Placement of endosteal implants in the zygoma after maxillectomy: a Cadaver study using surgical navigation

Learning curve of dynamic navigation-assisted zygomatic implant surgery: An in vitro study

STATEMENT OF PROBLEM

Dynamic computer-assisted zygomatic implant surgery (dCAZIS) has been reported to provide clinical efficacy with high accuracy and low risk of complications. However, the learning curve before performing dCAZIS effectively is unknown.

PURPOSE

The purpose of this in vitro study was to explore the learning curve of dCAZIS in dentists with different levels of experience in implant dentistry and navigation surgery.

MATERIAL AND METHODS

Six senior dental students were randomly divided into 3 groups for initial training (FH-CI group: pretraining on freehand conventional implant surgery; FH-ZI group: pretraining on freehand ZI surgery; DN-CI group: pretraining on conventional implant surgery under dynamic navigation). Then, every operator conducted 6 repeated dCAZIS training sessions on edentulous 3-dimensional (3D) printed skull models and was asked to complete a self-report questionnaire after each training session. A total of 36 postoperative cone beam computed tomography (CBCT) scans with 144 ZI osteotomy site preparations were obtained and superimposed over the preoperative design for accuracy measurements. The operation time, 3D deviations, and results of the self-reports were recorded. Comparisons among groups were analyzed with independent-sample Kruskal-Wallis tests (α=.05), and correlations between study outcomes and the number of practices were calculated.

RESULTS

Operator experience and increased practice times did not significantly affect the accuracy of dCAZIS (P>.05). However, the operation time varied among groups (P<.001), and significantly shortened with more practice, reaching 11.51 ±1.68 minutes at the fifth attempt in the FH-CI group (P<.001 compared with the first practice), 14.48 ±3.07 minutes at the third attempt in the FH-ZI group (P=.038), and 8.68 ±0.58 minutes at the sixth attempt in the DN-CI group (P<.001). All groups reached their own learning curve plateau stage within 6 practice sessions. As the number of practice sessions increased, the results from the self-report questionnaires gradually improved.

CONCLUSIONS

Among dentists with different levels of experience in implant dentistry and navigation surgery, dCAZIS was found to have a learning curve with respect to operation time but not implant accuracy. Experience in ZI surgery had little impact on the learning curve of dCAZIS, but experience in navigation surgery was a key factor.

Clinical efficacy of computer-assisted zygomatic implant surgery: A systematic scoping review

STATEMENT OF PROBLEM

Digital technology can improve the success of zygomatic implant (ZI) surgery. However, the reliability and efficacy of computer-assisted zygomatic implant surgery (CAZIS) need further analysis.

PURPOSE

The purpose of this scoping review was to provide an overview of the placement accuracy, implant survival, and complications of CAZIS.

MATERIAL AND METHODS

A systematic search of English and Mandarin Chinese publications up to May 2023 was conducted in PubMed, Web of Science, Embase, and Wanfang database. The nonpeer-reviewed literature was searched in the trial register (clinicaltrials.gov). Clinical studies and cadaver studies on CAZIS were included. After data extraction and collection, the findings were critically reviewed, analyzed, interpreted, and discussed.

RESULTS

Forty-one studies met the inclusion criteria. After excluding publications with duplicate data, retaining the most recent, 28 articles were included in this scoping review. Of these, 18 were on static computer-assisted zygomatic implant surgery (sCAZIS), 8 on dynamic computer-assisted zygomatic implant surgery (dCAZIS), and 2 on robot-assisted zygomatic implant surgery (rAZIS). Excluding the outliers, the mean deviations of ZIs in the sCAZIS group (with 8 articles reporting implant placement accuracy, 183 ZIs involved) were: 1.15 ±1.37 mm (coronal deviation), 2.29 ±1.95 mm (apical deviation), and 3.32 ±3.36 degrees (angular deviation). The mean deviations of dCAZIS (3 articles, 251 ZIs) were: 1.60 ±0.74 mm (coronal), 2.27 ±1.05 mm (apical), and 2.89 ±1.69 degrees (angular). The mean deviations of rAZIS (2 articles, 5 ZIs) were: 0.82 ±0.21 mm (coronal), 1.25 ±0.52 mm (apical), and 1.46 ±0.35 degrees (angular). Among the CAZIS reported in the literature, the implant survival rate was high (96.3% for sCAZIS, 98.2% for dCAZIS, and 100% for rAZIS, specified in 14 of 21 clinical studies). The incidence of complications was low, but, because of the few relevant studies (4/21 specified), valid conclusions regarding complications could not be drawn.

CONCLUSIONS

CAZIS has demonstrated clinical efficacy with high implant survival rates and placement accuracy. Of the 3 guided approaches, rAZIS showed the smallest 3-dimensional deviation.

Application of titanium 3D-printed double-sleeve guide for zygomatic implants: A technique report

The unique anatomical structure of the atrophic edentulous maxilla limits the placement of endosteal root form dental implants without bone grafting and augmentation. Surgical placement of zygomatic implants in an optimal position remains challenging. This technique report illustrates a novel digital guide technology, including the design workflow, application method, and indications for assisting with the placement of zygomatic implants using a bone-supported titanium double-sleeve guide. In addition, when the implant body reaches the zygomatic bone following an intra-sinus path, including ZAGA type 0 and ZAGA type 1 cases, a matching window osteotomy surgical guide is used to locate the lateral window boundary and protect the sinus membrane. With this technique, the surgical procedure is simplified, and the precision of guided zygomatic implant placement is improved.

The Accuracy of Zygomatic Implant Placement Assisted by Dynamic Computer-Aided Surgery: A Systematic Review and Meta-Analysis

PURPOSE

The present systematic review aimed to investigate the accuracy of zygomatic implant (ZI) placement using dynamic computer-aided surgery (d-CAIS), static computer-aided surgery (s-CAIS), and a free-hand approach in patients with severe atrophic edentulous maxilla and/or deficient maxilla.

METHODS

Electronic and manual literature searches until May 2023 were performed in the PubMed/Medline, Scopus, Cochrane Library, and Web of Science databases. Clinical trials and cadaver studies were selected. The primary outcome was planned/placed deviation. Secondary outcomes were to evaluate the survival of ZI and surgical complications. Random-effects meta-analyses were conducted and meta-regression was utilized to compare fiducial registration amounts for d-CAIS and the different designs of s-CAIS.

