- Skulls aren’t imaged using radiographs as much now.
- Not used in the trauma setting – any ideas why?
- However, it is still important to know your skull anatomy!
- The cranium is part of the skull that holds and protects the brain in a large cavity.
- The facial bones form the lower front of the skull and provide the framework for most of the face.
- The skull bones form other smaller cavities besides the cranial vault, including those for the eyes, the internal ear, the nose and the mouth.
Bones of the skull
- Parietal x2
- Temporal x2
- A suture is an immovable joint, in most cases in an adult skull, that holds the cranial bones together.
- Sutures in the skulls of infants and children are often movable.
Four main sutures
- The coronal suture unites the frontal bone and both parietal bones.
- The sagittal suture unites the two parietal bones on the superior midline of the skull.
- The lambdoid suture unites the two parietal bones to the occipital bone.
- The squamous sutures unite the parietal and temporal bones on the lateral aspects of the skull.
- Foetal skulls.
- Membrane filled spaces between the cranial bones.
- The posterior fontanelle usually closes by the time an infant is 1 – 2 months old.
- The anterior fontanelle usually closes between 7 – 19 months old.
2 main functions of fontanelles
- Enables the skull to change in size and shape as it passes through the birth canal.
- Allows for rapid brain growth as a young child develops.
- A Angle of mandible
- B Nasion
- C Glabella
- D Inferior orbital margin
- E Outer canthus of eye
- F External auditory meatus
- G Occipital protuberance
Planes used in skull / facial bone imaging
Median sagittal plane
Outer canthus of eye to EAM
Anthropological baseline (Frankfurt plane)
Infra-orbital margin to superior EAM.
Facial Bones & sinuses
Most sources state 14 facial bones:
- Maxilla (2)
- Zygomatic bones (2)
- Palatine bones (2)
- Lacrimal bones (2)
- Inferior nasal concha (2)
- Nasal bones (2)
- Paired air-filled cavities in certain cranial and facial bones.
- Lined with mucous membranes that are continuous with the nasal cavity.
- All open to the lateral wall of the nose through ostia, which allow entry of air to ventilate them and drainage of secretions.
- Lighten the skull bones.
- Add resonance to the voice.
- 2 Maxillary sinuses – pyramidal in shape, lie on either side of the nasal cavity below the orbits.
- 2 Frontal sinuses – irregular and varied in shape and size. Above nasal cavity and orbits, posterior to superciliary arches of the frontal bone.
- 3 Groups of ethmoid sinuses – anterior, middle, posterior. Numerous small cavities, irregular in shape. Between medial wall of orbit and nasal cavity.
- Spheniodal sinus – cuboid in shape. Lie within the body of the spheniodal bone below the sella turcica.
The Nasal Cavity
The Nasal Septum
The Inferior Nasal Conchae
The Inferior and Middle Nasal Conchae
- The mandible is the bone of the lower jaw.
- It is composed of a horse-shoe shaped body which lies horizontally, and 2 broad processes which run vertically and are called the rami
Body of the Mandible
- Symphysis menti.
- Mental protuberance.
- Mental foramen.
- Submandibular fossa.
- Sublingual fossa.
Ramus of the Mandible
- Mandibular foramen
- Mandibular canal
- Angle of the mandible
- Coronoid process
- Condylar process
- Mandibular notch
- Tempro-mandibular joint
The Mandible on a radiograph
Basic components are:
- head of the condyle.
- articular disc.
- glenoid fossa and articular eminence.
- capsule surrounding the joint.
Normal movements include:
- Hinge or rotation of the condyle within the fossa.
- Movement of the condyle down the articular eminence.
- The disc being attached to the condyle also moves forward.
Dentation Anatomy, Physiology and Pathology
Sagittal section of a mandibular (lower) molar.
Anatomy of the teeth
- Each tooth is composed mainly of dentine, which is a living material with the radiodensity of lamellar bone. The crown is the intraoral part of the tooth and this has a covering of enamel, which is the hardest and most radio-opaque tissue in the body
- The root is covered with a thin layer of cementum, which has the same radio-density as dentine, and which is too thin to show on a radiograph.
- The root is surrounded by the periodontal membrane, which is visible as a as a radiolucent line outlining the root.
- Beyond this lies the lamina dura which forms a continuous radio-opaque line around the root, and which is continuous with the lamina dura of the adjacent teeth at the level of the alveolar crest.
