A crown, sometimes known as a tooth cover, is a type of dental restoration that completely covers or surrounds a dental or dental implant. Crowns are often needed when large cavities threaten ongoing dental hygiene. They are usually bonded with teeth using cement gear. Crowns can be made from many materials, which are usually created using indirect methods . Crowns are often used to enhance the strength or appearance of teeth. Although very useful for dental health, procedures and materials can be relatively expensive.
The most common method of dental coronation involves using a dental impression of a tooth prepared by a dentist to make a crown out of the mouth. The crown can then be entered on the next dental appointment. Using this indirect method of dental restorations allows the use of strong restorative materials that require time-consuming fabrication methods that require intense heat, such as metal casting or porcelain burning that are impossible to solve in the mouth. Due to the nature of expansion, relatively equal material costs, and cosmetic benefits, many patients choose their crowns made with gold.
As new technology and materials science have evolved, computers have increasingly become part of the fabricating of crowns, as in CAD/CAM dentistry.
Video Crown (dentistry)
Indications for dental crown
Crowns are usually used for:
- Returns the worn, worn, or fractured shape, function and appearance of the tooth, in which other simpler form of restoration is inappropriate or has been found to be clinically unsuccessful.
- Improve unsightly tooth aesthetics that can not be managed with simpler cosmetic procedures.
- Maintaining structural stability and reducing the risk of extensively restored tooth fractures including root-filled teeth such as Root Canal Treatment, especially posterior teeth worn by higher occlusal forces.
- Restore dental implants
Since there is still no strong evidence in the current literature that crowns are better than other routine restorations to restore rooted teeth, dentists are still advised to use their clinical experience in the view of patient preference when making decisions using a crown. crown material
Full metal crown
As the name implies, this crown is fully cast in a metal alloy. There are many available alloys and the selection of certain alloys above others depending on several factors including cost, handling, physical properties, biocompatibility. The American Dental Association groups alloys in three groups: precious, noble, and precious metal alloys.
The noble and noble alloy
The high and noble alloys used in crown casting are generally based on gold alloys. Gold is not used in its pure form because it is too soft and has poor mechanical strength. Other metals included in the gold alloy are copper, platinum, palladium, zinc, indium and nickel. All types of gold casting alloys used in prosthodontics (Type I - IV) are categorized according to the percentage of gold and hardness content, with the softest Type I and Type IV most difficult. Generally, alloy types III and IV (62 - 78% and 60 - 70% gold content respectively) are used in full crown casting, as these are hard enough to resist occlusal forces. The gold crown (also known as the golden shell crown) is generally indicated for posterior teeth for aesthetic reasons. They are durable in function and strong in thinner parts, therefore require minimal dental preparation. They also have similar wear properties to emails, so they are unlikely to cause excessive wear on the opposing teeth. They have good dimensional accuracy when the cast minimizes seat-side/promise time and can be relatively easy to polish if any changes are required. Palladium-based alloys are also used. It was introduced as a cheaper alternative to gold alloys in the 1970s. Palladium has a strong bleaching effect giving most of its alloy its silvery appearance.
Metal-base alloy
Cast base metal alloys are rarely used to make full metal crowns. They are more commonly used as part of metal-ceramic crowns as bonding alloys. When compared to noble and noble alloys, they are stronger and harder; they can be used in thinner parts (0.3 mm as opposed to 0.5 mm) but they are more difficult to adjust and are more likely to cause excessive wear on opposing teeth. In addition, there can be problems with people with nickel allergies.
The basic metal alloys commonly used in dentistry are:
- Silver-palladium
- Silver-palladium-copper
- Nickel-Chromium
- Nickel-chromium-beryllium
- Cobalt-chromium
- Titanium
Titanium
Titanium and titanium alloys are highly biocompatible. Its strength, stiffness and tenacity are similar to other foundry alloys used in dentistry. Titanium is also ready to form a layer of oxide on its surface which gives it an anti-corrosive properties and allows it to bind to a ceramic, useful property in the manufacture of metal-ceramic crowns.
Full ceramic crown
See also: Porcelain gear
Dental or porcelain ceramics are used for crowning especially for their aesthetic properties compared to all metal restorations. These materials are generally quite fragile and fragile. Many classifications have been used to categorize dental ceramics, with the simplest, based on the material from which they are made, ie silica, alumina or zirconia.
