Full Crown Module: Learner Level 3

Full Crown Module

Restoration / Tooth #

Full Gold Crown (FGC) / mesially tilted 30

Extensions:

Porcelain Fused to Metal (PFM) / lingually 21 All Ceramic / rotated 12

Estimated Set Up Time: 2 hour Estimated Completion Time: 6 hours

I. Module Information

In level 3 of the Full Crown Module, we are going to prepare a tooth that is mesially tilted (Fig. 1). This would demand a thorough understanding of the principles of tooth preparation. This presents an unusual challenge to the learner because it requires an understanding of path of insertion or line of draw in

correcting a malpositioned tooth to receive a full crown restoration (Fig. 2). You will be guided to steps on dealing with this problem. These steps include (1) diagnostic wax up to correct the position of the tooth, (2) fabricating a working cast, and (3) fabricating a vacuum-formed stent to serve as your (a) preparation guide and eventual use for (b) provisional crown. In the extension part of this level, you will have the opportunity to practice your knowledge and skills in preparing a lingually tilted tooth as well a rotated tooth.

Fig. 1. Pre-operative photo of mesially tilted tooth #30

Fig. 2. Prepared tooth #30with Vacuum-formed stent as preparation guide

II. Setting up of the Articulated Teeth

These simulated exercises require the use of Natural teeth (extracted teeth, instead of a typodont teeth) mounted on a stone cast.

1. Get a natural tooth #30 (Fig. 3)

2. You may also start setting up for your extensions and get natural tooth #21 and #12 (Fig. 3)

Fig. 3. Natural Teeth #30,21,12 Fig. 4. Frassaco ® rubber mold

3. On your Frassaco ® rubber mold (Fig. 4), mount the teeth on thier corresponding positions. Follows the instructions for each tooth.

a. Mesially tilted #30

i. Place tooth #30 in the rubber mold

ii. Initially, position the tooth in such a way that the long axis of the tooth is perpendicular to the occulsal plane (Fig. 5). Note that the occlusal surface of the tooth is parallel to the

occlusal plane.

iii. Using current position as reference, push the root tip portion of your tooth distally (Fig. 6). This will then tilt the long axis of the tooth mesially once the stone cast is formed. Note that the occlusal surface of the tooth is at an angle

(approximately 45 degrees) to the occlusal plane.

Fig. 5. Initial position / angulation of the tooth in the rubber mold. Note the 2

black dots are aligned straight.

Fig. 6. Tipping the root tip distally to change the angulation of the tooth. Note

b. Lingually tilted #21

i. Place tooth #21 in the rubber mold

ii. Initially, position the tooth in such a way that the long axis of the tooth is perpendicular to the occulsal plane (Fig. 7). Note that the occlusal surface of the tooth is parallel to the

occlusal plane.

iii. Using current position as reference, push the root tip portion of your tooth buccally (Fig. 8). This will then tilt the long axis of the tooth lingually once the stone cast is formed. Note that the occlusal surface of the tooth is at an angle

(approximately 45 degrees) to the occlusal plane

Fig. 7. Initial position / angulation of the tooth in the rubber mold. Note the distance of the 2 black dots from each

other

Fig. 8. Tipping the root tip buccally to change the angulation of the tooth. Note

the distance of the 2 black dots decreased.

c. Rotated #12

i. Place tooth #12 in the rubber mold

ii. Initially, position the tooth in such a way that the long axis of the tooth is perpendicular to the occulsal plane (Fig. 9). Note that the occlusal surface of the tooth is parallel to the

occlusal plane.

iii. Using current position as reference, rotate the tooth

clockwise about quarter of a turn (Fig. 10). This will rotate the tooth mesially once the stone cast is formed.

Fig. 9. Initial position of the tooth in the rubber mold. Note the relationship of

the 2 black dots from each other

Fig. 10. Rotating the tooth clockwise at a quarter of the turn. Note the rotation of

the tooth relative to the dot.

4. Pour the rubber mold with the stone together with the mounting screws (Fig. 11).

5. Once the stone cast has set, clean the teeth involved by removing the stone plaster that may be covering the teeth (Fig 12-14).

Fig. 11. Rubber Mold and Mounting Screw

Fig. 12. Mesially tilted tooth #30 on a set stone cast

Fig. 13. Lingually tilted tooth #21 on a set stone cast

Fig. 14. Rotated tooth #12 on a set stone cast

III. Preparing Tooth for Full Crown Restoration

In restoring a mesially drifted tooth, one should examine the position of the tooth and recognize that angulation and tilt of the tooth relative to the long axis. Since, the long axis is not perpendicular to the occlusal plane, the occlusal surface of the tooth is not at the level of occlusal plane as well, thus not achieving maximum intercuspation. Given this clinical condition, how do we then prepare the tooth to correct the angulation, correct occlusal plane and be able to fabricate a crown on a maximum intercusaption position? The succeeding steps that you will be guided through will include, diagnostic waxing to correct the morphology, tilt and occlusion, fabrication of a working cast and fabrication of a vacuum-formed stent to be used as a preparation guide and provisionalization.

A. Diagnostic Wax Up

The goal of diagnostic Wax Up is to fabricate a three dimensional model of the malpositioned teeth that has been waxed up to a corrected anatomical form and established occlusion.

6. Make an alginate impression (read the instructors note) of the upper and lower arches of your patient (the stone cast with mounting screws) (Fig. 15).

