Indications for cone-beam computed tomography in the area of oral and maxillofacial surgery.

The aim of this study was to identify specific indications for dental cone-beam computed tomography (CBCT) in the field of oral and maxillofacial surgery. To this end, we compared the efficacy of CBCT to that of panoramic radiography, the standard imaging modality, for the evaluation of different surgical questions in the oral and maxillofacial region. Dentall CBCT proved to be particularly useful in cases where visualization of a second plane is necessary for implant planning or for pre-surgical evaluation of retained and displaced teeth posing a risk to adjacent structures. It is also indicated for precise localization of luxated teeth and dental implants dislocated into surrounding areas, localization of the mandibular canal to assess its anatomical relationship to overfilled root canal filling materials, assessment ofthe extent of osseous lesions, and evaluation of patients with suspected mandibular or condylar fractures. The main advantages of CBCT are reduction of the risks of surgery due to the free selection of imaging planes, maindibular canal marking, 1:1 magnification, and the ability to use DICOM data in other implant or surgical planning software. Adequate user experience is important for proper evaluation of dental CBCT scans, as is the diagnosis of incidental findings falling into areas not primarily related to dentistry and therefore requiring additional investigation.

Influence of the rotation centre in panoramic radiography.

The aim is to present the curve of the rotation centre in dental panoramic radiography and to examine its influence on organ doses. A screenless film was fixed between the layers of an Alderson Rando phantom in the centre of the mandible. The phantom was positioned in two different X-ray units [Scanora (Soredex, Helsinki, Finland) and Orthophos (Sirona, Bensheim, Germany)] and exposed. Organ doses and effective doses were determined. The curves of the rotation centre showed clear differences especially in the area of the parotid gland. These differences corresponded to the differences in organ doses and in effective doses (Scanora: 29.9 microGy; Orthophos Plus: 14 microGy). Artefacts might be shown (Orthophos, result of a plate osteosynthesis) or not (Scanora) due to the different rotation centres. Differences in organ doses and in image quality, e.g. artefacts, were explained with the curve of the rotation centre and beam geometry.

[High-contrast resolution of film-screen systems in oral and maxillofacial radiology]. / Hochkontrastauflösung von Film-Folien-Systemen in der Zahn-, Mund- und Kieferheilkunde.

PURPOSE: The aim was to determine differences in high-contrast resolution of film-screen systems used in dental panoramic and cephalometric radiography by calculating the modulation transfer function (MTF). The radiographs used to determine the MTF should be taken by the same x-ray units as those used for patient radiographs. MATERIALS AND METHODS: The MTF was determined using a lead grid and according to DIN 6867-2 for 11 film-screen systems (speed 250, speed class 200 and 400) used in dental radiographic diagnostics. The optical density was measured using a microdensitometer developed by PTB. RESULTS: With 10% of the modulation transfer factor, newly developed film-screen systems (speed class 200 and 400) demonstrated a resolution of 4.9 to 6 line pairs per mm (panoramic radiography). In cephalometric radiography a film-screen system (speed class 400 and green-sensitive film) had a resolution of 4.2 line pairs per mm and surpassed two film-screen systems (speed class 400, resolution of 3 line pairs per mm, blue-sensitive films). CONCLUSION: The relevance of this study is underlined by the diagnostic reference doses defined in the German X-ray Ordinance (RöV) which are also intended for dentistry. Film-screen systems (speed 250, speed class 200) previously used in dental panoramic and cephalometric radiography can be replaced by newly developed film-screen systems (speed class 400). In dental radiography dose reductions are possible with film-screen systems (speed class 400) without impairing diagnostic accuracy. The introduction of newly developed film-screen systems (speed class 400) requires lower milliampere-seconds and therefore an adjustment of the x-ray units to lower milliampere settings.

Conventional cross-sectional tomographic evaluation of mandibular third molars.

