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Research Article_______________________________________________________________________________________________________________________________________________________________

Evolution of apical formation on immature necrotic permanent teeth ASUNCIÓN MENDOZA MENDOZA, MD, DMD, PHD, ENRIQUE SOLANO REINA, MD, DMD, PHD& FRANKLIN GARCÍA-GODOY, DDS, MS

ABSTRACT: Purpose: To evaluate the evolution of apical formation on 28 necrotic immature permanent teeth treated with calcium hydroxide at different stages of root development. Methods: Apical formation in 28 necrotic incisors was carried out (27 upper and one lower incisors), in children between the ages of 6 and 13 years old (11 males, 10 females). Following anesthesia and rubber dam isolation, the chamber was opened and the coronal and root pulp tissue was removed. Next, after measuring the canal, the root canal was irrigated with 5% sodium hypochlorite. Once the canal was dried, it was filled with the CaOH2 powder mixed with physiologic saline solution to a dense consistency but malleable. This paste was compressed into the canal using a cotton pellet. The canal was completely filled up to the apex. Finally, the cavity opening was sealed with zinc oxide-eugenol (IRM) and glass-ionomer (Vitrebond). Follow-up appointments were made every 3 months in order to evaluate the evolution of the periapical radiolucency and the formation of the apical barrier. Results: The duration of the apical induction was 8.6 ± 5.36 months. Increase or lack of growth in the length of the root canal and the type of root end closing was as follows: cementoid tissue (85.72%); osseous tissue (14.28%), with a 100% overall success rate. The evolution of these teeth was monitored over a 2-year period with re-infections occurring in 7.1 percent of the cases. (Am J Dent 2010;23:269-274).

CLINICAL SIGNIFICANCE: The use of calcium hydroxide in immature necrotic permanent teeth after 2 years showed an overall success rate of 100% for root end induction with 7.1% of the cases showing re-infections.

: Dr. Asunción Mendoza Mendoza, Plaza de Cuba, 6-1º Centro, 41011- Seville, Spain. E- : coinsol@telefonica.net

Introduction During tooth formation, the pulp can suffer traumas that produce pulp necrosis that can affect root development.1 In teeth with incompletely formed roots it is crucial to maintain pulp vitality. Therefore, the treatment of choice should favor the one which offers the highest probability of main-taining the pulp in a healthy condition to promote satisfactory root development. Prior to the introduction of apical closure induction techniques, surgery was the common treatment for necrotic permanent teeth and for those with open apices.2 Although it proved to be a successful treatment, surgery was inconvenient from a mechanical standpoint of view due to the difficulty of obtaining a well-sealed apex without cutting part of the root. When dealing with a young permanent tooth with an open apex, the best treatment should aim to preserve pulp vitality to allow continuous root development. If possible, pulp capping and pulpotomy should be carried out before apexification or apexogenesis. If these treatments are contraindicated, for instance because pulp tissue necrosis or a periapical lesion, the treatment of choice would be apexification. The objective of this treatment is the induction of apical closure by means of the apposition of hard tissues so that the root canals with open apices may be plugged with the filling material while avoiding extrusion of the materials to the periapical area.3 On the other hand, the apical barrier should prevent the flow of fluids from the periapical area into the root canal to dry the dentin properly allowing maximum adaptation of the sealing material.4

In 1960, Cooke & Rowbotham5 made the first reference to the root canal therapy of nonvital teeth with open apices, but it was not described until 1964 by Kaiser;6 later, in 1966, Frank7

published his procedure which has been referred to as “Frank’s technique”. Many materials can successfully stimulate the formation of

apical closure. Kaiser6 was the first to report on the use of calcium hydroxide in apexification. Since then, different mixtures of this material have been tested: camphorated parachlorophenol,6.7 methacresilacetate,8 crenasol-mixture of both; with physiologic serum,9 distilled water,10 iodoform,11

Ringer solution and sterile water,5 anesthetic solution,12 gly-cerine,13 and methylcellulose.14 Other compounds that promote successful apical formation include zinc oxide blends, poly-antibiotic pastes,15 Walkoff paste,14 Diaket compounds,16 as well as tri-calcium phosphate.17

