Indications, clinical and laboratory stages of production the combined crown. Indications, clinical and laboratory stages of production the plastic crowns

Dental crowns

A dental crown is a tooth-shaped cap that is placed over a tooth – covering the tooth to restore its shape and size, strength, and/or to improve its appearance.

The crowns, when cemented into place, fully encase the entire visible portion of a tooth that lies at and above the gum line.

A dental crown may be needed in the following situations:

• To protect a weak tooth (for instance, from decay) from breaking or to hold together parts of a cracked tooth
• To restore an already broken tooth or a tooth that has been severely worn down
• To cover and support a tooth with a large filling when there isn’t a lot of tooth left
• To hold a dental bridge in place
• To cover misshapen or severely discoloured teeth
• To cover a dental implant
• Metals used in crowns include gold alloy, other alloys (for example, palladium) or a base-metal alloy (for example, nickel or chromium). Compared with other crown types, less tooth structure needs to be removed with metal crowns, and tooth wear to opposing teeth is kept to a minimum. Metal crowns withstand biting and chewing forces well and probably last the longest in terms of wearing down. Also, metal crowns rarely chip or break. The metallic colour is the main drawback. Metal crowns are a good choice for out-of-sight molars.
• Porcelain-fused-to-metal dental crowns can be colour-matched to your adjacent teeth (unlike the metallic crowns). However, more wearing to the opposing teeth occurs with this crown type compared with metal or resin crowns. The crown’s porcelain portion can also chip or break off. Next to all-ceramic crowns, porcelain-fused-to-metal crowns look most like normal teeth. However, sometimes the metal underlying the crown’s porcelain can show through as a dark line, especially at the gum line and even more so if your gums recede. These crowns can be a good choice for front or back teeth.
• All-resin dental crowns are less expensive than other crown types. However, they wear down over time and are more prone to fractures than porcelain-fused-to-metal crowns.
• All-ceramic or all-porcelain dental crowns provide the best natural colour match than any other crown type and may be more suitable for people with metal allergies. However, they are not as strong as porcelain-fused-to-metal crowns and they wear down opposing teeth a little more than metal or resin crowns. All-ceramic crowns are a good choice for front teeth.
• Temporary versus permanent. Temporary crowns can be made at your dental practice whereas permanent crowns are made in a dental laboratory. Temporary crowns are made of acrylic or stainless steel and can be used as a temporary restoration until a permanent crown is constructed by the dental laboratory.

Preparing a tooth for a crown usually requires two visits to the dentist — the first step involves examining and preparing the tooth, the second visit involves placement of the permanent crown.

First Visit: Examining and preparing the tooth.

At the first visit in preparation for a crown, your dentist may take a few X-rays to check the health of the roots of the tooth receiving the crown and the surrounding bone. If the tooth has extensive decay or if there is a risk of infection or injury to the tooth’s pulp, a root canal treatment may first be performed.

Before the process of making your crown begins, your dentist will anaesthetise (numb) your tooth and the gum tissue around the tooth. Next, the tooth receiving the crown is filed down along the chewing surface and sides to make room for the crown. The amount removed depends on the type of crown used (for instance, all-metal crowns are thinner, requiring less tooth structure removal than all-porcelain or porcelain-fused-to-metal ones). If, on the other hand, a large area of the tooth is missing (due to decay or damage), your dentist will use filling material to “build up” the tooth to support the crown.

After reshaping the tooth, your dentist will use impression paste or putty to make an impression of the tooth to receive the crown. Impressions of the teeth above and below the tooth to receive the dental crown will also be made to make sure that the crown will not affect your bite.

The impressions are sent to a dental laboratory where the crown will be manufactured. The crown is usually returned to your dentist’s surgery in two to three weeks. If your crown is made of porcelain, your dentist will also select the shade that most closely matches the colour of the neighbouring teeth. During this first visit your dentist will make a temporary crown to cover and protect the prepared tooth while the crown is being made. Temporary crowns are usually made of acrylic and are held in place using a temporary cement.

Because temporary dental crowns are just that — a temporary fix until a permanent crown is ready, most dentists suggest that a few precautions be taken with your temporary crown. These include:

• Avoid sticky, chewy foods (for example, chewing gum, caramel toffees), which have the potential of grabbing and pulling off the crown.
• Minimise use of the side of your mouth with the temporary crown. Shift the bulk of your chewing to the other side of your mouth.
• Avoid chewing hard foods (such as raw vegetables), which could dislodge or break the crown.

Second visit: Receiving the permanent dental crown.

At your second visit, your dentist will remove your temporary crown and check the fit and colour of the permanent crown. If everything is acceptable, a local anaesthetic may be used to numb the tooth and the new crown is permanently cemented in place.

• Slide flossing material out-rather than lifting out-when cleaning your teeth. Lifting the floss out, as you normally would, might pull off the temporary crown.

 

 

Over many decades metal alloys have been used for making dental crowns. One classic is the gold alloy crown. Although we may refer to this type of crown as a gold crown, it is typically composed of a number of different elements, including but io way limited to gold, palladium, platinum and silver.

Benefits of Gold Crowns

There are numerous reasons why one might choose to have a gold crown applied. Gold has always been a favorite among dentists for it’s workability. Its physical properties enables the dentist to achieve an exact fit. Another benefit of using a gold crown is that gold as a pure metal, gives the crown the strength that is required to tolerate the pressure of biting and chewing, also, a gold crown is not prone to chipping.

Although the rate at which a gold crown wears down is the same as enamel another positive characteristic of a gold crown is that it does not create so much wear on the teeth it bites against.

These days gold crowns are usually applied to the molars or teeth that are not so visible when a person smiles.

Indications

1. The only option remaining.

2. Usually reserved for molar and lower premolar teeth.

3. Flame-shaped diamond

4. Excavator

 

Procedure

If the problem is such that a partial crown will not function, the only option is the full crown restoration, and it is the treatment court of last appeal. Full crowns are most frequently placed on molar teeth and occasionally on lower bicuspids.

The situations that require a complete crown include teeth that have exten­sive but questionable restorations or extensive carious involvement. A significant contributor to this difficulty is a large defective Class V amalgam restoration, and the only way a casting will perform is to make a complete crown. Another situation requiring this type of crown is presented by teeth that are very short and do not provide resistance unless a full crown is utilized.

