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Written by Thomas O. Marxen DDS, MSD Wednesday, 01 March 2006 00:00
In the early-to-mid 1980s the literature described techniques for bonding veneers to enamel with predictable results.1-4 Porcelain veneers fabricated during this time period were made of stacked or feldspathic porcelain using either a foil or refractory die technique.5,6 These veneers were used to cover, or increase the color value, of tetracycline-discolored teeth; however they appeared bulky, excessively opaque, and monochromatic.7,8 The advantage of the first-generation feldspathic porcelain veneer technique was that it conserved tooth structure, since minimal or no enamel preparation was required.4,5,9 Although there are other product choices to upgrade first-generation veneers, many dentists prefer feldspathic porcelain veneers because of preservation of tooth structure.5,10,11
Figure 1. Tetracycline-stained teeth restored with resin veneers. Note internal areas of discoloration, marginal failure, and fracture.
Figure 2. The same patient after removal of the resin veneers. Note marked tetracycline discoloration. Both the resin veneers and the featured feldspathic veneers (Figures 3 to 17) are examples of the techniques recommended in the 1980s.
Other materials and techniques used to fabricate veneers have proven less satisfactory. Resin composite restorations were also a conservative option in place of feldspathic veneers. The restorations, however, are susceptible to discoloration, wear, and marginal fractures, thereby reducing their usefulness as a long-term aesthetic solution (Figures 1 and 2).12,13 In a patient satisfaction study, indirect resin composites and direct resin composites received a lower approval rating compared to feldspathic veneers.14 Golub-Evans compared composite bonding to porcelain veneers and concluded that the composite restorations required more restorative maintenance.15
The aesthetic characteristics of feldspathic veneers have improved markedly in recent years with a modification that involves removal of enamel and dentin in the gingival one third of teeth.8 This reduction provides sufficient thickness for translucent, natural-appearing porcelain without concern for bonding to the exposed dentin, since predictable dentinal bonding agents are now available. Most veneers require the standard reduction of 0.5 mm. However, tetracycline discoloration or other intrinsic discolorations caused by a variety of factors require greater tooth reduction.16,17 The enamel layer of many teeth ranges from 0.3 mm to 0.5 mm at the gingival one third of the tooth.18 With the later-generation dentinal bonding agents, reduction of more than 0.5 mm of enamel to expose the dentin is not a critical concern.19
This additional reduction creates space for restorative material that can help mask the moderate to dark dentin discolorations. For moderate tetracycline discoloration, the laboratory technician may incorporate opacious modifiers in the feldspathic veneers to block out the discoloration; however, this process demands skill to produce translucent, natural-appearing veneers.7,8 This technique also requires removal of an additional 0.2 mm of tooth structure for a total of 0.7 mm of reduction. For moderate to severe tetracycline discoloration, the modified subopaquing procedure consists of layers of hybrid composite and an opaquer. Here 0.7 mm of tooth reduction is also required.7 Still another technique uses hybrid resin only to mask the dark intrinsic dentin; however, this approach requires an additional 0.3 mm of tooth structure for a total reduction of 0.8 mm.8
The ability to bond porcelain in the gingival one third of the tooth makes the upgraded veneers possible. Ideally, however, a porcelain veneer should be designed so that it has no less than 70% exposed enamel after preparation.20 It is well documented that the bond strength to enamel is consistently better than the bond strength to dentin.5
The dental literature rarely discussed tooth whitening prior to 1990. Therefore, surface whitening was not a treatment option in the 1980s. There is recent evidence that many whitening materials are effective for most tetracycline-stained teeth.21,22 Patients who are unhappy with their first-generation veneers that were fabricated with no enamel preparation may now benefit from the new whitening products after the veneers are removed. In these cases there is no need for additional restorative procedures. However, for some patients tooth whitening alone is not sufficient due to a variety of factors, including malposition of the teeth or discrepancies in soft-tissue height or contour. In these cases, replacement of the existing veneers provides an aesthetic yet conservative solution.