OBJECTIVE: The purpose of this study was to locate the mandibular canal in relation to the impacted mandibular third molar by conventional cross-sectional tomography. METHOD AND MATERIALS: Conventional axially corrected cross-sectional tomograms of 347 successive impacted mandibular third molars of 234 patients referred for removal of the impacted teeth were acquired with a Scanora x-ray unit. The images were assessed for location of the mandibular canal and the impacted mandibular third molar. Descriptive analysis was performed. RESULTS: Examination of the tomograms revealed the alveolar nerve to have, in relation to the mandibular third molar, a lateral (buccal) course in 53.6% (n = 186), a course between the roots in 26.8% (n = 93), a lingual course in 13.0% (n = 45), and an inferior course in 6.0% (n = 21). Supplementary canals were found in 6.3% (n = 22). Two of the tomograms (0.6%) could not be evaluated, in 1 case because of incorrect patient positioning, resulting in an incorrectly adjusted transverse cut, and in the other case because of a mandibular carcinoma. CONCLUSION: Conventional axially corrected cross-sectional tomograms offer additional information in cases where there is a close relationship between impacted third molars and the alveolar nerve (superimposition of the roots and the canal, grooving, or a varied direction of the canal on the panoramic radiograph) and may contribute to a higher level of intrasurgical safety.

New radiographic programs for transverse conventional tomograms in the dentomaxillofacial region.

Using only 7 programs, Orthophos Plus permits transverse conventional tomograms of all maxillomandibular regions. The precision of the magnification factors of these programs is very high. Factors influencing the image quality of the 7 programs were assessed. Image quality depends on technical precision and on correct patient positioning, i.e., jaw axis alignment to the direction of projection. This procedure with 7 programs is more demanding than the procedure for x-ray units that use many programs for the different projections. Especially for implantology, it is important that the patient's jaw be positioned in accordance with the projection to avoid oblique cuts and incorrect information about the jaw dimensions. The correct region is best selected by positioning a cast in the positioning aids prior to exposure and using the same setting for the patient's exposures. For correct implant planning, it is helpful to digitize the tomograms with Friacom so that, despite different magnification factors of the programs, the correct implant dimensions are determined. If these suggestions are followed, use of these programs in dental practice can be recommended.

Radiographic imaging of the hard palate and maxillary third molars with spiral tomography: a novel technique of patient positioning.

The Scanora spiral tomography system can be used to solve a range of imaging problems in the maxillofacial region. However, the system has no specific programs for imaging bony lesions of the hard palate or medially and cranially displaced maxillary third molars. New patient-positioning techniques were therefore developed on the basis of phantom radiographs, and their successful application in patients is presented. With the novel techniques, good radiographic representations of the hard and soft palates in the posteroanterior and lateral projections and of maxillary third molars were achieved.

Possibilities of dose reduction in lateral cephalometric radiographs and its effects on clinical diagnostics.

OBJECTIVES: The aim of the present study was to determine (1) the absorbed and the exit radiation doses for cephalometric exposures on a phantom head with various exposure settings and image receivers, and (2) the diagnostic image quality for various modalities assessed on cephalometric radiographs of patients. METHODS: The dose measurements for lateral cephalometric radiographs were performed with a semiconductor detector, and also with thermoluminescent detectors and an Alderson phantom. Both the integral and the effective doses were determined. Two radiographs of each patient (n=119) were taken at two different times, one at a low tube potential setting, 75+/-5 kV, and one with a decreased dose. Film-screen systems with speed class 400 and one storage phosphor plate were used. Five observers assessed the radiographs for the visualization of six cephalometric reference points on a three-point scale with -1, 0 and 1. Twenty-seven image pairs were rescored to determine inter- and intrarater reliability. The statistical analysis was done using analysis of variance and Tukey's HSD (honestly significant difference) post hoc test. RESULTS: Increasing the tube potential setting led to an average dose reduction to 83% (integral dose) or to 87% (effective dose). Instead of taking the radiograph at a low tube potential setting (75 kV), a dose reduction of about 15% was feasible at a high tube potential setting (90 kV). A significant difference in reference point visibility existed between film radiographs at low tube potential settings (mean score 0.984) and at high tube potential settings (90 kV, mean score 0.958). For the storage phosphor plates, there was no significant difference to the film-screen combinations at low tube potential and halved milliampere seconds settings. In the second assessment, there was a high degree of agreement (96.6%) compared with the first assessment (unadjusted for random agreement). CONCLUSIONS: As there is only minimal dose reduction at increased tube potential settings, for a dose reduction, it seems to be more useful to use storage phosphor plates at unchanged tube potential and halved milliampere seconds settings compared with the film-screen combination.