Many times the locations of the gingival margins are predetermined by the existing restoration or caries and decalcification that must be enclosed. This often dictates that these margins, with emphasis on the interproximal and facial, will be in the gingival sulcus. If adequate resistance for the restoration and effec­tive coverage can be met without placing the margin in the sulcus, that is the rec­ommendation. Many times the lingual surface will be intact and it is easy to ter­minate the margin above the level of the gingiva, which eases the maintenance problems of the marginal gingiva.

The initial procedure is the occlusal reduction. The reduction may be done using a wheel diamond or a tapered round-end diamond. The same amount of reduction is required as for other posterior teeth, with a minimum of 1 mm wherever function occurs. The occlusal reduction should show correlation with occlusal morphology of the tooth and not be an arbitrary flattening of the occlusal surface.

Followin;g the occlusal preparation, proceed to the buccal and lingual reduction. A tapered round-end diamond is useful for this purpose. The gingival finish line will have been predetermined by the needs of retention, defective restorations, or caries. The reduction should reflect a chamfer effect at the gingi­val cavosurface. The buccal and lingual morphology is observed, and the reduc­tion is done to produce an even thickness of metal in the completed restoration consistent with the shape of the tooth.

The buccal and lingual walls are structured to provide good resistance to displacement. There is a danger of over-angulating the walls and losing the potential resistance for the casting. This reduction is carried toward the adjacent teeth. To avoid overcutting at the interproximal, a thin flame-shaped diamond is selected.

The finish line must be located gingival to the contact and be on healthy enamel. If an amalgam core or restoration  is part of the prepa­ration, it is expected that the finish line for the casting will terminate gingival to the restoration. The proximal walls must relate to each other in the same man­ner as to the buccal and lingual to provide optimal resistance. They will be slightly inclined toward each other.

This should complete most of the reduction, and now with a fine grit fin­ishing diamond or a No. 1170 bur the preparation is made smooth. All sharp corners or angles are slightly rounded. For some of the smoothing it is best that the bur run at a reduced speed to avoid excess cutting.

The occlusal clearance is checked in the same manner as discussed for pre­vious posterior cast preprations.

 

 

Consideration must be given to clearance when the patient goes through eccentric movements, and the preparation must have adequate reduction to allow the restoration to have a acceptable function in all movements. This information must be placed into a suitable articulator to allow for a reliable wax-up and casting.

The final segment of the preparation is the placement of a groove on the buccal surface, and usually this will be in the anatomical buccal groove. This groove is of value, as it helps to provide positive orientation during the placement of the casting. It will tend to limit the potential for slight rotation of the crown during seating, as the groove will guide or key it into the specific placement. At times it will prove of value by providing a degree of supplemental retention, which may be helpful to a restoration with marginal retention. On occasion when the buccal segment of the tooth is badly destroyed this groove may be placed on the lingual portion of the preparation. If the preparation  requires a pin-supported amalgam or resin buildup, the groove may be placed m the amalgam or resin.

This groove may be formed by using a thin, tapered round-end diamond, or a No. 171 bur may be used effectively for this purpose. If the bur is used, it is advised to use it at reduced speed to avoid overcutting. This groove extends just short of the gingival finish line.

Resume of Partial and Full Crown Preparation

1. Gingival finish line when possible should be located occlusal to the gingiva.

2. Grooves with adequate length are preferred over proximal boxes for resistance form.

3. Do not terminate a finish line through a wear facet.

4. Occlusal reduction should occur first using wheel or football-shaped diamond. With a wax bite check for a minimum clearance of 1mm.

5. Lingual reduction with bullet-nose diamond 2D-T.

6. Interproximal reduction with thin or flamed-shaped diamond to avoid cutting adjacent tooth.

7. Proximal grooves are located for maximum length and will line up toward the buccal cusp tip.

8. Place buccal bevel toward facial to complement esthetics and function.

9. A V-shaped connector may be used between grooves.

10. With a seven-eighths crown one groove is located on the facial surface.

11. For a full crown preparation the facial reduction is done with the same instrument as for the lingual. A definite chamfer is needed for the buccal finish line.

12. Place a groove on the facial surface of the preparation for positive seating and use of tapered diamond or a No. 171 bur.

 

 THE ABRASIVES

In the manner that all forms of prostheses require thorough and complete (to mirror brightness) polishing, some of the important auxiliary materials become abrasives – means for the polishing of prostheses. First prosthesis is ground, then they polish with the aid of the abrasives (from Lat. abrazio – erasure).

Abrasives can be before the powder, they can be before the bound state.

As bonding agents are used:

– Ceramic:mixture from the clay, the feldspar, the talc, the quartz. They are high-strength, thermally stable, moisture proofed.

– Bakelite: on the basis of the pasting Bakelite, natural rubber and other well elastic, high-impact.

– Vulcanite: on the basis of the vulcanized natural rubber with the gray (30%). Highly resilient, water-resistant, high-strength.

 All abrasives are divided:

1. Natural, that are encountered before nature.

2. Artificial,obtained by chemical means.

Natural

Diamond– most solid mineral. They use for preparing of separator discs and grindstones.

Corundum– before nature in the form of aluminum oxide. For preparing the grindstones. Distinguish the powder of №10, 20, 30 and so forth

Emery –in the form of the rock, contains corundum, oxide of iron and others make polishing paper and fabrics. It is divided about the numbers.

Pumice –volcanic origin: 70% of silica both oxides of metals and giving to it different painting.

Artificial

Carborundum –alloy: 36 h. fluxes before the electric furnace with 2000°[S]of the mixture 30% coke, 52% of quartz sand, 10% of sawdust, 2% of chloride sodium. Has crystalline structure. For preparing of grindstones, disks.

Electrocorundum –is obtained via the melting of bauxite with the coke before the electric furnaces. Very hard, thermo resistant. For the stones, the disks.

Pumice and emeryuse in the form aqueous pulp.

 The thinnest layer of surface is removed with the polishing. Polishing pastes are used for this.

            Basis of the pastes:

– Oxide of chromiumsolid, fine powder of green color, they obtain tempering bichromate potassium and sulfur = 5: 1.

Before the composition of paste GOI: 81% oxide of chromium, 2% silica gel, 10% stearin, 5 % fat, 2% kerosene. They divide beside the rough, the average, the thin. For the polishing of steel.

