Can ultra-low-dose computed tomography reliably diagnose and classify maxillofacial fractures in the clinical routine?

Purpose: Maxillofacial trauma predominantly affects young adults between 20 and 40 years of age. Although radioprotection is a legal requirement, the significant potential of dose reduction in computed tomography (CT) is still underused in the clinical routine. The objective of this study was to evaluate whether maxillofacial fractures can be reliably detected and classified using ultra-low-dose CT. Materials and Methods: CT images of 123 clinical cases with maxillofacial fractures were classified by two readers using the AOCOIAC software and compared with the corresponding results from post-treatment images. In group 1, consisting of 97 patients with isolated facial trauma, pre-treatment CT images at different dose levels (volumetric computed tomography dose index: ultra-low dose, 2.6 mGy; low dose, <10 mGy; and regular dose, <20 mGy) were compared with post-treatment cone-beam computed tomography (CBCT). In group 2, consisting of 31 patients with complex midface fractures, pre-treatment shock room CT images were compared with post-treatment CT at different dose levels or CBCT. All images were presented in random order and classified by 2 readers blinded to the clinical results. All cases with an unequal classification were re-evaluated. Results: In both groups, ultra-low-dose CT had no clinically relevant effect on fracture classification. Fourteen cases in group 2 showed minor differences in the classification code, which were no longer obvious after comparing the images directly to each other. Conclusion: Ultra-low-dose CT images allowed the correct diagnosis and classification of maxillofacial fractures. These results might lead to a substantial reconsideration of current reference dose levels.

Comparability of dental implant site ridge measurements using ultra-low-dose multidetector row computed tomography combined with filtered back-projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction.

OBJECTIVE: To assess the linear measurements of edentulous ridges recorded from multidetector row computed tomography (MDCT) images obtained by a previously untested ultra-low dose in combination with filtered back-projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR). METHODS: Three cadavers were imaged using a reference protocol with a standard dose and FBP (volume CT dose index (CTDIvol): 29.4 mGy) and two ultra-low-dose protocols, LD1 and LD2 (CTDIvol: 0.53 and 0.29 mGy). All test examinations were reconstructed with FBP, ASIR 50, ASIR 100, and MBIR. Linear measurements from the images of the edentulous ridges recorded from the test protocols were compared with those from the reference using a one-sample t test, Bland-Altman plots, and linear regression. Statistical significance was set at a p value of 0.05. RESULTS: The one-sample t test demonstrated a statistically significant difference between the measurements from the reference protocol and all test protocols. The difference was not clinically significant for the following three test protocols: LD1/FBP, LD1/ASIR 50, and LD2/FBP. Bland-Altman plots with linear regression showed no systematic variation between the measurements obtained with the reference protocol and these three test protocols. CONCLUSIONS: The lowest-dose protocol to demonstrate comparable measurements with a standard MDCT dose was CTDIvol 0.29 mGy with FBP. These results must be considered with caution for areas of the jaws with thin cortication. The results in areas of thin cortication should be verified by studies with larger sample sizes at such areas and comparison with true gold standard measurements.

Accuracy of computer-aided design models of the jaws produced using ultra-low MDCT doses and ASIR and MBIR.

