Clinical Outcomes of Artificial Root-end Barriers with Mineral Trioxide Aggregate in Teeth with Immature Apices David T. Holden, DMD,* Scott A. Schwartz, DDS,* Timothy C. Kirkpatrick, DDS,† and William G. Schindler, DDS, MS* Abstract The purpose of this retrospective study was to evaluate the clinical outcomes of ProRoot mineral trioxide aggregate used as an artificial apical barrier in teeth with immature apices. Twenty teeth from 19 patients were included in this study. A healed diagnosis was based on periapical index scores of 1 or 2 and no clinical signs or symptoms at recall examinations. Eighty-five percent (17/20) of these teeth were healed, and improvements in periapical index scores at recall appointments were shown to be statistically significant (P ⬍ .001, Wilcoxon signed-rank test). Chi-square test indicated that age, gender, primary treatment versus retreatment, presence of preoperative lesion, and differences in recall times did not significantly influence healing outcome. Overall, these results indicated that the mineral trioxide aggregate apical barrier technique is a successful method for obturating teeth with immature apices. (J Endod 2008;34:812– 817)
Key Words Apexification, barrier, clinical outcomes, immature apices, MTA
From the *Department of Endodontics, University of Texas Health Science Center at San Antonio, San Antonio; and † Wilford Hall Medical Center Endodontics Residency, Wilford Hall Medical Center, Lackland AFB, Texas. Address reprint requests to Dr David T. Holden, Department of Endodontics, UTHSCSA School of Dentistry, 7703 Floyd Curl Dr, Mail Code 7892, San Antonio, TX 78229-3900. E-mail address: [email protected]
0099-2399/$0 - see front matter Copyright © 2008 American Association of Endodontists. doi:10.1016/j.joen.2008.04.003
f a pulp has become necrotic as a result of trauma or other insults in an immature root, long-term apexification procedures with calcium hydroxide [Ca(OH)2] have historically been used to establish apical closure by an induction of a hard tissue barrier (1, 2). This technique was first introduced by Kaiser in 1964 and later made popular by Frank (1). The long-term Ca(OH)2 apexification technique has been a very successful clinical procedure, resulting in success rates in the mid-90% range (3). Despite this high success rate, there are several disadvantages to this technique. The treatment requires multiple appointments during an extended period of time, resulting in challenging patient compliance issues. There are several additional negative factors, ranging from esthetic demands to the susceptibility to fracture and coronal microleakage during the extended period of treatment time (4 –7). A recent study by Andreasen et al. (8) has shown that immature roots that had Ca(OH)2 placed within the root canals for 100 days showed a significant reduction in fracture resistance versus the controls. With all of these concerns taken together, an alternative treatment to long-term apexification with Ca(OH)2 might offer a more predictable and better long-term prognosis for these compromised teeth. Artificial apical barriers with a variety of materials have been suggested as an alternative to traditional Ca(OH)2 apexification (9 –14). In 1999 Torabinejad and Chivian (15) published an article recommending the use of mineral trioxide aggregate (MTA) as an artificial apical barrier. It has since become the material of choice in artificial apical barrier procedures (16). MTA’s popularity as an artificial apical barrier can be attributed to several factors. It might be placed in as little as 1 visit (17, 18) or after 1 or 2 applications of Ca(OH)2 (16), thus eliminating the 3- to 54-month waiting time required for Ca(OH)2 apexification (4, 19, 20). MTA is biocompatible (21–25), can induce the formation of hard tissue (26, 27), and has good sealing properties (28 –33). Studies have shown that both hand condensation and ultrasonic condensation produce acceptable results against leakage (31, 34). A 4-mm segment has been shown to resist displacement from the apex (35) and provides an adequate seal in vitro (31). The placement of a permanent bonded restoration after a short treatment time serves to increase fracture resistance of the immature root (31, 36). With all the apparent advantages of the MTA barrier technique, it should be recognized that the clinical success of this treatment is based on a limited number of studies (37– 40). Thus, there is a gap in knowledge regarding the assessment of this method in larger numbers of patients to provide more precise estimates of success and the possible impact of patient factors that might modify the success. The purpose of this retrospective study was to determine the clinical outcomes of ProRoot MTA (DENTSPLY Tulsa Dental Specialties, Tulsa, OK) used as an artificial apical barrier and to assess whether age, gender, primary treatment versus retreatment, presence of preoperative lesions, and differences in recall times had a significant influence on healing outcomes.
