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The effect of pH of rosin on setting time of root canal cements
JOURNAL OF ENDODONTICS I VOL 8, NO 7, JULY 1982
The effect of pH of rosin on setting time of root canal cements
L o u i s I. G r o s s m a n ,
DDS, ScD
M o s t r o o t c a n a l c e m e n t s c o n t a i n r o s i n , as w e l l as z i n c o x i d e , i n t h e i r p o w d e r c o m p o n e n t . T h e p u r p o s e o f r o s i n is to i m p a r t a d h e s i v e n e s s to t h e c e m e n t . It w a s f o u n d t h a t t h e r o s i n s u s e d i n d e n t i s t r y h a v e a w i d e v a r i a t i o n i n p H , r a n g i n g f r o m 4.5 to 7.9. I n t h i s s t u d y , r o s i n s h a v i n g a p H of 6.2 or l o w e r a c c e l e r a t e d t h e s e t t i n g t i m e of c e m e n t s ; w h e r e a s , t h o s e h a v i n g a p H of 7 o r h i g h e r r e t a r d e d o r i n t e r f e r r e d w i t h t h e s e t t i n g of t h e c e m e n t s . Z i n c o x i d e - e u g e n o l c e m e n t w i t h o u t r o s i n d i d n o t set h a r d i n 24 h o u r s a n d w a s f r i a b l e w h e n it d i d set. T h e a d d i t i o n of r o s i n to z i n c - o x i d e p o w d e r g a v e it b o d y , c o h e r e n c e , a n d a l l o w e d it to set i n a r e a s o n a b l e t i m e .
Most root canal cements are comp o u n d s consisting of zinc oxide a n d eugenol as a base, together with certain additives that supply adhesiveness a n d smoothness to the cement mix, a n d control the setting time of the cement. Rosin, either n a t u r a l or synthetic, is generally used to impart adhesiveness to the cement. Because of the rosin content, it m a y also influence the setting time of the cement a n d affect the periapical tissues. This study was u n d e r t a k e n to determine the p H of six rosins, both n a t u r a l a n d synthetic, a n d to assess the effect of these rosins on setting time. T h e powder of a c o m m o n l y used root canal c e m e n t ' (zinc oxide, rosin, b a r i u m sulphate, b i s m u t h subcarbonate, a n d sodium borate) was modified in only one respect--the rosin content. All other ingredients r e m a i n e d the same. T h e liquid used in c o n j u n c t i o n with powder to pro-
326
duce the cement was eugenol. T h e same rosins were also c o m p o u n d e d with zinc oxide, without the heavy metal salts in a ratio of 2.1 zinc oxide to 1.35 rosin. The resultant zinc oxide-rosin powders were mixed with eugenol, a n d the setting times were determined.
MATERIALS AND METHODS The following rosins were used to modify the root canal cement powder: Amend, Hakusui, Penresina, Primavera, Staybelite, and WW rosin. The pH of the rosins was determined in the following manner. One gram of rosin was crushed to a fine powder, and placed in a 15-ml centrifuge tube. Deionized water (9ml) was added. The tubes were stoppered and centrifuged in a Sorval Superspeed RC2B centrifuge at 5,000 rpm for five minutes. The pH of the supernatant fluid was determined with a London no. 26 pH meter (Table). Approximately 35 mg of each of the powders was mixed slowly with 0.8 mg of
eugenol to obtain a smooth mixture, which would conform to the consistency tests. ~ Dormann spacers (1 mm thick) were fixed to a polished glass plate and filled to the top surface of the spacers with each of the cements. The mixing time was recorded for each of the cements. The glass plate supporting the cements was placed in an incubator at 37 C with 100~7c humidity. Tests for setting cements were made every half hour for a total of eight hours. The tests were made with a 100-gm weight attached to a sharp, pointed instrument. The instrument was placed on the surface of the cements, and it was noted whether it made an indentation. Cement was considered hard-set when the instrument could no longer make an indentation. All tests were made at least five times and then averaged. Similar tests were made of the cements composed of zinc oxide-rosin powder and eugenol. RESULTS T h e p H of the rosins varied from 4.5 to 7.9 (Table). Both A m e n d a n d
JOURNAL OF ENDODONTICS ] VOL 8, NO 7, JULY 1982
Table 9 p H and setting time o f cements in hours. Hours
Brand
pH
Group A*
Group B+
Amend Hakusui Penresina Primavera Stavbelite WW
7.9 4.5 7.3 5.4 6.2 4.7
