Eggshell Provisionals: Full Arch Cases [Part II]

As discussed in Part I of this series, an easy way to transfer the esthetics and occlusion from the diagnostic wax-up to the mouth is to use the “eggshell” provisional technique. As I explained, rather than lightly prepping the model, I inject the provisional material into the putty itself. Once the material that has been injected into the putty is set, the next step is to trim and hollow the shell. This is done in two distinct steps and can take a little bit of time to do.

Step 1: Trim the provisional shell to the free gingival margin. In this step you’re essentially trimming back to the gingival margin, or more accurately, back to where the bulk-out wax ended on the gingival margin. If the wax margin is not well delineated it will be very difficult to determine how much needs to be trimmed off the shell. This first step in the trimming process should be done by orienting the acrylic bur perpendicularly to he axial wall along all the buccal and palatal surfaces.

Step 2: “Hollow” out the internal of the shell to allow it to freely seat over the preparations without binding. Once your first step is completed you can use a rounded acrylic burr or a #6 round burr to hollow out the internal of the shell. Upon completion, the provisional should be very thin once the internal is thinned out – which is exactly why this technique is called an “eggshell” provisional. The palatal and buccal walls of the provisionals usually measure around .5mm thick.

On the incisal edges and occlusal table, the walls can be ~1mm thick, since more preparation depth is anticipated in these areas. At this point, you will also want to verify that you aren’t leaving too much material interproximally which could impinge on the interproximal soft tissue and prevent complete seating. Lastly, a disc is used to open up the facial and palatal gingival embrasures to help ensure that the shell doesn’t impinge on the papillae.

At this point, the shell is ready to take to the mouth. After prepping the teeth, you’ll want to try the shell in the mouth. It should be noted that when trying the shell over the preps, it should not bind on the teeth at all. It’s will actually be the soft tissue that helps determine the seating of the shell. This trying in and fitting the shell properly is the most important step when using the shell technique. Rushing this step can affect the seating of the provisional and cause problems both with the occlusion and esthetics.

The best way to know if the shell is seated correctly (not over-seated or under-seated) is to use calipers to measure from incisal edge to gingival margin on the diagnostic wax-up, and verify the measurement in the mouth when fitting the shell. This verification can be done on multiple teeth to ensure that it isn’t binding somewhere or being over seated. This is typically done after the prep is essentially completed, but before cords are packed on the anterior teeth and the margins dropped.

The reason is that once cord is placed, your reference position for the gingival margin is no longer accurate. To make the sure the shell will be repositioned accurately after packing cord, place some Triad material in the incisal 1/3 of the centrals, seat and manipulate the shell until its seated correctly (using measurements and the opposing occlusion) and cure the Triad. Now you can pack your cords and refine the preparation without losing the ability to re-seat the provisional accurately.

 

Eggshell Provisionals: Full Arch Cases [Part I]

If you happen to be creating provisionals for an exceptionally large case, such as a full arch, an easy way to transfer the esthetics and occlusion from the diagnostic wax-up to the mouth is to use the “eggshell” provisional technique. This concept utilizes a prefabricated shell in the desired tooth form (made from the diagnostic wax-up).

Although this technique is typically used with larger cases, it is versatile enough that it can be used in any situation, all the way from a single unit to a three-unit bridge, or even a quadrant. This series will concentrate on using the “shell” provisional in a full arch situation.

To make provisionals in a full arch case while using a matrix (putty or clear matrix) requires the presence of hard tissue stops. If you are leaving parts of teeth untouched (ie. anterior veneer preparations or posterior partial coverage restorations) using a matrix is easy and predictable. If you don’t have enough hard tissue stops remaining to secure the matrix, the matrix will then have to rely on the soft tissue to determine the proper “seating” position. The problem when using soft tissue only to seat the matrix is that it is movable/resilient and pressing too hard can compress the soft tissue and hence produce a distorted provisional with regard to esthetics and occlusion. If you don’t have enough tooth structure to key the matrix because everything will be full coverage, or if you are opening the VDO, using the eggshell provisional technique can efficiently help transfer the esthetics, occlusion and vertical dimension from the diagnostic wax-up back to the patient in a very efficient and predictable manner.