RESULTS

A total of 14 studies with 511 ZIs were included (Nobel Biocare: 274, Southern Implant: 42, SIN Implant: 16, non-mentioned: 179). The pooled mean ZI deviations from the d-CAIS group were 1.81 mm (95% CI: 1.34-2.29) at the entry point and 2.95 mm (95% CI: 1.66-4.24) at the apex point, and angular deviations were 3.49 degrees (95% CI: 2.04-4.93). The pooled mean ZI deviations from the s-CAIS group were 1.19 mm (95% CI: 0.83-1.54) at the entry point and 1.80 mm (95% CI: 1.10-2.50) at the apex point, and angular deviations were 2.15 degrees (95% CI: 1.43-2.88). The pooled mean ZI deviations from the free-hand group were 2.04 mm (95% CI: 1.69-2.39) at the entry point and 3.23 mm (95% CI: 2.34-4.12) at the apex point, and angular deviations were 4.92 degrees (95% CI: 3.86-5.98). There was strong evidence of differences in the average entry, apex, and angular deviation between the navigation, surgical guide, and free-hand groups (p < 0.01). A significant inverse correlation was observed between the number of fiducial screws and the planned/placed deviation regarding entry, apex, and angular measurements.

CONCLUSION

Using d-CAIS and modified s-CAIS for ZI surgery has shown clinically acceptable outcomes regarding average entry, apex, and angular deviations. The maximal deviation values were predominantly observed in the conventional s-CAIS. Surgeons should be mindful of potential deviations and complications regardless of the decision making in different guide approaches.

Dynamic navigation for zygomatic implant placement: A randomized clinical study comparing the flapless versus the conventional approach

OBJECTIVES

The assessment of the accuracy of flapless placement of zygomatic implants in edentulous maxilla using dynamic navigation.

METHODS

A randomized controlled trial was carried out on 20 patients. Patients were randomized into two groups, the flapless (Group 1; n=10) and the conventional (Group 2; n=10). In each case two zygomatic implants were inserted under local anaesthesia, one on the right and one on the left side guided by a dynamic navigation system. The surgical procedure was identical in the two groups except for the reflection of the mucoperiosteal flap which was eliminated in the flapless cases. Postoperative CBCT scans were used to assess the accuracy of the placement of zygomatic implants.

RESULTS

Osseointegration was achieved for all the implants, except one case in the flapless group. Statistically significant differences in the accuracy of the position of the zygomatic implants was found between the flapless and the conventional groups, measured at the apex and the entry points of the implants (p < 0.01). The average apical and coronal deviations were 5 mm and 3 mm, respectively; the angular deviation was 6°, and 2 mm vertical apical disparity was detected between the planned and the achieved surgical position. Perforation of the Schneiderian membrane was noted in three cases, one in flapless group and two in the conventional group.

CONCLUSIONS

Flapless placement of zygomatic implants guided by dynamic navigation offered satisfactory safety and accuracy.

CLINICAL SIGNIFICANCE

This is the first clinical trial to prove the feasibility and accuracy of flapless placement of zygomatic implant with minimal morbidity. The study highlights the innovative reflection of the Schneiderian membrane under guided surgical navigation. The procedure can be performed under local anaesthesia, which offers clinical advantages. Adequate training on the use of dynamic navigation is mandatory before its use in clinical cases.

Augmented Reality-Based Surgery on the Human Cadaver Using a New Generation of Optical Head-Mounted Displays: Development and Feasibility Study

Background

Although nearly one-third of the world’s disease burden requires surgical care, only a small proportion of digital health applications are directly used in the surgical field. In the coming decades, the application of augmented reality (AR) with a new generation of optical-see-through head-mounted displays (OST-HMDs) like the HoloLens (Microsoft Corp) has the potential to bring digital health into the surgical field. However, for the application to be performed on a living person, proof of performance must first be provided due to regulatory requirements. In this regard, cadaver studies could provide initial evidence.

Objective

The goal of the research was to develop an open-source system for AR-based surgery on human cadavers using freely available technologies.

Methods

We tested our system using an easy-to-understand scenario in which fractured zygomatic arches of the face had to be repositioned with visual and auditory feedback to the investigators using a HoloLens. Results were verified with postoperative imaging and assessed in a blinded fashion by 2 investigators. The developed system and scenario were qualitatively evaluated by consensus interview and individual questionnaires.

Results

The development and implementation of our system was feasible and could be realized in the course of a cadaver study. The AR system was found helpful by the investigators for spatial perception in addition to the combination of visual as well as auditory feedback. The surgical end point could be determined metrically as well as by assessment.

Conclusions

The development and application of an AR-based surgical system using freely available technologies to perform OST-HMD–guided surgical procedures in cadavers is feasible. Cadaver studies are suitable for OST-HMD–guided interventions to measure a surgical end point and provide an initial data foundation for future clinical trials. The availability of free systems for researchers could be helpful for a possible translation process from digital health to AR-based surgery using OST-HMDs in the operating theater via cadaver studies.

Reliability and accuracy of dynamic navigation for zygomatic implant placement

Objectives

To assess the accuracy of a real‐time dynamic navigation system applied in zygomatic implant (ZI) surgery and summarize device‐related negative events and their management.

Material and methods

Patients who presented with severely maxillary atrophy or maxillary defects and received dynamic navigation‐supported ZI surgery were included. The deviations of entry, exit, and angle were measured after image data fusion. A linear mixed‐effects model was used. Statistical significance was defined as p < .05. Device‐related negative events and their management were also recorded and analyzed.

Results

Two hundred and thirty‐one zygomatic implants (ZIs) with navigation‐guided placement were planned in 74 consecutive patients between Jan 2015 and Aug 2020. Among them, 71 patients with 221 ZIs received navigation‐guided surgery finally. The deviations in entry, exit, and angle were 1.57 ± 0.71 mm, 2.1 ± 0.94 mm and 2.68 ± 1.25 degrees, respectively. Significant differences were found in entry and exit deviation according to the number of ZIs in the zygomata (p = .03 and .00, respectively). Patients with atrophic maxillary or maxillary defects showed a significant difference in exit deviation (p = .01). A total of 28 device‐related negative events occurred, and one resulted in 2 ZI failures due to implant malposition. The overall survival rate of ZIs was 98.64%, and the mean follow‐up time was 24.11 months (Standard Deviation [SD]: 12.62).