Silica
Silica-based ceramics are highly aesthetic because of their high glass content and excellent optical properties due to the addition of particle fillers that increase opalescence, fluorescence that can mimic the color of enamel and natural dentine. These ceramics, however, suffer from poor mechanical strength, and are therefore often used for the coating of stronger substructures.
Examples include aluminosilicate glass, eg. feldspathic, synthetic porcelain, and leucite-strengthened tiles.
The mechanical properties can be increased by adding filler particles, eg. lithium disilicate, and is therefore called glass ceramics. Glass-ceramics can be used alone to make all-ceramic restorations either as single shapes (called uni-layered) or can act as substructures for subsequent veneering (or layering) with weaker feldspathic porcelain (restorations called bi-layered).
Alumina
Alumina was introduced as a dental substitute (core) in 1989 when the material was slip cast, sintered, and infiltrated with glass. Recently, the alumina-core infiltration glass is produced by electrophoretic deposition, a rapid nanofabricating process. During this process, the slip particles are brought to the surface of the tooth die by an electric current, thereby forming a precision-fitting atomic nucleus within seconds. Margin then trimmed and greenbody sintered and infiltrated with glass. Glass-infiltration alumina has significantly higher porcelain bond strength over CAD/CAM producing zirconia core and glassless alumina.
The non-glass alumina core is produced by grinding pre-sintered block materials using the CAD/CAM dental technique. The glassless core must be large to compensate for the shrinkage that occurs when the core is fully sintered. The milled core is then sintered and shrunk to the correct size.
All alumina cores are coated with feldspathic porcelain like teeth to create real colors and shapes. Dental artists called ceramists, can adjust the "look" of this crown to each patient and dentist requirements. Now, the crown of porcelain that blends with alumina becomes the standard for dental appearance.
Zirconia
Yttria-stabilized zirconia, also known only as zirconia, is a very hard ceramic which is used as a strong base material in some full ceramic restorations. Relatively new zirconia in dentistry and published published clinical data are also limited. The zirconia used in dentistry is stabilized zirconium oxide with the addition of yttrium oxide. Stabilized zirconia Yttria is also known as YSZ.
Zirconia substructure (core) is usually designed on the digital representation of the patient's mouth, which is captured by a digital 3d scan on the patient, impression, or model. The core is then milled from a zirconia block in a soft pre-sintered state. Once ground, zirconia is sintered in a furnace where it shrinks up to 20% and reaches a full strength of 850 MPa to 1000MPa.
The structure of the zirconia core can be coated with tooth-like feldspathic porcelain to create the final color and shape of the tooth. Because the strength of the layered porcelain bonds that coalesce with zirconia is not strong, the "monolithic" zirconia crown is often made entirely of porcelain zirconia ceramics such as dental tissue laid on it. Zirconia is the hardest ceramic known in the industry and the strongest ingredient used in dentistry. Monolithic zirconia crowns tend to be opaque in appearance with high grades and they are less opaque and fluorescence. For the sake of appearance, many dentists will not use the monolithic crown on the front teeth (front).
For the most part, the selection of ingredients in dentistry determines the strength and appearance of the crown. Some monolithic zirconia materials produce the strongest crowns in dentistry (listed strengths for some zirconia crowns are close to 1000MPa.), But these crowns are usually not considered natural enough for the teeth at the front of the mouth; though not as strong, some of the newer zirconia materials have better looks, but generally they are not as good as crowned porcelain crowns. When the porcelain blends with the zirconia core, it is more natural than the monolithic zirconia crown but not strong. Conversely, when porcelain blends with alumina-infused glass, the crown is very natural and very strong, though not as strong as the monolithic zirconia crown. Another monolithic material, lithium-disilicate, produces a highly transparent highly pink crown that often appears too gray in the mouth, and to counter this, the bright colors of polyvalent dyes take on a distinctly unnatural, bright white look. Other properties of crown material considered are thermal and radiolucent conductivity. The stability/conformity of the prepared tooth and the cement gap at the edge is sometimes related to the selection of the material, although the nature of the crown is also generally associated with fabrication systems and procedures.
