0099-2399/90/1606-0269/$02.00/0 JOURNAL OF ENDODONTICS Copyright 9 1990 by The American Association ofEndodontists
Printed in U.S.A.
VOL. 16, NO. 6, JUNE 1990
An In Vitro Study of the Effect Endodontic Access Preparation and Amalgam Restoration Have Upon Incisor Crown Retention A. F. McMullen III, DDS, V. T. Himel, DDS, and N. K. Sarkar, PhD
MATERIALS AND M E T H O D S
Endodontic access preparation leads to a significant reduction in crown retention. This study sought to determine whether this retention can be regained after access. Eighteen extracted human maxillary incisors had PFM crowns fabricated. Crowns were cemented, retention measured, recemented, access preparations cut, and retention once again measured. Then, crowns were recemented and accesses restored with dental amalgam and new retention measured. This format allowed each crown to be used as a control of itself. For crowns cemented with zinc phosphate cement and restored with amalgam, a 126% increase over original retention was measured. For crowns cemented with polycarboxylate cement and restored with amalgam, a 237% increase over original retention was measured. For crowns cemented with polycarboxyiate cement and restored with amalgam, a 237% increase over original retention was measured. These results suggest that recementing crowns secondary to endodontic access and restoring the access with amalgam regains and even surpasses the original retention.
Eighteen extracted h u m a n maxillary central incisors stored in saline solution from the time of extraction throughout the course were studied. The teeth were radiographed from facial and proximal angulations utilizing a constant film-to-object distance at 15 mA, 70 kVp for 0.6 s. The teeth were assigned a random number and placed into two groups. Group 1 was designated the zinc phosphate group and group 2 was designated the polycarboxylate group. The teeth were prepared for PFM crowns by the method previously described by McMullen et al. (2). Once crown preparations were completed, the teeth were sent to a commercial dental laboratory where all crowns were fabricated by the same technician. Care was taken to ensure that during the course of the experiment the teeth were kept moistened by saline, utilizing either saline in a designated specimen bottle or holding the root in a saline-moistened gauze. The roots of the teeth were embedded in acrylic resin cubes to facilitate crown removal. There was also a supracoronal extension projecting from the incisal edge of the PFM crown to aid in crown removal. Following application of two coats of Copalite cavity varnish with a camel's hair brush and 10 min of drying, the crowns were cemented with their designated cement utilizing a static load of 11.5 kg for 10 min. The crowns were allowed to set for 24 h at 37~ and 100% relative humidity. The crowns were then displaced with the MTS-810 mechanical testing machine and original retentive forces recorded. Figure 1 illustrates the manner in which the teeth were fixed in the MTS-810 for crown removal. It was shown in the earlier study (2) that dental cement can be removed from a displaced crown, and the crown recemented without a significant effect upon the crown's retention. This was accomplished by treatment in an ultrasonic cleaner for 30 min with 30% nitric acid. Therefore, each crown can be used as a control of itself. Following displacement of the crowns, they were treated in the ultrasonic cleaner as described so they could be recemented without affecting the retention. Following ultrasonic cleaning, crowns were recemented and allowed to set under the same circumstances as before. Then, endodontic access preparations were cut through the lingual
Many dentists are confronted with the need to gain access to a root canal through an existing procelain or metal crown. In such a case one must remove the crown or cut an endodontic access preparation through the crown; either of which may lead to permanent deformation of the crown. It has been noted that crowns may become displaced during endodontic access preparation in a clinical situation (1). A previous study showed that endodontic access preparation through an existing PFM crown of maxillary central incisors causes a significant reduction in crown retention (2). The next logical question is whether this decrease in retention can be regained without refabrication of the crown. The purpose of this study was to determine whether recementation of the crown and or restoration of the access preparation with dental amalgam returns the retention to an acceptable level.