Conclusions

The navigation‐supported ZI implantation is an accurate and reliable surgical approach. However, relevant technical negative events in the navigation process are worthy of attention.

A Novel Guided Zygomatic and Pterygoid Implant Surgery System: A Human Cadaver Study on Accuracy

The aim of this human cadaver study was to assess the accuracy of zygomatic/pterygoid implant placement using custom-made bone-supported laser sintered titanium templates. For this purpose, pre-surgical planning was done on computed tomography scans of each cadaver. Surgical guides were printed using direct metal laser sintering technology. Four zygomatic and two pterygoid implants were inserted in each case using the guided protocol and related tools. Post-operative computed tomography (CT) scans were obtained to evaluate deviations between the planned and inserted implants. Accuracy was measured by overlaying the real position in the post-operative CT on the virtual presurgical placement of the implant in a CT image. Descriptive and bivariate analyses of the data were performed. As a result, a total of 40 zygomatic and 20 pterygoid implants were inserted in 10 cadavers. The mean deviations between the planned and the placed zygomatic and pterygoid implants were respectively (mean ± SD): 1.69° ± 1.12° and 4.15° ± 3.53° for angular deviation. Linear distance deviations: 0.93 mm ± 1.23 mm and 1.35 mm ± 1.45 mm at platform depth, 1.35 mm ± 0.78 mm and 1.81 mm ± 1.47 mm at apical plane, 1.07 mm ± 1.47 mm and 1.22 mm ± 1.44 mm for apical depth. In conclusion, the surgical guide system showed accuracy for all the variables studied and allowed acceptable and accurate implant placement regardless of the case complexity.

A comparative evaluation of parasymphyseal fracture fixation in edentulous patients performed using dynamic navigation systems and Herbert screws with the conventional two-plate method: A study on models

PURPOSE

The investigators performed this study to compare the rigidity outcomes for minimally invasive fixation of edentulous mandibular parasymphyseal fractures without flap creation using Herbert screws with a dynamic navigation system and the conventional two-plate method.

METHODS

The investigators implemented an in-vitro study design, and 20 polyurethane edentulous mandibular models covered with flexible plastic to simulate the gingiva were used. Parasymphyseal fractures were created in all models using a reciprocal saw. In the study group, the fracture segments in each model were planned to be fixed using two 30-mm Herbert screws. The Herbert screws were placed using a screwdriver with the dynamic navigation system guiding the process. In the control group, to simulate open reduction, the fracture fragments were fixed using two 4-hole straight titanium plates and 6-mm titanium screws. All mandibular models on the prepared platform were attached to the biomechanical testing machine. They were subjected to a continuous linear compression until plastic deformation occurred. Displacement resistance was measured once for every model when the displacement reached 1, 3, 5, 10, and 15 mm. Furthermore, the maximum breaking forces that the models could withstand before deformation were measured. Data were analyzed using independent samples t-test. A value of p < .05 was considered statistically significant.

RESULTS

Manual examination of the models did not reveal any mobility between the fragments. In all evaluated displacement steps, the models fixed using Herbert screws showed significantly higher resistance to mechanical loading compared to the models fixed using parallel miniplates.

CONCLUSION

In present study, parasymphyseal fracture of edentulous mandible models were fixed successfully using Herbert screws with the dynamic navigation system. The results of this study may encourage future clinical studies.

Comparative accuracy of cone-beam CT and conventional multislice computed tomography for real-time navigation in zygomatic implant surgery

BACKGROUND

Cone-beam computed tomography (CBCT) and conventional multislice CT (MSCT) are both used in zygomatic implant navigation surgery but the superiority of one technique versus the other remains unclear.

PURPOSE

This study compared the accuracy of CBCT and MSCT in zygomatic implant navigation surgery by calculating the deviations of implants.

MATERIAL AND METHODS

Patients with severely atrophic maxillae were classified into two groups according to the use of CBCT- or MSCT-guided navigation system. The entry and apical distance deviation, and the angle deviation of zygomatic implants were measured on fused operation images. A linear effect model was used for analysis, with statistical significance set at P < .05.

RESULTS

A total of 72 zygomatic implants were inserted as planned in 23 patients. The comparison of deviations in CBCT and MSCT groups showed a mean (± SD) entry deviation of 1.69 ± 0.59 mm vs 2.04 ± 0.78 mm (P = .146), apical deviation of 2 ± 0.68 mm vs 2.55 ± 0.85 (P < .001), and angle deviation of 2.32 ± 1.02° vs 3.23 ± 1.21° (P = .038).

CONCLUSION

Real-time zygomatic implant navigation surgery with CBCT may result in higher values for accuracy than MSCT.

The influence of dental experience on a dental implant navigation system

Background

This study evaluated the operating performance of an implant navigation system used by dental students and dentists of prosthodontic background with varying levels of experience. A surgical navigation system and optical tracking system were used, and dentists’ accuracies were evaluated in terms of differences between the positions of actually drilled holes and those of the holes planned using software before surgeries.

Methods

The study participants were 5 dental students or dentists who had studied in the same university and hospital but had different experience levels regarding implants. All participants were trained in operating the AqNavi system in the beginning of the study. Subsequently, using 5 pairs of dental models, each participant drilled 5 implant holes at 6 partially edentulous positions (11, 17, 26, 31, 36, and 47). In total, each participant conducted 30 drilling tests.

Results

In total, 150 tests among 5 dentists at 6 tooth positions (11, 17, 26, 31, 36, and 47) were conducted. Although a comparison of the tests revealed significant differences in the longitudinal error (P < .0001) and angular error (P = .0011), no significant difference was observed in the total error among the dentists.

Conclusions

A relatively long operating time was associated with relatively little implant experience. Through the dental navigation system, dental students can be introduced to dental implant surgery earlier than what was possible in the past. The results demonstrated that the operational accuracy of the dental implant navigation system is not restricted by participants’ implant experience levels. The implant navigation system assists the dentist in the ability to accurately insert the dental implant into the correct position without being affected by his/her own experience of implant surgery.