The crown of sengon is said to be less abrasive against the opposing teeth of the metal-ceramic crown.
Metal-ceramic crown
It is a hybrid of metal and ceramic crown. Metal parts are usually made of basic metal alloys (called alloy bonds). The properties of the selected metal alloy should be suitable and complementary of the ceramic to be bonded if problems such as delamination or ceramic cracking may occur. To obtain an aesthetic solution that can function with normal mastication activities, a minimum thickness of ceramic and metal materials, which must be planned during the preparation stage of the tooth.
Tie the ceramic to the metal frame with three methods:
- Compression fit (through ceramic shrinkage when enabled)
- Micro-mechanical retention (via irregular surfaces)
- Chemical unity (via oxide formation)
Maps Crown (dentistry)
Goal preparation
The preparatory design for the teeth to receive the crown follows five basic principles:
- Retention and resilience
- Preservation of tooth structure
- Structural resistance
- Marginal integrity
- Preservation of periodonsium
Aesthetics can also play a role in design planning.
Retention and robustness
Since there is currently no biologically compatible cement capable of holding the crown in solely through its adhesive properties, the geometric shape of the preparation is essential in providing retention and resistance to holding the crown in place. In a prosthodontic context, retention refers to the resistance of restoration movements along the insertion path or along the length of the dentition. Resistance refers to the resistance of the crown movement to the applied force apically or in an oblique direction preventing movement under the occlusal forces. Retention is determined by the relationship between the opposite surface of the preparation (eg buccal and lingual wall connections).
Lengket
Theoretically, the more parallel the opposite wall of the preparation, the more retention is achieved. But this is almost impossible to achieve clinically. This is the standard for preparation for a full cap crown to slightly tapered or fused in the occlusal direction. This allows preparation for visual inspection, prevention of deficiencies, compensates for the inappropriateness of crown fabrication and allows, at the cementation stage, for excess cement to escape with the ultimate goal of optimizing the seat of the crown on preparation. Generally the axial walls created using high speed burs with tapered lengths provide 2 - 3 Â ° jumps on each wall and a whole 4 - 6 Â ° taper for preparation. As the taper increases, retention decreases so that the taper should be kept to a minimum while ensuring undercut elimination. The overall decrease of 16 Â ° is said to be clinically achievable and able to meet the previously mentioned requirements. Ideally, the taper should not exceed 20 degrees because it will have a negative impact on retention.
Length
The length of the occlusal-gingiva or height of the crown preparation affects both resistance and retention. Generally, the higher the preparation, the greater the surface area. In order for the crown to be strong enough, the length of preparation should be greater than the height formed by the bow of the player spinning around the point on the margin on the opposite side of the restoration. The arc is affected by the diameter of the prepared tooth, therefore the smaller the diameter, the shorter the crown length it is necessary to withstand removal. Retention of short-stemmed teeth with wide diameter can be increased by placing a groove on the axial wall, which has the effect of reducing arc size.
Freedom to move
Retention can be increased by geometrically limiting the number of paths along the crown to be removed from the dental presentation, with maximum retention achieved when only one transfer path exists. Resistance can be enhanced by including components such as grooves.
Preservation of tooth structure
Preparing the teeth to receive the crown of full coverage is relatively destructive. This procedure can damage the pulp irreversibly, through mechanical, thermal and chemical trauma and make the pulp more susceptible to bacterial invasion. Therefore, preparation should be as conservative as possible, while producing a strong retention restoration. While this may be seen as contradictory to previous statements, sometimes, a healthy dental structure may need to be sacrificed to prevent the loss of larger and uncontrolled tooth structures.
Structural resistance
Finally, the crown should be made of sufficient material to withstand normal mastication functions and must contain within the space created by dental preparation, otherwise the problem may arise with aesthetics and occlusal stability (ie high restorations) and cause periodontal inflammation. Depending on the material used to make the crown, minimal occlusal and axial reductions are required to place the crown.
Occlusal Reduction
For gold alloys there should be a distance of 1.5 mm, while the crown metal-ceramic and full ceramic crown requires 2.0 mm. The occlusal permit must follow the natural line of the tooth; if not, there may be a restoration area where the material may be too thin.
