Indications and clinical stages of making of metal-ceramic dental bridges. Laboratory stages of making metal-ceramic crowns and dental bridges.
Dental Bridge or Pontic or Fixed Bridge
Fixed bridges or pontics or prosthetic devices used to replace missing teeth cannot be taken out of your mouth compare with removable partial dentures.
The teeth to be crowned (abutment teeth) are prepared in a very specific way (filing down the tooth to make room for crowns and bridge) by a dentist. Records are given to a dental technician to fabricate the dental bridge, which can then be inserted at another dental appointment.
The main advantages of dental procedures and solve dental problems with the indirect method of teeth restoration:
· you do not need to be in the dental chair
· use of materials that require intense heat to be processed with superior mechanical properties, such as gold and natural looking porcelain
· produce a restoration of much higher quality
Indication to Restore with a Dental Bridge
·
Re-establish your smile
· Bring back your ability to properly chew
· Help improve speech
· Preserve the shape of your face
· Distribute the forces in your bite properly by replacing missing teeth
· Limit remaining teeth from drifting out of position
· Correct some bite problems
· Reduce the risk of gum disease
Before
After
CLINICAL TECHNIQUE
The clinical techniques for using this class of metal-ceramic materials are the same as conventional metal-ceramic systems, which can be a benefit over many of the all-ceramic systems on the market. Teeth can be prepared with any traditional margin design, but for truly esthetic metal-ceramic restorations, a shoulder preparation that allows for the creation of a 1-mm porcelain margin is preferred. Ideally, a minimum of a 270° or 360° shoulder preparation on teeth in the anterior region facilitates optimal esthetics. Facial reduction can be slightly less than conventional metalceramics as the granular gold surface of Captek gives a light scattering effect that improves the perception of depth in the restoration. Generally, an overall facial thickness of
Diagram of ideal preparation for maximum esthetics for metal-ceramic restorations.
Production of metal skeleton is very hard process, its better to see one time, that ten times read.
Any construction starts with the model. This time with sectional model.
The working surface is covered by the compensation varnish, which serves to compensate for the space under the cement and partial shrinkage of the metal after casting. The varnish is covered to the whole teeth but leave
The gypsum stamps is covered with isolated fluid.
We are doing the cap with submersible wax, the thickness is
For fixing the intermediate part of the prosthesis we put on sticky wax (
There are different companies that produce the standart wax form for the composition.
We put the intermediate part of the prosthesis on the model
Composition elements are connected.
The superfluous wax removed from the stamp. The material easily remove under preparation line.
We put wax on the thin parts of the stamp. We need to do that on the model, especially if we are doing the correction of the shape.
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On the next step we are forming the garland and put some wax on the neck part of the cap.
We correct the form of . Its width varies between ±
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A view of the finished element. The wax composition is collected.
The casting system (3-
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We stick the casting system to the compositoin. We connect the interdental spaces.
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On our days there are different types of waxes, the main condition for all are small contraction, certain hardness and stickiness.
From the correct placement the composition in the casting form depends the density of the metal.
The carcass after the casting cuts from the casting system. We mark and remove places which trouble putting on and out the carcass.
We polish the places where casting system was. We finish the neck part of the crown.
We control the thickness of the carcass. The construction should not be thinner
2 laboratory step
The finished carcass. The surface should not have sharp edges or wedges
Before putting ceramics on it, we wash with oxide aluminum oxide with 150-250 microns, and with pressure 4-6 Bar.
On this slide we see the first layer of putting opaque (powder).
The layer should be the minimum thin and thoroughly rub into the surface of metal.
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The second layer of opaque. Its much more thicker than first. Its better to use glass cane with the round end.
The view of burned model.Its important that opaque have a smooth and straight surface. If there are any defects on the surface we need to polish it, but very carefully with the diamond and cover that parts with opaque again.
The first step in the production process is putting the matherial that allow to get the necessary saturation of color
in the thin parts of the construction. That’s why we put it near the neck of the teeth and in the area of fissures on the occlusual surface, also on the oral surface of the incisors.
Then with the dentine color we form the midle platen. He helps to see the height of the teeth and direction of the teeth. The prosthesis controls in the articulator in the position of central and lateral oclusion.
Now we model the messial and distal platen of buccal surface ot the teeth with the same dentine color.
The construction controls in the articulator
The view of ceramics after burning.
The steps of putting enamel is the same like dentine.
The view after the burniong.
We fit the work on the model.
The tracing paper must easily pass over the teeth and leave the mark, as you can see on the picture.
We polish the surface with backed diamond boron.
We do the first separation with rough disc
We do the finished separation with disc (
It is necessary to provide the smooth surface, that contact with gums.
we polish the chewing surface with balls from baked diamond and carbide boron.
We control the bridge in the articulator.
3 laboratory step
The we do the work with glazing . We need to put the glaze with the thin layer on the teeth.
The view of the work after glazing.
The oven for burning ceramics.
This invention relates to a method of making crowns, such as gold crowns, for teeth, and a method of making a form for use in making such crowns by an investment casting technique.
The conventional technique for producing crowns, such as gold crowns, utilises an impression which is made by the dentist in a hardenable resilient material such as a hardenable rubber composition. This impression will include an impression of at least the teeth surrounding the one to be crowned and will also include an impression of the decayed tooth which has been ground down by the dentist in preparation for crowning.
This impression is then utilised, usually by a dental laboratory, to produce a crown. A plaster cast of the stump remaining after the dentist has ground down the decayed tooth is produced on a brass pin and a model of the teeth in that jaw is also cast in such a way that the stump can be removably located in it by means of the brass pin.
The next stage of the process is to cast a layer of wax on the stump and to carve the wax by hand to give the external shape of the desired crown. The carved shape will generally be such as to be compatible with the other teeth. After carving, a rod of wax, generally referred to as a sprue, is attached at one end to the carved wax and at the other end to a conical wax reservoir.
This assembly can then be used to produce a mould which is achieved by casting in an investment casting ring a heat-resisting investment compound with the wax reservoir at the base of the ring. When the plaster compound is set hard it is heated in a furnace to remove all the wax and subsequently a gold crown is cast by introducing molten gold through the sprue into the mould cavity formed by the carved wax.
The specification for
The external surface of the crown form is then ground using a grinding stone until it matches the surrounding teeth in the mouth.
An investment casting moulding may then be produced from the crown form, from which a crown can be cast in the investment casting mould.
According to one aspect of the present invention there is provided a method of making a crown for a tooth such as a gold crown comprising;
· forming a sheet of formable material into a crown form having the desired shape of the crown;
· producing an investment casting mould from the crown form and burning out the crown form; and
· casting the crown in the investment casting mould.
