Penetration of metallic ions from restorations into teeth

Penetration

of metallic

ions from

restorations

Rune Siiremark, L.D.S., O.D., D.M.D.,* Kenneth Wing, Kurt Olsson, L.D.S.,*** and Joel Goldin, D.M.D.**** Umea” University School of Dentistry, Umea”, Sweden, School of Dental Medicine, Boston, Mass.

into

teeth

D.M.D.,** and Harvard

P

revious investigation? established that metallic ions (corrosion products) from restorations, crowns, and clasps flow into enamel and dentin. Analysis of the metallic ions showed a marked increase over the trace quantity of the same elements in teeth which did not bear restorations or clasps. Thermal neutron activation with subsequent gamma-ray spectrometric analysis established the concentration of the metallic ions. However, a single analysis required nearly all the enamel or coronal dentin of each tooth. The results, therefore, represented the concentration of the element averaged over the entire sample. The investigations failed to show concentration gradients within the enamel or dentin. This study extended the results of preliminary report+ z and, by means of laser-emission spectrometric analyses and radionuclide tracer techniques, established the concentration gradients of the metallic ions. MATERIALS

AND

METHODS

Thermal neutron activation followed by gamma-ray spectrometric analysis. The experimental teeth were 40 sound premolars to be removed from orthodontic patients 15 to 17 years of age. The teeth were randomly divided into 8 groups of 5 teeth each which were treated as follows: Group 1 contained Class I preparations of equal size which were restored with dental amalgam. This study was supported in part by the Swedish Medical Research Council, Grant 24X-628, and in part by the United States Public Health Service Fellowship 5-F2-DE-33, 610-02 from the National Institute of Dental Research. *Professor Harvard School tory,

of Prosthetics, Ume% of Dental Medicine.

**Postdoctoral Research Umei University. ***Instructor

****Presently, Surgery.

in Prosthetics, Instructor

Fellow

University, (National

Ume&

and Institutes

Lecturer of Health)

in

Orofacial

Rehabilitation,

at the Biophysical

Labora-

University.

in Prosthetics,

Columbia

University,

School

of Dental

and

Oral

531

1. PIOS. Dent. Drcemhrr, 1933

In Group 2: cast chromittm-cobalt clasps (circumferential retainer with att occlusal rest i wtW mechanically attachc~cl to the ertamcbl surfaces. No preparatiott or grinding was perforrnc,d. Group 3 c.ontaittt:d CYass \* prepat’attotls of equal 6.r. Cast inlays prel~art~d byconventional indirec,t techniques were r~chrnrnted with Snc-phosphate cement. ‘l’vpt> 1 dental gold alloy \\-a~ crnployed (ADA Specification 5, 1962‘

Groul~ 5 c~ontaitt~d (:lass 1‘ preparations of equal size with cohesive gold restoratiotis instWec1 by cottvrtttiottal teclinicl\tc~s. ‘l‘hr teeth in Group 6 \vverc: treated in tile same manner as those in Group 3. ?‘h(% gold alloy used itt this group was a mu tvpc (99.35 prr crnt Au and 0.65 per ct‘nt Ge -. (to I .‘i Group 7 c~orttairtecl teeth prepartd for full-cro\vtt restorations, Artificial crowyns cast of ‘Type III tlrtttal gold alloy \vt’rt: cemented in plac-c with zinc-phosphatr cement. The gold \vas not heat-treated. Ko liner or \rarnish was used. Group 8 contained cavity preparations similar to those in Group 3. A thin layer acrylic resin of*% polystyrt~n~ liner* co\-cred each cavity wall!’ and self-polymerizing was inserted. ‘I’his gulp served as a control group for studying possible cotttatrtination due to preparation. After three WC~S. the, teeth wer(~ cstractccl, and the restorations were remo\~~l. The enamel and the coronal dentin were mechanically separated by chipping, by breakittg. and by employing rotating diamond instruments. Great care \\‘as taken to avoid contacting the samples with metal instruments.‘; r; The samples (all the enamel and the clntirt, coronal portion of the dentin from each tooth) were WI)arately stored at 1” C:. for no more than c,ight clays and then irradiated overnight in a nf~utron reactor with a thermal neutron flux of 1.4 V 10”’ neutrons/cm.-2/sec. ‘.t After irradiation. the samples wt~ dissol\,ed in 4 ml. d concentrated HCl, and 1 mg. each of gold: copl~r, and zinc \vns added as a carrier along with a few drops of 30 per cent H,O,, A 256~channel cramma-rav spectromcrtcr i3 measured the sample activity. Quantitative data based on the wcat weights of the enamel and dentin the gamma-ray intensity of the identified samples were obtained by comparing elements in the samples with those of the appropriate standards which hat1 been irradiated at the satttt’ titrtc~. La\cr-cviission \p( c~froscopic vricroar2alyti\. In sis vital premolars of the same type as descrihrd previously, Uass \’ c.aI,itirBs were prepared. Two teeth were rcstored w?th amalgam and two with cast-gold inlays using Type II gold alloy. ‘i‘he castings were bench-cooled for 2 minutes, quenched, anti cemented with zincphosphate cement. The rernaining two teeth served as controls. They were restored with heat-cured acrylic resin restorations which were cemented with zinc-phosphate cement. Three weeks after inset tion of the restorations, the teeth were txtractecl. *Tubulitec (5 parts Ca[OH] Forssbergs Dentaldepot, Stockholm, tThe

