An evaluation of two resin systems for restoration of abraded areas

An evaluation abraded Ronald

of two

resin systems for restoration

of

areas K.

Marjorie

Harris,

D.D.S.,

1. Swartz,

Indiana

University

M.S.D.,*

Ralph

W.

Phillips,

D.Sc.,**

and

M.S.***

School

of

Dmtistry,

Indianapolis,

Ind.

T

reatment of noncarious lesions of the cervical region of teeth, resulting from dentifrice abrasion, has long been a concern in clinical dentistry. In a random snirrple of 10,000 extracted teeth, Sognnaes, Wolcott, and Xhongal found that 18 per cent showed evidence of cervical tissue loss. Regardless of whether lesions of nonbacterial origin are the result of softening of tooth structure by acid,2 improper brushing habits,” traumatic occlusion,’ or soft-tissue hyperactivity,” the problem exists and requires a solution. In the past, dentifrice abrasion usually has been treated by topical applications of fluorides or by the placement of metallic restorations. The latter necessitates further removal of tooth structure and may be esthetically unacceptable. More rccently. it has been proposed that a filled resin might be used for this purpose.‘; A conventional cavity preparation would not be used; but rather an acid etching tec~lmiclue lvould be employed to obtain a mechanical bond between the resin restoration and the tooth. However, only one study has reported on the efficacy of such ;I tcchnique.7 That was the purpose of this research, which involved both laboratory and clinical evaluations. METHODS

AND

MATERIALS

T\VO materials designed for this intended OIIC \tas a commercially available material,

of

Portions of this :he requirements

article were taken for the M.S.D.

purpose were included in the study. Enamelite,? while the other was an

from a thesis by the senior degree, Indiana University

author in partial fulfillinent School

of Dentistry,

June,

19i3.

The opinions or assertions not to lx: construed as official \PTT ice al 1ar~yg-e. *Commander Drpartment: Parris **4ssistant . ***Professor $l.ee

(DC) Island,

Dean

for

of Dental

Pharmaceuticals,

contained herein or reflecting the

USN; S. C.

currently

Research

at

and Research

are the private ones of the views of the Navy Department Dental Professor

Detachment, of Dental

Marine

writer and are or the naval Corps

Recruit

Materials.

Materials. South

El Mor.te,

Calif.

537

538

Harris,

Phillips,

J. Prosthct. Dent. May, 1974

and Swartz

Fig. 1. (A) A 67-year-old man with an advanced lesion on a maxillary The same patient at the base-line examination. The lesion was restored material. (C) An 82-year-old man with numerous cervical wear lesions. tient at the base-line examination, The lesions were restored with Enamelite.

lateral incisor. (B) with experimental (D) The same

pa-

experimental resin.* Both were basically composite formulations, but according to information supplied by the respective manufacturers, the fillers differed in type and amount. The procedures of manipulation and insertion were carefully standardized in accordance with the recommendations of the respective manufacturers. The same techniques were employed in the clinical and laboratory phases of the investigation. Clinical

procedure

One dentist placed the two materials in 75 contralateral pairs of teeth of 25 patients, using premolars and anterior teeth whenever possible. Kodachrome transparencies were made of the lesions before treatment was initiated. Random selection was used in determining which material was to be placed in each member of a pair. All restorations were placed within a period of three weeks, at the end of which the base-line evaluation was conducted. Restorations were re-evaluated at three and six months. Prior to placement of the restorations, the teeth were carefully polished with pumice, rinsed with water, and dried. Areas to be restored were isolated by means of a heavy rubber dam and a cervical clamp. Anesthesia was not required. As previously stated, restorations were placed according to the manufacturers’ instructions; however, the “adhesion booster” supplied with Enamelite and sug*Furnished

by Research

Division,

Johnson

& Johnson,

New

Brunswick,

N. J

TEO

resins for

restoring

abraded

area!

539

gestrd for use when inadequate enamel is present at the margins was not employed. Preliminary laboratory tests suggested that this agent exerted minimal influence on the bond strength and sealing properties of the material. Thus by eliminating this step. it Lvas possible to use the same procedure with both materials. ‘I’hc pretreatment etchants (both were phosphoric acid solutions) supplied by the manufacturers were applied for 120 seconds to the involved area and 1 mm. beyond. The area was thoroughly rinsed with a stream of water to remove the etch.mt and debris and then dried by means of an air syringe. Both materials were supplied in the form of t\vo pastes. In each instance, the materials were prepared by combining equal quantities of the two components and spatulating for 15 seconds. The restoration was inserted by flowing the material to plac,r: with a Teflon-coated instrument. The rubber dam clamp ivas removed two minutes after insertion of the material. Finishing was accomplished no sooner than 15 minutes following placement and was done with a fine diamond stone*% at high speed, and contour refinement was done by means of a white finishing stone.+ The finni surface was finished with a plastic disc coated with extra-fine diamond abrasive partic1es.S I-he evaluations at the base line were made by two trained examiners at threeand six-month periods, using the criteria of the United States Public Health Service as described in a previous study from this laboratory.” Color transparencies were made of all restorations at the time Iof each examination. Representative lesions befon and after restoration (base-line examination) are shown in Fig. 1. Laboratory

