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.

Camouflage in orthodontics refers to the strategic use of orthodontic treatment to mask or disguise underlying skeletal discrepancies, particularly in cases where surgical intervention may not be feasible or desired by the patient. This approach aims to improve dental alignment and occlusion while minimizing the appearance of skeletal issues, such as Class II or Class III malocclusions.

Key Concepts of Camouflage in Orthodontics

1. Objective:

   • The primary goal of camouflage is to create a more aesthetically pleasing smile and functional occlusion without addressing the underlying skeletal relationship directly. This is particularly useful for patients who may not want to undergo orthognathic surgery.

2. Indications:

   • Camouflage is often indicated for:
     • Class II Malocclusion: Where the lower jaw is positioned further back than the upper jaw.
     • Class III Malocclusion: Where the lower jaw is positioned further forward than the upper jaw.
     • Mild to Moderate Skeletal Discrepancies: Cases where the skeletal relationship is not severe enough to warrant surgical correction.

3. Mechanisms:

   • Tooth Movement: Camouflage typically involves moving the teeth into positions that improve the occlusion and facial aesthetics. This may include:
     • Proclination of Upper Incisors: In Class II cases, the upper incisors may be tilted forward to improve the appearance of the bite.
     • Retroclination of Lower Incisors: In Class III cases, the lower incisors may be tilted backward to help achieve a better occlusal relationship.
   • Use of Elastics: Orthodontic elastics can be employed to help correct the bite and improve the overall alignment of the teeth.

4. Treatment Planning:

   • A thorough assessment of the patient's dental and skeletal relationships is essential. This includes:
     • Cephalometric Analysis: To evaluate the skeletal relationships and determine the extent of camouflage needed.
     • Clinical Examination: To assess the dental alignment, occlusion, and any functional issues.
     • Patient Preferences: Understanding the patient's goals and preferences regarding treatment options.

Advantages of Camouflage

1. Non-Surgical Option: Camouflage provides a way to improve dental alignment and aesthetics without the need for surgical intervention, making it appealing to many patients.
2. Shorter Treatment Time: In some cases, camouflage can lead to shorter treatment times compared to surgical options.
3. Improved Aesthetics: By enhancing the appearance of the smile and occlusion, camouflage can significantly boost a patient's confidence and satisfaction.

Limitations of Camouflage

1. Not a Permanent Solution: While camouflage can improve aesthetics and function, it does not address the underlying skeletal discrepancies, which may lead to long-term issues.
2. Potential for Relapse: Without proper retention, there is a risk that the teeth may shift back to their original positions after treatment.
3. Functional Complications: In some cases, camouflage may not fully resolve functional issues related to the bite, leading to potential discomfort or wear on the teeth.

SEQUENCE OF ERUPTION OF DECIDUOUS TEETH

Upper/Lower   A B D C E 

SEQUENCE OF ERUPTION OF PERMAMENT TEETH 

Upper:   6 1 2 4 3 5 7           Lower:    6 1 2 3 4 5 7   
      
or       6 1 2 4 5 3 7              or  6 1 2 4 3 5 7 
 

ANTHROPOID SPACE / PRIMATE SPACE / SIMIEN’S SPACE  

The space mesial to upper deciduous canine and distal to lower deciduous  canine is characteristically found in primates and hence it is called primate space.  

INCISOR LIABILITY 

When the permanent central incisor erupt, these teeth use up specially all the spaces found in the normal dentition. With the eruption of permanent lateral incisor the space situation becomes tight. In the maxillary arch it is just enough to accommodate but in mandibular arch there is an average 1.6 mm less space available. This difference between the space present and space required is known as incisor liability. 
These conditions overcome by;  

      1. This is a transient condition and extra space comes from slight increase in arch width.   
      2. Slight labial positioning of central and lateral incisor. 
      3. Distal shift of permanent canine.        

      
LEE WAY SPACE (OF NANCE)  

The combined mesiodistal width of the permanent canines and pre molars is usually less that of the deciduous canines and molars. This space is 
called leeway space of Nance.     

Measurement of lee way space: 
 
Is greater in the mandibular arch than in the maxillary arch  It is about 1.8mm [0.9mm on each side of the arch] in the maxillary arch. 
And about 3.4mm [1.7 mm on side of the arch] in the mandibular arch. 
 
