Veneers

Indications

Veneers are an important tool for the cosmetic dentist. A dentist may use one veneer to restore a single tooth that may have been fractured or discolored, or multiple teeth to create a "Hollywood" type of smile makeover. Many people have small teeth resulting in spaces that may not be easily closed by orthodontics. Some people have worn away the edges of their teeth resulting in a prematurely aged appearance, while others may have malpositioned teeth that appear crooked. Multiple veneers can close these spaces, lengthen teeth that have been shortened by wear, fill the black triangles between teeth caused by gum recession, provide a uniform color, shape, and symmetry, and make the teeth appear straight. Dentists also recommend using thin porcelain veneers to strengthen worn teeth. Thin veneers is an effective option for aging patients with worn dentition. In many cases, minimal to none tooth preparation is needed when using porcelain veneers.

Contraindications

The problem of overuse of porcelain veneers by certain cosmetic dentists in 'Confessions of a Former Cosmetic Dentist'. He suggests that the use of veneers for 'instant orthodontics' or simulated straightening of the teeth is harmful, especially for younger people with healthy teeth. Leading dentists caution that minor cosmetic or wear is not justification for porcelain or ceramic veneers, the tooth preparation of which may destroy 3-30% of the tooth surface during tooth preparation for veneers, and after 10 years, 50% of veneers are gone, need retreatment, or no longer in satisfactory condition.

Veneers: Find A Cosmetic Dentist For Dental Veneers

What Are Dental Veneers?

There are many cosmetic dentistry situations which arise that lend themselves to treatment with dental veneers by your cosmetic dentist. One indication is for restoring teeth with discoloration that have been unaffected by the more conventional teeth bleaching approaches. Some examples of this are teeth that have severe tetracycline (an antibiotic) staining or discoloration from a previous injury to the tooth.

Another major indication is for teeth that require significant changes in their shape or contour. By placing dental veneers, small or misshapen teeth can be built up to regain a more natural appearance, spaces between teeth can be closed by making the teeth wider and teeth that are too short can be lengthened.

Porcelain dental veneers or composite veneers are a very popular dental care treatment option for a variety of reasons. They are one of the most conservative restorations that can be done by your cosmetic dentist. This means that the amount of tooth structure that must be removed is very small. Generally, only 0.3 to 0.7 mm needs to be removed from the surface of your tooth.

Dental veneers are then made and bonded to the teeth, incorporating the desired changes in shape and color. Since veneers are so thin and there is no metal in them, the esthetic potential is very high. Veneers can be made of two different materials, either composite or porcelain.

Composite Veneers

The major advantage of composite veneers is treatment time. If composite is used, the dental veneers can be done in one appointment. The dentist will actually make the veneers directly on the prepared teeth.

The veneers are then smoothed and polished to look like your natural teeth. Since it takes only one appointment, you can leave your dentist's office with a brand new smile.

One of the disadvantages of composite veneers is that they are not as strong as porcelain veneers and therefore are more prone to fracture. However, if a fracture does occur, they can be easily repaired because the same material that was used initially to make the veneers can be added in the same manner to fix it.

Another disadvantage is that the color, although stable, is not as stable as the same porcelain veneer restoration. This means that over time the veneers may get darker or turn yellow. Eventually, this change in color can warrant the replacement of the composite veneers.

Porcelain Veneers

Porcelain veneers require a longer treatment time. At the first appointment, your teeth are prepared and an impression is made of them. Temporary dental veneers are made out of plastic and placed on your teeth. They are used to protect your teeth while the real porcelain veneers are being fabricated. You can also use them to evaluate the look and feel of your teeth so that any changes you desire can be incorporated into your real veneers.

At the second appointment, the temporary veneers are removed and the porcelain veneers bonded to your teeth. Although they are thin, porcelain veneers are much stronger than composite veneers, so the risk of fracture compared to the composite veneers is much less. However, if a fracture does occur, repairing it is more difficult and may result in the veneers having to be remade.

