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The physical properties of four endodontic sealer cements
JOURNAL OF ENDODONTICS [ VOL 8, NO 3, MARCH 1982
The physical properties of four endodontic sealer cements J. A. v o n Fraunhofer, PhD, MSc, and J. Branstetter, DMD
The physical properties of t h r e e w i d e l y u s e d sealer c e m e n t s a n d a recently i n t r o d u c e d material h a v e b e e n studied. The e v a l u a t e d properties w e r e compressive s t r e n g t h , w a t e r sorption a n d solubility, d i m e n sional c h a n g e , p H a n d electrical c o n d u c t i v i t y . It was f o u n d that one material, w h i c h possessed the h i g h e s t compressive s t r e n g t h , s h o w e d little c h a n g e d u r i n g three m o n t h s " i m m e r s i o n in water. T w o eugenolc o n t a i n i n g c e m e n t s s h o w e d e v i d e n c e of e u g e n o l l e a c h i n g c o m b i n e d w i t h l o n g - t e r m d i m e n s i o n a l c h a n g e . The n e w n o n - e u g e n o l material r e t a i n e d a r u b b e r y consistency t h r o u g h o u t the test period, together w i t h a large positive d i m e n s i o n a l change. It is possible t h a t positive d i m e n s i o n a l c h a n g e (expansion) m i g h t i m p r o v e sealing efficacy w i t h time.
Endodontic cements are routinely used to help provide a hermetic seal in the obturation process for endodontically treated teeth. To achieve this objective, the sealer must satisfy certain criteria; possibly the most important of these are low solubility, good compressive strength, and long-term dimensional stability. A variety of sealer cements are commercially available, but the literature is somewhat confusing on their characteristics. Consequently, the literature pertaining to the three widely used materials used in this study--ProcoSol, Tubliseal, and Diaket--together with the available data on Nogenol, a newly introduced product, will be summarized. Proco-Sol, also known as Grossman's sealer, is a powder-liquid sys-
126
tern, the liquid being eugenol; whereas, the powder comprises a mixture of zinc oxide, hydrogenated resin, bismuth subcarbonate, barium sulphate, and sodium borate. The material's sealing ability was reported to be good by some workers, 1~ but others found that it showed greater leakage than other sealers. (' The solubility of ProcoSol during a seven-day test period was reported to be very low,; but other workers found a higher percentage solubility that approached the solubility of other eugonol-based sealers. 7 Proco-Sol has a reported compressive strength of approximately 230 kg/cm 2 and after it had set, the material shrank after 90 days at room temperature. 8 Diaket is a powder-liquid system; the powder is a mixture of zinc oxide
and bismuth phosphate: whereas, the liquid consists of vinyl copolymers in a ketone vehicle. Leakage studies on Diaket have produced variable results: some workers have suggested that it produced a satisfactory seal although some leakage had occurred3.4; other reports have indicated that there was little or no leakage with this material. 2,6The compressive strength of Diaket (approximately 340 kg/cm 2) was greater than that of Proco-Sol, 7 and the water solubility was significantly lower. 2,3,7
Tubliseal, a paste-paste system, consists of a base paste that is primarily zinc oxide with some bismuth trioxide, and the accelerator consists of various oleo resins and eugenol. Leakage studies on the material again produced variable results. Tubliseal leaked slightly more than Diaket, 6'9
JOURNAL OF ENDODONTICS I VOL 8, NO 3, MARCH 1982
although others have found that it produced a better seal than Diaket. 4 Similarly, some reports have indicated that Tubliseal is more effective than Proco-Sol, >'9 although others found that Tubliseal leaked more than Proco-Sol. 1~ A recent study m has shown t h a t Tubliseal has a sealing ability similar to another eugenol-based seale r and Nogenol, a non-eugenol material. The compressive strength of Tubliseal is low 7 (approximately 65 k g / era2), and although it has a moderate water solubility, 27 it also has a tendency to shrink consistently during a 90day period at room temperature and humidity, s Nogenol, a recently introduced paste-paste system that does not contain eugenol, consists of a base containing primarily zinc oxide and barium sulphate, and an accelerator that contains vegetable oil and fatty acids. There has been only one report on this material, m but ,that study indicated that the leakage of the material was of the same order as that of eugenolbased materials. Similar hardness and pH values were found for Nogenol, Tubliseal, and Kerr's sealer, m It is clear that the literature on root canal sealers is somewhat conflicting. In particular, leakage studies have yielded many inconsistencies although }issue-toxicity studies do show more of a consensus. H There is also a lack of information on many physical properties of root canal sealers: Studies on }ertain physical properties of several toot canal sealers are reported that should have clinical significance. Experimental
techniques
Three widely used commercial sealer cements and a newly introduced material were studied (Table 1). All ~aaterials were mixed in accordance ~'ith the manufacturer's instructions
Table 1 .