– Iron oxide– is obtained with interaction of iron vitriol and oxalic acid. They do not use for steel since are decreased anticorrosive properties.

– Mel– for the polishing of metals and plastics.

– Oxide of tin– for the polishing of porcelain.

 

Into the composition of pastes, besides abrasives enter the surface-active and binding agents (stearin, paraffin, wax, fat, vaseline). Pastes are brought down the circles, the cones from the skin, the felt, the fabric, the bristle, the hair and the threads.

Abrasive tools are characterized:

1. by birth abrasive (E – electrocorundum; E corundum is natural; KC – carborundum is black; KZ – carborundum is green)

2. with number of granularity (№10- 320 – powders; №28 – 45 – micropowder)

3. of hardness (ES – extremely soft, VS – very soft, S – soft, MS – middlesoft, H – medium-hard, SD–  solid, HS – very solid, EH – extra-hard)

 

With the work with different materials it is necessary to select different hardness cutting tools. With the large difference of the hardness of material and cutting tool the stone ceases to cut, cavities are driven in by shaving. The premature wear of stone occurs with the smaller hardness of stone. Stone before the process of work must gradually be destroyed in order to free the underlying grains of abrasive, they are not oppressed by shaving. The greater the speed, the less must be its hardness.

 

CHILLS

 As a result the heat working of the components (of metallic) prostheses occurs interaction of metal with the atmospheric oxygen, which leads to the formation of oxide film. The film worsens grinding and polishing of prostheses, it is capable of causing poisoning organism. Descaling is accomplished by the chemical reagents. Film hampers the soldering of components due to worsening in the interdiffusion of metals. The removal of oxide film is produced for the sake of chills.

As the chills the solutions of acids are used.

Hydrochloric acid. (HCl) – in air separate the hydrogen chloride (fuming acid). For the bleaching of gold (crown with the presence of the remainders of fusible alloy during the upholstering they are destroyed). 40% aqueous solution is used. Article is heated red hot, and then they lower beside the vessel with the solution of hydrochloric acid and in 1-2 min. they extract; they wash. Work based on HCl only in the exhaust hood.

Sulfuric acid.Colorless, oily liquid. They use for the bleaching of silver, it enters into the composition of electrolytes.

 Nitric acid.Colorless, smoking liquid with the sharp smell. Are dissolved all metals, except gold and platinum. Mixture from 30% – nitric acid and 60% hydrochloric acid “aqua regia” – for the dissolution of gold and platinum with the refining. Chills for the stainless steel:

 

 

 Before this solution article boil 1-2 min.

 

FLUXES

For the removal of oxides and protection of articles from oxidation before the process of soldering use the fluxes (fluxes), capable of dissolving oxide film and in this case of surfacing of solder.

Requirements at the point of the fluxes:

1. the melting point of flux must be lower than the melting point of solder,

2. it must dissolve oxide film,

3. it is good to spread by means of the surface of article before the hot state,

4. not to volatilize before the process of soldering,

5. weld face after soldering.

Borax– the colorless crystals, water-soluble and glycerin of t° of 700-740°C is brought down the heated parts of the components. The remainders of borax based on the surface of prosthesis with the aid of the acids are moved away.

Boric acid.Colorless crystals, are dissolved before alcohol and water. Application before the combination with the brown and oxide of silicon is effective. Rosin.

 

THE INSULATION

Isocol– alginate separating material, used for preventing the entry of gypsum beside the plastic before the polymerization. Composition: alginate 1,5-2,0%, salt of aluminum 0,02, 40% solution of formalin – 0,3; dye food 0,005%; distillate water 98,0%. They bring down the model by brush beside 2 layers. Layer must be thin and uniform.

Moldin– mixture of the kaolin for the sake of the glycerin, elastic mass, is packed on250 g. They use during casting of the combined models, during casting of the combined models, with the production of crowns by the method of external stamping.

Varnish of cover “Eudes”.It adapts for masking the metallic parts of the prostheses; composite from the acrylic copolymers and the epoxy resin. It possesses grow prettier by permeability to the metal and the plastic.

 

MELOT

For creating of the stamped crowns and similar constructions is required the manufacture of dies. For this purpose adapt special fusible alloys on the basis of lead – Melot.   These alloys, besides low (70-95^oC) melting point, have a sufficient hardness, insignificant thermal contraction.

Into the composition of Melot enter tin, lead, bismuth (it fulfills role “of the extinguisher” of shrinkage), cadmium. Alloy is mechanical mixture.

With the work with the alloy one should remember that it cannot be overheated. This leads down the combustion of alloy, it makes for the sake of its more brittle, the shrinkage (it burns bismuth) increases. In addition to this, with the intensive heating are separated the vapors of cadmium, which are toxic for the organism.

Is also inadmissible entry down the surface of Melot of gold and platinum – they are connected for the sake of lead and bismuth, disrupting the structure of the latter.

 

 

 

 

