- Email: [email protected]
Furcation Perforation Repair Comparing Gray and White MTA: A Dye Extraction Study
Basic Research—Technology
Furcation Perforation Repair Comparing Gray and White MTA: A Dye Extraction Study Hatim A. Hamad, DDS, MS, Patricia A. Tordik, DMD, and Scott B. McClanahan, DDS, MS Abstract The purpose of this study was to evaluate the ability of gray and white ProRoot MTA to seal furcation perforations in mandibular molars using a dye extraction leakage model. Sixty-four mandibular molars were randomly divided into four experimental groups. Six teeth with perforations were used as positive controls and six teeth without perforations were used as negative controls. Perforations in groups 1 and 2 were repaired with white MTA. Groups 3 and 4 were repaired with gray MTA. Dye leakage was tested from an orthograde direction (groups 1 and 3) and a retrograde direction (groups 2 and 4). After dye extraction, absorbance was measured on a spectrophotometer at 550 nm. No statistically significant difference in leakage was found between gray and white MTA when used as a furcation perforation repair material. However, there was significantly more leakage when the perforations were challenged from the orthograde than the retrograde direction (p ⬍ 0.001). (J Endod 2006;32:337–340)
Key Words Dye extraction, furcation perforation, furcation repair, gray ProRoot MTA, white ProRoot MTA
From the Naval Postgraduate Dental School, Bethesda, Maryland. Address requests for reprint to Dr. Scott B. McClanahan, 5419 Flint Tavern Place, Burke, VA 22015-2109. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2006 by the American Association of Endodontists. doi:10.1016/j.joen.2005.10.002
T
he American Association of Endodontists (AAEs) Glossary of Endodontic Terms defines perforations as the mechanical or pathologic communication between the root canal system and the external tooth surface (1). The etiology of perforations is caries, resorption, or iatrogenic factors. Regardless of the cause, a perforation allows bacterial invasion into the supporting structures that initially incites inflammation and loss of attachment, which eventually may compromise the prognosis of the tooth (2, 3). Furcation perforation is followed by bacterial contamination, periradicular tissue injury, inflammation, bone resorption, periodontal fiber destruction, epithelium proliferation, and periodontal pocket development (4). A principle goal of endodontic therapy is to remove bacteria and seal the root canal to promote osseous regeneration (5). Several studies have demonstrated that perforation of the root surface complicates our ability to achieve this goal (2– 4). Ideally, to prevent bacterial contamination, perforations should be repaired as quickly as possible with a biocompatible material (4). Gray mineral trioxide aggregate (MTA) was investigated to seal the root canal system from the external environment (6). Gray MTA was introduced to endodontics in 1993 as a root-end filling and lateral perforation repair material (7). ProRoot MTA is the commercial version introduced in 1998 by Dentsply Tulsa Dental. The original MTA and the ProRoot MTA have the same overall composition; however, ProRoot MTA is manufactured under FDA guidelines for medical devices (8). White ProRoot MTA was introduced by Dentsply in 2002. The white version eliminated the grayness of the original MTA, which can create a shadow under thin tissue (8). It was reported that primary, rat osteoblasts reacted differently in contact with the surface of white compared to gray ProRoot MTA (9). Asgary et al. concluded the most significant differences between gray and white ProRoot MTA were the measured concentrations of Al2O3 (⫹122%), MgO (⫹130%), and especially FeO (⫹1000%) (10). A recent PUBMED search for “mineral trioxide aggregate” produced 204 articles published between 1993 and 2005. However, there is limited research comparing the sealing ability of white and gray MTA (11, 12). Matt et al. found that gray MTA demonstrated significantly less leakage than white MTA when used as an apical barrier (11). Ferris et al. found no significant difference between the two types of MTA in preventing leakage of Fusobacterium nucleatum past furcal perforation repairs (12). Al-Hezaimi and others compared the sealing ability of gray and white MTA as a root filling and noted no significant difference in saliva leakage past the two preparations (13). Different leakage models have been used to assess the ability of materials to seal furcation perforations including fluid-filtration, dye penetration, dye extraction, and bacterial-leakage models. Camps and Pashley showed that the dye extraction method yielded the same results as fluid filtration while saving laboratory time (14). The purpose of this study was to evaluate the ability of gray and white ProRoot MTA to seal furcation perforations in mandibular molars using a dye extraction leakage model.
