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i. Definitions:
- Radiology: is a clinical science based on the diagnostic (radiodiagnosis) or therapeutic (radiotherapy) use of ionizing radiation. Diagnostic radiology is the field that most directly serves dentistry.
- X-ray: The term “x-ray” commonly applies to taking pictures of a patient.
Radiography is the photographic reflection of an object, recorded on a radiological image obtained by passing X-rays through this object.
- Imagery: An image is by definition the printed representation of any subject.
- biophysical principles of X-rays:
- When the cathode filament is heated to a high temperature by the current, a cloud of electrons is formed in the vacuum.
- These electrons projected at high speed will hit the target (tungsten plate) which will give rise to the X-ray
- It is by hitting the tungsten atom that the electron, abruptly stopped , releases its energy to form an X-ray photon.
- Electrons from the cathode can strip one or more K electrons from the tungsten atom.
ii. Radiographic materials:
1. generators
- The generator consists of:
- of the X-ray tube,
- power supply
- There are two types of Generator:
► Fixed kilovoltage generator : only the exposure time is variable.
► Variable power generators (from 50 to 100kv)
2- the cones:
The length of the cone varies from 10-50cm and therefore there are two types:
- Short cones:
- bisector technique.
- Due to their short length:
- Scattered radiation that impairs the quality of the radiological image
- They irradiate the patient unnecessarily and are gradually abandoned.
- long cones:
They come in different lengths.
- length from 35 to 50 cm
- collimation can be:
Different forms:
– circular 7.5 cm in diameter
– or rectangular with a section of 3.5-4.5 cm.
These cones are preferable because
- of image quality
- and the significant reduction of irradiation in the deep structures of the face
- .It requires a greater focus-object distance .
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3-the timers:
It ensures the passage of high voltage current in the X-ray tube, giving the correct exposure value depending on the area to be X-rayed.
They exist in three types:
- Mechanical timers.
- Electromechanical timers .
- Electronic timers.
4- The films; their accessories and their treatment:
- a. intraoral film:
The X-ray film is made of a 0.175 mm thick polyester support, covered on both sides with a thin adhesive layer (0.01 mm), a photosensitive emulsion (0.01 mm thick) and a protective layer of hard gelatin.
Silver halide crystals suspended in gelatin allow:
- increase the film sensitivity,
- improve X-ray absorption
- to reduce exposure time.
Intraoral films are presented in an opaque envelope to avoid exposure to light and any risk of humidity. In the film packaging there is a thin sheet of lead which helps reduce the irradiation of the tissues located behind the film, but whose purpose is mainly to limit blurring.
b. self-developing films:
Consisting of a hermetic main envelope in two-tone white-sky blue plastic material containing in its upper part, the X-ray film and in its slightly swollen lower part, a device containing an exclusive development and fixing solution. This film allows easier and instantaneous handling in full light.
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- Accessories:
a. the film doors:
- A support to keep the film flat and away from the tooth.
- means that eliminates exposure of the patient’s hand to radiation.
b- millimeter grids
These are accessories that are placed parallel to the film and allow, by simply reading the graduations on the film, to establish the root and canal lengths.
Rigid grids:
- Made from a very fine millimeter grid
- included in a plexiglass support of a slightly larger format than that of the honeycomb retro films.
- They are multi-use and sterilizable.
Flexible grids :
Made up of a sheet of self-adhesive paper carrying a radio-opaque millimetre.
They are expensive and single-use.
c. movie playback device:
The photographs are examined by transi lumination and enlargement using a viewing magnifying glass and variable intensity negatoscope:
- Negatoscope on dental chair for reading intraoral images
- negatoscope for extraoral images) .
- Film development:
- film development
a. classic manual development
It consists of developing the radiograph, that is to say going through four major stages: at a temperature of 20°C it is necessary:
- Soak the film after opening it in the developer for 4 minutes
- Rinse the film for 15sec
- Soak the film in the fixer for 10 minutes
- Finally, wash the film under running water for 20 minutes.
- Drying the film
b. Processing of self-developing film:
- Simply applying pressure with your hand to the lower part of the film allows the developer and fixer solution to pass quickly into the exposed area of the film.