PURPOSE: To compare the surface of computer-aided design (CAD) models of the maxilla produced using ultra-low MDCT doses combined with filtered backprojection (FBP), adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) reconstruction techniques with that produced from a standard dose/FBP protocol. METHODS: A cadaveric completely edentulous maxilla was imaged using a standard dose protocol (CTDIvol: 29.4 mGy) and FBP, in addition to 5 low dose test protocols (LD1-5) (CTDIvol: 4.19, 2.64, 0.99, 0.53, and 0.29 mGy) reconstructed with FBP, ASIR 50, ASIR 100, and MBIR. A CAD model from each test protocol was superimposed onto the reference model using the 'Best Fit Alignment' function. Differences between the test and reference models were analyzed as maximum and mean deviations, and root-mean-square of the deviations, and color-coded models were obtained which demonstrated the location, magnitude and direction of the deviations. RESULTS: Based upon the magnitude, size, and distribution of areas of deviations, CAD models from the following protocols were comparable to the reference model: FBP/LD1; ASIR 50/LD1 and LD2; ASIR 100/LD1, LD2, and LD3; MBIR/LD1. The following protocols demonstrated deviations mostly between 1-2 mm or under 1 mm but over large areas, and so their effect on surgical guide accuracy is questionable: FBP/LD2; MBIR/LD2, LD3, LD4, and LD5. The following protocols demonstrated large deviations over large areas and therefore were not comparable to the reference model: FBP/LD3, LD4, and LD5; ASIR 50/LD3, LD4, and LD5; ASIR 100/LD4, and LD5. CONCLUSIONS: When MDCT is used for CAD models of the jaws, dose reductions of 86% may be possible with FBP, 91% with ASIR 50, and 97% with ASIR 100. Analysis of the stability and accuracy of CAD/CAM surgical guides as directly related to the jaws is needed to confirm the results.

Localization of the inferior alveolar canal using ultralow dose CT with iterative reconstruction techniques.

OBJECTIVES: To compare subjective and objective localization of the inferior alveolar canal (IAC) on multidetector CT (MDCT) images obtained by ultralow doses in combination with the reconstruction techniques of filtered backprojection (FBP), adaptive statistical iterative reconstruction (ASIR), or model-based iterative reconstruction (MBIR) as compared to standard dose MDCT and FBP. METHODS: Three cadavers were imaged with a reference standard dose MDCT examination (volume CT dose index: 29.4 mGy) reconstructed with FBP and 5 low dose protocols (LD1-5) (volumeCT dose index: 4.19, 2.64, 0.99, 0.53, 0.29 mGy) reconstructed with FBP, ASIR 50, ASIR 100, and MBIR. Linear measurements from the crest of the ridge to the roof of the IAC were recorded. The results from the test protocols were compared with those from the reference using Bland-Altman plots. RESULTS: Only three test protocols allowed the identification of the position of the IAC on all the sample sites: LD1/FBP and LD1/ASIR 100 and LD2/FBP. All three protocols allowed identification of the IAC with comparable results to the reference dose protocol; the 95% confidence interval limits for the measurement differences were ± 0.41 mm, but the differences were not statistically significant. The calculated effective dose for the LD2 protocol, for a scan length of 5 cm, was 27.7 µSv. CONCLUSIONS: Using FBP, comparable IAC measurements were achieved with 91% reduction in dose compared with a standard exposure protocol. The use of ASIR and MBIR did not improve identification of the IAC in MDCT low dose images.

Human papillomavirus prevalence in a Mid-European oral squamous cell cancer population: A cohort study.

OBJECTIVES: Human papillomavirus infection has been investigated intensively regarding oropharyngeal carcinoma. However, there is still lack of knowledge about the impact of oral HPV infections concerning oral squamous cell carcinoma. This study investigates the prevalence of oral HPV infection in such patients, identifying possible differences between HPV+ and HPV- patients. SUBJECTS AND METHODS: One hundred and six consequent patients were investigated. After completion of a study questionnaire regarding risk factors, a brush smear sample was taken in each subject to identify the individual oral HPV status (overall/low risk/high risk). RESULTS: About 35.8% of the patients were tested positive for HPV in the oral cavity (14% low risk, 28.3% high risk). Patients with oral HPV infection and high-risk HPV infection were significantly younger (p < 0.001) and had a higher alcohol consumption (p = 0.0075 resp. p = 0.0022). A high number of different sexual partners were significantly correlated with any type of HPV infection. At last, patients with high-risk oral HPV infection had experienced more tooth extractions during their lifetime. CONCLUSION: Oral HPV infections may influence the course of disease of oral squamous cell carcinoma as HPV+ patients are about 10 years younger. It seems that high alcohol consumption facilitates high-risk HPV infection. It may be presumed that both alcohol consumption and high-risk oral HPV infection act synergistically, explaining earlier cancer onset.

