zirconia dental caps

7/29/2019 Zirconia Dental Caps

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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

zirconia dental caps

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