Polishing porcelain veneers: an SEM and specular reflectance analysis Haywood VB, Heymann HO, Kusy RP, Whitley JQ, Andreaus SB. Polishing porcelain veneers: an SEM and specular reflectance analysis. Dent Mater 1988: 4: 116--121.

Abstract - Techniques for placement of etched porcelain laminate veneers require that the glazed porcelain veneer be cemented prior to finishing and polishing. Finishing the veneer margins corrects the inherent marginal defects but results in removal of the glaze from the porcelain. This invites a poor tissue response unless the porcelain can be polished to a smooth surface. Using scanning electron microscopy (SEM) and specular reflectance, the surface texture of autoglazed porcelain was compared with that of polished porcelain. Emphasis was placed on those instruments which are suitable for gingival and interproximal finishing. Finishing with a fine diamond instrument followed only by diamond polishing paste produced an unacceptable surface. A finish equal or superior in smoothness to glazed porcelain was achieved through the use of a series of finishing grit diamonds (Micron Finishing System) followed by a 30- fluted carbide bur and diamond polishing paste. Other finishing combinations produced surface textures which were not as smooth as glazed porcelain, but which were better than that attained by the diamond polishing paste alone.

V. B. Haywood*, H. O. Heymann**, R. P. Kusy***, J. Q. Whitley***, S. B. Andreaus . . . . *Department of Fixed Prosthodontics, **Department of Operative Dentistry, ***Dental Research Center/Department of Orthodontics/ Biomedical Engineering and . . . . Student Research Assistant, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina, USA

Key words: dental polishing, dental porcelain, dental restorations, dental materials.

Dr. Van B. Haywood, Department of Fixed Prosthodontics, UNC School of Dentistry, Chapel Hill, NC 27514, USA.

Received February 10; accepted May 23, 1987.

The recent advent of etched porcelain laminate veneers has added a new di- mension to esthetic dentistry. Howev- er, finishing of the margins' post-ce- mentation removes the glaze from the porcelain. If the porcelain cannot be polished to a smooth surface, a poor tissue response will result, producing an unesthetic restoration. Using a bench lathe, Sulik and Plekavich (1) showed that a mixture of pumice and tin oxide produced a polished porcelain surface which was equal to a glazed porcelain surface. Bessing and Wik- torsson (2) confirmed this observation using a straight handpiece with the Shofu porcelain polishing system*, while Smith and Wilson (3) achieved similar results with 3M Soflex discs*. While these instruments perform satis- factorily on flat accessible surfaces at high speeds, none are well-suited for finishing the crucial gingival or inter-

* Porcelain Adjustment Kit, Shofu Dental Corp., 4025 Bohannon Drive, Menlo Park, CA 94025, U.S.A.

* Soflex Polishing Discs, 3M Dental Prod- ucts Division, St. Paul, MN 55144, U.S.A.

proximal regions of a bonded porcelain veneer. In these areas several tech- niques have been suggested, including the direct progression from a fine dia- mond instrument to a rubber prophy cup with diamond polishing paste. This study evaluates finishing and polishing techniques which might produce a sur- face texture comparable to glazed por- celain using instruments suitable for gingival and interproximal areas.

Material and methods

SEM photographs were made of vari- ous instruments suitable for gingival and interproximal surfaces, and of sev- eral different diamond polishing pastes to evaluate the particle sizes of the abrasives*.

Ten disks of conventional dental por- celain w measuring 10 mm x 4 mm were stacked and fired in a vacuum oven at

Etec U-1 Autoscan Scanning Electron Microscope. Ceramco II body porcelain, Shade C4, Ceramco Inc., Johnson & Johnson Co., 20 Lake Drive CN 7065, East Windsor, NJ 08520, U.S.A.