Swedish

Atomic

Energy

+ 5 parts Sweden.

ZnO.

Company,

Studsvik,

2 parts Sweden.

polystyrrnc,

88 parts

chloroform\,

Penetration

of metallic ions 533

Fig. 1. A longitudinal section, 100 w thick, of a premolar with a Class V gold inlay. Such sections were used for spot analysis by laser-emission spectroscopy of the enamel and dentin at various distances from the restoration as indicated by circles.

Immediately after extraction, each tooth was embedded in cold-curing acrylic resin. Sections about 100 p thick were made through the entire tooth and restoration by cutting the block under water with a diamond disk. These sectionswere used for semiquantitative analysis of various elements in different areas (50 p in diameter) of the enamel and dentin by means of laser-emissionspectroscopic microanalysis.* Fig. 1 showsa typical section usedin these experiments. Autoradiographic studies of the penetration of mercury and gold into teeth. Immediately after extraction, Class V cavities were prepared in four sound vital premolars. In two teeth, the cavity preparations were filled with amalgam. The mercury used had been irradiated with thermal neutrons for two days in order to produce radioactive mercury, Hg lg7. In one of the two cavities, a linert covered all prepared surfaces extending to the margins.g No liner or other isolation material was used in the other cavity. Direct cast-gold inlays were made with Type II gold alloy for the two remain*Jarrell Ash Laser Spectroscopic Analyzer, Jarrell Ash Company, TTubulitec, Forssbergs Dentaldepot, Stockholm, Sweden.

Waltham,

Mass.

534

Siiremark,

Wing,

Olsson,

and

J. PI-OS. Dent. December, 1968

Goldin

ing teeth. One of the two inlays was heat treated at 7250 C. for 75 minutes. The inlays were irradiated with thermal neutrons for two days in order to produce radioactive gold, Au’“~. The four teeth were then placed in separate beakers of Ringer’s solution. After six days, the restorations were removed from the teeth, and the cavity walls were cleaned mechanically. Four longitudinal sections, each approximately 100 p thick, were made from each tooth. The sections were placed with both surfaces in contact with Structurix films for five days of exposure in order to autoradiographically register the possible penetration of Hg’“’ or Aul”’ into the enamel and dentin. The Ringer’s solution, in which each tooth had been kept, was also monitored for the presence of HgrB7 or Au? Thermal neutron activation followed by gamma-ray Jpectrometric analysis of goZd in hair. Cranial hair samples from two groups, each consisting of ten girls 15 to 19 years of age, were analyzed for the presence of gold. One group had not been in contact with gold alloys for any appreciable period of time, while the other

Table I. Changes of the concentrations expressed in parts per millon” “Normal”

Gold E D

/

in enamel

(E)

and dentin

(D)

aft

/

/

Elements

of minerals

I

(X-2+(X

20)

/

1, Class

I

amalgam

2, Chromiumcobalt clasps

’ 3, Class V inla: Type I gold

0.00-0.04 0.01-0.05

0.07-0.14 0.07-0.23

0.04-0.48 0.01-0.41

0.32-0.67 0.38-0.73

Copper

E D Zinc

E D

64-488 43-355

3 lo-486 350-410

0.001-0.009 0.000-0.008

20-43 41-86

461-1605 521-941

Silver E D Mercury
E D

Chromium E D

28-67 64--96

0.001-0.009 0.000-0.011

0.3-2.6 0.02-0.06

0.0000-0.0004 0.0001-0.0005

0.02-1.2 0.001-0.003

Cobalt E D *The cent

values in columns confidence).

