Written by Leendert Boksman, DDS, and Brad Carson, DDS Tuesday, 01 November 2005 00:00
There are many treatment alternatives for the conservative clinical management of noncarious enamel defects such as enamel hypoplasia, enamel hypocalcification, localized enamel malformations and wear, rotations and simple malalignment, fluorosis, and discoloration of teeth due to trauma or tetracycline staining. These modalities may involve the placement of labial composite veneers, vital and nonvital bleaching1-3, or the placement of labial porcelain veneers.
Glazed feldspathic porcelain has long been regarded as the most aesthetic and biocompatible dental material available. It is stain resistant, abrasion resistant, nonporous, and color stable. True, lifelike appearance with fluorescence is available with some dental porcelains, creating a surface that matches the natural enamel in different lighting conditions. The clinician has control of opacity and better control of labial contour and anatomy than with direct composite veneers.
Many different types of porcelain and methods are currently used to create porcelain veneers. The authors prefer the use of stacked porcelain on a refractory die or foil matrix because of the ability to add opacious dentin underneath the veneer surface, helping to characterize and define the final color, translucency, and opacity. These veneers typically tend to be thinner than pressed ceramics, requiring less tooth reduction. As a result it is easier to maintain the preparation in enamel, thereby retaining tooth rigidity.
Etched porcelain surfaces as seen under the scanning electron microscope are porous, deeply honeycombed structures that seem to be more diffuse and easily penetrated than etched enamel surfaces. Early studies by Simonsen4 have shown that the tensile bond strength of etched porcelain to composite resin could be as high as 1,100 psi (7.5 MPa). His early work utilized a 7.5% hydrofluoric acid for 20 minutes to create the highest tensile bond strength. One critical control step is to make sure that regardless of the type or concentration of hydrofluoric acid used, the labial marginal area of the veneer must be blocked out. Inadvertent etching of the surface that contacts the gingival tissue can create a severe inflammatory tissue response.5 The current use of etching gels creates a problem in that the gel tends to migrate to the middle of the inner curvature, creating a lateral border of porcelain at the cavosurface margins that is not etched as deeply as the center.
Further, Calamia, et al6 in 1985 have conclusively shown that each porcelain has a specific concentration and time of hydrofluoric acid etching for maximum bond strength. In another study7 Calamia reported that shear bond strengths of different porcelains were higher for a 2.5-minute etch than for a 20-minute etch. Bond strengths of the feldspar-type porcelains were higher than the aluminous porcelain, the range being 1,716 psi (11.7 MPa) to 3,079 psi (21 MPa) for the 2.5-minute etch. It is logical, therefore, that the acid-etch gels must be used in a protocol designed for the particular porcelain being used. Recent research has conclusively shown that silanes used to increase the reactivity of the etched porcelain surfaces can be used incorrectly (N. Barghi, personal communication, 2005).
The organofunctional silanes react with glass through the ethoxy-, chloro-, or amino groups, leaving the vinyl group to react and form a bond with the composite.8 Silanes, if prehydrolysed, are active only for a period of less than a year; therefore it is best to use freshly mixed 2-part silanes. In addition, silanes should be used only in the thinnest of monolayers immediately after etching the porcelain for maximum bond strength. In fact, multiple layers or too thick a layer can act as a separating medium.
The porcelain veneer preparation and cementation techniques have not changed significantly in the last 20 years. The philosophy of adding porcelain laminates to unprepared teeth has been accepted by some clinicians since the inception of using porcelain for this restorative modality. In the authors' view, adding porcelain to unprepared teeth will create a labial overcontour with poor aesthetic results and negative tissue response. However, certain clinical situations exist where this approach can be used. If teeth are retroclined or have severe labial erosion, and the clinician is not trying to alter the tooth shade, then a no-preparation technique might give an acceptable result. However, the fact remains that porcelain cannot be fabricated to a feather edge, resulting in an overcontouring of the cavosurface margin postin-sertion. Trying to reduce this inevitable ledge with diamond finishing burs will almost always score the cementum. Also, remember to round over the incisal labial line angle to facilitate seating of the veneer and to minimize the potential for the underlying tooth structure to show through in the incisal third.
