The Integrated National Board Dental Examination (INBDE) is the 500-item licensing exam administered by the American Dental Association (ADA) which allows graduate dental students to practice in the United States of America. The content of the INBDE is formulated by the Joint Commission on National Dental Examinations (JCNDE).
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.
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. |
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The dentist who has got his or her bachelor dental degree from a non-Australian institution needs to pass the skill assessment test/examination conducted by the Australian Dental Council and register themselves in Dental Board of Australia to practice as a general dentist in Australia or to get a job in public or private sector.
The ADC test/examination is a screening examination to establish that dentists trained in dental schools which have not been formally reviewed and accredited by the ADC have the necessary knowledge and clinical competence to practice dentistry.
Following are the steps, an overseas dentist needs to go through to qualify the ADC examination:
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.
1. 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. When 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 esthetically 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. Enhanced
esthetics: For patients who have discolored or uneven teeth, or even for those
who have large fillings the use of crowns can greatly improve the esthetics 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.
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. Illnesses
where the use of anesthesia is contraindicated: These may include severe heart
disease, recent strokes and allergic reactions to anesthesia.
2. The use of
crowns is not indicated in cases where the problem can be solved with a
filling.
3. There is a
risk that during the preparation phase, the tooth’s surface can become too thin
or be perforated by an instrument.
4. 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.
You must know the properties of the materials used in dentistry to understand its function and how and why it works in oral cavity. It also helps in manipulating it. The main properties you should know about are following:
Regular oral hygiene by mechanical brushing and cleaning between the teeth removes soft dental plaque. When dental plaque becomes mineralised (calculus), it must be removed by a dental practitioner. Dental plaque and calculus can cause periodontal disease (eg gingivitis) and dental caries.
Frequent exposure to dietary sugar and carbohydrates leads to an increase in the risk of dental caries. Avoid sucrose in sticky forms and limit other sugars (eg acidic drinks) and carbohydrates as snacks between meals.
Avoid drinks other than water at bedtime after brushing teeth (including milk, formula and expressed breastmilk)—saliva flow diminishes during sleep and the sugar from the drink remains on the teeth overnight. This is a common cause of dental caries in children and the elderly.
Interdental cleaning using floss or interdental brushes is recommended once each day before brushing the teeth. Brushing teeth with a toothbrush does not remove plaque from between the teeth or below the gum line.
Dental floss can be used to wipe the interdental tooth surface to remove plaque (back and forth, then up and down several times on each tooth surface). Manual dental floss, floss-holding devices or automated flossing devices are available—the choice is based on personal preference or level of dexterity.
Interdental brushes areas effective as dental floss in plaque removal, and often more effective for debris removal. They require less dexterity than dental floss. Interdental brushes are particularly useful in patients with gum recession or disease, where the spaces between the teeth are larger.
Interdental wood sticks can remove food particles, but do not effectively remove plaque.
Water jets do not effectively remove plaque.
Soft-bristle toothbrushes are recommended; hard-bristle toothbrushes are not more effective and can damage the gums and the softer root surface. Children younger than 6 years should use a children’s toothbrush. Powered toothbrushes with a rotation oscillation action are slightly more effective at plaque removal than manual brushes. Powered toothbrushes are useful for people with dexterity or disability problems, and for carers. Toothbrushes should be replaced once damaged or when the bristles become deformed.
Advise patients to use a fluoride-containing toothpaste; for recommended concentrations of fluoride in toothpaste. Toothpastes that do not contain fluoride provide little protection against dental caries. Toothpastes also contain other additives (eg abrasives, detergents, antibacterial, bleaches, remineralising agents).
Toothpastes that do not contain fluoride provide little protection against dental caries.
Advise patients to brush teeth for 2 minutes, twice each day with fluoride toothpaste. Toothpaste should be spat out and not swallowed to minimise fluoride ingestion; the mouth should not be rinsed to allow increased uptake of fluoride from the saliva.
