The polishability of posterior composites

The polishability Anthony Loma

Linda

of posterior

H. L. Tjan, Dr. Dent., D.D.S.* University,

School

of Dentistry,

Loma

composites

and Clayton Linda,

A. Chan, B.A.**

Calif.

The polishability of six brands of posterior composites was evaluated by means of a stylus profile instrumentation and scanning electron microscopy and was compared with that of an anterior microfilled composite. A sedigraphic study was performed to estimate the size and distribution of their inorganic particles. The extent of the filler loading as well as the hardness values were also assessed to determine any relevant characteristics. Some of the findings indicated that posterior composites with large particles produced significantly higher surface roughness than those with small fiber particles. A direct correlation was also found between the hardness value and surface roughness value, indicating that a composite with higher hardness value yielded a higher roughness value. (J PROSTHET DENT 1989;61:138-46.)

A

unique drawback inherent to most compositesis the difficulty in polishing that often resultsin a rough or dull surface.lm6This problem has been attributed to the differencein hardnessbetweenthe inorganic filler component and the polymeric matrix. ‘* 4,5,7 Increased plaque retention, gingival irritation, and staining of the restoration are probable results of improperly finished restorations.‘*4,5,s-lo In addition, rough, unpolishable posterior compositesincrease the coefficient of friction, and thus increase the rate of wear.l’ Compositesdiffer mainly in their inorganic component. Thctype of inorganic filler, the size of the particles, and the extent of the filler loading vary widely among composites. Such factors influence the polishability of the composite.” This investigation evaluated and compared the polishability of several commercially available posterior composites by using stylus profile instrumentation and scanning electron microscopy. A particle size analysiswasperformed to estimate the size and distribution of their inorganic particles. The extent of the filler loading and hardnessvalues was also assessed to determine relevant characteristics.

MATERIAL

AND

METHODS

Six brands of posterior composite (one chemically activated system and five visible light-activated systems)were studied, and an anterior microfilled compositewasincluded for comparison. The product names,batch numbers, and manufacturers are listed in Table I. Cylindrical specimens2.5 mm thick and 6 mm in diameter were prepared in a stainlesssteelsplit mold (Fig. 1). The compositewasinjected into the mold, covered with a micro-

*Professor and Director of Biomaterials Restorative Dentistry. **Dental Student, Work-Study Dental

138

Research, Research

Department Program.

of

coverglass(V.W.R. Scientific Inc., San Francisco,Calif.) and irradiated for 40 set with a visible light (Elipar Visio, EspePremier SalesCorp., Norristown, Pa.). The specimenswere then immersedin distilled water for 1 week in an incubator at 37’ C. Ten specimenswere prepared from each tested composite.

Hardness

value

The hardnessof five randomly chosenspecimensof each compositetested wasmeasuredwith a Rockwell superficial hardnesstester (15T, l/is inch indenter, Wilson Mechanical Instrument Div., New York, N.Y.). Three hardnessreadings were madefrom each specimen,and the hardnessvalue was recorded as the average of these three readings. The hardnessvalue of the tested product wascomputed asthe arithmetic mean of the hardnessvalues of the five specimens.

Surface

roughness

measurement

After the test for hardness,all specimenswere randomly assignedinto a group consisting of one specimenof each compositetested. Each group was potted in a plastic ring (Fig. 2) with a clear autopolymerizing acrylic resin (Orthocryl, Stratford-Cookson Co., Newnan, Ga.). The exposed surfacesof the specimenswere roughened with white stone (Shofu Co., Menlo Park, Calif.) for 15 secondsand baseline measurementswere established. Two polishing systems were included in this study, (1) AleO,-coated Sof-Lexdisks (3M Co., St. Paul, Minn.) and (2) SiO,-impregnated rubber polisher (Vivadent Inc., Buffalo, N.Y.). The surface roughness(Ra value or arithmetic average roughness)was determined by using a Surftester (Surftest III, Mitutoyo, Tokyo, Japan) instrument with a diamond stylus traveling at 2 mm/set (tip radius 10 + 2.5 pm, tip angle90 k 10degrees,measuringforce 1.5gf or 15mN) and was recorded on a Surfcorder (Mitutoyo) machine with a cutoff

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POLISHABILITY

Fig.

