Morphology: Traditional Wax-up Technique for Anterior and Posterior Teeth

Jan 01. 2021

Advancement of CAD/CAM technology has been a game-changer for both dental clinicians and technicians. It provides consistency with natural anatomy and aesthetics in the production of dental prosthetics without the possessions of highly trained hands-on technical skills.

Understanding the anatomy of natural dentition – morphology – in depth is, however, essential for all dental professionals. The traditional way of reproducing teeth in wax remains critical as a way of training because the knowledge and technique are utilised in the application of composite restorations, diagnostic wax-up, and better understanding in the aesthetics and functions.

The following technique is what I presented at King’s College London for a postgraduate masters course in Prosthodontics and Aesthetics candidates, and was well received with high praises.

Model Preparation:

After the fabrication of the model, mark the sectioning lines on the model. The line should be drawn in all aspects – labial (Fig 1), palatal and radix (Fig 2).

Use either a handsaw (Fig 3) or a diamond separation disc for separation (Fig 4). When the margins are close with each other, use a scalpel blade first to cut and navigate the separation line.

Trim the margin in two steps. First, with a carbide bur, being away from the margin by 1mm or so (Fig 5). Then the precise trimming can be made using a silicon wheel with no more than 10,000rpm (Fig 6).

Mark the defined margin with a red pencil (Fig 7).

Now we can start the preparation for the wax-up. Apply two layers of the die spacer (Fig 8). Apply the second layer after the first layer is dried out. It should also be away from the margin by 1-2mm, and this step serves as the cement gap in actual cases (ideal cement gap is around 30-50 μm).

Protect the margin by applying a die hardner (Fig 9). I do this step after the die spacer so that the spacer won’t peel off from the die. Then lube is applied to prevent the wax from sticking with the die (Fig 10).

Air-dry the excess lube (Fig 11), and now it is ready for the commencement of the wax-up of initial coping. I always start with the cervical wax; which has a decent softness/stickiness (i.e., not brittle) with little shrinkage (Fig 12).

Apply subtle finger pressure until it cools down (Fig 13). The shrinkage occurs the most with the temperature change of the material, so the subtle presser holds the wax in the right place with minimum deformation. Upon completion of the wash layer, I use a sculpturing wax over the initial layer (Fig 14). The characteristic of the wax is more brittle, but it is suitable to form the desired shape with an appropriate hardness to carve the material in detail.

Again, apply subtle finger pressure while it’s cooling down (Fig 15). No need to continue this step further, as this initial coping is instead purely for the clean and smooth internal surface that affects the fit of the restoration. Fig 16 shows the quality of the fitting surface of the initial coping.

Now, moving on to the master / solid model, I apply a separator on the contact points (Fig 17), then air-dry it (Fig 18). I’m not a big fan of using the pinned model as once it’s sectioned, it loses the accuracy in the contacts (horizontal inaccuracy) and the occlusion (vertical inaccuracy).

Anterior Wax-up:

Fig 19 a-c shows the master model. The image on the left indicates the labial view, the middle image is from the incisal perspective, and the one on the right shows the palatal view.

Transfer the initial coping onto the master model (Fig 20 a-c).

I always start with the contact points (Fig 21 a-c). Note the difference in height between the mesial and distal position.

Determine Ideal incisal edge position (Fig 22 a-c).

Determine labial marginal ridges (Fig 23 a-c).

Fill the middle 1/3 of the labial surface (Fig 24 a-c).

Determine palatal marginal ridges (Fig 25 a-c).

Complete palatal aspect without trimming (Fig 26 a-c).

Complete labial aspect (Fig 27 a-c). Note that I haven’t trimmed to this point – additional only. Adapting to this technique is essential because I apply the same protocol on the application of ceramics and composite resin. Additive preserves the colour; trimming gets rid of the colour.

Finally start trimming the tooth to mimic the adjacent dentition. It should be minimum, and then add some details following the natural anatomy/morphology (Fig 28 a-b).

Smooth and polish the surface with a brush (Fig 29) and tissue paper if necessary for high gloss effect when necessary. Don’t forget to check the bite/occlusion (Fig 30).

Fig 31 a-c shows an example of completed anterior wax-up.

See the video of ‘Anterior wax-up – labial’:

See the video of ‘Anterior wax-up – incisal’:

See the video of ‘Anterior wax-up – Palatal’:

Posterior Wax-up:

Fig 32 a-c shows the master model. The image on the left indicates the buccal view, the middle image is from the occlusal perspective, and the one on the right shows the palatal view.

Transfer the initial coping onto the master model (Fig 33 a-c).

Determine the ideal position of the cusp tips (Fig 34 a-c).

Determine the ideal position of the cusps and interproximal marginal ridges (Fig 35 a-c).

Fill the buccal surface (Fig 36 a-c).

Fill both palatal and interproximal area (Fig 37 a-c).

Fill the occlusal surface, and determine the main grooves and pitts (Fig 38 a-c).

Complete all aspects – buccal, occlusal, palatal – without trimming (Fig 39 a-c) – i.e., it is only additive as explained in the anterior example. It is at this point that I start sculpturing and finalising the shape, then check the occlusion in the end (again, following the protocol in the composite build-up or ceramic layering technique).