960~ To evaluate whether or not the instrument used to finish the porcelain prior to glazing would affect the smoothness of the glaze, one-half of the flat surface of each disk was smoothed with either an F. G. green stone II or a fine diamond instrumentL To produce the smoothest glazed surface possible without rounding the corners of the disks, the samples were fired at 960~ for six 2 min cycles.

After these disks were attached to SEM studs with cyanoacrylate cement, 3 notches were placed in the edge of each disk to orient and to identify the left and right halves. Disks were sput- ter-coated with gold-palladium * and examined with the SEM. Photographs of the entire disk at 100 • and 10 • magnifications were taken, and the two

II Dura-Green Stone, Shofu Dental Corp., 4025 Bohannon Dr., Menlo Park, Ca 94025, U.S.A. Brasseler 8862 Diamond, Brasseler USA, Inc., 800 King George Boulevard, Savannah, GA 31419, U.S.A. Polaron 5200 Sputter Coater, Polaron Instruments Inc., 2293 Amber Dr., Hat- field, PA 19440, U.S.A.

Polishing porcelain veneers 11 7

Fig. 1. Scanning electron micrograph of glazed porcelain previously finished with an EG. green stone.

sides were c o m p a r e d for smoothness (Figs. 1 and 2). Based upon these re- sults, t he f ine d i a m o n d ins t rumen t was chosen to gene ra t e a base l ine surface texture before the glazing and polishing tests.

The disks were resurfaced with the fine d i a m o n d ins t rumen t , t h e n one half of each disk was pol i shed with d i amond pol ishing pas te • using a w e b b e d r u b b e r p rophy cup. Rep re sen t a t i ve pho tomi - c rographs were t a k e n (Fig. 3) and com- pa red to those of the previously glazed porce la in (Fig. 2). The disks were re- surfaced with the fine d i a m o n d instru- men t , t hen two disks were pol ished

Truluster Polishing System, Brasseler USA, Inc., 800 King George Boulevard, Savannah, GA 31419, U.S.A.

with each f inishing sequence (Table 1) in accordance wi th the manufac tu r e r ' s ins t ruct ions for each ins t rument . A1- *Codes: though some ins t rumen t s listed in the FD = fine table do not lend themse lves to the fin- ishing of gingival and in te rprox imal ar- DPP = eas, they were inc luded for purposes of compar i son to previous studies. F rom MFS = SEM p h o t o g r a p h s of all samples at • 100, compar i sons were m a d e to the

30 = p h o t o m i c r o g r a p h s of the glazed porce- 9 = lain s t andard (Fig. 2). Based upon the 12 = a p p a r e n t surface texture achieved, the Hy = pho tog rap h s r ep resen t ing each tech- Wh = n ique were g raded as: 1) i nadequa te ; 2) 3M = adequa te ; or 3) super ior (Table 2). RW =

Once the var ious sequences for pol- ishing had b e e n eva lua ted by the SEM, Whs = the samples were resurfaced with the ET = fine d i a m o n d ins t rument . O n e pair was

pol i shed wi th the best me t h o ds indi- cated via S E M (M) , one pair was pol- ished by the d i a m o n d pol ishing pas te a lone (P), and o n e pair was autoglazed (A). A f t e r the appropr ia t e t r ea tmen t , each sample was placed in an acrylic ho lder an d eva lua ted by specular re- f lectance (4, 5). O n the assumpt ion tha t a perfect ly s m o o t h surface should re- flect l ight at an angle ( f rom the no rma l of the t a rge t surface) which equals the inc ident angle (ct) and wi th an in tensi ty which equals the inc ident beam, any angular shift or in tensi ty loss indicates some fo rm of roughness . Using a he- l ium-neon laser ~ having a 6328 A wave-

Metrologic Instruments, Inc., Bellmawr, NJ, U.S.A.

Table 1. Sequences of instrumentation uti- lized to polish porcelain.

