Virtual implant planning and fully guided implant surgery using magnetic resonance imaging-Proof of principle

Influence of clinical expertise and practical experience on transfer accuracy in guided dental implant placement - an in vitro study

PURPOSE

To investigate whether inexperienced users applying a static navigation system can perform in-vitro a fully guided implant placement protocol and achieve similar results in terms of accuracy compared to experienced clinicians.

METHODS

Based on 36 identical resin models, a computer-assisted implant planning was performed and a surgical guide was produced accordingly. Three study groups were composed with 12 operators, each: control group with experienced surgeons (DOC), test group 1 with dental technicians (TEC) and test group 2 with non-specialists (OFC). Using a fully guided drilling protocol, two implants were placed into each of the 36 models. Subsequently, the differences between the virtually planned and final implant positions were determined and the transfer accuracy was evaluated.

RESULTS

For the control group DOC, the mean value of axial deviation was 1.90 ± 1.15 degrees, for 3-dimensional deviation at the implant base 0.52 ± 0.33 mm, for 3-dimensional deviation at the implant tip 0.76 ± 0.39 mm and for vertical deviation at the implant tip - 0.11 ± 0.51 mm. For corresponding parameters, the mean values of test group TEC were 1.99 ± 0.87 degrees, 0.42 ± 0.21 mm, 0.68 ± 0.30 mm and - 0.03 ± 0.33 mm and for test group OFC 2.29 ± 1.17 degrees, 0.63 ± 0.35 mm, 0.89 ± 0.43 mm and - 0.24 ± 0.57 mm, respectively. The results did not reveal any statistically significant differences between the control and the 2 test groups (p˃0.05).

CONCLUSION

The results of the present in-vitro study demonstrated that inexperienced users applying a static navigation system can perform a fully guided implant placement protocol and achieve similar results in terms of accuracy compared to experienced clinicians in this specific in vitro setup.

Effect of magnetic resonance imaging protocol on decision-making for positioning of dental implants in edentulous cases

PURPOSE

This study aimed to assess the influence of magnetic resonance imaging (MRI) protocol on the decision-making for the positioning of dental implants in edentulous arches in comparison to planning based on cone beam computed tomography (CBCT).

MATERIALS AND METHODS

One phantom was scanned with CBCT and two MRI protocols (T1- and T2-weighted). Two calibrated examiners performed digital implant planning (coDiagnostiX, Dental Wings), considering a digital prosthetic planning and alveolar ridge surface scan. Four implants were planned for each patient dataset, and the angular deviation between the long axis of the implants and the prosthetic planning occlusal plane was measured.

RESULTS

Each examiner planned 40 implants, 12 implants with CBCT and 28 implants with MRI (16 with T1 and 12 with T2 images). Significant differences in angle deviation were observed between CBCT, T1, and T2 in the anterior region for both examiners (p = 0.009 for examiner 1 and p = 0.042 for examiner 2). Implants planned with CBCT showed significantly lower angular deviation than those based on the T1 and T2 scans for both examiners (p = 0.028 and p = 0.046 for examiner 1 and p = 0.028 and p = 0.027 for examiner 2). No significant difference in angular deviation was found between T1 and T2 for both examiners (examiner 1: p = 0.600, examiner 2: p = 0.916).

CONCLUSION

Compared to CBCT planning, the MRI protocol influenced decision-making for anterior dental implants, with angular deviations within acceptable clinical thresholds, but further studies are needed to validate these findings.

Magnetic resonance imaging for jawbone assessment: a systematic review

PURPOSE

To evaluate the accuracy of magnetic resonance imaging (MRI) for jawbone assessment compared to reference-standard measurements in the literature.

MATERIALS AND METHODS

An electronic database search was conducted in PubMed, EMBASE, Scopus, Web of Science, and the Cochrane Library in June 2022, and updated in August 2023. Studies evaluating the accuracy of MRI for jawbone assessment compared with reference-standard measurements (histology, physical measurements, or computed tomography) were included. The outcome measures included bone histomorphometry and linear measurements. The risk of bias was assessed by the Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS-2). The review was registered in the PROSPERO database (CRD42022342697).

RESULTS

From 63 studies selected for full-text analysis, nine manuscripts were considered eligible for this review. The studies included assessments of 54 participants, 35 cadavers, and one phantom. A linear measurement error ranging from 0.03 to 3.11 mm was shown. The accuracy of bone histomorphometry varies among studies. Limitations of the evidence included heterogeneity of MRI protocols and the methodology of the included studies.

