Dental Traumatology 2015; 31: 380–384; doi: 10.1111/edt.12175
Effect of three calcium hydroxide formulations on fracture resistance of dentin over time Jeremiah James Hawkins, Mahmoud Torabinejad, Yiming Li, Bonnie Retamozo Department of Endodontics, Loma Linda School of Dentistry, Loma Linda, CA, USA
Key words: crown fracture; crown-root fracture; dental trauma; permanent tooth; root fracture; tooth injury Correspondence to: Jeremiah Hawkins, 1046 Sirron Ave, Richland, WA 99253, USA Tel.: (208) 989-6109 Fax: (509) 735 9598 e-mail: [email protected] Accepted 28 February, 2015
Abstract – Background: The long-term use of calcium hydroxide has been discouraged throughout the recent decade due to a proposed decrease in fracture resistance of dentin. This weakening has grave implications when used on immature teeth with thin dentinal walls in procedures such as apexogenesis. Aim: The purpose of this study was to identify the effects of three commercial calcium hydroxide formulations (Vitapex, Ultracal XS and Pulpdent) on the fracture resistance of dentin in relation to time. Materials and Methods: Two-hundred and forty deciduous lamb incisors were collected, cleaned and shaped, and filled with one of the three calcium hydroxide formulations and one negative saline control. At one, three, and 6 months, these teeth were fractured on an Instron machine to determine fracture resistance. Results: No statistical differences were observed among any of the experimental groups, nor between any of the experimental groups and negative control groups. Conclusions: Based on our findings, there appears insufficient evidence to support that either Vitapex, Ultracal XS, or Pulpdent will cause a decrease in fracture resistance of dentin within a 6-month period.
Since its introduction in 1920 by BW Hermann, calcium hydroxide (Ca(OH)2) has been recommended for various dental procedures (1). Calcium hydroxide is commonly used by the general practitioner as a deep cavity liner or base owing to its bactericidal and healing properties (2). Due to these properties, endodontists have found it useful as an intracanal medicament as well. Its application has been suggested to arrest internal and external resorptive processes (3, 4). Studies have shown that Ca(OH)2 has sufficient antibacterial properties to decrease cultivable bacteria when used as an interappointment medication and therefore increase root canal therapy success (5). In the case of an avulsed tooth, the International Association of Dental Traumatology (IADT) guidelines suggest its placement for up to 1 month before final obturation of the root canal system (6). For a tooth with a necrotic pulp and an incompletely formed apex, Ca (OH)2 was for many years the medication of choice for apexification (7). Mineral trioxide aggregate (MTA) has largely assumed this role in recent years (8). Today, Ca (OH)2 is used frequently within the root canal system for a varying degree of time according to its intended application. The length of time that Ca(OH)2 has been and continues to be used varies dramatically. In Sheehy and Robert’s review of the use of Ca(OH)2 for apical barrier formation, they describe its use for 5 to 20 months (9). Kvist et al. (10) in 2004 demonstrated its use as an interappointment medication for as little as a week. In 1988, Stormer discussed a negative outcome associated with teeth that had undergone apexification 380
using Ca(OH)2. An increased incidence of cervical root fracture due to a weakening effect owing to the use of Ca(OH)2 was suggested (11). Cvek et al. (12) investigated this suggestion in a retrospective study and found a significant increase in cervical root fracture in teeth that had undergone apexification with Ca(OH)2. Andreasen et al. examined the impact of duration of Ca (OH)2 use on immature root dentin weakening. They demonstrated a 50% decrease in fracture resistance after 1-year exposure to Ca(OH)2 in vitro (13). Andreasen et al. further investigated this weakening phenomenon on account of Ca(OH)2 by comparing its effect with that of MTA over a 100-day period. They found that Ca(OH)2 significantly decreased the fracture resistance of dentin while MTA did not (14). Many additional studies have been conducted to measure the fracture resistance of dentin after being exposed to Ca(OH)2 (15–26). Doyon et al. examined the fracture resistance of human dentin after exposure to Ca(OH)2 from 30 to 180 days. After 180 days, dentin disks exposed to Ca(OH)2 paste were shown to be statistically weaker (16). Sahebi et al. evaluated the short-term effects of Ca(OH)2 on human dentin; their results indicated that 30 days of exposure to Ca(OH)2 were enough to statistically weaken human root dentin (23). There exists a considerable difference in the methods and materials used to test the weakening effect among these