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.

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.

Orthodontic Force Duration

1. Continuous Forces:

   • Definition: Continuous forces are applied consistently over time without interruption.
   • Application: Many extraoral appliances, such as headgear, are designed to provide continuous force to the teeth and jaws. This type of force is essential for effective tooth movement and skeletal changes.
   • Example: A headgear may be worn for 12-14 hours a day to achieve the desired effects on the maxilla or mandible.

2. Intermittent Forces:

   • Definition: Intermittent forces are applied in a pulsed or periodic manner, with breaks in between.
   • Application: Some extraoral appliances may use intermittent forces, but this is less common. Intermittent forces can be effective in certain situations, but continuous forces are generally preferred for consistent tooth movement.
   • Example: A patient may be instructed to wear an appliance for a few hours each day, but this is less typical for extraoral devices.

Force Levels

1. Light Forces:

   • Definition: Light forces are typically in the range of 50-100 grams and are used to achieve gentle tooth movement.
   • Application: Light forces are ideal for orthodontic treatment as they minimize discomfort and reduce the risk of damaging the periodontal tissues.
   • Example: Some extraoral appliances may be designed to apply light forces to encourage gradual movement of the teeth or to modify jaw relationships.

2. Moderate Forces:

   • Definition: Moderate forces range from 100-200 grams and can be used for more significant tooth movement or skeletal changes.
   • Application: These forces can be effective in achieving desired movements but may require careful monitoring to avoid discomfort or adverse effects.
   • Example: Headgear that applies moderate forces to the maxilla to correct Class II malocclusions.

3. Heavy Forces:

   • Definition: Heavy forces exceed 200 grams and are typically used for rapid tooth movement or significant skeletal changes.
   • Application: While heavy forces can lead to faster results, they also carry a higher risk of complications, such as root resorption or damage to the periodontal ligament.
   • Example: Some extraoral appliances may apply heavy forces for short periods, but this is generally not recommended for prolonged use.

Late mandibular growth refers to the continued development and growth of the mandible (lower jaw) that occurs after the typical growth spurts associated with childhood and adolescence. While most of the significant growth of the mandible occurs during these early years, some individuals may experience additional growth in their late teens or early adulthood. Understanding the factors influencing late mandibular growth, its implications, and its relevance in orthodontics and dentistry is essential.

Factors Influencing Late Mandibular Growth

1. Genetics:

   • Genetic factors play a significant role in determining the timing and extent of mandibular growth. Family history can provide insights into an individual's growth patterns.

2. Hormonal Changes:

   • Hormonal fluctuations, particularly during puberty, can influence growth. Growth hormone, sex hormones (estrogen and testosterone), and other endocrine factors can affect the growth of the mandible.

3. Functional Forces:

   • The forces exerted by the muscles of mastication, as well as functional activities such as chewing and speaking, can influence the growth and development of the mandible.

4. Environmental Factors:

   • Nutritional status, overall health, and lifestyle factors can impact growth. Adequate nutrition is essential for optimal skeletal development.

5. Orthodontic Treatment:

   • Orthodontic interventions can influence mandibular growth patterns. For example, the use of functional appliances may encourage forward growth of the mandible in growing patients.

Clinical Implications of Late Mandibular Growth

1. Changes in Occlusion:

   • Late mandibular growth can lead to changes in the occlusal relationship between the upper and lower teeth. This may result in the development of malocclusions or changes in existing malocclusions.

2. Facial Aesthetics:

   • Continued growth of the mandible can affect facial aesthetics, including the profile and overall balance of the face. This may be particularly relevant in individuals with a retrognathic (recessed) mandible or those seeking cosmetic improvements.

3. Orthodontic Treatment Planning:

   • Understanding the potential for late mandibular growth is crucial for orthodontists when planning treatment. It may influence the timing of interventions and the choice of appliances used to guide growth.

4. Surgical Considerations:

   • In some cases, late mandibular growth may necessitate surgical intervention, particularly in adults with significant skeletal discrepancies. Orthognathic surgery may be considered to correct jaw relationships and improve function and aesthetics.

Monitoring Late Mandibular Growth

1. Clinical Evaluation:

   • Regular clinical evaluations, including assessments of occlusion, facial symmetry, and growth patterns, are essential for monitoring late mandibular growth.

2. Radiographic Analysis:

   • Cephalometric radiographs can be used to assess changes in mandibular growth and its relationship to the craniofacial complex. This information can guide treatment decisions.

3. Patient History:

   • Gathering a comprehensive patient history, including growth patterns and any previous orthodontic treatment, can provide valuable insights into late mandibular growth.

Steiner's Analysis

Steiner's analysis is a widely recognized cephalometric method used in orthodontics to evaluate the relationships between the skeletal and dental structures of the face. Developed by Dr. Charles A. Steiner in the 1950s, this analysis provides a systematic approach to assess craniofacial morphology and is particularly useful for treatment planning and evaluating the effects of orthodontic treatment.

Key Features of Steiner'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.

2. Reference Lines:

   • SN Plane: A line drawn from Sella to Nasion, representing the cranial base.
   • 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.
   • Facial Plane (FP): A line drawn from Gonion (Go) to Menton (Me), used to assess the facial profile.

3. Key Measurements:

   • ANB Angle: Indicates the anteroposterior 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.

Clinical Relevance

• Diagnosis and Treatment Planning: Steiner'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.