Calcium Oxide as a Root Filling

Calcium oxide, available for decades as a root canal filling material, has been little used in recent years due to its lack of radioopacity, and an expectation that it would lead to an excess of root fractures. In this study, four general dentists submitted 79 cases of endodontically treated teeth whose roots were filled with either Biocalex 6/9, or Endocal-10, and rendered adequately radio-opaque with yttrium oxide. 57 teeth were available for follow up at three years. Criteria for success were comfort, function, radiographic signs of healing. The overall success rate was 89%. The percentage of teeth retained in function was 98%; aside from one equivocal case, no teeth were lost to root fractures. These numbers are indistinguishable from success rates reported for conventional root filling materials. Conclusion: Calcium oxide may be considered a safe and viable alternative to other current methods of root obturation. This study was supported by a grant from the International Academy of Oral Medicine and Toxicology Calcium Oxide as a Root Filling Material: a Three Year Prospective Clinical Outcome Study Root canal therapy has always depended on the bedrock principles of instrumentation, canal disinfection, and obturation, but there has been relatively little attention given to disinfection of the deeper, microscopic spaces in the root, the dentinal tubules. There hasnʼt been a consistently successful technique for disinfecting the tubules. Canal irrigants donʼt penetrate very deeply into the tubules, and three dimensional obturation techniques, while they can often reach lateral canals and isthmuses, donʼt enter the tubules either. Interest in more penetrating disinfection may be revived by new high tech methods, such as the radially-firing endo tips for the Waterlase® (Biolase, Irvine, CA), or the cannula for fumigating canals with ozone using the forthcoming Healozone® unit (Kavo, Lake Zurich, IL). Meanwhile, the classic method of deepening the disinfection of root canals is to use a treatment dressing of calcium hydroxide, often mixed with chlorhexidine or iodine, that is left in the canal between appointments. However, calcium hydroxide preparations were never suitable for long term root fillings because they remain soluble and subject to leaking and washing out. For many years, at the fringes of dentistry, there has been another material for permanent filling of root canals that merges the advantages of calcium hydroxide with a hard setting, canal sealing, three dimensional obturation: calcium oxide. Although calcium oxide (CaO) was introduced as an endodontic filling material by Bernard in 1952 (1), the decades since have seen remarkably little clinical research on it. In fact, a search of the literature yields not even one longitudinal clinical follow-up study. There have been limited case reports and opinion pieces, and a few papers describing its properties in extracted teeth. In vitro studies have established that CaO root fillings are biocompatible (2); produce high alkalinity throughout the thickness of the dentin (3); dissolve organic predentin, resulting in an intimate apposition of the material to the dentin wall (4); produce a translocation of calcium into dentinal tubules (5); and produce an apical seal that is resistant to dye penetration (6). The fact remains, though, that CaO has not been studied clinically in an organized way. On the face of it, CaO should be an advantageous root filling material, giving the treated root the benefit of what might essentially be a perpetual calcium hydroxide treatment, while setting hard and providing an apical seal. However, there have been three persistent objections to its use. First, the commercial products that have been available for the CaO technique, Biocalex 6/9 ( Spad Laboratories, Saint Quentin en Yvelines, France), which is no longer on the market, and Endocal-10 (Albuca, Montreal, Canada), have not been radioopaque enough to be distinguished from tooth structure. This problem has been solved with the addition of non-toxic, moderately radio-opaque yttrium oxide, as will be described in this paper. Second, the expansive nature of CaO in an aqueous environment has led to the fear that the material will expand with force and fracture of the roots of teeth treated with it. While the proponents of CaO have maintained that it acts more by penetration of the tooth structure, does not expand with force, and does not cause excess root fractures, the perception of it as a hazard still prevails (7). This anticipation of negative outcomes has prevented the endodontic community from embracing the CaO technique, leading to the third objection: the lack of validation from university based research. The fact that no academic endodontic program teaches the use of CaO as a root filling