The Journey of Panoramic Radiography – A Review (Part I)

Category: Review

Author: Dr Manish Kumar, House Surgeon, NSVK Sri Venkateshwara Dental College and Hospital, Bangalore, Karnataka

Co-Author: Dr Gaurav, BDS, SCADA (USA), MDS, Consultant Oral Physician and Maxillofacial Radiologist, Assistant Professor, Dept of Oral Medicine and Maxillofacial Radiology, NSVK Sri Venkateshwara Dental College and Hospital, Bangalore, Karnataka.

Abstract

Head and neck imaging has undergone tremendous improvement and progress since the time of its inception. The growing complexity of various pathologies have increased the demand for better and more equipped imaging tool as a mode of investigation in various arenas. Amongst the various conventional imaging modalities, Orthopantomography (OPG) which is now known as the Panoramic Radiograph has been an important adjunct to clinical evaluation since the very beginning. The scout image that is obtained by this method gives physicians and clinicians an overall idea of the maxillary and mandibular components in toto. This 2 part series on OPG therefore aims to discuss and highlight various aspects of this imaging modality or in other words, its journey from 'then' to 'now'.

Keywords

Panoramic, orthopantomogram, imaging modality

Introduction

“The eyes only see what the mind knows”. Is this proverb apt? In diseases of the oro-facial region, clinical evaluation is indeed a great tool to detect, understand and treat pathologies. In fact this was the only means that existed for a very long time. But in the present days due to limitless emerging technologies, newer methods of disease detection are available. Most important among them has been the invention and use of X-rays which is a form of ionising radiation. This magical ray has indeed developed over the years by leaps and bounds and has almost taken up a lion share among the many investigative modalities.1,2 In the field of dentistry and investigations of oro-facial diseases, X-rays play a vital role. Both conventional and digital forms of this investigation are being used routinely in screening, diagnostic and therapeutic procedures. Among them, one of the most used screening X-ray tool is OPG, used in order to analyse the overall status of the teeth and their associated structures in maxilla and mandible.

But it needs more to gain more, human race has had to pay dearly in terms of detrimental effects of radiation and health hazards at large. In the present scenario we are addressing the question whether X-rays are absolutely mandatory or is clinical evaluation enough in diagnosing the same. The clinical dental examination includes, in addition to assessment of the mucous membranes, the condition of the teeth – healthy or carious, the restorative and prosthetic treatment of the teeth – sufficient or insufficient, as well as sensitivity testing and determination of the periodontal situation. 3, 4

Hence the present review aims to take us through a timeline of the journey of Panoramic Radiography from its inception to its present scenario and to find out if imaging is mandatory or optional for diagnosis & treatment.

Clinical Evaluation in Oral Diagnosis

Oral examination, is an area of physical diagnosis that for a variety of reasons traditionally receives minimal emphasis in the predoctoral medical curriculum. Nevertheless, much information can be gained through a systematic evaluation of the oral hard and soft tissues. While the primary objective is to distinguish between health and disease, a comprehensive oral examination in conjunction with a thorough medical and dental history can also provide valuable insight into the overall health and well-being of a patient. 5, 6

While the vast majority of soft tissue lesions in the oral cavity represent infectious, traumatic, or reactive processes rather than neoplasms, the precise etiology can often be determined through a careful history and clinical examination. For e g, medication adverse effects like xerostomia can have a profound effect on oral health. For that reason, a detailed drug history should be routinely obtained.7 When the clinical diagnosis of an oral lesion cannot be confirmed on the basis of its signs and symptoms, an oral examination can be supplemented by a biopsy of the oral soft tissues. In the vast majority of cases, the microscopic findings, in conjunction with the clinical examination, are sufficient to confirm the diagnosis. In addition to this, various radiological aids, from the conventional to the advanced modalities have always been an adjunct to the clinical evaluation when landing onto a diagnosis becomes a dilemma. 8, 9, 10

