Clinical questions of the application of dental bridges

Clinical questions of the application of dental bridges.

Indications and clinical and laboratory stages of manufacture stamped-soldered dental bridges.

Kennedy Classification

In 1923, Kennedy devised a system that became popular due to its simplicity and ease of application. A tremendous number of possible combinations can be reduced to four simple groups.

Class I – bilateral edentulous areas

located posterior to all remaining teeth.

Class II – unilateral edentulous area

located posterior to all remaining teeth.

 

 

Class III – unilateral edentulous area

bounded by anterior and posterior natural teeth.

Class IV – a single, but bilateral (crossing the midline) edentulous

area located anterior to remaining teeth

Applegate’s Rules for Applying the Kennedy Classification

Rule 1: Classification should follow rather than precede extraction.

Rule 2: If the 3rd molar is missing and not to be replaced, it is not considered in the

classification.

Rule 3: If the 3rd molar is present and to be used as an abutment, it is considered in the

classification.

Rule 4: If the second molar is missing and not be replaced, it is not considered in the

classification.

Rule 5: The most posterior edentulous area determines the classification.

Rule 6: Edentulous areas other than those determining classification are called modification

spaces.

Rule 7: The extent of the modification is not considered, only the number.

Rule 8: There is no modification space in Class

Classification of dentition defects after A.I. Betellmann.

 

 

 

 

Bridge prostheses.

      Bridge prostheses are most common category of prostheses in partial included defects of the dentitions.

      The dental arch consists of two symmetrical halves and in loss of one of them another one can take its function. It is considered that the periodontium of each tooth, because of the special reserve possibilities, is capable of maintaining dual masticatory load. The construction of any bridge-shaped prosthesis is based on this principle, when two and more crowns bear intermediate part, body on themselves, which compensates the defect of the absent tooth or teeth. When the tooth load, i.e., width of the intermediate part is more than the reserve possibilities of the periodontium of the teeth, on which abutment crowns are located, it will give arise to physiological irritation, the injury, which will lead to the teeth loosening.

      The loss of teeth on one of the jaws frequently leads to the reconstruction of the bone tissues of the alveolar processes, protrusion of the teeth- antagonists on the opposite jaw, contributing to the formation of block in the sagittal direction (Popov -Godon phenomenon). To prevent these phenomena it is necessary to make bridge prostheses as early as possible with the restoration of the lost function of the dentition.

      All bridge prostheses can be divided regarding the material into: plastic, metallic, combined. Metallic and combined dentures are also divided into: soldered (at first supporting crowns are made, then the intermediate part, later on all elements are soldered by the solder) and whole cast (at first all parts of the prosthesis are made of wax, and then wax is substituted by the metal by the method of precision casting). The soldered bridge prostheses become the thing of the past, preserving the major advantages – cheapness, easiness of construction, abrading of insignificant quantity of hard tissues of the teeth. The whole cast prostheses with the wide acceptance of precision casting and its significant development acquire greater popularity in dentists and dental technicians.

 The following postulate is the more generalized formulation of indications to the bridge prosthesis: the partial defects of the dentition when the sum of the coefficients of the masticatory effectiveness of supporting teeth according to Agapov is more or equal to the sum of the coefficients of the masticatory effectiveness of the absent teeth.

BRIDGES

 

A bridge is a permanent replacement for missing teeth which cannot be removed by the patient;  A bridge is constructed by preparing the teeth on both sides of a space so they can receive crowns.  The teeth are reduced and shaped around the outside and across the top so a crown can fit tightly over them.  Crowns are joined together to replace the missing teeth and cover the prepared teeth on each side providing support of the replacement. 

 

A bridge can be used only if there is enough strength to support the replacement teeth.  This generally means there should be as many teeth provide support as there are being replaced.  The type of replacement needed is also determined by careful evaluation of bone loss, size and shape of the tooth structure, the force which will be generated on the bridge and the strength of the remaining tooth structure.

 

INDICATIONS:

1.  Absence from 1-4 teeth before the frontal section.

2.  Absence of the 2 molars  with of distal support.

3.  Absence of the 3rd lateral teeth through one with the presence of distal support.

4. Absence of the 3rd next confronting teeth the presence of distal support (to consider the standing of supporting teeth and antagonists)

 

CONTRA-EVIDENCE:

1. Included defects with in 4-5 teeth.

2. Mobility of the teeth (atrophy of bone hole down 1/2 and more).

3 Deformations of a bite and dental numbers with the partial loss of teeth.

4. Production of cantilever prothesis in the region of molars.

Bridges

A bridge, also known as a fixed removable denture, is made to replace one or more missing teeth. Bridges can be supported in any of three ways:

By natural teeth

By implants

By a combination of teeth and implants

 

Dental Bridges

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.

Types of bridges may vary, depending upon 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.

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”.^[1]

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 a pontic, 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.

Dental bridges are false teeth, which are anchored onto neighbouring teeth in order to replace one or more missing teeth. The false tooth is known as a pontic and is fused in between two crowns that serve as anchors by attaching to the teeth on each side of the false tooth, thereby bridging them together.

