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A Step-by-Step Approach to Natural Morphology
Documenting a technique that emphasizes the method of application and a pattern of repetition
In years past, there was a definitive difference between laboratories focused on producing high-quality restorations and laboratories focused on high volume with average quality. Due to the evolution of materials and their esthetics, the difference in “high quality” and “high volume” has become marginal in many ways. Yet many hold onto the mindset that the two are mutually exclusive. It is still common to think that a quality technician is usually slow, and a high-producing technician usually produces lower-quality restorations. This could not be further from the truth, as long as each type of technician has a standard operating procedure (SOP).
The truth is, a technician who knows morphology can produce a restoration more quickly than one who has to “bounce” around a full-contour wax-up or buildup trying to make it look like a tooth. Creating a restoration is a step-by-step process, and creating a restoration that looks natural has a step-by-step procedure as well. Posterior anatomy that has a “natural” appearance is created through technique. The following article documents a simple approach to creating “a natural appearance” using a technique that focuses on correct instrumentation combined with correct application of materials.
The purpose in documenting this technique is to emphasize a method of application, a pattern of repetition, a SOP. Therefore, no opposing teeth will be included, allowing the primary focus to be on the technique of building a tooth and not the occlusal aspects of the fabricated restoration. Regardless of the materials used for fabrication, this technique remains the same and offers a compromise between the philosophies of high quality and high production by building or waxing to contour. Contour building of wax or porcelain requires minimal adjustments post pressing or firing.
This article will demonstrate this technique by deftly applying porcelain. In order to correctly perform or implement a procedure, understanding the principles upon which the procedure is based helps tremendously. For example, let’s evaluate a tooth’s contour and occlusal anatomy. Each is formed one of two ways—reducing down a bulk of material to create a shape through carving or grinding—such as milling—or through the building up of a material to the desired shape, such as 3D printing. The following describes a combination of building and carving. This approach requires minimal grinding and produces a more natural result than carving or grinding alone.
Dentin Build-Up Technique
The following steps should be completed first using a dentin buildup, then with an enamel buildup for the upper one-third to one-half of the restoration while gradually fading thinner down to the margin. Since the purpose of this article to emphasize production while producing high-quality, a larger size brush (lay:art #6 Slim, Renfert USA, www.renfert.com) is recommended for ceramic application other than for the occlusal anatomy. Prior to the application of any ceramic material to the substructure, each contact area should be sealed (Pico-Fit, Renfert USA) (Figure 1) to prevent the porous stone from absorbing the porcelain’s moisture during application. For the next step, simply apply dentin or deep dentin to the substructure, completely covering it (Figure 2). This is much like how a waxer creates a coping by dipping it prior to waxing full contour. As with waxing, we are now ready to begin “building” a tooth with porcelain. As with all restorative procedures, basic fundamentals of reconstruction must be met.
Step 1 As we begin building the tooth, we must first establish the plane of occlusion and arch form. Each of these planes will be achieved through building up porcelain in a series of dots, creating cusp tips that reach the same height as other cusp tips (plane of occlusion), while at the same time being in line with the contours of the adjacent dentition (arch form). Creating the cusp tips should be done on the buccal as well as on the lingual in harmony with each plane for as long as the opposing dentition allows. When applying the porcelain to create the cusp tips, keep in mind that the dots should be placed in a position that enhances the geometric shape of the dentition being restored. In this particular scenario, a “rhomboid-shaped” maxillary molar is to be built.
Step 2 The mesial and distal interproximal areas are to be filled in, thus creating the contact areas. This step not only establishes contact, but also creates corners at each interproximal on the buccal as well as the lingual. The contact area should be built up high enough to create a marginal ridge on each side of the restoration (Figure 3).
Step 3 We are now ready to connect the dots (cusp tips) and corners (interproximal ending points). This step creates the “occlusal table,” within which anatomy will be placed in a future step (Figure 4). At this stage, the occlusal parameters have been established, and now line angles and heights of contour are ready to be placed.
