Principles of Tooth Preparation: Part-1

CROWN, BRIDGE, VENEER PREPARATION KIT BY MIK DENTAL

Design Concept

This is a bur kit designed by Dr. Moez I. Khakiani, on the tenet that the most important aspect of a bur is its tip. Knowing the shape and dimensions of the bur used is of prime importance, as this helps to ensure the desired margin architecture and the desired amount of tooth reduction can be achieved. When used in accordance to its design concept, sinking the bur tip into the tooth leaves a groove of known dimension; a factor most important in ensuring uniform and predictable reduction each time.

There are 19 golden shank burs in this kit that are strategically divided into 7 clusters; each for a specific material or design purpose. The kit contains all the burs necessary for performing predictable tooth preparations for all prosthetic materials used in fixed prosthodontics.

For ease of recognition and communication, the burs are named on the basis of either their tip design (e.g. DC for Deep Chamfer, MS for Modified shoulder, etc.) or on the basis of their function (e.g. IR for Incisal reduction, OR for Occlusal reduction, etc.).

In order to use any bur prudently, it is important to memorize the tip diameter/ working dimension of the bur. This task has been made extremely simple in this kit, as the number associated with each bur indicates the diameter of the bur at its tip or its functional length, e.g. DC 1.4 bur is a Deep Chamfer bur with tip diameter of 1.4 mm, IR 2.0 is an Incisal Reduction bur with a functional length of 2 mm.

BURS OF 4 DIFFERENT DIAMOND GRITS HAVE BEEN INCLUDED IN THIS KIT

Blue ring burs: Medium grit.

These burs are used for routine tooth preparations. No specific designation code is used for these burs, as they are considered to be the base grit of this kit.

Green ring burs: Coarse grit.

These burs are designated by the letter ‘C’ in the name, e.g. DC 1.4C. The coarse bur has the ability to reduce tooth faster and thus, requires less effort to be applied for effective reduction. This has the advantage of saving time, while also reducing the possibility of pulpal damage and post preparation hypersensitivity that result from friction and heat produced during tooth reduction. However, it calls for good handpiece skills by the clinician, in order to prevent inadvertent over-reduction of the tooth structure.

Red ring burs: Fine grit.

These burs are designated by the letter ‘F’ in the name, e.g. DC 1.2F. The fine grit burs are used to finish the preparation. Regardless of the grit used to prepare the tooth, it is imperative that the preparation be finished using fine grit burs.

Yellow ring bur: Extra Fine grit.

These burs are designated by the letter ‘EF’ in the name, e.g. DC 1.2EF. This bur is used to achieve an extremely smooth surface for PLV preparations.

CLUSTER 1: PFM MARGIN (1ST ROW: LEFT)

1. MS 1.0 (Fig. 4.17)

This is a Modified Shoulder bur with a tip diameter of 1.0 mm. The classic shoulder bur creates a sharp internal line angle (butt) at the preparation margin. This area is prone to stress concentrations, possibly causing abutment fracture.

The MS bur has been designed as a flat tip bur, but with rounded edges that produce a rounded junction between the finish line and the axial walls. Such a modification helps reduce stress concentrations at this vulnerable part of the preparation.

This bur is to be used by sinking the tip to it’s full depth, thereby leaving a 1.0 mm groove in the tooth. Use: For preparing the buccal/labial margin when planning a PFM prosthesis.

This bur is also available in its coarse grit (green ring).

2. DC 1.0 (Fig. 4.18)

This is a Deep Chamfer bur with a tip diameter of 1.0 mm.

This bur is to be used only half it’s depth, in order to avoid formation of a lip of enamel at the margin. Thus when used correctly, the 1.0 bur leaves a 0.5 mm groove on the tooth.

Uses: For preparing the lingual/palatal margin when planning a PFM prosthesis with a lingual/palatal metal collar. It is also used for preparing all the margins (360°) when planning a

monolithic zirconia or a monolithic metal prosthesis and for a PLV preparation.

This bur is also available in its coarse grit (green ring).

