Year : 2008 | Volume
: 26 | Issue : 2 | Page : 53--58
Evaluation of a mixture of zinc oxide, calcium hydroxide, and sodium fluoride as a new root canal filling material for primary teeth
HS Chawla, S Setia, N Gupta, K Gauba, A Goyal
Unit of Pedodontic and Preventive Dentistry, Oral Health Sciences Center, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India
H S Chawla
Oral Health Sciences Centre, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
Endodontic treatment was performed on 25 pulpally involved mandibular primary molars in 4 to 9-year-old children; the root canals were obturated with a new root canal filling material consisting of a mixture of calcium hydroxide, zinc oxide, and 10% sodium fluoride solution, using hand-operated lentulo-spirals. All cases were evaluated clinically every 3 months and also radiographically every 6 months to assess the success of the treatment; we also examined the resorption of the root canal filling material from the root canals and the status of overpushed material, if any, as the tooth resorbed with the passage of time. At 6 months, endodontic treatment in 2 of the 25 teeth had failed and one tooth had exfoliated; the remaining 22 teeth were without any signs or symptoms. At the end of 2 years, 14 teeth could be evaluated; out of these 12 had physiologically exfoliated. It was observed that the rate of resorption of this new root canal obturating mixture was quite similar to the rate of physiologic root resorption in primary teeth. In three cases, where there was an overpush of the mixture, a gradual partial resorption was noted.
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Chawla H S, Setia S, Gupta N, Gauba K, Goyal A. Evaluation of a mixture of zinc oxide, calcium hydroxide, and sodium fluoride as a new root canal filling material for primary teeth.J Indian Soc Pedod Prev Dent 2008;26:53-58
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Chawla H S, Setia S, Gupta N, Gauba K, Goyal A. Evaluation of a mixture of zinc oxide, calcium hydroxide, and sodium fluoride as a new root canal filling material for primary teeth. J Indian Soc Pedod Prev Dent [serial online] 2008 [cited 2020 Dec 2 ];26:53-58
Available from: https://www.jisppd.com/text.asp?2008/26/2/53/41616
Endodontic treatment of primary teeth is more challenging than that of their permanent counterparts; ,,, this is because of the anatomical complexities of their root canal systems ,,, and their proximity to the developing permanent tooth, coupled with the difficulty in behavior management in children. ,,, A major requirement for the success of root canal treatment of the primary teeth is that the root canal material should resorb at the same rate as the physiologic resorption of the roots; the other factors are that the root canal material should be radiopaque, nontoxic to the periapical tissue and tooth germ, easy to insert, and non-shrinkable; it should also have disinfectant properties. ,
Various root canal filling materials for primary teeth have been used from time to time; the most commonly used and readily available materials are zinc oxide eugenol (ZnOE) ,,,,,,, and calcium hydroxide. ,,, ZnOE has a slow rate of resorption ,, and has a tendency to be retained even after tooth exfoliation; ,,, in some cases unresorbed material has been found to cause deflection of the succedaneous tooth. , ZnOE has also been used in combination with different fixative agents, viz, formaldehyde, , formocresol, , paraformaldehyde, , and cresol,  all of which have inherent cytotoxicity apart from other drawbacks. ,,, Calcium hydroxide, despite its antiseptic and osteoinductive properties, ,, has a tendency to get depleted from the canals earlier than the physiologic resorption of the roots.  Besides these materials, various iodoform-based root canal filling materials are currently in use. Iodoform paste (after Walkhoff's paste)  is commercially available as KRI* and contains iodoform, camphor, para-chlorophenol, and menthol. Iodoform paste in combination with Zinc oxide is available as Maisto's paste which, in addition to the above-mentioned constituents, also contains thymol and lanolin.  Iodoform paste in combination with calcium hydroxide has also been used; it is commercially available as Vitapex**  and Metapex***.  These iodoform-containing products resorb if inadvertently pushed beyond the apex, but the rate of resorption of the material from within the canals is faster than the rate of physiological root resorption.  Another root canal filling material - a mixture of iodoform, calcium hydroxide, and zinc oxide - is commercially available as Endoflas;  in addition, it has eugenol (triiodomethane, Zinc oxide, calcium hydroxide, barium sulphate, and iodine di-btiloorthocresol, with the liquid consisting of eugenol and paramonochlorophenol). It is reported to resorb when extruded beyond the apex but resists resorption intraradicularly.  Eugenol, one of its constituents, is known to cause periapical irritation.  However, there is a questionable safety with the use of iodoform or its combinations because of reports of allergic reactions to iodine in some individuals.  It also has the drawback of causing discoloration of the teeth.  Moreover, a few studies have shown that iodoform is irritating to the periapical tissues and can cause cemental necrosis.  In addition, bismuth iodoform paste has been reported to cause encephalopathy when used as wound dressing following head and neck surgery. 