studies. Even though these differences exist, a strong body of evidence has been accumulated showing that Ca(OH)2 can negatively affect dentinal © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Effect of calcium hydroxide on dentin strength. This effect has been examined cumulatively by Yassen et al. in a recent systematic review (27). On the other hand, the concentration of Ca(OH)2 examined in various studies has been consistent. A variety of commercial Ca(OH)2 products are available for use as intracanal medicaments, and each product has its own composition and percentage concentration of Ca(OH)2. The effect on fracture resistance of dentin depending on concentration percentage over time has not been clearly identified in the literature. It is possible that the concentration of Ca(OH)2 used has an impact on the results of these published studies. The purpose of this study was to identify the effects of three Ca(OH)2 formulations, including Vitapex, Ultracal XS, and Pulpdent, on the fracture resistance of dentin in relation to time. Materials and methods
Thirty-five frozen lambs’ heads were purchased from a local food-grade meat market after being imported from New Zealand. These lambs were slaughtered at approximately the same time being less than 2 months of age. The lower anterior mandible was then sectioned with a band saw and stored frozen until time for tooth extraction. Eight deciduous incisor teeth were extracted from each lamb mandible to provide a total of 240 teeth, which were placed in 10% buffered formalin solution immediately after the extraction until evaluation (28). To prepare the teeth for instrumentation and experimental treatment, each tooth was measured 10 mm from the CEJ toward the apex and then sectioned horizontally with a diamond burr. The remaining radicular and coronal pulp tissue was then extirpated with a hedstrom file. Root canal preparation was completed with Profile NiTi files 0.04 to a size #30. Each canal was then rinsed with 5 ml NaOCl, followed by another rinse with 5 ml of sterile saline. Each canal was then dabbed dry with paper points. Seventy-five roots were randomly assigned to each brand of Ca(OH)2, and 5 roots were randomly assigned to each control group. This pattern was repeated three times for a total of 12 groups, as shown in Table 1. Once divided, the commercial Ca(OH)2 paste was spun into the canals until completely filled using a lentulo spiral on a slow speed handpiece (29). Four millimeters of Cavit was then used to temporize each sample at the apex (30). The samples were stored in physiologic saline at 37°C that was replenished weekly for the dura-
381
tion of the experiment (13). Each experimental group was isolated from the other groups and housed in individual plastic containers throughout the experiment. The three test formulations were Vitapex, Ultracal XS, and Pulpdent, as described in Table 2. They were chosen because of their common use in practice as well as their varying concentrations of Ca(OH)2. After the experimental time had elapsed for each group, being either 1, 3, or 6 months, the samples were removed from their containers and placed in dye stone (Die-Keen Green, Heraeus Kulzer, Inc., South Bend, IN, USA) submerging the root to the depth of the buccal CEJ. Once the stone had set, it was trimmed to the level of the buccal CEJ and any misplaced stone was removed to ensure uniformity. A stainless steel 3/8 inch nut was used as a matrix to hold the dye stone and facilitate stabilization during fracture. The mounted roots were then secured in a vise and measured for fracture resistance by an Instron testing machine (Instron, High Wycombe, UK) at a rate of 1 mm per minute. A metal blade connected to the Instron machine directly applied force to the facial aspect of each tooth. The blade was placed approximately 1 mm coronal to the buccal CEJ (Fig. 1). Force was Table 2. The tested formulations are shown along with manufacturer and percentage calcium hydroxide Material
Manufacturer
Ca(OH)2%
Saline Vitapex
0.9% NaCl solution Neo Dental Chemical Products Co. Lt, Tokyo, Japan Ultradent Productions, Inc., South Jordan, UT Puldent Corp., Watertown, MA
0 30
Ultracal XS Pulpdent
35 42
Table 1. At each time point, 25 teeth will be tested from each formulation of calcium hydroxide and 5 teeth will be tested from each control group Organization and distribution of groups Month 1 Control (n = Material 1 (n Material 2 (n Material 3 (n
Month 3 5) = 25) = 25) = 25)
Control (n = Material 1 (n Material 2 (n Material 3 (n
Month 6 5) = 25) = 25) = 25)
Control (n = Material 1 (n Material 2 (n Material 3 (n
5) = 25) = 25) = 25)
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Fig. 1. The instron blade is placed approximately 1 mm coronal to the buccal CEJ. Force is applied at a rate of 1 mm per minute until dentin fracture.
