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Written by Jürgen Manhart, DDS, MS, PhD Tuesday, 01 April 2008 00:00
In combination with an adhesive technique, ceramic veneers can offer a minimally invasive treatment approach to modify shape and position of teeth as well as mask discolorations. The following article will first review and discuss the principles for successful all-ceramic veneer placement. A case report will then be presented that demonstrates the application of this gentle therapy variation on a patient who suffered trauma to multiple anterior teeth from a bicycle accident.
INDICATIONS/CONTRAINDICATIONS FOR ALL-CERAMIC VENEERS
Ceramic veneers are thin shells made from all-ceramic materials that are cemented to the tooth with the assistance of an adhesive bonding technique. In suitable cases, veneers enable a conservative and aesthetic treatment that may often replace the preparation of complete crowns in anterior teeth. They may also offer an alternative when anterior teeth with extremely large defects, demanding shade and texture situations, or patients with high aesthetic demands are in many cases beyond the scope of direct composite restoration indications.
Indications for all-ceramic veneers can include the following: improvement of aesthetics, discolorations, moderate to severe hypocalcification and other enamel defects, erosion, abrasion, large and aesthetically inadequate composite restorations, improvement of surface texture, correction of tooth shape and/or position, dysplastic anterior teeth, diastema closures, palatal veneers for the reconstruction of functional oral guidance surfaces (eg, maxillary cuspids), as well as selected minor tooth fractures.
Contraindications can include the following: insufficient enamel quantity and/or quality, cervical margins of the veneers that are not limited within enamel, circular carious lesions at the gingival level, severely discolored teeth that cannot be masked sufficiently, extremely large diastemas, patients with severe parafunction and/or untreated occlusal disease, and other small defects that could be handled with an even more conservative treatment modality.
PLANNING AND ANALYSIS OF AESTHETICS
An exact plan is drawn out for each veneer treatment. It contains analysis of the cause of discoloration, the possibility of orthodontic pretreatment with serious tooth position anomalies, and an evaluation of the possible need for preoperative bite elevation in cases of decreased vertical dimension. In this respect, it is important to involve the dental technician from the outset in the planning process. Good communication with the dental technician is an indispensable and basic requirement for optimal aesthetics and function. The distribution of different hues, as well as degrees of translucency and opacity within the tooth surfaces in the region of the mouth to be restored, must also be evaluated within the scope of an aesthetic analysis. Moreover, an age-dependent reconstruction that is linked to the general wear and existing tooth colors of the individual patient is advisable. Individual characteristics of the tooth, such as enamel cracks and surface texture, are assessed for the buildup of the restoration. Thus, the goal is to provide each patient with veneers that create ideal tooth positioning, shape, and shade. Documenting the initial situation with digital photographs is highly recommended. In addition, a preoperative wax-up is also recommended for situations involving significant changes. A diagnostic wax-up often serves multiple purposes and can provide a wealth of information. For the dentist, a wax-up helps to develop a treatment game plan for minimal tooth preparation that will be done only on the necessary sites. For the patient and the dentist, this enables visualization of the proposed treatment option while offering the possibility of modifications before preparation begins.
ANTERIOR VENEER PREPARATION
Generally, several varying styles of preparations are utilized for preparing anterior all-ceramic veneers. In addition to the in-enamel preparation extending to the incisal edge, with reduction approximately one half of the thickness of the enamel (contact lens veneer), there are also versions with varying incisal-horizontal reduction of the tooth and/or incisal overlay.
After creating 0.3- to 0.5-mm cuts with special depth-cutting diamond burs, the facial enamel is reduced, maintaining the anatomical shape. A reduction of less than 0.3 mm is not recommended to lower the risk of veneer fracture. With darker teeth, an additional labial reduction of 0.2 mm is advisable in order to mask discoloration sufficiently. If more than 50% of the facially reduced surface is in dentin, the risk of fracture and/or debonding of the veneer is significantly increased. The incisal reduction, if necessary after considering any significant pre-existing wear, should be approximately 1.5 to 2.0 mm. If the incisal edge preparation is wrapped onto the lingual aspect of a tooth (eg, of the maxillary anterior teeth), the tooth-porcelain margin interface should not be allowed to lie within the zone of static occlusion contact.
The gingival preparation line is prepared with a chamfer, and it should be limited completely within enamel. In the case of maxillary anterior teeth, the finish line should be prepared at the level of the gingival crest to a maximum subgingival placement not to exceed 0.5 mm. The functional zone of the lower lip can often allow for placement of the preparation margin to be up to 1.0 mm above the gingival crest for lower anterior teeth. However, when correcting the shade of very dark teeth in the mandibular arch, the aim should be to place the finish line at the gingival margin.
