First step in cavity preparation

# Which of the following describes the 1st step in cavity preparation according to G.V. Black?
A Retention form
B. Outline form
C. Resistance form
D. Convenience form

The correct answer is B. Outline form.

The 1st step in cavity preparation according
to G V Black is to establish the outline form.
The initial extension or the outline form of
the tooth preparation should be visualized
preoperatively by estimating the extent of
the defect, the preparation form requirements of the amalgam, and the need
for the adequate access to place amalgam
into the tooth.

G.V Blacks various steps of cavity preparation are:
- Establish outline form
- Obtain retention form
- Obtain resistance form
- Obtain convenience form

Least distance between tooth and implant:

# The implant should be positioned at least ____ away from natural tooth:
a) 0.5 mm
b) 1.0 mm
c) 1.5 mm
d) 2.0 mm

The correct answer is C. 1.5 mm.

When the implant is closer than 1.5 mm to an adjacent root of a tooth, the wedge-shaped vertical defect may become a horizontal defect, creating bone loss on the adjacent tooth root. 

Initial vertical bone loss around an implant during the first year of loading varies and ranges from 0.5 to more than 3 mm. this effect is utmost importance because the interseptal bone height in part determines the incidence of presence or absence of interdental papillae between the teeth or implants. As a result, an implant should be at least 1.5 mm from adjacent teeth whenever possible.

Natural tooth roots are often close than 1.5 mm to each other. Therefore the ideal mesiodistal implant size is usually less than the natural root dimension. Most often, the ideal implant diameters used to replace the average size anterior tooth correspond to a 4.2 mm implant for a central incisor and canine, and a 3 to 3.5 mm implant for a lateral incisor.

The two conditions that determine the ideal anterior tooth implant size in the mesiodistal dimension are:

• The ideal diameter most often corresponds to the width of the missing natural tooth, 2 mm below the CEJ.

• In addition, the implant diameter plus 1.5mm on each side should be equal to or less than the mesiodistal dimension between the two natural roots at the level of the crest of the residual ridge.

When implants are placed adjacent to each other, a minimum distance of 3 mm is suggested, especially when crestal bone is expected around the implants, to accommodate for eventual crestal bone loss and maintain interseptal bone levels.

The four conditions that determine the ideal implant size in the posterior maxilla are:

1. The implant dimension should correspond to the natural tooth (2 mm below the CEJ).

2. The implant should be at least 1.5 mm from the adjacent teeth.

3. The implant should be at least 3 mm from an adjacent implant.

4. The implant should be at least 4 mm in diameter.

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Denture cleaning powder

# Which of the following is a main ingredient of denture cleaning powder or tablets?
a) Hydrogen peroxides
b) Detergents
c) Sodium perborates
d) Alkaline compounds

The correct answer is C. Sodium Perborates

All the denture cleansing powder and tablets contain detergent, flavouring agent, alkaline compounds and sodium perborat e. The main component is sodium perborate. It decomposes in water to form a peroxide solution which inturn breaks down to liberate oxygen. It is this oxygen bubbles that remove the debris on the denture surfaces.

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Most common reason to repeat impression is:

# Most common reason to repeat impression is?
a) Improper positioning of tray
b) Too less or excess material
c) Voids that are irreparable
d) Improper mixing

The correct answer is A. Improper positioning of tray.

The most common reason to repeat an impression is improper positioning of the impression tray. If the tray position is improper, the flange of the impression which lies on the side of deviation will be excessively thick and the flange of the impression opposite to the deviation will be thin.

The other reasons are improper consistency, large voids, movement of the tray during setting and too little or too much impression material.

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