study

Laboratory tests which were corsidered pertinent to the performance of these materials included (1) bond strength of the materials to enamel and dentin, (2) adaptation as determined by microleakage of restorations in extracted teeth: and (3 penetration of dentin by the phosphoric acid etchant. Bond strength. The strength of the bond between the materials and enamel and dentin was evaluated by means of the adhesion test described by Lee, Cupples, and S~artz.” An area on the labial surface of a bovine tooth, which had been stored in \vater from the time of extraction, was wet ground to produce a flat area of enamel or dentin as desired. Final grinding was done with a 400 grit wet Carborundum pafler. follobved by light buffing wi.lh a slurry of flour of pumice. After the teeth were rinsed thoroughly to remove al:. traces of the pumice? they were etched for 120 seconds, rinsed, and dried, as described previously. The material was then loaded into a cone-shaped depression cut in the end of a stec 1 rod and immediately placed on the prepared tooth surface. This rod served as an attachment in the grips of the testing machine. Fifteen minutes after the specimens were prepared, they were immersed in water until testing. The bond to enamel NX~ assessed at 24 hours, one week, and 30 days. Each test series consisted of trn specimens. Specimens tested at 24 h’ours were stored at 37” C. Groups tested at one *F t46P

3/qA,

Densco,

mounted

$. 1900-4

disc,

Denver, point,

Dental

Colo.

Chayes EZ Corp.,

Dental

Instrument

Des Moines,

Corp., Iowa.

Danbury,

Conn.

540

Harris,

Phillijx,

Table

I. Status of restorations

J. I’rosrhrt. Dent. May. 1974

and Swartz by individual

teeth --

No. 01 I--___-.

__.-

I I

-_resloratiotls

Missing

Present

..-.

.-

.-

.-.

.--..

Total

Base line

Experimental Enamclite Three

(6.7%)

3

c4.0S.j

70 (93.3%) 7"w (96.0%)

75 75

45 53

70 69

months

Experimental Enamelite Six

5

25

(35.7%)

16 (‘32%)

(64.3X,) (76.8%)

months

Experimental Enamelite

35 (50.0%)

35 (50.0%)

"6

44

(37.1%)

(62.9%)

70 70

week and at 30 days were held at a constant temperature of 37’ C., while a similar group was subjected to 2,500 temperature cycles at a 40’ C. differential. The bond to dentin was determined after 24 hours storage in water at 37” C. Bond strength was measured under tensile loading using a crosshead speed of 0.025 inches per minute. Microleakage. Extracted human teeth which had lesions similar to those in the clinical portion of the study were selected. The sealing ability of 20 restorations of each material ~vas tested at one week, 30 days, and 60 days. Half of the specimens tested at each time period were held at 37’ C., and half were subjected to the temperature-cycling procedure described above. Leakage was tested according to a method previously described,” using *%a as a tracer. The teeth were covered with :I combination of tinfoil and nail polish, except for the area of the restorations and 1 to 2 mm. surrounding the restoration. They were immersed in a solution of WaCL _ (0.1 mCi./ml.) for two hours. Upon removal from the solution, the teeth were hemisectioned, and autoradiographs were made from the sections. Acid penetration. The depth of dentin penetrated by the phosphoric acid of the pretreatment cleansers was investigated by incorporating azP at a concentration of 0.2 mCi./ml. into solutions supplied by the two manufacturers. Extracted human teeth were ground on the labial surface to obtain a flat area of dentin. A piece of electrical tape with a hole 4 mm. in diameter was placed on each flattened surface. These areas of dentin were then swabbed with the radioactive pretreatment solutions for two minutes: Sixteen teeth were treated, eight with each material. The teeth were then serially sectioned (0.5 mm. sections) toward the pulp chamber on a Gillings-Hamco sectioning machine. Penetration of the acid was determined by the presence of radioactive substance in the dentin sections. Three counts were made on each surface of each section by means of a proportional counter, and the average of the six counts was recorded. Corrections were made for background radiation and decay rate.

