IDEAL PROPERTIES OF LA

source – don’t remember, had written it a lot time ago

DISLOCATION OF CONDYLES/LUXATION OF TMJ

Image source: SlideShare

Let’s first understand the terms Luxation, Subluxation & Habitual Dislocation👇🏻

  • Luxation of joint refers to complete dislocation – Non self reducing.
  • Subluxation is partial dislocation or Self-reducing.
  • Repeated anterior dislocation & self reduction leads to Habitual/Recurrent dislocation.

➡️ Condylar dislocations can be divided into Anterior (Luxation/Subluxation), Cranial & Posterior Dislocations.

Etiology:

  1. Fracture of condyle (due to acute trauma)
  2. Stretching of capsule of TMJ
  3. Yawning/mouth opened too widely (during extraction/ Tonsillectomy/ Endoscopy)

Clinical Features:

  1. Sudden locking & immobilization of jaw when the mouth is open. Hence mouth cannot be closed and patient becomes panicky.
  2. Spasmodic contractions of Temporal, internal pterygoid & masseter muscle with protrusion of jaw.
  3. Severe pain, excessive salivation & depression of skin around preauricular area
  4. Eating/talking – impossible.

Treatment:

  1. Relaxation of Muscles – Inferior & superior pressure of thumbs in mandibular molar area.
  2. General anesthesia
  3. Tiring the masticatory muscles: Cupping the chin in palm of hand & applying pressure 5-10 min.
  4. Recurrent Dislocation – Alter the ligament, bony musculature.
  5. Repositioning Dislocated Temperomandibular Joint..Do watch till the end! (Video credits: Youtube channel-The General Medicine)👇🏻

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Amelogenesis Imperfecta

➡️ Represents a group of hereditary defects of enamel unassociated with any other generalized defects. It is entirely an ectodermal disturbance, since the mesodermal components of the teeth are basically normal.

➡️ Otherwise known as…

  • AI
  • Hereditary enamel dysplasia
  • Hereditary brown enamel
  • Hereditary brown opalescent teeth
AI can be inherited as an X-linked Autosomal Recessive or Autosomal Dominant condition

Prevalence: 1 in 700 to 1 in 15,000

Etiology:

  • Dental enamel is a highly mineralized tissue with over 95% of the volume occupied by unusually large, organized structures called the hydroxyapatite crystals.
  • The formation of these is controlled in Ameloblasts through the interaction of a no. of organic matrix molecules that include –
MMP20 (Matrix Metallopeptidase 20)
DSPP (Dentin sialophosphoprotein)

Develoment of Enamel:

➡️ 3 stages:

  1. Formative – deposition of organic matrix
  2. Calcification – Matrix mineralization
  3. Maturation – Crystallites enlarge & mature

Types of AI classification (Witkop and Sauk)

Based on clinical, histological & genetic criteria:

🔹 TYPE I HYPOPLASTIC

  • Pitted Autosomal dominant
  • Local Autosomal dominant
  • Local Autosomal Recessive
  • Smooth Autosomal dominant
  • Smooth, X-linked dominant
  • Rough Autosomal dominant
  • Enamel agenesis, Autosomal Recessive

🔹 TYPE II HYPOMATURATION

  • Diffuse Pigmented, Autosomal Recessive
  • Hypomaturation
  • Snow-capped teeth, X-linked
  • Autosomal Dominant

🔹 TYPE III HYPOCALCIFICATION

  • Diffuse Autosomal dominant
  • Diffuse Autosomal Recessive

🔹 TYPE IV COMBINATION TYPE

  • Hypomaturation – Hypoplastic with taurodontism
  • Hypomaturation – Hypoplastic with taurodontism, Autosomal Dominant
  • Hypoplastic – Hypomaturation with taurodontism, Autosomal Dominant

Clinical Features:

1) Hypoplastic – Enamel not formed to full normal thickness.

2) Hypomaturation –

  • The enamel can be pierced by an explorer point under firm pressure.
  • Can be lost by chipping away from the underlying normal appearing dentin.
  • Teeth normal in shape but exhibit a mottled, opaque white, brown-yellow discoloration.
  • Snow capped pattern – Zone of white opaque enamel on the incisal or occlusal third of crown.

3) Hypocalcified

  • The enamel is so soft that it can be removed by a prophylaxis instrument.
  • Yellow, brown or orange on eruption. Stained brown to black with time.
  • Rapid calculus apposition.
  • Coronal enamel lost with function except for the cervical portion which is mineralized better.
  • Autosomal Recessive – More severe.

