Response of the human dental pulp to amalgam restorations

Response of the human dental pulp to amalgam restorations

Section of the FEDERAL . . . DENTAL . RESPONSE . . . SERVICES . . OF THE HUMAN . . . . DENTAL . . . . . . . . . . . PULP ...

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Section

of the

FEDERAL .

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DENTAL .

RESPONSE

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SERVICES .

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OF THE HUMAN

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DENTAL

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PULP TO AMALGAM

RESTORATIONS Herbert Swerdlow, B.A., D.D.S., M.S.D.,’ N.S., B.S.,“” Bethesda, Md. National

Institutes

of Health,

United

and

Harold

States Public Health

R, Stanley, D.D.S.,

Service

the use of high-speed techniques for cutting tooth structure has been found biologically acceptable to the human dental pulp,lA5 the attention of investigators is now being focused on the additional effects of filling materials. During our previous studies in the evaluation of the traumatic capacity of the newer high-speed cutting techniques on the human dental pulp, a large number of teeth were experimentally prepared with Class V cavities and filled with zinc oxide and eugenol cement (ZNOE:) .I, 2y4 With the information that was gained from a study of this material as a base line, realistic comparative studies can now be carried out on similarly prepared teeth restored with other materials. PaffenbargerO recently noted that amalgam is one of the most important agents that the dentist has at his disposal. Amalgam, which is used in three of every four restorations, is a metallurgic triumph. It can be plastic and yet harden at body temperature; it has nearly the strength of a casting; it can withstand the rigorous and corrosive mouth environment, and yet it is bland to the host. Although its physical propert,ies and manipulation have been extensively studied, there is a relative paucity of research material concerning its biologic effects on the dental pulp. Although previous studies have demonstrated mild inflammatory pulpal reactions under cavities restored w&h amalgam,7-g usually within four to eight weeks a layer of reparative dentine has formed directly under the cut dentinal tubules. Amalgam is thought by some to be nonirritating to tooth structure,l’ while others consider its high thermal conductivit,y the cause ol’ the result,ant, in juryl’ and secondary dentine formation.

S

INCE

*Clinical Center, Dental Department, National Institutes of Health. **National Institute of Dental Research, National Institutes of Health. 499

2.00

1.33

Average degree of superficial response (0, 1, 2, 3, 4)

=\verage degree of deep response (0, 1, 2, 3, 4)

Number

of focal abscesses

0

88.9

1.89

average degree of displacement (0, 1, 2, 3, 4 )

Per cent, of lesions predominating in neutrophils

O.i3

of re(mm. j

Average thickness maining dentinc

39.4

2.78

time

tooth size (code)

40.8

l-6

9

XVALGAM (HAND)

Average preparation (seconds)

Average

Average age of patients (years)

interval

of specimens

Range of time (days)

Number

-

.

0

80.0

l.‘(I

-0.00

7.00

0.6-I

33.6

2.60

39.7

l-6

5

AMALGAM .\II%:IIAxwAL)

.~~\IALG‘\~[ i II*4SD,

0 .---.-

88.9

1.89

2.44

2.56

0.83

28.9

2.78

36.5

l-14

9

‘zxALcAl\l ( IIE(‘IIASICAl.,

1

0

1 .“Q -.

2.00

I.71

O.il

34.3

3.5 i

40.0

l-15

7

AMALGAl (HASD)

2

‘I

il.-4

1 .3fi

I.36

(J.91

0.84

25.6

l-40

bMALGAX (MECHAXCAT.

X.4

)

41.2

1.10

1.47

1.35

1.13

21.7

3.18

39.8

l-37

17

~4x!Ir.ca~r (HAKI?