269
270
Journal of Endodontics
McMullen et al.
the cotton pellet was removed during the cementation procedure to remove all cement from the access preparation. When cementation had been allowed to set for 24 h, the crowns were displaced and displacement forces again recorded. Once again, the crowns were cleaned and recemented with a cotton pellet placed in the access. Before the cement was set, with the 11.5-kg load still applied to the crown, the cotton pellet and exoess cement were removed from the access preparation. The root canal was filled with thermoplasticized gutta-percha and seared off at the cementoenamel junction. Then a high copper amalgam, Tytin, was packed into the access preparation after the application of cavity varnish. These crowns were allowed to set under the previously described conditions. The crowns were then displaced and final retention was measured. Values at different cementation times were compared and an analysis of variance conducted.
of the P F M crowns utilizing a high-speed rotary cutting instrument under water spray with a #8 then a #256 bur. The teeth were not hand-held during the access preparation as in the previous study but were affixed to the cuspidor with a "C" clamp and a rubber dam sleeve to more closely simulate the bone and periodontal ligament. Once entrance was gained, the canals were instrumented to a #30 largest apical file 1 m m from the apex. Sodium hypochlorite was used as the irrigant. The canals were flared with Gates Glidden drills in a low-speed rotary instrument. The crowns were then displaced with the MTS-810 machine and retentive forces secondary to endodontic access preparation measured. Next, the crowns were cleaned in the ultrasonic cleaner and recemented. This time, a cotton pellet was placed inside the access preparation and, with the I 1.5-kg force still applied,
Upper MTS-810 "JAWS"
RESULTS The retentive values obtained at each successive crown removal are listed in Tables 1 and 2. Duncan's multiple range test for variance was conducted for groups 1 and 2. There was no significant difference in either group between original cementation, access preparation, and cementation without amalgam secondary to access preparation. There was a significant difference among those three variables and cementation with amalgam restoration secondary to access preparation for both groups. The results o f the Duncan's multiple range tests are given in Table 3.
Supracoronal crown removal extension 'Jaws" of crown emoval apparatus Jaws" rotate 180 egrees about this axis during crown referral Crown removal apparatus
~-~-Lower
~
DISCUSSION
MTS-180 "JAWS" *
* An alignment table was affixed on the lower MTS-180 "JAWS" to allow the other 180 degree rotation to ensure strict parallelism during crown removal. FiG 1. This is an illustration of the manner in which the teeth were affixed to the MTS-810 machine.
It has once again been shown that endodontic access preparation through an existing P F M crown causes a decrease in crown retention. Except under these experimental conditions, the results were not significant as they were in the previous experiment. Several reasons are postulated to account for this finding. First, the direction o f crown removal forces is different in this experimental design from that in the first experiment. The first experiment utilized the Instron Constant Rate Displacement Machine, whereas this experiment utilized the MTS-810 machine. The "jaws" that attach the tooth to the
TABLE 1. Group 1
Crown #
Original Retention (kg force)
Retention Secondary to Access
80 96 15 16 21 3 7 47 2
16.3 25.4 22.2 21.5 20.1 13.3 8.0 16.3 9.8
12.5 23.8 19.0 17.5 11.0 8.0 10.0 14.0 15.9
Retention Secondary to
Access~Cementation 12.6 23.1 24.0 19.2 17.7 20.9 11.7 24.4 20.1
Retention Secondary to
Access~Cementation~Amalgam 31.0 35.2 43.7 28.6 35.0 36.6 33.0 40.5 35.4
Vol. 16, No. 6, June 1990
Amalgam Restoration after Access
271
TABLE 2. Group 2
Crown #
Original Retention (kg force)
Retention Secondary to Access
77 44 1 95 35 57 92 86 43
12.3 3.5 12.2 5.6 4.0 9.1 8.0 7.0 5.4
11.0 3.9 0.0 7.2 2.7 4.8 8.2 3.3 0.0
TABLE 3. Duncan's multiple range test Group
Mean (kg force)
Significance
Original retention Retention-access Retention-recementation Retention-amalgam
17.0 14.6 19.3 35.4
No No No Yes
Original retention Retention-access Retention-recementation Retention-amalgam
7.5 4.6 7.5 21.7
No No No Yes
1