According to another aspect of the present invention there is provided a method of making a crown form for a tooth such as a gold crown, for use in an investment casting technique comprising;
· (a) forming a first sheet of formable material to a shape which approximates to the desired shape of the crown;
· (b) disposing the formed shape around a layer of deformable hardenable material;
· (c) applying a compressive force to the formed shape to deform the underlying hardenable material to the desired shape of the crown;
· (d) hardening the hardenable material to produce a crown form precursor;
· (e) removing the formed shape from the hardened crown form precursor; and
· (f) utilising the hardened crown form precursor to form a second sheet of formable material into a crown form of the desired shape of the crown.
Preferably in step (b) the hardenable material is applied between a cast model of the tooth stump to which the crown is to be fixed and the formed shape.
Desirably the assembly of the cast model of the tooth stump, hardenable material and formed shape is disposed in a model of at least the teeth surrounding the tooth to be crowned and the compressive force of step (c) is applied to the assembly by means of a model of the occluding tooth or teeth in the jaw opposite to that in which the tooth to be crowned is situated to deform the underlying hardenable material to the desired shape.
Preferably the method further includes the steps of:
· (a) producing an investment casting mould from the crown form of step (f) and burning out the crown form; and
· (b) casting the crown in the investment casting mould.
Conveniently, the first sheet is formed by means of a deep-drawing technique. The second sheet may also be formed by a deep-drawing technique.
Advantageously, additional material is added to the second formed sheet in order to produce the final desired shape of the form. Preferably the additional material is wax.
In one method according to the present invention a plaster model of the teeth in one jaw and a plaster cast of the stump of the tooth to be crowned is produced in the conventional way. An artificial tooth is then chosen from a selection of stock teeth to match approximately the remaining teeth in the mouth. Supplies of such stock teeth are readily available as they are used in the preparation of dentures. When a stock tooth of the desired shape is selected it is used to make a first plastics impression in a sheet of formable plastics material. This can be effected by a process known as deep-drawing in which the sheet is heated to a temperature at which it is formable and the stock tooth pushed into it. Usually a backing of a deformable material which will control the forming of the plastics sheet is employed for this step.
The first plastics impression, which is a female mould of the approximate shape of the desired tooth, is then cut from the sheet of plastics material filled with hardenable material and pressed on to the plaster cast of the stump. The stump is then inserted in the model of the teeth in that jaw and a model of the teeth in the other jaw impressed upon it so that the occluding tooth on the opposite jaw can depress contacting areas of the plastics impression. The hardenable material is then allowed to harden on the plaster cast of the stump.
The plastics impression is then removed and discarded and any excess of hardenable material around the margin of the stump is removed to give a smooth surface. The smooth hardened material at this stage is in the shape of the desired crown but is smaller by an amount governed by the thickness of the material of the first plastics impression, and is referred to herein as the crown form precursor.
The crown form precursor is then used to produce a second plastics impression by a method of deep-drawing as described above. The plastics impression so formed will have the desired shape of the crown to be produced as it has been derived by way of the crown form precursor from a selected stock tooth and has been adjusted for occlusion.
This impression is then cut from the sheet placed over the cast of the stump from which the hardenable material has been removed and the margins filled with wax of a type which is normally used for the investment casting process. Thus, in the region of the margin there will be a wax coating but in the remaining region of the impression there will be layer of shaped plastics material which will be spaced from the casting of the tooth at least in certain areas thereof. The plastics impression together with the wax margin is then removed from the cast of the stump and provided with a wax sprue and reservoir in the conventional manner. The sprued crown form of wax and plastics material is then used to produce a conventional investment casting mould and the gold crown cast in the normal way.
The process described above has two marked advantages over the conventional method of producing gold crowns. Firstly, the amount of time taken to produce the crown is considerably reduced particularly in view of the fact that it is not necessary to carry out any carving of a wax coating on the cast of the stump; this carving is both skillful and very time consuming.
Secondly, the thickness of the gold crown is governed only by the thickness of the plastics material which is used to form the impression. Thus, a much thinner crown can be achieved with the attendant saving in the amount of gold employed. It will be seen therefore that the process provides a much cheaper product which when cemented in position on the stump is indistinguishable from a conventional cast gold crown.
The use of the wax in the marginal portion will ensure that the crown has a very close fit in the important marginal areas of the stump.
The materials which are employed in producing the plaster cast and models may be those normally employed for this purpose by dental technicians. Suitable materials other than plaster may of course be used. Similarly any known material may be employed for the investment casting process which is carried out in a conventional manner.
The plastics material which is used for the first and second impressions should be capable of being formed to the desired shape when heated and should retain that shape when cooled to ambient temperature. A further requirement for the second impression is that the plastics material should be capable of being “burned-out” in the investment casting step. Poly unsaturated hydrocarbon sheets such as polypropylene and, preferably, polyethylene have been found to be suitable but it will be appreciated that other formable materials can be employed provided that they exhibit the desired characteristics outlined above.
The hardenable material which is used for producing the crown form precursor should be capable of being shaped whilst in a plastic state and preferably hardens to form a resilient material which can be distorted at least sufficiently to enable removal of the plastics impression and will subsequently regain substantially its original shape. Hardenable elastomeric materials may be employed for this purpose, particularly cold-curing elastomeric materials. One example of such a material is available commercially under the Trade Mark “IMPREGUM”.
The deformable material which may be used as a backing in the deep-drawing steps may be any material which has the desired resistance to deformation at the deep-drawing temperature so as to control the plastic deformation of the heated plastics sheet to the desired degree. Such a material is available commercially and known in the art as MASTIC.
Reference is now made to the accompanying drawing which is a schematic representation of the steps involved in a preferred method according to the invention for producing a crown form suitable for use in producing an investment casting mould.
Stage I shown in the drawing is an illustration of the deep-drawing of a first sheet of plastics material 21 to the shape of a stock tooth 11 which has been selected to match the teeth surrounding the tooth to be crowned. The plastics sheet is preferably polyethylene.
The deep-drawing technique is carried out by heating a sheet of the plastics material in a frame until it is in a formable state. The stock tooth 11 is then pressed into the sheet 21 over a supporting body of a “Mastic” material which serves to support the plastics sheet 21 during the forming operation. The resulting first plastics impression 10 is shown in step I.
A plaster cast of the stump of the tooth which is to be crowned is produced in a conventional way. The first plastics impression is trimmed from the remainder of the plastics sheet and is filled with hardenable cold-curing elastomer such as “IMPREGUM” and pressed on to the cast model stump as shown in step. This produces a layer 12 of hardenable material between the model stump and plastics impression and, the excess elastomer is expelled in the region of the margin as can be seen in step.
When the dentist makes an impression of the patients mouth he makes an impression of the teeth in both the upper and lower jaw as well as a specific impression of the stump of the tooth which is to be crowned. Plaster models of the teeth in the upper and lower jaw and the stump to be crowned are then made from the impressions taken by the dentist.
The assembly of the cast model stump, the layer of hardenable elastomer and first plastics impression is inserted in the plaster model of the appropriate jaw and the model of the other jaw pressed against it so that the occluding tooth can bear upon the first plastics impression and suitably shape the underlying layer of hardenable elastomer.