382
Hawkins et al. Table 3. The statistical mean, standard deviation, and confidence intervals are given for each formulation at each time point tested Confidence interval Formulation
Month
Mean
SE
Lower bound
Upper bound
PulpdentXS
1 3 6 1 3 6 1 3 6 1 3 6
0.038 0.04 0.038 0.039 0.043 0.037 0.039 0.04 0.04 0.041 0.038 0.032
0.002 0.002 0.001 0.002 0.002 0.001 0.002 0.002 0.001 0.004 0.004 0.003
0.034 0.037 0.035 0.036 0.04 0.034 0.035 0.037 0.037 0.034 0.031 0.025
0.041 0.043 0.041 0.042 0.046 0.04 0.042 0.043 0.043 0.048 0.045 0.039
Ultacal
Vitapex
Saline
Fig. 2. IMAGE J software was used to calculate the square millimeters of fractured dentin. A standard endodontic ruler was used to calibrate each image prior to calculation.
The cumulative data support that the fracture resistance of dentin is not affected by the concentrations of Ca(OH)2 within these formulations over time. Discussion
measured in Newtons and recorded at the point of fracture (31). The cross-sectional diameter of the fractured incisor was photographed, and IMAGE J software (National Institutes of Health, Bethesda, Maryland, USA) was used to calculate the surface area of fractured dentin (Fig. 2). Newtons of force per square millimeters was then converted to megapascals (MPa). The data were collected and subjected to a related-samples Friedman’s two-way analysis of variance by ranks. The level of significance was set at 0.05. Results
The mean load at fracture, standard error, and confidence intervals is presented in Table 3. The mean fracture resistance of Vitapex was 0.0386, 0.0399, and 0.0404 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of Ultracal XS was 0.0392, 0.0430, and 0.0369 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of Pulpdent XS was 0.0377, 0.0394, 0.0380 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of the saline control was 0.0409, 0.0376 and 0.0321 Mpa at 1, 3, and 6 months, respectively. Graphical representation of the comparison is illustrated in Fig. 3. The Pulpdent group showed no significant decrease (P = 0.527) in fracture resistance at any of the time points; 1, 3, or 6 months. The Ultracal XS group showed no significant difference (P = 1.79) between time points. Interestingly, the fracture strength of the 3-month group of Ultracal XS was higher than Ultracal at 1 month or 6 months, although still insignificant. The Vitapex group showed no significant difference (P = 0.141) between time points. The control group showed an insignificant decrease (P = 0.247) in strength at each time point 1, 3, and 6.
The suggestion that Ca(OH)2 used for an extended period of time results in a detrimental effect on the fracture resistance of dentin has become well accepted since Cvek’s report in 1992 (12). This observation has also been corroborated by Andreasen’s research reports on lamb’s incisors with incompletely formed root apices (13, 14). The results of the present study are different than the above reports, showing that the use of Vitapex, Ultracal XS, or Pulpdent does not have the same weakening effect on the fracture resistance of dentin. The dissimilar results generated in the present study may be attributed to the following reasons. First, the present study used deciduous lamb incisors instead of permanent underdeveloped incisors, as the later could not be obtained. Secondly, and perhaps the most influential cause for our results when compared to previous studies is the formulations of Ca(OH)2 tested. The differences in results become even greater when our findings are compared with those of other studies that tested the modulus of elasticity or microhardness of dentin after long-term exposure to Ca(OH)2 (17, 19, 25, 26, 32). Given the large body of evidence confirming the weakening effect of pure Ca(OH)2, we did not include pure Ca(OH)2 as a positive control group. Therefore, sterile saline was included as a negative control group. Although insignificant, the sample size of the control group may have contributed heavily to the apparent decrease in strength over time of teeth exposed to sterile saline. A limitation of our investigation is the sample size of the controls. However, the experimental groups had a sample size appropriate to offer sufficient statistical power. It is possible that this experiment failed to show a statistically significant decrease in dentin fracture resistance on account of the formulations of Ca(OH)2 evaluated. The commercial varieties examined have © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Megapascals
Effect of calcium hydroxide on dentin
Fig. 3. The fracture resistance of the samples is given in Mpa at all tested time points.
