Retainers in FPDRestraining what is left

By: Ghida Lawand Hind Tabbal

What is a Retainer?It’s that component of an FPD which takes

support from the abutment tooth and provides retention to the prosthesis.

Ideal Requirements:

1) Should cause least amount of destruction to the abutment

2) Least destroys the outline form of the tooth

3) Marginal line should be finished with great accuracy

4) Rigidity withstand requisite load

Functional adaptation and protect the tooth against its fracture

Least destroys the cervical marginal ridge Positioned margins at less susceptible to caries

or recurrence of caries Preparation should be made without trauma to

the pulp or surrounding tissue Accurate complement to the lost tooth

structure Cleansable Esthetic

Retainers

Extracoronal

Complete Crowns

-All Metal-All Ceramic

-Metal Ceramic

Partial Veneer Crowns

-3/4th crown-Mesial half Crown

-7/8th crown

Intracoronal

-Inlay-onlay

Radicular

-Cast Post-Prefabricated post

Criteria of selecting type of retainer

Full Veneer crown

Partial Veneer crown

All Ceramic

Abutment teeth are aligned parallel to one another

Non carious abutments /abutments with large

restorations but intact buccal and lingual surfaces

Classification of retainers

Based on the tooth coverage

Based on the location

Based on mode of retention

Based on material being

used

Based on the tooth coverage

Partial coverage retainer

Full coverage retainer

Conservative retainer

Telescopic retainer

A- Full coverage retainer

These retainers cover all the five surfaces of the abutment tooth.

Advantages

Contact area can be properly developed Embrasure area can be enhanced Buccal contours can be correctly developed Facilitate occlusal plane modifications Indicated for endodontically treated abutments Ideal for restoring edentulous area in patients with craniofacial

anomalies

Disadvantages

Extensive tooth preparation Poor supportive tissue response (subgingival finish line) Gingival decay is prevalent Poor esthetics (metal crowns), restricted to posterior teeth

Indications

1. Short clinical crown

2. For a patient with a history of active caries and poor hygiene

3. In both vital and pulpless teeth

4. Metal ceramic crowns and all ceramic crowns are used in situations that require good cosmetic results with maximum resistance and retention requirements.

It is an artificial metallic restoration used to cover the all surfaces of the clinical crown.

It is made only from metal, e.g. gold.

Can be either partial or full veneer crown. Require minimal tooth reduction. Strong even in thin sections.

Preperation:Occlusal reduction:

non centric cusp – 1mm centric cusp – 1.5mm

Margin:

chamfer – allows 0.5mm thickness

1. Full metal crown:

1.As single crown or as a bridge.2.Only for posterior teeth.3.In patients with high caries index. 4.For an endodontically treated tooth/or teeth. 5.For malalignment tooth/or teeth.6.For teeth with a short occluso-gingival height. 7.For a badly broken clinical crown.8. In a long span bridge.

Indications

1. In case of anterior teeth, for esthetic reasons.2. In a situation where anther conservative preparation can be

used.3. When less than maximum resistance and retention is needed.4. When caries extend gingivally, as that the finish line cannot

be made.5. In case of uncontrolled caries.

Contraindications

ADVANTAGES DISADVANTAGES1. Great resistance form.

2. Great retention.

3. High strength.

4. Good protection for a tooth to be restored.

5. Can modify occlusion in case of overeruption.

6. Can modify tooth contour in case of open contact or in buccal or lingual contour in a tooth used as a retainer for FPD.

7. Ideal restorations for teeth with developmental defects.

1. Bad esthetics (especially for anterior teeth).

2. Pulp vitality can-not be detected.

3. Incipient caries can-not be detected.

4. Extensive amount of tooth reduction

Tare full cast crowns having porcelain or acrylic facing on facial or lingual surface. They require more tooth reduction

• Can be fabricated over full veneer crown or partial veneer crown • Indicated on teeth that require complete coverage & esthetic demand • Can accommodate cast or soldered connectors • Can afford high force—metal

Preparation:Incisal reduction

- 2mm Occlusal reduction - 1.5mm – for metal coverage - 2mm – for metal with ceramic veneer

Margins - facial surface- shoulder - lingual surface- chamfer - Shoulder must extend at least 1mm lingual to proximal contact area.

