Microleakage of four root canal sealer cements as determined by an electrochemical technique

Microleakage of four root canal sealer cements as determined by an electrochemical technique

Microleakage of four root canal sealer cements as determined by an electrochemical technique Biruta A. Osiris. D.M.D.,* J. Malcolm Carter, Ph.D.,** Mi...

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Microleakage of four root canal sealer cements as determined by an electrochemical technique Biruta A. Osiris. D.M.D.,* J. Malcolm Carter, Ph.D.,** Ming Shih-Levine, D.D.S., MS.,* Bu$alo, N. Y. SCHOOL

OF DENTISTRY,

STATE

UNIVERSlTY

OF NEW

YORK

and

AT BUFFALO

Eighty-eight teeth were used to determine the sealing quality of four root canal sealer cements-Kerr, Diaket, AH-26, and ProcoSol-via the vertical condensation of warm gutta-percha technique. In addition, limited studies were carried out to determine the sealing quality of injected Hydron and thermoplasticized gutta-percha. A comparison was also made between the lateral condensation of gutta-percha and vertical condensation of warm gutta-percha when Kerr sealer was used. Teeth filled with vertical condensation of warm gutta-percha and AH-26 sealer cement showed lower leakage in one experiment but higher leakage in another. Hydron showed the highest leakage of any material. Teeth filled via vertical condensation of warm gutta-percha and Diaket showed less leakage than the other groups. A statistically significant difference was also found between lateral condensation of gutta-percha and vertical condensation of warm gutta-percha using Kerr sealer cement.

N

umerous studies over past decades have endeavored to assess quantitatively the leakage potential of root canal filling materials. Studies of seal integrity of filling materials include methods using bacteria,’ air under pressure,2 dye penetration3 fluorometric assays,4 radioactive isotope penetration,sv6 and scanning electron microscopic examination.7 The results of the various investigations have varied not only with the techniques of obturation but also with the type of sealer used, particularly AH-26, Diaket, Kerr, and ProcoSol sealer cements.6,7,8-‘2 Previous electrochemical methods have used the electrical resistance between an Ag/AgCl electrode in the experimental tooth and an indifferent electrode13 or a galvanic cell where an iron probe within the test tooth generated an electromotive force and current, the latter being measured via zero-resistance ammetry.14 The method used here incorporated an Ag/AgCl

Abstracted from of the requirements sity of New *Department **Department

80

a thesis by the senior author in partial fulfillment for certification in endodontics, State Univer-

York at Buffalo, June, of Endodontics. of Dental Materials.

198 1.

electrode sealed in a prepared tooth that, as leakage progressed, gave increasing electrical potential when measured against a standard calomel electrode (SCE) by a voltmeter of finite impedance. Values for fully leaking teeth (where the output had leveled off), were just less than that for a bare Ag/AgCl electrode, the output of which was corroborated by the Nernst equation. MATERIALS AND METHODS Preparation of teeth

Eighty-eight extracted human anterior maxillary and mandibular teeth were collected and stored in 0.9 percent saline solution at 5” C. The teeth were intact and caries-free, although a few had very small composite restorations. The teeth were externally cleaned of soft-tissue attachments by soaking for 24 hours in a 2.5 percent NaOCl solution. Routine access cavities were prepared in all the teeth, which were cleaned and shaped according to the procedure proposed by Schilder.lS The patency at the apical foramen of each tooth was routinely established with a No. 25 reamer. The canals were copiously irrigated with 2.5 percent NaOCl solution, dried with paper points and sealed by means of Schilder’s techniquei with one of the four sealers:

Volume Number

Microleakage

56 1

of four root canal sealer cements

81

Table I. Numbers Experiment Categories

of teeth in study

1. Vertical condensation of warm guttapercha only-VGP 2. Vertical condensation of warm guttapercha plus Kerr Sealer VGP + K 3. Vertical condensation of warm guttapercha plus ProcoSol VGP + P 4. Vertical condensation of warm guttapercha plus Diaket VGP + D 5. Vertical condensation of warm guttapercha plus AH-26-VGP + A 6. Teeth filled with Hydron*-H 7. Teeth filled with thermoplasticized gutta-percha using motorized reverse HedStrom files-TGP 8. Lateral condensation of gutta-percha and Kerr sealer-LGP + K TS = Test specimen. c = Control. *2-Hydroxyethyl methacrylate,

Hydron

Experiment

2

Experiment

3

C

TS

c

TS

C

4

1

4

I

4

1

4

1

4

I

4

1

4

I

4

I

4

1

4

1

4

1

4

1

4

1

4

I

4

1

4

I

4

1

2

1

-

-

-

-

Canada Limited, Etobicoke,

(Stock #54003) made Products Department,

1

in each group

TS

-

-

Ont., Canada.

