CORONAL MICROLEAKAGE

Transcription

1 CORONAL MICROLEAKAGE Author: Title: Journal: Keywords: Running title: Martin S Gale BDS, MDSc, PhD, FRACDS Coronal microleakage Annals of the Royal Australasian College of Dental Surgeons dentistry, endodontics, periapical periodontitis, apical seal, failure. Gale MS: Coronal microleakage Footnote: This paper was presented in Auckland, New Zealand on 23 October 2000 at the Fifteenth Convocation of the Royal Australasian College of Dental Surgeons. Correspondence should be addressed to: Martin Gale, Specialist Endodontist, The Endodontic Unit, The School of Dental Science, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, 711 Elizabeth Street, Melbourne, Victoria 3000, Australia. m.gale@dent.unimelb.edu.au 0

2 CORONAL MICROLEAKAGE ABSTRACT The microbiological aetiology of periapical periodontitis of endodontic origin is generally accepted. Therefore, bacterial entry into the tooth both initially and secondarily to endodontic therapy is not desirable. Dental restorations and then root fillings in series are intended to prevent recurrent bacterial entry by blocking the access cavity and pulp canal system. This paper reviews whether this intent is realised practically, and what effect an incomplete seal might have on expressed recurrent disease. The aim is to communicate more recent research findings to a wider clinical audience. CORONAL MICROLEAKAGE The cause of periapical inflammation of endodontic origin is generally accepted to be primarily due to the leakage of microbial products and perhaps microbes out of the dentinopulpal space. 1 In endodontically treated teeth, these microbes may be from populations inadvertently remaining in the tooth after preparation, or else new ones from the oral cavity passing through the tooth. For the former, a root filling is required to prevent microbial movement to the apex, and for the latter both a coronal filling and then a root filling in series (Fig. 1) are intended to prevent apical reinfection. 2,3 The aim of this paper is to communicate some more recent research findings to the general clinical community. the leakage process to differentiate effective and ineffective materials and techniques with tracer tests, or even to create a correct ranking. 20,22 The central problem is that the microleakage system is multifactorial, such that with different circumstances different groups of variables become relevant to the final clinical outcome. This makes identification of relevant test variables extremely difficult. Even if test variables were well defined, an often excessive system variability makes it very difficult to determine clear effects. 20 Furthermore, some effects can be tolerated without leading to clinical failure, so long as they are below an often unknown and also variable threshold. These serious research problems effectively hinder proper study of this subject. Suffice it to say that despite their excessive prevalence in the literature, leakage tests including those using a microbial tracer are of unknown relevance to clinical performance. 20,22 They will remain so until this multifactorial system is much better understood and thresholds identified in vivo. Both stronger theoretical analysis and practical comparison of leakage data sets with clinical outcomes are advised. 23 More simplistically, there are two fundamental clinically relevant questions, and some evidence is presented here. Firstly, can temporary or permanent coronal restorations seal their cavities, and secondly can root fillings seal their canals, at least against salivary microbes if not their smaller products and substrates? Various tracers have been used to demonstrate leakage paths including bacteria, water, and dye solutions. Fig 2. shows leakage of an ionic silver tracer around a resin composite restoration into dentine. The ability of the root filling, the coronal restoration, or both to obstruct reinfection of the apical region with oral microbes and their products has been repeatedly investigated, 1,2,4-19 taking up about a quarter of endodontic journal publications. 20 However, dental leakage is an extremely difficult subject to study effectively, although a few papers have grasped the issues well and are worth careful reading by those who can tolerate complexity and uncertainty. If these papers are to be accepted, it appears that we have neither a sufficient understanding nor an adequate simulation of The associated interfacial gap can be clearly seen. Generally, all materials have been found to leak to some extent 10 and it is therefore surprising that most coronal 1

