of opposing enamel. This s t u d y c o m p a r e d t h e e f f e c t s o f g o l d alloy, g l a z e d p o r c e l a i n , a n d a l a b o r a t o r y - p r o c e s s e d c o m p o s i t e o n o p p o s i n g e n a m e l . T e n s a m p l e s o f a t y p e III g o l d alloy, a p o r c e l a i n , a n d a visible-light, heat, and vacuum-processed composite were abraded against cusps of e x t r a c t e d m o l a r s for 10,000 c y c l e s o n an a b r a d i n g m a c h i n e . P r e t e s t a n d p o s t t e s t profilometric measurements of the restorative materials demonstrated no statistical difference. Pretest and posttest tracings of the cusps were made on an optical c o m p a r a t o r to d e t e r m i n e l o s s o f v e r t i c a l h e i g h t a n d s u r f a c e area. T h e p o r c e l a i n c a u s e d s i g n i f i c a n t l y m o r e loss o f v e r t i c a l h e i g h t a n d s u r f a c e a r e a t h a n t h e g o l d a l l o y or t h e c o m p o s i t e , w h i c h w e r e similar. (J PROSTHET DENT 1995;74:647-54.)

I t is the desire of the restorative dentist to provide a material t h a t has the function and appearance of the enamel t h a t it replaces, but the goal has been elusive because the materials t h a t function most like enamel do not resemble it esthetically, and materials t h a t resemble enamel do not necessarily function like enamel. This disparity is readily a p p a r e n t w h e n the wear of enamel surfaces, opposed by different restorative materials, is considered. All materials (including enamel) can wear or abrade other materials. Ideally, a restorative material that replaces enamel and/or opposing enamel should have functional characteristics similar to enamel. Seghi et al.1 stated t h a t such a material should wear at the same rate as enamel and should not cause more wear to the enamel it opposes t h a n enamel itself would. Lambrechts et al. 2 reported t h a t the wear of enamel opposing enamel is approximately 20 to 40 ~m per year. Excessive wear of a single tooth, restoration, or a n entire dentition has been associated with overeruption of opposing teeth, mesial drift of teeth distal to a n eroding contact, 3 ,4 t r a u m a t i c occlusion,5 a n d t e m p o r o m a n d i b u l a r disorders. 6 Gold alloy has been and is still considered the most ideal

Presented before the Greater New York Academy of Prosthodontics Spring meeting, June 10, 1994; and the International Association for Dental Research, 72nd General Session, Seattle, Wash., March, 1994. aClinical Assistant Professor, Division of Restorative and Prosthodontic Sciences. bDirector of Prosthodontic Research, Division of Restorative and Prosthodontic Sciences. CAdjunct Assistant Professor, Division of Restorative and Prosthodontic Sciences. Copyright 9 1995 by The Editorial Council of THE JOURNALOF PROSTHETICDENTISTRY. 0022-3913/95/$5.00 + 0. 10/1/67764

D E C E M B E R 1995

restorative material because it most resembles enamel in function a n d wear characteristics. 7-9 However, its esthetic limitations often cause it to be overlooked in favor of the more "natural" appearing alternatives. Porcelain has been used for m a n y years, and in m a n y forms, as the esthetic alternative to gold alloy. Feldspathic porcelain fused to a metal substructure is the most widely used form of this restoration. Its greatest shortcoming is its abrasiveness. 9 If it is well polished or glazed it becomes less abrasive, b u t it is still more abrasive t h a n a n enamel-toenamel coupling. 7' 9, 10 Modern porcelain systems, such as Dicor (Dentsply International, York, Pa.), Cerestore (Johnson & J o h n s o n Dental Products, Inc., East Windsor, N. J.), and Optec (Jeneric/Pentron, Wallingford, Conn.) have sought to address this problem b u t with only limited results.i, s, 10 The severity of this problem is best noted by Wiley, 11who stated, "Group function in porcelain can elicit group destruction." The search for other acceptable esthetic alternatives has focused on composite materials. The ability of composites to cause enamel wear has been documented clinically by C h a p m a n and N a t h a n s o n 12 and recently in the laboratory by Suzuki and LeinfelderJ 3 However, composites have most often been reported excessively worn by enamel and/or other restorative materials. 14-1sThis limitation has led to the development of newer composite materials that are more resistant to wear from the opposing dentition. The most promising of these newer materials requires t h a t the restoration be fabricated in a dental laboratory much as a porcelain restoration. This study compared the wear rate of enamel abraded against a new composite system, porcelain, and gold alloy. MATERIAL

