FIXED PARTIAL DENTURE OR BRIDGE

 
FIXED PARTIAL DENTURE OR BRIDGE

Table of Contents

Introduction

Terms used in Bridge work

Types of Bridges

Bridge Designs

Conventional Bridges

Advantages and Disadvantages

Indications and Contraindications

Laboratory procedures for Fixed Partial Denture

General considerations in bridge work

Factors affecting bridge design etc.

Introduction

What is fixed partial denture or FPD or Bridge ?

Fixed Partial Dentures or bridge is  a vital branch of prosthodontics,  focused on the replacement and/or restoration of teeth using artificial substitutes that are firmly on standing neighboring teeth. These substitutes, known as FPDs or Bridge, serve to replicate the function and aesthetics of natural teeth seamlessly.

Fixed options for tooth replacement include the following:

None

Resin bonded bridge

Conventional bridge

Implant

A dental bridge is a partial prosthesis fitted permanently to one or more prepared natural teeth or implants. It occupies no more space than the natural teeth it replaces.

It restores masticatory efficiency, appearance, speech and prevents collapse of the dental arch.

Terms used in bridge work

Abutment: the tooth which supports the bridge or part of the bridge and to which the retainer is cemented.

Retainer: the part of a bridge which is cemented to an abutment tooth and is joined either to another retainer or to a pontic.

Major and minor retainers: The retainer in a fixed – movable bridge that is rigidly united to the terminal pontic is known as the major retainer. The retainer that is united to a pontic by a semi- rigid joint is called a minor retainer.

Pontic: Each artificial tooth replacement. One or more pontic may make up a span. A pontic is not always the reproduction of the tooth it replaces.

Unit: Each part of a bridge. A retainer or a pontic may be referred to as a unit.

Span: Horizontal distance between two abutments or that part of a bridge which covers the edentulous area.

Pier: Any abutment other than the terminal abutments. Also known as the intermediate abutment.

Joint/ Connector: Junction between any two units of a bridge.

Advantages of fixed partial denture FPD/BRIDGE OVER a REMOVABLE partial denture/ RPD

• Requires less support from the mucous membrane and in many instances, not even in contact with it. ( Less of a tissue irritant).
• Only occupy the same space as the natural teeth which they replace apart from the spring cantilever bridge. They therefore feel more natural in the mouth  and are better tolerated.
• Can withstand greater masticatory load than partial dentures. ( Except tooth borne).
• Habit of playing with prosthesis is less; therefore they are less subject to patient mismanagement.

Disadvantages of Fixed Partial Denture/FPD/BRIDGE

• Confined to short spans bounded  by healthy teeth in good positions and alignment.
• Construction, time consuming and requires great precision. It is therefore more expensive.
• If damaged, repair is difficult and costly.
• Sound natural teeth might have to be prepared for inlay’s and crown’s abutment.
• Cannot be added onto.
• If not well taken care of – food stagnation and recurrent caries . Caries might be very much advanced before it is discovered.

INDICATIONS for Fixed Partial Denture/FPD/BRIDGE

• Patient’s wish.
• Improvement of appearance.
• To prevent collapse of dental arch – there is drifting or tilting which leads to loss of contact which could eventually cause periodontal disease or caries.
• Psychological reasons
• e.g. ( i ) Young cleft palate patients
•                     ( ii ) Wind instrument players who require a lip seal, which is difficult to achieve with a partial denture in the anterior region.
•                     ( iii ) Public speakers – teachers, politicians.
• Cases with ridge resorption where a RPD will not be stable or retentive.

CONTRA INDICATIONS for Fixed Partial Denture/FPD/BRIDGE

• The very young patient because of possible further tooth movement. ( Jaw growth) and size of the dental pulp.
• High caries susceptibility
• Too long span
• Bruxism
• Congenitally malformed teeth, which do not have adequate tooth structure to offer support.
• Uncooperative patient.
• Kennedy class I or II cases.