Materials and Methods A search of all patients treated with MTA at the University of Texas Health Science Center at San Antonio (UTHSCSA) Advanced Education Program in Endodontics and the Air Force Endodontic Residency Program at Wilford Hall Medical Center (WHMC), Lackland AFB, Texas was made. From this search, patients were chosen on the basis of the following inclusion criteria: (1) a tooth with a single canal and the presence of an
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Clinical Research open apex, (2) Ca(OH)2 treatment for at least 1 week before obturation, (3) use of MTA to produce an artificial apical barrier, (4) placement of a final restoration, and (5) radiographs documenting pretreatment and immediate post-treatment condition of the tooth. All patients meeting these criteria were invited for a 1-year minimum post-treatment follow-up examination. Patients were excluded from the study on the basis of the following exclusion criteria: (1) those who received the MTA artificial apical barrier and subsequently had the tooth extracted (no patients fit this criteria), (2) those who did not desire to take part in the study (2/43 patients), or (3) those who could not be contacted during the recruitment process (22/43 patients). The patients who met the above criteria had treatment previously completed by endodontic residents during routine patient care. All treatment was completed in a similar manner and is outlined as follows. Patients were seated in the operatory, had their medical and dental histories evaluated, and had appropriate vital signs taken (blood pressure, pulse). The patient’s chief complaint and history of the chief complaint were recorded. Clinical preoperative testing was performed to arrive at a pulpal and periradicular diagnosis for the tooth/teeth in question. The testing included pulpal tests with refrigerant, electric pulp testing when appropriate, percussion, palpation, periodontal probing, evaluation of tooth mobility, and visual examination for any swelling or sinus tracts. At least 1 preoperative digital radiograph was taken, more if necessary, to visualize the radiographic status of the periradicular tissues. After testing, the pulpal diagnosis was determined to be either necrosis or previous root canal treatment. The periradicular diagnosis was determined to be normal, acute periradicular periodontitis, chronic periradicular periodontitis, chronic periradicular periodontitis with symptoms, acute periradicular abscess, or suppurative periradicular periodontitis. When endodontic treatment was necessary on a tooth with an immature root or apex and vital pulp treatment was not a possible treatment option, the artificial root-end barrier procedure with MTA was initiated. The patient was anesthetized with up to 2 cartridges of 2% lidocaine HCl with 1:100,000 epinephrine and/or 3% mepivacaine HCl. A rubber dam was placed and disinfected per operator’s preference. Caries, if present, was removed, and the tooth was accessed. Instrumentation was performed with a combination of Gates-Glidden drills, hand files, and/or LightSpeed instruments (LightSpeed Technology Inc, San Antonio, TX), with copious irrigation of 5.25%– 6% NaOCl. After the canals were dried with paper points, Ca(OH)2 was placed, and the access was closed with a sterile cotton pellet or sponge followed by a provisional restorative material. The patient was then reappointed for continuation of treatment approximately 1 week from the initial appointment. At the next appointment, the patient was anesthetized and had the rubber dam placed as described above. The tooth was reaccessed, and Ca(OH)2 was removed, with 5.25%– 6% NaOCl irrigation and instrumentation. Before obturation, the canal was irrigated with 5.25%– 6% NaOCl, 17% ethylenediaminetetraacetic acid, and 5.25%– 6% NaOCl. The canal was then dried with paper points. If the operator judged it appropriate, CollaTape (Integra, Plainsboro, NJ) was placed in the periapical tissues as an internal matrix to prevent extrusion of MTA. Gray or white ProRoot MTA was then mixed according to manufacturer’s instructions and placed to the apex with a minimum 4-mm thickness. The MTA was condensed by using an indirect ultrasonic technique. This technique consists of the placing of a hand instrument, such as a condenser, in direct contact with the MTA segment. An ultrasonic instrument is then placed in contact with the shaft of the hand instrument and activated for several seconds. After the placement of MTA, the operator could elect to place a wet cotton pellet/paper point in the canal for 24 hours or immediately restore the tooth. The restoration of the tooth