OF POSTERIOR

COMPOSITES

1. Stainlesssteel split mold used to make specimens.

value of 0.8 mm. These measurementsof surface roughness were madeafter eachsuccessivestageof finishing or polishing. Three transversesof different directions (0, 45, and 90 degrees)were made for each specimen,and the roughness value was recorded as the average of these three readings. Five groups of the potted specimenswere polished with the Sof-Lex systemby using a sequenceof stepsfrom coarse to superfine (150,360,600, and 1200grit size) culminating in a final polish with a 0.3 pm alumina paste (Luster paste, Sybron/Kerr, Romulus,Mich.). After eachsuccessivechange in abrasive,the specimenswere rinsed thoroughly to remove all debris from the previous abrasive. Large size Sof-Lex disks with a diameter of 20.3 cm (8 in) were mounted on a metallurgical polisher (Ecomet II, Buehler Ltd., Lake Bluff, Ill.) and usedto polish the potted group of specimenssimultaneously for 40 secondsfor each abrasivestep. The specimenswere rotated 45 degreesevery 10 secondsto assurea uniform grinding. Sof-Lex polishing sheetsprovided by 3M Co. were usedto make the large-size disks. This grouping of the specimensand simultaneous polishing on a large disk with a metallurgical polisher provided equal pressure,time, and rotational speedduring polishing for eachspecimen.Every effort wasalsomadeto control these factors when a slow-speedhandpiece had to be used.All finishing and polishing proceduresweredoneby the sameinvestigator to reduce variability. As suggestedby the manufacturer, no water coolant was used during polishing with Sof-Lex disks. However, to prevent thermal damageto the specimens,the polishing disk was run at a low speed.A speedof 187to 200 rpm wasestimated by using a noncontact digital photoelectric tachometer that measuredrpm by reflection of light from a sensing strip (Mitutoyo), and a pressureof 50 to 75 gf/cm* was recorded with a modified pressuregauge(Mitutoyo). A final polish was done with Luster paste by using a rubber cup

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Fig. 2. One specimen from each composite tested was potted in plastic ring with autopolymerizing acrylic resin.

Table I. Codes,batch numbers, and manufacturers of compositesstudied Code

Product

Batch number

SL

Silux*

4C2

HL

Heliomolar

850384

HR

Herculite

504A

FF

Ful-Fil

P-30

P-30

1102837 032784

P-10

P-lot

CII

Curay II

*Anterior tChemically activated

microfilled composite, activated posterior posterior composite.

A3420, B-3A7 BB-389 for comparison. composite. All

Manufacturer

3MCo.

St. Paul, Minn. Vivadent (USA), Inc. Tonawanda,N.Y. Sybron/Kerr Romulus,Mich. The L.D. Caulk Co. Milford, Del. 3M Co.

Sci-Pharm,Inc. Duarte,Calif. others

are

visible

light-

(Crescent Dental Mfg. Co., Lyons, Ill.) on a slow-speed handpiece at approximately 3000rpm for 60 seconds. In contrast to the Sof-Lex system,where the potted specimens were polished simultaneously with a large disk, the compositesin the other five groupsof potted specimenswere polishedindividually with SiO,-impregnated rubber polishers on a slow-speedhandpiece. After the baselinemeasurements were establishedas describedearlier, the initial polishing w.asdone with a gray rubber polisher for 15 seconds and a green rubber polisher for an additional 15 seconds. This time increment wasestimated to deliver an equal number of strokesto each specimenpolishedwith the Vivadent

139

TJAN

AND

CHAN

Am

1.40

1.30

1

T

0

3Y

0

VIVADENT

8OF-LEX

I

I

P-30

P.10

: 0.90 a >

0.80

t

3 0.70 E 3

0.80

z

0.50

0.10 0.00

t I

I

1

8L

HL

I

HR BRAND

I

OF

I

FF CF COMPOSITE

II

Fig. 3. Graph depicts means and standard deviations of surface roughness of composites studied.

Table

II.

