Dental Crown and Bridge

When you need a Crown?

Tooth that cannot be restored with traditional filling material may require a crown. Dental crowns fit snuggly over teeth to conceal cracked, discolored, injured, or chipped teeth.  Dental crown look and feel like natural teeth and restore them back to their functional use, leaving the teeth more resistant to injury. Dental crowns are often used to support a tooth that already has a large filling to prevent breakage and can also be used to align a tooth that is out of position.

There are also many other reasons for dental crown treatments; most often being because of insufficient remaining tooth structure like root canal treatment, large amalgam. Large dental fillings can cause fractures in teeth over time.

Once the dentist can detect the fracture with his or her instruments, it is likely that that tooth will fracture at some point. Doing the dental crown procedure can prevent that from happening.

Dental crowns could be more expensive, but if it is not done and the tooth fractures, it is possible that that tooth may be lost, or need to be root canaled. If your tooth is extracted, dental bridge restoration is required. Both of which would be much more expensive than that single crown.  

When you need a Bridge?

Dental Bridge may be necessary if you are missing one or more teeth. When teeth are missing, you may notice a difference when chewing and speaking. Dental crown is comprised of two crowns and one pontic(fake tooth).  A bridge is used to replace missing teeth, help maintain the shape of your face, and alleviate the stress in your bite. A fixed bridge replaces missing teeth with artificial teeth, looks great, and literally bridges the gap where one or more teeth may have been. Once the bridge has been constructed, it will be permanently bonded onto surrounding teeth for support, filling the spots where missing teeth used to be. A bridge, when necessary, offers a great solution for a strong, natural-looking smile.

Dental Crown and Bridge Procedures

It normally takes 2-3 appointments to complete dental crown, the preparation appointment, the installation appointment and post treatment examination.

The first appointment of the dental crown procedure is the preparation. The tooth is reduced on all 4 sides plus the top in order to make room for the crown. This is also when any decay is removed and filled accordingly. The dentist will take an impression of the tooth and make a temporary crown. The impression will be sent to model in dental lab, which take around a week until the final crown is seated (at the second appointment).

The second appointment of the dental crown procedure involves seating the crown. The temporary crown is removed and the final crown is fitted onto the tooth. This normally involves some adjustments, and then the crown is cemented onto the tooth.  After an impression is made, your crown will be delivered at a second appointment and permanently bonded.

The third appointment is for examination whether patient feel comfortable with new teeth. Minor adjustment as color or shape will be applied.

Dental Crown and Bridge Materials

Dental crown and bridge can be GOLD, PROCELAIN, or PORCELAIN FUSED TO GOLD/METAL (PFM/PFG) depending on patient preference.

GOLD The hardness of gold is very close to natural tooth hardness, therefore it does not wear against the opposing tooth. PORCELAIN is much harder than natural tooth structure, therefore can wear down the opposing tooth/teeth. Gold crowns also require less reduction of tooth structure during the dental crown procedure, which in general is better for the longevity of the tooth.

In the current day of everyone wanting whiter teeth and looking more natural, gold is esthetically less acceptable, unless it is in the back of your mouth. Gold alloy is used when strength is desired and appearance is not a factor. There are many formulations of gold, varying from 1% to 99%.

Non-Precious Alloy Non-precious alloys are used when maximum strength is desired, appearance is not a factor, but cost is most important. Since it does not contain any gold, cost is less. There are two basic formulations, one that contains nickel and one that is nickel-free. The controversial issue is that nickel, beryllium, cobalt, chromium, and palladium may cause immune problems and/or toxicity.

ALL PORCELAIN All Porcelain is used when appearance and wear resistance is the most important factor. It is much more fragile than metal and may break easily. Porcelain alone is not normally recommended for bridges. As mentioned in the gold crown and bridge section, when porcelain crown and bridge are done, the preparation phase of the dental crown or bridge procedure requires more tooth structure to be removed in order to make room for the porcelain on porcelain crowns.

Indirect Composite Indirect composites are used when appearance is an important factor but when the risk of porcelain fractures and wearing down the other teeth is to be avoided. These are not quite as wear-resistant or esthetic as porcelain but very acceptable for normal situations.

Titanium Titanium is used when maximum strength is desired, appearance is not a factor, and a gold alloy is not biocompatible. There are different purities of titanium, with grade-1 being the purest. This is used in joint replacement, dental implants, and bone pins. Cost is the same as for gold alloy.

