Retention In Complete Denture Notes

Retention In Complete Denture Notes

Retention in fixed partial denture.

Fixed Partial Denture Definition

Retention in Fixed Partial Denture

Retention prevents removal of the restoration along the path of insertion or along the path of the tooth preparation.

It is the quality of preparation that prevents the restoration from becoming dislodged by such forces parallel to the path of withdrawal.

Resistance in Fixed Partial Denture

Prevents dislodgement of the restoration, by forces directed in an apical or oblique direction and prevents any movement of restoration under occlusal forces.

Read And Learn More: Fixed Partial Denture Short Essay Question And Answers

Factors Affecting Retention in Fixed Partial Denture

• The magnitude of the dislodging forces
• Geometry of the tooth preparation
• Roughness of the fitting surface of the restoration
• Type of restorative materials being cemented
• Type of luting agent/film thickness of the luting agent.

The magnitude of the dislodging forces

Factors influencing dislodging forces:

• Stickiness of the food
• The surface area of the restoration
• The texture of the restoration is being pulled.

Of all the types of forces, sticky food exhibits large dislodging forces floss placed beneath the connectors presents the same type of effect as sticky food.

Geometry of the Tooth Preparation

Factors influencing geometry of tooth preparation:

• Taper
• Surface area
• Stress concentration
• Type of preparation.

Taper

• Maximum retention is obtained if a tooth preparation has parallel walls
• Smaller degrees of taper have more retention
• Two opposing surfaces each with a 3° taper provide a 6° taper for the preparation
• The ideal convergence between opposing walls is 6°
• This amount of convergence is required to restrain the cemented restoration.

Factors decreasing retention with regard to taper

• Less amount of taper will form an undercut in an occlusocervical direction
• An increased amount of taper increases the free movement of the restoration and retention will be reduced (experimented by Jorgensen in 1955).

Preparation rule in Fixed Partial Denture

• A rotary instrument of the desired taper held at a constant angulation produces the amount of taper required
• The rotary instrument of ideal taper when moved through a cylindrical path during tooth preparation will produce the desired axial wall taper on the completed preparation.

Surface area in Fixed Partial Denture

• The greater the length of the clinical crown, the more is the retention
• Short clinical crowns require the help of grooves and box preparation for increased retention
• The greater the width of the clinical crown, the better the retention
• A restoration with a limited path of withdrawal is more retentive depending on the length of the surface area in sliding contact.

Stress Concentration in Fixed Partial Denture

• Round margins reduce stress concentrations and increase the retention of the restoration
• Stresses are generally concentrated around the junction of the axial and occlusal surfaces.

Type of preparation  in Fixed Partial Denture

• Additional grooves and boxes to preparation with a limited path of withdrawal increase the retention
• Retention is double for complete crowns than for a partial crown
• Luting agent is only effective if the restoration has a single path of withdrawal
• The occlusoaxial line angle of the tooth preparation should be a replica of the gingival margin geometry
• Fixed prostheses depend on the geometric form rather than on the adhesion of the luting agents for retention.

Roughness of the surfaces

• Retention is increased if the restoration is roughened or grooved by air-abrading the fitting surface with alumina
• If the internal surface of a restoration is very smooth, retentive failure can occur.

Materials being cemented

• The more reactive base-metal alloys have more adhesion with certain luting agents than less reactive high-gold content metals
• Cement adheres better to amalgam than to composite resin or cast gold.

Type of luting agent

Adhesive resin cements are the most retentive.

Instructions to crown and bridge patients regarding care and maintenance.

Fixed Partial Dentures Significance

After placement and cementation of fixed dental prostheses improper maintenance programs are the major cause of failures in fixed partial dentures.

Hence, the maintenance program is aimed at reinforcing meticulous plaque control habits, identifying incipient caries/gingivitis, and introducing corrective treatment wherever required.

Post cementation instructions

• The patient is advised to chew food only one hour after cementation
• Is instructed to avoid biting on hard foods for at least 24 hours to achieve maximum strength
• The patient is warned to expect mild to moderate sensitivity to hot and cold food/drink for a few days after cementations over vital teeth
• The patient is advised against flossing for a couple of days but brushing can commence almost immediately
• If the bite does not feel normal the patient is asked to report to the dentist
• The patient is instructed in special plaque control measures to use floss and floss threaders
• The patient is instructed on the importance of attending recall visits every six months.