CONCLUSION

Few studies have suggested the feasibility of MRI for jawbone assessment, as MRI provides comparable results to those of standard reference tests. However, further advancements and optimizations are needed to increase the applicability, validate the efficacy, and establish clinical utility of these methods.

Magnetic resonance imaging in dental implant surgery: a systematic review

PURPOSE

To comprehensively assess the existing literature regarding the rapidly evolving in vivo application of magnetic resonance imaging (MRI) for potential applications, benefits, and challenges in dental implant surgery.

METHODS

Electronic and manual searches were conducted in PubMed MEDLINE, EMBASE, Biosis, and Cochrane databases by two reviewers following the PICOS search strategy. This involved using medical subject headings (MeSH) terms, keywords, and their combinations.

RESULTS

Sixteen studies were included in this systematic review. Of the 16, nine studies focused on preoperative planning and follow-up phases, four evaluated image-guided implant surgery, while three examined artifact reduction techniques. The current literature highlights several MRI protocols that have recently investigated and evaluated the in vivo feasibility and accuracy, focusing on its potential to provide surgically relevant quantitative and qualitative parameters in the assessment of osseointegration, peri-implant soft tissues, surrounding anatomical structures, reduction of artifacts caused by dental implants, and geometric accuracy relevant to implant placement. Black Bone and MSVAT-SPACE MRI, acquired within a short time, demonstrate improved hard and soft tissue resolution and offer high sensitivity in detecting pathological changes, making them a valuable alternative in targeted cases where CBCT is insufficient. Given the data heterogeneity, a meta-analysis was not possible.

CONCLUSIONS

The results of this systematic review highlight the potential of dental MRI, within its indications and limitations, to provide perioperative surgically relevant parameters for accurate placement of dental implants.

Jawbone measurements of edentulous sites related to implant planning using magnetic resonance imaging compared to cone beam computed tomography: An ex vivo study

AIM

To compare measurements on images obtained by magnetic resonance imaging (MRI) and cone beam CT (CBCT) for height, width, and area in alveolar bone sites in human jaw specimens.

MATERIAL AND METHODS

Forty edentulous alveolar posterior sites in human cadaver specimens were imaged using CBCT scanners, and with zero-echo-time MRI (ZTE-MRI). Semi-automatic volume registration was performed to generate representative coronal sections of the sites related to implant planning. ZTE-MRI sections were also presented after grayscale inversion (INV MRI). Three observers measured bone height, bone width 5 mm from the alveolar crest, and bone area stretching from the width measurement to the top of the alveolar crest in the images. Interobserver agreement was assessed by intra-class correlation coefficients (ICC). The measurements were analyzed using two-way repeated measures ANOVA factoring observer and image type.

RESULTS

ICC was >0.95 for bone height, width, and bone area. No significant differences among observers (p = 0.14) or image type (p = 0.60) were found for bone height. For bone width, observer (p = 0.14) was not a significant factor, while ZTE-MRI produced width estimates that were significantly different and systematically smaller than CBCT-based estimates (p ≤ 0.001). Observer (p = 0.06) was not a significant factor regarding the bone area measurements, contrary to the imaging type where ZTE-MRI led to significantly smaller area estimates than CBCT (p ≤ 0.001).

CONCLUSION

Bone height measurements were essentially equivalent using CBCT and MRI. This was found regardless of grayscale choice for the MRI. However, ZTE-MRI resulted in smaller estimates of bone width and area.

Dental MRI-only a future vision or standard of care? A literature review on current indications and applications of MRI in dentistry

MRI is increasingly used as a diagnostic tool for visualising the dentoalveolar complex. A comprehensive review of the current indications and applications of MRI in the dental specialities of orthodontics (I), endodontics (II), prosthodontics (III), periodontics (IV), and oral surgery (V), pediatric dentistry (VI), operative dentistry is still missing and is therefore provided by the present work.The current literature on dental MRI shows that it is used for cephalometry in orthodontics and dentofacial orthopaedics, detection of dental pulp inflammation, characterisation of periapical and marginal periodontal pathologies of teeth, caries detection, and identification of the inferior alveolar nerve, impacted teeth and dentofacial anatomy for dental implant planning, respectively. Specific protocols regarding the miniature anatomy of the dentofacial complex, the presence of hard tissues, and foreign body restorations are used along with dedicated coils for the improved image quality of the facial skull.Dental MRI poses a clinically useful radiation-free imaging tool for visualising the dentoalveolar complex across dental specialities when respecting the indications and limitations.