The most beautiful crown for a tooth is, without question, all-porcelain or all-ceramic. With porcelain fused to metal crowns, there has to be an opaque layer put over the metal to block out its color. This makes it impossible to have a translucent restoration that mimics the translucency of natural teeth. Only with pure porcelain or pure ceramic can you have such translucency. To define some terminology, porcelain is a particular type of ceramic that is built by stacking and firing. When we say ceramic, we include porcelain—porcelain is a type of ceramic.   The reason all dentists don’t use all-porcelain crowns for front teeth is that the technique for placing them is very demanding and isn’t generally taught in dental schools. They are translucent, and their color is influenced by the color of the underlying teeth. General dentists aren’t usually very skilled at color manipulation in these situations. Also, placing them requires the use of sophisticated bonding techniques that aren’t fully taught in dental schools. At mynewsmile.com we recommend that if you want one of these beautiful crowns for your front tooth, have it done by an expert cosmetic dentist such as we have listed on our site.          Here is a photograph of a patient’s front teeth. One of these teeth is an all-porcelain crown, done by an expert cosmetic dentist in our referral network. Can you tell which one it is? The crown is on the patient’s left lateral incisor, the smaller tooth just to the right of the two larger front teeth in our photograph.   Ceramic crowns 12, 11, 21, 22   The work was done by Dr. Duane Delaune, of Metairie, Louisiana. Notice how closely it mimics the appearance of the natural teeth.  CHOICES IN ALL-PORCELAIN AND ALL-CERAMIC CROWNS There are various types of all-porcelain or all-ceramic crowns. Let’s explain the differences between some of them: ·    Feldspathic porcelain is the standard, traditional porcelain that is used for crowns. Many cosmetic dentists feel that this is the most beautiful porcelain. ·    The Empress crown – Empress is strictly speaking not a porcelain, but is more like a glass. It can be called a ceramic material. The Empress material is cast rather than baked as a feldspathic porcelain crown is. The fit of Empress is more precise than the baked feldspathic porcelain. However, the color in Empress is mostly baked on the outside. Empress can be very beautiful. For appearance’s sake, some expert cosmetic dentists prefer the feldspathic porcelain, and some prefer the Empress. ·    The Procera crown – Procera is a milled ceramic on the inside with a more traditional porcelain baked onto the outside. The advantage of Procera is its exceptional strength. However, the milled ceramic core is opaque white, so many cosmetic dentists feel that it isn’t as natural-looking as the more translucent materials. An advantage of Procera is that it doesn’t have to be bonded to the tooth but can be cemented with ordinary crown and bridge cement, a technique familiar to all dentists. ·    The Lava crown – Lava is similar to Procera, but the milled ceramic on the inside is a more translucent Zirconia, rather than an opaque white material. The Zirconia is shaded, and then the final esthetics of the crown are achieved in the baked-on outer layer. The Lava crown can also be cemented with traditional techniques. However, any crown cemented with a traditional crown and bridge cement is going to be susceptible to a compromise in the appearance if that cement line ever shows.       ·    Zirconia crowns, if they are done right, can be translucent enough to look natural. And if they are bonded to the teeth, instead of being cemented with conventional dental cement, they won’t show a black line at the gumline. ·    The Cerec crown – Cerec is are also milled from a block of very hard ceramic material. What’s unique about Cerec is that the crown is milled by a computer in the dentist’s office rather than in a separate dental laboratory. Thus, the dentist doesn’t have to send out for it to be made—it can be made on the spot. So, no second appointment is required, and no wearing of a temporary crown between appointments. Cerec is milled from a block of ceramic that is a single color, so it is generally not considered esthetic enough for demanding cosmetic dentists. A few exceptional dentists who are artists, however, are able to custom stain Cerec for front teeth so that they are truly beautiful. Some even make Cerec veneers that can be placed the same day. To be precise, Cerec is actually a technique and not a material. There are several companies that make ceramic materials for use in Cerec machines. ·    The InCeram crown – InCeram is made of a very dense and very tough aluminous porcelain. It also has excellent esthetics, but is more opaque than feldspathic porcelain. InCeram is also strong enough to be cemented with traditional dental cement. ·    There are other types of all-ceramic crowns. We’re not going to list all of them here.         ADVANTAGES AND DISADVANTAGES OF ALL-PORCELAIN AND ALL-CERAMIC CROWNS Let’s compare all-porcelain with porcelain fused to metal. ·    All-porcelain is generally not as strong as porcelain fused to metal. It has to be bonded to the tooth in order to have adequate strength for oral function. The bonding technique is very demanding and is not fully taught in dental schools. We recommend that you only have an expert cosmetic dentist place this type of crown. ·    With porcelain fused to metal, the porcelain has to be opaque in order to block out the appearance of the metal underneath. They all also eventually develop an unsightly dark line at the margin where the edge of the crown meets the tooth. ·    Some of the all-ceramic systems that have an inner ceramic core with an outer layer of porcelain baked on require more tooth reduction. Grinding away more of the tooth is ofteot desirable. ·    Some of the ceramic materials that are very tough and fracture resistant are also quite abrasive against the opposing teeth. Of the crowns listed above, the Empress is the kindest to the teeth it chews against.       GENERAL RECOMMENDATIONS FOR ALL-CERAMIC CROWNS     ·    There are several factors that need to go into the selection of a crown material: strength requirements, esthetic requirements, the abrasivity of the material against the opposing teeth, and the skills of the dentist. There is not a single crown that is clearly superior for all situations. Many cosmetic dentists will have several types that they will use, each for a different situation. ·    It is generally a poor idea for a patient to go to a dentist and request a specific type of all-porcelain or all-ceramic. We have received many e-mails from patients who have done this and have been very disappointed with the results, because they were pushing their dentist to use a material the dentist was not comfortable with, and many dentists will try very hard to conceal from patients any discomfort they feel with a procedure. There is also the factor of the dental ceramist, whom you will most likely never meet. The material that is used for the crown should be intimately familiar to the dentist and to the ceramist for the best results. ·    You cannot learn, as a patient doing online research, which crown is best. First of all, there simply isn’t one all-ceramic material that is always best. Second, in a web page such as this, we can’t list all the properties of all them. Third, in evaluating these crowns, there is a great deal of background information needed in order to evaluate which research claims are fully established and which claims should be questioned. ·    Our recommendation, at mynewsmile.com, is that you find a cosmetic dentist you can trust and that understands your needs and is passionate about creating beautiful dentistry. Then ask that expert cosmetic dentist to use the technique that he or she is most comfortable with in creating the all-ceramic crown that will be best for you. The choice of the material is secondary to the skills of the dentist and of the ceramist in working with that particular material. There are subtleties in working with all of these all-porcelain and all-ceramic materials that need to be mastered by the dentist and the ceramist to produce the most beautiful result.

 

Ceramic crown on 22 tooth

 

Ceramic crown on 11 tooth

 

 

 

 

 

 

Why Is a Dental Crown Needed?

A dental crown may be needed in the following situations:

1.     To protect a weak tooth (for instance, from decay) from breaking or to hold together parts of a cracked tooth

2.     To restore an already broken tooth or a tooth that has been severely worn down

3.     To cover and support a tooth with a large filling when there isn’t a lot of tooth left

4.     To hold a dental bridge in place

5.     To cover misshapened or severely discolored teeth

6.     To cover a dental implant

 

What Types of Crowns Are Available?

Permanent crowns can be made from all metal, porcelain-fused-to-metal, all resin, or all ceramic.

·         Metals used in crowns include gold alloy, other alloys (for example, palladium) or a base-metal alloy (for example, nickel or chromium). Compared with other crown types, less tooth structure needs to be removed with metal crowns, and tooth wear to opposing teeth is kept to a minimum. Metal crowns withstand biting and chewing forces well and probably last the longest in terms of wear down. Also, metal crowns rarely chip or break. The metallic color is the main drawback. Metal crowns are a good choice for out-of-sight molars.