AND

METHODS

Three different commercially available restorative systems were used in this study: a type III gold alloy, a porcelain, and a visible-light, heat, a n d vacuum-treated composite (VLHC) (Table I). The VLHC material is a microhybrid oligocarbonate dimethylacrylic ester resin based

T H E J O U R N A L OF P R O S T H E T I C D E N T I S T R Y

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Fig. 1. Prepared type III gold sample in autopolymerizing resin matrix.

Fig. 3. Prepared composite sample in autopolymerizing resin matrix.

Fig. 2. Prepared porcelain sample in autopolymerizing resin matrix.

Fig. 4. Prepared restorative material in autopolymerizing resin mat~x with screw to attach to weighted cup and rod.

material 19 classified as a direct/indirect composite resin. The gold alloy samples (Fig. 1) were used as they were received from the manufacturer. Each 2 pennyweight (dwt) ingot was sectioned in half and the surface repolished with tripoli and rouge. The porcelain samples (Fig. 2) were prepared by the manufacturer and fired to a medium glaze. The composite samples (Fig. 3) were prepared by compressing the material in a split stainless steel ring (20 mm diameter, 2 mm high) between two glass slides, light cured (Optilux 400, Demetron, Danbury, Conn.) for 40 seconds on each side, and then placed in the curing unit (Conquest curing unit, model 001, Jeneric/Pentron) and fired at 107 ~ C for 15 minutes in 29 inches of mercury vacuum followed by a 2-minute cooldown. The composite samples were then finished with medium, fine, and superfine Soflex disks (3M Dental Products; St. Paul, Minn.).

The restorative samples were positioned in an autopolymerizing resin matrix (Shur Tray acrylic tray resin; Mode m Materials, South Bend, Ind.) (Fig. 4) and attached with a screw to a weighted cup and rod that would provide a constant load of 178.35 gm (Fig. 5). This load was selected for its ability to maintain the "heads" in contact with the restorative materials throughout the testing. The opposing enamel samples were obtained from the cusps of unrestored, recently extracted molar teeth. Individual cusps were selected and sectioned from the teeth and mounted in the autopolymerizing acrylic resin (Fig. 6). These mounted teeth could then be transferred to a holder that allowed the cusp tips to remain under room temperature water while undergoing testing. This method of enamel selection for testing is consistent with previous studies by Jacobi et al. 8 and DeLong et al. 11

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F i g . 6. P r e p a r e d enamel s a m p l e m o u n t e d in autopolymerizing acrylic resin.

Table II. Profilometric readings m e a n Ra (microns)

Pretest Posttest

Gold (SD)

Porcelain (SD)

(n 10)

(n 10)

V L H C (SD) (n 10)

1.3 (1.0) 1.8 (3.0)

14.6 (3.0) 9.6 (5.0)

8.4 (7.0) 5.3 (3.0)

F i g . 5. Weighted cup and rod (178.35 gm) with restorative sample attached.

T a b l e I. Restorative m a t e r i a l s included in w e a r testing Material

Manufacturer

Composition

Gold

Degussa, Degular C (type III) South Plainfield, (74% Au) N.J. Porcelain Dentsply Int. Biobond body porcelain York, Pa. (shade A2) VLHC Jeneric/Pentron Conquest Crown and Bridge Wallingford, Conn. (Body shade A3)

The restorative m a t e r i a l and tooth samples were placed in a w e a r machine for testing (Fig. 7). The tooth specimens were positioned in holders and a t t a c h e d to the machine, t h e n i m m e r s e d in w a t e r for the d u r a t i o n of the testing (Fig. 8). The restorative samples were positioned above the cusp tips u n d e r a constant load of 178.35 gm (Fig. 9). The w e a r machine provided abrasion between the diss i m i l a r samples with a 6.0 m m back-and-forth stroke. The s a m p l e s were r u n for 10,000 cycles or 20,000 strokes. The restorative material/tooth couples were assigned randomly as were the positions on the machine.