Further, using porcelain polishing pastes in a rubber cup to polish this surface after the use of diamond finishing burs will preferentially remove the cementum, creating a ledge and the potential for postoperative sensitivity. Full labial chamfer shoulders are preferred, with labial reduction of 0.4 to 0.7 mm, with best effort to maintain the preparation in enamel. This minimal reduction maintains much of the strength of the tooth and provides better bond strengths than can be achieved when bonding to dentin. Magne, et al9 showed that the tooth is far more flexible (about 2x) when all the enamel is removed than when only some or no enamel is removed. If minimal or no color correction is needed, the preparation ends cervically just short of the free gingival margin, taking care to extend interproximally with a "dog leg" preparation so the margins cannot be seen from a lateral angle.
If a significant color change is anticipated, for example when treating tetracycline discoloration or changing the color of a nonvital tooth, the preparation is carried 1 mm under the collar of the gingival tissue. The preparation can extend to the crest of the incisal edge or have an incisal overlap. An incisal overlap has 2 distinct advantages. Reducing the incisal will give the technician the ability to create incisal translucency. Further, an incisal overlap creates a positive stop when inserting the veneer filled with the luting composite, facilitating a predictable insertion. Castelnuevo, et al10 demonstrated that the strongest veneer has 2 mm of unsupported incisal porcelain and a butt joint on the lingual, with a lingual chamfer not adding strength. A veneer with no overlap has a tendency to float on insertion, making it difficult to verify if the veneer is in the desired luting position.
|Figure 1. Preoperative stone model of ankylosed lateral incisor with tissue height discrepancy.|
Figure 1 shows the preoperative model of the patient post orthodontics. The gingival contours make the central incisors look too short and bulky. The maxillary left central incisor has a wider root than the crown and presents as an inverted taper. This unusual presentation of the root form precludes moving the gingival margin apically on the central incisor, as it would make the tooth appear wider at the gingival. This tooth also had a distal subgingival morphologic defect and was one shade darker than the left central incisor. The maxillary left lateral incisor was ankylosed in linguoversion. The lower arch was asymmetric, with the lower jaw positioned to the patient's right.
|Figure 2. Three-day postoperative after gingivectomy on the lateral incisor.||Figure 3. Putty reduction guide showing lingual displacement of lateral incisor.|
Figure 2 shows the 3-day postoperative result of a gingivectomy on the maxillary left lateral incisor, creating a balance in length with the opposite side and exposing the distal defect on the central incisor. After an initial wax-up of the proposed contour of the lateral incisor, a reduction guide was fabricated using Affinity Putty (Clinician's Choice). The putty was cut back to allow insertion of the guide intraorally with support on the occlusal surfaces of the bicuspids. Figure 3 demonstrates from an incisal view the lingual placement of the lateral incisor and also the incisal taper of the central incisor, which reveals that the tooth is much thinner distally than mesially. This degree of taper was not taken into account on the first reduction, and as will be seen, the laboratory feedback was invaluable to help create a satisfactory postoperative result.
Clearly Affinity (Clinician's Choice), a water-clear silicone impression/matrix material, was used in a disposable tray without adhesive to create a matrix for temporization of the preparations. This material was cut back on the lingual surface 1 mm short of the incisal edge to allow access for removal of excess temporary material before light curing to minimize postinsertion finishing. A shade was taken of the existing color of the maxillary left central incisor, matching the Vita A2 shade guide. The shade of the right central and lateral and of the ankylosed lateral incisor was Vita A1. It is always best to err on the light side in the prescription to the laboratory and in cementation, as most luting composites darken with time. Following is a short list of tips for better shade communication to the laboratory:
(1) Choose the best practical area, preferably in a properly lit room, with a north light combined with fluorescent natural daylight tubes of 6,500ºK and a color rendering of 92 or higher.