Fig. 15. Alginate Impression

Instructor’s Note

I suggest that you soak your casts in water for 10 minutes prior to impression. If you don’t, the “dry” cast will absorb all the water of the alginate thus making it impossible to remove the impression without tearing off the alginate. Another approach to avoid this is to lubricate your cast with Vaseline ® for ease of removal.

You may use other impression materials you are comfortable with. Alginate material is just a cheap and quick material of choice to use for duplication of casts.

7. Pour your impression with mounting stone (white plaster of paris). Make sure you have adequate base of the cast for mounting.

8. Now you have your upper and lower duplicate casts. 9. Bring out your Whipmix ® articulator.

10. Arbitrarily mount the duplicate casts on the articulator. Establish the occlusal plane parallel the floor.

11. Make sure that your duplicate casts and mounting are neat and clean. 12. Prepare your waxing instruments.

13. Begin waxing the tooth to correct anatomical form and contour (Fig. 16). 14. Check wax up for correct occlusion (Fig. 17).

Fig. 16. Waxing mesially-tilted tooth #30 in proper anatomical form

Fig. 17. Waxing mesially-tilted tooth #30 in proper occlusion

15. Finish and Polish your diagnostic wax up. Be ready for fabricating a working cast out of your diagnostic wax up.

B. Fabrication of Working Cast from Diagnostic Wax Up

16. To fabricate your working cast, you need your Sil-tech ® putty material. 17. Make an impression of your diagnostic wax up using the putty material

(Fig. 18)

Fig. 18. Putty material impression of the diagnostic wax up to fabricate the

working cast

18. Once set, remove the putty material from the diagnostic wax up. 19. Pour the putty impression with mounting stone (white plaster of paris). 20. Once set, trim the working cast clean and neat (Fig. 19).

C. Fabrication of the Vacuum-formed Stent / Template

21. Place the working cast on the vacuum-forming machine (Fig. 20).

Fig. 20. Working cast ready for stent fabrication

22. Read the operation manual or request for a demonstration on how to use the vacuum-forming machine if needed.

23. Remove the working cast from the vacuum-forming machine (Fig.21 & 22). Care should be observed so you are not going to burn yourself.

Fig. 21. Working cast with the vacuum-formed stent

Fig. 22. Working cast with the vacuum-formed stent (close-up view)

24. Remove the stent from the working cast. With your scissor, trim the stent properly. This means that you have to include the tooth you are planning to prepare and the 2 adjacent teeth. Just like your putty matrix, you need a reference (the adjacent teeth) so you will be able to orient your stent and place it on the patient accordingly as your guide in tooth preparation (Fig. 23)

Fig. 23. Vacuum-formed stent

D. Using the Vacuum-formed Stent / Template as a Preparation Guide

25. Place the stent on the tooth to be prepared (Fig. 24). Evaluate! Plan your preparation based on the guide that you just created. Your preparation should be confined within the stent.

Fig. 24. Evaluating and Planning the preparation

Clinical Relevance

The vacuum-formed stent / template serve as your guide in tooth preparation. Assuming that your diagnostic wax up is accurate (or at least useful), the stent tells you basically what your final restoration would look like (dimension-wise). It is very important for you to evaluate and plan your tooth preparation. Ask yourself the following questions. (1) What is my planned restoration (PFM, FGC, All ceramic, etc.)? (2) What are the dimensional requirements for the planned restoration? (3) Where should I establish my path of insertion? Once you have answered these questions, prepare the teeth accordingly. For mesially-tilted tooth, you may need to reduce more on the distal side of your occlusal surface and probably less on the mesial side. For lingually tilted tooth, you may reduce a lot on your lingual surface and not so much on the buccal surface. For the rotated tooth, you may require reshaping and reangulating your tooth. All is based on the stent you just fabricated. In all this situations, you should be able to establish your path of insertion. Again, evaluate, plan and execute your preparation!

26. Proceed in tooth preparation. From time to time, use the stent to check your reduction (Fig. 25).

27. You should also be aware where your path of insertion is. For most situations, the path of insertion should be parallel to the line perpendicular to the occlusal plane.

Fig. 25. Using the stent as a guide in preparation

29. Once done, check your preparation. By this time, your preparation should have corrected the malpositioning of the tooth. You have established path of insertion and reduce the tooth based on the requirements of the restoration (Fig. 26 & 27).

Fig. 26. Pre-operative orientation of the mesially-tilted tooth

Fig. 27. Corrected path of insertion after tooth preparation

30. Provisionalizing the tooth should be easy. You can use the stent as your matrix for direct or indirect provisional procedure (Fig. 28 & 29).

Fig. 29. Provisional material on the patient

Fig. 28. Provisional material on the stent

CONGRATULATIONS! You made it once again! You have finished Level 3 of

the Full Crown Module. You may proceed doing the Level Extensions for further practice and efficiency. Good Job!

Clinical Relevance

Teeth vary in size, shape, form and position. These variations our due to several reasons which includes genetic factors and clinical factors. Often, as a consequence of tooth loss, there is an imbalance in patient’s occlusion and caused mesial driftings, rotations and other forms of

malpositions. In time, such sequela may lead to either adaptation of the dentition or pathological dentition. Either way, a clinician should be able to recognize when a therapeutic intervention is needed.