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 (without teeth) 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 eithermesially 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.

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 requiringparallelism 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.

Full dental bridge being machined usingWorkNC Dental CAD/CAM software.

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.^[2] 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.

What are dental bridges?

Dental bridges are false teeth, which are anchored onto neighbouring teeth in order to replace one or more missing teeth. The false tooth is known as a pontic and is fused in between two crowns that serve as anchors by attaching to the teeth on each side of the false tooth, thereby bridging them together.

What are the parts of a typical dental bridge (fixed)?

A dental bridge essentially consists of:

·         A pontic or false tooth used to replace the missing tooth, which is made from gold, alloys, porcelain or a combination of these materials.

·         Two crowns – serving to anchor the false tooth in place.

 

When are dental bridges needed?

Bridges are recommended when there are one or more teeth missing that affect:

·         Your smile and appearance.

·         Your bite, as a result of adjacent teeth leaning into the space and altering the way the upper and lower teeth bite together.

·         Your speech.

·         The shape of your face.

·         The rate of gum disease and tooth decay as a result of food accumulated in the gap.

Must missing teeth be replaced?

Yes, missing teeth must be replaced for many reasons:

·         To improve your appearance.

·         To reduce the strain on the teeth at either side of the missing tooth.

·         To prevent the neighbouring teeth from leaning into the resulting gap and altering the bite.

·         To prevent gum disease and tooth decay due to accumulation of food in the g

There are three main types of dental bridges:

1. Traditional fixed bridge
This is the most commonly used type of bridge and consists of a pontic fused between two porcelain crowns that are anchored oeighbouring teeth or implants. The pontic is usually made of either porcelain fused to metal or ceramics. These are fixed and cannot be removed.

2. Resin-bonded bridges or Maryland-bonded bridges
These are chosen when the gap to be filled is in between the front teeth, or when the teeth on either side of the missing tooth are strong and healthy without large fillings. The false tooth is made of plastic and is fused to metal bands that are bonded to the adjacent teeth using resin that is hidden from view.

3. Cantilever bridges
These are opted for in areas such as the front teeth that are susceptible to lower stress. Cantilever bridges are used when there are teeth present on only one side of the space, where the false tooth is anchored to one or more adjacent teeth on one side.

What are bridges made of?

Bridges may be made of

·         Porcelain.

·         Porcelain bonded to precious metal.

·         All-metal dental bridges (gold).

How are dental bridges fitted?

At the first appointment:

·         The dentist will numb the area with a mild anaesthetic.

·         The teeth on either side of the space are prepared by trimming away a small area in order to accommodate the new crown over them.

·         The dentist then uses dental putty to make an impression of the teeth, which will be used to make the bridge and crown in the laboratory.

·         A temporary bridge is fitted in to protect the exposed gums and teeth.

·         A Vita shade guide may be used to determine the right shade for the dental bridge, by selecting a shade that resembles natural colour variations in your teeth, as well as suits your complexion, hair colour, the colour of your natural teeth and even your eye colour.

At the second appointment:

·         The temporary bridge is removed and the custom-made bridge is fitted, checked for its fit and bite, and adjusted accordingly. It is then cemented into place

·         Multiple visits are often required to check and adjust the fit.

·         In case of permanent or fixed bridges, the bridge is temporarily cemented for a couple of weeks and checked for its fit. It is permanently cemented only after several weeks.

How long will dental bridges last?

Dental bridges can last 10-15 years, provided that you maintain good dental hygiene and eating habits.

How to take care of your dental bridges?

Practise good dental hygiene:

·         Clean the dental bridge every day to prevent tooth decay, bad breath and gum disease.

·         Clean under the false tooth every day.

·         Keep the remaining teeth healthy, as these serve as the foundation for the dental bridge.

Brushing and flossing:

·         Brush twice and floss daily.

·         To floss, use a bridge floss threader, which is a flexible piece of plastic with a loop at one end to thread the floss.

·         Thread one end of a 14-to-18-inch piece of dental floss through the loop, making sure to leave one side about half as long as the other.

·         Insert the end of the flosser without the hole between the bridge and the gumline.

·         Hold onto the longer piece of floss, gently bring it up and pull the pointed end all the way through.

·         Floss using both hands, moving the floss back and forth under the bridge.

·         Floss the bridge completely from one end to the other.

Diet and eating habits:

·         Eat soft foods or food cut into small pieces until you get accustomed to the dental bridge.

·         Eat a balanced and nutritious diet for good general and dental health.

What are the advantages of dental bridges?

·         They are natural in appearance.

·         They generally require only two appointments with the dentist.

·         They have a good life period, lasting for 10-15 years, providing you maintain good dental hygiene.

·         They improve your appearance, bite issues and speech problems occurring as a result of missing teeth.

What are the disadvantages of dental bridges?

·         Teeth become mildly sensitive to extreme temperatures for a few weeks.

·         They require healthy tooth tissue from neighboring teeth to be prepared.

·         Your teeth and gums are vulnerable to infection as a result of accumulation of bacteria due to the food acids (if proper hygiene is not maintained).