Instron machine have a self-aligning component that allows the forces of crown removal to adjust relative to the path of draw for the appropriate crown. Therefore, the forces of crown removal are not only vertical but have horizontal component incorporated so that the tooth is not fractured during crown removal. The MTS-810 machine had no self-aligning component associated with its path of draw. Since there is no selfaligning component associated with the MTS-810, horizontally directed forces are not incorporated into its crown removal. Hence, a more complicated crown removal apparatus was needed with the MTS-810 to ensure that the path of draw for each crown was exactly parallel to the path of crown removal for the MTS-810, or the tooth would have been fractured (Fig. 1). Thus, the direction of retentive forces measured with the MTS-810 and the Instron machine are different and the magnitude of the forces might be expected to be different. Second, the speed of crown removal in the two experiments was different. Once again, this relates to the differences in the test machines. The speed of crown removal in the first experiment with the Instron machine was 0.5 m m per min, as compared with 10 m m per min with the MTS-810 machine. This can cause differences in the amount of retention measured. Third, this experiment had the teeth affixed to the cuspidor with a C clamp with a rubber dam interposed to more closely simulate the human situation of the tooth to periodontal ligament to bone. In the first experiment, the teeth were handheld during access preparation, which does not simulate the human condition. Fourth, different operators cut the access preparations through these crowns in the two experiments. It is accepted
Retention Secondary to
Access~Cementation 9.1 4.0 9.7 10.8 6.4 9.0 6.0 4.4 7.8
Retention Secondary to
Access~Cementation~Amalgam 19.2 18.2 15.5 16.0 18.0 33.5 22.8 20.5 31.4
that different operators use different amounts of force and different directions of force during operative procedures. Fifth, once an endodontic access preparation is cut through a crown, it may have an effect similar to venting the crown. Venting is done to facilitate complete seating and to increase the crown's retention (3). However, venting in this experiment seems to have had little effect upon the retention because the crowns were recemented with the dental cement alone and no significant difference was seen relative to the original retention. The retention significantly increased only when the amalgam was plugged into the access preparation. Different retentive forces were seen when zinc phosphate or polycarboxylate cements were used, with zinc phosphate being the more retentive cement. No statistical comparison was made between the zinc phosphate and polycarboxylate cement groups because the cements have different physical properties and a direct comparison would be useless. But regardless of which cement was used originally, recementation and amalgam restoration following access preparation regained and even surpassed the original retention. The primary purpose of this project has been to determine whether or not restoration of an endodontic access preparation with dental amalgam secondary to recementation can regain the original retention. The results indicate that it does, regardless of whether zinc phosphate or polycarboxylate cement is utilized for crown cementation. The fact that the retention after restoring the access with dental amalgam is greater than the original crown retention may be deceiving. This may once again relate to the fact that the forces of crown removal of the MTS-810 are exactly vertical. The amalgam rsetoration placed into the access preparation is tangential to this vertical force and may add to crown retention by providing an intracoronal retentive feature. This supposition is supported because most of these crowns fractured through the amalcore upon removal; the crowns were not simply removed in toto as they were in the previous cementations. Regardless of the effect of access preparation or subsequent amalgam restoration had on crown retention, it seems that crown retention can be restored to an acceptable level following recementation and amalgam restoration. One aspect of retention which has not been addressed is that of microscopic leakage. The fact that mechanical retention is restored or even increased by restoring the access with amalgam may be misleading. When the amalgam restoration is holding a leaking crown in place, the long-term results could be disastrous. This may explain the situation of recur-
272
McMullen et al.
rent decay beneath a crown with a history of endodontics through the crown. Therefore, when recementing a crown secondary to endodontic access preparation, the marginal integrity must be checked as with any other crown to prevent leakage. This research was funded by NIDR-BRSG Grant S07RR05704. Dr. McMullen is now in private practice in Monroe, Louisiana. Dr. Himel is the coordinator of the postgraduate endodontic program, LSU School of
Journal of Endodontics Dentistry, New Orleans, LA. Dr. Sarkar is the head, Department of Biomaterials, LSU School of Dentistry.
References 1. Bergenholtz G. Endodontic complications following periodontal and prosthetic treatment of patients with advanced periodontal disease. J Periodontal 1984;55:63-8. 2. McMullen AF, Himel VT, Sarkar NK. An in vitro study of the effect endodontic access preparation has upon the retention of procelain fused to metal crowns of maxillary central incisors. J Endodon 1989; 15:154-6. 3. Phillips RW. Skinner's science of dental materials. 8th ed. Philadelphia: WB Saunders, 1982:461.