Kerr, Diaket, AH-26, and ProcoSol. No more than two teeth were filled with each individual mix of sealer cement. In all, three experiments were carried out and the categories of teeth in each group were divided as outlined in Table I. All teeth were randomly selected for the experimental conditions, except that in experiment 3 the samples were limited to maxillary teeth to decrease the influence of anatomy as an indirect variable. The teeth in experiments 1 and 2, after obturation, were allowed to dry for 7 and 14 days to facilitate the total application of silicone rubber* on the external root surfaces, particularly the root apex. Initial studies indicated that sticky wax and enamel varnish produced a totally unacceptable seal of the apical foramen for controls, but silicone produced a hermetic seal. One control tooth was provided in each category of teeth, by leaving the silicone coating undisturbed at the root apex and surrounding the root. On the test specimens, the silicone coating was removed circumferentially within 1 mm. from the apical foramen with a scalpel. A later pilot study indicated that teeth sealed with *Clear Silicone Auto Seal Electric Company, Silicone N. Y. 12188.

of teeth and controls

by General Waterford,

vertical condensation of warm gutta-percha and Kerr sealer and tested 12 hours later (to allow the silicone to set) resulted in lower leakage readings than 7- and lCday-old specimens. Consequently, experiment 3 was modified so that the teeth were immersed within 12 hours of obturation. A No. 6 Gates-Glidden burr was used to provide space in each canal to approximately within 5 mm. of the apex of each tooth. An Ag/AgCl electrode was placed in the canal within 5 mm. from the apex. Each tooth with the projecting anode was sealed with Concise* for stability and insulation. The teeth were then immersed in the 0.9 percent NaCl solution and readings in millivoltage were recorded at intervals of time against the SCE. At the end of each experiment, the silicone coating of the controls was removed circumferentially from within 1 mm. of the apex to determine whether the controls were capable of leakage. Also, the electrodes were randomly removed from the teeth to determine whether they were capable of producing the expected saline potential. Preparation

of electrodes

No. 35 endodontic silver cones of 99.9 percent purity were used to prepare the Ag/AgCl electrodes *Minnesota 55101.

Mining

and Mfg.

Co., 3M

Center,

St. Paul, Minn.

82

Osiris, Carter, and Shih-Levine

1----_---_ em------‘d------FPi’C

1 /-k-..--~-~I IL L

Oral Surg. July, 1983

3 inches was used as a cathode. Anodizing conditions were similar to those used in biomedical telemetry,“. I8 namely, about 3,000 mA-sec./cm.* Representative electrodes were measured, and an average surface area value was calculated. The following equation was used to estimate the current required for the above deposit:

I I+ .c, -_

-----

-----

-_

11111---= ---

1



DXAXn I = 60t

2 , 1

Fig. 1. Anodizing apparatus: a, Constant current source; 6, electronic breadboard; c, silver cones; d, NaCl electrolyte; e, pure silver cathode.

L-

where D = 3000 mA.-sec./cm.*, the desired deposit A = 0.239 cm.*, mean electrode surface area n = number of electrodes t = time in minutes I = current in mA. Example: n = 30 and t = 20 minutes, total current I = 18 mA. After preparation, electrodes were rinsed in distilled water and stored dry. Apparatus and instrumentation

L Fig. 2. Experimental cell: a, Calomel reference electrode; b, sampletooth containing electrodeand coated within 1 mm. of foramen;c, Ag/AgCl electrode for saline reading; d, connecting wire; e, copper terminal rod; J internal specimentray; g, 0.9 percent NaCl solution; h, Lucite cell; i, cell lid.

used in all the experiments. Initial work showed that complete and even anodizing to form AgCl could be obtained only on clean specimens. Also, it was found that grit-blasting improved the electrical stability and life of electrodes. Electrodes were individually grit-blasted* with 60-mesh A&O3 grit and immediately immersed in distilled water. Batches, usually of thirty electrodes, were mounted in a small electronic breadboard, which was then inverted over a 0.9 percent saline bath so that about 16 mm. of length was immersed. Then the silver cones were made anodic in an electrical circuit as shown in Fig. 1. The power source? used could be set to deliver a constant anodizing current. A pure silver plate measuring 2 by *Williams tHeathkit 12424.