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could be done with a segment of gutta-percha placed in the canal followed by a bonded restoration or by a bonded restoration beginning at the level of the MTA and ending at the access. Immediate post-treatment digital radiographs were then taken, postoperative instructions were given, and the patient was dismissed. An example of this technique can be seen in Fig. 1. Patients meeting these criteria were invited for a 1-year minimum post-treatment follow-up examination initially by phone. If the patient could not be contacted by phone, a postcard was sent to the patient’s last known address inviting them to participate in the study and asking them to contact the endodontic clinic. The post-treatment follow-up examination was accomplished as follows. An evaluation was performed on each patient by the designated investigators to assess whether there was any spontaneous pain or whether any pain could be elicited clinically by percussion, palpation, or biting on the treated tooth. A visual inspection of the soft tissues was made for any signs of pathosis of endodontic origin (eg, sinus tracts, swelling). Any pain or soft tissue lesions associated with the tooth were designated as signs and/or symptoms. Tenderness to percussion was allowed if unaccompanied by any other clinical sign or symptom (41). At least 1 postoperative digital radiograph was taken, more when necessary, to visualize the radiographic status of the periradicular tissues.
Subjective Radiographic Assessment After all participants were evaluated, the data were assigned a random number, and personal identifiers were removed by the principal investigator. All digital radiographs necessary for this study had the contrast and brightness adjusted by the principal investigator to obtain the best viewing image. These radiographs were then randomized in a PowerPoint presentation. These radiographs were evaluated by 2 independent examiners who were calibrated for use of the periapical index (PAI) (42). Two board-certified endodontists served as the examiners. They were calibrated as described by Delano et al. (43). After the completion of the calibration sessions, both immediate post-treatment and follow-up radiographs from this study were evaluated one at a time in random order and in a blinded manner by using the PAI, and this was repeated on a separate occasion 7 days later. For any disagreement on a PAI score for a particular tooth, the observers jointly reevaluated the radiograph, and a consensus score was reached. On the basis of clinical and radiographic measures from the follow-up examination, each tooth was assigned an outcome according to the criteria found in Table 1. Data Analysis Primary Outcomes (1) The number of cases that were healed, healing, and not healed was analyzed by percent frequencies. (2) The change in PAI scores for each case was analyzed with the Wilcoxon signed-rank test. Secondary Outcomes Outcomes were compared by using 2 tests to evaluate whether they were affected by age (ⱕ10 years old vs ⬎10 years old), gender (male vs female), initial treatment versus retreatment, preoperative lesion (present vs not present), and recall time (12–23 months vs ⱖ24 months). Examiner Agreement Interexaminer and intraexaminer agreement scores were calculated by using the Cohen kappa statistic.
MTA Apical Barrier Outcomes
Figure 1. A case showing the MTA root-end barrier technique. (A) Preoperative radiograph. (B) Ca(OH)2 placement verified at the end of the first appointment. (C) MTA segment in place at the second appointment. (D) Postoperative radiograph with final restoration in place.
