Dental caries is ranked as the second disease that most widely affects the health of human populations [1], and it has a multifactorial and dynamic etiology [2]. The development of carious lesions results from an imbalance between the demineralization and remineralization of dental hard tissues, influenced by the frequent consumption of high-sugar foods and poor oral hygiene practices [3]. As carious lesions do not regress naturally and are not effectively treated with short-term pharmacological interventions, they can negatively affect individuals’ quality of life [4–10] and become the major cause of dental pain [5, 11, 12].
In the clinical setting, the diagnosis of dental caries can be challenging for clinicians due to the diverse characteristics of lesions at different stages of development; therefore, they require distinct treatment approaches [13]. Early lesions, known as white spots, are reversible and can be managed through noninvasive interventions such as fluoride therapy in association with control over sugar consumption [14]. Cavities, on the other hand, involve loss of the tooth structure and require moderately to highly complex restorative procedures, depending on the depth and severity of the lesion [15].
Recognizing and detecting the various stages of carious lesions, mainly the early ones, is crucial in this context, as it allows for early disease control and the implementation of treatment strategies using minimally invasive procedures [16] in order to preserve healthy tooth structures to the greatest extent possible [3, 17]. Also, detection of early carious lesions enables more conservative and cost-effective treatments, avoiding repetitive and complex treatments that could eventually lead to tooth loss [17].
Visual examination conducted in the dental office under artificial lighting with the aid of a blunt-tipped probe is still the main diagnostic method for the detection of carious lesions [13]. This reliable, noninvasive, cost-effective, and easily performed method allows detecting the initial stages of carious lesions [18]. Moreover, unlike other diagnostic methods, visual examination permits evaluating the activity, depth, and retention potential of carious lesions [15]. Some detection systems have been devised to preserve the sensitivity and high precision of this method, thus reducing the influence of the clinician’s experience during the procedure [19, 20]. The International Caries Detection and Assessment System (ICDAS), proposed by Ismail [21], has been widely used because it allows for the measurement of healthy and carious surfaces, including early lesions, encompassing multiple clinical aspects and providing a comprehensive assessment of tooth condition. Studies have shown that ICDAS has a diagnostic accuracy comparable to that of histological analysis in dental caries detection [22, 23]. Nevertheless, the accuracy of ICDAS relies directly on the clinician’s expertise and previous training [21].
Numerous auxiliary exams, such as radiographs, computed tomographic scans, transillumination, and histological analysis, can help detect carious lesions [22]. These methods, however, have major limitations for their clinical application and they show variable effectiveness in the detection of carious lesions, especially in earlier stages [25]. Hence, in recent years, there has been a growing demand for automated methods, such as convolutional neural networks (CNNs), which leverage deep-learning techniques to assist clinicians in detecting dental caries in the very first clinical signs [26–29].
CNNs are trainable algorithms capable of automating the detection of patterns and classifying changes by extracting data, such as shape, illumination, and color distribution, from images [30]. A large number of dental images can be utilized for CNN training, including radiographs [31, 32] and infrared transillumination images [33, 34], but intraoral photographs, regarded as the best diagnostic method for the detection of early carious lesions, closely resemble visual examination [35–42].
Assessing the effectiveness of CNN training based on dental images for the detection of dental caries is still incipient in dentistry, and to the best of our knowledge, only eight studies have addressed it [35–42] and only two studies have assessed the effectiveness of neural networks in the detection of early lesions [37, 38]. Despite the growing interest of researchers in automated detection of carious lesions, no studies have tested the use of CNN as a diagnostic aid by examiners with different levels of clinical experience. Therefore, the effectiveness of CNNs in dentistry should be further investigated by training a network capable of detecting early carious lesions and assisting clinicians in their diagnosis.
The aim of this study was to assess the application of CNNs in the detection and classification of health teeth and early carious lesions using occlusal images of extracted teeth, and to verify the effectiveness of neural networks as an auxiliary tool for the diagnosis of dental caries.