Development of a dental handpiece angle correction device

Background

Preparation of a uniform angle of walls is essential for making an ideal convergence angle in fixed prosthodontics. We developed a de novo detachable angle-correction apparatus for dental handpiece drills that could help the ideal tooth preparation.

Methods

We utilized a gyro sensor to measure the angular velocities to calculate the slope of an object by integrating the values, acceleration sensor to calculate the slope of an object by measuring the acceleration relative to gravity, and Kalman filter algorithm. Converting the angulation of the handpiece body to its drill part could be performed by a specific matrix formulation set on two reference points (2° and 6°). A flexible printed circuit board was used to minimize the size of the device. For convergence angle investigation, 16 volunteers were divided randomly into two groups for performing tooth preparation on a mandibular first molar resin tooth. All abutments were scanned by a 3D scanner (D700^®, 3Shape Co., Japan), the convergence angle and tooth axis deviation were analyzed by a CAD program (SolidWorks 2013^®, Dassault Systems Co., USA) with statistical analysis by Wilcoxon signed-rank test (α = 0.05) using SPSS statistical software (Version 16.0, SPSS Inc.).

Results

This device successfully maintained the stable zero point (less than 1° deviation) at different angles (0°, 30°, 60°, 80°) for the first 30 min. In single tooth preparation, without this apparatus, the average bucco-lingual convergence angle was 20.26° (SD 7.85), and the average mesio–distal (MD) convergence angle was 17.88° (SD 7.64). However, the use of this apparatus improved the average BL convergence angle to 13.21° (SD 4.77) and the average MD convergence angle to 10.79° (SD 4.48). The angle correction device showed a statistically significant effect on reducing the convergence angle of both directions regardless of the order of the directions.

Conclusions

The angle correction device developed in this study is capable of guiding practitioners with high accuracy comparable to that of commercial navigation surgery. The volume of the angle correction device is much smaller than that of any other commercial navigation surgery system. This device is expected to be widely utilized in various fields of orofacial surgery.

Assessment of tumor margins in head and neck cancer using a 3D-navigation system based on PET/CT image-fusion - A pilot study

OBJECTIVES

Determination of tumor margins in patients with squamous cell carcinoma of the head and neck (SCCHN) is mostly based on preoperative magnetic resonance imaging (MRI) or computed tomography scans (CT). Local recurrence of disease is often correlated with the presence of positive resection margins after surgical treatment. Positron emission tomography/computed tomography (PET/CT) imaging plays a crucial role in the assessment of patients with SCCHN. The purpose of this study was to determine whether PET/CT could predict tumor extension.

METHODS

In 12 patients who underwent surgical treatment of primary SCCHN (Stage III-IV) F18-FDG PET/CT image-fusion was performed on a 3D navigation-system based workstation. Image-guided needle biopsies were obtained from four different, color-coded metabolic areas within the tumor. The histopathological findings were correlated with findings on corresponding PET/CT scans.

RESULTS

81.3% of biopsies from the central area were positive. Specimens taken from the outer metabolic zone were positive in 66.7% of the patients. The highest incidence of positive biopsies was found in the zone adjacent to the outermost area. There was a statistically significant difference in positive tumor histopathology when comparing the various metabolic zones (p = 0.03).

CONCLUSION

Exact determination of tumor is an important research topic, although results remain controversial. The results of this study suggest that in some cases PET scans may overestimate tumor extension.

Development of a surgical navigation system based on augmented reality using an optical see-through head-mounted display

The surgical navigation system has experienced tremendous development over the past decades for minimizing the risks and improving the precision of the surgery. Nowadays, Augmented Reality (AR)-based surgical navigation is a promising technology for clinical applications. In the AR system, virtual and actual reality are mixed, offering real-time, high-quality visualization of an extensive variety of information to the users (Moussa et al., 2012) [1]. For example, virtual anatomical structures such as soft tissues, blood vessels and nerves can be integrated with the real-world scenario in real time. In this study, an AR-based surgical navigation system (AR-SNS) is developed using an optical see-through HMD (head-mounted display), aiming at improving the safety and reliability of the surgery. With the use of this system, including the calibration of instruments, registration, and the calibration of HMD, the 3D virtual critical anatomical structures in the head-mounted display are aligned with the actual structures of patient in real-world scenario during the intra-operative motion tracking process. The accuracy verification experiment demonstrated that the mean distance and angular errors were respectively 0.809±0.05mm and 1.038°±0.05°, which was sufficient to meet the clinical requirements.

Accuracy of a flapless protocol for computer-guided zygomatic implant placement in human cadavers: expectations and reality

BACKGROUND

This work evaluated the accuracy and safety of a protocol for minimally-invasive flapless zygomatic implant placement that uses computer-guided stereolithographic mucosa-supported surgical templates.

METHODS

A total of six zygomatic implants were placed in three formalin-fixed human cadaver heads, with edentulous and severely atrophic posterior maxillae. CT scans of each cadaver head were performed after zygomatic implant placement, to evaluate the lateral error (LE) at implant tip and base, and the angular error (AE) of the implant body.

RESULTS

Excluding the implant placed outside the drilling channel, the LE at the implant base was less than 1 mm in all cases. The average LE at the tip was 3.86 mm, and the AE was less than 6° in all cases, with an average of 4.5°.

CONCLUSION

Computer-guided minimally-invasive flapless zygomatic implant surgery remains challenging. Careful planning and perfect stability of the surgical guide are essential.

Zygomatic implants: a critical review of the surgical techniques

PURPOSE

The purpose of the present study is to identify and describe the different surgical techniques for placement of zygomatic implants reported in the literature and discuss the differences between them.

METHODS

An electronic search was undertaken in July 2011. The titles and abstracts from these results (n = 130) were read for identifying studies, which reported different surgical techniques for placement of zygomatic implants, which resulted in 41 articles.

RESULTS

Five different surgical approaches were identified: (1) the classical approach, (2) the sinus slot technique, (3) the exteriorized approach, (4) the minimally invasive approach by the use of custom-made drill guides, and (5) the computer-aided surgical navigation system approach. When the maxilla is severely resorbed, the concavity formed by the ridge crest is small, and the original classical technique should be used. When maxillary resorption generates a large concavity, it would be better to exteriorize the zygomatic implant. The externalized technique has fewer surgical steps than the classical and sinus slot methods, is less invasive, and reduces surgical time. It is recommended that utilization of the sinus slot technique together with the CT-based drilling guide would enhance the final results. Although the technique that uses the computer-aided surgical navigation system approach may produce an improved precision in the clinical procedure, its use is expensive, prolongs the operation time, and is limited to centers that have the necessary equipment for the surgery.