After the elastomer has hardened the first plastics impression is removed and the excess hardened elastomer removed from the region of the margin in step III and then smoothed down to give a smooth marginal area. This step produces the crown form precursor as shown in step lV. The crown form precursor 16 is then utilised in a second deep-drawing step similar to the one employed for producing the first plastics impression. Again it is preferred to use a sheet of polyethylene for this purpose.
The impression is then trimmed from the plastics sheet to produce a second plastics impression 18 which will have the shape of the crown form precursor 16 which in turn has the general shape of the original chosen stock tooth modified to suit the occluding tooth 15. Thus, the second plastics impression will correspond to the desired shape of the crown but when it is assembled on the cast model stump there will be a spacing over at least a portion thereof.
In order that the crown should fit the stump accurately further material in the form of wax is added in the marginal portions as shown in step V. The wax is smoothed down to the desired external configuration and then the second plastics impression together with the wax is removed from the cast model stump to produce the crown form shown in step VI.
This crown may then be provided with a conventional wax sprue and wax reservoir and utilised to produce the investment casting mould. Both the polyethylene and the wax are burned out to leave the mould cavity which is subsequently employed to mould the crown material such as gold to produce the crown.
It will be apparent from the above description, and particularly with reference to step V, that the crown which is produced is considerably thinner than the crown which would be produced by a conventional technique in which crown material would extend from the stump to the outer profile of the second plastics impression. It has been found that the production of such thin crowns does not produce an inferior product as when the dentist applies the crown to the stump the space therebetween is filled with cement and the important marginal area is made to fit the stump precisely by virtue of addition of the wax as shown in step V.
In certain circumstances the sheet formed in accordance with step is sufficiently close to the desired shape of form that steps can be eliminated. Also, where a thick crown is required this form can be used with the hardened material in place to produce an investment casting mould.
The sheet of formable material may be formed by using a convenient forming technique other than the deep-drawing technique described above. Vacuum forming could be used and in this case it would be possible to vacuum form a plurality of forms in a single sheet of formable material.
The method of the invention enables a high quality crown to be produced in a relatively short time and requires less skill than the conventional method involving a carving technique. The method can be employed for producing crowns of any castable material. The thickness of the crown is, of course, predetermined by the thickness of the formed sheet, unless a crown of other than constant thickness is required, in which case material such as wax, can be added in selected areas.
The first sheet of formable material may be preformed and supplied, for example, to a dental laboratory as part of a kit for making crowns. The preformed sheet may include a number of shapes of teeth from which the technician can select a suitable form for his purpose. This avoids the technician having to carry out step of the method and also he does not need to carry a selection of stock teeth for this purpose.
It will be appreciated that the method described above is a particularly attractive commercial method for producing crowns of a precious metal such as gold, as the amount of precious metal used is considerably less than would be used in producing an equivalent crown by a conventional technique.
Dental-crown alloys: High noble (precious), Noble (semiprecious), Base (nonprecious).
When making plans to have a crown placed, your dentist may ask you to make a decision about what type of metal alloy is used when it is fabricated. (This is a decision that needs to be made for all-metal and porcelain-fused to metal dental crowns.)
In general, there are 3 basic types of dental alloys that can be used. They are: high noble, semiprecious, and nonprecious (this classification system based upon the metal’s composition). Each type has its own advantages and disadvantages, including: cost, insurance plan coverage, color (gold or “white”), as well as general physical properties.
Related Page
· Selling scrap
dental crowns.
This page discusses each of the above considerations. However, if cost is not a factor, the alloy having the highest precious metal content typically makes the best choice.
What types of metals are used to make crowns?
Crowns (all-metal and porcelain-fused-to-metal) are made using specific types of dental alloys. No pure metals are used for crowns, not even gold. This is because the physical properties of dental alloys are superior.
The classification of dental alloys.
Here’s the formal classification system that is used to categorize dental alloys.
1) High noble alloys (Precious metals)
This group of alloys has a composition that is over 60% noble metal (gold, palladium and/or platinum), of which more than 40% must be gold.
These metals constitute the “gold standard” of dental alloys; all others are compared to them. High noble alloys are the easiest type of metal to work with (for both the dentist and dental laboratory) and create the most predictable bond with porcelain.
2) Noble alloys (Semiprecious metals)
These alloys have a noble metal content that is, at minimum, over 25%.
3) Non-noble (Nonprecious metals)
These alloys are also referred to as base metals. Their noble metal content is less than 25%. They often contain large percentages of nickel, chromium or beryllium.
Why should I care what metal is used to create my dental crown?
There are several reasons why the type of dental alloy that is used to fabricate your dental crown should be important to you. Some of these reasons will affect you directly. Others will be more of a concern to your dentist, or the dental laboratory that makes it.
A) Color – Dental alloys can be white or yellow.
In those cases where an all-metal dental crown is being placed, you might have a preference as to whether it should have a yellow (like gold) or silver (“white”) coloration. The alloy’s composition determines its color.
B) Costs – High noble metal alloys cost more.
The “noble” dental metals are gold, platinum and palladium. These metals are pricey. And the greater the percentage of them found in the composition of an alloy, the greater its cost will be. With some applications, the overall cost between using a high noble or base metal alloy might be small. But in the case of an all-metal crown for a large molar, it might be a consideration.
C) Dental plan and insurance policy limitations.
If some type of dental plan is paying a part of your bill, you might check to see if there are any limitations as to the type of metal that can be used for crowns. The policy might state that they do not cover the cost of high noble alloys. Or the level of coverage might change based on the type of alloy that is used.
D) Some people have metal allergies.
Studies report that about 10% of the female population and 5% of the male have an allergic response to nickel, chrome and/or beryllium alloys. These metals are often found in the composition of nonprecious dental alloys.
E) The physical properties of the alloy are an important consideration.
Dentists and dental laboratories often have a set opinion about which types of dental alloys they will consider working with. This is because their goal is getting the job done right, the first time. They know that any difficulties or problems experienced will just end up costing them money. So, if choosing a certain type of alloy makes getting a positive result more likely, then that’s the one they are probably going to want to work with.
Advantages of precious dental alloys.
In general, dentists and dental labs prefer to work with high noble alloys. These metals are easiest to cast, provide the most accurate fit on the tooth, offer some degree of malleability (so the fit of the metal can be adjusted, if needed), and offer the most predictable bond with porcelain.
Finishing lines:
Is the final margin that separate between the prepared axial tooth surface and the remaining unprepared tooth surface.