Parts of Dental Bridges

1. Crown: It is a cemented extra coronal restoration that covers the surface of underlying tooth and the part that the crown has to cover is the length of clinical visible tooth structure and the main part is the coronal part of it. This serves as the function of restoring and protecting the underlying tooth structure and to maintain the outer appearance perfect.

2. Abutment: When the Dental Bridges are to be placed the support is required from the near by teeth and these are considered as the abutments in Dentistry.

3. Pontic: The artificial tooth in Dental Bridges that replaces the missing tooth. These Pontics are attached to retainers and the forces that act in various directions on Dental Bridges are transferred by the Pontics to Abutments through the passage of Retainers.

4. Connectors: This is the connection between the pontic and retainer in the Dental Bridges and these are the flexible and flexible one. The nonflexible are immovable attachments between the pontic and retainer and on the other hand flexible are the one having movable attachments with a key-keyway mechanism and these are the mainly stress breakers.

Materials frequently used in bridges include:

Full gold alloy bridges: While these are not that common anymore, it is possible to cast and cement solid gold bridges. Composed of a combination of gold, copper and other metals, these materials are tough and strong. They are highly resistant to tarnishing, corrosion, fracture and wear. These materials do not tend to require as much removal of healthy tooth material as other bridge materials. They are gentle to the nearby teeth and are well tolerated by patients. However, many patients do not like the metallic gold color.

Base metal alloys: These materials are composed of a combination of base metals and are quite tough. They are highly resistant to fracture, wear, tarnishing and corrosion. However, they have a metallic silver color that many patients do not like. Sometimes they may also cause an allergic reaction or initial discomfort with hot and cold in some patients.

Porcelain Dental Bridge: These are composed of porcelain, ceramics or glasslike materials. These materials have a color and translucency that closely matches natural teeth, and highly recommended by cosmetic dentist abroad and in India They are also highly resistant to wear. However, they may become prone to fracture eating very solid foods and can wear dowearby teeth if the porcelain surface becomes rough.

Porcelain fused to metal (PFM): These are more commonly sought teeth bridges at dental clinics in India, and have the added advantage of having a metal substructure for rigidity and marginal fit. The combination is composed of porcelain crown bonded to a metal base.  It is strong and durable and highly resistant to wear. However, it can wear dowearby teeth if the surface of the porcelain in PFM Bridge becomes rough due to more solid foods. It may also cause an allergic sensitivity or initial discomfort with hot and cold in some patients.

Composite resin: This material tends to be relatively inexpensive and looks like natural teeth. However, since these are composed of a type of composite plastic, it may stain more readily than porcelain. This material is not as strong or durable as porcelain, but also does not excessively wear dowearby teeth. These materials or combinations of these materials can be used to produce many different types of bridges.

There are three types of dental bridges regularly made available.

1) Bonded (Maryland) dental bridges uses the adjacent teeth to help support the bridge. The resin bonded is primarily used for your front teeth. Less expensive, this bridge is best used when the abutment teeth are healthy and don’t have large fillings. The false tooth is fused to metal strips that are bonded to the abutment teeth with a resin which is hidden from view. This type of bridge reduces the amount of preparation on the adjacent teeth. This is achieved by bonding a very thin piece of metal or tooth-colored material to the back of the adjacent teeth, which holds the replacement tooth in place. Bonded bridgeworks depend on the strength of the bonding, and unfortunately one out of four bonded bridges comes off within the first five years. However, the advantage is that there is no damage done to the adjacent teeth.

2) Cantilevered dental bridges are recommended by dentists when there are only teeth on one side of the gap. It takes one adjacent tooth to support the bridge and can work similar to bonded bridges, by attaching a piece of material to the back of the tooth, but typically involve using a full crown to support the missing tooth. These are used only in areas of your mouth that are under less stress, such as your front teeth. Cantilever bridges are used when there are teeth on only one side of the open space. This procedure involves anchoring the false tooth to one side over one or more natural and adjacent teeth. The traditional bridges have a crown on either side of the pontic, while in contrast the cantilever bridges consist of two side-by-side crowns and only one is connected to the pontic. By using a crown these bridges last much longer than bonded bridges, however they do affect the adjacent tooth because it has to be grinded down in order to place the crown.

3) Conventional dental bridges procedure is used to replace one or more missing teeth. Conventional bridges utilise crowns on the existing teeth at each end of the gap with an additional tooth hooked together to support the replacement tooth. A false tooth known as a pontic is fused between two crowns to fill in the area left by a missing tooth. These two crowns hold it in place that is attached onto your teeth on each side of the false tooth. This is known as a traditional fixed bridge. Fixed bridges cannot be taken out of your mouth as you might do with removable partial dentures. This is usually the bridge of choice when the adjacent teeth already need to be crowned for other reasons.