Basic Designs, Combinations and Variations of Fixed Partial Denture/FPD/BRIDGE

Four basic designs

• Fixed - fixed
• Fixed - movable
• Cantilever
• Spring cantilever

Of the four basic designs, the first three may be either conventional or RBB type. 

The last design ( spring cantilever) only applies to the conventional.

Combination designs

The four basic designs can be combined in a variety of ways.

It is possible to combine two or more of the four basic designs (complex/ compound ) and to combine conventional and minimal preparation retainers ( Hybrid bridges)

Fixed – fixed design Fixed Partial Denture/FPD/BRIDGE

All units are rigidly attached to each other

Advantages Fixed – fixed design Fixed Partial Denture/FPD/BRIDGE

• Robust design with maximum retention and strength.
• Abutment teeth are splinted together and the load is more evenly distributed via the entire periodontal attachment, thus making the weaker element to be adequately supported by the stronger neighbour.
• The design is the most practical for larger bridges, particularly when there has been periodontal disease.

• The construction is relatively straight forward in the laboratory because there are non movable joints to make.
• Can be used for long spans.

Disadvantages of Fixed – fixed Fixed Partial Denture/FPD/BRIDGE

• Requires preparations to be parallel and this may mean more tooth destruction
• All the retainers are major and require extensive preparation of the abutment teeth.
• Has to be cemented on as one piece so cementation is difficult.

Fixed – movable  Fixed Partial Denture/FPD/BRIDGE

This incorporates a stress breaking device which allows limited movement at one of the joints between pontic and retainer.

Advantages of  Fixed – movable  Fixed Partial Denture/FPD/BRIDGE

• Preparations do not need to be parallel to each other, so divergent abutment teeth can be used.
• More conservative of tooth tissue.
• Fixed movable
• Allows minor movement of teeth.
• Parts can be cemented separately, so cementation is easy.

Disadvantages of Fixed – movable  Fixed Partial Denture/FPD/BRIDGE

• Limited  to short span replacements.
• More complicated to construct in the laboratory than fixed – fixed design.
• Difficult to make temporary bridges.
• Unless articulation is constructed so tightly that the joint can only be  assembled with considerable force, some latitude for movement and food stagnation within the joint is always present.
• Sticky food will exert considerable traction on the pontic area which is then transmitted to the major abutment causing mobility of this.

Cantilever Design of Fixed Partial Denture/FPD/BRIDGE

Has a pontic connected to a retainer at one end only. The pontic may be attached to a single  retainer or to two or more  retainers splinted together, but has no connection at the other end of the pontic.

Advantages of  Cantilever Design of Fixed Partial Denture/FPD/BRIDGE

• The most conservative design when only one abutment tooth is needed.
• Construction in the laboratory is relatively straight forward.
• Cantilever Design
• , there is no need to make preparations parallel to each other; if two or more abutment teeth are used, they are adjacent to each other, so it is easier to make preparations parallel.

Disadvantages of  Cantilever Design of Fixed Partial Denture/FPD/BRIDGE

• Limited to short span
• Imposes leverage on the abutment tooth.
• Restricted to areas where occlusal forces on the pontic will not be heavy.
• The design is not suitable in the lower anterior  region of the mouth because of rotational factor.
• The construction of the bridge must be rigid to avoid distortion.

Spring Cantilever of Fixed Partial Denture/FPD/BRIDGE

This supports a pontic at some distance from the retainer. It is  tooth  and tissue supported. The connecting palatal  bar may either be  cast or  fashioned from wrought metal and should be well finished on the fit surface.

Should be oval in cross section so that food passes easily over it.

Should follow a wide curve to provide the additional mucosal support to limit adverse leverage.

Spring Cantilever

Advantages of Spring Cantilever of Fixed Partial Denture/FPD/BRIDGE

• It solves the problem of replacing an upper central incisor when the anterior teeth are spaced.
• It preserves intact anterior teeth when posterior teeth need crowning.