Requirements of finishing line:
1. It must be clear, well defined and smooth, so it can be reproduced on working model.
2. It must be continuous from one surface to another.
3. Whenever possible the finishing line should be placed on sound tooth structure.
Position of finishing line:
1. With the level of free gingival margin.
2. Supra gingival finishing line,: its better to place the finishing line supragingivally for the following reasons:
A. Easily to be prepared without trauma to the soft tissues.
B. Easy to be prepared and finished by dentist.
C. Patient can keep it clean easily.
D. Impression is easily made and can be removed without tearing or deficiency.
3. Subgingival finishing line: indicated in
A. Esthetic.
B. Caries or filling at the area of finishing line.
C. To increase retention of short teeth.
Types of finishing line:
1. Feather edge (knife edge).
2. Chamfer.
3. Shoulder.
4. Bevel shoulder.
The selection of certain type of finishing line depends on:
1. The materials used to construct the restoration.
2. The position of the tooth.
3. The tooth aspect to be prepared.
Feather edge (knife edge):
In this type all convexities coronal to the margin are removed only, its mostly unacceptable but it was advocated already before the development of high speed cutting instruments and improvement of impression materials and techniques, this type of margins lack strength, difficult to locate on the cast and difficult to fabricate the wax pattern, however it provide the best marginal seal and it’s the most conservative type.
Chamfer finishing line:
This type is prepared with a tapered round ended fissure diamond bur, its regarded as the line of choice for most veneer cast metal restorations and lingual margins of porcelain fused to metal restoration. It has been shown to exhibit the least stress.
Shoulder finishing line:
This is the best choice for jacket crowns; the wide ledge provides resistance to occlusal forces and minimizes stresses that might lead to fracture of the restoration, and its less conservative. This finishing line is prepared with flattened end tapered diamond fissure bur. Its very well defined finishing line so it’s easily detected on the cast.
Shoulder with bevel:
In this type we create a bevel on the end margin of unprepared tooth structure, this lies between the prepared and unprepared tooth structure and is very critical area. This type of finishing line is recommended for extremely short walls, since the axial walls of this type is nearly parallel to each other so enhances retention. This type of finishing lines is used for porcelain fused to metal and full cast veneer with acrylic facing.
Types of crowns:
1. Full metal (veneer) crown:
This provides better retention and resistance because all the axial surfaces of the teeth are included in the preparation.
Indication:
1. Posterior abutment teeth with excessive caries.
2. As retainer on tooth receive clasp (posterior teeth).
3. High caries index.
4. Necessity of maximum retention and strength.
Contraindication:
1. Teeth located in the appearance zone.
2. Low caries index.
Advantage:
1. Strong.
2. More conservative and easy to prepared.
3. Provide more retention and resistance compared to partial veneer crowns.
Disadvantage:
1. Poor esthetic.
2. Tarnish and corrosion, so it needs prophylactic measures.
3. Difficulty to test the vitality of the abutment teeth.
Steps of preparation:
Depth orientation grooves must be prepared on the surface of the tooth to act as guide or reference to determine when sufficient amount of tooth structure is removed, without these grooves we may remove much or less tooth structure or we loss time in repeated checking.
1. The preparation for a full veneer crown is begun with the occlusal reduction. By accomplishing this step first, the occlusso gingival length of the preparation can be determined. The potential retention of the preparation can then be assessed, and auxiliary features can be added if necessary there should be
The tooth structure remaining between the orientation grooves is removed to accomplish the occlusal reduction then smooth any roughness left by the grooves. Keeping the occlusal surface in the configuration of the geometric inclines that make up the occlusal surface of any posterior tooth after that a wide bevel is placed on the functional cusp again using the No. 170 buy or rounded tapered diamond. The functional cusp bevel placed on the buccal inclines of mandibular buccal cusps and the lingual inclines of maxillary lingual cusps after completion of occlusal surface preparation we should check the occlusion of the patient in centric and eccentric positions of jaw relationship.
3. Buccal surface: because of the anatomy of the buccal surface of the lower posterior teeth, this surface should be divided into two parts: gingival two thirds and occlusal one third for the gingival two thirds we should place a (DOG) in the center of this surface parallel to the long axis of the tooth and by moving the bur mesially and distally following the inclination of the surface so this surface prepared. For the occlusal one third a (DOG) is placed in the center of this area by placing the bur 45 degree with the long axis of the tooth and by moving the bur with the curvature of the surface to be prepared. This type of preparation is called two plane preparation or two steps
4.
preparation The two plane preparation is done on the buccal surface of the lower molar and the palatal surface of the upper molar.
3. Lingual surface :the (DOG) is placed in the middle parallel to the long axis of the tooth and by moving the bur mesially and distally so we complete the reduction, this type of preparation is done in one plane as it is indicated for the lingual lower and buccal upper molar and premolar teeth.
4. Proximal surfaces: we start with a fine tapered diamond fissure bur (needle type) to open and remove the contact area carefully without touching the adjacent tooth because caries will be developed in the damaged surface later on, because we are going to create a rough surface in addition to removing the outer layer of enamel which is saturated with fluoride. The bur should be rested on the prepared tooth itself and by moving the bar up and down the contact will be removed, finally any sharp angle should be removed to prevent fracture due to stress concentration, sometimes seating groove is placed in the buccal surface of the lower and the palatal surface of the upper molar teeth which act as a guide during placement of the crown, to prevent the rotation of the restoration, increase the surface area of preparation so it enhance the retention and the resistance, finally it improves the seating of crown as it let the escape of the excess cement during cementation.
2-Full metal crown with facing
It is a full metal crown having the labial or buccal surface covered by a tooth colored materials (acrylic, Porcelain), it combines the strength of full metal crown and the cosmetic effect of the tooth colored material, and it is not a conservative type of crown since it includes excessive tooth preparation to provide enough space for the metal and the facing material in addition to that there is excessive contact with the gingival tissue when the margin of the crown is placed close or below the gingival margin ,it can be used on anterior and posterior teeth
Indication:
1. Improvement of esthetics (carious teeth, malposed teeth, peg shaped lateral incisor, discolored teeth).
2. Fracture of tooth without pulp exposure.
3. Teeth with large filling.
4. As a bridge retainer especially in long span bridge.
5. Endodontically treated teeth with sufficient remaining tooth structure.
Contraindications:
1. Teeth with large pulp.
2. Teeth with short crown.
3. Patient with poor oral hygiene.
Advantage:
1. It combines the strength of full metal crown and the cosmetic effect of the tooth colored material.
2. Natural appearance can be closely matched by good technique and if desired through characterization of the restoration with internally or externally applied stains.
Disadvantages:
1. Requires significant tooth reduction to provide sufficient space for the restorative materials.
2. Increases the potential for periodontal disease.
3. Because of the glasslike nature of the veneering material, a metal-ceramic crown is subject to brittle fracture (although such failure can usually be attributed to poor design or fabrication of the restoration).
Preparation
1. Preparation for posterior teeth
We should follow the same principles as in full metal crown as in the full metal crown with one exception only, by doing a deep reduction on the buccal surface to provide enough space for the metal and the facing material and also to gain bulk for proper shade of the final crown The finishing line is shoulder on the buccal surface and chamfer all around the remaining tooth aspects.
