The intercanine width in the mandible is completed by:

 # The intercanine width in the mandible is completed by:

A. 4 to 5 years

B. 7 to 8 years

C. 9 to 10 years

D. 10 to 12 years

The correct answer is C. 9 to 10 years.

The intercanine width in the mandible is typically completed by the time a child is 9 to 10 years old, which is when the mandibular canine teeth have fully erupted and have reached their final position in the arch. This timing can vary slightly between individuals, and it is important to consider other factors such as dental crowding or spacing when evaluating intercanine width.

The reference for this explanation is: Naini FB. Biological basis of orthodontics. John Wiley & Sons; 2015. Chapter 5: Growth and development of the mandible.

The main growth site for mandible is:

 # The main growth site for mandible is:

A. Condyle 

B. Angle

C. Symphysis 

D. Body

The correct answer is A. Condyle.

The mandibular condyle is the main growth site for the mandible. The condyle is a specialized growth center that contributes to both the length and width of the mandible. The condyle grows through endochondral bone formation, which involves the transformation of cartilage into bone tissue. The growth of the condyle is regulated by various factors such as growth hormones, growth factors, and mechanical stimuli.

While the other parts of the mandible also contribute to its overall growth and development, the condyle is the primary growth site for the mandible.

Therefore, the correct answer is A, the condyle.

Reference: Proffit, W. R., Fields, H. W. Jr, & Sarver, D. M. (2013). Contemporary Orthodontics. (5th ed.). St. Louis, MO: Mosby/Elsevier. Chapter 4: Growth of the Face and the Jaws.

Meckel's cartilage is essential for mandibular growth because:

 # Meckel's cartilage is essential for mandibular growth because:

A. It is converted into bone 

B. It is a template for bone deposition

C. It is a skeletal unit

D. It is a secondary cartilage

The correct answer is B. It is a template for bone deposition.

Meckel's cartilage is a temporary cartilage structure that forms the basis of the mandibular skeleton in the early embryo. During development, the cartilage acts as a template for the formation of bone, and the mandible grows around it. Meckel's cartilage eventually undergoes resorption, and the mature mandible is formed through a combination of endochondral and intramembranous ossification.

Therefore, the correct answer is B, that Meckel's cartilage is essential for mandibular growth because it serves as a template for bone deposition.

Reference: Proffit, W. R., Fields, H. W. Jr, & Sarver, D. M. (2013). Contemporary Orthodontics. (5th ed.). St. Louis, MO: Mosby/Elsevier. Chapter 4: Growth of the Face and the Jaws.

The mandibular condyle grows by:

 # The mandibular condyle grows by:

A. Endochondral bone formation

B. Subperiosteal surface addition

C. Interstitial growth

D. Sutural bone growth

The correct answer is A. Endochondral bone formation.

The mandibular condyle is a part of the temporomandibular joint (TMJ) and it is a specialized growth center. The growth of the mandibular condyle occurs through endochondral bone formation, which involves the transformation of cartilage into bone tissue. This process is regulated by various factors such as growth hormones, growth factors, and mechanical stimuli. The endochondral bone formation process is essential for the development and growth of many bones in the body, including the long bones of the limbs and the mandible.

Reference: Proffit, W. R., Fields, H. W. Jr, & Sarver, D. M. (2013). Contemporary Orthodontics. (5th ed.). St. Louis, MO: Mosby/Elsevier. Chapter 4: Growth of the Face and the Jaws.

Center of resistance of maxilla is at:

 # Center of resistance of maxilla is at:

A. Point A

B. Palatal suture

C. Above the roots of premolar

D. Maxillary tuberosity

The correct answer is C. Above the roots of  premolar.

In theory, the movement of the maxilla can be controlled in the same way as a single tooth is controlled: by managing forces and moments relative to the center of resistance of the jaw. In practice, it is difficult to analyze exactly where the center of resistance and center of rotation of the maxilla might be, but they are above the teeth and most likely above the premolar teeth. Directing the line of force closer to the center of resistance is another major reason for including an upward direction of pull for most children who have headgear force to the maxilla.

Reference: Contemporary Orthodontics, Proffit

Age of closure of sphenooccipital synchondrosis is:

 # Age of closure of sphenooccipital synchondrosis is:

a) 6 years 

b) 12 years

c) 18 years 

d) 25 years

The correct answer is C. 18 years.

The spheno-occipital synchondrosis (also known as the basiocciput or basicranial synchondrosis) is the synchondrosis between the basisphenoid and basiocciput bones, which together when joined form the clivus. When fused, the synchondrosis is often called the spheno-occipital suture - this is a misnomer - as anatomically it is not a suture.

Fusion of the spheno-occipital synchondrosis initiates in girls at 12-13 years, and in boys at 14-15 years and is complete by 17-18 years. Fusion begins superiorly and progresses inferiorly, and also starts at the inner surface of the skull base proceeding towards the ectocranial surface.

Purpose of the post treatment retention of an orthodontic case is:

 # Purpose of the post treatment retention of an orthodontic case is:

A. To allow bony changes

B. To prevent tongue thrusting

C. To encourage the space closure

D. To let the patient get used to the new functional position of the teeth

The correct answer is D. To let the patient get used to the new functional position of the teeth

The purpose of post-treatment retention of an orthodontic case is to let the patient get used to the new functional position of the teeth. After completing orthodontic treatment, the teeth are in a new position, and the surrounding bone and soft tissues need time to adapt to this new position. During the retention period, the teeth are held in place while the surrounding structures adjust to the new position of the teeth. This helps to ensure the long-term stability of the treatment results. The retention period also allows the patient to become accustomed to the new position of their teeth and develop new habits such as proper oral hygiene practices and speech patterns.