Zirconia (Zirconium Oxide) Zirconia crown and bridge are like porcelain fused to metal excepting the metal substructure is primarily cubic zirconia, which has a white appearance rather than a silver or gold appearance. This allows for much better esthetics, but may still not be suitable for all posterior teeth under high stress.  One of the most difficult areas in dentistry today is the restoration of dental structures with biocompatible materials that are strong enough to withstand the forces of chewing (500-1000lbs pressure on molar teeth). Recent technology from Germany now offers a material that has overcome most of the pitfalls of present day products. Patients now have a choice of a material that is esthetic, strong, pure, biocompatible and capable of being used for single and long span dental bridgework. That material is called Zirconium oxide.

Zirconium oxide forms the core of each crown and provides the cross-link that bridges the gap of missing teeth. The precision fit of the Zirconium core is derived from computer guided Swiss lathes that cut the form out of a solid Zirconium oxide block. The cutting instructions are obtained from a laser beam that reads 120 points per millimeter from the anatomy of a model of the prepared teeth. Once formed, new synthetic porcelain (99.9% pure) is baked on to the Zirconium core and then shaped like a tooth. Because of the extreme accuracy of the crown fit, the crowns can be cemented with biocompatible dental luting material. This avoids the use of an invasive procedure of etching the tooth with acid and injuring the pulp or nerve of the tooth. This latter procedure often times results in the pulp dying and necessitating root canal therapy.

Zirconium oxide ceramic primarily stands out due to its high crack resistance. Crack resistance is the resistance with which the material counteracts the spreading of cracks. If a material is stressed, it usually comes to excessively high tension within a defect area (pores, surface deficiencies, cavities) or it cracks. While with metals under high tension in the area of cracks, plastic deformation appears and the top of the tension can be reduced by rounding the cracks; in ceramics due to missing plastic deformation possibility the cracks continue to grow. The unusual feature of zirconium oxide ceramic in comparison with other ceramics is that at the appearance of a high-tension area a transformation of the crystal structure can take place. This process is also accompanied by a volume expansion. By this volume increase it builds wedges in the crack and therefore it reduces the continuation of the crack. While the critical tensile strength (KIC) e.g. of Dicor, Vita Mark II and Empress is in the area of 1-2.5 Mpam-1/2, zirconium oxide shows values in the range of 10 Mpam-1/2. Even In-Ceram (glass infiltrated Al203 ceramic) and Procera aluminum oxide (pure Al203 ceramic) show values less then 5 Mpam-1/2.

In connection with the tensile strength there also stands the characteristic of bending strengths. While conventional glass ceramics show results of 100-200 Mpa and aluminum oxide ceramics lie in the area of 400-600 Mpa, zirconium oxide reaches a bending strength of over 1000 Mpa.

Because of the high tensile strengths exhibited in test results, it is now possible to fabricate posterior bridges with zirconium oxide. Further decisive advantages of zirconium oxide are its high resistance to corrosion; stability to hydrolysis and its high biocompatibility in comparison with other ceramics makes this material ideal for restorative dentistry.

In medicine, zirconium oxide is being used more and more as the material of choice especially for hip prosthesis. For years there has existed substantial clinical tests and examinations which confirm the high quality of zirconium oxide.

ALL PORCELAIN vs PORCELAIN FUSED TO METAL

Like gold, the metal hardness is closer to that of natural tooth structure, so part of the tooth can be PORCELAIN (for esthetics) and part of it can be metal/gold (part that hits the opposing tooth). The metal is normally an alloy of gold, with the amount of gold and other metals varying depending on the type of crown.

Choosing Dental Material

Conventional: Except in rare situations, currently used dental materials are safe in the mouth. The important criteria are how durable, natural looking, inexpensive, and practical they are for the dentist and dental laboratory to use. Concerns therefore are economics and aesthetics. Because some people have a sensitivity to certain substances, the choice of dental materials may have to be limited. A special blood test may be used to determine sensitivity to corrosion by-products of components.

Toxicity: Some dental materials contain toxic substances that, depending on exposure and other factors, may impact total toxic body load. Non-toxic alternatives should be used to decrease exposure to and accumulation of scientifically confirmed environmental toxins. Some dental treatment and materials can be disruptive to the normal flow of energy through the acupuncture meridians. Eastern philosophy believes chronic disruption of energy flow causes dysfunction and resultant health problems on the associated meridian; therefore, the choice of dental materials and treatments is limited.

