Reversed layer position in rotational panoramic radiography

In rotational panoramic radiography, the image layer is generally positioned between the rotation center of the beam and the film. It is also possible to create a layer that is positioned between the rotation center and the x-ray source. The reversed layer position is useful clinically and gives rise to image properties that are somewhat different from the conventional geometry.     

Third molar position following Bionator treatment

Third molar eruption is an unpredictable event. The position of the third molar continuously changes during development. The purpose of this study was to evaluate the influence of Bionator treatment on third molar position against an untreated control group. A Bionator is a loose‐fitting intra‐oral appliance that postures the mandible forward, thereby producing skeletal and dentoalveolar changes. Data were obtained from direct measurements of existing longitudinal panoramic radiographs taken during the course of a randomized study investigating Class II malocclusion treatment options. The following variables were analyzed: mandibular third molar depth in relation to the cemento‐enamel junction of the second molar; anterior–posterior (A–P) position in relation to the anterior border of the ramus; and angulation registered at the functional occlusal plane. Analysis of variance and ordinal logistic regression were used to investigate relationships between the variables. Angulation of the third molars changed substantially with varying depths (p<0.0008) and A–P positions (p<0.0001), but did not appear to relate appreciably to dental age (p>0.5) or treatment condition (p>0.4). The A–P position was significantly correlated to dental age (p>0.004) and Bionator treatment (p<0.0001), whereas depth was marginally associated with dental age (p<0.07) and not influenced by Bionator treatment (p>0.5). Third molars adopt a position further anterior in relation to the ramus with Bionator treatment than they do in controls. As dental age increases, Bionator use appears to positively influence third molar position.     

Inferior alveolar nerve demage following removal of mandibular third molar teeth. A prospective study using panoramic radiography

Permanent alteration of sensation in the lip after the removal of mandibular third molar teeth is an unusual but important complication. Studies have been performed to assess the risk of nerve damage but most of these have been retrospective and poorly controlled.
This prospective trial predicted the outcome of altered sensation prior to surgery based on assessment of a panoramic radiograph and correlated this with the result postoperatively in the consecutive removal of 479 third molar teeth.
Result indicated that 5.2 per cent had transient alteration in sensation but only one patient (0.2 per cent) had prolonged anaesthesia. As 94.8 per cent of teeth extracted had no neurological sequelae the figures for prediction were skewed and a kappa statistical analysis of 0.27 illustrated a fair level of agreement between prediction and outcome.
This study supports previously reported levels of neurological damage and confirms that panoramic radiography is the optimum method for radiological assessment for mandibular third molar teeth prior to their removal.     

Radiation exposure during panoramic radiography in children.

In an effort to determine the amount of radiation exposure a child receives during a panoramic radiograph and to evaluate the effect of a protective thyroid collar, dosimeter readings were made on twenty-nine child patients at fourteen anatomic sites. The levels of radiation recorded were similar to those previously recorded for adults and phantoms, except for greater doses in the thyroid area. Placement of a lead-lined thyroid collar resulted in significant reduction of the thyroid doses.     

Intraoral or panoramic radiography?

When panoramic radiographs are used to replace full-mouth radiographic series for the pediatric patient, certain advantages and disadvantages of this technique should be understood. The panoramic exposure offers ease of operation, shorter working time, and greater coverage than does the intraoral full-mouth series. However, certain shortcomings are noted. Rotations of maxillary premolars appear where there are none, and confusion exists in the anterior region about rotated teeth. Supernumerary teeth are frequently missed on the panoramic film in the anterior region. Because of this it is wise to supplement the panoramic image with anterior periapical films. Posterior bitewing films are a necessary supplement to the panoramic examination and with them interproximal caries, periapical lesions, and other details not visualized on the panoramic film are noted. It is imperative that the dentist understand confusing panoramic images that result from motion, superimposed structures, and apparent rotations, so that missed diagnoses do not occur.     

