Dental Dentures: Partial | Cosmetic Dentistry
Dental Dentures
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8.4.3 Anchorage with Telescoping Attachments part 2
 101 (Partial Dentures: Anchorage with Precision Attachments) The telescoping denture base is fabricated without a separate lingual bar. Therefore, the lingual walls of the secondary crowns and the occlusal surfaces must be adequately sturdy. The retentive framework here is designed to lie under the artificial teeth, similar to a typical saddle retention latticework (Fig. 101). The connection between the retentive framework and the secondary crowns must be as thick as possible in the gingivo-occlusal dimension
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 102 (Partial Dentures: Anchorage with Precision Attachments) The two retentive frameworks are soldered together at the anterior midline. Proximal flares are not waxed up on the secondary crowns. The labial and occlusal surfaces are designed with retentive beads for the acrylic veneer (Fig. 102). The secondary crowns and saddle retention exhibit all the characteristics of a typical cast denture base. |
 103 (Partial Dentures: Anchorage with Precision Attachments) The facing of the secondary crown is completed only after the rest of the telescoping denture is processed in acrylic. There are no problems with retention of the acrylic veneer on the secondary crown, since it can be polymerized directly onto the denture base acrylic interproximally (Fig. 103). |
 104 (Partial Dentures: Anchorage with Precision Attachments) A correctly designed denture base will produce a prosthesis which replaces only those dental and periodontal structures missing after tooth loss and bone resorption. Such telescoping dentures are very pleasant for patients to wear (Fig. 104). |
 105 (Partial Dentures: Anchorage with Precision Attachments) If, for static reasons, we elect to do without dental support, then a resilient telescoping denture is required. Only the lower half of the primary crowns of a resilient telescoping denture are parallel and thus able to generate some degree of friction and to a larger extent, bracing of horizontal forces (Fig. 105). |
106 (Partial Dentures: Anchorage with Precision Attachments)
When the denture base is seated, the internal occlusal surface of the secondary crown should not contact the occlusal surface of the primary crown.
The secondary crowns of the resilient telescoping denture are fabricated on the primary crowns, as usual, except that in the final step a space maintainer is used to raise the secondary crowns half a millimeter (Fig. 106).
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8.4.3 Anchorage with Telescoping Attachments part.1
 94 (Partial Dentures: Anchorage with Precision Attachments) The presence of recesses and spaces around bar-type attachments is a disadvantage encountered by other types of precision attachments as well, especially extracoronal attachments (Fig. 93 + 94).
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 95 (Partial Dentures: Anchorage with Precision Attachments) For the preceding reason and because of static advantages in many cases, telescoping attachments are a very practical means of anchorage. Veneered, telescopic crowns are often somewhat plump. One can avoid such results if, during design and construction, certain rules are observed. The procedure shall be described for the case of two restored canines in the lower arch: The teeth are prepared and an impression is taken during the first appointment (Fig. 95). |
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 96 (Partial Dentures: Anchorage with Precision Attachments) An occlusal bite plate is prepared on the master cast and used during the second appointment to obtain a bite registration. The primary crowns are then fabricated in the laboratory (Fig. 96).
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 97 (Partial Dentures: Anchorage with Precision Attachments) The artificial teeth are set up in wax. Therein lies the most crucial step as far as the esthetic result is concerned. The teeth adjacent to the primary crown are set up such that an interproximal space of ca. 7 mm exists between them. In this case, 7 mm from the distal of the lower lateral incisors to the mesial of the first premolars (Fig. 97). In addition, the artificial teeth must be set in an occlusal plane that is approximately 1.0 – 1.5 mm higher than that of the primary crowns, depending upon whether full cast (all metal) or veneered secondary crowns are fabricated, respectively. |
 98 (Partial Dentures: Anchorage with Precision Attachments) During planning, one must take into consideration that the secondary crown has a wall thickness of 1.2 – 1.5 mm if veneered and 0.5 – 0.8 mm if non-veneered (Fig. 98). |
99 (Partial Dentures: Anchorage with Precision Attachments)
100 (Partial Dentures: Anchorage with Precision Attachments)
The try-in of the wax set-up, prior to fabrication of the secondary crowns and framework, is of critical importance. If the wax set-up meets the patient’s esthetic demands, then a plaster index will be prepared in the laboratory; the metal framework and secondary crowns must be adapted to the wax set-up and not vice versa (Fig. 99 + 100).
