porcelain veneers (2)

7/27/2019 Porcelain Veneers (2)

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Porcelain veneersThey enable the dentist to change

the appearance, size, color, spacing, and, to a minor extent,

thepositioning of the teeth. Many veneering procedures can be

accomplished with little or no preparation of the naturaldentition,

and commonly, anesthesia is not required.


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Bonded porcelain veneers have a number ofsignificant advantages over either metal-ceramic or all-ceramic crowns.

they are extremely conservative in terms of tooth structure

their durability

lack of potential for pulpal involvement


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THE RELATIONSHIP BETWEEN APPEARANCEAND SUCCESS


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DIRECT RESIN VENEERS

THE BONDING THAT MADE IT ALL POSSIBLE

INDICATIONS AND CONTRAINDICATIONS


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Hypocalcification. The so-called white"discoloration", these spots can be as perplexing

to the patient and dentist as staining


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Diastemas. These are frequently seen in patients whose jaw and teeth sizes do notmatch. The mandible may be too large, or the teeth may be too small, or possibly acombination of both. There may be anterior spacing due to early loss of theposterior teeth and the subsequent drifting.


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


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


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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


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Lingual position. These malpositionedteeth are most often corrected orthodontically, but can be treated withporcelain veneers as well.


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Stained restorations. Composite restorations

may be acceptable dentally, but not esthetically. For patients who smoke, ordrink coffee or tea, replacing these with new composites is often at best a shortterm solution.


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Foreshortened teeth. Some patients have

worn away some part of their incisors through clenching or grinding. Once theproblem of decreased vertical dimension has been attended to, these anteriorscan be esthetically restored.


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Malpositioned midlines. In cases wherethere is a moderate amount of midline displacement, especially when this isassociated with diastemas, porcelain veneers may be a desirable treatmentmodality


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Toothbrush abrasion. The non-invasivenature of veneering, and the resistant surface presented after treatment, makeporcelain veneers the restoration of choice


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Worn acrylic veneers. There are manypatients 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 patientsbecome ideal candidates for porcelain laminates.


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Missing lateral incisors. This common problem is often solved by disguisingthe cuspid as a lateral incisor. Since the facial aspect of the premolars exhibit

caniniform anatomy, the result can be esthetically dramatic.


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CONTRAINDICATIONS

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


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Labial version. Teeth that are positionedlabially 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 hasalways remained below acceptable levels for this technique. As already indicated, it ishoped that with the new generations of dentin bonding agents this restriction will belifted. Until such time, however, we would continue to recommend that wheneverpossible such cases should be treated orthodontically


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Excessive interdental spacing. This type of situation does not allow fullclosure of the spaces without creating another esthetic problem-oversized

looking teeth. Porcelain laminates can still be used to improve the estheticsituation, but the experienced CosmeticDentist will leave some interproximalspace.


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Poor oral hygiene. The lack of homecare is a contraindication to any type ofmajor dental restorative work, including

veneers


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When mouth breathing is present, there is arelatively poor prognosis for the case due to both the eventualdecay under the veneers and the potentially shortened lifespan of

the materials themselvesSome contact sports. Chipped anteriors are sometimes theresult of playing various sports without a protective face ormouthguard.

Clenching or bruxing. Clenchers and bruxers are sometimespoor candidates for porcelain veneers for a perhaps surprisingreason.

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


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THE SMILE ANALYSIS

Obviously, the first step in the fabrication of porcelain veneersmust be to establish the need for this kind of restorative work andthe conditions upon which ultimate success (or failure) will bepredicated.

When restoration of a larger section of the

dentition is considered, however, the initial evaluation should bethe smile analysis. This should be done to help both the dentistand patient examine the general problems that exist and thepotential for their solution.

The Diagnostic Wax Up


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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 isreduced 0.75 mm to 1 mm, and the lingual surface of the tooth reduced 1mm past the prepared incisal edge. The lingual finish line is in the form

of a shoulder 0.5 mm in depth.


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

Ifthe mandibular teeth are not going to be restored, the lingual finish lineis 1 mm from the prepared incisal edge as stated previously Carrying thepreparation over the incisal edge limits the path of placement of the veneers buthas two important advantages.The veneers can be more esthetic when this is done, and incisal translucencycan be created if indicated .

The second potential advantage is that some clinicians feel such veneers maybe stronger than veneers that terminate at the incisal edge, and the incidence offracture and/or debonding due to shear stress may be reduced.


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First, diagnostic casts should be mounted in an articulator of choiceand a diagnostic wax-up completed. This will give an indication of theamount of tooth lengthening required to establish function and thedesired esthetic result. It will also indicate whether it is desirable toincrease the vertical dimension. This wax-up can be duplicated ingypsum and a polypropylene matrix fabricated on the duplicate cast.Tooth-colored photo-cured acrylic resin can be used to form a try-inrestoration to preview the final esthetic result prior to irreversibletooth preparation.

