Role of Intraoral Scanners in the Detection of Dental Caries: A Review
Correspondence Address :
Dr. Paras Mull Gehlot,
Reader, Department of Conservative Dentistry and Endodontics, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysuru, Karnataka, India.
Dental caries is an irreversible, microbial disease of the tooth which is characterised by demineralisation and dissolution of the hard tissues. Conventional methods such as visual and tactile examination, radiography, laser or light induced fluorescence methods help in the diagnosis of dental caries, though they lack sensitivity. Being an irreversible process, it is important to detect the caries process in its incipient stages. Very recently, intraoral scanners have also found their way through to the detection and diagnosis of dental caries, particularly, the incipient lesions. Use of advanced technology for the detection of dental caries in its incipient stages has enabled a change in the paradigm to minimally invasive dentistry which focuses more on a preventive approach to caries management. The present review paper attempts to summarise the available literature on the role of intraoral scanners in caries diagnosis by performing a online search on PubMed, Embase, SCOPUS and MEDLINE databases. Only full text studies authored in English and published in peer reviewed journals between 2010 and 2022 were included in the research. Keywords and terms from both review articles and original research papers were taken. A total of 36 papers were reviewed including full texts and abstracts.
Bitewing radiograph, Early enamel caries, Fluorescence, Near infrared radiation
Early identification of dental caries is still one of dentistry's most difficult tasks (1). The current protocol for the detection of dental caries relies on methods such as visual inspection, clinical and radiographic examination. These methods are known to have limited sensitivity and specificity which is a prerequisite to detect caries early on, when the tooth structure is still capable of remineralising. Recent advances in detection of caries include digital imaging, fibre optic transillumination, quantitative light/laser-induced fluorescence, tuned aperture computed tomography, ultrasound caries detector, Diagnodent (1).
The past decade saw the advent of the use of intraoral scanners in the field of dentistry and very recently its use in the detection of caries has been identified. Intraoral scanners are devices that use image sensors to acquire optical impressions of dentogingival tissues and then build point clouds using built-in scanning software (2). A laser or Light Emitting Diode (LED) light source facilitates the capture of surface topography of the intraoral tissues by the camera of the scanner. The images are then fed into a software that filters out aberrations before being fed into the manufacturing machine (3),(4).
TYPES OF INTRAORAL SCANNERS
Standalone scanners: These scanners convert intraoral scanning data into 3D models, which they either store as image files or finish the design using Computer-Aided Design (CAD) software (4) (Table/Fig 1).
All-in-one scanning platforms with Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) solutions: These scanners design the prosthetic appliances immediately from the optical impression. Hence, it is also called as ‘one-day treatment’ device (3) (Table/Fig 1).
MECHANISM OF ACTION
The various mechanisms of action of the intraoral scanner systems are demonstrated in (Table/Fig 2) (4),(5),(6).
ROLE OF INTRAORAL SCANNERS IN CARIES DETETCTION
Current methods for the diagnosis of dental caries have mainly relied on visual and tactile methods in combination with radiographic examination. However, each of these methods have a set of drawbacks which render them non ideal. With visual examination being highly subjective and technique sensitive, and exposure to ionizing radiation being an area of concern, there is a huge demand for newer imaging technologies that have an increased efficiency and accuracy for the early diagnosis of a carious lesion (7).
The current treatment concept in restorative dentistry mainly focuses on the early detection and diagnosis of caries in order to prevent and avoid an extensive intervention.
Near Infrared Imaging (NIRI) is a useful diagnostic tool for early detection of caries. The scanners based on NIRI use a light having a wavelength of 850 nm in the electromagnetic spectrum which on penetration and interaction with the tooth forms images which are based on the optical properties of the tooth due to the scattering, absorption and transmission of dental tissues in near infrared radiation wavelength (7),(8),(9). Various studies carried out previously demonstrate NIRI and bitewing radiography to have reproducible results (10),(11),(12). However, NIRI would serve to be further advantageous over bitewing radiography in terms of the use of non ionizing radiation.
The scanner systems capable of caries detection work on the principle of confocal laser scanning microscopy which is based on the concept of preserving and gathering the in-focus reflected light from the specimen and discarding the off-focus light (13).
Further, imaging technologies utilising this principle employ different sources of light for caries detection.
Near Infrared Transillumination Technology
The iTero Element 5D scanner (Table/Fig 3)a, and Planmeca Emerald S scanner (Table/Fig 3)c utilises this technology wherein sound enamel which is transparent to near-infrared radiation due to the limited scattering of light, appears as a dark area by allowing the light to pass through it entirely, whereas sound dentin, due to its orientation of the dentinal tubules, appears bright in a NIRI image due to enhanced scattering of light (14),(15). The iTero Element 5D produces a 3D model, 2D colour photographs, and NIRI images mapped to the 3D model after scanning the area of interest using an optical, non contact mode. However, in early enamel lesions, demineralised enamel would contain gaps that scatter light substantially in the near infrared region. The difference between optical properties of sound enamel, demineralised enamel and the contrast between sound enamel and demineralised enamel, illuminated with near infrared range light with wavelength of 480 nm, which is high, resulting in enamel lesions looking bright (16),(17) (Table/Fig 4).
