Angle's Classification of Malocclusion

Developed by Dr. Edward Angle in the early 20th century, this classification is based on the relationship of the first molars and the canines. It is divided into three main classes:

Class I Malocclusion (Normal Occlusion)

• Description: The first molars are in a normal relationship, with the mesiobuccal cusp of the maxillary first molar fitting into the buccal groove of the mandibular first molar. The canines also have a normal relationship.
• Characteristics:
  • The dental arches are aligned.
  • There may be crowding, spacing, or other dental irregularities, but the overall molar relationship is normal.

Class II Malocclusion (Distocclusion)

• Description: The first molars are positioned such that the mesiobuccal cusp of the maxillary first molar is positioned more than one cusp width ahead of the buccal groove of the mandibular first molar.
• Subdivisions:
  • Class II Division 1: Characterized by protruded maxillary incisors and a deep overbite.
  • Class II Division 2: Characterized by retroclined maxillary incisors and a deep overbite, often with a normal or reduced overjet.
• Characteristics: This class often results in an overbite and can lead to aesthetic concerns.

Class III Malocclusion (Mesioocclusion)

• Description: The first molars are positioned such that the mesiobuccal cusp of the maxillary first molar is positioned more than one cusp width behind the buccal groove of the mandibular first molar.
• Characteristics:
  • This class is often associated with an underbite, where the lower teeth are positioned more forward than the upper teeth.
  • It can lead to functional issues and aesthetic concerns.

2. Skeletal Classification

In addition to Angle's classification, malocclusion can also be classified based on skeletal relationships, which consider the position of the maxilla and mandible in relation to each other. This classification is particularly useful in assessing the underlying skeletal discrepancies that may contribute to malocclusion.

Class I Skeletal Relationship

• Description: The maxilla and mandible are in a normal relationship, similar to Class I malocclusion in Angle's classification.
• Characteristics: The skeletal bases are well-aligned, but there may still be dental irregularities.

Class II Skeletal Relationship

• Description: The mandible is positioned further back relative to the maxilla, similar to Class II malocclusion.
• Characteristics: This can be due to a retruded mandible or an overdeveloped maxilla.

Class III Skeletal Relationship

• Description: The mandible is positioned further forward relative to the maxilla, similar to Class III malocclusion.
• Characteristics: This can be due to a protruded mandible or a retruded maxilla.

3. Other Classifications

In addition to Angle's and skeletal classifications, malocclusion can also be described based on specific characteristics:

• Overbite: The vertical overlap of the upper incisors over the lower incisors. It can be classified as:

  • Normal Overbite: Approximately 1-2 mm of overlap.
  • Deep Overbite: Excessive overlap, which can lead to impaction of the lower incisors.
  • Open Bite: Lack of vertical overlap, where the upper and lower incisors do not touch.

• Overjet: The horizontal distance between the labioincisal edge of the upper incisors and the linguoincisal edge of the lower incisors. It can be classified as:

  • Normal Overjet: Approximately 2-4 mm.
  • Increased Overjet: Greater than 4 mm, often associated with Class II malocclusion.
  • Decreased Overjet: Less than 2 mm, often associated with Class III malocclusion.

• Crossbite: A condition where one or more of the upper teeth bite on the inside of the lower teeth. It can be:

  • Anterior Crossbite: Involves the front teeth.
  • Posterior Crossbite: Involves the back teeth.

Mixed Dentition Analysis: Tanaka & Johnson Analysis

 This analysis is crucial for predicting the size of unerupted permanent teeth based on the measurements of erupted teeth, which is particularly useful in orthodontics.

Mixed Dentition Analysis

Mixed dentition refers to the period when both primary and permanent teeth are present in the mouth. Accurate predictions of the size of unerupted teeth during this phase are essential for effective orthodontic treatment planning.

Proportional Equation Prediction Method

When most canines and premolars have erupted, and one or two succedaneous teeth are still unerupted, the proportional equation prediction method can be employed. This method allows for estimating the mesiodistal width of unerupted permanent teeth.

Procedure for Proportional Equation Prediction Method

1. Measurement of Teeth:

   • Measure the width of the unerupted tooth and an erupted tooth on the same periapical radiograph.
   • Measure the width of the erupted tooth on a plaster cast.

2. Establishing Proportions:

   • These three measurements form a proportion that can be solved to estimate the width of the unerupted tooth on the cast.

Formula Used

The following formula is utilized to calculate the width of the unerupted tooth:

[ Y_1 = \frac{X_1 \times Y_2}{X_2} ]

Where:

• Y1 = Width of the unerupted tooth whose measurement is to be determined.
• Y2 = Width of the unerupted tooth as seen on the radiograph.
• X1 = Width of the erupted tooth, measured on the plaster cast.
• X2 = Width of the erupted tooth, measured on the radiograph.

Application of the Analysis

This method is particularly useful in orthodontic assessments, allowing practitioners to predict the size of unerupted teeth accurately. By using the measurements of erupted teeth, orthodontists can make informed decisions regarding space management and treatment planning.

