Introduction

Dental Anatomy refers to tooth morphology, location and position, and their relationship to dental occlusion and the other components of the masticatory system (e.g., jaw bones, temporomandibular joint, gingivae, and neuromuscular components) during function and dysfunction. Dental anatomy is also an important determinant for an esthetic smile. Therefore, the knowledge of dental anatomy is fundamental for the preservation and restoration of a physiologic and esthetic occlusion that is in harmony with the functions of the masticatory system. This dental procedures education system (DPES) video provides step-by-step instructions of waxing-up and carving teeth using an electric waxing instrument that can facilitate the development of manual dexterity for the fabrication of correct dental anatomy¹.

Background and Objective

As part of the Dental Anatomy laboratory assignments, dental students practice waxing-up teeth with missing tooth structure in order to restore correct dental morphology. Each assignment simulates a different clinical situation in which a clinician needs to restore missing tooth structures in the deciduous or permanent dentition. Such exercises can improve students’ psychomotor skills² while acquiring the knowledge needed to identify teeth, their normal anatomy³ and possible morphological variations.

The purpose of this article is to present educational material that will allow dental students understand and apply principles of tooth morphology by waxing-up cast models.

Procedure

Armamentarium:

• Cast molds with preparations on anterior and posterior teeth for direct and indirect restorations.
• Ultra-waxer 2 (Kerr) with the following heating tips (spatulas):
  • Small PK Thomas, blue
  • Large PK Thomas, Teal
  • Needle, Red
  • Half Hollenback, Black
• Small alcohol Torch: This alcohol torch produces a needle-point flame with only a gentle squeeze of the plastic bottle. It is useful in applying heat to small and localized areas of the wax. Either ethyl or methyl alcohol may be used as a fuel.
• Sharp red pencil.
• Clear nail polish or liquid Vaseline.
• Inlay casting wax: This pattern material accurately represents desired mold space for inlays, onlays, and crowns.
  • Optimal characteristics of a casting wax include:
    • good adaptation
    • homogeneity
    • thermal stability at ambient temperatures
  • General composition:
    • ̴60% Paraffin Wax (base wax)
    • ̴25% Carnauba Wax (modifier wax)
    • ̴10% Ceresin (modifier wax)
    • ̴05% Bees Wax (modifier wax)
    • <1% Colorants
• Dental explorer: A sharp and pointed dental instrument used to conduct tactile examination and appraisal of teeth pits and fissures, carious lesions, root surfaces, and margins of restoration.
• PK Thomas waxing instrument #3: Used to perfect and enhance the supplemental grooves and developmental grooves.
• Half Hollenback instrument: Used for carving and shaping the wax.
• LeCron instrument: Has a small spoon at one end and a ‘knife’ at the other. Used for carving and trimming wax.
• Wax spatula #7: Used to hold small bits of wax over the flame.

Procedure Description

• Cover your work area with a white paper so that you do not get wax spills on the counter.
• Mark the cavity margins with the red pencil to clearly identify them all around.
• Apply nail polish or liquid Vaseline outside of the cavity preparation to make the surface impermeable to wax.
• Operation of Ultra-Waxer 2 (for more details refer to the manufacturer’s instructions brochure):
  • Connection: plug power cord into the back of the unit and connect two heating tips by inserting them into the jacks on the front of the unit.
  • Touch pad operation: use enter button for power off/on; use up/down buttons to scroll through equipment options; use menu button to access different applications.
  • Heating tip operation: to remove tip, retract the blue collar of the tip handle (0.3 cm) and gently remove the heating tip in the opposite direction. After replacing the heating tip, use the quick heat feature (it will bring the cold tip to a working temperature).
• Insert wax to preparations: Use PK Thomas instruments or wax spatula #7 to carry wax to the tooth preparation. The instruments should be adequately heated and the wax added to the preparation in small amounts to avoid trapped bubbles as wax starts to cool and gain viscosity. If the wax is too hot, it will flow all over the preparation without control. Sink the heated instrument down to the base of the preparation when melting a new wax layer to the previously placed wax, so that they do not separate during carving. Using the heated half Hollenback waxing pen, start building up contact areas, embrasures and marginal ridges, tooth outer surfaces, then cusps and cusp ridges. Add a slightly greater amount of wax than that needed to restore tooth morphology (0.5 to 1.0 mm above margins). Make sure all margins around the preparation are properly sealed.
• Carving: Use the wax carving instruments to refine the tooth morphology. PKT #3 is good to enhance grooves. The LeCron and the manual half Hollenback will refine the whole morphology, removing all flash and excess material so that no wax is extending over the pencil mark. Lay the sharp cutting side of the manual half Hollenback carver on a cusp (around 45° inclination) with the point of the instrument in the groove at the centre of a tooth. Scrape away the excess wax following the line of the cusps. This will give you a proper groove anatomy as well as shaping the cusps correctly. You will aim to mimic the mirror image of the same tooth in the adjacent quadrant. The marginal ridges should be at the same level as the adjacent teeth. You can check if you carved your wax enough by occluding your upper and lower models together. If they do not occlude properly (i.e., seem too high or are contacting more on the side of the preparation) you will need to reduce the height of the wax.
• Finishing: In the presence of voids or if too much wax was removed, add an additional amount of wax by repeating step 5 and re-carving. Polish your restoration with a toothbrush, gauze, and/or a piece of nylon or cotton.

General wax-up characteristics:

• Margins: Wax should be flush with the margin of the tooth preparation with no overhangs, sub margins or open-margins.
• Contour: Should be smooth and curved with no flat (under) or bulbous (over) contour.
• Outer surfaces (facial, lingual, mesial, distal): Should respect proper convexity, appear smooth, even and polished (with no scratches, waviness or voids).
• Morphological structures: All ridges, fossae, cingulum area and grooves should exhibit a polished surface with no scratches. The junctions between these structures should flow naturally.

Instrument care:

• Always keep your instruments clean and sharp.
• PK Thomas #3 and wax spatula #7 can go into the flame.
• Dental explorer, manual half Hollenback and LeCron should not go into the flame. They might lose sharpness or break.

Research and Clinical Implications

Clinically, the preservation of the anatomical features of teeth such as height of contour, embrasures, proximal contacts and contour are important to protect and ensure the health of the surrounding soft tissues. Adequate interproximal contacts serve to anchor all teeth within the same arch, to avoid tooth migration or inclination and avoid food trapping between the teeth. Proper occlusal anatomy and interocclusal contacts confer comfort to the patient as well as harmony and stability of the occlusion. Harmonious incisal planes, anterior lines and point angles, and overall anatomy relate especially to patients’ aesthetics but also functional satisfaction. Therefore, the knowledge and maintenance of tooth morphological characteristics will certainly lead to restorations with improved aesthetics and oral functions.

Don’t forget: the more you practice the better you get!

References:

1. Wax-up Technique DPES-Pro
2. Obrez A, Briggs C, Buckman J, Goldstein L, Lam C, Knight WG. Teaching clinically relevant dental anatomy in dental curriculum: description and assessment oa an innovative module. Journal of Dental Education 75:797-804; 2011.
3. Nayak MT, Sahni P, Singhvi A, Singh A. The perceived relevance of tooth carving in dental education: views of practicing dentists and faculty in west India. Education for Health 27:238-242; 2016.