1 through

8 represent

the

minimum

and

maximum

values

from

five

teet;

Penetration

2%: ” ‘6”

of

metallic

ions

535

group had regularly worn gold-alloy jewelry for at least two years prior to this analysis. The analysis procedures used have been described previously.7l 8 RESULTS Table I presents the uptake of metal ions (corrosion products) into enamel and dentin from amalgam restorations, chromium-cobalt clasps, inlays, and full crowns as measured by thermal neutron activation with subsequent gamma-ray spectrometry. For comparison, Table I also presents “normal” values from intact premolars from boys and girls of the same age and from the same geographical area as in the present study.3 After only three weeks, teeth with amalgam restorations showed marked increases in the concentrations of silver and mercury and moderate increases of zinc in enamel and dentin. Similarly, chromium and cobalt penetrated the enamel and even the dentin after bearing clasps of the same metals for three weeks. Significant increases in the concentrations of gold, copper, and zinc occurred

aving been in contact 4, As in 3, heatireated (725” C., 24 hr.)

with

restorative

materials

for three weeks in vivo, with

values

8, Class 5, Class

V, cohesive gold

6, Class V inlay, new type golde

7, Full Type

crown, III gold

V,

self-curing acrylic

0.05-O. 11

0.03-0.06 0.03-0.09

0.03-0.06 0.03-0.07

3.8-5.6

0.04-0.05 0.03-0.05

0.30-0.33 0.28-0.47

0.22-0.36 0.14-0.36

0.20-0.38 0.21-0.35

0.76-1.84

0.2C-0.33 0.22-0.39

509-1440 473-952

234-314 174-225

459-932 526-l 184

706-1496

331-406 216-240

0.06-0.09

0.003-0.004 0.003-0.005

0.005-0.006 0.005-0.006

lose in the “Normal”

column represent the limits

0.0001-0.0002 0.0001-0.0002 two standard deviations from the mean (95 per

536

S%emark,

Wing, Ohon,

J. Pros. Dent. December, 1968

and Goldin

in both the enamel and dentin of teeth with Class V inlays of Type I dental gold alloy. Heat treatment at 725’ C. for 24 hours reduced the migration of gold and copper from the gold inlays into the teeth. Lesser uptake of gold and copper was demonstrated from pure cohesive-gold or nearly pure (99.35 per cent) cast-gold restorations. “Normal” zinc concentrations prevailed in the enamel and dentin beneath the cohesive-gold restorations. The greatest accumulations of gold, copper, and zinc infiltrated dentin which was covered with gold crowns. Comparison of the “normal” values with those of teeth with Class V acrylic restorations showed that no significant contamination of the samples occurred during preparation or subsequent manipulation. Laser-emission spectroscopic microanalysis provided data on 8 to II points in the enamel and in the dentin at various distances from the restorations (Fig. 1). The major constituents of enamel and dentin were calcium and phosphorus, There was a slightly lower concentration of phosphorus in the dentin Point analysis of enamel adjacent to amalgam fillings revealed relatively large amounts of mercury and tin and trace amounts of zinc, silver, and iron. Areas in the dentin near the amalgam were also very high in mercury content, with tin, zinc, silver, and iron present in tract, amounts. Areas of the enamel close to the gold restorations displayed significant amounts of gold and zinc and trace amounts of sil\xr, aluminum, and iron. Dentinal areas bordering on these restorations contained large amounts of gold, copper, and zinc: and trace amounts of silver, aluminum, and iron. Teeth with acrylic restorations showed no significant concentrations of metallic elements other than zinc, which was

present

in the

Fig. 2. An autoradiogram

rnamel

and

dentin

near

the

restorations.

and the corresponding 100 m/.t section of a premolar which had had a Class V amalgam for 6 days. The amalgam was made with radioactive mercury, Hgls?. The black areas on the autoradiogram correspond to regions of the tooth to which the HglQ7 had migrated. Note the high uptake in the dentin between the preparation and the pulp.

