Curve Of Wilson

L, Lingual; 0, distal; M, mesial; B, buccal; C, central. ( Courtes if Dr. A. G. Gegaujf.)

fossa (see Figs. 18-28, H to K, Fig. 18-31, and Tables 18-1 and 18-2).

Evaluation (Fig. 18-32). The cones should be positioned so they follow an anteroposterior curve (the curve of Spee). The mandibular cusps should become taller farther distally, and the maxillary cusps should become shorter. They should also follow a compensating plane (the curve of Wilson) when viewed from the front, with the noncentric (or nonfunctional) cusps slightly shorter than the centric cusps. All eccentric movements should be reproduced on the articulator; if unwanted contact results in protrusive, working, and nonworking excursions, they should be eliminated by either reducing or repositioning the cones. Proper cone height and position are the key to proper occlusal form.

Completion of Axial Contours (Fig. 18-33).

4. Complete the axial contours (marginal ridges and cuspal ridges). Be especially careful not to alter the location or height of the cusps as previously determined with the cones.

5. After each addition of wax, check for occlusal contact by closing the articulator. Do not increase the vertical dimension of occlusion.

Evaluation. At this stage, the buccal, mesial, lingual, and distal surfaces have been completed (see Fig. 18-33, D and E). When viewed from these perspectives, the wax pattern should appear identical to an intact tooth. When viewed from the buccal perspective, each cusp should have a distinct profile, with the cusp tip highest and a gentle slope down to the marginal ridges. Adjacent marginal ridges should be of the same height. Occlusal contacts in excursive movements must also be evaluated. If there is unwanted contact, grooves can be created in the cuspal ridges to allow the passage of opposing cusps.

Triangular Ridges (see Fig. 18-28, A, and Fig. 18-34)

6. Give each cusp a triangular ridge that runs toward the center of the occlusal surface. The apex (or point) of the triangle should be at the

Guiding Non Centric CuspsCurve Spee
Fig. 18-31. A, Cusp-marginal ridge occlusion. B, Cusp-fossa occlusion. (The numbers refer to Tables 18-1 and 18-2.)
Wilson Curve Occlusion
Fig. 18-32. Cones should follow an anteroposterior curve (of Spee) and a lateral curve (of Wilson).

cusp tip, and the base should be in the center of the occlusal surface.

7. Make the bases of the buccal and lingual triangular ridges convex mesiodistally and buc-colingually.

8. As each ridge is added, close the articulator. Where the occlusal surface meets an opposing tooth, note the small depression and ad j ust this to form a convex surface so that pinpoint contact exists.

Evaluation (see Fig. 18-28, B, and Fig. 18-35). The triangular ridges are dusted with zinc stearate or powdered wax. The cusps should still have their correct sharp contour and should not be rounded by improper polishing.

Secondary Ridges (see Fig. 18-28, F, and

9. Make two secondary or supplemental ridges adjacent to each triangular ridge. All cusps should have a single triangular ridge and two secondary ridges. The degree of specific delineation between the triangular and secondary ridges varies, depending on the prominence of the cusp within the occlusal table of the tooth that is being waxed.

Occlusal Buccal DistalOcclusal Buccal Distal
Fig. 18-33. Completing axial contours. A and B, Add the maxillary buccal cusp ridges. C, Add the mandibular buccal cusp ridges. D and E, At this stage, the buccal surface is complete and should be evaluated for correct contour.
Occlusal Diagram Tooth
Fig. 18-34. Waxing maxillary triangular ridges.
Occlusal Buccal DistalTriangular Ridge Tooth

10. Make the secondary ridges convex with grooves where they meet the convexities of the triangular ridges. The most mesial and most distal secondary ridges are often contiguous with the marginal ridges.

Evaluation (Figs. 18-37 and 18-38). If the ridges have been carefully formed, only a small amount of finishing will he needed at this stage. Any pits can he filled with wax and the grooves carefully smoothed (see Fig. 18-28, G). Initially, obtaining smooth transitions between the occlusal components may be difficult. Smoothing from the grooves onto the individual occlusal features, rather than back and forth, prevents unnecessary accumulations of wax residue in the grooves.

The occlusal surfaces are redusted with zinc stearate or powdered wax, and the occlusal contacts are checked. If a contact has inadvertently been polished away, it can be quickly re-formed by adding a drop of wax, closing the articulator to verify that contact was restored, and subsequently reflowing and reshaping the occlusal feature to reestablish a convex contour.

Margin Finishing. To optimize the adaptation of the wax pattern (and the cast restoration) to the die, the margins must be reflowed and refinished immediately before investing the wax pattern. The two principal objectives are (1) minimizing dissolution of the luting agent and (2) facilitating plaque control.