Results The weighted kappa statistic for the calibration exercises ranged from 0.67– 0.86 between the 2 observers. The Cohen kappa statistics for the immediate postoperative and recall radiographs for intrarater reliability ranged from 0.68 – 0.80. Inter-rater reliability ranged from 0.71– 0.85 between the 2 observers. All kappa statistics indicated substantial agreement (44). All patients evaluated were free of signs and symptoms at recall appointments. Patient data and outcomes are found in Table 2. As determined from the criteria for this study, 85% (17/20) healed, whereas 5% (1/20) were considered healing. Ten percent (2/20) had not 814
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healed. The overall improvement in PAI scores was shown to be statistically significant by the Wilcoxon signed-rank test (P ⬍ .001) (Fig. 2). Chi-square test indicated that age, gender, primary treatment versus retreatment, presence of preoperative lesion, and differences in recall times did not significantly influence healing outcomes (P ⬎ .05).
Discussion The primary purpose for this retrospective clinical study was to evaluate the clinical outcomes of the MTA root-end barrier. An important aspect of this outcome assessment was to compare the results against the outcomes of long-term Ca(OH)2 apexification treatment. JOE — Volume 34, Number 7, July 2008
Clinical Research TABLE 1. Criteria Used To Determine Outcomes Outcome
PAI 1 or 2 PAI 3 or 4, with score improved at follow-up from immediate post-treatment radiograph Not healed PAI 1–5 PAI 3–5, with score not improved or worse at followup from immediate posttreatment radiograph
Signs/Symptoms None present None present Present None present
PAI, periapical index.
Historically, long-term Ca(OH)2 has been a very successful treatment for teeth with immature roots and apices, with success rates from 87% (45) to 95% (3, 4). Directly comparing the 2 techniques, El Meligy et al. (45) treated children with 2 permanent incisors diagnosed with necrotic pulps by placing an MTA barrier in one incisor and performing long-term Ca(OH)2 treatment in the other. Their findings indicated that at 12-month recalls, 13 of15 teeth treated with Ca(OH)2 were symptomfree and radiographically successful, whereas 15 of 15 teeth treated with MTA were symptom-free and radiographically successful. Although the results were not statistically significant, they did show that MTA apical barriers can achieve similar results to long-term Ca(OH)2 treatment. In a recent study by Pradhan et al. (46), healing times of MTA root-end barriers and long-term Ca(OH)2 apexification were compared. Their results indicated that MTA and Ca(OH)2 treatment modalities showed similar healing times (4.6 ⫾ 1.5 months vs 4.4 ⫾ 1.3 months, respectively), again confirming that both techniques are comparable in resolving periapical radiolucencies. In addition, there was a statistically significant shorter treatment time for the MTA group versus the Ca(OH)2 group (0.75 ⫾ 0.49 months vs 7 ⫾ 2.5 months, respectively). In the present study, 85% of the teeth showed an absence of periapical pathosis (PAI 1 or 2) and signs or symptoms at recall, with an additional 5% showing signs of healing. Three recent studies (38 – 40) have also reported on the success of MTA root-end apical barriers, ranging from 76.5% (39) to 91% (38). These percentages, on a whole,
Figure 2. Effect of MTA as a root-end barrier on PAI in incompletely formed permanent teeth (n ⫽ 20).
are lower than those reported for long-term Ca(OH)2 apexification. One potential explanation might be the length of recall. Sarris et al. (39) reported a 76.5% radiographic success, with recall lengths ranging from 6 –16 months. By way of comparison, Pace et al. (38) reported 0 of 11 cases healed at a 12-month recall but saw 10 of 11 healed cases (91%) in the same teeth at 24 months. Although the current study did not detect changes in outcomes with longer recall intervals, the study by Pace et al. suggested that longer recall intervals might be an important factor for a more favorable treatment outcome. It must be acknowledged that the greater success rate of long-term Ca(OH)2 might result from treatment intervals ranging from as little as 3 months to as long as 54 months, with a mean of 24 months (4). This could potentially give the periapical tissues sufficient time to heal during the course of treatment, whereas the healing from MTA root-end barriers occurs after treatment. It should also be noted that the 95% success rate reported by Cvek (4) had decreased to 91% at a 4-year recall, suggesting that long-term follow-up is important.