Diagnostic accuracy of in vitro panoramic radiographs depending on the exposure.

OBJECTIVES: The aim was to evaluate the effect of dose reduction on diagnostic accuracy in panoramic radiographs with increased tube potential and reduced milliampere settings. METHODS: Panoramic radiographs of 12 dried human skulls prepared with lesions in the bone, teeth and peri-implant bone in ascending size were taken. Medium and regular film--screen combinations and a storage phosphor system were used for imaging. All systems were exposed at a low and a high tube potential level. To compare the dose at different tube potential settings, dose length product was measured at the secondary collimator. Five observers assessed the presence (response: 1) or absence (response: 0) of lesions. Sensitivity, specificity and diagnostic accuracy were evaluated and 36 000 ratings were made in all. All settings were repeated once. Intrarater agreement was expressed by Cohen's kappa coefficient. RESULTS: There was no significant difference in diagnostic accuracy between a medium and a regular film--screen combination at a low tube potential level (70 kV; 0.935 and 0.930) and the medium film--screen system at a high tube potential level (85 kV; 0.926). Compared with this group, the regular film-screen combinations at high tube potential level (85 kV, 0.906) and all digital radiographs were significantly different (0.886 and 0.866), irrespective of the tube potential level. The digital panoramic radiograph was only comparable with the best film--screen combinations with an exposure for a medium film-screen system and at a low tube potential level. Sensitivity was 89.9% and specificity 93.7%. The kappa coefficient for intrarater agreement was high (0.81). CONCLUSIONS: The medium intensifying screen can be used at high tube potential settings instead of low tube potential settings, or the regular intensifying screen can be used at low tube potential settings with the same diagnostic value. A dose reduction of about 40% is possible. The storage phosphor plates should be exposed at least like a regular film-screen system and at a low tube potential level.

Influence of tube potential setting and dose on the visibility of lesions in intraoral radiography.

OBJECTIVES: The objectives were to determine the diagnostic accuracy of different image receptors when first, the tube potential setting was increased from 60 kV to 90 kV and second, when the milliampere setting was reduced at unchanged tube potential for storage phosphor plates. METHODS: Intraoral radiographs (films of speed class F, storage phosphor plates) were taken of 12 dried human skulls prepared with lesions in both teeth and peri-implant bone, in ascending size. Five observers assessed the presence (response=1) or absence (response=0) of lesions. The digital intraoral radiograph was exposed at 60 kV and 90 kV with half and a quarter of the film exposure. Some of the radiographs were assessed a second time. In total, 6000 assessments were made. Intrarater agreement was expressed by Cohen's kappa coefficient. RESULTS: The digital combinations showed the lowest diagnostic accuracy in all combinations, but the results demonstrated an equivalence of all combinations of films and storage phosphor plates. The differences in diagnostic accuracy were low (94-96.5%). The kappa coefficient for intrarater agreement was high (0.85). CONCLUSIONS: Regarding peri-implant and decayed lesions, intraoral films and storage phosphor plates demonstrated equal quality in this in vitro study regardless of exposure at 60 kV or 90 kV.

Factors influencing the absorbed dose in intraoral radiography.

