Dental bridge dentures with different supporting elements. Clinical and laboratory stages of making dental bridges with different supporting elements.
A bridge, also known as a fixed partial denture, is a dental restoration used to replace a missing tooth by joining permanently to adjacent teeth or dental implants. A bridge is used to span, or bridge, an edentulous area (space where teeth are missing), usually by connecting to fixed restorations on adjacent teeth. The teeth used to support the bridge are called abutments. A bridge may also refer to a single-piece multiple unit fixed partial denture (numerous single-unit crowns either cast or fused together). The part of the bridge which replaces a missing tooth and attaches to the abutments is known as a «pontic.» For multiple missing teeth, some cases may have several pontics.
There are different types of bridges, depending on how they are fabricated and the way they anchor to the adjacent teeth. Conventionally, bridges are made using the indirect method of restoration however, bridges can be fabricated directly in the mouth using such materials as composite resin.
Fixed prosthodontics in dentistry is a technique used to restore teeth, using fixed restorations (also referred to as indirect restorations), which include crowns, bridges, inlays, onlays, and veneers. Prosthodontists are specialist dentists who have undertaken training recognized by academic institutions in this field. Fixed prosthodontics can be used to restore single or multiple teeth, spanning areas where teeth have been lost. In general, the main advantages of fixed prosthodontics when compared to direct restorations is the superior strength when used in large restorations, and the ability to create an aesthetic looking tooth. As with any dental restoration, principles used to determine the appropriate restoration involves consideration of the materials to be used, extent of tooth destruction, orientation and location of tooth, and condition of neighboring teeth.
A dental bridge (or pontic) is a custom-made false tooth or teeth, that is permanently placed between two healthy teeth, filling in the area left by a missing tooth or teeth. The bridge is held in place by porcelain crowns placed on the healthy teeth on each side of space to be filled. A bridge created by a cosmetic dentist is completely metal-free. As a result, the bridge absorbs light, creating a natural looking smile. (Bridges made of porcelain fused to metal actually reflect light, creating an “unnatural” look for the tooth or teeth.) Bridges reduce the risk of gum disease, limit the shifting of remaining teeth, help correct some bite problems and help improve speech.
A bridge is fabricated by reducing the teeth on either side of the missing tooth or teeth by a preparation pattern determined by the location of the teeth and by the material from which the bridge is fabricated. In other words, the abutment teeth are reduced in size to accommodate the material to be used to restore the size and shape of the original teeth in a correct alignment and contact with the opposing teeth. The dimensions of the bridge are defined by Ante’s Law: “The root surface area of the abutment teeth has to equal or surpass that of the teeth being replaced with pontics”.
The materials used for the bridges include gold, porcelain fused to metal, or in the correct situation porcelain alone. The amount and type of reduction done to the abutment teeth varies slightly with the different materials used. The recipient of such a bridge must be careful to clean well under this prosthesis.
When restoring an edentulous space with a fixed partial denture that will crown the teeth adjacent to the space and bridge the gap with apontic, or “dummy tooth”, the restoration is referred to as a bridge. Besides all of the preceding information that concerns single-unit crowns, bridges possess a few additional considerations when it comes to case selection and treatment planning, tooth preparation and restoration fabrication.
Case selection and treatment planning.
When a single tooth requires a crown, the prosthetic crown will in most instances rest upon whatever tooth structure was originally supporting the crown of the natural tooth. However, when restoring an edentulous area with a bridge, the bridge is almost always restoring more teeth than there are root structures to support. For instance, in the photo at right, the 5-unit bridge will only be supported on three abutment teeth. To determine whether or not the abutment teeth can support a bridge without failure from lack of support from remaining root structures, the dentist employs Ante’s rule – which states that the roots of abutment teeth must have a combined surface area in three dimensions that is more than that of the missing root structures of the teeth replaced with a bridge. When the situation yields a poor prognosis for proper support, double abutments may be required to properly conform to Ante’s rule.
