ORIGINAL ARTICLE How does triangular-shaped radiolucency affect caries diagnosis? Najmeh Movahhedian 1 • Sadaf Adibi 1 • Hanie Sadat Tavakoli 2 • Hasan Baseri 3 Received: 9 December 2015 / Accepted: 13 March 2016 / Published online: 16 April 2016 Ó Japanese Society for Oral and Maxillofacial Radiology and Springer Japan 2016 Abstract Objectives Dental radiographs provide valuable infor- mation for dentists. However, during radiographic evalua- tion, dental practitioners may come across radiolucent shadows that closely mimic carious lesions and lead to false-positive diagnoses. Among these is triangular-shaped radiolucency (TSR), which can occur on the mesial surface of maxillary deciduous and permanent molars and arises from their anatomic structures. Because of its resemblance to dentinal caries, this study aimed to evaluate dental practitioners’ knowledge of TSR and the effect of clinical experience on TSR diagnosis. Methods Ninety-four observers (47 final-semester dental students and 47 dentists with [ 4 years of clinical experi- ence) evaluated four digital images of 11 extracted human teeth (nine deciduous molars and two first permanent maxillary molars), among which six proximal surfaces showed TSR. Histologic sectioning was used as the gold standard for differentiating between caries and TSR. Two oral and maxillofacial radiologists defined TSRs with agreement. Custom-made software was used for image display. Results Overall, 20 ± 9.34 % of observers mistakenly diagnosed TSR as a carious surface, 79.37 ± 10.53 % diagnosed it as a sound surface or Mach band effect, and only a few observers (0.53 ± 1.31 %) correctly diagnosed it as TSR. There was no significant difference between students and dentists for number of caries misdiagnoses of TSR (P = 0.859). Conclusions Dental practitioners and students have hardly any knowledge about TSR, leading to a considerable rate of false-positive caries diagnosis. It is highly likely that training dental practitioners in this phenomenon will improve their diagnostic performance and subsequent treatment plans. Keywords Triangular-shaped radiolucency Á False- positive diagnosis Á Clinical experience Introduction Dental radiographs are valuable complementary tools for clinical dental examination, and provide important infor- mation that would otherwise not be accessible for caries diagnosis [1, 2]. It is claimed that radiographs can help to increase the detection of proximal caries by at least twofold compared with clinical inspections [3]. Nevertheless, dur- ing radiographic evaluation, dental practitioners may come across deceptive radiolucent shadows that closely mimic carious lesions, thus leading to a false-positive diagnosis (FPD) and unnecessary treatments. Therefore, accurate interpretation of radiographs is of great importance and requires thorough knowledge of dental anatomy and pathologic processes [2, 4]. & Sadaf Adibi adibisa@sums.ac.ir Najmeh Movahhedian movahedian@sums.ac.ir 1 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Shiraz University of Medical Sciences, Ghasroddasht Street, Ghomabad Ave, Shiraz, Iran 2 Student Research Committee, School of Dentistry, International Branch, Shiraz University of Medical Sciences, Nader Kazemi Clinic, Valiasr Square, Shiraz, Iran 3 Department of Computer Engineering, Faculty of Engineering, Arak University, Arak University Sardasht Campus, Arak, Iran 123 Oral Radiol (2017) 33:32–37 DOI 10.1007/s11282-016-0243-y