Disadvantages of Spring Cantilever of Fixed Partial Denture/FPD/BRIDGE

• Difficulty in designing accessible embrasures between the connecting bar and retainers
• Some degree of chronic mucosa change may be inevitable beneath the bar.
• A slight variation in seating during cementation may affect the position of the retainer.
• If the bar is flexible, functional value of the replacement is markedly reduced, while if too rigid, the added leverage may unseat the retainers. 

Factors Influencing Component Selection

The selection of components in fixed partial dentures is influenced by various factors, including:

• Oral Health: The condition of the abutment teeth and surrounding oral tissues.
• Aesthetic Considerations: Ensuring the FPD blends seamlessly with the natural dentition for a harmonious smile.
• Functional Requirements: Designing FPDs that facilitate proper occlusion and chewing efficiency.
• Material Choice: Selecting appropriate materials based on durability, aesthetics, and biocompatibility.

Art and Science in Fixed Bridge Design

Crafting a successful fixed partial denture involves a delicate balance of scientific principles and artistic flair. The practitioner must consider not only the structural integrity and functional aspects but also the aesthetic harmony and patient satisfaction.

Proper Placement of Connectors

The placement of connectors in fixed partial dentures, particularly in the anterior and posterior regions, is crucial for both functional and aesthetic reasons. Properly positioned connectors ensure adequate support for the pontic(s) while maintaining the natural contours of the dental arch and gingival tissues.

Components of FPD

FPDs consist of three primary components:

•     Retainer: This component connects the abutment teeth to the rest of the restoration.
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•  Pontic: An artificial tooth on the FPD that replaces a missing natural tooth.
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• Connector: The portion of the FPD that links the retainers and pontics.

Retainer

Classification of FPD Retainers

Retainers are classified based on:

1.      Amount of Tooth Coverage:

·         Complete Coverage: Covering all surfaces of abutment teeth.

·         Partial Coverage: Involving only some surfaces of abutment teeth.

·         Conservative Retainers: Minimally invasive options suitable for specific cases.

2.      Mechanism of Retention:

·         Extracoronal Retainers: Providing retention from external surfaces.

·         Intracoronal Retainers: Offering retention from within the tooth structure.

·         Radicular Retainers: Obtaining retention from within the root of the abutment.

3.      Materials Used:

·         Various materials like metal, metal-ceramic, all-ceramic, and acrylic are utilized based on strength, aesthetics, and clinical requirements.

Criteria for Selection of Retainers

Selection of retainers depends on factors such as abutment angulation, condition of the abutment, aesthetics, retention requirements, and cost considerations. Each factor plays a crucial role in determining the most suitable retainer for a particular case.

Pontic

Ideal Requirements

Pontics must meet specific criteria to ensure optimal performance:

• Restore Function: Replicate the function of the replaced tooth effectively.
• Aesthetic and Comfort: Provide natural appearance and comfort to the patient.
• Biologically Acceptable: Compatible with oral tissues and hygiene.
• Preserve Underlying Ridge and Mucosa: Maintain the integrity of surrounding structures.
• Adequate Strength: Withstand masticatory forces and daily wear.

Classification

Pontics are classified based on mucosal contact, materials used, and method of fabrication. Each type offers unique advantages and is chosen based on clinical requirements and patient preferences.

Connectors

Types of Connectors

Connectors play a crucial role in the stability and integrity of FPDs. They can be classified into:

• Rigid Connectors: Provide stability without movement.
• Non-Rigid Connectors: Allow limited movement to accommodate variations in abutment alignment.

General Considerations in bridge work

The patient

The span

The occlusion

Health of the mucosa

Strength

Appearance

Function

The patient

Explain to the patient the aim and the procedure with the aid of models, photographs or diagrams.