When a posterior tooth intended for an abutment tooth already possesses an intracoronal restoration, it might be better to make that bridge abutment into an inlay or an onlay, instead of a crown. However, this may concentrate the torque of the masticatory forces onto a less enveloping restoration, thus making the bridge more prone to failure.
In some situations, a cantilever bridge may be constructed to restore an edentulous area that only has adequate teeth for abutments either mesially or distally. This must also conform to Ante’s rule but, because there are only abutments on one side, a modification to the rule must be applied, and these bridges possess double abutments in the majority of cases, and the occlusal surface area of the pontic is generally decreased by making the pontic smaller than the original tooth. Once you and your dentist determine that a dental bridge is the best replacement for your missing tooth or teeth, you will be advised of different materials that the dental laboratory can use to make your restoration. Material availability will depend upon where in the mouth the bridge will be placed, whether or not you grind or clench your teeth (bruxism), your dental insurance coverage, and other factors outlined by your dentist. Dental bridges today can be fabricated from a combination of porcelain and metal, porcelain and gold, or exclusively with high-strength metal-free materials such as zirconia or alumina. Your dentist will take X-rays and impressions of the area requiring a bridge, as well as preoperative photographs, for use in planning the ideal bridge restoration for you. Depending upon the number of consecutive teeth you are missing, your bridge could be three or more units; two crowns that are cemented to the teeth on either side of the space (called abutments), plus one or more false teeth (called pontics) to fill the space. Additional impressions will be taken after your dentist prepares the abutment teeth for the bridge. During the first visit, your dentist examines the health of your gums and other teeth to evaluate if you are a candidate for a dental bridge. If you are a candidate for a dental bridge, you are given a local anesthetic so your dentist can prepare the teeth required to support the bridge. If the support teeth are decayed or badly broken down, your dentist may have to build them back up before they can be used as support teeth for a bridge. Next, your dentist takes an impression of the prepared teeth with a putty-like material that is used to create a model of your teeth. Your bridge is fabricated based on this model by a skilled lab technician so that it precisely fits the prepared teeth. It is important that your restoration fit perfectly to avoid additional oral health problems such as tooth decay. While your bridge is being fabricated, your dentist fits you with a temporary bridge so the teeth and gums can be protected from damage until your permanent bridge is ready.
Tooth preparation
As with preparations for single-unit crowns, the preparations for multiple-unit bridges must also possess proper taper to facilitate the insertion of the prosthesis onto the teeth. However, there is an added dimension when it comes to bridges, because the bridge must be able to fit onto the abutment teeth simultaneously. Thus, the taper of the abutment teeth must match, to properly seat the bridge. This is known as requiring parallelism among the abutments.
When this is not possible, due to severe tipping of one of more of the abutments, for example, an attachment may be useful, as in the photo at right, so that one of the abutments may be cemented first, and the other abutment, attached to the pontic, can then be inserted, with an arm on the pontic slipping into a groove on the cemented crown to achieve a span across the edentulous area.
Preparation of a tooth for a crown involves the irreversible removal of a significant amount of tooth structure. All restorations possess compromised structural and functional integrity when compared to healthy, natural tooth structure. Thus, if not indicated as desirable by an oral health-care professional, the crowning of a tooth would most likely be contraindicated. It should be evident, though, that dentists trained at different institutions in different eras and in different countries might very well possess different methods of treatment planning and case selection, resulting is somewhat diverse recommendations for treatment.
Traditionally more than one visit is required to complete crown and bridge work, and the additional time required for the procedure can be a disadvantage; the increased benefits of such a restoration, however, will generally offset these considerations.