The following case demonstrates the upgrading of first-generation feldspathic porcelain veneers so that they are more aesthetically pleasing. This case illustrates (1) tooth preparation guides and design, (2) the ability to bond to dentin, (3) the ability to mask the dentin, and (4) whitening materials that are effective on tetracycline-discolored teeth. Obsolete restorations can now be upgraded to natural-appearing feldspathic veneers while still conserving tooth structure.
Figure 3. Case describing this report. Evaluation of tooth position reveals that the maxillary teeth do not follow the curvature of the mandibular lip. Teeth Nos. 6 and 11 touch the lower lip. Teeth Nos. 9 to 13 have gingival margins that are more coronally positioned than what is present on the maxillary right side.
Figure 4. First-generation feldspathic veneers on teeth Nos. 6 to 11.
A 34-year-old female had first-generation veneers fabricated in 1987. The patient was pleased that her teeth looked whiter but was disappointed that they did not have a natural appearance (Figures 3 and 4). To her knowledge there was no tooth preparation as part of the original veneer fabrication. She had accepted her smile, but when told that techniques were now available to fabricate veneers with a more natural appearance, she chose that option.
Figure 5. Notice the symmetrical difference when one half of the veneers are removed (teeth Nos. 6 to 8). Even after the veneer is removed from the maxillary right canine, it still does not have the appropriate axial inclination. It is also apparent that the bicuspids are inclined too far to the lingual.
Figure 6. The lingual torque of the bicuspid teeth causes more of the facial surface to be displayed in this occlusal view than is ideal. Poor smile design is enhanced by the added thickness of the veneers on the natural, unprepared teeth.
After a thorough examination, it was evident that the desired aesthetic results would not be possible by simply removing the old veneers and whitening her natural teeth. Changes in tooth position through cosmetic dentistry or orthodontic tooth movement would be required. At the consultation, the patient stated that she was not interested in orthodontic treatment (Figures 5 and 6).
Discrepancies in soft-tissue height existed when comparing the maxillary left anterior and bicuspid teeth to the teeth on the right side (Figure 3). Without the gingiva in a more apical position, tooth No. 11 would be short if it was prosthetically modified so that it no longer contacted the lower lip (Figure 3). Fortunately, the patient had a wide band of attached gingiva and a 4-mm gingival sulcus. Removing 2.0 mm of gingival tissue on the facial aspect of the maxillary left cuspid tooth would not cause invasion of the biological width.23 The result would be symmetrical gingival margins on the left and right sides.
Before the maxillary left gingivectomy was accomplished, the first step would be to whiten the mandibular teeth and ultimately match the new maxillary veneers to the whitened mandibular anterior teeth. A custom tray was fabricated for use with Opalescence Regular 10% carbamide peroxide (Ultradent Products), which was used for 2 weeks at home. The patient was not completely satisfied with the results of the 10% carbamide peroxide, therefore she was given Opalescence Quick 35% carbamide peroxide, (Ultradent Products) to use for one week. Whitening results were acceptable after this regimen.
The maxillary teeth would not be whitened for 3 reasons: (1) rebound discoloration of whitened teeth after 18 to 24 months has been reported,24,25 (2) bond strength is reduced after tooth whitening,26-28 and (3) dark intrinsic colors at the cervical aspect of most tetracycline-stained teeth are difficult to whiten.
Preoperative Work-Up (Stage 1)
Clinical records included radiographs, preoperative photographs, periodontal charting, evaluation of the occlusion/temporomandibular joint, preoperative impressions, maximum intercuspation bite registration, and face-bow transfer.
Preoperative Work-Up (Stage 2)
Figure 7. A diode laser was used to perform a gingivectomy.
Figure 8. After healing, the gingival margins are more symmetrical, and sufficient attached tissue remains. The mucogingival junction is greater than 5 mm apical to the gingival margin for most of the maxillary teeth.
