Magnetic Resonance Imaging in Digital Dentistry: The Start of a New Era

In June 2024, at the European Congress of Dentomaxillofacial Radiology (ECDMFR) in Germany, the first-ever magnetic resonance imaging (MRI) system dedicated to dentistry was introduced. The MAGNETOM Free.Max Dental Edition (developed by Dentsply Sirona and Siemens Healthineers) is a groundbreaking advancement in dental imaging. On this occasion, it is only fit to have a glance at the fascinating history of MRI, specifically focusing on its applications in digital dentistry.

MRI has emerged as a cornerstone of modern medical diagnostics. Its non-invasive nature, lack of ionizing radiation, and exceptional soft tissue contrast make it an invaluable tool. MRI excels at distinguishing between various soft tissues without the need for contrast agents. This capability aids in early disease detection, precise tumor localization, and treatment planning. Additionally, MRI provides high-resolution images in multiple planes (sagittal, axial, and coronal), allowing clinicians to explore the human anatomy comprehensively. MRI does not employ ionizing radiation and thus is safe for children and pregnant women. It provides detailed images for assessing congenital anomalies, brain development, and pediatric tumors. In addition, due to its capability of detecting fluids and blood flow, MRI can be used for visualizing blood vessels without invasive procedures (known as MR angiography). Additionally, it allows for quantitative measuring of the fluid content within lesions, as demonstrated by diffusion-weighted imaging (DWI) [1]. Last but not least, functional MRI reveals not only a patient’s anatomy but also brain activity by tracking blood flow changes during cognitive tasks [2]. In summary, MRI’s versatility, safety, and ability to reveal both structure and function have elevated it to have a central role in modern medicine, impacting patient care across specialties.

In March 1973, Paul Lauterbur, then working at the State University of New York at Stony Brook, achieved a remarkable milestone: he published the first magnetic resonance (MR) image in the prestigious scientific journal Nature [3]. His pioneering work laid the foundation for what would become an indispensable diagnostic tool in medicine. In his experimental setup, Lauterbur placed two 1 mm diameter tubes filled with water inside a powerful 1.4T magnet. By applying magnetic field gradients that rotated successively by 45°, he obtained four different one-dimensional projections of the nuclear magnetic resonance (NMR) signal. He mathematically “back-projected” these four projections to reconstruct a two-dimensional tomographic image. The result was a spatial map of water distribution within the tubes. Shortly after his groundbreaking publication, Lauterbur extended his experiments to living organisms. His first living subject was a tiny clam. Although the resulting images were still crude, they marked the beginning of a new era in medical diagnostics [4].

Also in 1973, Peter Mansfield, from the University of Nottingham, demonstrated a groundbreaking technique for localizing the NMR signal on a slice-by-slice basis. His experimental setup involved stacking multiple 1 mm thick sheets of solid camphor inside an NMR spectrometer. By applying a magnetic field gradient perpendicular to the sheets, Mansfield measured the transient NMR signal response to an applied radiofrequency (RF) pulse. Mansfield used inverse Fourier transformation to reveal discrete layers of the camphor sample from the interference peaks observed in the signal. This technique allowed for precise localization of the NMR signal within the sample. Later in that decade, Mansfield collaborated with Andrew Maudsley to further refine this method. Their contributions paved the way for producing the image of a human body part, a finger of Maudsley in 1976.

Raymond Damadian, a physician and Associate Professor of Medicine at the State University of New York—Brooklyn (Downstate), approached NMR from an innovative perspective. In 1971, Damadian published a landmark paper in Science, where he demonstrated that cancer cells exhibited longer T1 and T2 values compared to normal cells [5]. His pioneering work hinted at the potential of NMR as a tool for probing the human body and diagnosing diseases. In 1972, Damadian filed a US patent application for an apparatus and method to detect cancer in tissue. The device his team created was named “Indomitable”. By July 1977, they achieved a groundbreaking milestone: the first whole-body MR images. Among these images was one showing the chest of Damadian’s assistant, Larry Minkoff. Remarkably, the image took nearly 5 h to produce. Damadian coined the term “field-focused NMR” to describe his imaging method [4]. Subsequent versions of MRI scanners incorporated the methods developed by Lauterbur and Mansfield, which allowed for faster and more practical clinical imaging, ultimately shaping the future of MRI. Lauterbur and Mansfield received the Nobel Prize in Medicine in 2003 for their contribution to developing MRI. Figure 1 provides a timeline of relevant events in the history of MRI and its applications in dentistry.