- Massage for 30-45 seconds with your thumb from top to bottom.
- Turn the film upwards and bring the liquid towards its lower part.
- Open the envelope and grab the film with tongs and rinse it under water for 2 minutes and dry it afterwards.
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- Causes of failure of conventional radiography:
- Insufficient milliamperage and kilovoltage: clear X-ray image
- Excessive milliamperage and kilovoltage: image too dark and insufficient contrast
- Zero exposure: timer not triggered: clear transparent film.
- Overexposure: image too dark
- Underexposure image too bright and insufficient contrast
- Folded film before exposure: emulsion breakage, black lines after film processing.
- Film exposed twice: double image film uninterpretable in the majority of cases
- Film placed upside down: the radiation first reaches the lead sheet, and is largely absorbed, hence the underexposure of the film
- Tube mobilization during irradiation: blurred image
- Fingerprints: They are clear when you touch the film
- Transparent film: film mistakenly immersed first in fixer
- Yellow haze: resulting from the use of an exhausted or too weak developer
- Brown haze resulting from using an exhausted or too weak fixative
- Developer temperature too low: radiolar image.
- Developer temperature too high: dark image.
- Light yellow cliché after insufficient washing
iii. Radiographic techniques in conservative dentistry
Essential parameters in radiology:
- Exposure time: Or exposure time corresponds to the duration of the X-ray emission. This duration has an influence on the quality of the radiography with regard to density and contrast.
- Milli amperage (10 and 15 Milliamps): This is the number of electrons bombarded per second, i.e. the quantity of electricity passing through the tube
- Voltage (70KV): The voltage or potential difference between the anode and the cathode is expressed in Kilovolt. The kilovoltage determines the speed of the electrons and therefore the nature and quantity of the radiation.
- Focal length: This is the distance between the focus and the film , it influences the intensity of the X-rays which vary, according to Kepler ‘s law , inversely proportional to the square of the focus-film distance. The more this distance decreases, the more the radiological intensity increases at the object. If the focal length is doubled, the exposure time must be multiplied by 4
- Intraoral (conventional) radiography techniques
Commonly used intraoral radiographs are of three types
- periapical
- Inter proximal
and the occlusal .
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A- Periapical radiography techniques:
a. Preoperative X-ray:
It provides valuable information on:
- the general appearance of the tooth at the root and canal level ,
- it also reveals the possible existence of periapical or latero-radicular lesions , radiologically visible
b. Intraoperative radiography:
- It allows you to control the different phases of the treatment.
- the X-ray with the files in place helps to define the working length ;
- X-ray with gutta cones in place: this is the final check to be carried out after shaping the canals and before obturation.
- Other images: in the event of difficulties encountered during treatment (calcifications, search for a canal, stop, negotiation of curvature), images can be taken to facilitate the continuation of the treatment.
c. Post-operative X-ray:
- It plays an important role in endodontics and remains essential for immediately controlling the value of root canal fillings .
- It allows to monitor periapical and periodontal development and to verify in the long term the effectiveness of endodontic treatments
1. Orthogonal incidences:
This type of radiography can be used with the Bisector or parallel planes
- The “DIECK DITE” bisector technique:
Described in 1911, this is the old method of taking the retroalveolar image by the practitioner in the chair.
- Principle The director ray is perpendicular to the bisector of the angle formed by the major axis of the tooth and the plane of the film ( Cieszinski isometry rule ). The rules of the technique imply that the operator can virtually conceive the position of the bisector of this angle.
- Film placement and angulation technique in the bisector technique:
1)-In the upper jaw:
- Incisor and canine region:
The operator applies the film against the patient’s palate so that his thumb and the film are in contact with the free edge of the incisors. The lower edge of the film thus extends 5 mm beyond the free edge. The patient’s thumb of the opposite hand replaces that of the practitioner to hold the film in the chosen position, and the other fingers are as far away from the field as possible to allow maximum visibility. The operator must imagine the bisector of the angle formed between the plane of the film and the axes of the teeth, and he must orient the main ray on the middle of the tooth, perpendicular to the virtual bisector.