A diamond bur was used to carefully remove all of the bonded porcelain without contacting the enamel surface. This is the point in the preoperative work-up that is ideal for completing an intraoral mock-up. This mock-up helped determine the amount of gingiva to be removed from the facial aspect of teeth Nos. 9 to 13 and also establish the proper position of the incisal edge of the central incisors.29 Subsequently, a gingivectomy was performed using a diode laser (Aurora). A minimal amount of gingiva (0.5 mm) was removed from tooth No. 7, no gingiva was removed from tooth No. 8, 0.5 mm was removed from tooth No. 9, 1.0 mm was removed from tooth No. 10, and the amount of tissue removed increased to 2.0 mm for teeth Nos. 11, 12, and 13 (Figures 7 and 8).
The decision was made to fabricate feldspathic porcelain veneers for teeth Nos. 4 to 14 after consultation with the laboratory technician. Photographs of the natural teeth prior to preparation (after removal of the first-generation veneers) and Polaroid photographs with shade tabs adjacent to the prepared teeth were reviewed.
After soft-tissue healing, alginate impressions were taken. The casts allowed the laboratory technician to study the natural contours of the patientís teeth while correcting tooth length and rotation discrepancies in the diagnostic wax-up (Figure 9).
Figure 9. Tooth position and contour changes fabricated in the diagnostic wax-up. Blockout resin is added to the facial contours of teeth Nos. 4, 5, 12, and 13, which will help properly develop the buccal corridor.
Figure 10. The mandibular teeth have been whitened, the maxillary veneers have been removed, and the tissues have healed from the gingivectomy. Tetracycline discoloration is especially evident on the gingival third of the maxillary central incisors.
Photographs were sent to the laboratory for evaluation of tooth color and to allow comparison of the whitened mandibular teeth with the maxillary teeth (Figure 10). The laboratory technician determined that he could match the shade of the mandibular whitened teeth using the new maxillary feldspathic veneers if provided with at least 0.7 mm of tooth reduction.
Figure 11. The clear plastic stent has a passive fit after selected areas of enamel removal.
Tooth preparation requires discipline and care to accomplish the proper amount of tooth reduction. Clear plastic stents were used for aesthetic pre-recontouring of the enamel with a diamond bur (Figure 11).30 Any enamel that was impeding the stent from seating properly was removed, because this enamel extends outside the ideal contours established in the diagnostic wax-up. After this was ac-complished, the silicone index (ExaFlex Putty [GC America]) and the clear plastic stent fit passively.30,31 The silicone index was used to check reduction of the teeth in all 3 facial planes (incisal, middle, and cervical portions). To help guide the gross reduction, 0.5-mm depth cutting burs (No. 828-026 [Axis Dental]) were used. The interproximal extension of each preparation was determined by the tooth position and color of the dentin.32 The preparation of teeth with dark intrinsic color must include a break in the contact with the proximal teeth to decrease the risk of a dark shadow around the margins of the veneers.33 The plastic stent was used for both evaluation of the preparation design and fabrication of the provisional restorations (Luxa-temp [Zenith DMG]).
The final impression was made. A face-bow was taken for the Panadent articulator (Panadent), and maximum intercuspation bite registrations were taken. The diagnostic wax-up was anatomically accurate and aesthetic, and the provisional restorations were a precise preview of the final result.31,34,35
Contouring and occlusal adjustments were made to the provisionals prior to polishing with pumice and a polishing paste. The units of the provisional restoration were luted with a temporary cement (TempBond NE [Kerr USA]). An opaque temporary cement was advisable to cover up preparations with low color value. The provisional restorations were adjusted a few days later when the patient was not anesthetized.
|Figure 12. The provisional restorations closely follow the curvature of the lower lip; however, the central incisors appear too long.|| |
Figure 13. Provisional restorations after the central incisors were shortened. Luxaflow (DMG) was also added to the mesial gingival line angles of teeth Nos. 8 and 9, closing the interproximal space.