0.0500 0.0450 0.0400 0.0350 0.0300 0.0250 0.0200 0.0150 0.0100 0.0050 0.0000
383
Fracture resistance by formulation and month
1 month
3 months
6 months
Vitapex
0.0386
0.0399
0.0404
Ultracal
0.0392
0.0430
0.0369
PulpDent
0.0377
0.0394
0.0380
Control
0.0409
0.0376
0.0321
different properties than pure Ca(OH)2 mixed with saline. Vitapex has the lowest concentration of Ca(OH)2 at only 30%, while Pulpdent has the highest concentration at 42%. The mere decrease in available Ca(OH)2 could have been sufficient to lessen the weakening effect on fracture resistance. It is also possible that the additional ingredients of each formulation create a buffering effect on the damage created by the free hydroxyl ions. It has been postulated that matrix metalloproteases, (MMP-2, MMP-14) contribute to the degradation of type I collagen in dentin during exposure to Ca(OH)2. TIMP-2, on the other hand, is an inhibitor of MMP-2 and -14 and has been shown to be reduced in Ca(OH)2 exposed dentin (18). MTA appears to have a much smaller weakening effect on dentin even though calcium remains to be one of the major active ingredients promoting biocompatibility and hard tissue repair (33). Interestingly, MTA has been shown to induce the protective expression of TIMP-2 in the dentin matrix (18). Based on these findings, MTA appears to be the obvious solution unless the case requires removal of the material several months later. However, as long as Ca(OH)2 decreases the expression of TIMP-2 and increases the expression of MMP-2 and -14, the weakening potential will likely exist. The added ingredients (iodoform, cellulose/water gel, barium sulfate) of Vitapex, Ultracal XS, and Pulpdent could affect either the expression of MMPs or TIMP-2 in a favorable way. Further investigations may shed
light on either the positive or negative effects of these additives. Consideration was given to the use of pure Ca(OH) mixed in a gradient of 10% (i.e. 10%, 20%. . . 100%) concentration in an attempt to find the point at which statistical weakening occurs, but was abandoned for the lack of clinical relevance. With the information gained from the present study, additional investigation is needed to determine the effect of various gradients of Ca(OH)2 on the fracture resistance of dentin. An additional finding of the experiment was the ‘washout’ or solubility rate of the groups when compared radiographically (Fig. 4). Vitapex consistently maintained the most mix within the root at all time points. However, the fracture resistance of the Vitapex groups was not significantly different from that of Ultracal XS and Pulpdent. This finding shows a lack of correlation between the radiographic presence of a material in a canal and its effect on fracture resistance of dentin. Conclusion
Under the conditions of this study, there appears insufficient evidence to support that either Vitapex, Ultracal XS, or Pulpdent will cause a decrease in fracture resistance of dentin within a 6-month period. It is possible, however, that if the interappointment dressing was refreshed regularly throughout this time period that different results could be obtained. Additional research to examine effects caused by supplemental ingredients in common commercial dressings is encouraged.
Fig. 4. Teeth containing Vitapex, Ultracal, and Puldent at 6 months showing the degree of soluable washout. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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Hawkins et al.