When preparing a tooth for a crown, the enamel should be totally removed and the finished preparation should, thus, exist entirely in dentin. As elaborated on below, the amount of tooth structure required to be removed will depend on the material(s) being used to restore the tooth. If the tooth is to be restored with a full gold crown, the restoratioeed only be
If there is not enough tooth structure to properly retain the prosthetic crown, the tooth requires a build-up material. This can be accomplished with a pin-retained direct restoration, such as amalgam or a resin like fluorocore, or in more severe cases, may require a post and core. Should the tooth require a post and core, endodontic therapy would then be indicated, as the post descends into the devitalized root canal for added retention. If the tooth, because of its relative lack of exposed tooth structure, also requires crown lengthening, the total combined time, effort and cost of the various procedures, together with the decreased prognosis because of the combined inherent failure rates of each procedure, might make it more reasonable to have the tooth extracted and opt to have an implant placed.
The prepared tooth also needs to possess a certain degree of taper to allow for the restoration to be properly placed on the tooth. Fundamentally, there can be no undercuts on the surface of the prepared tooth, as the restoration will not be able to be removed from the die, let alone fit on the tooth (see explanation of lost-wax technique below for understanding of the processes involved in crown fabrication). At the same time, though, too much taper will severely limit the grip that the crown has while on the prepared tooth, thus contributing to failure of the restoration. Generally, 6º of taper around the entire circumference of the prepared tooth, giving a combined taper of 12º at any given sagittal section through the prepared tooth, is appropriate to both allow the crown to fit yet provide enough grip.
The most coronal position of untouched tooth structure (that is, the continual line of original, undrilled tooth structure at or near the gumline) is referred to as the margin. This margin will be the future continual line of tooth-to-restoration contact, and should be a smooth, well-defined delineation so that the restoration, no matter how it is fabricated, can be properly adapted and not allow for any openings visible to the naked eye, however slight. An acceptable distance from tooth margin to restoration margin is anywhere from 40-100 nm. However, the R.V. Tucker method of gold inlay and onlay restoration produces tooth-to-restoration adaptation of potentially only 2 nm, confirmed by scanning electron microscopy; this is less than the diameter of a single bacterium.
Naturally, the tooth-to-restoration margin is an unsightly thing to have exposed on the visible surface of a tooth when the tooth exists in the esthetic zone of the smile. In these areas, the dentist would like to place the margin as far apical (towards the root tip of the tooth) as possible, even below the gum line. While there is no issue, per se, with placing the margin at the gumline, problems may arise when placing the margin too subgingivally (below the gumline). First, there might be issues in terms of capturing the margin in an impression to make the stone model of the prepared tooth (see stone model replication of tooth in photographs, above). Secondly, there is the seriously important issue of biologic width. Biologic width is the mandatory distance to be left between the height of the alveolar bone and the margin of the restoration, and if this distance is violated because the margin is placed too subgingivally, serious repercussions may follow. In situations where the margin cannot be placed apically enough to provide for proper retention of the prosthetic crown on the prepared tooth structure, the tooth or teeth involved should undergo a crown lengthening procedure.
There are a number of different types of margins that can be placed for restoration with a crown. There is the chamfer, which is popular with full gold restorations, which effectively removed the smallest amount of tooth structure. There is also a shoulder, which, while removing slightly more tooth structure, serves to allow for a thickness of the restoration material, necessary when applying porcelain to a PFM coping or when restoring with an all-ceramic crown (see below for elaboration on various types of crowns and their materials). When using a shoulder preparation, the dentist is urged to add a bevel; the shoulder-bevel margin serves to effectively decrease the tooth-to-restoration distance upon final cementation of the restoration.
The single most important consideration when restoring with a crown is, undeniably, the incorporation of the ferrule effect. As with the bristles of a broom, which are grasped by a ferrulewhen attached to the broomstick, the crown should envelop a certain height of tooth structure to properly protect the tooth from fracture after being prepared for a crown. This has been established through multiple experiments as a mandatory continuous circumferential height of 2mm; any less provides for a significantly higher failure rate of endodontically-treated crown-restored teeth. When a tooth is not endodontically treated, the remaining tooth structure will invariably provide the 2mm height necessary for a ferrule, but endodontically treated teeth are notoriously decayed and are often missing significant solid tooth structure. Contrary to popular belief, endodontically treated teeth are not brittle after being devitalized according to the following study -CM Sedglay & Messer 1992 Journal of Endodontics. Contrary to what some dentists believe, a bevel is not at all suitable for implementing the ferrule effect, and beveled tooth structure may not be included in the 2 mms of required tooth structure for a ferrule.