not set 11/2 not set 1 21/2 ILk
24 11/2 24 1t/2 3 11/2
* S t a n d a r d tenlen
pllwder except tor Ihe resin
- Z i m " oxide a n d resin
Penresina c l a i m e d to contain a diluent, a n d they h a d the highest p H (7.9 and 7.3, respectively). A c c o r d i n g to one m a n u f a c t u r e r the diluent is Bentonite, which has a p H of 9.6. O b s e r v a t i o n of the setting times of the cements showed t h a t the p H of the rosins did indeed have an effect on the setting time ( G r o u p A, Table). In general, the lower the p H of the rosin, the shorter the setting time. The setting time was the shortest for cement containing Primavera, 1 hour; H a k u s u i a n d W W rosin set in 11/2 hours; Staybelite rosin set in 21/2 hours; a n d A m e n d a n d Penresina did not set in eight hours. H i g h alkaline content a c t u a l l y prevented Cements from setting within the time range of the e x p e r i m e n t ; both Amend a n d Penresina were soft a n d tacky even after 24 hours. T h e setting time of the zinc oxiderosin cements differed only slightly from the a f o r e m e n t i o n e d ( G r o u p B, Table). C e m e n t m a d e with zinc oxide a n d H a k u s u i , P r i m a v e r a , a n d W W rosin set in 11/2 hours; A m e n d and Penresina set in 24 hours; a n d zinc oxide w i t h o u t the rosin could still be i n d e n t e d after 24 hours. DISCUSSION It has been k n o w n for some time that an acid or acidic salt will accelerate the setting of zinc oxide-euge-
nol cement. Benzoic acid a n d zinc acetate have been r e c o m m e n d e d to hasten the setting time. However, the fact that the a d d i t i o n of a rosin to zinc oxide-eugenol root canal cements affects the setting time, either accelerating or r e t a r d i n g it, has not been reported in d e n t a l literature. It was found that, in general, the lower the p H of the rosin, the faster the c e m e n t set; conversely, a p H of 7 or higher interfered with setting. O n e w o u l d expect that H a k u s u i ( p H 4.5) or W W rosin (pH 4.7) would be the first to set hard, b u t this was not the case. P r i m a v e r a rosin ( p H 5.4) set e q u a l l y as fast or faster most of the time. This m a y suggest t h a t slight variations in the m a n n e r of m i x i n g the cement, or a m b i e n t t e m p e r a t u r e and humidity during mixing may have a c c o u n t e d for the slight differences in setting time because not all tests were c o n d u c t e d on the same day. Because zinc oxide alone when mixed with eugenol a n d m a d e into a wafer (1 m m thick) did not set h a r d after 24 hours at 37 C a n d 100% relative h u m i d i t y , its use as a c e m e n t i n g agent for g u t t a - p e r c h a or silver cones is open to question. It did, however, become hard-set in c o m b i n a t i o n with a rosin u n d e r the same conditions in this e x p e r i m e n t . Even after 24 hours, zinc oxide-eugenol c e m e n t was a friable mass. Rosin
gave coherence to zinc oxide-eugenol m a k i n g it a more solid substance a n d p r o b a b l y less likely to dissolve. Therefore, a c c o r d i n g to the results of this e x p e r i m e n t , zinc oxide-eugenol should be used as a root canal cement in c o n j u n c t i o n with a rosin. Finally, as the p H range of those rosins, which b r o u g h t a b o u t setting of the cements within one or 21/2 hours ( p H 4.5 to 6.2), is different from the p H of b o d y tissues, their effect on periapical tissue should be investigated. SUMMARY Rosins used in the composition of root canal sealer cements vary considerably in respect to pH. In this study, those having a p H of 7 or above, r e t a r d e d or interferred with the setting properties of the cements. Zinc oxide-eugenol cement w i t h o u t rosin d i d not set h a r d in 24 hours a n d was friable when it did set. T h e a d d i t i o n a l of rosin to zinc-oxide powder gave it b o d y a n d coherence, a n d allowed it to set in a reasonable time. T h e biologic effect of grossly acidic rosins should be investigated. Dr. Grossman professor emeritus of endodontics, and director of postdoctoral endodontic research, School of Dental Medicine, University of Pennsylvania. Requests for reprints should be directed to Dr. Grossman, 4001 Spruce St, Philadelphia, 19104.