TABLE 2. Patient Data and Outcomes PAI Gender
Primary vs Retreatment
Patient Age at Treatment (y)
Months of Follow-up
At Treatment Completion
M M F F F F F M M M F F M F F F M M M M
Primary Retreatment Primary Primary Primary Primary Primary Primary Primary Primary Primary Primary Primary Retreatment Primary Primary Primary Primary Retreatment Primary
12 82 15 15 7 13 16 11 14 8 11 8 20 44 8 23 15 27 37 20
32 12 28 28 26 44 28 24 22 15 12 23 38 16 21 33 12 19 15 41
4 2 5 3 2 3 5 2 3 3 2 3 3 3 2 3 3 3 3 3
2 2 3 3 2 2 2 1 2 2 2 2 2 2 2 2 2 2 3 2
Healed Healed Healing Not healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Healed Not healed Healed
F, female; M, male; PAI, periapical index.
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MTA Apical Barrier Outcomes
Clinical Research The shorter treatment time with MTA root-end barriers can be advantageous. The first advantage is that the success of treatment is less dependent on patient compliance. Long-term Ca(OH)2 requires a motivated patient who will return for multiple follow-up appointments. The MTA root-end barrier can be completed in little as one (17, 18) or two (16) appointments. Another advantage for MTA root-end barriers is that they allow for immediate restoration. Ca(OH)2 treatment requires that a patient be left in a provisional restoration for an extended period of time to allow for a change in the Ca(OH)2 paste. This will leave a tooth with a weakened root and compromised crown exposed to forces that might lead to a catastrophic fracture. In studies by Lawley et al. (31) and Pene et al. (36), the placement of a bonded restoration in the crown of a treated tooth made them significantly stronger than unrestored crowns, reducing the potential of fracture. Finally, Andreasen et al. (8) showed that long-term Ca(OH)2 has a significantly negative effect on the strength of the root. The fracture resistance was significantly reduced if Ca(OH)2 was left in the tooth longer than 30 days. Because the root structure in these teeth is already compromised, care should be given not to reduce it any further. The MTA root-end barrier reduces the time needed for Ca(OH)2 apexification and eliminates the additional weakening of the tooth. The treatment in the current study made use of Ca(OH)2 for approximately 1 week, as in several other studies (38, 39). One study, however, did not make use of Ca(OH)2 as an intracanal medicament, treating the tooth with an MTA root-end barrier in one visit (40). Although the results from that study were favorable, additional benefit could potentially be gained by the short-term application of Ca(OH)2. Immature roots and apices can be difficult to chemomechanically debride in one visit. Very immature roots can have canal diameters that exceed the size of our largest instruments. Thin root thickness might make mechanical instrumentation of all the walls undesirable, because it might further weaken the root or result in perforation. Sjögren et al. (47) showed that Ca(OH)2 for 7 days was highly effective in killing root canal flora. Hasselgren et al. (48) demonstrated that Ca(OH)2 can be effective in dissolving necrotic pulp tissue. It would appear in these compromised cases that a 1-week dressing with Ca(OH)2 would benefit the patient while still enabling completion of treatment during a minimal period of time and not significantly reducing the root strength. Two studies looking at MTA root-end barriers (39, 40) evaluated radiographic success by the standard published by the European Society of Endodontology (ESE) (49) or by a modified version of this standard. The ESE standard defines success as radiographic evidence of normal periodontal ligament space, decrease in the size of the periapical lesion as compared with preoperative radiographs, and no evidence of inflammatory external root resorption. That description of success differs from the definition used in this study. Although the reduction in lesion size is promising, a radiograph only captures one moment in time. A smaller but persistent lesion might represent a lesion that might begin increasing in size. It is important that persistent lesions continue to be recalled until they heal or until it is determined that additional treatment is required (50). As mentioned in the Results, age, gender, primary treatment versus retreatment, presence of preoperative lesion, and differences in recall times did not significantly influence healing outcomes (P ⬎ .05, 2). Perhaps with sufficient power, the above factors could indeed be found to be significant. Because relatively few studies exist at this time looking at success of the MTA root-end barrier, increased power could be gained by means of meta-analysis. This would, in turn, give more accuracy to the reported clinical success rates of the MTA root-end barrier and determine potential significance of the secondary outcomes. Because the studies to date have used different criteria to determine success, a meta-analysis would be difficult, if not impossible, to perform. If 816