Assessment of patient’s enthusiasm and affordability

Medical conditions that may require caution e.g. DM, xerostomia

Caries index and OH

Patient must be able to maintain a high standard of oral hygiene (OH) and appreciate necessity of good plaque control.

The patient

Periodontal condition of the mouth – poor periodontal conditions that are likely to deteriorate contraindicates bridge work because the potential abutments must be able to support the bridge.

The span/ edentulous space

Small groups with strong teeth at either end in an otherwise complete arch are ideal for bridges.

Ideal span: The longer the span, the less rigid is the bridge.

Ideal span( 2 or fewer posterior, 4 or fewer incisors ).

Compared with a bridge having a single tooth pontic span, a two- tooth pontic span will bend or deflect 8 times as much. A three - tooth pontic will bend 27 times as much.

Over erupted un opposed tooth reduces the vertical height of the edentulous space.

The span/ edentulous space

Grind this down to the occlusal level of the adjacent teeth.

Excessive dentine exposure might necessitate an onlay covering.

The space available for the pontic should be assessed.

The space may be diminished by drifting, rotating or tilting of the abutment teeth.

Reduced space in the anterior region may be managed by

Orthodontic means

The use of narrower retainers

The use of overlapping ponitic design

The span/ edentulous space

For such cases, diagnostic wax up should form part of the treatment plan.

Increased / wider space can be closed orthodontically, or midline diastema maintained with the use of a cantilever or a spring cantilever bridge.

Occlusion

The abutment support and the amount of retention required vary not only with the length of the span but also with the force exerted by the opposing teeth.

Occlusal readjustment carried out if necessary. This removes premature contact thus diminishing lateral stresses.

Presence of faceting or attrition suggest occlusal disharmony.

Bruxism may cause accelerated destruction of periodontal support of an abutment or loosening of a retainer. It is a contraindication to bridge work.

Mucosal health

All pontics have some tissue contact except the all gold ”self- cleansing or sanitary” pontic.

Contact when present should be minimal and the self- cleansing pontic should have enough clearance to prevent stagnation.

Bridge designed such that mucosal stimulation can occur during mastication, tooth brushing ( and with interdental cleaners.)

Strength

This is limited by strength of individual units and the materials used.

Points of potential weakness are joints, gold backings for pontics and incisal edges.

Requirement for strength depends on the masticatory force the prosthesis has to resist.

Appearance

This is more significant towards the front of the mouth.

Use of bonded porcelain reduces problem of showing gold with resultant good appearance but more tooth tissue need to be removed.

Where occlusal stress is minimal an all- porcelain bridge is excellent.

Function

A bridge should have a dynamic function as an effective part of the masticatory apparatus in addition to its static function of maintaining continuity of the dental arch and restoring appearance ( i.e. It is not just for decoration).

Factors influencing the design of a bridge

The design of a bridge varies with

The strength, shape and angulation of the abutment.

The  length of the span of and number of abutment.

Space available for the pontics

Occlusal forces acting on the bridge

Final appearance

Abutments

The classic requirement for an abutment are

Reasonably long clinical crowns

Vertically correct alignment

Good periodontal support.

The first two relate to retentivity  and parallelism of the prepared surfaces and the third  to amount of surface over which the load can be shared.

Abutment crowns

Crown size: abutments with small crowns cannot provide adequate retention for the bridge. Any crown less than 4mm in interproximal height ( i.e. from marginal ridge to gingival attachment is unsuitable for most extra coronal retainers.

Pins and posts may be used for extra coronal retention.

Crown strength

Caries, existing restorations, or endodontic treatment may weaken the crown.

Large losses best restored with pin retained amalgam.

Root treated teeth may require a metal core retained by a post in the root canal, this reduces the leverage on the coronal portion of the crown and lowers the centre of thrust on the periodontal attachment. ( This arrangement often favoured when only a few abutment teeth remain to support what would otherwise be a full denture).