In general, porcelain veneers can be used in a greater variety of situations with a higher level of predictability. Since they are made outside the mouth, the shape and color can be easier to control, thus enhancing the final result.

Composite Bonding

Advantages

The main advantage of a direct dental composite over traditional materials such as amalgam is improved aesthetics. Composites can be made in a wide range of tooth colors allowing near invisible restoration of teeth. Composites are glued into teeth and this strengthens the tooth's structure. The discovery of acid etching (producing enamel irregularities ranging from 5-30 micrometers in depth) of teeth to allow a micromechanical bond to the tooth allows good adhesion of the restoration to the tooth. This means that unlike silver filling there is no need for the dentist to create retentive features destroying healthy tooth. The acid-etch adhesion prevents micro leakage; however, all white fillings will eventually leak slightly. Very high bond strengths to tooth structure, both enamel and dentin, can be achieved with the current generation of dentin bonding agents.

Disadvantages

Clinical survival of composite restorations placed in posterior teeth has been shown to be significantly lower than amalgam restorations. However, improvements in composite technology and techniques have improved their longevity.

Direct dental composites

A hand-held wand that emits primary blue light (λmax=450-470nm) is used to cure the resin within a dental patient's mouth.

Direct dental composites are placed by the dentist in a clinical setting. Polymerization is accomplished typically with a hand held curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved. When using a curing light, the light should be held as close to the resin surface as possible, a shield should be placed between the light tip and the operator's eyes, and that curing time should be increased for darker resin shades. Light cured resins provide denser restorations than self-cured resins because no mixing is required that might introduce air bubble porosity.

Direct dental composites can be used for:

• Filling cavity preparations
• Filling gaps (diastemas) between teeth using a shell-like veneer or
• Minor reshaping of teeth
• Partial crowns on single teeth

Crowns

All-ceramic restorations

Inlays, onlays, porcelain veneers, crownlays and all varieties of crowns can also be fabricated out of ceramic materials, such as in CAD/CAM Dentistry or traditionally in a dental laboratory setting. CAD/CAM technology can allow for the immediate, same day delivery of these types restorations which are milled out of blocks of solid porcelain which matches the shade or color of the patients teeth. Traditionally, all-ceramic restorations have been made off site in a dental laboratory either out of feldspathic porcelains or pressed ceramics. This indirect method of fabrication involves molds and temporaries, but can yield quite beautiful end-results if communication between the laboratory and the dentist is sound. The greatest difference between these two differing modalities lies in the fact that the CAD/CAM route does not require temporization, while the laboratory-fabricated route does. Some argue that this lack of temporization can result in a decreased need for root canal therapy, as there is no temporary leakage between visits.

Restorations that are all-ceramic require wide shoulder margins and reductions of at least 1.0 - 1.5 mm across the occlusal (chewing) surfaces of the teeth. There are times where this reduction would be considered excessive, just as there are times when previous restorations or pathology require this much removal or more. Arguments against using all-ceramic restorations include a greater chance of fracture, when little to no enamel remains for proper adhesive bonding, or potentially when the patient clenches or grinds their teeth ("bruxes") excessively. Indications for using all-ceramic restorations include more aesthetic results, when metal compatibility issues exist, and when removal of less tooth structure is desired. All-ceramic restorations do not require resistance and retention form and consequently less surface area need be removed and the restoration will still stay in place by virtue of micromechanical and chemical bonding.

Ceramic materials such as lithium disilicate dental ceramics have recently been developed which provide greater strength and life-expectancy of dental restorations.

Longevity

Although no dental restoration lasts forever, the average lifespan of a crown is around 10 years. While this is considered comparatively favorable to direct restorations, they can actually last up to the life of the patient (50 years or more) with proper care. One reason why a 10 year mark is given is because a dentist can usually provide patients with this number and be confident that a crown that the dental lab makes will last at least this long. It should be noted that many dental insurance plans in North America will allow for a crown to be replaced after only five years.

The most important factor affecting the lifespan of any restorative is the continuing oral hygiene performed by the patient. Other factors depend on the skill of the dentist and their lab technician, the material used and appropriate treatment planning and case selection.

