Dental crowns in Bucharest

Dental crowns in Bucharest

In dentistry, a crown refers to a type of dental restoration that completely covers/surrounds a tooth or implant. A crown is needed when deep and extensive decay threatens dental health.

The crown is fixed to the tooth using dental cement. Crowns can be made from many types of materials, and are often made by indirect methods.

Crowns are used to improve the hardness and aesthetics of the tooth and to prevent it from being damaged. Although beneficial to dental health, the procedure and materials can be expensive.

The most common method of fitting a crown to a tooth involves having an impression of the tooth made by the dentist, and then manufacturing the crown in a laboratory.

The crown can then be cemented in place at a future appointment. This indirect method of dental restoration allows the use of strong restorative materials that require time under intense heat, such as metal casting or porcelain firing, which would not be possible inside the oral cavity.

Thanks to compatible thermal expansion, similar cost and aesthetic benefits, some patients choose to have the crown made of gold.

Computer-aided technology is increasingly used for crown fabrication in CAD/CAM dentistry.

Indications for dental crowns

Crowns are indicated for:

• Replacing existing crowns that have failed
• Restoring the form, function and aesthetics of a fractured or abraded tooth where other forms of restorations are not indicated or have failed clinically in the past.
• Improving the aesthetics of teeth that cannot be achieved by a simple cosmetic and restorative procedure.
• Maintaining structural stability and reducing the risk of fracture in extensively restored teeth, including those that have been treated endodontically.
• It is applicable to dental implants for prosthetic restoration.

Restoration of endodontically treated teeth

Dental crowns in Bucharest

Conventionally, it has been stated that teeth that have undergone root canal treatment are more likely to fracture and therefore require cusp protection by providing occlusal coverage with an indirect restoration such as crowns. This has led to the routine use of crowns for endodontically treated teeth.

Nevertheless, a recent review of the literature reveals that there is no solid evidence to show how crowns are better than other routine restorations for repairing root canal treated teeth.

The general advice is that dentists should use their clinical experience with the patient’s preferences in mind when making the decision to use a crown. As a rule, the use of crowns and other indirect restorations for endodontically treated teeth is justified when the surface area of the access cavity exceeds one third of the occlusal surface area of the tooth, when the lingual or buccal walls are undermined, or when the mesial and distal marginal ridges are missing.

Clinical stages of dental crown application

• Patient assessment
• Choice of restoration
• Tooth preparation
• Construction and cementation of the temporary restoration
• Dental impressions
• Fitting the permanent restoration
• Final check – revision

Patient assessment

To ensure optimal conditions and longevity of crowns, a number of factors need to be examined through a comprehensive patient history and clinical examination. These factors include:

Patient factors

• Patient expectations
• Patient motivation to adhere to the treatment plan and maintain outcomes
• Financial costs and patient time

Dental crowns in Bucharest

Biological factors

• Periodontal health status and risk of periodontal disease
• Dental pulp health and risk of endodontic complications
• Caries and caries risk
• Occlusion and risk of occlusal problems

Mechanical factors

• Extent of the remaining tooth structure
• Height and diameter of the tooth to be prepared
• Level of adhesion of the gum to the level of the tooth to be prepared
• Shape and root length of the tooth to be prepared

Aesthetic factors

Choice of restoration

The choice of a dental crown restoration can be described by:

• The size and percentage coverage of the natural crown
• Total crowns
• 3/4 and 7/8 crowns

The material to be used

• Metal
• Metal-ceramic crowns
• Ceramic crowns

These restorations are a hybrid between an onlay and a full crown. They are named based on the estimated coverage of the walls of the tooth; for example, the 3/4 crown aims to cover three of the four walls, with the buccal wall usually uncovered, therefore reducing the healthy tooth tissue that needs to be prepared. They are normally made of gold. Some grooves are made in the preparation as close to the intact wall as possible to increase crown retention. Despite its advantages of not reducing healthy tooth tissue, these crowns are not commonly prescribed in practice because they are technically difficult and have poor patient acceptability due to the metal being unsightly.