Evaluation of impacted maxillary canine position using panoramic radiography and cone beam computed tomography

IntroductionLocalization of impacted maxillary canine (IMC) position is essential in orthodontic treatment for accurate orthodontic treatment as well as prognosis.ObjectivesThis study aimed to: 1- investigate the relationship between the locations of IMC in panoramic radiograph (PR) using sectors in relation to their labio-palatal position in cone beam computed tomography (CBCT): 2- report the incisor root resorption in CBCT in relation to its sector location of IMC in PR.Material and MethodsThe study is a retrospective imaging assessment of 60 IMCs in multiple centers in Riyadh, Saudi Arabia. Sector location of IMC was determined on the PR and correlated with each of their labio-palatal positions and resorption of the root of permanent incisors using CBCT.ResultsThere is a significant correlation between sector location and impaction location of IMC. No statistical correlation was found between IMC sector location and lateral incisor root resorption, whereas a significant correlation was found between sector location and central incisor root resorption.ConclusionsFor Sectors I and II, IMC tended to be in either the mid-alveolus or labial location, whereas Sectors III and IV tended to show palatal impaction. Therefore, sector could be a good tool for localization of IMC and to predict the possibility of incisor root resorption.     

Patient-selection criteria for panoramic radiography

The purpose of this study was to determine whether selection criteria could be developed for the use of panoramic radiographs in the treatment planning of patients seeking dental care. A total of 1,424 patients were included in this 10-month study. Clinicians were asked to indicate what signs or symptoms caused them to order a panoramic radiograph. After the radiograph was taken, the referring clinician was asked to indicate the extent that the panoramic radiograph influenced the patient's care. The panoramic examination was found to be most productive in dentulous patients when no other radiographs were ordered and least productive in dentulous patients who had already had a full-mouth set of radiographs. Considering all patients, it is possible to reduce the number of panoramic examinations by 73% while missing 6% of the findings that influence patient treatment. The most important selection criteria for the panoramic examination are whether the radiograph was ordered for a "general screening examination" (a negative predictor) and whether the radiograph was ordered for any specific examination (a positive predictor).     

Nonrotational scanning in panoramic radiography

A mathematical analysis of orthoradiography, nonrotational scanning in panoramic radiography, and rotational panoramic radiography shows that they may all be described by the same set of equations. The other two techniques may be regarded as special cases of rotational panoramic radiography.     

Fine-detail panoramic radiography by free-focus radiography. A clinical demonstration of diagnostic radiographs

Previous comprehensive clinical studies have shown that free-focus radiography (FFR) may be used to improve image detail and diagnostic value in panoramic radiography of the teeth and jaws. This study demonstrated the clinical image quality in fine-detail panoramic FFR surveys relative to conventional surveys made by rotational panoramic or intraoral radiography. Cases of particular diagnostic interest with respect to common dental disease and changes in the jaws were included. The radiographic area of diagnostic interest depicted in FFR surveys generally resembled that of conventional dental radiographic surveys with the use of intraoral films rather then those of conventional rotational panoramic surveys.     

Aspects of panoramic radiography in general dental practice.

OBJECTIVES: To gather information on the types of panoramic x-ray equipment used in NHS dental practice and whether dentists satisfy the legal requirements for safety, to determine which practice personnel take panoramic radiographs and to assess the prevalence of the practice of 'routine' panoramic radiography among NHS dentists. DESIGN: Postal questionnaire survey of general dental practitioners carried out during 1997 in selected FHSAs in England and Wales. RESULTS: 542 dentists returned the questionnaire, a 73.3% response. Panoramic x-ray equipment ranged in age from 27 years old to new, with 42.2% exceeding 10 years in age. The overwhelming majority of GDPs satisfied the requirement for regular maintenance and surveying of equipment. Almost all dentists (95.9%) performed a history and clinical examination prior to panoramic radiography but 42% practised 'routine screening' of new adult patients. A substantial proportion (36.7%) of dentists used unqualified personnel to take panoramic radiographs. CONCLUSIONS: While some aspects of this study give reassurance about the prevalence of good practice, widespread panoramic screening and using unqualified staff to take radiographs causes concern. These findings have implications for educators and for those involved in maintaining clinical standards.     