Surface roughness (Ba value in pm) of composites polished with 3M Sof-Lex disk system White

Brand

Silux

Heliomolar Herculite Ful-Fil P-30 P-10

Curay II Vertical

stone

Coarse

Medium

Luster

paste

SD

Ra

SD

Ra

SD

Ra

SD

Ra

SD

Ra

SD

0.45 0.41 0.43 0.62 0.70 0.67 0.68

0.13 0.11 0.15 0.24 0.20 0.12 0.18

0.95 1.01 0.84 0.94 1.10 1.06 1.10

0.32 0.51 0.19 0.30 0.33 0.17 0.23

0.24 0.36 0.25 0.35 0.47 0.41 0.45

0.03 0.11 0.08 0.06 0.06 0.07

0.19 0.21 0.16 0.27 0.32 0.31 0.32

0.04 0.04 0.04 0.05 0.06 0.04 0.02

0.12 0.14 0.11 0.21 0.28 0.27 0.27

0.01 0.04 0.03 0.04 0.03 0.01 0.02

0.14 0.15 0.11 0.18 0.26 0.28 0.27

0.02 0.01 0.02 0.03 0.03 0.02 0.01

lines denote no significant

difference

0.01

at p 5 .Ol.

analysis

Specimens polished with both polishing systems were prepared for examination with a scanning electron micro-

140

Superfine

Ra

system as delivered to the specimens polished with the SofLex system, considering the differences in speed between the handpiece and the Ecomet II polisher. A total of 105 minutes per step was spent to polish a group of seven specimens with the handpiece and Vivadent system. A final polish with Luster paste and a rubber cup on a slow handpiece for 60 seconds was done to evaluate the effectiveness of this extra step on the final results.

SEM

Fine

scope (SEM) (Amray Inc., Bedford, Mass.). The specimens were coated with a 2OOA layer of gold-platinum. Scanning electron micrographs made at original magnifications of x20 and X500 were evaluated and compared for surface texture and roughness.

Particle

size analysis

Particle size at 10% sedimentation level (larger particles) and the median particle size of the fillers of the posterior composites were determined by using a particle size analyzer (Sedigraph 5000 D, Micromeretics Instrument Corp., Norcross, Ga.) that detected the sedimentation rates of compos-

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Table

III.

OF POSTERIOR

COMPOSITES

Surface roughness

(Ra value in pm) of composites

White Brand Silux Heliomolar Herculite Ful-Fil P-30 P-10 Curay II Vertical

stone

Gray

polisher

polisher

system

polisher

Luster

SD

Ra

SD

Ra

SD

0.45 0.41 0.43 0.62 0.70 0.67 0.68

0.13 0.11 0.15 0.24 0.20 0.12 0.18

0.32 0.32 0.24 0.39 0.73 0.62 1.04

0.10 0.14 0.09 0.07 0.13 0.13 0.11

0.25 0.23 0.19 0.36 0.74 0.78 1.14

0.09 0.08 0.06 0.03 0.05 0.07 0.18

0.28 0.23 0.19 0.32 0.64 0.73 1.05

0.11 0.07 0.07 0.04 0.08 0.04 0.20

difference

3M Sof-Lex disk

at p 4 .Ol.

technique Vivadent polisher

Ra

SD

Ra

SD

Total

0.12 0.14 0.11 0.21 0.28 0.27 0.27 1.40

0.01 0.04 0.03 0.04 0.03 0.01 0.02

0.25 0.23 0.19 0.36 0.74 0.78 1.14 3.69

0.09 0.08 0.06 0.03 0.05 0.07 0.18

0.37 0.37 0.30 0.57 1.02 1.05 1.41

Table

V.

Summary

of ANOVA

Total Brands of composite (rows) Polishing systems (columns) Error

sum of squares

df

Variance estimate

6.301 2.803

69 6

0.467

93.4

s

1.893

1

1.893

374.6

S

0.257

56

0.005

Product

ite filler particles in a slurry by a finely collimated beam of low-energy x-rays. Samples of each tested posterior composite were prepared, tested, and graphed.

loading

The weight percentage of the filler loading was determined by burning off the resin and weighing the filler portion that was not thermally decomposed in this process. A two-way analysis of variance was performed to analyze the data with the composites’ brands and polishing systems as the variables. The means were compared by using Duncan multiple range tests. Student t-tests were used to determine the significance of an additional polishing with a polishing paste. Pearson’s product moment (r) was used to analyze the strength and direction of the relationship between surface roughness and hardness value.

