Porcelain Veneers (2)

Porcelain veneers They enable the dentist to change the appearance, size, color, spacing, and, to a minor extent, the positioning of the teeth. Many veneering procedures can be accomplished with little or no preparation of the natural dentition, and commonly, anesthesia is not required.

Bonded porcelain veneers have a number of  significant advantages over either metalceramic or all-ceramic crowns. they are extremely conservative in terms of tooth structure their durability  lack of potential for pulpal involvement

THE RELATIONSHIP BETWEEN APPEARANCE  AND SUCCESS

DIRECT RESIN VENEERS

THE BONDING THAT MADE IT ALL POSSIBLE

INDICATIONS AND CONTRAINDICATIONS

Hypocalcification. The so-called white "discoloration", these spots can be as perplexing to the patient and dentist as staining

Diastemas. These are frequently seen in patients whose jaw and teeth sizes do not match. The mandible may be too large, or the teeth may be too small, or possibly a combination of both. There may be anterior spacing due to early loss of the posterior teeth and the subsequent drifting.

Peg laterals. These malformed incisors occur relatively frequently, often being seen in patients who have congenitally missing teeth and the related problems of diastemas. Peg laterals are hereditary, and if a patient is affected, it is likely that his siblings will require treatment also.

Chipped teeth. This kind of breakdown may be attributable to external influences, such as sports or fights, or to intraoral forces, such as bruxing, grinding, and clenching.

Rotated teeth. These teeth erupt or grow  incorrectly, often as a result of crowding during the mixed dentition period. Their cosmetic treatment will sometimes include the use of orthodontics

Lingual position. These malpositioned teeth are most often corrected orthodontically, but can be treated with porcelain veneers as well.

Stained restorations. Composite restorations may be acceptable dentally, but not esthetically. For patients who smoke, or drink coffee or tea, replacing these with new composites is often at best a short term solution.

Foreshortened teeth. Some patients have  worn away some part of their incisors through clenching or grinding. Once the problem of decreased vertical dimension has been attended to, these anteriors can be esthetically restored.

Malpositioned midlines. In cases where there is a moderate amount of midline displacement, especially when this is associated with diastemas, porcelain veneers may be a desirable treatment modality 

Toothbrush abrasion. The non-invasive nature of veneering, and the resistant surface presented after treatment, make porcelain veneers the restoration of choice

 Worn acrylic veneers. There are many  patients who have preformed plastic veneers bonded to their teeth. Unfortunately, preformed plastic laminates have a relatively short esthetic lifetime in the mouth.  When the positive esthetic effect of the plastic veneer is lost, these patients  become ideal candidates for porcelain laminates.

Missing lateral incisors. This common problem is often solved by disguising the cuspid as a lateral incisor. Since the facial aspect of the premolars exhibit caniniform anatomy, the result can be esthetically dramatic.

CONTRAINDICATIONS

Insufficient fusible substrate. The technique used to attach porcelain  veneers to teeth has always been most effective with etched enamel.

Labial version. Teeth that are positioned labially to the arch contour beyond the reasonable depth to which preparation can be taken traditionally have not been veneered. The anticipated bond strength to dentin has always remained below acceptable levels for this technique. As already indicated, it is hoped that with the new generations of dentin bonding agents this restriction will be lifted. Until such time, however, we would continue to recommend that whenever possible such cases should be treated orthodontically 

Excessive interdental spacing. This type of situation does not allow full closure of the spaces without creating another esthetic problem-oversized looking teeth. Porcelain laminates can still be used to improve the esthetic situation, but the experienced CosmeticDentist will leave some interproximal space.

Poor oral hygiene. The lack of home care is a contraindication to any type of  major dental restorative work, including  veneers

 When mouth breathing is present, there is a relatively poor prognosis for the case due to both the eventual decay under the veneers and the potentially shortened lifespan of  the materials themselves Some contact sports. Chipped anteriors are sometimes the result of playing various sports without a protective face or mouthguard. Clenching or bruxing. Clenchers and bruxers are sometimes poor candidates for porcelain veneers for a perhaps surprising reason.

Extreme midline deviation. In those few cases where one of  the upper central incisors actually straddles the midline, laminate  veneering is not a good solution to the problem

THE SMILE ANALYSIS Obviously, the first step in the fabrication of porcelain veneers must be to establish the need for this kind of restorative work and the conditions upon which ultimate success (or failure) will be predicated.  When restoration of a larger section of the dentition is considered, however, the initial evaluation should be the smile analysis. This should be done to help both the dentist and patient examine the general problems that exist and the potential for their solution.

The Diagnostic Wax Up

Labial reduction of 0.5 mm is recommended, terminating in a chamfer  margin in a slightly supragingival location.  A depth-cutting diamond (Brasseler USA, Savannah, Ga.) is useful for providing the proper depth reduction

If the tooth is to be neither lengthened nor shortened, the incisal edge is reduced 0.75 mm to 1 mm, and the lingual surface of the tooth reduced 1 mm past the prepared incisal edge. The lingual finish line is in the form of a shoulder 0.5 mm in depth.

On maxillary teeth, the location of the lingual finish line is determined by   whether the mandibular incisors are to be restored. If the mandibular teeth are to be restored with crowns or veneers, the finish line on the maxillary teeth is carried gingivally past the point of centric occlusion contact with the mandibular incisal edges.