Full metal crowns

Dental crowns in Bucharest

As the name suggests, these crowns are cast entirely from a metal alloy. There are a multitude of alloys available and the choice of one alloy over another depends on several factors including cost, handling, physical properties, and biocompatibility. The American Dental Association classifies alloys into three groups: high-grade, noble and basic noble metal alloys.

High-noble and noble metal alloys

These types of alloys used in dental crowns are generally based on gold alloys. Gold is not used in its pure form as it would be too soft and have poor mechanical strength. Other metals included in gold alloys are copper, platinum, palladium, zinc, indium and nickel. All types of gold alloys used in prosthetics are divided according to the percentage of gold and hardness, type I being the softest and type IV the hardest. In general, types III and IV alloys (62 – 78% and 60 – 70% gold content) are used for full crowns, as they have sufficient hardness to withstand occlusal forces. Gold crowns are generally indicated for lateral teeth for aesthetic reasons. They are hard during the functions and strong in thinner sections, so require minimal preparation. They also have enamel-like wear properties, so are unlikely to cause severe abrasion to opposing teeth. They exhibit good dimensional accuracy when cast which minimizes patient chair time and can be relatively easy to polish if certain changes are required. Palladium-based alloys are also used. These were introduced as a cheaper alternative to gold alloys in the 1970s. Palladium has a strong whitening effect, giving most of its alloys a silvery appearance.

Metal-based alloys

These alloys are rarely used for making full crowns. They are more commonly used as part of a metal-ceramic crown as bonding alloys. Compared to noble alloys, they are harder and stronger, can be used in thin sections, however, are too hard to fit and are more likely to cause excessive abrasion on opposing natural teeth. Additionally, there are potential complications for people with nickel allergies.

Base metal alloys used in dentistry

The base metal alloy systems most commonly used in dentistry today include stainless steels, nickel-chromium, and cobalt-chromium, titanium, and nickel-titanium alloys. Titanium easily forms an oxide layer on its surface which gives it anti-corrosive properties and allows it to bond to ceramics, a useful property in the manufacture of metal-ceramic crowns.

Ceramic crowns

Dental crowns in Bucharest

Dental ceramics or porcelains are used to make crowns primarily for their aesthetic properties compared to all metal restorations. These materials are generally quite brittle and prone to fracture. Many classifications have been used to divide dental ceramics, the simplest being according to the material they are made of, i.e. silica, alumina or zirconia.

Silica

Silica-based ceramics are highly aesthetic due to their high glass content and excellent optical properties with incorporated filler particles that enhance opalescence, fluorescence and can mimic the color of natural enamel and dentin. These ceramics, however, have poor mechanical strength and are therefore often used for veneering stronger substructures.

Examples include aluminosilicate glass, e.g. feldspathic ceramics, synthetic porcelain and leucite-reinforced porcelain.

Mechanical properties can be improved by adding filler particles, e.g. lithium disilicate, and is therefore referred to as glass ceramics. Glass-ceramics can be used individually to make all-ceramic restorations either as a single form (uni layered) or can act as substructures for subsequent veneering (or layering) with weaker feldspathic porcelain (bi-layered restorations).

Alumina

Alumina (aluminum oxide) was introduced as a dental substructure (core) in 1989, when the material was cast, sintered and infiltrated with glass. More recently, glass-infiltrated alumina cores are produced by electrophoretic deposition, a rapid nanofabrication process. During this process, sliding particles are brought to the surface of a dental mold by an electric current, forming a precisely fitting cored body within seconds. The edges are then cut and the body is sintered and infiltrated with glass. Glass-infiltrated alumina has significantly higher resistance to porcelain adhesion than zirconia and alumina cores produced by CAD/CAM technology without glass.

Glass-free alumina cores are produced by milling presintered blocks of the material using a CAD/CAM technique. They must be oversized to compensate for the shrinkage that occurs when the core is fully sintered. The milled cores are then sintered to the correct size.