Dental Bridge Work Process

Dental bridges usually require two or more trips to the dentist’s office listed. A bridge is a type of indirect restoration. Before a bridge can be created and placed, a patient needs to have an initial consultation and evaluation by a general dentist or a prosthodontist at the chosen dental clinic India. This will include a dental examination and a medical and dental history. During the initial visit, the surrounding teeth are numbed with a local anesthetic. The dentist prepares the surrounding teeth by cleaning any plaque or decay that remains and reducing them so that the dental crowns can be fitted. The dentist makes a mold of the teeth and sends it off to a dental lab, where the customized impression is prepared. The customized mold takes one to two weeks to return to the office. In the interim, patients are fitted with a temporary dental bridge constructed of acrylic resin. When the patient returns to the dental office, the dentist removes the temporary dental bridge and replaces it with the permanent one. The dentist then adjusts the dental bridge for the proper bite and fit, and the dental bridge is permanently bonded into the mouth.

 

What are the parts of a typical dental bridge (fixed)?

A dental bridge essentially consists of:

§                     A pontic or false tooth used to replace the missing tooth, which is made from gold, alloys, porcelain or a combination of these materials.

§                     Two crowns – serving to anchor the false tooth in place.

 

 

When are dental bridges needed?

Bridges are recommended when there are one or more teeth missing that affect:

§                     Your smile and appearance.

§                     Your bite, as a result of adjacent teeth leaning into the space and altering the way the upper and lower teeth bite together.

§                     Your speech.

§                     The shape of your face.

§                     The rates of gum disease and tooth decay as a result of food accumulated in the gap.

Must missing teeth be replaced?

Yes, missing teeth must be replaced for many reasons:

§                     To improve your appearance.

§                     To reduce the strain on the teeth at either side of the missing tooth.

§                     To prevent the neighbouring teeth from leaning into the resulting gap and altering the bite.

§                     To prevent gum disease and tooth decay due to accumulation of food in the gap.

 

There are three main types of dental bridges:

Dental Bridge Type 1 — Fixed Bridges (Traditional)

Your dentist prepares the neighbouring teeth (abutments) in order to hold the false tooth (pontic). The false tooth is fused afterwards to the other teeth (abutment crowns). Or to put in another way: it is fastened securely to the teeth or implants next to it. The place where it can be used is not limited, good for replacing either front teeth or back teeth (molars).

This type of bridge can be made of metal, ceramic or a combination of those two – though generally porcelain fused to either metal or ceramics.

Advantages of Fixed Bridges

• Possible alternatives to  dental implants, mostly because they are moderately less expensive

• They last around 10-15 years the longest amongst bridges.

Disadvantages of Fixed Bridges

• There is only a subtle difference in the price between this type of bridge and dental implants.

• Keeping good oral hygiene could be more challenging  and possibly require new habits of cleaning under this type of dental bridges

• Due it is fixed position, it cannot be removed.

• As dental work is needed on the teeth nearby, they may be more delicate temporarily. In some very rare cases the abutment tooth becomes eventually requiring a root canal treatment though only if a severe toothache is present

Dental Bridge Type 2 — Maryland Bridges (Resin Bonded)

This type of bridge is typically used for replacing front teeth as they do not require extensive dental work done on the neighboring teeth. Also it is especially recommended if there is no harm done to the teeth either side of the gap. Another reason why it is more suitable for front teeth is that pressure is smaller in these areas and the binding can be made hidden at the rear of the adjacent teeth.

Commonly the false tooth (pontic) is created by fusing plastic with metal and it is attached via metal wings to the inside wall of the neighboring teeth using resin.  This type of bridge can be made of metal, ceramic or a combination of those two – similarly as the previous type.

Advantages of Maryland Bridges

• Bridges can be made faster as for traditional bridges less clinical and lab time is necessary. It can be cheaper in this manner, especially in places dedicated to dental tourism.

• Because of nearly no preparatory work needed of the neighboring teeth, they can be literally untouched. Therefore your teeth can be preserved for longer period of time.

• They can be easily adjusted and fitted

• Less impact on the surrounding teeth

• No need for a local anaesthetic shot

Disadvantages of Maryland Bridges

• Generally unsuitable for back missing teeth (molars).

• The chance of the dental bridge falls off is greater than conventional bridges.

• They last around 5 years maybe longer.

• It could be more expensive than a conventional bridge because of the fitting and the skill required to accommodate a Maryland Bridge they are generally cost more than a normal bridge. 

 

Dental Bridge Type 3 — Cantilever Bridges

It comes down to cantilever bridges when only one tooth (abutment) is available to support. The false tooth (pontic) is then anchored to that tooth (sometimes more) on one side of the gap only. However, it is only appropriate for teeth having little strain such as the ones in the front or more ideally the lower front teeth. These can be made of metal, ceramic or a combination of those two – alike previous types.

Advantages of Cantilever Bridges

• Most of the cases it is less expensive than conventional bridges as less clinical time and lab time is required (similarly as Maryland bridges)

• It is a preferred option as opposed to dentures as cantilever bridges are fixed.

• Keeping good oral hygiene is effortless comparing to the traditional bridges.

Disadvantages of Cantilever Bridges

• As some dental work is needed on the teeth nearby, they may be more delicate for temperature changes temporarily.

• It can be applied only to a limited area (typically front lower) and may be not suitable for all dental needs.