2. Metal ceramic crown:

ADVANTAGES DISADVANTAGES Have the strength of cast metal crowns

with the esthetic of the all ceramic crowns

Have good retention.

Permit easy correction of the axial walls.

X Their preparation requires more tooth reduction to provide sufficient space for the restorative materials.

X Their facial margins for anterior teeth, is often placed sub-gingivally which increase the risk for periodontal disease.

X The laboratory casts are expensive.

X A frequent problem is the difficulty of accurate shade selection.

3. Non- metal crown (ALL Ceramic)It is also called the jacket crown is an artificial non-metallic restoration made of porcelain.It is used to cover the all surfaces of the clinical crown. May be fabricated as full or partial coverage crown.

Primary purpose: to achieve best possible esthetic results.Risk of reduced restoration longevity—potential for fracture

Preparation:Incisal reduction: 2mm clearance ( this enables cosmetically pleasing restoration & provides adequate strength )Facial reduction: 1mm clearance Lingual reduction: 1mm clearance Margin: shoulder preparation – 90 degree angle

3. Non- metal crown (ALL Ceramic)It is also called the jacket crown is an artificial non-metallic restoration made of porcelain.It is used to cover the all surfaces of the clinical crown. May be fabricated as full or partial coverage crown.

Primary purpose: to achieve best possible esthetic results.Risk of reduced restoration longevity—potential for fracture

Preparation:Incisal reduction: 2mm clearance ( this enables cosmetically

pleasing restoration & provides adequate strength )Facial reduction: 1mm clearance Lingual reduction: 1mm clearance Margin: shoulder preparation – 90 degree angle

INDICATIONS CONTRAINDICATIONS1. For anterior teeth (especially

incisors).

2. For severely discolored anterior teeth.

3. over an existing post and core substructure.

1. In Posterior teeth.

2. In case of tooth with short clinical crown

3. In case of edge to edge or overbite

4. As a retainer for FPD.

ADVANTAGES DISADVANTAGES1. Have the best cosmetic effect of dental restorations.

2. Are very strong.

3. Are the best to use on the incisors.

1. Have high risk of fracture because they’re brittle.

All acrylic retainersUsed as temporary fixed partial dentures Not indicated for permanent restorations

B- Partial coverage retainer

Advantages

Conservative tooth preparation Guides for coronal contours Embrasure forms are pre-established Improved periodontal health as limited contact between margin of restoration and gingiva. Marginal fit and Complete seating of casting can be easily verified before and during cementation Margin accessibility for finishing and cleaning Uncovered portion of tooth can be used for electric pulp testing Acceptable esthetics.

Disadvantages Are not as retentive as complete coverage

retainers. There is a limited display of metal. Tooth preparation is difficult because only

limited adjustments can be made in the path of placement.

Indications

• Intact or minimal restored teeth • Normal anatomic clinical crown • Teeth with adequate labiolingual thickness

Contraindications 1. Teeth with short clinical crowns 2. Thin teeth bucco-lingually 3. Teeth that are proximally bulbous 4. Poorly aligned tooth 5. Bad oral hygiene and high caries index 6. Retainers for long span bridges 7. Endodontically treated teeth 8. Malformed teeth

Types of partial coverage retainers

1 Posterior three quarter

crowns

2 Anterior three quarter

crown

3 Pin modified three

quarter crown

II. Partial coverage

1. ¾ crown:Indications Contraindications

1. Carious or damaged tooth with intact facial surface 2. As bridge retainer in short span bridge 3. Long clinical crown

4. Splinting

1. Short clinical crown

2. Damaged facial surface of teeth

3. Long span bridge

4. Anterior teeth with thin labio-lingual dimension

5. Malformed tooth Ex: Pig shaped tooth, tilted tooth, etc

Advantages Disadvantages1. More conservative than full metal

crown

2. More esthetics as facial surface remains intact

3. Pulp vitality test can b done as one surface is un covered

4. Less gingival irritation

1. Less retentive than full coverage

2. Needs skill from operator

3. Metal display may occurs

2. ½ crown:• It is a partial coverage restoration that restores the

occlusal surface (or incisal edge), the mesial surface and a portion of the facial or lingual surfaces.

• This type is indicated for mesially tilted tooth.

3. Pin ledge:• It is a technique that employs parallel long pins

prepared in the lingual or palatal surface of the clinical crown, in order to increase retention of the restoration.