3 and root fillings are clinically successful. This indicates the importance of leakage thresholds and factors other than leakage in the pathogenesies of dental diseases. The results of some tracer studies are shown in Table 1 and are reported in more detail below to illustrate the extent to which restorations can be shown to leak, and the effect of some system variables. Bacterial penetration studies Bacterial tracer studies have been perceived as more relevant than dye tracer studies as, for periapical periodontitis at least, bacteria are known to be required within the tooth. 1,24 However, whether remaining internal bacteria can be sufficiently supplied with soluble nutrients through gaps smaller than bacteria is uncertain, 9 but may be moot when the practical difficulty of getting even a bacterial seal is recognised. Torabinejad et al demonstrated full penetration of two bacterial types through root filled canals in less than 73 days. Root filled teeth were used to separate an artificial saliva containing Proteus vulgaris (motile, acidogenic) or Staphyloccus epidermidis (non-motile, acidogenic) from a sterile broth with phenol red (yellow in acid conditions). Positive and negative controls were instituted. Full penetration occurred in 15 to 51 d (mean 24 d, 0.4 mm/d) for S. epidermidis, and 10 to 73 d (mean 49 d, 0.2 mm/d) for P. vulgaris, as shown by a colour change of the indicator broth. Penetration times were very variable, but the motility of P. vulgaris appeared to be of little consequence. 8 This penetration was reconfirmed by Khayat et al who used a similar experimental apparatus to Torabinejad et al , but they used mixed oral bacteria and measured broth turbidity rather than ph. They aimed to measure the time taken for bacteria in human saliva to penetrate 10 mm along laterally and vertically condensed root fillings. Mixed saliva from several students was collected every two days and applied to the coronal chamber until the lower chamber's broth became turbid. Positive and negative controls confirmed internal validity. India ink was then used after bacterial penetration to identify the distribution of any leakage paths. Penetration of laterally condensed (mean 28.8 d " 4.7 d, range 8 to 48 d) and vertically condensed (mean 25.4 d " 13.6 d, range 4-46 d) roots were similar, but all leaked within 48 d. Again this demonstrated the inadequacy of root fillings to seal their root canals in the laboratory. Obligate anaerobes predominate in endodontic reinfections and so Barrieshi et al decided that mixed Peptostreptococcus micros (Gram positive), Fusobacterium nucleatum (Gram negative rod) and Campylobacter rectus (Gram negative rod) would be more relevant tracers than aerobic microbes. They aimed to measure the presence and rate of travel of these different anaerobic bacterial species through laterally condensed obturated root canals. Five millimetre lengths of gutta percha were left remaining after post space preparation with a hot plugger. The root filled tooth was used to separate an upper chamber containing a suspension of the anaerobic bacteria from a lower chamber of Hank's balanced salt solution. The time taken for the lower chamber to become contaminated with each species, and the scanning electron microscope detection of bacteria in split samples of the teeth were measured. P. micros did not penetrate test teeth although it did go through all positive control teeth in 9 d. F. nucleatum and C. rectus penetrated all test specimens between 48 d and 84 d, and all three bacteria were seen by electron microscopy in the split teeth. It seems that obligate anaerobes are equally adept as facultative anaerobes at penetrating the gaps around and within laterally condensed root fillings. Sometimes temporary fillings leak or are lost completely while intracanal dressing are present. Saliva may wash out and dilute the canal medication, and allow bacterial recontamination. Siqueira et al tested whether the presence of either calcium hydroxide, camphorated