Materials and Methods Seventy-six extracted, human mandibular molars were used in this study. The molars had minimal restorations and/or minimal caries, and nonfused roots. The teeth were stored in 0.2% sodium azide. One investigator performed all procedures under 13.1⫻ using a dental operating microscope (Global Surgical Corp., St. Louis, MO). Molars were decoronated 3 mm above the cemento-enamel junction and roots were amputated 3 mm below the furcation. A standardized endodontic access opening was
JOE — Volume 32, Number 4, April 2006
A Dye Extraction Study
337
Basic Research—Technology
Figure 1. (A) Pulpal floor view and (B) furcal view of perforation. Dye challenge from the (C) orthograde direction. (D) Tooth after submergence in dye for retrograde challenge.
made in each tooth, sticky wax placed over the orifice of each canal, and the teeth, including the pulpal floor, coated with two layers of clear nail varnish. To ensure each perforation was centered between the roots, a defect 1 mm in diameter was made from the external surface with a #2 high-speed carbide bur (Fig. 1). The chamber and perforation were flushed with water and dried. Teeth were randomly divided into four groups and perforations sealed as follows: ● ●
Groups 1 (n ⫽ 16) and 2 (n ⫽ 16) repaired with white ProRoot MTA (Lot # 03081235, Dentsply Tulsa Dental, Tulsa, OK) Groups 3 (n ⫽ 16) and 4 (n ⫽ 16) repaired with gray ProRoot MTA (Lot # 03061887, Dentsply Tulsa Dental).
Six teeth with unrepaired perforations were used as positive controls and six teeth without perforations were used as negative controls. Teeth were placed in a saline-soaked Oasis (Smithers-Oasis North America, Kent, OH), a wet floral foam product. To replicate common clinical procedures, an internal matrix (15) was placed before repair in all groups. A standardized amount of CollaTape (Zimmer/dental, Carlsbad, CA) served as the matrix. Gray and white ProRoot MTA were mixed according to manufacturer’s recommendations, placed with a Messing gun, and compacted with hand pluggers. 338
Hamad et al.
Teeth were kept in the Oasis at 37°C and 100% humidity for 24 h to allow the MTA to set. Each group was removed from the Oasis and placed in petri dishes. Methylene blue dye was added to the access chambers of groups 1 and 3. Groups 2 and 4 were immersed in dye to the CEJ. All samples were stored in methylene blue for 48 h (Fig. 1). After removal from the dye, teeth were rinsed under tap water for 30 min and varnish removed with a polishing disc. Each tooth was stored in a vial containing 1000 l of concentrated (65 wt %) nitric acid for 3 days. Vials were centrifuged (Sorvall RC-5B centrifuge, Asheville, NC) at 14,000 rpm for 5 min, and 100 l of the supernatant from each was transferred to a 96-well plate. Samples were read by an automatic microplate spectrophotometer (Anthos Labtec Instruments, Pasadena, CA) at 550 nm using concentrated nitric acid as the blank. A two-way ANOVA was performed for each technique to compare groups.
Results Figure 2 illustrates experimental findings. Results showed no statistically significant difference in dye absorbance between gray and white ProRoot MTA. Regardless of the material used, dye absorbance was greater from an orthograde direction than a retrograde direction (p ⬍ 0.001). JOE — Volume 32, Number 4, April 2006
Basic Research—Technology
Figure 2. Leakage of repaired furcation perforations for experimental groups and controls.