(2) Compare the patient's teeth with a top-quality shade guide such as the Vita Classical, Vita 3D shade master, Chromoscope, etc.
(3) Characterize on the shade chart all the characteristics present, trying to be as accurate as possible as defined by the tooth divisions of gingival, middle, and incisal. Include the details of surface characteristics and glaze. Particular anomalies such as mamelons, surface cracks, and decalcifications can always be shaded in with simple pastel colored pencils. Note: If the underlying color is dark and needs to be masked out, consider asking for some die relief so that the luting composite can have some influence on the final shade. Without die relief a well-adapted porcelain veneer will displace most of the luting resin, and thus the luting resin will have little effect on the final postinsertion shade.
(4) Digital pictures are very useful tools in visualizing where characteristics might be present. Capturing the shade guide on the same plane of the tooth often helps in determining the brightness, but it must be remembered that these camera shots don't determine shade. Send preoperative as well as post-preparation photos so the technician can see the underlying color map.
(5) If shade scans are also taken, include all printouts.11
|Figure 4. Reduction guide placed intraorally to verify reduction of lateral incisor.||Figure 5. Tissue Goo hemostatic agent placed with First String Retraction Cord (Clinician's Choice).|
|Figure 6. Hemostasis and vertical reduction grooves on central incisor.|
The reduction guide is shown intraorally in Figure 4. For better control of the newly healing gingivectomy, Tissue Goo (Clinician's Choice), a 25% aluminum sulfate, was placed (Figure 5). Figure 6 shows the tissue on the lateral incisor retracted with cord (post hemostasis) and vertical reduction grooves placed for controlled reduction of the labial surface with a tapered diamond. Alternatively, self-limiting diamond wheel burs can be used to place depth cuts in the cervical, middle, and incisal thirds of the labial surface prior to tooth reduction. Depending on the depth required as shown by the reduction guide, these are available in various depth configurations.
|Figure 7. Spot etching for retention and OraSeal Putty block out.||Figure 8. Ronald E. Jordan instruments No. 02 used to "walk" the cord into place.|
The initial tooth reduction created a well-defined chamfer finishing line, with the irregular hypocalcified distal wall of the central incisor evident in Figure 7. First String retraction cord size L (Clinician's Choice) was placed using 2 Ronald E. Jordan No. 02 (Clinician's Choice) instruments to "walk" the string into the sulcus (Figure 8). The decision to use a single or double retraction cord depends on the type of tissue and the sulcus depth. The authors prefer to take the impression with an extra assistant to remove the cord as we follow the created sulcus space with the polyvinyl siloxane impression material. The best retraction is immediately after the cord is removed, therefore the clinician should not wait for the tissue to collapse. Do not remove all the cords and then start to impress. It is helpful to use one long cord for multiple labial retractions so there is only one cord to place; this also facilitates its easy removal prior to impressioning.
|Figure 9. Entire preparation captured in Affinity Light Body Regular Flow.||Figure 10. The 5- to 7-second preset of the Intro Temporary Veneer Composite to facilitate margination.|
Hydroactive polyvinyl siloxane Affinity Light Body Regular Flow and Affinity Heavy Body (Clinician's Choice) were used in a rigid fiberglass Border-Lock tray (Clinician's Choice). Note that the heavy-body material did not displace the light-body material, thereby creating a much more accurate impression of the preparations (Figure 9). After placement of OraSeal Putty (Ultradent), which would prevent flow of the temporary material into unwanted areas in order to facilitate finishing and tissue healing, the teeth were spot-etched with Ultra-Etch 35% phosphoric acid (Ultradent, Figure 7). A thin layer of D/E Bond Resin (Bisco) was placed over the preparations. Intro Temporary Veneer Composite (Clinician's Choice) was placed inside the clear matrix. Due to its thixotropic nature, it is easy to place a small amount of translucent followed by the color of choice. A thin composite instrument can then be used to "preadapt" the material to the labial surface, thereby minimizing the amount of flash postinsertion. The matrix is carried intraorally, gently seated with a small amount of labial pressure to adapt it to the gingival tissue, and then light-cured for 5 to 7 seconds (Figure 10). The idea is to set it just enough so that the material can be easily contoured and the excess removed with a No. 12B Bard Parker blade. If the material starts to tear, just cure it for a few more seconds. When the excess flash is removed, cure the material and remove excess palatally with finishing burs. A thin layer of Tempglaze (Clinician's Choice) was placed over the Intro material and cured with an Ultra-Lume 5 (Ultradent) broadband curing light.