Synergy between artificial intelligence and precision medicine for computer-assisted oral and maxillofacial surgical planning

OBJECTIVES

The aim of this review was to investigate the application of artificial intelligence (AI) in maxillofacial computer-assisted surgical planning (CASP) workflows with the discussion of limitations and possible future directions.

MATERIALS AND METHODS

An in-depth search of the literature was undertaken to review articles concerned with the application of AI for segmentation, multimodal image registration, virtual surgical planning (VSP), and three-dimensional (3D) printing steps of the maxillofacial CASP workflows.

RESULTS

The existing AI models were trained to address individual steps of CASP, and no single intelligent workflow was found encompassing all steps of the planning process. Segmentation of dentomaxillofacial tissue from computed tomography (CT)/cone-beam CT imaging was the most commonly explored area which could be applicable in a clinical setting. Nevertheless, a lack of generalizability was the main issue, as the majority of models were trained with the data derived from a single device and imaging protocol which might not offer similar performance when considering other devices. In relation to registration, VSP and 3D printing, the presence of inadequate heterogeneous data limits the automatization of these tasks.

CONCLUSION

The synergy between AI and CASP workflows has the potential to improve the planning precision and efficacy. However, there is a need for future studies with big data before the emergent technology finds application in a real clinical setting.

CLINICAL RELEVANCE

The implementation of AI models in maxillofacial CASP workflows could minimize a surgeon's workload and increase efficiency and consistency of the planning process, meanwhile enhancing the patient-specific predictability.

Buccal bone thickness assessment for immediate anterior dental implant planning: A pilot study comparing cone-beam computed tomography and 3D double-echo steady-state MRI

PURPOSE

To evaluate image quality and diagnostic accuracy of buccal bone thickness assessment in maxillary and mandibular anterior region using cone-beam computed tomography (CBCT) and 3-dimensional double-echo steady-state (DESS) MRI for preoperative planning of immediate dental implants in healthy individuals.

METHODS

One hundred and twenty teeth in 10 volunteers were retrospectively evaluated for image quality and artifacts using Likert scale (4 = excellent to 0 = decreased). Buccal bone thickness was measured at three measurement points (M1 = 2 mm from the cementoenamel junction, M2 = middle of the root, and M3 = at the root apex) for each tooth in the maxillary (13-23) and the mandibular anterior region (33-43). Descriptive statistics and two-way ANOVA with Tukey's Post-hoc test were performed to evaluate the significant differences (α = 0.05) between both imaging modalities.

RESULTS

Image quality showed little to no artifacts and enabled confident diagnostic interpretation (CBCT (3.72 ± 0.46); MRI (3.65 ± 0.49)), with no significant differences between both imaging modalities (p > 0.05). Regarding the assessment of buccal bone thickness at M1-M3 for the teeth 13-23 and 33-43, no significant differences were noted (p > 0.05). MRI demonstrated slight, nonsignificant overestimation of thickness with the canines having mainly a thick buccal bone wall, where thin buccal wall was evident for the central incisors.

CONCLUSION

Black bone MRI sequences, such as 3D-DESS MRI, for immediate implant planning provided confidential diagnostic accuracy in bone thickness assessment without significant disadvantages compared to CBCT. Thus, the implementation of no-dose protocols for dental rehabilitation using an immediate loading approach seems promising and could further improve the treatment strategy for dental rehabilitation.

SEMAC + VAT for Suppression of Artifacts Induced by Dental-Implant-Supported Restorations in Magnetic Resonance Imaging

The purpose of this study was to assess the feasibility of SEMAC + VAT to reduce artifacts induced by dental implant-supported restorations, such as its impact on the image quality. Dental-implant supported restorations were installed in a dry mandible. Magnetic resonance scans were acquired on a 3-Tesla MRI system. Artifact suppression (SEMAC + VAT) was applied with different intensity modes (weak, moderate, strong). Artifacts assessment was performed by measuring the mandible volume increase in MRI images prior (reference dataset) and after installation of dental implant-supported prosthesis. Image quality was assessed by two examiners using a five-point scale. Inter-examiner concordance and correlation analysis was performed with Cronbach's alpha and Spearman's test with a significance level at p = 0.05. Mandible volume increased by 60.23% when no artifact suppression method was used. By applying SEMAC + VAT, the volume increase ranged from 17.13% (strong mode) to 32.77% (weak mode). Visualization of mandibular bone was positively correlated with SEMAC intensity degree. SEMAC + VAT reduced MRI artifacts caused by dental-implant supported restorations. A stronger suppression mode improved visualization of mandibular bone in detriment of the scanning time.