OBJECTIVES: The aim of the present study was to find out whether it was more effective to achieve a dose reduction in intraoral radiography with an increase in the tube potential setting (and a decrease of milliampere seconds) by an additional attenuation of the X-ray beam behind the film plane or by the use of digital radiography. A second aim was to find out if there were differences between the integral doses determined by two different detectors and two different phantoms. METHODS: The X-ray attenuation in this in vitro study was carried out using additional lead foils from the dental film packet fixed behind the film plane and with a metal film holder. The dose measurements were performed with two semiconductor detectors (Quart, Diados). Patient simulation was achieved by the Alderson phantom or by the use of a filter (6Al+0.8Cu). The absorbed doses were calculated by integrating an exponential function between the entrance dose and the body exit dose. In addition, organ doses were measured and the effective dose was determined according to the Implementation of the 1990 Recommendations of the ICRP (ICRP-60). RESULTS: The increase in tube potential levels did not provide a substantial reduction of the absorbed dose (90 kVp instead of 60 kVp: reduction to 92.4%), only a reduction of the entrance dose (by 30% to 35% at 90 kVp compared with 60 kVp). The use of three lead foils behind the film plane instead of one resulted in a 14.0% reduction of the absorbed dose (60 kVp); the use of a metal film holder resulted in a 27.8% reduction (60 kVp). When tube potential settings were increased, the dose reduction decreased. The absorbed dose was reduced to 52% when a storage phosphor plate was used instead of a film (60 kVp). It was possible to determine the amount of dose reduction with both the calculated absorbed dose and the effective doses. The integral doses obtained from the Alderson phantom showed values 5% higher than those obtained by the filter (r(2)=96.7%). For the comparison of the integral doses, the measurements performed with Quart had values higher by a factor of 1.139 than those performed with Diados. CONCLUSIONS: Instead of increasing the tube voltage or using additional lead foils or metal film holders, a substantial dose reduction is provided by digital radiography or more sensitive films while a low tube potential level is maintained and the milliampere seconds setting is reduced.

The effect of dose reduction on the detection of anatomical structures on panoramic radiographs.

OBJECTIVES: The aim was to evaluate the effect of dose reduction on diagnostic accuracy using different screen-film combinations and digital techniques for panoramic radiography. METHODS: Five observers assessed 201 pairs of panoramic radiographs (a total of 402 panoramic radiographs) taken with the Orthophos Plus (Sirona, Bensheim, Germany), for visualization of 11 anatomical structures on each side, using a 3-point scale -1, 0 and 1. Two radiographs of each patient were taken at two different times (conventional setting and setting with decreased dose, done by increasing tube potential settings or halving tube current). To compare the dose at different tube potential settings dose-length product was measured at the secondary collimator. Films with medium and regular intensifying screens (high and low tube potential settings) and storage phosphor plates (low tube potential setting, tube current setting equivalent to regular intensifying screen and halved) were compared. The five observers made 27 610 assessments. Intrarater agreement was expressed by Cohen's kappa coefficient. RESULTS: The results demonstrated an equivalence of regular screens (low tube potential setting) and medium screens (high and low tube potential settings). A significant difference existed between medium screens (low tube potential setting, mean score 0.92) and the group of regular film-screen combinations at high tube potential settings (mean score 0.89) and between all film-screen combinations and the digital system irrespective of exposure (mean score below 0.82). There were no significant differences between medium and regular screens (mean score 0.88 to 0.92) for assessment of the periodontal ligament space, but there was a significant difference compared with the digital system (mean score below 0.76). The kappa coefficient for intrarater agreement was moderate (0.55). CONCLUSIONS: New regular intensifying screens can replace medium screens at low tube potential settings. Digital panoramic radiographs should be taken at low tube potential levels with an exposure equivalent at least to a regular intensifying screen.

Radiographic imaging of the mastoid process with conventional tomography: a novel positioning technique.

The Scanora (Soredex, Helsinki, Finland) is a multimodal unit for maxillofacial imaging combining narrow beam radiography and pluridirectional spiral tomography. We describe a novel technique for imaging the mastoid process based on a modification of the program for coronal tomography of the ear. This technique is of potential clinical value for implant planning and postoperative evaluation in the temporal bone.

Triple images on panoramic radiographs.

OBJECTIVE: To explain the formation of triple images on panoramic radiographs. METHODS: A metal test object was placed in defined positions in relation to movement path of a panoramic X-ray beam. RESULTS: The test object was portrayed once, twice or three times with varying degrees of distortion depending on its location. Triple images were formed when the test object was located in a specific diamond-shaped area distal to the path of the rotation centre of the X-ray beam. CONCLUSIONS: The formation of triple images on panoramic radiographs can be explained on the basis of known projection geometry.

Intra-oral storage phosphor and conventional radiography in the assessment of alveolar bone structures.