Radiological Perspective in Oral Diagnosis

An image is the representation of a real or virtual object. Although the human brain can conjure up images of both perceptible and intangible objects, in the realm of medical imaging, we largely deal with perceptible images of tangible, though often inaccessible objects. The interpretation of the images, however, involves many unseen thought processes and levels of sophistication which only the brain can contrive.11 Medical science thrived and flourished out of man’s eternal curiosity and fascination for his own body and his urge to unravel its internal mysteries. Roentgen’s discovery of X-rays revolutionised his efforts and paved the way for ‘looking inside’ the body from outside. Indeed, the X-ray has given access to every nook and corner of the human body, and 100 years on, it continues to be the cornerstone of many imaging modalities. Technological progress in the last three decades alone has been amazing in every sphere of human endeavour and contributed to the advancement of medical science through the accelerated pace of scientific research. The continuous and rapid transition of techniques from research laboratory into clinical practice has been the pattern of development in radiology, imaging and intervention over this phase of time. Apart from refining and perfecting X-ray systems and techniques, pioneering imaging modalities and technologies like CT, MRI, ultrasound were developed and utilised. 12, 13, 14 Thus, in the 105 years since Roentgen’s ‘new kind of ray’ surfaced, technology has grown leaps and bounds, transforming diagnostic imaging into a sophisticated science with ever-broadening clinical applications based interventional radiology. This has added a whole new dimension and scope to the medical practice itself, substantially altering the treatment options for several ailments. All this has put the concept and role of clinical imaging into a different scenario with growing relevance. 15

Radiological practice over the years went alongside its mainline clinical specialities and although the system continues, the current exalted status of radiology gives its proponents a niche of their own. Gone are the days of the armchair radiologist who, in the eyes of the public and even for educated medics was just a technician who dwelled with few films and predicted some diagnosis. The radiologist’s role was one of pattern recognition; whether a radiograph was normal or abnormal. 16 Often we have to be content in saying a lesion is present without giving a definite pathological diagnosis. The tools at their disposal has transformed the radiologist today, elevating their task of reporting to a comprehensive clinical imaging assay, giving information at a level profound enough to be useful for scientists working in allied fields. To extract the best out of any image and give it scientific meaning it must be analysed with the backdrop of the clinical history, findings, laboratory data, previous imaging information, etc. It is the radiologist’s prerogative to see the patient, gather history, undertake clinical examination and analyse laboratory data if they so wish. It cannot be overemphasised that clinical information and imaging findings are mutually complementary.17,18 The radiologist and their clinical colleague are two different realms on either side of a coin; the common core being the patient at the centre of their interests.

A complex and multisystem disease invariably requires imaging support to land onto a confirmatory diagnosis. It provides an easy tool to assess the extent of disease spread and is invaluable in staging neoplasms. 19, 20, 21 Imaging also permits an easy noninvasive follow-up of patients. Often imaging is undertaken just to document a known abnormality. Interventional radiology has paved the way for rewriting earlier textbooks regarding the management of several diseases. Currently available high precision gadgets allow entry to surgically inaccessible areas. Another major advantage is that most of these procedures can be repeated many times over, unthinkable with open surgery. 22, 23 As a symptom per se does not yield any clinical diagnosis, radiographic appearance is also not specific most of the time. With modern imaging techniques the presence of an abnormality is often obvious. Diagnostic accuracy is central to maintaining the larger relevance of the specialty.

A high percentage of today’s clinical work in imaging depends on well-established radiological techniques, the interpretation of the image being dependent on clearly defined and accepted anatomical and pathophysiological correlations. 24, 25 This basic corpus of accepted knowledge must however be kept up-to-date by the specialist. Keeping pace with expanding knowledge in medical science is a major challenge. One way to deal with this problem is to broaden the knowledge base of everyone who later specialises in this as a career choice. The liberal education of the radiologist is the cornerstone of all radiological practice. 26 One approach has been to subspecialise, thereby narrowing the range of knowledge required to do a good job, but in doing so, we have in many instances diminished the role, content and generalism in radiology. In Einstein’s words, no man can ever learn everything in this world, the ultimate you can do is appreciate the mysterious. 27, 28 It is important that radiology maintains its role in integrating the various disciplines involved in medical care. For that, the personnel involved must have an appreciation of the breadth and scope of the entire field. 29, 30 Imaging science has kept pace with the developments and has been at the cutting edge of advances in technology ever since the introduction of newer imaging modalities, like CT and MRI, which are in fact the greatest breakthroughs in imaging science since the discovery of X-rays themselves. These pioneering innovations moved the speciality from conventional methods of static imaging, providing purely anatomical information to more dynamic options helping to acquire useful pathophysiological data. 31, 32, 33

Probably, no field of medicine is advancing as rapidly at present as imageology. Technological advances have elevated diagnostic imaging to the level of a sophisticated science, to the extent that images are more easily interpretable as straightforward representations of anatomy. But science, scientific education and medical practice are evolutionary processes that require constant tuning, refinement and overhaul of its faculties. 34, 35 The imageologist apart from being adept in their chosen field requires equipping his mind simultaneously to be a handy physician, a surgeon, a pathologist and an effective therapeutist. 36 Only then can they make efficient use of the technological marvels at their disposal, upgrade their acumen and utility and contribute to the advancement of medical science itself. Radiological practice with a flawless clinical attitude and aptitude alone will thrive in a ruthlessly competitive world and help maintain the pivotal role radiology has in integrating the various disciplines involved in medical and dental care. 37, 38 Hence, in this enormously advancing field of oral and maxillofacial radiology, the role of panoramic radiography which was the first ever tomography to be carried out, still holds good in establishing the lesions of hard tissue at the first instance, being used as a scout image. 39