                                                                              Before Dental Bridge                        After Dental Bridge 

 

Stamped-soldered dental bridges

Stamped solder-prostheses are made of base (stainless steel + silver Cadmium free solder) and precious alloys (an alloy of gold 900-carat, gold alloy 750 standard (“Super TK”), silver-palladium alloys PD 190 and PD 250 + gold Cadmium free solder 750-carat “Superbekam”

The figure schematically presents the construction of the soldered bridge prosthesis constructed from the stainless steel, on which three sections are isolated: crown 1, solder 2 and the cast intermediate part 3 of the dental prosthesis.

      The case, from which the crown 1 was constructed, was stretched and then swaged. The artificial teeth 3 were obtained by casting. The place of junction between the crown 1 and intermediate part 3 was filled with the solder 2; therefore the structure of all sections was not identical. The most unsatisfactory of three sections indicated is the solder.

      The solder testing as to the strength of junction of the soldered parts carried out in the Research Institute of nonferrous metallurgy as early as the 30s showed that the solder possessed satisfactory mechanical properties, although it was unstable to the effect of even weak acids.

      At the same time the literature data analysis of the results of experimental studies and clinical observations on the study of effect of different solder alloys on the biological medium, gives grounds to assert that the solder does not meet the requirements, to the dental prostheses, which are in the biological medium, as to physicomechanical properties.

      The main drawbacks of the solders are their low stability to the corrosive destruction in the oral cavity, electro-potential difference with the soldered metals, as well as change of the structure of the soldered metal during the process of soldering.

      This specifies a number of the positions, which have a negative nature.

      1. There is a formation of metal oxides in the oral cavity of people using soldered prostheses of chromium nickel steel. Depending on the nature of saliva, composition of other metal ware, being in the oral cavity (prostheses, metallic fillings, inlays) as well as individual peculiarities of the organism, the formation of oxides may have the more or less expressed character.

      Blackening of the sites of soldering or presence of the sharply outlined spots on the steel prosthesis surface is evidence of the presence of such oxides. In this case a quantitative increase of the microcells in the saliva and the formation of salts of heavy metals are noted in the oral cavity of people using such prostheses, which adversely affects the secretary function of the stomach. The mechanism of effect of metal oxides on the organism during the electrolytic dissociation in the oral cavity is still studied insufficiently; however, their nonphysiological state is completely obvious and incompatible with the principles of preventive medicine.

      2. The pathologic state, which was called the phenomena of galvanism, develops in the oral cavity of those, who use soldered prostheses, which are associated with a potential difference and can appear both in presence of different metals or alloys and as a result of heterogeneity of one alloy.

 Both factors, which specify a potential difference, can develop in presence of soldered bridge prostheses, since these prostheses consist of different alloys – chrome-nickel steel and solder, and the structure of each of these alloys acquires heterogeneous nature during the process of their manufacture.

 While conducting the metallographic examination of the soldered bridge prostheses of chrome-nickel steel, it is revealed that even during thorough observance of technology along the contact line there are many nonsoldered sections. There are micropores in the layer of solder dividing them. Although the decrease of the thickness of the solder layer provides more durable junction of the soldered parts, however, it does not improve the alloy structure at the site of their junction, but in this case a quantity of micropores in the solder layer even increases. The two-phase structure of steel is observed both in the crown and in the intermediate part. There are sections of metal with the precipitation of chromium carbides on the margins of the metal grains.

 It is impossible to improve the alloy structure by heat treatment (recrystallization), since the prosthesis should be heated to the temperature of 1, 000-1,1000C, and this will lead to deformation and separation of its parts.

 But if we examine the clinical stages of construction of swaged-soldered prostheses, they included up to 5 visits of the patient to the dentist:

 1 visit: Preparation of the teeth and taking of the impressions for constructing the swaged – soldered crowns.

 2 visit: Fitting of the swaged crowns and their trimming as well as taking of the impressions for constructing soldering of the intermediate parts of the prosthesis (cast teeth).

 3 visit: Fitting of the unpolished swaged – soldered constructions of the bridge prostheses and their trimming.

 4 visit. Fitting of the polished swaged – soldered constructions of the bridge prostheses and constructions with their subsequent fixation.

 5 visit. In spraying of the dental prostheses – the prosthesis construction takes from 20 to 30 days.

Thus, analyzing the aforesaid it is possible to make the following conclusions, namely:

 1. At present the swaged crowns and soldered bridge prostheses do not meet the necessary modern requirements as the methods of swaging do not ensure the precise construction of the crown.

 2. Presence of different alloys and metals in the soldered bridge prosthesis leads to the phenomenon of galvanism in the oral cavity.

 3. Breakdown occurs very frequently at the site of soldering of the dental prosthesis elements.

 4. The technical process of construction of different elements of the swaged- soldered dental prosthesis provides for the use of the strong acids.