As with single-unit crowns, bridges may be fabricated using the lost-wax technique if the restoration is to be either a multiple-unit FGC or PFM. Another fabrication technique is to use CAD/CAM software to machine the bridge. As mentioned above, there are special considerations when preparing for a multiple-unit restoration in that the relationship between the two or more abutments must be maintained in the restoration. That is, there must be proper parallelism for the bridge to seat properly on the margins. Sometimes, the bridge does not seat, but the dentist is unsure whether or not it is only because the spatial relationship of the two or more abutments is incorrect, or whether the abutments do not actually fit the preparations. The only way to determine this is to section the bridge and try in each abutment by itself. If they all fit individually, it must have simply been that the spatial relationship was incorrect, and the abutment that was sectioned from the pontic must now be reattached to the pontic according to the newly confirmed spatial relationship. This is accomplished with a solder index.
The proximal surfaces of the sectioned units (that is, the adjacent surfaces of the metal at the cut) are roughened and the relationship is preserved with a material that will hold on to both sides, such as GC pattern resin. With the two bridge abutments individually seated on their prepared abutment teeth, the resin is applied to the location of the sectioning to reestablish a proper spatial relationship between the two pieces. This can then be sent to the lab where the two pieces will be soldered and returned for another try-in or final cementation.
A resin retained bridge
A resin retained bridge is a dental prosthesis replacing a missing tooth that relies for its retention on a composite resin cement. The resin retained bridge is a good treatment option for many missing teeth as it is relatively cheap when compared to alternatives such as dental implants, requires little or no damage to the surrounding teeth during preparation for placement, and it is well tolerated by patients. Typical success rates are quoted as being as high as 80% after 15 years in the anteriormaxilla. Far lower success rates are seen in the posterior mandible.
Thus case selection is important. As with any dentistry, good oral hygiene is paramount for success.
One major advantage of the resin retained bridge over a conventional bridge is the failure mode is likely to be debonding of the retainer. In conventional bridges the failure mode is likely to be complete fracture of the abutment tooth with difficult to manage sequelae, possibly requiring root canal treatment. With a resin retained bridge the prosthesis can usually be cleaned off and rebonded in position with minimal inconvenience to the patient.
The resin retained bridge has gone through a number of iterations. Perhaps the best known is the Maryland bridge. Other designs used in the past include the Rochette bridge .
The resin retained bridge requires a very specific set of design principles.
The wing or retainer must be rigid and is usually fabricated from a metal alloy. The inner surface must fit closely to the abutment tooth. The intaglio is treated in some way to enhance the micromechanical adhesion between the prosthesis and the composite resin cement. In the past various methods have been used, ranging from metal-weave patterns to tin plating. The modern resin retained bridge retaining wing is usually sandblasted with an alumina powder.
The pontic is usually made from dental porcelain. The whole restoration is thus a porcelian fused to metal restoration.
Current cement brands commonly used for this procedure include Panavia, Nexus. All are either auto cure or dual cure to ensure complete polymerisation of the resin under the wing. Great care must be taken during cementation to avoid contamination of the operative field as this will lower the bond strength of the cement and lead to premature failure. For this reasonrubber dam is often advocated for placement, though this can bring its own difficulties.
Impression materials are used to record the shape of the teeth and alveolar ridges. There are a wide variety of impression materials available each with their own properties, advantages and disadvantages. Materials in common use can be classified as elastic or non-elastic according to the ability of the set material to be withdrawn over undercuts. Impression materials, in the fluid or plastic state, are carried to the mouth in a suitably sized tray. Hardening of the material takes place either on cooling or through a chemical reaction. There is no clear line between mucostatic and mucodisplacing impression materials.
