for a given load below which the tool will not cut. Greater the load, lower is the minimum rotation speed. MODIFICATIONS IN BUR DESIGNS 1. Smaller bur heads are being used as they are more effective. 2. Increased effectiveness of carbide burs at high speeds. LATEST TRENDS IN BUD DESIGNS 1. REDUCED USE OF CROSS CUT BURS: Crosscuts are needed on fissure burs to obtain adequate cutting effectiveness at low speeds, but at high speeds they are not needed. As cross cut burs used at high speeds tend to produce unduly rough surfaces. 2. EXTENDED HEADS ON FISSURE BURS: Extended head lengths for carbide fissure burs help in reaching deeper regions. Carbide burs can be used at high but only with an extended head. (5000-6000 rpm) 3. ROUNDING OF SHARP TIP ANGLES: Bur heads with rounded corners result in lower stresses in restored teeth, enhance the strength of the tooth by preserving dentine and facilitate in adaptation of restorative materials. ADDITIONAL FEATURES IN HEAD DESIGN These features include: 1. Head Length: It is determined according to area of use. 2. Taper Angle: Like the head length it is determined according to function. 3. Neck Diameter: Too small a diameter will result in a weak instrument and too large a diameter will cause visibility problems. # as length or diameter of head of a bur increases, moment arm exerted by lateral forces also increases, and the neck diameter needs to be larger. 4. Spiral Angle: For efficient high speed cutting the spiral angles are reduced. 5. Crosscutting: In order to increase cutting pressure from rotation of the blade and perpendicular pressure holding the blade edge against the tooth,
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