Step 4 Fabricating line angles and heights of contour on the buccal and lingual is quite simple. For the buccal line angles, follow the buccal cusp tips down onto the buccal at a 45-degree angle towards the center of the tooth without intersecting (Figure 5). The lingual line angles should be closer to a 90-degree angle directed towards the margin (straight). Each line angle should be built outward enough to be in arch form with the adjacent teeth. This creates the height of contour (Figure 6). A good metaphor for this step would be building the framework of a wall before putting up the wall itself.
Step 5 Next, we fill in the area between our heights of contour and our interproximal with porcelain. This step can be thought of as fabricating the actual walls upon the previously built framework. Filling in or building the “body” of the restoration should be done completely around the prosthesis (Figure 7 and Figure 8). We then detail the contours, forming a natural shape while keeping in mind our geometric shape, the plane of occlusion, and the arch form. Now the morphological shape has been created.
Step 6 In the last step, we place the anatomy within the occlusal table. Start by establishing ridges followed by the primary anatomy as usual. A fine-tip instrument is commonly used to divide lobes, segment any areas of overlapping porcelain, and map out anatomy for future enamel placement. At this point, the buildup should look complete (but with dentin porcelain) and should be slightly out of or minimally in occlusion. Adjacent dentition should be in occlusion when the articulator is closed.
The Enamel Buildup
At this point, we have created a dentin ceramic tooth. Depending on the amount of translucency required, a cutback might be necessary, but keep in mind that minimal shrinkage will occur. The addition of enamel slightly overbuilt in regards to height and contour will shrink as well. The author has found that this technique usually requires little to no cutback once the ceramist learns the material’s shrink ratio. Now, applying the same technique we used in Step 1, apply enamel porcelain in a series of dots on top of the existing cusp tips. Build the height taller than the adjacent dentition, violating the plane of occlusion about 1 mm. From this point on, the adjacent teeth should be held open by the lingual cusp tips of the enamel buildup when the articulator is closed. Be sure to adjust your pin on the articulator to this new vertical to prevent breaking the buildup in the event the articulator closes.
Now, using the same technique used in Steps 2 and 3, apply enamel porcelain to the marginal ridge areas (Figure 9 and Figure 10) and then connect the corners to the cusp tips, naturally creating the occlusal table (Figure 11). Next, create line angles and height of contour on the lingual and buccal as when we used dentin as our building material. Remember to go 45 degrees on the buccal, coming down from each cusp tip and straight down (90 degrees) on our lingual from each cusp tip. Build the line angles out beyond the adjacent dentition, violating arch form about 1 mm (Figure 12 and Figure 13). Now we are ready to repeat Step 4 and “put up our walls” around the tooth between the line angles and corners and the line angles and developmental lobe grooves on the buccal and the lingual (Figure 14 and Figure 15). Remember to fade the enamel the closer you get to the margin. Last, finalize the anatomy within the occlusal table by adding enamel porcelain on top of the dentin anatomy that was previously mapped out. Once ridges and fossa have been created within the occlusal table, use a pointed instrument to define fossa depth and pits, thus creating negative contour (Figure 16) (Pizzi Instrument Line). After defining fossas and pits, use a fine-tip brush to apply small amounts of porcelain (lay:art #2, Renfert USA) (Figure 17) on either side of where anatomy has been cut. Building up around the cut anatomy is a positive contour technique, which contributes to the illusion of natural depth and creates a much more natural look than simply “cutting” in anatomy after firing. Last, remove the crown and minimally add enamel to the contact areas and prepare for firing. Figure 18 and Figure 19 depict a first bake firing prior to any contour adjustments.
These steps detail an excellent SOP for any laboratory technician looking to create a natural-looking tooth, regardless of experience. Through repetition, the process of building porcelain will become more familiar to a novice technician. The post-firing result is much more anatomical than building teeth with no cusp tips, fossas, or ridges, and relying on grinding to create the anatomical shape. This standardization of the application process reduces the learning curve and produces more consistent results. Also, as a ceramist gains more experience, this technique can be adjusted as skill level and confidence increase. Each technician will find his or her own way to achieve the best final outcome in the most efficient manner, but starting with a standard procedure is paramount to achieving the expected final result consistently and productively.
About the author
Keith Miolen, CDT
Director of Education
Gibson Dental Designs