Dental Equipment

RADIOLOGY AND IMAGING EQUIPMENT

Dental x-ray machine

Learning objectives

Student should be able to describe the components and functions of dental equipment

Dental radiograph: A photographic image produced on film by the passage of x-rays through teeth and related structures.

Dental radiography: The production of radiographs of the teeth and adjacent structures by the exposure of an image receptor to x-rays.

Dental radiographer: Any person who positions, exposes, and processes dental x-ray image receptors.

COMPONENT AND FUNCTIONS OF DENTAL EQUIPMENT

Dental Equipment

Dental imaging is the creation of digital, print, or film representations of anatomic structures of the teeth for the purpose of diagnosis.

Dental X-rays (radiographs) are used with low levels of radiation to capture images of the interior of teeth and gums to limit the amount of radiation to patients.

Why dental radiograph?

Detection of pathology associated with the teeth and their supporting structures such as caries, periodontal disease and periapical pathology.

Detection of anomalies/injury associated with the teeth, their supporting structures, the maxilla and the mandible.

Determination of the presence/absence of teeth and the localisation of any unerupted teeth.

Root length determination of teeth prior to endodontic therapy.

• Detection of the presence/absence of radio-opaque salivary calculi and foreign bodies.
• Detection of anomalies/injury/pathology of adjacent facial structures.

Evaluation of skeletal and /or soft tissues prior to orthodontic treatment.

Monitoring the progress of orthodontic treatment and dental disease.

The preoperative assessment of skeletal and soft-tissue patterns prior to orthognathic surgery.

Assessment of bone levels prior to implant placement.

Monitoring the healing and effectiveness of surgical treatment of the patient postoperatively.

Dental Equipment

Dental radiography involves techniques in which the image receptor is placed either inside the mouth (intraoral radiography) or outside the mouth (extraoral radiography).Extraoral X-rays show teeth, but their main focus is the jaw and skull.

X-RAY MACHINE

X-rays are produced in the dental x-ray machine. The dental x-ray machine can be divided into four study areas:

• (1)The component parts
• (2) The x-ray tube
• (3)Image receptors

(4) The x-ray generating apparatus.

component part

This includes conventional dental X-ray units, panoramic X-ray machines, and cone beam computed tomography (CBCT) units.

There are several conventional dental x-ray units available from various manufactures.

They vary in appearance, complexity and cost,but all consist of three main visible components;

(Figure 1)

(A) control panel, (B) extension arm, and (C) tubehead.

• B
• C

A

Control Panel and circuitry

The control panel of the dental x-ray machine contains an on-off switch and indicator light, an exposure button and control devices (time, kilovoltage, and milliamperage selectors) to regulate the x-ray beam.

The control panel is plugged into an electrical outlet and appears as a panel or a cabinet mounted on the wall outside the dental operatory.

Extension Arm

The wall-mounted extension arm suspends the x-ray tubehead and houses the electrical wires that extend allows for movement and positioning of the tubehead.

Tubehead

The x-ray tubehead is a tightly sealed, heavy metal housing that contains the x-ray tube that produces dental x-rays. The component parts of the tubehead include the following;

Dental Equipment

A: Metal housing, or the metal body of the tubehead that surrounds the x-ray tube and transformers and is filled with oil-protects the x-ray tube and grounds the high-voltage components.

B:Insulating oil, or the oil that surrounds the x-ray tube and transformers inside the tubehead- prevents overheating by absorbing the heat created by the production of x-rays.

Dental Equipment

C:Tubehead seal, or the aluminum or leaded-glass covering of the tubehead that permits the exit of x-rays from the tubehead-seals the oil in the tubehead and acts as a Filter to the x-ray beam. (Figure 2)

Dental Equipment

Also known as the heart of the x-ray generating system it is critical to the production of x-rays and warrants a separate discussion from the rest of the x-ray machine.

The x-ray tube is a glass vacuum tube from which all the air has been removed. The x-ray tube used in dentistry measures approximately several inches long by 1 inch in diameter.

X-ray tube

The component parts of the x-ray tube include a leaded-glass housing, negative cathode, and positive anode (Figure 3).

Leaded-Glass Housing

The leaded-glass housing is a leaded-glass vacuum tube that prevents x-rays from escaping in all directions. One central area of the leaded-glass tube has a “window” that permits the x-ray beam to exit the tube and directs the x-ray beam toward the aluminum disks, lead collimator, and Position-indicating device (PID).Figure 4

Cathode

The cathode, or negative electrode, consists of a tungsten wire filament in a cup-shaped holder made of molybdenum. The purpose of the cathode is to supply the electrons necessary to generate x-rays.

