Magnetic resonance imaging in dental implant surgery: a systematic review

In recent years, three-dimensional cross-sectional imaging and navigation have made dental implant placement a popular and well-established treatment modality in modern dentistry. Taking into account medical, economic, psychological and social aspects, dental implants stand out as the optimal long-term solution for the replacement of one or more teeth with high survival rates [1]. Nonetheless, many local and systemic factors, such as patient-specific, implant-related, surgical technique, and environmental factors, are relevant and key to the long-term success of dental implant surgery [2].

In the pursuit of a multidisciplinary, personalized, and minimally invasive treatment approach, the comprehensive initial preoperative evaluation of the implant site commonly includes both clinical and radiographic assessments. Typically, a two-dimensional X-ray-based panoramic radiograph (PAN) is performed initially and is sufficient for many cases. In high-risk cases where it is challenging to accurately visualize important surgical details such as the quality and quantity of osseous structures, nearby vulnerable anatomical structures, or other concomitant pathologies, three-dimensional imaging such as cone-beam computed tomography (CBCT) is recommended [3]. Widely recognized as the gold standard for oral and maxillofacial solid tissue imaging, CBCT has further consolidated its integral role in dental implantology by becoming the imaging technique of choice for virtual surgical planning and subsequent CAD/CAM template fabrication for guided implant surgery [4]. Although experienced surgeons can achieve comparable results with freehand implant placement techniques, the incorporation of advanced biomedical imaging into the clinical workflow in combination with surgical planning has led to better outcomes in terms of positional accuracy while simultaneously improving the protection of vulnerable adjacent anatomical structures [5]. However, the use of CBCT in dental implantology comes with certain drawbacks, including radiation exposure, higher costs, potential overdiagnosis and overtreatment, and susceptibility to image artifacts, mainly in the presence of dense materials such as metals [4]. The increasing use of 3D imaging with higher radiation doses [4] may be associated with an elevated lifetime risk of radiation-induced tumors, particularly among genetically predisposed adolescents [6, 7]. Even though the age of the population undergoing dental implant surgery is generally higher, this stochastic radiation effect should always be taken into account, considering the continuous striving towards reducing or even eliminating radiation exposure in biomedical imaging according to the As Low As Reasonably Achievable (ALARA) principle and the upcoming suggested paradigm shift towards the As Low As Diagnostically Acceptable (ALADA) principle using CBCT [8].

Recently, magnetic resonance imaging (MRI), a non-invasive, non-ionizing radiation imaging modality, has undergone significant advancements in a wide range of technical improvements coupled with the development of novel MRI sequences, positioning it as a leading imaging modality for the head and neck region, especially for the visualization of soft tissues [9]. Given the increasing application of MRI in the dental field, it also represents a valuable tool for indication-specific implementation in perioperative dental implant diagnostics and treatment planning [10]. The shift towards radiation-free imaging techniques could potentially lead to more robust imaging regarding artifact susceptibility when dealing with metal or ceramic dental implants [11]. However, this transition is associated with challenges, as the pursuit of diagnostic accuracy must not be compromised. Challenges of MRI in dental implantology include high cost, limited accessibility, motion-induced distortions, accurate differentiation of complex anatomy with various small-sized nerves and blood vessels, and image distortion due to magnetic field inhomogeneities caused by dental restorations [12]. However, dental MRI protocols developed in recent years have made it possible to overcome limitations in imaging bone structures, one of the most essential parameters in dental implant surgery, by using, e.g., black bone MRI sequences [13] or ultrashort echo time (UTE) sequences [14]. Furthermore, integrating innovations such as intraoral [15] or mandibular coils [16] combined with specialized dental MRI protocols has led to novel high-resolution, high-contrast imaging of dentomaxillofacial structures within short acquisition times. The MRI signals generated can be digitized and combined so that variably mineralized hard and soft tissues can be simultaneously depicted, illustrating the potential emerging for improving perioperative diagnostics in dental implant surgery [17].

This systematic review aims to comprehensively assess the existing literature regarding the rapidly evolving in vivo application of MRI in dental implant surgery, explicitly emphasizing newly developed dental MRI protocols and technical innovations. By systematically evaluating the available evidence, this review aims to highlight the potential benefits, indication-specific limitations, and current evidence-based case-specific guidelines of MRI in the context of dental implantology. Additionally, this review aims to investigate the novel MRI protocols and techniques that have been developed to enhance their performance in assessing osseointegration, peri-implant soft tissues, and surrounding anatomical structures relevant to implant placement by addressing the following research question: Does the use of dental MRI and newly introduced MR protocols and techniques, considering their potential advantages and limitations, provide a comprehensive set of perioperative quantitative and qualitative diagnostic information for dental implant surgery in healthy subjects and patients?