Create Diagnostic Wax-Up
The first step is to create a diagnostic wax-up on the mounted models. Once this is complete, you have two options to fabricate the shell. The first option is to have the lab fabricate the shell for you. These days this would be done with a CAD/CAM approach. Scan the wax-up, create a very light prep on the model, scan the prepped model, and then have the shell “milled” via a CAD/CAM technique. This can be a very quick and efficient way to have a shell fabricated. The only downside with this approach is that there will be a lab fee for milling the shell that could be quite significant.

Another way to fabricate the shell is to have the technician complete the diagnostic wax-up and then fabricate the shell using more traditional techniques: using your hands! With this, you will first need to duplicate the diagnostic wax-up, so as to leave the original wax-up undisturbed. The easiest way to duplicate a wax-up is to soak the model in very soapy water until it is saturated, then make a traditional alginate impression of the model and pour the impression in stone. This stone model of the diagnostic wax-up will be used to add “bulk-out” wax to help account for the shrinkage of the provisional material.

When working with provisional materials, it’s important to remember that virtually all of them shrink. I typically make my shells out of a BisAcryl type of provisional material, although any material can be used. If we don’t account for the shrinkage of the material, the shell may shrink to such a point that it won’t fit around the margins of the preparation. In order to overcome any shrinkage, a small layer of wax is applied over the cervical 1/3 on both the facial and palatal surfaces of the teeth on the duplicated model of the wax-up. The thickest portion of the wax (~1/2 mm) is started on the gingival margin and then feathers down to nothing in the junction of the cervical and middle 1/3s.

End on the Gingival Margin
It should be noted that the gingival portion must not end on the tooth but rather on the gingival margin itself. This will enable the cervical 1/3 to be over-contoured compared to the original wax-up and in the process, help accommodate any shrinkage of the material. Doing this on a stone model of the wax-up better allows you to visualize where the bulk out wax is applied and how much is placed. Once completed, a putty impression of the “bulked out” model can be taken.

At this point, rather than lightly prepping the model and using the putty as a matrix carrying the material back to the model, I will inject the provisional material into the putty itself.  Essentially, the provisional shell will start out in more of a “block form” and then have to be trimmed and hollowed into “shell form” after it sets. Why do I choose to do this rather than lightly prep the model and seat the matrix over the preps? Because BisAcryl tends be a rather brittle when it is very thin and will typically end up breaking when you first try to remove it from the model.

In the next article in this series I discuss trimming the eggshell provisional.

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Creating Gingival Harmony

Many patients who have changed their smiles by restoring their teeth are quick to notice a discrepancy in the tooth length/gingival margin on even a single tooth. In the absence of a soft tissue grafting procedure, they would have had to tolerate a longer looking tooth.

When we restored with PFM restorations, we could build pink porcelain onto the metal framework and create gingival harmony; however, I've recently been informed that this can be done on lithium disilicate restorations also.

My patient was thrilled that despite all the implants, grafting procedures and pink ceramic on her bridgework in the posterior quadrant, that she wouldn't have that “long" eye tooth by having an all-ceramic crown with pink at the margin.

This is an excellent option when treating a gingival recession case. A smile improves dramatically when we don't have to seat long restorations apically.

Mary Anne Salcetti, DDS, PC, Spear Education Visiting Faculty. [ www.maryannesalcettidds.com ]

Placing Composite in Large Non-Carious Cervical Class V Lesions

We all have had large non-carious cervical lesions to restore on the facial or buccal surfaces of teeth. The challenge in finishing them is usually over adjusting when removing the excess in two directions (cervical 1/3 and facial 1/3). This often results in a less than desirable root form when finished.

I have always used this end (see photo) of the composite instrument to place composite and condense it when restoring posterior Class II preparations. I have discovered that it is the perfect shape for smoothing down the last application of composite on large Class V lesions.

When held against the cavosurface margin to the gingival margin it shapes the composite so nicely that there remains almost no other finishing to be completed.

Restorative Treatment Option for Ankylosis in Young Patients

Limited treatment options are available for young patients that have ankylosis of teeth after traumatic avulsion and re-implantation. Generally, we choose to treat these patients by extracting the ankylosed tooth prior to the patient entering their growth phases so as to minimize the potential bony defect. However, since many variables exist each situation must be evaluated individually to determine the most appropriate treatment option.