Volume 15 Number 4

PULP

RESPONSE

TO

AMALGAM

RESTORATIONS

501

The investigation reported here dealt with the comparative pulpal effects produced by manual and mechanical condensation and with the possible differences between amalgam and ZNOE fillings. MATERIALS

AND

METHODS

Typical Class V cavity preparations were made on the facial surfaces in the gingival region of seventy-three intact human teeth with inverted-cone No. 37 diamond stones or No. 35 tungsten carbide burs at speeds ranging from 20,000 to 300,000 r.p.m. (Tables I and II). The proper air-water spray coolant was used with each procedure. All preparations were carefully air-dried and restored with uncontaminated amalgam or ZNOE. The amalgam was condensed with either a hand condenser or a low-speed mechanical condenser, each with a plugger point 2.0 mm. in diameter. The mechanical condenser was an eccentric cam type of contra-angle driven by a belt and engine to a maximum of 6,000 r.p.m. The alloy-to-mercury ratio of the amalgam and its mechanical trituration were achieved according to the manufacturers’ directions. The amalgam-restored teeth in each speed category were kept similar with respect to the patient’s age, the postoperative extraction interval, the remaining dentine thickness, and tooth size. The pertinence of these factors has been previously established. 2*4 Three of the amalgam-restored teeth (prepared with the Page-Chayes instrument) with longer postoperative intervals were not included in this first phase of the study in order that the postoperative intervals might be more comparable when the methods of amalgam insertion were evaluated (Table I). All the amalgam-restored teeth were then matched as closely as possible to sixty-four ZNOE-restored teeth from the aforementioned baseline material on the basis of the following criteria: patient’s age, tooth size (molar, incisor, etc.), postoperative interval, and remaining dentine thickness. Except for the ZNOErestored teeth in the 20,000 r.p.m. category, which were extracted under local anesthesia, all teeth were removed under general anesthesia. Microscopic comparisons were made between the various categories by recording the incidence and intensity of cellular displacement into the dentinal tubules, the inflammatory response in the superficial tissues (odontoblastic layer, zone of Weil, and the cell-rich zone) and in the deeper tissues, and the percentage of lesions predominating in neutrophilic leukocytes. The intensity of a characteristic was recorded according to an arbitrary degree scale (0, 1, 2, 3, and 4 degrees). Specimens exhibiting less than 1 degree of intensity for any characteristic usually represented one or two discernible inflammatory cells and/or displaced cells and were coded “0” for the computations in Tables I and II. The incidence of reparative dentine formation was recorded in the specimens treated with the Borden air turbine technique, since a sufficient number of specimens 20 days old or older were obtained only for this technique. RESULTS

The most frequent and characteristic histopathologic feature in the amalgam-restored teeth was a dense accumulation of neutrophilic leukocytes between

4.

Fig.

5.

Fig.

#580069. Borden air turbine, the odontoblastic layer (arro\r) Magnification, Xl25 ; retluced I,&)

5.-Specimen #5704X1. Borden air turbine, and eosin stain. Magnification, XlGO ; reduced

Fig. 6.-SpccimPn the distance between lin and eosin stain.

toxylin

r.p.m.,

one day,

restored

with

amalgam,

with ZNOE, odontoblnsts

6.

remaining

dentine

O.i5

mm.

(Hema-

remaining dentine 0.64 mm. Note the as compared to the specimens shown

Fig.

200,000 r.p.m., two days, restored with amalgam, remaining dentine 1.80 mm. Note and the dentine. the number of leukocytes a.nd the hemorrhage (H). (Hematoxy-

200,000 $6.)

Fig. 4.-S~ccimen #57018fl. Borden air turbine, 200,000 r.p.m., one day, restored small number of inflammator’y cells, the scarcity of displaced cells, and the recognizable in Figs. 5 and F. (Hematoxylin and eosin stain. Magnification, X 160 ; recicced x,)

Fig.

Fig.

9.

Fig.

10.

Uensco Air Turbex 301),01)11 I’.P.IW one day, restored with Y.-Specimen #590266. Compare u ith hr. IO. (Hemntoxylin and eosin stain. O.il mm. ZN’OE. remaining dentine Magnification, X125 ; reduced %. 1 Fig. IO.-Specimen #590272. Densco Air Turbex, 300,000 r.p.m., one day, restored with amalgam, remaining dentine 0.90 mm. Note the pooling of leukocytes between the predentine Magnification, x 125 : reduced $4. ) and surviving odontoblasts. (Hematoxylin and eosin stain. Fig.