Bevel cusp functional
For posterior teeth, wide bevels are required on functional valves, palatal palatal for maxillary tooth and buccal valve for mandibular teeth. If this functional bevel cusp does not exist and the crown is thrown to replicate the correct tooth size, most of the material may be too small at this point to hold the occlusal surface.
Axial Reduction
This should allow sufficient thickness for the selected material. Depending on the type of crown to be installed, there is a minimum preparation thickness. Generally, full metal crown requires at least 0.5mm, whist metal-ceramic and full ceramic crowns require at least 1.2mm
Marginal_Integrity> Marginal Integrity
In order for the final cast restoration in the oral environment and to protect the underlying tooth structure, the margins between the plaster and the tooth preparation must be tightly adjusted. The design and position of marginal lines should facilitate plaque control, allowing adequate thickness of the restoration material to be chosen because it provides sufficient strength to crown at the edges. Several types of final line configurations have been advocated, each having some advantages and disadvantages (see table below). Finish Chamfer is usually recommended for full metal margins and shoulders generally required to provide enough for a metal-ceramic crown and full ceramic crown margin. Some evidence suggests adding bevels to the margins, especially where this is heavy, to reduce the distance between crown and dental tissue.
Preservation periodontium
Connected with marginal integrity, the placement of the finish line directly affects the ease of crowning and the health of the periodontium. The best results are achieved where the finish line is above the gum line as it is fully cleansable. They should also be placed on the enamel as this creates a better seal. If circumstances require that the margins fall below the gum line, care should be taken as some problems may arise. First, there may be a problem in terms of capturing margins when creating impressions during the manufacturing process leading to inaccuracies. Second, the biological width, the compulsory distance (approximately 2 mm) is left between the height of the alveolar bone and the restoration margin; if this distance is violated, it can cause gingival inflammation with pocket formation, gingival recession and loss of alveolar bone peak. In this case, the crown elongation operation should be considered.
Special considerations
Ferrule effect
Endodontically treated teeth, especially those with small tooth tissue, are susceptible to fractures. The success of clinical outcomes for these teeth depends not only on adequate root canal care, but also on the type of restorative treatments used, including the use of pegs and the core system and the type of selected coronal restoration. Some evidence suggests the use of ferrules to optimize the bio-mechanical behavior of root-filled teeth, especially where the post and core systems need to be used.
In dentistry, the ferrule effect, as defined by Sorensen & amp; Engelman (1990), a 360-degree metal collar from a crown that surrounds the parallel wall of dentine that extends coronally to the preparation shoulder. Like the pencil ferrule that surrounds the junction between the rubber and the pencil rod, the ferrule effect is believed to minimize the pressure concentration at the post and core junctions, ultimately providing a protective effect against the fracture. It also reduces the transmission of voltage to the root because of the non-axial force applied by the post during placement or during normal functioning. Ferrule can also help to preserve the airtight seal of the luting cement. It has been suggested that the protection gained by the use of ferrule occurs due to the functional lever force holding the ferrule, the indentation effect of the pointy post and lateral force during post insertion. To make full use of the ferrule effect, preparations should allow for continuous dentin bands that must be at least 2 mm from the margin level of preparation and with bands that are at least 1 mm in thickness.
It has been shown, however, that while the absence of a 360 ferrule â € <â € <â € <â €
Preformed stainless steel metal crowns are the preferred treatment for posterior primary tooth restorations. A systemic review found that it had the highest success rate (96.1%). To receive a stainless steel crown, the entire occlusal surface should be reduced by 1 - 1.5 mm and the interproximal contact should be cleaned by cutting the mesial and distally thin parts or subgingiva slices by holding the tip. from a thin high speed bur at 15-20 ° relative to the long axis of the tooth, to avoid shoulder formation. No buccal or lingual/palatal surface preparation required.
Hall Technique
Hall technique is a noninvasive treatment for decayed posterior deciduous teeth in which caries is sealed under a stainless steel crown. This technique does not require tooth preparation.
Temporary and temporary crown
See also: Temporary crown
It is likely that once a tooth has been prepared and while waiting for a definitive restoration, the preparation of the tooth is equipped with a temporary crown.