• These restorations used the both grooves and pins to improve retention.

4. ¾ reversed crown:• It is a partial coverage restoration that restores the occlusal

surface (or incisal edge), and three axial surface of the clinical crown (the lingual surface is not included).

• This type is indicated for lower posterior teeth. And it is useful for server lingual indications.

5. 7/8 crown:• It is a partial coverage restoration that restores all surfaces of

the crown except the mesio-buccal cusp.• This type is only used for the upper 1st molar.

6. Modified type: Indications Contraindications

1. For both anterior and posterior teeth.

2. When the coronal portion is intact.

3. When there is a good crown length.

4. as a retainer for FPD (short edentulous span).

5. When there is a minimum occlusal stress.

1. When maximum retention is required.

2. in case of a thin or short clinical crown.

3. for patient with high caries index.

4. When there is active periodontal disease.

5. In case of mal formed tooth, e.g. Bellshaped canine.

Advantages Disadvantages

1. Preservation of tooth structure.

2. More esthetic than full coverage restorations.

3. The finish line is easy to place.

4. Less periodontal irritation due to the less contact with the tissues.

5. Pulp damaged is reduced.

1. Less retentive than the full coverage.

2. Difficultly of placing the grooves and pins properly.

3. In some restorations, the metal is displayed and this is not acceptable by the patient.

Complete or Partial coverage? (Periodontal point of view)

• The complete retainers accumulate more plaque, which leads to gingivitis and increases pocket depth than abutment with partial retainers.

• The difference may not be evident if the patient practices meticulous oral hygiene.

• Complete retainers are performable in patients with long span FPDs or splints with few abutment teeth.

• Partial veneer retainers have less resistance to deformation than complete retainers.

C- Conservative retainers

• Require minimal tooth reduction• Do not accept heavy loads, therefore indicated for

anterior teeth.• Have a small metallic extension which are designed

to be luted directly onto the lingual surface of the abutment tooth using resin cement.

Resin bonded FPD

Missing anterior teeth

Retainer with wings

Wings bonded to the lingual surface of the

abutment teeth

Why resin-bonded FPD ?• Conventional FPD’s requires abutment preparation which leads to destruction of adjacent teeth.• Various solution tried for this problem but not of much result oriented

1.Inlay retainer2.Cantilever FPD

loss of PDL support of abutment teeth3.Unilateral RPD

lack of retention stability and risk of aspirated if dislodged

Classification of RBFPD• Classified on the basis progression of development:

–Rochettebridge–Maryland bridge–Cast Mesh–Virginia bridges

Rochette bridge

wing-like retainers, with funnel-shaped perforations through them to enhance

resin retention combined mechanical retention with a silanecoupling agent

to produce adhesion to the metal

Disadvantage• Weakening of the metal retainer by the perforations• Limited adhesion of the metal provided by the perforations• Wear of composite resin• Thick lingual retainers• Plaque accumlation• 50% fail in about 110 months

Maryland Bridge: Etched-metal prosthesis

Done in either two step process or one step process –equally

retentive.

Advantages over the caste perforated restorations: resin-to-etched metal bond can be substantially stronger than the resin-to-

etched enamel The retainers can be thinner and still resist flexing oral surface of the cast retainers is highly polished and resists plaque

accumulation

Two-step process• Livaditisand Thompson• Electrochemical pit corroding technique• 1ststep

o 3.5 % Nitric acid at 250 mA/sq cm (current) for 5 min –non-beryllium-containing nickel-chromium alloy

o 10% sulfuricacid at 300 mA/cm2 (current) for 5 min -beryllium nickel-chromium alloy

• 2nd step : 18% HClfor 10 minutes in an ultrasonic cleaner bath

1-step• McLaughlin• Faster technique• Combined solution of sulfuricand

hydrochloric acids placed in an activated ultrasonic cleaner for 99 seconds passing electrical current.