- PM and M region:
The film is placed horizontally. Once the film is in place, the thumb of the patient’s hand on the opposite side to be radiographed is introduced into the mouth. The film thus placed, the main ray is oriented perpendicular to the bisector of the angle formed between the plane of the film and the axis of the tooth.
2)-At the mandible:
- Central, lateral and canine incisor region:
The film is placed in a vertical direction. The upper edge of the film is against the free edge, which it protrudes by approximately 5 mm; The main ray is directed between the central and lateral incisors. For the canine, the ray must be centered on it.
- PM and M region:
For lower premolars and molars, the operator should stand in front of or to the right of the patient to place the film. The film should be held firmly against the tooth to be radiographed, taking care not to bend it. The tongue should be moved before placing an intraoral film in the lower premolar region.
B)- The technique of parallel planes:
More recent than the bisector method, the long cone technique , also called “parallel beams”, due to Ms Cormack , was perfected and disseminated by Fitzgerald .
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- Principle :
The film is held in the mouth behind and parallel to the major axis of the tooth being examined. Since the director ray is perpendicular to the tooth and the surface of the film, the latter must form a plane parallel to the major axes of the teeth to be radiographed. This technique requires the greatest possible focus-object distance (which is why the long cone is used to compensate for distortion by increasing the focus-object distance).
- Setting up the cliché and angulation procedure in the parallelism technique:
The strict conditions of orthogonality and parallelism of the radiation are ensured by the use of special angulators in which a bite block keeping the film parallel to the tooth is secured to a metal rod, on which a sighting ring slides.
Once the film positioning system is in the mouth, the end of the “long cone” cylinder is placed in contact with the ring and the parallelism of the rod and the cylinder is checked, which ensures the correct direction of the radiation.
1)-In the upper jaw:
Incisor and canine region:
The film is positioned vertically in contact with the palatal vault 2.5 cm behind the apices. It is parallel to the long axis of the central incisors. To achieve this positioning, the film must be held in place with cotton rolls, or fixed on a tongue depressor or, use a plastic film holder. The orientation of the long cone is such that the main ray is directed above the nasal region directly onto the interproximal space of the 2 central incisors, thus the radiation will be perpendicular to both the teeth and the film.
Premolar region: the operator introduces the film into the mouth deeply and in a horizontal position, without touching the tongue or the palate; the main ray is oriented perpendicular to the plane of the film and the tooth with an angulation of 30 to 40°, at the level of the suborbital region.
Molars region:
The film should be positioned a little more distally than that of the PM
The main ray is perpendicular to the plane of the film with an angulation of 20 to 30° on the region of the zygomatic arch.
2). In the mandible:
Incisor region:
Once the film is in place, the cone is oriented on the interproximal space between the central and lateral incisors, while directing the main ray perpendicular to the plane of the film, at the level of the submental region, with an angulation of –15 to –20°.
Premolar region:
The cone is oriented on the interproximal space of the PM perpendicular to the teeth and the film at the level of the middle of the horizontal branch of the mandible, with an angulation of – 10 to – 15 °.
Molars region:
The film is placed parallel to the teeth, applying it against the inner surface of the mandible with the index finger of the hand on the opposite side. The film should extend beyond the free edge of the molars by about 3 mm. Its distal edge should be posterior to the distal surface of the 3rd molar , the main ray is oriented perpendicular to the tooth and the film at the angle of the mandible, with an angulation of –0 to –5 °.
C)- Comparison between the two techniques
The majority of authors all agree that the Parallel Plane Technique is the most favorable:
- X-rays are superior in quality
- allow a reduction in the risks of irradiation,
- They provide better definition and more accurate relationships between neighboring anatomical structures
2. Specific implications:
It is a good rule to perform on a dental sector, in addition to the orthogonal image , a distal or mesial oblique lateral incidence in order to discriminate contiguous structures such as two roots merged in orthogonal incidence .
- CLARK’S RULE : Clarck’s rule states that the root furthest from the film undergoes the greatest displacement in the direction of radiation. To take an eccentric mesial radiograph, the localizing cone should be placed at an angulation of 20° mesially to the orthogonal position.
