A panoramic radiograph is a panoramic scanning dental X-ray of the upper and
lower jaw. It shows a two-dimensional view of a half-circle from ear to ear.
Panoramic radiography is a form of tomography; thus, images of multiple
planes are taken to make up the composite panoramic image, where the
maxilla and mandible are in the focal trough and the structures that are
superficial and deep to the trough are blurred.
Other nonproprietary names for a panoramic radiograph are dental
panoramic radiograph and pantomogram; trade names are Panorex and
Orthopantomograph. Abbreviations include PAN, DPR, OPT, and OPG.
Types Dental panoramic radiography equipment
consists of a horizontal rotating arm which holds an X-ray source and a moving
film mechanism arranged at opposed extremities. The patient's skull sits
between the X-ray generator and the film. The X-ray source is collimated
toward the film, to give a beam shaped as a vertical blade having a width of
4-7mm when arriving on the film, after crossing the patient's skull. Also the
height of that beam covers the mandibles and the maxilla regions. The arm moves
and its movement may be described as a rotation around an instant center which
shifts on a dedicated trajectory. The manufacturers propose different
solutions for moving the arm, trying to maintain constant distance between the
teeth to the film and generator. Also those moving solutions try to project
the teeth arch as orthogonally as possible. It is impossible to select an
ideal movement as the anatomy varies very much from person to person. Finally
a compromise is selected by each manufacturer and results in
magnification factors which vary strongly along the film. The patient
positioning is very critical in regard to both sharpness and distortions.
= Films = There are two kinds of film moving
mechanisms, one using a sliding flat cassette which holds the film, and
another using a rotating cylinder around which the film is wound. There are two
standard sizes for dental panoramic films: 30 cm × 12 cm and 30 cm x 15 cm.
The smaller size film receives 8% less X-ray dosage on it compared to the
bigger size. = Digital =
Dental X-rays' radiology is moving from film technology to digital X-ray
technology, which is based on electronic sensors and computers. One of the
principal advantages compared to film based systems is the much greater
exposure latitude. This means many fewer repeated scans, which reduces costs and
also reduces patient exposure to radiation. Lost X-rays can also be
reprinted if the digital file is saved. Other significant advantages include
instantly viewable images, the ability to enhance images, the ability to email
images to practitioners and clients, easy and reliable document handling,
reduced X-ray exposure, that no darkroom is required, and that no chemicals are
used. One particular type of digital system
uses a photostimulable phosphor plate in place of the film. After X-ray exposure
the plate is placed in a special scanner where the latent formed image is
retrieved point by point and digitized, using a laser light scanning. The
digitized images are stored and displayed on the computer screen. This
method is in between old film based technology and the current direct
digital imaging technology. It is similar to the film process because it
involves the same image support handling and differs because the chemical
development process is replaced by the scanning process. This is not much
faster than film processing and the resolution and sensitivity performances
are contested. However it has the clear advantage of being able to fit with any
existing equipment without any modification because it replaces just
the existing film. Also sometimes the term "digital X-rays"
is used to designate the scanned film documents which further are handled by
computers. The other types of digital imaging
technologies use electronic sensors. A majority of them first convert the
X-rays in light which is further captured using a CCD or a CMOS image
sensor. Few of them use a hybrid analog-to-digital arrangement which
first converts the X-ray into electricity and then this electricity is
rendered as an image by a reading section based on CMOS technology.
In current state-of-the-art digital systems, the image quality is vastly
superior to conventional film-based systems. The latest advancements have
also seen the addition on Cone Beam 3D Technology to standard digital panoramic
devices. Indications
OPTs are used by health care professionals to provide information on:
Impacted wisdom teeth diagnosis and treatment planning - the most common use
is to determine the status of wisdom teeth and trauma to the jaws.
Periodontal bone loss and periapical involvement.
Finding the source of dental pain Assessment for the placement of dental
implants Orthodontic assessment. pre and post
operative Diagnosis of developmental anomalies
such as cherubism, cleido cranial dysplasia
Carcinoma in relation to the jaws Temporomandibular joint dysfunctions and
ankylosis. Diagnosis of osteosarcoma,
ameloblastoma, renal osteodystrophy affecting jaws and hypophosphatemia.
Diagnosis, and pre- and post-surgical assessment of oral and maxillofacial
trauma, e.g. dentoalveolar fractures and mandibular fractures.
Salivary stones. Other diagnostic and treatment
applications. Mechanism
Normally, the person bites on a plastic spatula so that all the teeth,
especially the crowns, can be viewed individually. The whole orthopantomogram
process takes about one minute. The patient's actual radiation exposure time
varies between 5.5 and 22 seconds for the machine’s excursion around the
skull. The collimation of the machine means
that, while rotating, the X-rays project only a limited portion of the anatomy
onto the film at any given instant but, as the rotation progresses around the
skull, a composite picture of the maxillo-facial block is created. While
the arm rotates, the film moves in a such way that the projected partial
skull image scrolls over it and exposes it entirely. Not all of the overlapping
individual images projected on the film have the same magnification because the
beam is divergent and the images have differing focus points. Also not all the
element images move with the same velocity on the target film as some of
them are more distant from and others closer to the instant rotation center.