All alumina cores are layered with feldspathic porcelain similar to dental tissue to achieve a realistic color and shape. The dental technician can customize the appearance of these crowns to the individual requirements of the patient and dentist. Alumina cores have greater translucency than zirconia, but inferior to lithium disilicate.

Zirconia

Dental crowns in Bucharest

Yttria-stabilized zirconia, known simply as zirconium, is a very hard ceramic that is used as a strong base material in some all-ceramic restorations. Zirconia is relatively new to dentistry and published clinical data is limited. Zirconia used in dentistry is zirconium oxide (ZrO2) which has been stabilized through the addition of yttria.

The zirconia substructure (the core) is usually projected onto a digital representation of the patient’s oral cavity, which is captured with a three-dimensional digital scan of the arch, impression or model.

The core is then made of a block of zirconia in a pre-sintered soft state. Once realized, the zirconium is sintered in a furnace where it shrinks by 20% and reaches its maximum strength of 850-1000 MPa. Recently, the strength of zirconia for dental restorations has been reported to reach 1200 MPa.

The zirconia core structure can be layered with dental tissue-like feldspathic porcelain to create the final shade and shape of the tooth.

Because the bond strength of layered porcelain fused to zirconia is not strong; chipping of conventional ceramics occurs frequently, crowns and bridges are now increasingly made of monolithic zirconia produced from a block of zirconia graded in color and structure and coated with a thin layer of glaze.

Aesthetic prosthetic restorations with natural reflection, interior color and shade gradations influenced by the anatomy of the internal dentinal core can best be achieved with conventional zirconia rather than monolithic zirconia crowns.

In the making of dental restorations custom designed for a single patient, dental technicians, with their problem-solving skills, dexterity and cognitive abilities, provide porcelain with the aesthetics, individuality and artistry required. Fear of long-term chipping of conventional single-component zirconia porcelain and price pressures on manual porcelain application are possible factors for monolithic zirconia restorations.

Yet, by applying multi-glass components to porcelain, chipping will no longer occur, especially in the case of mimetic prosthetic restorations where the crown follows a two-layer natural tooth model: a histo-anatomical dentin layer mimicking the shape of the patient’s dentin and an enamel layer.

Dental crowns in Bucharest

Such restorations that mimic the structure of natural teeth by cognitively designing the dentin core present a new manufacturing paradigm to fabricate natural zirconia restorations using high-strength CAD/CAM porcelain. These crowns are produced with a tooth-colored tetragonal zirconia core, to which a layer of translucent high-strength porcelain has been applied and subsequently milled to the appropriate size.

In the subtle cooperation between dentine-colored zirconia and veneering porcelain, the zirconia shines through the translucent porcelain layer, the thinner the porcelain layer. This creates a natural color dynamic. As a result, the natural tooth, aesthetically and in terms of hardness, is similar to monolithic solid zirconia crowns. Thus, the histo-anatomical dentine core is the key to aesthetic crowns.

Zirconia is the hardest of the ceramic class in the industry and the most durable material used in dentistry; it is required to be fabricated using the CAD/CAM process, not conventional dental hand technology.

Because monolithic zirconia does not wear through the normal 25-75 micron vertical wear of natural enamel and porcelain, there is no clinical evidence that oversized zirconia crowns will cause long-term damage to the opposing dentition.

Although wear tests on the two monolithic zirconia veneered and glazed bodies and corresponding enamel antagonists showed similar wear, at least twice as much enamel micro cracking was observed in the samples opposite the monolithic zirconia.

Monolithic zirconia

Monolithic zirconia crowns tend to be opaque in appearance and lack translucency and fluorescence. For better appearance, many dentists will not use monolithic crowns on anterior (front) teeth.

Monolithic zirconia crowns are produced from a block of zirconia graded in color and structure and coated with a thin layer of glaze that also provides a degree of fluorescence.

The “graded” zirconia crown has a darker cervical area consisting of tetragonal zirconia, a main tooth color in the central area and a translucent incisal edge consisting of cubic zirconia. The only thing a dental technician has to do is to use the appropriate height of the zirconia block so that the crown fits in all the different colored areas.

