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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Relieving mid-palatine area in complete dentures

# The purpose of relieving mid-palatine area in complete dentures is to prevent:
a) Pressure on palate
b) Midline fractures in dentures
c) Incorrect centric relation
d) Resorption of bone

The correct answer is A. Pressure on palate.

Mid palatine raphe is the median suture area covered by a thin submucousa and the mucosa layer is practically in contact with the underlying bone. For the reason the soft tissue covering the median palatal sutures is non resilient and may need to be relived to avoid trauma from the denture base.

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Maxillary canine missing FPD

# In a case where maxillary canine is missing and we have to make a tooth-supported FPD, the abutment will be:
a) Central incisor, Lateral incisor and 1st premolar
b) Lateral incisor, 1st premolar 2nd premolar
c) Lateral incisor and 1st premolar
d) It depends upon periodontal status of remaining teeth

The correct answer is A. Central incisor, lateral incisor and first premolar.

Missing maxillary canine or mandibular canine (one tooth) come under complex fixed partial dentures and central incisor, lateral incisor and 1'1 premolar acts as abutments, whereas for other teeth(incisors, premolars and molars) the adjacent teeth in relation to the missing tooth are enough

to act as abutments.

FPD replacing canines can be difficult because the canine often lies outside the inner abutment axis.

An edentulous space created by the loss of a canine and any two contiguous teeth is best restored with a RPD.

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The posterior tooth that gives a better support is:

# The posterior tooth that gives a better support is:
a) With convergent roots
b) Divergent roots
c) Conical roots
d) Curved roots

The correct answer is B. Divergent roots.

- Roots with greater labiolingual width than mesiodistal width are preferable to roots that are round in cross section.

• Long, irregularly shaped and divergent roots offer great support.

• Short, conical and blunted roots offer poor support.

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Functional cusp Bevel

# The functional cusps are bevelled in the preparation of posterior cast crowns:
a) To reduce the stress at the line angles
b) To prevent the fracture of the tooth structure
c) For the structural durability of the restoration
d) To help in the retention

Bevelling of the functional cusp (lingual inclines of maxillary lingual cusps and the buccal inclines of mandibular buccal cusps) is an integral part in obtaining the structural durability of the restoration.

- Lack of functional cusp bevel can cause:

• A thin area or perforation on the casting.

• Overcontouring and poor occlusion of the restoration.

• Loss of tooth structure and retention.

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