Material Proco-Sol Diaket Tubliseal Nogenol
Endodontic sealer cements.
System Powder-liquid Powder-liquid Paste-paste Paste-paste
Batch no. 13829 LE 262 (powder) LE 276 (liquid) 0208 79-1032 and 0418 78-1081 110278
Table 2 9 Water sorption, solubility, and d i m e n s i o n a l change (at three months).
Material Proco-Sol Diaket Tubliseal Nogenol
Water sorption Mean % SD -3.07 _+ 0.49 +1.59 + 0.58 +0.30 + 1.74 +3.41 + 0.08
Water solubility Mean % SD 10.92 _-'20.22 0.91 + 0.08 5.22 _+ 1.89 2.98 + 0.33
Dimensional change Mean % SD +2.93 _+ t.42 0.0 +_ 0.00 +8.63 _+ 1.66 +15.59 _+ 3.11
Table 3 9 Mean compressive strengths + SD (kg/cm~).
Material Proco-Sol Diaket Tubliseal Nogenol
One week 47.43 _ 7.92 144.05 _+ 20.43 50.37 _ 8.39
Coefficient of variation 16.7% 14.2% 16.7%
and packed into polymeric cylinders (1.0 X 0.5 cm in diameter); five samples of each cement were prepared. After setting for 48 hours at 100% r H and 37 + I ~ excess cement was ground back on water-lubricated, 800grit silicon carbide paper until the cement was flush with the ends of the cylinders. Thereafter, the specimens were measured and weighed to find the initial weights (Wo), then placed in 100 ml of distilled water in separate sealed containers at 37 _+ I~ An empty polymeric cylinder, also ira-
Three 41.27 179.46 34.63
months 4- 10.78 + 30.57 _+ 4.52
Coefficient of variation 26.1% 17.0% 13.1%
mersed in 100 ml of distilled water, served as the control. Specific conductance (YSI Model 31 Conductivity Bridge) and p H (Corning Model 12 p H Meter) measurements were performed periodically on the immersion water. Specific conductance measurements were made by inserting the conductivity electrode, which comprised two 1 mm 2 platinized platinum electrodes mounted 1 cm apart in an open-ended glass tube, in the solution in the specimen container. The conductance bridge imposed a 1-KHz alternating current between 127
JOURNAL OF ENDODONTICS [ VOL 8, NO 3, MARCH 1982
the platinized electrodes, and the solution conductance was read directly from an internal meter when the measuring bridge of the conductivity meter was in balance. Specific conductance and pH measurements were made at 24-hour intervals for the first week of immersion and at weekly intervals thereafter for 12 weeks. At the end of the test period, excess water was removed from the specimens by gentle blotting with paper tissues, which were then weighed to find the saturated weights (Wt). The specimen dimensions were then measured to determine the percentage extrusion of the cements out of the containing cylinders. Finally, the specimens were dried to constant weight over a desicant and a final weight (Wf) was found for each specimen. The water sorption and solubility values were found for each specimen, using the relations given in the formula; mean values and their standard deviations were calculated for each material. Water sorption and solubility values were calculated, using the standard relations: water sorption = Wt - Wo 100 X I%; Wo 1 water solubility = Wo
-
Wo
Wf
100
X--%. 1
In performing water sorption tests, there is always concomitant sorption and dissolution of the specimens, and these two factors cannot be separated. Consequently, the water sorption figures referred to later have positive values when sorption exceeds any dissolution that occurs, whereas, a negative figure indicates that dissolution
128
has exceeded any water uptake, and there was an overall loss in weight. Similarly, water solubility measurements do not take account of sorbed water that becomes bound within the structure of the test material and is not released by drying of the specimen. Consequently, these two parameters, which are routinely measured during the assessment of dental materials, have inherent limitations but are useful in indicating behavior rather than being definitive material characteristics. After drying, the polymeric cylinders were carefully slit open, and the specimens were removed, and their cross-sectional areas measured. The compressive strengths were determined, using an universal testing machine (Universal Calibration Corporation Unite-O-Matic) at a crosshead speed of 5 mm/min. For purposes of comparison, samples of each cement were prepared as described and allowed to set for one week at 100% r H and 37 +__ 1~ before compressive testing. RESULTS