References
1. Grossman, L.I. Endodontic Practice, eft 10. Philadelphia, Lea & Febiger, 1981, p 297. 2. Grossman, L.I. An improved root canal cement. JADA 56: 381-385, 1958. 327
The effect of pH of rosin on setting time of root canal cements
L o u i s I. G r o s s m a n ,
DDS, ScD
M o s t r o o t c a n a l c e m e n t s c o n t a i n r o s i n , as w e l l as z i n c o x i d e , i n t h e i r p o w d e r c o m p o n e n t . T h e p u r p o s e o f r o s i n is to i m p a r t a d h e s i v e n e s s to t h e c e m e n t . It w a s f o u n d t h a t t h e r o s i n s u s e d i n d e n t i s t r y h a v e a w i d e v a r i a t i o n i n p H , r a n g i n g f r o m 4.5 to 7.9. I n t h i s s t u d y , r o s i n s h a v i n g a p H of 6.2 or l o w e r a c c e l e r a t e d t h e s e t t i n g t i m e of c e m e n t s ; w h e r e a s , t h o s e h a v i n g a p H of 7 o r h i g h e r r e t a r d e d o r i n t e r f e r r e d w i t h t h e s e t t i n g of t h e c e m e n t s . Z i n c o x i d e - e u g e n o l c e m e n t w i t h o u t r o s i n d i d n o t set h a r d i n 24 h o u r s a n d w a s f r i a b l e w h e n it d i d set. T h e a d d i t i o n of r o s i n to z i n c - o x i d e p o w d e r g a v e it b o d y , c o h e r e n c e , a n d a l l o w e d it to set i n a r e a s o n a b l e t i m e .
Most root canal cements are comp o u n d s consisting of zinc oxide a n d eugenol as a base, together with certain additives that supply adhesiveness a n d smoothness to the cement mix, a n d control the setting time of the cement. Rosin, either n a t u r a l or synthetic, is generally used to impart adhesiveness to the cement. Because of the rosin content, it m a y also influence the setting time of the cement a n d affect the periapical tissues. This study was u n d e r t a k e n to determine the p H of six rosins, both n a t u r a l a n d synthetic, a n d to assess the effect of these rosins on setting time. T h e powder of a c o m m o n l y used root canal c e m e n t ' (zinc oxide, rosin, b a r i u m sulphate, b i s m u t h subcarbonate, a n d sodium borate) was modified in only one respect--the rosin content. All other ingredients r e m a i n e d the same. T h e liquid used in c o n j u n c t i o n with powder to pro-
326
duce the cement was eugenol. T h e same rosins were also c o m p o u n d e d with zinc oxide, without the heavy metal salts in a ratio of 2.1 zinc oxide to 1.35 rosin. The resultant zinc oxide-rosin powders were mixed with eugenol, a n d the setting times were determined.
MATERIALS AND METHODS The following rosins were used to modify the root canal cement powder: Amend, Hakusui, Penresina, Primavera, Staybelite, and WW rosin. The pH of the rosins was determined in the following manner. One gram of rosin was crushed to a fine powder, and placed in a 15-ml centrifuge tube. Deionized water (9ml) was added. The tubes were stoppered and centrifuged in a Sorval Superspeed RC2B centrifuge at 5,000 rpm for five minutes. The pH of the supernatant fluid was determined with a London no. 26 pH meter (Table). Approximately 35 mg of each of the powders was mixed slowly with 0.8 mg of
eugenol to obtain a smooth mixture, which would conform to the consistency tests. ~ Dormann spacers (1 mm thick) were fixed to a polished glass plate and filled to the top surface of the spacers with each of the cements. The mixing time was recorded for each of the cements. The glass plate supporting the cements was placed in an incubator at 37 C with 100~7c humidity. Tests for setting cements were made every half hour for a total of eight hours. The tests were made with a 100-gm weight attached to a sharp, pointed instrument. The instrument was placed on the surface of the cements, and it was noted whether it made an indentation. Cement was considered hard-set when the instrument could no longer make an indentation. All tests were made at least five times and then averaged. Similar tests were made of the cements composed of zinc oxide-rosin powder and eugenol. RESULTS T h e p H of the rosins varied from 4.5 to 7.9 (Table). Both A m e n d a n d
JOURNAL OF ENDODONTICS ] VOL 8, NO 7, JULY 1982
Table 9 p H and setting time o f cements in hours. Hours
Brand
pH
Group A*
Group B+
Amend Hakusui Penresina Primavera Stavbelite WW
7.9 4.5 7.3 5.4 6.2 4.7
not set 11/2 not set 1 21/2 ILk
24 11/2 24 1t/2 3 11/2
* S t a n d a r d tenlen