paramonochlorophenol (CMCP) or a mixture of calcium hydroxide and CMCP in root canals could prevent viable bacteria in saliva in an upper chamber from penetrating through a tooth to a lower chamber filled with brain heart infusion broth. A cotton wool ball was placed coronally, but without a restoration. Infection of the broth was detected by its turbidity. Positive and negative controls were arranged. All canals leaked eventually. Specimens containing calcium hydroxide alone took a mean of 15 d (range 4 to 34 d), those with CMCP alone took a mean of 7 d (range 2 to 13 d) and those with a mixture of calcium hydroxide and CMCP took 17 d (range 4 to 34 d) to leak. It was advised that calcium hydroxide provided a longer antimicrobial action than CMCP against saliva in case of a coronal seal loss. This may not be applicable to patients where food and saliva flows would quickly displace the bulk of any dressings exposed to the mouth. The seal of temporary restorations have also been tested. Deveaux et al conducted an in vitro leakage test of a resin reinforced zinc oxide eugenol (Intermediate Restorative Material [IRM], Dentsply, NY, USA) a methacrylate material (Temporary Endodontic Restorative Material [TERM], Dentsply) and a gypsum and zinc oxide based material (Cavit, ESPE, Seefeld, Germany). They found that Cavit (3 mm thick, 1/13 leaked) and TERM (5 mm thick, 0/9 leaked) provided better seals than IRM (3 mm thick, 6/10 leaked) over the 12 d period against the Streptococcus sanguis (Gram positive facultative anaerobe) tracer with thermal cycling. Cavit linearly expands by 14% with setting and water sorption, taking up water equivalent to 9.6% of its own weight in the first 3 h. This water sorption expansion of Cavit was given as the reason for such a good seal. TERM also absorbs water after the initial shrinkage of polymerisation. Temporary restorations need durably to seal out oral fluids, and seal in medications. For this they must be impermeable, adapt well to the cavity walls, have sufficient compressive strength and abrasion resistance to withstand occlusion, and be Table 1. Tracer penetration tests of teeth containing coronal and root fillings. 2

4 REFERENCE TRACER / MEASURE FILLING TYPE RESULTS Bacteria Torabinejad et al Staphylococcus epidermidis GP root filling All leaked within d Proteus vulgaris " " All leaked within d Deveaux et al Streptococcus sanguis IRM temp. rest. 6/10 leaked within 12 d TERM " 0/9 leaked within 12 d Cavit " 1/13 leaked within 12 d Khayat et al Mixed saliva (bacteria) GP root filling Leaked within 4-48 d Barrieshi et al Peptostreptococcus micros " " Only partial penetration Fusobacterium nucleatum " " Leaked within d Campylobacter rectus " " " " Siqueira et al Mixed saliva (bacteria) Ca(OH) 2 Leaked within 4-34 d " " CMCP Leaked within 2-13 d " " Ca(OH) 2 + CMCP Leaked within 4-34 d Dyes Madison and Methylene blue dye GP root filling All specimens leaked Zakariasen Swanson and India ink Roth's sealer RF 33% linear leakage at 7 d Madison " " Sealapex RF 49% linear leakage at 7 d " " AH26 RF 80% linear leakage at 7 d McRobert and India ink Lateral Cond. RF 3.0 mm mean linear leakage Lumley " " Obtura RF 0.3 mm mean linear leakage " " AlphaSeal RF 4.9 mm mean linear leakage " " System B RF 0.5 mm mean linear leakage Fox and India ink Cast post + RF 2/10 leaked in 7 d Gutteridge " " Parapost + RF 0/10 leaked in 7 d " " Temporary post + RF 10/10 leaked in 7 d ( mm) Freeman Basic fuchsin 0.5% + loading Posts, cores and crowns 5/10 or 6/10 leaked in 3 groups Caliskan et al India ink (vacuum) Ca(OH) 2 + Diaket 3.2 ± 0.78 units " " CRCS + RF 2.0 ± 0.82 units Pai et al % basic fuchsin, 7 d Caviton (Ca 2SO 4) 0.92 ± 0.61 mm " " IRM 3.18 ± 1.31 mm " " Caviton + IRM 1.02 ± 0.29 mm Pressurised water Wu et al Pressurised water AH26 / Ultrafil 15/20 leaked " " AH26 / Ultrafil+10N 13/20 leaked " " Ketac Endo / Ultrafil 11/20 leaked " " Ketac Endo / Ultrafil+10N 10/20 leaked Fan et al " " RF + immediate post prep. 0/40 leaked " " RF + delayed post prep. 7/40 leaked Animal histological Friedman et al Bacteria/inflammation Sealer + Gutta Percha Inflam.: 3 none, 6 mild, 0 severe " " Gutta Percha only Inflam.: 3 none, 5 mild, 1 severe " " Sealer only Inflam.: 1 none, 5 mild, 3 severe " " Controls (No bacteria) Inflam: 6 none, 3 