Novel and accurate 3D-Printed surgical guide for mandibular reconstruction with integrated dental implants

PURPOSE

Patients with mandibular defects due to trauma or infiltrated disease are in a need of functional mandibular implants that will completely restore the function of their lower jaw. One of the most important roles of well-functioning jaw is mastication, a complex mechanism. A conventional approach used in oral and maxillofacial surgery accomplish this aim via two major surgeries- mandibular reconstruction and surgical placement of dental implants. Little work has been done on combining the two surgeries into with using Additive Manufacturing (AM) and digital planning.

MATERIAL AND METHODS

This case study offers a mandibular implant design solution with pre-positioned dental implants that can reduce the requirement to only one surgery. Mandibular implant was designed using 3-Matic software (Materialise, Belgium). Positions for dental implants were restoratively-driven and planned on the designed mandibular implant in Blue Sky Plan 4 software (Blue Sky Bio, USA) and placed prior to mandibular reconstruction using a 3D-printed surgical guide. Finite Element Analysis (FEA) was used to evaluate the mechanical behaviour of the 3D-printed surgical guide during dental implant placement.

RESULTS

The surgical guide was fabricated using SLA and stress distribution was evaluated in ANSYS Workbench FEM software (Ansys Inc Swanson, Houston, USA). Results showed that the designed surgical guide can withstand the forces occurring during the surgery.

CONCLUSION

The proposed method substantially reduces the surgical procedure and recovery time, increases the accuracy, and allows for a predictable restorative solution that can be visualised from the beginning.

A Novel Approach to Guided Implant Surgery: A Technical Note

Computer-guided software and kits have significantly improved the clinical applications of implant surgery. Nonetheless, some technical problems are still in evidence during clinical procedures because of cumbersome surgical tools that can limit access to implant sites, mainly in posterior areas of the mouth in the presence of bulky anatomical structures and in patients with reduced mouth-opening capacity. The present paper aimed to present a novel approach to guided implant surgery, describing the technical characteristics of an innovative guided surgical kit made up of modified sleeves and modular surgical drills. The proposed guided surgical kit is based on a novel patented system of sleeves and modular burs, with an increased length of the metal sleeves and a reduced height of the drills. The innovative design of the proposed system would allow the clinician to position guided fixtures in all clinical situations; the reduced encumbrance would be particularly helpful to gain access to the posterior areas of both maxilla and mandible, which have limited inter-arch space, with an easy and user-friendly approach. The modular system could overcome anatomical limitations, such as reduced mouth-opening capacity, and permit clinicians to maintain the stability and integrity of the surgical templates, even in cases where there is very limited intermaxillary space.

Artifacts in magnetic resonance imaging caused by dental materials: a systematic review

OBJECTIVES

The purpose of this systematic review was to search in literature in which severity unintended effects are caused by dental materials in magnetic resonance imaging (MRI), such as to evaluate whether these artifacts hamper the diagnosis in the head and neck region.

MATERIALS AND METHODS

Clinical studies showing the severity of artifacts which dental materials are capable of causing in MRI of head and neck, such as their influence on diagnostic accuracy, were included in this review. The searches were conducted in four electronic databases (PubMed/Medline, Embase, Scopus and Web of Science), and a manual search was made in the reference lists of papers screened for full-text reading. Risk of bias was assessed using "Quality Assessment Tool for Diagnostic Accuracy Studies-2" (QUADAS-2). The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) was used to assess the quality of evidence.

RESULTS

From 151 studies selected for full-reading, 19 were considered eligible for this review. Artifacts caused by orthodontic appliances were well-documented, and stainless steel brackets were the materials most likely to cause artifacts in MR imaging of head and neck. The literature was scarce for dental implants and restorations. Diagnoses within the oral cavity, but also those of the brain and craniofacial structures, were affected.

CONCLUSION

Artifacts caused by orthodontic appliances may affect the diagnosis in oral cavity and craniofacial structures. Data regarding dental implants and prosthodontics restorations were inconclusive. The severity of artifacts in MRI and their influence on diagnosis is dependent on dental material features, location in the oral cavity, and magnetic resonance parameters.