Discussion Dye penetration techniques are the most frequently used methods to evaluate the sealing ability of dental materials (14, 16). These are commonly used because they are easy to complete and do not require sophisticated materials. Despite their popularity, dye leakage studies have several disadvantages: (a) molecular size of most dye particles is smaller than bacteria; (b) most studies measure penetration in one plane rather than total leakage; and (c) they are static and do not reflect the dynamic interaction with periradicular tissues (16). Dye-extraction provides more reliable results because it measures all of the dye taken up in the root. Our study closely followed an established protocol for dye extraction (14). Methylene blue was placed in nitric acid and evaluated with the spectrophotometer. Maximum optical density was read. Interestingly, Wu et al. (17) found that methylene blue was decolored by MTA obtained from Loma Linda University. They concluded the calcium oxide contained in MTA may, with water, form Ca(OH)2 that decolors methylene blue, and that dye may be further diluted with cooling water used in sectioning teeth for a linear penetration study. Considering these findings, we might expect there to be less overall measurable dye penetration for the gray ProRoot MTA. However, the results should be consistent among samples, because a single lot of MTA was used. Whether white ProRoot MTA decolors methylene blue is unknown. It appears that gray MTA has gone through a series of alterations since 1993. Torabinejad et al. observed fine hydrophilic particles with calcium and phosphorous as the main ions present in gray MTA powder. They noted the principle compounds present were tricalcium silicate, tricalcium aluminate, tricalcium oxide, and silicate oxide, with small amounts of a few other mineral oxides (7, 18). A recent study by Asgary et al. detected only minute amounts of phosphorus and showed that the
JOE — Volume 32, Number 4, April 2006
predominant oxides in ProRoot MTA were CaO, SiO2, and Bi2O3, respectively (10). According to the MSDS of gray ProRoot MTA, Portland cement accounts for the majority of the product: calcium silicate compounds, calcium compounds containing iron and aluminum, hydrated calcium sulfate, and bismuth oxide. The MSDS of the white ProRoot MTA indicates that the composition includes calcium silicate compounds, tricalcium aluminate, hydrated calcium sulfate, and bismuth oxide. Gray and white ProRoot MTA differ by less than 6% in any one component. No components are new and none are eliminated in the white formula compared to the gray. The difference between white and gray is primarily a result of the lower iron oxide content used in the white ProRoot MTA (10, 19). Reasonably, the absence of significant FeO in white MTA causes the color change from gray to white, and changes the percentage of calcia, alumina, and silica in each material (10). Since 2003, Dentsply changed the size distribution of crystals in both the gray and white ProRoot MTA to be less than 10 m (8). It was shown that crystal size can affect the physical properties of cements. Smaller particle size increases the surface available for hydration and causes greater early strength. A small particle size would be an important characteristic of perforation repair materials (19). Although several investigations were completed to determine the sealing properties of gray MTA (20 –23), only three studies have been published comparing the sealing ability of gray and white MTA. Our results were consistent with two of the three studies. Ferris et al. established no significant difference between the gray and white ProRoot MTA in sealing furcal perforations of extracted human molars (12). Al-Hezaimi et al. found no significant difference in saliva leakage between gray and white MTA when it was used as an orthograde root canal filling material (13).
A Dye Extraction Study
339
Basic Research—Technology However, the third study by Matt et al. used a linear dye leakage model with ProRoot MTA obtained from Dentsply before 2003 and demonstrated significantly less dye penetration with gray MTA compared to white MTA (11). Our study evaluated furcation perforation repairs using the dye extraction model with the most current formulations of gray and white ProRoot MTA. Regardless of the material used, we found significantly more leakage from an orthograde direction than a retrograde direction. This may be a consequence of the methodology. We chose to use a collagen matrix because of direct, vertical compaction forces resulting from placement of the repair material into the furcation. It was noted that the ProRoot MTA could easily be over-extended even though an internal matrix was placed. Over-extension of the material may be related to sealing capabilities and requires further study. Gravity may also have played a role in allowing more orthograde than retrograde dye penetration. Coronal microleakage of bacteria and their by-products is a problem in endodontics. This study demonstrated significantly greater dye penetration from an orthograde direction, which may be an important factor influencing the long-term outcome of perforation repairs. Although it is not known if this implies clinical significance, clinicians may consider the placement of a barrier material over a perforation repair for additional protection against coronal microleakage. Under the conditions of this study, white and gray ProRoot MTA performed similarly as a furcation perforation repair material and regardless of the material used, there was significantly more leakage when the perforations were challenged from the orthograde than the retrograde direction (p ⬍ 0.001).
Acknowledgment The authors would like to thank Mark E. Cohen, PhD, Naval Institute for Dental and Biomechanical Research, Great Lakes, IL, for his assistance with the statistical analysis. The opinions or assertions expressed in this article are those of the authors and are not to be construed as official policy or position of the Department of the Navy, Department of Defense or the U.S. Government.