Printed in U.S.A.
VOL. 16, NO. 6, JUNE 1990
An In Vitro Study of the Effect Endodontic Access Preparation and Amalgam Restoration Have Upon Incisor Crown Retention A. F. McMullen III, DDS, V. T. Himel, DDS, and N. K. Sarkar, PhD
MATERIALS AND M E T H O D S
Endodontic access preparation leads to a significant reduction in crown retention. This study sought to determine whether this retention can be regained after access. Eighteen extracted human maxillary incisors had PFM crowns fabricated. Crowns were cemented, retention measured, recemented, access preparations cut, and retention once again measured. Then, crowns were recemented and accesses restored with dental amalgam and new retention measured. This format allowed each crown to be used as a control of itself. For crowns cemented with zinc phosphate cement and restored with amalgam, a 126% increase over original retention was measured. For crowns cemented with polycarboxylate cement and restored with amalgam, a 237% increase over original retention was measured. For crowns cemented with polycarboxyiate cement and restored with amalgam, a 237% increase over original retention was measured. These results suggest that recementing crowns secondary to endodontic access and restoring the access with amalgam regains and even surpasses the original retention.
Eighteen extracted h u m a n maxillary central incisors stored in saline solution from the time of extraction throughout the course were studied. The teeth were radiographed from facial and proximal angulations utilizing a constant film-to-object distance at 15 mA, 70 kVp for 0.6 s. The teeth were assigned a random number and placed into two groups. Group 1 was designated the zinc phosphate group and group 2 was designated the polycarboxylate group. The teeth were prepared for PFM crowns by the method previously described by McMullen et al. (2). Once crown preparations were completed, the teeth were sent to a commercial dental laboratory where all crowns were fabricated by the same technician. Care was taken to ensure that during the course of the experiment the teeth were kept moistened by saline, utilizing either saline in a designated specimen bottle or holding the root in a saline-moistened gauze. The roots of the teeth were embedded in acrylic resin cubes to facilitate crown removal. There was also a supracoronal extension projecting from the incisal edge of the PFM crown to aid in crown removal. Following application of two coats of Copalite cavity varnish with a camel's hair brush and 10 min of drying, the crowns were cemented with their designated cement utilizing a static load of 11.5 kg for 10 min. The crowns were allowed to set for 24 h at 37~ and 100% relative humidity. The crowns were then displaced with the MTS-810 mechanical testing machine and original retentive forces recorded. Figure 1 illustrates the manner in which the teeth were fixed in the MTS-810 for crown removal. It was shown in the earlier study (2) that dental cement can be removed from a displaced crown, and the crown recemented without a significant effect upon the crown's retention. This was accomplished by treatment in an ultrasonic cleaner for 30 min with 30% nitric acid. Therefore, each crown can be used as a control of itself. Following displacement of the crowns, they were treated in the ultrasonic cleaner as described so they could be recemented without affecting the retention. Following ultrasonic cleaning, crowns were recemented and allowed to set under the same circumstances as before. Then, endodontic access preparations were cut through the lingual
Many dentists are confronted with the need to gain access to a root canal through an existing procelain or metal crown. In such a case one must remove the crown or cut an endodontic access preparation through the crown; either of which may lead to permanent deformation of the crown. It has been noted that crowns may become displaced during endodontic access preparation in a clinical situation (1). A previous study showed that endodontic access preparation through an existing PFM crown of maxillary central incisors causes a significant reduction in crown retention (2). The next logical question is whether this decrease in retention can be regained without refabrication of the crown. The purpose of this study was to determine whether recementation of the crown and or restoration of the access preparation with dental amalgam returns the retention to an acceptable level.