If a zone of superior adaptation (i.e., minimum marginal gap width) between the casting and the prepared tooth surface is created, cement dissolution will be reduced.27 To obtain this superior adaptation, the pattern should be reflowed over a band approximately 1 mm wide, measured from the margin onto the prepared surface (Fig. 18-39).

Plaque control is facilitated by producing cast restorations that exhibit a smooth transition from

Fig. 18-37. Evaluating the completed wax patterns.

(CourtesyDr. A.G. Gegauff.)

Marginal Ridge Tooth
Fig. 18-38. Completed cusp-marginal ridge waxing. The occlusal contacts have been marked.

restoration to tooth without any sudden directional change. In addition, the axial surface of the restoration must be highly polished (see Chapter 29). Because the use of any metal polishing compound or abrasive will result in removal of material, metal finishing procedures should be kept to a minimum near the margin. The best way to prepare for this step is to ensure superior smoothness of the wax pattern when the Rflowing process is complete. This should be verified under magnification with loupes or a binocular microscope.

Fig. 18-39. Reflowing the margins. The objective is to create a well-adapted, 1-mm zone to prevent cement dissolution.

Step-by-step Procedure

1. Relubricate the die and reseat the wax pattern (Fig. 18-40, A). Because of the time and attention devoted to developing occlusal and axial form, the margins of the pattern are not properly adapted at this stage. A large, well-heated waxing instrument is used to melt completely through the wax.

2. Push the heated instrument through the pattern and completely remelt the marginal 1 to 2 mm (Fig. 18-40, B).

3. Draw the instrument along the margin until resistance is felt because the instrument has begun to cool and no longer easily melts the wax.

4. Reheat the instrument and repeat the procedure, always overlapping with the previously melted area to remelt it and to preclude internal folds, voids, and defects. When the entire margin has been reflowed circumferen-tially, a depression will be seen around the margin as a result of the readaptation.

5. Fill the depression with additional wax (Fig. 18-40, C.

6. Trim excess wax from beyond the margin (Fig. 18-40, D).

7. Rectify any pits or defects in the axial surfaces and smooth the wax pattern. Wax chips can be removed from the occlusal surface

Marginal Discrepancy

Fig. 18-40. Reflowing margins. A, After waxing, a marginal discrepancy is normally apparent (arrow). This must be corrected before investing. B, Use a large, well-heated instrument to melt completely through the wax. C, Continue around the preparation margin; then add wax to fill the depression. D, When the pattern has cooled, carefully trim or burnish the marginal excess.

Fig. 18-40. Reflowing margins. A, After waxing, a marginal discrepancy is normally apparent (arrow). This must be corrected before investing. B, Use a large, well-heated instrument to melt completely through the wax. C, Continue around the preparation margin; then add wax to fill the depression. D, When the pattern has cooled, carefully trim or burnish the marginal excess.

with a cotton pellet; however, the surface should not be rubbed. Otherwise, the occlusal contacts that were so carefully generated will be destroyed.

The wax pattern is removed from the die without distortion and replaced for final evaluation before investing.

Evaluation. Being thorough at this stage will pay dividends later. Because of the wax pattern's color and glossy surface, small defects can be difficult to identify. If they are not noticed, a later remake may be necessary.

NOTE: Avoid overwaxing. Very little finishing of a cast metal margin is possible without damaging the die. Any flash of wax that extends beyond the finish line must be trimmed. Otherwise, it will cause distortion as the pattern is removed or prevent the cast metal restoration from completely seating. A gap between the wax and the die, resulting in an open margin, can be difficult to detect. The die should be oriented so that the observer's line of sight is precisely along the wax-die interface. If the wax is not well adapted, a black shadow line will be visible. This is hard to see in wax but easier to see (but too late) in metal. A binocular microscope or loupe is very helpful for this stage (Fig. 18-41). To ensure that new debris has not accumulated during the finishing procedures, a final evaluation of the occlusal and axial surfaces is performed. The pattern is now ready for investing. (See Chapter 22.)

Waxing Inlays and Onlays (Fig. 18-42). The sequence of steps for fabricating a wax pattern for an inlay or onlay is similar to that for a complete crown, although the unprepared tooth can often serve as a guide to axial and occlusal contour. Sometimes manipulation of a small inlay can be difficult. One approach is to embed a loop of floss into the pattern for easier removal (Fig. 18-42, E).

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Responses

  • sebastian
    How to carve the occlusal surface of tooth on wax?
    8 years ago
  • gundahar banks
    What are the centric cusps?
    8 years ago

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