The secret to any restoration is operator technique – from correct diagnosis and proper preparation to material choice. Whether a restoration is temporary or permanent, it must be designed to allow proper cleaning, to support periodontal health, and to function like the natural tooth it replaces.
Teeth that have carious lesions or that have lost structure or anatomy due to fracture, abrasion, or erosion should be restored to their original form, function, and esthetics. By necessity, cavity preparations must be larger than the size of the carious lesion, but with today’s emphasis on minimally invasive dentistry, it is important to carefully follow the appropriate protocols both to conserve tooth structure and to ensure long-term stability of the restoration and the remaining tooth.
After assessing the amount of decay, the clinician can choose the preparation form. The preparation form and the amount of tooth structure removed will contribute to mechanical, biological, and esthetic restorative success. Unless enamel will be unsupported by dentin, which may make it break more easily, it is best to preserve as much natural tooth as possible. Well-designed restorations can last 10 to 40 years.
Preparations are the first step in restoring a tooth that either has a carious lesion or has been fractured or otherwise physically damaged. After removal of decayed tissue, preparations are based on outline, retention, and resistance forms. The steps must be followed meticulously and attention to detail is critical.
Clinical examination and X-ray assessment help determine the size and shape of the lesion and the outline form of the preparation, which usually is slightly larger than the decayed area. Retention forms are what help a restoration stay in place. Resistance forms prevent fracture either of the remaining tooth structure or the restoration itself. The convenience form involves removing healthy tooth structure so the clinician can see and access carious areas that require treatment. Cavity depth is determined by the extent of the lesion.
The outline form and prep are created using carbide or diamond burs with a high-speed handpiece. A slow-speed handpiece with a steel bur and hand instruments typically are used to remove decayed dentin and finish the preparation.
For example, in a Class I carious lesion involving all the occlusal fissures on a molar tooth, the approach would be to use a pear-shaped bur in a high-speed handpiece to a depth of less than 2 mm. Stopping at 2 mm enables the clinician to remove remaining decayed dentin with a spoon excavator.
The pear-shaped bur creates a subtle convergence toward the occlusal opening. This creates an “undercut” effect or the retention form, which will help keep the restoration in place.
A large round bur in a slow-speed handpiece can be used to remove decayed dentin from the subfloor of the preparation. Slow-speed burs can be used to finish the walls and floor of the cavity.
If a carious occlusal lesion in a molar is connected to another lesion on the buccal or lingual surface, it will be necessary to perform a Class I cavity preparation with a buccal or lingual extension. If the second lesion is below the level of the pulpal floor, the preparation for the extension may need to include a “step.”
A freestanding lesion may occur on the buccal or lingual side of a molar, or on the lingual side of incisors. The outline form for this preparation usually is a little larger than the lesion. The preparation is round, oval, or triangular.
A convenience form used for access to a two-surface cavity preparation results in a proximal box preparation. The retention form is created when the floor is larger than the occlusal opening. Carefully creating retention grooves can help prevent horizontal sliding of the proximal portion of the restoration.
To further protect the stability of the remaining tooth structure in maxillary molars, the clinician may need to remove areas of unsupported enamel by beveling the gingival cavosurface to reduce fracture risk.
Using proper cavity preparation techniques and choosing the appropriate design is the best way to provide long-lasting restorations. It is important to use sharp, new burs for these procedures as well as proper isolation and moisture control. When restoring with composites, moisture control, polymerization shrinkage, and light curing also impact the success and longevity of a restoration.
The best tools for successful cavity preparations
Dental burs are integral to creating long-lasting restorations. Choice is influenced by what they’ll be used for, how they impact handpiece vibration, and personal preferences. Generally speaking, carbide burs are highly efficient for cavity preparation and diamond burs are ideal for intracoronal cavity preparation.
Carbide burs are the most common type of dental bur and come in a variety of shapes and sizes for different applications. They can be used to remove both tooth structure and restorative materials. Carbide burs create a smoother surface than diamond burs. They also can be sharpened and reused. Carbide burs come with a coating that helps increase tool life.
Patterson Dental carries hundreds of carbide burs, including its proprietary brand. Head shapes include barrel, end cutting, inverted cone, straight fissure, tapered fissure, needle, flame, egg, pear, wheel, cylinder, football, round, cone and amalgam prep. End types range from bevel to flat, point and round. Available shank lengths include short, standard, long and extralong/surgical. Applications range from implant to endodontic, restorative, laboratory, surgical, orthodontic, trimming and finishing, operative, and preparation and exploration.
Diamond burs offer precise drilling and finishing that result in cleaner cuts and a higher polish than carbide burs. Users should choose diamond burs based on grit, which determines the speed and type of polish. Finer grits result in high polish and coarser grits are used for removing heavy material. Diamond bur uses include intraoral grinding and cutting procedures as well as precise drilling and finishing. Applications range from restorative and endodontic to implant, laboratory, trimming and finishing, and orthodontic. Diamond burs come in a variety of shank types, head shapes, end types, shank lengths, and grits. They’re available as both disposable and reusable.
Ask your Patterson representative for the best dental bur options to suit the needs of your practice.
Disposable vs. reusable burs
Deciding whether to use disposable or reusable burs may present a conundrum. On the one hand, it makes sense to sterilize and reuse all items possible to prevent waste. However, infection control and cross-contamination also are concerns in the dental office.
Most diamond burs can’t be effectively cleaned because of their irregular shape and surfaces. In fact, the Food and Drug Administration issued this statement in 2019: “The FDA considers all diamond-coated burs single-use unless the manufacturer has a 501k clearance on file.” After repeated sterilization cycles, cutting surfaces can become dull, making them more likely to break during use. Carbide burs also can be difficult to clean.
Following the manufacturer’s instructions is critical. Bur manufacturers should indicate whether a particular item can be reused and include instructions on cleaning and sterilization methods that will maintain the integrity of a bur’s usefulness as well as meet infection control standards. If reprocessing instructions aren’t evident, the item shouldn’t be used more than once.
Although disposable burs may produce more waste and seem less cost-effective, perhaps the consequences of cross-contamination outweigh those concerns. Cost savings will be in the form of reduced team time for processing as well as their increased safety by eliminating the potential for sharps exposures.
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Lively T. Preps: Preparing for success with your composite restorations. Dental Products Report. August 19, 2019.
Molinari JA. Single-use devices and burs: Disposable or reusable? Dental Economics. October 1, 2009.
Simon JF, George LA. Factors for successful composite restorations. Inside Dentistry. June 2014.
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A version of this article originally appeared in the May 2022 edition of OnTarget. Read the latest edition and view current promotions at pattersondental.com/dental/ontarget.