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Before a n d after testing, the occluding surfaces of the restorative materials,were scanned at six sites per sample with the use of a profilometer (Mitutoyo Suftest 4, Tokyo, Japan). The unit has an accuracy of 1.0 pro. When calibrated before e a c h s e s s i o n , it can reproduce a reading with 100% precision. The scanner length was 1.5 m m and the d a t a were recorded for Ra, which is the arithmetic average roughness value of the roughness curve. Before a n d after testing, the e n a m e l (cusp) samples were examined w i t h an optical comparator (Nikon Profile Projector, V-12) (Fig. 10). This procedure produced a shadow graph of t h e cusp t h a t enabled a tracing of the cusp tips to be m a d e before and after testing (Fig. 11). The extracted and sectioned teeth h a d been m o u n t e d in an acrylic resin block with flat sides. This p e r m i t t e d visualization of the cusp tip from four sides and ensured the s a m e projection before a n d after testing. The tracing of the cusp tip and its slopes before testing ensured the exact s a m e view when it was realigned with the tracing after testing. A comparison of these tracings provided the d a t a for determination of vertical h e i g h t loss a n d surface a r e a loss of the cusp. RESULTS The averages and s t a n d a r d deviations of pretest and posttest profilometric m e a s u r e m e n t s recording the surface

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Fig. 7. Wear machine used in testing with weighted cups and rods in place.

Fig. 8. Close-up view of weighted cups and rods with restorative sample attached.

smoothness of the gold alloy, porcelain, and VLHC samples are presented in Table II. An ANOVA and Scheffe analysis (p < 0.01) demonstrated no significant difference between the pretest and posttest profilometric readings. Comparison of pretest and posttest tracings of the cusp tips allowed the determination of the wear of enamel as measured by both surface area loss and the vertical height loss of the cusps. The ANOVA and Scheffe analysis (p < 0.01) are presented in Tables III through VI. Porcelain

650

caused a statistically significant loss of vertical height and surface area of the opposing enamel when compared with either gold alloy or VLHC. There was no significant difference in the wear of enamel opposing gold alloy or VLHC. DISCUSSION In this experiment, feldspathic porcelain, polished and glazed, caused significantly more enamel wear than the gold alloy, and a relatively new composite restorative

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F i g . 9. Close-up view of restorative sample attached to rod and positioned in contact with enamel sample.

Table III. Analysis of variance for area and material Source

DF

Sum of squares

Mean squares

F Ratio

F Probability

Between groups Within groups Total

2 27 29

8115180667 1274518000 9389698667

4057590333 47204370.37

85.9579

0.0000

Table IV. Group statistical analysis for area a n d material Group

Gold Porcelain VLHC Total Effects model Fixed Random

Count

Mean

Standard deviation

Standard error

10 10 10 30

3170.0 37580.0 2230.0 14326.7

3514.75 11207.32 1911.98 17993.96

1111.46 3544.06 604.62 3285.23

6870.54

1254.38 11629.83

95% C o n f i d e n c e interval for mean

655.70 To 5684.30 29562.8 To 45597.2 862.25 To 3597.75 7607.61 To 21045.72

SS Sub

A B A

1752.88 To 16900.45 -35713.01 To 64366.34

Random effects model estimate of between-component variance 401038596.296.

material caused enamel wear similar to that of the gold alloy. The profilometric tracings revealed no degradation of the surfaces of the restorative materials tested. Although a change in the reflective qualities of the surfaces of the gold alloy a n d porcelain samples was noted, no change in

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their surfaces could be detected by scanning electron microscopy. However, scanning electron micrographs at x 150 magnification demonstrated minor degradation of the surface of the composite sample, which visually exhibited the most a p p a r e n t wear (Fig. 12). When viewed at • magnification (Fig. 12), the

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Fig. 11. Shadow graph ofposttreatment cusp tip. Difference between original tracing and posttreatment tracing allows for measurement of lost tooth surface.