These viscous impressions materials are called mucocodisplacive impression materials. These record an impression of the mucosa under load. This results in a wider distribution of load during function, making it more stable it also compensates for the differing compressibility of the denture bearing area reducing the risk of a fracture due to flexion. However the retention of the dentures may be compromised as the soft tissues wish to return to their original position at rest.
An impression is a negative reproduction of a given area of the oral cavity. The area reproduced may be composed of either hard or soft tissues or both. The material must be inserted into the mouth while it is too soft to retain its shape. A rigid base is needed to carry it to the mouth and hold it against the tissues until it hardens. For this purpose, a variety of trays, called stock trays, are available. These are shaped to fit over the average maxillary and mandibular arches. Some can be trimmed and bent to the requirements of the individual patient. Trays may also be fabricated for each individual patient.
The resin retained bridge is increasingly being used in modern dentistry as an alternative to more destructive treatments. This has been driven by the advent of evidence based dentistryshowing the benefits to patients of reduced tooth preparation and the importance of an intact enamel structure for the longterm health of the teeth.
There has been a long-standing need in the dental art for a superior means for replacing a missing tooth. Many different types of dental bridges have been developed, but in recent years many dental professionals have shown a preference for resin bonded systems which can be utilized for the replacement of a single anterior tooth. Resin bonded systems have the advantage over other types of dental bridges in that preparation of the patient’s mouth and existing teeth is minimal.
Some prior resin bonded systems, though conservative iature, utilize a metallic bridge framework over which an enamel or porcelain is applied. In such systems there always exists the potential aesthetic disadvantage of mental “shine-through” at the incisal edge of the abutment teeth. Further, the prior systems typically have a fixed pontic color, which is frequently more opaque than desired.
In an effort to avoid the problems associated with the use of metals in a dental bridge, all-porcelain bridges have been developed which also require minimal tooth reduction. A problem associated with all-porcelain bridges is that they exhibit a higher incidence of porcelain fracture due to movement of the abutment teeth. This problem exists even when the teeth are just slightly mobile. Further, the all-porcelain bridge has a pontic color which is set during the manufacturing process, and which cannot be adjusted at the chair.
Accordingly, there has been a need for a novel dental bridge which integrates the strength and resiliency of a resinous bridge framework, with the aesthetic advantages of a porcelain-like veneer. Additionally, there exists a need for a novel dental bridge and process of manufacturing the same which requires conservative tooth preparation, which allows bridge flexure permitting class 1 mobility without fracture, and which utilizes non-metallic materials for optimum aesthetics and reduced risk of allergy. Further, a novel dental bridge and related method of manufacturer is needed which permits a two-phase placement technique in the mouth of a patient, thus eliminating pontic over-contouring, and gives chairside control to the dental professional over the final pontic shade. Moreover, a method of manufacturing such an improved dental bridge is needed which provides for maximum polymerization of the resinous bridge framework. Such a method should further provide for a high bond strength between the bridge framework and the abutment teeth, on the one hand, and a porcelain veneer on the labial surface of the pontic, on the other. The present invention fulfills these needs and provides other related advantages.
The present invention resides in an improved winged composite dental bridge for attachment to two abutment teeth, and a process for manufacturing the winged dental bridge. The dental bridge comprises, generally, a relatively flexible bridge framework which is fixed to the abutment teeth, and a relatively hard veneer which is subsequently fixed to the framework. The bridge framework includes a pontic and means attachable to the abutment teeth for supporting the pontic therebetween. The pontic is permitted limited flexure relative to the supporting means to give the bridge class 1 mobility without fracture.
In a preferred form of the invention, the means attachable to the abutment teeth for supporting the pontic therebetween includes a first wing which extends laterally outwardly from the pontic for attachment to a first abutment tooth, and a second wing which extends laterally outwardly from the pontic opposite to the first wing for attachment to a second abutment tooth. The bridge framework is formed of at least two laminated cured resin materials which, when manufactured in accordance with a preferred method, permit limited flexure of the pontic relative to the wings.