In the field of imaging, the Intra Oral Periapical Radiographs (IOPARs) are widely used as the commonest aids which could complement the clinical evaluation. However there are various disadvantages in this field of imaging which can be overcome with a radiograph that has a wider field of view and covers not only the structures of maxilla and mandible but some of the surrounding structures as well. Owing to its huge panorama of coverage, besides the pathological findings of our interest, there are numerous incidental findings as well that can be encountered on a panoramic radiograph which are termed as 'occult' findings. These incidental or the Occult findings on the panoramic radiograph form the mainstay of our study. 40, 41, 42

Panoramic Radiography – An Important Wing in Oral Radiology

Also known as the rotational panoramic radiography method or 'Pantomography' was first proposed and experimented by Dr H Numata of Japan in the year 1934. 43 The panoramic radiograph continues to offer today's dentist, a unique patient view, covering the entire dentition and surrounding structures, the facial bones and condyles and parts of the maxillary sinus and nasal complexes. The equipment used to obtain panoramic radiographs has continued to improve with recent advances, including automatic exposure and multiple image programs. However, achieving diagnostic panoramic images requires attention to the basic steps and correct patient positioning. Once the error has been assessed, possible solutions to the problem are suggested. The result will be panoramic radiographs with the maximum diagnostic detail and information that the equipment and technique allow. 44

History of Panoramic Radiography

Panoramic radiographs were made using basically two different methods

1. Intra oral source of radiation
2. Extra oral source of radiation

Intra oral Source of Radiation

The radiation is directed from inside the mouth through the jaws and exposes a film moulded to the outside of the face of the patient

• X-ray tube is inside the mouth
• No screen or slow speed screen films are used
• X-ray source, Patient and Film 45, 46

within time however, the intra oral film method was abandoned due to

• The limited space within the oral cavity to reveal all necessary structures.
• Separate exposures were required for each of the jaws

Extra Oral Source of Radiation

1946

• Dr Y Veli Paatero, Finland The Father of Panoramic Radiography experimented slit beam method of panoramic radiography for dental arches
• Patient was moved by means of a rotating chair
• X-ray source was stationary
• Paatero called this technique 'Parabolography'. 47, 48

1949

• Paatero used parabolographic technique by placing the film extra orally
• Film cassette and patient revolved with same velocity on a single vertical axis
• X-ray remained stationary
• This technique is called 'Pantomography'. 48, 49

1958

• Dr Eiko Sairenji of Japan suggested name Orthopantomography to Dr Paatero
• Patient sits or stands immobile while the X-ray tube rotates behind neck and a curved film cassette moves around the face, rotating on its own axis
• It revolves on 3 successive rotational axes: one concentric rotational axis for anterior portion of jaw and two eccentric axes for each side of the jaws. 48, 49, 50

History of Digital Panoramic Imaging

1985-1991: The first attempt to build a dental digital panoramic was of McDavid et al. at UTHSCSA. Their idea was based on a linear pixel array (single pixel column) sensor which was not appropriate for such an application because

1. There was no tomographic effect;
2. Huge difficulties to collimate the x-rays beam and to control the x-ray dose delivered to the patient;
3. Poor generator efficiency.

DXIS – real time display

1995: DXIS, the first dental digital panoramic x-ray system available on the market, created by Catalin Stoichita at Signet (France). DXIS targeted to retrofit all the panoramic models.

1997: SIDEXIS, of Siemens (currently Sirona Dental Systems, Germany) offered a digital option for Ortophos Plus panoramic unit, DigiPan of Trophy Radiology (France) offered a digital option for the OP100 panoramic made by Instrumentarium (Finland).

1998-2004: Many panoramic manufacturers offered their own digital systems.

2006: SCAN300FP, of 'Ajat' (Finland) is the latest innovation offered. It shows the feature to acquire many hundreds of megabytes of image information at highframe rate and to reconstruct the panoramic layer by post acquisition computing. 51, 52

Panoramic Theory

Why is panoramic radiography inherently technique sensitive? Panoramic radiography is a modified type of tomography or image layer radiography. The patient’s dental arch must be positioned within a narrow zone of sharp focus known as the “focal trough”/imaging plane, designed by panoramic machine manufacturers as the ideal patient position to produce the optimum image. Distortion of the image quality occurs when patients are not properly positioned, such as if the chin is tipped up or down too much, midline rotated off machine centre, anterior teeth/jaws too far forward or back. 53, 54 These result in vertical and horizontal magnification and distortion, superimposition of anatomical structures, and some structures being projected out of the field of view. In such cases, the interpretation of the resultant image is severely compromised. The adjoining figure shows the various normal anatomical landmarks as observed on an ideal panoramic radiograph.