Electrogalvanism: Dissimilar metals in the mouth, including different formulations of the “same” metal, create microamps of current which could cause oral pain, corrosion of the metal (black mercury amalgam fillings), dry mouth, metallic taste, erythema (red & swollen gums), and possible dysfunction of other organ systems, endocrine glands, etc..

Crown and Bridge Failures issues

After crown or bridge is placed, the tooth still needs to be flossed and brushed, because it is still possible to get cavities under a crown.

There are other issues that can arise after crown placement.

• Decay: If you get recurrent decay under the crown/bridge, most likely the crown will need to be redone.

• Open Margins: This means that there is a space between the crown/bridge and tooth, and is not a good situation. If you have open margins around any part of the crown, the crown/bridge should be redone, because leaving open margins leaves the tooth at a much higher risk for getting decay. Open margins around new crowns can often cause sensitivity to hot, cold, air, and or sweets.

• Occlusion: This is one of the more common concerns with new crown/bridge and bridge. If your bite feels off, your dentist can probably just adjust the crown/bridge to feel better. When a tooth is contacting prematurely, it can cause a great deal of discomfort to that tooth, any opposing tooth, sensitivity to hot/cold or biting, or a variety of other symptoms. This is one of the first things dentists check if a patient is having problems with a new crown/bridge.

• Open Contacts: If the crowned tooth does not contact the adjacent teeth, you will likely get food packed in the space. This should be addressed before the crown is cemented, but if not, the only way to fix this is to either redo the crown/bridge, or do a filling or modify the adjacent tooth.

• Fractured Porcelain: If you have a porcelain fused to metal/gold crown/bridge and the porcelain fractures off, the metal/gold underneath will still protect the tooth. The crown/bridge does not necessarily need to be replaced, as long as the margins of the crown are intact. Some people elect to replace crowns when this happens if there is an esthetic concern, or if there are open contacts as explained above.

Denture

Dentures are removable replacements for missing teeth. They are made from acrylic, stainless steel, and chromium-cobalt, but can be made of nylon, a gold alloy, or titanium. Most pink-colored acrylics and vinyls contain cadmium, which is considered toxic and/or immune reactive. The alternative is to use cadmium-free pink or clear materials. Metals are used to increase rigidity and increase retention of the prosthesis in the mouth during function. If metals are not used, the opposite is true, which is not desirable from a functional perspective.  If your dentures are well looked after, you will have a very natural looking smile. Your dentures will also help strengthen muscles controlling your expressions and you will be free of any speech problems which were caused by missing teeth. If you've lost, or are losing, all of your teeth a Complete Denture replacement could be the perfect solution for you.

Complete Dentures

These replace all of your teeth filling the entire upper or/and lower jaws. The level of comfort depends on your muscles, bones, tongue, and saliva. Upper Dentures are a little easier to adjust to. Complete dentures can be either "conventional" or "immediate." Made after the teeth have been removed and the gum tissue has begun to heal, a conventional denture is ready for placement in the mouth about 8 to 12 weeks after the teeth have been removed.

Unlike conventional dentures, immediate dentures are made in advance and can be positioned as soon as the teeth are removed. As a result, the wearer does not have to be without teeth during the healing period. However, bones and gums shrink over time, especially during the healing period following tooth removal. Therefore a disadvantage of immediate dentures compared with conventional dentures is that they require more adjustments to fit properly during the healing process and generally should only be considered a temporary solution until conventional dentures can be made.

Partial Dentures

Partial dentures are placed to fill the gaps in your smile when only some of your teeth are missing. The dentures are anchored to your teeth with metal attachments. They maintain tooth alignment because they prevent your remaining teeth from shifting. They can also help prevent your loss of more teeth due to decay or gum disease. A removable partial denture or bridge usually consists of replacement teeth attached to a pink or gum-colored plastic base, which is connected by metal framework that holds the denture in place in the mouth. Partial dentures are used when one or more natural teeth remain in the upper or lower jaw. A fixed (permanent) bridge replaces one or more teeth by placing crowns on the teeth on either side of the space and attaching artificial teeth to them. This "bridge" is then cemented into place. Not only does a partial denture fill in the spaces created by missing teeth, it prevents other teeth from changing position. A precision partial denture is removable and has internal attachments rather than clasps that attach to the adjacent crowns. This is a more natural-looking appliance.