Stamp-soldered dental bridge with facet intermediate part – non-removable orthopedic construction that is used for replacement of included defects in the frontal and lateral areas. Structurally it consists of metal or combined metal acrylic crowns (by Belkin or Borodyuk), between which is placed the intermediate part, lined with plastic (standard or cast individually). It is more aesthetic than integrally-metal, so has wider indications for the use. However, it is necessary to remember that the crown by Belkin is structurally weaker than the metal, and the crown by Borodyuk has worse fixation. Therefore, with the large size of the gap between abutment crowns should be preferred the metal. Veneering of the intermediate part can be accomplished only from the vestibular surface, from the vestibular and chewing or completely from all surfaces. The degree of veneering is dictated by aesthetic requirements and the need to reduce the pressure of chewing on the abutment teeth and teeth-antagonists due to the fact that plastic has a lower specific mass and lower hardness than metal. However, the plastic chewing surface is quickly erased that smooth its relief and reduce interalveolar height. Therefore, this feature should be considered in orthopedic treatment of excessive abrasion of teeth and deformations of bite. On the other hand, the plastic chewing surface is easy to correct to the downside and to the upside of interalveolar height that can be used for gradual normalization of interocclusive relations.

After the end of teeth preparation imprints are removed from both jaws. One of them is working, the other – subsidiary, may be working both. Working imprint must clearly display the teeth, their cervix, cutting edges and chewing surfaces, alveolar portion in defect area. Supporting imprint should contain imprints of the dentition, especially cutting edges of the front and chewing surface of the side teeth. With getting imprints is completed the first stage. According to the imprints are cast models, they are made up in the position of central occlusion according to peculiarities specific to each type of bite, or using wax patterns. When the central occlusion is known, the gypsum models are fixed in such position by binding with thick thread or clueing using a match, filling them with boiling wax.

Models are fixed in occludator, moreover the top model is fixed to the upper arch, and the lower – to the bottom. Remnants of gypsum are cut from the models so that the pin of occluder height would bear against the area. After preparing of models the gypsum is mixed, it is placed on a smooth surface and immersed in it the lower frame of the occluder. Then is added a small layer of gypsum and fixed model are situated on them. With the spatula the gypsum is smoothed down, and then layers of gypsum are put on the model of the upper jaw and lower the upper frame of the occluder. After hardening of gypsum its remnants are removed, the thread is taken, the occluder is opened and the modeling of the dentures begins. Then are made modeling of stump of all abutment teeth, manufacture of imprints, gypsum and metal, stamping of abutment crowns. This concludes the first laboratory stage. Crowns are sometimes bleached, preferably in black form are sent to the hospital, where they conclude the second or third clinical stages. The last consist of fitting the abutment crowns, testing the central occlusion and getting the imprint along with crowns for the manufacture of intermediate part of dental bridge. After receiving the imprint are taken all the basic bits and sent to the laboratory.

If the imprint is of gypsum, it is carefully collected and glued together. When gluing the imprint, the crowns are carefully established in its bed, watching that closely adjoiot only to walls, but also in the region of the cell. Wax is not poured into the crown only when the crown is lined. Model is cast and spared from pieces of imprint, compared with the model of antagonist jaw and plasterer in the occluder. After fixation in the occluder proceed to model the intermediate part of dental bridge.

The space between crowns is filled with roller made ​​of wax. Roller should be a little bit taller and wider than the crown. The roller is installed; the models are closed, allowing getting the imprint of antagonists on the roller. From the roller with the trowel are modeled teeth, then it is marked according to the number of missing teeth, and is started the modeling of each tooth, creating the appropriate anatomical shape on the vestibular and chewing surfaces for premolars and molars for and vestibular, cutting and oral surfaces for front teeth. When the side of the crown, facing the defect, is of small height, from the body of dental bridge on the tongue side of the crown should be taken the process. This helps to increase the surface of connection the crown with the body of the bridge. Technician in modeling of the crown does not model the chewing surface – it is formed when modeling the intermediate part and is poured together with crown. Thus there is a combination of metal with the crown.

From the point of view the hygiene to dental bridges are imposed special requirements. Very important is the form of intermediate part of the bridge and its relation to surrounding tissues of dental bed – mucosa of toothless alveolar process, lips, cheeks, tongue. In the tactile form, the absence of pressure on the mucosa is checked with probe. If its tip is easily injected under the body of the bridge, this means that the pressure on the gums is absent and at the same time there is no visible crack, which has unaesthetic look during smile or conversation. Wash space is enough large, especially on the lower jaw, approximately on the thickness of a match. On the upper jaw the wash space is a little smaller than on the lower, and in the area of ​​premolars and canines it can be built deep into the contact with mucosa. After modeling the vestibular, chewing and masticator surfaces, begin to design the parts directed to the gums. For this with the sharp trowel is cut the bridge at an angle to the vestibular surface departing from the place of transition of the chewing surface into the tongue of 2-4 mm. Then, when the wax is cooled, it is removed from the model. On cross-section the form of intermediate part of the bridge resembles a triangle.

Then begins the casting process for getting metal parts. This process involves a series of successive operations:

•manufacture of wax models of parts;

•installation of sprue making pins and creation of gating system;

•covering of models with fire-resistant layer;

•formation of the model with fire-resistant mass in muffel;

•melting of wax;

•drying of form;

•melting of alloy;

•casting of alloy;

•liberation of parts from fire-resistant mass.

