What is a crown?
One of the most common questions we get at the dental practice is: “What is a crown”
This is difficult to answer. Its a bit like asking a “What is a car?”
A “Dental Crown” is a bit of precision engineering. It is a thimble which wraps around the whole surface of a tooth or dental implant to mimic a natural tooth.
A Dental Veneer is a partial crown which covers the usually the front surface of the tooth, but can also extend around the sides and over the biting edge.
There are many questions, decisions, techniques, material and factors which influence the successful outcome.
Lets look at some of the questions, factors and choices that you and your dentist have to make.
- Why is it needed.
- To replace decayed or broken teeth.
- To strengthen a weak tooth.
- To protect a tooth that has had root canal therapy
- To improve the appearance - the shape or the colour.
- Is it for back teeth or front.
- What do you want?
- What can we offer you?
- What standards shall your dentist choose for you?
- What do you want it to look like?
- How long should it last?
- How much of the remaining tooth is left to cement a crown onto.
- What load or function will the neighbouring and opposing teeth be imposing on it?
- What is the status of the nerve ( is the tooth alive or dead?)
- How healthy are the gums and bone.
How is a crown made
The outer layer of tooth structure is removed and shaped to give a thimble like shape.
Any decay must be removed and the margins of the preparation shaped to suit the chosen material characteristics of the crown to be used.
Some dentists will use “Loupes” or microscopes to aid the accuracy of the procedure and the fine finishing required to give the best results.
Two visit crowns with a physical Impressions
The dentist will take impressions with a “paste-like material” that sets in the mouth.
A temporary crown is then fitted and the impression goes to the technician who makes a model of the teeth and builds the crown
Of equal importance is the skill, the training and the experience of the technician and the rapport and communication that the dentist and technician have together.
The technician has to pour a stone model ( if physical impressions were used ). He has to create the correct anatomical features to replace the lost tooth structure. He has to create a margin or fit of the crown as perfect as possible to prevent later decay. He has to contour the material to give a beneficial soft tissue response. He has to create a perfect “contact point” where the crown touches to teeth beside it. He has to make it look like a “real tooth”, in form, “colour”, translucency, reflectivity, and surface texture. and returns it to be fitted on a second visit
One visit Crowns with computerised technology
Using newer digital technology such as the CEREC system Digital Impressions use a digital camera to capture the data electronically using infra-red wavelength camera technology. This provides instant models that can be inspected for inaccuracies and if necessary retaken there and then.
The opposing teeth can also be recorded and the way they relate to each other captures the “Occlusion” or the functional shape
Usually a shade “guide” will be used by the dentist to draw a little map of the distribution of colour that they choose for you. Preferably records using photography and or digital photo-spectrometry can be used to give the technician the best chance of accurately reproducing the closest possible likeness to the natural tooth that matches and blend with your other teeth.
The better the communication between dentist and technician the better the chance of your tooth matching your Matching a single front tooth to the other front tooth is considered one of the most difficult challenges in modern dentistry,
Using digital photo-spectrometry to analysis the colour can help the technician replicate the natural tooth “colours” no matter the difference between light source that the dentist and the dental technician are working with.
Colour is the sum total perception of the combination of;
The characteristics, hue, chroma, value, surface texture, translucency.
It is the interpretation of the brain. Patient judge the result by the blend of the “colour” to the natural teeth
Porcelain bonded to metal crowns done well can be a good solution to many problems, but it doesn’t matter whether it’s a high quality gold or a base metal, neither will allow the light to shine through the tooth.
This creates an aesthetic / cosmetic issue that the crown cannot transmit light like a normal tooth.
The experience and skill of the clinician, - the choice of material, the precision of the preparation, the impression technique ( physical or digital ), the preparation of the model, the design of the crown, the surrounding and opposing teeth, the health of the gums, the proximity / health of the nerve of the tooth, the experience and skill of the technician, the manufacturing technique, the cement, the cementation or application of the cement, the aftercare and follow up.
We have to factor in a multitude of considerations to suit your needs, your philosophy, your expectations and your budget. The truth is there are a vast range of options for you and us to consider. Our job is to try and give you the best choice and result for the resources and expectations that you have. There is a lot to consider.