RESULTS The arithmetic means and standard deviations of the surface roughness values (Ra value) for the seven brands of composite tested, finished with both polishing systems, are presented in Tables II and III. Table IV compares the surface roughness of the composites polished with the two pol-

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F

ps.01

Table VI. Hardness value (RHN), filler loading, mean particle size, and particle size at 10% sedimentation level of composites studied Particle

Filler

paste

Ra

Polishing

Curay II Total

Green

rubber

SD

Table IV. Comparison of surface roughness (Ra value in pm) of composites polished with Sof-Lex disks and Vivadent rubber polisher system

Silux Heliomolar Herculite Ful-Fil P-30 P-10

with Vivadent

Ra

lines denote no significant

Brand

polished

Silux Heliomolar Herculke Ful-Fil P-30 P-10 Curay II *Measured tllilicrofilled

size in rm

Hardness W-W

Filler wt%

Mean

10% level*

75.0 73.8 81.4 81.9 87.4 88.4 86.8

52.0 59.1 78.0 75.8 84.5 83.2 87.0


--t --t >1.3 >6.8 >7.8 >ll.O >lS.O

large particles at 10% sedimentation level. composites; particle size below 0.1 pm not measurable.

ishing systems tested. Fig. 3 graphs the means and the standard deviations. Statistical analysis of the data with a two-way analysis of variance indicated significant differences between the brands of composite and between the polishing systems at p < .Ol. The summary of the ANOVA is presented in Table V. The surface roughness values of the composites with larger filler particles (Curay II, P-10, P-30, and Ful-Fil) were significantly higher than those of composites with smaller filler particles (Herculite, Heliomolar, and Silux) finished with either 3M Sof-Lex disks or Vivadent rubber polishers

141

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Fig. 4. Surface profile tracing of composites finished with series of four Sof-Lex disks (range = 3 pm): A, Silux; B, Heliomolar; C, Herculite; D, FulFil; E, Curay II; F, P-30; and G, P-10.

Fig. 5. Surface profile tracing of composites finished with Vivadent rubber polisher (range = 3 pm): A, Silux; B, Heliomolar; C, Herculite; D, FulFil; E, Curay II; F, P-30; and G, P-10.

(p < .Ol). Figs. 4 and 5 show the surface profile tracings of all the composites polished with both polishing systems. 3M Sof-Lex disks produced significantly smoother polished surfaces than Vivadent rubber polishers for all of the composites tested except Herculite. The surface roughness values of Herculite (small-particle hybrid) composite polished with both systems were not found significantly different statistically. Analysis of the data by using Student t-tests revealed that additional polishing with 0.3 pm alumina paste (Luster paste) produced no significant improvement of surface polish. SEM analysis showed, in general, a strong agreement with the profilometric data. The Sof-Lex disk system produced surface scratches or striations on all specimens at each successive finishing step, although no exposed filler particles were evident (Fig. 6). Scanning electron micrographs of 142

composites finished with rubber polisher systems showed no striations on any of the tested surfaces. However, exposed particles were observed (Fig. 7). Table VI depicts the hardness values (RNH), filler loading (filler percent by weight), mean particle size, and the particle size at the 10% level of all the composites studied. A statistically significant linear correlation (r =.845, a = .Ol) was observed between the hardness values (RHN) and surface roughness (Ra value). Those composites with a higher hardness value produced a correspondingly higher Ra value.

DISCUSSION The specimens that were finished with aluminum oxide (Al,O,)-coated Sof-Lex disks showed smoother surfaces than those finished with silicon dioxide (SiO,)-impregnated rubber polishers. Nonetheless, an analysis of the SEM photographs (origFEBRUARY

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Fig. 6. #Scanning electron micrographs depicting surface profiles of composites with Sof,-Lex system: A, Silux; B, Heliomolar; C, Herculite; and D, FulFil.

Fig. 6. E, Curay II: F, P-30; and G, P-10. Striations ticles. (see legend for Fig. 6, A through D.) TAE

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finished

but no exposed par143

TJAN

Fig. 7. Scanning with Vivadent

electron micrographs depicting surface profiles of composites system: A, Silux; B, Heliomolar; C, Herculite; and D, Ful-Fil.

inal magnification x20 and x500) revealed clearly that SofLex finishing disks produced surface striations or scratches at each successive stage of finishing. A similar observation was also reported by Norteast and Van Noort.13 These scratches were not evident when Vivadent rubber polishers were used. The Sof-Lex finishing disks system appeared to effectively abrade and polish the large filler particles as well as the resin matrix, thus giving a more even surface profile. On the other hand, the Vivadent polishing system did not produce surface striations, but it seemed to remove the resin matrix more easily, leaving the larger filler particles exposed and unfinished. Thus a rougher and more uneven surface profile was evident. Silicon dioxide, the abrasive used in the manufacture of Vivadent rubber polishers, is also the main filler component of microfilled composites. These rubber polishers were found effective only on microfilled composites and possibly smallparticle hybrid composites. The results of this study agreed with others’ findings that for a composite finishing system to be effective, the cutting particles (abrasive) must be relatively harder than the filler materials.4 Otherwise, the polishing agent will only remove the soft polymer and leave the filler particles protruding from the surface. Reported data indicate that the hardness of aluminum oxide (Mohs value) is significantly higher than that of silicon dioxide, and, in general, higher than most filler materials used in composite formulation.7, 14, l5 144