CONCLUSIONS

Preference for one technique over the other should take into consideration the concavity formed by the ridge crest, maxillary sinus, and region of implant insertion in the zygomatic bone.

Image guided oral implantology and its application in the placement of zygoma implants

The application of zygoma implants proposes a successful treatment for functional reconstruction of maxillary defects. However, the placement of zygoma implants is not without risk due to anatomically complex operation sites. Aiming at minimizing the risks and improving the precision of the surgery, an image guided oral implantology system (IGOIS) is presented in this study to transfer the preoperative plan accurately to the operating theatre. The principle of IGOIS is introduced in detail, including the framework, 3D-reconstruction, preoperative planning, registration, and the motion tracking algorithm. The phantom experiment shows that fiducial registration error (FRE) and TRE (target registration error) of IGOIS are, respectively, 1.12mm and 1.35mm. With respect to the overall accuracy, the average distance deviations at the coronal and apical point of the implant are, respectively, 1.36+/-0.59mm and 1.57+/-0.59mm, while average angle deviation between the axes of the planned and the actual implant is 4.1 degrees +/-0.9 degrees . A clinical report for a patient with a severely atrophic maxilla demonstrates that the major advantage of this computer-aided navigation technology lies in its accuracy, reliability, and flexibility.

Case Report: Fusion of positron emission tomography (PET) and computed tomography (CT) images for image-guided endoscopic navigation in maxillofacial surgery: Clinical application of a new technique

INTRODUCTION

Surgery based on computed tomography (CT) data is becoming increasingly important in the head and neck region. The technique for hardware fusion between positron emission tomography (PET) and computed tomography (CT) has only been established commercially in the last 4 years. The advantages over CT alone are obvious. The surgeon is simultaneously provided with a map of anatomical as well as of functional (metabolic) details. The fused images offer improved localization of malignant lesions and improved targeting of biopsy, especially for small lesions.

PURPOSE

A new technique for image-guided tumour localization for maxillofacial surgery based on PET/CT-image fusion is described.

PATIENT AND METHOD

A 78-year-old woman was admitted to this department with a tumour of the skull base. Three dimensional fusion of computed CT with positron PET images on a commercially available navigation system is described. After patient-to-image registration, a high-resolution endoscope was calibrated intraoperatively. Image-guided biopsy specimens were taken under direct visual control.

CONCLUSION

PET/CT-image fusion proved extremely helpful to navigate the endoscope to the target lesion and to identify the tumour.

Tilting of splinted implants for improved prosthodontic support: A two-dimensional finite element analysis

STATEMENT OF PROBLEM

Presence of the maxillary sinus or the mental foramen may prevent implant treatment in the posterior maxilla or mandible. Tilting of distal implants supporting fixed restorations may be a valid treatment alternative.

PURPOSE

The aim of this study was to evaluate if tilting of splinted implants affects stress distribution in the bone surrounding the implant cervix, and to investigate if the use of tilted implants as distal abutments is biomechanically superior to the use of distal cantilevers.

MATERIAL AND METHODS

A 2-dimensional (2-D) model for finite element analysis was developed using two 13-mm implants splinted by a titanium beam, 16 x 3 mm. The implants were embedded in bone blocks, simulating different bone properties. A small crater was created in the marginal bone around the tilted implant to simulate physiologic bone remodeling. The model with a distal cantilever 7 mm long and a distal implant was compared to a model in which the distal implant (13 or 19 mm) was tilted 45 degrees and supported the distal end of the cantilever. A force of 50 N was applied via the beam.

RESULTS

The stress at the most coronal bone-to-implant contact was identical irrespective of the angle of tilt, demonstrating that tilting of splinted implants does not result in increased stress. The cantilevered model showed that the use of cantilevers results in higher stress in the marginal bone around implants. This stress is reduced to "normal" levels when the cantilever arm is negated by the distal implant being apically inclined to support the distal end of the cantilever. Use of a longer implant only reduces the stress marginally.

CONCLUSIONS

Within the limitations of this 2-D finite element analysis, it appears that distal tilting of implants splinted by fixed restorations does not increase bone stress compared to normally placed, vertical implants. There is a biomechanical advantage in using tilted distal implants rather than distal cantilever units.

Zygoma implant-supported prosthetic rehabilitation after partial maxillectomy using surgical navigation: A clinical report

The rehabilitation of patients with acquired defects of the maxilla is a challenge in terms of reestablishing oronasal separation. In most patients these goals are met by means of prosthetic rehabilitation with an obturator prosthesis. If the remaining dentition does not offer sufficient retention and support, the placement of zygoma implants can enhance the stability of the prosthesis. Due to the anatomic intricacies of the zygomatic bone and the implant length, computer-supported navigated implant placement can be advantageous. In the following clinical report, a diabetic patient with a status of posthemimaxillectomy secondary to aspergillusis infection is presented, in whom a zygoma implant was placed using a CT scan-based navigation system. A special retentive anchoring abutment was used to integrate the zygoma implant into a telescopic crown-retained denture on the residual dentition. This tooth-implant-supported obturator prosthesis restored function and phonetics, as well as esthetics, for this young patient.

Computer-guided flapless transmucosal implant placement in the mandible: a new combination of two innovative techniques

OBJECTIVE

To assess whether computer-guided flapless transmucosal implant bed preparation without mucosal punching allows placement of dental implants in edentulous mandibles.

STUDY DESIGN

Twenty patients with fully edentulous mandibles (11 male; 9 female) were included in the study. Each patient was scheduled to receive 4 screw-shaped Ankylos (Dentsply Friadent, Mannheim, Germany) implants in the interforaminal region. The StealthStation Treon navigation system (Medtronic, Minnesota, MN) was used for computer-guided drilling. Using conventional implant drills the mucosa was penetrated without flap elevation or mucosal punching. The study protocol did not allow direct visualization of the bone surface during surgery.

