The coefficient of thermal expansion of which of the following dental materials is the highest?

 # The coefficient of thermal expansion of which of the following dental materials is the highest?

A. Amalgam

B. Gold inlay

C. Silicate cement

D. Acrylic resins

The correct answer is D. Acrylic resins.

Linear coefficient of thermal expansion (α = coefficient of linear expansion (°C−1))

Tooth 9 - 11

Silicate 8

Unfilled acrylate 81

Composites 28 - 45

Amalgam 25

Direct gold 18

Aluminous porcelain 6 - 7

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The glass ionomer cement is not recommended for:

 # The glass ionomer cement is not recommended for:

A. Class V restoration

B. Class III restoration

C. Class IV restoration

D. None of the above

The correct answer is C. Class IV restoration 

INDICATIONS OF GIC

- The restoration of caries lesions on the roots of patients with active caries is the primary indication for the use of a glass ionomer as a restorative material.

- Because of their limited strength and wear resistance, glass ionomers are indicated generally for the restoration of low-stress areas (not for typical Class I, II or IV restorations), where caries activity potential is of significant concern.

- In addition to being indicated for root-surface caries lesions in Class V locations, slot-like preparations in Class II or III cervical locations (not involving the proximal contact) may be restored with glass ionomers, if access permits.

- Cervical defects of idiopathic erosion or abrasion origin (or any combination) also may be indications for restoration with glass ionomers, if esthetic demands are not critical.

 Reference: Sturdevant’s Art and Science of Operative Dentistry Second South Asia Edition 2019, Page No: 540

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Antibiotic prophylaxis is not recommended in:

 # Antibiotic prophylaxis is not recommended in:

a) Making of impressions 

b) Dental extraction

c) Replantation of tooth 

d) Gingivectomy

The correct answer is A. Making of impressions.

All dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa need antibiotic prophylaxis to prevent Bacterial endocarditis. Procedures such as anesthetic injections through non infected areas, taking dental radiographs, placement of removable prosthodontic/orthodontic appliances, adjustment of ortho appliances, placement of brackets, shedding of deciduous teeth, bleeding from trauma to lips or oral mucosa do not need antibiotic prophylaxis.

Cardiac conditions requiring prophylaxis include prosthetic cardiac valve, previous infective endocarditis, congenital heart disease, cardiac transplantation recipients who develop cardiac valvulopathy. They may be given oral Amoxicillin 2 gm/ Azithromycin SOOmg/ Cephalexin 2gm/ Clindamycin 600mg (OR) Ampicillin 2 gm IM or IV/ Cefazolin or Ceftriaxone 1 gm IM or IV/ Clindamycin phosphate 600mg IM or IV.

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# Serial extraction is contraindicated in:

 # Serial extraction is contraindicated in:

A. Open bite

B. Deep bite

C. Class II and III malocclusion with skeletal abnormalities

D. All of the above

The correct answer is D. All of the above.

Contraindications to Serial Extraction are:

1. Mild to moderate crowding—tooth size arch length deficiency < 5 mm per quadrant.

2. Class II division 2 and Class III malocclusions.

3. Spaced dentition.

4. Congenital absence—anodontia/oligodontia.

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

6. Open bite and deep bite, which should be corrected first.

Reference: Textbook of Orthodontics, 2nd Edition, Gurkeerat Singh, Page No: 569

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Pericision is carried out as an adjunct retention for:

 # Pericision is carried out as an adjunct retention for:

A. Midline diastema

B. Rotation

C. Proclination

D. Extrusion

The correct answer is B. Rotation.

It is generally assumed that a stable position of the teeth in the dental arch after orthodontic tooth

movement can only be established when the connective tissues of the gingiva have been allowed to adapt to the newly created situation. Supracrestal gingival fibers of an orthodontically moved tooth get

stretched and undergo readaptation very slowly. The pull of these fibers is a major factor in relapse. If these supracrestal fibers are sectioned and allowed to heal while the teeth are held in the proper position, relapse caused by gingival elastic fibers is greatly reduced.

Reattachment of these fibers at a new relaxed position on the root surface stabilizes the tooth in its new

position. This procedure is effective in controlling relapse of derotated teeth.

Reference: Textbook of Orthodontics, 2nd Edition Gurkeerat Singh, Page 279

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Anterior crossbite should be corrected:

 # Anterior crossbite should be corrected:

A. During mixed dentition

B. After all permanent teeth have erupted

C. As soon as possible

D. Any time

The correct answer is C. As soon as possible.

Lingually positioned incisors limit lateral jaw movements and they or their mandibular counterparts sometimes suffer significant incisal abrasion, so early correction of the crossbite is indicated.

Early correction of dental cross bites in the mixed dentition is recommended because it eliminates functional shifts and wear on the erupted permanent teeth, and possibly dentoalveolar asymmetry. There are three basic approaches to the treatment of moderate posterior crossbites in children:

i) Equilibration to eliminate mandibular shift

ii) Expansion of a constricted maxillary arch, and

iii) Repositioning of individual teeth to deal with intra-arch asymmetries.

Reference: Contemporary Orthodontics, Proffit, 4th Edition Page no 248

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# If the permanent canines are lost prematurely, the permanent incisors may drift:

 # If the permanent canines are lost prematurely, the permanent incisors may drift:

A. Labially

B. Distally

C. Medially

D. Lingually

The correct answer is B. Distally.

When a primary first molar or canine is lost prematurely, there is also a tendency for the space to close. This occurs primarily by distal drift of incisors, not by mesial drift of posterior teeth. The impetus for distal drift appears to have two sources: force from active contraction of transseptal fibers in the gingiva, and pressures from the lips and cheeks. 

Reference: Contemporary Orthodontics, 4th Edition, Profitt, Page no. 140

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