Do Ultra-Low Multidetector Computed Tomography Doses and Iterative Reconstruction Techniques Affect Subjective Classification of Bone Type at Dental Implant Sites?

PURPOSE: To investigate whether ultra-low-dose multidetector computed tomography (MDCT) combined with the reconstruction techniques filtered backprojection (FBP), adaptive statistical iterative reconstruction (ASIR), or model-based iterative reconstruction (MBIR) alters the subjective classification of revised Lekholm and Zarb (LZ) bone types at prospective dental implant sites. MATERIALS AND METHODS: Three cadavers underwent a reference MDCT examination using a standard dose volume (CT dose index [CTDIvol]: 29.4 mGy) and reconstructed with FBP in addition to five test protocols (LD1-LD5) using ultra-low doses (CTDIvol: 4.19, 2.64, 0.99, 0.53, and 0.29 mGy, respectively) and reconstructed with FBP, ASIR 50, ASIR 100, and MBIR. Transverse cross-sectional images of the jawbones were obtained, and three examiners subjectively classified the bone type in each image using the revised LZ classification. The bone type classifications obtained using the reference examination were compared with those obtained from the test protocols for each examiner, and kappa statistic was used to analyze the level of agreement between the reference and test protocols. The clinical significance of the differences was analyzed with Wilcoxon signed rank test. RESULTS: Examiners 1 and 2 found moderate to strong agreement between the reference and test protocols, while Examiner 3 found strong to almost perfect agreement (P < .001). The Wilcoxon signed rank test did not demonstrate a clinical significance of the differences between the reference and test protocols for any of the three examiners. CONCLUSION: MDCT dose reductions of up to 99% did not significantly alter the subjective classification of bone at dental implant sites.

Spatial and contrast resolution of ultralow dose dentomaxillofacial CT imaging using iterative reconstruction technology.

OBJECTIVES: The objective of this study was to determine how iterative reconstruction technology (IRT) influences contrast and spatial resolution in ultralow-dose dentomaxillofacial CT imaging. METHODS: A polymethyl methacrylate phantom with various inserts was scanned using a reference protocol (RP) at CT dose index volume 36.56 mGy, a sinus protocol at 18.28 mGy and ultralow-dose protocols (LD) at 4.17 mGy, 2.36 mGy, 0.99 mGy and 0.53 mGy. All data sets were reconstructed using filtered back projection (FBP) and the following IRTs: adaptive statistical iterative reconstructions (ASIRs) (ASIR-50, ASIR-100) and model-based iterative reconstruction (MBIR). Inserts containing line-pair patterns and contrast detail patterns for three different materials were scored by three observers. Observer agreement was analyzed using Cohen's kappa and difference in performance between the protocols and reconstruction was analyzed with Dunn's test at α = 0.05. RESULTS: Interobserver agreement was acceptable with a mean kappa value of 0.59. Compared with the RP using FBP, similar scores were achieved at 2.36 mGy using MBIR. MIBR reconstructions showed the highest noise suppression as well as good contrast even at the lowest doses. Overall, ASIR reconstructions did not outperform FBP. CONCLUSIONS: LD and MBIR at a dose reduction of >90% may show no significant differences in spatial and contrast resolution compared with an RP and FBP. Ultralow-dose CT and IRT should be further explored in clinical studies.

Kooperation von Kieferorthopädie, Kieferchirurgie und Prothetik bei der umfassenden Rehabilitation von DysgnathiepatientInnen. Teil 2: Fallbeispiel Klasse-II-Malokklusion, Tiefbiss, Hypodontie.

Dental aplasia of heterogenous etiology may cause jaw growth disturbance, malocclusion, esthetic discontent and psychosocial impairment. By a case report of a young patient suffering from hypodontia, class II malocclusion and a deep bite the intricate interdisciplinary diagnosis- and treatment-protocol targeting the functional and esthetic rehabilitation is illustrated.

Kooperation von Kieferorthopädie, Kieferchirurgie und Prothetik bei der umfassenden Rehabilitation von DysgnathiepatientInnen. Teil 1: Fallbeispiel Klasse-III-Malokklusion, Unterkiefer-Schaltlücken.