- The pulp of the tooth appears radiolucent as it consists of soft tissues. Each tooth contains a pulp chamber in the crown, which is continuous with one or more rooted canals.
- Each canal runs to the root where the blood vessels and nerves of the pulp communicate with those of the maxilla or mandible.
- The part of a tooth, which is nearest to the midline of the dental arch, is described as “medial“, and the part of the tooth furthest from the midline of the dental arch is described as “distal“.
Number and Position of Teeth
- The human being develops two sets of teeth.
- The milk or deciduous set numbering 20 which appear between the ages of 6 months and 2 years and the permanent set which are 32 in number and erupt from the sixth year onward.
- These 32 teeth consist of each quadrant having 2 incisors, 1 canine, 2 premolar and 3 molars.
- Dental requests are made in accordance with the dental formula.
- Milk teeth are often referred to by serial letters from “a” to “e” on passing from central incisor laterally to second milk molar.
- Permanent teeth are often referred to by serial numbers from “1” to “8” on passing laterally from central incisor to third molar.
- The milk teeth as mentioned earlier begin to erupt at 6 months and should be all present by 2½ years.
Milk Tooth Type Approx. Eruption (months)
- A Central incisors 6-8 months
- B Lateral incisors 8-10 months
- C Canines 16-20 months
- D First molars 12-16 months
- E Second molars 20-30 months
- The permanent teeth begin to appear at the age of 6 years and should all be present by 20 years.
- The lower teeth erupt 6-12 months earlier than the uppers.
Tooth Type Approx. Eruption (months)
- 1 Central incisors 6-8 years
- 2 Lateral incisors 7-9 years
- 3 Canines 9-12 years
- 4 First premolars 10-12 years
- 5 Second premolars 10-12 years
- 6 First molars 6-7 years
- 7 Second molars 11-13 years
- 8 Third molars 17-21 years
Pathologies of the teeth
- Dental caries, otherwise known as tooth decay, is one of the most prevalent chronic diseases of people worldwide; individuals are susceptible to this disease throughout their lifetime.
- Dental caries forms through a complex interaction over time between acid-producing bacteria and fermentable carbohydrate, and many host factors including teeth and saliva.
- The disease develops in both the crowns and roots of teeth, and it can arise in early childhood as an aggressive tooth decay that affects the primary teeth of infants and toddlers.
Risk for caries includes physical, biological, environmental, behavioural, and lifestyle-related factors:
- High numbers of cariogenic bacteria
- Inadequate salivary flow
- Insufficient fluoride exposure
- Poor oral hygiene
- Inappropriate methods of feeding infants
- The approach to primary prevention should be based on common risk factors.
- Secondary prevention and treatment should focus on management of the caries process over time for individual patients, with a minimally invasive, tissue-preserving approach.
- Caused by: acute inflammation, chronic inflammation and other priapical conditions.
- In the apical tissues the inflammation accumulates in the apical periodontal ligament space – this results in swelling.
- The affected tooth becomes painful, especially when subjected to pressure. The patient will avoid biting on the tooth.
- Destruction and resorption of the tooth root and surrounding bone occurs as a periapical abscess develops.
- On a radiograph this can be seen as a periapical radiolucent area.
- Develops from acute inflammation. As the body tries to prevent spread of the infection, destruction and healing occur at the same time.
- In the apical tissues a granuloma forms at the apex of the tooth and dense bone is laid down around the area of resorption.
- On a radiograph the apical radiolucent area becomes surrounded by dense sclerotic bone.
- Sometimes a periapical cyst or another abscess forms.
Other periapical conditions:
- These conditions may also result in radiographic periapical radiolucency, as a result of one of the following:
- Benign and malignant bone tumours
- Langehans cell disease
- Fibro-cemento-osseous lesions.
- Periodontal disease can be classified as either inflammatory or systemic conditions that affect the periodontium
Inflammatory periodontal disease:
- Gingivitis: Acute: caused by trauma
- Acute ulcerative gingivitis
- Acute herpetic gingivostomatitis or acute non-specific.
- Chronic: hyperplastic or desquamative causes.
- Periodontitis: Acute: caused by acute periodontal abscess, or chronic causes.
Systemic or generalised conditions that can affect the periodontium:
- causes include:
- Uncontrolled diabetes
- Down’s syndrome
- Secondary metastases