References 1. Hermann B. Calciumhydroxyd Als Mittel Zum Behandein und Fullen Von Zahnwurzelkanalen (Dissertation): Wurzburg; 1920. 2. King JB Jr, Crawford JJ, Lindahl RL. Indirect pulp capping: a bacteriologic study of deep carious dentine in human teeth. Oral Surg Oral Med Oral Pathol 1965;20:663–71. 3. Haapasalo M, Endal U. Internal inflammatory root resorption: the unknown resorption of the tooth. Endod Topics 2006;14:60–79. 4. Majorana A, Bardellini E, Conti G, Keller E, Pasini S. Root resorption in dental trauma: 45 cases followed for 5 years. Dent Traumatol 2003;19:262–5. 5. Sj€ ogren U, Figdor D, Sp angberg L, Sundqvist G. The antimicrobial effect of calcium hydroxide as a short-term intracanal dressing. Int Endod J 1991;24:119–25. 6. Andersson L, Andreasen JO, Day P, Heithersay G, Trope M, DiAngelis AJ et al. International Association of Dental Traumatology guidelines for the management of traumatic dental injuries: 2. Avulsion of permanent teeth. Dent Traumatol 2012;28:88–96. 7. Frank AL. Therapy for the divergent pulpless tooth by continued apical formation. J Am Dent Assoc 1966;72:87–93. 8. Bakland LK, Andreasen JO. Will mineral trioxide aggregate replace calcium hydroxide in treating pulpal and periodontal healing complications subsequent to dental trauma? A review Dent Traumatol 2012;28:25–32. 9. Sheehy E, Roberts G. Use of calcium hydroxide for apical barrier formation and healing in non-vital immature permanent teeth: a review. Br Dent J 1997;183:241–6. 10. Kvist T, Molander A, Dahlen G, Reit C. Microbiological evaluation of one-and two-visit endodontic treatment of teeth with apical periodontitis: a randomized, clinical trial. J Endod 2004;30:572–6. 11. Størmer KJI, Attramadal A. Hvor funksjonsdyktige blir rotfylte unge permanente incisiver? Nordisk forening for pedo donti. Bergen, Norway: Arsmøte; 1988. 12. Cvek M. Prognosis of luxated non-vital maxillary incisors treated with calcium hydroxide and filled with gutta-percha. A retrospective clinical study. Dent Traumatol 1992;8:45–55. 13. Andreasen JO, Farik B, Munksgaard EC. Long-term calcium hydroxide as a root canal dressing may increase risk of root fracture. Dent Traumatol 2002;18:134–7. 14. Andreasen JO, Munksgaard EC, Bakland LK. Comparison of fracture resistance in root canals of immature sheep teeth after filling with calcium hydroxide or MTA. Dent Traumatol 2006;22:154–6. 15. Batur YB, Erdemir U, Sancakli HS. The long-term effect of calcium hydroxide application on dentin fracture strength of endodontically treated teeth. Dent Traumatol 2013;29:461–4. 16. Doyon GE, Dumsha T, von Fraunhofer JA. Fracture resistance of human root dentin exposed to intracanal calcium hydroxide. J Endod 2005;31:895–7. 17. Grigoratos D, Knowles J, Ng YL, Gulabivala K. Effect of exposing dentine to sodium hypochlorite and calcium hydrox-
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© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Effect of three calcium hydroxide formulations on fracture resistance of dentin over time Jeremiah James Hawkins, Mahmoud Torabinejad, Yiming Li, Bonnie Retamozo Department of Endodontics, Loma Linda School of Dentistry, Loma Linda, CA, USA
Key words: crown fracture; crown-root fracture; dental trauma; permanent tooth; root fracture; tooth injury Correspondence to: Jeremiah Hawkins, 1046 Sirron Ave, Richland, WA 99253, USA Tel.: (208) 989-6109 Fax: (509) 735 9598 e-mail: [email protected] Accepted 28 February, 2015
Abstract – Background: The long-term use of calcium hydroxide has been discouraged throughout the recent decade due to a proposed decrease in fracture resistance of dentin. This weakening has grave implications when used on immature teeth with thin dentinal walls in procedures such as apexogenesis. Aim: The purpose of this study was to identify the effects of three commercial calcium hydroxide formulations (Vitapex, Ultracal XS and Pulpdent) on the fracture resistance of dentin in relation to time. Materials and Methods: Two-hundred and forty deciduous lamb incisors were collected, cleaned and shaped, and filled with one of the three calcium hydroxide formulations and one negative saline control. At one, three, and 6 months, these teeth were fractured on an Instron machine to determine fracture resistance. Results: No statistical differences were observed among any of the experimental groups, nor between any of the experimental groups and negative control groups. Conclusions: Based on our findings, there appears insufficient evidence to support that either Vitapex, Ultracal XS, or Pulpdent will cause a decrease in fracture resistance of dentin within a 6-month period.