3. MS 1.3F (Fig. 4.19)

This is a Modified Shoulder Finishing bur with a tip diameter of 1.3 mm.

This bur is used by sinking the tip slightly short of its full depth, thereby developing a margin that is 1-1.2 mm in width.

Use: For finishing the buccal/labial and proximal margins whenpreparing the tooth for a PFM prosthesis.

4. DC 1.2F (Fig. 4.20)

This is a Deep Chamfer Finishing bur with a tip diameter of 1.2 mm. As this is a deep chamfer design, it is to be used only half its depth to avoid formation of a lip of enamel at the margin. Thus when used correctly, this bur leaves a 0.5-0.6 mm deep chamfer margin.

Uses: For finishing the lingual/palatal margin when preparing the tooth for a PFM prosthesis with a metal collar.

It is also used for finishing all the prepared margins (360°) when planning a monolithic zirconia or a monolithic metal prosthesis.

In addition, it is also used to finish the proximal and palatal/lingual margins for a PFZ or a LiDiSi prosthesis, especially anterior teeth.

CLUSTER 2: METAL FREE MARGIN (1ST ROW: RIGHT)

5. DC 1.4 (Fig. 4.21)

This is a Deep Chamfer bur with a tip diameter of 1.4 mm.

This bur is also to be used only half its depth. Thus when used correctly, it leaves a 0.5-0.7 mm deep chamfer margin.

Use: For preparing all the margins (360°) when planning for a PFZ or a LiDiSi prosthesis.

This bur is also available in its coarse grit (green ring).

6. DC 1.8F (Fig. 4.22)

This is a Deep Chamfer Finishing bur with a tip diameter of 1.8 mm.

This bur is also to be used only half its depth. Thus when used correctly, it leaves a 0.8-0.9 mm deep chamfer margin.

Use: For finishing the buccal/labial aspect when preparing the tooth for a PFZ or a LiDiSi prosthesis.

CLUSTER 3: MODIFIED INTERDENTAL (2ND ROW: LEFT)

7. MI 0.8 (Fig. 4.23, 4.24)

This is a Modified Interdental bur with a tip diameter of 0.8 mm.

The Modified interdental bur is safe ended (no diamonds at the tip). This prevents the bur from slipping gingivally as one moves from the labial/buccal towards the lingual/palatal surface.

This prevents gouging of the margin and trauma to the gingival col, a common occurrence during interproximal reduction.

When using this bur, it is important to start above the interdental papilla on the buccal/labial aspect and then run it across the inter proximal tooth structure. During the entire stroke, it is essential to ensure the bur is oriented perpendicular to the tooth.

Use: For opening interproximal contacts when preparing the tooth for a PFM prosthesis, especially for molars.

8. MI 0.5 (Fig. 4.25)

This is a Modified Interdental bur with a tip diameter of 0.5 mm.

This bur is also safe ended and is to be used in the same manner as that described for the MI 0.8 bur.

Use: For opening interproximal contacts when preparing the tooth for a PFZ, a LiDiSi, a monolithic metal or a monolithic zirconia prosthesis, especially for anterior and premolar teeth.

CLUSTER 4: OCCLUSAL REDUCTION (2ND ROW: CENTER)

9. OR 1.6 (Fig. 4.26)

This is an occlusal reduction bur with a diameter of 1.6 mm through it’s entire length (straight bur).

It is used by sinking the bur to its full depth, ensuring the bur follows the preexisting cuspal incline; thereby allowing anatomic reduction of the occlusal aspect.

Use: For occlusal reduction of the functional cusps when preparing a tooth for a PFM prosthesis.

10. OR 1.2 (Fig. 4.27)

This is an occlusal reduction bur with a diameter of 1.2 mm through it’s entire length (straight bur).

Uses: For occlusal reduction of non-functional cusps when preparing a tooth for a PFM prosthesis.

Also used for reducing the entire occlusal table (both, functional and nonfunctional cusps) when preparing a tooth to receive a PFZ, a LiDiSi, a monolithic metal or a monolithic zirconia prosthesis.