RESULTS

For 78 implants (97.5%) the preoperative plan could be transfered to the patient by intraoperative navigation with a mean deviation of 0.9 mm (Implant tip 0.8 +/- 0.6 mm; coronal implant end 1.1 +/- 0.7 mm) as measured by comparing pre- and postoperative computerized tomography images. Two implants (2.5 %) were not primarily stable and failed to osseointegrate.

CONCLUSIONS

Computer-guided transmucosal interforaminal implant placement without mucosal punching is a precise and predictable procedure. It is, however, not yet suitable for all bone morphologies. Future developments may include miniaturization of hardware and simplification of the drilling procedure.

Accuracy of image-guided implantology

OBJECTIVES

The accuracy of two commercially available systems for image-guided dental implant insertion based on infrared tracking cameras was compared with manual implantation.

MATERIAL AND METHODS

Phantoms of partially edentulous mandibles were used. In a master phantom, pilot boreholes for dental implants were placed. These boreholes were reproduced in slave phantoms using either of the two image-guided systems and manual implantation. The resulting positions were determined using a coordinate measurement machine and compared with the master model.

RESULTS

In comparison with manual implantation, the difference of borehole positions to the master phantom was significantly lower using either of the systems for image-guided implant insertion.

CONCLUSION

Image-guided insertion of dental implants is significantly more accurate than manual insertion. However, the accuracy that can be achieved with manual implantation is sufficient for most clinical situations.

Accuracy of navigation-guided socket drilling before implant installation compared to the conventional free-hand method in a synthetic edentulous lower jaw model

In this study, the three-dimensional (3D) accuracy of navigation-guided (NG) socket drilling before implant installation was compared to the conventional free-hand (CF) method in a synthetic edentulous lower jaw model. The drillings were performed by two surgeons with different years of working experience. The inter-individual outcome was assessed. NG drillings were performed using an optical computerized tomography (CT)-based navigation system. CF drillings were performed using a surgical template. The coordinates of the drilled sockets were determined on the basis of CT scans. A total of n=224 drillings was evaluated. Inter-individual differences in terms of the surgeons' years of work experience were without statistical significance. The mean deviation of the CF drilled sockets (n=112) on the vestibulo-oral and mesio-distal direction was 11.2+/-5.6 degrees (range: 4.1-25.3 degrees ). With respect to the NG drilled sockets (n=112), the mean deviation was 4.2+/-1.8 degrees (range: 2.3-11.5). The mean distance to the mandibular canal was 1.1+/-0.6 mm (range: 0.1-2.3 mm) for CF-drilled sockets and 0.7+/-0.5 mm (range: 0.1-1.8 mm) for NG drilled sockets. The differences between the two methods were highly significant (P<0.01). A potential benefit from image-data-based navigation in implant surgery is discussed against the background of cost-effectiveness.

Validation of 3D-laser surface registration for image-guided cranio-maxillofacial surgery

AIM

Image-data-based navigation plays an important role during surgical treatment in anatomically complex areas. Conventional patient-to-image registration techniques on the basis of skin and bone markers require expensive and time-consuming logistic support. A new markerless, high-resolution laser surface scan technique for patient registration has been tested in experimental and clinical settings.

METHODS

In a phantom study, a skull model was registered with laser scanning and marker-based algorithms. The registration procedure was repeated 25 times in each group. The values for the root mean-square error were calculated as a measure of the deviation of the forecast position from the actual position and the target difference. In a clinical setting, 21 consecutive patients who presented with cranio-maxillofacial disorders were scheduled for navigational surgery using laser surface scanning for patient-to-image registration. Here the accuracy was determined by anatomical landmark localization.

RESULTS

In the experimental study, a root mean-square error of 1.3+/-0.14 mm, and a mean target deviation of 2.08+/-0.49 mm were found for laser scanning. In contrast, a root mean-square error of 0.38+/-0.01 mm and a mean target deviation of 0.99+/-0.15 mm were found for marker registration. The differences were statistically significant (p<0.005). A strong correlation between the root mean-square error and the target deviation was found for laser (r=0.96) and marker registration (r=0.95). During the 21 clinical procedures, the overall accuracy of laser scan registration determined by the root mean-square error was 1.21+/-0.34 mm, and the mean clinical precision was 1.8+/-0.5 mm.

CONCLUSIONS

Three-dimensional laser surface registration offers an interesting approach for selected image-guided procedures in cranio-maxillofacial surgery.

Long-term implant survival in the grafted maxilla: results of a 12-year retrospective study

OBJECTIVE

The aim of this study was to determine the long-term outcome of implant insertion in the augmented severely atrophied maxilla.

STUDY DESIGN

Three hundred and twenty-four implants were inserted in 35 patients (eight males, 27 females, average age 57.6 years) in extremely atrophied maxillae after osteotomy and interposition of iliac crest bone. One hundred implants were installed in 12 patients simultaneously with the osteotomy and grafting; 224 implants were placed in 23 patients in a second procedure 6-12 months later. Implant parameters like osseointegration and peri-implant bone loss; peri-implant tissue parameters like bleeding, gingival and plaque index; and patients' satisfaction were evaluated.

RESULTS

Of 324 implants, 29 (8.9%) were lost during the entire follow-up: 14 in six patients of the one-step and 15 in 11 patients of the two-step group. The overall input-output survival in 141.1 months was 91.1%. The overall 2-year failure-free fraction of implants was 95.5%; the 5-year failure-free fraction was 89.3%. In the one-step group, the 2 (5)-year failure-free fraction was 95.9% (86.9%), and in the two-step group 95% (91.3%) (log-rank test P=0.57). Marginal peri-implant bone loss was 1.7+/-1.3 mm mesial and 1.8+/-1.3 mm distal.

CONCLUSION

Implant insertion after osteotomy and iliac bone grafting is a reliable operation method for the dental rehabilitation of the severely atrophied maxilla showing good long-term results.