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a standard criterion for defining success could be agreed on, we could compare apples to apples and realize the advantages that a meta-analysis would offer. As it is now, we are left to compare apples with oranges. Recent case reports (51, 52) have suggested the use of revascularization/regeneration as perhaps new alternative forms of treatment in teeth with immature roots and apices. These cases have shown continued root development and maturation in teeth with previously necrotic pulps. The advantage over a more traditional endodontic technique such as the MTA root-end barrier is the strength added by increased hard tissue thickness and root length. Because these techniques have not yet proved to be predictable in every case, treatment such as the MTA root-end barrier can still be used in cases in which revascularization/ regeneration has failed. In summary, 85% (17/20) of teeth treated with MTA root-end barriers healed, and improvements in PAI scores at recall appointments were shown to be statistically significant (P ⬍ .001, Wilcoxon signed rank test). Short treatment times reduce the need for patient compliance and allow the crown to be strengthened quickly by means of a bonded restoration. Overall, these results indicate that the MTA apical barrier technique is a successful method for obturating teeth with pulp necrosis and immature apices. However, additional studies with appropriate follow-up are still necessary to better assess long-term clinical success of this technique.
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Clinical Research 19. Finucane D, Kinirons MJ. Non-vital immature permanent incisors: factors that may influence treatment outcome. Endod Dent Traumatol 1999;15:273–7. 20. Yates JA. Barrier formation time in non-vital teeth with open apices. Int Endod J 1988;21:313–9. 21. Holland R, de Souza V, Nery MJ, Otoboni Filho JA, Bernabe PF, Dezan Junior E. Reaction of dogs’ teeth to root canal filling with mineral trioxide aggregate or a glass ionomer sealer. J Endod 1999;25:728 –30. 22. Keiser K, Johnson CC, Tipton DA. Cytotoxicity of mineral trioxide aggregate using human periodontal ligament fibroblasts. J Endod 2000;26:288 –91. 23. Osorio RM, Hefti A, Vertucci FJ, Shawley AL. Cytotoxicity of endodontic materials. J Endod 1998;24:91– 6. 24. Torabinejad M, Pitt Ford TR, Abedi HR, Kariyawasam SP, Tang HM. Tissue reaction to implanted root-end filling materials in the tibia and mandible of guinea pigs. J Endod 1998;24:468 –71. 25. 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. 26. Apaydin E, Shabahang S, Torabinejad M. Hard-tissue healing after application of fresh or set MTA as root-end-filling material. J Endod 2004;30:21– 4. 27. Shabahang S, Torabinejad M, Boyne PP, Abedi HR, McMillan P. A comparative study of root-end induction using osteogenic protein-1, calcium hydroxide and mineral trioxide aggregate in dogs. J Endod 1999;25:1–5. 28. Al-Hezaimi K, Naghshbandi J, Oglesby S, Simon JH, Rotstein I. Human saliva penetration of root canals obturated with two types of mineral trioxide aggregate cements. J Endod 2005;31:453– 6. 29. Al-Kahtani A, Shostad S, Schifferle R, Bhambhani S. In-vitro evaluation of microleakage of an orthograde apical plug of mineral trioxide aggregate in permanent teeth with simulated immature apices. J Endod 2005;31:117–9. 30. De Leimburg ML, Angeretti A, Ceruti P, Lendini M, Pasqualini D, Berutti E. MTA obturation of pulpless teeth with open apices: bacterial leakage as detected by polymerase chain reaction assay. J Endod 2004;30:883– 6. 31. Lawley GR, Schindler WG, Walker WA 3rd, Kolodrubetz D. Evaluation of ultrasonically placed MTA and fracture resistance with intracanal composite resin in a model of apexification. J Endod 2004;30:167–72. 32. 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. 33. Torabinejad M, Watson TF, Pitt Ford TR. Sealing ability of mineral trioxide aggregate when used as a root end filling material. J Endod 1993;19:591–5. 34. Aminoshariae A, Hartwell GR, Moon PC. Placement of mineral trioxide aggregate using two different techniques. J Endod 2003;29:679 – 82. 35. Hachmeister DR, Schindler WG, Walker WA 3rd, Thomas DD. The sealing ability and retention characteristics of mineral trioxide aggregate in a model of apexification. J Endod 2002;28:386 –90.