Fig. 10. Optical comparitor demonstrating shadow graph of cusp tip.

Table V. Analysis of variance for vertical height and material Source

DF

Sum of squares

Mean squares

Between groups Within groups Total

2 27 29

21856.47 6220.50 28076.97

10928.23 230.39

abraded area (A) appears to be more highly polished than the unabraded area (B). The pretest profilometric reading of this sample was R a 8.0 Dm and the posttest reading was Ra 5.0 Din. This demonstrates that the treated sample was smoother than the pretest sample, probably as a result of the "polishing effect" of the opposing cusp. The two readings (8.0 and 5.0 l~m) are extremely low and indicate smooth surfaces. Because posttest tracings were made perpendicular to the cusp tracks, if the Rmax(highest reading of any isolated groove) was significant, indicating wear of the material caused by abrasion, it would have a large effect on these low Ras. It was not the purpose of this re-

652

F

F

Ratio

Probability

47.43

0.0000

search to determine the amount of wear to the restorative samples. Future research will address this issue. Composites have historically demonstrated occlusal wear in the oral environment 14-B and have had limited usage in occlusal rehabilitation. More recent treatment of composites have included heat curing in addition to visiblelight curing. Covey et al. 2~reported that heat treatment of composites significantly increased their tensile strength. A similar study by Waknine et al. m demonstrated that the visible-light, heat, and vacuum-cured composite, Conquest C & B, had a high flexural strength (21880 psi), a linear coefficient of thermal expansion (17.33 • 106/~ C) ap-

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F i g . 12. SEM p h o t g r a p h (upper box • magnification; lower boxes • magnification) of composite s a m p l e t h a t visually showed most e n a m e l wear. A b r a d e d areas, labeled A, a p p e a r to be more highly polished t h a n u n a b r a d e d areas, B.

T a b l e VI. Group statistical analysis for vertical height and m a t e r i a l Group

Gold Porcelain VLHC Total Effects model Fixed Random

Count

Mean

Standard deviation

Standard error

10 10 10 30

12.0 69.8 13.1 31.6

6.749 24.022 8.279 31.115

2.134 7.596 2.618 5.681

15.179

2.771 19.086

95% C o n f i d e n c e i n t e r v a l for m e a n

7.17 52.61 7.17 20.01

To 16.83 To 86.98 To 19.02 To 43.25

SS Sub

A B A

25.95 To 37.32 -50.49 To 113.75

R a n d o m effects model estimate of between-component variance: 1069.7844.

proaching t h a t of tooth structure (12 o 10-6/o C), and most important---an in vitro w e a r r a t e t h a t corresponds to an in vivo w e a r r a t e of 3 p m per year. This m a t e r i a l (VLHC) seems to have overcome m a n y of the limitations of composites t h a t are placed directly in a tooth with visible light as the sole method of cure. Conquest Crown and Bridge composite should not be confused w i t h Conquest DFC composite, which is intended for direct placement in the m o u t h and is solely light cured. Conquest C & B is of a h i g h e r molecular weight. It h a s two additional initiators a n d accelerators t h a t are not p r e s e n t in Conquest DFC. CLINICAL

IMPLICATIONS

The d a t a support the conclusions of previous studiesi, 7, i i t h a t porcelain m a y cause excessive e n a m e l wear. They h a v e also d e m o n s t r a t e d t h a t a laboratory-processed com-

DECEMBER 1995

posite s y s t e m causes less e n a m e l w e a r t h a n does porcelain and a s i m i l a r amount of e n a m e l wear w h e n compared with a gold alloy. To achieve predictable results in prosthodontics it is imperative t h a t wear be controlled. M a h a l i k et al. have stated, "the a m o u n t of w e a r depends on such factors as n e u r o m u s c u l a r forces, lubricants, foreign objects, patient habits a n d the type of restorative m a t e r i a l used. "9 Of these, the d e n t i s t h a s the most control of t h e m a t e r i a l selected. Because a visible-light, heat, a n d vacuum-fired composite was shown to cause w e a r of e n a m e l t h a t is similar to gold alloy, p e r h a p s a m a t e r i a l exists t h a t can be a n alternative to p o r c e l a i n - - o n e t h a t provides esthetics y e t does not w e a r t h a t which it opposes. Only in vivo clinical trials can d e t e r m i n e the u l t i m a t e efficacy of a restorative material, and such trials are pending for this material.