Dental professionals recognized the potential of MRI due to its ability to provide excellent soft tissue differentiation. However, the application of MRI in dentistry was limited, and conventional techniques like panoramic radiography and cone beam computed tomography (CBCT) remained the standard imaging methods [6,7,8], while MRI was primarily used for head and neck imaging, focusing on areas like the temporomandibular joint, airway, salivary glands, and soft tissue pathologies [9,10,11]. MRI offers advantages including non-ionizing radiation and soft tissue differentiation [12]. While acknowledging the exceptional diagnostic value of other imaging modalities, MRI stands unrivaled in its capacity to integrate anatomic imaging with quantitative tissue function evaluation across macroscopic, microscopic, and even molecular scales [13]. On the other hand, the challenges of incorporating MRI in day-to-day dentistry include the complex anatomy of the dentomaxillofacial region containing various hard and soft tissues as well as air- and fluid-filled cavities, the presence of metallic and motion artifacts, and its high cost and limited accessibility. While most day-to-day dental procedures are focused on hard tissues including teeth and alveolar bones, conventional MRI systems are not the best option for providing images of tissues with tightly bound hydrogen atoms, i.e., cortical bone, dentin, and enamel. Dental practitioners lack clear guidance on the beneficial indications for MRI and have limited access to MRI facilities in dental clinics and centers. However, ongoing efforts, involving the introduction of specialized sequences and equipment designed for dental imaging, with a focus on reducing acquisition time and overall costs, aim to integrate MRI into dentistry [13,14]. A recent literature review published in 2023 reported that in dental research, possible applications of MRI have been investigated for a variety of purposes, including cephalometry for orthodontics and dentofacial orthopedics, detecting dental pulp inflammation, characterizing periapical and marginal periodontal pathologies, identifying caries, and visualizing the inferior alveolar nerve, impacted teeth, and dentofacial anatomy for dental implant planning. Specialized protocols and dedicated coils enhance image quality, particularly for the intricate dentofacial structures [13]. Despite these attempts, many of these applications have remained in dental research. While promising, their practical implementation has faced challenges. Notably, a dedicated MRI machine specifically tailored for dental imaging had not been fully realized.

Things changed this June when the first MRI system dedicated to dentistry was introduced in Freiburg, Germany. According to the manufacturers, the device is designed to include a dental-dedicated receiver coil, enhancing patient setup and ensuring excellent image quality. Tailored scan protocols specific to dental indications simplify MR image acquisition. An automated focus view on dental anatomy provides crucial guidance to operators. This streamlined workflow aims for an in-room setup, scan time, and cleanup duration of 20 min or less, comparable to a dental CBCT scan. Additionally, the system has a significantly smaller footprint compared to existing MRI scanners (24 sqm) and incorporates virtually helium-free cooling technology, reducing infrastructure requirements. The newly developed device primarily targets dental schools and universities worldwide and the involved companies have made it clear that the workflow is designed with dentists in mind as operators and users [15]. Initial research has shown its promising features for radiation-free imaging for purposes such as third molar extraction, endodontics, temporomandibular disorders, orthodontics, and periodontitis [16].

The journey toward integrating MRI into routine dental practice involves overcoming challenges related to cost, accessibility, and imaging protocols. Researchers and clinicians continue to explore ways to optimize MRI for dentomaxillofacial diagnostics, with the ultimate goal of enhancing patient care and early disease detection. It is foreseeable that dental MRI will become an integral part of the routine digital workflow for various dental treatments, much like CBCT has become a staple in everyday dental practice, including prosthodontics [17,18,19]. To achieve optimal functional and esthetic outcomes in prosthodontic treatments, dental MRI can provide valuable insights. For instance, it allows for precise visualization of temporomandibular joint structures, aiding in the assessment of joint disorders, disc displacement, and degenerative changes. Additionally, dental MRI assists in evaluating the integrity of peri-implant soft tissues, detecting inflammation, and assessing bone quality around dental implants. Prosthodontic treatment planning often involves complex cases, such as full-mouth rehabilitation or implant-supported prostheses. Dental MRI can contribute to these treatments by revealing anatomical variations, identifying hidden pathology, and guiding the placement of implant abutments. Additionally, it facilitates the assessment of muscle function during mastication, which is crucial for designing occlusal schemes and achieving harmonious occlusion. Overall, integrating dental MRI into the digital workflow of prosthodontics promises enhanced diagnostics, personalized treatment, and improved patient outcomes.