In 1961, Nygaard-Otsby18 achieved apical closure by stimulating bleeding inside the root canal and lacerating the granulation tissue of the periapical area. However, others19,20

did not report satisfactory results after using the blood clot formation method. England & Best21 determined that a thorough cleaning of the root canal could be the main factor responsible for apical closing. Similarly, Chawla et al22 in 1980 considered the use of a catalytic paste unnecessary for the induction of the formation of an apical barrier. Likewise, Das et al23 showed apical closing by just controlling the infection, without placing any filling material inside the root canal. Tetracycline, a non-caustic substance capable of diminishing the bacterial flora of the root canal, was used and proved not to adversely affect root growth.23

Currently, the most widely accepted method for the forma-tion of an apical barrier is by using a calcium hydroxide and physiological saline mixture, with a duration of 4-6 months.24

In recent years, there has been support for the formation of apical barriers through the application of mineral trioxide aggregate (MTA) cement that hardens in 4 hours, permitting the definitive filling of the apex.25 Both procedures call for the total elimination of necrotic tissue present in the root canal and carrying out a proper seal aiming to prevent bacterial filtration towards the interior of the root canal. When dealing with immature teeth, one of the most im-

270 Mendoza Mendoza et al

Fig. 1. Stages of root development: Stage 6: Two-thirds formed roots and divergent walls; Stage 7: Two-thirds formed roots and parallel walls; Stage 8: Between 2/3 and 3/3 of the root formed and very open apex; Stage 9: Almost 3/3 of the root formed and open apex; Stage 10: 3/3 of the root formed and close apex.

portant and complex issues is the radiographic diagnosis of pulp necrosis due to the apparently normal radiolucency presented by the apices of these teeth during the process of root maturation. As a result, root formation should be always compared to that of the adjacent or contralateral tooth. In order to confirm the diagnosis, it is important as well to analyze the presence of sharp or chronic pain, sensitivity to percussion, changes in color, and mobility of the tooth.

Materials and Methods Apical formation in 28 necrotic incisors was carried out (27 upper and one lower incisors), in children between the ages of 6 and 13 years old (11 males, 10 females). The following parameters were taken into account for each incisor, regardless of the patient’s age and sex:

1. The tooth’s stage of apical development according to the classifications shown in Fig. 1. 2. Number of replacements of the calcium hydroxide paste and interval of time in which they were carried out. 3. Presence of mobility, swelling and/or fistula, internal or external root resorption and the presence of periapical image, grading the size of the latter as +, ++ or +++, corresponding to between 0 and 2 mm, from 2 to 4 mm, and over 4 mm, respectively. 4. Type of tissue forming in response to the filling material placed in the root canal, be it cementoid or osteoid (Fig. 2), observed in the periapical radiograph using a magnifying glass. 5. The initial length of the tooth and the final length following apical formation treatment measured by means of root canal measurement. 6. The duration of treatment required in order to carry out the sealing of the root canal with gutta-percha. 7. The evolution of the tooth over a 2-year period, following filling with gutta-percha.

Technique - Following anesthesia and rubber dam isolation, the chamber was opened and the coronal and root pulp tissue was removed. Next, after measuring the canal, the root canal was irrigated with 5% sodium hypochlorite. Once the canal was dried, it was filled with the CaOH2 powder mixed with physio-logic saline solution to a dense consistency but malleable. This paste was compressed into the canal using a cotton pellet. The canal was completely filled up to the apex. Finally, the cavity

American Journal of Dentistry, Vol. 23, No. 5, October, 2010

Fig. 2. Type of tissue formation in response to the filling material placed in the root canal (cementoid or osteoid).

Table 1. Sample distribution. ____________________________________________________________________________________________________

Age Female Male Teeth ____________________________________________________________________________________________________

6 1 1 7 3 2 5 8 2 3 7 9 2 2 10 3 2 8 11 1 2 12 1 2 13 1 1 ____________________________________________________________________________________________________

Total 10 11 28

Table 2. Frequency of affected teeth. ____________________________________________________________________________________________________

Maxillary incisor Frequency % ____________________________________________________________________________________________________

Right central 12 42.9 Right lateral 2 7.1 Left central 13 46.4 Left lateral 1 3.6 ____________________________________________________________________________________________________

Total 28

opening was sealed with IRMa and glass-ionomer (Vitrebondb).Paste replacement and follow-up - Follow-up appointments were made every 3 months in order to evaluate the evolution of the periapical image and the formation of the apical barrier. Calcium hydroxide replacements were made only when the radiograph revealed a lower paste density or an unsatisfactory evolution of the periapical area. Once the apical closing was complete and root canal intervention had been carried out, clinical and radiographic follow-up sessions were scheduled every 6 months over a 2-year period, thus ensuring that no re-infection had taken place. Fischer exact test was used to evaluate any association among the different qualitative variables, and in cases where this test was not appropriate, it was substituted by the Chi-square test. The Cramer V served as a measure of the association among nominal variables while the lineal association coefficient was used to measure relationship among ordinal variables. For the analysis of the total time of treatment and its relationship with the different variables, the Mann-Whitney and Kruskal-Wallis non parametric tests were carried out. Student t-test for paired samples was employed to evaluate increases in length. In all cases differences and associations have been considered significant to P< 0.05.

