Written by Jacinthe M. Paquette, DDS Sunday, 31 March 2002 19:00
Porcelain veneers are being used today for many different indications and have in fact become a reliable and effective means of replacing coronal or incisal volume and length in the anterior dentition. The conservative and minimally invasive nature of the preparation, coupled with the ability to provide excellent aesthetics and blending capabilities with natural teeth and other porcelain restorations, has made the bonded porcelain restoration a well-accepted part of our restorative options.
The porcelain inlay veneer and the porcelain onlay veneer, extensions of the porcelain veneer design, have become an effective way to address functional or occlusal discrepancies for the posterior dentition as part of extensive restorative reconstructions. The benefits of enhanced aesthetics, idealized functional and periodontal compatibility, and matching to other porcelain restorations has created a restoration that can greatly enhance the outcome of any dental treatment.
This article demonstrates some of the key features necessary for idealized success with porcelain bonded restorations and their various designs by outlining the steps involved in their fabrication from diagnosis to delivery. The well-established guidelines for ideal tooth preparation, and the potential clinical variations of these preparations, will be illustrated through a patient treatment involving an extensive use of these restorations in the overall aesthetic rehabilitative care.
THE AESTHETIC REHABILITATION PATIENT
|Figure 1. An anterior view of the four maxillary incisors of the aesthetic rehabilitative patient. The patient was dissatisfied with wear, chipping, and shade of natural dentition.||Figure 2. An occlusal view of a maxillary arch of a patient treatment planned for an aesthetic dental rehabilitation. The proposed treatment would eliminate the ill-contoured and ill-matching restorations, restore length to the worn and fractured incisor teeth, and re-create a more aesthetic complete dentition.|
|Figure 3. An occlusal view of the same patient as in Figure 1. The same restorative discrepancies of defective margins, overcontoured restorations, and wear are present in this opposing arch.|
This 50-year-old patient initially presented in need of extensive dental treatment. Her pre-existing dentistry was dated, with defective margins, ill-matching restorations of various types and materials, and a remaining natural dentition with localized areas of moderate wear (Figures 1 through 3).
A comprehensive examination including an evaluation of periodontal health, temporomandibular joints, dental occlusion, restorative status, and aesthetic assessment was accomplished. The completeness of a thorough examination is crucial in providing appropriate treatment goals and the best preventive care for each individualized patient. An initial treatment plan was derived that included periodontal therapy to establish idealized periodontal health and serve as an opportunity to educate the patient on periodontal home care for long-term plaque control. Additionally, initial attention to the re-establishment of ideal periodontal health provides the dental team with the ability to educate the patient on their treatment goals and desires. Because of the patient’s aesthetic desires the treatment plan included a combination of porcelain veneers, porcelain inlay veneers, porcelain onlays, and PFM restorations as part of full-mouth reconstruction.
COMPREHENSIVE TREATMENT PLANNING
The comprehensive wax-up assists the dentist and the dental technologist in properly planning for the ideal restoration selection and serves as a guide to the necessary modifications required of the preparations to achieve the desired treatment objectives.
|Figure 4. Patient undergoing jaw recordings for future programming of fully adjustable articulator. Electronic data gathered can be stored for future comparative evaluations for patients using the CADIAX device by Water Pik Technologies.|
Historically, jaw recordings were accomplished in a somewhat time-consuming and cumbersome manner, with most systems available being similar. A newly introduced system records these measurements in a simple way rather quickly and easily. This animated system records protrusive, lateral, and opening paths (Figure 4). A software program then translates and calculates the appropriate settings for various articulators. From its recordings, any articulator can be programmed to the individual patient’s chewing pattern, allowing the dental technologist to more accurately create an anatomical occlusal and functional scheme to the wax-up and subsequent restorations to be created. This level of accuracy at the planning and laboratory stages results in fewer adjustments at the time of delivery, thereby reducing the required chair time for that phase of treatment.
|Figure 5. A complete diagnostic wax-up was done to create a blueprint in wax of the proposed treatment. A diagnostic wax-up such as this not only serves as a restorative guide but also is very useful as a communicative tool to describe to the patient the restorative objectives to be achieved.|
The diagnostic wax-up is especially powerful in planning for porcelain-bonded restorations. This initial phase provides an opportunity to pre-assess a number of parameters toward the final porcelain tooth form (Figure 5). Because the porcelain-bonded veneer is conservative in nature, it is less forgiving in the preparation requirements than are PFM restorations. As the restorative objectives of natural emergence, maintenance of enamel for bond strength, and aesthetic alignments within the surrounding dentition are borne in mind, variations in the standardized porcelain veneer preparation begin to emerge. These variations can become quite significant when attempts to close large diastemas or correct malalignments are involved.
Although at the surface porcelain-bonded restorations appear to be a somewhat simple restorative option, they can become quite sophisticated and technique sensitive under certain clinical situations. The few failures that occur are typically failures related to inappropriate tooth preparation, improper restoration choice, insufficient enamel for bonding, or structural defects within the porcelain itself. Maximizing success with these restorations is achieved through proper planning, accurate preparations, precise laboratory fabrication, and a well-coordinated delivery.
