Oral Health Group

Detecting Caries at the Restoration Margins: Clinical Challenge, Technological Solution – The Canary System

July 1, 2014
by Stephen Abrams, DDS

There are many reasons for the replacement of restorations including esthetics, loss of anatomical form, fracture and loss. Secondary caries is, however, the major factor.1-3 The detection of secondary caries in its early stages is not easy,4 especially with current detection methods including radiography, explorer and visual examination.

Discoloration next to the restoration or ditched amalgam margins are not necessarily predictive of secondary caries.5 Bitewing radiographs may not be the ideal detection tool in detecting enamel secondary caries,6-8 particularly if they are located on the occlusal or smooth surfaces. The restoration also masks the ability of radiographs to detect caries along the preparation walls.9 All of these factors create clinical challenges for the practitioner.


There are various caries detection devices on the market today but they have their limitations, especially fluorescence-based devices. A number of studies have concluded that measuring fluorescence is not suitable for detecting caries around restoration margins or beneath dental sealants due to false positive readings.10-13 The CR Clinicians’ Report (March 2012) found that existing restorations interfered with readings.14 Further, fluorescence does not give any information about lesion size or depth, and does not penetrate beneath the tooth surface due to the scattering of light from stain, plaque, organic deposits and surface features such as pits and fissures.15,16

The Canary System, (Fig. 1) uses energy conversion technology (PTR-LUM) to image and examine the tooth. Pulses of laser light are aimed at the tooth, and the light is then converted to heat (Photothermal Radiometry or PTR) and light (luminescence or LUM), which are emitted from the tooth surface between pulses. These harmless pulses of laser light enable the clinician to examine sub-surface caries up to 5mm below the surface.17,18

FIGURE 1. The Canary System.

Caries modify the thermal properties (PTR) and glow (LUM) of healthy teeth. As a lesion grows, there is a corresponding change in the signal. In effect, the heat confined to the region with crystalline disintegration (dental caries) increases the PTR and decreases the LUM. As remineralization progresses and enamel prisms start to reform their structure, the thermal and luminescence properties begin to revert towards those of healthy tooth structure.19-21

The Canary System creates a Canary Number (ranging from 0–100) from an algorithm combining the PTR and LUM readings, which are directly linked to the status of the enamel or root surface crystal structure22 (Fig. 2). A Canary Number of less than 20 indicates healthy crystal structure. A Canary Number greater than 70 indicates a large lesion that may justify restoration. Canary Numbers falling between 20 and 70 indicate the presence of early carious lesions or cracks that may require restoration, particularly at restorative margins.23 If the caries is located beneath a healthy layer of enamel, the Canary measures both healthy tissue and caries. The healthy crystal structure overlying the caries dampens the signal, decreasing The Canary Number.

FIGURE 2. The Canary Scale.

Research has shown that The Canary System can detect caries around the margins of restorations.24-27 The following case report provides an excellent example of how The Canary System can be used to detect caries around the margins of restorations.

A 30-year-old male was seen at his re-care appointment complaining of pain in the left posterior teeth. Visual examination (Fig. 3) and bitewing radiography (Fig. 4) did not reveal any pathology. There was a brown stain associated with the mesial marginal ridge of the maxillary left second molar but otherwise, the restoration seemed intact.

FIGURE 3. Occlusal view of the maxillary second molar.

FIGURE 4. Bitewing radiographs left side.

The Maxillary Left First and Second Molars were scanned with The Canary System. The Canary scan of the second molar (Fig. 5) indicated caries in the brown pit at the mesial marginal ridge, caries along the buccal margin of the composite, and possibly caries along the lingual aspect of the mesial marginal ridge. The Canary Scan of the first molar (Fig. 6) indicated caries on the distal proximal contact as well as caries around the buccal margin of the amalgam. Since The Canary Scan taken at that time indicated that both restorations needed to be opened and investigated, no further scanning was needed.

FIGURE 5. Canary scan of the maxillary second molar.

FIGURE 6. Canary scan of the maxillary first molar.

On opening the mesial marginal ridge of the second molar, extensive caries was detected (Fig. 7) in the mesial contact area. Caries and leakage were also found on the buccal margin at the distal aspect of the tooth. Since the caries on the mesial aspect was located beneath a 4 mm thick ridge of enamel, The Canary Number was dampened but still indicated that a lesion was present.

FIGURE 7. Large caries found on the mesial aspect of the second molar and caries along the buccal margin.

On opening and removing the restorations on the maxillary first molar (Fig. 8), extensive caries were found along the walls of the amalgam and also in the interproximal region. In this situation, the caries was extensive in
both the mesial and distal areas. In the distal interproximal region, the caries was large, close to the occlusal surface and located towards the buccal aspect of the contact area resulting in a Canary Number of 61. On the mesial aspect around the margin of the amalgam, the caries was large with Canary Numbers of 57 and 66 on the buccal and lingual walls of the restoration. This is a good example of how The Canary System can scan and detect caries beneath intact enamel surfaces, around restorations and in interproximal contact regions. Even with intact enamel overlying the lesion, The Canary was able to detect caries which were not seen on the bitewing radiograph.

FIGURE 8. Large caries found on the mesial and distal aspects of the first molar.