American Journal of Dentistry, Vol. 23, No. 5, October, 2010

Table 3. Treatment duration in months. ____________________________________________________________________________________________________

Treatment duration (months) ________________________________________________________________

Mean SD Total N 8.69 5.36 ____________________________________________________________________________________________________

Stage 6 3 10.40 3.24 7 8 14.41 5.89 8 9 6.82 2.34 9 8 4.41 1.63 X2 =15.61 P= 0.001 No. of 1 16 5.85 2.87 replacements 2 4 7.07 2.69 2 4 11.52 3.04 4 4 18.77 2.85 X2 =14.97 P= 0.002 Radio- + 20 6.92 3.56 lucency ++ 5 8.84 4.32 +++ 3 20.20 0.00 X2 =8.35 P= 0.015 Swelling No 22 7.60 3.82 Yes 6 12.67 8.34 U=0.236 P= 0.236 Mobility No 25 7.53 4.30 Yes 3 18.30 3.29 U=3.0 P= 0.004 Fistula No 25 7.30 3.71 Yes 3 20.2 0.00 U=0.0 P= 0.001 Internal No 27 8.44 5.29 resorption Yes 1 15.4 0.00 U=3.0 n.s. External No 26 8.93 5.49 resorption Yes 2 5.55 0.49 U=15.5 n.s. Apical Cementoid 24 6.97 3.37 closure Osteoid 4 19.00 2.40 U=0 P< 0.001 ___________________________________________________________________________________________________

Results Tables 1 and 2 show the 28 treated teeth organized by age and sex. Some subjects had more than one affected incisor. The upper central incisors were the most frequently treated teeth with a distribution of 42.9 in the upper right central incisors and 46.4 in the upper right central incisors left. Duration of the treatment - The development stage in which the apical formation was carried out revealed that that the lower the root development stage was, the longer the duration of treatment, in some cases up to 20 months even if the measures were widely varied and highly significant (Table 3). Number of replacements - In the majority of cases (16), only one paste replacement was needed with an average treatment time of 5.85 ± 2.87 years. In cases where a greater number of replacements were necessary, the duration of the treatment increased significantly. Radiolucency - Only three of the 28 teeth presented radiolucency over 4 mm in diameter with an average treatment period of 20 months, while the remaining 25 teeth underwent an average treatment period of 1 year or less. Swelling - Only six of the 28 teeth presented swelling, but these were asymptomatic. In a longer treatment period, they were significant (P= 0.236). Mobility - 25 of the 28 treated teeth did not present mobility, with an average treatment period of 1 year (7.53 ± 4.30), while the remaining three were treated for an average of 2 years (18.30 ± 3.29).

Apical formation of immature necrotic teeth 271

Table 4. Increase in length. ____________________________________________________________________________________________________

Mean (mm) SD ____________________________________________________________________________________________________

Initial length 20.98 2.54 Final length 21.01 2.54 ____________________________________________________________________________________________________

t= 1.441 n.s.

Fistula - The same three teeth that presented mobility had suppuration leading to a considerable increase in the duration of their treatment (20 months).

Resorption - internal and external - There was only one case of internal resorption and two cases of external resorption. In the internal resorption case, the duration of the treatment was longer than in other cases. Nevertheless, this difference in recovery time was not significant. On the contrary, the two cases of external resorption required a shorter treatment period, though again the difference was also insignificant. Apical closure - In 85.72% of the cases (24) apical closure was achieved with cementoid tissue in less than a year (6.97 ± 3.37), while in only 14.28% of the cases (4) did apical closure occur by osseous tissue over a 2-year treatment period (19 ± 2.40) (Tables 4,5).