The mean water sorption and solubility figures for the four cements after 12 weeks' immersion are given in Table 2. The mean dimensional changes of the cements expressed as percent of extrusion out of the containing cylinders during three months, are also given (Table 2). The two eugenolcontaining cements, Proco-Sol and Tubliseal, showed weight losses in the water sorption studies as well as pronounced solubilities. Proco-Sol had a water sorption more than ten times greater and a solubility more than double that of Tubliseal. The dimensional change of Tubliseal, however, was three times greater than that of
Proco-Sol. Diaket showed a moderate water sorption and a low water solubility, although it showed zero dimensional change during the test period. Nogenol bad a high water sorption and moderate solubility as well as a high dimensional change. The changes in the pH and conductivity of the immersion waters are shown in Figures 1 and 2. The control liquid (that is, water covering the empty polymeric cylinder) showed a small but progressive drop in pH and a small rise in conductivity during the test period. This drop in pH suggests there was some absorption of acidic substances (possibly the oxides of carbon, sulphur, and nitrogen) from the atmosphere by the water. This effect would be present with all specimens so that small changes in solution pH would tend to be masked. Consequently, the p H changes reported are comparative rather than absolute values. The liquids covering Diaket, Nogenol, and Tubliseal showed little change in pH during 12 weeks, although there was a small but progressive rise in conductivity in this period. The ProcoSol liquid showed little change in pH, but a large rise in specific conductance during the first four weeks, with a smaller but continuous rise during the remaining test period. The compressive strengths of the cements after three months' water immersion and after storage for one week at 100% r H and 37 + 1~ are given in Table 3. No compressive strength values could be determined for Nogenol as the material had a rubbery consistency and remained pliable even at three months. The compressive strength of Proco-Sol did not decrease during three months (P > .05). Student's t test was used to compare the mean values and obtain probability values), although that of
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i
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,~
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Fig 1--Changes in pH.
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Fig 2--Changes in conductivity
Tubliseal showed a significant ( P < . 0 1 ) decrease after long-term water immersion. The compressive strengths of Proco-Sol and Tubliseal were not significantly different ( P > .05). Diaket had the greatest compressive strength, and there was no significant (P > .05) decrease during three months. The coefficients of variation of all three materials had a similar magnitude, with the exception of Proco-Sol at three months, which )roduced the relatively large value of 26.1%. DISCUSSION The two eugenol-containing sealer cements, Proco-Sol and Tubliseal, showed similar behavior. The rapid rise in specific conductance for ProcoSol during the first four weeks, followed by a slower but continuous
increase for the remaining test period, indicates that leaching occurred with this material. The negative water sorption figure and high water solubility clearly indicate that significant dissolution occurred with time. The high pH of the supernatant fluid, presumably resulting from the described leaching/dissolution affects, appears beneficial because an elevated pH is accepted as less cytotoxic than more acidic conditions. Despite the leaching/dissolution effects, there is no statistically significant decrease in compressive strength with Proco-Sol for 12 weeks. The material also had a small but positive dimensional change during the test period, indicating that canal-sealing efficiency might improve with time. The results reported here for ProcoSol differ somewhat from those of other studies, and these differences
may have a variety of sources. First, previous studies were performed several years ago, and there may have been changes and improvements in the material in the meantime. Second, the testing conditions adopted here differed from those in other studies (for example, storage at 37~ rather than at room temperature), but the conditions are possibly more clinically relevant than previously assumed with sealer cements in the past. Tubliseal also showed significant leaching/dissolution, but less than for Proco-Sol, although the dimensional change was considerably greater during the three months. The latter indicates a possible significant improvement in sealing efficacy with time. The specific conductance of the supernatant liquid showed a small, progressive rise with time while the pH stayed virtually