Caries is a disease that results in the destruction of the crystal structure of the tooth. The ability to examine crystal structure integrity has a direct impact on the effectiveness of the treatment plan. Detecting caries around the margins of restorations and in interproximal regions is a challenging situation. Visual examination and radiography all have limitations in terms of their ability to detect, diagnose and monitor caries. While visual examination addresses the tooth surface, early lesions typically begin and grow beneath. Using an explorer to probe lesions is often inaccurate, and can damage tooth structure and inoculate the pits and fissures with oral bacteria. Dental radiographs can detect interproximal lesions, but only after they’ve demineralized at least 60% of the outer enamel shell. Even at this stage, they do not provide an accurate system to measure and monitor lesion size.

Fluorescence-based devices are designed to detect surface changes such as stain and bacterial by-products, but they are not capable of identifying early-stage pathological changes or cracks in crystal structure. The Canary System, uniquely powered by the energy conversion technology (PTR-LUM) has the ability to quantifiably identify defects in the structure of teeth. With this technology, dental clinicians for the first time have the ability to identify and measure crystal structure defects more accurately, and detect caries in clinically challenging situations.

Dr. Stephen Abrams is the President and Co-Founder of Quantum Dental Technologies which has developed The Canary System mentioned in this article. He has not received any compensation for the preparation of this article. OH

Stephen Abrams is a general dental practitioner with over 33 years of clinical experience. Upon graduation from the University of Toronto, Faculty of Dentistry in 1980, he established a group practice in Toronto Canada which has grown to involve both general dentists and dental specialists. He is a fellow of the Pierre Fauchard Academy, the Academy of Dentistry International and the American College of Dentistry. He is a member of the European Association for Caries Research and International Association of Dental Research. He has published over 90 articles in various international publications on topics ranging from early caries detection, and prevention to removable prosthetics and restorative dentistry. In 2002, Dr. Abrams was awarded the Barnabus Day Award from the Ontario Dental Association for 20 years of distinguished service to the dental profession. He can be contacted at (416)-265-1400 or email dr.abrams4cell@sympatico.ca

Disclaimer: Dr. Abrams founded Quantum Dental Technologies, a company developing laser-based technology for the early detection and ongoing monitoring of dental caries.

Oral Health welcomes this original article.


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17. Jeon, RJ., Phan TDT., Wu, A., Kulkarni, G., Abrams, SH., and Mandelis, A., “Photothermal radiometric quantitative detection of the different degrees of demineralization of dental enamel by acid etching”, Proc. 13th Int. Conf. Photoacoustic & Photothermal Phenomena, July 5 – 8, 2004, J. Physique IV France, 2005: 125: 721 – 723

18. Jeon R.J., Matvienko A., Mandelis A., Abrams S.H., Amaechi B.T, Kulkarni G. “Detection of interproximal demineralized lesions on human teeth in vitro using frequency-domain infrared photothermal radiometry and modulate
d luminescence”, J. BioMed. Optics, 2007; 12(3); 034028 1 – 13

19. Matvienko, A., Jeon, R. J., Mandelis, A., Abrams, S. H., Amaechi, B. T., “Photothermal Detection of Incipient Dental Caries: Experiment and Modeling”, Proc. of SPIE, 2007, 66759; 67590J-1 – 67590J-10

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22. Garcia, J., Mandelis, A., Abrams, S. H., Matvienko A., “Photothermal Radiometry and Modulated Luminescence: Application to Dental Caries Detection”, Chapter 71 page 1047, published in “Handbook of Biophotonics, Vol. 2: Photonics for Health Care” editors: Jürgen Popp (Editor), Valery V. Tuchin (Editor), Arthur Chiou (Editor), Stefan H. Heinemann (Editor) December 2011, Wiley-VCH

23. Abrams, S. H., Sivagurunathan, K., Jeon, R. J., Mandelis, A., Silvertown, J. D., Hellen, A., Hellen, W. M. P., Elman, G. I., Ehrlich, B. R., Chouljian, R., Finer Y., and Amaechi, B. T., “Multi-Center Clinical Study to Evaluate the Safety and Effectiveness of ‘The Canary System’ (PTR-LUM Technology)”. Caries Res. 2011; 45:174–242 [58th Annual ORCA Congress July 6–9, 2011, Kaunas, Lithuania].

24. Kim, J., Mandelis, A., Matvienko, A., Abrams, S. H., Amaechi, B. T., “Detection of Dental Secondary Caries Using Frequency – Domain Infrared Photothermal Radiometry (PTR) and Modulated Luminescence (LUM)”, International Journal of Thermophysics 2012 (December) 33: 1778 – 1786

25. Abrams, S. H., “Detecting Caries at the Margins of Restorations with The Canary System”, Dental Tribune 2012 (May); 6: 14

26. Kim, J., Mandelis, A. Matvienko, A. Abrams, S. H., Amaechi B. T., “Detection of Dental Secondary Caries Using Frequency-Domain Infrared Photothermal Radiometry (PTR) and Modulated Luminescence” (LUM) XVI International Conference on Photoacoustic and Photothermal Phenomena, November 2011

27. Wong, B., Abrams, S. H., Silvertown, J. D., Sivagurunathan, K., Klausze, R., Mandelis, A., Amaechi, B. T. “Detection of caries around ceramic crown restorations with The Canary System and DIAGNOdent”. ORCA Abstract # 86, Caries Res 2013;47:433-531 [60th ORCA Congress. July 3-6, 2013, Liverpool, UK].