Unilateral sagittal split mandibular ramus osteotomy: indications and geometry.

Small mandibular asymmetries may be corrected by unilateral sagittal split ramus osteotomy (USSO). This study had two objectives: first to define the geometric changes in the mandibular condyle and the lower incisor teeth that result from the rotation of the major segment (n=26), and secondly to examine in a clinical study the temporomandibular joints (TMJ) of 23 patients after correction of mandibular asymmetry by USSO to find out if there were any long-term adverse effects. Small mandibular asymmetries (<5mm) can be corrected by USSO. Secondary anteroposterior changes as a result of setback or advancement on the operated side should be taken into account during the planning of treatment. The small rotational changes of the condyle did not adversely affect the TMJ.

Application of cone beam computed tomography in facial imaging science.

The use of three-dimensional (3D) methods for facial imaging has increased significantly over the past years. Traditional 2D imaging has gradually being replaced by 3D images in different disciplines, particularly in the fields of orthodontics, maxillofacial surgery, plastic and reconstructive surgery, neurosurgery and forensic sciences. In most cases, 3D facial imaging overcomes the limitations of traditional 2D methods and provides the clinician with more accurate information regarding the soft-tissues and the underlying skeleton. The aim of this study was to review the types of imaging methods used for facial imaging. It is important to realize the difference between the types of 3D imaging methods as application and indications thereof may differ. Since 3D cone beam computed tomography (CBCT) imaging will play an increasingly important role in orthodontics and orthognathic surgery, special emphasis should be placed on discussing CBCT applications in facial evaluations.

Comparison between two-dimensional and midsagittal three-dimensional cephalometric measurements of dry human skulls.

The aim of this study was to compare two- and three-dimensional cephalometric values by using a three-dimensional analysis based on the midsagittal plane. Spherical metal markers were fixed on to the anatomical landmarks of 10 human skulls, which were examined radiographically with conventional lateral cephalograms and cone-beam computed tomographic (CBCT) scans. Preprogrammed analyses calculated the 18 angular and linear two- and three-dimensional cephalometric values. An error study was made to assess the accuracy and reliability of the methods used. Both sets of values were compared using Wilcoxon's signed-rank test. Probabilities of less than 0.05 were accepted as significant. Reliability of the measurements was assessed by intraclass correlation coefficients (ICC) based on absolute agreement. The method error (ME) was tiny (mean ME<0.61 measuring unit) and reliable (ICC>0.97). Comparison of the two- and three-dimensional measurements showed that that they were reliable (ICC>0.88) and that there were no significant differences (P=0.41-1.00). The values from the cephalometric analyses were comparable and interchangeable when using the midsagittal three-dimensional approach as described.

Accuracy and reliability of facial soft tissue depth measurements using cone beam computer tomography.

It is important to have accurate and reliable measurements of soft tissue thickness for specific landmarks of the face and scalp when producing a facial reconstruction. In the past several methods have been created to measure facial soft tissue thickness (FSTT) in cadavers and in the living. The conventional spiral CT is mostly used to determine the FSTT but is associated with high radiation doses. The cone beam CT (CBCT) is a relatively new computer tomography system that focuses on head and neck regions and has much lower radiation doses. The aim of this study is to determine the accuracy and reliability of CBCT scans to measure the soft tissue thicknesses of the face. Seven cadaver heads were used. Eleven soft tissue landmarks were identified on each head and a punch hole was made on each landmark using a dermal biopsy punch. The seven cadaver heads were scanned in the CBCT with 0.3 and 0.4mm resolution. The FSTT at the 11 different sites (soft tissue landmarks) were measured using SimPlant-ortho volumetric software. These measurements were compared to the physical measurements. Statistical analysis for the reliability was done by means of the interclass coefficient (ICC) and the accuracy by means of the absolute error (AE) and absolute percentage error (APE). The intra-observer (0.976-0.999) and inter-observer (0.982-0.997) correlations of the CBCT and physical measurements were very high. There was no clinical significant difference between the measurements made on the CBCT images and the physical measurements. Increasing the voxel size from 0.4 to 0.3mm resulted in a slight increase of accuracy. Cone beam CT images of the face using routine scanning protocols are reliable for measuring soft tissue thickness in the facial region and give a good representation of the facial soft tissues. For more accurate data collection the 0.3mm voxel size should be considered.

Simple technique to achieve a natural position of the head for cone beam computed tomography.

We developed a modified laser level technique to record the natural position of the head in all three planes of space. This is a simple method for use with three-dimensional images and may be valuable in routine craniofacial assessment.