References 1. American Association of Endodontists Glossary of Endodontic Terms. 2003; 7th ed; 2003. 2. Ruddle CJ. Nonsurgical Endodontic Retreatment. In Cohen S, Burns RC (eds). Pathways of the pulp, 8th ed. St Louis: Mosby Inc., 2002:917.
340
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3. Sinai IH. Endodontic perforations: their prognosis and treatment. J Am Dent Assoc 1977;95:90 –5. 4. Seltzer S, Sinai I, August D. Periodontal effects of root perforations before and during endodontic procedures. J Dent Res 1970;49:332–9. 5. Hirsch JM, Ahlstrom U, Henrikson PA, Heyden G, Peterson LE. Periapical surgery. Int J Oral Surg 1979;8:173– 85. 6. Torabinejad M, Chivian N. Clinical applications of mineral trioxide aggregate. J Endod 1999;25:197–205. 7. Lee SJ, Monsef M, Torabinejad M. Sealing ability of a mineral trioxide aggregate for repair of lateral root perforations. J Endod 1993;19:541– 4. 8. DENTSPLY. Testing of the White Version of ProRootTM MTA Root Canal Repair Material. Literature from the manufacturer. Tulsa, OK: Dentsply, Tulsa Dental, 2003. 9. Perez AL, Spears R, Gutmann JL, Opperman LA. Osteoblasts and MG-63 osteosarcoma cells behave differently when in contact with ProRoot MTA and White MTA. Int Endod J 2003;36:564 –70. 10. Asgary S, Parirokh M, Eghbal MJ, Brink F. Chemical differences between white and gray mineral trioxide aggregate. J Endod 2005;31:101–3. 11. Matt GD, Thorpe JR, Strother JM, McClanahan SB. Comparative study of white and gray mineral trioxide aggregate (MTA) simulating a one- or two-step apical barrier technique. J Endod 2004;30:876 –9. 12. Ferris DM, Baumgartner JC. Perforation repair comparing two types of mineral trioxide aggregate. J Endod 2004;30:422– 4. 13. Al-Hezaimi K, Naghshbandi J, Oglesby S, Simon H, Rotstein I. Human saliva penetration of root canals obturated with two types of mineral trioxide aggregate cements. J Endod 2005;31:453– 6. 14. Camps J, Pashley D. Reliability of the dye penetration studies. J Endod 2003;29:592– 4. 15. Lemon RR. Nonsurgical repair of perforation defects. Internal matrix concept. Dent Clin North Am 1992;36:439 –57. 16. Torabinejad M, Rastegar AF, Kettering JD, Pitt Ford TR. Bacterial leakage of mineral trioxide aggregate as a root-end filling material. J Endod 1995;21:109 –12. 17. Wu MK, Kontakiotis EG, Wesselink PR. Decoloration of 1% methylene blue solution in contact with dental filling materials. J Dent 1998;26:585–9. 18. Torabinejad M, Hong CU, McDonald F, Pitt Ford TR. Physical and chemical properties of a new root-end filling material. J Endod 1995;21:349 –53. 19. Asgary S, Parirokh M, Eghbal MJ, Brink F. A comparative study of white mineral trioxide aggregate and white Portland cements using X-ray microanalysis. Aust Endod J 2004;30:89 –92. 20. Arens DE, Torabinejad M. Repair of furcal perforations with mineral trioxide aggregate: two case reports. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;82:84 – 8. 21. Ford TR, Torabinejad M, McKendry DJ, Hong CU, Kariyawasam SP. Use of mineral trioxide aggregate for repair of furcal perforations. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:756 – 63. 22. Weldon JK, Jr., Pashley DH, Loushine RJ, Weller RN, Kimbrough WF. Sealing ability of mineral trioxide aggregate and super-EBA when used as furcation repair materials: a longitudinal study. J Endod 2002;28:467–70. 23. Sluyk SR, Moon PC, Hartwell GR. Evaluation of setting properties and retention characteristics of mineral trioxide aggregate when used as a furcation perforation repair material. J Endod 1998;24:768 –71.