Other Features:

  • Both dentition affected
  • Crown – Yellow to dark brown
  • Enamel might have numerous parallel vertical wrinkles or grooves.
  • Open Contact points.
  • Occlusal & incisal edges frequently abraded.

Radiographic Features:

Source: SlidePlayer
  • The enamel may appear totally absent.
  • When present may appear as a thin layer, chiefly over tip of cusps & on inter-proximal surfaces.
  • In some cases, calcification is so much affected that enamel and dentin seem to have the same radio density, making differentiation b/w the two difficult.

Histological Features:

  1. Hypoplastic: Disturbance in the differentiation/viability of Ameloblasts. Defect in matrix formation.
  2. Hypomaturation: Alteration in enamel rod & rod sheath structures.
  3. Hypocalcified: Defects of matrix structure & of mineral deposition.

Management:

  • Sealants/bonding
  • Prosthetic reconstruction

References: Shafer’sTextbook Of Oral Pathology; Internet

Pit & Fissure Caries

➡️ Morphology of Fissures:

Based on morphological alphabetical description of shape – 4 types:

  1. V + U (Self-cleansing)
  2. U
  3. K

Note: Pit & fissure with high steep walls & narrow bases are more prone to caries.(Developmental faults)

Occlusal fissures: Deep invagination of enamel, described as broad/narrow funnels, constricted hour glasses, multiple invaginations with inverted Y-shaped divisions & irregularly shaped.

Deep and narrow Pit & Fissure

⬇️

Retention of food debris & microbes

⬇️

Fermentation of food by microbes

⬇️

Formation of Acid

⬇️

Caries

➡️ The lesions develops from attack on their walls.

  • Cross section: Inverted “V” (A narrow entrance & wider involvement closer to DEJ)
  • Therefore, Greater no. of Dentinal Tubules are involved.
  • Early dentin involvement – When enamel at bottom of Pit & fissure is thin.

Caries when occur at Pit & Fissure follow direction of ENAMEL RODS

ENAMEL LAMELLAE – Initiation of Caries

The Initial Carious lesion of Enamel:-

• Clinical View:

  • Visual Changes – Chalkiness, yellow/brown/black discoloration.
  • Soft & ‘catch’ a fine explorer point.
  • Enamel bordering them is opaque bluish white & undermined ➡️ Lateral spread of caries at DEJ
  • Sign on stained tooth (Brown P/F)
  • Newly erupted teeth – underlying decay; Older: Arrested lesion

References: Wheeler’s Textbook, Google images

PHYSIOLOGIC TOOTH MOVEMENT

➡️ Orthodontic tooth movement is a unique process where a solid object (teeth) is made to move through a solid medium (bone).

➡️ Orthodontic treatment is possible due to the fact that whenever a prolonged force is applied on a tooth, bone remodeling occurs around the tooth resulting in its movement.

➡️ Physiologic tooth movements are naturally occurring tooth movements that take place during and after tooth eruption. They include:

  • a. Tooth eruption
  • b. Migration or drift of teeth
  • c. Changes in tooth position during mastication

a) Tooth Eruption:

➡️ Tooth eruption is the axial movement of the tooth from its developmental position in the jaw to its final position in the oral cavity. A number of theories have been put forward to explain how the eruption process take place.

a. Blood pressure theory: According to this theory, the tissue around the developing end of the root is highly vascular. This vascular pressure is believed to cause the axial movement of the teeth.

b. Root growth: According to the proponents of this theory, the apical growth of root results in an axially directed force that brings about the eruption of the teeth. This theory has not been accepted. Teeth move a greater distance during eruption than the increase in root length. In addition the onset of root growth and eruption do not seem to coincide. Teeth that are malformed and lack roots also erupt in a no. of cases.

c. Hammock ligament: According to Sicher, a band of fibrous tissue exists below the root apex spanning from one side of the alveolar wall to the other. This fibrous tissue appears to form a network below the developing root and is rich in fluid droplets. The developing root forces itself against this band of tissue, which in turn applies an occlusally directed force on the tooth.

d. Periodontal ligament traction: This theory states that the periodontal ligament is rich in fibroblasts that contain contractile tissue. The contraction of these periodontal fibres result in axial movement of the tooth.


b) Migration or drift of teeth:

