Indications and Contraindications of a Dental Crown

Crown and bridges are being served to dental patients routinely as its manufacturing has become fast, readily available. It is a dependable option. 

Although, the crown & bridge is generally considered very safe and it is associated with a low incidence of complications, there are some precautions that need to be considered. 

Indications of a Dental Crown

1. Damage of crown beyond repair
2. Large filling needing replacement
3. Fractured tooth
4. Esthetic enhancement
5. Dental implant coverage
6. To fix dental bridges or dentures
7. Erosion of teeth

1. Damage beyond repair: Cases where the tooth has been damaged beyond repair: If the patient has a large cavity that cannot be fixed with a filling, but the dentist determines that the dentine and pulp are in good condition then he will recommend that a crown be placed to save the tooth.

2. Large fillings need replacing: Fillings need replacing every so often, your dentist may recommend installing a crown instead of re-filling the tooth, the reasons for this are the crown is a long term solution and it is aesthetically more pleasing.

3. Fractured tooth: In the case that a tooth gets fractured due to a dental trauma or progressive tooth decay, it is highly recommended that a procedure known as post and core be performed. The post and core procedure simply put, is the placement of an implant without extracting the root. In this procedure a small rod is inserted into the root of the affected tooth, this rod will slightly protrude and the core or crown will be attached to it. For this procedure, the tooth in question will require a root canal before the post and core can be done.

4. Esthetic enhancement: For patients who have discoloured or uneven teeth, or even for those who have large fillings the use of crowns can greatly improve the esthetic of their smile.

5. To cover dental implants: When a patient has lost a tooth for any reason, and an implant is required to maintain proper function, the implant will be covered by a porcelain crown that has been made to match your existing teeth.

6. To affix dental bridges or dentures: A dental bridge is a prosthetic used to replace missing teeth, these bridges are permanently adjoined to either dental implants or crowned teeth. The dental crowns are used to hold the prosthetic in place.

7. Dental erosion: The tooth enamel can be dissolved by the acidity in foods; when the enamel has been compromised, porcelain crowns are the ideal solution to prevent the progression of tooth decay to the dentine and pulp. Other forms of erosion include tooth abrasion which occurs from improper uses of toothbrushes, brushing too hard, improper flossing or biting on hard foods. And it also includes conditions where natural tooth to tooth friction happens, as in the case of involuntary grinding known as bruxism.

Contraindications

1. Where anaesthesia is contraindicated
2. Where filling can solve the problem
3. Insufficient tooth material
4. Chances of nerve damage
5. Bite misalignment
6. Allergy

As with any medical procedure, it is possible that complications can arise. Among the risk factors and contraindications of dental crown procedures, we can list the following:

1. Contraindication of anaesthesia: Illnesses where the use of anaesthesia is contraindicated. These may include severe heart disease, recent strokes and allergic reactions to anaesthesia.

2. The use of crowns is not indicated in cases where the problem can be solved with a filling.

3. Insufficient tooth material: There is a risk that during the preparation phase, the tooth’s surface can become too thin or be perforated by an instrument.

4. Nerve damage: During the preparation procedure, nerve damage can occur, if this should happen, it will be necessary to perform a root canal.

5. Bite misalignment, although in most cases dental crowns can correct TMJ (temporomandibular joint), if the crown is incorrectly placed, it can exacerbate the problem in some patients. Once the dental crown is in place, your dentist should check the fit taking into account the surrounding teeth as well as the whole bite.

6. Allergic reactions to one or more of the materials. Dental crowns can be made from a variety of materials, choosing the right material will minimize the chances of an allergic reaction.

7. Infections, if the dental crown is not properly sealed or if the damaged tissue was not properly removed, the area might become infected.

 

 

Crown and Bridge

Introduction

A crown is provided to protect the weakened natural tooth, regain its shape, maintain or enhance the esthetics and regain the functional ability of a person. A bridge is a prosthesis that is constructed to replace the one or more missing teeth and is supported by the neighbouring teeth.

A posterior tooth prepared for full crown (pink area)
B-Buccal aspect, L-Lingual aspect

They can be constructed in variety of the materials as follows:

1. All Metal
2. Porcelain fused to metal
3. All ceramic material
4. Pressed ceramic
5. All acrylic

There are various types of crown based on the surfaces they cover.

1. Full coverage crown
2. 3/4 crown
3. 4/5 crown
4. Inlay
5. Onlay

All metal includes precious metals like gold alloys, semi-precious that contains lesser amount of gold and non-precious alloys that are basically chrome- cobalt or nickel- chrome alloys.

Porcelain fused to metal crowns and bridges are made in any one of the above mentioned alloys. This metal crown, in the later phase of construction, is sintered with ceramic powders and chemo-mechanically fuses with metals in ceramic furnace.

“All ceramic” crown is made in Ceramic only. Aesthetically they are the best. Their con is that they are not as strong as metal ceramic or pressed ceramic.