The basis for long-term success of porcelain-bonded veneers lies to a great extent in a properly designed substructure—the tooth preparation. A proper preparation is the key to porcelain aesthetics, longevity, and retention. Although slight variations in the preparation have been described in the literature, some key characteristics to the preparation must be universally met. The tooth preparation design determines the pattern of stress distribution within the porcelain, therefore determining the longevity of the overall restoration.
One of the key requirements for the preparation is a controlled and uniform tooth reduction to create an even and adequate thickness of porcelain. A 0.3-mm or 0.5-mm reduction bur is an effective means of ensuring a minimally even reduction over the entire surface of the tooth being prepared initially.
Bi-plane reduction of the facial surface provides a reduction pattern that will follow the appropriate contours of the tooth being restored. Finish lines must be clear and distinct in order to create a sufficient bulk of porcelain at the margin to prevent fragile finish lines of porcelain. Thin extensions of porcelain can be vulnerable to breakage during the fabrication and delivery processes. A light chamfer is the best form of a finish line to meet these objectives. The contours of the preparation must be smooth, with the absence of any undercuts to prevent any stress propagation within the final porcelain. Lastly, enamel preservation must be kept in mind during the preparation to maximize the bond strength and resistance to underlying stresses to the future porcelain restoration.
|Figure 6. An occlusal view of the maxillary arch wax-up. Note the planned closure of diastemas and incisal overlap of future veneers for anteriors.||Figure 7. An occlusal view of the mandibular arch wax-up of the same patient. The entire dental reconstruction was to include a combination of aesthetic restorations of porcelain veneers, porcelain veneer inlays, porcelain onlays, and PFM.|
Variations on the standardized preparation design are often required under clinical situations. The most common variation is when diastemas are being closed through the use of porcelain veneers. The closure of the diastemas requires a palatal or lingual extension of the preparation that will enable the dental technologist to create a natural emergence and tooth contour to the interproximal porcelain. The necessary extensions of the preparation required are initially assessed through the diagnostic wax-up models (Figures 6 and 7). The larger the interproximal diastemas being closed, the greater the need for extension both in the lingual direction and in the gingival direction of the preparation. As margin locations unfold clinically in extensive preparations, one must pay close attention to proper draw for the restoration. Additionally, as undercuts are removed, a corresponding sacrifice of supportive enamel takes place, potentially compromising the bond strength of the future restoration. Once the preparations are completed, clinical photographs of the prepared teeth provide the laboratory technologist with information on the underlying shade of the prepared teeth, to assist in the porcelain fabrication.
|Figure 8. A polyvinylsiloxane guide, created from the diagnostic wax-up, serves as a useful guide to assist in idealized incisal tooth reduction. In this view, the porcelain veneer preparations are being re-evaluated against the incisal reduction guide to assess the appropriate reduction.|
A number of techniques have been described in the literature to assist in proper tooth reduction for the anterior dentition, including reduction guides or silicone matrices created from a diagnostic wax-up. Reduction guides can be especially effective in evaluating the appropriate incisal reduction. Although one would typically aim for 2 mm of final porcelain at the incisal edge of the final veneer, reduction of the incisal edge of the tooth may sometimes not be necessary if significant wear of the incisal edge was pre-existing. Therefore, the silicone guides of the projected future incisal length can serve to accurately guide the clinician to the appropriate reduction for the clinical situation at hand (Figure 8).
For the posterior dentition, clear vacuform stent replicas of the diagnostic wax-up help evaluate reduction objectives as the preparation of the posterior teeth evolves. These guides assist in evaluating the uniformity of the occlusal reduction of the overall posterior dentition, degree of parallelism between the preparations, and other preparation objectives.
|Figure 9. A diagrammatic view of the preparation objectives for the porcelain onlay veneer restoration. This view illustrates the smooth flowing contours of the preparation with the absence of any undercuts.|
In complete rehabilitation, the diagnostic wax-up guides the restorative team, the restorative dentist, and the dental technologist toward the appropriate restorative treatment option for the individual teeth within the reconstruction. The increasing successes with porcelain-bonded veneers have resulted in growing variations and extensions of available preparation designs. Therefore, a more critical evaluation of the clinical parameters that present is required to make the correct treatment choices and is provided by the diagnostic wax-up. Examples of such variations in our restorative armamentarium are the porcelain inlay veneer and porcelain onlay veneer (Figure 9).
|Figure 10. With final impressions taken, the final steps to laboratory fabrication begin. This epoxy resin working cast of the maxillary arch preparations illustrates the various preparation designs utilized throughout this arch combining porcelain veneers, porcelain inlay veneers, porcelain onlays, and full-coverage crowns.|
This preparation design provides the unique opportunity to more conservatively address the restoration of posterior teeth for the correction of the facial and the occlusal or intracoronal portion of the tooth being restored. The same preparation objectives of the conventional veneer preparation are followed and incorporated, with the addition of an inlay preparation. Because of the extent of the tooth preparation, extra attention to the elimination of any undercuts must be examined as the tooth preparation unfolds. Additionally, as the preparation becomes more extensive, one must once again bear in mind the amount of enamel remaining to ensure an appropriate bond of the restoration. Functional loads, occlusal loads, and contact schemes for the future posterior bonded porcelain restorations need to be considered and well understood for the longevity of the restoration (Figure 10).