·         Porcelain-fused-to-metal dental crowns can be color matched to your adjacent teeth (unlike the metallic crowns). However, more wearing to the opposing teeth occurs with this crown type compared with metal or resin crowns. The crown’s porcelain portion can also chip or break off. Next to all-ceramic crowns, porcelain-fused-to-metal crowns look most like normal teeth. However, sometimes the metal underlying the crown’s porcelain can show through as a dark line, especially at the gum line and even more so if your gums recede. These crowns can be a good choice for front or back teeth.

·         All-resin dental crowns are less expensive than other crown types. However, they wear down over time and are more prone to fractures than porcelain-fused-to-metal crowns.

·         All-ceramic or all-porcelain dental crowns provide the best natural color match than any other crown type and may be more suitable for people with metal allergies. However, they are not as strong as porcelain-fused-to-metal crowns and they wear down opposing teeth a little more than metal or resin crowns. All-ceramic crowns are a good choice for front teeth.

·         Temporary versus permanent. Temporary crowns can be made in your dentist’s office whereas permanent crowns are made in a dental laboratory. Temporary crowns are made of acrylic or stainless steel and can be used as a temporary restoration until a permanent crown is constructed by the dental laboratory.

·          

 What Steps Are Involved in Preparing a Tooth for a Crown?

Preparing a tooth for a crown usually requires two visits to the dentist — the first step involves examining and preparing the tooth, the second visit involves placement of the permanent crown.

First Visit: Examining and preparing the tooth.

At the first visit in preparation for a crown, your dentist may take a few X-rays to check the roots of the tooth receiving the crown and surrounding bone. If the tooth has extensive decay or if there is a risk of infection or injury to the tooth’s pulp, a root canal treatment may first be performed.

Before the process of making your crown is begun, your dentist will anesthetize (numb) your tooth and the gum tissue around the tooth. Next, the tooth receiving the crown is filed down along the chewing surface and sides to make room for the crown. The amount removed depends on the type of crown used (for instance, all-metal crowns are thinner, requiring less tooth structure removal than all-porcelain or porcelain-fused-to-metal ones). If, on the other hand, a large area of the tooth is missing (due to decay or damage), your dentist will use filling material to “build up” the tooth to support the crown.

After reshaping the tooth, your dentist will use impression paste or putty to make an impression of the tooth to receive the crown. Impressions of the teeth above and below the tooth to receive the dental crown will also be made to make sure that the crown will not affect your bite.

The impressions are sent to a dental laboratory where the crown will be manufactured. The crown is usually returned to your dentist’s office in 2 to 3 weeks. If your crown is made of porcelain, your dentist will also select the shade that most closely matches the color of the neighboring teeth. During this first office visit your dentist will make a temporary crown to cover and protect the prepared tooth while the crown is being made. Temporary crowns usually are made of acrylic and are held in place using a temporary cement.

Second Visit: Receiving the permanent dental crown.

At your second visit, your dentist will remove your temporary crown and check the fit and color of the permanent crown. If everything is acceptable, a local anesthetic will be used to numb the tooth and the new crown is permanently cemented in place.

How Should I Care for My Temporary Dental Crown?

Because temporary dental crowns are just that — a temporary fix until a permanent crown is ready, most dentists suggest that a few precautions be taken with your temporary crown. These include:

·         Avoid sticky, chewy foods (for example, chewing gum, caramel), which have the potential of grabbing and pulling off the crown.

·         Minimize use of the side of your mouth with the temporary crown. Shift the bulk of your chewing to the other side of your mouth.

·         Avoid chewing hard foods (such as raw vegetables), which could dislodge or break the crown.

·         Slide flossing material out-rather than lifting out-when cleaning your teeth. Lifting the floss out, as you normally would, might pull off the temporary crown.

 What Problems Could Develop With a Dental Crown?

·         Discomfort or sensitivity. Your newly crowned tooth may be sensitive immediately after the procedure as the anesthesia begins to wear off. If the tooth that has been crowned still has a nerve in it, you may experience some heat and cold sensitivity. Your dentist may recommend that you brush your teeth with toothpaste designed for sensitive teeth. Pain or sensitivity that occurs when you bite down usually means that the crown is too high on the tooth. If this is the case, call your dentist. He or she can easily fix this problem. 

·         Chipped crown. Crowns made of all porcelain can sometimes chip. If the chip is small, a composite resin can be used to repair the chip with the crown remaining in your mouth. If the chipping is extensive, the crown may need to be replaced.

·         Loose crown. Sometimes the cement washes out from under the crown. Not only does this allow the crown to become loose, it allows bacteria to leak in and cause decay to the tooth that remains. If your crown feels loose, contact your dentist’s office.

·         Crown falls off. Sometimes crowns fall off. Usually this is due to an improper fit or a lack of cement. If this happens, clean the crown and the front of your tooth. You can replace the crown temporarily using dental adhesive or temporary tooth cement that is sold in stores for this purpose. Contact your dentist’s office immediately. He or she will give you specific instructions on how to care for your tooth and crown for the day or so until you can be seen for an evaluation. Your dentist may be able to re-cement your crown in place; if not, a new crown will need to be made. 

·         Allergic reaction . Because the metals used to make crowns are usually a mixture of metals, an allergic reaction to the metals or porcelain used in crowns can occur, but this is extremely rare.

·         Dark line on crowned tooth next to the gum line. A dark line next to the gum line of your crowned tooth is normal, particularly if you have a porcelain-fused-to-metal crown. This dark line is simply the metal of the crown showing through.

 

What Are “Onlays” and “3/4 Crowns?”

Onlys and 3/4 crowns are variations on the technique of dental crowns. The difference between these crowns and the crowns discussed previously is their coverage of the underlying tooth. The “traditional” crown covers the entire tooth; onlays and 3/4 crowns cover the underlying tooth to a lesser extent.

How Long Do Dental Crowns Last?

On average, dental crowns last between 5 and 15 years. The life span of a crown depends on the amount of “wear and tear” the crown is exposed to, how well you follow good oral hygiene practices, and your personal mouth-related habits (you should avoid such habits as grinding or clenching your teeth, chewing ice, biting your fingernails, and using your teeth to open packaging).