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CONCLUSIONS Under the conditions of this study, the following conclusions were made. 1. Gold alloy and a visible-light, heat, and vacuum-fired composite caused similar wear of enamel. 2. Polished and glazed feldspathic porcelain caused a significant amount of enamel wear when compared with gold alloy or a visible-light, heat, and vacuum-fired composite. REFERENCES

1. Seghi RR, Rosenstiel SF, Bauer P. Abrasion of human enamel by different dental ceramics in vitro. J Dent Res 1991;70:221-5. 2. Lambrechts P, Braem M, Vanherle G. Evaluation of clinical performance for posterior composite resin and dental adhesives. Oper Dent 1987;12:53-78. 3. Leinfelder KF. Composite resin in posterior teeth. Dent Clin North Am 1981;25:357-64. 4. Wilder AD, May KN Jr, Leinfelder KF. Three year clinical study of UV-cured composite resins in posterior teeth. J PROSTHET DENT 1983;50:26-30. 5. Ramtjord S, Ash MM. Occlusion. 3rd ed. Philadelphia: WB Saunders, 1983:203. 6. Okeson JP. Management of temporomandibular disorders and occlusion. 2nd ed. St Louis: CV Mosby, 1989:204. 7. Monasky GE, Taylor DF. Studies on the wear of porcelain, enamel and gold. J Dent Res 1971;25:299-306. 8. Jacobi R, Shillingburg HT, Duncanson MG Jr. A comparison of the abrasiveness of six ceramic surfaces and gold. J PROSTHETDENT 1991; 66:303-9. 9. Mahalick JA, Knap FJ, Weiter EJ. Occlusal wear in prosthodontics. J Am Dent Assoc 1971;82:154-9.

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10. DeLong R, Sasik C, Pintado MR, Douglas WH. The wear of enamel when opposed by ceramic systems. Dent Mater 1989;5:266-71. 11. Wiley MG. Effects of porcelain on occluding surf ~cesof restored teeth. J PROSTHETDENT 1989;61:133-7. 12. Chapman RJ, Nathanson D. Excessive wear of natural tooth structure by opposing composite restorations. J Am Dent Assoc 1983;106:51-3. 13. Suzuki S, Leinfelder KF. Wear of enamel cusps opposed by posterior composite resin. Quintessence Int 1993;24:885-90. 14. Waknine S, Gold AJ, Leinfelder KF. Comparative evaluation of clinical and laboratory wear of posterior composites [Abstract]. J Dent Res 1988;67:361. 15. Sakaguchi RL, Douglas WH, DeLong R, Pintado MR. The wear of a posterior composite in an artificial mouth: a clinical correlation. Dent Mater 1986;2:235-40. 16. Embong A, Glyn Jones J, Harrison A. The wear effects of selected composites on restorative materials and enamel. Dent Mater 1987;3:23640. 17. Powell JM, Phillips RW, Norman RD. In vitro wear response of composite resin, amalgam and enamel. J Dent Res 1975;54:1183-95. 18. Sulong MZAM, Aziz RA. Wear of materials used in dentistry: a review of the literature. J PROSTHET DENT 1990;63:342-9. 19. Waknine S, Prasad A, Jia W, Schulman A. Direct/indirect commercial composites: characterization of strength, shrinkage and wear [Abstract]. J Dent Res 1991;70:481. 20. Covey DA, Tahaney SR, Davenport JM. Mechanical properties of heattreated composite resin restorative materials. J PROSTHET DENT 1992;68:458-61. Reprint requests to: DR. JAMES D. HUDSON 630 FIFTH AVE. SUITE 1810 NEW YORK, NY 10111

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