In accordance with a preferred process for manufacturing the winged dental bridge, the abutment teeth are first prepared to receive the dental bridge by cutting the lingual surfaces of the abutment teeth to form reduction or shaved areas. These shaved areas are contoured in a manner to receive the wings of the bridge framework and to facilitate a secure attachment between the wings and the abutment teeth. An impression is taken of the patient’s mouth after the abutment teeth have been prepared, and a first cast is created from the impression. A separator is then applied to all surfaces of the cast which will come into contact with the dental bridge itself during subsequent manufacturing steps.
A resinous composite bridge framework is formed over the separator on the cast, which extends between the two abutment teeth. This is accomplished by applying a polishable resinous material to the saddle area of the cast, then applying an etchable resinous material to create the labial surface of the pontic and the attachment surfaces for the wings, and finally laminating a polishable resinous material to the etchable material, to entirely cover the lingual surface of the etchable material.
The uncured composite bridge framework is then light cured, while still mounted to the cast, in a pressurized nitrogen gas environment for seven minutes at a pressure of approximately 80 PSI. The partially cured bridge framework can then be removed from the cast and heat and light cured for an additional seven minutes at approximately 130° C. The pressurized nitrogen gas environment in which the uncured bridge framework is placed includes a chamber having a base on which the cast is positioned, and an overlying transparent dome which forms an air-tight chamber. A gas inlet passageway is provided through the base for pressurizing the chamber, and a separate air purge passageway insures that a pure nitrogen environment is attained.
After the bridge framework has been cured, the pontic portion is contoured to receive a porcelain-like veneer. The bridge framework is then secured to the first cast using sticky wax, an impression is taken, and a second cast is created. From this second cast, a relatively hard (porcelain) veneer is fabricated for placement over the labial surface of the bridge framework pontic.
Prior to installing a dental bridge in the mouth of the patient, the exposed surfaces of the etchable material, as well as the interior surfaces of the hard veneer, are acid-etched utilizing a hydroflouric acid. The exposed surfaces of the polishable material are polished. The dental bridge is then installed in the mouth of the patient by fixing the wings to the prepared abutment teeth, and subsequently attaching the hard veneer to the labial surface of the pontic. More particularly, the wings are fixed within the shaved areas of the abutment teeth by means of direct composite bonding. The hard veneer is attached to the labial surface of the bridge framework pontic by utilizing a dental composite cement which is colored, if necessary, in order to match the color of the veneer when fixed to the pontic, to the color of the abutment teeth. This advantageously gives chairside control during the final installation step, over the final color of the normally visible portions of the winged dental bridge.
The use of nonmetallic components in the winged dental bridge of the present invention permits the manufacture of a bridge having sufficient hardness and aesthetic properties, while permitting some bridge flexure without fracture thereof. The nonmetallic materials reduce the risk of allergy, and the two phase placement technique eliminates pontic over contouring.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The present invention is concerned with an improved dental bridge, generally designated in the accompanying drawings by the reference number 20. The dental bridge comprises, generally, a relatively flexible resin composite bridge framework which is manufactured for attachment to a pair of abutment teeth, and a relatively hard (porcelain) veneer which is attached at chairside to a pontic portion of the bridge framework.
In accordance with the present invention, and as illustrated best in FIGS. 5 through, the bridge framework includes the pontic portion, a first wing extending laterally outwardly from the pontic 28 for attachment to a first abutment tooth, and a second wing which extends laterally outwardly from the pontic opposite to the first wing for attachment to a second abutment tooth. The bridge framework is formed of two laminated cured resinous materials which permit limited flexure of the pontic relative to the wings and.
The construction and characteristics of the winged dental bridge will become more clear from the following discussion of a novel process for manufacturing the winged dental bridge and preparing the abutment teeth, which process is illustrated in logic diagram form.