Digital versus conventional panoramic radiography in predicting inferior alveolar nerve injury after mandibular third molar removal

The aim of the study was to compare the accuracy of conventional and digital panoramic radiography (OPG) in relation to 4 specific high-risk signs (interruption of the superior cortical line, diversion, narrowing of the canal, and dark band of the root), which would indicate a close anatomic relationship between third molar roots and the inferior alveolar canal.Four hundred mandibular third molar surgical removals after conventional and 272 after digital radiographs were evaluated in the study. The association between postoperative inferior alveolar nerve (IAN) paresthesia and the presence of any preoperative high-risk signs in the OPG was investigated. Bivariate and multivariate logistic regression analyses were completed to compare the accuracy of conventional and digital radiographic techniques detecting high-risk signs predicting possible IAN paresthesia.Digital OPG results showed significantly higher sensitivity in diversion (P = 0.014) and narrowing (P < 0.002) of the canal, whereas the specificity of these signs was significantly lower (P < 0.001 and P = 0.035). The likelihood ratio analysis and multivariate logistic regression analysis did not prove the significant difference between digital and conventional imaging according to the examined high-risk signs. Positive predictive values of the signs were found in conventional radiography between 3.6% and 10.9%, whereas in the digital images, it ranged from 2.9% to 7.9%.The results of this study failed to prove significant difference between the accuracy of digital and conventional OPG for predicting IAN paresthesia, whereas low positive predictive values indicate both imaging techniques as inadequate screening methods for predicting IAN paresthesia after mandibular third molar removal.     

The current status of panoramic radiography

The current status of dental panoramic tomography (rotational panoramic radiography) is reviewed. This technique is based on a combination of tomography and slit-beam radiography to provide an image of both jaws on a single film. There is a greater degree of image degradation when compared with conventional radiographic techniques due to tomographic blurring, magnification and distortion, secondary images and burn-out. Meticulous patient position is essential to accommodate their jaws to the image layer determined by the manufacturers. The absorbed doses from panoramic radiography are of a similar order to that from bitewing radiography and lower than those from a full-mouth periapical series. The individual risk of 1.3 X 10(-6) is compared with that from other radiographic examinations and smoking. The collective risk, 1.04 deaths in the UK in 1981, is relatively insignificant as is the genetic dose. The risk to the dentist and his staff is also low compared to other risks. The methods of dose limitation currently available are reviewed. The clinical indications are considered in relation to the guidelines of the American Dental Association and the Dental Estimates Board in the UK. The problems associated with attempts to measure diagnostic yield are considered. In view of the world-wide public concern at the potential dangers of ionising radiation, dentists are urged to maximize the diagnostic yield from their panoramic radiography by taking such radiographs only when clinically necessary, ensuring meticulous positioning and processing, followed by scrupulous assessment of the radiography for any sign of pathological change.     

颅骨-锁骨发育不全综合征在曲面体层片上的影像特点

目的 分析颅骨-锁骨发育不全综合征在曲面体层片上的特征性表现。方法 颅骨-锁骨发育不全综合征18例，在曲面体层片上观察牙，颌骨及颧弓等发育情况。对7例进行了随访观察。结果 （1）牙发育异常；乳牙滞留（14/18），恒牙迟萌（16/18），牙发育畸形（11/18），多生牙及阻生牙（各18/18），含牙囊肿形成（5/18）及继生多生牙（4/7）；（2）颌面骨发育异常；牙槽骨致密（9/18），骨小梁粗糙（18/18），升支前后继呈平行（14/18），喙突尖小（12/18）及颧弓下弯畸形（18/18）。结论 （1）建议用骨-牙发育异常综合征命名较妥；（2）只需一张曲面体层片即可对本病作出正确诊断；（3）因本病进行正畸治疗应定期曲面体层片随访，以便早发现继生多生牙，早处理。     

全颌曲面体层片和根尖片测量线距准确性的对比研究

目的：探讨全颌曲面体层片和根尖片在测量颌骨牙根区域线距时准确性的差异。方法：选取20例12～16岁的恒牙列正畸患者的记存模,在模型中嵌入5.00 mm钢珠作为标准参照物,分别拍摄全颌曲面体层片和根尖片,测量磨牙区、前磨牙区、尖牙区和切牙区影像中钢珠的水平径和垂直径,比较两种拍摄方法的测量值在各区域的变化,并与钢珠的真实值进行比较。结果：全颌曲面体层片测量值的失真率在后牙区较小,前牙区较大;根尖片的所有测量值中,失真率除少数前牙区较大外,其余区域的测量值接近;全颌曲面断层片水平测量值失真率较垂直测量值失真率大,根尖片则两者相近;全颌曲面断层片测量值较根尖片更接近实际值,但影像的放大率变化较大,而根尖片影像的放大率较大,但其失真率更恒定。结论：如使用标准参照物校正测量值,根尖片对颌骨内牙根区域线距的测量结果更可靠。