In a case report the stomatognathic rehabilitation of a patient with class III malocclusion and mandibular bilateral interdental gaps from the diagnosis and treatment planning through to the stepwise realization of the orthodontic, surgical and prosthetic treatment is presented. Explicit information about the proposed treatment, risks and the prospective outcome beforehand ensured the patient’s compliance during the extensive procedure.

Cone Beam Computed Tomography vs Multislice Computed Tomography in Computer-Aided Design/Computer-Assisted Manufacture Guided Implant Surgery Based on Three-Dimensional Optical Scanning and Stereolithographic Guides: Does Image Modality Matter?

PURPOSE: Cone beam computed tomography (CBCT) is increasingly overtaking multislice computed tomography (MSCT) for implant planning and computer-aided design/computer-assisted manufacturing (CAD/CAM) surgical guide fabrication. The purpose of this study was to evaluate whether the image modality has a significant influence on the accuracy of image-fusion stereolithographic guides. MATERIALS AND METHODS: A total of 240 implants were placed in 30 polymer models using surgical guides fabricated using CBCT or MSCT and optical scanning of dental casts and diagnostic wax-up. Postsurgical image data were fused with the planning data for evaluation of the following errors: total error (Euclidean error), mesiodistal and buccolingual error, depth error, and angular error. The CBCT and MSCT results were statistically compared using a t test (P = .05). RESULTS: CBCT showed a statistically significantly higher total error with mean (± SD) of 0.36 ± 0.13 mm vs 0.27 ± 0.13 mm (P = .000), mesiodistal error with 0.20 ± 0.14 mm vs 0.16 ± 0.11 mm (P = .018), and depth error with 0.17 ± 0.12 mm vs 0.07 ± 0.07 mm (P = .000). Buccolingual and angular errors did not statistically significantly differ with 0.16 ± 0.11 mm vs 0.15 ± 0.12 mm (P = .613), and 0.96 ± 0.47 degrees vs 0.85 ± 0.59 degrees (P = .111). CONCLUSION: Using CBCT for image-fusion stereolithographic guides may provide lower accuracy than MSCT. The results should be confirmed on alternative CBCT scanners. Due to the total volume of tissues, image artifacts, and patient movements, the advantages seen using MSCT on models could be nonexistent or exacerbated on patients. Patient studies are required to demonstrate clinical relevance.

Ultralow dose dentomaxillofacial CT imaging and iterative reconstruction techniques: variability of Hounsfield units and contrast-to-noise ratio.

OBJECTIVE: The aim of this study was to evaluate whether application of ultralow dose protocols and iterative reconstruction technology (IRT) influence quantitative Hounsfield units (HUs) and contrast-to-noise ratio (CNR) in dentomaxillofacial CT imaging. METHODS: A phantom with inserts of five types of materials was scanned using protocols for (a) a clinical reference for navigated surgery (CT dose index volume 36.58 mGy), (b) low-dose sinus imaging (18.28 mGy) and (c) four ultralow dose imaging (4.14, 2.63, 0.99 and 0.53 mGy). All images were reconstructed using: (i) filtered back projection (FBP); (ii) IRT: adaptive statistical iterative reconstruction-50 (ASIR-50), ASIR-100 and model-based iterative reconstruction (MBIR); and (iii) standard (std) and bone kernel. Mean HU, CNR and average HU error after recalibration were determined. Each combination of protocols was compared using Friedman analysis of variance, followed by Dunn's multiple comparison test. RESULTS: Pearson's sample correlation coefficients were all >0.99. Ultralow dose protocols using FBP showed errors of up to 273 HU. Std kernels had less HU variability than bone kernels. MBIR reduced the error value for the lowest dose protocol to 138 HU and retained the highest relative CNR. ASIR could not demonstrate significant advantages over FBP. CONCLUSIONS: Considering a potential dose reduction as low as 1.5% of a std protocol, ultralow dose protocols and IRT should be further tested for clinical dentomaxillofacial CT imaging. ADVANCES IN KNOWLEDGE: HU as a surrogate for bone density may vary significantly in CT ultralow dose imaging. However, use of std kernels and MBIR technology reduce HU error values and may retain the highest CNR.