pllwder except tor Ihe resin
- Z i m " oxide a n d resin
Penresina c l a i m e d to contain a diluent, a n d they h a d the highest p H (7.9 and 7.3, respectively). A c c o r d i n g to one m a n u f a c t u r e r the diluent is Bentonite, which has a p H of 9.6. O b s e r v a t i o n of the setting times of the cements showed t h a t the p H of the rosins did indeed have an effect on the setting time ( G r o u p A, Table). In general, the lower the p H of the rosin, the shorter the setting time. The setting time was the shortest for cement containing Primavera, 1 hour; H a k u s u i a n d W W rosin set in 11/2 hours; Staybelite rosin set in 21/2 hours; a n d A m e n d a n d Penresina did not set in eight hours. H i g h alkaline content a c t u a l l y prevented Cements from setting within the time range of the e x p e r i m e n t ; both Amend a n d Penresina were soft a n d tacky even after 24 hours. T h e setting time of the zinc oxiderosin cements differed only slightly from the a f o r e m e n t i o n e d ( G r o u p B, Table). C e m e n t m a d e with zinc oxide a n d H a k u s u i , P r i m a v e r a , a n d W W rosin set in 11/2 hours; A m e n d and Penresina set in 24 hours; a n d zinc oxide w i t h o u t the rosin could still be i n d e n t e d after 24 hours. DISCUSSION It has been k n o w n for some time that an acid or acidic salt will accelerate the setting of zinc oxide-euge-
nol cement. Benzoic acid a n d zinc acetate have been r e c o m m e n d e d to hasten the setting time. However, the fact that the a d d i t i o n of a rosin to zinc oxide-eugenol root canal cements affects the setting time, either accelerating or r e t a r d i n g it, has not been reported in d e n t a l literature. It was found that, in general, the lower the p H of the rosin, the faster the c e m e n t set; conversely, a p H of 7 or higher interfered with setting. O n e w o u l d expect that H a k u s u i ( p H 4.5) or W W rosin (pH 4.7) would be the first to set hard, b u t this was not the case. P r i m a v e r a rosin ( p H 5.4) set e q u a l l y as fast or faster most of the time. This m a y suggest t h a t slight variations in the m a n n e r of m i x i n g the cement, or a m b i e n t t e m p e r a t u r e and humidity during mixing may have a c c o u n t e d for the slight differences in setting time because not all tests were c o n d u c t e d on the same day. Because zinc oxide alone when mixed with eugenol a n d m a d e into a wafer (1 m m thick) did not set h a r d after 24 hours at 37 C a n d 100% relative h u m i d i t y , its use as a c e m e n t i n g agent for g u t t a - p e r c h a or silver cones is open to question. It did, however, become hard-set in c o m b i n a t i o n with a rosin u n d e r the same conditions in this e x p e r i m e n t . Even after 24 hours, zinc oxide-eugenol c e m e n t was a friable mass. Rosin
gave coherence to zinc oxide-eugenol m a k i n g it a more solid substance a n d p r o b a b l y less likely to dissolve. Therefore, a c c o r d i n g to the results of this e x p e r i m e n t , zinc oxide-eugenol should be used as a root canal cement in c o n j u n c t i o n with a rosin. Finally, as the p H range of those rosins, which b r o u g h t a b o u t setting of the cements within one or 21/2 hours ( p H 4.5 to 6.2), is different from the p H of b o d y tissues, their effect on periapical tissue should be investigated. SUMMARY Rosins used in the composition of root canal sealer cements vary considerably in respect to pH. In this study, those having a p H of 7 or above, r e t a r d e d or interferred with the setting properties of the cements. Zinc oxide-eugenol cement w i t h o u t rosin d i d not set h a r d in 24 hours a n d was friable when it did set. T h e a d d i t i o n a l of rosin to zinc-oxide powder gave it b o d y a n d coherence, a n d allowed it to set in a reasonable time. T h e biologic effect of grossly acidic rosins should be investigated. Dr. Grossman professor emeritus of endodontics, and director of postdoctoral endodontic research, School of Dental Medicine, University of Pennsylvania. Requests for reprints should be directed to Dr. Grossman, 4001 Spruce St, Philadelphia, 19104.
References
1. Grossman, L.I. Endodontic Practice, eft 10. Philadelphia, Lea & Febiger, 1981, p 297. 2. Grossman, L.I. An improved root canal cement. JADA 56: 381-385, 1958. 327