Basic research and 12 years of clinical experience in computer-assisted navigation technology: a review

Computer-aided surgical navigation technology is commonly used in craniomaxillofacial surgery. It offers substantial improvement regarding esthetic and functional aspects in a range of surgical procedures. Based on augmented reality principles, where the real operative site is merged with computer generated graphic information, computer-aided navigation systems were employed, among other procedures, in dental implantology, arthroscopy of the temporomandibular joint, osteotomies, distraction osteogenesis, image guided biopsies and removals of foreign bodies. The decision to perform a procedure with or without computer-aided intraoperative navigation depends on the expected benefit to the procedure as well as on the technical expenditure necessary to achieve that goal. This paper comprises the experience gained in 12 years of research, development and routine clinical application. One hundred and fifty-eight operations with successful application of surgical navigation technology--divided into five groups--are evaluated regarding the criteria "medical benefit" and "technical expenditure" necessary to perform these procedures. Our results indicate that the medical benefit is likely to outweight the expenditure of technology with few exceptions (calvaria transplant, resection of the temporal bone, reconstruction of the orbital floor). Especially in dental implantology, specialized software reduces time and additional costs necessary to plan and perform procedures with computer-aided surgical navigation.

Navigated vs. conventional implant insertion for maxillary single tooth replacement

Abstract Introduction: Computer-guided navigation has proven a valuable tool in several surgical disciplines. During oral implant placement, its application is intended to accomplish optimal implant localization and to reduce the risk of damage to adjacent structures. The aim of this study was to compare the precision limits of conventional vs. navigated implant insertion in practice.

MATERIALS AND METHODS

In cast models of the maxilla, implants were inserted to replace the left central incisor (n = 40) and the right canine (n = 40); each of those were inserted either conventionally (n = 20) or navigated (n = 20). Implant position, angulation and insertion depth were calculated from computer tomography scans of the implants that were connected to an index abutment of 40 cm length.

RESULTS

The variations of implant positions were reduced for implants that were inserted by navigation (P < 0.05). In both the axial and the transversal plane, the variations of implant angulations were reduced for implants that were inserted by a navigation protocol (P < 0.05). The variations of insertion depth were less (P < 0.05) when the implants were placed by navigation in comparison with conventional insertion procedures.

CONCLUSIONS

Given the experimental conditions, although they tried to mimic a clinical situation, no final conclusions can be drawn. The in vitro application of a navigation system resulted in an improved precision of insertion surgery regarding the position, angulation and depth of an implant. Clinical studies will have to prove if routine image guidance will result in superior surgical outcome.

Rehabilitation of the severely atrophied maxilla by horseshoe Le Fort I osteotomy (HLFO)

OBJECTIVE

The purpose of this study was to determine the long-term outcome of the horseshoe Le Fort I osteotomy (HLFO) as a preprosthetic operation technique for implant insertion in the extremely atrophied maxilla.

STUDY DESIGN

36 patients (8 male, 28 female, average age 57.6 years) underwent HLFO combined with iliac crest bone grafting. They were divided into 2 groups: group A with 12 patients who simultaneously received 100 implants; group B with 24 patients where 176 implants were inserted in 18 patients in a second-stage procedure. Clinical and radiographic outcome with regard to implant osseointegration, alveolar bone height in the canine and molar regions, peri-implant bone loss and satisfaction of patients (esthetics, masticatory function, overall treatment) were investigated in all cases.

RESULTS

The overall 2-year failure-free fraction of implants was 95.5%; the 5-year failure-free fraction was 89.3%. In the 1-step group the 2-year and 5-year failure-free fractions were 95.9% and 86.9%, respectively, in the 2-step group 95.0% and 91.3% (log rank test P=.57). A total of 27 implants were lost during the entire follow-up: 14 in 6 patients of the 1-stage and 13 in 9 patients of the 2-stage group. The mean loss of alveolar bone after augmentation in the canine and molar regions was almost equal in both groups (overall means for the 2 regions 3.67 +/- 2.77 and 4.42 +/- 2.72 mm, respectively). The relationship between the jaws and thereby the esthetic profile could be improved in all cases. All patients were satisfied with the dental rehabilitation and the achieved new esthetic appearance.

CONCLUSIONS

HLFO combined with iliac bone grafting is a feasible preprosthetic technique prior to implant insertion in cases of severe atrophy of the maxillary alveolar ridge, leading to satisfying implant survival and rehabilitation of function.

Computer-aided navigation in dental implantology: 7 years of clinical experience

PURPOSE

This long-term study gives a review over 7 years of research, development, and routine clinical application of computer-aided navigation technology in dental implantology. Benefits and disadvantages of up-to-date technologies are discussed.

MATERIALS AND METHODS

In the course of the current advancement, various hardware and software configurations are used. In the initial phase, universally applicable navigation software is adapted for implantology. Since 2001, a special software module for dental implantology is available. Preoperative planning is performed on the basis of prosthetic aspects and requirements. In clinical routine use, patient and drill positions are intraoperatively registered by means of optoelectronic tracking systems; during preclinical tests, electromagnetic trackers are also used.

RESULTS

In 7 years (1995 to 2002), 55 patients with 327 dental implants were successfully positioned with computer-aided navigation technology. The mean number of implants per patient was 6 (minimum, 1; maximum, 11). No complications were observed; the preoperative planning could be exactly realized. The average expenditure of time for the preparation of a surgical intervention with navigation decreased from 2 to 3 days in the initial phase to one-half day in clinical routine use with software that is optimized for dental implantology.

CONCLUSIONS

The use of computer-aided navigation technology can contribute to considerable quality improvement. Preoperative planning is exactly realized and intraoperative safety is increased, because damage to nerves or neighboring teeth can be avoided.

Quantification and Clinical Relevance of Head Motion During Computed Tomography

OBJECTIVE

To quantify the 3-dimensional translation and rotation components of head motion during computed tomography and to analyze the influence of such motion on perceptible artifacts and distortion of volume image data sets.

METHODS

Using high-precision optoelectronic motion-capture technology, changes in patient head position during axial CT scanning were registered in 20 cases and 2 phantoms with a spatial relative resolution better than 0.003 cm. Statistical analysis was performed on a base of 6-dimensional measurement-vectors, each with 3 translation and 3 rotation values. Because of the recording frequency of the tracking system, more than 80000 values were included in a statistical analysis.

RESULTS

All 20 patients had head motion during the CT scanning, with only 4 of 20 patients showing perceptible motion artifacts. The frequency, the extent, and the direction of the movements did not correlate with either the observations made by the radiologic staff or with the patient's subjective estimation of comfort. Translation movements of the head during CT accounted for a maximum of 0.5 cm and rotations of more than 2 degrees without perceptible motion artifacts. The extent of positional changes of the head was found to correlate with the duration of scanning (Pearson's correlation coefficient: 0.647 for translation shifts, 0.453 for rotation shifts). The mean direction of head motion could be characterized predominantly as a rotation around the longitudinal axis of the body (xy plane) at a significance level of 0.01.