OBJECTIVES: To compare storage phosphor (SP) with conventional film radiography for accuracy of linear measurements of the marginal alveolar bone and visibility of anatomical structures. METHODS: Linear measurements were made in paired SP and conventional images of dried human mandibles with a metal pin fixed 10 mm below the alveolar crest. One observer measured the distance from the alveolar crest to the reference point on the radiographs. The difference between the measured and the true distance was calculated. Two observers rated the visibility of bony structures (periodontal ligament space, periapical bone tissue, alveolar crest) in 51 paired digital and conventional images of 21 patients on a 3-point scale. Overall agreement and Kappa index were calculated. RESULTS: Accuracy of linear measurements was higher in digital radiography (mean difference 0.17 mm) than in conventional radiography (mean difference 0.59 mm). Overall, the two observers rated visibility higher in conventional radiographs. The Kappa indices for the periodontal ligament space and periapical bone indicated fair to almost perfect agreement (kappa = 0.38 and 0.5; kappa = 0.39 and 0.84) while for the alveolar crest there was only poor or moderate agreement (kappa = 0.2 and 0.5). CONCLUSIONS: The small differences in linear measurements indicate that the Digora system is suitable for clinical assessment of periodontal and peri-implant bone loss. The visibility of dental structures depends as much on the individual features assessed, as the radiographic system.

[Quality of cardiopulmonary resuscitation by dentists in dental emergency care]. / Qualität von Herz-Lungen-Weiderbelebungsmassnahmen von Zahnärzten in der zahnärztlichen Notfallversorgung.

The crucial factor deciding the success of cardiopulmonary resuscitation is a sufficient oxygen supply. At about 4 min after cardiac arrest, cerebral death results because of hypoxia, and cardiopulmonary resuscitation has to be started regardless of the pathogenesis of the cardiac arrest. The purpose of the study was to assess the application of guidelines for cardiopulmonary resuscitation by participants at a dental surgery congress (n = 96) and to evaluate previous knowledge in cardiopulmonary resuscitation and knowledge after instruction. The present study was based on the standards and guidelines for cardiopulmonary resuscitation issued by the American Heart Association. The group was divided into four groups of doctors experienced or inexperienced in clinical emergencies or with dummies. For the study the Skillmeter-ResusciAnne (Laerdal, Stavanger, Norway) was used, which has automatic data recording. After analysis of the individual errors, the success of new instruction was assessed. Good previous knowledge was registered, particularly with respect to checking respiration and hyperextension of the head (67.7%), primary insufflation (93.8%), closed-chest cardiac massage (99%) and correct compression rate (68.4%). The participants demonstrated post-instruction improvement in all subdivisions except in the group without practice on dummies (primary insufflation: from 94.4 to 88.9%; correct order of checking consciousness and respiration, primary insufflation, the carotid pulse and closed-chest cardiac massage: from 22.2 to 5.6%). Good results with marked improvements in the second passage were achieved in checking consciousness and the carotid pulse, closed-chest cardiac massage and correct implementation of compression. The participants were, however, found to be in need of further education and training in diagnostics and certain cardiopulmonary resuscitation measures. Knowledge should be improved concerning recognition of the emergency (42.7%), checking the carotid pulse (22.9%), the correct order of primary insufflation and closed-chest cardiac massage (9.4%), correct implementation of compression (21.8%) and ventilation (36.4%), and the correct ratio of compression and ventilation (21.9%). Regular courses should be targeted at these specific aspects.

A clinical evaluation of some factors affecting image quality in panoramic radiography.

AIM: To evaluate the suitability of panoramic radiographs obtained with two different machines for clinical use. MATERIAL AND METHODS: Three observers assessed 111 pairs of panoramic radiographs taken with the Scanora (Soredex, Orion Corp., Helsinki, Finland) programme 001, and the Orthophos Plus (Sirona, Bensheim, Germany), programme P1 respectively, for visualisation of seven anatomical structures on each side, on a 5-point scale where 1 = very good. The median values were computed and a descriptive analysis performed. Interrater and intrarater agreement were expressed as weighted kappa. RESULTS: The median values of both Scanora and Orthophos radiographs were the same, scoring 2. The intra- and inter-observer agreement was generally poor and similar for both machines. CONCLUSIONS: The two panoramic machines were both given good ratings for evaluation of anatomical structures. The differences were very small and suggest that both machines are suitable for clinical use.