  • Migration refers to the minor changes in tooth position observed after eruption of teeth. Teeth show a lifelong ability to drift through the alveolar bone, a process called physiologic tooth migration.
  • It is generally believed that the direction of tooth migration varies from species to species. The dentition in humans and primates shows a natural tendency to move in a mesial and occlusal direction. This is largely true in case of the maxillary dentition. However the lower jaw could show certain variations.
  • Tooth migration is usually a result of proximal & occlusal wear of teeth. As the teeth undergo occlusal and proximal wear, they move in a mesial and occlusal direction to maintain inter-proximal and occlusal contact. Change in state of equilibrium such as by loss of neighbouring or opposing teeth may induce further movement.
  • The remodeling process that accompanies physiologic migration is a normal function of the supporting structures. Osteoclasts are seen in lacunae along the alveolar bone wall towards which the tooth is moving. This is the resorptive surface. The alveolar bone wall on the opposite side from which the tooth is moving away is the depository surface and is characterized by osteoblasts depositing non mineralized osteoid which later mineralizes to form mature bone. In addition to this mesio-distal movement of teeth, they also exhibit a continued eruption throughout life accompanying the vertical development of their surrounding tissue.

C) TOOTH MOVEMENT DURING MASTICATION:

➡️ During mastication, the teeth and periodontal structures are subjected to intermittent heavy forces, which occur occur in cycles of one second or less and may range from 1-50 kg based on the type of food being masticated. A tooth subjected to these heavy forces, exhibits slight movement within its socket and subsequently returns to its original position as soon as the load is removed.

➡️ When a tooth is subjected to such heavy forces, the tissue fluid present in the periodontal space, being incompressible, prevents major displacement of the tooth within the socket. Therefore the forces are transmitted through the tissue fluids to the adjacent alveolar bone. Recent studies have shown that the alveolar bone can bend in response to heavy masticatory forces.

➡️ Whenever the forces of mastication are sustained and are more than the usual one second cycle, the periodontal fluid is squeezed out and pain is felt as the tooth is displaced into the PDL space.


References: Textbook of Orthodontics The Art and Science 6th Edition By Bhalajhi!…Image source: Google

Oral Radiograph Anatomical landmarks

Common to Maxilla & Mandible:

  • Teeth – Enamel, Dentin, Cementum, pulp
  • Lamina dura
  • Alveolar crest
  • Periodontal ligament space
  • Cortical bone

Maxillary landmarks:

Mandibular landmarks:

Radiolucent vs. Radiopaque

➡️ Structures that are cavities, depressions or openings in bone such as a sinus, fossa, canal or foramen will allow x-rays to penetrate through them and expose the receptor. These areas will appear radiolucent or black on radiographic images.

➡️ Structures that are bony in origin absorb or stop the penetration of the x-rays and, therefore, do not reach the receptor. These areas appear radiopaque or white on radiographic images. Some structures partially absorb radiation and are represented in varying degrees of radiopacity.

Detailed description:

1) Landmarks common in Maxilla & Mandible

  • Teeth– Consist of enamel & dentin. Enamel cap covers the coronal portion & cementum over the root surface.
  • Enamel– Most radio-opaque & 92% mineralized. Seen on the coronal portion of teeth.
  • Dentin– Less radio-opaque as compared to enamel & 65% mineralized.
  • Cementum– Radiopacity less than enamel but similar to dentin & 50% mineralized.
  • Pulp– Consists of pulp chamber, root canals, pulp horns & apical foramina. It contains soft tissues, blood vessels & nerves.
  • Lamina dura- Is the dense cortical bone of the tooth socket that surrounds the teeth.
  • Alveolar crest– It is the gingival margin of alveolar process. It is the most coronal portion of alveolar bone b/w the teeth covered with dense cortical bone.
  • Cancellar or trabecular bone- Lies b/w the cortical plates in both jaws & forms lattice like network of inter-communicating spaces filled with bone marrow.