PITLP

RESPONSE

TO AMALGAM

RERTORATIOSS

505

the predentine and the odontoblastic layer (Figs. 2, 3, 5, 6, and 10). The quantity of leukocytes in several instances was sufficient to lift the odontoblastic layer away from the predentine and press it into the deeper pulpal tissues. This characteristic was so pronounced in three manually condensed specimens as to present localized pools of exudate (Fig. 6) which were classified as abscesses (graded at 4 degrees). Such lesions represented merely extreme degrees of lcukocytic accumulation and not the conversion of necrotic tissue to abscesses as seen in specimens subjected to operative techniques employing inadequate coolants.4s I* Except in the three cases just cited, no significant differences in pulpal responses were found between the two methods of amalgam condensation when the average intensities of the histopathologic characteristics were compared. TABLE II.

Number

COMPARING AMALGAM RESTORATIONS WITH ZNOE

18

of specimens

Range of time intervals (days)

l-6

l-6

Average time interval (days)

2.77

3.14

,\verage age of patients (years) Average

tooth

size (code)

Average preparation (seconds)

37.0 2.69

40.8 2.71

time 34.2

37.4

2-37

28

RESTORATIONS

28

11

l-44

1-42

l-40

l-15

l-15

12.5

12.4

18.89

18.39

6.18

3.15

37.2

41.8

41.8

38.6

2.33 14.8

2.89 29.8

2.96 19.6

3.13 23.4

42.3 2.55 21.7

49.0 3.46 29.6

Average thickness of remaining dentine (mm.)

0.89

0.70

0.78

0.81

0.81

1.05

0.68

0.63

Average degree of displacement (0, 1, 2, 3, 4)

1.53

1.93

0.83

2.06

0.57

1.10

0.36

1.77

Average degree of superficial response (0, 1, 2, 3, 4)

1.69

2.00

0.33

2.00

0.32

1.39

0.18

1.77

Average degree of deep response (0, 1, 2, 3, 4)

1.23

1.29

0.33

1.61

0.46

1.19

0.18

1.08

Per cent of lesions predominating in neutrophils

14.3

39.3

0

0

2

Number of specimens 20 days or older

15

15

Number of specimens with secondary dentine

3

8

Per cent of specimens with secondary dentine

20

53

of focal

abscesses

Average remaining dentine of all specimens 20 days or older

85.7

0

0

0.0

78.6

Number

69.2

0

0.72

0.96

0.00 0

77.0 1

DI,SCUSSION

It appears that the biologic advantage ol’ high-speed cutting, as manifested 1)~ minimal pulpal rcsponscs,4 is modified or lost when the cavity preparation involving tlentinal tubules in an intact tooth unsupported k~?; irregular dentino is restored with amalgam, regardless of the method of amalgam wndensation. (Clomparc Fig. 1 with Figs. 2 and 3, Figs. 4 and 7 with Figs. 5, 6. and 8, and Fig. 9 with Fig. 10.) Because the pulpal wsponses of the one-da) amalganr slwc?irncws \vwe greater than those of the XVOE spccimrw, it, is reasonable t,o assume that the physical insertion of the> amalgam might 1~~1 0310 of the contributing factow responsible for the greater responses than the toxica, chemical, 01’ thermal propert) of tlic restorative material itself. Previously it has been she\\-ri that, the k&or* of load 01’ force (pressure) in grinding proc.edurw can contribute to an intwsification of the pulpal response.lCi Ewn ihough frictional heat was neutralized with adequate coolants, greater pIllpa wspouscs n;crc! elicited in twth ~~~~~l~ar’ctl Possibl>. t tic forrcs with low-speed techniques rquiring increased forces. r~tilixcd in condensing amalgam a t*e similarly capable of increasing tllo pull~al YcspoIlsc. It was interesting to note that. the degree of response to carit>preparation with the 20,000 r’.p.m. technique, even though follo\vecl IJ~ %NOE restorations, was suficicntl~~ great that any addcd c#wl s of arni~lgalr~ ins&ion were not tletectablv. In those categories in which the post,operative pclriod was longer than fifi.ectl iufiamrnatory cells in amalgam-l,c~;toi,e(~ twlh clays, tllcs number of infiltrat,ing persisted rather t,han decrcasrd, as was the case with the ZNOE-restored twill. Because thcb initial rcsponscs in the amalgam-l~esto~ed teeth mew greater than in the %L~OE-rf%tOred teeth, a lotigct. wsolution period ~vould bc wquitwl iTi th!* former. Howevrr, definit P wsolution in thn amalgalrl-rcslored icetlr was iuclicated by tlw gradual replacement, 01’ the ucut,e inflatnnlat,ory ~11s 1)). the c*htmic* types and by the production of reparative dentine. A point. implicating the injury attendant to amalgam insertion as the cause