Type of apical closure - Apical closure with cementoid tissue coincides with rounded apices, probably due to continuous root canal and apical closure, until a normal appearance was obtained. However, there was no increase in length, while in cases of apical closure by osseous tissue the barrier may not have shown up in the radiograph due to its plateau shape; regardless, a clear upper limit was detected clinically, allowing the definitive filling to be carried out (Table 5). The data in Table 5 shows that the four osseous closings coincided with stage 7. In other words, they presented open apices and root development less than 2/3, yet had parallel walls and, in turn, required a greater number of replacements. Three of them presented a periapical radiolucency greater than 4 mm, swelling and fistula; two out of four closings presented mobility and only one showed signs of internal resorption. We can also confirm that the number of replacements was greatly reduced in those cases where closure was obtained using cementoid tissue. None of them presented a periapical radiolucency over 3 mm, and although there were three with swelling and one with mobility, none presented fistula although two of them showed signs of external resorption. Apical closure with osseous tissue took place in the four teeth presenting the worst overall prognosis.

Increase in root length - After measuring the length of the root canal before introducing the filler paste and once apical closure took place, the new level of root development was measured again, taking the highest level achieved previous to filling with gutta-percha as a reference. An increase in length did not take place after the initial length was 20.98 ± 2.54 and the final length was 21.01 ± 2.54 (Table 4).

Evolution - After 2 years, two of the teeth (7.1%) suffered re- infection; they were the two teeth that had undergone closure with osseous tissue and in turn had presented signs of swelling, mobility and fistula, and presented the same symptoms again after re-infection, making it necessary to carry out an apicoectomy (Table 6).

272 Mendoza Mendoza et al American Journal of Dentistry, Vol. 23, No. 5, October, 2010

Table 5. Apical closure type. _______________________________________________________________________________________________________________________________________________________________________________________________________________

No. of Internal External Total Stage replacements Radiolucency Swelling Mobility Fistula resorption resorption _______________________________________________________________________________________________________________________________________________________________________

6 7 8 9 1 2 3 4 + ++ +++ No Yes No Yes No Yes No Yes No Yes _______________________________________________________________________________________________________________________________________________________________________________________________________________

Good 85.7%-24 3 4 9 8 16 4 3 1 19 5 0 21 3 23 1 24 0 24 0 22 2 Poor 14.28%- 4 0 4 0 0 0 0 1 3 1 3 0 1 3 2 2 1 3 3 1 4 0 _______________________________________________________________________________________________________________________________________________________________________________________________________________

Total 100% 28 3 8 9 8 16 4 4 4 20 5 3 22 6 25 3 25 3 27 1 26 2

X2 X2 =11.667 X2 =15.750 P P= 0.009 P= 0.001 P= 0.001 P= 0.022 P= 0.045 P= 0.001 ns. n.s. Association R= 2.912 R= 12.742 R= 12.182 V= 0.533 V= 0.519 V= 0.849 V= 0.471 V= 0.113 P n.s. P< 0.001 P= 0.003 P= 0.005 P= 0.006 P< 0.001 P= 0.013 n.s _______________________________________________________________________________________________________________________________________________________________________________________________________________

Table 6. Evolution after 2 years. _______________________________________________________________________________________________________________________________________________________________________________________________________________

No. of Internal External Stage replacements Radiolucency Swelling Mobility Fistula resorption resorption Apical closure ______________________________________________________________________________________________________________________________________________________________________________

Total 6 7 8 9 1 2 3 4 + ++ +++ No Yes No Yes No Yes No Yes No Yes Cementoid Osteoid _______________________________________________________________________________________________________________________________________________________________________________________________________________

Good 92.85%-24 3 6 9 8 16 4 4 2 20 5 1 22 4 25 1 25 1 25 1 24 2 24 2 Poor 7.15%- 4 0 2 0 0 0 0 0 2 0 0 2 0 4 0 2 0 2 2 0 2 0 2 0 _______________________________________________________________________________________________________________________________________________________________________________________________________________

Total 100% 28 3 8 9 8 16 4 4 4 20 5 3 22 6 25 3 25 3 27 1 26 2 26 2

X2 X2 = 5.385 X2 = 12.923 P P= 0.146 P= 0.005 P= 0.008 P= 0.040 P= 0.0008 P= 0.008 ns. n.s. P= 0.016 Association R= 1.344 R= 7.537 R= 11.847 V= 0.531 V= 0.801 V= 0.801 V= 0.053 V= 0.077 V= 0.679 P n.s. P= 0.016 P= 0.008 P= 0.040 P= 0.001 P< 0.001 P= 0.013 n.s P< 0.001 _______________________________________________________________________________________________________________________________________________________________________________________________________________

