accordingly , with reference to fig1 - 3 , a self - limiting depth gauge spherical dental burr 30 comprises a shank 32 which is adapted to be held at one end 34 by the bit of a drilling machine of conventional construction . a spherical cutting element 36 of diamond , carbide or other useful drilling material is secured to the shank at its opposite end 38 by any conventional means . a shield 40 , acting as a self - limiting depth gauge , is integrally secured to the shank , and directly behind the burr . shield 40 is essentially flat , having a smooth surface 42 which is designed to contact the enamel without harming it or , if the enamel is missing , onto the remaining tooth surface . shield 40 is terminated at its periphery with a rounded or curved surface to avoid any sharp corner . spherical cutting element 36 has a specified diameter 46 ( e . g ., see fig2 and 3 ) which determines its cutting depth , as enforced by shield 40 . the burr may be manufactured with a variety of diameters , such as depicted in fig4 - 6 , the most utilized being those of 0 . 5 mm , 1 . 0 mm and 1 . 2 mm to provide cutting depths of those dimensions . accordingly , burrs with differently sized spherical cutting elements are used to establish a predetermined maximum depth for creating a depression . this avoids any undesirable grinding into the tooth and possibly completely through the enamel or further , if desired , into the dentin . alternately stated , the depth of tooth removal is restricted , when the tooth is prepared for placement of a crown , usually over the dentin , or of a veneer over whatever tooth surface that may exist . thus , tooth reduction is made more predictable and prevents excessive or inadequate removal of the tooth structure , and avoids guess - work . in practice , the dentist marks dots on the tooth where work is to be performed . then , the burr with its integral shield is applied to form precisely the penetrations . the size of the burr is tailored to the specific procedure desired and , therefore , a host of different diameter burrs with their integral , self - contained , depth - limiting shields are made available . as examples , for preparation for crown placements , the burr typically ranges from 1 mm to 1 . 5 mm in diameter and for veneer work , the burr typically ranges from 0 . 3 to 0 . 6 mm in diameter . fig7 - 16 illustrate a porcelain veneer technique while fig1 - 20 illustrate a technique for preparing a porcelain crown , which techniques are both utilized for anterior ( front ) teeth . referring to fig7 - 16 , in fig7 , penetrations 48 of 0 . 5 mm depths are made into an anterior tooth 50 by a drill formed with a burr 30 a ( also see fig4 ), with fig8 depicting a multiple of such hole depth drillings 48 . a cylindrical , rounded end diamond burr 52 ( fig9 ) is used to reduce the remaining tooth structure , as existing between penetrations 48 , to 0 . 5 mm by using these penetrations as reference markers . fig1 illustrates the thus prepared tooth showing what was removed by burr 52 , where the removed tooth material is denoted therein by dashed line 54 . fig1 - 16 illustrate an incisal view of teeth being prepared for the placement of a porcelain veneer thereon . here , in tooth 50 , a spherical burr 30 a forms penetrations 56 ( fig1 and 12 ), which form reference points for further tooth removal as depicted in fig1 by a burr 58 which is moved in the direction of arrow - headed line 60 . further preparation proceeds ( fig1 - 16 ), utilizing a cylindrically shaped burr 62 having a pointed end , which procedure terminates ( fig1 ) in a tooth having removed material as denoted therein by dashed line 64 . in fig1 - 15 , the dentin is identified by indicium 65 . referring to fig1 - 20 which illustrate a technique for preparing a porcelain crown on tooth 66 , a spherical burr 30 forms penetrations 68 and 70 ( fig1 ), which form reference points for further tooth removal as depicted in fig1 by burrs 72 and 74 , leaving a tooth showing removed material as denoted therein by dashed lines 76 and 78 . reference is now made to fig2 - 23 which illustrate a veneer tooth preparation on a premolar or posterior ( back tooth ) of a typical half millimeter depth . in fig2 , a burr 30 a , such as that depicted in fig4 , forms penetrations 80 in a tooth 82 which , in the same manner as previously described , form reference points for further removal of tooth material by a cylindrical , rounded end diamond burr 84 , thus leaving a product having removed material as denoted by dashed line 86 . in fig2 - 26 which illustrate a porcelain crown tooth preparation on a premolar for reducing the biting surface by 1 . 2 mm and the remainder of the tooth by 1 . 0 mm , burrs 30 c and 30 b , respectively , such as that depicted in fig6 and 5 , form penetrations 88 and 90 in a tooth 92 . cylindrical , rounded end diamond burrs 92 and 94 respectively reduce the remaining tooth portions between the precisely cut holes to the tooth , as shown in fig2 , with reduced surfaces as referred to by dashed line 96 . although the invention has been described with respect to particular embodiments thereof , it should be realized that various changes and modifications may be made therein without departing from the spirit and scope of the invention .