Radiation Dosage

Generally, intraoral digital radiography is touted as requiring 70 – 90% less radiation than that for traditional film radiography. Making such claims is not necessarily valid. The key to understanding these reductions is knowing what is being compared. 55 The 70 – 90% reductions compare to Ultra speed “D” film, the slowest film used in dentistry today. If comparison is made to faster 'F' film, such reductions are negated and the exposure is in a similar range for digital radiography. Patient size influences the amount of radiation necessary to produce a diagnostically useful radiographic image. 55, 56 Larger patients require more radiation than smaller, meaning an increase or decrease in both the X-ray energy (kVp) and the amount of X-ray as determined by either the milliamperage (mA) and/or exposure time. Recent studies comparing the effective patient dose for digital to conventional panoramic radiography have reported varied results. Reported effective doses for digital are 4.7 μSv to 14.4 μSv and 45 μSv. For conventional film panoramic radiography, effective values are 16–21 μSv and 54 μSv. Results from Visser and Gijbels are similar and indicate a digital advantage ranging from a 13 – 77% reduction. The actual dose values reported by Kiefer are greater than for the other studies but the digital advantage is within range at 17% reduction. Variations in study design and machines used for evaluation tend to produce wide ranging data, but overall, the results support the notion that digital imaging does reduce patient exposure for panoramic radiography. 57, 58

OPTs are used by healthcare professionals to provide information on

• Impacted wisdom teeth diagnosis and treatment planning – the most common use is to determine the status of wisdom teeth
• Trauma to the jaws
• Periodontal bone loss and periapical involvement
• Assessment for the placement of dental implants
• Orthodontic pre and post-operative assessment of occlusion and other factors
• Diagnosis of developmental anomalies such as cherubism, cleido cranial dysplasia etc
• Carcinoma in relation to the jaws
• Temporomandibular joint dysfunctions and ankylosis
• Detection of several conditions like osteosarcoma, ameloblastoma, renal osteodystrophy affecting jaws
• Diagnosis, and pre- and post-surgical assessment of oral and maxillofacial trauma, e g dentoalveolar fractures and mandibular fractures
• Salivary stones (Sialolithiasis). 59, 60

Advantages of Panoramic Radiography

Patient convenience and compliance where in the entire oral cavity can be imaged in a single film due to its wide coverage.

• In patients with trismus and gagging where there is reduced mouth opening and the intraoral examination cannot be carried out
• Maxilla, mandible and their supporting structures seen due to broader field of coverage and vision
• Visual aid in patient education where in various impending disorders could be explained to the patients using the panoramic radiographs as teaching aids
• Better visual relationship of teeth with each other and adjacent structures
• Assessment of unerupted supernumerary and impacted teeth
• Demonstrates periodontal disease in general way that includes the presence of pockets, localised or generalised bone loss
• Assessment of primary dentition
• In localisation of an object with other views, i e, once the findings are suspected on the panoramic radiographs, their exact location and dimension can be assessed with the help of other radiographs. Hence the OPG works as a scout image. 38, 62

Disadvantages of Panoramic Radiography

• Does not display fine anatomic details
• Does not display fine carious lesions, periapical disease, fine structures of periodontium
• Proximal surface of premolars overlap
• Unequal magnification and geometric distortion
• Clinically important objects outside the line of focus get distorted or are not seen
• Early alveolar bone loss not seen
• Poor detection of incipient dental caries
• Analysis of trabecular bone changes associated with early periapical lesions. 17, 19, 61

Panoramic Radiography as an Emerging Research Tool

There is a keen interest amongst the researchers in order to use panoramic radiographs as a screening tool, however further data is needed with regard to, if it is able to make a meaningful difference in outcomes. Taking this aspect and growing trend into consideration, our study was planned in order to compare the radiographic examination (using panoramic radiography) with that of the clinical in terms of efficacy and accuracy and to find out occult pathologies missed out in the clinical examination. 63

The next and the concluding volume of this article would include various studies that have been conducted in order to highlight the significance of panoramic radiography exclusively in addition to the various indications and conditions in which panoramic radiography is a mandatory investigative imaging modality.

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