mild, 0 severe Human radiographic Ray and Trope Radiolucencies in/around Coronal Root % with no apical radiolucency fillings and periapex None None 91.4% None Yes 67.6% Yes None 44.1% Yes Yes 18.1% Results of some dental leakage studies demonstrating the generally inadequate seal of restorations and root fillings even under laboratory conditions. Clinical relevance of these data is largely unknown, although it can be concluded that the absence of leakage is unrelated to any pathogenesis. Abbreviations: Root filling (RF), Gutta Percha (GP), Intermediate Restorative Material (IRM), Temporary Endodontic Restorative material (TERM), Camphorated paramonochlorophenol (CMCP). See main text for manufacturers details. 3

5 unreactive with canal medications. Good aesthetics are also desirable. 2 Dye penetration studies Soluble dyes used as leakage tracers have been very common in the literature. Being soluble, their particle size is in the order of nanometres rather than the micrometres of bacteria, and could be regarded to represent bacterial substrates and products. Small tracers have been advised because the absence of leakage is known to be non-contributory to disease. 20 Methylene blue dye has the approximate width of a benzene ring, and has been used to test the seal of root fillings after post space preparation. Madison and Zakariasen aimed to test 0.2% methylene blue penetration of remaining laterally condensed gutta percha root fillings after post space preparation had been made with either engine driven reamers, heated endodontic pluggers or files with chloroform, either immediately or 48 h after obturation. The teeth were sectioned longitudinally and then the pieces dissolved in nitric acid. Measurements were made of both linear dye penetration from the coronal end and total dye mass using the spectrophotometric method. All the specimens leaked to some extent but there were no significant differences between any of the treatments for either linear or mass measurements. There was a weak correlation between linear and mass dye measurements. This report is an excellent example of the difficulty encountered when trying to interpret leakage test results, and shows well the inability of even statistical tests to deliver meaningful conclusions. 21 A further test of the ability of root fillings to seal when the coronal restoration was absent was conducted by Swanson and Madison Teeth were root filled, and then after 48 h storage were exposed to artificial saliva (1 mm CaCl 2, 3 mm NaH 2PO 4, 20 mm NaHCO 3) with their access cavities open for between 3 and 56 days. They were then immersed in India ink for 48 h, demineralised with 5% nitric acid and made transparent with methyl salicylate. Positive and negative controls also were instituted. Linear dye penetration lengths from the coronal end were then measured. No tracer entry into or past the root filling was seen unless artificial saliva had been applied, when there was then little difference in the amount of leakage (0 to 17 mm) with exposure time to artificial saliva. They speculated that Roth's sealer (Roth's, IL, USA) dissolution was important. The authors actually recognised and stated that the clinically relevant threshold amount of leakage was unknown. Such explicit recognition is mandatory but unusual in dental leakage studies. The same authors 6 then went on to test the leakage of three sealers: Roth's (zinc oxide and eugenol, Roths), Sealapex (calcium hydroxide, Kerr, Romulus, MI, USA and AH26 (epoxy resin, Dentsply) with the same method, but with exposure to artificial saliva for just 7 d. Mean linear percentage leakage for Sealapex specimens was 33%, for Roth's sealer specimens was 49% and for AH26 specimens was 80%. As the authors mentioned in their earlier paper, clinical significance remained uncertain, but clearly any intention to seal completely the root canals had not been met. The effect of obturation technique on root filling leakage was also investigated by McRobert and Lumley They compared coronal leakage of canals filled with the Obtura II (Obtura Corp., MO, USA), System B (Analytic Tech., Redmont, WA, USA), Alphaseal (NiTi Co, Chattanooga, TN, USA), or lateral condensation methods. After obturation, the teeth were exposed to India ink for 65 h and then cleared to measure linear