Reliability and accuracy of dental MRI for measuring root canal length of incisors and canines: a clinical pilot study

To evaluate whether high-resolution, non-contrast-enhanced dental MRI (dMRI) can reliably and accurately measure the canal length of incisors and canines compared with cone-beam computed tomography (CBCT). Three-Tesla dMRI was performed in 31 participants (mean age: 50.1 ± 14.2 years) with CBCT data. In total, 67 teeth were included (28 from the upper jaw and 39 from the lower jaw; 25 central incisors, 22 lateral incisors, and 20 canines). CBCT and dMRI datasets were reconstructed to visualize the root canal pathway in a single slice in the vestibulo-oral (V-O) and mesio-distal (M-D) direction. Root canal length was measured twice by two radiologists using dMRI and CBCT. Data were statistically analyzed by calculating intraclass correlation coefficients (ICCs) and performing Bland–Altman analysis. The reliability of dMRI measurements was excellent and comparable to that of CBCT measurements (intra-rater I/intra-rater II/inter-rater was 0.990/0.965/0.951 for dMRI vs. 0.990/0.994/0.992 for CBCT in the M-D direction and 0.991/0.956/0.967 for dMRI vs. 0.998/0.994/0.996 for CBCT in the V-O direction). According to Bland–Altman analysis, the mean (95% confidence interval) underestimation of root canal lengths was 0.67 mm (− 1.22 to 2.57) for dMRI and 0.87 mm (− 0.29 to 2.04) for CBCT in the M-D direction/V-O direction. In 92.5% of cases, dMRI measurements of canal length had an accuracy within 0–2 mm. Visualization and measurement of canal length in vivo using dMRI is feasible. The reliability of dMRI measurements was high and comparable to that of CBCT measurements. However, the spatial and temporal resolution of dMRI is lower than that of CBCT, which means dMRI measurements are less accurate than CBCT measurements. This means dMRI is currently unsuitable for measuring canal length in clinical practice.

Impact of radiographic field-of-view volume on alignment accuracy during virtual implant planning: A noninterventional retrospective pilot study

OBJECTIVE

To evaluate the impact of reducing the radiographic field-of-view (FOV) on the trueness and precision of the alignment between cone beam computed tomography (CBCT) and intraoral scanning data for implant planning.

MATERIALS AND METHODS

Fifteen participants presenting with one of three clinical scenarios: single tooth loss (ST, n=5), multiple missing teeth (MT, n=5), and presence of radiographic artifacts (AR, n=5) were included. CBCT volumes covering the full arch (FA) were reduced to the quadrant (Q) or the adjacent tooth/teeth (A). Two operators, an expert (exp) in virtual implant planning and an inexperienced clinician, performed multiple superimpositions, with FA-exp serving as a reference. The deviations were calculated at the implant apex and shoulder levels. Thereafter, linear mixed models were adapted to investigate the influence of FOV on discrepancies.

RESULTS

Evaluation of trueness compared to FA-exp resulted in the largest mean (AR-A: 0.10 ± 0.33 mm) and single maximum discrepancy (AR-Q: 1.44 mm) in the presence of artifacts. Furthermore, for the ST group, the largest mean error (-0.06 ± 0.2 mm, shoulder) was calculated with the FA-FOV, while for MT, with the intermediate volume (-0.07 ± 0.24 mm, Q). In terms of precision, the mean SD intervals were ≤0.25 mm (A-exp). Precision was influenced by FOV volume (FA<Q<A) but not by operator expertise.

CONCLUSIONS

For single posterior missing teeth, an extended FOV does not improve registration accuracy. However, in the presence of artifacts or multiple missing posterior teeth, caution is recommended when reducing FOV.

Inductively Coupled Intraoral Flexible Coil for Increased Visibility of Dental Root Canals in Magnetic Resonance Imaging

OBJECTIVES

Accurate visualization of dental root canals is vital for the correct diagnosis and subsequent treatment. This work assesses the improvement of a dedicated new coil for dental magnetic resonance imaging (MRI) in comparison to conventional ones in terms of signal-to-noise ratio (SNR) and visibility.

MATERIALS AND METHODS

A newly developed intraoral flexible coil was used to display dental roots with MRI, and it provides improved sensitivity with a loop design and size adjusted to a single tooth anatomy. Ex vivo and in vivo measurements were performed on a 3 T clinical MR system, and results were compared with conventional head and surface coil images. Additional comparison was performed with a modified fast spin echo sequence and a constructive interference in steady-state sequence.