Crown shape

Shape of the abutment crown may present retention problems, e.g. Conical teeth. Retention of the retainer on this type of tooth can be improved by slots placed in the approximal surfaces, such slots should be as long as possible.

The pulp

Size of the pulp should be assessed on radiographs and vitality with a pulp tester.

Angulation

The inclination of the abutment teeth determines the path of insertion of the bridge and may contraindicate a fixed – fixed bridge.

 Tilted teeth can sometimes be improved by orthodontic treatment.

 If the same path of insertion cannot be achieved without pulp exposure, then an elective root canal therapy should be done. Partial and telescopic crowns may also be used as retainer.

Abutment roots

The root support must be adequate and periodontium must be healthy.

 The root support is related to the amount of root area secured in healthy bone. If this is insufficient the abutment is liable to become loose.

Supporting bone level should be consistent with patients age.

As  a general rule the combined root area of the abutments should not be less than that of the teeth to be replaced. ( Ante’s law) ? Periodontal support.

Abutment roots

The number , length and shape of the roots will indicate the amount of support available for the bridge.

Preference for abutment support is given in the following order

    i. Upper  - 6,7,3,4,5,1,2.

                ii. Lower – 6,7,3,5,4,2,1

Third molars may be used but exhibit a lot of variation of form – both crown and root.  

Abutment roots

If only half of the root length is in bone, the effective loss of support is greater than half since the root tapers towards the apex.

Assess each case separately and not by any rule of thumb.

Posterior teeth with diverging roots are preferred to those with fused conical roots.

The length of the span

The length of the span, position in relation to abutment teeth and position in the arch all influence the number of abutment teeth.

In anterior region, number of abutment is related to the curvature of the arch which imposes additional stresses on the bridge. Here design of bridge depends more on presence or absence of the canine.

Bridge Retainers

Choice of retainers: a major consideration in bridge design

The choice of retainer will depend on:

Retention  required

Amount of abutment crown available

Strength of the dentine remaining after tooth preparation

Extent of existing restoration to be covered

Aesthetics

The material used for the pontic

Occlusal and Incisal protection required

Factors affecting the retention required

Length of span – the longer the span the greater the stress and the more the retention needed.

Type of bridge – fixed – fixed bridge requires more retention than fixed movable.

Strength of the bite – the heavier the bite the greater the retention required.

Teeth to be replaced – molars require more retention than anteriors.

Para functional habits – these require more retention

Factors affecting retention available

Teeth involved – the bigger the abutment teeth, the greater the retention.

Surface area of the retainer – the greater the surface area the more the retention. Incorporating grooves and slots in the tooth preparation can increase retention.

Degree of parallelism between the walls of the tooth preparation.

Rigidity of the casting.

Type of luting cement used.

Material used in the construction of the bridge.

Pontics

The design is critical and dictated by:

Aesthetics

Function

Ease of cleaning

Maintenance of healthy tissue on the edentulous ridge

Patient’s comfort

Design considerations

Stein and Eissman outlined the ideal pontic form that is compatible with both hygienic and aesthetics as :

Posterior pontic

Smooth surfaces, well finished and convex in all directions

Pin point pressure free tissue contact on the buccal slope of the ridge,

Occlusal table in functional harmony with the opposing teeth,

The buccal and lingual contours should be confluent with the adjacent teeth.

The overall buccal surface length equal to that of the adjacent abutments or pontics.

Anterior pontic

Smooth properly finished and convex on all surfaces,

Pinpoint pressure free contact on the labial mucosa.

Emergence profile and pontic length harmonious with the adjacent pontic or abutment teeth to maximize aesthetic considerations.

Lingual contours confluent with adjacent teeth and pontic.