neutral (pH'~ 7), compared with the slowly increasing acidity of the control. The virtually unchanged pH, small increase in conductivity, but relatively high sorption and solubility figures indicate that, although dissolution/leaching occurred with this material, the leached material was neutral in nature (presumably eugenol). The decrease in compressive strength indicates that some breakdown of the matrix occurred, supporting the contention that eugenol was the leached entity. Diaket had little water sorption and solubility, with no dimensional change during three months. The pH of the supernatant liquid remained essentially neutral throughout the test period, although there was a small but progressive rise in conductivity. This material showed the greatest compressive strength, and this did not significantly (P > .05) decrease during the test period. The virtually unchanged nature of this material with time suggests that it might be stable in the 129
J O U R N A L OF E N D O D O N T I C S ] VOL 8, N O 3, M A R C H 1982
clinical environment. Sealing efficacy would depend on its initial placement as no post-setting dimensional changes were observed. The new material, Nogenol, differed from the other sealers in a number of respects. It did not set hard, remaining rubbery throughout the test period. T h e pH and conductivity behavior were similar to those of Tubliseal and Diaket; however, Nogenol had a positive water sorption together with a moderate solubility, although Nogenol showed the greatest dimensional change with time. This high positive dimensional change, together with the rubbery consistency, suggests that the material might have a good sealing effect that could increase with time. CONCLUSIONS
the clinical significance of the eugenol leaching (whether it is beneficial) is unknown at this time. Diaket was the strongest sealer cement, and it remained virtually unchanged during the test period. The absence of dimensional change indicates that sealing efficacy is primarily dependent on a good initial placement technique. Nogenol differed significantly from the other materials, particularly in appearing to show a long-term rubbevy consistency. This characteristic might be beneficial in that long-term dimensional changes could possibly result in an improved seal by wedging the material within the root canal. In view of these findings and the reported biocompatibilitym of Nogenol, the material is worthy of further study, particularly with regard to its clinical USe.
The compressive strengths of ProcoSol, Diaket, and Tubliseal would appear satisfactory as there have been no reports in the literature of mechanical breakdown during post-and-core placement. The positive dimensional changes found with Proco-Sol and Tubliseal suggest that sealing efficiency might improve with time, although
130
Dr. von Fraunhofer is professor of biomaterials science, University of Louisville School of Dentistry, Louisville. Dr. Bransteuer is in private practice in Horse Cave, Ky. Requests for reprints should be sent m Dr. von Fraunhnfer, Department of Restorative Dentistry, University of Louisville School of Dentistry, Louisville, Ky 41.)292.
References 1. Marshall, F.J., and Massler, M. Sealing of pulpless teeth evaluated with radioisotopes. J Dent Med 16:172, 1961. 2. Higginbotham, T.L. A comparative study of five commonly used root canal sealers. Oral Surg 24:89, 1967. 3. Curson, I., and Kirk, E.E. An assessment of ront canal sealing cements. Oral Surg 26:229, 1968. 4. Kapsimalis, P., and Evans, R. Sealing properties of endodontic filling materials using radioactive polar and nonpolar isotopes. Oral Surg 22:386, 1966. 5. Barry, G., and Fried, I. Sealing quality of two polycarboxylate cements used as root canal sealers J Endod, 1:107, 1975. 6. Grieve, A.R., and ParkhoIm, ..I.D. The sealing properties of root filling cements. Br Dent J 132:19, 1972. 7. McComb, D., and Smith, D.C. Comparison of physical properties of polycarboxylatebased and conventional rout canal sealers. J Endod 2:228, 1976. 8. Weiner, B.M. and Schilder, H. A comparative study of important physical properties of various root canal sealers. Evaluation of setting times. Oral Surg 23:768, 1971. 9. Grieve, A.R. Sealing properties of cements used in root filling. Br Dent J 132:19, 1972. 10. Crane, D.L., and others. Biological and physical properties of an experimental root canal seaIer without eugenoL J Endod 6:438, 1980. 11. Antrim, D.D. Evaluation of the cytoxicity of root canal sealing agents on tissue culture cells in vitro: Grossman's sealer, N2 (permanent), Rickert's sealer and Cavit. J Endod 2:111, 1976.