- 2- WALTON’s rule:
To take a distal image, according to Walton’s rule, the tube is moved in the horizontal plane by approximately 20° distally . This image is mainly used for maxillary molars to avoid superposition of the malar bone on the apices and also to locate the 4th canal.
- 3- SLOWEY rule
Used to detect vestibular or palatal bends of incisors and canines.
According to SLOWEY, if the elbow projects in the direction of the principal (incident) ray, it is therefore a palatal elbow and vice versa.
B. Inter-proximal radiographs: (or Bite Wing):
- a- Definition:
- This is a technique proposed by Raper in 1913. This type of examination is a variant of the retro-alveolar, it uses horizontal films carrying a paper fin intended to be bitten by the patient.
b- Interest of the technique:
- the image of the dental crowns and the upper part of the roots.
- This examination allows for the fine detection of proximal coronal or cervical caries,
- to assess the shape and type of the alveolar rim, the importance of the lamina dura and the desmodontal space,
- the details of the restorations and especially the pulp modifications.
C. Occlusal examination
a- Definition:
An old method, disseminated in France by Belot since 1907, it uses a 57×76 mm film called a bitten film ( because it is held in the occlusal plane by the patient’s light bite). It is a technique that complements the fundamental incidences (panoramic or retroalveolar) which provides the 3rd , horizontal dimension of the maxillo-dental volume.
- Placement of the occlusal film and angulation procedures:
The occlusal film is introduced into the mouth in the direction of its greatest dimension; to keep it in place the patient must clench their teeth as if biting into a sandwich.
The directing ray of the source is orthogonal (ortho-occlusal images) or oblique (dysocclusal images), relative to the axis of the film.
c- Interest of the technique:
- vision in another plane of space often perpendicular to that of the dental panoramic view over a limited sector.
- the vision of the morphology of a tooth, the position of an included tooth, to locate the sector of a dental trauma
- allows to visualize the reports of a bone lesion
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II- Extra-oral techniques:
- Dental panoramic
Dental panoramic is a radiographic exploration method which allows to have on a single film, at the cost of a low exposure, the image of the dental arches and the ATMs.
- Benefits of this exam:
— Complete examination of the masticatory system including the temporomandibular joints and maxillary sinuses
— Analysis of functional or morphological anomalies and their impact on the masticatory system
— Overview allowing the planning and evaluation of treatments
— Reduction of patient exposure through a rational exploration strategy
III-Digital radiography techniques:
radiovisiography (RVG)
Fast, low-dose, digital imaging system obtained using a small intraoral probe.
The device consists of:
- X-ray source
- An X-ray sensor
- Processing unit
- Advantages of RVG:
- sensor robustness
- low maintenance cost with single-use protections
- image without delay on screen
- More precise reading thanks to the possibility of zooming.
- Less and not insignificant exposure to x-rays.
- Color dimensional representation of the image
- To keep the data of each file, for each patient.
- Sending radio
- by email to facilitate the exchange of information with our colleagues.
- Invert the contrast and be able to have a color image.
- Rotate the image in 3D
- Measuring the working length.
IV-the Beam cone:
- The “cone beam” uses the principle of volumetric tomography. The technique consists of using a conical X-ray beam which will be captured by an extended detection surface.
- The X-ray source, emitting a conical beam, and the detection surface synchronously perform a single 360° rotation around the patient’s head.
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Perspectives of cone beam imaging
- Determination of the number of roots and canals
- Detection of cracks and root fractures
- highlighting root resorptions
- Early diagnosis of periapical lesions
- Determination of the extent of maxillary lesions of dental origin, as well as their relationship with anatomical elements
V-Radiation protection measures
- Protective aprons to protect pregnant women and X-ray personnel
- Positioning yourself in the safety position, which offers the operator and his assistant the greatest safety during the exposure, consists of standing between 90° and 135° to the beam and if possible behind the patient.
- Move away from the ray source (at least 2 m)
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Wisdom teeth can be painful if they are misplaced.
Composite fillings are aesthetic and durable.
Bleeding gums can be a sign of gingivitis.
Orthodontic treatments correct misaligned teeth.
Dental implants provide a permanent solution for missing teeth.
Scaling removes tartar and prevents gum disease.
Good dental hygiene starts with brushing twice a day.