Cast Mesh FPD• Non etching method after casting • Produce roughness before the alloy is

cast.• Net-like nylon mesh –lingual surfaces

of the abutment teeth on the working cast

• Covered by and incorporated into the retainer wax pattern

• Mesh-like surface when the retainer is cast

• Eliminates the need for etching

Advantage: Use of noble-metal alloysDisadvantage: stiff, making it somewhat difficult to adapt to detail of the

abutment tooth Wax runs too freely into mesh –blocks undercut compromising

retentivity

Virginia bridge Lost salt technique Particle roughened retainers by incorporating salt

crystals into the retainer patterns to produce roughness on the inner surfaces

1. Sieved cubic salt crystals (NaCl) -sprinkled over the outlined area sparing 0.5-1.0 mm wide crystal free margin

2. Retainer patterns were fabricated from resin

3. Removed from the cast-resin was polymerized

4. Cleaned with a solvent5. Placed in water in an ultrasonic cleaner

to dissolve the salt crystals6. Left cubic voids in the surface

Steps

ADVANTAGES DISADVANTAGES

Non invasive to dentin with lingual and proximal tooth preparation including occlusal rest.

Conservative preparation. Good esthetics. Tissue tolerant because of

Supragingival margin, and no pulpal irritation.

Reduced cost and less chair side time

- Demanding technique and tooth prep.

- plaque accumulation - bulky contours may be intolerable

to some patients - not ideal for replacing more than

one tooth - Graying out of teeth that are thin

labiolingually.

INDICATIONS CONTRAINDICTIONS

• As retainers of FPD, on abutment with sufficient enamel to etch.

• Splinting of periodontally compromised teeth.

• Stabilizing dentition after orthodontic treatment.

- In patients with sensitivity to base metal alloys.

- When facial esthetic of abutment require improvement.

- Inadequate enamel surface to bond eg; caries, existing restoration.

- Incisor with extremely thin faciolingual dimension.

D-Telescopic retainers

• These are used when path of insertion of the fixed partial denture does not coincide with the long axis of the abutment tooth.

• Indicated in tilted abutment.

• The design involves the fabrication of two copings one over the other:

- Primary coping: Functions to modify the morphology of the tooth and helps to change the path of insertion.

- Secondary coping:Designed to fit over the primary coping along the new path of insertion.

• Thus accurate parallelism of the copings is necessary.

2. Based on location

• Extra-coronal (complete coverage or partial coverage)

• Intra-coronal (Inlay / onlay) • Intra-radicular (Post and core)

Intra-coronal Retainers

Intra-coronal retainers can either beI. InlayII. Onlay

I. Inlay• Inlay is defined as a restoration which has been constructed

out of the mouth from gold, porcelain or other metal and then cemented into the prepared cavity of the tooth.

• It is mostly used.

II. Onlay• It is essentially an inlay that covers one or more cusp and

adjoining occlusal surface of the tooth.• It is retained by mechanical or adhesive mean.

INDICATIONS CONTRAINDICATIONS1. Onlay is used in large restorations

2. Endodontic ally treated teeth

3. Teeth at risk for fracture

4. Dental Rehabilitation with cast Metal Alloys

5. Diastema closure and occlusal plane correction

6. Removable prosthodontic abutment

1. High caries rate

2. Young patients

3. Esthetics

4. Small restorations

ADVANTAGES DISADVANTAGES1. Strength 2. Bio-compatibility

3. Low wear

4. Control of contours

1. Number of appointment 2. Higher chair time

3. Temporary Restoration 4. Cost

5. Technique sensitive

6. Splitting forces

Intra-radicular Retainers

• Radicular retained prosthesis consists of a post or dowel with an attached core that obtains its retention and resistance to displacement from the prepared root portion of an endodontically treated teeth.

• While the root preparation retains the post, the core establishes retention and resistance for a complete veneer crown that restores the pulp less tooth to normal form and function.

• The post or dowel and core may be custom cast, where the radicular retainer is fabricated to fit the root preparation or prefabricated where the root preparation is designed to fit a stock post and core is build up with silver amalgam or composite resin.

Post1. Custom made 2. Prefabricated

Tapered smooth sided postsTapered serrated posts Tapered threaded posts Parallel threaded posts Parallel serrated posts Parallel smooth side posts

1. Detached dowel crown (Davis):

All porcelain crown with a post that is detached and can be placed on a prepared root end by cementation of both the post in the root and the cementation of crown on the post.