Since its introduction in 1920 by BW Hermann, calcium hydroxide (Ca(OH)2) has been recommended for various dental procedures (1). Calcium hydroxide is commonly used by the general practitioner as a deep cavity liner or base owing to its bactericidal and healing properties (2). Due to these properties, endodontists have found it useful as an intracanal medicament as well. Its application has been suggested to arrest internal and external resorptive processes (3, 4). Studies have shown that Ca(OH)2 has sufficient antibacterial properties to decrease cultivable bacteria when used as an interappointment medication and therefore increase root canal therapy success (5). In the case of an avulsed tooth, the International Association of Dental Traumatology (IADT) guidelines suggest its placement for up to 1 month before final obturation of the root canal system (6). For a tooth with a necrotic pulp and an incompletely formed apex, Ca (OH)2 was for many years the medication of choice for apexification (7). Mineral trioxide aggregate (MTA) has largely assumed this role in recent years (8). Today, Ca (OH)2 is used frequently within the root canal system for a varying degree of time according to its intended application. The length of time that Ca(OH)2 has been and continues to be used varies dramatically. In Sheehy and Robert’s review of the use of Ca(OH)2 for apical barrier formation, they describe its use for 5 to 20 months (9). Kvist et al. (10) in 2004 demonstrated its use as an interappointment medication for as little as a week. In 1988, Stormer discussed a negative outcome associated with teeth that had undergone apexification 380
using Ca(OH)2. An increased incidence of cervical root fracture due to a weakening effect owing to the use of Ca(OH)2 was suggested (11). Cvek et al. (12) investigated this suggestion in a retrospective study and found a significant increase in cervical root fracture in teeth that had undergone apexification with Ca(OH)2. Andreasen et al. examined the impact of duration of Ca (OH)2 use on immature root dentin weakening. They demonstrated a 50% decrease in fracture resistance after 1-year exposure to Ca(OH)2 in vitro (13). Andreasen et al. further investigated this weakening phenomenon on account of Ca(OH)2 by comparing its effect with that of MTA over a 100-day period. They found that Ca(OH)2 significantly decreased the fracture resistance of dentin while MTA did not (14). Many additional studies have been conducted to measure the fracture resistance of dentin after being exposed to Ca(OH)2 (15–26). Doyon et al. examined the fracture resistance of human dentin after exposure to Ca(OH)2 from 30 to 180 days. After 180 days, dentin disks exposed to Ca(OH)2 paste were shown to be statistically weaker (16). Sahebi et al. evaluated the short-term effects of Ca(OH)2 on human dentin; their results indicated that 30 days of exposure to Ca(OH)2 were enough to statistically weaken human root dentin (23). There exists a considerable difference in the methods and materials used to test the weakening effect among these studies. Even though these differences exist, a strong body of evidence has been accumulated showing that Ca(OH)2 can negatively affect dentinal © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Effect of calcium hydroxide on dentin strength. This effect has been examined cumulatively by Yassen et al. in a recent systematic review (27). On the other hand, the concentration of Ca(OH)2 examined in various studies has been consistent. A variety of commercial Ca(OH)2 products are available for use as intracanal medicaments, and each product has its own composition and percentage concentration of Ca(OH)2. The effect on fracture resistance of dentin depending on concentration percentage over time has not been clearly identified in the literature. It is possible that the concentration of Ca(OH)2 used has an impact on the results of these published studies. The purpose of this study was to identify the effects of three Ca(OH)2 formulations, including Vitapex, Ultracal XS, and Pulpdent, on the fracture resistance of dentin in relation to time. Materials and methods
Thirty-five frozen lambs’ heads were purchased from a local food-grade meat market after being imported from New Zealand. These lambs were slaughtered at approximately the same time being less than 2 months of age. The lower anterior mandible was then sectioned with a band saw and stored frozen until time for tooth extraction. Eight deciduous incisor teeth were extracted from each lamb mandible to provide a total of 240 teeth, which were placed in 10% buffered formalin solution immediately after the extraction until evaluation (28). To prepare the teeth for instrumentation and experimental treatment, each tooth was measured 10 mm from the CEJ toward the apex and then sectioned horizontally with a diamond burr. The remaining radicular and coronal pulp tissue was then extirpated with a hedstrom file. Root canal preparation was completed with Profile NiTi files 0.04 to a size #30. Each canal was then rinsed with 5 ml NaOCl, followed by another rinse with 5 ml of sterile saline. Each canal was then dabbed dry with paper points. Seventy-five roots were randomly assigned to each brand of Ca(OH)2, and 5 roots were randomly assigned to each control group. This pattern was repeated three times for a total of 12 groups, as shown in Table 1. Once divided, the commercial Ca(OH)2 paste was spun into the canals until completely filled using a lentulo spiral on a slow speed handpiece (29). Four millimeters of Cavit was then used to temporize each sample at the apex (30). The samples were stored in physiologic saline at 37°C that was replenished weekly for the dura-
