Characteristics of Middle-Third Facial Fractures

Middle-third facial fractures, often referred to as "midfacial fractures," involve the central portion of the face, including the nasal bones, maxilla, and zygomatic arch. These fractures can result from various types of trauma, such as motor vehicle accidents, falls, or physical assaults. The following points highlight the key features and clinical implications of middle-third facial fractures:

1. Oedema of the Middle Third of the Face

• Rapid Development: Oedema (swelling) in the middle third of the face develops quickly after the injury, leading to a characteristic "balloon" appearance. This swelling is due to the accumulation of fluid in the soft tissues of the face.

• Absence of Deep Cervical Fascia: The unique anatomical structure of the middle third of the face contributes to this swelling. The absence of deep cervical fascia in this region allows for the rapid spread of fluid, resulting in pronounced oedema.

• Clinical Presentation: In the early stages following injury, patients with middle-third fractures often present with similar facial appearances due to the characteristic swelling. This can make diagnosis based solely on visual inspection challenging.

2. Lengthening of the Face

• Displacement of the Middle Third: The downward and backward displacement of the middle third of the facial skeleton can lead to an increase in the overall length of the face. This displacement forces the mandible to open, which can result in a change in occlusion, particularly in the molar region.

• Gagging of Occlusion: The altered position of the mandible can lead to a malocclusion, where the upper and lower teeth do not align properly. This can cause discomfort and difficulty in chewing or speaking.

• Delayed Recognition of Lengthening: The true increase in facial length may not be fully appreciated until the initial oedema subsides. As the swelling decreases, the changes in facial structure become more apparent.

3. Nasal Obstruction

• Blood Clots in the Nares: Following a middle-third fracture, the nares (nostrils) may become obstructed by blood clots, leading to nasal congestion. This can significantly impact the patient's ability to breathe through the nose.

• Mouth Breathing: Due to the obstruction, patients are often forced to breathe through their mouths, which can lead to additional complications, such as dry mouth and increased risk of respiratory infections.

• Q – switching: Shortens pulse time to limit lateral tissue damage (e.g., ruby laser for tattoo removal).
• CO₂ laser:
  • Zone of coagulation necrosis: ~500 microns; reduced to <100 microns with superpulse/ultrapulse.
  • Common for cosmetic skin resurfacing.
• Tissue interactions with lasers: Reflection, scatter, transmission, absorption.
• Tissue reactions to laser energy: Photothermal, photoablative, photochemical, photoacoustic.
• Delivery systems: Fiberoptic guide, articulated arm, hollow wave guide (most recent).

Osseointegration Testing

Torque Testing (Primary Assessment)

• Force required: 10 – 20 N/cm without unscrewing
• Lateral force test: 5 lb should show no movement
• Failed implant indicators:
  • Horizontal mobility >1mm
  • Movement with <500gm force

Clinical Signs of Successful Integration

• Percussion test (no mobility)
• Immobility when placing fixture mount
• Immobility with impression coping placement

Implant Failure

• Most useful radiographic sign: Loss of crestal bone
• Imaging compatibility: MRI and CT scans NOT contraindicated with pure titanium implants
• CT advantage: Can subtract titanium from images, eliminating scatter

Joint Lubrication Mechanisms

Weeping Lubrication

• Occurs at high loads
• Hydrostatic pressure > osmotic pressure
• Water squeezed from extracellular matrix
• Contributes to joint surface lubrication

Boundary Lubrication

• Occurs under low loads

Cartilage Loading Physiology

• Joint movement → increased internal hydrostatic pressure
• When hydrostatic pressure exceeds proteoglycan osmotic pressure
• Water expulsion from extracellular matrix occurs

Radiological Signs Indicating Relationship Between Mandibular Third Molars and the Inferior Alveolar Canal

In 1960, Howe and Payton identified seven radiological signs that suggest a close relationship between the mandibular third molar (wisdom tooth) and the inferior alveolar canal (IAC). Recognizing these signs is crucial for dental practitioners, especially when planning for the extraction of impacted third molars, as they can indicate potential complications such as nerve injury. Below are the seven signs explained in detail:

1. Darkening of the Root

• This sign appears as a radiolucent area at the root of the mandibular third molar, indicating that the root is in close proximity to the IAC.
• Clinical Significance: Darkening suggests that the root may be in contact with or resorbing against the canal, which can increase the risk of nerve damage during extraction.

2. Deflected Root

• This sign is characterized by a deviation or angulation of the root of the mandibular third molar.
• Clinical Significance: A deflected root may indicate that the tooth is pushing against the IAC, suggesting a close anatomical relationship that could complicate surgical extraction.

3. Narrowing of the Root

• This sign is observed as a reduction in the width of the root, often seen on radiographs.
• Clinical Significance: Narrowing may indicate that the root is being resorbed or is in close contact with the IAC, which can pose a risk during extraction.

4. Interruption of the White Line(s)

• The white line refers to the radiopaque outline of the IAC. An interruption in this line can be seen on radiographs.
• Clinical Significance: This interruption suggests that the canal may be displaced or affected by the root of the third molar, indicating a potential risk for nerve injury.

5. Diversion of the Inferior Alveolar Canal

• This sign is characterized by a noticeable change in the path of the IAC, which may appear to be deflected or diverted around the root of the third molar.
• Clinical Significance: Diversion of the canal indicates that the root is in close proximity to the IAC, which can complicate surgical procedures and increase the risk of nerve damage.

6. Narrowing of the Inferior Alveolar Canal (IAC)

•  This sign appears as a reduction in the width of the IAC on radiographs.
• Clinical Significance: Narrowing of the canal may suggest that the root of the third molar is encroaching upon the canal, indicating a close relationship that could lead to complications during extraction.

7. Hourglass Form

• This sign indicates a partial or complete encirclement of the IAC by the root of the mandibular third molar, resembling an hourglass shape on radiographs.
• Clinical Significance: An hourglass form suggests that the root may be significantly impinging on the IAC, which poses a high risk for nerve injury during extraction.

• Osteomyelitis in mandible: Poor blood supply from single endosteal vessel.
• Sentinel lymph node: First node receiving lymphatic drainage from tumor.
• Carcinoma – in – situ: Dysplasia involving all epithelial layers, not beyond basal layer.
• Ulcers >2 weeks: Biopsy recommended, esp. with rolled borders.
• Selective neck dissection: Preferred for N0 neck in oral SCC.
• Radical neck dissection: Removes SAN, SCM, IJV, and lymphatics (regions I – V).