The need for temporization
Tempuran important after preparing the teeth to receive the crown for several reasons:
- Protect from and prevent bacterial invasion of newly exposed dentine tubules, causing pulpal inflammation and necrosis
- Prevent gingival growth in areas created by dental preparations
- Allows the area to be cleaned more effectively, reducing the incidence of bleeding and gingival inflammation at the time of definitive recovery.
- Maintains occlusal contacts and estimates thus preventing eruption, rotation and space closure
- Aesthetic reasons
The temporary crown can also play a diagnostic role in treatment planning where there is a need for occlusal, aesthetic or periodontal change.
Temporary crown type
There are many types of temporary crowns available. There are also several ways to classify the crown. One is to classify the temporary crown by approximate or approximate the length of temporalization. Temporary crown can be described as short-term, if used for several days, medium term, if planned use for several weeks and long term if plan they are used for several months. Options in the length of temporization are often related to the complexity of planned restorative work. Short-term temporary crowns are generally appropriate for simple restorative cases whereas complicated cases involving more than one tooth often require long-term temporary crowns.
The temporary crown may also be explained by being made or installed on the crown preparation. Temporary crowns can be direct , if constructed by a dentist in the clinic, or indirectly if made offsite, usually in dental laboratories. Generally the temporary crown instantly tends to short term use. Where medium or long-term temporalisation is required, the use of an indirect, temporary crown must be considered.
Materials
There are several ingredients that can be used to build a temporary crown. The temporary crown is either made using preformed metal or plastic crowns, chemically preserved or cured resins with light or composite resins. Indirect restorations can be made of chemically-dried acrylic, heat-preserved acrylics, or metal castings.
Cementation
Unlike a definitive crown cement, the temporary crown should be relatively easy to release. For this reason a softer cement is used when cementing a temporary crown. This tends to zinc oxide of cement eugenol.
Clinical stage of crown making
- Gear preparation
- Impressions
- Temporary crown creation
Stage of crown-making dental laboratory
Preparation of crowns using CAD/CAM
- CERAC
Dental CAD/CAM on the side of the seat
The CAD/CAM method for falsifying the restoration of all ceramics is by electronically capturing and storing prepared dental photographic images and, using computer technology, devising a 3D restoration design that conforms to all required specifications of the proposed inlay, onlay or sole. single crown; no impression. After selecting the right features and making decisions on the computer model, the dentist directs the computer to send information to the local milling machine. This machine will then use a diamond burs specially designed to grind the restoration of a predetermined solid ceramic rod to fit the patient's teeth. After about 20 minutes, the restoration is complete, and the dentist divides it from the rest of the unmade ingot and tries it in the mouth. If the restoration is suitable, the dentist can cement the restoration immediately. CAD/CAM gear machines cost around $ 100,000, with continued purchases of ceramic ingots and drill milling. Due to the high costs, the usual and usual cost of making crowns of CAD/CAM in the dentist's office is often slightly higher than having the same crown made in dental laboratories.
Typically, over 95% of restorations made using CAD/CAM gear and Vita Mark I and Mark II are still clinically successful after 5 years. Furthermore, at least 90% of the restoration is still functioning successfully after 10 years. The advantages of Mark II blocks over ceramic blocks include: they wear out quickly like natural teeth, their failure load is very similar to natural teeth, and Mark II wear pattern to enamel is similar to enamel to enamel.
In recent years, technological advances provided by CAD/CAM dentistry offer a viable alternative to traditional crown restoration in many cases. Where an indirectly engineered crown traditionally requires a large amount of surface area to maintain a normal crown, potentially resulting in the loss of a healthy natural tooth structure for this purpose, a porcelain CAD/CAM crown can be predicted to be used with significantly fewer surfaces. area. In fact, the more enamel that is maintained, the more likely the results are successful. During the thickness of the porcelain at the top, the chewing section is as thick as 1.5mm or larger, the restoration can be expected to be successful. The side walls that are usually completely sacrificed in traditional crowns are generally left much more intact with the CAD/CAM option. Associate posts & amp; core buildup, this is generally contraindicated in the CAD/CAM crown as the resin bonding material performs the best bonding porcelain interface etched into the natural dental enamel/dentin interface. The crownlay is also an excellent alternative to post & amp; the accumulation of the core while restoring the teeth that are treated root of the tooth.