Surgical treatment of mandibular condyle fractures using the retromandibular anterior transparotid approach and a triangular-positioned double miniplate osteosynthesis technique: A clinical and radiological evaluation of 124 fractures.

OBJECTIVE: Different modalities have been described regarding the treatment of mandibular condyle fractures. The most advantageous and safest one is still a topic of discussion. The present analysis describes the combination of a retromandibular, transparotideal approach combined to a triangular-positioned double-miniplate osteosynthesis, with a special regard for the patients' long term outcomes. MATERIAL AND METHODS: Clinical data of 102 patients with 124 condyle fractures treated with the mentioned surgical procedure were evaluated. Functional parameters such as the maximal interincisal distance, deviations/deflections, facial nerve function, occlusion as well as complications regarding the parotid gland, osteosynthesis, and esthetics were evaluated 1 week, 2 weeks, 3 months, and 6 months postoperatively. RESULTS: The mean maximal interincisal distance ranged from 38 mm after 1 week to 45 mm after 6 months. Deviations/deflections were seen in 22.5% of the cases 1 week postoperatively and decreased to 2% at 6 months postoperatively. A temporary facial palsy was diagnosed in 3.9% during the first follow-up, whereas no impairment was recorded after 3 or 6 months. At the same time, no patient had occlusional disturbances or complications regarding the parotid gland or the osteosynthesis 6 months postoperatively. CONCLUSIONS: Direct fracture visualization and a stable three-dimensional fracture stabilization are the main advantages of the presented combination of a surgical approach and osteosynthesis technique. Additionally, the absence of long-term complications confirms the safety of the procedure. Therefore, it may be considered as a successful treatment option for mandibular condyle fractures.

Accuracy of Image-Fusion Stereolithographic Guides: Mapping CT Data with Three-Dimensional Optical Surface Scanning.

BACKGROUND: Computer-assisted implant surgery usually requires a radiographic scan template as the basis for prosthetic-driven implant planning and surgical guide fabrication. PURPOSE: The study aims to evaluate the accuracy of image-fusion stereolithographic guides in which a computed tomography (CT) scan is mapped with three-dimensional optical scans of cast and diagnostic wax-up. MATERIALS AND METHODS: Three-dimensional error at the base and tip of the implants, angular deviation of the implant-axis, and the inserting-depth error of 120 implants with a length of 10 mm and a caliber of 4.1 mm in 15 polymer-models were examined. A control CT was performed and fused with the planning data for accuracy evaluation. RESULTS: The mean three-dimensional error was 0.21 ± 0.10 mm (0.00-0.48 mm) at the implant base, 0.32 ± 0.17 mm (0.03-0.75 mm) at the implant tip, and the mean angular error was 0.85 ± 0.59° (0.00-2.50°). The mean depth error was 0.07 ± 0.07 mm (0.00-0.32 mm). CONCLUSIONS: Within the limitations of an in vitro study, the novel technique showed excellent accuracy. Errors from fabrication and scanning of a radiographic scan template can be avoided, and the workflow and costs of computer-assisted implant surgery may be reduced.

Ultralow-dose CT of the craniofacial bone for navigated surgery using adaptive statistical iterative reconstruction and model-based iterative reconstruction: 2D and 3D image quality.