TYPES OF CROWN AVAILABLE
All the crown materials below will have their applications.
Choosing the correct material for the patient’s needs depends on multiple clinical factors.
There is not one type fits all and each of these below has variations! Your dentist has plenty of choice.
Each type of crown will have different strengths and appearance to suit different situations.
Gold crown: Made of a gold alloy. Solid metal cast by a “lost wax technique”. Mechanically excellent and still a good choice of back teeth
Metal crown: A variety of metals can be used with a lower gold or no gold content.
Feldspathic crown: Feldspathic porcelain only. Usually referred to as a PJC.
Feldspathic / metal fused crown: Metal core fused to feldspathic porcelain.
Feldspathic / Zirconium crown: Zirconium core fused to feldspathic porcelain
Zirconium crown: Zirconium one piece crown
Zirconium / feldspathic crown: Zirconium core fused to feldspathic porcelain.
Lithium Di-silicate crown: Reinforced solid porcelain. “E-Max”.
Lithium Di-silicate / zirconium core: Zirconium core fused to “E-max”
Composite crown: A glass resin and filler material.
“Enamic” Crown: A Ceramic Polymer Composite
Black lines around the crowns :
Micheal had these two front crowns for many years, the darkness at the roots of the crowns and the discoloured fillings were a cause of concern so we placed two 360degree veneers /crowns and two veneers with all porcelain high translucency crowns.
These restorations were placed in one visit using the CEREC system. They are designed and cut from solid blocks of homogenous porcelain to within 45 microns tolerance of fit.
This is equivalent to half the diameter of a human hair.!
This customised design process gives the dentist full control over the decision process and
The final characterisations applied by the dentist to blend the colours and tones to suit the individual patient.
The surface texture of the porcelain can be varied to give a “brilliance”, just as a multifaceted diamond sparkles because it reflects the light.
Smooth teeth can look dull and “old”.
Here we have mimicked the natural “mottling” on the real teeth
Usually the dentist who took the optical impression will make your crown there and then. This avoids any communication or record taking for shade etc. You are present and the dentist can compare the work in progress with the real you as he proceeds!
Allow the dentist to be in sole control of the design of your crown. Here we show a right central incisor made to match the left.
At the fitting of the crown the choice of the best cement relates to the material used for the crown and the remaining tooth structure. Non metal crowns can be cemented with x-ray visible cements to assist monitoring long term
With advances continuously in adhesive technology and research the correct choice and application of
technique will give a greater chance of success.
The choice of material, of preparation finish line (or edge of the crown) and the cements used will determine any possibilities of “Black “Lines around the edges at a later date.
The margins of this all porcelain crown are not below the gum line and the cement is the same colour as the tooth and the crown. This makes it easy to clean and to watch and means the less removal of the tooth structure in a “sensitive” area of the root surface.
We want you to be as proud of your new teeth as we are. This we can only achieve with attention to detail from start to finish. Here we show how a new smile has allowed the patient to smile again.
Veneers /crowns to rebuild worn teeth
The initial photos show worn and chipped edges with a “restricted or “guarded”smile.
One year later see how the patient lip musculature has relaxed and adapted to the new smile line.
As important as all of the above is that you continue to attend preferably the same dentist or dental practice to continuously monitor the crown once fitted.
To keep the gums healthy and to monitor with x rays to compare to the original.
It’s worth reiterating: Non Metal crowns have the advantage that x-rays will see through the material and allow early detection of any later developing problems.
How long will it last? Its a fair enough question.
It depends on all the above being done as well as possible,
It depends on how you treat and look after your teeth and gums. We would ask you to see the hygienist at least every 6 months.
It depends on what you eat. Sugar will undo even the best dentistry, no matter the materials and care.
Its depends on the skill of the dentist, the technician, the choice of materials by the dentist.
It depends on your investment.
So once again, how to answer the first question.
What is a Crown.
My best answer is come and talk to us. We can listen to what you would like. We can inspect examine and assess your needs. We can advise you what your options are. We can tell you what we think would do best and the limitations of alternatives.
Given the choice we will offer you our best techniques, materials and technicians.
You can tell us what you would like to choose.
DR PAUL MOORE BDS 091 547592