dye penetration. The authors also compared radiographic density of the root fillings with leakage results, finding that fewer radiolucencies indicating fewer voids were related to less leakage. This seems rational and affirms the clinical intention of creating root fillings without radiographically visible voids. However, they correctly understood that even a radiographically voidless filling may still leak microscopically. As with other reports, variation was very high but Alphaseal specimens appeared to have more radiographic voids and leakage than System B and Obtura II specimens. The Obtura II group had the most specimens without any leakage. Contamination of root canal walls with residual endodontic dressings as root fillings are placed may be one reason for the generally observed poor seal. Caliskan et al tried to determine whether calcium hydroxide dressings may have this effect. Canals were dressed with water or glycerine suspensions of calcium hydroxide or nothing for 7 d before obturation by lateral condensation with either Diaket (ESPE) or Calcibiotic Root Canal Sealer (CRCS, Hygienic, Akron, OH, USA). The teeth were exposed to India ink for 7 d under vacuum, and then sectioned for linear ink penetration measurements from the apex. Other teeth were not obturated, but split after dressing removal, and viewed with scanning electron microscopy. While all groups including those not dressed showed apical leakage with high variations, specimens treated with water based calcium hydroxide paste and then Diaket generally leaked less. Perhaps ultrasonic agitation to remove dressings might make a cleaner canal surface for sealing. Pai et al investigated the leakage through the interfaces not only between temporary filling materials and tooth structure, but also with other permanent filling materials. Access cavities were filled with either amalgam (Valiant-PhD, Dentsply) or IRM (Dentsply). Then parts of these restorations were replaced with either Caviton (a gypsum based material, GC Dental, Tokyo, Japan), IRM or both Caviton and then IRM in a double layered seal. After 50 thermal cycles from 5EC to 55EC the teeth were immersed in 0.5% basic fuchsin at 37EC for 7 d and sectioned to allow linear measurement of dye penetration along the interfaces. Dye penetration in the interface between restorative materials was generally less than that between any of the materials and tooth structure. Variations were high though, and no material could be said to seal completely. At least a 3.5 mm depth of Caviton was advised to make a reliable seal, and here a 6 mm depth was used. In this study the double layered seal of Caviton and IRM sealed better than IRM alone, and should be encouraged. Many endodontically treated teeth are subsequently restored with endodontic posts and then crowns. Fox and Gutteridge investigated the leakage around 4

6 posts. This study aimed to compare the leakage around permanent cast posts cemented with zinc phosphate, permanent preformed stainless steel posts (Parapost, Coltene/Whaledent, NJ, USA) cemented with resin, and temporary aluminium posts (also Parapost) cemented with zinc oxide eugenol material. India ink with a mean particle size of 10 µm was applied for 7 d at 37 C and then the teeth were cleared with nitric acid and methyl salicylate. Linear ink penetration measurements were made from the coronal margin of the post. Only two of ten cast post specimens leaked compared with none of the preformed post specimens. All the temporary post specimens leaked, with a range of 1.47 to mm. While permanent post and cores may reduce coronal leakage, temporary posts may be inadequate and allow significant leakage. Clearly, temporary posts are likely to allow recontamination of root fillings and permanent prostheses should be placed as soon as practicable after endodontic therapy. Freeman went one step closer to a clinical simulation and measured leakage under post crowns with load cycling. Teeth were root filled and then the following posts were fitted. Preformed serrated Paraposts (Coltene/Whaledent), preformed threaded Flexi-posts (Essential Dental Systems, NJ, USA) and cast Paraposts (Coltene/Whaledent) with cores were all fixed with zinc phosphate cement. Crowns were cemented over the cores with the same cement, and a strain gauge