AND

CAAN

finished

The data also indicated that some posterior composites (for example, small-particle hybrids) can be successfully polished to a clinically acceptable surface smoothness similar to that of the microfilled anterior composite. A series of aluminum oxide-coated flexible disks is suitable for finishing and polishing directly accessible convex surfaces. However, these disks do not allow precise finishing of small delineated areas or concave and occlusal surfaces. Therefore, rigid rotary instruments, such as abrasive points, are still needed for that particular purpose. With some composites a clinically acceptable surface smoothness may be achieved by finishing with white stones. The data in Table II suggest the use of medium- instead of coarse-grit Sof-Lex disks as the next sequence after finishing with white stone, because the coarse-grit disk created deeper grooves or a higher Ra value than the white stone. Finishing or polishing is also a function of time, meaning that the results depend on the amount of time spent in the finishing procedure. The results presented in this study may not be optimal and may be at variance with other studies, but the time increments used in each successive step of finishing are considered clinically realistic. From simple observation, it can be deduced that posterior composites with smaller filler particles produced a smoother surface. The American Dental Association (ADA) Council on Dental Materials considered composites containing filler particles size up to 5 grn as “polishable” composites.16 FEBRUARY

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Fig. 7. E, Curay II: F, P-30; and G, P-10. Exposed tions. (see legend for Fig. 7, A through D.)

Analysis of the data revealed that increased hardness resulted in increased surface roughness. In addition, the data tend to indicate that the hardness of the composite increased with an increase in the filler content, which agreed with the findings of Li et a1.17

SUMMARY

AND

CONCLUSIONS

Six brands of posterior composite were evaluated for polishability. Two polishing systems were used, (1) Sof-Lex finishing disks (3M) and (2) composite rubber polishers (Vivadent). Correlation was sought between polishability and certain characteristics of the composite such as the hardness, filler loading, and filler particle size. The results were as follows. 1. Posterior composites with large filler particles produced a significantly higher surface roughness value (Ra) than those with small filler particles with either the Sof-Lex disks or the Vivadent rubber polishers system (p < .Ol). 2. Polishing posterior composite with a Sof-Lex disk system produced significantly smoother surfaces than with the Vivadent polishing system at p < .Ol. 3. No reduction in surface roughness values was obtained by additional polishing with 0.3 pm alumina paste (Luster paste). 4. Statistical correlation was observed between the hardness value (RHN) and surface roughness value (Ra). ComTHE

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particles

were evident,

but no stria-

posites with a higher hardness value produced a correspondingly higher roughness value (r = 645). 5. Scanning electron micrographic study indicated that (a) Sof-Lex disks produced some surface scratches, but no exposed filler particles, and (b) Vivadent rubber polishers showed no scratches, but exposed filler particles were observed. 6. When polishing posterior composites, an abrasive that is significantly harder than the fillers of the composite being polished should be used. We gratefully acknowledge the technical assistance provided Kerr Dental Material Center, Santa Ana, Calif.

by

Sybron/

REFERENCES 1. Lee

HL,

Scanning electron microscope study of composite J Dent Res 1970;49:149-58. Johmon LN, Jordan RE, Lynn JA. Effects of various finishing devices of resin surfaces. J Am Dent Assoc 1971;83:321-31. Dennison JB, Craig RG. Physical properties and finished surface texture of composite restorative resins. J Am Dent Assoc 1972;85:101-8. Chandler HH, Bowen RL, Paffenbarger GC. Method for finishing composite restorative materials. J Am Dent Assoc 1971;83:344-8. Weitman RT, Eames WB. Plaque accumulation on composite surfaces after various finishing procedures. J Am Dent Assoc 1975;91:101-6. Savoca DE, Felkner LL. The effect of finishing composite resin surfaces at difFerent times. J PROSTHET DENT 1980;44:167-70. Christensen RP, Christensen GJ. Comparison of instruments and commercial pastes used for finishing and polishing composite resin. Gen Dent 1981;21:40-5.

restorative

2. 3. 4. 5. 6. 7.