In order to overcome the disadvantages of ZnOE, calcium hydroxide, and iodoform, and their different formulations, Chawla et al .  reported the use of a mixture of zinc oxide powder and calcium hydroxide as a root canal filling material in primary molars. This mixture, like calcium hydroxide, was also reported to resorb earlier than the physiologic resorption of the roots of the primary teeth. Since intracanal and the overpushed material get resorbed, and do so at a rate faster than the rate of physiological root resorption, one of the authors (HSC) felt that if the root canal filling material contained fluoride, it would leach out fluoride, which could be beneficial to the erupting tooth. In addition, there was the possibility that the combination of zinc oxide powder and calcium hydroxide might form a mixture that would delay resorption.
The present study was therefore undertaken to evaluate a mixture of zinc oxide powder, calcium hydroxide, and sodium fluoride as a root canal filling material in primary mandibular molars.
Materials and Methods
The present investigation was carried out on 25 mandibular molars in 4 to 9-year-old children. The cases were selected from amongst the patients attending the outpatient department of the Unit of Pedodontics and Preventive Dentistry, Oral Health Sciences Center, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India. Primary mandibular molars requiring endodontic treatment, showing adequate bone support and root length, with no radiographically discernable internal or pathological external resorbtion, and without any sinus were included in the study; care was taken to select the sample from children with no history of any systemic disease.
The root canal procedure involved primarily single-sitting pulpectomy, which was carried out by the same operator (SS) in all cases. The root canal treatment in each case was carried out under rubber dam after administration of local anesthesia. The procedure involved cavity preparation, removal of all carious tooth structure, making a straight-line access, and extirpation of pulpal debris from the root canals using files, and copious irrigation with 2.5% sodium hypochlorite. A diagnostic radiograph was taken to ascertain the exact length of the root canal, with snugly fitting files extending periapically to an average length of the root canal of that particular tooth. A good fit of the file into the canal is desirable to avoid error due to increase or decrease of the inserted file length during the radiographic procedure. The radiographic procedure involved the removal of the rubber dam sheet from the frame and tying of the free ends of the sheet together by slipping the rubber band over it. After establishing the working length, the canals were prepared with H-files (30-35 size), using a pullback motion. Care was taken to do selective filing, i.e., while filing the root canal, more pressure was maintained along the outer wall of the canal as the walls towards the interradicular areas are generally thin due to physiological resorption and there is an associated risk of perforation. The root canals were thoroughly irrigated with sodium hypochlorite; I.V. metronidazole solution (0.5%) was used as the last irrigating solution. The root canals were filled using the mixture made out of calcium hydroxide paste and zinc oxide powder, with 10% sodium fluoride solution as the liquid. To standardize the quantity of each ingredient in the mixture, 70 mg of zinc oxide powder was preweighed, placed in empty capsules, and sterilized. A standard length of 7.5 cm of calcium hydroxide paste (Reogan Rapid)* was placed on the mixing pad and the zinc oxide powder from the preweighed capsule was emptied beside it. The two were mixed together along with drops of 10% sodium fluoride solution to achieve the desired consistency. Hand lentulo spiral was used with a clockwise rotatory motion to fill the material into the root canals. The lentulo spiral was rotated in a clockwise direction while inserting the material into the canal and once the predetermined length was obtained, an agitating motion was done several times. Anticlockwise rotation was carried out while withdrawing the lentulo spiral from the canals. The access cavity was sealed with a fast-setting ZnOE paste followed by permanent filling; in some cases stainless steel crowns were given.
