Internal or in-scan validation: a method to assess CBCT and MSCT gray scales using a human cadaver.

OBJECTIVE: This study aimed to explore whether cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) can be used to quantify tissue density and to determine if the Hounsfield unit scale is applicable. STUDY DESIGN: A clinical MSCT scanner and effective energy adjusted photon beam attenuation references were used to compare the gray scale of CBCT images of the mandible region. A phantom was scanned using axial cadaver slices and 4 different homogeneous reference objects. The consistency of the references' gray values and 12 linear profile lines from both scanner data sets were compared. RESULTS: The gray values of the 2 scans showed strong correlation with quantified position-dependent differences as an outcome of the validation process. CONCLUSIONS: The introduced internal, in-scan validation is able to estimate and has a potential to compensate for the differences between MSCT and CBCT protocols. This validation serves as a guide in situations where the users can expect deviations.

High-quality image acquisition by double exposure overlap in dental cone beam computed tomography.

OBJECTIVE: With a double exposure overlapping cone beam computed tomography (CBCT) scan technique, using CBCT acquisition radiation dose, the objective was to obtain apparent density similar to that of multidetector computed tomography (MDCT). STUDY DESIGN: Factory quality-assurance phantom and water phantom were used for the evaluation of apparent density fidelity of iCAT scans in different modes. Each scan's apparent density was analyzed for identical regions using ImageJ, version 1.42q. RESULTS: The iCAT Classic extended height acquisition with 4-cm central overlap and reconstruction of 2 groups of 300 projections per rotation for the water and quality-assurance CBCT phantoms resulted in improved apparent density fidelity. This apparent density accuracy was superior to that of iCAT scan at high resolution (600 projections during 1 rotation). CONCLUSIONS: Using double exposure overlapping CBCT scans allows the analysis quality to be comparable with that of MDCT.

The biomechanical aspects of reconstruction for segmental defects of the mandible: a finite element study to assess the optimisation of plate and screw factors.

A bone plate is required to restore the load-bearing capacity of the mandible following a segmental resection. A good understanding of the underlying principles is crucial for developing a reliable reconstruction. A finite element analysis (FEA) technique has been developed to study the biomechanics of the clinical scenarios managed after surgical resection of a tumour or severe trauma to assist in choosing the optimal hardware elements. A computer aided design (CAD) model of an edentulous human mandible was created. Then 4 common segmental defects were simulated. A single reconstruction plate was designed to span the defects. The hardware variations studied were: monocortical or bicortical screw fixation and non-locking or locking plate design. A standardized load was applied to mimic the human bite. The von Mises stress and strain, spatial changes at the screw-bone interfaces were analysed. In general, the locking plate and monocortical screw fixation systems were most effective. Non-locking plating systems produced larger screw "pull-out" displacements, especially at the hemimandible (up to 5% strain). Three screws on either side of the defect were adequate for all scenarios except extensive unilateral defects when additional screws and an increased screw diameter are recommended. The simplification of screw geometry may underestimate stress levels and factors such as poor adaptation of the plate or reduced bone quality are likely to be indications for bicortical locking screw fixation. The current model provides a good basis for understanding the complex biomechanics and developing future refinements in plate or scaffold design.

Three-dimensional computer-aided surgical workflow to aid in reconstruction: From diagnosis to surgical treatment.

The development of three-dimensional computer-aided surgical workflow has simplified the planning of complex reconstruction cases. It can also be helpful in planning distraction osteogenesis cases. This article examines the evolving role of three-dimensional computer-aided surgical workflow in maxillofacial surgery.

A finite element analysis of bone plates available for prophylactic internal fixation of the radial osteocutaneous donor site using the sheep tibia model.

INTRODUCTION: The strengthening effect of prophylactic internal fixation (PIF) with a bone plate at the radial osteocutaneous flap donor site has previously been demonstrated using the sheep tibia model of the human radius. This study investigated whether a finite element (FE) model could accurately represent this biomechanical model and whether stress or strain based failure criteria are most appropriate. METHODS: An FE model of an osteotomised sheep tibia bone was strengthened using 4 types of plates with unilocking or bicortical screw fixation. Torsion and 4-point bending simulations were performed. The maximum von Mises stresses and strain failure criteria were studied. RESULTS: The strengthening effects when applying stress failure criteria [factor 1.76-4.57 bending and 1.33-1.80 torsion] were comparable to the sheep biomechanical model [factor 1.73-2.43 bending and 1.54-2.63 torsion]. The strongest construct was the straight 3.5mm stainless steel unilocking plate. Applying strain criteria the strongest construct was the straight 3.5mm stainless DCP plate with bicortical screw fixation. CONCLUSIONS: The FE model was validated by comparison with the sheep tibia model. The complex biomechanics at the bone-screw interface require further investigation. This FE modelling technique may be applied to a model of the human radius and other sites.

Measurement of orbital volume after enucleation and orbital implantation.