If the mandibular teeth are not going to be restored,

the lingual finish line is 1 mm from the prepared incisal edge as stated previously Carrying the preparation over the incisal edge limits the path of placement of the veneers but has two important advantages. The veneers can be more esthetic when this is done, and incisal translucency  can be created if indicated . The second potential advantage is that some clinicians feel such veneers may   be stronger than veneers that terminate at the incisal edge, and the incidence of  fracture and/or debonding due to shear stress may be reduced.

First, diagnostic casts should be mounted in an articulator of choice and a diagnostic wax-up completed. This will give an indication of the amount of tooth lengthening required to establish function and the desired esthetic result. It will also indicate whether it is desirable to increase the vertical dimension. This wax-up can be duplicated in gypsum and a polypropylene matrix fabricated on the duplicate cast. Tooth-colored photo-cured acrylic resin can be used to form a try-in restoration to preview the final esthetic result prior to irreversible tooth preparation. The final, optional, step in preparation of the veneers is the breaking of  interproximal tooth contact using diamond-impregnated strips. Removal of the interproximal contacts facilitates laboratory steps but necessitates the fabrication of provisional restorations, which is readily  accomplished using a clear matrix and light-cured acrylic resin (Unifast, G.C. America, Scottsdale, Ariz.). Impressions are made in a (poly) vinylsiloxane impression material and the veneers are fabricated in the laboratory  cementing a veneer with medium to high viscosity resin luting agent

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 1-Preoperative view of tooth stained for  demonstration prior to preparation for   porcelain laminate veneer   2-Position LVS1 (.5mm) or LVS2 (.3mm) depth 4 cutters so that the three striations are evenly  placed across the labial surface of incisor   3-Move the LVS depth cutter across the labial  surface—developing the striations. The depth cutter  5 has been specifically designed so that placement in the middle and incisal third of the tooth will result  in a shallower reduction in the cervical third of the tooth where the enamel is thinner  6

 4-View shows initial reduction with depth cutter and preparation on mesial half of tooth with coarse grit of the two grit diamond   LVS3, following contour of gingival margin.  5 -Next use the appropriate size of two grit  diamond LVS3 or LVS4, (red & green band) to reduce the remaining enamel to the depth of the striations. 6- In addition to reducing the remaining enamel with the coarse part of the diamond, the fine grit on the tip establishes the finish line of the

preparation

 VENEER MARGIN PLACEMENT

PREPARATION TYPES  With these factors in mind, here are the six basic preparation types:

Type I. Minimal Preparation. This preparation type is well described by its name. In a minimal preparation, no tooth reduction is undertaken except for that necessary to provide a path of insertion that is free from undercuts. Often this means that no preparation is necessary.

Type II. Incisal Preparation. On occasion, for reasons of shade control, it is advantageous to have a greater thickness of porcelain at the incisal edge than at the knife edged finish line provided by the Type I preparation. In these cases, it is suggested that the dentist cut into the incisal edge in such a way  as to allow for an even thickness of porcelain as the incisal edge is approached. This is easily achieved with a cylindrical instrument, such as a 556 bur or a diamond cylinder. The dentist should be aware of the direction of  the enamel prisms to avoid undercutting them.

Type III. Over the Incisal Edge. In this design, the porcelain extends beyond the incisal edge. If the tooth is already shortened, then all that is needed is to ensure that there are no sharp angles protruding from the tooth in the areas where the veneer is to be placed (including the incisoproximal angles) and to be certain that the path of  insertion is free from undercuts. In addition, the margin of the veneer should terminate on enamel if at all possible. Often this means a slight reduction of the lingual aspect of the incisal edge to make room for the porcelain

Type IV. Over the Incisal Edge with a Lingual Ledge. The Type IV preparation is  very similar to the Type III preparation. They both extend past the incisal edge of the tooth and wrap around to the lingual surface. In fact, from the facial, the two preparation types are identical

The difference is found in the gingival margin of the lingual porcelain. In the Type III preparation, the laminate ends in a knife edge. In the Type IV preparation, the gingival porcelain on the lingual is a deep chamfer or even a shoulder. Theoretically this increased  bulk is designed to provide increased strength in situations where the fusing strengths are expected to be below optimal.

Type V. Maximal Preparation. The Type  V preparation consists of a general reduction of the entire labial surface of the tooth to be  veneered. In addition, it is usual with a Type  V preparation to include some sort of chamfer finish line at the gingival. This preparation type is used whenever maximum bulk of  porcelain is desired for masking out underlying discolorations, or whenever any increase in labial bulk must be minimized. Such  would be the case when treating an individual tooth that is correctly aligned with the neighboring teeth, as seen in these views, or  whenever the teeth to be laminated are already in slight labio-version

Type VI. Double Preparation. This finding suggests the method for maximum control of the final color by the dentist. Since the dentist has control of the density and shade of the luting agent, the thicker the layer of composite, the greater the amount of control he will have. As a direct result of this observation, in May 1987 McLaughlin published the sixth preparation category (Type VI),' called the "double preparation". The double preparation is used when the dentist desires maximum change between the natural color of the tooth and the final shade. This preparation consists of two stages. In the first stage the dentist prepares the tooth using a Type I (minimal) preparation and then takes an impression. When the veneers arrive, and after they are tried on for shape and size, the areas of  the tooth requiring maximum change in color are reprepared into a Type V (maximal). preparation. This creates a gap between the  veneer and tooth sufficient enough to place a totally opaque masking layer of composite. Although the composite used should  be totally opaque, it must also be the final shade desired for the restoration