Restoring large tooth defects and tooth replacement

SECTION VI RESTORING LARGE TOOTH DEFECTS AND TOOTH REPLACEMENT

When a tooth is too badly broken down to be restored with a conventional restoration and only a thin shell of enamel remains, it may be necessary to protect the remaining tooth structure with a crown. Before preparing a tooth for a crown, the dentist first removes decay and then restores some or all of the lost tooth structure with amalgam or composite. This restoration that replaces defective and carious tooth structure prior to preparing a tooth for a crown may be called a restoration under crown (RUC) or crown buildup. When there is too little remaining tooth, particularly on an anterior tooth, a custom cast metal core (resembling a tooth prepared to receive a crown) with a metal post can be designed. The post provides the retention by fitting snugly into a previously endodontically treated and prepared root canal. This restoration is called a cast post and core (Fig. 10-44). Prefabricated posts are also available in metal, or esthetic materials (such as fiber posts), which can be cemented into the prepared canal and then be bonded with a composite crown buildup.

Photos A, B, C, and D show a cast post and core.

FIGURE 10-44. Cast post and core. A. On a cast metal post and core before cementation, you can distinguish the post, which fits snugly in the prepared root canal (after endodontic treatment), and the core, which is the portion that the crown will cover. B. The visible portion of the gold post and core is the core that can be seen forming the missing part of the crown preparation. C. The post can be seen on this radiograph extending well down within the root to provide retention for the crown that will be placed over the post and core. D. Almost all of this tooth crown is now a core that has been prepared for a replacement crown.

Description

On posterior teeth, a crown can be constructed entirely of cast metal and is called a complete cast metal crown (Fig. 10-45B). To prepare a tooth for a complete crown, the previously restored anatomic tooth crown (or prepared crown buildup) is externally reduced with specially shaped burs in a dental drill to make room for the required thickness of the cast metal crown (Fig. 10-45A). Crowns obtain retention from the nearly parallel preparation walls that slightly converge toward the occlusal, an accurate fit, and the cement. The preparation ideally extends gingivally beyond the margins of the cast post and core or crown buildups so that the crown margins end on sound tooth structure. Full cast metal crown preparations end at the gingival cavosurface with a rounded shape called a chamfer (Figs. 10-45A and 10-46A).

Photos A and B show a complete cast metal crown.

FIGURE 10-45. Complete cast metal crown. A. Crown preparation on tooth #20 for a full cast metal crown. The reduction at the gingival cavosurface is called a chamfer (at arrow). B. The complete cast metal crown cemented in place.

Description

Photos A and B show the proximal views revealing crown preparations with their facial surface toward the right.

FIGURE 10-46. Proximal views: crown preparations with their facial surface toward the right. A. Full cast metal crown (no porcelain veneer) preparation on a mandibular premolar. B. Preparation on a maxillary canine that will have a facial fused porcelain veneer over metal to provide esthetics. Greater facial tooth reduction was necessary (arrow).

Description

When esthetics is important, especially on anterior teeth and maxillary premolars, one option is a metal crown covered facially with porcelain. The preparation for this type of crown requires more reduction of facial tooth structure to make room not only for the thin cast metal but also for an additional thickness of a tooth-colored porcelain veneer, which is fused onto the facial surface of the metal (Fig. 10-46B). This restoration is called a metal ceramic restoration (also called a porcelain fused to metal crown) and is seen on tooth #30 in Figure 10-47. Another esthetic solution for a full coverage restoration is an all-ceramic restoration. Since there is no internal metal support under the porcelain, the resultant increased translucency more closely resembles a natural tooth (seen on the maxillary incisor teeth in Fig. 10-48). Zirconia is a newer esthetic restorative material that is ideal for crowns since it is translucent and biocompatible, less susceptible to fracture than porcelain, and requires less tooth reduction than porcelain.25

A photo shows tooth #31 restored with a complete cast metal crown, tooth #30 restored with a metal ceramic restoration, and teeth #28 and #29 both having metal ceramic crowns.

FIGURE 10-47. Types of crowns. Tooth #31 is restored with a complete cast metal crown, #30 is restored with a metal ceramic restoration (porcelain fused to metal crown), and #28 and #29 both have metal ceramic crowns (metal is not visible).(Photographs courtesy of Dr. Julie Holloway.)

Photo A shows thin, badly damaged maxillary incisors. Photo B shows the same incisors after placing all ceramic restorations.

FIGURE 10-48. A. Thin, badly damaged maxillary incisors. B. Same incisors after placing all ceramic restorations. (Photographs courtesy of Dr. Julie Holloway.)

