zirconia dental caps
TRANSCRIPT
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ZIRCONIA DENTAL CAPS
Using CAD-CAM Technique
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Girraj Maheshwari
Amisha Chhajlani
Raivent Nahar
Paridhi Choudhary
Srijan AgrawalVaibhav Tamrakar
Karan Kumbhare
Group 1
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What is a Crown?
A crown is a restorative to cap a tooth or dentalimplant
After being fabricated according to required
dimensions, bonded to tooth using dental cement Materials involved in making crowns have been
evolving
We witnessed the fabrication of:
1. Zirconia crowns (Reductive technique) and
2. Chrome-Cobalt Alloy crowns (Additive technique)
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What is Zirconia?
Zirconia is a very hard ceramic that is used as a
strong base material
The zirconia used in dentistry is zirconium oxide
which has been stabilized with the addition ofyttrium oxide
The structure is milled from a block of zirconia in a
soft pre-sintered state
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Why Zirconia?
Strength- 800 to 1000 Mpa
Durability- 10 to 15 years warranty
Aesthetics-
Naturally translucent
Available in number of shades
Metal caps start showing black marks over time
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Procedure
Modeling
Scanning
Milling
Sintering
Ceramic Layering
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Modelling
Impression of teeth (negative) taken by placing a
viscous liquid into the mouth. Eg. polyvinyl siloxane.
At portions closer to the crown preparation site,
impression material of lower viscosity is used tocapture greater detail.
Then a POP model (positive) is prepared using this
mould This model is exact replica of patients teeth
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Scanning (CAD-CAM)
3-D Optical Scanner- Light Source + Camera
The model of the tooth (or set of teeth) is placed for
scanning
The system software is used to adjust alignment and
set margins (for gums) Light exposure time is
adjusted, if any shiny portion is detected on the
model by the camera After all parameters are fed, about 13 pictures are
taken from different angles
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Scanning Contd.
The camera takes pictures using a self-adjusting
feature
The images are compiled into a single 3-D file
The entire process is repeated for rest of the jaw
After obtaining 3-D design, surfaces are
smoothened digitally (advantage over conventional)
Shape is readjusted to create better support, alsotaking into account sintering shrinkage (about 20-
25%)
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CAD-CAM
When the design is ready, the system sends
command for milling
CEREC software and Delcam software are in wide
use for dental design
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Milling
The 3D shape is milled from the pre-sintered ZrO2
blank using hard metal tools.
The average milling time for a crown is 35 minutes,
for a 3-unit bridge about 75 minutes.
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Types of Dental Milling Machine Used
3-Axes and 5-Axes machines areused.
3-Axes machines use X, Y and Z-axis inputs to create the replica ofthe design given by CAD machine.
Machine tools with 3 axes areintended for simple parts or formachining freeform surface withsmooth curves that are as flat aspossible.
The work piece or the tool cannotbe tilted: the tools' orientation inspace does not change.
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Rotary axes in 5-axes Milling Machine
Rotary axes also known as
Tilting axes
Perform the orientation of
the workpiece or tool.
Linear axes are mostly
responsible for the
machining.
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Milling
The machine has a magazine capacity of 21
blanks; new blanks can be inserted and finished
frameworks removed while milling continues.
Different frameworks can be milled automatically,even overnight, because of the automatic tool
changer.
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Removing of the milled framework
Removal of the Milled Framework from the Holding Device
Turbine hand piece to remove the framework due to thelower degree of vibration as compared to other handpieces! If no turbine is available, fine cross-cut tungsten
carbide mills can also be used - rotary speed 20 rpm/min!
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Preparation for Sintering
Milled Copings are removed from the zirconia blockusing a hand piece which is similar to a drill.
The coloring of the frame-works also takes place
before the sintering process according to theprescribed shade (16 possible shades, keyed toVITA Classic).
The zirconia block being porous absorbs the color
completely This block is chalk-like in nature and can break
easily and is therefore sintered
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Sintering
Manual finishing can becarried out beforesintering takes place.
The fully-automated,monitored sinteringprocess then takes placewith no manual handling ina special furnace, the Lava
Therm (approx. 11 hoursincl. heating and coolingphases).
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Sintering
Sintering fuses particles together and the finalstrength achieved is 850-1000 MPa
Milled coping or single-piece framework is tested
for fit. Any adjustments are easily made with arubber bur.
Coping or framework is then infiltrated two timesfor 40 minutes each time in a furnace at 1400C-
1500C.
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Cementation of Restorations
Dental Cements are hard, brittle materials formed
by mixing powder and liquid together
Before Cementation, restorations should be
sandblasted in order to increase surface roughness. Sufficient surface is required for optimal bonding
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METAL DENTISTRYTooth filling using metal
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Criteria
Must not be poisonous or harmful to the body.
excellent thermal conductivity.
ability to be shaped (malleability).
Must not be harmful or irritating to the tissues of the
oral cavity.
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Alloy Composition
Co-Cr alloy of the following composition is used for making tooth.
Cobalt 61%
Chromium 27%
Molybdenum 6 %
Others 7 %
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Process
The CAD-CAM file of the tooth is sent to the machine
Cr-Co alloy plates are used as the base plates in the machine on which 20
micron thick powder layer is added. The milling machine compresses and
shapes the powder into solid layer.
Another powder layer is added above this layer and the same process
repeats until we get the desired crown.
The tooth structure is removed from the base plate using hammer.
The base plate can only be used once. To reuse it, it has to be sent to the
manufacturer for polishing.
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Using Metal alloy over Zirconia
Benefits
it is reasonably durable and easy to work with in
aesthetic dentistry
It is relatively inexpensive.
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Disadvantages
Metal filling contains mercury, has been known to
cause significant harm particularly to ones nervous
system as well as damaging ones kidneys and
stomach. While ceramic are mercury 100% mercuryfree
For those concerned with environmentally- concious
dentistry and to limit their exposure to metal toxins,
then ceramic fillings are a viable alternative to
filling your cavities.
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Ceramic fillings are generally much more resilient
and less susceptible to their metal counterparts
Metal fillings are, aesthetically speaking, abrasive
with placed on the teeth. Ceramic fillings, on theother hand, restore the natural appearance of the
tooth filled and are difficult to spot by an
unknowing observer