Although on the outside the color gradient mimics natural teeth, they are still far from the optical, physical, biomimetic and aesthetic properties of natural teeth.

To a large extent, the selection of materials in dentistry determines the strength and appearance of a crown. Monolithic zirconia materials produce the strongest crowns in dentistry (recorded strength for some zirconia crown materials is nearly 1200 MPa), but these crowns are usually not considered to be natural looking enough to be used in the anterior area.

Lithium disilicate

Dental crowns in Bucharest

Another monolithic material, lithium disilicate, gives a high translucency in leucite-fused crowns, which often appear grey in the oral cavity. To overcome this drawback, light-toned polyvalent dyes provide a bright, unnatural white appearance.

Metal-ceramic crowns

These are a hybrid between metal and ceramic crowns. The metal part is usually made of a metal-based alloy. The properties of the chosen metal alloy should match the ceramic to be bonded; otherwise problems such as delamination or fracture of the ceramic may arise. In order to achieve an aesthetic result with the functional capacity for normal masticatory activity, a minimum thickness of ceramic and metal is required and should be planned for throughout the tooth preparation phase.

Ceramics are bonded to the metal framework by 3 methods:

• by compression (by shrinking the ceramic during firing)
• micromechanical retention (by surface irregularities)
• chemical (by oxide formation)

Tissue control and gingival retraction

Gingival retraction refers to the displacement of loosened gums. For crowns with supragingival margins, there is no need for gingival retraction, as long as there is good moisture control.

For crown preparations that have subgingival margins, tissue control is required during the preparation and impression phase to ensure visibility, good moisture control and that there is enough space for the impression material to be correctly positioned and capture the marginal areas.

The options available are gingival retraction floss, Magic Foam floss and ExpaSyl.

Another method to expose the subgingival margins of the preparation is using electrosurgery and coronal elongation technique.

Tooth preparation

The design of the tooth preparation to accept a crown follows 5 basic principles:

• Strength and retention
• Preservation of tooth structure
• Structural durability
• Marginal integrity
• Periodontal preservation

Aesthetics can also play a role in design planning.

Strength and retention

Dental crowns in Bucharest

Currently there are no biologically compatible cements that can hold the crown in place solely through their adhesive properties, so the geometric shape of the preparation is crucial to ensure retention and strength to secure the crown in place.

In the denture context, retention refers to the resistance to movement of a restoration along the path of insertion or along the long axis of the tooth.

Resistance refers to the resistance to movement of the crown by forces applied apically or in an oblique direction that prevent movement under occlusal forces. Retention is determined by the relationship between the opposing surfaces of the prepared tooth (e.g. the relationship between the palatal and lingual walls).

Taper

Theoretically, the more parallel the opposing walls of the preparation, the more retention is achieved. However, this is almost impossible to achieve clinically.

It is a standard criterion for preparations made for full-coverage crowns to have a slight taper or coverage in an occlusal direction.

This allows the preparation to be visually inspected, prevents over-shearing, compensates for inaccuracies in crown fabrication, and allows, in the cementation stage, for excess cement to flow back with the ultimate goal of optimizing the fit of the crown on the preparation.

In general, axial walls prepared using long; tapered cutters at high speed give a 2-3° taper on each wall, and a 4-6° taper of the entire preparation. As taper increases, retention decreases, so taper should be kept to a minimum.

An overall taper of 16° can be achieved clinically and can meet the above requirements. Ideally the taper should not exceed 20° as this will negatively influence retention.

Length

The occlusal-gingival length or coronal height of the preparation affects both strength and retention. In general, the higher is the preparation, the greater is the surface area. For the crown to be sufficiently retentive, the length of the preparation must be greater than the height formed by the arch pivoting around a point on the opposite edge of the restoration.

The arch is affected by the diameter of the prepared tooth, so the smaller the diameter, the shorter the crown length must be to resist removal. Retention of short-walled, large-diameter teeth can be improved by placing grooves in the axial walls, which has the effect of reducing the size of the arch.