material, means, consequently, that they lack the cases with which to do clinical research. If the outcomes of this technique are to be examined, it must necessarily fall to the clinicians who use it to provide the material for such studies. This paper reports on prospectively collected clinical observation data derived from root canal treatments done in private general practice. It is not a report of a randomized clinical trial, and it is the authorʼs hope that the information presented here may provide a justification for such a clinical trial at an appropriate academic institution. Materials and Methods Four general dentists in private practice, who routinely provide endodontic services, and use CaO as their root filling material of choice, submitted cases to this study. Issues of diagnosis, indications for treatment, and informed consent for root canal treatment with CaO, were handled privately between doctor and patient, but each patient whose case was submitted signed written permission to communicate his or her private data to the study. Cases eligible to be included in the study were any teeth whose endodontic treatment was performed successfully, without compromises in the initial treatment result, that had a reasonable chance of surviving into the future. Criteria for exclusion were: 1. Primary teeth 2. Previous endodontic treatment 3. Excess periodontal risk 4. Root fracture 5. History of full or partial avulsion 6. Non-restorable 7. Procedural errors in initial treatment, e.g. inability to fully instrument and fill roots; perforation; broken instruments; etc. Participants in this study were provided by the author with yttrium oxide (Alfa Aesar, Ward Hill, MA), to improve the radio-opacity of the CaO paste. Yttrium oxide (Y2O3) is nearly identical to zinc oxide in its physical and chemical properties (8), is non-toxic (9), and is moderately radio–opaque. It has been approved by the US Food and Drug Administration as a substitute for zinc oxide in this application (10). The original manufacturerʼs instructions for Biocalex 6/9 recommended that in cases where the canal was instrumented to its full length, that one-third more zinc oxide be added to the mix. In this study, we substituted yttrium oxide for this extra zinc oxide, which solved the problem of lack of radioopacity without changing the working properties of the root filling material. Figure A shows tooth #19 (36) eight years after it was re-treated with Biocalex 6/9. The clinical outcome is good but the lack of radio-opacity of the filled root is unacceptable. In figure B, tooth #30 (46) is filled with conventional gutta percha, while #31 (47) is filled with the CaO/ Y2O3 material, and has acceptable radioopacity. Both Biocalex 6/9 and Endocal-10 were used in this study without distinction, because they were manufactured using identical formulas. The intent of this study was to follow up on the use of the CaO technique in the context of root canal treatment as it is practiced in every day general dentistry, with all the inherent variations that exist between operators. Therefore, no attempt was made to standardize instrumentation, irrigation, use of interappointment treatment dressings, or other treatment strategies available to the clinicians. Since the CaO is a paste filling material, it was recommended that they use a wide root preparation design, to allow free passage of a Lentulo spiral to the full working length. Before declaring the case successfully treated and reporting it to the study, the treating dentist was asked to confirm, on a follow-up appointment, that the paste filling had fully hardened. It is a peculiarity of the CaO root filling that, while it usually hardens on the first application, it doesnʼt always. It is necessary to examine the hardness of the root filling before proceeding with restorative procedures. Only when the hardness of the root filling had been confirmed by the treating dentist would the case be eligible for registration in the study for prospective follow-up. Initial clinical data included information on the patientʼs demographic data, signs and symptoms, and on the vitality or non-vitality of the pulp. Radiographs of diagnostic quality were also submitted. Follow-up data were collected at one year and three years following initial treatment and submission to this study. Questions asked on the data reporting form related to the classical criteria of endodontic success, after Bender et. al. (1966) (11): • Absence of pain or swelling • Disappearance of any sinus tracts • No loss of function • Radiographic evidence of resolved or arrested areas of rarefaction after a post-treatment interval of one year To be considered successful, a case would, in addition, have to have undergone no form of retreatment, and have been restored in a way adequate to provide a coronal seal.