The final, optional, step in preparation of the veneers is the breaking ofinterproximal tooth contact using diamond-impregnated strips.Removal of the interproximal contacts facilitates laboratory steps butnecessitates the fabrication of provisional restorations, which is readilyaccomplished using a clear matrix and light-cured acrylic resin (Unifast,

G.C. America, Scottsdale, Ariz.). Impressions are made in a (poly) vinyl-siloxane impression material and the veneers are fabricated in thelaboratory

cementing a veneer with medium to high viscosity resin luting agent


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1-Preoperative view of tooth stained fordemonstration prior to preparation for

porcelain laminate veneer2-Position LVS1 (.5mm) or LVS2 (.3mm) depthcutters so that the three striations are evenly

placed across the labial surface of incisor3-Move the LVS depth cutter across the labialsurfacedeveloping the striations. The depth cutterhas been specifically designed so that placement inthe middle and incisal third of the tooth will resultin a shallower reduction in the cervical third of thetooth where the enamel is thinner


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4-View shows initial reduction with depth cutterand preparation on mesial half of toothwith coarse grit of the two grit diamondLVS3, following contour of gingival margin.5-Next use the appropriate size of two gritdiamond LVS3 or LVS4, (red & green band)to reduce the remaining enamel to the depthof the striations.6-In addition to reducing the remainingenamel with the coarse part of thediamond, the fine grit on the tip

establishes the finish line of thegingival and proximal margins.


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preparation


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VENEER MARGIN PLACEMENT


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PREPARATION TYPES

With these factors in mind, here are the six basic preparationtypes:

Type I. Minimal Preparation. This preparationtype is well described by its name.In a minimal preparation, no tooth reduction isundertaken except for that necessary to providea path of insertion that is free from undercuts.

Often this means that no preparation is necessary.


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Type II. Incisal Preparation. On occasion,for reasons of shade control, it is advantageousto have a greater thickness of porcelainat the incisal edge than at the knife edgedfinish line provided by the Type I preparation.

In these cases, it is suggested that thedentist cut into the incisal edge in such a wayas to allow for an even thickness of porcelainas the incisal edge is approached. This iseasily achieved with a cylindrical instrument,such as a 556 bur or a diamond cylinder. The

dentist should be aware of the direction ofthe enamel prisms to avoid undercuttingthem.


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Type III. Over the Incisal Edge. In this design,

the porcelainextends beyond the incisal edge. If the tooth isalready shortened, then all that is needed is toensure that there are no sharpangles protruding from the tooth in the areas wherethe veneer is to be placed (including the inciso-

proximal angles) and to be certain that the path ofinsertion is free from undercuts.In addition, the margin of the veneer shouldterminate on enamel if at all possible.Often this means a slight reduction of the lingualaspect of the incisal edge to make room for the

porcelain


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Type IV. Over the Incisal Edge with aLingual Ledge. The Type IV preparation isvery similar to the Type III preparation.They both extend past the incisal edge of thetooth and wrap around to the lingual surface.In fact, from the facial, the two preparationtypes are identical

The difference is found in the gingivalmargin of the lingual porcelain. In the TypeIII preparation, the laminate ends in a knifeedge. In the Type IV preparation, the gingivalporcelain on the lingual is a deep chamferor even a shoulder. Theoretically this increasedbulk is designed to provide increasedstrength in situations where the fusingstrengths are expected to be below optimal.


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Type V. Maximal Preparation. The TypeV preparation consists of a general reduction

of the entire labial surface of the tooth to beveneered. In addition, it is usual with a Type

V preparation to include some sort of chamferfinish line at the gingival. This preparation

type is used whenever maximum bulk ofporcelain is desired for masking out underlying

discolorations, or whenever any increasein labial bulk must be minimized. Such

would be the case when treating an individualtooth that is correctly aligned with the

neighboring teeth, as seen in these views, orwhenever the teeth to be laminated are

already in slight labio-version


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Type VI. Double Preparation. This finding suggests themethod 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 theamount of control he will have. As a direct result of this

observation, in May 1987 McLaughlin published the sixth preparationcategory (Type VI),' called the "double preparation".

The double preparation is used when the dentist desiresmaximum change between the natural color of the tooth and the

final shade. This preparation consists of two stages. In the firststage 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 ofthe tooth requiring maximum change in color are reprepared intoa Type V (maximal). preparation. This creates a gap between the

veneer and tooth sufficient enough to place a totally opaquemasking layer of composite. Although the composite used shouldbe totally opaque, it must also be the final shade desired for the

restoration


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porcelain veneers (2)

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