Once the preparation phase is completed, provisional restorations provide a thermal guard and aesthetic replacement. Additionally, the provisionalization phase of treatment provides an opportunity for an exacting guide toward the final aesthetic treatment outcome. The provisional restorations provide valuable information to the laboratory technologist on the appropriateness of tooth contour, tooth alignment, incisal/occlusal planes, and patient satisfaction with the existing temporary tooth arrangement derived from the original diagnostic wax-up. Accurate provisionalization provides the patient with a precise preview of the final, special tooth arrangement. Any slight corrections or modifications can be easily achieved with the provisionals and assessed for correctness before the porcelain veneers are created. Using provisional restorations as a template for progressive aesthetic refinement helps prevent any potential dissatisfactions with the final porcelain veneers at the delivery appointment.
|Figure 11. The refined mandibular provisional stone model is cross-mounted against the maxillary arch working cast to assist in creating the porcelain restorations. The working cast has been modified to incorporate the refractory dies for the all-ceramic restorations. The metal copings for the PFM crowns have already been opaqued in this view.||Figure 12. A polyvinylsiloxane putty guide affixed to the mandibular model is created to replicate the incisal edges of the maxillary arch provisional model to serve as a guide to create the appropriate incisal length and tooth contour of the porcelain veneers.|
|Figure 13. The maxillary epoxy resin working cast with completed porcelain veneers. The dimensional accuracy of the epoxy resin cast creates the correct inter-tooth relationship that will minimize the need for interproximal adjustment at the time of delivery.||Figure 14. The mandibular epoxy resin cast with completed porcelain veneers. The recreation of slight variation in tooth alignment maintains an uncompromised individual tooth width and assists in creating a natural appearance to the restorations.|
Once final impressions have been taken and the laboratory work-up is initiated, study casts of the full-mouth provisionals are mounted to assist in the final porcelain fabrication. These study casts are further corrected for any necessary aesthetic refinement and finalization in the occlusal scheme. Once refined, the mounted models are cross-mounted with the prepared arches for the fabrication procedures of the final restorations (Figures 11 and 12). The porcelain restorations are created with the use of solid gypsum master casts and epoxy resin working casts. The porcelain veneers are created on refractory dies, which have been accurately transferred into the epoxy resin working cast (Figures 13 and 14).
|Figure 15. An occlusal view of the maxillary epoxy resin model with the completed restorations in place. The varying lingual extensions of the porcelain veneers on the incisors illustrate the available flexibility within this preparation design as lingual or interproximal defects can be incorporated within the restoration.||Figure 16. An occlusal view of the mandibular epoxy resin model with the completed restorations in place. The various restorative treatment options selected for each individual tooth provide an opportunity to preserve tooth structure where possible. The bicuspid teeth restored with porcelain veneer inlays are a good example of such a treatment option.|
At the time of delivery, the attention to detail and precision achieved in the dental laboratory are reflected in the accuracy of fit and precision in the clinic (Figures 15 and 16). The greater the attention to detail at the time of fabrication of the restorations within the laboratory, the easier the delivery phase of treatment becomes. This results in less chair time required, with the ability to maintain the high polish of the porcelain achieved in the lab for the best aesthetic and hygienic results.
|Figure 17. A full close-up view of the patient’s treatment completed with all bonded porcelain veneers in place.||Figure 18. A close-up view of the completed mandibular incisors with the restored length and an enhanced natural aesthetic result. Precise porcelain margins and natural emergence provide a favorable tissue response adjacent to the restorations.|
|Figure 19. An intraoral occlusal view of the completed maxillary arch. The porcelain-bonded restorations provided the ability to create more favorable tooth contours and arrangements for a more idealized overall arch symmetry.||Figure 20. An intraoral occlusal view of the completed mandibular arch. The combination of the various restorative options described create an ideally aesthetic and functional result.|
Treatment success with porcelain-bonded restorations is best achieved with attention to detail at every phase of the treatment. A complete diagnosis through a diagnostic wax-up provides valuable information relating to the possibilities that exist with the combined use of the various restorative options available, allowing an opportunity to create more aesthetic treatment outcomes for our patients. An understanding of treatment objectives and well-executed preparations provides appropriate required spaces for the restorative materials being utilized in the laboratory. Lastly, precision at both the clinical level and the laboratory level of fabrication enhances the potential for success and longevity of the results achieved (Figures 17 through 20).
Longevity of the final result is further assured with the nighttime use of a protective occlusal splint, which is recommended for all patients entering into extensive aesthetic rehabilitative treatments. This type of appliance should maintain an ideal occlusal position and functional scheme and be made of hard acrylic.
The author would like to thank Tadanori Taniguchi, RDT, for the fabrication of the excellent restorations shown in this case.
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