Burs

Experts weigh in: Which bur is right for your dental practice?

From general practitioners to endodontists and prosthodontists, clinicians rely on burs – or rotary instruments – for a range of applications.  “Burs have been a staple product for years within the dental industry,” says Michael Vranesevic, MBA, global product manager, Rotary and Private Label Business Unit, Coltene. Over the years the industry has seen technological improvements, such as the creation of one-piece carbide burs, eliminating the brazed joint of two-piece burs, he points out. More recently, new delivery methods have been developed, such as sterile packaged products, he adds.

“The combination of high-quality natural diamond and the diamond attachment process remains key,” says Dr. Jason Goodchild, director of clinical affairs, Premier Dental (who formerly taught at Creighton University and currently practices in Philadelphia part-time). “Manufactured or synthetic diamond quality has improved slightly, however the attachment process, which primarily is some form of electroplating, has not changed. The alternative to plated diamond is a braze technique, and the original brazed dental bur has undergone continuous quality improvements.”

Bur selection often is determined by the material being worked on, as well as the procedure. Tungsten carbide burs, for instance, are generally used for caries removal, rapid reduction of PFM (porcelain fused metals) materials and contouring/finishing prior to the use of polishers. Diamond burs are useful for such restorations as veneering, crown preparations, bridges and contact point adjustments. Zirconia burs can be used to create an access through a zirconia crown. Shape, too, factors into the choice of burs: Typically, round-shaped rotary burs are used to create an access, while safe-end burs are used to flatten and flare the access.

Efficiency in Group Practice asked the experts to weigh in.

Efficiency in Group Practice: What are the pros and cons of different types of burs?

Dr. Jason Goodchild: The two main cutting surfaces of burs are tungsten carbide and diamond. Stainless steel is typically used for the shank of modern burs because tungsten carbide is three times as hard as steel, making it a more useful cutting tool for tooth, bone and dental restorations. Both tungsten carbide and diamond burs come in numerous shapes and sizes. Rotary tooth preparation for crowns and bridges with quality diamond burs is often faster and more precise than preparations using carbides. One paper states “The enormous advantage of using diamond burs for grinding human teeth was found by Westland in 1980. He discovered that under the same circumstances, the specific grinding energy is three times lower with diamond burs than with carbide burs. Moreover, an increase in loading force did not change the outcome.” (Cohen BD, Bowley JF, Sheridan PJ.  An evaluation of operator preference of diamond burs in coronal tooth preparation.  Compend Contin Educ Dent 1997;18(2):160-4.

Michael Vranesevic: Carbide, diamond and zirconia burs each offer benefits, depending on the application. It is important to understand the method by which each type of bur functions in order to achieve the desired outcome (i.e. caries preparation, crown removal, crown preparation, etc.). Carbide burs act in a cutting/chipping manner. Diamond and zirconia burs act in an abrasive wearing/grinding manner. Both of these mechanisms for reducing tooth structure – cutting/chipping and abrasive wearing/grinding – are beneficial when applied appropriately. For instance, metal cutting carbide burs with aggressive profile characteristics work well for rapidly cutting amalgam, metal, enamel and dentin. Both carbide and diamond burs work well on natural tooth structure (e.g., enamel and dentin), while zirconia burs are best utilized on a zirconia-based surface (e.g., a zirconia crown).

Efficiency in Group Practice: What applications are different shaped burs used for?

Goodchild: Form follows function in rotary tooth preparation. A football-shaped diamond is ideal for shaping the lingual aspect on anterior teeth, and the occlusal aspect on posterior teeth. It is important to remember that many shapes can be used to achieve the same restorative outcomes. It often comes down to what the clinician learned to use in school, or what they have become comfortable with in their clinical practice. For crowns and bridges, often the type of restorative material helps to dictate the marginal finish design, as well as the appropriate diamond bur tip shape and diameter to achieve that design. In addition, understanding the dimensions of any diamond bur (tip dimension, major diameter and cutting length) used for crown and bridge preparation enables the dentist to gauge the proper occlusal reduction, based on the manufacturer guidelines. There are calibrated depth guide burs, and some clinicians like the training wheels approach they provide. However, they can add an extra step to the procedure and prolong chairtime. The primary advantage of calibrated reduction burs – not only for the occlusal, but for the facial of anterior teeth – is the ability to achieve a consistent balance between creating enough reduction for the intended restorative material and preserving of natural tooth structure.

Vranesevic: Burs can be used in various procedures. Following are some of the more commonly used burs, as well as a few unique burs with potential applications. Of course, depending on the procedure at hand, the manner of application and/or burs used may differ based on the dental professional’s assessment.

Carbides

• Round (i.e. 2, 4, 6): Caries preparation, removal of old fillings, working on fillings, and endodontic access creation.
• Pear (i.e. 330): Caries preparation and removal of old materials, such as amalgam.
• Cross cut fissure (i.e. 557): Creating preparation with straight, parallel sides and flat floors, as well as gaining access to carious dentin.
• Round end fissure cross cut metal cutter (i.e. 1558G): Rapid reduction of metal, amalgam, enamel and dentin.
• Endodontic burs (219EZ and 152EZ): Safe-end (non-cutting tip) burs used for flattening and flaring access points during root canal preparation.