Instrumentation sequence* Category

FD - DPP Inadequate (P) FD - 30 Adequate FD - 3 0 - DPP Adequate FD - Wh Adequate FD - Wh - DPP Adequate FD - MFS Adequate FD - MFS - 3M Adequate FD - MFS - 3M - DPP Adequate FD - MFS - DPP Adequate FD - MFS - 30 Adequate FD - 3 M - DPP Adequate FD - RW Adequate FD - RW - DPP Adequate FD - Wh - RW Adequate FD - Whs - RW Adequate FD - H y - 30 - DPP Adequate FD - MFS - Wh - DPP Adequate FD - W h - 30 - DPP Adequate FD - W h - 3M - DPP Adequate FD - ET - DPP Adequate FD - E T - 30 - DPP Adequate FD - 9 - DPP Adequate FD - 9 - 30 - D P P Adequate FD - 12 - DPP Adequate FD - 1 2 - 30 - D P P Adequate FD - M F S - 30 - DPP Superior (M)

diamond instrument (8862 Brasseler) diamond polishing paste (Bras- seler Truluster on webbed rubber prophy cup) Micron Finishing System dia- monds 1, 2, 3 (Abrasive Tech- nology) 30-fluted carbide bur (Midwest) 9-fluted carbide bur (Brasseler) 12-fluted carbide bur (Midwest) Hybrid diamond (Shofu) white stone friction grip high speed (Shofu) Soflex disk series (3M) three rubber wheels (Shofu Polish- ing Kit) white stone straight handpiece slow speed (Shofu Polishing Kit) Esthetic Trimming diamonds, fine and extra fine (Brasseler)

118 Haywood et al.

Table 2. Criteria for evaluation of surface smoothness of polished porcelain.

Category Criteria

Inadequate

Adequate

Superior

Surface characterized by significant roughness in form of grooves, chips, or pitting. Deviates significantly from glazed porcelain standard.

Surface characterized by shallow grooves, chips or pitting. Nearly resembles glazed porcelain standard, but not equal.

Surface characterized by absence of grooves, chips or pitting. Surface is comparable or superior to that of glazed porcelain standard.

length and a 0.6 mm beam diameter , the relative smoothness was deter- mined by measuring the reflected power of each sample (Ix) in microwatts (~tW) and comparing it with the inten- sity of the incident beam (Io). Using the notches on the samples for or ientat ion, scans of each sample were taken at 3 different locations at a single ct = 70 ~ The value, Ix, was de termined from the maximum value on the spectral map of the reflected coherent light beam as the photodetec tor was rotated through an angle (0) which was + 15 ~ about the theoretical angle of reflectance, 70 ~ . Prior to each run, the initial power of the laser (Io = 600 ~tW) was verif ied by placing the detector coaxial with the beam. Since the determinat ions were made within such a short per iod of time, power at tenuat ion from tube ag- ing was not a problem. Consequent ly , in the preliminary data repor ted here , either the absolute or the relat ive

Fig. 2. Scanning electron micrograph of glazed porcelain previously finished with a fine dia- mond instrument.

Table 3. Approximate particle size of various abrasive instruments used to polish porcelain.

Company Instrument Particle Size (~tm)

Abrasive Technology: MF 1 25-35 Micron Finishing System MF 2 10-20

MF 3 2-5

Brasseler: OS1 - F 30-75 Esthetic Trimming diamonds OS1 - EF 17-24

3-M: Black 300 Soflex disks Dark blue 45-80

Medium blue 10-22 Light blue 3-5

Shofu Hybrid diamond 10-22

Brasseler: Diamond polishing paste 2-5 Truluster

power gave a good indication of the relative surface roughnesses: the grea- ter the I x or Ix/I o of the sample, the smoother the surface relative to anoth- er. Future work will quantify these roughnesses in terms of R M S or aver- age roughness values using multiple, grazing ct's.