CLUSTER 5: CINGULUM REDUCTION (2ND ROW: RIGHT)

11. CR 2.3 (Fig. 4.28)

This is a Cingulum Reduction bur with a diameter of 2.3 mm at its widest circumference.

It is used by positioning the bur such that its widest portion sits into the deepest concavity on the palatal/lingual aspect of the tooth being prepared.

Use: For reduction of the lingual fossa when preparing the tooth for a PFZ, a LiDiSi or a PFM facing prosthesis, especially for maxillary lateral incisors and for mandibular anteriors.

12. CR 2.8 (Fig. 4.29)

This is a Cingulum Reduction bur with a diameter of 2.8 mm at its widest circumference.

This bur is used following the same protocol as that mentioned for the CR 2.3 bur.

Use: For reduction of the lingual fossa when preparing the tooth for a PFM prosthesis, especially for maxillary central incisors and for maxillary canines.

CLUSTER 6: ALLIED (3RD ROW)

13. EC 1.4F (Fig. 4.30, 4.31)

This is an End Cutting Finishing bur with a tip diameter of 1.4 mm.

This bur has diamonds incorporated only at it’s tip and has a noncutting shank.

The non-cutting shank of the bur allows for it to be used on proximal surfaces of the prepared tooth, without the fear of inadvertent damage to the adjacent teeth.

This bur is to be used with pull strokes only, as a push stroke carries the risk of ploughing/digging the bur into the prepared margin.

Use: For removing irregular/unsupported tooth structure around the prepared margins.

14. IR 2.0 (Fig. 4.32)

This is a self-limiting Incisal Reduction bur with a working length of 2.0 mm and a tip diameter of 1.0 mm

This bur is used by holding its shank flush with the incisal edge of the tooth (i.e. long axis of bur is oriented perpendicular to the incisal edge) and then moving it straight through from the labial into the palatal/lingual aspect (in one sweeping motion). When used correctly, it leaves a groove that is 2.0 mm deep and 1.0 mm wide.

Use: For preparing depth grooves, when reducing the incisal edge for all types of prosthetic materials.

15. CA 1.6F (Fig. 4.33)

This is a Ceramic Adjustment bur with a diameter of 1.6 mm at its widest circumference.

The tip of this bur is shaped like a semi-circle (half round) and is to be used for adjusting static occlusal interferences. The remainder of its length is to be used for reducing incline interferences during excursive movements.

Use: For reducing interferences on porcelain crowns and bridges during the occlusal adjustment appointment.

16. DC 1.0SS (Fig. 4.34)

This is a Super Short Shank bur with a tip diameter of 1.0 mm and a Deep Chamfer tip design.

When used correctly, this bur leaves a 0.5 mm deep chamfer margin.

Use: For tooth preparation in difficult to access areas of the oral cavity, e.g. distal margin of a maxillary 2nd molar.

CLUSTER 7: PORCELAIN LAMINATE VENEER (4TH ROW)

17. PLV 0.3 (Fig. 4.35)

This is a single tier, self-limiting depth gauge bur with a working diameter of 0.3 mm.

This bur has a non-cutting shank that extends above and below the working surface. This ensures that depth grooves of 0.3 mm are created, regardless of the labial curvature of the tooth.

Use: To scribe depth grooves when preparing the tooth for ultraconservative Porcelain Laminate Veneers.

18. PLV 0.5 (Fig. 4.36)

This is also a single tier, self-limiting depth gauge bur with a working diameter of 0.5 mm.

Works on the same principle as that described for the PLV 0.3 bur. It ensures the depth grooves achieved are 0.5 mm deep, regardless of the labial curvature of the tooth.

Use: To scribe depth grooves when preparing Porcelain Laminate Veneers that require comparatively more reduction.

19. DC 1.2EF (Fig. 4.37)

This is an Extra Fine Deep Chamfer Polishing bur with a tip diameter of 1.2 mm and is the only yellow ring bur in this kit.

Use: To polish the Porcelain Laminate Veneer preparations.