Minicor, regulated

Williams Gold Refining Co., Buffalo, L.V. power supply, Model IP-27,

N. Y. Series

A Lucite cell was constructed (Fig. 2), with an internal specimen tray and tightly fitting lid that had provision for a ceramic-junction standard calomel electrode.* The lid was drilled so that the copper lead wires from the specimens could be clamped with short l%-AWG copper-wire rods to which electrical connections could be made. Sample teeth were attached to the internal specimen tray with sticky wax so that about 5 mm. of their root apices projected from the underside of the tray. The lead wires were coiled to facilitate positioning into drilled holes in the cell cover as this was lowered into place. The cell was then filled with saline solution so that the liquid was just level with the internal specimen tray. To get a base reading for saline, a separate Ag/AgCl electrode was inserted. The reference electrode was then installed, and the readings in millivolts were started immediately through a highimpedance digital multimeter.? When subsequent readings were taken, the auxiliary Ag/AgCl electrode was included to monitor any changes in concentration of the saline. Any decrease of these readings indicated an increase in concentation of saline by evaporation. *Corning

#476109.

‘!Simpson Digital Multimeter, Model Company,Elgin,III. 60120.

#461,

Simpson

Electric

Volume Number

Table

Microleakage

56 I

of four root canal sealer cements

83

II. Resultsof analysisof varianceof the three experiments(p < 0.05)

Experiment

Source

I

Between Within

groups groups

Total

2

Between Within

groups groups

Total

3

Between Within

groups groups

Total

Calculation

D.F.

Sum of squares

5 298 303 5

2198.17 3616.44 1293.13 691 1.76

198

203 5

8204.89 3661.57 4662.02 8329.60

210

potential

When a metal (M) is in a solution containing its own ions (M”+), the electrode potential established is given by the Nernst equation: (Equation

1)

where E” = standard electrode potential of the metal against the standard hydrogen electrode (SHE) R = universal gas constant T = temperature in degrees Kelvin n = valency of the ion involved F = faraday constant aMn+ = activity of ion involved A silver wire coated with AgCl can be used to measure the concentration of chloride ions in solution. For silver, equation 1 becomes: E = EOAg++ s

In aAp,

(Equation

squares

439.63

F. ratio

F prob.

35.64

.oooo

7.405

.oooo

33.04

.oooo

12.34

5874.61

215

of Ag/AgCI

Mean

2)

The silver ions originate from the silver chloride, and their activity is governed by the chloride ion activity via the solubility product principle:

KS6%$X = (aAs+)(ad K, (AgCl), the solubility product of AgCl, is calculated from the solubility and the molecular weight and is 1.793 X lo-lo mol* at 25°C. Substituting in equation 2, we have:

258.63 34.91

733.62 22.20

rithm conversion to log at the base 10, for a univalent ion is given by 0.05915, giving: E = EoAg++ 0.05915 (log KS - 1% acl-)

(Equation 4)

Since K, is constant at constant temperature, E is governed by a,,-, the chloride activity. The chloride activity, a,,- = TM, where y = chloride ion activity coefficient M = chloride molal concentration where y = 0.7525, the chloride ion activity coefficient, found by interpolating standard tables, and M = 0.1544, the molal concentration of chloride ions in 0.9 percent saline solution. Substituting the above values into equation 4 yields: E = EoAg++ 0.05915 (log 1.793 X lo-‘O - log 0.1162) now EoAg+= 0.799 (versus SHE at 25C.) from standard tables giving E = 0.2778 volts. When the Ag/AgCl electrode is used with the standard saturated calomel electrode that has a potential of 244.4 mV at 25°C. versus the SHE, the potential of the cell is given by: E = 277.8 - 244.4 = 33.4 mV From equation 4, as the concentration of NaCl increases, the cell output E decreases. This was verified experimentally and a millivolt output curve is drawn for concentrations between 0.1 and 10 percent weight NaCl. Millivoltage versus log concentrations gave the expected straight line as predicted by the Nernst equation. RESULTS

E = E”Ag+ + z At 25°C

(In K, - In a,,-)

(Equation

3)

the constant R$ and the natural loga-

The results of the three experiments were statistically tested at the 0.05 level by analysis of variance (Table II) and by Duncan’s multiple range test for differences between the means (Table III) and between experiments (Table IV).