Classification of pontics

Based on mucosa contact

Based on type of the material used

Based on method of fabrication

1. Based on mucosa contact

A.) with mucosa contact

Saddle pontic/ ridge

Ridge lap pontic

Modified ridge lap

Ovate pontic

B.) without mucosa contact

Conical/ bullet pontic

Hygienic/ sanitary pontic

2. Type of material used

Metal and porcelain veneered pontic

Metal and resin veneered pontic

All metal pontic

All ceramic pontic

Glazed porcelain and highly polished gold are preferred because they are easier to clean. All ceramic pontics ideal for aesthetic zone.

3. Based on method of fabrication

Custom made pontic

Prefabricated pontic e.g. Trupontic, Harmony pontic, Pin facing pontic, PFM pontic etc.

Prefabricated ,custom modified pontic

Saddle pontic

Looks like a tooth

Replaces all the contour of the missing tooth

Forms a large concave contact with the ridge, obliterating the facial, lingual and proximal embrasures.

The design is unclean and uncleanable

Causes tissue inflammation

Should be avoided

Sometimes called ridge lap.

Modified ridge lap

 Gives an illusion of a tooth but has nearly all convex surfaces.

Lingual surface has a slight deflective contour to prevent food impaction and minimize plaque accumulation.

Tissue contact is narrow MD and FL.

Most commonly used in the appearance zone.

Ovate

Rounded end design

For appearance zone

Tissue contact segment bluntly rounded.

It is easily flossed.

Conical or Bullet

Rounded and cleanable.

Tip small in relation to the overall size

Suited for use on a thin mandibular ridge in non appearance zone.

Hygienic or sanitary pontic

No tissue contact

For non appearance zone

Has  an all convex configuration MD and FL

Restores occlusal function and stabilizes adjacent and opposing teeth.

Design with rounded under surface is called Fish belly pontic.

Design with a concave archway  mesiodistally is called Perel pontic

Custom made pontics

Made for individual

Most of the above mentioned are custom made.

Offer superior aesthetics and flexibility because of wide number of materials that can be used.

Prefabricated pontic facings

Commercially available as porcelain pontics

Can be adjusted to fit individual requirements

The metal back is custom made and has a tug which will engage the slot in the occlusal/ lingual surface of the facing.

Connectors/ Joints

Used to unite retainers and pontics.

Could be rigid ( for F – F design) or non rigid.

Non rigid connectors:

Indicated where a single path of insertion cannot be achieved due to non parallelism of the abutments

Examples – Tenon Mortise (M –F)

                      -   Loop connector( used where you want to preserve an existing diastema e.g. A spring cantilever bridge

                                                   -   Split pontic connectors

Bridge Designs for Adhesive / Resin Bonded Bridges

Rochette

Maryland

Virginia

Fiber reinforced composite bridges( Ribbond)

Carolina bridges etc.

 Stages of Fabrication

After crown prep

Impression

       -Locating imp

       -wash imp

       -Single imp technique

       -Double imp technique

       -Single paste imp

       -Double paste imp

       -Alternate cast imp tech

TEMPORIZATION

Peel off crown form (cellulose acetate)

Polycarbonate crown

Aluminium shell crown

Stainless steel crown?

Cold cure acrylic crown / bridge

Heat cure acrylic crown / bridge

Laboratory Procedures

Die fabrication

Wax pattern fabrication

Investment

Burn out

Casting

Finishing

Firing of ceramic /porcelain

Fitting of Crown/bridge

Recall patient

Remove temporal bridge

Trial  fit of the final bridge

       Check: fit on individual abutment

                   approximal contacts/relationship

                   labial &buccal contour/bulbosity

                   occlusal surface & occlusion

       Adjust occlusion if necessary

 Cementation

Conclusion

In conclusion, fixed partial dentures represent a cornerstone of restorative dentistry, offering patients a reliable solution for replacing missing teeth and restoring oral function and aesthetics. By understanding the classifications, components, and factors influencing design, dental practitioners can create bespoke FPDs that meet the unique needs and preferences of each patient. Through a blend of science and artistry, we embark on a journey towards excellence in dental prosthetics, transforming smiles and restoring confidence, one restoration at a time.