Clinical Corner: Information on Dental Procedures

Articles

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Combating Hidden Decay with Early Detection
Atraumatic Removal of Defective Crowns
Balancing: The Art, Science and Business of Dentistry
Intra-Oral Preparation of Titanium Abutments in Order to Obtain Ideal Angulations and Contours
SS White Express Line High Speed Laboratory Metal Finishing Burs
Direct Preparation Of Preexisting Implant Abutments For Case Rehabilitation
Flextime Xtreme: The 80/20 Rule
Fast and Smooth - Efficient Crown Preparation With Carbide Instruments
When Advancing the Bur, One Can Feel the Presence of Dentinal Caries
Precision Trimming and Finishing of Current Dental Restorations Using the Safe End Bur System
Indirect Restorative Tooth Preparation: Extreme Efficiency and Accuracy
Creating Maximum Efficiency and Accuracy In Indirect Restorative Tooth Preparation
Preparation Protocol To Ensure Predictable Aesthetic Restorations
Tooth Preparation Mastering Quality and Efficiency
Fissurotomy: Proactive Treatment for Incipient Decay
Anatomically Adapted Carbide Finishing Burs - Creating Super-Smooth Composite Surfaces in Two Steps
Directions for Use: Dr. David Clark Kit
Placing Traditional Sealants with Enhanced Magnification: Methodology to Increase Both Short-term and Long-term Success - David Clark, DDS
How to Quickly and Conservatively Restore a Natural Shine after Orthodontic Bracket Removal
SS White Surgical Length Oral Surgery Burs: Atraumatic Removal of Teeth for Maximum Bone Preservation

"Fast and Smooth - Efficient Crown Preparation with Carbide Instruments"

Dr. Michael Leistner 

In crown preparation, dental professionals really have to prove their skills. The entire dental arch and the opposing dentition must be taken into account. During preparation, dentists must already see the planned restorations in their mind’s eye. To allow practitioners to fully concentrate on these tasks, the instruments used should cut neatly and efficiently. A newly launched series of carbide burs will do a very good job in this respect.

Diamond burs are regarded as the gold standard for crown preparations. A well-known disadvantage, however, is their tendency to clog. The spaces between the diamond particles quickly clog with debris, and, as a consequence, their effectiveness in material reduction decreases rapidly (Siegel and von Fraunhofer 1999). Instrument processing in an ultrasonic bath and the use of special cleaning stones can only partially restore the original performance. Even in the case of coarse-grit diamonds, a certain drop in effectiveness cannot be avoided. If the dentist reacts to this problem by increasing the contact pressure, this will result in a higher development of heat, as compared to the use of new and clean instruments.

Carbide burs work according to a completely different principle, so they cannot clog. The clear spaces between the blades ensure a proper removal of the debris created in the cutting process. And if some debris remains in these wide flutes, it can easily be removed in an ultrasonic bath or with the aid of nylon or metal brushes. Another benefit of carbide burs is their neat cutting action, resulting from their sharp and smooth blades. This is why specialists in all-ceramic restorations recommend reworking and smoothing (diamond) preparations with carbide finishers.

A new series of carbide burs, named Great White Ultra (SS White Burs, Freiburg, Germany), also features wide flutes, ensuring an effective removal of tooth substance, composites, alloys or amalgam. These burs maintain their high torque throughout the preparation procedure. The combination of a special dentate design of the working part with a reinforced shank makes the material reduction step particularly efficient. The burs work quickly and reliably, and practitioners can fully concentrate on the shape and extent of the preparation, the insertion path of the restoration, and the correct distance to the opposing dentition.

Another interesting aspect of these new carbide burs is the creation of a rough surface on the tooth stump by their lateral dentate blades. Most university teachers and opinion leaders still recommend careful finishing of the entire preparation. The background to this opinion is the idea that smooth surfaces will lead to more precise impressions and thus to more accurately fitting restorations. In dental scientific studies, however, one will hardly find any evidence supporting this recommendation.