Full gold crowns last the longest, as they are fabricated as a single piece of gold. PFMs, or porcelain-fused-to-metal crowns possess an additional dimension in which they are prone to failure, as they incorporate brittle porcelain into their structure. Although incredibly strong in compression, porcelain is terribly fragile in tension, and fracture of the porcelain increases the risk of failure, which rises as the amount of surfaces covered with porcelain is increased. A traditional PFM with occlusal porcelain (i.e. porcelain applied to the biting surface of a posterior tooth) has a 7% higher chance of failure per year than a corresponding full gold crown.

When crowns are used to restore endodontically treated teeth, they decrease the potential of the tooth fracturing due to the brittle devitalized nature of the tooth and provide a better seal against invading bacteria. Although the inert filling material within the root canal blocks against microbial invasion of the internal tooth structure, it is actually a superior coronal seal, or marginal adaptation of the restoration in or on the crown of the tooth, which prevents reinvasion of the root canal.

Advantages and disadvantages

The main disadvantages of restoration with a crown are extensive irreversible tooth preparation (grinding away) and higher costs than for direct restorations such as amalgam or dental composite. The benefits, as described above, include long-term durability and evidence-based success as compared to other restorations or no treatment.

The crowning of two fairly large molars to sling a bridge between them for a missing tooth is a costly and sometimes oversold procedure. The increased food and bacteria trapping of the underside of the bridge often offsets the benefits of the bridge element in maintaining the positions of the opposing teeth and the loss of the ease of use and mouth feel of two big natural teethIt is usually the damage to a tooth that dictates the need for a crown, and alternative treatments are usually less effective. Risks and benefits can be weighed based on the priorities of the patient.

An example of this occurs when a patient would like to restore an edentulous area between healthy adjacent teeth. Before implants, there were three options:
• Fixed partial denture (bridge)
• Removable partial denture
• No treatment

Those who could afford it were usually told by their dentists that a bridge was their best choice, because it is much sturdier than removable dentures and requires less looking after. When implants became available, however, they were recommended as the best possible treatment, because the virgin teeth adjacent to the edentulous area no longer needed to be cut in order to fit the bridge. The affluent are thus told that a fixed partial denture is no longer desirable, now that implants are available. However, implants are significantly more expensive than a bridge, and the results are generally much less immediate.

Types and materials

Comparison between a porcelain-metal dental crown, an all-porcelain dental crown and a porcelain veneer laminate

There are many different methods of crown fabrication, each using a different material. Some methods are quite similar, and utilize either very similar or identical materials.

Metal-containing restorations

Full gold crown

Full gold crowns (FGCs) consist entirely of a single piece of alloy. Although referred to as a gold crown, this type of crown is actually composed of many different types of elements, including but not limited to gold, platinum, palladium, silver, copper and tin. The first three elements listed are noble metals, while the last three listed are base metals. Full gold crowns are of better quality when they are high in noble content. According to the American Dental Association, full gold crown alloys can only be labeled as high noble when they contain at least 60% noble metal, of which at least 40% must be gold.

The process of constructing a full gold crown begins at the dentist's office. The clinician will begin by preparing the tooth by removing enough tooth tissue to allow for the crown. Once the preparation has been finalized the clinician will take an impression which is basically a mold of the patient's mouth. The impression and patient details are sent to a dental laboratory where the dental technician will flow dental gypsum into the impression to make a dental model. This model is an exact reproduction of the situation in the patient's mouth. The dental technician now has the information required to model a wax pattern of the final restoration allowing for the tooth shape, occlusion and preparation. The wax pattern can be removed from the model and a wax sprue pattern is attached. The pattern is now ready to use in the Lost-wax casting technique. It is invested in a gypsum or phosphate-bonded investment material, allowed to set then put into a furnace where the wax is completely burnt out leaving a hole for the gold to be poured in. Once the crown has cooled, the technician can remove the sprue, fit and polish the crown ready for cementation. The crown is returned to the dentists office where they can remove any temporary crown and cement the finished gold crown.