fitted to the margin to detect any flexure between the crown and the root. This mobility was expected to indicate cement fracture before it was obvious macroscopically. The teeth were loaded with a cyclical 3.5 kg force some 72 times per minute until the strain gauge detected some crown movement. Then, an additional 100,000 cycles of a 1 kg force was applied with the tooth in 0.5% basic fuchsin dye. If still not macroscopically failed then the teeth were soaked without further loading in the dye for a further 24 h. Sections 1 mm apart were made by serial grinding to allow measurement of any linear dye penetration into the canal. Although variable (10 to 4970 cycles), there was no statistically significant difference in the number of cycles to initial failure for any of the post types, and again casts doubt on the usefulness of statistics with these small and variable specimen groups. Only four of the 30 teeth had failed macroscopically after loading in dye. At least four out of ten specimens with each post type experienced some leakage into the canal, typically by about 3 mm, but no significant differences between post types was detected. The main conclusion was that macroscopically intact post crowned teeth did still leak. The importance of a ferrule was emphasised. Pressurised liquid penetration studies Some authors considered that the amount of a tracer passing right through a specimen is a clinically relevant measure, although this has also not been demonstrated practically. Consequently, Wu et al used a pressurised water tracer to test the seal of root fillings created with molten gutta percha, Shrinkage of the gutta percha on cooling may lead to its poorer fit in the canal. Its compression with pluggers during cooling to reduce or fill these contraction spaces was tested. The standardised film thickness occurring between two loaded glass plates was also adjunctively tested for the two sealers used (Ketac Endo, ESPE and AH26, Dentsply). Five millimetre long root sections with 1.5 mm diameter canals were made and obturated with either a solid 1.5 mm diameter rod of gutta percha or molten gutta percha (Ultrafil, Hygienic). The molten gutta percha was either vertically condensed with a 10 N force or left uncondensed during solidification. The teeth were pressurised to 25 kpa above atmospheric pressure and any water flow measured in µl/d from the linear movement of a small bubble marker in a graduated constant diameter capillary tube. In other sectioned specimens, gaps between gutta percha and canal walls were measured. The leakage test showed similar water flow with heated uncondensed gutta percha irrespective of the sealer, but when condensed, Ketac Endo specimens leaked less than AH26 specimens. Gaps of 5 to 37 µm were found between condensed heated gutta percha and canal walls where sealer had not been used. Mean standardised cement film thicknesses were 29 µm for AH26 and 22 µm for Ketac Endo. It seems that Ketac Endo was the better sealer in this test, but again clinical relevance is difficult to establish. The seal of root fillings after post space preparation was also tested with the pressurised water method by Fan et al A test variable was whether post preparation was done with unset or solidified sealer cement. Human mandibular premolars were root filled with AH26 (Dentsply) or Pulp Canal Sealer (Kerr) using lateral condensation. Excess gutta percha was melted away and the softened remainder compressed vertically into the single canal. Then, the post spaces were created with 0.9 mm diameter Gates Glidden drills at about 5000 rpm to within 5 mm of the apices either immediately or one week later after the sealers had set. No leakage occurred for any specimen where the post space was prepared immediately, but seven of 40 specimens leaked where post preparation was done later. They then concluded that an aseptic (rubber dam and antiseptic irrigation) technique should be used for post space preparation. Histological and radiological animal studies In vivo animal studies are expected to avoid many of the limitations associated with laboratory studies, and so may have much greater relevance to the human clinical system than laboratory tests ever can. Accordingly, Friedman et al used dogs to test whether coronal bacterial leakage in vivo could