Close adaptation between the PLV and the underlying tooth structure is extremely important for ensuring long-term success with this treatment protocol. A smooth polished surface helps in achieving this requirement.

The MIK Dental kit is a contemporary and technical approach for achieving consistent tooth preparations for all material categories used in fixed prosthodontics. The use of such a controlled method of reduction takes the guess work out of tooth preparation, thereby ensuring predictability to the workflow.

Tooth preparation burs should be frequently replaced, as a clogged/dull bur often prompts the operator to apply excessive pressure against the tooth. The combination of heat and increased lateral force is extremely detrimental for the pulp and is a leading cause of irreversible pulpal inflammation and sensitivity following tooth preparation. Such excessive forces may also prematurely damage the handpiece cartridge, often requiring replacement.

CHECKING FOR ADEQUACY OF CLEARANCE ACHIEVED

One of the biggest hurdles most laboratories face with tooth preparations, is that of inadequate occlusal or incisal clearance. In such a situation, the technician has to accommodate the prosthesis into a restricted space, thereby compromising the long-term prognosis.

Although clinicians are aware of the amount of clearance desired, it is routinely difficult to precisely gauge this amount intra-orally. Clinically, occlusal clearance is usually estimated on the basis of visual inspection of the ‘space’ available between the antagonist teeth when in MIP. This canbe extremely subjective, as teeth have cuspal slopes that can obscure the
amount of lingual or palatal reduction achieved.

A simple, yet effective solution to this problem would be the use of ‘PrepGauge’ from MIK Dental.

Each of these have their own indications:

1 mm gauge: Non-functional cusps for LiDiSi, PFZ, monolithic metal and monolithic zirconia preparations.

1.5 mm gauge: Functional cusps for LiDiSi, PFZ, monolithic metal and monolithic zirconia preparations. Non-functional cusps for PFM preparations.

2 mm gauge: Functional cusps for PFM preparations.

3.5 mm gauge: PFM reductions involving maxillary and mandibular antagonist teeth.

Their wider extension (10 mm) is to be used for molar teeth, while the narrower extension (7 mm) is designed for use with teeth having a narrower diameter. The rounded end of the narrow extension (1 mm) can be used for mandibular anterior teeth which have the smallest mesio-distal width.

TECHNIQUE FOR USE

Once the desired amount of reduction has been achieved, the patient is asked to bite onto the corresponding PrepGauge in MIP. The clinician is to then try and pull the gauge through the buccal aspect (feeler gauge concept), as seen in Fig. 4.42 .

One of the following three possibilities exist:

Possibility 1: The gauge can be pulled out through the buccal aspect with minimal resistance.

Clinical conclusion: The preparation is adequate in relation to the PrepGauge used.

Possibility 2: The gauge cannot be pulled out through the buccal aspect. Clinical conclusion: The clearance is inadequate and requires further reduction.

Possibility 3: The gauge can be pulled out through the buccal aspect without any resistance.

Clinical conclusion: The preparation is over-reduced. Although this technique helps gauge the adequacy of the preparation, it does not indicate specific areas where the preparation may need further reduction (if any).

The PrepGauge (with the paint/spray) should be used to evaluate not just the static clearance, but also the clearance in all excursive movements. This small step helps avoid the creation of an excursive interference or perforation/ fracture of the prosthesis.

Evaluating excursive clearance is especially important for anterior teeth, where uniform reduction along the entire path of anterior guidance is extremely crucial for long-term prognosis of the case. This can easily be evaluated with the use of PrepGauge.

In this manner, predictability when performing fixed prosthetic preparations can be greatly enhanced with the use of burs of known tip diameters (to gauge margin width) and the use of PrepGauge (to evaluate the clearance).

Note: This article is a direct extract from the book “Clinical Fixed Prosthodontics” by Dr. Moez I. Khakiani. With over 1700 colored illustrations, clustered into 23 chapters that span over 400 pages, this book is the ideal atlas for every clinicians who wishes to improve on their clinical skills and serve their patients with the highest level or oral care. To purchase the same call on +919111212912.