The physical properties of four endodontic sealer cements J. A. v o n Fraunhofer, PhD, MSc, and J. Branstetter, DMD
The physical properties of t h r e e w i d e l y u s e d sealer c e m e n t s a n d a recently i n t r o d u c e d material h a v e b e e n studied. The e v a l u a t e d properties w e r e compressive s t r e n g t h , w a t e r sorption a n d solubility, d i m e n sional c h a n g e , p H a n d electrical c o n d u c t i v i t y . It was f o u n d that one material, w h i c h possessed the h i g h e s t compressive s t r e n g t h , s h o w e d little c h a n g e d u r i n g three m o n t h s " i m m e r s i o n in water. T w o eugenolc o n t a i n i n g c e m e n t s s h o w e d e v i d e n c e of e u g e n o l l e a c h i n g c o m b i n e d w i t h l o n g - t e r m d i m e n s i o n a l c h a n g e . The n e w n o n - e u g e n o l material r e t a i n e d a r u b b e r y consistency t h r o u g h o u t the test period, together w i t h a large positive d i m e n s i o n a l change. It is possible t h a t positive d i m e n s i o n a l c h a n g e (expansion) m i g h t i m p r o v e sealing efficacy w i t h time.
Endodontic cements are routinely used to help provide a hermetic seal in the obturation process for endodontically treated teeth. To achieve this objective, the sealer must satisfy certain criteria; possibly the most important of these are low solubility, good compressive strength, and long-term dimensional stability. A variety of sealer cements are commercially available, but the literature is somewhat confusing on their characteristics. Consequently, the literature pertaining to the three widely used materials used in this study--ProcoSol, Tubliseal, and Diaket--together with the available data on Nogenol, a newly introduced product, will be summarized. Proco-Sol, also known as Grossman's sealer, is a powder-liquid sys-
126
tern, the liquid being eugenol; whereas, the powder comprises a mixture of zinc oxide, hydrogenated resin, bismuth subcarbonate, barium sulphate, and sodium borate. The material's sealing ability was reported to be good by some workers, 1~ but others found that it showed greater leakage than other sealers. (' The solubility of ProcoSol during a seven-day test period was reported to be very low,; but other workers found a higher percentage solubility that approached the solubility of other eugonol-based sealers. 7 Proco-Sol has a reported compressive strength of approximately 230 kg/cm 2 and after it had set, the material shrank after 90 days at room temperature. 8 Diaket is a powder-liquid system; the powder is a mixture of zinc oxide
and bismuth phosphate: whereas, the liquid consists of vinyl copolymers in a ketone vehicle. Leakage studies on Diaket have produced variable results: some workers have suggested that it produced a satisfactory seal although some leakage had occurred3.4; other reports have indicated that there was little or no leakage with this material. 2,6The compressive strength of Diaket (approximately 340 kg/cm 2) was greater than that of Proco-Sol, 7 and the water solubility was significantly lower. 2,3,7
Tubliseal, a paste-paste system, consists of a base paste that is primarily zinc oxide with some bismuth trioxide, and the accelerator consists of various oleo resins and eugenol. Leakage studies on the material again produced variable results. Tubliseal leaked slightly more than Diaket, 6'9
JOURNAL OF ENDODONTICS I VOL 8, NO 3, MARCH 1982
although others have found that it produced a better seal than Diaket. 4 Similarly, some reports have indicated that Tubliseal is more effective than Proco-Sol, >'9 although others found that Tubliseal leaked more than Proco-Sol. 1~ A recent study m has shown t h a t Tubliseal has a sealing ability similar to another eugenol-based seale r and Nogenol, a non-eugenol material. The compressive strength of Tubliseal is low 7 (approximately 65 k g / era2), and although it has a moderate water solubility, 27 it also has a tendency to shrink consistently during a 90day period at room temperature and humidity, s Nogenol, a recently introduced paste-paste system that does not contain eugenol, consists of a base containing primarily zinc oxide and barium sulphate, and an accelerator that contains vegetable oil and fatty acids. There has been only one report on this material, m but ,that study indicated that the leakage of the material was of the same order as that of eugenolbased materials. Similar hardness and pH values were found for Nogenol, Tubliseal, and Kerr's sealer, m It is clear that the literature on root canal sealers is somewhat conflicting. In particular, leakage studies have yielded many inconsistencies although }issue-toxicity studies do show more of a consensus. H There is also a lack of information on many physical properties of root canal sealers: Studies on }ertain physical properties of several toot canal sealers are reported that should have clinical significance. Experimental
techniques
Three widely used commercial sealer cements and a newly introduced material were studied (Table 1). All ~aaterials were mixed in accordance ~'ith the manufacturer's instructions
Table 1 .