The provisional restorations required a few contour modifications (Figure 12). The central incisors appeared to be too long; therefore, it was decided to shorten them. This compromised their appearance in relation to the lower lip. This same situation existed for the natural teeth after the first veneers were removed (Figure 10). There was also a black cervical triangle space present between teeth Nos. 8 and 9 (Figures 12 and 13).
In consideration of the difficulty of matching feldspathic veneers to the whitened mandibular teeth, the tooth colors were mapped, and Polaroid photographs of the maxillary anterior preparations were taken. All records were sent to the laboratory technician, including preoperative photographs, 2 impressions of the maxillary arch, a stone model of the mandibular teeth, a bite registration, diagnostic wax-up, and photographs of the patientís smile taken a few days after the provisional restorations were placed.
In 6 weeks the feldspathic porcelain veneers were ready for a try-in. After anesthesia was achieved, the temporary restorations were removed. The veneers were rinsed with water, etched with hydrofluoric acid (Porcelain Etch [Ultradent]), and silanated (Silane Primer [Kerr]). Using try-in paste (3M ESPE), the veneers were all placed on the teeth to evaluate marginal integrity, color and value, contour, and contacts.
The laboratory ceramist was able to match the feldspathic veneers with the underlying shade of the preparations. A clear luting agent (Opal Luting Composite [3M ESPE]) provided a cosmetically pleasing result. Slight modification of the contacts was the only correction required prior to bonding.
A tissue deflection cord (Ultrapak No. 000 [Ultradent Products]) was placed just apical to all finish lines to help prevent gingival fluid from contaminating the surface of the preparations. A dental dam was placed to isolate the maxillary teeth from saliva.36 The preparations were microetched (Micadent 25-µm aluminum oxide [Medidenta International]), and the veneers were bonded using the "two-by-two" technique.37 With this technique the central incisors were placed, first followed by the right lateral and canine, and then the left lateral and canine. Then the right premolars were placed, and the veneer bonding process was completed with the left premolars. After the veneers were bonded, excess cement was removed. Any margins with residual resin were cleared with a No. 12 scalpel blade (Bard-Parker). Some margins were finished with a finishing diamond bur and a 30 fluted carbide bur (Axis Dental).
The rubber dam was removed and occlusion was checked. Minimal adjustment was needed to ensure the presence of proper cuspid disclusion and anterior guidance. Any porcelain glaze on the margin or elsewhere that was touched with finishing instruments was polished with a sequence of porcelain polishing discs, points, and cups (CeraGlaze [Axis Dental]).
Figure 14. Postoperative evaluation of 10 feldspathic porcelain veneers bonded to the prepared teeth.
Figures 15 and 16. Before-and-after portraits. To create vitality and natural aesthetics, the ceramist chose high fusing porcelain.
|Figure 16.|| |
Figure 17. Patient in conversation 5 years after her veneer upgrade.
The patient returned in a week for an assessment of her occlusion, contacts, gingival health, and any aesthetic concerns (Figure 14). Alginate impressions were made for a nightguard. The result was successful (Figures 15 and 16).
In this case the patientís smile has been improved as a result of careful attention to detail. The teeth met proper smile design criteria (incisal edges in harmony with the smile line; appropriate midline; appropriate axial inclinations; proper incisal embrasures; natural progressive increase in the incisal embrasure size from central incisor to cuspid; adherence to principles of proportion and central incisor dominance; cervical/incisal tooth length symmetrical from right to left; contralateral teeth in harmony in terms of size, shape, and position; buccal corridor properly developed; proper cervical embrasures). The contours of her new veneers were very similar to her natural teeth. They also matched the mandibular teeth in color, translucency, surface anatomy, and texture.
The feldspathic veneers require only conservative tooth removal, which will allow future replacement of the veneers. Five years later the patient remains pleased with the result (Figure 17).
The author wishes to express thanks to his mentor Dr. Robert Faucher, and to Dr. Robert Johnson, professor and Undergraduate Program Director, Department of Periodontology, University of Washington, for their help with editing this manuscript. Thanks are also expressed to ceramist Arnie Larson of Larson Ceramic Arts (Seattle, Wash).
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