CONCLUSION

Computed tomography evaluations of the head performed without rigid fixation suffer a spatial distortion of the volume image data sets, caused by interimage motion. The absence of motion artifacts is not correlated with the absence of motion.

Computer-aided placement of endosseous oral implants in patients after ablative tumour surgery: assessment of accuracy

The objective of this study was to evaluate the feasibility and accuracy of a novel surgical computer-aided navigation system for the placement of endosseous implants in patients after ablative tumour surgery. Pre-operative planning was performed by developing a prosthetic concept and modifying the implant position according to surgical requirements after high-resolution computed tomography (HRCT) scans with VISIT, a surgical planning and navigation software developed at the Vienna General Hospital. The pre-operative plan was transferred to the patients intraoperatively using surgical navigation software and optical tracking technology. The patients were HRCT-scanned again to compare the position of the implants with the pre-operative plan on reformatted CT-slices after matching of the pre- and post-operative data sets using the mutual information-technique. A total of 32 implants was evaluated. The mean deviation was 1.1 mm (range: 0-3.5 mm). The mean angular deviation of the implants was 6.4 degrees (range: 0.4 degrees - 17.4 degrees, variance: 13.3 degrees ). The results demonstrate, that adequate accuracy in placing endosseous oral implants can be delivered to patients with most difficult implantologic situations.

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Computer-enhanced stereoscopic vision in a head-mounted operating binocular

Based on the Varioscope, a commercially available head-mounted operating binocular, we have developed the Varioscope AR, a see through head-mounted display (HMD) for augmented reality visualization that seamlessly fits into the infrastructure of a surgical navigation system. We have assessed the extent to which stereoscopic visualization improves target localization in computer-aided surgery in a phantom study. In order to quantify the depth perception of a user aiming at a given target, we have designed a phantom simulating typical clinical situations in skull base surgery. Sixteen steel spheres were fixed at the base of a bony skull, and several typical craniotomies were applied. After having taken CT scans, the skull was filled with opaque jelly in order to simulate brain tissue. The positions of the spheres were registered using VISIT, a system for computer-aided surgical navigation. Then attempts were made to locate the steel spheres with a bayonet probe through the craniotomies using VISIT and the Varioscope AR as a stereoscopic display device. Localization of targets 4 mm in diameter using stereoscopic vision and additional visual cues indicating target proximity had a success rate (defined as a first-trial hit rate) of 87.5%. Using monoscopic vision and target proximity indication, the success rate was found to be 66.6%. Omission of visual hints on reaching a target yielded a success rate of 79.2% in the stereo case and 56.25% with monoscopic vision. Time requirements for localizing all 16 targets ranged from 7.5 min (stereo, with proximity cues) to 10 min (mono, without proximity cues). Navigation error is primarily governed by the accuracy of registration in the navigation system, whereas the HMD does not appear to influence localization significantly. We conclude that stereo vision is a valuable tool in augmented reality guided interventions.

Computer-enhanced stereoscopic vision in a head-mounted display for oral implant surgery

We developed a head-mounted display (HMD) with integrated computer-generated stereoscopic projection of target structures and integrated it into visit, a specific oral implant planning and navigation software. The HMD is equipped with two miniature computer monitors that project computer-generated graphics stereoscopically into the optical path. Its position is tracked by the navigation system's optical tracker and target structures are displayed in their true position over the operation site. In order to test this system's accuracy and spatial perception of the viewer, five interforaminal implants in three dry human mandibles were planned with visit and executed using the stereoscopic projection through the HMD. The deviation between planned and achieved position of the implants was measured on corresponding computed tomography (CT) scan images recorded post-operatively. The deviation between planned and achieved implant position at the jaw crest was 0.57 +/- 0.49 mm measured from the lingual, and 0.58 +/- 0.4 mm measured from the buccal cortex. At the tip of the implants the deviation was 0.77 +/- 0.63 mm at the lingual and 0.79 +/- 0.71 mm at the buccal cortex. The mean angular deviation between planned and executed implant position was 3.55 +/- 2.07 degrees. The present in vitro experiment indicates that the concept of preoperative planning and transfer to the operative field by an HMD allows us to achieve an average precision within 1 mm (range up to 3 mm) of the implant position and within 3 degrees deviation for the implant inclination (range up to 10 degrees ). Control during the drilling procedure is significantly improved by stereoscopic vision through the HMD resulting in a more accurate inclination of the implants.

A head-mounted operating binocular for augmented reality visualization in medicine--design and initial evaluation

Computer-aided surgery (CAS), the intraoperative application of biomedical visualization techniques, appears to be one of the most promising fields of application for augmented reality (AR), the display of additional computer-generated graphics over a real-world scene. Typically a device such as a head-mounted display (HMD) is used for AR. However, considerable technical problems connected with AR have limited the intraoperative application of HMDs up to now. One of the difficulties in using HMDs is the requirement for a common optical focal plane for both the realworld scene and the computer-generated image, and acceptance of the HMD by the user in a surgical environment. In order to increase the clinical acceptance of AR, we have adapted the Varioscope (Life Optics, Vienna), a miniature, cost-effective head-mounted operating binocular, for AR. In this paper, we present the basic design of the modified HMD, and the method and results of an extensive laboratory study for photogrammetric calibration of the Varioscope's computer displays to a real-world scene. In a series of 16 calibrations with varying zoom factors and object distances, mean calibration error was found to be 1.24 +/- 0.38 pixels or 0.12 +/- 0.05 mm for a 640 x 480 display. Maximum error accounted for 3.33 +/- 1.04 pixels or 0.33 +/- 0.12 mm. The location of a position measurement probe of an optical tracking system was transformed to the display with an error of less than 1 mm in the real world in 56% of all cases. For the remaining cases, error was below 2 mm. We conclude that the accuracy achieved in our experiments is sufficient for a wide range of CAS applications.

Evaluation of accuracy of computer-aided intraoperative positioning of endosseous oral implants in the edentulous mandible

The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96 +/- 0.72 mm (range 0.0-3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.