Material Proco-Sol Diaket Tubliseal Nogenol
Endodontic sealer cements.
System Powder-liquid Powder-liquid Paste-paste Paste-paste
Batch no. 13829 LE 262 (powder) LE 276 (liquid) 0208 79-1032 and 0418 78-1081 110278
Table 2 9 Water sorption, solubility, and d i m e n s i o n a l change (at three months).
Material Proco-Sol Diaket Tubliseal Nogenol
Water sorption Mean % SD -3.07 _+ 0.49 +1.59 + 0.58 +0.30 + 1.74 +3.41 + 0.08
Water solubility Mean % SD 10.92 _-'20.22 0.91 + 0.08 5.22 _+ 1.89 2.98 + 0.33
Dimensional change Mean % SD +2.93 _+ t.42 0.0 +_ 0.00 +8.63 _+ 1.66 +15.59 _+ 3.11
Table 3 9 Mean compressive strengths + SD (kg/cm~).
Material Proco-Sol Diaket Tubliseal Nogenol
One week 47.43 _ 7.92 144.05 _+ 20.43 50.37 _ 8.39
Coefficient of variation 16.7% 14.2% 16.7%
and packed into polymeric cylinders (1.0 X 0.5 cm in diameter); five samples of each cement were prepared. After setting for 48 hours at 100% r H and 37 + I ~ excess cement was ground back on water-lubricated, 800grit silicon carbide paper until the cement was flush with the ends of the cylinders. Thereafter, the specimens were measured and weighed to find the initial weights (Wo), then placed in 100 ml of distilled water in separate sealed containers at 37 _+ I~ An empty polymeric cylinder, also ira-
Three 41.27 179.46 34.63
months 4- 10.78 + 30.57 _+ 4.52
Coefficient of variation 26.1% 17.0% 13.1%
mersed in 100 ml of distilled water, served as the control. Specific conductance (YSI Model 31 Conductivity Bridge) and p H (Corning Model 12 p H Meter) measurements were performed periodically on the immersion water. Specific conductance measurements were made by inserting the conductivity electrode, which comprised two 1 mm 2 platinized platinum electrodes mounted 1 cm apart in an open-ended glass tube, in the solution in the specimen container. The conductance bridge imposed a 1-KHz alternating current between 127
JOURNAL OF ENDODONTICS [ VOL 8, NO 3, MARCH 1982
the platinized electrodes, and the solution conductance was read directly from an internal meter when the measuring bridge of the conductivity meter was in balance. Specific conductance and pH measurements were made at 24-hour intervals for the first week of immersion and at weekly intervals thereafter for 12 weeks. At the end of the test period, excess water was removed from the specimens by gentle blotting with paper tissues, which were then weighed to find the saturated weights (Wt). The specimen dimensions were then measured to determine the percentage extrusion of the cements out of the containing cylinders. Finally, the specimens were dried to constant weight over a desicant and a final weight (Wf) was found for each specimen. The water sorption and solubility values were found for each specimen, using the relations given in the formula; mean values and their standard deviations were calculated for each material. Water sorption and solubility values were calculated, using the standard relations: water sorption = Wt - Wo 100 X I%; Wo 1 water solubility = Wo
-
Wo
Wf
100
X--%. 1
In performing water sorption tests, there is always concomitant sorption and dissolution of the specimens, and these two factors cannot be separated. Consequently, the water sorption figures referred to later have positive values when sorption exceeds any dissolution that occurs, whereas, a negative figure indicates that dissolution
128
has exceeded any water uptake, and there was an overall loss in weight. Similarly, water solubility measurements do not take account of sorbed water that becomes bound within the structure of the test material and is not released by drying of the specimen. Consequently, these two parameters, which are routinely measured during the assessment of dental materials, have inherent limitations but are useful in indicating behavior rather than being definitive material characteristics. After drying, the polymeric cylinders were carefully slit open, and the specimens were removed, and their cross-sectional areas measured. The compressive strengths were determined, using an universal testing machine (Universal Calibration Corporation Unite-O-Matic) at a crosshead speed of 5 mm/min. For purposes of comparison, samples of each cement were prepared as described and allowed to set for one week at 100% r H and 37 +__ 1~ before compressive testing. RESULTS
