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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