A new craniofacial diagnostic technique: the Sydney diagnostic system.

INTRODUCTION: A new nonradiographic craniofacial imaging technique is described and evaluated. The Sydney diagnostic system (SDS) image is formed from a standardized lateral head digital photograph and a standardized digital photograph of the study models. The SDS image was designed for orthodontic diagnosis and treatment planning without a lateral cephalogram. METHODS: Measurements from the composite facial and study model images of 35 randomly selected patients were compared with the same measurements from cephalograms to assess their validity and reliability. The measurements involved soft-tissue profile landmarks, landmarks on the ear, and hard-tissue landmarks identified on the study models including Point A, Point B, and dental landmarks. RESULTS AND CONCLUSIONS: The new imaging technique is reliable and valid for orthodontic treatment planning when compared with a lateral cephalogram if the inherent distortion between images is considered. Most soft-tissue measurements were more reliable than hard-tissue measurements, but some soft-tissue landmarks were less reliable. The ear was a reliable soft-tissue landmark. Maxillary incisor edge was the most reliable hard-tissue landmark, and neither Point A nor Point B could reliably be found on the study model images.

Validity and reliability of ear landmarks as reference points for cephalometric analysis.

AIM: A cephalometric analysis was designed to determine whether the external ear is a suitable reference structure for the superimposition of cephalometric analysis. METHODS: The sample consisted of 21 orthodontic patients with an average age of 16.5 years. Tracings of pretreatment and posttreatment cephalograms were superimposed on the cranial base. The landmarks on the ear, namely upper ear (UE), posterior ear (PE), and ear point (Ea), as well as the planes, namely UE-PE and EaP were defined to depict the position of the ear. The differences in these parameters between 2 timepoints were identified to indicate the stability of the ear position relative to the craniofacial complex. The paired t tests were used to evaluate the significance of displacement of these landmarks and planes at the 95% confidence interval. RESULTS: The results showed that the angulation between EaP and SN showed no difference between pre- and posttreatment (mean, 0.000 degrees) and the angulation between E-line and SN changed very little (mean, 0.095 degree). However, the change in linear distance between S and N was significant (mean, 1.19 mm; P <.01). CONCLUSIONS: It is suggested that the ear and its related landmarks are reliable and feasible reference structures or points for cephalometric analysis.

Comparison of radiation levels from computed tomography and conventional dental radiographs.

BACKGROUND: With the increasing use of computed tomography (CT) in oral diagnosis and treatment planning, concern has been expressed about the high levels of radiation used, and the associated risks. OBJECTIVES: The purpose of this study was to compare the radiation doses of facial CT scans with the radiation doses taking a lateral cephalometric radiograph, a panoramic radiograph (OPG), an occlusal film, and an intra-oral periapical radiograph. METHODS: An Alderson-Rando anthropomorphic phantom head was used for the analysis. Thirty-six lithium fluoride thermoluminescent dosimeters were placed in the phantom head in locations representing radiosensitive sites. Standard facial CT scans and conventional radiographs (lateral cephalometric, OPG, maxillary occlusal, intra-oral periapical) were then taken of the phantom head. RESULTS: The following radiation doses were measured: maxillo-mandibular CT scan, 2.1 mSv; maxillary CT scan, 1.40 mSv; mandibular CT scan, 1.32 mSv; lateral cephalometric radiograph, 0.005 mSv; OPG, 0.010 mSv; maxillary occlusal, 0.007 mSv; intra-oral periapical radiograph, 0.005 mSv. CONCLUSIONS: CT scans produce significantly more ionising radiation than conventional radiographs. This factor should be taken into account when considering a CT scan as an alternative to a survey with conventional radiographs. While CT scans offer many advantages over conventional radiography the high radiation dose to patients, and the cost of this procedure should be considered.

The reliability of crown-root ratio, linear and angular measurements on panoramic radiographs.

The aim of this study was to evaluate the reliability of crown and root length, crown-root ratio and angular measurements of teeth relative to constructed reference lines and to other teeth in the same region on consecutive (T1 and T2) panoramic radiographs (OPGs). This retrospective study employed 20 cases; ten with five implants in each jaw (age range between 20 and 60 years) and ten with a full permanent dentition (age range between 12 and 16 years). The consecutive pairs of OPGs ranged from 6 months to 3 years apart. Four variables were measured and compared: 1) the crown or coronal segment length and the root or apical segment length; 2) the crown-root ratio; 3) the angulations of teeth and implants relative to specific reference lines in each jaw; 4) the angle between teeth and implants in the same sextant. The results revealed that comparisons of measurements taken of the same structures at T1 and T2, there were no statistically significant differences (p>0.05) between vertical linear measurements. The crown-root ratios and coronal-apical segment ratios too, showed no significant differences (p>0.05). Whereas, angulations of teeth or implants relative to respective reference lines showed significant differences (p=0.001) for some of the teeth. These differences, however, were less than 5 degrees; a clinically acceptable range. Angles measured between teeth or implants in the same sextant showed no significant differences (p>0.05). These results seem to support the hypothesis, therefore, that the linear vertical measurements, ratio calculations and angular measurements can be used to compare crown and root lengths, crown-root ratios and tooth angulations on OPGs taken of the same patient at different times with consistent accuracy.

Accuracy of linear and angular measurements on panoramic radiographs taken at various positions in vitro.

The accuracy of measurement of tooth length and angulation on dental panoramic tomograms (DPTs) is thought to be highly dependent on head positioning technique. A model representing the dentition and the functional occlusal plane was designed using an acrylic framework and stainless steel wires. The aim was to investigate whether varying the position of the model affects the linear and angular measurements on DPTs. Four different positions were investigated: initial position representing natural head posture (NHP) (T1); lateral right cant of the occlusal plane (T2); lateral left cant of the occlusal plane (T3); and tilting the occlusal plane up anteriorly (T4). On each DPT, four sets of measurements were recorded: (1) Vertical linear measurements of the stainless steel pins and ratio calculations of the 'crown' and 'root' segments (represented by the wire above and below the occlusal plane, respectively); (2) angular measurements of the pins relative to the occlusal plane; (3) angular measurements of the pins relative to a constructed reference line; and (4) angular measurements of pins relative to each other in the same segment. The results showed a significant error (P < 0.05) in all measurements when the occlusal plane was tilted up anteriorly by 8 degrees. A lateral cant of the occlusal plane by less than 10 degrees without an upward anterior rotation showed no significant effect on the measurements. This would suggest that there is some tolerance of variation in head position.