84

Osiris, Carter, and Shih-Levine

Oral July,

Table 111.Duncan multiple (p < 0.05)

range test for the difference in the means between the experimental

Experiment

Lower

subset

Central

values

VGP + A 22.65

I

VGP VGP VGP VGP VGP VGP VGP VGP VGP LGP VGP VGP+ VGP

2

VGP + D 10.41

3

VGP VGP

= Vertical gutta-percha alone. + A = Vertical gutta-percha plus

VGP VGP VGP

+ D = Vertical + K = Vertical + P = Vertical

gutta-percha gutta-percha gutta-percha

IV. Duncan multiple Sealer

cement

obturation

subset

values

Ii 32.59

VGP + A 27.77

VGP + P VGP+ A VGP VGP + K

20.98 21.36 21.14 22.44

Kerr.

range test for differences in the means for sealer cements between experiments

or

method

Lower

subset

(2) (3) (3) (2) (2) (3) (3) (I) (3)

VCP+K VGP+P VGP+A VGP+D (I), (I?), (3) are experiment numbers. VGP = Vertical gutta-percha alone. VGP + A = Vsrtical gutta-percha plus VGP + D = Vertical gutta-percha plus + K = Vertical + P = Vertical

+ K 26.33 + P 26.49 21.23 + D 21.34 + P 20.58 + D 20.71 2 1.a + K 22.49 22.66 + K 19.37 + P 20.98 A 21.36 21.74

Upper

groups

AH-26.

VGP

VGP VGP

values

1983

plus Diaket. plus Kerr. plus ProcoSol

LGP + K = Lateral gutta-percha plus H = Hydron. TGP = Thermoplastized gutta-percha.

Table

subset

Surg.

gutta-percha gutta-percha

Central

values

21.52 21.74 22.45 22.49 20.58 20.98 21.36 22.65 IO.41

subset

values

Upper

subset (I)

27.23

(I)

26.44

(I)

26.49

values

(2) 27.71

-

(2) 20.71

(I)

27.34

.4H-26. Diaket.

plus Kerr. plus ProcoSoi.

In experiment 1, VGP + A showed significantly lower leakage than all the other methods of obturation. Hydron showed significantly higher leakage. Experiment 2, however, presented VGP + A as having significantly higher leakage than the other groups. In experiment 3, VGP + D leakage was significantly lower than the rest of the groups, and LGP + K showed significantly lower leakage than VGP + K. The rest of the groups were comparable to each other. In performance comparisons across the three experiments (Table IV), all groups except VGP + A

showed significantly higher leakage in experiment 1. Therefore, under the experimental conditions, the results at p < 0.05 showed that Diaket produced significantly less leakage. Also, with Kerr sealer, lateral condensation of gutta-percha had a significantly lower mean value than that of vertical condensation of warm gutta-percha with the same sealer. Vertical condensation of warm gutta-percha without sealer did not differ significantly from that in the technique with Kerr, AH-26, and ProcoSol sealer cements.

Volume 56 Number I

Microleakage

of four root canal sealer cements

C

rD

32

0 VGP only

AA

VGP&

l

A n

o VGP&

0

16

8

0

VGP only

.

VGP 8 Kerr

A

VGP 8 AH 26

1

VGP 8 Dlokat

0

VGP 8 Procosol

l

Hydron

0

Soline

Gutto-perctm

Sohe

8

A

0

4%

,

8 TIME

Fig.