be shown to be related with periapical periodontitis. Teeth in four dogs were endodontically prepared and obturated under aseptic conditions. Some teeth were obturated with sealer only, some with gutta percha only and some with both. Two weeks later the teeth were reopened to inoculate the root fillings with the dogs' own plaque, and then resealed. Positive control teeth were unobturated and inoculated, while for negative control teeth, some were obturated and others were left unfilled, but all were not inoculated. At times of up to 14 w the dogs were killed and their jaws histologically prepared to allow measurement of periradicular inflammation and bacterial presence. Radiographs were taken before and after a 14 w period. Bacterial colonies were detected within the root filling for 11 of 12 (four test and eight control) roots with severe inflammation. Bacteria were 5

7 seen in none of the 19 roots with mild inflammation and only one of the 15 roots with no inflammation. Periapical radiolucencies were only visible if severe inflammation was present. Whether canals were filled with just gutta percha, just sealer or both was not obviously related with periapical inflammation. Importantly, any inflammation was seen to occur within weeks of reinfection of root fillings. However, although root fillings failed to seal canals, they did allow less inflammation than if canals were empty. This indicates that the amount or rate of bacterial leakage, or the volume available for bacteria to multiply, is important. For dogs at least, it was concluded that coronal seal is crucial to the success of a root filling, second only to the initial disinfection of the root canal system. Human radiographic studies While dog studies provide a better simulation of the human condition than laboratory tests, there is no better simulation than that with real people. Hence, Ray and Trope conducted a retrospective human study in which a comparison was made of the occurrences of radiolucencies in coronal fillings, root fillings and periapical bone. The radiolucencies in filling materials were assumed to be macroscopic leakage paths, and those in bone were assumed to indicate the presence of periapical periodontitis. Although crude, these indirect measures were accepted to allow some comparison of leakage with periapical periodontitis for 1010 teeth treated at least one year previously. The reported distribution of periapical health with coronal and radicular filling voids (Table 1) is demonstrative. They calculated that a good root filling conferred a 4.3 times greater risk of periapical health than a poor root filling. However, a good coronal restoration conferred an 11.3 times greater risk of periapical health than a poor coronal filling. The sequential requirement for leakage to pass through both the crown and then the root filling was clear with 91.4% of periapical regions showing health when both fillings were without radiographic voids, but only 18.1% when both fillings contained voids. The design of this study is weak; it is retrospective and radiographic assessment of restoration seal is obviously of limited reliability. However, the data show such a difference that some real effect is likely to be operating. Conclusions The above studies repeatedly demonstrate that coronal and root fillings are generally incapable of reliably sealing against bacteria, dyes and pressurised water tracers in laboratory tests. Bacteria within root canals are related to periapical peridontitis in vivo. Such leakage is expected to lead to clinical failure but reported clinical success rates of 66% to 95% 25 do not confirm this, indicating that factors other than leakage dominate in the clinical system, or else the laboratory tests are at fault. 