Numerous articles in the literature have investigated and evaluated the feasibility and accuracy of MRI in dental implantology, focusing on its potential to provide surgically relevant quantitative and qualitative parameters. Subsequently, the analysis in this review has focused on the impact of MR protocols and device-specific technical features in perioperative imaging, aiming to assess their indications and limitations and provide recommendations for the most appropriate decision-making. The results of this review highlight the significant contribution of dental MRI to the comprehensive assessment of surgically relevant clinical parameters of the implant site, including details of the osseous tissue structure, bone dimensions (height and width), proximity to the mandibular canal, respectively nerves and foramina, and delineation of the osseous boundaries of the maxillary sinus. This is particularly important in cases where conventional imaging techniques such as CBCT may be inadequate due to limitations in visualizing soft tissue structures.

For more than three decades, MRI has been used to image the pathoanatomy of the dentomaxillofacial region, allowing simultaneous radiation-free visualization of soft and hard tissues [20]. Several previously conducted clinical studies have demonstrated that MRI has the potential to be used for dental implant planning, even though the aspect of template-guided implant positioning was not initially considered [12, 21‐23]. Nonetheless, the long scan times of up to 30 min and suboptimal image quality with insufficient resolution at slice thicknesses of up to 4 mm have, until recently, proved unsuitable for daily clinical routine. However, the data obtained support that MRI using conventional MRI sequences (T1-weighted gradient‐echo (GE) and fast spin echo (SE) sequences) has been shown to provide similar, non-inferior information to CBCT or CT in the preoperative planning of dental implants [23, 24]. It should be noted that the conventional MRI protocols used in these studies allowed the acquisition of signals from nonmineralized soft tissues but could not directly visualize mineralized crystalline tissues such as teeth or bone, presenting them as dark voids or regions devoid of signal. In clinical practice, X-ray-based three-dimensional sectional imaging modalities, particularly CBCT, have established themselves as the gold standard for patient-specific preoperative virtual surgical planning, and the subsequent fabrication of CAD/CAM-generated drilling templates for guided implant surgery [4, 25]. The use of planning software enables the virtual positioning of implants, taking into account prosthetic and anatomical considerations and the available bone level so that the virtually planned implant position can be transferred to the surgical site with appropriate clinical accuracy [25]. However, with the increasing use of CBCT in medical imaging, potential concerns have been raised due to cumulative radiation exposure, resulting in an increased susceptibility to thyroid cancer and meningiomas [26, 27]. Ongoing research is still being conducted to understand further the exact relationship between radiation exposure and the implementation of X-ray-based scans in routine clinical dental procedures.

Recent developments advancing the field of dental imaging towards innovative MRI protocols optimized specifically for dental applications, along with the integration of dedicated novel coils, have enabled the acquisition of high isotropic 3D resolution, with significant improvement in resolution, signal-to-noise ratio, contrast-to-noise ratio, as well as significant reduction in acquisition times and effective suppression of artifacts [15, 28, 29]. As a result, MRI is emerging as a promising and reliable alternative to CBCT for dental implant surgery, both for accurate diagnosis and perioperative treatment planning, when indicated. Previous studies have shown that CT, CBCT, and MRI have excellent intermodal agreement for dimensional and positional measurements, including parameters such as bone height and width and bone dimensional volume [23, 29‐31].

