PREPARATIONS FOR PARTIAL VENEER

CROWNS

Rani RanabhattDepartment of Prosthodontics

CONTENTINDICATIONSCONTRAINDICATIONSADVANTAGESDISADVANTAGESARMAMENTARIUMPOSTERIOR PARTIAL VENEER

CROWNPREPARATION MAXILLARY PREMOLAR THREE QUARTER CROWNS MAXILLARY MOLAR THREE QUARTER CROWN MAXILLARY MOLAR SEVEN-EIGHTHS CROWN MANDIBULAR PREMOLAR MODIFIED THREE QUARTER

CROWNANTERIOR PARTIAL VENEER CROWN PREPARATION MAXILLARY CANINE THREE QUARTER CROWN PINLEDGE PREPERATION ON MAXILLARY CENTRAL INCISOR

Introduction •An extracoronal metal

restoration that covers only part of the clinical crown is considered a partial veneer crown.

•An intracoronal cast metal restoration is called an inlay or an onlay if one or more cusps are restored.

•Partial veneer crowns generally include all tooth surfaces except the buccal or labial wall in the preparation. Therefore, these restorations preserve more of the tooth’s coronal tissue than does a complete crown.

•Buccolingual displacement of the restoration is prevented by internal features (e.g., proximal boxes and grooves)

•Can be used as single tooth restorations or as retainers for a fixed dental prosthesis (FDP).

•They can be used on both anterior and posterior teeth

•Because they cover less of the coronal surface, partial coverage restorations tend to be less retentive than complete crowns and also less resistant to displacement

INDICATIONS1) Intact buccal wall & well supported

by sound tooth structure.

2) Teeth with crown length that is average or exceeds average.

3) Teeth with normal anatomic crown form, i.e. without cervical constriction.

4) Anterior teeth with adequate labio-lingual thickness.

CONTRAINDICATIONS1) High caries rate2) In short clinical crown because retention may

not be adequate. 3) In endodontically treated teeth or non-vital

teeth4) In teeth that are proximally bulbous 5) Deep cervical abrasion6) Teeth with extensive core restorations7) Bell shaped teeth (severe cervical

constriction)8) Thin teeth or restricted faciolingual dimension

ADVANTAGES1) Conserves tooth structure.2) Easy access to supra-gingival margins for

finishing.3) Less gingival involvement than with

complete cast crown.4) Aesthetics are superior to that of the

complete crowns.5) Complete seating of the restoration can be

easily verified during cementation.6) Reduced pulpal and periodontal insult

during tooth preparation.

DISADVANTAGES

1) Retention is less than that of complete veneer crown

2) Skillful preparation is crucial to avoid metal display

3) Preparation is limited to teeth with normally shaped, average length clinical crown.

4) It is not indicated for use in cases of non vital teeth

POSTERIOR PARTIAL VENEER CROWN PREPARATION

•Maxillary premolar three-quarter crown

•Maxillary molar three-quarter crown

•Maxillary molar seven-eighth crown

•Mandibular premolar modified three quarter

MAXILLARY PREMOLAR THREE QUARTER CROWNS

A. Occlusal reductionB. Axial reductionC. Groove placementD. Bucco-occlusal

contrabevelE. Occlusal offsetF. Finishing

Occlusal reduction

Before any partial veneer crown preparation , mark the proposed location of the margin of the completed preparation on the tooth with a pencil.

Recommended minimum clearances for reduction of a partial veneer crown preparation. Slight hollow grinding of the lingual incline of the buccal cusp results in an acceptable clearance with the least display of metal.

Assess the amount of occlusal clearance in the intercuspal position and in all excursive movements of the mandible.

After verifying the alignment, remove tooth structure between the guide grooves (with a smooth continuous motion) and place a cervicalchamfer.

A periodontal probe placed in each groove should be carefully viewed in both planes (mesiodistal and buccolingual).

Axial reduction

Buccal wall are flared to leave no

unsupported enamel

Occlusocervical height for a proximal groove is 4 mm

Floor of the groove should be flat and smooth, chamfer extend cervically

As the cervical chamfer extends closer to the cemento-enamel junction, more axial tooth structure is removed. Consequently, the deepest portion of the groove (its pulpal wall) will be located slightly closer to the center of the tooth.

THREE QUARTER CROWN FOR MAXILLARY MOLAR

Some additional leeway may exist for groove placement because more tooth structure is present on molars than on premolars. Also, because of their less prominent position in the dental arch, molars are less visible.

As a result, the mesioproximal flare can sometimes be extended onto the buccal surface without incurring esthetic liability.

MAXILLARY MOLAR SEVEN-EIGHTHS CROWNSThe seven-eighths crown preparation includes, in addition to the surfaces covered by the three-quarter crown, the distal half of the buccal surface. Therefore the mesial aspect of this preparation resembles that for a three-quarter crown; the distal aspect resembles that for a complete crown

A. Occlusal reduction

B. Axial reduction

C. Groove placement, flaring, contrabevel

Occlusal reduction

Occlusal depth grooves

Mesial half of occlusal reduction completed

Occlusal reduction completed

Parallel guiding groove placed in the lingual tooth surface

Groove placement, flaring, contrabevel

Proximal groove placed Buccal groove with flaring of the mesial groove

Connect the two grooves with a smooth contrabevel that follows the ridge of the mesiobuccal cusp.