All wax compositions and alloys during the transition from liquid to solid stage are reduced in volume, i.e. shrink. Shrinkage of alloys is compensated with special compensating masses with double coefficient of expansion. Shrinkage of wax compositions is reduced by the formation of compounds with the introduction of carnauba, montanic and other types of wax.

Before soldering, for fixation of the bridge is required plastering. For this is applied gypsum with the addition of pumice, marble dust, sand. For plastering steel bridges, Citrin mass is used sometimes. The bridge is dipped in a small amount of fire-resistant mass with upper and chewing surfaces down. Crowns are filled with mass and is cover the inside surface of the cast teeth, leaving open the places of soldering. Then begins the process of soldering. Soldering – a connection of metal parts by heating a homogeneous alloy with a low melting point. Connecting alloy is called solder.

Solder must meet the following requirements:

•have a melting point lower than in base metals on 50-100 degrees;

•well spill;

•well penetrate into the thickness of base metals ;

•be resistant to acids and alkalis;

•match base metals with color;

•be resistant to corrosion;

•do not give shells and blisters.

Depending on the density and melting point, solders are divided into soft and hard. When soldering the connecting parts are solid and solders are molded. The metal surfaces to be soldered should be cleaned of oxides and contaminants, for which is used mechanical method of cleaning. Since the soldering takes place during heating in an open fire, on the surface of metal can be formed oxide cover that prevents the diffuse of solder.

Therefore it is necessary to counteract the formation of oxide cover to the moment of reaching operating temperature. This is achieved by using different soldering materials, or fluxes. The largest spread has got borax. When heated the borax absorbs oxygen, thereby preventing it from getting to the metal and the formation of oxides on its surface. After soldering, the denture bridge is immersed with molding mass into cold water, cleaned from fire-resistant mass, bleached and washed in boiling water. Then start grinding and polishing.

 

For whitening products are immersed in the boiling solution and boiled for about 1 minute. Then the bridge is removed from the solution, washed with water, cleaned of scale. After bleaching the bridge is grinded with various circles, bevels, hard and soft brushes. Then polished using a variety of pasta, depending on the material from which dental bridges are made. Facet intermediate part is modeled of wax and then replaced with plastic. After polishing the bridge is washed with water and soap and sent to the clinic for applying and fixing the bridge in the mouth cavity.

In the past, present, and also in the future, “soldering” as a joining technique has been and will be an important part of dental-lab procedures. Soldering is the most frequently used joining technique for metals. In order to obtain a soldering joint, the necessary materials must be processed with utmost care. It also involves thorough

knowledge of the materials and their correct technical application. Nevertheless, the ultimate objective of the users should be to work in such a way that joining metals is largely unnecessary.

The ancient Egyptians melted gold and used the material to fabricate beautiful artifacts as testimony to their sophisticated culture. Soldering has also been practiced

since the earliest days of history. The soldering technique of those days involved copper ore and helped goldsmiths fabricate the finest jewelly.

In dentistry, soldering has been used for more than 100 years.

 

Given its universal application possibilities in dental-lab technology, soldering has not lost its importance despite modern welding techniques and adhesive procedures. In dental laboratories, the number of daily soldering procedures still clearly exceeds that of other joining methods.

Soldering is a procedure to join metal components with the help of a molten joining metal with a processing temperature below the solidus temperature of the alloys to be joined. The solder wets these alloys without melting them during soldering.

During the soldering procedure a reciprocal diffusion between the liquid solder and the solid-hot alloy takes place.

 

Solders

Given the required resistance to the oral environment, only hard solders are used in dental-lab technology. Depending on the designated use, solders are classified as high-fusing solders with a processing temperature of approximately 950–1,200 °C / 1742–2192 °F and low-fusing solders with a processing temperature of approximately 700–900 °C / 1292–1652 °F. A high fusing solder should always be selected first. To allow additional repair procedure to be accomplished with a flow fusing solder. A solder with the correct processing temperature is selected according to the alloys to be soldered. Dental solders must be corrosion resistant and demonstrate a composition similar to that of the alloys to be joined.

The solder and alloy must be compatible with each other. Please refer to the solder table in the Appendix for recommended solder / alloy combinations. Metallurgical compatibility and similar coefficients of thermal expansion of solders and alloys are the prerequisites for the ideal solder joint.

A solder with the correct processing temperature is selected according to the alloys to be soldered. Dental solders must be corrosion resistant and demonstrate a composition similar to that of the alloys to be joined.

 

 

Surface Tension / Diffusion

Good wetting of the alloy with the molten solder is a prerequisite for a successful soldering procedure.

Good

Not good

With optimum wetting, the solder spreads out evenly over the alloy, wets both

surfaces, and fills the soldering gap. The formation of droplets by the solder is a

sign of poor wetting. As a result, the solder does not flow and diffusion does

not occur.