|Figure 11. Laboratory diagnostics of initial preparation design.||Figure 12. Suggested modifications of the preparations to allow better final contour.|
|Figure 13. Incisal view of laboratory wax-up compensating for size discrepancy.|
After submission of the final impression and digital photographs to the laboratory, the laboratory sent back digital images of our original preparations (Figure 11) along with suggested alterations to our preparations (Figure 12), which would allow more room to create the proper angulation and width of the lateral incisor to match the contralateral side. The returned wax-up (Figure 13) showed the obvious shortcomings of the original diagnostic wax-up. This is the type of laboratory relationship that we should all thrive on. All too often the laboratory is afraid or unwilling to make corrective suggestions to the practitioner for fear of insulting the dentist and losing the business. This should be a truly symbiotic relationship.
|Figure 14. Repreparation of the teeth as suggested by the laboratory feedback.||Figure 15. Excellent aesthetic result of temporization with good tissue healing and final contour.|
The teeth were reprepared (Figure 14) with more reduction on the distal aspect of the central incisor, creating more of an incisal-gingival taper without an incisal overlay. Figure 15 shows the temporization 2 weeks postinsertion. There is excellent tissue health with a good color match and visualization of incisal translucency using the Intro material.
|Figure 16. Side view of the lateral porcelain veneer showing the amount of bulk to be added.|
The veneers were verified for marginal adaptation on the dies, with Figure 16 demonstrating the extent to which the gingival margin of the lateral incisor was contoured to place the labial surface in proper alignment. The removal of the temporary restoration was difficult, with the gingival tissue slightly injured by the scaler when it broke trying to lift off the temporary.
The veneers were tried in using Prevue (Cosmedent), a water-soluble try-in gel system that matches the shade of the final cured luting composite. It must be noted here that many try-in pastes do not accurately reflect the color of the luting cement post cure.
|Figure 17. View of try-in with 80% white opaque and 20% clear Insure Light.|
The color of the veneers using the clear was too gray, and therefore opaque white was added in a number of different proportions to get the veneers to match the uncut teeth. Figure 17 shows the final match using 80% white opaque and 20% clear. As stated earlier, always err on the light side when cementing porcelain veneers, as all luting resins darken with time. Never use a dual-cure resin for cementing veneers, as the amine reaction will cause a noticeable yellowing with time. In a study by Nathanson,12 "the aged dual-cured resin cement samples revealed significantly higher changes in color compared to light-cured resin cements." Even with light-cured luting resins there is a great variation in the delta E or color change over time.