Even when little or no caries or breakdown is evident, a crown may be recommended if the tooth is cracked or when needed to support an adjacent false tooth that replaces a missing tooth. The replacement tooth crowns can be attached to other crowns that cover the adjacent supporting teeth, and this is called a fixed dental prosthesis (also called a fixed partial denture [FPD] or a bridge by many people) (Fig. 10-49). The false tooth is called a pontic, and the teeth that support the pontic are called the abutment teeth. Abutment teeth are covered by crowns called retainers that are attached to the pontic. In Figure 10-49B, a fixed dental prosthesis is used to replace tooth #4 by attaching it to an abutment metal ceramic crown on tooth #5 and a complete cast metal crown on tooth #3. The metal pontic replacing #4 is veneered with porcelain. A fixed dental prosthesis is seen before cementation in Figure 10-49C.

Photos A, B, and C show fixed dental prosthesis.

FIGURE 10-49. Fixed dental prosthesis, also called a “bridge” by many persons. A. Buccal view of tooth abutments: tooth #3 is prepared for a full crown and #5 is prepared for a crown veneer abutment. B. The completed three-tooth fixed dental prosthesis (fixed partial denture or bridge) is cemented on the prepared teeth: The retainer for abutment tooth #5 and pontic replacing #4 are restored with porcelain fused to metal. The retainer for #3 is covered with a complete cast metal crown. C. This porcelain fused to metal fixed dental prosthesis is ready to cement in the mouth. It is reflected in a mirror so you can see the space in the molar retainer that will fit over the prepared molar abutment. (This photo was provided by Burak Yilmaz, DDS, PhD, the Ohio State University College of Dentistry.)

Description

Lost teeth can also be replaced with dental implants (Fig. 10-50). A dental implant involves embedding an artificial root into the bone. Three to six months after surgical placement, the embedded implant can be used to provide retention for a crown or provide retention as an abutment for a screw-retained fixed dental prosthesis or to provide support for a removable partial denture. See Chapter 7, Section X, for more discussion about dental implants.

Photos A, B, and C show a dental implant. Tooth #29 was lost and replaced with a dental implant.

FIGURE 10-50. A dental implant. Tooth #29 was lost and was replaced with a dental implant. A. A radiograph of the implant with the screw-retained component and porcelain crown. B. The screw-retained component (crown support) is attached to the implant and extends above the tissue prior to placement of the crown. C. The porcelain crown is cemented on the screw-retained component of the implant. (Photographs courtesy of Ed McGlumphy, D.D.S., M.S., Ohio State University, College of Dentistry.)

Description

Groups of lost teeth can also be replaced with multiple implants, a longer fixed dental prosthesis, or a removable dental prosthesis, which is also called a removable partial denture. One type of removable dental prosthesis is made with an acrylic saddle that adapts comfortably over the edentulous area, artificial replacement tooth crowns on the acrylic saddle, and a framework (usually metal) with parts that adapts around adjacent teeth to provide stability and retention (Fig. 10-51A). The part of the framework that connects the left and right sides of the prosthesis is called a major connector. The framework has clasps, which surround and contact abutment teeth just cervical to the height of contour facially or lingually to provide retention, and rests that fit into small depressions (rest seats) prepared mostly into occlusal enamel in order to keep the partial denture from seating too firmly against the mucosa.

Photos A and B show a removable partial dental prosthesis.

FIGURE 10-51. A. Removable partial dental prosthesis (also known as a removable partial denture) on a teaching model (typodont) replacing teeth #30 and #31 and attached to abutment teeth #19 and #29 using clasps (a) and rests (b) that retain and position the prosthesis in the mouth. The major connector (c) of the metal framework that connects the left and right sides of the prosthesis has a lingual plate that adapts to the lingual surfaces of all of the mandibular anterior teeth, providing additional stability. B. Complete removable dental prosthesis (also known as a complete denture). The upper denture on the left is designed to cover the palate, while the lower denture on the right is designed to maintain room for the tongue.

When all teeth have been lost, a complete removable dental prosthesis (also called a complete denture or false teeth) can be constructed (Fig. 10-51B).

LEARNING EXERCISE

Without looking at the key for each photograph of restorations in this chapter, identify the material used, the surfaces involved, and the abbreviation that could be used to denote the restoration. Do the same with clean extracted teeth that have existing restorations. Look into your mouth using an excellent light source, and identify the classification of any existing restorations (according to Dr. G.V. Black). Repeat this when looking into the mouth of a friend as they retract their lips and cheeks. Do you suspect any areas of decay? If so, check with a dentist.

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Sep 12, 2021 | Posted by in General Dentistry | Comments Off on Restoring large tooth defects and tooth replacement
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