Bruxism

Bruxism is the involuntary grinding or clenching of teeth, often occurring during sleep (nocturnal bruxism) or while awake (awake bruxism). It can lead to various dental and health issues, including tooth wear, jaw pain, and temporomandibular joint (TMJ) disorders.

Etiology

1. Central Nervous System (CNS):

   • Bruxism has been observed in individuals with neurological conditions such as cerebral palsy and mental retardation, suggesting a CNS component to the phenomenon.

2. Psychological Factors:

   • Emotional disturbances such as anxiety, stress, aggression, and feelings of hunger can contribute to the tendency to grind teeth. Psychological stressors are often linked to increased muscle tension and bruxism.

3. Occlusal Discrepancy:

   • Improper interdigitation of teeth, such as malocclusion or misalignment, can lead to bruxism as the body attempts to find a comfortable bite.

4. Systemic Factors:

   • Nutritional deficiencies, particularly magnesium (Mg²⁺) deficiency, have been associated with bruxism. Magnesium plays a role in muscle function and relaxation.

5. Genetic Factors:

   • There may be a hereditary component to bruxism, with a family history of the condition increasing the likelihood of its occurrence.

6. Occupational Factors:

   • High-stress occupations or activities, such as being an overenthusiastic student or participating in competitive sports, can lead to increased clenching and grinding of teeth.

Clinical Features

• Tooth Wear: Increased wear on the occlusal surfaces of teeth, leading to flattened or worn-down teeth.
• Jaw Pain: Discomfort or pain in the jaw muscles, particularly in the masseter and temporalis muscles.
• TMJ Disorders: Symptoms such as clicking, popping, or locking of the jaw, as well as pain in the TMJ area.
• Headaches: Tension-type headaches or migraines may occur due to muscle tension associated with bruxism.
• Facial Pain: Generalized facial pain or discomfort, particularly around the jaw and temples.
• Gum Recession: Increased risk of gum recession and periodontal issues due to excessive force on the teeth.

Management

1. Adjunctive Therapy:

   • Psychotherapy: Aimed at reducing emotional disturbances and stress that may contribute to bruxism. Techniques may include cognitive-behavioral therapy (CBT) or relaxation techniques.
   • Pain Management:
     • Ethyl Chloride: A topical anesthetic that can be injected into the TMJ area to alleviate pain and discomfort.

2. Occlusal Therapy:

   • Occlusal Adjustment: Adjusting the occlusion to improve the bite and reduce bruxism.
   • Splints:
     • Volcanite Splints: These are custom-made occlusal splints that cover the occlusal surfaces of all teeth. They help reduce muscle tone and protect the teeth from wear.
     • Night Guards: Similar to splints, night guards are worn during sleep to prevent grinding and clenching.
   • Restorative Treatment: Addressing any existing dental issues, such as cavities or misaligned teeth, to improve overall dental health.

3. Pharmacological Management:

   • Vapo Coolant: Ethyl chloride can be used for pain relief in the TMJ area.
   • Local Anesthesia: Direct injection of local anesthetics into the TMJ can provide temporary relief from pain.
   • Muscle Relaxants: Medications such as muscle tranquilizers or sedatives may be prescribed to help reduce muscle tension and promote relaxation.

BONES OF THE SKULL  

A) Bones of the cranial base: 

    A)  Fontal  (1) 
    B)  Ethmoid  (1)      
    C)  Sphenoid (1)  
    D)  Occipital  (1)
    
B) Bones of the cranial vault: 
 
       1. Parietal (2)          
       2. Temporal (2) 
       
C) Bones of the face:
  
        Maxilla (2) 
        Mandible (1) 
        Nasal bone (2) 
        Lacrimal bone (2) 
        Zygomatic bone (2) 
        Palatine bone(2) 
        Infra nasal concha (2)  

FUSION BETWEEN BONES 

1. Syndesmosis: Membranous or ligamentus eg. Sutural point. 
2. Synostosis: Bony union eg. symphysis menti. 
3. Synchondrosis: Cartilaginous eg. sphenoccipital, spheno-ethmoidal. 

GROWTH OF THE SKULL: 
          A)     Cranium: 1. Base   2. Vault   
          B)     Face:  1. Upper face 2.Lower face  

CRANIAL BASE: 

Cranial base grows at different cartilaginous suture. The cranial base may be divided into 3 areas.  

1. The posterior part which extends from the occiput to the salatercica. The most important growth site spheno-occipital synchondrosis is situated here. It is active throughout the growing period and does not close until early adult life.  

2. The middle portion extends from sella to foramen cecum and the sutural growth spheno-ethmoidal synchondrosis is situated here. The exact time of closing is not known but probably at the age of 7 years. 

3. The anterior part is from foramen cecum and grows by surface deposition of bone in the frontal region and simultaneous development of frontal sinus. 

CRANIAL VAULT:  

The cranial vault grows as the brain grows. It is accelerated at infant. The growth is complete by 90% by the end of 5th year. At birth the sutures are wide sufficiently and become approximated during the 1st 2 years of life. 