Before taking an impression of the portion of a patient’s mouth where the bridge is to be installed, the abutment teeth must first be prepared. With reference to FIGS. 1 and 2, which illustrate a cast of a patient’s mouth after the preparation has been accomplished, it will be seen that preparation of the abutment teeth involves the cutting of the lingual surfaces to form reduced or shaved areas which are contoured and dimensioned to receive the wings and of the bridge framework. Tooth preparation for the winged dental bridge is predominantly a lingual surface preparation with a slight proximal extension. The basic outline form resembles a half-watermelon and encompasses appoximately one-half of the lingual surface of each abutment tooth from the mesiolingual transition angle to the distolingual transition angle.
A 379-
To increase general retention and resistance form, a horizontal groove 44 about
Following preparation of the lingual surfaces of the abutment teeth 24, an impression is taken of the patient’s mouth and a first cast is created utilizing standard techniques. The resultant cast structure is illustrated in. 1 through. Before fabrication of the dental bridge is begun in connection with the cast, the tissue areas on the cast are trimmed so that all margins are visible. Preferably, these margins are outlined using an indelible pencil. A saddle area is scraped with a knife approximately three pencil scrapings, and any undercuts are blocked out.
Next, a separator is applied by means of a brush to all surfaces of the cast which are likely to come into contact with the bridge framework. These areas include the saddle area and all shaved areas 38 on the lingual surfaces of the abutment teeth. Preferably, the separator is a silicone or latex based, semi-tranparent separator which has been thinned to leave a very thin layer of separator only on the cast. Use of a lacquer thinner to thin the separator has been found to be acceptable. After the separator is applied to the cast, it is allowed to dry approximately twenty minutes.
Following application of the separator to the cast, a flexible, translucent, highly polishable resin (resin #1) is placed over the separator
After the #1 resin is applied to the saddle area, a #2 resin 58, which is acid-etchable, is applied to the cast to create a labial surface and body of the pontic portion of the bridge framework, and attachment surfaces for the wings. The etchable resin may overlie a portion of the polishable resin previously applied to the saddle area, and a sufficient amount of the etchable resin (#2 resin) is applied to cover all of the preparation areas of the cast and fill the center of the pontic portion. Preferably, the etchable resin is a composite comprising, in approximate percentages, 44% acid-etched, semiporous glass filler, 35% submicron (0.04 u) silica, 16% Bis-GMA, 5% diluent monomer, 0.05% CQ, 0.5% amine and 0.4 percent hydroperoxide. Both the #1 and #2 resins are manufactured by BISCO, Inc. of Downers Grove, Ill.
Next, the polishable resin (#1 resin) is applied as a laminate over the etchable resin (#2 resin), to entirely cover the lingual surface of the etchable resin. With the polishable and etchable resins applied as described to the cast, the basis for the bridge framework has been formed, but it exists in an uncured state. The polishable resin (#1 resin) preferably has a depth of approximately
The next step in the process for preparing the novel winged dental bridge 20 is to cure the composite bridge framework, wherein at least a portion of the curing of the bridge framework is accomplished with the bridge framework mounted to the cast. For this purpose, as illustrated best in FIGS. 9 and 10, the cast with the uncured bridge framework applied is placed within a pressurized chamber apparatus. This pressurized chamber apparatus includes a base having an inlet fluid passageway and an outlet fluid passageway. Overlying the base is a transparent dome which is threaded, at its lower end, to a retention flange. An 0-ring is interposed between the base and a lower portion of the dome to form an air-tight seal between the base and the dome.
The retention flange includes a plurality of keyways which are dimensioned to pass over the heads of bolts secured in the base, in order the lock the dome in place onto the base. The inlet fluid passageway is connected to a nitrogen gas source, and a valve and a pressure gauge are provided in the line between the base and the nitrogen gas source, in order to allow a user to monitor and control the introduction of nitrogen into a chamber 88 defined between the base and the dome. Further, an outlet valve is provided adjacent to the outlet fluid passageway, to provide a means for purging air within the chamber.