Penetration

of metallic ions 537

The sample points in the enamel and in the dentin which lay furthest from the restoration showed the lowest concentrations of the elements (metals) under study. The points of highest concentration in every case were in the dentin between the restoration and the pulp. The autoradiographic studies revealed an uptake of radioactive mercury in the cavity walls adjacent to the amalgams. The tooth under the amalgam in which no cavity liner was used showed a penetration of mercury through the cut dentinal tubules into the pulp (Fig. 2). N o such penetration was observed when a cavity liner (Tubulitec) was used. Radioactive gold from the inlays accumulated in the cement layer and in the cavity walls. However, penetration of gold from the inlays into the deeper layers of the dentin was not demonstrated. Less activity occurred in the cavity restored with heat-treated gold inlays. The Ringer’s solutions, in which the teeth for the autoradiographic study had been kept for six days, exhibited considerable radioactivity. Thus, corrosion and an efflux of metal ions from the external surfaces of the restorations had also taken place. Each of the ten girls wearing gold jewelry showed a significant amount of gold in her cranial hair. The concentration was several times greater than that found in the control group.

DISCUSSION radiochemical separation procedures, and The neutron activation techniques, gamma-ray spectrometry methods have previously been discussed.7j 8 The “normal” values in Table I were based on the ‘
538

S&remark,

Wing, Olsson, and Gddin

J. 1’10s. Dent. December, 1968

due to an efflux of zinc from the zinc-phosphate cement. I’he zinc concentrations appeared to be independent of the type of gold used. The use of radioactive restorations for the autoradiographic study required that that part of the investigation be done in vitro on freshly extracted teeth. A previous study’ established that experiments of this type produce similar results in vitro as in viva. In the first two phases of this study, tilt: restorations were left in situ for 21 days. In the autoradiographic study, third phasth, the radioactive amalgam (HglD7) and gold ( Aul=) were left in the teeth for only six days since the half-values of these radioactive nuclides precluded longer experimental periods. Despite these short time periods, marked accumulations of mercury, gold, copper, zinc, and other elements effused into the enamel and dentin. These accumulations were more marked in the layers closer to the restorations and were especially high in the dentinal tubules which had been cut in making the preparations. In a.ddition, the Ringer’s solution, in which the teeth with radioactive restorations had been stored, demonstrated radioactivity. Therefore. it is likrly that there is also a continuous efflux of metal ions into the saliva. It was further demonstrated that the migration of gold and copper from cast inlays into enamel and dentin can be reduced by heat treating (homogenizing) the inlays before cementation. The length of the heat-treatment period appears to be critical. Relatively long periods of time reduce the corrosion of gold castings, while the commonly employed shorter time periods are ineffccti\:e.“. “, ’ Gold alloys ol’ higher purity also show less corrosion. While the use of a cavity liner probably does not affect corrosion, it does appear to prevent the migration of metal ions into the tooth substance. The results of the prcscnt study are in agreement with those of earlier studies.1, 2, 1, ~, 1!,-12 In one study, the dentin underlying old amalgam restorations was found to be deeply and darkly discolored in 85 per cent of the 300 teeth examined. The gradual diffusion of metallic ions into the contiguous dentin was found to be effectively prevented by a base of zinc oxide and eugenol cerncnt.‘l The causes for a continuous efflux of ions from metal restorations into tissues have been previously discussrcl.‘, ‘-c In mst:nct>, the milieu in which the restorations are placed is responsible for the. existence of ;I high corrosion potential on all surfaces of the restorations causing an efflux of ions which subsequently migrate into the various tissues and body fluids.‘> 4-6 The mechanism of ion migration into the tooth structure is not clearly understood. Howcvcr, we know that the rate of diffusion in enamel and dentin is inversely related to the degree of mineralization. In general, this implies that the enamel and dentin of older patients, which are more mineralized, permit less penetration of ions through the enamel and dentin toward the pulp. The penetration rate can also be lowered if the water phase in enamel and dentin is reduced as in a nonvital tootle. Metal ions from restorations can also migrate into the gingiva.’ Ions diffuse rather freely into soft tissues. It can be expected that some of the metal ions taken up by the gingiva, the dental pulp, and the saliva will be rapidly transported throughout the body to specific target organs. This evidence of the accumulation of corrosion products in oral tissues from metal restorations and the further ob-