Especially in the perioperative assessment of sinus lift surgery [32] or onlay bone grafting [33], excellent results seem to be obtained with a significant correlation between MRI and CBCT. Sinus floor elevation procedures showed the best intermodality agreement for sinus graft height, buccolingual width, and anteroposterior depth [32, 34], whereas onlay bone grafts allowed accurate longitudinal visualization, with image artifacts in some cases causing volumetric measurement deviations [33]. Thus, it can be concluded that MRI allows accurate assessment of the outcome of sinus floor elevation with high image quality and little or no artifacts. Mineralized dental tissue is challenging to depict using conventional MRI sequences due to its low proton density and biological composition, which limit the molecular motion of hydrogen nuclei within water molecules, coupled with rapid signal decay after radiofrequency excitation [35, 36]. For effective visualization of teeth and critical bony structures, such as the osseous boundaries of the maxillary sinus and mandibular canal, along with the inferior alveolar nerve, specialized sequences are required. These sequences should be capable of acquiring rapidly decaying signals, a feat achieved by implementing ultra-short echo time (UTE) and zero echo time (ZTE) techniques. These techniques offer the advantage of generating CT-like contrast while simultaneously enabling the visualizing soft tissue signals [37, 38]. Thereby, ultrashort hard pulse excitations and three-dimensional center-out radial sampling are utilized, resulting in high-quality imaging. Due to its ultra-short echo time, the UTE protocol is also particularly well suited for reducing metal or field inhomogeneity artifacts, highlighting its enormous potential in dental implant imaging [14]. Regarding the visualization of neural tissues, especially the continuous depiction of the trigeminal nerve and its peripheral branches, such as the inferior alveolar or lingual nerve, the combination of black bone MRI sequences, such as 3D-double echo steady state (DESS) sequences with novel mandibular coils provides excellent perioperative imaging of the surgical site [9], [39]. For high-risk procedures near vulnerable soft tissue anatomy, such as vessels, nerves, gingiva, and adjacent periodontal ligaments, DESS MRI could enhance the procedure's safety and improve patient outcomes. However, both CBCT and MRI can have limitations in terms of accurate visualization of the occlusal surfaces, which is required for precise tooth-guided implant positioning. Both in vitro and in vivo studies are currently demonstrating the feasibility and accuracy of the MRI-based approach regarding the accuracy of partially and fully guided dental implant surgery for the restoration of single-tooth gaps and for partially edentulous and edentulous mandibles [40, 41]. Probst et al. conducted a study to demonstrate the feasibility of 3D T1-weighted bone sequence and 3D T2-weighted short tau inversion recovery (STIR) MRI for computer-assisted template-guided 3D dental implant planning, which was achieved in three-quarters of cases, with the resulting deviation between the virtual planned and the actual implant position being clinically acceptable [13]. Another study supported the feasibility by effectively visualizing all anatomical structures relevant to implant placement comparing various MRI protocols, with 3D HR T1w TSE being superior and showed no significant differences compared to CBCT [31]. Hilgenfeld and colleagues conducted a study in 2020 to demonstrate the usefulness of a multi-slab acquisition with view-angle tilting gradient was used, based on a sampling perfection with application-optimized contrasts using different flip-angle evolution (MSVAT-SPACE) prototype sequence for implant planning and surgical guide fabrication. The MRI datasets were co-registered with the CBCT datasets to evaluate angular discrepancies between planned and surgically guided implant positions. For implant planning, inter-rater and inter-modality agreement for MRI-based treatment planning was excellent, but CBCT-based adjustments to MRI plans were required for implant position in 30% and implant axis in 7%, with almost all guides being suitable for clinical use [42]. Thereby, the mean three-dimensional deviations between MRI- and CBCT-based implant position were 1.1 mm at the entry point and 1.3 mm at the apex, with a mean angular deviation of 2.4°. Furthermore, another study integrating intraoral surface scanning and 3D printing into guided implant surgery has demonstrated the need for an imaging modality that can effectively and accurately visualize mucosal details [43]. However, another evaluation of MSVAT-SPACE-MRI compared to CBCT in assessing the geometric reproducibility of 3D implant planning using a backward planning approach showed higher reproducibility and inter- and intra-rater reliability for CBCT [44]. Obviously, MRI of the oral cavity is challenged by artifacts that may compromise the accuracy and quality of the acquired images due to the presence of dental restorations, depending on their composition and physical properties, field inhomogeneity, breathing, or tongue and deglutition movements [12]. Addressing and minimizing these artifacts is critical to the reliability and interpretability of dental MRI scans in the comprehensive assessment of dental implant therapy. Efforts are therefore being made to optimize MRI protocols, patient preparation, and technical software and hardware. However, in clinical practice, the presence of artifacts in all imaging modalities, including CT and CBCT, needs to be considered as dental restorations causing image artifacts are more prevalent in patients undergoing dental implant surgery due to their tendency to be older, which may affect the accuracy of transferring the surgical plan to the surgical site [45]. In CBCT imaging, metallic artifacts appear as black-and-white streaks, predominantly arising due to X-ray diffraction and photon starvation [46]. In the context of dental implant surgery, the challenge of metallic artifacts extends beyond implant materials themselves. Even the drilling procedures performed during surgery that result in metal debris can cause severe degradation of image quality, as they can become embedded in surrounding tissues [47]. Although artifacts in MRI may originate from similar sources, their underlying physical mechanisms, mainly due to magnetic field distortions, and their visual manifestation vastly differs from X-ray based imaging modalities. While the streak artifacts induced by CBCT are usually less severe in MRI, the presence of these artifacts can still compromise the diagnostic utility of images the images [48]. However, in contrast to titanium implants, zirconia implants showed minimal artifacts and were visualized together with the surrounding tissue with an accurate signal-to-noise ratio [30, 49]. Initial efforts have included the implementation of specific dental MRI protocols, including view angle tilting (VAT) and slice-encoding metal artifact correction (SEMAC) techniques, already successfully established in orthopedics [50] and neurosurgery [51], which have resulted in a reduction in metal artifacts and further improved image quality, but have been associated with a blurring effect [52, 53]. Similarly, in oncological imaging such as PET/MRI in the head and neck region, several studies have aimed to reduce metal artifacts from dental implants by applying deep learning-based assessment to predict the missing information [54]. The results showed promising performance of the proposed approach and reduction of artifacts in the completion of MR images affected by metal artifacts and/or body truncation in PET/MR imaging. Burger et al. developed another algorithm to reduce metal artifacts from dental implants in Dixon-based attenuation map generation using a multi-acquisition variable-resonance image combination sequence, showing robust results in all patients with a 70% reduction in artifact size, allowing MR image-based attenuation correction in critical areas, leading to improved diagnostics [55]. In addition, the use of lower magnetic field strengths in combination with dedicated intraoral or mandibular coils is a promising diagnostic approach that allows fixation of the patient's head and jaw, faster imaging and thus shorter examination times (up to three minutes), which plays a key role in reducing artifacts and making MRI a viable option for clinical applications [16]. However, further research and technological advancements, particularly in light of the ongoing shift toward the use of ultra-low field MRI are still needed to establish standardized approaches aiming at minimizing implant-related artifacts and enhancing the diagnostic potential of dental MRI.

