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Spectrum dialogue – Vol. 9 No. 2 – February 2010

Introduction

“The Carrot Model”

In this article we describe the “Carrot Model” technique, also known as the “Geller Model”. Model work is a step that is often Olivier Tric, MDT, CDT neglected by dental technicians, or in some cases a task that is assigned the soft tissue untouched. This type of cast, or model to the least experienced person in the laboratory. We preparation technique, presents several advantages: first it disagree with this philosophy and strongly believe that is esthetically pleasant. Second, we can repour one single model work is a crucial step in the fabrication of a dental die on a large case, without (re-)preparing a complete new prosthesis. As a reminder, this is the first phase in any new cast. In addition, the “Carrot Model” allows us to switch case and subsequently, the precision achieved on a the dies from investment to stone material very easily. porcelain crown/veneer will have no meaning if the cast is Lastly, and most importantly, it allows us to focus on the not treated with proper care. Additionally, the cast is our tooth tissue relationship and design crowns, veneers, or only reference of the patient’s mouth, and it is the link bridges with a more adequate emergence profile in order to between the laboratory and the dental office. This close dark spaces or push the papillae. Despite these significance is the reason why we developed a reliable advantages, just as you would observe with the Pin Model, technique to achieve a highly esthetic and precise model. we have found that we still need a master cast to control The Technique contacts with the adjacent teeth and the occlusion in order to reduce or eliminate clinical adjustments. The “Carrot Model” consists of a slightly conical die(s) that is removable from the alveolar base, while keeping

Fig. 1: Original cast

Fig. 2: Original cast ready to be duplicated

Fig. 3: Duplication of the master cast

Spectrum dialogue – Vol. 9 No. 2 – February 2010

Fig. 4

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Fig. 5

Figs. 4 and 5: Testing the hardness of the impression material Fig. 6: Reduplication of the master cast

Figs. 7 and 8: Testing the hardness of the second impression material

Fig. 7

This Specific Case This particular case presents diastemas in the anterior region. Teeth 6 through 11 are unprepared teeth which will be later restored with some “no prep veneers”. Because the original impression was not available, the first step is to duplicate the master cast (Fig. 1). Manufacturers offer different type of duplicating materials. A proper material selection is essential when

Fig. 8

having diastemas or undercuts. Figures 3-5 illustrate the first duplicate made with a material with an insufficient coefficient of elasticity for the teeth shape/positioning of this specific case. The silicone was not resistant enough and was breaking between the central (Fig. 5). A new duplicate with appropriate physical properties was made (vinyl polysiloxane from GC America) (Fig. 6). Identical stretch does not tear the material now (Figs. 7-8).

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Spectrum dialogue – Vol. 9 No. 2 – February 2010

Preparing the Carrots The next step is to create a new cast (Figs. 9-10). We use a type 4 stone (Fujirock from GC America). Every tooth or die is separated using a diamond disk (Fig. 11). In order to properly trim the dies into “carrots” we trace with a pencil the shape of a cone on the slice of each tooth/preparation (Figs. 13- 14). The bulk of the carrot can be first shaped with a disk (Fig.15). Controlling the precision of carrot trimming is a key step to achieving a high quality cast. Using the right instrumentation is

important (Figs. 16-19). Each die/ carrot must be of a conic shape, very smooth without undercuts while leaving enough space in between the other dies and silicone (Figs. 21-24). The different level of angulations or shape of each die (from base to CEJ) will determine the tightness of each carrot onto its alveoli (Fig. 20). A more parallel shape will bring more stability but may be technique sensitive (Fig. 20 –right die). A less parallel shape (Fig. 20-left die) is suggested when starting this technique; however, it may decrease the stability of the dies into their base.

Fig. 9: Pour of the silicon impression

Fig. 10: Duplicated cast

Fig. 11: Cutting each tooth

Fig. 12: Each tooth is separated

Fig. 13: Side view of a tooth/die

Fig. 14: Visualization of the carrot before trimming

Spectrum dialogue – Vol. 9 No. 2 – February 2010

We can also create a groove or a flat site to minimize any rotation or movement. After the master dies are created, we must duplicate them. It is not recommended to use the master dies to make the alveolar base. Because of the small diameter at the base of each die, we prefer to use a different duplicating material (Figs. 26-30). Double Take (from Ivoclar) has a higher modulus of elasticity than the previous vinyl polysiloxane and will allow us to stretch the material at the entrance of each die while pouring stone or investment into it (Fig. 52).

Fig. 15: Shaping the carrot

Fig. 18

Pouring and “Glazing” the “Sacrificed” Dies. The replicas of the master dies are made (Figs. 34-35). Because, we will not use those dies for anything else other than to create the alveolar base, we also call them the “sacrificed” dies. In order to facilitate their separation from the base, we find advantages to pour them with a softer stone such a mounting stone (Whip-Mix). We like to call the following steps “glazing the carrot”. We add a thin, smooth and homogenous coat of paraffin wax around each duplicate die.

16: Proper bur shape

17: Incorrect bur shape

Fig. 19

Figs. 18 and 19: Refining the carrot shape

Fig. 20: Comparison of different carrot shapes

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Fig. 21: Replacing the tooth/die in the silicon impression

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Spectrum dialogue – Vol. 9 No. 2 – February 2010

Fig. 23

Fig. 22 Figs. 22 and 23: Verification of space around the tooth/die

Fig. 24: Flat sides are created to increase stability of the dies and allow room for the buccal wall of the base.

Fig. 26: Master dies with sticky wax on porcelain bottle cap.