RESULTS

Ex vivo, an SNR gain of 6.3 could be achieved with the intraoral flexible coil setup, and higher visibility down to 200 μm was possible, whereas the external loop coil is limited to 400 μm. In vivo measurements in a volunteer resulted in an SNR gain of up to 4.5 with an improved delineation of the root canals, especially for the branch tissue splitting of the mesial root canal into mesial-buccal and mesial-lingual.

CONCLUSIONS

In summary, we showed the feasibility of implementing a wireless coil approach with readily available dental practice materials for sealing and placement. Highly improved MRI scans can be acquired within clinically feasible scan times, and this might provide additional medical findings to supplement available x-ray images.

Geometric Reproducibility of Three-Dimensional Oral Implant Planning Based on Magnetic Resonance Imaging and Cone-Beam Computed Tomography

This study aimed to investigate the geometric reproducibility of three-dimensional (3D) implant planning based on magnetic resonance imaging (MRI) and cone-beam computed tomography (CBCT). Four raters used a backward-planning approach based on CBCT imaging and standard software to position 41 implants in 27 patients. Implant planning was repeated, and the first and second plans were analyzed for geometric differences regarding implant tip, entry-level, and axis. The procedure was then repeated for MRI data of the same patients. Thus, 656 implant plans were available for analysis of intra-rater reproducibility. For both imaging modalities, the second-round 3D implant plans were re-evaluated regarding inter-rater reproducibility. Differences between the modalities were analyzed using paired t-tests. Intra- and inter-rater reproducibility were higher for CBCT than for MRI. Regarding intra-rater deviations, mean values for MRI were 1.7 ± 1.1 mm/1.5 ± 1.1 mm/5.5 ± 4.2° at implant tip/entry-level/axis. For CBCT, corresponding values were 1.3 ± 0.8 mm/1 ± 0.6 mm/4.5 ± 3.1°. Inter-rater comparisons revealed mean values of 2.2 ± 1.3 mm/1.7 ± 1 mm/7.5 ± 4.9° for MRI, and 1.7 ± 1 mm/1.2 ± 0.7 mm/6 ± 3.7° for CBCT. CBCT-based implant planning was more reproducible than MRI. Nevertheless, more research is needed to increase planning reproducibility—for both modalities—thereby standardizing 3D implant planning.

Interdisciplinary management of skull base surgery

Skull base surgery remains one of the challenging areas in the field of cranio-maxillofacial surgery, otolaryngology and neurosurgery. Subsequent reconstruction of bone and soft tissue are an essential component to restore function and appearance after ablative surgery. Establishment of interdisciplinary tumor boards with presentation of the individual patient cases have become standard. Multiplanar reconstruction using MRI or CT imaging techniques combined with virtual 3D planning allow precise planning of the procedures. Intraoperative navigation helps for complete resection of malignant findings with safety margins; surgical approaches provide a good overview of the surgical site. Reconstruction using local flaps have a low complication rate with equally reliable results in reconstruction of small tissue defects. Free flap surgery makes reconstruction of large tissue defects possible. Alloplastic materials are alternatively used for reconstruction of bone defects. Based on selected patients, treatment algorithms and standard surgical procedures in extracerebral skull base surgery will be illustrated. Current techniques and new approaches will be discussed with emphasize on hard and soft tissue reconstruction.

Three-dimensional accuracy of partially guided implant surgery based on dental magnetic resonance imaging

OBJECTIVES

To measure in vivo 3D accuracy of backward-planned partially guided implant surgery (PGIS) based on dental magnetic resonance imaging (dMRI).

MATERIAL AND METHODS

Thirty-four patients underwent dMRI examinations. Tooth-supported templates were backward planned using standard dental software, 3D-printed, and placed intraorally during a cone beam computed tomography (CBCT) scan. Treatment plans were verified for surgical viability in CBCT, and implants were placed with guiding of the pilot drill. High-precision impressions were taken after healing. The 3D accuracy of 41 implants was evaluated by comparing the virtually planned and definitive implant positions with respect to implant entry point, apex, and axis. Deviations from the dMRI-based implant plans were compared with the maximum deviations calculated for a typical single implant.

RESULTS

Twenty-eight implants were placed as planned in dMRI. Evaluation of 3D accuracy revealed mean deviations (99% confidence intervals) of 1.7 ± 0.9mm (1.2-2.1mm) / 2.3 ± 1.1mm (1.8-2.9 mm) / 7.1 ± 4.8° (4.6-9.6°) for entry point / apex / axis. The maximum deviations calculated for the typical single implant surpassed the upper bounds of the 99% CIs for the apex and axis, but not for the entry point. In the 13 other implants, dMRI-based implant plans were optimized after CBCT. Here, deviations between the initial dMRI plan and definitive implant position were only in part higher than in the unaltered group (1.9 ± 1.7 mm [0.5-3.4 mm] / 2.5 ± 1.5 mm [1.2-3.8 mm] / 6.8 ± 3.8° [3.6-10.1°] for entry point / apex / axis).