Swarts

ML.

materials.

145

TJANANDCHAN

8. Chan KC, Fuller JL, Hormati AA. The ability of foods to stain two composite resins. J PROSTHET DENT 1980;43:542-5. 9. Larato DC. Influence of a composite resin restoration on the gingiva. J PRWTHET DENT 1972;28:402-4. 10. Wise MD, Dykema RW. The plaque-retaining capacity of four dental materials. J PRO~THET DENT 1975;33:178-90. 11. *Jorgensen KD. Microfills in posterior occlusion. In: DF Taylor, ed. Proceedings of the International Symposium on Posterior Composite Resins. Chapel Hill, North Carolina, 1982;174. 12.
Endodontic

This

study

teeth.

and

dies

for

stone fabrication

endodontic

access

College

determines

the

extracted

of human

and

D.M.D., M.S.,* D.M.D., M.S.***

of Saskatchewan,

Forty-two

Crown

The

dies

of the

restorations.

access

openings The

crowns

stereomicroscopy,

crowns

during

fractured 29 crowns

or carbide fractures

There

exhibited was craze

were

polysulfide

by

were

removed and

of the

did

ceramic

luted using examined electron

seven

carbide diamond

and

scanning

difference

(Dicer) the

crowns material

in the

extent

instrumentation instrumentation.

crowns.

various

types

impressions

to a commercial were

chipping

than

completed,

crowns

However, lines

to represent

completed

and

Canada

on all-ceramic

were

preparation,

Sask.,

MS.,**

selected

forwarded The

D.M.D.,

opening

were were

no significant

instrumentation. and

access

crowns

Saskatocm,

of access teeth

preparations

poured.

preparation.

opening.

DR. ANTHONY H. L. TJAK LOMA LINDA UNIVEFXIY SCHOLL OF DENTISTRY LOMA LINDA, CA 92350

P. E. Teplitsky,

of Dentistry,

effects

permanent

transillumination, and

Reprint requeststo:

access of all-ceramic

J. K. Sutherland, M. B. Moulding, University

15. Kanter J, Koski RE, Graham DA. An evaluation of diamond polishing disks and pastes upon composite restorative resins. J Calif Dent Assoc 1980$43-7. 16. ADA Council on Dental Materials, Instruments and Equipment: Visible light-cured composites and activating units. J Am Dent Assoc 1985; 110:100-3. 17. Li Y, Swarm ML, Phillips RW, Moore BK, Roberta TA. Effect of filler content and size on properties of composites. J Dent Res 1985;64:13961401.

dental

to the

made, laboratory

prepared

established by direct

adjacent of chipping

for

vision,

microscopy. exhibited

teeth

criteria Two craze

lines,

to the

access

with

caused (J PROSTHET

diamond

more DENT

1989;61:146-9)

P

reparation of endodontic access openings through porcelain or ceramic metal restorations may cause fracture of the porcelain.’ This problem is not surprising in light of our knowledge of the structure and properties of dental porcelain,‘. 3 yet it is not well documented by scientific studies. A recent article examined the effects of access openings on Cerestore crowns (Johnson & Johnson Products Co., East Windsor, N.J.).4 Clinical examples of porcelain fracture are commonplace.

Presented to the Canadian Association for Dental Research, MidWest Section, Saskatoon, Canada. This work was supported by Dean’s Medical Research Council Grant MA 3489. *Associate Professor, Chairman, Department of Restorative and Prosthetic Dentistry. **Associate Professor, Director, Division of Endodontics. ***Assistant Professor, Director, Division of Prosthoclontics.

146

One source advises dentists to forewarn patients of this possibility before initiating therapy.5 Advance knowledge of the expected frequency of damage during access preparation would be useful practical information for both prosthodontist and endodontist. The Dicer crown (Dentsply International Inc., York, Pa.) is entirely ceramic in structure (Fig. 1). It consists of a cast ceramic crown that is heat-treated and then custom-shaded with surface colorants. Dicer crowns have been marketed in North America for approximately 3 years for use in both anterior and posterior teeth. This project determined the effect of preparing endodontic access openings through DiLor crowns.

MATERIAL

AND

METHODS

Forty-two extracted permanent teeth were selected to represent the various types of human teeth; seven each of maxillary anteriors, mandibular anteriors, maxillary premo-

FEBRUARY1989

VOLUME61

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