2. Preparation for anterior teeth
A. Incisal edge reduction:
We started by basing a depth orientation groove of
B. Preparation of the labial surface:
This surface should be divided into two parts, gingival and incisal, for the gingival part a DOG of
C. Lingual surface preparation:
For the cingulum area a DOG of
Why we do the two steps preparation on the lower buccal, upper palatal surfaces of the posterior and labial surfaces of anterior teeth:
1. To follow the anatomy and the inclination of the tooth and not to disturb the surface geometry.
2. To increase the surface area this will give increase in retention and resistance of the final restoration.
3. To avoid hitting of the pulp chamber during preparation.
4. To give enough space for the restorative material so this will enhance the structural durability other vise we will have bulky restoration, bulky facing or poor shade of the tooth.
CAD/CAM dentistry (Computer-Aided Design and Computer-Aided Manufacturing in dentistry), is an area of dentistry utilizing CAD/CAM technologies to produce different types of dental restorations, including crowns, crownlays, veneers, inlays and onlays, fixed bridges, dental implant restorations and orthodontic appliances.
Typically CAD/CAM dental restorations are milled from solid blocks of ceramic or composite resin closely matching the basic shade of the restored tooth. Metal alloys may also be milled or otherwise digitally produced. After decayed or broken areas of the tooth are corrected by the dentist, an image (scan) is taken of the prepared tooth and the surrounding teeth. This image, called a digital impression, draws the data into a computer. Then proprietary software is used to create a replacement part for the missing areas of the tooth, essentially creating a virtual restoration. This is called reverse engineering. The software sends this virtual data to a milling machine where the replacement part for the defect (the dental restoration) is carved out of a solid block of ceramic or composite resin. Stains and glazes are fired to the surfaces of the milled ceramic crown or bridge to correct the otherwise monochromatic appearance of the restoration. The resulting restoration can then be adjusted in the patient’s mouth and cemented or bonded in place. Depending on the restorative material, cementing/bonding surface areas on the tooth and the restoration may be respectively etched and silanized. Resin cement is then used to fuse the restoration to the prepared tooth, completing the restorative treatment process.
An in-house (chairside) CAD/CAM system enables the dentist to create a finished inlay in as little as an hour, in contrast to two or more weeks using an outsourcing service. But there are some drawbacks to CAD/CAM treatments, whether they are done chairside or outsourced to a dental laboratory fabricating service.
Because milled fits are typically 60 to 100 micrometres, CAD/CAM dental restoration fits are not comparable to traditionally fabricated dental restorations with fits typically between 25 to 50 micrometers. Each monolithic CAD/CAM crown or bridge is machine-cut from a solid monochromatic block. Because of this, these one-color restorations depend on superficial staining to achieve any kind of aesthetic value. CAD/CAM crowns and bridges are machine-produced substitutes for more aesthetic hand-layered porcelain restorations with colors built deep within the layered porcelain. Feldspathic porcelain is the material utilized in making hand-layered crowns and bridges, and when this porcelain is fused to glass-infiltrated aluminum-oxide (an alumina substructure) a high-strength, high-aesthetic, metal-free crown or bridge is created. Traditional dental restorations, where this porcelain is layered onto a metal substructure, however, are not translucent and often display color brightness (an opaque “headlight”) and dark oxide lines (a “black line”) in the vicinity of the gum line. As these dark metal substructures are not conducive to a natural appearance, metal-free restorations are typically more aesthetically pleasing to the patient.
If the CAD/CAM restorative material is zirconium-oxide (zirconia) or lithium-disilicate, the restoration is going to be “radio-opaque” just as metal restorations are. That is, these materials block x-rays. Only alumina and some composite resin materials are “radio-lucent.” Dentists are able to keep track of potential decay underneath an alumina all-ceramic restoration. Zirconia, lithium-disilicate, conventional porcelain-to-metal, and traditional gold crowns block x-ray radiation, disallowing such an evaluation over time.
CAD/CAM technologies are used frequently in the dental laboratory industry, providing for the fabrication of dental prostheses ranging from orthodontic appliances to dental implants, and from crowns to long-span fixed bridges. The accuracy of crowns and bridges using this technology is not as consistent as some other dental fabricating processes. This is because crowns and bridges require extremely precise fits on tooth abutments or stumps that the dentist has prepared by hand. Scanning and mathematically calculating the stump surface typography is called reverse engineering and this process is known to have accuracy limitations. Then, machines that do the actual fabricating are computer-numeric-control (CNC) milling machines, and these machines also have accuracy limitations. Essentially, crowns and bridges made on CAD/CAM dental systems often have fit issues including open margins and loose fits. These fit issues can lead to tooth decay and gum disease.
Shaping Dentistry with CAD/CAM Technology
CAD/CAM is an acronym for computer-aided design/computer-aided manufacturing. Used for decades in the manufacturing industry to produce precision tools, parts and automobiles, CAD/CAM technology has been increasingly incorporated into dentistry over the past 20 years.
CAD/CAM technology and metal-free materials are used by dentists and dental laboratories to provide patients with milled ceramic crowns, veneers, onlays, inlays and bridges. Dental CAD/CAM also is used to fabricate abutments for dental implants, used to replace missing teeth.
As the materials and technology available for CAD/CAM dentistry have improved over the years, so too have the restorations that patients can receive from this form of digital dentistry. Today’s CAD/CAM restorations are better-fitting, more durable and more natural looking (multi-colored and translucent, similar to natural teeth) than previously machined restorations.
In-Office and Dental Laboratory CAD/CAM Options
How affordable are dental implant restorations?
Dental CAD/CAM technology is available for dental practices and dental laboratories, enabling dentists and their staff (or a laboratory technician) to design restorations on a computer screen. The CAD/CAM computer displays a 3-D custom image of your prepared tooth or teeth obtained by digitally capturing the preparations with an optical scanner. Alternatively, the 3-D images can be obtained by scanning a traditional model obtained from conventional impressions of the preparations.
The dentist or laboratory technician then uses those 3-D images and CAD software to draw and design the final restoration. The amount of time it takes for a dentist, in-office restoration designer or laboratory technician to design a restoration varies based on skill, experience, and complexity of case and treatment. Some cases could take minutes, while others could require a half-hour or more of design time to ensure quality.
Once the final restoration is designed, the crown, inlay, onlay, veneer or bridge is milled from a single block of ceramic material in a milling chamber. The restoration then can be customized with stains and glazes to create a more natural look, before being fired in an oven (similar to ceramics and pottery), and then finished and polished.
Benefits of CAD/CAM Dentistry
Research suggests that today’s milled CAD/CAM restorations are stronger than those milled from earlier materials. They also are less likely to fracture.
One of the advantages of CAD/CAM technology is that if your dentist has the technology in office, same day dentistry may be a treatment option for you. CAD/CAM dental technologies such as CEREC in-office or the E4D Dentist System can be used to make an inlay, onlay, crown or veneer restoration in a single appointment, while you wait.
If your dentist offers in-office CAD/CAM, you do not require traditional impressions, a temporary restoration or a second appointment. You will only receive local anesthetic (be numbed) once for any necessary tooth preparations.
