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