JOE — Volume 32, Number 4, April 2006
Furcation Perforation Repair Comparing Gray and White MTA: A Dye Extraction Study Hatim A. Hamad, DDS, MS, Patricia A. Tordik, DMD, and Scott B. McClanahan, DDS, MS Abstract The purpose of this study was to evaluate the ability of gray and white ProRoot MTA to seal furcation perforations in mandibular molars using a dye extraction leakage model. Sixty-four mandibular molars were randomly divided into four experimental groups. Six teeth with perforations were used as positive controls and six teeth without perforations were used as negative controls. Perforations in groups 1 and 2 were repaired with white MTA. Groups 3 and 4 were repaired with gray MTA. Dye leakage was tested from an orthograde direction (groups 1 and 3) and a retrograde direction (groups 2 and 4). After dye extraction, absorbance was measured on a spectrophotometer at 550 nm. No statistically significant difference in leakage was found between gray and white MTA when used as a furcation perforation repair material. However, there was significantly more leakage when the perforations were challenged from the orthograde than the retrograde direction (p ⬍ 0.001). (J Endod 2006;32:337–340)
Key Words Dye extraction, furcation perforation, furcation repair, gray ProRoot MTA, white ProRoot MTA
From the Naval Postgraduate Dental School, Bethesda, Maryland. Address requests for reprint to Dr. Scott B. McClanahan, 5419 Flint Tavern Place, Burke, VA 22015-2109. E-mail address: [email protected]. 0099-2399/$0 - see front matter Copyright © 2006 by the American Association of Endodontists. doi:10.1016/j.joen.2005.10.002
T
he American Association of Endodontists (AAEs) Glossary of Endodontic Terms defines perforations as the mechanical or pathologic communication between the root canal system and the external tooth surface (1). The etiology of perforations is caries, resorption, or iatrogenic factors. Regardless of the cause, a perforation allows bacterial invasion into the supporting structures that initially incites inflammation and loss of attachment, which eventually may compromise the prognosis of the tooth (2, 3). Furcation perforation is followed by bacterial contamination, periradicular tissue injury, inflammation, bone resorption, periodontal fiber destruction, epithelium proliferation, and periodontal pocket development (4). A principle goal of endodontic therapy is to remove bacteria and seal the root canal to promote osseous regeneration (5). Several studies have demonstrated that perforation of the root surface complicates our ability to achieve this goal (2– 4). Ideally, to prevent bacterial contamination, perforations should be repaired as quickly as possible with a biocompatible material (4). Gray mineral trioxide aggregate (MTA) was investigated to seal the root canal system from the external environment (6). Gray MTA was introduced to endodontics in 1993 as a root-end filling and lateral perforation repair material (7). ProRoot MTA is the commercial version introduced in 1998 by Dentsply Tulsa Dental. The original MTA and the ProRoot MTA have the same overall composition; however, ProRoot MTA is manufactured under FDA guidelines for medical devices (8). White ProRoot MTA was introduced by Dentsply in 2002. The white version eliminated the grayness of the original MTA, which can create a shadow under thin tissue (8). It was reported that primary, rat osteoblasts reacted differently in contact with the surface of white compared to gray ProRoot MTA (9). Asgary et al. concluded the most significant differences between gray and white ProRoot MTA were the measured concentrations of Al2O3 (⫹122%), MgO (⫹130%), and especially FeO (⫹1000%) (10). A recent PUBMED search for “mineral trioxide aggregate” produced 204 articles published between 1993 and 2005. However, there is limited research comparing the sealing ability of white and gray MTA (11, 12). Matt et al. found that gray MTA demonstrated significantly less leakage than white MTA when used as an apical barrier (11). Ferris et al. found no significant difference between the two types of MTA in preventing leakage of Fusobacterium nucleatum past furcal perforation repairs (12). Al-Hezaimi and others compared the sealing ability of gray and white MTA as a root filling and noted no significant difference in saliva leakage past the two preparations (13). Different leakage models have been used to assess the ability of materials to seal furcation perforations including fluid-filtration, dye penetration, dye extraction, and bacterial-leakage models. Camps and Pashley showed that the dye extraction method yielded the same results as fluid filtration while saving laboratory time (14). The purpose of this study was to evaluate the ability of gray and white ProRoot MTA to seal furcation perforations in mandibular molars using a dye extraction leakage model.