Take for instance the 14-year-old female in the photograph; she had a traumatic injury at the age of nine that caused her right central to be avulsed. What the literature reveals is that the longer the tooth is kept out of the mouth, the incidence of ankylosis increases dramatically. Ideally, the tooth should be re-implanted within 15-18 minutes to help decrease the chances of ankylosis. In this situation, the tooth was found and re-implanted within an hour.

Now, at age 14 it can be verified radiographically that the tooth has ankylosed as well as esthetically by comparing the discrepancies in the gingival margin and the incisal edge positions. The good news is the ankylosis is occurring at a very slow rate (this was verified by comparing radiographs and clinical images taken from the age of nine through the age of 14). What treatment options do we have for this patient?

What this patient currently has is an esthetic problem because of the discrepancies in the incisal edge and gingival margins. What we know is that at the age of 14, she is near the completion of her growth phase, meaning that most of the damage from the ankylosis and eruption during growth has already taken place. We’ve also established that although replacement resorption is occurring, it is occurring at a very slow rate.

In evaluating her smile line, it was noticed that she has a low smile line with less than average lip mobility. Her lip mobility was such that she didn’t show the gingival margin of the teeth during either a posed or spontaneous smile. Given this information, the treatment option chosen was not to extract the tooth, but rather keep the tooth and add length to the incisal edge. Simply bonding composite or placing a veneer on the tooth will address the esthetic component in this case. The tooth can later be extracted and the ridge grafted for implant placement at any time (either after growth is complete or at a later date when the progression of the replacement resorption necessitates treatment)

What I hope you’re realizing is that rather than just “extracting” the ankylosed tooth, many factors need to be taken into consideration when treating young patients that have undergone traumatic avulsion. We not only have to manage the site at the time of the trauma, but also continue to manage the area until the patient has reached an age suitable for implant placement whether the tooth has been extracted or maintained. However, it must be noted that depending on the age of the patient and the potential for growth, it is typically advisable to extract the tooth (or decoronate the tooth) before the patient enters their growth phase so as to minimize the potential bony defect.

Ridge Evaluation of Ovate Pontics

The goal of an ovate pontic is to create the illusion that the tooth is emerging from the gingiva with a cuff of tissue surrounding it on the facial. In order to achieve this, it’s necessary to identify when an ovate pontic is possible and when it is not.

In fact, the ridge the patient has and whether it is adequate or can be grafted determines the feasibility of an ovate pontic. There are three things we look at in order to decide whether the ridge is adequate, or if it would need augmentation to accommodate the pontic.

1. Interproximal height: If we drew lines on this patient’s photograph between the natural teeth and the height of the papillae in the pontic area, it shows what appears to be a vertically deficient ridge.

The condition of the ridge can be very deceiving however because this particular pontic is sitting on top of the ridge casting a very dark shadow interproximally. To actually evaluate the interproximal height of the ridges, this patient’s bridge needed to be removed to expose the real tissue height. After doing that, the tissue was revealed to be adequate in height vertically towards the palatal aspect of the ridge, but deficient in height towards the facial.

2. Free gingival margin: If we compare the tooth that is present (right central incisor) with the tooth that’s missing (left central incisor) it’s revealed that the pontic is shorter than the natural tooth. However, the only reason it is shorter is because it’s rolled in with an extreme convexity. If this particular pontic had the correct contour, it would be significantly longer than the adjacent tooth.

3. Facial prominence: The most important view to look at is down from the incisal. Because the tissue has to be facial to the pontic to make it seem like the pontic is emerging out of tissue instead of resting on top of it. The cervical portion of the tooth is where the white line is; the right central and left lateral have at least another 1-1.5mm of gingiva facial to that line. In the pontic area the tissue is lingual to that line, which is causing that dark shadow. This ridge needed to be augmented significantly on the facial to allow an ovate pontic to be created and make the pontic appear like a natural tooth growing out of that tissue.

The augmentation for this patient was done with a connective tissue graft to make the ridge prominent enough to embed the pontic and produce a natural appearance.