A variety of factors have to be considered for the construction of a bridge.

1. Span of the edentulous area
2. Type of the teeth being replaced
3. Quality of supporting teeth
4. Conditions of the teeth in the opposing arch
5. Age of the patient
6. Patients’ ability to bear the treatment cost

Span of the edentulous area means how many teeth have to be replaced by bridge. The more number of teeth to be replaced, the longer will be the bridge; that in turn, will cause more stress in the bridge itself as well as onto the supporting teeth known as abutments. More stressed bridge will get more fractured ceramic from the metal part.

Type of the teeth decides as to how much masticatory load will have to be borne by the abutments. In case of the lateral incisor pontic, supported by one central incision and one canine, the masticatory load over abutments will be minimum. As we move from the Canines through Premolars to Molars, the quantity of masticatory load increases. Accordingly, we need to increase the number of abutments.

Quality of supporting teeth means how healthy the attachment apparatus of the supporting teeth is present. The healthier the apparatus, the better will be the masticatory load bearing ability of the abutments. It will result in a relatively longer life span of the bridge with minimum number of abutments. If the available healthy root surface area of the abutments will be less than the root surface area of the tooth or teeth being replaced, then more number of teeth should be used as abutment to prevent the overloading of any particular abutment tooth and ultimately bridge failure.

Conditions of the teeth present in the opposite dental arch includes the considerations of occlusal surface of the tooth and whether it is extruded. Is it causing mandible deviation during chewing?

Age wise a very young patient cannot be given crown and bridge as their pulp chambers are usually large and the trauma caused by heat during crown preparation or acids of luring agents may render the pulp tissue dead. This may lead to pulpal or periapical pathology ultimately leading to the failure of the bridge.

Preparation features for anterior crowns [1]

Treatment cost of the PFM bridges are very high. Therefore, the patient must understand the importance of the maintenance of the oral hygiene for the longer life of the prosthesis. The patient should be able to bear the cost of this treatment, otherwise a less expensive treatment needing easy maintenance should be chosen.

Preparation features of the posterior crowns [1]

Further Reading: Read BDJ article by clicking at the link

1. Crowns and other extra-coronal restorations: Preparations for full veneer crowns

An Introduction to Dental Crowns

 

• Dental Crowns

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• Crowns are a far more complex procedure than most people realise. To make a good quality crown, a dentist has to work in within a fraction of a millimetre. There is almost no margin for error. Getting the appearance correctly and communicating accurately with the dental lab can be an issue. Added to these, discussions about the balance between appearance and maintaining tooth tissue can be tricky. It can take a lot of painstaking adjustment at every step. Add in time pressure and any other added difficulties and it's a recipe for a stressed dentist, particularly if the dentist has recently graduated with limited experience. 

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• A calm and supportive dental nurse can work slickly with the dentist and makes the entire procedure easier. The roles of a good dental nurse and efficient lab technician are vital to the success of crowns.

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  Diagram showing transvers view of a tooth showing shape and thickness of a dental crown in pink colour.

  
  

• Planning for Making a Crown

• The first stage is the treatment planning, and deciding whether or not to place a crown. A decision has to be made about whether a filling is sufficient, whether a crown is most appropriate, or whether the tooth has become unrestorable and an extraction is the only choice. Crowns can be quite destructive due to the amount of tooth material to be removed. On the contrary, the advantage of the crowns is that they can be protective to the tooth and can help to hold the tooth together just like a helmet on the head, preventing the tooth splitting outwards, specifically after a root canal treatment. No restorative material can replace original tooth tissue so unnecessary tooth destruction must be avoided. so although they certainly have their place, crowns should not be placed without good reason.

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• The next big question comes is whether the patient's priority is the appearance or saving tooth tissue. Sometimes choosing to aim for the optimum appearance can be done without endangering the pulp of the tooth but at other times a compromise has to be made in order to keep the tooth alive and healthy. Some patients will be willing to accept a metal-coloured tooth quite happily to keep as much of their own tooth as possible because the metal crowns can be made much thinner, but for others that will not be an acceptable option.

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• At most occasions, compromises are done and agreed upon, like a metal band around the gingival margin of the tooth, or just having the visible part of the crown tooth coloured and the rest metal coloured. Discussing the patients' priorities and making sure that they know what exactly they will get end of treatment is a very important part of the process, to ensure their happiness and satisfaction.

• Another important part of the planing is checking whether the tooth is vital. Often crowns are placed following root canal treatment. Therefore, it is important to check that any infection under the tooth has improved. If the tooth is not root canal treated, then vitality tests and radiographic examination is a must for long term prognosis.

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• Crown Preparation

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• The first stage of the crown preparation appointment is normally making an impression for making a temporary crown while the permanent crown is being fabricated. The impression can be made using alginate or putty. Alginate needs to be mixed smoothly and the impression needs to be accurate with no big air bubble in the relevant area specially the margins. Putty needs to be used if the impression may be needed at a later date, as alginate impressions soon lose their shape.