269
270
Journal of Endodontics
McMullen et al.
the cotton pellet was removed during the cementation procedure to remove all cement from the access preparation. When cementation had been allowed to set for 24 h, the crowns were displaced and displacement forces again recorded. Once again, the crowns were cleaned and recemented with a cotton pellet placed in the access. Before the cement was set, with the 11.5-kg load still applied to the crown, the cotton pellet and exoess cement were removed from the access preparation. The root canal was filled with thermoplasticized gutta-percha and seared off at the cementoenamel junction. Then a high copper amalgam, Tytin, was packed into the access preparation after the application of cavity varnish. These crowns were allowed to set under the previously described conditions. The crowns were then displaced and final retention was measured. Values at different cementation times were compared and an analysis of variance conducted.
of the P F M crowns utilizing a high-speed rotary cutting instrument under water spray with a #8 then a #256 bur. The teeth were not hand-held during the access preparation as in the previous study but were affixed to the cuspidor with a "C" clamp and a rubber dam sleeve to more closely simulate the bone and periodontal ligament. Once entrance was gained, the canals were instrumented to a #30 largest apical file 1 m m from the apex. Sodium hypochlorite was used as the irrigant. The canals were flared with Gates Glidden drills in a low-speed rotary instrument. The crowns were then displaced with the MTS-810 machine and retentive forces secondary to endodontic access preparation measured. Next, the crowns were cleaned in the ultrasonic cleaner and recemented. This time, a cotton pellet was placed inside the access preparation and, with the I 1.5-kg force still applied,
Upper MTS-810 "JAWS"
RESULTS The retentive values obtained at each successive crown removal are listed in Tables 1 and 2. Duncan's multiple range test for variance was conducted for groups 1 and 2. There was no significant difference in either group between original cementation, access preparation, and cementation without amalgam secondary to access preparation. There was a significant difference among those three variables and cementation with amalgam restoration secondary to access preparation for both groups. The results o f the Duncan's multiple range tests are given in Table 3.
Supracoronal crown removal extension 'Jaws" of crown emoval apparatus Jaws" rotate 180 egrees about this axis during crown referral Crown removal apparatus
~-~-Lower
~
DISCUSSION
MTS-180 "JAWS" *
* An alignment table was affixed on the lower MTS-180 "JAWS" to allow the other 180 degree rotation to ensure strict parallelism during crown removal. FiG 1. This is an illustration of the manner in which the teeth were affixed to the MTS-810 machine.
It has once again been shown that endodontic access preparation through an existing P F M crown causes a decrease in crown retention. Except under these experimental conditions, the results were not significant as they were in the previous experiment. Several reasons are postulated to account for this finding. First, the direction o f crown removal forces is different in this experimental design from that in the first experiment. The first experiment utilized the Instron Constant Rate Displacement Machine, whereas this experiment utilized the MTS-810 machine. The "jaws" that attach the tooth to the
TABLE 1. Group 1
Crown #
Original Retention (kg force)
Retention Secondary to Access
80 96 15 16 21 3 7 47 2
16.3 25.4 22.2 21.5 20.1 13.3 8.0 16.3 9.8
12.5 23.8 19.0 17.5 11.0 8.0 10.0 14.0 15.9
Retention Secondary to
Access~Cementation 12.6 23.1 24.0 19.2 17.7 20.9 11.7 24.4 20.1
Retention Secondary to
Access~Cementation~Amalgam 31.0 35.2 43.7 28.6 35.0 36.6 33.0 40.5 35.4
Vol. 16, No. 6, June 1990
Amalgam Restoration after Access
271
TABLE 2. Group 2
Crown #
Original Retention (kg force)
Retention Secondary to Access
77 44 1 95 35 57 92 86 43
12.3 3.5 12.2 5.6 4.0 9.1 8.0 7.0 5.4
11.0 3.9 0.0 7.2 2.7 4.8 8.2 3.3 0.0
TABLE 3. Duncan's multiple range test Group
Mean (kg force)
Significance
Original retention Retention-access Retention-recementation Retention-amalgam
17.0 14.6 19.3 35.4
No No No Yes
Original retention Retention-access Retention-recementation Retention-amalgam
7.5 4.6 7.5 21.7
No No No Yes
1