An exception to this process is the all-ceramic bridge, since it is created in a laboratory using the CAD/CAM technology. All-ceramic bridge restorations require a second office visit to insert the bridge. In such cases, a temporary restoration would be necessary.
Don’t let your anxiety get in the way of treatment.
Another exception is if your dentist prefers to fabricate the CAD/CAM restoration while you are not in the office, making it a two-appointment process. Some dentists prefer this approach in order to dedicate more time to the design and characterization processes involved with creating a CAD/CAM restoration. A temporary also would be required in this instance.
Special Considerations for CAD/CAM Dentistry
CAD/CAM technology is not a replacement for the accuracy and talent provided by a dentist or dental laboratory technician. Dentists must be precise in creating the initial tooth preparation; both dentists and laboratory technicians must be accurate when taking the digital impression and drawing the restoration.
Equally important is the accuracy and skill with which they design a restoration, particularly since the fit of a restoration is critical to preventing future tooth damage. For example, an ill-fitted crown, veneer, inlay or onlay can leave space between the teeth, or between the tooth preparation and the restoration. This could lead to an increased risk of infection or disease.
When to Choose CAD/CAM Dentistry
It is important to note that not every tooth can be treated with a CAD/CAM restoration. Your dentist will determine if a CAD/CAM restoration is among the appropriate treatment options for your condition. Additionally, despite improvements in the esthetics of CAD/CAM materials, patients may find that some CAD/CAM restorations look too opaque and lack natural characterizations.
Depending on the type of restoration that’s needed (such as inlays/onlays), your dentist may prefer conventional laboratory fabrication techniques that have a longer and more proven track record for accuracy of fit. Therefore, patients must discuss their particular situation and desires with their dentist, who will make the final treatment decision based on a thorough examination.
Cost of CAD/CAM Restorations
All-ceramic restorations, including those fabricated at a dental laboratory using CAD/CAM technology, tend to be a more expensive restorative solution. However, even though the materials for CAD/CAM restorations might cost more, the expense incurred by the dental laboratory and/or the dentist may not be passed onto the patient.
Also, there is no additional fee or cost to have a restoration placed in one visit as opposed to two. Insurance reimbursement is similar for in-office, same day dentistry or laboratory-fabricated restorations.
The Application of Zirconium Oxide Frameworks
Accurate and precisely fitting superstructures are a prerequisite for long-term success of implant-retained restorations. Casting of multi-unit frameworks requires considerable knowledge and skill of the dental technician, and is often associated with time-consuming adjustments performed by the clinician and the technician to achieve adequate fit.
Combinations of newly developed dental materials and computer technology have led to new restorative treatment options for dental implants. Increased processing power of computers over the past decade, computer-designed and computer-generated copings, frameworks, and abutments for conventional and implant-supported restorations have significantly altered treatment protocols for dentists and dental technicians. The technology of computer-aided design (CAD) and computer-aided manufacturing (
The introduction of CAD/CAM systems for single-implant restorations eliminated many shortcomings, such as incorrect abutment selection, poor support of soft tissues, and concerns about dissimilar metal alloys and interfaces between cast and machined components.
Until recently, the majority of CAD/CAM systems only allowed the fabrication of single-unit components, such as crown copings, single- implant abutments, or small fixed-partial-denture (FPD) frameworks.
Numerous studies have evaluated precision, strength, and handling characteristics of these CAD/CAM components. New hardware and software refinements and high-strength ceramics have led to the introduction of systems to design and fabricate FPD frameworks exceeding three units, as well as bar superstructures for implant-retained restorations.
CAD programs are a combination of hardware and software components that allow a three- dimensional scan of an object, such as a tooth abut-ment, and virtually design a congruent coping. A major advantage is that the computer program tracks design-dependent parameters; for example, when one value is altered, all other values that depend on it are automatically changed accordingly. The data are transferred to a remote production unit where the object is fabricated.
A wide range of materials can be used for CAD/CAM manufacturing. Aspects to be considered are long-term stability in the oral cavity, biocompatibility, and post-processing options (eg, type of veneering material). Numerous clinical trials support the use of all-ceramic restorations for conventional prosthodontic rehabilitation. In implant dentistry, various studies demonstrated the successful application of ceramic and titanium abutments regarding long-term stability and biocompatibility. Despite the superior fracture strength of metal-ceramic crowns cemented to titanium abutments as compared to all-ceramic crowns cemented to ceramic abutments, the use of all-ceramic materials is greatly increasing. Ceramic abutments have an excellent esthetic potential when associated guidelines are meticulously followed, and offer outstanding biocompatibility and long-term stability. The first all-ceramic abutments were densely sintered aluminium oxide (Al2O3) and were available in only one size. Disadvantages included time-consuming preparation in the laboratory and finishing in the dental office, which increased the risk of microcrack formation, possibly leading to catastrophic failure during preparation or placement.
Currently, one very auspicious and interesting material for framework and abutment manufacturing is zirconium oxide (ZrO2) ceramic. Yttria-stabilized zirconium oxide (Y-TZP-zirconium dioxide, Yttria-stabilized Tetragonal Zirconia Polycrystals) is a highly biocompatible ceramic material which provides fracture strength properties that allow application in any area of the oral cavity. Although long-term clinical data are not yet available, current studies show encouraging results.
Recent in vitro and in vivo studies have de-monstrated that zirconia ceramic surfaces accumulate fewer bacteria than commercially pure titanium. Another in vitro investigation evaluated the fracture resistance of implant-supported all-ceramic abutments (Al2O3 and ZrO2). The strength for both abutment materials exceeded the established maximum values for incisal load reported in the literature. However, ZrO2 abutments were twice as resistant to fracture than Al2O3 abutments. The very fine-grain structure of this material (0.3 to 0.5 um) and its chemical composition (Yttria -Y2O3– stabilized) are among the reasons for its high flexural strength (1,000 to 1,200 MPa) and fracture toughness (10 MPam). Numerous current trials investigate static fatigue behavior of all-ceramic materials and the long-term prognosis of such abutment materials.
High biocompatibility with reduced bacterial adhesion and the high flexural strength render it an excellent material for implant-retained superstructures in close contact with surrounding soft tissues.
Most
This article illustrates current techniques and options for fabrication of long-span zirconium oxide frameworks for implant restorations. The primary objective is accurate fit of the mating components to prevent premature screw loosening during function and thus improve long-term stability. Other important factors are optimal biocompatibility and natural esthetics.
A 41-year-old female patient presented with an insufficient FPD restoration. Clinical and radiographic diagnostics revealed severe hard and soft tissue deficiencies and a skeletal Class III malocclusion. Extensive vertical and horizontal bone loss and severe inflammation of the oral tissues were present. The patient desired an implant-retained restoration.