2) Maxillary Anterior landmarks:

  • Nasal fossa – The nasal fossae are the nasal openings located above the maxillary anterior teeth. Radiographically, the nasal fossae appear as vertically oblong radiolucent structures bounded by bone.
  • Anterior Nasal spine – Located at the anterior & inferior portion of Nasal cavity situated in the midline. Appears as a V-shaped or triangular radiopacity.
  • Nose – Soft tissue tip of nose is seen in projection of maxillary central & lateral incisor. Appears with uniform opacity.
  • Nasal Septum – Vertical bony wall that divides the nasal cavity into right & left fossae formed by Vomer & ethmoid bone.
  • Inferior concha – Appears as diffuse radiopaque mass within nasal cavity.
  • Intermaxillary suture – Immovable b/w two palatine process of maxilla.
  • Nasal cavity – Pear shaped, air filled conpartment of bone located superior to maxilla, appears as radiolucent area.
  • Incisive foramina – Nasopalatine vessels & nerves lies in midline on lingual aspect of hard palate. Radiographically, it appears between the roots of the central incisor teeth as a round to oval radiolucency less than one centimeter in diameter.
  • Floor of nasal cavity – Bony wall formed by palatal process of Maxilla & horizontal portion of palatine bone. Appears as dense radio-opaque band that cuts the maxillary process.
  • Lateral/canine fossa – Great depression in the maxilla in the region of apex of lateral incisor. Inferior to infra-orbital foramen b/w laterals & canines.
  • Y line of Ennis – The inverted Y is a radiographic landmark that depicts where the nasal fossa crosses the maxillary sinus. The boundary between them is shaped like an upside-down letter Y, hence its name.

3) Maxillary Posterior Landmarks:

  • Zygomatic bone – The zygomatic bone or cheek bone attaches to the right and left sides of the posterior maxilla. The zygomatic bone, quadrangular in shape, broadens as it extends posteriorly. This bilateral radiopaque structure is also known as the malar bone.
  • Zygomatic process – Extension of lateral surface of maxilla. Radiopaque U-shaped structure.
  • Nasolabial fold – It is seen in periapical region of premolar. It is seen as oblique line demarcating the region that appears to be covered by a slight radiopacity.
  • Pterygoid plate – Mesial & lateral pterygoid plates immediately posterior to tuberosity of maxilla with homogenous radiopacity.
  • Hamular process – Small hook like projection of the bone extending from the medial plate of sphenoid bone inferiorly downward & forward.
  • Maxillary tuberosity – Rounded bony prominence present posterior to third molar.
  • Maxillary sinus – Largest paranasal sinus occupies entire body of maxilla. Pyramidal in shape. Superior wall forms floor of mouth.
  • Nasolacrimal canal – Formed by nasal & maxillary bones. Ovoid in shape.

4) Mandibular Anatomical Landmarks

5) Mandibular Anterior Landmarks

  • Genial tubercle/Mental Spine– This structure serves as the locus of attachment for the genioglossus and geniohyoid muscles. It appears as spiny protuberance or prominence of bone (Doughnut-shaped) located in the midline on the lingual aspect of the mandible below the roots of the incisor teeth(2-4mm)
  • Lingual foramen – Small openings located on lingual surface of mandible situated in midline & surrounded by genial tubercle.
  • Mental fossa – Depression on labial surface. It has a diffuse radiolucent appearance above the mental ridge.
  • Symphysis – It is fused by end of first year of life, seen as radiolucent line through the midline of jaw b/w the images of developing deciduous central incisor.
  • Mental ridge/Triangle – Linear prominence of cortical bone located on central portion of anterior region of mandible. Occasionally seen as two bilateral inverted V-shaped radiopaque lines. Forward & upward to midline.

6) Mandibular Posterior Landmarks

  • Mental foramen – Appear as round slit like irregularity, partial or completely cortical radiolucency located in apical region of premolars.
  • External oblique ridge – The external oblique ridge or line is the bony anterior border of the ramus located on the outer aspect of the mandible. This ridge has a downward diagonal course. Radiopaque.
  • Internal oblique ridge – Irregular crest of bone on lingual surface of body of mandible. It runs parallel to but below the external oblique ridge. The internal oblique ridge is sometimes referred to as the mylohyoid line.
  • Mandibular canal – Tube like passage through bone that travels along the length of mandible in contact with the apex of third molar.It is also referred to as the inferior alveolar nerve canal.
  • Submandibular fossa – It is scooped but depressed area on bone located lingually below the myelohyoid ridge.This structure is also referred to as the submandibular gland fossa or mandibular fossa.
  • Inferior border of mandible is the lower most part of the mandible. Appears as dense broad radiopaque band of bone.
  • Coronoid process – It appears as triangular radiopacity with its apex divided & in the region of the third molar. Narrow in lateral dimension. The coronoid process is the only mandibular structure recorded on maxillary molar periapicals.
  • Lingula – It is a tongue shaped projection of the bone, located anteriorly to the mandibular foramen.

References: https://www.dentalcare.com/en-us/professional-education/gail-f-williamson