OBJECTIVE. The purpose of this article is to evaluate 2D and 3D image quality of high-resolution ultralow-dose CT images of the craniofacial bone for navigated surgery using adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) in comparison with standard filtered backprojection (FBP). MATERIALS AND METHODS. A formalin-fixed human cadaver head was scanned using a clinical reference protocol at a CT dose index volume of 30.48 mGy and a series of five ultralow-dose protocols at 3.48, 2.19, 0.82, 0.44, and 0.22 mGy using FBP and ASIR at 50% (ASIR-50), ASIR at 100% (ASIR-100), and MBIR. Blinded 2D axial and 3D volume-rendered images were compared with each other by three readers using top-down scoring. Scores were analyzed per protocol or dose and reconstruction. All images were compared with the FBP reference at 30.48 mGy. A nonparametric Mann-Whitney U test was used. Statistical significance was set at p < 0.05. RESULTS. For 2D images, the FBP reference at 30.48 mGy did not statistically significantly differ from ASIR-100 at 3.48 mGy, ASIR-100 at 2.19 mGy, and MBIR at 0.82 mGy. MBIR at 2.19 and 3.48 mGy scored statistically significantly better than the FBP reference (p = 0.032 and 0.001, respectively). For 3D images, the FBP reference at 30.48 mGy did not statistically significantly differ from all reconstructions at 3.48 mGy; FBP and ASIR-100 at 2.19 mGy; FBP, ASIR-100, and MBIR at 0.82 mGy; MBIR at 0.44 mGy; and MBIR at 0.22 mGy. CONCLUSION. MBIR (2D and 3D) and ASIR-100 (2D) may significantly improve subjective image quality of ultralow-dose images and may allow more than 90% dose reductions.

Comparison of the prevalence of human papilloma virus infection in histopathologically confirmed premalignant oral lesions and healthy oral mucosa by brush smear detection.

OBJECTIVE: The role of human papilloma virus (HPV) infections in oral carcinogenesis is an important topic of research in maxillofacial oncology. Nevertheless, the association between such infections in the oral cavity and the development of oral precancerous lesions remains unclear. The aim of this study was to evaluate the association between oral HPV infections and oral leukoplakia or erythroplakia. STUDY DESIGN: The case control study included 118 patients with manifest oral leukoplakia or erythroplakia, who underwent surgical biopsy, including a histopathologic grading of the lesion, and 100 control patients without any oral lesions. HPV detection was achieved with a noninvasive brush smear method (Digene Cervical Sampler, Hybrid Capture II-Test). Logistic regression analysis was performed to assess the associations. RESULTS: A significant association was found between high-risk oral HPV infection and the presence of oral premalignant lesions (P = .001). Among all other evaluated parameters, only smoking showed a significant association with the presence of oral lesions. CONCLUSIONS: Oral HPV infections may play a role in the pathogenesis of premalignant oral lesions.

Surgical resection technique of a fused supernumerary lateral incisor: a clinical report and review of the literature.

This case report presents the surgical and restorative management of a fused supernumerary left lateral incisor. The diagnosis was confirmed using conventional radiographs and CT. The case report discusses the value of CT for evaluation of the root relationships and describes the varied morphology associated with supernumerary incisors, the surgical resection technique, partial pulpotomy, and restoration with composite resin after mechanical exposure of the remaining tooth's pulp.

Do image modality and registration method influence the accuracy of craniofacial navigation?

PURPOSE: Cone-beam computed tomography (CBCT) is increasingly used in craniofacial imaging and may be an interesting option for navigated surgery. The purpose of this study was to evaluate the accuracy of various registration techniques in CBCT compared with intraoperative and diagnostic multislice spiral computed tomography (MSCT). MATERIALS AND METHODS: High-resolution images of an anthropomorphic skull phantom with target markers were obtained using 2 CBCT machines (KaVo 3D eXam, ILUMA), an intraoperative MSCT (Sensation Open), and the standard diagnostic MSCT (LightSpeed VCT). Bone markers, a registration template, and an external registration frame were used for registration with an optical-based navigation system. Target registration errors (TREs) were evaluated and statistically analyzed in SPSS (P < .05). RESULTS: The mean ± standard deviation for overall TREs of the KaVo 3D eXam, ILUMA, Sensation Open, and LightSpeed VCT devices were 1.37 ± 0.54, 1.67 ± 0.65, 1.27 ± 0.52, and 1.31 ± 0.30 mm, respectively. The KaVo 3D eXam showed no significant differences compared with the MSCTs. The ILUMA imaged the external registration frame only marginally and showed significant higher TREs compared with the other registration methods (P < .001). In the 2 MSCTs, no significant differences between the registration methods were found. CONCLUSIONS: CBCT and intraoperative MSCT may show comparable TREs as standard diagnostic MSCT. Bone markers are the gold standard. Registration templates and external registration frames are valuable alternatives. When using only external registration frames, CBCTs with a large scan field are recommended.