At least for conventional cementation, only a finished preparation margin is desirable, according to the data currently available. Conventionally cemented crowns are retained exclusively by increased friction between tooth stump and restoration. And a certain degree of stump roughness will help to increase friction, in comparison with smooth surfaces (Wiskott, Belser and Scherrer 1999, investigation at the University of Geneva). This applies to all types of cement, including composites and phosphate or glass ionomer cements. However experts agree that an axial roughness of 30 micrometers should not be exceeded (Hellwig 1998).

Figure 1 Original finding I: After periodontal pretreatment, the patient (aged 45) wished to have harmonious and markedly lighter maxillary anterior teeth. Apart from the yellowish color, extensive composite restorations (e.g. tooth 11, buccal), enamel cracks and the inharmonious overall appearance were considered unsatisfactory	Figure 2 Original finding II: Despite extensive brushing defects and gingival recession with a substantial attachment loss, the patient was not willing to undergo gingivoplasty (view from the right, mirror photo)	Figure 3 A chamfer preparation was performed with the newly developed Great White Ultra carbide burs by SS White Burs (Freiburg). Their special blade design ensures a very effective removal of debris (bur shown in this photo: No. 856-020)
Figure 4 While the lateral blades feature a dentate design for high cutting efficiency, the smooth blades at the tip provide a precise preparation margin	Figure 5 Great White Ultra carbide burs are also very well-suited for the removal of old fillings, which can be done in one procedure together with the preparation (bur shown in this photo: No. 847-016)	Great White Ultra carbide burs take account of the demand for smooth preparation margins by offering smooth blades at the tip of the working part. These smooth blades ensure precise preparation margins without the need for an additional finishing step (Fig. 4). If dentists wish to complete the preparation by finishing the margins without any additional material reduction, they can use the instrument head at a low speed and in minimal axial contact with the stump. The lateral blades with their distinct dentate design, by contrast, will create a relatively rough surface (Fig. 3). In order to avoid distortion of the impression material finishing with normal (ISO 524) or fine grit (ISO 514) diamonds is recommended.

Turbine or Micromotor?

The question as to whether a turbine or a micromotor is used for preparation is, at least in part, a matter of taste. According to a comprehensive study conducted by the U.S. Army, micromotors have a number of advantages (Eikenberg 2000). The benefits of micromotors include: better control of the speed selected (presetting, display), constant speed even after prolonged use, and better torque. The higher costs of a micromotor are definitely outweighed by its lower fault proneness and longer service life.

Great White Ultra carbide burs can be used with both turbines and micromotors. The speed depends on the working part diameter (Hellwig 1998, Statement by the German Society of Dental, Oral and Craniomandibular Sciences, DGZMK). In micromotors, burs with diameters of up to ISO 016 can be used at maximum speeds between 230,000 and 300,000 revolutions per minute (min-1). Turbines permit a maximum idling speed of 400,000 min-1. This is equivalent to a working speed of approx. 240,000 min-1.

If the working part diameters are larger, the recommended maximum speeds will be lower, for example approx. 50,000 min-1 at ISO 023 (Kimmel 1997). Ideally, the speed is preprogrammed on a dental treatment unit with a display. If an instrument with a large-diameter working part begins to rattle, it will be necessary to increase the speed and provide better cooling with the aid of a spray insert.

Figure 6 Result after the placement of metal-ceramic crowns (IPS d.SIGN Metallkeramik, Ivoclar Vivadent): Because of the patient’s low smile line, the cervical tooth areas will not be visible at any time (view from the left, mirror photo)

Figure 7 The crowns harmonize with the dental arch, are considered successful in terms of color and light optics, and meet the patient’s wish for light and uniform teeth (view from the right, mirror photo)

Figure 8 In addition to various burs for crown and bridge preparations, the Great White Ultra carbide preparation kit by SS White Burs also offers special instrument shapes for partial crowns, inlays and onlays

Conclusion

Great White Ultra carbide burs feature a particularly effective removal of both tooth substance and composite, amalgam or alloy debris. In contrast to diamond burs, which tend to clog, the flutes of these carbide burs remain clear of debris. The instruments maintain their torque, so that preparations for crowns, bridges and partial crowns can be accomplished in a highly efficient and economical manner.

Originally Published in The ZMK December 2005 Issue