Instron machine have a self-aligning component that allows the forces of crown removal to adjust relative to the path of draw for the appropriate crown. Therefore, the forces of crown removal are not only vertical but have horizontal component incorporated so that the tooth is not fractured during crown removal. The MTS-810 machine had no self-aligning component associated with its path of draw. Since there is no selfaligning component associated with the MTS-810, horizontally directed forces are not incorporated into its crown removal. Hence, a more complicated crown removal apparatus was needed with the MTS-810 to ensure that the path of draw for each crown was exactly parallel to the path of crown removal for the MTS-810, or the tooth would have been fractured (Fig. 1). Thus, the direction of retentive forces measured with the MTS-810 and the Instron machine are different and the magnitude of the forces might be expected to be different. Second, the speed of crown removal in the two experiments was different. Once again, this relates to the differences in the test machines. The speed of crown removal in the first experiment with the Instron machine was 0.5 m m per min, as compared with 10 m m per min with the MTS-810 machine. This can cause differences in the amount of retention measured. Third, this experiment had the teeth affixed to the cuspidor with a C clamp with a rubber dam interposed to more closely simulate the human situation of the tooth to periodontal ligament to bone. In the first experiment, the teeth were handheld during access preparation, which does not simulate the human condition. Fourth, different operators cut the access preparations through these crowns in the two experiments. It is accepted
Retention Secondary to
Access~Cementation 9.1 4.0 9.7 10.8 6.4 9.0 6.0 4.4 7.8
Retention Secondary to
Access~Cementation~Amalgam 19.2 18.2 15.5 16.0 18.0 33.5 22.8 20.5 31.4
that different operators use different amounts of force and different directions of force during operative procedures. Fifth, once an endodontic access preparation is cut through a crown, it may have an effect similar to venting the crown. Venting is done to facilitate complete seating and to increase the crown's retention (3). However, venting in this experiment seems to have had little effect upon the retention because the crowns were recemented with the dental cement alone and no significant difference was seen relative to the original retention. The retention significantly increased only when the amalgam was plugged into the access preparation. Different retentive forces were seen when zinc phosphate or polycarboxylate cements were used, with zinc phosphate being the more retentive cement. No statistical comparison was made between the zinc phosphate and polycarboxylate cement groups because the cements have different physical properties and a direct comparison would be useless. But regardless of which cement was used originally, recementation and amalgam restoration following access preparation regained and even surpassed the original retention. The primary purpose of this project has been to determine whether or not restoration of an endodontic access preparation with dental amalgam secondary to recementation can regain the original retention. The results indicate that it does, regardless of whether zinc phosphate or polycarboxylate cement is utilized for crown cementation. The fact that the retention after restoring the access with dental amalgam is greater than the original crown retention may be deceiving. This may once again relate to the fact that the forces of crown removal of the MTS-810 are exactly vertical. The amalgam rsetoration placed into the access preparation is tangential to this vertical force and may add to crown retention by providing an intracoronal retentive feature. This supposition is supported because most of these crowns fractured through the amalcore upon removal; the crowns were not simply removed in toto as they were in the previous cementations. Regardless of the effect of access preparation or subsequent amalgam restoration had on crown retention, it seems that crown retention can be restored to an acceptable level following recementation and amalgam restoration. One aspect of retention which has not been addressed is that of microscopic leakage. The fact that mechanical retention is restored or even increased by restoring the access with amalgam may be misleading. When the amalgam restoration is holding a leaking crown in place, the long-term results could be disastrous. This may explain the situation of recur-
272
McMullen et al.
rent decay beneath a crown with a history of endodontics through the crown. Therefore, when recementing a crown secondary to endodontic access preparation, the marginal integrity must be checked as with any other crown to prevent leakage. This research was funded by NIDR-BRSG Grant S07RR05704. Dr. McMullen is now in private practice in Monroe, Louisiana. Dr. Himel is the coordinator of the postgraduate endodontic program, LSU School of
Journal of Endodontics Dentistry, New Orleans, LA. Dr. Sarkar is the head, Department of Biomaterials, LSU School of Dentistry.
References 1. Bergenholtz G. Endodontic complications following periodontal and prosthetic treatment of patients with advanced periodontal disease. J Periodontal 1984;55:63-8. 2. McMullen AF, Himel VT, Sarkar NK. An in vitro study of the effect endodontic access preparation has upon the retention of procelain fused to metal crowns of maxillary central incisors. J Endodon 1989; 15:154-6. 3. Phillips RW. Skinner's science of dental materials. 8th ed. Philadelphia: WB Saunders, 1982:461.