Discussion

In the present study, apical formation using calcium hydroxide showed a high success rate in the 28 necrotic immature permanent incisors treated. Apical closure was achieved in 100% of the teeth treated, 92.85% of which have evolved satisfactorily over the course of the 2-year follow-up period (Figs 3-5). The existing literature on apical formation using calcium hydroxide also shows the highly satisfactory nature of this technique.24,26-29

Although many authors are in favor of carrying out frequent calcium hydroxide paste replacements every 3 months, in the present study we have opted to make replacements only when radiographs showed a decrease in paste density in the root canals, obtaining excellent results with less treatments. Only 28% of the sample required more than one replacement. This agrees with Chosak et al,3 who concluded that frequent paste replacements did not lead to noteworthy improvements. Though in the present study the mixture of calcium hy-droxide powder was made with physiologic solutions, other authors have also obtained good results by mixing it with other substances such as distilled water,30,31 camphorated parachloro-phenol,6,7 and methylcellulose.8 It seems that the technique’s success does not depend so much on the substance mixed with calcium hydroxide, but in the correct cleaning of the root canal and in the filling of the canal with filler material, allowing the tooth to reorganize and repair the periapical tissue.32

Regarding the duration of the treatment, Kleier24 found a median time between 6 and 24 months. This agrees with the present study in general terms as our average treatment duration

was 8.6 ± 5.36 months, although three of the cases reached 20 months. Therefore, it seems that the duration of the treatment is a function of variables such as root development stage, size of the radiolucency, the presence of swelling or fistula, type of apical closure and number of paste replacements. As far as the apical closure type, of the four types of closures described by Frank,7 the present study found only two: first, types which can take place by way of a steady closing of the canal and apices until a normal appearance is obtained (cementoid tissue), occurring 85.72% of the time (24 cases); and secondly, closure types in which the apical barrier did not show up on the radiographs, but where a clear upper limit was detected during the clinical observation period allowing definitive root canal filling. This was attributed to osseous tissue closure and it represents 14.28% (4) of the cases in our study. The present findings did not show continued root develop-ment following treatment. However, others30-33 observed an increase in root length, demonstrating the capacity of the cells comprising the Hertwig epithelial sheath to remain intact and ward off infection. As for evolution, 2 years after the apical closing it was noticed that despite apical closure in all the cases, the risk of re-infection occurred in two of the cases (7.1%), coinciding with two of the four teeth that closed by way of osseous tissue and in turn showed signs of swelling, mobility and fistula. Immature teeth, in spite of being treated with this technique, have thin, fragile walls and any trauma, insignificant as it may be, can easily produce root fracture. In a retrospective study, Cvek34 observed that the frequency with which fractures occurred among immature teeth, depended on the develop-mental stage of the tooth in question, being 77% in the most

American Journal of Dentistry, Vol. 23, No. 5, October, 2010 Apical formation of immature necrotic teeth 273

Fig. 3A. Necrotic maxillary right central incisor with open apex following dental trauma. B. Root canal filling with calcium hydroxide. C. Replacement root canal filling with calcium hydroxide after 6 months. D. 1 year after filling with gutta-percha.

Fig. 4A. 9 year-old child 3 months after traumatic dental injury. A widened periodontal ligament area in the right central incisor as well as periapical radiolucency in both incisors. B. Initial calcium hydroxide placement. C. Third calcium hydroxide replacement. D. Final gutta-percha filling after apical closure and after three calcium hydroxide replacements

Fig. 5A. 9 year-old 1 month after enamel-dentin fracture. B. Calcium hydroxide placement. C. 8 months after root canal filling with gutta-percha.

immature teeth and 28% in the most developed ones. In the present study no root fracture was noticed; however Robertson & Andreasen35 reported that the immature teeth that were subjected to apical formation treatment suffered a root fracture over time. Further longer term studies are recommended to evaluate

the outcome of the treatments. a. LD Caulk Dentsply, Milford, DE, USA. b. 3M ESPE, St. Paul, MN, USA. Disclosure statement: The authors have no conflict of interest.

Dr. Mendoza Mendoza is Titular Professor, Department of Pediatric Dentistry; Dr. Solano Reina is Titular Professor, Department of Orthodontics, Faculty of

274 Mendoza Mendoza et al

Dentistry, University of Seville, Seville, Spain. Dr. García-Godoy is Senior Executive Associate Dean for Research and Director, Bioscience Research Center, College of Dentistry, University of Tennessee Health Science Center, Memphis, Tennessee, USA.

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