The mean water sorption and solubility figures for the four cements after 12 weeks' immersion are given in Table 2. The mean dimensional changes of the cements expressed as percent of extrusion out of the containing cylinders during three months, are also given (Table 2). The two eugenolcontaining cements, Proco-Sol and Tubliseal, showed weight losses in the water sorption studies as well as pronounced solubilities. Proco-Sol had a water sorption more than ten times greater and a solubility more than double that of Tubliseal. The dimensional change of Tubliseal, however, was three times greater than that of
Proco-Sol. Diaket showed a moderate water sorption and a low water solubility, although it showed zero dimensional change during the test period. Nogenol bad a high water sorption and moderate solubility as well as a high dimensional change. The changes in the pH and conductivity of the immersion waters are shown in Figures 1 and 2. The control liquid (that is, water covering the empty polymeric cylinder) showed a small but progressive drop in pH and a small rise in conductivity during the test period. This drop in pH suggests there was some absorption of acidic substances (possibly the oxides of carbon, sulphur, and nitrogen) from the atmosphere by the water. This effect would be present with all specimens so that small changes in solution pH would tend to be masked. Consequently, the p H changes reported are comparative rather than absolute values. The liquids covering Diaket, Nogenol, and Tubliseal showed little change in pH during 12 weeks, although there was a small but progressive rise in conductivity in this period. The ProcoSol liquid showed little change in pH, but a large rise in specific conductance during the first four weeks, with a smaller but continuous rise during the remaining test period. The compressive strengths of the cements after three months' water immersion and after storage for one week at 100% r H and 37 + 1~ are given in Table 3. No compressive strength values could be determined for Nogenol as the material had a rubbery consistency and remained pliable even at three months. The compressive strength of Proco-Sol did not decrease during three months (P > .05). Student's t test was used to compare the mean values and obtain probability values), although that of
pit
z~
0
~
9
,
0
O--
-0
0
g o
6-' W n"
5-
"~,------.,.....~,
_
O-PROCOSOL e-DIAKET O-NOGENOL ~-TUBLISEAL m=CONTROL
i
i
w
,~
.4
g
"~
I~
w
lb
1'1
1'2
WEEK9
Fig 1--Changes in pH.
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Fig 2--Changes in conductivity
Tubliseal showed a significant ( P < . 0 1 ) decrease after long-term water immersion. The compressive strengths of Proco-Sol and Tubliseal were not significantly different ( P > .05). Diaket had the greatest compressive strength, and there was no significant (P > .05) decrease during three months. The coefficients of variation of all three materials had a similar magnitude, with the exception of Proco-Sol at three months, which )roduced the relatively large value of 26.1%. DISCUSSION The two eugenol-containing sealer cements, Proco-Sol and Tubliseal, showed similar behavior. The rapid rise in specific conductance for ProcoSol during the first four weeks, followed by a slower but continuous
increase for the remaining test period, indicates that leaching occurred with this material. The negative water sorption figure and high water solubility clearly indicate that significant dissolution occurred with time. The high pH of the supernatant fluid, presumably resulting from the described leaching/dissolution affects, appears beneficial because an elevated pH is accepted as less cytotoxic than more acidic conditions. Despite the leaching/dissolution effects, there is no statistically significant decrease in compressive strength with Proco-Sol for 12 weeks. The material also had a small but positive dimensional change during the test period, indicating that canal-sealing efficiency might improve with time. The results reported here for ProcoSol differ somewhat from those of other studies, and these differences
may have a variety of sources. First, previous studies were performed several years ago, and there may have been changes and improvements in the material in the meantime. Second, the testing conditions adopted here differed from those in other studies (for example, storage at 37~ rather than at room temperature), but the conditions are possibly more clinically relevant than previously assumed with sealer cements in the past. Tubliseal also showed significant leaching/dissolution, but less than for Proco-Sol, although the dimensional change was considerably greater during the three months. The latter indicates a possible significant improvement in sealing efficacy with time. The specific conductance of the supernatant liquid showed a small, progressive rise with time while the pH stayed