Preoperative selection of the type of definitive restoration is not always feasible in complex cases where surgeries will be performed in several steps. Some uncertainties remain with regard to the interarch relationship in both vertical and horizontal planes (especially following orthognathic surgery) and the amount of available bone for implant placement after extensive augmentation procedures. Once the interarch relationship is stable, a diagnostic waxup can be utilized to decide whether a fixed or removable implant-retained restoration is the ideal option. This protocol was followed in the present case and a treatment plan was outlined in cooperation with the restorative dentist, the oral surgeon, and the dental technician.
First, all remaining maxillary and posterior mandibular teeth were extracted and a provisional complete maxillary denture was fabricated. Intensive hygiene instructions were given to the patient regarding the remaining dentition to evaluate the patient’s compliance before any further treatment steps were initiated. After complete healing of the mandible following orthognathic surgery, maxillary ridge augmentation was performed with autogenous bone harvested from the iliac crest. A new diagnostic waxup was made 6 months after the initial surgery, and the prospective implant locations were selected based on radiographic diagnostics and the anticipated final restoration. The information obtained from the diagnostic waxup and the radiographs was transferred to surgical templates made of clear autopolymerizing acrylic resin (Paladur Clear, Heraeus Kulzer).
In a second surgery, eight maxillary and three mandibular implants (TiUnite MK III, Nobel Biocare) were placed. After second-stage surgery, impressions were made following standard protocols. Master casts (Fuji Rock EP, GC) with a rigid-polyurethane gingival mask (Alpha Pur, Alpina) were mounted in the appropriate vertical dimension of occlusion. A full-contour esthetic waxup was fabricated to evaluate tooth proportion and position in relationship to lip line, smile line, profile, function, and phonetics.
Due to limited available bone, only one implant was placed in the mandibular left quadrant and an implant-tooth-retained FPD was fabricated. Space management for maximum esthetics required a high-noble gold alloy framework. The right mandibular quadrant was restored with an implant-retained FPD and two metal-ceramic crowns (Reflex, Wieland Dental).
The definitive maxillary restoration comprised two zirconium oxide custom bars, a galvanic mesostructure for optimized fit, and a ZrO2 secondary structure. One anterior implant was not integrated into the definitive restoration due to its labial position and was subsequently covered with soft tissue in a minimally invasive procedure. The superstructure was retained by three horizontal screws (gib-type, Security Lock, Bredent) luted into the secondary framework (Durobond, ZL Microdent). Due to the complex geometric form of the anticipated superstructure, a five-axis
Twelve individual Procera AllZirkon zirconia copings (Nobel Biocare) were scanned on a duplicate die of the secondary framework and veneered with corresponding ceramics (NobelRondo Zirconia, Nobel Biocare) for maximum esthetics. Missing soft tissues were imitated by veneering the superstructure with a gingiva-colored composite resin (Gradia Gum, GC). To achieve adequate bond strength between components, the galvanic mesostructures were silica/silane treated with the Rocatec system (Rocatec, 3M ESPE). Before application of the composite resin, the two-bar ZrO2 framework was sandblasted (Al2O3; 120 um), and a bonding agent was applied (Clearfil Porcelain Bond Activator/Clearfil SE Bond Primer, Kuraray).
Complex clinical situations require thorough treatment planning. The patient must be aware that fixed implant-retained restorations are not always feasible, despite new technical advances. The design of a definitive restoration must follow basic restorative requirements, such as function, phonetics, and esthetics, as well as required material properties.
Advances in dental materials and improved hardware and software components for computers provide a broader range of applications for CAD/CAM techniques in dentistry. The major benefits of CAD/CAM-generated frameworks, copings, and abutments are the customized design options and the industrialized manufacturing process of modern materials. This ensures homogenous high-strength components. Also, software programs for design and control of the manufacturing processes have improved considerably, allowing the fabrication of precisely fitting components. Only thorough assessment on an individual basis can determine whether a CAD/CAM system is the right choice for a restoration. Even though time-consuming steps like casting of wax patterns can be avoided, other equipment- related costs and laboratory time have to be considered.
Combinations of CAD/CAM technology and modern materials (eg, zirconium oxide ceramic) offer promising perspectives for the future. However, long-term clinical evaluations of these new techniques and materials are necessary before they can be recommended for standard use in private practice.
Dental CAD/CAM systems
A 20-year success story
The stage was set for exciting advances in dentistry in the 1950s and 1960s when prototypes of computer-aided design (CAD) and computer-aided manufacturing (
Early dreamers like Mörmann, Duret and colleagues and me were intrigued by the possibilities. But the road was far less smooth than any of us imagined. Computing power was limited; a gigabyte drive was unheard of, yet design of the complex geometries of crowns was computationally intensive.
In this supplement, you will read about the success of one of the systems that emerged as an effective in-office automated system known as the CEREC system (Sirona Dental Systems GmbH, Bensheim, Germany), though much of what you read will apply to any CAD/CAM system. The CEREC system has been available commercially for 20 years, is used by more than 17,000 dentists and in 28 dental schools in the
At first blush, the thought of machining a brittle material like dental ceramics was ridiculous. But as Giordano describes in the second article of this supplement, innovations in materials created esthetic materials that could withstand potential damage introduced by CAD/CAM operations. When created with an in-office CAD/CAM system, esthetic restorations provided in a single appointment are a reality.
But can an automatically produced restoration fabricated in the dental office perform as well and deliver the same esthetics as those created by skilled artist technicians? In the third article of this supplement, Fasbinder reviews the literature pertaining to performance of CEREC-generated restorations. He provides insight into the types of restorations that could be produced over time and the successful fit, esthetics and survival of ceramic restorations produced in the dental office.
While thousands of dentists have incorporated CAD/CAM systems into their offices, there still are many dentists who have not. In the fourth article of this supplement, Trost and colleagues summarize the practice management considerations, providing guidance for clinicians to make informed decisions about incorporating the technology into their own practices. While this article focuses on decisions relating to the CEREC system, the same kinds of considerations will apply to future in-office systems. In this month’s issue of JADA, Strub and colleagues have summarized how CEREC’s successes have catalyzed the development of other systems.
Without question, the dreams of automation have had an irreversible impact on dentistry. With in-office systems, esthetic, long-lasting restorations can be produced in a single appointment. Laboratory-based systems expand the possibilities for restoration type and material selection. But clinicians must be concerned with more than just the initial product, whether it is produced by CAD/CAM systems or using traditional approaches. Ceramics, including those used in dentistry, have interesting performance characteristics. Even when highly polished, they lose strength when subjected to repeated loading, like normal occlusal contact. Over 1 million cycles (approximately five years of clinical function), both alumina- and zirconia-based veneered structures lose 50 percent of their strength.
Damage caused by sandblasting, by chairside adjustments with a bur or even during the CAD/CAM fabrication process can reduce the restoration’s strength further and compromise its life expectancy. For some materials, researchers have recorded as much as a 30 percent reduction in strength after sandblasting. This information is especially important for posterior restorations, which are subject to the highest stresses in the mouth.
