What is a second-order bend in orthodontic wire?

# What is a second-order bend in orthodontic wire? 

A. Bend to position a tooth buccolingually 

B. Bend to provide angulation of a tooth in mesiodistal direction (tip) 

C. Bend to provide correct angulation of a tooth in labiolingual direction (torque) 

D. Bend to rotate a tooth 

The correct answer is B. Bend to provide angulation of a tooth in mesiodistal direction (tip) 

A second-order bend is placed to provide angula tion of a tooth in the mesiodistal direction, also called “tip.” A first-order bend is placed in an arch wire to position a tooth in the labiolingual direc tion (in-out bend) or to rotate a tooth as seen in the occlusal plane. A bend to provide angulation in the labiolingual direction is called a third-order bend (torquing bend). 

The membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called:

 # The membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called:

A. Inner enamel epithelium

B. Outer enamel epithelium

C. Membrana preformativa

D. Cell-free zone

The correct answer is C. Membrana preformativa.

The dental papilla is enclosed in the invaginated portion of the enamel organ. Before the inner enamel epithelium begins to produce enamel, the peripheral cells of the mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium. First, they assume a cuboidal form; later they assume a columnar form and acquire the specific potential to produce dentin. The dental papilla ultimately gives rise to dental pulp, once the dentin formation begins at the cuspal tip of the bell stage tooth germ. The basement membrane that separates the enamel organ and the dental papilla just prior to dentin formation is called the membrana preformativa.

Which of the following is true of cellular cementum?

 # Which of the following is true of cellular cementum?

A. Forms during root formation

B. Forms after eruption of the tooth

C. Seen at the coronal portion of the tooth

D. Formation is a slow process

The correct answer is B. Forms after eruption of the tooth. 

The cellular cementum is also known as secondary cementum as this is formed later than the AEFC (Acellular Extrinsic Fiber Cementum). The cellular cementum found in the apical third is mainly of two types—the cellular mixed fiber cementum which forms the bulk of secondary cementum and occupies the apical interradicular regions and the CIFC (Cellular intrinsic fiber cementum) which is present in the middle and apical third. These types are mainly involved in the adaptation and repair of cementum. Since the secondary cementum is formed rapidly the incremental lines are placed further apart than in AEFC (Acellular Extrinsic Fiber Cementum).

Reference: Orban's Oral Histology and  Embryology

Which of the following is indicative of ageing?

 # Which of the following is indicative of ageing?

A. Expression of dead tracts

B. Widening of predentin

C. Increase in tubular diameter

D. Increase in peritubular dentin

The correct answer is A. Expression of dead tracts. 

It is rather difficult to separate age and functional changes in dentin. Dentin is laid down throughout life. This dentin is termed secondary dentin. If dentin forms as a result of pathological process, like caries, it is termed tertiary dentin. Tertiary dentin shows irregularity in size, shape, number and arrangement of dentinal tubules. Dentinal tubules degenerate due to injury resulting in the formation of dead tracts. Mineralization of dentinal tubules results in the formation of sclerotic dentin. This makes the tooth to appear transparent in these areas.

Reference: Orban's Oral Histology and Embryology