INDICATIONS CONTRAINDICATIONS

1. When impossible to restore crown by other means so that vitality can be maintained.

2. Mostly on anterior teeth, occasionally on posterior teeth.

3. When there is normal occlusal relationship.

4. Sufficiently long and thick root structure.

5. Only when peri-apical and periodontal conditions are favorable.

1. Heavy and close bite cases.

2. Poor oral hygiene.

3. Patients with para-functional habits.

4. Thin narrow roots.

ADVANTAGES DISADVANTAGES

1. Esthetics.

2. Adequetely strong.

3. Permits alignment with other teeth.

4. Good tissue adaptability.

5. Easily removed for treatment of required.

1. Tooth must be non vital.

2. Weakening of root face and canal by enlarging.

2. Richmond crown: A dowel retained crown made for an endodontically treated tooth using porcelain facing.

3. Detached post crown with a cast base: When the coronal portion of the remaining tooth is missing to a point below gingiva and it is impossible to adapt the crown and root face, a cast metal base is interposed between the base of the crown and root face.This cast base is rigidly attached to the dowel.

INDICATIONS CONTRAINDICATIONS

1. Tooth broken or destroyed by caries to a point sub-gingivally.

2. Mostly anterior teeth, occasionally bicuspids.

3. In cases with heavy bite.

4. Sufficiently long or thick roots.

5. All periodontal factors favorable.

1. Poor oral hygiene.

2. Thin and narrow roots.

3. If possible to design other variety, such as core and jacket restoration.

ADVANTAGES DISADVANTAGES

1. Quite strong and lasting.

2. Strengthens remaining tooth structures.

3. Esthetics.

1. Tooth must be non vital.

2. Difficult to construct in comparison to the restoration without a cast base.

3. Based on mode of retention

• Encircling the tooth (Full coverage ) • Mainly by grooves (Partial coverage) • Mainly by Dowel pins (Pin ledge) • Post in root canal • Conservative restorations (Resin bonded)

4. Based on material being used

• All metal retainers • Non-metallic retainers (Ceramic / Acrylic) • Combined retainers (Veneered / full veneered) • Resin bonded bridge retainers

FACTORS AFFECTING SELECTION OF RETAINERS

1-RETENTION

A- amount of remaining tooth structure influence retentive properties of retainers

B- teeth with extensive defective restorations or fractures may need intentional endodontic treatment and post & core.

C- crown lengthening when caries, restoration, or fracture are present.D- crown morphology and quantity of sound enamel & dentin. Resin bonded bridge needs intact enamel to be etched for microretention.

2-ESTHETICS :A- Drifting of teeth into edentulous area may lead to reduce pontic space. This affects selection of retainer.B- Diastema may lead to exccessive mesiodistal width.C-long clinical crown due to recession or bone loss may need full coveraage retainer & gingival porcelainD- precision attachment to replace unesthetic clasp arm. E – Porcelain on occlusal surfaces of post teeth is not recommended unless opposing occluding teeth are with porcelain occlusal surfaces.

3- AGE OF PATIENT Below 18—20 years A- large pulp size & high pulp horns lead to pulp exposureB- If a crown is made when the gingival attachment level is high (at young age), the margin of restoration will become exposed with nomal gingival recession leading to poor esthetics .

4- EXISTING CARIES A- Simple proximal caries (partial coverage crowns) B - MO or MOD caries ( inlay retained restoration or full coverage crowns)

5- Amount & direction of stress Deep overbite: complete coverage6- Type of opposing restoration RPD + complete dentures create less force than natural dentition, so use either partial or complete coverage.7- Size & position of abutment

8- Condition of abutment

Crown, roots, bone level, gingiva, mobility, tilting , pulp vitality, post & core all affect retainer selection.

9- Caries Index poor oral hygiene +high caries index necessitate full coverage retainers

10- length of edentulous span Increased span length needs retentive & strong retainers (complete coverage restoration)

11- Patient musculature males have heavy muscules (complete coverage restoration)

References:• A.E. Kahn, Partial Versus Full Coverage. J. Prosthet.

Dent. 10:167-178, 1960.• Johnstons, Modern Practice in Fixed Prosthodontics

4th edition 1986.• T.Shillinburg.Fundamentals of Fixed Prosthodontics,

III edition• •T.Shillinburg.Fundamentals of Fixed

Prosthodontics, IV edition• •Rosenstiel, Land, Fujimoto. ContemperoryFixed

Prosthodontics, III edition

Thank You