Advise patients to brush or gently scrape the tongue, but not to brush or massage the gums.
Mouthwash is usually not required as part of a standard oral hygiene routine, provided mechanical cleaning (toothbrushing, interdental cleaning) is performed properly. Mouthwash should not be used as substitute for proper mechanical teeth cleaning.
Fluoride-containing mouthwashes can be used as an additional source of fluoride for people at high risk of dental caries on the recommendation of a dentist.
Mouthwash that inhibits plaque formation (eg chlorhexidine) can be used for a short duration in addition to mechanical tooth cleaning, usually when pain associated with periodontal disease restricts mechanical cleaning (see Management of necrotising gingivitis and Gingivitis).
Alcohol-containing mouthwashes may be associated with oral cancer and are not recommended. See here for further information on mouthwashes.
People with dental implants, bridges, crowns that are joined together, and orthodontic brackets should follow the oral hygiene advice from their dentist.
Dentures should be regularly cleaned twice a day to remove food particles and plaque. Advise patients to remove dentures from the mouth and clean them with warm water, mild soap and a toothbrush, denture brush or soft nail brush. Avoid cleaning dentures with hot water, toothpaste, kitchen detergents, laundry bleaches, methylated spirits, antiseptics or abrasives (unless instructed to by a dental practitioner). Patients should clean their gums and remaining teeth with a soft toothbrush and toothpaste.
Advise patients to place dentures in a dry environment overnight after cleaning them. Traditionally, it was recommended that dentures were kept in liquid overnight. However, allowing the cleaned denture to dry out at night is more effective for reducing yeast colonisation and plaque accumulation, compared with both denture cleansers and water. Although repeated cycles of hydration and dehydration can change the shape of the denture, these changes are small and not clinically significant.
Dentures should be cleaned then placed in a dry environment at night. If there is a build-up of hard deposits (tartar, calculus), dentures can be soaked overnight in a solution of white vinegar (diluted 1:4), then cleaned as usual. Advise patients to see their dentist for professional cleaning if hard deposits cannot be removed.
Denture-associated erythematous stomatitis is prevented by regular cleaning of the dentures and storing them in a dry environment overnight. Advise patients with denture-associated erythematous stomatitis to optimise denture hygiene—it can take 1 month for symptoms to improve; see Oral candidiasis and Candida-associated lesions for further information.
Ref: Therapeutic Guidelines Limited 2019 (www.tg.org.au)
Enamel: This is the hard, calcified substance that makes the surface of a crown of a tooth.
Pulp: This is the organ at the centre of a tooth that contains blood vessels, connective and neural tissue, and cells that produce dentine-odontoblast. Blood vessels and neural tissue enter the tooth from the apex of the root.
Periodontal ligament: This is the ligament that connects a tooth, by its root, to the supporting bone.
Cementum: This is the calcified tissue on the surface of the root of a tooth, which provides attachment for the periodontal ligament.
Fissure: It is a naturally occurring crevice in the enamel.
Crown: This is the part of the tooth that is visible and is above the gingival margin.
Root: This is the part of the tooth below the gingival margin; it is connected through cementum on its surface and the fibres of the periodontal ligament to the supporting bone.
There are numerous dental numbering systems to identify teeth and their
maturity. The most commonly used system in Australia is the Federation Dentaire
Internationale (FDI) system
The FDI numbering system divides the mouth into quadrants. The first
number indicates the quadrant and whether it is a primary or secondary tooth.
The second number indicates the tooth; tooth numbering begins at the central
incisor and counts backward to the molars.
Using the FDI numbering system, for adults, the quadrants are numbered as:
1. patient’s upper right is quadrant 1
2. patient’s upper left is quadrant 2
3. patient’s lower left is quadrant 3
4. patient’s lower right is quadrant 4
For primary teeth in children, the quadrants are numbered as:
1. patient’s upper right is quadrant 5
2. patient’s upper left is quadrant 6
3. patient’s lower left is quadrant 7
4. patient’s lower right is quadrant 8