Diffusion refers to the process in which certain metals of the alloy and the solder are mixed. A diffusion structure is formed at the interface. A sufficiently high temperature of the framework elements to be joined by soldering is required for good flow behaviour and optimum wetting. The temperature at the soldering site must

be higher than the processing temperature of the solder, but must not exceed the solidus temperature of the alloy.

 

 

Solder Joint

 

Good gap

 

 

A “solder gap” is an even distance of 0.05 to 0.2 mm between the framework

elements to be joined by soldering. For that purpose, the soldering surfaces must be parallel.

Not good gap

Wider gaps are not suitable. During cooling, the solder contracts more than the soldering base and the framework element expand during heating. This is due to a solidification shrinkage of the liquid solder. The consequences are torsion of the

framework elements, inadequate flow of the solder and solder joint crack.

To maximize the capillary effect, framework elements should be parallel to one another with the recommended gap between parent alloys.

Oxidation

 

Soldering requires heating of the alloy, which always results in oxidation. Oxidation is a reaction with oxygen. It occurs in all the alloys. The higher the base metal content, the more pronounced is the oxidation.

In order to prevent oxide formation, an appropriate flux may be used.

The flux breaks down the oxygen compound of the alloy surface. During this dissolution procedure, the oxides are absorbed by the flux and protect parent alloys from further oxidation. A non contaminated surface then enables optimum wetting by the solder.

Soldering Accessories

The prerequisites for a sound soldering procedure are as follows: clean metallic

surfaces, a flux that will dissolve the oxides, framework elements that have

been evenly preheated to the processing temperature, and a soldering gap

(0.05–0.2 mm) with walls as parallel as possible.

High-fusing Bondal™ Flux

Flux for solder with a high processing temperature: > 960 °C (soldering before ceramic firing)

Bondal™ Flux

Flux for solder with a low working temperature: < 900 °C (soldering after ceramic firing and for universal solders)

 

Magic wand

A torch system with a safety valve enables controlled flow of gas and oxygen during the soldering and casting of alloys.

Torch and Flame Control

For dental soldering procedures, mainly propane torches with compressed air or

oxygen are used. 

The correct setting of the flame, oxygen/propane or air/propane mixture, and the selection of the burner nozzle/ burner head are critical for reliable soldering.

Multi-orifice torches produce a large, soft flame. In conjunction with a propane-compressed air mixture or a propane-oxygen mixture, these torches are suitable for even heating of the object to be soldered.

Single-orifice torches produce a pointed, hot flame of up to 2900 °C/5252 °F in

temperature. A propane-oxygen mixture enables spot soldering without excessively heating up the surrounding areas.

 

Surface Preparation

Clean soldering contact surfaces are a basic requirement for optimum wetting.

The surfaces of the soldering contact areas have to be prepared by grinding and/or sand blasting.

Evenly roughen the soldering contact surfaces in the direction of flow of the solder using a suitable (ceramic-bonded) grinding instrument.

The soldering contact surfaces may also be blasted with 50 micron Al2O3.

The soldering contact surfaces should have dimensions adequate for the intended stress bearing situation.

Pre-Soldering

(Before Ceramic Firing)

Once the surfaces of the framework elements to be soldered are prepared, the individual components are placed on the model and secured.

The soldering gap is filled with wax and the individual framework

elements joined using modelling wax, sticky wax, or modelling resin.

Important: Use low shrinkage materials that fire without leaving residue to secure the

components.

The individual framework elements must be secured in an absolutely stress-free manner and then lifted off the model. Design the soldering base as small as possible and with rounded edges. Too large a soldering block withdraws heat from the soldering object. The soldering gap must be freely accessible from all sides so that the flame can reach it. Only in this way can the framework elements be evenly

heated.

Once the soldering investment has set, remove the sticky wax with steam or hot water. Burn out the modelling resin in the pre-heating furnace. Pre-heat the soldering object in the pre-heating furnace at approximately 600 °C/ 1112 °F) for 10 minutes.

Apply flux to the soldering gap and evenly heat the object to be soldered to the

processing temperature of the solder using the torch.

Once the working temperature of the object to be soldered has been reached as a result of the heat from the flame being applied to the exposed soldering contact surfaces, the solder quickly and reliably flows into the soldering gap and fills it.

Allow the solder joint to cool slowly. Remove the soldering investment. Blast the object with 50 or 100 micron Al2O3 to remove oxides and flux residue. Instead of

blasting precious metal alloys can be pickled (PCT AScid).

Carefully grind the soldering site and prepare it for the subsequent veneer.

Post-Soldering

(After Ceramic Firing)

A basic requirement for functional furnace soldering is the correct design of the framework. The connecting area must demonstrate adequate dimensions.

The soldering surfaces act as heat centers, towards which the solder can flow. The smaller the alloy surface in the heat center, the more difficult it is for the solder to flow into the soldering gap. The soldering gap should be 0.05 mm to 0.2 mm.

Secure the ceramic veneered bridge components using a stress-free wax that fires without leaving residue and lift the bridge off the model.

Cover the soldering gap and all the ceramic parts with wax so that they will not come into contact with the soldering investment.