Anatomical Landmarks the Radiographic Recognition of Diseases Requires a Sound Knowledge of the Radiographic Appearance of Normal Structure

Lec.8 Radiology Dr.Sura Anatomical landmarks The radiographic recognition of diseases requires a sound knowledge of the radiographic appearance of normal structure. Intelligent diagnosis mandates an appreciation of the wide range of variation in the appearance of normal anatomic structure. Accordingly, the absence of one or two or even several landmarks in any individual should not necessarily be considered abnormal. Most patients demonstrate many of the normal radiographic landmarks, but it is rare patient who shows them all. Radiolucent: Radiolucent refers to that portion of a processed radiograph that is dark or black. A structure that appears radiolucent on a radiograph lacks density and permits the passage of the X-ray beam with little or no resistance. For example, air space freely permits the passage of dental X-rays and appears mostly radiolucent on a dental radiograph. Radiopaque: Radiopaque refers to that portion of a processed radiograph that appears light or white. Radiopaque structures are dense and absorb or resist the passage of the X-ray beam. Normal Tooth Anatomy Enamel: Enamel is the densest structure found in the human body. Enamel is the outer most radiopaque layer of the crown of the tooth. Dentine: Dentine is found beneath the enamel layer of the tooth and surrounds the pulp cavity. Dentine appears radiopaque and comprises most of the tooth structure

Lec.8 Radiology Dr.Sura

Red arrow indicates for enamel while yellow arrow indicates for dentin and blue arrow for DEJ Dentinoenamel junction (DEJ): It is the junction between the dentine and the enamel of a tooth. The DEJ appears a line where the enamel (very radiopaque) meets the dentine (less radiopaque). The alveolar bone: is the bone of the maxilla and mandible that supports and encases the root of teeth. Alveolar bone is composed of dense cortical bone and cancellous bone. A) Cortical bone: also referred to as compact bone, is the dense out layer of bone. Cortical bone resists the passage of X-ray beam, and appears radiopaque on the radiograph. The inferior border of the mandible is composed of cortical bone and appears radiopaque.

Arrows in figure(A)and squares in figure(B) indicate for cortical bone

Lec.8 Radiology Dr.Sura B) Cancellous bone: is the soft spongy bone located between two layers of dense cortical bone. it is composed of numerous bony trabeculae that form a lattice like network of intercommunicated spaces filled with bone marrow. The trabeculae resist the passage of the X- ray beam and appear radiopaque; in contrast, the marrow spaces permit the passage of X ray beam and appear radiolucent.

Black arrow indicates cancellous bone show predominant radiolucency

Landmarks in radiographs of the mandible 1. Mental fossae: slight depression in bone on the labial aspect of mandibular lateral incisors (diminished radiopacity). 2. Mental ridge: bony prominence extending from midline of the mandible to the area of premolars (Radiopaque). 3. Lingual foramen: single radiolucent area in the midline of the mandible. 4. Genial tubercles: radiopaque zones located in the radiographs of lower incisors area. 5. Mental foramen: oval, round, or irregular radiolucency in the radiographs of premolars, when superimposed of the apex of a tooth it may misdiagnose as periapical pathology. 6. Mandibular canal (inferior dental canal) radiolucent structure extends from the mental foramen to the mandibular. 7. Mandibular foramen: Foramen in the ramus: Mandibular foramen is funnel shaped area radiolucency that varies greatly in size and location.

Lec.8 Radiology Dr.Sura 8. External oblique line: radiopaque structures that corresponds to the anterior border of the ramus and descend to the area of the third molar. 9. Internal oblique line: radiopaque structure that descends downward and forward from coronoid process below the external oblique line it possesses down ward and forward from the ramus and gradually fades in bicuspid area. 10. Submaxillary gland fossa: Zone of relative radiolucency below the molars, it may mistake with radiolucent lesion. 11. Nutrient canals: seen most frequently in the incisor area of lower arch appear as radiolucent linear shadows between the roots. Landmarks in radiographs of maxilla 1. Median suture: radiolucent line between central incisors 2. Incisive or anterior palatine foramen: oval radiolucency, but sometimes appear round, heart shaped or diamond- shaped, located between or above maxillary central incisors. If the foramen is larger, distinction between it and small incisive canal cyst is often difficult. 3. Anterior nasal spine: V- shaped radiopacity seen in the inferior aspect of nasal fossae above or superimposed on it. 4. Nasal septum: separates the two nasal fossae in the midline, appear gray or white shadow above central incisors. 5. Nasal cavity: bilateral radiolucency in radiographs of incisors area. The floor of the nasal cavity overlaps the radiolucency of maxillary sinus in the radiographs of caspid area. 6. Maxillary sinus: not seen until after 5 years of age, it is a dominant radiolucency in radiographs of bicuspid area and molars and extend to the tuberosity. 7. Lateral fossa. Bony depression in the labial cortical plate of maxillary lateral incisor area (Diminished radiopacity). 8. Zygomatic (malar) process of maxilla and zygomatic bone: zygomatic process seen as V- shaped radiopacity in the apical films of molar area. Zygomatic arch appears as a radiopaque bond extending posteriorly from the V- shaped radiopacity of the zygomaticomaxiilary Junction. 9. Coronoid process of mandible: a triangular radiopaque structure in radiographs of posterior maxillary teeth and is easily identified.

Lec.8 Radiology Dr.Sura 10. Hamulus and lateral plate of pterygoid process: pterygoid process of sphenoid bone has two plates, lateral plate wide round radiopacity behind the maxillary sinus. The inferior end of the medial place ends in a thin curved process called pterygoid hamulus.

RADIOGRAPHIC APPEARANCE OF RESTORATIVE MATERIALS 1. Radiopaque restorative materials: Gold, Silver amalgam, Zinc oxide – eugenol, Zinc phosphate cement, Gutta – percha, Silver points, Metal bands & crowns, & Metal wires. 2. Radiolucent restorative materials: Acrylic, Silicates, Calcium hydroxide pastes, &Porcelain.