Freedom of movement

Dental crowns in Bucharest

Retention can be improved by geometrically limiting the number of paths along which the crown can be removed from the prepared tooth, with maximum retention achieved when only one path of movement is available. Strength can be improved by making retentions like grooves.

Preservation of tooth structure

Preparing a tooth to accept a full crown is relatively destructive. The procedure can irreversibly destroy the pulp through mechanical, thermal and chemical trauma and make the pulp more susceptible to bacterial invasion.

However, the preparation should be as conservative as possible while achieving a restoration with strong retentivity. Although it may be seen contradictory to the previous statement, sometimes tooth structure requires to be sacrificed in order to prevent uncontrollable and substantial loss of tooth structure in the future.

Structural durability

In order to last, the crown must be made of material that supports normal masticatory function and must be contained within the space created by the tooth preparation, otherwise aesthetic and occlusal stability problems (i.e. high restorations) may occur and cause periodontal inflammation.

Depending on the material used to create the crown, minimal occlusal and axial reductions are required to accommodate the crown.

Occlusal reduction

For gold alloys, a clearance of 1.5 mm is required, whereas for metal-ceramic and all-ceramic crowns, 2 mm is required. The occlusal surface must follow the natural contour of the tooth; otherwise there may be areas of the restoration where the material may be too thin.

Weaving of functional cusps

For posterior teeth, a broad chamfer is required on the functional cusps, palatal cusps for maxillary teeth and buccal cusps for mandibular teeth. If this functional cusp bevel is not present and the crown is cast to reproduce the correct tooth size, the volume of material may be too small at this point to resist the occlusal surfaces.

Axial reduction

Dental crowns in Bucharest

This should provide sufficient thickness for the selected material. Depending on the type of crown to be made, there is a minimum of preparation thickness. In general, all-metal crowns require at least 0.5 mm, while metal-ceramic and all-ceramic crowns require at least 1.2 mm.

Marginal integrity

In order for the restoration to withstand the oral environment and protect the underlying tooth structure, the margins between the crown and the prepared tooth must be as tightly aligned as possible.

The design and position of the marginal line should facilitate plaque control, allow for adequate thickness of the preferred restorative material, thus providing sufficient strength for the crown at the marginal level.

Several types of gingival margin configurations have been advocated, each with some advantages and disadvantages (see table below).

Rounded thresholds are normally recommended for full metal margins, and straight ones are generally required to provide sufficient volume for metal-ceramic crowns and all-ceramic crown margins. Some evidence suggests adding bisection to the margins to reduce the distance between the crown and dental tissue.

Periodontal preservation

Dental crowns in Bucharest

Being related to marginal integrity, the placement of preparation margins can directly affect the easiness of crown fabrication and periodontal health.

Best results are achieved when the preparation margin is supragingival, as this makes hygiene easier to achieve. It should also be positioned at enamel level as in this way a better seal is created.

When circumstances require the edges to be subgingival, caution is necessary as some problems may arise. Firstly, there may be problems in terms of indentation of this margin during the manufacturing process leading to inaccuracies.

Secondly, the biological height must be at a mandatory distance of 2 mm between the alveolar bone height and the edge of the restoration; if this distance is exceeded, gingival inflammation with periodontal pocket formation, gingival recession and loss of alveolar bone ridge height may result. In these circumstances, dental crown augmentation should be considered.

Special considerations

Ferrule Effect

Endodontically treated teeth, especially those with limited healthy tooth tissue, are prone to fractures. Successful clinical outcome for these teeth is based not only on proper root canal treatment, but also on the type of restorative treatment used, including the use of teeth as abutments and the type of extra-coronal restoration selected. Some evidence supports the use of a ferrule to optimize the bio-mechanical performance of root filled teeth, particularly where a pivot is required.

In dentistry, the ferula effect is, as defined by Sorensen and Engelman (1990), a “360° metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation.”. Like the ferrule of a pencil surrounding the junction between the rubber and the pencil rod, the ferrule effect is thought to minimize stress concentration at the pivot junction, ultimately providing a protective effect against fracture.

