DENTAL MICROSURGERY TERMINOLOGY

Magnification

The use of a surgical operating microscope unlike loupes offers a number of different magnification options within the same instrument. That used by the author has six steps of magnification (X 2.5, X 4.0, X6.7, X10, X 16, and X 24).

Under lowest power (X 2.5) almost the whole mouth is observable. This is useful for general screening of the dentition.

Medium powers (X 4.0 and X 6.7) are beneficial for initial conservative and restorative procedures, together with general surgery and periodontics.

Under higher magnification (X 10 and X 16) fine details are easily observed permitting precise instrument placement. This is useful for finishing the margins of crown preparations, inspecting impressions, examining root apices and finalising cavity outlines.

Due to the limited depth of field, in the author's opinion, the highest magnification (X 24) is not easy to operate under. Visibility of the surgical site is limited with only a fraction maintained in focus. This requires constant adjustment of the fine focus and microscope body. The highest magnification is used predominantly for assessment, and in comparison to the other magnifications rarely utilised.

Working Distance [WD]

The working distance is determined by the linear measurement of the objective front lens to the surgical site. For dental microscopes this distance is normally 150-250mm.

The shorter the focal length of lens, the closer the lens to the operating field. The immediacy of shorter focal length lenses to the operating site; limits the working distance and can be awkward. The proximity of the lens can restrict the latitude of movement of hand instruments and equipment such as turbines.

A longer working distance enables the operator to work comfortably under its magnification. In order to accomodate a longer focal length lens, and therefore the benefits of an increased working distance, it may be necesarry to use an inclinable head.

Depth of Field [DOF]

The Depth of field is the range that the operator can visually distinguish an image both in front of and behind the main object. Objects found within the depth of field will appear sharp while those found in front and behind the depth of field will appear blurry. It is obviously beneficial for the clinician to keep the maximum amount of the image in sharp focus.

Depth of field is expressed in terms of the nearest and furthest confines within which the object remains focused (e.g. from 20 to 23cm). It may also be recorded in terms of the difference between these limits (e.g. a 3-cm depth of field). DOF is not influenced by the focal length of the lens.

Unfortunately with increasing the magnification the depth of field reduces.