Results

SEM photographs of the instruments, which were used to polish the porce- lain, revealed a wide range of particle sizes (Table 3). Only one d iamond pol- ishing paste (Truluster) was used in all polishing techniques, but SEM photo- graphs were taken of several o ther available pastes. These revealed some radical differences in particle size. Tru-

Polishing porcelain veneers 119

Fig. 3. Scanning electron micrograph of porcelain polished with a fine diamond instrument and diamond polishing paste.

luster and Instaglaze* polishing paste had fairly uniform diamond particles of 2-5 gin. Chameleong polishing paste and Den-mat h had no apparent dia- mond particles as large as 1 ~tm.

When the glazed porcelain samples which had previously been finished with a green stone were compared to those which were previously finished with a fine diamond instrument, the surface morphologies at x 100 magnifi- cation appeared identically smooth.

The polishing sequence using a fine diamond instrument followed by dia- mond polishing paste was "inadequate" (Table 1). Most of the other finishing techniques produced "adequate" re- sults when compared to the glazed por- celain standard using the SEM. A "su- perior" finish was achieved by pro- gressing from the fine diamond instrument through the Micron Finish- ing System diamonds ~ to a 30-fluted carbide bur II followed by Truluster dia- mond polishing paste on a webbed rub- ber prophy cup (Fig. 4). This polishing technique was used to polish the sam- ples for Group M.

Representative laser spectra of the three different porcelain surfaces (M, A, and P) at a = 70 ~ show that both M

* George Taub Prod. Inc., Jersey City, NJ 07307, U.S.A.

t Chameleon Diamond Paste, Chameleon Dental Products, Two Gateway Center, Kansas City, KS 66101, U.S.A.

* Den-mat Corp., P.O. Box 1729, Santa Maria, CA 93456, U.S.A. Micron Finising System, Premier Dental Products, Romano Drive, P.O. Box 111, Norristown, PA 19404, U.S.A.

II Midwest Division of Sybron Corp., Des Plaines, IL, U.S.A.

Table 4. Specular reflectance of dental porcelain.

Group Sample Absolute intensity*, I x (~tW)

Range Mean Low High

Standard deviation

M: Best method M~ 19.2 25.6 indicated M e 13.7 27.5 by SEM

23.4 18.5

3.64 7.82

MIM~ 13.7 27.5 20.9 6.09

A: Autoglazed A 1 6.9 10.8 9.23 2.06 A 2 6.4 10.2 8.43 1.91

A1A ~ 6.4 10.8 8.83 1.83

P: Diamond polishing P1 0.13 0.16 paste alone P2 0.25 0.36

0.15 0.29

0.01 0.06

P1pz 0.13 0.36 0.22 0.08

*Initial intensity, Io = 600 lxW.

120 Haywood et al.

•

~o a_

eo .>_

+ 1'5 (3 - 15 ~ + 1'5 C C W ~ C W ~

S c a n A n g l e , e (~

Fig. 5. Typical laser spectra of three differ- ent porcelain surfaces at c~ = 70~ A = auto- glazed; P = diamond polishing paste only; M = Micron Finishing System, 30-fluted carbide bur, and diamond polishing paste. Spectra shows both the relative intensity (IJIo) and the absolute intensity (I• as the detector is scanned + 15 ~ in both the coun- terclockwise (CCW) and the clockwise (CW) directions.

and A have similar overall peak widths (Fig. 5). In contrast, both the relative and the absolute powers are generally greater for M than A at scan angles which are _+ 10 ~ about the angle of re- flectance. By superposing these scans, P appears to be little more than back- ground noise compared to either A or M.

When the peaks were considered alone, the average spectral reflectivities of the 3 different groups equalled 20.9 + 6.09 ~tW, 8.83 + 1.83 ~W, and 0.22 + 0.08 ~W for groups M, A, and P, respectively (Table 4). When a one-way analysis of variance and a Tukey post- hoc test were applied to determine the level of significance between the 18 measurements of the 6 samples, no sig- nificant intragroup difference was found; however, a significant inter- group difference was observed (p -< 0.01).