Mesial groove is smooth and has a 90-degree cavosurface

angle

MANDIBULAR PREMOLAR MODIFIED THREE-QUARTER CROWN

1. Additional retention is required because of the shorter crown lengths of mandibular teeth. This can be obtained by extending the preparation buccally, although because of their rather prominent position in the dental arch, these teeth should be modified only distal to their height of contour.

2. The axial surface that is not prepared (the buccal) includes the functional cusp. This means that additional tooth structure must be removed to provide sufficient bulk of metal for strength.

Occlusal reductionPlace 0.8-mm depth grooves on the buccal inclines of the lingual cusp and 1.3-mm grooves on the lingual inclines of the buccal cusp.

.

Axial reduction1. Mesial is prepared as three-quarter and seven-

eighth crown.

2. Reduce the distal surface as for a complete crown, extending the preparation to the transitional line angle and onto the buccal surface. However, it should not extend mesially beyond the middle of the distal half of the buccal surface, and the chamfer should not extend too far cervically;

Finishing• the grooves of the three-quarter crown should

be slightly buccal. Care must be taken so that the distal groove is slightly closer to the center of the distal wall (so the distobuccal line angle will not be undermined).

Mesial and buccal groove

The chamfer must be heavy enough to allow 1.5 mm of clearance in the area of occlusal contact. A regular or thick diamond is used to place the chamfer, which should connect the grooves and provide a protective "staple" linkage of alloy in the completed restoration.

ANTERIOR PARTIAL VENEER CROWN

PREPARATION

Maxillary canine three-quarter crown

Maxillary central incisor pinledge

MAXILLARY CANINE THREE-QUARTER CROWN

A. Incisal and lingual reduction

B. Axial reduction and groove placement

C. Incisal offset and lingual pinhole

Incisal reduction Half lingual surface reduction

Lingual reduction

Axial reduction Groove Flare

Proximal flare on premolars and canines

Required interproximal clearance

Incisal offset and lingual pinholeAnterior partial veneer crowns require a means of reinforcement for preserving the casting's integrity. For an anterior tooth, an incisal offset or groove is needed to create a band of thicker metal to provide a "staple" configuration. This provides additional rigidity and resistance against bending of the casting.

PINLEDGE PREPARATIONA pinledge is occasionally used as a single restoration, generally to reestablish anterior guidance, in which case only the lingual surface is prepared. More commonly, however, it is used as a retainer for a fixed partial denture or to splint periodontally compromised teeth..

Four unit FPD with modified pinledge

Modified pinledge serving as a retainer for a four unit FPD

Indication1. undamaged anterior teeth2. high esthetic requirement3. prepared on bulbous teeth4. to establish the desired anterior

guidance.

Contraindication1. Patients with poor oral hygiene or a high

caries rate

2. Often it is not possible to place pinholes of adequate size and length in teeth that are thin labiolingually.

3. Pinledges are contraindicated on non-vital teeth and when the alignment of the abutment will conflict with the proposed path of withdrawal of the fixed partial denture.

A, Guiding grooves are placed for lingual reduction. B, The lingual reduction is completed, and an incisal bevel is placed. C, Incisal and cervical ledges are prepared. D, Indentations have been made. E, Pinholes are prepared to a depth of 2 mm. The junction between the ledge and the pinholes has been countersunk.

Ledges & Indentations •Two ledges are prepared across the

reduced lingual surface. These provide room for additional bulk of metal to ensure rigidity.

•Without them, the restoration would not be very strong because it would consist of only a thin sheet of metal.

•Recommended minimum ledge width is 0.7 mm.

•The ledges are prepared parallel to the incisal edge of the tooth, as viewed from the lingual aspect, and parallel to one another, as viewed from the incisal aspect

MAXILARY CENTRAL INCISOR PINLEDGE

A. Conventional pinledge

B. Pinledge with proximal slice

C. Pinledge with proximal groove

Mesio-occlusal or Disto-occlusal Inlays

Indications •An inlay can be used instead of amalgam

for patients with a low caries rate who require a small interproximal restoration in a tooth with ample supporting dentin.

• It is among the least complicated cast restorations to make and can be very durable when it is done carefully

Contraindications •Because these restorations rely on

intracoronal (wedging) retention, inlays and onlays are contraindicated unless there is sufficient bulk to provide resistance and retention form.

•MOD inlays may increase the risk of cusp fracture and are generally not recommended.

Advantage •Cast inlays and onlays can be extremely

long-lived restorations because of the excellent mechanical properties of the gold alloy

•Unlike an inlay or amalgam, an onlay can support cusps, reducing the risk of tooth fracture.

Disadvantage •In the restoration of a small carious

lesion, an inlay is not very conservative of tooth structure

•High occlusal force may lead to cusp fracture as a result of wedging from the inlay.

Mesio-occluso-distal onlay

To summarise…• Preparations for restorations should be based on

fundamental principles i.e a preparation must satisfy all the three principles i.e biologic, mechanical & esthetic principles which inturn are responsible for the success of the prosthodontic treatment

• Also, it should be carefully decided which restoration to choose based on each case.