The Prevue was washed from the inner aspect of the veneers, and the surface was acidified with 35% phosphoric acid, washed, and dried. A thin monolayer of silane (Hydro-Cast Silane Porcelain Primer, Kay-see Dental) was placed with a microbrush, and then carefully air dried with an air-only syringe. Most 3-way syringes leak water into the air stream when air only is used, compromising drying and the bonding procedure. We use dedicated air-only lines for all drying/bonding techniques. The inner surface of the veneer was coated with air-thinned D/E Resin (Bisco), our mixture of Insure Light Cured Luting Resin (Cosmedent), and placed in a Resin Keeper (Cosmedent). The prepared teeth were etched for 15 seconds, washed, and lightly air-dried, and 2 coats of One Step Plus (Bisco) were applied to the surface of the enamel with air thinning. The layer of bonding resin was cured for 10 seconds per tooth (this step can be omitted, and all materials can be cured simultaneously if you are confident of the light penetration through the veneer). The loaded veneers were adapted into place, and gross excess was removed with a periodontal probe followed by a No. 1 Cosmedent brush. An Ultra-Lume LED 5 with a Pointcure lens (Ultradent) was used to spot tack the veneers, allowing for removal of interproximal and gingival excess before final cure. A full curing cycle per tooth was then applied.
|Figure 18. Adjustment of lateral protrusive to regain cuspid rise without interference.||Figure 19. Full-face view of patient demonstrating obvious facial asymmetry.|
|Figure 20. Two weeks postinsertion with lateral incisor labially displaced and central incisor recontoured with modified shade.|
The veneers were adjusted for protrusive movements of the mandible, and even more critically, for lateral protrusive movements. Lateral protrusive interference is one of the main causes for fracturing the distal incisal corner of the central incisor and the distal incisal of the lateral incisor. Figure 18 shows canine rise without interference from the lower incisors. The full-face view shows the patient's obvious facial asymmetry (Figure 19). The final intraoral view taken 2 weeks postinsertion shows a good color match with the lateral incisor placed labially and lengthened to match the contralateral side (Figure 20).
1. Boksman L, Jordan RE, Skinner DH. Non-vital bleaching: internal and external. Aust Dent J. 1983;28:149-152.
2. Boksman L, Jordan RE, Skinner DH. A conservative bleaching treatment for the nonvital discolored tooth. Compend Contin Educ Dent. 1984;5:471-475.
3. Boksman L, Jordan RE. Conservative treatment of the stained dentition: vital bleaching. Aust Dent J. 1983;28:67-72.
4. Simonsen RJ, Calamia JR. Tensile bond strength of etched porcelain [abstract]. J Dent Res. 1983;61:297. Abstract 1154.
5. Jones GE, Boksman L, McConnell RJ. Effect of etching technique on the clinical performance of porcelain veneers. Quintessence Dent Technol. 1986;10;635-637.
6. Calamia JR, et al. Shear bond strength of etched porcelains. IADR/AADR Abstract No. 355 J Dent Res 65, spec. issue (June) 765, 1986.
7. Calamia JR, Vaidyanathan J, Viadyanathan TK, et al. Shear bond strength of etched porcelains. J Dent Res. 1986;64;296.
8. Craig RG, Powers JM, eds. Restorative Dental Materials. 11th ed. St Louis, Mo: CV Mosby; 2001.
9. Magne P, Douglas WH. Cumulative effects of successive restorative procedures on anterior crown flexure: intact versus veneered incisors. Quintessence Int. 2000;31:5-18.
10. Castelnuovo J, Tjan AH, Phillips K, et al. Fracture load and mode of failure of ceramic veneers with different preparations. J Prosthet Dent. 2000;83:171-180.
11. Pow Laboratories Inc, Woodstock, Ontario. Shade Communication "Tips and Procedures" 2005 (In-house publication).
12. Nathanson D, Banasr F. Color stability of resin cements â€“ an in vitro study. Pract Proced Aesthet Dent. 2002;14:449-455.
Special thanks to Rotsaert Dental Laboratory Services in Hamilton, Ontario for its support in this case.
Dr. Carson received his DDS degree from the University of Western Ontario, Canada. He maintains a private practice in London, Ontario. He was awarded the Johnson and Johnson Restorative Award in 1983. He has published articles and in-office research for several dental corporations. He is a member of the Thames Valley Dental Study Club, London and District Dental Society, where he held the positions of treasurer, secretary, vice president, president and past president. He is also a member of Ontario Dental Association, Canadian Dental Association. He can be reached at (519) 660-1066.
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