While radiation-free dental MRI offers several advantages and new possibilities in implant dentistry, the results of this systematic review highlight the potential of several MRI protocols for planning, placement, and follow-up of dental implant rehabilitation, with comparable results to CBCT-based surgical planning. The ongoing transition to radiation-free dentomaxillofacial imaging should always consider well-defined case-specific indications and limitations. This approach aims to achieve the best possible patient outcome in a comprehensive, multidisciplinary coordinated, personalized and minimally invasive therapeutic approach. Given the existing heterogeneity in the literature regarding scan parameters and coils used, additional studies, including randomized control trials, are needed to evaluate comparisons between MRI and conventional radiography. Some studies in this systematic review focused on feasibility assessments using MRI alone, highlighting the need for further research. At the same time, adherence to radiation safety guidelines is essential to contribute to an evidence-based understanding of the effectiveness and impact of MR protocols on clinical outcomes. For future meta-analyses, standardization of study designs, outcomes, and methods across studies is essential to ensure a more homogeneous and comparable database. From today's perspective, dental MRI can be used on an indication- and patient-specific basis to replace or complement established X-ray-based imaging modalities such as CBCT or CT. The additional insights derived from soft-tissue information may have a positive impact on surgical planning. This, in turn, might allow better prediction of postoperative outcomes, leading to potentially safer surgical approach and minimizing postoperative discomfort or complications. However, with increased accessibility, improved cost-effectiveness and considering the improved benefit-risk ratio, the use of UTE or ZTE protocols with clinically acceptable acquisition times represents a promising alternative that can be used for oral rehabilitation planning, enabling advanced treatment options such as guided implantation.

In conclusion, this systematic review investigates the existing literature on the feasibility and accuracy of MRI in dental implantology. The analysis focuses on the impact of MR protocols and technical features and provides insight into their indications and limitations for perioperative imaging. The results emphasize the significant contribution of dental MRI in the assessment of critical clinical parameters, including osseous tissue structure, bone dimensions, and proximity to vital structures. While conventional X-ray-based imaging techniques remain the gold standard, Black Bone MRI and MSVAT-SPACE MRI protocols, which offer improved hard and soft tissue resolution and higher sensitivity in detecting pathologic changes compared to conventional X-ray-based modalities, may establish themselves as a valuable alternative in targeted cases where CBCT is insufficient. The results of this review indicate that further studies, including randomized control trials, are needed to evaluate the efficacy and impact of MRI protocols on clinical outcomes. Therefore, standardization of study designs is essential for future meta-analyses to ensure a homogeneous and comparable database. While the benefits of MRI in implant dentistry are currently being demonstrated, further research is needed to evaluate its long-term efficacy, cost-effectiveness, and broader applicability. However, implementing dental MRI into the perioperative workflow has the potential to redefine treatment strategies, increase precision, and improve patient outcomes while minimizing radiation exposure.