CONCLUSIONS

The 3D accuracy of dMRI-based PGIS was lower than that previously reported for CBCT-based PGIS. Nonetheless, the values seem promising to facilitate backward planning without ionizing radiation.

Geometric accuracy of magnetic resonance imaging-derived virtual 3-dimensional bone surface models of the mandible in comparison to computed tomography and cone beam computed tomography: A porcine cadaver study

BACKGROUND

Providing accurate 3-dimensional virtual bone surface models is a prerequisite for virtual surgical planning and additive manufacturing in craniomaxillofacial surgery. For this purpose, magnetic resonance imaging (MRI) may be a radiation-free alternative to computed tomography (CT) and cone beam computed tomography (CBCT).

PURPOSE

The aim of this study was to assess the geometric accuracy of 3-dimensional T1-weighted MRI-derived virtual bone surface models of the mandible in comparison to CT and CBCT.

MATERIALS AND METHODS

Specimens of the mandible from porcine cadavers were scanned with (1) a 3-dimensional T1-weighted MRI sequence (0.6 mm isotropic voxel) optimized for bone imaging, (2) CT, and (3) CBCT. Cortical mandibular structures (n = 10) were segmented using semiautomated and manual techniques. Imaging-based virtual 3-dimensional models were aligned with a high-resolution optical 3-dimensional surface scan of the dissected bone (=ground truth) and global geometric deviations were calculated (mean surface distance [MSD]/root-mean-square distance [RMSD]). Agreement between the imaging modalities was assessed by equivalence testing and Bland-Altman analysis.

RESULTS

Intra- and inter-rater agreement was on a high level for all modalities. Global geometric deviations (MSD/RMSD) between optical scans and imaging modalities were 0.225 ± 0.020 mm/0.345 ± 0.074 mm for CT, 0.280 ± 0.067 mm/0.371 ± 0.074 mm for MRI, and 0.352 ± 0.076 mm/0.454 ± 0.071 mm for CBCT. All imaging modalities were statistically equivalent within an equivalence margin of ±0.3 mm, and Bland-Altman analysis indicated high agreement as well.

CONCLUSIONS

The results of this study indicate that the accuracy and reliability of MRI-derived virtual 3-dimensional bone surface models is equal to CT and CBCT. MRI may be considered as a reliable alternative to CT and CBCT in computer-assisted craniomaxillofacial surgery.

MRI for the display of autologous onlay bone grafts during early healing-an experimental study

OBJECTIVES

Autologous bone grafts are the gold standard to augment deficient alveolar bone. Dimensional graft alterations during healing are not known as they are not accessible to radiography. Therefore, MRI was used to display autologous onlay bone grafts in vivo during early healing.

METHODS AND MATERIALS

Ten patients with alveolar bone atrophy and autologous onlay grafts were included. MRI was performed with a clinical MR system and an intraoral coil preoperatively (t0), 1 week (t1), 6 weeks (t2) and 12 weeks (t3) postoperatively, respectively. The graft volumes were assessed in MRI by manual segmentation by three examiners. Graft volumes for each time point were calculated and dimensional alteration was documented. Cortical and cancellous proportions of bone grafts were assessed. The intraobserver and interobserver variability were calculated. Statistical analysis was performed using a mixed linear regression model.

RESULTS

Autologous onlay bone grafts with cortical and cancellous properties were displayed in vivo in eight patients over 12 weeks. The fixation screws were visible as signal voids with a thin hyperintense fringe. The calculated volumes were between 0.12-0.74 cm³ (t1), 0.15-0.73 cm³ (t2), and 0.17-0.64 cm³ (t3). Median changes of bone graft volumes of -15% were observed. There was no significant difference between the examiners (p = 0.3).

CONCLUSIONS

MRI is eligible for the display and longitudinal observation of autologous onlay bone grafts. Image artifacts caused measurements deviations in some cases and minimized the precise assessment of graft volume. To the knowledge of the authors, this is the first study that used MRI for the longitudinal observation of autologous onlay bone grafts.

