This is a comprehensive explanation of what goes into a Niho restoration. 

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THE PATIENT 

 

Typically patients are referred to us by their dentists.  Along with the dentists' prescribed treatment we endeavour to discover what it is patients wants.  

 

The patient, whose case is shown above, had a crown made with a different dentist and dental laboratory a few years ago and had never been happy with it.  It was the wrong colour, unacceptable shape and stood out from the other teeth in his mouth.  He mentioned he wanted the new crown to blend in with his smile, the shape to be natural as well the shade but wanted some the staining to be reduced.

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THE SHADE TAKE

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In order to make a crown we need to know which colour to make it.  This is our process which ensures we get the correct colour

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First we use a Digital Photo Spectrometer (DPS) to measure the base colour or shade of the tooth.  A DPS is a small hand held device that shines a small beam of light into your tooth and tells us the colour.  We measure the colour at the neck, the centre and incisal edge of the tooth as each third of the tooth has a variance in base shade colour. We confirm colour with a shade tab (a colour sample) and take a few photographs so we can see how to replicate the tooth.  We note any other colours that might be present in the tooth. How translucent the tooth is and where. We also note any light behaviours like fluorescence, opalescence, iridescence or light absorption .

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In the example above there is fluorescence in the neck of the tooth.  A little blue opal tinge in the incisal corners and a cream haze next to that.  There is translucency at the incisal edge with some yellow hue and orange stains on the surface.  There is a light absorbing low value area in the centre of the tooth and an orange line in the tooth's surface.  All of these intricacies are what makes a crown look natural and what we hope to emulate.

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THE SHAPE

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With a Niho restoration we make a wax replica of the final shape and size of the restoration. This is made before we move to the next stages as it is a great diagnostic tool.  It helps us resolve problems like lack of space for ceramic, or what will look best when making a tooth in a space which is too big or small.  We also have a better idea of how to layer the different colours of ceramic to ensure they are in the right area and at the right depth within the crown. 

 

This is an added process used to create our Niho restorations and ensures we get the best results possible.

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THE FRAME

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A crown is typically made of two parts, a frame work for strength and ceramic veneering to achieve the right aesthetics.  The framework needs to be the correct thickness for strength, there must also be enough space for the layering of ceramic to achieve the correct colour and depth of colour so the crown looks natural.  

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Having a wax replica of the final shape our restoration means we can make our frame work with more accuracy.  We can measure the thickness of the wax to know the thickness of the final restoration.  How much room we have  for our frame work and how much room we have for ceramic.  We can take an impression of this wax and use this to see how much room we have between the prepared tooth and final restoration.  With this impression we can  see exactly where we need support for ceramic and areas which may not have ideal space for ceramic veneering. 

 

Depending on which material we use, we need between .4mm and .8mm thickness for the frame work . 1.5mm is the ideal space for ceramics for one material, PFM, with another, high translucent zirconia,  .5 would be suitable.  Having this added information helps us choose the best material for the situation and indicates where any colour modifications of the framework might be needed to achieve a great result. 

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In the example above, the area between the prepared tooth and the final desired outcome was only 1mm in the incisal edge and corners of the tooth and only 0.3mm from the face of the tooth.  We choose high translucent zirconia as this case has less  ideal amount of room for ceramics. This was a very tricky case to get a good result and this gives us the highest chance of success. 

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THE BUILD UP

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Once the framework is ready we can build up our ceramic, the aesthetic portion of the crown.  We need to build our ceramic to the right size, right shape and with the appropriate coloured ceramic in the appropriate place to achieve the acceptable result. 

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A basic crown has two ceramics that are layered on top of the frame work and fired in a furnace to set.  The two ceramics typically used are a dentine ceramic, as a tooth coloured base,  The dentine is added to the neck, body and a thin layer in the incisal third.  An enamel ceramic is layered on to the dentine ceramic in the incisal half.

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This will resemble a tooth to a degree but natural teeth have multiple colours and intricacies that make them look like teeth.  We believe two ceramics are not enough to achieve a high aesthetic result. 

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With our standard crowns we use six ceramics.  First  we apply a slightly orange ceramic at the neck and in between the teeth. Then dentine ceramic is added as above.  On top of the dentine ceramic a translucent ceramic is added at the incisal edge and a slight blue translucent ceramic is placed in the corners of the crown. The final layer is a dentine enamel in the neck and an incisal enamel on the incisal half.  Ceramic shrinks by 10% once fired so care is taken to ensure the ceramics are in the correct area of tooth and at the right depth.

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This achieves a great result but doesn't have the individual details required when making a crown to a custom shade.

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In our Niho restorations we take this process to the next level.  We use multiple dentine colours, enamel colours and ceramics with different optical properties to more closely replicate nature.  Fluorescence, opalescence, iridescence and light absorption are what make teeth look the way they do.  We need ceramics that act like teeth so our crowns look natural.  These ceramics have specific firing parameters and need to be fired at different stages to achieve the necessary result.  This takes more time and knowledge but truly enhances the final product. 

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In the case above we used 15 different ceramics, as per our shade take, to achieve the correct shade.  As our frame work was custom made to our wax replica the shrinkage is better controlled, which is essential when using multiple ceramics and firing procedures.

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THE FINE DETAILS

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With the ceramics fired and in the correct place it is time to focus on the final shaping of the crown.  We shape the length and width of the crown to match the tooth next to it.  We make sure it doesn't protrude too far forward of the adjacent tooth.  Next we focus on the small ridges and valleys of the tooth and copy any small indents.  This means light should reflect on the crown as it does on the natural teeth. 

 

Although this is the process with all our crowns we take extra care at this stage with a Niho restoration.  Gold dust is added to the crown and model to highlight the micro details of the tooth and crown.  These details are incorporated in the crown.  With the shape finalised we can do our final glaze of the crown and add the surface staining. 

 

Once glazed we take photographs of the crown next to the shade tabs and compare to our first photographs.  Another extra step in the manufacture of a Niho crown.  Happy with the result the crown is sent to the dentist.

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THE FIT DAY

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This is the day you will return to your dentist to have your final crown fitted.  The dentist will temporarily cement you're crown  so you can see your crown in place.  It is up to you to decide whether you are happy with the crown's colour, shape and overall appearance.  No two teeth ever look exactly the same but your new crown should look harmonious and natural.  This patient was very happy with his crown and had it permanently cemented then and there. 

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Sometimes the smallest difference can make a crown stand out from the tooth next to it.  Because of this, minor modifications to the crown may be needed.  The patient will return to us with the crown temporarily cemented in place or with photographs of the crown in place. The modifications are made, usually within a few hours and the crown fitted.  Our ultimate aim is to ensure that all parties, the patient, the Dentist and the technician are happy with the outcome.