It also reduces stress transmission to the root due to non-axial forces inflicted by the tooth during insertion or during normal function.

Dental crowns in Bucharest

The ferrule can also help keep the luting cement hermetically sealed. It has been suggested that the protection gained through the use of a ferrule occurs due to the functional forces of the lever, the locking effect of taper pins and lateral forces during their insertion.

To fully utilize the ferrule effect, the preparation must allow for a continuous portion of dentin that is at least 2 mm high from the preparation margin and at least 1 mm thick.

It has been shown, however, that while the absence of a 360° ferrule may increase the risk of fracture in teeth with pivots and crowns, restored root canal fillings, having insufficient crown walls presents an even greater risk.

Stainless steel crowns for posterior temporary dentition

Stainless steel made before metal crowns is a treatment option for restoring primary posterior teeth. A systematic study found that they have a high success rate (96.1%).

In order to accept a stainless steel crown, the entire occlusal surface should be reduced by 1-1.5 mm and the interproximal contacts should be left free by milling a mesial and distal or subgingival portion by keeping the tip of a thin high-speed milling cutter at 15-20° to the long axis of the tooth to avoid creating a threshold. No preparation of the buccal or lingual/palatal surfaces is required.

Stainless steel crowns can be esthetic by composite veneering using the open technique or composite veneering performed after sandblasting the stainless steel crown. Composite veneering can also be completed after preparation of retention grooves on the buccal surface of stainless steel crowns.

Hall technique

The Hall technique is a non-invasive treatment for decayed temporary posterior teeth, where the caries is sealed under a pre-formed stainless steel crown. This technique does not require tooth preparation.

Making and fixing temporary crown restorations

It is quite possible that once the tooth has been prepared and during the waiting time for the permanent restoration, a temporary crown will be applied to the tooth.

The need for temporary restorations

Dental crowns in Bucharest

Temporization is essential after the tooth has been prepared in order to:

• Protect/prevent bacterial invasion of exposed dentinal tubules, which can lead to pulpal inflammation and necrosis
• Prevent gingival growth in the area of the prepared tooth
• Allows the area to be cleaned more effectively, decreasing the incidence of bleeding and gingival inflammation when fitting the final restoration
• Maintains occlusal and approximal contacts, thus preventing extrusion, rotation and space closure
• Aesthetic purposes

Temporary crowns can also play a diagnostic function in treatment planning, where occlusal, aesthetic or periodontal changes are required.

Types of temporary crowns

Temporary crowns can be described according to expected or planned duration of temporization:

• Short-term
• Medium term
• Long-term

The manner or location from which/where the temporary crown is made:

• Directly or in the dental practice
• Indirectly or in the dental laboratory

Aesthetics of the material from which it is made:

• Metal
• Tooth color
• Preformed plastic (acrylic)
• Composite resin

Timing duration

Dental crowns in Bucharest

Temporary crowns can be described as short term if they are maintained for a few days, medium term if they are planned to be maintained for a few weeks and long term if they are planned to be used for a few months. The choice of temporization duration is often in accordance with the complexity of the restoration.

Short-term temporary crowns are generally indicated for simple restorations, while complex cases involving more than one tooth require long-term temporary crowns.

Direct vs. indirect restorations

Temporary crowns can be either direct, if they are made by the dentist in the clinic, or indirect, if they are made outside the office, usually in a dental laboratory. In general, direct temporary crowns tend to be used for a short time. When medium or long-term temporization is required, the use of indirect temporary crowns should be considered.

Materials used for temporary crowns

There are several materials that can be used to make temporary crowns. Direct crowns are fabricated using metal or pre-formed plastic, light-curing or chemically-curing resins and composite resins. Indirect restorations are either made from chemically polymerisable acrylic, heat-cured acrylic or metal.

Cementing temporary crowns

The purpose of temporary luting cements is to fill the space between the crown preparation and the temporary restoration. Unlike cementing permanent crowns, temporary crowns should be relatively easy to remove.

Adhesive cements should not be used and softer cements are preferred to allow easy removal of both temporary cements and crowns.

