2-9. MOTOR DRIVEN ROTARY INSTRUMENTS USED FOR CAVITY PREPARATION
(1) Characteristics. In discussing the preparation of a cavity for restoration in a modern clinic, it is essential that we talk about the many different kinds of burs available to the dentist. Regardless of the procedure being done, the burs will probably be used in preparing the cavity for restoration. They are manufactured in different sizes and shapes suited to the various types and forms of the cavity preparation desired. You will be expected to know four different things about the burs that you are given: The shape (name) of the working end, the series number of the bur, the material of which it is made, and in which hand piece each type of bur may be used. Series numbers and bur shapes are associated with each other: A round bur is in the ten series, an inverted cone bur is in the thirty series, a straight crosscut fissure bur is in the five hundred series, and the tapered fissure bur is in the seven hundred series. Burs may be made of one of two materials: A stainless steel bur will have a smooth shank, and a tungsten carbide alloy, bur will have a ring, a set of parallel rings, or possibly a ring of X's around the shank. Tungsten carbide burs will stay sharp longer than stainless steel burs, and they may be used repeatedly without marked reduction in cutting efficiency. There are three different hand piece attachments for the burs. The slow-speed straight hand piece (SHP) uses a friction grip attachment and accepts a bur with a long shank. This means that the end of the bur that goes into the hand piece is smooth and is held in the hand piece by friction. The shank of the straight hand piece bur is not only longer but also larger than the other burs. The bur that goes into the slow-speed contra-angle hand piece (AHP) is almost as large around as the straight handpiece bur, but it is much shorter and has a notched end with a groove opposite the working end that fits into the latch attachment on the angle hand piece. The bur for all high-speed hand pieces (HSHP) is smaller and shorter than the other burs; it also has a friction grip attachment (that is, the end is smooth). The Midwest Quiet-Air hand piece accepts the friction grip bur, but the hand piece is designed with a chuck that must be tightened on the bur. Burs are an essential part of the setup for the dentist performing a restorative procedure. They are the rotary cutting instruments that replace many of the hand instruments used in a cavity preparation procedure. You will be required to know four identifying characteristics about dental burs.
(a) The first type is a description of the shape of the working end as illustrated in figure 2-2.
Figure 2-2. Bur shapes.
NOTE: The first letter of each bur type is underlined. These four letters, in order, spell RIST. This key word will help you learn the burs in increasing numerical sequence.
(b) The second identifier is the number:
- 10 series--(Round bur)
- 30 series--(Inverted cone bur)
- 500 series--(Straight crosscut fissure bur)
- 700 series--(Tapered fissure bur)
(c) The third is composition.
(d) The fourth is the hand piece attachment. Burs are attached to one of three hand pieces. To establish which hand piece a bur is used in, you may look at the end away from the working end, as illustrated in figure 2-3.
(e) Any of the independent factors describing burs may be combined when designing a bur. Obviously, the use and series numbers correspond with the name or shape of the bur. However, any shape bur may be made of either of the two materials, and it may be made to fit into any of the three types of hand pieces.
(2) Availability. Available stainless steel burs include the following for both AHP and SHP except as noted: round burs numbers 1/2, 2, 4, 6, and 8; inverted cone burs numbers 33 1/2, 35, 37, and 39 (39 is available for AHP only); straight crosscut fissure burs numbers 557, 558, 559, and 560 (560 is available for AHP only); and tapered crosscut fissure burs numbers 700, 701, 702. Angle hand piece steel burs numbers 4, 35, and 558 are available in either the standard or short-neck lengths. Tungsten carbide burs are available for the AHP in the same sizes except for numbers 1/2 and 560. An end-cutting tungsten carbide bur is available as number 901. The tungsten carbide burs function best at high-speed operations; they are harder than stainless steel burs. See figure 2-4. Available friction grip tungsten carbide burs include the following for high-speed angle hand pieces: round burs. Numbers 1/2, 2, 4, and 6; inverted cone burs numbers 33 1/2, 34, and 35; straight, crosscut fissure burs number 557 and 558; straight, plain fissure bur number 57; tapered, crosscut fissure burs number 699, 700, and 701; and tapered, plain fissure bur number 170L.
Figure 2-3. Bur hand pieces.
Figure 2-4. Friction-grip tungsten carbide bur.
b. Diamond Stones and Wheels Diamond stones and wheels (figure 2-5) are used to cut enamel and are manufactured in various sizes and shapes. These instruments create heat during use and require water or air-cooling if used for any length of time.
Figure 2-5. Diamond points.