virtually neutral (pH'~ 7), compared with the slowly increasing acidity of the control. The virtually unchanged pH, small increase in conductivity, but relatively high sorption and solubility figures indicate that, although dissolution/leaching occurred with this material, the leached material was neutral in nature (presumably eugenol). The decrease in compressive strength indicates that some breakdown of the matrix occurred, supporting the contention that eugenol was the leached entity. Diaket had little water sorption and solubility, with no dimensional change during three months. The pH of the supernatant liquid remained essentially neutral throughout the test period, although there was a small but progressive rise in conductivity. This material showed the greatest compressive strength, and this did not significantly (P > .05) decrease during the test period. The virtually unchanged nature of this material with time suggests that it might be stable in the 129
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clinical environment. Sealing efficacy would depend on its initial placement as no post-setting dimensional changes were observed. The new material, Nogenol, differed from the other sealers in a number of respects. It did not set hard, remaining rubbery throughout the test period. T h e pH and conductivity behavior were similar to those of Tubliseal and Diaket; however, Nogenol had a positive water sorption together with a moderate solubility, although Nogenol showed the greatest dimensional change with time. This high positive dimensional change, together with the rubbery consistency, suggests that the material might have a good sealing effect that could increase with time. CONCLUSIONS
the clinical significance of the eugenol leaching (whether it is beneficial) is unknown at this time. Diaket was the strongest sealer cement, and it remained virtually unchanged during the test period. The absence of dimensional change indicates that sealing efficacy is primarily dependent on a good initial placement technique. Nogenol differed significantly from the other materials, particularly in appearing to show a long-term rubbevy consistency. This characteristic might be beneficial in that long-term dimensional changes could possibly result in an improved seal by wedging the material within the root canal. In view of these findings and the reported biocompatibilitym of Nogenol, the material is worthy of further study, particularly with regard to its clinical USe.
The compressive strengths of ProcoSol, Diaket, and Tubliseal would appear satisfactory as there have been no reports in the literature of mechanical breakdown during post-and-core placement. The positive dimensional changes found with Proco-Sol and Tubliseal suggest that sealing efficiency might improve with time, although
130
Dr. von Fraunhofer is professor of biomaterials science, University of Louisville School of Dentistry, Louisville. Dr. Bransteuer is in private practice in Horse Cave, Ky. Requests for reprints should be sent m Dr. von Fraunhnfer, Department of Restorative Dentistry, University of Louisville School of Dentistry, Louisville, Ky 41.)292.
References 1. Marshall, F.J., and Massler, M. Sealing of pulpless teeth evaluated with radioisotopes. J Dent Med 16:172, 1961. 2. Higginbotham, T.L. A comparative study of five commonly used root canal sealers. Oral Surg 24:89, 1967. 3. Curson, I., and Kirk, E.E. An assessment of ront canal sealing cements. Oral Surg 26:229, 1968. 4. Kapsimalis, P., and Evans, R. Sealing properties of endodontic filling materials using radioactive polar and nonpolar isotopes. Oral Surg 22:386, 1966. 5. Barry, G., and Fried, I. Sealing quality of two polycarboxylate cements used as root canal sealers J Endod, 1:107, 1975. 6. Grieve, A.R., and ParkhoIm, ..I.D. The sealing properties of root filling cements. Br Dent J 132:19, 1972. 7. McComb, D., and Smith, D.C. Comparison of physical properties of polycarboxylatebased and conventional rout canal sealers. J Endod 2:228, 1976. 8. Weiner, B.M. and Schilder, H. A comparative study of important physical properties of various root canal sealers. Evaluation of setting times. Oral Surg 23:768, 1971. 9. Grieve, A.R. Sealing properties of cements used in root filling. Br Dent J 132:19, 1972. 10. Crane, D.L., and others. Biological and physical properties of an experimental root canal seaIer without eugenoL J Endod 6:438, 1980. 11. Antrim, D.D. Evaluation of the cytoxicity of root canal sealing agents on tissue culture cells in vitro: Grossman's sealer, N2 (permanent), Rickert's sealer and Cavit. J Endod 2:111, 1976.