CathodeThe negative electrode. It carries the focusing cup and the filament.
AnodeThe positive electrode: a tungsten target set in a copper stem. The copper carries the heat away.
FilamentA small coil of wire. Heated until it glows, it gives off electrons.
Tungsten targetThe plate of tungsten the electrons strike. The X-rays are made here.
Focusing cupThe cup that holds the filament. It is part of the cathode.
Focal spotThe small area of the target that the electrons hit.
Electron streamElectrons pulled across from the filament to the target. The high voltage between the two ends moves them.
Glass envelopeThe sealed glass tube around the two electrodes. It keeps the air out.
VacuumThe space inside the glass, with the air pumped out.
The tubehead 7
Metal housingThe metal case of the tubehead. The tube sits inside it.
Insulating oilOil that fills the housing around the tube. It takes up the heat the tube gives off.
Tubehead sealThe plate that closes the opening in the housing. It keeps the oil in and lets the X-rays out.
Aluminum filterA thin aluminum disk in the path of the beam. It absorbs the low-energy X-rays.
Lead collimator (diaphragm)A lead plate with a hole in it. It restricts the beam to the size wanted.
Cone (position-indicating device)The open-ended tube the beam leaves through. Cone, tube and PID are names for the same part.
X-ray beamThe X-rays that leave the target and pass out through the cone.
How this list was compiled: Every name checked on 2026-10-01, and again with four dental textbooks on 2026-10-02, and kept only where two independent sources use it. (1) US Army Medical Department Center and School, subcourse MD0512, Dental Radiography, lesson 1 and figures 1-2 to 1-8 (a public-domain training text), full text at https://archive.org/details/md-0512-dental-radiography-edition-200 : inside the metal tube housing is the x-ray tube; cathode, filament, anode, tungsten target, target surface, the copper end of the anode, leaded glass tube, electrons, focal spot; aluminum filter, lead collimator (diaphragm), and the cone, tube or position indicating device (PID), three names for one part; the filter absorbs the low-energy, long-wavelength x-rays; the collimator restricts the beam to the desired size. (2) J. Selman, The Fundamentals of X-ray and Radium Physics, fifth edition (1972), full text at https://archive.org/details/B-001-014-315 : a glass bulb with the air evacuated; the cathode consists of the filament, its supporting wires and the focusing cup; the filament is a small coil of tungsten wire that gives off electrons when heated; a tungsten button embedded in a block of copper, which conducts the heat away; the focus or focal spot; the electron stream; immersion in insulating oil in a metal housing. (3) Wikipedia, X-ray tube, text only, https://en.wikipedia.org/wiki/X-ray_tube : cathode, filament, anode, tungsten target, focal spot, the anode set in copper, the envelope, a vacuum tube, aluminum filters in the path of the beam, the tube head. (4) US War Department, TM 8-280, Military Roentgenology (1944), public domain, https://archive.org/details/unitedstates_militaryroentgenology_1944 : filament, focusing cups, focal spot, an anode of copper with a block of tungsten set in it, oil around the tube, cones and diaphragms. (5) J. Iannucci Haring and L. Jansen, Dental Radiography: Principles and Techniques (1996), read by full-text search at https://archive.org/details/dentalradiograph1996iann : the tubehead holds the metal housing, insulating oil, tubehead seal, x-ray tube, transformers, aluminum disks, lead collimator and position-indicating device; the tubehead seal is the aluminum or leaded-glass covering that lets the x-rays out and seals the oil in; the aluminum disks sit between the collimator and the tubehead seal; the oil takes up the heat made in the tube. (6) P. Anderson, The Dental Assistant (2000), read by full-text search at https://archive.org/details/dentalassistant0000ande : the tubehead houses the x-ray tube, transformers, oil, tubehead seal and aluminum filters; the filter sits in the opening of the tubehead between the tubehead seal and the collimator. (7) D. Miles and others, Radiographic Imaging for Dental Auxiliaries (1993), https://archive.org/details/radiographicimag0000unse_02ed : in a dental x-ray tube the cathode consists of the tungsten filament and a focusing cup. (8) H. Frommer, Radiology for Dental Auxiliaries (1992), https://archive.org/details/radiologyfordent00from_0 , with the study guide to its eighth edition (2005) and D. Phinney and J. Halstead, Dental Assisting Coloring Book (2011): the tungsten filament is surrounded by the molybdenum focusing cup; both workbooks print copper stem beside tungsten target and focusing cup as a name to match to the tube. (9) T. Razmus and G. Williamson, Current Oral and Maxillofacial Imaging (1996), https://archive.org/details/currentoralmaxil00razm : the tubehead contains the x-ray tube and two transformers surrounded by oil, which passes the heat to the casing. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry and redrawn on 2026-10-02; nothing traced. Licence: own work
How it works
A dental X-ray tube is a sealed glass tube with a cathode at one end and an anode at the other. The second view lets you label the parts of the dental X-ray tubehead that holds it.
Read the full guide
Inside the tube
The cathode is the negative end: an arm that carries the focusing cup, with the filament in the cup. The anode is the positive end: a copper stem with a tungsten target set in its slanted face. Electrons cross the vacuum from the filament and strike the target at the focal spot, where the X-rays are made.
Inside the tubehead
The tube sits in a metal housing filled with insulating oil, and a tubehead seal closes the opening in the housing. Under the seal are an aluminum filter, a lead collimator with a hole in it, and the open-ended cone the beam leaves through.
Cone, tube and position-indicating device (PID) are three names for the same part.
Questions and answers
What are the parts of a dental X-ray tube?
A glass envelope with a vacuum inside, a cathode with its filament and focusing cup, and an anode: a copper stem with a tungsten target. The small area of the target that the electrons strike is the focal spot.
What are the parts of a dental X-ray tubehead?
The X-ray tube sits in a metal housing filled with insulating oil, and a tubehead seal closes the opening. Below the seal are an aluminum filter, a lead collimator and the cone, or position-indicating device. The two transformers in the housing are not drawn.
What is the difference between the cathode and the anode of an X-ray tube?
The cathode is the negative electrode and gives off electrons from its heated filament. The anode is the positive electrode: the electrons strike its target, and its copper stem carries the heat away.
What does the aluminum filter do in a dental X-ray tubehead?
It sits in the path of the beam and absorbs the low-energy, long-wavelength X-rays. The high-energy, short-wavelength X-rays pass through it.