This is essential as the residual of temporary cement remaining on the tooth surface can compromise the health of the gums and interfere with the accurate setting of the final restoration and permanent cement attachment.

Temporary cements must also be strong enough to avoid warping or fracturing during the time of use.

Zinc oxide eugenol (ZOE) based temporary luting cements

These are commonly used because of their low tensile strength and lack of adhesion, which ensures easy removal. These products should not be used when composite resin is to be used for definitive crown fixation, as eugenol is able to infiltrate and diffuse through dentin; contaminating the tooth surface and compromising fixation by blocking resin polymerization.

Non-eugenol temporary luting cements

Non-eugenol cements replace eugenol with several types of carboxylic acids that do not suppress permanent cementation. These cements are compatible with resinous temporary materials and resin permanent cements and have increased retention when compared to ZOE-containing cements.

Polycarboxylate-based temporary luting cements

This hydrophilic cement has the advantage of minimal effects on resin-containing temporary luting agents and poor adhesion to dental tissue which increases ease of removal. This cement is the easiest to clean of all types of temporary cement.

Resin-based temporary luting cements

Dental crowns in Bucharest

Advantages of these cements include superior aesthetics, high strength, good retention and ease of cleaning. However, the disadvantages of this cement include a high rate of discoloration, the appearance of micro-leaks and unpleasant smell.

Impression of dental preparation

After the tooth in question has been prepared to the appropriate dimensions, it is equally important to make an accurate and dimensionally stable impression of the dental preparation or implant, surrounding the hard and soft tissues as well as the opposing dental arch, so that the restoration created matches the required dimensions and to ensure that the fit is as close as possible, without the doctor having to make many changes in the cabinet.

Impressions can be made digitally or by conventional technique. With regard to conventional impression techniques, the materials selected should have adequate physical properties and handling properties to allow faithful reproduction of detail and durability when casting the model, including the ability to withstand effective decontamination procedures. In general, the impressions of the dental arch where the dental preparation is placed are made of silicone and the “wash” technique is used; the impressions of the opposing arch are made of alginate.

Digital impressions can be made using dedicated optical scanners. A review suggests that digital impressions offer the same accuracy as conventional impressions and have been shown to be more comfortable for patients and convenient for dentists.

Dental crown fabrication using CAD/CAM technique

The CAD/CAM method of fabricating all-ceramic restorations is by electronically capturing and storing a photographic image of the prepared tooth and, using computer technology, producing a 3D restoration design that meets all the specifications required for the inlay, onlay or crown; there is no dental impression.

After selecting the appropriate features and making various decisions on the computer design, the dentist directs the computer to send the information to a local milling machine.

Dental crowns in Bucharest

This machine will then use its specially designed diamond burrs to mill the restoration from a solid ingot of a ceramic with a predefined shade to match the patient’s tooth.

After about 20 minutes, the restoration is complete, and the dentist cuts it from the rest of the ungrounded ingot and places it in the patient’s mouth. If the restoration fits well, the dentist can cement the restoration immediately.

A CAD/CAM dental machine costs around $100,000, with the ongoing purchase of ceramic ingots and milling cutters. Because of the high cost, the fee for making a CAD/CAM crown in a dental office is often slightly higher than having the same crown made in a dental lab.

Typically, over 95% of dental restorations made using CAD/CAM and Vita Mark I and Mark II blocks are still clinically successful after five years. In addition, at least 90% of restorations still perform successfully after 10 years. Advantages of Mark II blocks over ceramic blocks include the fact that: they wear as fast as natural teeth, and their chances of failure are very similar to those of natural teeth.

Recently, advanced technology supported by CAD/CAM dentistry has offered viable alternatives to traditional crown restorations in many cases.

Classically made indirect crowns require a large surface area for retention of the normal crown, potentially resulting in a loss of health of the natural tooth structure, whereas CAD/CAM porcelain crowns can be used on significantly smaller surfaces.

In fact, the more enamel used for retention, the greater the chance of success. As long as the thickness of the porcelain on the upper, occlusal side of the crown is 1.5 mm thick or greater, the restoration is expected to be successful.