 

Does a Crowned Tooth Require Special Care?

While a crowned tooth does not require any special care, remember that simply because a tooth is crowned does not mean the underlying tooth is protected from decay or gum disease. Therefore, continue to follow good oral hygiene practices, including brushing your teeth at least twice a day and flossing once a day-especially around the crown area where the gum meets the tooth.

 

What are dental crowns?

Dental crowns are restorations that protect damaged, cracked or broken down teeth. A crown strengthens your existing, damaged tooth so as to preserve its functionality. Dental crowns are also commonly known as caps (because a crown sits over your existing tooth, covering the entire outer surface). The animations below graphically illustrate the procedure of placing dental crowns:

Why might I need crowns?

§  If your tooth has undergone significant decay and there is not enough tooth structure remaining to support a filling or an inlay and maintain functionaility.

§  If a large portion of your tooth has fractured and it cannot be built up using traditional composite bonding techniques .

§  If you have a large cavity and opt for the additional protection a crown offers to your tooth over a large composite filling or an inlay.

§  If you have had a dental implant to replace a missing tooth, a crown will be fitted to the abutment of the titanium implant.

§  Following root canal treatment, a crown is ofteeeded to strengthen the tooth.

§  If you grind your teeth and have a poor diet, acid errosion may reduce your teeth to a point where the only option available is to crown them.

§  For cosmetic reasons, to improve the aesthetics of your smile, you may opt for all porcelain cosmetic crowns.

 

Are dental crowns always the best option?

Crowns should not be the first choice just to improve the aesthetics of your teeth, because a dentist needs to grind a significant portion of the original tooth away. Less invasive alternatives include veneers or dental bonding. Crowns are required when the strength of the tooth supporting the restoration is compromised, since veneers and dental bonding restorations are only as strong as the supporting tooth.

What materials can crowns be made from?

In modern-day dentistry. there is a wide variety of dental materials to choose from. Some crowns are made from full gold, where as others are made from an alloy of metals fused to a porcelain outer shell. After time, crowns that are made from a combination of metal fused to porcelain can begin to show dark gum lines that are not aesthetically attractive. All-porcelain or -ceramic crowns are the best choice for a natural cosmetic look. There are many different brands and types of porcelain crowns, and the variation between the costs of dental crowns at different dental practices may well reflect the quality of the materials used.

What does the procedure of having dental crowns fitted involve?

Once you have had a consultation with your dentist and discussed all the treatment options, he/she will prepare the tooth for crowning. The first stage is to clean the tooth, remove any decay and reshape it using a burr (a special dental drill for shaping teeth) under local anaesthesia. The shape of the prepared tooth is usually tapered to allow the crown sit comfortably over the top of it. Once the tooth is prepared, an impression (mould) of your teeth will be taken using a special “dental putty”. This impression is sent to a dental laboratory, which will use the impression of the prepared tooth as a guide to fabricate the new crown to fit perfectly. It usually takes between two to three weeks for a laboratory technician to custom-fabricate your new crown. During this time, your dentist will fit you with a temporary crown to cover and protect your prepared tooth.

On your second visit, your dentist will remove the temporary crown and roughen the outer surface of your prepared tooth with a special etching acid to give the dental cement a good surface to bond to. Your dentist will sit the crown over your tooth to see if it fits with your smile correctly and is the right colour and shape. Once you are both happy with the restoration and how it looks, your dentist will cement the crown firmly into place.

How long do crowns last?

This will depend largely on how well you look after your teeth. Dental crowns require the same level of care and attention as your natural teeth. Provided you have a good oral hygiene program, attend regular checkups at your dentist, don’t grind your teeth, maintain a tooth-kind diet and don’t do things like open beer bottles with your teeth, a high-quality dental crown can last 10-15 years.

Combined dental crowns

A combination dental crown is crafted from both porcelain and metal and often referred to as “porcelain fused to metal” or PFM. The advantage of using both materials is that metal provides the inner added strength of the crown and the porcelain-coated shell gives it the look and color of a natural tooth. The look of a natural tooth is typically why a PFM is considered for teeth that can be seen when you smile. One drawback to a PFM crown is if the porcelain shell chips or becomes rough it can wear down surrounding teeth. 

The procedure for getting a combination dental crown is often done in phases over two office visits. Each visit should take about one to three hours, depending on the extent of the damage or decay of the tooth that will be covered by the crown. The visits will take longer if the tooth is badly damaged or needs a root canal. Ask your dentist to estimate how long you should allow for each visit.

The following outlines the basic steps of the procedure, including what to expect and an estimate of how much time is involved:

During the first visit, the dentist prepares the tooth that will receive a crown by filing it down to make it smaller so that a crown can fit over it. Next, the dentist will have you bite down on a rubber-like substance in order to make a mold that’s used as a guide for shaping the permanent combination dental crown. The mold is typically sent to a dental lab where the dental crown will be made. There are some dental offices that have a machine that can make the crown the same day. Before you leave, the dentist will use dental glue to secure a temporary crown over your tooth. The temporary crown will remain on your tooth until your next visit when it will be replaced with the permanent crown.

When the permanent crown is ready you will return to the dental office to have it attached to the tooth. The dentist will test the dental crown to see how it fits over your tooth and may need to polish or shave it a bit to get the best fit. Once the combination crown has been properly fitted, the dentist will use cement glue to permanently attach it over your tooth.

Cost and appearance are the main differences between a combination dental crown and other types of dental crowns, all of which are designed to cover and restore a decayed or fractured tooth.

The combination dental crown can be more expensive than a traditional silver dental crown, but less money than the  stronger alternative of a porcelain-only crown. A combination dental crown has the double advantage of the strength of metal and the natural look of a tooth. The two other types of dental crowns are made either of all metal (gold or silver) or porcelain.

A downside to the combination dental crown is that more of the original tooth must be removed than with metal crowns, in order to put it in place. Also with a combination dental crown, the porcelain portion can wear dowearby teeth if it becomes jagged or rough.

 

 

Porcelain Crown Photos

Case #1 – Dark Front Teeth with Black Line Syndrome

Tom was concerned about the appearance of his two front teeth.  The one on the left had turned very dark.  The one on the right had been crowned only two years ago, but he didn’t like the way it looked.  It was opaque and had “black line syndrome” at the gumline.  As with many cases, the solution was a combination of treatments.  First, we whitened (bleached) all of Tom’s teeth.  The dark tooth required root canal therapy due to a “dead nerve” (the reason it turned dark).  The final step was to place two all-ceramic crowns on the front teeth.  The result completely changed his whole appearance.