3/4 and 7/8 knob
There is even a restoration that falls between the full onlay and crown when it concerns the preservation of natural tooth structure. In the past, it was rather common to find dentists preparing teeth for 3/4 and 7/8 crowns . Such restorations will generally be made for the second or second molar premolar teeth, which may be only slightly visible when the patient smiles. Thus, the dentist will maintain a healthy natural tooth structure that is at the mesiobuccal angle of the teeth for the sake of natural appearance, the rest of the tooth will be covered in a restorative material. Even when the porcelain-fused-to-metal and all-ceramic crowns are developed, maintaining a number of dental structures adds to the overall strength of the teeth. Some dentists feel that the structural benefits of maintaining some of the original tooth structure are more than offset by potential problems having significantly longer marginal lengths ("sutures" on the surface between the crown and the teeth).
Longevity
Although there is no dental restoration that lasts forever, the average age of the crown is about 10 years. While these are considered relatively favorable for direct restoration, they can actually last up to a patient's life (50 years or more) with proper care. One of the reasons why the age of 10 is quoted is that dentists can usually provide patients with this number and believe that crowns made by dental laboratories will last for at least this long. Many dental insurance plans in North America will allow the crown to be replaced after only five years.
The most important factor that affects the lifespan of any recovery is the patient's continuous oral hygiene. Other factors are the skills of their dentists and lab technicians, materials used and proper care planning and case selection.
Full gold crowns last the longest, as they are made as a single piece of gold. PFM, or porcelain-fused-to-metal crowns have an additional dimension where they are prone to failure, because they incorporate fragile porcelain into their structures. Although very strong in compression, porcelain is very fragile in tension, and porcelain fractures increase the risk of failure, which increases as the number of closed surfaces of porcelain increases. Traditional PFM with occlusal porcelain (eg porcelain applied to the surface of posterior tooth bites) has a 7% greater chance of failure per year than the corresponding full gold crown.
When the crown is used to restore endodontically treated teeth, the tooth reduces the possibility of tooth fracture due to the delicate teeth and provides better protection against attacking bacteria. Although an inert filler inside the root canal blocks the microbial invasion of the internal tooth structure, it is actually a superior coronal seal, or a marginal adaptation of the restoration in or to the dental crown, preventing reinvasion of the root canal.
Type of dental crown and material used
There are many different methods of crown making, each using different materials. The available evidence suggests that all ceramic crowns survive around the same time or less than metal-ceramic crowns. Gold crowns are desirable because they require less reduction of dental tissue than other types of crowns and are the most durable crown type.
Crown of porcelain-melted into metal
Porcelain-Fused-to-Metal Porcelain Teeth (PFMs) have metal shells that blend with porcelain veneers in a high-heat oven. These metals provide powerful compression and tensile strength, and porcelain gives the crown a white-like appearance, suitable for front teeth restoration. This crown is often made with a partial layer that only covers the visible aspect of the crown. The remaining surface of the crown is an empty iron. Various metal alloys containing precious metals and base metals may be used. Porcelain can be matched with adjacent tooth color or gingiva.
Leucite reinforced
Known as the "Queen's Crown," a superficially reinforced leucite system is similar to the gold crown technique in a vacuum investment pattern created, but the similarity stops there. A specially-designed specially designed pressure-injected ceramic is then pressed into the mold by using a pressable porcelain oven, as if the final ceramic restoration has been "thrown." The constructed crown can be stained and glazed or cut into pieces and coated with a feldspathic ceramic to match the natural color and shape of the patient.
A study by UmeÃÆ'  ¥ University in Sweden, led by GÃÆ'¶ran SjÃÆ'¶gren, seeks to study the effectiveness of leukite reinforced crowns. Entitled "Clinical examination of leucite-reinforced ceramic crowns (Empress) in common practice: a restrospective study" , found the initial crown cracking at about a mere 6% level, with the integrity of 86% of the remaining sample called "excellent. "
History of the dental crown
There is some evidence of gold dental prostheses dating back to Etruscans.
See also
- Tooth recovery
- Posts and cores
- Teeth restorative material
- Inlay and onlays
- Preformed metal crown
References
External links
- Media related to Dental Crown on Wikimedia Commons
- Dental Health: Dental Crown
- Video from Sheffield University shows gold crown production
Source of the article : Wikipedia
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