Discussion

Upon comparing the particle size of the various abrasive instruments used in this study (Table 3 ) t o the effect pro- duced on the porcelain, a longtime maxim of metallurgical sample prepa- ration is reinforced: all else being equal, the production of an acceptable surface requires the particle size of the abrasive to decrease systematically.

Fig. 4. Scanning electron micrograph of porcelain polished with a fine diamond instrument, MFS diamonds, 30-fluted carbide bur, and diamond polishing paste.

This difference in particle size of the 4 different diamond polishing pastes could affect their polishing efficiency, depending on the particle size of the instrumentation used prior to their use. In the final analysis the Truluster dia- mond polishing paste was used because its diamond particles are fairly uniform (2-5 p,m).

The sequence (M) which included the Premier Micron Finishing System and a Midwest 30-fluted carbide fin- ishing bur produced a significantly su- perior finish. However, to finish a ve- neer using 5 different instruments and polishing paste is extremely time-con- suming. Moreover, MFS diamonds should be used in a high speed hand- piece at low speed with water coolant to improve cutting efficiency and pre-

vent overheating. This requirement makes the surface finish difficult to evaluate without periodic drying. This protocol should be followed, however, since these diamonds were designed for composite resins, and the binder life against a porcelain surface is undocu- mented. The 30-fluted carbide burs polished satisfactorily only after the scratches had been reduced in size by previous abrasive instruments. It should be noted that the 9- or 12-fluted carbide burs did not produce this same kind of smoothness because they tended to chip or cleave the porcelain. No attempt was made to further differ- entiate or rank order the other "ade- quate" finishing techniques owing to the complexity of their rough surfaces.

One inherent disadvantage of the

Polishing porcelain veneers 121

SEM is that samples viewed at higher magnifications often appear decep- tively smoother. If the magnification is reduced to obtain a representative f i e ld of view, the topography varies so widely as to make quantitative meas- urements impossible. The advantage of the specular reflectance technique is that quantitative results can be ob- tained provided the surfaces are rela- tively smooth. In subsequent specular reflectance work, the actual (or abso- lute) surface roughnesses of the present as well as other finishing techniques will be determined and compared with autoglazed porcelain.

Conclusions

Porcelain which has been polished in- traorally can equal or even surpass the smoothness of glazed porcelain. To

achieve this smoothness, instruments must be used which progressively de- crease in particle size. A polishing se- quence which uses a fine diamond in- strument followed by diamond polish- ing paste produces an "inadequate" surface. In contrast, a polishing se- quence which uses a fine diamond in- strument followed by the Premier Mi- cron Finishing System diamonds, the Midwest 30-fluted bur, and the Trulus- ter diamond polishing paste on a webbed rubber prophy cup produces a surface which is "superior" to that of a glazed porcelain standard. While the SEM provided a qualitative assessment of the surface finishes, only specular reflectance provided the necessary quantitative results.

Acknowledgements - This study was sup- ported by a Junior Faculty Development

Award from the R. J. Reynolds Fund and by NIH grant numbers DE02668 and RR05333.

References

1. Sulik WD, Plekavich EJ. Surface finish- ing of dental porcelain. J Prosthet Dent 1981: 46: 217. Bessing C, Wiktorsson A. Comparison of two different methods of polishing porce- lain. Scand J Dent Res 1983: 91: 482.

3. Smith GA, Wilson NHE The surface fin- ish of trimmed porcelain. Br Dent J 1981: 151: 222. Konishi RN, Whitley JQ, Kusy RP. Sur- face roughness of a dental amalgam via a laser scattering test. Dent Mater 1985: 1: 55. Kusy RP, Whitley JQ. In situ replication techniques. II. Quantitative methodolo- gies for replicate materials. J Biomed Mater Res 1985: 19." 35.

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9 Dental Materials 4:3, 1988