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.

The Nance Appliance is a fixed orthodontic device used primarily in the upper arch to maintain space and prevent the molars from drifting forward. It is particularly useful in cases where there is a need to hold the position of the maxillary molars after the premature loss of primary molars or to maintain space for the eruption of permanent teeth. Below is an overview of the Nance Appliance, its components, functions, indications, advantages, and limitations.

Components of the Nance Appliance

1. Baseplate:

   • The Nance Appliance features an acrylic baseplate that is custom-made to fit the palate. This baseplate is typically made of a pink acrylic material that is molded to the shape of the patient's palate.

2. Anterior Button:

   • A prominent feature of the Nance Appliance is the anterior button, which is positioned against the anterior teeth (usually the incisors). This button helps to stabilize the appliance and provides a point of contact to prevent the molars from moving forward.

3. Bands:

   • The appliance is anchored to the maxillary molars using bands that are cemented onto the molars. These bands provide the necessary anchorage for the appliance.

4. Wire Framework:

   • A wire framework may be incorporated into the appliance to enhance its strength and stability. This framework typically consists of a stainless steel wire that connects the bands and the anterior button.

Functions of the Nance Appliance

1. Space Maintenance:

   • The primary function of the Nance Appliance is to maintain space in the upper arch, particularly after the loss of primary molars. It prevents the adjacent teeth from drifting into the space, ensuring that there is adequate room for the eruption of permanent teeth.

2. Molar Stabilization:

   • The appliance helps stabilize the maxillary molars in their proper position, preventing them from moving forward or mesially during orthodontic treatment.

3. Arch Development:

   • In some cases, the Nance Appliance can assist in arch development by providing a stable base for other orthodontic appliances or treatments.

Indications for Use

• Premature Loss of Primary Molars: To maintain space for the eruption of permanent molars when primary molars are lost early.
• Crowding: To prevent adjacent teeth from drifting into the space created by lost teeth, which can lead to crowding.
• Molar Stabilization: To stabilize the position of the maxillary molars during orthodontic treatment.

Advantages of the Nance Appliance

1. Fixed Appliance: As a fixed appliance, the Nance Appliance does not rely on patient compliance, ensuring consistent space maintenance.
2. Effective Space Maintenance: It effectively prevents unwanted tooth movement and maintains space for the eruption of permanent teeth.
3. Minimal Discomfort: Generally, patients tolerate the Nance Appliance well, and it does not cause significant discomfort.

Limitations of the Nance Appliance

1. Oral Hygiene: Maintaining oral hygiene can be more challenging with fixed appliances, and patients must be diligent in their oral care to prevent plaque accumulation and dental issues.
2. Limited Movement: The Nance Appliance primarily affects the molars and may not be effective for moving anterior teeth.
3. Adjustment Needs: While the appliance is generally stable, it may require periodic adjustments or monitoring by the orthodontist.

Relapse

Definition: Relapse refers to the tendency of teeth to return to their original positions after orthodontic treatment. This can occur due to various factors, including the natural elasticity of the periodontal ligament, muscle forces, and the influence of oral habits.

Causes of Relapse

1. Elasticity of the Periodontal Ligament: After orthodontic treatment, the periodontal ligament may still have a tendency to revert to its original state, leading to tooth movement.
2. Muscle Forces: The forces exerted by the lips, cheeks, and tongue can influence tooth positions, especially if these forces are not balanced.
3. Growth and Development: In growing patients, changes in jaw size and shape can lead to shifts in tooth positions.
4. Non-Compliance with Retainers: Failure to wear retainers as prescribed can significantly increase the risk of relapse.

Prevention of Relapse

• Consistent Retainer Use: Adhering to the retainer regimen as prescribed by the orthodontist is crucial for maintaining tooth positions.
• Regular Follow-Up Visits: Periodic check-ups with the orthodontist can help monitor tooth positions and address any concerns early.
• Patient Education: Educating patients about the importance of retention and the potential for relapse can improve compliance with retainer wear.

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.

Growth is the increase in size It may also be defined as the normal  change in the amount of living substance. eg. Growth is the quantitative aspect and measures in units of increase per unit of time.

Development

It is the progress towards maturity (Todd). Development may be defined as natural sequential series of events between fertilization of ovum and adult stage.

Maturation

It is a period of stabilization brought by growth and development.

CEPHALOCAUDAL GRADIENT OF GROWTH

This simply means that there is an axis of increased growth extending from the head towards feet. At about 3rd month of intrauterine life the head takes up about 50% of total body length. At this stage cranium is larger relative to face. In contrast the limbs are underdeveloped. 

By the time of birth limbs and trunk have grown faster than head and the entire proportion of the body to the head has increased. These processes of growth continue till adult.  

SCAMMON’S CURVE

In normal growth pattern all the tissue system of the body do not growth at the same rate. Scammon’s curve for growth shows 4 major tissue system of the body;

• Neural

• Lymphoid 

• General: Bone, viscera, muscle.

• Genital

The graph indicates the growth of the neural tissue is complete by 6-7 year of age. General body tissue show an “S” shaped curve with showing of rate during childhood and acceleration at puberty. Lymphoid tissues proliferate to its maximum in late childhood and undergo involution. At the same time growth of the genital tissue accelerate rapidly. 

Mesial Shift in Dental Development

Mesial shift refers to the movement of teeth in a mesial (toward the midline of the dental arch) direction. This phenomenon is particularly relevant in the context of mixed dentition, where both primary (deciduous) and permanent teeth are present. Mesial shifts can be categorized into two types: early mesial shift and late mesial shift. Understanding these shifts is important for orthodontic treatment planning and predicting changes in dental arch relationships.

Early Mesial Shift

• Timing: Occurs during the mixed dentition phase, typically around 6-7 years of age.
• Mechanism:
  • The early mesial shift is primarily due to the closure of primate spaces. Primate spaces are natural gaps that exist between primary teeth, particularly between the maxillary lateral incisors and canines, and between the mandibular canines and first molars.
  • As the permanent first molars erupt, they exert pressure on the primary teeth, leading to the closure of these spaces. This pressure causes the primary molars to drift mesially, resulting in a shift of the dental arch.
• Clinical Significance:
  • The early mesial shift helps to maintain proper alignment and spacing for the eruption of permanent teeth. It is a natural part of dental development and can influence the overall occlusion.

Late Mesial Shift

• Timing: Occurs during the mixed dentition phase, typically around 10-11 years of age.
• Mechanism:
  • The late mesial shift is associated with the closure of leeway spaces after the shedding of primary second molars. Leeway space refers to the difference in size between the primary molars and the permanent premolars that replace them.
  • When the primary second molars are lost, the adjacent permanent molars (first molars) can drift mesially into the space left behind, resulting in a late mesial shift.
• Clinical Significance:
  • The late mesial shift can help to align the dental arch and improve occlusion as the permanent teeth continue to erupt. However, if there is insufficient space or if the shift is excessive, it may lead to crowding or malocclusion.