 

 

 

Case #2 – Large Stained Fillings Restored with Porcelain Crowns

The following case illustrates four crowns.  Cynthia had several large fillings in her upper front teeth.  The central incisor (the middle tooth on the left) had a large bonded composite which had been redone several times over the years.  Notice the dull surface.  She desired a more permanent cosmetic solution.  Prior to the crowns, home bleaching was done.  The final result is very pleasing and natural.

 

Case #3 – Crown That Didn’t Match Other Teeth Replaced with All-Ceramic Crown

Annette had been living with a mismatched crown on her front tooth for many years.  The color is obviously too light.  Furthermore, the porcelain is very opaque giving what dentists call the “chiclet” appearance.  The tooth also had drifted and appeared longer than the other teeth.  Smile solutions discussed included a complete makeover.  However, Annette preferred to address the one tooth.  The result from such a simple approach is astounding.  

 

Summary

 

 

A crown is a dental restoration typically made in a dental laboratory that is placed over a natural tooth to replace damaged or unsupported tooth structure. Natural crowns may need to be replaced if they have been damaged by tooth decay, chipping or breaking. Artificial crowns can also be used as part of a bridge or as a restoration over an implant. They are commonly used after root canal treatment because the procedure can make the tooth brittle. A crown will protect the tooth structure from fracture.

Crown restorations range from full crowns that cover the entire natural crown of the tooth (the top surface of the tooth) to three-quarter crowns that leave the front of the tooth exposed (commonly used on front teeth). Crowns may be made of metal alloys (e.g., gold, copper, nickel, chromium), porcelain, porcelain fused to metal, or a type of plastic called composite resin.

The restoration process for a crown is a multistep process, beginning with a dental examination and x-rays. In many cases, root canal treatment is the first step. A diseased or decayed tooth has its pulp removed from its root canal and replaced with material called gutta percha.

  After the initial examination and any preliminary dental work, crowns typically require two or more visits: one to prepare the tooth and take impressions and another to cement the permanent crown to the tooth. Between these visits, the patient wears a temporary crown. There is usually little or no discomfort after a crown has been placed, although some patients may experience some sensitivity to hot and cold. If any additional problems arise, patients should speak with their dentist.

 

 

 

Crowns can closely match the color, shade, shape and length of neighboring teeth and are often difficult to detect as artificial. However, various problems (e.g., chipping, fracture, breaking, loosening, falling out) may require that crowns be replaced. In some of these cases, the crown may be able to be repaired in the mouth or re-cemented, depending on the amount of damage that has occurred.

In general, crowns require the same care as natural teeth. However, it is typically recommended that patients with crowns avoid chewing on extremely hard substances (e.g., nuts, ice), grinding their teeth and biting their fingernails. These activities can damage the crowns or reduce how long they last. Crowns do not protect the teeth from tooth decay, periodontal disease and other common oral concerns. Therefore, diligent dental hygiene remains extremely important

A crown is an artificial cap made to cover a natural tooth. The term “crown” can refer to a natural crown (the part of a tooth that is visible in the mouth) or a dental restoration that covers the top part of the tooth. 

An artificial crown is a dental prosthesis that covers or replaces the natural crown of a tooth. It typically covers the entire natural crown, on all sides and chewing surfaces. Artificial crowns can be used to cover and strengthen teeth that have been damaged. They may be used to improve the appearance of a tooth that is oddly shaped, badly discolored, or not in proportion with the neighboring teeth. Crowns can be used in cavity restoration when the tooth decay is too widespread for a filling, to restore a broken or cracked tooth, or prevent a tooth from breaking.

Crowns are commonly used as the last step after root canal treatment. Teeth become brittle as a result of this treatment and a crown will prevent further damage to the tooth (e.g., fracture). In these cases, the pulp of the tooth is removed from the root canal and the canal is filled with material such as gutta percha. A post may be placed in the root canal if there is insufficient natural tooth to support a crown. A crown is then typically placed in the area. Crowns can also be used to support a bridge or cover an implant.

Other types of dental restorations include inlays and onlays. These restorations cover smaller portions of the tooth, such as only the top part of the chewing surface. Inlays cover the smallest portion and may be slightly larger than a filling, while onlays cover at least one cusp of a tooth. Because onlays cover the cusps of teeth they offer better structural support. Inlays and onlays are more conservative restorations than crowns because less tooth structure is drilled away to fit.

Multiple visits to a dental office are required to prepare, place and adjust a crown. The crown is constructed in a dental laboratory based on impressions taken by the dentist. The multiple visits and labor crowns require means they usually cost more than simpler restorations, such as fillings.

 

 

Crowns require the same dental hygiene (regular brushing and flossing) as natural teeth. Crowns can last many years, depending on the location in the mouth and the level of dental hygiene.

Types and differences of crowns

The term “crown” can refer to either the natural crown which is part of a tooth or an artificial crown which is a dental restoration.

The natural crown of a tooth may be defined in two ways:

Anatomical crown. The part of the tooth covered by enamel, which may be above or below the gumline.

Clinical crown. The portion of the tooth visible inside the mouth and not covered by soft or hard tissue.

Different types of artificial crowns include:

Full crown. An artificial crown that covers the entire natural crown.

Jacket crown. A thin crown that covers large areas of the natural crown in the front teeth. It may not be strong enough for use in the back teeth, which endure greater levels of chewing stress and pressure.

Dowel crown. A full crown that is anchored by a dowel pin that extends into the root canal of a tooth that has undergone a root canal treatment.

Three-quarter crown. A crown that covers all of a natural crown except the front surface of the tooth, which remains natural for aesthetic purposes.

Abutment crown. An artificial crown used to support a bridge or cover an implant.

Artificial crowns may also be classified by their materials:

Gold alloys. Composed of a combination of gold, copper and other metals. These materials are strong and highly resistant to tarnishing, corrosion, fracture and wear. These materials do not tend to require as much removal of the underlying natural tooth material as other crown materials. They are compatible with the nearby teeth and are well tolerated by patients. However, many patients find the metallic gold color displeasing for teeth that are visible when talking, smiling or laughing.