Importance:  

 This lee way space allows the mesial movement of lower molar there by correcting flush terminal plane.     
 LWS can be measure with the help of cephalometry.    

FLUSH TERMINAL PLANE (TERMINAL PLANE RELATIONSHIP) 

Mandibular 2nd deciduous molar is usually wider mesio-distally then the maxillary 2nd deciduous molar. This leads to the development of flush terminal plane which falls along the distal surface of upper and lower 2nd deciduous molar. This develops into class I molar relationship. 

Distal step relationship leads to class 2 relationship.
Mesial step relationship mostly leads to class 3 relationship.  

FEATURE OF IDEAL OCCLUSION IN PRIMARY DENTITION 

1. Spacing of anterior teeth. 
2. Primate space is present. 
3. Flush terminal plane is found. 
4. Almost vertical inclination of anterior teeth. 
5. Overbite and overjet varies.  

UGLY DUCKLING STAGE  

Definition:  
Stage of a transient or self correcting malocclusion is seen sometimes is called ugly duck ling stage. 
 
Occurring site: Maxillary incisor region 

Occuring age: 8-9 years of age.  

This situation is seen during the eruption of the permanent canines. As the developing p.c. they displace the roots of lateral incisor mesially this results is transmitting of the force on to the roots of the central incisors which also gets displaced mesially. A resultant distal divergence of the crowns of the two central incisors causes midline spacing.  

This portion of teeth at this stage is compared to that of ugly walk of the duckling and hence it is called Ugly Duckling Stage. 

Described by Broad bent. In this stage children tend to look ugly. Parents are often apprehensive during this stage and consult the dentist.  

Corrects by itself, when canines erupt and the pressure is transferred from the roots to the coronal area of the incisor.  
IMPORTANCE OF 1ST MOLAR
 
1. It is the key tooth to occlusion. 
2.  Angle’s classification is based on this tooth. 
3.  It is the tooth of choice for anchorage. 
4.  Supports occlusion in a vertical direction. 
5.  Loss of this tooth leads to migration of other tooth. 
6.  Helps in opening the bite.   

Types of Springs

In orthodontics, various types of springs are utilized to achieve specific tooth movements. Each type of spring has unique characteristics and applications. Below are a few examples of commonly used springs in orthodontic appliances:

1. Finger Spring

• Construction: Made from 0.5 mm stainless steel wire.
• Components:
  • Helix: 2 mm in diameter.
  • Active Arm: The part that exerts force on the tooth.
  • Retentive Arm: Helps retain the appliance in place.
• Placement: The helix is positioned opposite to the direction of the intended tooth movement and should be aligned along the long axis of the tooth, perpendicular to the direction of movement.
• Indication: Primarily used for mesio-distal movement of teeth, such as closing anterior diastemas.
• Activation: Achieved by opening the coil or moving the active arm towards the tooth to be moved by 2-3 mm.

2. Z-Spring (Double Cantilever)

• Construction: Comprises two helices of small diameter, suitable for one or more incisors.
• Positioning: The spring is positioned perpendicular to the palatal surface of the tooth, with a long retentive arm.
• Preparation: The Z-spring needs to be boxed in wax prior to acrylization.
• Indication: Used to move one or more teeth in the same direction, such as proclining two or more upper incisors to correct anterior tooth crossbites. It can also correct mild rotation if only one helix is activated.
• Activation: Achieved by opening both helices up to 2 mm at a time.

3. Cranked Single Cantilever Spring

• Construction: Made from 0.5 mm wire.
• Design: The spring consists of a coil located close to its emergence from the base plate. It is cranked to keep it clear of adjacent teeth.
• Indication: Primarily used to move teeth labially.

4. T Spring

• Construction: Made from 0.5 mm wire.
• Design: The spring consists of a T-shaped arm, with the arms embedded in acrylic.
• Indication: Used for buccal movement of premolars and some canines.
• Activation: Achieved by pulling the free end of the spring toward the intended direction of tooth movement.

5. Coffin Spring

• Construction: Made from 1.2 mm wire.
• Design: Consists of a U or omega-shaped wire placed in the midpalatal region, with a retentive arm incorporated into the base plates.
• Retention: Retained by Adams clasps on molars.
• Indication: Used for slow dentoalveolar arch expansion in patients with upper arch constriction or in cases of unilateral crossbite.

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.

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.