Procowl

. Thermoplostwed

> E

0

Kerr

A VGPSAH26

24

24

85

16 (days)

24

3. Leakage patterns with time for experiment 1.

The same interval between initial onset of leakage from 0.0 mV to the leveling off at the approximate maximum leakage value varied between the groups in the experiments. In experiment 1 (Fig. 3), Hydron and VGP + A preceded VGP + D and VGP + P. Last to reach the level were VGP and VGP + K. In experiment 2 (Fig. 4), the groups leveled off in the following order: VGP + K leveled off first, followed in succession by VGP + A, TGP, and then VGP + D, VGP + P, and VGP at approximately the same time. In experiment 3 (Fig. 5) however, the groups leveled off at approximately the same time. The control specimens maintained a constant zero potential reading and the saline readings approximated 33.4 millivolts throughout the experiments. At the conclusion of each experiment, removal of the silicone coating from the root apices of the control teeth produced increasing millivoltage readings with time. Ag/AgCl electrodes removed randomly from the test specimens produced millivoltage readings within the 33 f 1 mV range when immersed in the 0.9 percent saline solution. The impedance of a bare Ag/AgCl electrode versus the SCE was measured and found to be about 5.27 KQ. This value is near to that measured for a commercial laboratory reference Ag/AgCl elec-

C/

-$

I

a

IG

24

TI me (days) Fig.

4. Leakage patterns with time for experiment 2.

trode, which was 4.28 KQ. The impedance of the circuit with a prepared tooth varies according to the magnitude of the saline leakage. At the onset of leakage, the resistance was in the order of 4.5 MQ, and as leakage progressed this decreased to around 0.2 MQ, for a tooth which produced a few millivolts less than the Nernst voltage. DISCUSSION

Studies in the past largely represented attempts to determine root canal sealer leakage by visual estimation. Grieve” evaluated leakage by expressing the dye area as a percentage of the tooth area. Antoniazzi and associates” attempted to measure leakage quantitatively by means of a graded ocular. Foge120 assessed dye leakage by measuring marginal penetration of dye in each tooth with Cenco calipers. These methods, however, provided only a visual measurement that was subject to human error. In this study, the electrical potential between the silver/silver chloride electrode within the tooth and the standard calomel electrode was measured to indicate the leakage through cementum and dentin and sealer and gutta-percha filling in terms of an electrochemical reaction produced by the interaction of chloride ions and the silver/silver chloride electrode. An electrical potential in this system is produced

Osiris, Carter, and Shih-Levine

66

4c )-

C

,.

24

2

If

j-

E \.

c I-

Fig.

5. Leakage patterns with time for experiment 3.

upon onset of leakage into the root canal and when a continuous electrolytic path has been established. The time elapsed between immersion of the tooth containing the silver/silver chloride electrode and the appearance of electrical potential is dependent on the sealing qualities of the coating around the tooth (in the case of the control) or the root canal obturation technique and materials (in the case of the specimens). The potential values recorded depend on the electrical resistance of the cell formed by the experimental tooth containing the Ag/AgCl electrode and the SCE. The anatomic variation of the teeth studied seemed to influence. the quality of obturation attained; thus, a range of millivoltage values was obtained. Leakage values most likely differed according to the thickness of dentin and cementum in the apical root area as well as the presence of any accessory canals, since these factors would affect the electrical resistance of the tooth. Although a less exacting simulation of in vivo clinical conditions would be exercised, a more precise quantitation of sealer leakage may be possible with the use of glass capillary tubes.

Oral Surg. July. 1983

Some teeth gave a few millivolts less than the Nernst voltage after several days, while others gave much lower steady readings. With the latter, a loading effect was present when the digital multimeter was used, in spite of its high impedance (10 Ma), because of the comparable (3 MO) impedance of the voltage source. Even with zero current measurement of voltage used a potentiometer, non-Nernst voltages were observed. The reasons for this are complex and could include: 1. Insufficient input sensitivity of the potentiometer when matched with a high-impedance voltage source. 2. A nonequilibrium condition concerning the Ag/AgCl electrode, where insufficient saline is present as a result of efficient sealing for production of the Nernst potential by presently unknown ionic diffusion phenomena. In this study, sticky wax and enamel varnish were inadequate for coating the external root surface. The control group leaked when coated with these materials. The validity of controls in which these coatings were used for longer than 48 hours must be questioned. In this study, a coating of silicone on the outer root surface seemed to be adequate in providing impermeability to the detecting solution. Controls treated in this manner did not show leakage when immersed in saline solution for up to 30 days. Seidler2’ has emphasized that all sealers undergo dimensional changes. These changes occur in the form of “linear” contractionz3 cracking upon setting, and dissolution in fluids.12 Not only does statistically significant shrinkage of sealers occur upon setting, but the shrinkage is not uniform.6~22~23 The loss of mass by dissolution of sealers increases with time, the greatest loss of mass occurring within 30 days. Therefore, physical properties24,“5 of cement sealers are important factors in assessing seal and dimensional stability. There are several sites where leakage may occur: the sealer-tooth interface, the tilling material itself (due to porosities in the sealer), and the solid core material and cement sealer interface. The permeability of AH-2620 and gutta-percha appear to be negligible.30 Therefore, generally, leakage is due to the permeability of the interface between the filling material and the dentin. If a crevice 10 microns26 in diameter developed between the tooth root dentin and the filling material, this could permit access for bacteria the size of 2 microns--lactobacillus, or 0.5 micron-Streptococcus.27 The chloride ionzn having a covalent diameter of 1.98 A” or a van der Waals diameter of 3.6 A”, is a far more sensitive test since it has been established