The interproximal preparation geometry is determined by the tooth position and any existing discoloration. With normal tooth-to-tooth position, the preparation should extend to, but not break, the interproximal contact to retain further natural enamel. The use of oscillating preparation systems is suitable here to protect the neighboring dentition. If the interdental embrasure must be reshaped (eg, diastema closure) or if the discoloration is severe, then the preparation margin must extend lingually through the interproximal contact and slightly subgingival in order to provide ideal geometry. This will allow the dental technician to create ideal tooth morphology and/or to achieve the maximum masking of any discoloration.
The veneer must have a clearly defined final position to avoid seating problems during insertion. This problem arises only with pure contact lens veneers and can be elegantly solved by preparing two hemispherical recesses on the labial surface. Any existing composite fillings should be completely covered by the veneer preparation and must be replaced in advance if necessary. The entire veneer preparation is best carried out with a finegrit diamond bur.
PREMOLAR VENEER PREPARATION
If it is necessary to place veneers on the buccal aspects of maxillary premolars, then the preparation should be done in an analogous way to the anterior preparation technique. The occlusal porcelain-to-tooth margin should not be situated within a centric occlusal stop or within the functional glide path. If cuspid-protected anterior guidance is not present, and the patient has a dynamic occlusion on the working side (posterior group function), then extending the occlusal finish line down to the central groove while reducing the buccal cusp a minimum of 2 mm may be advantageous. For ceramic longevity and fracture prevention, veneers should not be placed on mandibular premolars. Placing a ceramic crown or onlay with coverage of the working cusp is preferable here.
VENEER LUTING PROCEDURES
When inserting multiple veneers, after checking the fit of each individual veneer, a collective try-in is conducted to verify fit. The interproximal contacts are evaluated as well to determine the sequence of insertion. A water-soluble (glycerin) try-in paste, which corresponds to the shade of the cured luting cement, is used to evaluate the shade and relative translucency or opacity. These pastes will also eliminate the influence of air on the overall optical (aesthetic) result due to differences in the refraction index between the involved materials. Minor color changes can be corrected by using luting cement with varying shade intensities. However, it must be noted that the shade is more heavily determined by the ceramic(s) used and not by an extremely thin layer (microns) of shaded luting cement. To avoid dehydration of the teeth, which will render the teeth higher in value and more opaque, as well as hinder aesthetic evaluation, this tryin process should always take place prior to application of a rubber dam. After placement of the rubber dam, and a dry working field has been secured, the veneers are luted with a low-viscosity luting cement according to the manufacturer’s instructions for the adhesive technique being used. By their optical nature, thin ceramic veneers allow the use of a high-intensity polymerization light-curing unit with a light-cured (LC) resin cement.
|Figure 1. Preoperative photograph (after the accident and palliative care) showing an aesthetically unacceptable composite restoration on tooth No. 8. Tooth No. 9 is shown here after it was adhesively reattached after being traumatically fractured.||Figure 2. The veneer preparation on tooth No. 8 and a modified shoulder preparation for tooth No. 9 have been completed.|
|Figure 3. Temporary restorations have been placed awaiting the definitive restorations.||Figure 4. The temporaries have been removed and the teeth cleaned. Note the healthy gingival tissues.|
A 30-year-old female presented with a fractured tooth No. 9 several months after a bicycle accident. As the result of the accident, the pulp had been traumatically exposed from a fracture extending from the distal-palatal area to the marginal gingiva of the tooth. In the course of the palliative emergency treatment, the exposed pulp had been directly capped with a calcium hydroxide dressing, and a large fragment of the fractured tooth crown was reattached using a flowable composite with an adhesive bonding technique.
Later, at the patient’s follow-up visit for definitive restorative treatment in our clinic, it was discovered that tooth No. 9 had lost its vitality since the time of the emergency treatment. Additionally, tooth No. 10 exhibited trauma-in-duced fracturing at and along the incisal edge. Tooth No. 8 had a large composite restoration that was aesthetically unacceptable due to discoloration. The patient want-ed to replace that composite with a more aesthetic all-ceramic veneer in the process of the restorative treatment (Figure 1). After successful endodontic treatment of the left upper central incisor (tooth No. 9), the preparation for the all-ceramic crown was performed 4 weeks later. A 1.0-mm wide, circumferential, modified shoulder preparation was prepared, with an incisal edge reduction of 2.0 mm. A ceramic veneer preparation was performed on tooth No. 8. Removing the old composite filling revealed that the remaining, post-traumatic tooth structure sloped toward the mesial gingival papilla (Figure 2). After taking an impression and bite registration, both teeth were fitted with provisional restorations until the insertion of the definite restorations could be done (Figure 3). The case was then sent into the dental laboratory for fabrication of the restorations (Sidebar).