Materials and Methods Seventy-six extracted, human mandibular molars were used in this study. The molars had minimal restorations and/or minimal caries, and nonfused roots. The teeth were stored in 0.2% sodium azide. One investigator performed all procedures under 13.1⫻ using a dental operating microscope (Global Surgical Corp., St. Louis, MO). Molars were decoronated 3 mm above the cemento-enamel junction and roots were amputated 3 mm below the furcation. A standardized endodontic access opening was
JOE — Volume 32, Number 4, April 2006
A Dye Extraction Study
337
Basic Research—Technology
Figure 1. (A) Pulpal floor view and (B) furcal view of perforation. Dye challenge from the (C) orthograde direction. (D) Tooth after submergence in dye for retrograde challenge.
made in each tooth, sticky wax placed over the orifice of each canal, and the teeth, including the pulpal floor, coated with two layers of clear nail varnish. To ensure each perforation was centered between the roots, a defect 1 mm in diameter was made from the external surface with a #2 high-speed carbide bur (Fig. 1). The chamber and perforation were flushed with water and dried. Teeth were randomly divided into four groups and perforations sealed as follows: ● ●
Groups 1 (n ⫽ 16) and 2 (n ⫽ 16) repaired with white ProRoot MTA (Lot # 03081235, Dentsply Tulsa Dental, Tulsa, OK) Groups 3 (n ⫽ 16) and 4 (n ⫽ 16) repaired with gray ProRoot MTA (Lot # 03061887, Dentsply Tulsa Dental).
Six teeth with unrepaired perforations were used as positive controls and six teeth without perforations were used as negative controls. Teeth were placed in a saline-soaked Oasis (Smithers-Oasis North America, Kent, OH), a wet floral foam product. To replicate common clinical procedures, an internal matrix (15) was placed before repair in all groups. A standardized amount of CollaTape (Zimmer/dental, Carlsbad, CA) served as the matrix. Gray and white ProRoot MTA were mixed according to manufacturer’s recommendations, placed with a Messing gun, and compacted with hand pluggers. 338
Hamad et al.
Teeth were kept in the Oasis at 37°C and 100% humidity for 24 h to allow the MTA to set. Each group was removed from the Oasis and placed in petri dishes. Methylene blue dye was added to the access chambers of groups 1 and 3. Groups 2 and 4 were immersed in dye to the CEJ. All samples were stored in methylene blue for 48 h (Fig. 1). After removal from the dye, teeth were rinsed under tap water for 30 min and varnish removed with a polishing disc. Each tooth was stored in a vial containing 1000 l of concentrated (65 wt %) nitric acid for 3 days. Vials were centrifuged (Sorvall RC-5B centrifuge, Asheville, NC) at 14,000 rpm for 5 min, and 100 l of the supernatant from each was transferred to a 96-well plate. Samples were read by an automatic microplate spectrophotometer (Anthos Labtec Instruments, Pasadena, CA) at 550 nm using concentrated nitric acid as the blank. A two-way ANOVA was performed for each technique to compare groups.
Results Figure 2 illustrates experimental findings. Results showed no statistically significant difference in dye absorbance between gray and white ProRoot MTA. Regardless of the material used, dye absorbance was greater from an orthograde direction than a retrograde direction (p ⬍ 0.001). JOE — Volume 32, Number 4, April 2006
Basic Research—Technology
Figure 2. Leakage of repaired furcation perforations for experimental groups and controls.