Volume Number

56 I

that tissue fluid and toxin penetration can lead to root canal failure in the absence of bacteria. The size of harmful tissue protein molecules has not been determined. At this time, it is not known what degree of leakage, histologically or microscopically, leads to clinical failure. The permeability of dentin is another variable factor that may have affected the results of experiments of the type described in this investigation. Going and co-authors29 suggested that dentin permeability in freshly extracted teeth is similar to that in teeth in vivo. However, it is difficult to determine the extent of the trauma produced at the root apex during the application of the extraction forceps to the crown of the tooth. Also, the time of storage may influence the dentin so that microfractures are more readily produced during the filling techniques. It is not known to what extent leakage is due to these microfractures. Both lateral and vertical gutta-percha condensation techniques can produce crazing or cracking of the dentin, possibly resulting in more leakage. The leakage of the teeth may also differ greatly because of the large variation in root canal anatomy. CONCLUSIONS

The quantitative data obtained by this leakage technique are capable of yielding information regarding the relative effectiveness of different sealers and techniques. However, the data give no information on the absolute amount of saline leaking into a tooth and therefore cannot be used to determine long-term prognosis for a root canal filling. This study supported the findings of other investigators5’ ‘32’ that all root canal fillings leak. One hundred percent hermetic obturation of canals occurs rarely, if ever. Leakage can be a potential source of failure in root canal fillings. Which is more critical: complete cleaning and shaping of the root canal system, hermetic obturation of the entire canal, or the integrity of the apical seal? All can contribute to success or failure. Clinical success or failure may be a mere function of the significance of microleakage. There may be a critical level of microleakage that is not acceptable to biologic tissues or beyond which biologic repair cannot occur. This may vary according to root canal anatomy and the biologic tissue tolerance of the individual. This may explain the phenomenon of the radiographically well-obturated tooth that is a clinical failure. The results of an in vitro study must be cautiously extrapolated to the in vivo situation. In spite of the fact that to date a total hermetic obturation of the root canal system on a microscopic level has not been

Microleakage

of four root canal sealer cements

achieved technologically, success clinically.