The teeth were clinically evaluated regularly after 3 months and also radiographically every 6 months or till the exfoliation of the teeth. At each follow-up visit, the teeth were assessed clinically for pain, tenderness on percussion, and mobility; the teeth were also radiographically assessed for resorption of overpushed material (if any) as well as for resorption from the root canals, comparisons being made with the immediate postoperative radiographs.
Single-stage pulpectomy, using a mixture of calcium hydroxide, zinc oxide, and 10% sodium fluoride solution as a root canal obturation material, was carried out in a total of 25 teeth (7 first and 18 second primary molars) in 25 children aged 4-9 years [Table 1]. The teeth were followed up at regular 3-month intervals for a period of 24 months. For the radiographic assessment, the mesial canals were considered as a single canal because of superimposition of the two canals seen on the intraoral periapical radiographs.
Initially, out of a total of 50 canals (25 mesial and 25 distal) in 25 teeth, adequate filling was observed in 33 canals (19 mesial and 14 distal), underfilling in 14 canals (5 mesial and 9 distal), and overpushing of the material in the periapical region in 3 canals (1 mesial and 2 distal) [Table 2]. After a follow-up period of 6 months, the treatments in 2 out of the 25 teeth were found to have been unsuccessful and therefore the teeth were extracted, one at 3 months and another at 6 months. After a follow-up period of 2 years, 14 children (involving 14 mandibular molars) could be assessed; the roots of 12 primary molars had naturally resorbed and got exfoliated. The timing of physiologic exfoliation is depicted in [Table 3]. In the 14 teeth, involving 28 canals, initial radiographic assessment showed adequate filling in 18, underfilling in 7, and overfilling in 3 canals. Over a period of 2 years, the resorption of the material matched the physiologic root resorption in all the 28 root canals, i.e., the root canal material from within the canal (intraradicularly) resorbed along with the resorption of the roots [Figure 1] and [Figure 2]. In three subjects in whom the material got overpushed, there was a slow resorption of the overpushed material but even after a follow-up period of more than 2 years the overpushed material did not resorb completely [Figure 3] and [Figure 4]. One tooth with overpushed material beyond the apex got exfoliated physiologically along with the remaining extruded material.
With predictable management and the cooperation of children in clinics for dental treatment, using nonpharmacological methods, nitrous oxide sedation and better understanding of the morphology of the root canals of primary teeth, more and more clinicians the world over are recommending and performing pulpectomy procedures in teeth. The primary goal of root canal treatment is to eliminate infection and retain the tooth in a functional state until it is normally exfoliated.
Pulp management of infected primary teeth involves not only thorough debridement of the root canal system but also obturation by using a material which is biocompatible and would resorb at the same rate as the roots of the involved tooth, without endangering the succedaneous permanent tooth and its eruption. Till date, a number of investigators have tested different materials but none of these have been shown to possess the requisite properties of an ideal root canal filling material for primary teeth, especially with regard to the major desirable property of having a rate of resorption matching that of the physiologic root resorption of the primary teeth. ZnOE paste is the most frequently used root canal filling material for primary teeth. Clinical studies conducted on animals and humans have shown the success rate of ZnOE paste used alone to range from 65-95%.  To improve its properties and success rate, ZnOE in combinations with different compounds like formocresol,  formaldehyde, , paraformaldehyde,  and cresol  have been tried out, but the addition of these compounds neither increased the success rate nor made the material more resorbable as compared to ZnOE alone. Moreover, the use of phenolic compounds are not advocated due to their fixative nature; they have been proven to have cytotoxic, mutagenic, and carcinogenic potential. ,,, Calcium hydroxide, virtually an all-purpose medicament in dentistry, , has been widely used in permanent teeth for pulp capping and apexification, but its use in pulpotomy in primary teeth has been limited due to the risk of internal resorption. , However, its use as a root canal filling material in primary teeth following pulpectomy has been reported by a few authors ,, to provide considerable success. A study conducted by Mani et al .  has however revealed the rate of calcium hydroxide resorption to be faster than the rate of physiologic resorption of the roots and the material was seen to deplete from the canals much before root resorption.