In the x-ray tube, the electrons produced in the negative cathode are accelerated toward the positive anode.

The cathode includes the following:

• The tungsten filament, or coiled wire made of tungsten, which produces electrons when heated.
• The molybdenum cup, which focuses the electrons into a narrow beam and directs the beam across the tube toward the tungsten target of the anode.

Anode

The anode, or positive electrode, consists of a wafer-thin tungsten plate embedded in a solid copper rod. The purpose of the anode is to convert electrons into x-ray photons. The anode includes the following:

• A tungsten target, or plate of tungsten, which serves as a focal spot and converts bombarding electrons into x-ray photons.
• The copper stem, which functions to dissipate the heat away from the tungsten target.

Dental Equipment

Transformer, or a device that alters the voltage of incoming electricity. A transformer is a device that is used to either increase or decrease the voltage in an electrical circuit.

Transformers alter the voltage of the incoming electrical current and then route the electrical energy to the x-ray tube.

In the production of dental x-rays, three transformers are used to adjust the electrical circuits:

• (1) The step-down transformer,
• (2) The step-up transformer.

(3) The autotransformer.

Dental Equipment

A step-down transformer is used to decrease the voltage from the incoming 110- or 220-line voltage to the 3 to 5 V used by the filament circuit. A step-down transformer has more wire coils in the primary coil than in the secondary coil.

NB;The coil that receives the alternating electrical current is the primary, or input, coil; the secondary coil is the output coil.

Dental Equipment

A step-up transformer is used to increase the voltage from the incoming 110- or 220-line voltage to the 65,000 to 100,000 volts used by the high-voltage circuit. A step-up transformer has more wire coils in the secondary coil than in the primary coil.

An autotransformer serves as a voltage compensator that corrects for minor fluctuations in the current.

Dental Equipment

• Aluminum disks, or sheets of 0.5-mm-thick aluminum placed in the path of the x-ray beam, filter out the non-penetrating, longer wavelength x-rays .
• Lead collimator, or a lead plate with a central hole that fits directly over the opening of the metal housing, where the x-rays exit-restricts the size of the x-ray beam.
• Position-indicating device (PID), or open-ended, leadlined cylinder that extends from the opening of the metal housing of the tubehead, aims and shapes the x-ray beam (Figure 5). The PID is sometimes referred to as the cone.

Figure :Position-indicating de vice (PID), or cone

Radiographic film

Digital receptors

Radiographic film; Has traditionally been employed as the image receptor in dentistry and is still widely used. There are two basic types ;

Direct action or non screen film(wrapped or packet film).This type of film is sensitive primarily to x-ray photons and produces a high resolution image that provides the fine detailed needed to assess pathological changes. Used for intraoral radiograph.

Image receptors

Dental image receptors

Indirect-action or screen film, so-called because it is used in combination with intensifying screens in a cassette.

This type of film is sensitive primarily to light photons, which are emitted by the adjacent intensifying screens by photoelectric effect.

They respond to shorter exposure of x-rays,enabling a lower dose of radiation to be given to the patient.

Digital receptors;

Many manufacturers are now producing digital imaging systems specifically for dental radiography. The two methods of image capture used are:

Solid state; manufacturers employ a range of electronic sensor technology within digital imaging systems.

Storage phosphor; these systems are commonly found in general radiography departments and may be referred to as computed radiography (CR).

Dental Equipment

To understand how the x-ray tube functions and how x-rays are produced, the dental radiographer must understand electricity and electrical currents, electrical circuits, and transformers.

X-Ray Generating Apparatus

Electricity and Electrical Currents

Electricity is the energy that is used to make x-rays. Electrical energy consists of a flow of electrons through a conductor; this flow is known as the electrical current.

The electrical current is termed direct current (DC) when the electrons flow in one direction through the conductor.

The term alternating current (AC) describes an electrical current in which the electrons flow in two, opposite directions.

Rectification is the conversion of AC to DC.

The dental x-ray tube acts as a self-rectifer in that it changes AC into DC while producing x-rays. This ensures that the current is always owing in the same direction, more specifically, from cathode to anode.

Circuits

A circuit is a path of electrical current. Two electrical circuits are used in the production of x-rays: (1) a low-voltage, or filament, circuit and (2) a high-voltage circuit.

The filament circuit uses 3 to 5 V, regulates the flow of electrical current by the milliampere settings.

The high-voltage circuit uses 65,000 to 100,000 V, provides the high voltage required to accelerate electrons and to generate x-rays in the x-ray tube, and is controlled by the kilovoltage settings.