The velocity of the film is controlled in such fashion to fit exactly the
velocity of projection of the anatomical elements of the dental arch side which
is closest to the film. Therefore they are recorded sharply while the elements
in different places are recorded blurred as they scroll at different velocity.
The dental panoramic image suffers from important distortions because a vertical
zoom and a horizontal zoom both vary differently along the image. The
vertical and horizontal zooms are determined by the relative position of
the recorded element versus film and generator. Features closer to the
generator receive more vertical zoom. The horizontal zoom is also dependent on
the relative position of the element to the focal path. Features inside the
focal path arch receive more horizontal zoom and are blurred; features outside
receive less horizontal zoom and are blurred.
The result is an image showing sharply the section along the mandible arch, and
blurred elsewhere. For example, the more radio-opaque anatomical region, the
cervical vertebrae, shows as a wide and blurred vertical pillar overlapping the
front teeth. The path where the anatomical elements are recorded sharply
is called "focal path". = Principal advantage of panoramic
images = Broad coverage of facial bones and teeth
Low patient radiation dose Convenience of examination for the
patient Ability to be used in patients who
cannot open the mouth or when the opening is restricted e.g.: due to
trismus Short time required for making the image
Patient's ready understandability of panoramic films, making them a useful
visual aid in patient education and case presentation.
Easy to store compared to the large set of intra oral x-rays which are typically
used. Preparation
Persons who are to undergo panoramic radiography usually are required to
remove any earrings, jewellery, hair pins, glasses, dentures or orthodontic
appliances. If these articles are not removed, they may create artifacts on
the image and reduce its usefulness. There is also a need for the person to
stay absolutely still during the 18 or so second cycle it takes for the machine
to expose the film. For this reason, radiographers often explain to the
person beforehand how the machine will move.
Adverse effects Like any medical imaging utilizing
ionizing radiation, there will be a minute degree of direct ionizing damage
and indirect damage from free radicals created during the ionization of water
molecules within cells. A rough estimate of the risk of fatal cancer from a
panoramic radiograph is about 1 in 20,000,000. The age of the person being
imaged also alters the risk, with younger people having a slightly higher
risk. E.g. the 1 in 10,000,000 risk would be doubled for someone in the 1-10
age group. History
= Historical milestones for Digital Panoramic Systems =
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 is was not appropriate for such application
because: a) there is no tomographic effect; b) huge difficulties to
collimate the X-rays beam and to control the X-ray dose delivered to the patient;
c) poor generator efficiency. 1995 - DXIS, the first dental digital
panoramic X-rays system available on the market, created by Catalin Stoichita at
Signet. DXIS targeted to retrofit all the panoramic models.
1997 - SIDEXIS, of Siemens offered a digital option for Ortophos Plus
panoramic unit, DigiPan of Trophy Radiology offered a digital option for
the OP100 panoramic made by Instrumentarium.
1998-2004 - many panoramic manufacturers offered their own digital systems. 2006
- SCAN300FP, of 'Ajat' is the latest innovation offered. It shows the feature
to acquire many hundreds of mega bytes of image information at high frame rate
and to reconstruct the panoramic layer by post acquisition computing.
Research Panoramic radiographs have the
capability to demonstrate a portion of the neck and display atheromas which are
an indication of both local and generalized atherosclerosis.
Atherosclerosis of the coronary arteries leading to myocardial infarction, and
atherosclerosis of the carotid artery leading to stroke are the number one and
number three most common causes of death in the United States.
There is interest to look at panoramic radiographs as a screening tool, however
further data is needed with regards if it is able to make a meaningful
difference in outcomes. = Epidemiology: General Public and High
Risk Groups = Additional research projects have
further determined the prevalence rate of these atheromas in the general
population and among high-risk groups. These findings have been corroborated by
other several other researchers. = Dental Infection and Atherosclerosis =
Atherosclerosis is attributed to risk factors that include cigarette smoking,
hyperlipidemia, obesity, diabetes mellitus, and hypertension. These
factors, however, do not fully account for the risk of disease. Atherosclerosis
has been conceptualized as a chronic inflammatory response to endothelial
cell injury and dysfunction possibly arising from chronic dental infection.
In 2010, using the previously validated Mattila panoramic radiographic index to
quantify the totality of dental infection, Friedlander’s group
determined that individuals with carotid artery atheromas on their panoramic
radiographs had significantly greater amounts of dental infection/inflammation
than atherogenic risk-matched controls devoid of radiographic atheromas. While
the Mattila index had been previously used to relate the extent of dental
infection to coronary artery disease, this research is the first to link the
full range of dental disease that it measures to panoramic radiographs
evidencing calcified carotid artery atherosclerosis.
References See also
Oral and maxillofacial radiology