Posterior Teeth

The following sequence is recommended for waxing posterior teeth:

1. Internal surface

2. Wax pattern removal and evaluation

3. Proximal surfaces

4. Axial surfaces

5. Occlusal surfaces

6. Margin finishing

Internal Surface. Forming a closely adapted internal surface is the first step in waxing. The wax must reproduce all retention features of the restoration.

Step-by-step Procedure

1. Apply die lubricant generously with a clean brush (Fig. 18-15, A). Allow it to dry and paint on a second coat (repeat periodically as needed). Waxing should not begin until the lubricant has soaked in completely.

2. Where pinholes have been prepared, fit in plastic pins that match the bur used to sink the hole. Seat the pins in the die and use a heated no. 7 instrument to flatten their tops to provide retention (Fig. 18-15, B).

3. Flow wax onto the die from a well-heated, large waxing instrument (Fig. 18-16, A), making sure that any previous application is par tially remelted. A large instrument will hold sufficient heat to partially remelt previous wax increments and to prevent folds or lines from developing in the fitting surface. Wax-

Fig. 18-15. Starting the waxing procedure. A, Lubricating the die. B, Adapting plastic pins.

Fig. 18-16. Forming the initial copings. A, Use a large instrument to keep the wax sufficiently hot. Ensure that previous applications are remelted as additional wax is added. B, Build up adequate bulk for rigidity. C, Build up the second coping while allowing the first to cool thoroughly. D, Trim the wax very carefully to the margin.

Fig. 18-16. Forming the initial copings. A, Use a large instrument to keep the wax sufficiently hot. Ensure that previous applications are remelted as additional wax is added. B, Build up adequate bulk for rigidity. C, Build up the second coping while allowing the first to cool thoroughly. D, Trim the wax very carefully to the margin.

ing will be easier if the instrument is kept clean and only its shank is heated.

4. When applying the initial layer, be sure that the wax is fully molten. If it is not, wax "memory" may cause distortion. Very hot wax flows rapidly over the die. Subsequent waxing of external anatomic details is accomplished with cooler instruments, which allows small additions to be placed accurately. Dipping the lubricated die in a pot of melted wax is an alternative method for making well-adapted internal surfaces (Fig. 18-17). This method is particularly suitable for complete-coverage restorations.

Fig. 18-17. Wax dipping pot.

5. Add sufficient wax with a large instrument to allow the coping to be handled without deformation or breakage (Fig. 18-16, B). A large instrument will keep the wax hot more effectively than a small instrument.

6. Give the proximal areas extra bulk to help grip the coping and prevent its distortion when it is removed from the die. The wax should cool between applications (Fig. 18-16,

C). At this point, no attempt should be made to contour the axial walls.

7. Trim the wax back to the margin (Fig. 18-16,

D) so the coping can be removed and evaluated. Excess bulk can be removed safely with a carving instrument. When only a thin ex

Posterior Tooth
Fig. 18-18. Wax pattern removal. A, A sheet of washed rubber dam increases friction and aids removal. B, The fingers of the left hand hold the die. The right hand holds the pattern. C, The die is pulled from the pattern by bending the fingers of the left hand.

cess layer remains, trimming is performed most safely with a burnisher. Careless use of a sharp carver at this stage may scratch the fragile margin of the die or chip it. Therefore, a slightly warmed blunt instrument should be used and the margins rubbed with a burnishing action. A carver can be used but requires meticulous technique and great care.

Wax Pattern Removal (Fig. 18-18). The wax should be allowed to cool thoroughly before the coping is removed from the die. A constant light grip is maintained on the pattern by the thumb and forefinger of one hand while pressure is applied against them with the thumb and forefinger of the other hand, which also holds the die (Fig. 18-18, B). A small square of washed rubber dam will increase friction between the fingers and the pattern. If the pattern fails to move, there may be excess wax gingival to the margin.

Evaluation (Fig. 18-19). The objective of the first waxing step is a perfectly adapted reproduction of the prepared tooth surfaces. Identifying defects may take some practice. The examiner rotates the pattern under a bright light and looks for shadows formed by folds or creases. A binocular microscope or high-quality magnifying loupe is helpful not only for this step but also throughout the laboratory phase. Ten-power magnification is practical

Tooth Surfaces Maganified
Fig. 18-19. Evaluation. A, Well-adapted pattern. B, Poor adaptation. Folds and creases (arrows) indicate that wax was not hot enough when applied.

and helpful. Using higher power makes maintaining orientation a problem.