‘l’rvo Table

rerins

Ior rrstoring

abraded

urea,

541

II. Bond to tooth structure

conditions

Storage

37” c. 37” c:. Thermal 37” c. Thermal 37”

c:.

cw~led c p-led

,

Experimental materiul (p.s.i., 180 170 130 150 130

+ * * ? -i-

1 ?(I 110 1 io 180 10

3 5 1

RESULTS Clinical

data

lYhc%results are presented in Table I. The failure rate among the restorations \t’a\ hi:11 : At the base-line examination, eight (5.0 per cent \ of the 150 restorations \\~rr rnissirlg: at three months, 41 (29.0 per crnt ! of 139 restorations examined were lost: at six nlonths. 61 (44.0 per cent) of 140 restorations examined were missing. Tllc, difference in loss between the 1~0 materials was not significant at the l!l per cell1 lr\~l. \Vith both materials, the greatc’st loss occurred within the first three moiiths. f relati\.el) high rate of loss, Four restorations kvith obvious marginal discoloration waist dislodyrd with the tip of a scaler at thr six-llwnth evaluation. Stain WLS apl)art~nt under t\so of these restorations. Several restorations exhibited of&t) at ttlc, ginsi\-al margins. suggestive of the presence of a gap or air space. Marginal adaptation scores sho\vtd a considerable dtcline in alfa score: (50 to 60 p:‘r cent ) over the six-month period. Caries was not detected with any of fhe r.cLtorations during the six-month observation interval. Laboratory

Borl~I rt>\torati\.e subjrc ted follo~cd rc,Lults on

data

.strength. The data obtairled in tests measuring the bond strength of the materials to tooth structure are shown in Table II. The data were TO a logarithmic transformation” to equalize variances among the groups. b>- a factorial analysis ol’ variance.‘” The statistical analysis of the test enamel are summarized in Tabk III.

542

Harris,

Phillips,

and Su;art:

.I. Prosthet. Dent. May. 1974

Fig. 2. Autoradiograph of 30 (top) and 60 day (bottom) specimens demonstrating leakage as assessed I)y means of aXa: A, Enamelite, uncycled: B, Enamelite, thermal cycled; C, experimental, uncycled; D, experimental, thermal cycled.

‘The strength of the bond of Enamelite to enamel was significantly greater than that of the experimental material to enamel under all of the test conditions. Although the statistical analysis indicates no difference with either material between the specimens tested at 24 hours and at 30 days, the mean data obtained for Enamelite do suggest that the bond may weaken with time and when subjected to thermal cycling. Laboratory values obtained with Enamelite used in conjunction with the “adhesion booster” Mere comparable to those presented here. There \vas virtually no bond of either material to dentin. During the 24 hour storage period, the material separated from the dentin in six of the ten Enamelite specimens and eight of the ten experimental resin specimens. Microleakage. Evaluation of leakage was done on an all-or-none basis, with any evidence of leakage at the margin considered as failure (Fig. 2). On this basis, 56 of the 60 Enamelite restorations exhibited leakage, and all 60 experimental resin restorations leaked. The degrees of penetration ranged from slight to great. Time of storage in water or thermal cycling had no apparent effect on leakage. When the adhesion booster was used with the Enamelite material, the incidence of leakage was not appreciably altered. Marginal penetration of ‘“Ca was minima1 or nonexistent in regions bordered by sufficient enamel (Fig. 3). However, the lesions which were involved in this study were invariably bounded at the gingival margin by dentin or cementum, and isotope penetration occurred in these areas. The lack of bonding of Enamelite to dentin or cementum has also been reported by Friedman and Retief.’ Penetration of dentin by acid. The average radioactive counts obtained for

Two

Fig. 3. Autoradiographs pared, at 30 days. Note

compared to uncycled the absence of leakage

resins for restoring

abraded

tooth where

which

specimens adequate

the material was feathered over the margin. A, Enamelite; Table III. Factorial analysis of variance two materials and five procedures?) --Source

of variation

Between two materials .tmong five procedures Interaction IVithin Totul

groups

Degrees freedom

1 4 4 90 99

for enamel

of

Mean square 6.423 1.245 0.305 0.616

from

areas

they

were

543

pre-

enamel was present or where B, experimental.

bond data”

(comparison

of

F

P

10.43 2.02 0.50

< 0.005

n.s.$ n.s.