Porcelain-fused-to-metal crowns

Porcelain-fused-to-metal dental crowns (PFMs) have a metal shell on which is fused a veneer of porcelain in a high heat oven. The metal provides strong compression and tensile strength, and the porcelain gives the crown a white tooth-like appearance, suitable for front teeth restorations. These crowns are often made with a partial veneer that covers only the aspects of the crown that are visible. The remaining surfaces of the crown are bare metal. A variety of metal alloys containing precious metals and base metals can be used. The porcelain can be color matched to the adjacent teeth.

Restorations without Metal

Chairside CAD/CAM Dentistry

The CAD/CAM method of fabricating all-ceramic restorations is by electronically capturing and storing a photographic image of the prepared tooth and, using computer technology, crafting a 3D restoration design that conforms to all the necessary specifications of the proposed inlay, onlay or single-unit crown; there is no impression. After selecting the proper features and making various decisions on the computerized model, the dentist directs the computer to send the information to a local milling machine. This machine will then use its specially designed diamond burs to mill the restoration from a solid ingot of a ceramic of pre-determined shade to match the patient's tooth. After about 20 minutes, the restoration is complete, and the dentist sections it from the remainder of the unmilled ingot and tries it in the mouth. If the restoration fits well, the dentist can cement the restoration immediately. A dental CAD/CAM machine costs roughly $100,000, with continued purchase of ceramic ingots and milling burs.

Typically, over 95% of the restorations made using Dental CAD/CAM and Vita Mark I and Mark II blocks are still clinically successful after 5 years. Further, at least 90% of restorations still function successfully after 10 years. Advantages of the Mark II blocks over ceramic blocks include: they wear down as fast as natural teeth, their failure loads are very similar to those of natural teeth, and the wear pattern of Mark II against enamel is similar to that of enamel against enamel.

Leucite Reinforced

Popularly known as the "Empress Crown," the leucite reinforced system is superficially similar to a gold crown technique in that a hollow investment pattern is made, but the similarities stop there. A specially designed pressure-injected leucite-reinforced ceramic is then pressed into the mold by using a pressable-porcelain-oven, as though the final all-ceramic restoration has been "cast." The crown that is constructed can be stained and glazed or cut-back and layered with feldspathic ceramic to match the patients natural color and shape.

A study by the Umeå University in Sweden, led by Göran Sjögren, sought to study the effectiveness of leucite-reinforced crowns. Titled “Clinical examination of leucite-reinforced glass ceramic crowns (Empress) in general practice: a restrospective study”, it found Empress crowns cracked at approximately only a 6% rate, with the integrity of 86% of the remaining samples being called "excellent."

Alumina

Alumina was introduced as a dental material in 1989 where the material was slip cast and infused with glass. More recently alumina core have been constructed with a CAD/CAM dentistry technique where a oversized core is milled from a pre-sintered block of Al2O3.[15] The block is sintered and shrinks to the correct size. This alumina core can be layered with feldspathic ceramics to make a true to life color and shape.

Zirconia

Zirconia is a very hard ceramic that is used as a strong base material in some full ceramic restorations. The zirconia used in dentistry is zirconium oxide which has been stabilized with the addition of yttrium oxide. The full name of zirconia used in dentistry is yttria-stabilized zirconia or YSZ.

The zirconia substructure of a crown is usually designed on a digital representation of the patients mouth, which is captured with a 3d digital scan of the patient, impression or model. The substructure is then milled from a block of zirconia in a soft pre-sintered state. Once milled the pre-sintered zirconia is sintered in a furnace, where it shrinks by 20% and reaches it full strength of approximately 850MPa.

On the core structure a dental technician can layer an aesthetic ceramic to create the final colour and shape of the tooth. Sometimes a 'monolithic' crown can be made exclusively of the zirconia ceramic with no aesthetic ceramic layered on top. These crowns tend to be dense in appearance with a high value and lack translucency and fluorescence.