go:“‘;;ng ‘4’ ”

PULP

RESPONSE

TO

AMALGBM

RESTORATl.ONS

207

of the increased responses is the fact, that pulpal injury was seen following the rrstorat.ive procedure despite the presence of a considerable t,hickness of remaining dentinc. The three specimens exhibiting abscess formations had remaining dentine thicknesses of 0.26 mm., 0.98 mm., and 1.80 mm. (Fig. 6). In our previous work4 all the abscess formations occurred in specimens with remaining dentine t,hicknesses of less than 0.70 mm., and five of the six abscesses were associated with operative techniques employing inadequate coolants. In the present study adequate coolant was used and two of the abscessed specimens had remaining dentine values greater than 0.70 mm. One plausible explanation for the occurrence of intrapulpal abscesses with the hand plugging method is that possibly there is an occasional excessive or erratic stroke during amalgam condensation, which is less likely to occur when a mechanical condenser is used. Although the teeth prepared with the Borden air turbine technique and restored with amalgam had an average remaining dentine value (0.959 mm.) greater than the Z?r’OE-restored specimens (0.715 mm..), the percentage incidence of reparative dentine in the amalgam-restored teeth was more than twice t,hat in the Zh’OE-restored teeth (Table II). It must be emphasized that pulpal responses resulting from experimental procedures arc exaggerated in comparison with those produced by similar procedures in clinical practice. In experimental cavity preparations on noncarious teeth, irregular dentine does not underlie the cut dcntinal tubules, as is usually the case when cavities are prepared in areas preceded by caries.14 In addition, teeth with as small a thickness of remainin g dentine as found in this study would not generally be subjected to the direct effects of amalgam condensation. In clinical practice the deep portion of a cavity preparation would usually either be lined on the pulp side by irregular dentine stimulated by caries or receive a cement base to raise that portion of the cavity floor to an optimal level. In an investigative situation, however, in order to compare the responses produced by various clinical procedures, it has been found necessary to work with rcmaining dentine thicknesses of less than 2.0 mm.4 SUMMARY

AND

CONCLUSIONS

Typical Class V cavity preparations were cut on the facial surfaces in the gingival regions on seventy-three intact human teeth. Water-cooled invertedcone cutting tools were used at speeds ranging from 20,000 to 300,000 r.p.m. Silver amalgam was inserted by manual and mechanical condensation methods. The teeth were extracted one to forty-four days after restoration. The effects on the human dental pulp of manual versus mechanical condensation of amalgam and of amalgam versus zinc oxide-eugenol restorations were compared. No significant histopathologic differences in the pulpal responses were found between the two methods of amalgam insertion. With the high-speed techniques, the amalgam raised the intensity of the initially mild response to cavity preparation to a level comparable to that obtained with the lower-speed technique followed by zinc oxide-eugenol restorations.