381
tion of the experiment (13). Each experimental group was isolated from the other groups and housed in individual plastic containers throughout the experiment. The three test formulations were Vitapex, Ultracal XS, and Pulpdent, as described in Table 2. They were chosen because of their common use in practice as well as their varying concentrations of Ca(OH)2. After the experimental time had elapsed for each group, being either 1, 3, or 6 months, the samples were removed from their containers and placed in dye stone (Die-Keen Green, Heraeus Kulzer, Inc., South Bend, IN, USA) submerging the root to the depth of the buccal CEJ. Once the stone had set, it was trimmed to the level of the buccal CEJ and any misplaced stone was removed to ensure uniformity. A stainless steel 3/8 inch nut was used as a matrix to hold the dye stone and facilitate stabilization during fracture. The mounted roots were then secured in a vise and measured for fracture resistance by an Instron testing machine (Instron, High Wycombe, UK) at a rate of 1 mm per minute. A metal blade connected to the Instron machine directly applied force to the facial aspect of each tooth. The blade was placed approximately 1 mm coronal to the buccal CEJ (Fig. 1). Force was Table 2. The tested formulations are shown along with manufacturer and percentage calcium hydroxide Material
Manufacturer
Ca(OH)2%
Saline Vitapex
0.9% NaCl solution Neo Dental Chemical Products Co. Lt, Tokyo, Japan Ultradent Productions, Inc., South Jordan, UT Puldent Corp., Watertown, MA
0 30
Ultracal XS Pulpdent
35 42
Table 1. At each time point, 25 teeth will be tested from each formulation of calcium hydroxide and 5 teeth will be tested from each control group Organization and distribution of groups Month 1 Control (n = Material 1 (n Material 2 (n Material 3 (n
Month 3 5) = 25) = 25) = 25)
Control (n = Material 1 (n Material 2 (n Material 3 (n
Month 6 5) = 25) = 25) = 25)
Control (n = Material 1 (n Material 2 (n Material 3 (n
5) = 25) = 25) = 25)
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Fig. 1. The instron blade is placed approximately 1 mm coronal to the buccal CEJ. Force is applied at a rate of 1 mm per minute until dentin fracture.
382
Hawkins et al. Table 3. The statistical mean, standard deviation, and confidence intervals are given for each formulation at each time point tested Confidence interval Formulation
Month
Mean
SE
Lower bound
Upper bound
PulpdentXS
1 3 6 1 3 6 1 3 6 1 3 6
0.038 0.04 0.038 0.039 0.043 0.037 0.039 0.04 0.04 0.041 0.038 0.032
0.002 0.002 0.001 0.002 0.002 0.001 0.002 0.002 0.001 0.004 0.004 0.003
0.034 0.037 0.035 0.036 0.04 0.034 0.035 0.037 0.037 0.034 0.031 0.025
0.041 0.043 0.041 0.042 0.046 0.04 0.042 0.043 0.043 0.048 0.045 0.039
Ultacal
Vitapex
Saline
Fig. 2. IMAGE J software was used to calculate the square millimeters of fractured dentin. A standard endodontic ruler was used to calibrate each image prior to calculation.
The cumulative data support that the fracture resistance of dentin is not affected by the concentrations of Ca(OH)2 within these formulations over time. Discussion
measured in Newtons and recorded at the point of fracture (31). The cross-sectional diameter of the fractured incisor was photographed, and IMAGE J software (National Institutes of Health, Bethesda, Maryland, USA) was used to calculate the surface area of fractured dentin (Fig. 2). Newtons of force per square millimeters was then converted to megapascals (MPa). The data were collected and subjected to a related-samples Friedman’s two-way analysis of variance by ranks. The level of significance was set at 0.05. Results
The mean load at fracture, standard error, and confidence intervals is presented in Table 3. The mean fracture resistance of Vitapex was 0.0386, 0.0399, and 0.0404 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of Ultracal XS was 0.0392, 0.0430, and 0.0369 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of Pulpdent XS was 0.0377, 0.0394, 0.0380 Mpa at 1, 3, and 6 months, respectively. The mean fracture resistance of the saline control was 0.0409, 0.0376 and 0.0321 Mpa at 1, 3, and 6 months, respectively. Graphical representation of the comparison is illustrated in Fig. 3. The Pulpdent group showed no significant decrease (P = 0.527) in fracture resistance at any of the time points; 1, 3, or 6 months. The Ultracal XS group showed no significant difference (P = 1.79) between time points. Interestingly, the fracture strength of the 3-month group of Ultracal XS was higher than Ultracal at 1 month or 6 months, although still insignificant. The Vitapex group showed no significant difference (P = 0.141) between time points. The control group showed an insignificant decrease (P = 0.247) in strength at each time point 1, 3, and 6.