Sidewalls that are normally sacrificed completely in the classic crown are generally left much more intact with the CAD/CAM option. As for making pivots, these are generally contraindicated in CAD/CAM crowns, as the resin luting materials best bond the etched porcelain interface to the etched enamel/dentin interfaces of the natural tooth itself.

The crown is also an excellent alternative to the pivot when restoring an endodontically treated tooth.

Crown removal

Dental crowns in Bucharest

Sometimes it may be necessary to remove the crown restoration in order to perform treatment of the tooth tissue under the crown, especially to perform non-surgical endodontic treatment of a previously necrotic/treated pulp. Several methods are available and the choice is guided by the nature and quality of the crown restoration, i.e. whether it is to be saved or be replaced.

Factors to consider when deciding whether the crown will be permanently preserved or replaced include:

• Cost of replacement
• Aesthetics
• Removability
• Marginal integrity
• Restoration planning (including changing from a crown to a bridge or adapting the crown to an abutment tooth design for a partial denture)
• Required access to treat the tooth safely and effectively

Temporary crowns are easy to remove and replace, so they don’t pose a problem.

Prior to the removal of the permanent crown restoration, it is important to plan for a temporary crown, especially in the event that the crown to be removed may deteriorate during the process.

It usually involves making an impression of the crown so that a temporary crown can be made in the office or dental laboratory.

Several instruments and methods are available, which can be categorized according to how conservative they are. Normally, the tooth, if badly damaged, should be restored before a new crown (whether temporary or permanent) is fitted.

Methods of crown removal depending on how conservative they are with dental preparation

Dental Bands

• Application of a strip of matrix which is inserted under the crown and pulled vertically.

Ultrasonic

Dental crowns in Bucharest

An ultrasonic tip can be applied to a cast metal crown to dislodge the luting cement. This method should be avoided in ceramic restorations as it can lead to fractures.

Pliers

These can be used to grasp the restoration and dislodge it from the dental preparation. Some special pliers are designed to have rubber grips and powder on the top of the restoration to reduce the risk of damage to the ceramic restoration. They are quite effective in removing crowns fixed with temporary cements.

Sticky sweet method or Richwill crown and bridge remover

A thermoplastic pliable resin is softened in warm water then placed on the occlusal surface of the crown to be removed. The patient is then asked to bite down, compressing the resin block to two-thirds of its original thickness. The patient is then asked to open the mouth quickly, which should generate enough force to displace the restoration. This method however, is not very effective and has a risk of damaging restorations on or accidentally extracting the opposing tooth. Therefore, before using this method, it is important to look at the state of the opposing tooth.

Pneumatic instruments

Sliding hammers work by using the tip to wedge the edge of the crown and sliding the weight along the shaft to loosen the restoration. Several versions are available. Some are weighted, others spring-loaded. This system is uncomfortable for the patient and is not always successful. It is also contraindicated for periodontally involved teeth as it can cause unwanted extractions. This system can also damage the ceramic margins.

Special instruments

A slot is cut using the side of a long tapered bur, normally on the buccal surface of the crown, all the way down to the cement. A flat plastic tool, Couplands elevators or dedicated systems such as WamKey, is inserted into the slot created to separate the crown from the tooth.

Special crown and bridge removal system (Metalift)

Dental crowns in Bucharest

Based on the jack-screw principle, the Metalift system works by precisely drilling a channel through the occlusal surface of a cast restoration, then with a special milling cutter, the area around the periphery of the hole is undetermined before a threaded screw is inserted into the space.

As the screw comes into contact with the core of the restoration, continuous rotation of the screw results in a lifting force that displaces the crown from the tooth.

This system can be used for the removal of both all metal and metal-ceramic crowns, although care must be taken to remove sufficient ceramic from the area where the hole is created to reduce the chance of fracture.

The minimum metal thickness required for the lifting action is approximately 0.5 mm. The damage can be repaired with a plastic filling material.

Burs

The crown can be simply sectioned using a bur.

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