LABORATORY FABRICATION OF VENEERS
After impressions are taken and any needed temporization is completed, the technical fabrication of the ceramic veneer is carried out in the dental laboratory. There are different techniques that the dental technician can utilize to fabricate ceramic veneers. Veneers made entirely from sintered ceramics on a refractory die can be extremely aesthetic, since they possess optimal 3-D shade depth. However, the technician must exercise caution in the fabrication process to minimize the inclusion of micro-bubbles; these can reduce the strength of the ceramic. Pressed ceramic veneers are made with a full-contour anatomic wax-up that is subsequently burned out using the lost-wax method. A specialized oven is then used to press the heated, molten ceramic, thus creating the ceramic veneer. The utilization of ceramic ingots with varied shades, translucency, and opacity in combination with a stain-and-glaze technique can result in excellent aesthetics and durability. Dental technicians can also utilize ceramic layering techniques if specialized shading and/or aesthetic effects are required. At this point in time, CAD/CAM veneers have not yet shown an ability to meet the high aesthetic expectations that are linked to all-ceramic veneer restorations.
|Figure 5. Try-in of the ceramic veneer on tooth No. 8.||Figure 6. Try-in of the ceramic veneer (No. 8) with try-in paste, shade A1.|
|Figure 7. Try-in of the ceramic veneer (No. 8) with try-in paste, shade A2.||Figure 8. Try-in of the ceramic veneer (No. 8) with try-in paste, shade BL.|
|Figure 9. Try-in of the ceramic veneer (No. 8) with try-in paste, shade WO.||Figure 10. A small retraction cord is placed prior to the adhesive cementation procedure on tooth No. 8.|
|Figure 11. Etching with phosphoric acid.||Figure 12. Gentle drying of the tooth surface to remove excess moisture.|
|Figure 13. Application of the primer solution.||Figure 14. Light polymerization from the labial direction.|
|Figure 15. Light polymerization from the palatal-incisal direction.||Figure 16. Postoperative photo of the adhesively bonded aesthetic restorations on tooth No. 8 and tooth No.9.|
The insertion appointment be-gan by removing the temporaries and thoroughly cleaning the teeth to remove all traces of temporary cement (Figure 4). The gingival tissue was in perfect condition. Next, the fit of the ceramic veneer was then checked by gently placing the veneer onto tooth No. 8 (Figure 5). With the assistance of the four shades of try-in paste (A1, A2, BL, WO) found in the Grandio Flow Veneer Kit (VOCO), the ideal shade of the light-curing composite cement was then determined (Figures 6 to 9). These try-in pastes consist of dyed, water soluble glycerin gel and correspond to the respective shade of the cured luting composite. After determining the ideal cement shade, the veneer was thoroughly cleaned and prepared for the adhesive luting procedure. For this purpose, the veneer was etched with hydrofluoric acid. (If this etching procedure is done by the laboratory technician prior to the delivery of the all-ceramic restorations to the doctor, it does not need to be repeated.) The internal, etched surfaces were then treated with silane and dried (Ceramic Primer [VOCO]). On No. 8, the right central incisor, the gingiva/tissue was gently displaced with an appropriately sized retraction cord (Figure 10). The entire preparation surface was subsequently conditioned with 37% phosphoric acid, while the interproximal surface of the neighboring tooth was protected with a clear matrix strip (Figure 11). After thorough rinsing to remove the acid and precipitation residue, the tooth surface was carefully dried (Figure 12) and subsequently prepared with Solobond Plus (VOCO) adhesive bond (Figure 13). The light-cured luting composite, Grandio Flow, chosen in the previously selected shade that was determined by use of the try-in pastes, was applied in a thin layer on the (etched and silanated) internal surface of the ceramic veneer. The veneer was then carefully seated on the prepared tooth. The excess cement was gently removed after the veneer was fully seated. Next, the resin cement was light-cured from multiple angles, 40 seconds at each position, with a high-intensity light polymerization unit (Figure 14 and 15). The all-ceramic crown on tooth No. 9 was adhesively luted (Figure 16) in an analogous fashion with a dual-cured luting resin (Bifix QM [VOCO]). Finally, the incisal edge on tooth No. 10 was repaired and modified aesthetically with a (direct) composite resin restorative material. The aesthetics and function of this patient’s maxillary anterior teeth were completely and successfully restored with resin-bonded all-ceramic restorations and a conservatively placed direct composite resin restoration.
All-ceramic restorations have reached an extraordinarily high standard of quality and have become an indispensable therapeutic instrument for conservative restorative and aesthetic dentistry. This material group is distinguished by its excellent aesthetics and excellent tissue biocompatibility. Data from clinical studies indicate that superb clinical survival rates are attainable when proper indications for all-ceramics are followed right from the start of treatment, the right type of ceramic is selected based on the case specifics, and, in addition to the dental laboratory’s correct manufacture of the ceramic restoration, when precise preparation and sound luting techniques are utilized.
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