Proximal Surfaces (Fig. 18-20). The proximal surfaces of natural teeth are not convex. They tend

Size Posterior Teeth
Fig. 18-20. Proximal surfaces gingival to the contact area are normally flat or concave. Note the triangular shape of the posterior embrasures.

to be flat or slightly concave from the contact area to the cementoenamel junction, and any restoration must reproduce this feature. Overcontouring often makes maintaining periodontal health difficult, particularly if drifting of teeth has led to increased root proximity. Excessively concave or undercontoured proximal surfaces also make flossing ineffective and must be avoided. 16

Contact Areas. The size and location of the contact areas should be established before waxing the remainder of the proximal surfaces. Reference is made to contacts between the contralateral teeth and knowledge of anatomic form.

Abnormally large proximal contact areas make plaque control more difficult and can lead to periodontal disease. Very small (point) contacts may be unstable and cause drifting. Deficient contacts can also lead to food impaction; although this is not a direct cause of chronic periodontal disease, it can be very uncomfortable and painful to the patient.

Most posterior contact areas (Fig. 18-21) are located in the occlusal third of the crown. However, contact between the maxillary first and second

Occlusal Food Impaction ToothProximal Contact Areas MaxillaryOcclusal Food Impaction ToothTooth Occlusal Contact Points

Fig. 18-21. Location of the proximal contact areas. A, On maxillary teeth-progressively more occlusal and buccal when progressing anteriorly. B, On mandibular posterior teeth-centrally located.

molar occurs in the middle third." The contact areas between mandibular teeth and maxillary molars are generally centrally located. Between maxillary premolars and molars, the contact areas are usually toward the buccal surface (making the lingual embrasure larger than the buccal).

Step-by-step Procedure

1. Replace the wax coping on the lubricated master cast or removable die. When a removable die system is used, extreme care must be taken to ensure that the locating pin and stone surfaces are absolutely free of excess wax or other debris that could prevent complete seating of the die (e.g., small stone particles) (Fig. 18-22).

2. Adjust the coping as necessary to be completely clear of the opposing occlusal surfaces. They will be developed with a wax additive technique later.

3. Add wax to the contact areas until they are the correct size, properly located, and consistent with anatomic form (Fig. 18-23).

4. When this has been accomplished, shape the proximal surfaces gingival to the contacts to the correct contour. A properly trimmed die is of great assistance in accomplishing this. The unprepared tooth structure that was reproduced in the "cuff" of the impression now serves as an effective guide to orienting the waxing instrument properly.

Evaiuation. The location of the contact area is checked once again. Where multiple restorations are being made, the proximal embrasure is shaped symmetrically to provide adequate room for the free gingival tissues of adjacent teeth (Fig. 18-24). The proximal surfaces should be flat or slightly concave and should be shaped to eliminate any directional change between the root surface and the finished restoration. The cervical contour of the restoration should be continuous, with the contour

Tooth Height Contur
Fig. 18-22. Wax chips that accumulate on the dowel pin or in the sleeve will prevent a die from seating. Periodic cleaning with a brush is recommended.

of the unprepared tooth structure immediately cervical to the preparation margin.

Axial Surfaces. The buccal and lingual surfaces should be shaped to follow the contours of the adjacent teeth. The location of the height of contour (or survey line for retainers for removable partial dentures) is particularly important. It is generally located in the gingival third of most teeth, although on mandibular molars it is usually in the middle third of the lingual surface.

Restorations are often made too bulky. Natural teeth are rarely more than 1 mm wider at their height of contour than at the CEJ. This should not be exaggerated when recreating a tooth in wax. The tooth surface gingival to its height of contour i mmediately adjacent to the gingival soft tissues, sometimes called the emergence profile,18 is usually flat or concave. Creation of a convexity in this area or a shelf or ledge19 makes bacterial plaque removal difficult and has been shown to cause inflammatory and hyperplastic changes in the marginal gingiva. Before dental plaque was identified as the direct etiologic agent in periodontal dis-ease,2° an excessive axial contour was considered necessary to keep food from entering the gingival sulci." However, there is no evidence to support this concept. Indeed, artificially reduced axial contours (as when a prepared tooth is left unprotected for an extended period) 22 are associated with

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  • manuela
    How to carve posterior teeth by wax in lab.?
    8 years ago

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