NEET MDS Lessons
Oral and Maxillofacial Surgery
Classification and Management of Impacted Third Molars
Impacted third molars, commonly known as wisdom teeth, can present in various orientations and depths, influencing the difficulty of their extraction. Understanding the types of impactions and their classifications is crucial for planning surgical intervention.
Types of Impaction
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Mesioangular Impaction:
- Description: The tooth is tilted toward the second molar in a mesial direction.
- Prevalence: Comprises approximately 43% of all impacted teeth.
- Difficulty: Generally acknowledged as the least difficult type of impaction to remove.
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Vertical Impaction:
- Description: The tooth is positioned vertically, with the crown facing upward.
- Prevalence: Accounts for about 38% of impacted teeth.
- Difficulty: Moderate difficulty in removal.
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Distoangular Impaction:
- Description: The tooth is tilted away from the second molar in a distal direction.
- Prevalence: Comprises approximately 6% of impacted teeth.
- Difficulty: Considered the most difficult type of impaction to remove due to the withdrawal pathway running into the mandibular ramus.
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Horizontal Impaction:
- Description: The tooth is positioned horizontally, with the crown facing the buccal or lingual side.
- Prevalence: Accounts for about 3% of impacted teeth.
- Difficulty: More difficult than mesioangular but less difficult than distoangular.
Decreasing Level of Difficulty for Types of Impaction
- Order of Difficulty:
- Distoangular > Horizontal > Vertical > Mesioangular
Pell and Gregory Classification
The Pell and Gregory classification system categorizes impacted teeth based on their relationship to the mandibular ramus and the occlusal plane. This classification helps assess the difficulty of extraction.
Classification Based on Coverage by the Mandibular Ramus
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Class 1:
- Description: Mesiodistal diameter of the crown is completely anterior to the anterior border of the mandibular ramus.
- Difficulty: Easiest to remove.
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Class 2:
- Description: Approximately one-half of the tooth is covered by the ramus.
- Difficulty: Moderate difficulty.
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Class 3:
- Description: The tooth is completely within the mandibular ramus.
- Difficulty: Most difficult to remove.
Decreasing Level of Difficulty for Ramus Coverage
- Order of Difficulty:
- Class 3 > Class 2 > Class 1
Pell and Gregory Classification Based on Relationship to Occlusal Plane
This classification assesses the depth of the impacted tooth relative to the occlusal plane of the second molar.
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Class A:
- Description: The occlusal surface of the impacted tooth is level or nearly level with the occlusal plane of the second molar.
- Difficulty: Easiest to remove.
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Class B:
- Description: The occlusal surface lies between the occlusal plane and the cervical line of the second molar.
- Difficulty: Moderate difficulty.
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Class C:
- Description: The occlusal surface is below the cervical line of the second molars.
- Difficulty: Most difficult to remove.
Decreasing Level of Difficulty for Occlusal Plane Relationship
- Order of Difficulty:
- Class C > Class B > Class A
Summary of Extraction Difficulty
- Most Difficult Impaction:
- Distoangular impaction with Class 3 ramus coverage and Class C depth.
- Easiest Impaction:
- Mesioangular impaction with Class 1 ramus coverage and Class A dep
- Pediatric mandibular fractures: Greenstick, esp. condyle
- TMJ ankylosis signs in child:
- Limited mouth opening
- Prominent antegonial notch
- Elongated coronoid
- Short ramus
- Bony bridging
- Fullness on affected side
Ridge Augmentation Procedures
Ridge augmentation procedures are surgical techniques used to increase the volume and density of the alveolar ridge in the maxilla and mandible. These procedures are often necessary to prepare the site for dental implants, especially in cases where there has been significant bone loss due to factors such as tooth extraction, periodontal disease, or trauma. Ridge augmentation can also be performed in conjunction with orthognathic surgery to enhance the overall facial structure and support dental rehabilitation.
Indications for Ridge Augmentation
- Insufficient Bone Volume: To provide adequate support for dental implants.
- Bone Resorption: Following tooth extraction or due to periodontal disease.
- Facial Aesthetics: To improve the contour of the jaw and facial profile.
- Orthognathic Surgery: To enhance the results of jaw repositioning procedures.
Types of Graft Materials Used
Ridge augmentation can be performed using various graft materials, which can be classified into the following categories:
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Autografts:
- Bone harvested from the patient’s own body, typically from intraoral sites (e.g., chin, ramus) or extraoral sites (e.g., iliac crest).
- Advantages: High biocompatibility, osteogenic potential, and lower risk of rejection or infection.
- Disadvantages: Additional surgical site, potential for increased morbidity, and limited availability.
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Allografts:
- Bone grafts obtained from a human donor (cadaveric bone) that have been processed and sterilized.
- Advantages: No additional surgical site required, readily available, and can provide a scaffold for new bone growth.
- Disadvantages: Risk of disease transmission and potential for immune response.
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Xenografts:
- Bone grafts derived from a different species, commonly bovine (cow) bone.
- Advantages: Biocompatible and provides a scaffold for bone regeneration.
- Disadvantages: Potential for immune response and slower resorption compared to autografts.
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Alloplasts:
- Synthetic materials used for bone augmentation, such as hydroxyapatite, calcium phosphate, or bioactive glass.
- Advantages: No risk of disease transmission, customizable, and can be designed to promote bone growth.
- Disadvantages: May not integrate as well as natural bone and can have variable resorption rates.
Surgical Techniques
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Bone Grafting:
- The selected graft material is placed in the deficient area of the
ridge to promote new bone formation. This can be done using various
techniques, including:
- Onlay Grafting: Graft material is placed on top of the existing ridge.
- Inlay Grafting: Graft material is placed within the ridge.
- The selected graft material is placed in the deficient area of the
ridge to promote new bone formation. This can be done using various
techniques, including:
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Guided Bone Regeneration (GBR):
- A barrier membrane is placed over the graft material to prevent soft tissue infiltration and promote bone healing. This technique is often used in conjunction with grafting.
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Sinus Lift:
- In the maxilla, a sinus lift procedure may be performed to augment the bone in the posterior maxilla by elevating the sinus membrane and placing graft material.
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Combination with Orthognathic Surgery:
- Ridge augmentation can be performed simultaneously with orthognathic surgery to correct skeletal discrepancies and enhance the overall facial structure.