Saturday, October 15, 2011

CHAPTER 5 INSTRUMENTATION/ EQUIPMENT


LIGHT-CURING REQUIREMENTS
< 2 mm thickness of composite resin ( light to medium shades); » 1 mm for dark shades
Wavelength: 450-490 nm
Intensity of power outage: ³ 280 mw/cm2
Exposure time = 60 sec.
Light curing tip < 6 mm from composite resin
800 mw/cm2 @ 80 sec. ineffective @ 3mm depth

Bur dimensions

bur
330
¼
½
557
169
diameter
.8 mm
.5 mm
.6 mm
1 mm
.9 mm

Bur Rake angles
     Negative rake angle = cutting burs
            Positive rake angle = finishing burs-when rake face is behind the axis line
            Concentricity: direct measurement of symmetry of bur head itself; a static measurement not directly related to function
            Runout: dynamic test measuring accuracy with which all blade tips pass through a single point when rotated; clinically significant because determines minimum diameter hole drilled

Matrix bands
Thickness
     Metal
0.0010" = 25 microns
0.0015" = 38 microns
     Mylar
0.0020" = 50 microns

Characteristics
Reproduce and/or establish contour
Proper adaptation to gingival cavosurface margin
Easy to apply and remove
Must remain rigid during condensation


Parts of a hand instrument
blade (or nib-part corresponding to the blade on non-cutting instruments)
shank
shaft (handle)

Black's formula
instrument balance is established by keeping the blade ( or nib) within 2 mm of the long axis of the handle
line
Black's instrument numbering formula  (Example: 10-7-14 enamel hatchet)
     1st number -     blade width in 1/10 mm (10 = 1 mm blade width)
     2nd number - blade length in mm (7 = 7 mm long blade)
     3rd (last) number -  blade angle, or angle the blade makes with the shaft of the handle using a Celsius
compass of 100 degrees (thus, a 90° right angle is expressed as 25° Celsius)
            Some instruments, such as gingival margin trimmers, are constructed with a cutting edge at an angle
other than a right angle: in these cases, a fourth number (in degrees centigrade) is placed in the
formula which indicates the degree of angle of the cutting edge to the long axis of the handle. The
fourth number is placed between the first and second numbers, and it specifies the primary
cutting edge angle or angle formed by the cutting edge and the handle.  Example: 13-80-8-14
gingival margin trimmer 1.3 mm wide, 8 mm long, 14° blade angle, with a primary cutting edge
80° to the handle.
Ref:  Baum’s Textbook of Operative Dentistry, 1981, W.B.Saunders Co, pp. 51-53

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