It is evident that if t,lw health ot’ t11v pnl p is I o twncfit ~‘IWIII t IIC minimal pulpal reactions associated x\ith the newer cott,ing methods, some troatn~cwi oi the freshly cut dentinal tubules not linctl by wparati\x dcntinv is irnpc~r;rl.iv~~ prior to restoration. This stucly demonst,ratcs the nwessity l’or dcrcloping :I c*arit,y liner or base material capable of protectin p ;rnd/or sealing the c~xposwl dcnt,inal tubules, not only fJ’OlJ1 thtb cr;tetmal stimuli JT?liitCd to chciniva1 iIrl(I t11(:1,1r1a1properties of amalgam hut also from stimuli associated with 1111,CorldeIWil’ l.iou of amalgam. The mechanical aspects of amalgam condensation apparently p1a.y a role in producing an increased pulpal response regardless oi’ the physical propertks of the rcstorativc material itwl1’. The question has not been comp1etel.v resol~wl, hoverer, and additional studies of other contributing factors are illdic.:rI cttl.

1. Swerdlow, 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

H., and Stanley, 11. B., Jr.: Human Pulpal Reactions %‘ollowing 20,000 autl 150,000 R.P.M. Cavity Preparations, J. D. lies. 37: 68, 1958 (abstrxt). Smerdlow, H., and Stanley, H. R., Jr.: Reaction of Human Dental Pulp to Cavity Preuaration. Part Il. AYt 150,000 R..P.M. With a\ir-Water SDrav. & . .I. I’ros. l)en. 9: i21, 1959. Nygaard Ostby, B.: Clinical and Experimental Expcrieuee With Bordou Airotor, Norskc Tannl. Tidskr. 68: 124, 1958. Reaction of the Human Pulp to Cavity Prepara. Stanley, H., Jr., and Swerdlow, H.: tion : Results Produced by Eight Different Operative Grinding Technics, .I. Am. Dent. A. 58: 49, 1959. Seltzer, S., and Bender, I.: Early Human l’ulp Reactions to Full Crown Prf~parations, J. Am. Dent. A. 59: 915, 1959. Materials Given at the 106th Meeting _, oP Paffenbarner. G. C.: Review of Dental A. ArAT 8. as Reported in Dental Times, February, 1960. Manley, E. B.: lnvestigations Into the Early Effect.s of Various Filling Materials ou the Human Pulp, D. Record 62: 1, 1942. S&off, F. R.: Effects of Filling Materials on the Dental Pulp, New Zealand 1). J. 42: 99, 145, 1946; 43: 35, 1947. Effects of Filling Silberkweit! M., Massler, X., Schour, I:, and Weintnaun, J. I’.: Materials on the Pulp of the Rat Incisor, J. D. Res. 34: 854, 1955. A New Pulpal Response to High-Spcctl Dental Bcrnier, J. L., and Knapp, M. J.: ORAL SUBG., ORAL JMED. & ORAL PATH. 11: 167, 1958. Instruments, Zander, H. A.: Pulp Response to Restorative Materials, J. Am. Dent. A. 59: 911, 1959. H., and Stanley, 11. R., Jr.: Reaction of Human Dental Pulp to Cavity Swerdlow, Prc~paration. I. Eflect of Water S11ray at 20$00 r.p.m., J. .
Department of Oral Pathology at Walter Reed Army Medical Center Lieutenant Colonel 8. N. Bhaskar, Ii. 8. Army Dental Corps, has been appointed chief of the newly created Department of Dental and Oral Pathology at the, United States Army Institute of Dental Research at the Walter Reed Army Medical Center. The Departa biopsy service, provides consultament, which serves the Army Dental Corps, maintains tion to clinicians in problem cases of oral diagnosis, conducts research, and gives a number These services are available to both the military and civilian of instructional courses. dentists. In addition to these functions, the Department sponsors a Registry of Clinical Oral Pathology in which cases of unusual interest are recorded.