Certain other caries detection scanner systems such as the 3Shape TRIOS 4 (Table/Fig 3)b utilise blue-violet light (415 nm) in contrast to near infrared range light (480 nm), which receive and detect fluorescence signals remitted from dental hard tissues. Such systems rest on a concept similar to the reliable quantitative light-induced fluorescence, allowing higher specificity and sensitivity in results compared to clinical visual examination and radiographic methods and are in fact seen to be comparable to histological assessment of caries detection (18),(19). Michou S et al., found only minor differences between in-vitro and in-vivo diagnostic performances of IOS devices, and concluded different approaches can be investigated for possible optimisation of the IOS devices in caries diagnosis (18).
When blue-violet light is illuminated onto a sound tooth surface, a portion of it is absorbed by fluorophores in the enamel and dentin and re-emitted at a longer wavelength as green fluorescent light. However, presence of demineralisation in the tooth causes the intensity of the green fluorescence to reduce and so the carious lesion appears dark on the fluorescent images (18),(19).
By collecting all of the colour information available on the 3D model and assessing any differences in colour signal intensity on the tooth surface, as well as fluorescence variations correlating to sound and demineralised tooth structure, four algorithms identifying red green fluorescence signals (Rfluo, Gfluo) were devised for the intraoral scanner systems - ALG1, ALG2, ALG3 and ALG4 [18,19]. The first three algorithms incorporate the fluorescent information i.e. (ALG1, ALG2, ALG3) while the last one, ALG4 is based on sound tooth colour information. For initial enamel caries, ALG1 and ALG4 were seen to be most accurate (0.70,0.69) and sensitive (0.74,0.71) whereas for caries extending into the outer and middle third of dentin, ALG3 and ALG4 were seen to be most accurate (0.87,0.86) and specific (0.88,0.86) (19).
Intraoral scanner systems have also utilised scoring systems that incorporated the red green fluorescent components on illuminated tooth surfaces into mathematical functions that help quantify the fluorescent signal (19).
f1 - Defined the ratio of red to green fluorescence at the examination sites and allowed quantification of severity of carious lesion.
f2 - The absolute green fluorescence measured at the examination site.
f3 - Defined the ratio of green fluorescence at the examination site and sound tooth surface and allowed quantification of demineralisation of the hard tissues.
f4 - Defined as the ratio of total red to green fluorescence at the examination site to the sound tooth surface.
Assessment of the specificity, sensitivity and accuracy of these functions, using histological evidence as a reference revealed highest collective specificity and sensitivity with f2, f3, and f4 while lowest was seen for f1 (19). Early detection of a carious lesion allows for preventive steps to be taken. To improve caries diagnosis, researchers have created better and newer approaches with more advanced and sensitive methods over time. (Table/Fig 5) includes various studies comparing intraoral scanners with other methods for incipient caries detection (10),(14),(20),(21),(22),(23),(24),(25),(26),(27),(28),(29).
Advantages and Disadvantages
The recent development of intraoral scanners as an aid for the detection of dental caries serve to be advantageous in early detection and intervention of incipient carious lesion and documentation for long-term follow-up. Also, they help in reducing chairside time and allow easier communication with the patient. However, its limitations can be described in terms of higher equipment costs, the need for a clear, isolated field and difficulty in the detection of caries around the restorative margins.
CURRENT CHALLENGES AND FUTURE PERSPECTIVES
Increasing adoption of dental technologies such as intraoral scanners for diagnosis and treatment planning have seemed to help both, dentists and patients alike in terms of treatment experiences. However, there is limited evidence on their efficiency in caries detection in patients. This could, in part, be due to its high cost, making it uneconomical for a clinical setup. There are various in-vitro and invivo studies that have proven intraoral scanners sensitive to detect initial caries which were corelatable with histological findings and have been accepted by standard caries research organisations such as European Organisation for Caries Research (ORCA), though not as gold standard or substitute but as an adjunct diagnostic aid (30).
Over the years, dentistry has undergone tremendous transformation from traditional, invasive methods to unconventional, reliable, minimalistic methods for caries detection. Increasing demand for highly sensitive methods of caries detection through intraoral scanners would not only allow a shift in the caries management protocol to conservative restorative procedures, but could also motivate dentists and patients to adopt caries preventive measures, owing to their high sensitivity.
By addressing one of the most challenging aspects of preventive dentistry, intraoral scanners have helped significantly in the diagnosis of incipient dental caries, enabling patients to avail preventive treatments. It also makes for a better medical experience by reducing patient discomfort, risks of cross infection and clinician’s chairside time. High adoption of intraoral scanners would be a huge step in the evolution of dental diagnosis, serving as efficient adjuncts to the conventional diagnostic aids.
The authors wish to thank Dr. Priyanka Keshav for the illustration and iTero®, 3Shape’s Trios and Planmeca for their product images.
Date of Submission: Jun 02, 2022
Date of Peer Review: Jul 01, 2022
Date of Acceptance: Aug 11, 2022
Date of Publishing: Oct 01, 2022
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? NA
• Was informed consent obtained from the subjects involved in the study? NA
• For any images presented appropriate consent has been obtained from the subjects. NA
PLAGIARISM CHECKING METHODS:
• Plagiarism X-checker: Jun 18, 2022
• Manual Googling: Aug 02, 2022
• iThenticate Software: Aug 08, 2022 (11%)
ETYMOLOGY: Author Origin
- Emerging Sources Citation Index (Web of Science, thomsonreuters)
- Index Copernicus ICV 2017: 134.54
- Academic Search Complete Database
- Directory of Open Access Journals (DOAJ)
- Google Scholar
- HINARI Access to Research in Health Programme
- Indian Science Abstracts (ISA)
- Journal seek Database
- Popline (reproductive health literature)