A dental bur is a small, rotating instrument used by dentists to perform precise modifications on hard tissues like tooth enamel, dentin, and bone. The bur is an indispensable tool that attaches to a motorized handpiece. This instrument allows for the high level of accuracy needed in modern dental procedures, ensuring both effectiveness and patient comfort.
The Anatomy of a Dental Bur
A dental bur is composed of three distinct parts: the shank, the neck, and the head, each serving a specific mechanical function. The shank is the longest portion, acting as the shaft that is inserted and held securely within the dental handpiece. The specific design of the shank determines the type of handpiece it can fit into and the speed at which it is intended to operate.
For example, a Friction Grip (FG) shank is used with a high-speed handpiece for bulk material removal. In contrast, a Right-Angle (RA) or Latch-type shank is designed for low-speed contra-angle handpieces, which are used for slower, more controlled tasks. The neck is the narrow section connecting the shank to the head, designed to be slim enough to maximize the dentist’s visibility during a procedure.
The head is the working end of the bur, containing the blades or abrasive material that performs the actual cutting or grinding action. The specific use of the bur is determined by the shape, size, and angle of these cutting blades or the coarseness of the abrasive material. The head’s design is the primary factor that dictates the instrument’s cutting characteristics and overall performance on tooth structure.
Materials and Shapes Used in Bur Design
The most common materials used are tungsten carbide, diamond grit, and stainless steel, each selected for its unique properties. Tungsten carbide burs are known for their exceptional hardness, being approximately three times stiffer than standard steel.
Carbide burs feature sharp-edged blades, or flutes, which are designed to cut and chip away tooth structure, leaving a smoother finish than abrasive tools. They are primarily used when a controlled, efficient cutting action is needed, such as excising old filling material or preparing the walls of a cavity. The sharp edges of these burs allow them to quickly cut through enamel, dentin, and even some metal restorations.
Diamond burs are manufactured by bonding fine particles of industrial-grade diamond onto a stainless steel substrate. Since diamond is the hardest known material, these burs function by abrasion, effectively grinding away hard tissues like tooth enamel and ceramics. They are often categorized by grit size, with coarser versions used for aggressive material reduction and finer grits used for smoothing and polishing.
The head’s shape is just as important as the material, as it determines the specific task the bur is best suited for. For initial entry into a tooth or for removing decay, a round bur is commonly selected due to its versatile ball-like shape. The inverted cone bur is designed with a flat end and sides that taper inward, which is useful for creating undercuts or retention grooves in a prepared cavity. Fissure burs, which can be straight or tapered, are used to shape the lateral walls of a cavity preparation, ensuring they are parallel or slightly convergent for the final restoration.
Common Uses of Burs in Modern Dentistry
Dental burs are routinely used for the removal of decayed tissue and the precise preparation of a tooth for a filling. For this common procedure, a round or pear-shaped carbide bur is used to gain initial access to the carious lesion and remove the infected dentin with minimal trauma to the healthy tooth structure.
Burs are utilized extensively in the process of shaping restorations and preparing the underlying tooth for crowns and bridges. Diamond burs are frequently employed to reduce the overall size of the tooth, creating the necessary space for a prosthetic crown to fit precisely. This preparation involves contouring the tooth structure to specific dimensions, ensuring the crown’s margins are perfectly adapted to the tooth.
Burs are also instrumental in the final stages of many procedures. After a filling has been placed, specialized finishing burs with a high number of shallow blades are used to smooth the rough edges of the composite or amalgam material. This ensures the restoration blends seamlessly with the natural tooth contour and minimizes areas where plaque could accumulate.