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There are various magnified illuminating lights and shade measuring light meters that can be used as an adjuct to shade matching. The best technique is for the patient to be seen directly by the dental ceramic technician for the shade taking.

Colour matching is an art rather than a science and is always less than 100% reliable, however a good colour match can usually be achieved by good communication between a dentist and his highly trained technician.  There are electronic measurers of shades but they are not fool-proof and the shade of one's crowns can change radically in different lights.

Generally, if one is not happy with a colour or shade match, the crowns can occasionally be changed subtely but sometimes a perfect match is not achievable which has to be accepted by patient and dentist alike.

Thanks for your question. Whole text-books have been written on the subject. There are digital machines which measure the average colour of teeth, and will give a technician a prescription for matching porcelains, but the best results are achieved by letting the patient visit the technician for colour matching, or by taking a digital photograph with a graded colour tab held next to the teeth. Either of these options will allow the technician to build in the subtle nuances that make good crowns look like natural teeth. There are other aspects to shade matching such as the ambient light and the hydration of the teeth when photographing them, but a good technician will be well aware of these matters.

From a ceramists point of view , there are many things to take into consideration when trying to match teeth perfectly:-
The first consideration is:-  If a ceramist receives photographs, they should come from a dentist who knows what a ceramist is looking for.  The dentist needs to look into the tooth itself and the camera needs to be of a minimum quality - if it is a digital camera even better.  A technician can then magnify the image, see all the internal characteristics as well as the surface textures.  The most important thing is that a dentist includes some sort of colour reference tab in the photograph so that the ceramist will also have this physically in view when making the teeth.  The ceramist/ technician can then refer to the colours using the colour tab in the photograph. The good thing about using photography for shade taking is that it gives the dentist the freedom to shop around for a very good ceramist.  It takes years and years to train and produce life-like teeth and so these people are hard to find. Once found they don't tend to change very easily.  With modern technology, patients' digital photographs can be sent/stored electronically and be accessed securely by both  dentist and technician (see www.ceramiccentre.com - Case Studies - Patients and click on either Anteriors or Combinations for example).  There are also excellent shade taking machines - and again see www.ceramiccentre.com - How We Work and click on Shade Taking.  

A good technician may see a patient but will have have seen quite a few patients in one day and this means that when the time comes to make the tooth, reliance will be upon recorded information.  The answer to a good tooth match is therefore not always about seeing the technician but about the use of modern technology in the transmission, storage and retrieval  of quality and key information.  The second consideration is :-  What is underneath the crowns to be made?  This will greatly influence the final crowns in shape and colour.  If the remaining tooth structure of the tooth to be made (preparations) are to big, it will mean that there is not always enough room to create the desired shape as the colour might end up opaque and solid looking.  If the preparations are too dark, this will influence the material used to make your crowns, as we will have to try and mask this colour  with a material that is very solid (metal) and which will influence the light reflective qualities.

1.  Enamel Shells or All Porcelain Crowns (without a sub-structure), get their strength from the underlying support of the dentine and remaining tooth structure by bonding on to them.  Light refractive qualities are at their best when a crown is translucent and allows all the light in and out and through a crown. Crowns like these are the most flexible in colour control. If the underlying tooth is a good colour, the technician has control of the shape and colour and the dentist can also influence the colour with different cement colours available on the market . These crowns are able to give the best aesthetics possible. When these crowns are being made and  the base tooth colour is dark, it can be bleached and the crowns are then made.  All variations of these kinds of crowns are great with colours. The down side is that they are very difficult to cement and can crack upon cementation due to no fault of the dentist or technician  (this is the reason that they are not readily offered amongst others).   They give the best result, however, if the money is available.  Look at case studies - Veneers www.ceramiccentre.com for examples of our best work in this category.  There are some dentists who charge enough to have the same teeth made 3 times and then have ultimate flexibility.  Please do not forget that your underlying colour might need addressing which adds cost.  If the occlusion is right (refer Occlusion) and they bond well, they will look great and last a very long time.  Some dentists put them on all teeth.  The underlying colour becomes part of the new crown.

2.  All Porcelain crowns with either metal or ceramic sub-structures get their strength from the underlying support that they are made on.  All-ceramic crowns with a harder ceramic substructure (more of a halfway house between the former and metal crowns which I will explain next) are very successful and have good colour matching abilities. This will of course be influenced by the underlying colour of the coping (harder ceramic substructure)  which refracts light more like that of a crack in a block of ice. This can cause a less natural appearance in different lights and also when light refracts at certain angles. These crowns are much more colour managed by the ceramist and if he knows the underlying colours he can compensate for many factors, like irregularities in thickness and discolourations.  They are more expensive to produce than metal substructure crowns as supply costs and equipment costs are higher generally. These are very strong and very good in compensating for problem areas. Most aesthetic dentistry is built on these sorts of crowns. With the demand for implants increasing, these materials provide the same foundation for all teeth being replaced and so produce more harmony with much more translucency than metal crowns and yet retaining some masking abilities.  More tooth structure is saved using these sorts of crowns than the following metal substructure crowns.

3.  Metal substructures with porcelain on top stop the light.   Light will go in and then shoot back out without having gone through the tooth causing a solid quality.  They are believed to be the strongest sort of porcelain crown. They do have an odd look to them even  when they are done by the best ceramist in the world. They do look fine in darker areas of the mouth and in fact in the front of the mouth they can also look very good. To achieve this a lot of tooth structure needs to be taken away so that their substructures can be made as discrete as possible. They also stop the light going into the root. This can make the soft tissues look grey.  In the front of the mouth, some people do not take to this.  These crowns are less expensive than all-ceramic crowns.  With long bridge-work, metal substructures still seem to be the strongest and most versatile.

So, in summary it is about communicating your needs and wishes to the dentist  who should translate and communicate all your information well to the ceramist.  If there is a problem you should be open to going back to the dentist and in complicated cases being open to seeing the technician/ceramist, especially with specific preferences to enhance communication between all.  The crowns which suit your situation should be used to give your particular case the best result.  If you want the very best, you need to make this clear to your dentist and be prepared to take on a long term treatment plan as well as being open to hidden costs.

By liaising carefully with a skilled ceramist via photography is one solution. Alternatively actually visit the ceramist - Whilst it is important to get the correct colour, the skill of the ceramist who builds the crown is just as important so that correct anatomy and shade nuances are also reproduced