INTRODUCTION: This article reports experience relating to the measurement of orbital volume by means of cone beam computed tomography (CBCT) and Cranioviewer program software in patients who have undergone enucleation and orbital implantation. PATIENTS AND METHODS: CBCT scans were made in 30 cases, 10 of which were later excluded because of various technical problems. The study group therefore consisted of 20 patients (8 men and 12 women). The longest follow-up time was 7 years, and the shortest was 1 year. In all 20 cases, the orbital volume was measured with Cranioviewer orbital program software. Slices were made in the ventrodorsal direction at 4.8 mm intervals in the frontal plane, in both bony orbits (both that containing the orbital implant and the healthy one). Similar measurements were made in 20 patients with various dental problems. CBCT scans were recorded for the facial region of the skull, containing the orbital region. The Cranioviewer program can colour the area of the slices red, and it automatically measures the area in mm. RESULTS: In 5 of the 20 cases, the first 4 or all 5 slices revealed that the volume of the operated orbit was significantly smaller than that of the healthy orbit, in 12 cases only from 1 to 3 of the slices indicated such a significant difference, and in 3 cases no differences were observed between the orbits. In the control group of patients with various dental problems, there was no significant difference between the two healthy orbits. The accuracy of the volume measurements was assessed statistically by means of the paired samples t-test. SUMMARY: To date, no appropriate method is avaliable for exact measurement of the bony orbital volume, which would be of particular importance in orbital injury reconstruction. However, the use of CBCT scans and Cranioviewer orbital program software appears to offer a reliable method for the measurement of changes in orbital volume.

Porous Hydroxyapatite and Aluminium-Oxide Ceramic Orbital Implant Evaluation Using CBCT Scanning: A Method for In Vivo Porous Structure Evaluation and Monitoring.

Objective. This study aimed to define CBCT as a technique for postimplantation in vivo examination of porous hydroxyapatite and aluminium-oxide orbital implant shape, volume and density changes. Methods and Materials. CBCT was used to evaluate 30 enucleated patients treated with spherical polyglactin 910 wrapped hydroxyapatite and aluminum-oxide orbital implants. The mean duration of patient followup was 3.2 years or 1338 days with a range of 0.2 to 7.2 years or 79 to 2636 days in a population with an average age of 40.8 years. Results. The resolution of currently clinically used CBCT equipment allowed detailed structural observation of the orbital hydroxyapatite implants with some modifications. Volume and shape estimations were possible while density evaluation was more complicated compared to medical source computed tomography. The mean densities of the orbital implants were followed and a consistent gradual decrease identified from the beginning of implantation which was better defined after the applied correction procedure. Conclusion. CBCT with lower dosages of radiation exposure can be used to follow changes in implanted high-density porous structures. The density evaluation is possible with calibration modifications. Changes in orbital implant densities identified in this study may correspond to healing and maturation of soft tissues surrounding and penetrating the implants.

[Possibilities of clinical testing of osseointegration in oral implants]. / Fogászati implantátumok csontintegrációjának klinikai vizsgálatával szerzett tapasztalataink.

The osseointegration of oral implants is of utmost importance as far as the success of implant prosthetics is concerned. In clinical practice osseointegration can only be tested indirectly. The loading of implants is usually linked to osseointegration as a condition. Under some circumstances implants can be loaded before osseointegration is completed. The present study reviews the various methods of testing osseointegration and the conditions of immediate loading. In the present study the changes in the stability of 59 implants restored with screw-retained superstructures and partly immediately loaded, were observed over a period of several years, with the help of the Periotest method. Based on the statistical evaluation of the results, a significant correlation was found between implant insertion torque and primary stability. A difference was found between the stability of implants in the upper and lower jaws. A typical curve in the temporal changes of implant stability was described.

Finite element analysis of the human mandible to assess the effect of removing an impacted third molar.

BACKGROUND AND AIM: Finite element analysis (FEA) was used to generate 3-dimensional models of a human mandible with impacted third molars. The aim was to analyze the effects of removing various amounts of bone around an impacted mandibular third molar and to predict the possibility of iatrogenic fracture. MATERIALS AND METHODS: Data were acquired from cone beam computed tomography (CBCT) scans of a patient using numerically calculated mechanical parameters. Virtual surgery was then performed on the mandibular models, and standardized chewing forces were applied to the resulting simulations. RESULTS: The modelling showed that the highest stress during normal clenching occurred if the surgical procedure involved the external oblique ridge. The peak stress occurred at the site of removal of the third molar, during contralateral loading of the mandible. DISCUSSION: Use of CBCT allowed production of high-quality models of an individual patient and simulation of various surgical scenarios. FEA identified the accumulation of stress and strain at specific parts of the mandible and predicted the responses of bone to mechanical activity. FEA could prove useful to dental practitioners in the future to predict the likelihood of iatrogenic fracture of the jaws after surgical removal of mandibular bone, such as occurs when the third molar is removed. This may allow dentists to change their approach to tooth removal in certain cases.

Finite element analysis of the human mandible at 3 different stages of life.

OBJECTIVE: This study analyzed detailed models of human mandibles at 3 different stages of life with simulation of supra normal chewing forces at static conditions. METHODS AND MATERIALS: Finite element analysis (FEA) was used to generate models from cone-beam computerized tomograms (CBCT) of 3 patients aged 12, 20, and 67 years, using numerically calculated material parameters. Estimated chewing forces were then applied to the simulations. RESULTS: The results reflect higher elasticity in younger models in all regions of the mandible. The experimental models show that physiologic load stress and strain distributional changes of the mandible vary according to age. CONCLUSION: The CBCT-based model generation used in this study provided high-quality model definition of the 3 individual patients of different ages. FEA has great potential to predict bone responses to paradigms of mechanical activity. Future applications of FEA will include surgical planning, surgical hardware testing, and the design of scaffolds and tissue-engineered constructs.