The suggestion that Ca(OH)2 used for an extended period of time results in a detrimental effect on the fracture resistance of dentin has become well accepted since Cvek’s report in 1992 (12). This observation has also been corroborated by Andreasen’s research reports on lamb’s incisors with incompletely formed root apices (13, 14). The results of the present study are different than the above reports, showing that the use of Vitapex, Ultracal XS, or Pulpdent does not have the same weakening effect on the fracture resistance of dentin. The dissimilar results generated in the present study may be attributed to the following reasons. First, the present study used deciduous lamb incisors instead of permanent underdeveloped incisors, as the later could not be obtained. Secondly, and perhaps the most influential cause for our results when compared to previous studies is the formulations of Ca(OH)2 tested. The differences in results become even greater when our findings are compared with those of other studies that tested the modulus of elasticity or microhardness of dentin after long-term exposure to Ca(OH)2 (17, 19, 25, 26, 32). Given the large body of evidence confirming the weakening effect of pure Ca(OH)2, we did not include pure Ca(OH)2 as a positive control group. Therefore, sterile saline was included as a negative control group. Although insignificant, the sample size of the control group may have contributed heavily to the apparent decrease in strength over time of teeth exposed to sterile saline. A limitation of our investigation is the sample size of the controls. However, the experimental groups had a sample size appropriate to offer sufficient statistical power. It is possible that this experiment failed to show a statistically significant decrease in dentin fracture resistance on account of the formulations of Ca(OH)2 evaluated. The commercial varieties examined have © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Megapascals
Effect of calcium hydroxide on dentin
Fig. 3. The fracture resistance of the samples is given in Mpa at all tested time points.
0.0500 0.0450 0.0400 0.0350 0.0300 0.0250 0.0200 0.0150 0.0100 0.0050 0.0000
383
Fracture resistance by formulation and month
1 month
3 months
6 months
Vitapex
0.0386
0.0399
0.0404
Ultracal
0.0392
0.0430
0.0369
PulpDent
0.0377
0.0394
0.0380
Control
0.0409
0.0376
0.0321
different properties than pure Ca(OH)2 mixed with saline. Vitapex has the lowest concentration of Ca(OH)2 at only 30%, while Pulpdent has the highest concentration at 42%. The mere decrease in available Ca(OH)2 could have been sufficient to lessen the weakening effect on fracture resistance. It is also possible that the additional ingredients of each formulation create a buffering effect on the damage created by the free hydroxyl ions. It has been postulated that matrix metalloproteases, (MMP-2, MMP-14) contribute to the degradation of type I collagen in dentin during exposure to Ca(OH)2. TIMP-2, on the other hand, is an inhibitor of MMP-2 and -14 and has been shown to be reduced in Ca(OH)2 exposed dentin (18). MTA appears to have a much smaller weakening effect on dentin even though calcium remains to be one of the major active ingredients promoting biocompatibility and hard tissue repair (33). Interestingly, MTA has been shown to induce the protective expression of TIMP-2 in the dentin matrix (18). Based on these findings, MTA appears to be the obvious solution unless the case requires removal of the material several months later. However, as long as Ca(OH)2 decreases the expression of TIMP-2 and increases the expression of MMP-2 and -14, the weakening potential will likely exist. The added ingredients (iodoform, cellulose/water gel, barium sulfate) of Vitapex, Ultracal XS, and Pulpdent could affect either the expression of MMPs or TIMP-2 in a favorable way. Further investigations may shed
light on either the positive or negative effects of these additives. Consideration was given to the use of pure Ca(OH) mixed in a gradient of 10% (i.e. 10%, 20%. . . 100%) concentration in an attempt to find the point at which statistical weakening occurs, but was abandoned for the lack of clinical relevance. With the information gained from the present study, additional investigation is needed to determine the effect of various gradients of Ca(OH)2 on the fracture resistance of dentin. An additional finding of the experiment was the ‘washout’ or solubility rate of the groups when compared radiographically (Fig. 4). Vitapex consistently maintained the most mix within the root at all time points. However, the fracture resistance of the Vitapex groups was not significantly different from that of Ultracal XS and Pulpdent. This finding shows a lack of correlation between the radiographic presence of a material in a canal and its effect on fracture resistance of dentin. Conclusion
Under the conditions of this study, there appears insufficient evidence to support that either Vitapex, Ultracal XS, or Pulpdent will cause a decrease in fracture resistance of dentin within a 6-month period. It is possible, however, that if the interappointment dressing was refreshed regularly throughout this time period that different results could be obtained. Additional research to examine effects caused by supplemental ingredients in common commercial dressings is encouraged.
Fig. 4. Teeth containing Vitapex, Ultracal, and Puldent at 6 months showing the degree of soluable washout. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
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