Fig. 28 Figs. 28 and 29: Duplication of the master dies

Fig. 25: Master dies/carrot

Fig. 27: Master dies/carrots ready to be duplicated

Fig. 29

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Fig. 31: Cutting and removing the container

33: Silicone impression ready to be poured

Fig. 35: Original and duplicated dies.

We must only apply it on the carrot area while avoiding the cervical margin, tooth or surface preparation. The wax we use is soft and has a low fusion temperature. The application of the wax to the surface of the dies fills all small pores of the stone and creates a thin space with the alveolar base which will help to separate each tooth or preparation from it (Fig. 36). Each die or tooth must be carefully replaced into the impression. A little bit of sticky wax can be used at the margin area to hold the carrots during the pour (Figs. 37-38). However, it is very difficult to access the circumference of every part when the case presents two or

Fig. 32: Removal of the stone dies

Fig. 34: Pour the second set of die

Fig. 36: Glazing of the stone dies

more consecutive carrots. In this case, we prefer to extend each tooth with a casting sprue which is also covered with a thin coat of wax. Each extension is then stabilized to the mold or the impression with some pins and sticky wax (Fig. 39).

Pouring the Alveolar Base The impression is poured with some type 4 stone (Fujirock from GC). There, the challenge is to capture every detail of the mold such as the papillaes without moving the carrots from their positioning. The use of a

Spectrum dialogue – Vol. 9 No. 2 – February 2010

vibrator is recommended, however, it should be set at the lowest power (Fig. 40). We fill the mold completely and we check if the contacts between the sticky wax and the silicone remain sealed (Fig. 41). The stone can now set for about 60-90 minutes, before removing the pins (Fig. 42) and using some water to separate the cast from the impression (Figs. 43-44).

Fig. 37

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Removing the Dies from the Base Removing the carrots from the alveolar base is sometimes intricate and it is more than ever the quality and the accuracy of the prior steps that will determine its simplicity. In order to avoid any breakage, we like to soften the wax in a bain-marie or water bath at 55-60 degree Celsius for 2-3 minutes (Fig. 45).

Fig. 38

Figs. 37 and 38: Setting and fixing carrot back to position into mold.

Fig. 39: Carrots in place.

Fig. 40: Pouring of the alveolar base with type 4 stone.

Fig. 41: Poured alveolar base.

Fig. 42: Alveolar base after 90 min.

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Fig. 43

Fig. 44

Figs. 43 and 44: Using water to separate the base from the mold.

Fig. 45: Bain-marie.

Fig. 46: Removal of the sprues

Fig. 47: Access to the bottom of the carrots.

Fig. 48: Pushing out the carrots.

The Paraffin wax is now soft and each sprue can be pulled from the bottom of the cast (Fig. 46). We now access the base of each die (Fig. 47). The previous step can be repeated if needed, before pushing each carrot with an instrument. The use of a steamer can also be recommended to melt the wax and facilitate the removal of the carrots (Fig. 48). All the dies are not being kept or reused. As said previously, they were only needed to create the base. Fig. 49: Trimming and cleaning the alveolar base.

Spectrum dialogue – Vol. 9 No. 2 – February 2010

Fig. 50: Finished alveolar base.

Fig. 51: Material for the refractory dies.

53: Thermo-treatment of the refractory dies in burn-out oven.

Fig. 52: Pouring the refractory dies.

54: Thermo-treatment of the refractory dies in porcelain oven.

55: Model with refractory dies in place.

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Figs. 56 and 57: Final cast with stone dies.

Fig. 56

Fig. 57

The base is totally cleaned from the melted wax with some steam or boiling water. The base is then trimmed and dried (Figs. 49-50). Different set of dies can be made from the silicone. In this particular case a first set is poured in refractory investment (orbit-vest from GC) (Figs. 51- 52). Two hours of setting time are necessary before removing them and proceeding with the usual steps for thermo treatment (Figs. 53-54). We can use different materials such as epoxy or gypsum to pour a final, clean, and untouched set of dies. Any material used must have its expansion controlled with the use of the appropriate liquids, in order for the dies to have the right tightness inside the alveolar base. The completed cast with its removable dies ready for presentation or delivery is shown in Figs. 56-57.

Conclusion The Geller Model is a simple project, but requires accuracy all along the process. No step is less important than another and each stage is determinant for a definite and trustworthy outcome. However, no cast can be more accurate than a plain uncut cast. All veneers and crowns we create must be verified on a master cast before being clinically tried. “Carrot Models” offer us essential information on the soft tissue, and therefore determine the contour of our porcelain work.

About the author Olivier Tric, MDT, CDT, began his studies in France at the College of Leonardo De Vinci and the University of Pharo while concurrently pursuing an apprenticeship in Dental Technology. After a 5 year apprenticeship, he launched a 15+ year career devoted to a thorough understanding of the principles of Dental Aesthetics and the mastery of specialized techniques in Dental Laboratory Technology. His specialties include all facets of porcelain restorations on both natural teeth and osseointegrated implants. He is recognized by his peers as a pioneer in the industry by developing new and unique methodologies that are taught worldwide. He is widely published on the topic of ceramic layering techniques and aesthetic dentistry in industry journals such as Dental Dialogue, Practical Procedures & Aesthetic Dentistry and Quintessence Dental Technology. He also serves on the Editorial Board for Spectrum dialogue, and TeamWork Magazine. His professional affiliations include Design Technique International (DTI), Oral Design International Foundation, and others. Mr. Tric is a highly respected lecturer and educator, teaching hands-on courses to dentists and technicians throughout the United States, Canada and Europe. He is regularly consulted by leading Dental Manufacturers and Laboratories for input on new product development. He currently operates Olivier Tric Dental Laboratory and Educational Center in the Chicago suburb of Elmhurst, Illinois.