Penetration

of

servation of the migration of gold from finger rings and ear clips us to believe that corrosion occurs in most metals in contact with penetration of metal ions (corrosion products) into the body is phenomenon. At this time, it is difficult to say what effects the presence products might have on the tissues of the body. A positive effect example, in the case of the efflux of fluoride ions from silicate Tubulitecg in resisting secondary caries. It is equally likely that be detrimental. In either case, the problem of corrosion of metal restricted to that of maintaining the integrity of the restorations. this area are definitely indicated.

metallic

ions

539

into the hair lead the body and that a rather common of these corrosion is possible as, for restorations and metal ions could restorations is not Further studies in

SUMMARY The efflux of metal ions from metal restorations and their penetration into dental tissues have been studied with the use of sophisticated techniques. The results show significant concentrations of metal ions in both enamel and dentin from amalgam, chromium-cobalt, and cast-gold restorations after short periods in or on the teeth. The highest concentrations occurred in the regions closest to the restorations, especially within the dental tubules cut during cavity preparation. It was also shown that use of pure cohesive-gold or nearly pure cast-gold restorations or heat-treatment (homogenization) of gold castings for sufficiently long periods reduced the corrosion of gold restorations and the penetration of corrosion products into dental tissues. Use of a cavity liner was found to prevent migration of corrosion products from metal restorations into teeth. References 1.

SGremark, R., Ingels, O., Plett, H., and Samsahl, K.: Influence of Some Dental Restorations on the Concentrations oE Inorganic Constituents of the Teeth, Acta odont. scandinav. 20: 215-224, 1962.

2.

Bergenholtz, A., Hedeghrd, B., and Saremark, R.: Studies of the Transport of Metal Ions from Gold Inlays Into Environmental Tissues, Acta odont. scandinav. 23: 135-146, 1965. Brudevold, F., and &remark, R.: Chemistry of the Mineral Phase of Enamel, in Miles, A. E. W., editor: Structural and Chemical Organization of Teeth, ed. 2, New York, 1967, Academic Press, Inc., pp. 247-277. Siiremark, R., Freedman, G., Goldin, J., and Gettleman, L.: Structure and Microdistribution of Components of Gold Alloys, J. D. Res. 45: 1723-1735, 1966. Hedin, M., and Siiremark, R.: Corrosion Studies on Heat-Treated Dental Gold Alloys, Odont. Revy. In press. Gettleman, L., Freedman, G., Shaw, B., Goldin, J., and SBremark, R.: Studies on a New Dental Casting Gold Alloy, J. D. Res. 46: 595-601, 1967. SGremark, R.: Micro Element Analyses by Neutron Activation, in Lawrence, J. H., editor: Progress in Atomic Medicine, ed. 1, New York, 1965, Grune & Stratton, Inc., pp. 54-78. Samsahl, K., and Siiremark, R.: Comparative and Absolute Measurements of 11 Inorganic Constituents of 38 Human Tooth Samples with Gamma-Ray Spectrometry, Program of 1961 International Conference of Modern Trends in Activation Analysis, A. and M. College of Texas, College Station, Texas, pp. 149-154. Scremark, R., Hedin, M., and Rlijmyr, R.: Studies on Incorporation of Fluoride in a Cavity Liner (Varnish), Odont. Revy. In press.

3.

4. 5. 6. 7.

8.

9.

540 10. 11. 12.

Shemark,

Wing, Olsson, and Goldin

J. Pros. December.

Dent. 1968

Guthrow, C. E., Johnson, I,. B., and Lawless, K. R.: Corrosion of Dental Amalgam and Its Component Phases, J. D. Res. 46: 1372-l 381, 1967. Ma&r, M., and Barher, T.: Action of Amalgam on Drntin. J. A. D. A. 47: 215-422. 1953. Schoonover, I. (1.. and Soudcr; \V.: Corrosion of Dental Alloya. J, ii. D. A. 28: 12781291, 1941. DRS.%REMARK SCHOOL

UMEK

OLSSON:

UNIVERSITY

UME& DR.

AND

OF DENTISTRY SWEDEN

901 87

WING:

SWEDISH

RESEARCH

COUNCIL’S

STUDSVIK,IVYKOPING,SWEDEN DR.

GOLDIN:

15 E. 48T~

ST.

NEW

N. Y. 10017

YORK,

LABORATORY 61100