Serial Extraction

# In the mandibular arch where the canines often erupt before the premolars, ________ technique of serial extraction is followed.
A. Dewel’s
B. Modified Dewel’s
C. Tweed’s
D. Nance’s

The correct answer is: B. Modified Dewel's.

Tweed defines it as “the planned and sequential removal of the primary and permanent teeth to intercept and reduce dental crowding problems”.

The term “serial extraction” was coined by Kjellgren in 1929 and popularized by Nance (1940) who has been called the ‘father of serial extraction'.

Indications of serial extraction:

Indications

1. Class I malocclusions with anterior crowding space discrepancy of 10 mm more.

2. Lingual eruption of lateral incisors.

3. Midline shift of mandibular incisors due to displaced lateral incisors.

4. Premature loss of deciduous canine.

5. Abnormal canine root resorption.

6. Severe proclination of mandibular and maxillary interiors with associated crowding.

7. Ectopic eruption.

8. Ankylosis.

Contraindications

1. Mild to moderate crowding (about 8 mm or less)

2. Congenital absence of teeth providing space

3. Class II div 2 and Class III malocclusion

4. Spaced dentition

5. Extensive caries involving permanent first molars which cannot be conserved.

6. Open bite and deep bite

7. Cleft up and palate cases, etc

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Undetectable death of embryo

# Undetectable death of embryo occurs during first few days of conception when exposure range is:
A. 0.1 – 0.3 Gy
B. 0.4 – 0.7 Gy
C. 0.8 - 1 Gy
D. 1 – 3 Gy

The correct answer is: D. 1-3 Gy.

Exposures of 1 to 3 Gy during the first few days after conception are thought to cause undetectable death of the embryo because many of these embryos fail to implant in the uterine wall. The period of organogenesis, when the major organ systems form, is 3 to 8 weeks after conception. The most common abnormalities among the Japanese children exposed early in gestation were reduced growth that persisted through life and reduced head circumference (microcephaly), often associated with mental retardation.

Ref: Oral Radiology, Principles and Interpretation, 7th E Page No. 25

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The plasma coating of a Titanium Dental implant (TPS) is done to:

# The plasma coating of a Titanium Dental implant (TPS) is done to:
A. To increase its acceptance in bone
B. To make the Implant Biocompatible
C. To avoid contamination of the implant
D. To improve implant anchorage power in bone

The correct answer is: D. To improve implant anchorage power in bone.

Applying calcium phosphate (CaP) coating on implants improves the osteoconductive
(osseointegration) properties. Different methods have been developed to coat metal
implants with CaP layer such as plasma spraying, biomimetic and electrophoretic
deposition. By means of plasma polymerization, positively charged, nanometric thin coating
can be applied to implant surfaces. Titanium plasma sprayed (TPS) surface results in
increased surface area and it has been proposed that TPS improves implant anchorage
power in bone (Osseo integration).

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The first bone formed in response to orthodontic loading is

# The first bone formed in response to orthodontic loading is:
a) Bundle bone
b) Composite bone
c) Lamellar bone
d) Woven bone

The correct answer is D. Woven bone.

When a force is applied, there is stretching of the periodontal fibres on the tension side with raised vascualarity. This raised vascularity causes mobilization of fibroblasts and osteoblasts into that area, which form osteoid. This lightly calcified bone in due course of time matures to form woven bone.

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