Discussion Dye penetration techniques are the most frequently used methods to evaluate the sealing ability of dental materials (14, 16). These are commonly used because they are easy to complete and do not require sophisticated materials. Despite their popularity, dye leakage studies have several disadvantages: (a) molecular size of most dye particles is smaller than bacteria; (b) most studies measure penetration in one plane rather than total leakage; and (c) they are static and do not reflect the dynamic interaction with periradicular tissues (16). Dye-extraction provides more reliable results because it measures all of the dye taken up in the root. Our study closely followed an established protocol for dye extraction (14). Methylene blue was placed in nitric acid and evaluated with the spectrophotometer. Maximum optical density was read. Interestingly, Wu et al. (17) found that methylene blue was decolored by MTA obtained from Loma Linda University. They concluded the calcium oxide contained in MTA may, with water, form Ca(OH)2 that decolors methylene blue, and that dye may be further diluted with cooling water used in sectioning teeth for a linear penetration study. Considering these findings, we might expect there to be less overall measurable dye penetration for the gray ProRoot MTA. However, the results should be consistent among samples, because a single lot of MTA was used. Whether white ProRoot MTA decolors methylene blue is unknown. It appears that gray MTA has gone through a series of alterations since 1993. Torabinejad et al. observed fine hydrophilic particles with calcium and phosphorous as the main ions present in gray MTA powder. They noted the principle compounds present were tricalcium silicate, tricalcium aluminate, tricalcium oxide, and silicate oxide, with small amounts of a few other mineral oxides (7, 18). A recent study by Asgary et al. detected only minute amounts of phosphorus and showed that the
JOE — Volume 32, Number 4, April 2006
predominant oxides in ProRoot MTA were CaO, SiO2, and Bi2O3, respectively (10). According to the MSDS of gray ProRoot MTA, Portland cement accounts for the majority of the product: calcium silicate compounds, calcium compounds containing iron and aluminum, hydrated calcium sulfate, and bismuth oxide. The MSDS of the white ProRoot MTA indicates that the composition includes calcium silicate compounds, tricalcium aluminate, hydrated calcium sulfate, and bismuth oxide. Gray and white ProRoot MTA differ by less than 6% in any one component. No components are new and none are eliminated in the white formula compared to the gray. The difference between white and gray is primarily a result of the lower iron oxide content used in the white ProRoot MTA (10, 19). Reasonably, the absence of significant FeO in white MTA causes the color change from gray to white, and changes the percentage of calcia, alumina, and silica in each material (10). Since 2003, Dentsply changed the size distribution of crystals in both the gray and white ProRoot MTA to be less than 10 m (8). It was shown that crystal size can affect the physical properties of cements. Smaller particle size increases the surface available for hydration and causes greater early strength. A small particle size would be an important characteristic of perforation repair materials (19). Although several investigations were completed to determine the sealing properties of gray MTA (20 –23), only three studies have been published comparing the sealing ability of gray and white MTA. Our results were consistent with two of the three studies. Ferris et al. established no significant difference between the gray and white ProRoot MTA in sealing furcal perforations of extracted human molars (12). Al-Hezaimi et al. found no significant difference in saliva leakage between gray and white MTA when it was used as an orthograde root canal filling material (13).
A Dye Extraction Study
339
Basic Research—Technology However, the third study by Matt et al. used a linear dye leakage model with ProRoot MTA obtained from Dentsply before 2003 and demonstrated significantly less dye penetration with gray MTA compared to white MTA (11). Our study evaluated furcation perforation repairs using the dye extraction model with the most current formulations of gray and white ProRoot MTA. Regardless of the material used, we found significantly more leakage from an orthograde direction than a retrograde direction. This may be a consequence of the methodology. We chose to use a collagen matrix because of direct, vertical compaction forces resulting from placement of the repair material into the furcation. It was noted that the ProRoot MTA could easily be over-extended even though an internal matrix was placed. Over-extension of the material may be related to sealing capabilities and requires further study. Gravity may also have played a role in allowing more orthograde than retrograde dye penetration. Coronal microleakage of bacteria and their by-products is a problem in endodontics. This study demonstrated significantly greater dye penetration from an orthograde direction, which may be an important factor influencing the long-term outcome of perforation repairs. Although it is not known if this implies clinical significance, clinicians may consider the placement of a barrier material over a perforation repair for additional protection against coronal microleakage. Under the conditions of this study, white and gray ProRoot MTA performed similarly as a furcation perforation repair material and regardless of the material used, there was significantly more leakage when the perforations were challenged from the orthograde than the retrograde direction (p ⬍ 0.001).
Acknowledgment The authors would like to thank Mark E. Cohen, PhD, Naval Institute for Dental and Biomechanical Research, Great Lakes, IL, for his assistance with the statistical analysis. The opinions or assertions expressed in this article are those of the authors and are not to be construed as official policy or position of the Department of the Navy, Department of Defense or the U.S. Government.
References 1. American Association of Endodontists Glossary of Endodontic Terms. 2003; 7th ed; 2003. 2. Ruddle CJ. Nonsurgical Endodontic Retreatment. In Cohen S, Burns RC (eds). Pathways of the pulp, 8th ed. St Louis: Mosby Inc., 2002:917.
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JOE — Volume 32, Number 4, April 2006