23 The poor clinical relevance and validity of laboratory dental leakage tests was poignantly stated seven years ago 20, but little improvement in the fundamental understanding of this difficult field has been evident in the literature since then. It seems that our theoretical understanding is still too inadequate to justify routine practical testing, and more attention should be directed towards identification of clinically relevant and good leakage measures. This must involve the practical comparison of dental leakage with clinical dental disease, ideally in the same clinical specimens over time. ACKNOWLEDGEMENTS The first draft of this paper was written while the author was enrolled in the Masters Program in Endodontics at the University of Melbourne directed by Professor Harold Messer. Professor Messer's invaluable advice with this paper and many other aspects of the author's training in endodontics is gratefully acknowledged. ADDRESS Correspondence should be addressed to: Martin Gale, Specialist Endodontist, The Endodontic Unit, The School of Dental Science, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, 711 Elizabeth Street, Melbourne, Victoria 3000, Australia. m.gale@dent.unimelb.edu.au 6

8 REFERENCES 1. Friedman S, Torneck C, Komorowski R, Quzounian Z, Syrtash P, Kaufman A. In vivo model for assessing the functional efficacy of endodontic filling materials and techniques. J Endodontics 1997;23: Deveaux E, Hildelbert P, Neut C, Boniface B. Bacterial leakage of Cavit, IRM, & TERM. Oral Surg, Oral Med, Oral Pathol 1992;74: Saunders WP, Saunders EM. Coronal leakage as a cause of failure in root-canal therapy: a review. Endod Dent Traumatol 1994;10: Madison S, Zakariasen K. Linear and volumetric analysis of apical leakage in teeth prepared for posts. J Endodontics 1984;10: Swanson K, Madison S. An evaluation of coronal microleakage in endodontically treated teeth. Part 1. Time periods. J Endodontics 1987;13: Madison S, Swanson K, Chiles SA. An evaluation of coronal microleakage in endodontically treated teeth. Part II. Sealer types. J Endodontics 1987;13: Torabinejad M, Ung B, Kettering JD. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endodontics 1990;16: Khayat A, Lee SJ, Torabinejad M. Human saliva penetration of coronally unsealed obturated root canals. J Endodontics 1993; 19: Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. International Endodontic J 1995;28: Barrieshi K, Walton R, Johnson W, Drake D. Coronal leakage of mixed anaerobic bacteria after obturation and post space preparation. Oral Surg, Oral Med, Oral Pathol, Oral Radiol, Endodontics 1997;84: Fox K, Gutteridge DL. An in vitro study of coronal microleakage in root-canal-treated teeth restored by the post and core technique. Int Endodontic J 1997;30: McRobert AS, Lumley PJ. An in vitro investigation of coronal leakage with three gutta-percha back filling techniques. Int Endodontic J 1997;30: Wu MK, De Gee AJ, Wesselink PR. Leakage of AH26 and Ketac Endo used with injected warm gutta percha. J Endodontics 1997;23: Caliskan MK, Turkun M, Turkum LS. Effect of calcium hydroxide as an intracanal dressing on apical leakage. International Endodontic J 1998;31: Freeman MA, Nicholls JI, Kydd WL, Harrington GW. Leakage associated with load fatigue-induced preliminary failure of full crowns placed over three different post and core systems. J Endodontics 1998;23: Siqueira JF, Lopes HP, de Uzeda M. Recontamination of coronally unsealed root canals medicated with camphorated paramonochlorophenol or calcium hydroxide pastes after saliva challenge. J Endodontics 1998; 24: Fan B, Wu MK, Wesselink PR. Coronal leakage along apical root fillings after immediate and delayed post space preparation. Endod Dent Traumatol 1999;15: Pai SF, Yang SF, Sue Wl, Chueh LH. Microleakage between endodontic temporary restorative materials placed at different times. J Endodontics 1999;25: Siqueira JF, Rocas IN, Lopes HP, de Uzeda M. Coronal leakage of two root canal sealers containing calcium hydroxide after exposure to human saliva. J Endodontics 1999;25: Wu MK, Wesselink PR. Endodontic leakage studies reconsidered. Part I. Methodology, application and relevance. Int. Endodontic J. 1993;26: Schuurs AHB, Wu MK, Wesselink PR, Duivenvoorden HJ. Endodontic leakage studies reconsidered. Part II. Statistical aspects. Int. Endodontic J. 1993;26: Roulet JF. Marginal integrity: clinical significance. J. Dentistry 1994(Suppl 1.);22:S9-S Gale MS. Dental filled resin restorations: seal integrity of the dentine bond. PhD Thesis, The University of Hong Kong Kakehashi S, Stanley HR, Fitzgerald, RJ. The effects of surgical exposures of dental pulps in germ free and conventional laboratory rats. Oral Surg, Oral Med, Oral Pathol. 1965;20: Carr, GB. Chapter 24. Retreatment. In: Eds. Cohen S, Burns, RC. Pathways of the pulp. (ISBN ) New York: Mosby. 1998: