Anchorage in orthodontics refers to the resistance that the anchorage area offers to unwanted tooth movements during orthodontic treatment. Proper understanding and application of anchorage principles are crucial for achieving desired tooth movements while minimizing undesirable effects on adjacent teeth.

Classification of Anchorage

1. According to Manner of Force Application

• Simple Anchorage:

  • Achieved by engaging a greater number of teeth than those being moved within the same dental arch.
  • The combined root surface area of the anchorage unit must be at least double that of the teeth to be moved.

• Stationary Anchorage:

  • Defined as dental anchorage where the application of force tends to displace the anchorage unit bodily in the direction of the force.
  • Provides greater resistance compared to anchorage that only resists tipping forces.

• Reciprocal Anchorage:

  • Refers to the resistance offered by two malposed units when equal and opposite forces are applied, moving each unit towards a more normal occlusion.
  • Examples:
    • Closure of a midline diastema by moving the two central incisors towards each other.
    • Use of crossbite elastics and dental arch expansions.

2. According to Jaws Involved

• Intra-maxillary Anchorage:
  • All units offering resistance are situated within the same jaw.
• Intermaxillary Anchorage:
  • Resistance units in one jaw are used to effect tooth movement in the opposing jaw.
  • Also known as Baker's anchorage.
  • Examples:
    • Class II elastic traction.
    • Class III elastic traction.

3. According to Site

• Intraoral Anchorage:

  • Both the teeth to be moved and the anchorage areas are located within the oral cavity.
  • Anatomic units include teeth, palate, and lingual alveolar bone of the mandible.

• Extraoral Anchorage:

  • Resistance units are situated outside the oral cavity.
  • Anatomic units include the occiput, back of the neck, cranium, and face.
  • Examples:
    • Headgear.
    • Facemask.

• Muscular Anchorage:

  • Utilizes forces generated by muscles to aid in tooth movement.
  • Example: Lip bumper to distalize molars.

4. According to Number of Anchorage Units

• Single or Primary Anchorage:

  • A single tooth with greater alveolar support is used to move another tooth with lesser support.

• Compound Anchorage:

  • Involves more than one tooth providing resistance to move teeth with lesser support.

• Multiple or Reinforced Anchorage:

  • Utilizes more than one type of resistance unit.
  • Examples:
    • Extraoral forces to augment anchorage.
    • Upper anterior inclined plane.
    • Transpalatal arch.

Anterior bite plate is an orthodontic appliance used primarily to manage various dental issues, particularly those related to occlusion and alignment of the anterior teeth. It is a removable appliance that is placed in the mouth to help correct bite discrepancies, improve dental function, and protect the teeth from wear.

Indications for Use

1. Anterior Crossbite:

   • An anterior bite plate can help correct an anterior crossbite by repositioning the maxillary incisors in relation to the mandibular incisors.

2. Open Bite:

   • It can be used to help close an anterior open bite by providing a surface for the anterior teeth to occlude against, encouraging proper alignment.

3. Bruxism:

   • The appliance can protect the anterior teeth from wear caused by grinding or clenching, acting as a barrier between the upper and lower teeth.

4. Space Maintenance:

   • In cases where anterior teeth have been lost or extracted, an anterior bite plate can help maintain space for future dental work or the eruption of permanent teeth.

5. Facilitation of Orthodontic Treatment:

   • It can be used as part of a comprehensive orthodontic treatment plan to help achieve desired tooth movements and improve overall occlusion.

Design and Features

• Material: Anterior bite plates are typically made from acrylic or thermoplastic materials, which are durable and can be easily adjusted.
• Shape: The appliance is designed to cover the anterior teeth, providing a flat occlusal surface for the upper and lower teeth to meet.
• Retention: The bite plate is custom-fitted to the patient’s dental arch to ensure comfort and stability during use.

Mechanism of Action

• Repositioning Teeth: The anterior bite plate can help reposition the anterior teeth by providing a surface that encourages proper occlusion and alignment.
• Distributing Forces: It helps distribute occlusal forces evenly across the anterior teeth, reducing the risk of localized wear or damage.
• Encouraging Proper Function: By providing a stable occlusal surface, the bite plate encourages proper chewing and speaking functions.

Management and Care

• Patient Compliance: For the anterior bite plate to be effective, patients must wear it as prescribed by their orthodontist. This may involve wearing it during the day, at night, or both, depending on the specific treatment goals.
• Hygiene: Patients should maintain good oral hygiene and clean the bite plate regularly to prevent plaque buildup and maintain oral health.
• Regular Check-Ups: Follow-up appointments with the orthodontist are essential to monitor progress and make any necessary adjustments to the appliance.

Key Cephalometric Landmarks

1. Sella (S):

   • The midpoint of the sella turcica, a bony structure located at the base of the skull. It serves as a central reference point in cephalometric analysis.

2. Nasion (N):

   • The junction of the frontal and nasal bones, located at the bridge of the nose. It is often used as a reference point for the anterior cranial base.

3. A Point (A):

   • The deepest point on the maxillary arch, located between the anterior nasal spine and the maxillary alveolar process. It is crucial for assessing maxillary position.

4. B Point (B):

   • The deepest point on the mandibular arch, located between the anterior nasal spine and the mandibular alveolar process. It is important for evaluating mandibular position.

5. Pogonion (Pog):

   • The most anterior point on the contour of the chin. It is used to assess the position of the mandible in relation to the maxilla.

6. Gnathion (Gn):

   • The midpoint between Menton and Pogonion, representing the most inferior point of the mandible. It is used in various angular measurements.

7. Menton (Me):

   • The lowest point on the symphysis of the mandible. It is used as a reference for vertical measurements.

8. Go (Gonion):

   • The midpoint of the contour of the ramus and the body of the mandible. It is used to assess the angle of the mandible.

9. Frankfort Horizontal Plane (FH):

   • A plane defined by the points of the external auditory meatus (EAM) and the lowest point of the orbit (Orbitale). It is used as a reference plane for various measurements.

10. Orbitale (Or):

    • The lowest point on the inferior margin of the orbit (eye socket). It is used in conjunction with the EAM to define the Frankfort Horizontal Plane.

11. Ectocanthion (Ec):

    • The outer canthus of the eye, used in facial measurements and assessments.

12. Endocanthion (En):

    • The inner canthus of the eye, also used in facial measurements.

13. Alveolar Points:

    • Points on the alveolar ridge of the maxilla and mandible, often used to assess the position of the teeth.

Importance of Cephalometric Landmarks

• Diagnosis: These landmarks help orthodontists diagnose skeletal and dental discrepancies, such as Class I, II, or III malocclusions.
• Treatment Planning: By understanding the relationships between these landmarks, orthodontists can develop effective treatment plans tailored to the individual patient's needs.
• Monitoring Progress: Cephalometric landmarks allow for the comparison of pre-treatment and post-treatment radiographs, helping to evaluate the effectiveness of orthodontic interventions.
• Research and Education: These landmarks are essential in orthodontic research and education, providing a standardized method for analyzing craniofacial morphology.

• Scammon's growth curve: Lymphoid tissue shows negative growth

• Fontanelle fusion:

  Fontanelle	Time of Fusion
  Anterior	3 years (last)
  Posterior	3 months
  Sphenoidal	6 months
  Mastoid	18 months

• Cranial base growth:

  • Birth: 55 – 60%
  • 4 – 7 years: 94%
  • 8 – 13 years: 98%

• Head-body proportion:

  • 3rd month IU: 50%
  • Birth: 30%
  • Adult: 12%

• Fontanelle fusion order: Posterior → Sphenoidal → Mastoid → Anterior

• Last cranial base growth center to fuse: Spheno-occipital synchondrosis

• Functional matrix theory: Melvin Moss

• Bone growth study via implants: Bjork (1969)

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.

Retention

Definition: Retention refers to the phase following active orthodontic treatment where appliances are used to maintain the corrected positions of the teeth. The goal of retention is to prevent relapse and ensure that the teeth remain in their new, desired positions.

Types of Retainers

1. Fixed Retainers:

   • Description: These are bonded to the lingual surfaces of the teeth, typically the anterior teeth, to maintain their positions.
   • Advantages: They provide continuous retention without requiring patient compliance.
   • Disadvantages: They can make oral hygiene more challenging and may require periodic replacement.

2. Removable Retainers:

   • Description: These are appliances that can be taken out by the patient. Common types include:
     • Hawley Retainer: A custom-made acrylic plate with a wire framework that holds the teeth in position.
     • Essix Retainer: A clear, plastic retainer that fits over the teeth, providing a more aesthetic option.
   • Advantages: Easier to clean and can be removed for eating and oral hygiene.
   • Disadvantages: Their effectiveness relies on patient compliance; if not worn as prescribed, relapse may occur.

Duration of Retention

• The duration of retention varies based on individual cases, but it is generally recommended to wear retainers full-time for a period (often several months to a year) and then transition to nighttime wear for an extended period (often several years).
• Long-term retention may be necessary for some patients, especially those with a history of dental movement or specific malocclusions.