But doesn’t sandblasting enhance adhesion? Perhaps, but it also introduces substantial damage. So my colleagues and I explored alternatives that can provide excellent bond strength without sandblasting. For alumina and zirconia cores, bond strengths equal to those on particle-abraded surfaces have been achieved by using metal primers in combination with adhesive cement formulations such as Panavia 21 (Kuraray America, New York City) and RelyX Unicem (3M ESPE, St. Paul, Minn.) on “as-received,” etched surfaces.
The performance of ceramics can be compromised by a mismatch between coefficients of thermal expansion of core and veneer materials. While this is not an issue for in-office–produced monolithic materials, it can play an important role in crown and bridge survival. It also may be a major factor in porcelain chipping, which is reported commonly for zirconia-based layered crowns.
While much remains to be learned and many innovations still are possible, there already has been much success with CAD/CAM systems’ producing ceramic restorations. Innovations will continue to affect and challenge dentistry. I hope you find this summary of 20 years of the success of one dream enlightening.
CAD /
Abstract
CAD/CAM systems (computer-aided design / computer aided manufacturing) used for decades in restorative dentistry have expanded its application to implant dentistry. This study aimed to look through CAD/CAM systems used in implant dentistry, especially emphasizing implant abutments and surgical templates manufacturing. A search of articles published in English at Medline and Scopus databases at present was conducted, introducing “dental CAD/CAM”, “implants abutments” and “surgical guide CAD/CAM” as key words.
These systems consist of three components:
1) data capture using optical systems or laser scanning, 2) CAD for the design of the restoration, and 3)
In 1971, Francois Duret introduced CAD/CAM in restorative dentistry and, in 1983, the first dental CAD/CAM restoration was manufactured. One of the main lines of implementation was the intra-operative use for dental restoration using prefabricated ceramic monoblocks.
The CAD /
Nowadays there is a greater interest in the CAD/CAM systems for implant-supported prosthesis, as they have been used for the manufacture of implant abutments and diagnostic templates in implant dentistry. The aim of this paper is to review the CAD/CAM systems used in implant dentistry, and describe its application in the construction of implant abutments and surgical templates.
Material and Methods
A search of articles published in English at Medline and Scopus databases at present was conducted, introducing “dental CAD/CAM”, “implants abutments” and “surgical guide CAD/CAM” as key words. 59 articles were found using this search strategy. All articles that described the construction of implant abutments and surgical templates using CAD/CAM technology were included, not excluding articles about clinical cases or in vitro studies. 29 articles were used finally.
Results
CAD/CAM components CAD/CAM systems are compound of three basic functional components:
1. Data capture or scanning to obtain the oral information. To conduct this process there are different trading systems:
– Intraoral capture. This method uses 3D optical systems for capturing single components anatomy. Some examples are: Interférométrie Moire, laser scan, colorcoding (such as CEREC (8) and Evolution 4D (Evolution 4D)).
– Anatomical dental duplicate capture (plaster cast), usually using a laser scan method. Comercial products such as RapidForm® (RapidForm), Slim® (Slim), poly Works® (polyWorks) and Geometric Studio® (Geometric Studio) are used for the 3D meshes post-process.
2. CAD for the geometric design of the restoration. These CAD systems have some simple functions to change the restauration geometry.
3.
Prosthetic abutments
Ideally, the abutment head should resemble a prepared tooth with good form, morphology and emergence profile. Proper implant positioning and appropiate preparation of hard and soft tissue are critical to creating optimal emergence profile, function, esthetics, and periodontal health. The types available can be separated into three categories:
Stock (prefabricated). They are milled in different materials (titanium, zirconium) using CAD/CAM technology. These are available either straight or preangled. UCLA (laboratory wax and cast). They are manufactured from a gold platform and a castable sleeve that allows to individualize the shape and height. Computer-milled solid abutment. A solid block of titanium is milled using a computerized milling machine to the operator ́s specifications.
CAD/CAM abutments in Implant Dentistry
Advantages of CAD/CAM abutments
Custom abutments created with CAD/CAM technology have the potential to provide the advantages of both stock and laboratory processed custom abutments without the disadvantages(2). First, like laboratory-made abutments, CAD/CAM abutments are specific for each patient (11), however the results are much more consistent. The technician ́s learning curve is less steep than that for handmade components. The technician controls the abutment design using CAD software that incorporates parameters to assist him or her. The virtually designed abutment is electronically transferred to a
Materials used
CAD/CAM technology has used metals such as titanium and titanium alloys, and ceramics such as aluminum oxide or zirconium oxide for the fabrication of implant abutments. The higher strength of these materials, which can be shaped only with CAD/CAM systems, has increased the longevity of these restorations and the demand between dentists recently. Some of these products are: CEREC 3D® (Sirona Dental Systems) (CEREC 3D), Everest® (Everest) and Lava® (LAVA).
CAD/CAM Custom Implant Abutments
Most implant systems offer these kind of abutments.
The sequence begins introducing the patient information in the software that employs CAD/CAM technology. The laboratory technician waxes the prosthesis over the corresponding abutment and scans it. Then this structure is adapted to the antagonist arch and to the emergency profile. These data are transferred to the
Some advantages of this technique are the possibility of shorten the overall treatment time and the minimal manipulation of the soft tissue. Heydecke et al. emphasizes the natural appearance using aluminum oxide ceramic implant abutments and the minimal necessity of postproduction adjustments if we compare with stock abutments. The accuracy of this system is reflected in the concept Teeth-in-an hourTM (20) for immediate functional loading in maxilla using CAD/CAM fixed prostheses manufactured from a block of milled titanium through the protocol
Advantages of this system are: 1) it provides an anatomical emergente profile for the definitive abutment; 2) it provides the ability to correct an implant angle of up to 30 degrees; 3) there is no need to wax or cast, so laboratory time and cost are decreased; 4) it is easy to use since there is an optioot to make an implant-level impression, and there is no need for intraoral abutment preparation. However, this technique does have its disadvantages: 1) its use is limited to a specific implant system (3i Implant Innovtions, Inc); 2) an inter arch space of at least
Placement of dental implants requires precise planning that accounts for anatomic limitations and restorative goals. Diagnosis can be made with the assistance of computerized tomographic scanning, but transfer of planning to the surgical field is limited. Recently, novel CAD/CAM techniques such as stereolithographic rapid prototyping have been developed to build surgical guides in an attempt to improve precision of implant placement. As a result of this technology, the surgical guide permits accurate and consistent position and orientation of the implants. Sarment et al. showed the advantage of this technique in a case-control study that compared the distances between planned implants and actual osteotomies using a conventional surgical guide or a stereolithographic surgical guide (SurgiGuide; Materialise Medical,
Conclusions
1 CAD/CAM technology applied to implant surgery allows the production of high resistance and high density crowns, and the manufacture of implant abutments and surgical guides.
3 CAD/CAM surgical templates allow to transfer the software planning to the surgical field.