endodontics

87

enjoys good

REFERENCES 1. Seltzer, S.: The Penetration of Microorganisms Between The Tooth and Direct Resin Fillings, J. Am. Dent. Assoc. 57: 560-566, 1955. 2. Fiasconaro, J., and Sherman, H.: Sealing Properties of Acrylics, N. Y. State Dent. J. 18: 189-198, 1952. 3. Massler, M., and Ostrovsky, A.: Sealing Qualities of Various Filling Materials, A.S.D.C. J. Dent. Child. 21: 228234, 1954. 4. Ainley, J. F.: Fluorometric Assay of the Apical Seal of Root Canal Fillings, ORAL SURG. 29: 753-762, 1970. 5. Marshall, F. J., and Massler, J.: The Sealing of Pulpless Teeth Evaluated With Radioisotopes, J. Dent. Med. 16: 172-184, 1961. 6. Kapsimalis, P., and Evans, R.: Sealing Properties of Endodontic Filling Materials Using Radioactive Polar and nonpolar isotopes, ORAL SURG. 22: 386-393, 1966. I. Wollard, R.R., Brough, S. O., Maggio, J., and Seltzer, S.: Scanning Electron Microscopic Examination of Root Canal Filling Materials, J. Endod. 2: 98110, 1976. 8. Grossman, L. 1.: Physical Properties of Root Canal Cements, J. Endod. 2: 166-178, 1976. 9. Grossman, L.1.: Solubility of Root Canal Cements, J. Dent. Res. 57: 921, 1978. IO. Younis, O., and Hembree, J. H.: Leakage of Different Root Canal Sealers, ORAL SURG. 41: 777-784, 1976. Il. Antoniazzi, J. H., Mjor, I. A., and Nygard-Ostby, B.: Assessment of the Sealing Properties of Root Filling Materials, Odontol. Tidskr. 76: 261, 1968. 12. McComb, D., and Smith, D. C.: Comparison of Physical Properties of Polycarboxylate-based and Conventional Root Canal Sealers, J. Endod. 2: 228-235, 1976. 13. Tidmarsh, B. G.: An Electrical Resistance Method of Determining Leakage Around Root Fillings, J. Dent. Res. 58D: 2233, 1979. 14. Jacobson, S. M., and Von Fraunhofer, J. A.: The Investigation of Microleakage in Root Canal Therapy, ORAI. SURG. 42: 817-823, 1976. 15. Schilder, H.: Cleaning and Shaping the Root Canal, Dent. Clin. North Am. 18: 269-296, 1974. 16. Schilder, H.: Filling Root Canals in Three Dimensions, Dent. Clin. North Am., pp. 723-744, November, 1967. 17. Rootare, H. M., and Powers, J. M.: Preparation of Ag/AgCI Electrodes, J. Biomed. Mater. Res. 11: 633-635, 1977. 18. Geddes, L. A.: Electrodes and the Measurement of Biolectric Events, New York, 1972, John Wiley & Sons, Inc. 19. Grieve, A. R.: Sealing Properties of Cements Used in Root Filling, Br. Dent. J. 132: 19-22, 1972. 20. Fogel, B. B.: A Comparative Study of Five Materials for use in Filling Root Canal Spaces, ORAL SURG. 43: 284-299. 1977. 21. Seidler, B.: The Technique and Rationale of Filling Root Canals, N.Y. J. Dent. 24: 276-285. 1954. 22. Weiner, B. H., and Schilder, H.: A Comparative Study of Important Physical Properties of Various Root Canal Sealers. I. Evaluation of setting times, ORAL SURG. 32: 769-777, 1971. 23. Weiner, B. H., and Schilder, H.: A Comparative Study of Important Physical Properties of Various Root Canal Sealers. II. Evaluation of Dimensional Changes, ORAL SURG. 32: 928-937, 1971. 24. Benatti, 0.. Stolf, W. L., and Rhunke, L. A.: Verification of the Consistency, Setting Time and Dimensional Changes of Root Canal Filling Materials, ORAL SURF. 46: 107-113, 1978. 25. Weisman, M. I.: A Study of the Flow Rate of Ten Root Canal Sealers, ORAL SURG. 29: 255-261, 1970.

88

Oral Surg. July, 1983

Osins, Carter, and Shih-Levine

26. Nelson, R. J., Wilcott, R. B., and Paffenbarger, G. C.: Fluid Exchange at the Margins of Dental Restorations, J. Am. Dent. Assoc. 44: 288-295, 1952. 27. Parris, L., and Kapsimalis, P.: The Effect of Temperature Change on the Sealing Properties of Temporary Filling Materials. Part 1. ORAL SURG. 13: 982-989, 1960. 28. Parry, R. W., et al.: Chemistry: Experimental Foundations, Englewood Cliffs, N.J., 1975, Prentice Hall. 29. Going, R. E., Massler, M., and Dute, H. L.: Marginal Penetration of Dental Restorations as Studied by Crystal Violet Dye and I’)‘, J. Am. Dent, Assoc. 61: 286-300, 1960.

30. Gurney, B. F., Best, E. J. and Gervasio, ments on Gutta-Percha, ORAL SURG. Hrprinr

rryursts

to:

Dr. J. Malcolm Carter Department of Dental Materials School of Dentistry State University of New York at Buffalo 3435 Main St. BuBalo, N. Y. 14214

G.: Physical

Measure-

32: 260-270, 197 1.