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36. Pene JR, Nicholls JI, Harrington GW. Evaluation of fiber-composite laminate in the restoration of immature, nonvital maxillary central incisors. J Endod 2001;27: 18 –22. 37. Giuliani V, Baccetti T, Pace R, Pagavino G. The use of MTA in teeth with necrotic pulps and open apices. Dent Traumatol 2002;18:217–21. 38. Pace R, Giuliani V, Pini Prato L, Baccetti T, Pagavino G. Apical plug technique using mineral trioxide aggregate: results from a case series. Int Endod J 2007:40:478 – 84. 39. Sarris S, Tahmassebi JF, Duggal MS, Cross IA. A clinical evaluation of mineral trioxide aggregate for root-end closure of non-vital immature permanent incisors in children: a pilot study. Dent Traumatol 2008:24:79 – 85. 40. Simon S, Rilliard F, Berdal A, Machtou P. The use of mineral trioxide aggregate in one-visit apexification treatment: a prospective study. Int Endod J 2007;40:186 –97. 41. Friedman S, Abitbol S, Lawrence HP. Treatment outcome in endodontics: the Toronto Study. Phase 1: initial treatment. J Endod 2003;29;787–93. 42. Ørstavik D, Kerekes K, Eriksen HM. The periapical index: a scoring system for radiographic assessment of apical periodontitis. Endod Dent Traumatol 1986;2: 20 –34. 43. Delano EO, Ludlow JB, Ørstavik D, Tyndall D, Trope M. Comparison between PAI and quantitative digital radiographic assessment of apical healing after endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92:108 –15. 44. Landis JR, Koch GG. An application of hierarchical kappa-type statistics in the assessment of majority agreement among multiple observers. Biometrics 1977;33:363–74. 45. El Meligy OA, Avery DR. Comparison of apexification with mineral trioxide aggregate and calcium hydroxide. Pediatr Dent 2006;28:248 –53. 46. Pradhan DP, Chawla HS, Gauba K, Goyal A. Comparative evaluation of endodontic management of teeth with unformed apices with mineral trioxide aggregate and calcium hydroxide. J Dent Child 2006;73:79 – 85. 47. Sjogren U, Figdor D, Spangberg L, Sundqvist G. The antimicrobial effect of calcium hydroxide as a short-term intracanal dressing. Int Endod J 1991;24:119 –25. 48. Hasselgren G, Olsson B, Cvek M. Effects of calcium hydroxide and sodium hypochlorite on the dissolution of necrotic porcine muscle tissue. J Endod 1988;14:125–7. 49. European Society of Endodontology. Consensus report of the European Society of Endodontology on quality guidelines for endodontic treatment. Int Endod J 1994;27:115–124. 50. Reit C. Decision strategies in endodontics: on the design of a recall program. Endod Dent Traumatol 1987;3:233–9. 51. Banchs F, Trope M. Revascularization of immature permanent teeth with apical periodontitis: new treatment protocol? J Endod 2004;30:196 –200. 52. Chueh LH, Huang GT. Immature teeth with periradicular periodontitis or abscess undergoing apexogenesis: a paradigm shift. J Endod 2006;32:1205–13.
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