Resection of a primary oral malignant melanoma and rehabilitative management using nasolabial flap: a case report.

BACKGROUND: The primary malignant melanoma is a rare neoplasm of melanocytic origin in the oral cavity. Only about 1% of all melanomas arise in the oral mucosa and these account for 0.5% of all oral malignancies CASE REPORT: This report describes an oral malignant melanoma occurring in the right maxilla of a 73-year-old patient. The interdisciplinary management using a nasolabial flap and prosthetic oral rehabilitation procedure is described. DISCUSSION: The nasolabial flap technique offers the possibility of an immediate reconstruction of the maxillary defect and obviated problems with speech, swallowing, and permitted oral intake. As a supplementary benefit, the resection area can support the prosthetic rehabilitation.

Comparison of the accuracy of invasive and noninvasive registration methods for image-guided oral implant surgery.

PURPOSE: Registration refers to the linkage of coordinates from an image with actual patient coordinates and has been shown to be the most influential factor in the accuracy of image-guided surgery. Invasive bone markers are the gold standard but require surgical placement prior to imaging. In contrast, registration templates or external registration frames are noninvasive, but their repositioning during imaging and surgery can be a source of error. The purpose of the present study was to determine whether noninvasive registration methods can achieve an accuracy similar to that of invasive bone marker registration. MATERIALS AND METHODS: Computed tomographic slices (1 mm each) of a maxillary and mandibular dental stone cast that had been prepared with target markers on the buccal and oral surfaces were registered with an optical-based navigation system simulating invasive bone markers, noninvasive registration templates, and a noninvasive external registration frame. Predicted error of the navigation system, fiducial registration error, and target registration error were evaluated. The use of five and seven registration markers was compared. RESULTS: A total of 696 error measurements was performed. The external registration frame showed significantly worse fiducial registration error compared with the other methods, but there was no significant difference in target registration error between invasive and noninvasive registration methods. The predicted error given by the navigation system significantly underestimated target registration error. Increasing the number of registration markers from five to seven resulted in no significant differences. CONCLUSIONS: Noninvasive registration based on registration templates or external registration frames showed accuracy that was equivalent to that of invasive registration. The use of five registration markers was sufficient. The predicted error given by a navigation system should not be mistaken as "navigation error" during clinical application.

Flapless implant surgery in the edentulous jaw based on three fixed intraoral reference points and image-guided surgical templates: accuracy in human cadavers.

OBJECTIVES: In edentulous patients, accurate and stable positioning of a surgical template is impeded by the mobile mucosal tissue. The objective was to evaluate the accuracy of flapless computer-assisted template-guided surgery in an edentulous human cadaver specimen using three fixed oral reference points (FRP) for fixation of the registration mouthpiece and the consecutive surgical template. MATERIAL AND METHODS: Oral implants were planned on the computed tomography (CT) of an edentulous human cadaver specimen. Surgical templates have been fabricated using a multipurpose navigation system. Both the registration mouthpiece and consecutive surgical template were supported via three FRP. Study implants were inserted through the guide sleeves and the accuracy was evaluated on a post-surgical CT of the cadaver jaws fused with the pre-surgical planning CT. A Matlab script enabled comparison of the planned surgical path with the study implants. RESULTS: In five maxillary and three mandibular edentulous human cadaver specimens, a total of 51 implants (35 implants in the maxilla and 16 implants in the mandible) have been placed. The mean+/-standard deviation total error (Euclidean distance)/lateral error (normal deviation) were 1.1+/-0.6/0.7+/-0.5 mm at the implant base and 1.2+/-0.7/0.9+/-0.7 mm at the implant tip. The mean angular error was 2.8+/-2.2 degrees. CONCLUSIONS: Flapless surgery based on FRP-supported image-guided surgical templates may provide similar accuracy as reported for tooth-supported surgical templates or surgical navigation.