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• Then comes the actual ‘crown preparation’ stage. Local anaesthetic is normally given to anaesthetise the tissues around the tooth being prepared. Cutting the tooth for the crown is the time where the dentist's real skill is needed. The amount of tooth tissue removed and the space needed for the crown depends on the material to be used for each part of the crown. A thicker porcelain is needed for porcelain whereas metal need to be kept thinner. For a patient, the difference between little tooth tissue removal and too much removal is fairly small. The dentist will try to create a clear margin, ideally finishing on natural tooth rather than filling material, for the dental lab to work on. On one hand, a written laboratory authorisation form will communicate a lot of the information about the crown to be made, the work done on the actual tooth can give a lot of information about what the dentist is intending for the tooth and how they want the lab to make the crown. The margin needs to be clear in order for it to be picked up clearly in the impression so that the lab has something useful to work with and so that the end result is good.

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• Shade Selection

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• After the crown prep is completed, the shade(s) for the crown needs to be decided on, in the case of porcelain. A shade guide is used and the dentist will look at different shades compared with the surrounding teeth. If the crown is full porcelain, rather than part porcelain with metal underneath, the dentist may also record the colour of the tooth underneath that is being crowned. This can then be communicated to the lab, to give them a greater idea of what they are working with, as the underlying colour can shine through and affect the colour of the crown needed. Any little details wanted, for example, stains or slight cracks on the tooth, can also be recorded and communicated.

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• Before the patient leaves, the tooth needs to be temporised. This is where the tooth is covered in order to keep it safe and healthy while the crown is made by the lab. It also helps to prevent movement or further eruption of the tooth that could prevent the crown fitting. The impression taken earlier in the process is used; temporary crown material is put into the impression and the impression is put back over the tooth. A small blob of the material is often put somewhere to give an indication of when the material is set. Once the material has set, the impression and temporary crown is removed. The edges are smoothed off using polishing discs. Temporary cement is then used for cementing the temporary crown in place.

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• The dental laboratory will then make the crown. This is also a very complex process, but largely falls outside of the clinical practice. The dental technician will fill the impression with dental stone to create a model/die of the tooth to work on. The lab will work to the instruction of the dentist, creating what has been asked for. The process will vary depending on whether it is a full metal, a porcelain fused to metal or a full porcelain crown.

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• Once the crown returns back from the lab, the dentist will check that it is as they expected. They will check if the crown goes on and off on the model perfectly.

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• Crown Cementation

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• The temporary crown will be removed, the temporary cement will be cleaned off the underlying tooth and a cement will be decided upon. The crown will be tried in and out so that the dentist is certain about the placement of the crown. Cement will then be mixed and put into the crown, the tooth will be dried, and the crown will be placed. Excess cement will be cleared away using floss and dental instruments. Pressure will be maintained on the crown so that the cement sets with the crown fully seated/in the correct position.

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• The patient will then be asked how it feels to bite on. Often it will be slightly ‘high’, so the dentist will mark the teeth using articulating paper, so that the heavy contacts show up. Adjustments will then be made so that the crown is comfortable and doesn't interfere with the patient's bite.

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• Crowns can be a fabulous restoration, helping to save teeth that would otherwise have to be extracted. They can also be a very aesthetic option, particularly those made of/with porcelain. Crowns can be a very complex and involved procedure, but really demonstrate the important roles that different members of the dental team play in producing an end result that really meets the needs of/pleases the patient.

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• Summary of stages:

1. Deciding whether a crown is the most appropriate restoration
2. Planning the material(s) of the crown
3. Taking an impression to allow a temporary crown to be made
4. Shaping the tooth ready for the crown
5. Temporising the tooth
6. The crown is made by the lab
7. The temporary crown is replaced with the permanent crown
8. Any necessary adjustments are made.

Ref: British Dental Journal

What is best during placement of Crown?

A ceramic crown being placed over a tooth. The excess cement is protruding at margin [1].

The placement of crown is an important step in the longevity of the crown and the comfort of the patient. There are certain points that should be taken into consideration by a dentist during placement i.e. cementation.

The gingival margins should not be inflamed at the time of crown cementation. This may happen due to gingivoplasty or crown lengthening. For a common man, it means, the gum margins of the tooth receiving the artificial crown should not have redness, swelling or puffiness. If there is any, better to wait till it subsides.

The choice of cement/luting agent should be decided based on the type and material of the crown. The available materials are Zinc phosphate, Glass ionomer, Polycarbonate, Zinc silicophosphate, and resin luting agents. The anterior crowns need different cementing material than that of posterior crowns. The all ceramic crowns are best cemented by resin luting agents, but the use is limited to the cementation of anterior crowns. The reason is, after cementation, it becomes extremely difficult to remove set resin from the interproximal area of posterior teeth. Rest luting materials are brittle enough to break and remove, therefore, they can be used in all areas-anterior as well as posterior.