Iodoform paste and its combinations with other compounds have been used by a number of authors, with a success rate ranging from 70-90%. ,,,, Good clinical results with Walkhoffs paste  have been reported in several studies. High rates of clinical and radiographic success has been reported using Vitapex,  a commercial paste containing calcium hydroxide and iodoform that is available in premixed form in syringes with disposables tips. The above-mentioned materials have the drawback of being resorbed earlier than the roots during physiologic resorption of primary teeth. Fuks et al .  carried out a retrospective study using Endoflas as a filling material; this is primarily a mixture of calcium hydroxide, zinc oxide, iodoform, and eugenol. The resorption of this material has been shown to be limited to the excess extruded extraradicularly and it does not get depleted intraradicularly. The authors observed a lower success rate of 58% when there was overfilling but 83% success in cases with flush and underfilled root canals. The overpushing of the root canal filling material in primary teeth is unavoidable in some cases because of the thin dentinal walls of the root canals toward the interradicular areas, which may give way during filing of root canals. However, the use of iodoform-containing products in dentistry is of questionable benefit because of reports of iodine allergy,  discoloration of teeth,  and even encephalopathy leading to coma.  Till such time as the doubt regarding the safety of iodoform as root canal filling material is cleared it seems unlikely that the material will gain much popularity for use in primary teeth.
To overcome the draw backs of calcium hydroxide (faster rate of resorption from within the canals) and ZnOE (slow rate of resorption), Chawla et al .  used a mixture of calcium hydroxide and zinc oxide as a root canal filling material, but this material also got depleted from the canals earlier as compared to the physiologic root resorption. In the present study, a mixture of calcium hydroxide, zinc oxide powder, and sodium fluoride (10%) was used, combining the advantages of both calcium hydroxide and zinc oxide. Calcium fluoride as a reaction product added radiopacity to the root canal filling material, without the need for addition of any other radiopaque material. The addition of fluoride was seen to give this material a resorption rate that matched the resorption rate of the roots of the primary pulpectomized teeth.
The extrusion of root canal material in the present study was seen in the periapical area and not in the interradicular area. This may be due, firstly, to the 'selective filing' procedure carried out while preparing the canals and, secondly, to the inclusion criteria for the teeth in the present study, i.e., absence of sinus and interradicular radiolucency. Taking into consideration the fact that the walls of the root canal toward the succedaneous tooth are thin and weak and are prone to perforation during instrumentation, one has to accept that at times extrusion of the material cannot be prevented. In the present study, in all three cases of overfilling, a slow resorption of the root canal filling material was noted and it was seen to be a continuous process; therefore, there seems little danger of the overpushed material being retained after natural exfoliation of the primary tooth. The overfilled material was not seen to completely resorb even after 2 years of follow-up and so care should be taken not to overpush the material beyond the apex.
A study is already in progress to evaluate the resorption of the root canal filling material intraradicularly, interradicularly, and periapically, using mixtures of zinc oxide and calcium hydroxide along with different concentrations (2, 6, and 8%) of sodium fluoride as a liquid. The mixture made by using 8% sodium fluoride is showing good results in the mid-term evaluation.
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