Device for measuring the residual bacterial burden during root canal treatments
Dr Rob Glen
In the UK alone, eight hundred thousand root canal treatments (RCT) are carried out each year, over 25% of which require revisions due to persistent infection within the root canal space. To date, it is impossible to establish if the root canal space is free from bacteria at the time of completion of this treatment. Currently clinicians estimate the bacterial load (BL) present in the root canal by means such as colour of removed dentine, smell, and absolute time of irrigation with disinfectants. Scientific literature shows however that the absence of bacteria favourably influences treatment outcome. The only current alternative technique is bacterial culture which requires up to a week for the growth response and might not be significant in case of inter-appointment reinfection. Furthermore, several endodontic pathogens are non-cultivatable. A method to directly measure the residual bacterial load would dramatically improve the modest 75% success rate of RCTs, saving clinician time and provider money while minimising patient suffering.
This new optical-based technique allows rapid detection of live bacteria within RCs (Fig. 1) and has been developed by a team of practicing dentists and physical scientists within the Faculty of Dentistry, Oral & Craniofacial Sciences. This highly sensitive and rapid (<3 min) test is based on fluorescence staining of biomaterial sampled using paper-points, conventionally discarded after drying the RC, and quantification of the BL using spectral-analysis. The method uses the a dye which fluoresces only when cleaved by cellular metabolic activity, making the measurements highly accurate on biofilms and significantly more sensitive than bacterial culturing. An initial proof of concept device has been built and tested successfully in a clinical pilot trial involving 65 patients. This trial measured a BL score, derived from bacterial fluorescence on the paper-point before final filling of the canal. Results indicated that 32% of canals show bacterial contamination prior to treatment completion. Patients were recalled after 12 months and a CBCT scan taken, from which independent experts made an accurate assessment of the success or failure of each RCT, yielding a global probability of failure in this trial of 15%. An optimised BL threshold was determined by correlation of this true clinical outcome and the BL measured prior to obturation. This shows that below the threshold, the probability of failure was 11%, while above it the probability of failure was 80%, demonstrating that the device could be used to reduce the probability of failure by a factor of about 8.
Two prototype readers have been developed comprising a cassette with an insert to hold the paper-point samples in place within the fluorescent agent and a cassette reader which receives the cassette which can hold up to 4 paper-point samples while avoiding cross-contamination (Fig. 3) and reads the fluorescence signal emitted by the sample following reaction. This clinically compatible device is easily incorporated into the existing endodontic treatment pathway, without requiring a significant change to practice and without the need of an external computer.
The device is best suited for use in general dentistry clinics which carry out RCT’s. The success rate in this sector is modest: <75% compared with that of expert endodontists (>90%). An increase in the success rate in this sector would bring increased performance and reputational benefit to these clinical practices. At present, most endodontic treatments require more than a single session to achieve completion of the root canal treatment, in many cases to check the outcome of the preparation. Successful development of the device would result in reduced time and cost to clinicians, patients and healthcare providers (whether national or private insurance schemes or out of pocket patient payment). it is also expected to decrease patient discomfort and increase patient convenience by reducing the time taken to achieve resolution and the number of visits required to complete treatment. The device will also improve clinicians’ confidence in committing to procedure completion such as filling and crowning.
This is a unique technology with patent protection, which should be of interest to a company with experience of commercialising dental devices, particularly those active in selling dental irrigation systems. A licensing opportunity is available to develop and sell a commercial device. The technology is at a stage where it is ready for industrial engineering by a licensee with suitable experience, and a route to shrink the current prototype to a small footprint device suitable for bench top location has been identified. Routes have been identified to develop a sealed system to apply the dye reagent to the paper-point and which can then be disposed of safely. Initial informal discussions of the concept with practising dentists have been highly positive, with no concerns about interruption to their current routines for RCT.
The American Association of Endodontists estimates that more than 15 million root canals are performed every year (2006 latest figures). There are approximately 186,000 dentists in the USA, most of who are in private practice and it would be expected that a majority would do at least basic RCT’s. A similar or possibly smaller number possibly can be applied to the EU. Overall an estimated 350,000 RCT practitioners may exist in the two territories, carrying out 30M RCT’s per annum. Revenue streams are indicated from both device and consumable materials (integrated cassette/reagent delivery unit). Indicative costing for both products have been made and found to be in an acceptable range.
Patent applications (published as WO2013024088A1) are granted in Europe, Japan and the USA.
Journal article in preparation and available under an NDA.
Fig. 1: (A) Root canal sampling followed by (B) rapid fluorescence staining and (C) optical detection of live cells. (D) Typical fluorescence image of the paper-point apex showing its autofluorescence and the stained live bacteria from a patient. The red circle shows the spectrometer’s sampling area.
Fig. 2: From left to right: Self-contained (no computer needed) research-grade prototype device with touch-screen, 3D model of the 3-sample cassette and 3 & 4 samples cuvette + 3D-printed insert cassette system.
Fig. 3: Potential commercial design of the sealed cross contamination-free cassette.