*Data for analysis are logarithmic transformations of original data. tprocedures refers to storage time and groups that were not thermal cycled. 1n.s. -= not significant. dentin treated for two minutes with ““P-tagged phosphoric acid cleansers are seen in ‘Table IV. The radioactive counts on sections of the underlying dentin indicate that: although the acid concentration decreases with depth, the acid is capable of considerable penetration. The standard deviations are high but not unusually so for this particular test. They reflect the inherent variation in permeability of dentin from tooth to tooth. .4 limited number of tests conducted with a one-minute treatment resulted in Iow.c:r counts: indicating a reduced concentration of acid, but the depth of penetration was not appreciably altered. DISCUSSION The laboratory tests on the strength of the bond of these resins to tooth structure as i! rrla tes to marginal leakage suggest that problems might be encountered clinirallv in the restoration of noncarious cervical lesions. The strength of the bond of the resins to enamel pretreated with etching agents supplied by the manufacturers \vas appreciable. However, practically no bonding was noted when the adhesion to dentin was measured. Additional tests were made using citric instead of phosphoric acid for pretreatment of dentin, and no improvement in bond strength was indicatcd. The leakage tests supported the adhesion tests in that the isotope penetrated the margins of these cervical restomtions wherever they were bordered by dentin but did not permeate margins that were located in enamel.

544

Harris,

Phillips,

and

.I. l’rosthet. Dent. May. 1974

SW&z

Table IV. Two-minute application of phosphoric acid tagged with 32P Enamelite Section 1

2 3 4 5

(c.p.m.)

4,872 + 2,259 1,355 i: 1,68.5 979 ?: 1,369 649f 915 634+ 764

Experimental (c.p.m.)

resin

6,998 + 3,082 1,380 k 1,285 51Of .557 .366 f. 428 2aa f. 337

The differences in the bond strength betiveen enamel and dentin are not surprising since acid treatment does not produce the same effect on dentin and enamel. Recent work suggeststhat the only effect on dentin is enlargement of the tubules’” and possibleopening of dead tracts.” The acid etch technique has been shown to improve the sealing and retentive qualities of conventional and composite restorative materials, and its use in Class III and IV resin restorations has been advocated. However, in these situations, it must be recognized that the margins of the restorations are invariably in enamel. Since the restorations in this study were without mechanical retention and involved areas of dentin or cementum, the high rate of lossamong the clinical restorations is not surprising. Undoubtedly, the greater the area of enamel underlying the restoration: the higher the probability of its retention. Friedman and Retief’ reported loss of only two of 150 clinical restorations with Enamel&e after one year. Personal communication with these investigators indicated that the area of enamel etched and overlaid by the restorative material was considerably greater in their study than in this one. This factor probably accounts for the difference in retention of material in the two studies. However, the leakage tests and the increase in marginal discoloration associated with the clinical restorations suggestthat, even when the restoration is retained, it may merely be tacked onto the enamel, and leakage might occur at the gingival margin. Such a situation conceivably would provide an environment suitable for the growth of microorganisms. For this reason, the restorations which remained in situ at the six-month evaluation are being closely monitored. However, if the margins of restorations are bordered entirely by enamel, the incidence of marginal leakage will undoubtedly decreaseand retention increase, just as for other restorative resins jvhen used with an acid etch technique. Likewise, the resin could probably perform effectively when used as a coating to mask enamel defects, as suggested by one manufacturer. The experiments conducted to determine the penetration of the phosphoric acid pretreatment solutions indicate that an appreciable thickness, as great as 4 mm., of dentin may be penetrated. It is true that neither the actual concentration nor the pH of the acid at the various levels is revealed by these tests. Neither is the effect of such penetration on the pulp, as demonstrated here, known. Furthermore, most of these noncarious Class V lesions are long standing; thus the dentin probably is sclerosedand relatively impermeable to acid penetration. Several recent studies suggest that the application of 50 per cent phosphoric acid to cut dentin for short

‘TLCO resins for restoring periods of time may not be injurious to the lack of improvement achieved in the bonding one, it would seem judicious to confine the r~n:tnlrl~ -at least until further information is rll‘cc~t upon the pulp. SUMMARY

AND

abraded

areas

545

dentin.“, “; However, in view of the of resins to dentin through acid etchuse of phosphoric acid principally to brought forth with respect to its exac:t

CONCLUSIONS

:\ clinical and laboratory study was conducted to evaluate the efficacy of restorirl,g ? c,r\+;rl wear lesions by mearls of a nonoperative procttdure employing a resin rrstolati\c in conjunction with an acid etch technique. SIlvellty-fi\.e pairs of clinical restorations were placed with two resins designed for this purpose. ‘I‘he restorations were examined at three and six months. At the tilret>-month recall, only 70 per cent of the restorations were retained, and at the \:s-month examination, onl) 55 per #:ent were still in place. Laboratory adhesion tests indicated relatively good “bonding” of the material to enamel but virtuail) none’ to dentin. Marginal leakage tests with radioactive isotopes revealed gross pent.iration at the margins of restorations bordered by dentin but little penetration \vllelI tllc margins were located in enamel. Although the observations made in tllis i:lvc.\tiyation do not establish \vhethe:r leakage at the dentin-resin interface will or v&ill ?lot lead to increased sensitivity or caries, the interface is a potential source for d(xtetior;ltion. Thus the use of this technique for the restoration of eroded areas \\.itl:t)ut ;I conventional cavity preparation when dentin or cementum is involved at tllf‘ ::largins appears questionable until further long-term evaluations are made.

thy

l’he authors .iata.

arc

indebted

to Dr.

Rosario

Potter

who

performed

the

statistical

analysis

oi

References i

2. ;. I. 7. 6. 7 t!

9. IO.

%gnnacs, R. F., Wolcott, R. B., and Xhonga, F. A.: Dental Erosion. I. Erosion-Like Pattern\ Occurring in Association M’ith Othrr Dental Conditions, J, 4m. Dent. i\ssoc. 34: ?il-576, 1972. !Hcnd, J.: Enamel Softrniq and Rehardening as a Factor in Erosion, Dent. Corrnos. 52: M-48, ‘1910. Stec~l, J,, and Brown?, R. C.: The Effect of Abrasion Upon the Acid Decalcification of Trcth. Br. Dent. J. 94: 285-288, 19513. Kidevkrr, C. F.: Dental Erosion: Its Possible Causes and Treatment, Dent. Cosmos. 75: I O’,li- I OFT 1933. Ko,t. T., and Brodie, A. G.: Ponsible Etiologic Factors in Dental Erosion, J. Dent. KP 40: :m, 1961. Ibvn, R. L.: Non-operative Treatment for Gingival Erosion, Dent. Sure. 48: 22.21, 1972. Fric,tlnlan. M.. and Reticf. D. H.: A Clinical and Laboratory Evaluation of a New Ctrmporitv Restcjrative Material, J. Dent. C, Afr. 28: 460-466. 1973. Phillip\, R. W.. Avrry. D. ,J.. Mehra. R., Swartz, M. L.. and McCune. R. J.: One-E‘c,ar !)l)\crvations on a Composite Resin for Class II Restorations, J, PROSTHET. DL:NT. 26: lifl-77, 1971. IAT. H. I,.. CuppIes, A. L., and Swartz, M. L.: Epoxy Resin Dental Materials, South El Monte, Calif., 1968, Epoxylite Corp. Sw,lrtT, M. I,., and Phillips, R. W.: In Vitro Studies on Marginal Leakage of Restorative .Materials. J. Am. Dent. Assoc. 62: 141-151, 1961.

546 I I. I?. I?. 14.

1.5. 16.

Harris,

Phillips,

and

Swartz

J. Prosthct. Dent. May, 1914

Li, J. C. R.: Statistical Inference, I, Ann Arbor, Mich., 1964, Edwards Bros., Inc., pp. 516~:ili. Winer, B. J.: Statistical Principles in Experimental Design, New York, 1962, McGrawHill Book Company, Inc., pp. 140-160, 302-318. Gwinnett. A. J.: Structural Changes in Enamel and Dentin of Fractured Anterior Teeth After Acid Conditioning in Vitro, J. Am. Dent. Assoc. 86: 117-122, 1973. Isokawa, S., Kubota, K., and Kuwajima, K.: Scanning Electron Microscope Study of Dentin Exposed by Contact Facets and Cervical Abrasion, J. Dent. Res. 52: 170-174, 1973. Goto. G., and Jordan, R. E.: Pulpal Effects of Concentrated Phosphoric Acid, Bull. Tokyo Dent. Coil. 14: 105-I 12, 1973. Mueller, H. E.: The Histopathologic Response of the Human Dental Pulp to Phosphoric .4cid Pretreatment of Enamel and Dentin, Master’s Thesis, University of Nebraska, May, 1972. DR.

HARRIS

DEXTAL MARIKE PAHRIS

DETACHMEXT CORPS RECRUIT ISLAW,

DR. PHILLIPS ISLXANA

DEPARTMENT

S. C. 29905 AND

USWERSITY

1 I21 W. MICHIGAN ISWANAPOLIS, IND.

Ms.

SWARTZ SCHOOL

ST.

46202

OF DENTISTRY