Base metal alloys. Composed of a combination of base metals (e.g., nickel, chromium). These materials have strength and resistance qualities similar to gold alloys. However, they have a metallic silver color that many patients do not like. They may also cause an allergic sensitivity or initial discomfort with hot and cold in some patients.

Porcelain. May be composed of porcelain, ceramics or glasslike materials. These materials have a color and translucency that closely matches natural teeth. They are also highly resistant to wear. However, they may be prone to fracture and can wear dowearby teeth if the porcelain surface becomes rough. They may also require the removal of a larger amount of natural tooth than metal alloy crowns to support enough porcelain to produce a strong crown.

Porcelain fused to metal (PFM). Composed of a porcelain crown bonded to a metal base. This combination is strong and durable and highly resistant to wear. However, it can wear dowearby teeth if the porcelain surface becomes rough. It may also cause an allergic sensitivity or initial discomfort with hot and cold in some patients. In addition, it may require the removal of a larger amount of natural tooth than metal alloy crowns to support the combined metal and porcelain.

Composite resin. Composed of a type of composite plastic similar to the material used in tooth-colored fillings. This material tends to be relatively inexpensive and looks like natural teeth. However, it may stain more readily than porcelain and is not as strong or durable as porcelain.

Before the crown procedure

Before a crown can be placed, patients need to see a dentist for a dental examination to determine what type of crown is right for them. The dentist may also evaluate the patient’s medical and dental history. In some cases, a root canal treatment may be necessary due to extensive tooth decay. This treatment may also be needed if the tooth has to be reduced to such an extent that the tooth’s pulp may be injured or risk infection.

If there is not enough natural tooth structure to support the crown, a foundation may need to be built up, frequently around a pin or a post. Pins are thin shafts, typically made of metal, that are inserted into a hole that has been drilled into the tooth. They are becoming less common due to advances in adhesive dental materials that now allow weaker or smaller teeth to support crowns. Posts are thicker rods, frequently made of metal, that are inserted into the root canal of a tooth that has undergone root canal treatment.

After the initial examination and any preliminary dental work, crowns typically require two or more visits: one to prepare the tooth and make impressions and another to cement the crown to the tooth. The tooth that will support a crown must first be prepared by reducing its size to make room for the crown. Surrounding teeth may also require some adjustments so the crown will fit.

During and after the crown procedure

After the tooth is prepared, the dentist takes an impression of the prepared tooth and nearby teeth. A medicated thread or cord may be used to separate the gum from the tooth, allowing a more accurate impression. The impression will be sent to the dental laboratory, where it will be used to make the crown. The dentist then places a temporary crown, which the patient will wear until the permanent crown is placed. Temporary crowns may be prefabricated or made from resin in the dental office. They do not last long, but keep the prepared tooth safe until the permanent crown is available.

Crowns are generally made in dental laboratories and may take several weeks. After the crown arrives, the dentist removes the temporary crown and checks the fit of the permanent crown. The dentist makes any necessary adjustments (e.g., polishing, glaze) and temporarily cements the crown onto the prepared tooth. The dentist also ensures that the patient’s bite is correct with the new crown. If the crown is comfortable and satisfactory to the patient, the crown will be permanently cemented. This may occur at a later date.

There is usually little or no discomfort after a crown has been placed, although some patients may experience some sensitivity to hot and cold. In some crowns (e.g., porcelain fused to metal crowns), a dark line may be visible along the gumline. This is a small, visible portion of the metal base of the crown. It is not noticeable in most cases.

If any additional problems arise, such as pain or sensitivity when biting down, patients are advised to speak with their dentist. Some issues can be fixed in the dental office in a single visit. Others may require replacement of the crown.

The multistep process of preparing a tooth for a crown and having the crown placed may take weeks. Researchers are investigating new techniques that may help to reduce this time, allowing dentists to place crowns much sooner after the tooth has been prepared.

 Potential risks and benefits of crowns

Crowns have a natural look and feel that many patients consider superior to bridges and other forms of dental restoration. They can closely match the color, shade, shape and length of neighboring teeth and are often difficult to detect as artificial. They are generally considered affordable and are usually covered by insurance.

Crowns also have drawbacks. Many problems may require the crowns be replaced. Crowns may chip, fracture or break. Sometimes, chips or fractures can be repaired with composite resin without removing the crown. However, in many cases, the crown must be removed and a new crown placed.

In some cases, the porcelain part of a porcelain fused to metal crown may detach from the metal. It may come apart cleanly, or parts of the porcelain may remain attached to the metal. In some cases, these crowns can be bonded back together. However, they often must be replaced.

Tooth decay can still occur in the underlying tooth. Poor placement of the crown may allow food to get under the crown, or the cement may partially wear or wash out, making the crown loose and unstable. Patients should continue daily dental hygiene (brushing and flossing) and monitor any unusual changes around the crown. To avoid tooth decay, it is important to see a dentist as quickly as possible when a crown becomes loose. The crown can often be re-cemented before any damage to the tooth itself occurs. If the tooth does become damaged, the crown will no longer fit properly and a new crown will need to be made.

Occasionally, a crown may become loose and fall out entirely.  It is important to see a dentist as soon as possible to ensure that the crown and tooth are not damaged. If either becomes damaged, the crown will no longer fit properly and a new crown will need to be made.

Finally, changes in the material of a crown (e.g., discoloration, wear) or changes in the surrounding teeth (e.g., whitening attempts) may cause a crown to become unattractive. Patients may wish to have such crowns replaced.

Lifestyle considerations with crowns

In general, crowns require the same care as natural teeth. However, it is typically recommended that patients with crowns avoid chewing on extremely hard substances (e.g., nuts, ice), grinding their teeth and biting their fingernails. These activities can damage the crowns and reduce durability.

Crowns can last many years. According to the Academy of General Dentistry, crowns tend to last for around five to eight years. However, diligently cared for crowns can last many decades.

It is important for all patients, whether or not they have artificial crowns, to see a dentist regularly for a dental examination and cleaning. Diligent dental hygiene is also extremely important. Crowns do not protect the teeth from tooth decay, periodontal disease and other common oral concerns. While patients with crowns are not generally required to do anything that is not recommended for natural teeth as well, they may be advised to pay particular attention to the area of the tooth by the gumline. This is where plaque and decay may get under the crown and damage the underlying natural tooth.