The development and extension of frontal sinus takes place particularly at the age of puberty and there is deposition of bone on the surfaces of cranial bone. 
 

Tweed's Analysis

Tweed's analysis is a comprehensive cephalometric method developed by Dr. Charles Tweed in the mid-20th century. It is primarily used in orthodontics to evaluate the relationships between the skeletal and dental structures of the face, particularly focusing on the position of the teeth and the skeletal bases. Tweed's analysis is instrumental in diagnosing malocclusions and planning orthodontic treatment.

Key Features of Tweed's Analysis

1. Reference Planes and Points:

   • Sella (S): The midpoint of the sella turcica, a bony structure in the skull.
   • Nasion (N): The junction of the frontal and nasal bones.
   • A Point (A): The deepest point on the maxillary arch between the anterior nasal spine and the maxillary alveolar process.
   • B Point (B): The deepest point on the mandibular arch between the anterior nasal spine and the mandibular alveolar process.
   • Menton (Me): The lowest point on the symphysis of the mandible.
   • Gnathion (Gn): The midpoint between Menton and Pogonion (the most anterior point on the chin).
   • Pogonion (Pog): The most anterior point on the contour of the chin.
   • Go (Gonion): The midpoint of the contour of the ramus and the body of the mandible.

2. Reference Lines:

   • SN Plane: A line drawn from Sella to Nasion, representing the cranial base.
   • Mandibular Plane (MP): A line connecting Gonion (Go) to Menton (Me), which represents the position of the mandible.
   • Facial Plane (FP): A line drawn from Gonion (Go) to Menton (Me), used to assess the facial profile.

3. Key Measurements:

   • ANB Angle: The angle formed between the lines connecting A Point to Nasion and B Point to Nasion. It indicates the relationship between the maxilla and mandible.
     • Normal Range: Typically between 2° and 4°.
   • SN-MP Angle: The angle between the SN plane and the mandibular plane (MP), which helps assess the vertical position of the mandible.
     • Normal Range: Usually between 32° and 38°.
   • Wits Appraisal: The distance between the perpendiculars dropped from points A and B to the occlusal plane. It provides insight into the anteroposterior relationship of the dental bases.
   • Interincisal Angle: The angle formed between the long axes of the maxillary and mandibular incisors, which helps assess the inclination of the incisors.

4. Tweed's Philosophy:

   • Tweed emphasized the importance of achieving a functional occlusion and a harmonious facial profile. He believed that orthodontic treatment should focus on the relationship between the dental and skeletal structures to achieve optimal results.

Clinical Relevance

• Diagnosis and Treatment Planning: Tweed's analysis helps orthodontists diagnose skeletal discrepancies and plan appropriate treatment strategies. It provides a clear understanding of the patient's craniofacial relationships, which is essential for effective orthodontic intervention.
• Monitoring Treatment Progress: By comparing pre-treatment and post-treatment cephalometric measurements, orthodontists can evaluate the effectiveness of the treatment and make necessary adjustments.
• Predicting Treatment Outcomes: The analysis aids in predicting the outcomes of orthodontic treatment by assessing the initial skeletal and dental relationships.

Forces Required for Tooth Movements

1. Tipping:

   • Force Required: 50-75 grams
   • Description: Tipping involves the movement of a tooth around its center of resistance, resulting in a change in the angulation of the tooth.

2. Bodily Movement:

   • Force Required: 100-150 grams
   • Description: Bodily movement refers to the translation of a tooth in its entirety, moving it in a straight line without tipping.

3. Intrusion:

   • Force Required: 15-25 grams
   • Description: Intrusion is the movement of a tooth into the alveolar bone, effectively reducing its height in the dental arch.

4. Extrusion:

   • Force Required: 50-75 grams
   • Description: Extrusion involves the movement of a tooth out of the alveolar bone, increasing its height in the dental arch.

5. Torquing:

   • Force Required: 50-75 grams
   • Description: Torquing refers to the rotational movement of a tooth around its long axis, affecting the angulation of the tooth in the buccolingual direction.

6. Uprighting:

   • Force Required: 75-125 grams
   • Description: Uprighting is the movement of a tilted tooth back to its proper vertical position.

7. Rotation:

   • Force Required: 50-75 grams
   • Description: Rotation involves the movement of a tooth around its long axis, changing its orientation within the dental arch.

8. Headgear:

   • Force Required: 350-450 grams on each side
   • Duration: Minimum of 12-14 hours per day
   • Description: Headgear is used to control the growth of the maxilla and to correct dental relationships.

9. Face Mask:

   • Force Required: 1 pound (450 grams) per side
   • Duration: 12-14 hours per day
   • Description: A face mask is used to encourage forward growth of the maxilla in cases of Class III malocclusion.

10. Chin Cup:

    • Initial Force Required: 150-300 grams per side
    • Subsequent Force Required: 450-700 grams per side (after two months)
    • Duration: 12-14 hours per day
    • Description: A chin cup is used to control the growth of the mandible and improve facial aesthetics.