The uncured bridge framework applied to the cast is placed within the chamber for purposes of an initial cure of the resin composite materials. Both the inlet and outlet valves are opened, and nitrogen from the nitrogen gas source is injected into the chamber 88. Once the air originally in the chamber has been purged, the outlet valve is closed, and the chamber is pressurized with nitrogen gas to approximately PSI. The bridge framework is illuminated with white light through the dome to effect a light cure of the bridge framework s applied to the cast, for seven minutes in the pressurized nitrogen environment.
Following this initial light/pressure curing step, the partially cured bridge framework s removed from the cast and placed within an oven to further cure the bridge framework under heat for seven minutes at approximately 130° C. Preferably, the oven is provided with tranparent walls which permit observation of the curing bridge framework, and also permit the bridge framework to be illuminated with white light for further light curing thereof.
After the bridge framework has been cured as described, the labial surface of the pontic is contoured in a standard manner to receive the veneer. The contour is shown generally. The bridge framework is secured to the cast using a sticky wax, and then an impression is taken of the cast and the bridge framework. A second cast is then made, and a porcelain veneer is fabricated, utilizing standard techniques, for application to the pontic of the bridge framework. The porcelain veneer rovides a rigid and aesthetically pleasing outer surface for the dental bridge in the pontic area, and is preferably designed to provide a hard bite surface.
With fabrication of the veneer complete, the internal surfaces of the veneer are etched utilizing a hydroflouric acid. Similarly, all of the areas of the bridge framework to be bonded to either the veneer or the abutment teeth are also acid-etched with a hydroflouric acid. The acid agent used is a 7% gel agent which is applied for thirty seconds and then brushed off using water. On the bridge framework, those portions to be attached to the veneer or the abutment teeth generally comprise the exposed surfaces of the etchable resin (#2 resin). Before installing the bridge, the surface areas of the polishable resin are all polished to provide a smooth lingual surface for the dental bridge, as well as a smooth surface between the bridge and adjacent gingival tissue. A cross-section of the pontic is illustrated.
Following completion of the above-listed manufacturing process steps, the winged dental bridge is ready for installation into the mouth of the patient. This is accomplished by affixing the wings and of the bridge framework to the shaved areas 38 on the lingual surfaces of the abutment teeth, by bonding the labial, etched surfaces of the wings directly to the prepared abutment teeth. Once the bridge framework 22 has been secured in place between the abutment teeth, the hard (porcelain) veneer is then attached to the labial surface of the pontic of the bridge framework. A dental composite resin cement such as found in the INSURE resin cement kit by Cosmodent, is preferably utilized in attaching the veneer to the pontic portion. The dental composite resin cement may be colored, if necessary, by the dental professional during installation in order to match the final color of the veneer when fixed to the pontic, to the color of the abutment teeth. This provides a significant advantage over prior dental bridges, by permitting the dental professional to fine tune the final color of the dental bridge at chairside.
From the foregoing it should be appreciated that the improved winged dental bridge of the present invention incorporates the advantages of a flexible composite bridge framework with the superior aesthetics of a hard porcelain veneer for the replacement of an anterior tooth. The bridge framework s capable of withstanding class 1 mobility without fracture. This is accomplished, at least in part, through the unique process of heat, light and pressure curing of the composite resin materials. Since no metal is used, there is no compromise of aesthetics due to “shine-through.” The two-phase placement technique eliminates pontic over contouring, permits conservative tooth preparation and allows chairside control of the pontic shade. Bonding of the bridge framework and the veneer is accomplished utilizing conventional light-cured resins. In some cases, the procedure does not require anesthesia and is accomplished in substantially less time at chairside than other crown and bridge procedures.
Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited, except as by the appended claims.
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.
2. 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
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.
Dental Bridge or Pontic or Fixed Bridge or Fixed Partial Denture is a custom-made fake tooth or false teeth or prosthetic device used to replace missing teeth, that is permanently placed between your natural healthy teeth or dental implants. Usually two tooth crowns (tooth caps, “caps”) are holding it in place that are cemented onto your teeth on each side of the false teeth. These two anchoring teeth are called abutment teeth.
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.