Dental MRI: a road beyond CBCT

KEY POINTS

• Three-dimensional (3D) imaging coupled with computer-guided surgery planning is the core of the contemporary dental implant practice.• Magnetic resonance (MR)-based dental implant planning can achieve results comparable to those with cone beam computed tomography (CBCT)-based planning.• MR-based dental implant planning without radiation dose could be a potential alternative to CBCT-based planning.

Use of dental MRI for radiation-free guided dental implant planning: a prospective, in vivo study of accuracy and reliability

OBJECTIVES

To evaluate the accuracy and reliability of dental MRI for static guided implant surgery planning.

MATERIALS AND METHODS

In this prospective study, a 0.4-mm isotropic, artifact-suppressed, 3T MRI protocol was used for implant planning and surgical guide production in participants in need of dental implants. Two dentists decided on treatment plan. Surgical guides were placed intraorally during a subsequent reference cone beam computed tomography (CBCT) scan. Inter-rater and inter-modality agreement were assessed by Cohen's kappa. For each participant, dental MRI and CBCT datasets were co-registered to determine three-dimensional and angular deviations between planned and surgically guided implant positions.

RESULTS

Forty-five implants among 30 study participants were planned and evaluated (17 women, 13 men, mean age 56.9 ± 13.1 years). Inter-rater agreement (mean κ 0.814; range 0.704-0.927) and inter-modality agreement (mean κ 0.879; range 0.782-0.901) were both excellent for the dental MRI-based treatment plans. Mean three-dimensional deviations were 1.1 ± 0.7 (entry point) and 1.3 ± 0.7 mm (apex). Mean angular deviation was 2.4 ± 1.5°. CBCT-based adjustments of MRI plans were necessary for implant position in 29.5% and for implant axis in 6.8% of all implant sites. Changes were larger in the group with shortened dental arches compared with those for tooth gaps. Except for one implant site, all guides were suitable for clinical use.

CONCLUSION

This feasibility study indicates that dental MRI is reliable and sufficiently accurate for surgical guide production. Nevertheless, more studies are needed to increase its accuracy before it can be used for implant planning outside clinical trials.

KEY POINTS

• An excellent reliability for the dental MRI-based treatment plans as well as agreement between dental MRI-based and CBCT-based (reference standard) decisions were noted. • Ideal implant position was not reached in all cases by dental MRI plans. • For all but one implant site surgical guides derived from dental MRI were sufficiently accurate to perform implant placement (mean three-dimensional deviations were 1.1 ± 0.7 (entry point) and 1.3 ± 0.7 mm (apex); mean angular deviation was 2.4 ± 1.5°).

Evaluation of magnetic resonance imaging artifacts caused by fixed orthodontic CAD/CAM retainers-an in vitro study

Objectives

Magnetic resonance imaging (MRI) image quality can be severely impaired by artifacts caused by fixed orthodontic retainers. In clinical practice, there is a trend towards using computer-aided design/computer-aided manufacturing (CAD/CAM) retainers. This study aimed to quantify MRI artifacts produced by these novel CAD/CAM retainers.

Material and methods

Three CAD/CAM retainers and a stainless-steel retainer (“Twistflex”; clinical reference standard) were scanned in vitro at 3-T MRI using a high-resolution 3D sequence. The artifact diameters and three-dimensional artifact volumes (AV) were determined for all mandibular (AV_mand) and maxillary (AV_max) retainers. Moreover, the corresponding ratio of artifact volume to retainer volume (AV/RV_mand, AV/RV_max) was calculated.

Results

Twistflex caused large artifact volumes (AV_mand: 13530 mm³; AV_max: 15642 mm³; AV/RV_mand: 2602; AV/RV_max: 2235). By contrast, artifact volumes for CAD/CAM retainers were substantially smaller: whereas artifact volumes for cobalt–chromium retainers were moderate (381 mm³; 394 mm³; 39; 31), grade-5 titanium (110 mm³; 126 mm³; 12; 12) and nickel–titanium (54 mm³; 78 mm³; 12; 14) both produced very small artifact volumes.

Conclusion

All CAD/CAM retainers caused substantially smaller volumes of MRI artifacts compared to Twistflex. Grade-5 titanium and nickel–titanium CAD/CAM retainers showed the smallest artifact volumes.

Clinical relevance

CAD/CAM retainers made from titanium or nickel–titanium may not relevantly impair image quality in head/neck and dental MRI. Artifacts caused by cobalt–chromium CAD/CAM retainers may mask nearby dental/periodontal structures. In contrast, the large artifacts caused by Twistflex are likely to severely impair diagnosis of oral and adjacent pathologies.