Diamonds

• Football: Crown preparations and working on the lingual and occlusal surfaces of the tooth, as well as adjustments.
• Round: Caries preparation, working on fillings and endodontic access creation.
• Round end taper (851 Safe-End variation): Safe-end (non-cutting tip) burs used for flattening and flaring access points during root canal preparation.
• Round end taper: Crown preparation, as well as crown cutting.
• Occlusal reduction: Reduction of the occlusal surface during restorative procedures.

Efficiency in Group Practice: Do all burs have crosscuts for greater efficiency?

Goodchild: Additional cuts across the blades – or crosscuts – can be added to increase cutting efficiency of tungsten carbide burs. These operative burs are either straight-bladed or crosscut. Straight-bladed burs cut smoothly, but are slower, especially with harder materials. Crosscut burs can cut faster due to the lack of debris build-up. In the case of diamond-coated burs, a smooth shape is created and a fine-, medium- or coarse-ground diamond coating is applied over it. (Little D.  Handpieces and burs: the cutting edge.  Available at:  https://www.dentalacademyofce.com/courses/1592/PDF/HandpieceandBurs.pdf.  Accessed February 12, 2018.)

Vranesevic: Not all carbide burs have crosscuts. The crosscut geometry is a feature of certain bur profiles, which can lend themselves to added cutting efficiency. That said, greater cutting efficiency is not always the goal. For example, in the finishing process, where a 30-bladed carbide may be used, the goal is not necessarily bulk reduction of the tooth structure, but refinement of the surface finish prior to polishing.

Efficiency in Group Practice: Can the bur blade be positioned at different angles?

Goodchild: Yes, they can. This is particularly necessary in the back of the mouth, where access is a challenge in hard-to-reach areas and complex preparation geometry is required.

Vranesevic: Whether burs are carbide, diamond or zirconia, they have unique profiles and angulations that aid in performing certain tasks. When utilizing burs during intraoral procedures, minimal space is available and only slight adaptations can be made to the position of the bur. These adaptions are made at the practitioner’s discretion, while working toward the ideal outcome for the given situation.

Efficiency in Group Practice: What is the cost, and how many burs do dentists need on hand?

Goodchild: Diamond burs are divided into lower-cost, single-use burs, which cost $1-2 each, and slightly more expensive, reusable types that cost $5-10 each. The costs of burs is not insignificant to dentists, however; it is considered a low overhead cost, which can impact the restorative outcome and patient comfort. (For example, efficient cutting burs work better and are more comfortable for the patient.) Typically, dentists routinely use 2-4 diamonds for a crown preparation, but often keep 10-12 shapes in their armamentarium for different sized teeth and specialty procedures. The same is true for tungsten carbide burs. A typical restorative preparation may require several different shapes, and the clinician may carry a larger variety to account for usual clinical situations.

Vranesevic: Rotary instruments can vary in price depending on the bur type, packaging and offering size. Generally, the more unique the bur is and/or the more complex the geometry is, the higher the cost. For instance, a metal cutting US# 330 carbide bur typically will cost more than a standard friction grip US# 330 carbide bur. The number of burs dental professionals keep on hand varies based on the practice type and procedures performed. For instance, a handful of burs may be all that is needed to perform most basic procedures, while additional specialty burs are added for more complex procedures.

Efficiency in Group Practice: What is the lifetime of a bur?

 Goodchild: Bur life is very difficult to quantify given the multiple factors involved, such as handpiece maintenance, the amount of water spray used, the pressure/load applied, the type/girth of the bur (e.g., very thin flame or large shoulder, or chamfer bur) and the material being cut. Brand and bur quality also play a significant role. Major manufacturers tend to produce longer lasting, better quality burs, but at a potentially higher cost; discount brand burs may not last as long, but they may be less expensive. Because the bur quality can impact the clinical outcome and patient experience, it is recommended that clinicians get the best tools they can afford.

Vranesevic: The average lifespan of a bur varies, depending on whether it is carbide, diamond or zirconia. Factors such as the number of uses, time under use and material the bur is used on have the potential to impact lifespan. To ensure burs are still viable for use, practitioners should inspect them for wear routinely and replace them as necessary. Wear may present itself as dulled and/or chipped blades on a carbide bur and lessening of partial coverage on diamond and zirconia burs.

Points to consider

When considering trying a new brand or type of bur, it’s important to consider all aspects of the crown and bridge – particularly tooth preparation, tissue management and conventional or digital impressions. Clinicians should consider the type of crowns they recommend to their patients and what their favorite margin design is for those materials; their techniques for cavity prep and finishing; and the growing need for proper rotary instruments for crown-removal.

Additional talking points may include:

• How can switching to a new bur make your life easier?
• What is your ideal outcome for each procedure you perform?
• Where do you see an opportunity for improvement when using burs?
• When working with your current rotary instruments, what takes you the most time?
• What are some of the most common procedures you perform on a daily basis?
• What are some of the more difficult procedures you perform with burs? What challenges do you face?
• How many burs do you use when performing an endodontic access?
• How many burs do you use when removing a crown?