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8.4.2 Anchorage with Bars
 92 (Partial Dentures: Anchorage with Precision Attachments) Custom-made, parallel-milled bars belong in the same category as precision attachments. Together with their corresponding secondary or female parts, they perform an excellent support and bracing function, but generally lack an adequate amount of retention. Therefore, additional retention must be added elsewhere (Fig. 92).
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 93 (Partial Dentures: Anchorage with Precision Attachments) A particular disadvantage of all bars is that despite precise design and construction, a series of corners and recesses are produced which hinder effective prophylaxis. Bars which are not designed to form to the mucosa, having light contact with the ridge and a narrow facial- lingual dimension, are subject to the danger that proliferation of the mucosa in search of contact will soon fill all spaces under the attachment (Fig. 93). |
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8.4.1 Anchorage with Extracoronal Precision Attachments
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 90 (Partial Dentures: Anchorage with Precision Attachments) The effectiveness of prefabricated, standardized precision attachments is often over-estimated. It is quite common that after a relatively short period of time the originally favorable amount of retention no longer exists. The performance of precision attachments is largely dependent upon the type of case in which they are employed. In the case of a Kennedy Class III, very few problems would be anticipated. Also relevant to success is the question of whether or not the precision attachments can be left as long as possible in their vertical dimension (Fig. 90).
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 91 (Partial Dentures: Anchorage with Precision Attachments) Generally, the capabilities of extracoronal attachments are exceeded in cases of a Kennedy Class I or Class II due to the special requirements for support, stabilization and retention. This is especially true of cases where the attachment’s vertical dimension has been shortened due to a minimal space available. In all cases it is beneficial to relieve the attachment of such functions as dental support and bracing by the use of additional rests and bracing elements located elsewhere on the abutment crown(s). If the abutment crown is correctly designed, the partial denture can indirectly assist in the functions of dental support and bracing without such an ill- proportioned burden on the attachment itself (Fig. 91). |
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8.3 Crown and Clasp
 84 (Partial Dentures: Crown and Clasp) If a tooth to be clasped is cariously destroyed or has an unsuitable form for retention, it must be crowned. The wax pattern for the required crown should be contoured using the parallelometer, or surveyor. This naturally assumes that even for single crowns, an impression of the entire arch is taken. The path of insertion of the partial denture is determined prior to designing the wax patterns (Fig. 84).
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 85 (Partial Dentures: Crown and Clasp) The contours of each wax pattern must be designed to satisfy the requirements set by the three elements of anchorage (dental rests, bracing, retention). To aid in bracing and guidance for the correct path of insertion, a parallel surface, or guiding plane, should be cut into the lingual and mesial and/or distal regions, depending on the location of the dental rest. In reference to preparing the dental rest, see Chap. 5.1 and 9.3. The undercut should be designed such that its angle of inclination from the path of insertion is approximately 25-30°. Optimal clasp retention is generated at this angle (Fig. 85). |
 86 (Partial Dentures: Crown and Clasp) A short explanation of the preceding statements: In its designed position, the clasp lies tension- free on the abutment tooth. It must first be moved toward the height of contour before retention occurs. The extent of retention is dependent upon the angle of the undercut and is defined by the functional equation: R = K • tan alfa (Fig. 86). |
 87 (Partial Dentures: Crown and Clasp) We recognize the validity of this equation with respect to the existing intraoral findings when the extreme values are tested. The tangent of a 0° angle is 0. The retention is, therefore, also 0. On a surface without undercuts, no clasp retention occurs. The tangent of a 90° angle is not defined. If the clasp lies under a 90° overhang, the retention is also undefined (Fig. 87). |
88 (Partial Dentures: Crown and Clasp)
The decisive advantages of a 25 – 30°
undercut are summarized as follows:
For 10° undercuts present on natural teeth
- the retentive arms of the clasp must travel a rather long distance before reaching the height of contour,
- the retention is delayed,
- the amount of retention generated is small
(Fig. 88a).
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