Direct retainers (general considerations) & Suprabulge direct retainers

Retention for denture its resistance to removal in a direction opposite that of its insertion. ( away from the supporting tissue in a vertical direction)

What are the forces that can displace the denture from tissue ?

Direct retainer is any unit of a removable dental prosthesisthat engages an abutment tooth to resist displacementof the prosthesis away from basal seat tissue.

Direct Retainers

Retention of partial denture

Mechanical means friction : • precision attachments ( direct retainers ) • guide planes flexibility

Physical forces of adhesion and cohesion could supplement the retention obtained by mechanical means

Types of Directs Rerainers

Intra-coronal retainer

extra-coronal retainer

Intracoronal retainer consists of a key and keyway

• Esthetics • Better support

•More abutment prep•Complicated •Difficult to repair •Cost•Least effective on short teethSize of the pulp of abutment teeth

Intracoronal retainer

Advantages Disadvantages

Extracornnal direct retainers (clasp retainers )

• Any clasp design should include 180 degree of circumference of the crown of the tooth

• Occlusal rest should prevent any movement of clasp cervically

• Each retentive arm should be opposed by a reciprocal arm

• The path of escapement of each retentive terminal must be other than that of the selected path of removal of prosthesis

• The amount of retention should always be minimum necessary to resistdisplaemnt

Basic Requirements of clasp :

• Clasp on abutment teeth adjacent to distal extension bases should avoid transmission of tipping and rotational forces to the abutment

• Ideally ,the reciprocal arm should be located at the junction of the gingival and middle third of the crown

• Unless guiding planes will positively control the path of removal and stabilize abutments against rotational movements ,retentive clasps should be bilaterally opposes

Extracornnal direct retainers (clasp retainers )

Basic Requirements of clasp :

FACTORS DETERMINING THE AMOUNT OF CLASP RETENTION

① Angle of cervical convergence ② Depth of undercut engaged ③ Flexibility Length Tapered Diameter Cross-sectional form Material

Functions of a Reciprocal Arm

Provides reciprocation against the action of retentive arm

Provided stability against horizontal forces

May acts as an indirect retainer

Classification of Extra coronal Direct Retainers

• A retainer that encircles a tooth by more than 180 degree and follows the contour of the tooth , with one terminal engages the undercut of the tooth from the occlusal direction .

A. supra-bulge or circumferential clasp

• A clasp whose body extends from minor connector or denture base , passing adjacent to the soft tissue , and approach the tooth from a gingivo-occlusal direction

B- Infra-bulge or Bar clasp

SUPRA-BULGE DIRECT RETAINERS

1-circlet 2-multiple clasp3-embrasure clasp4- ring clasp 5- reverse action 6- combination clasp 7- half &half clasp

Circlet clasp

Ring clasp

Embrasure clasp

Two retentive arm and two reciprocal arm either bilaterally or diagonally I

Always should be used with double occlusal rest. this is done to avoid interproximal wedging by prosthesis ,whish could cause separation of the abutment and result in food impaction and clasp displacement ,

In addition to providing support , occlusal rest also serve to shunt food away from

The contact area should not be eliminate entirelyUnmodified class II or class III

Multiple clasp

It is simply two opposing circlet clasp joined at the terminal ends of two reciprocal arms

It uses when additional retention and stabilition are need

Usually on tooth – supported partial dentureMultiple clasping when a partial denture replace an

entire half of the dental arch

Two embrasure approaches disadvantage

Multiple clasp

Consists of a circumferential retentive arm arisingfrom one direction and a reciprocal arm arisingfrom anotherRare Unilateral partial denture

Half & Half clasp

for tooth supported denture that proximal undercut below the points of origin & tissue undercut prevents use of a Bar clasp

• Covers to much of a tooth structure • its occlusal origin may increase the functional load

on the tooth ,and its flexibility is limitedes • Traps debris• Esthetics

Reverse action / Hairpin clasp

Indications

Disadvantages

• Its consist of a wrought wire retentive arm and cast reciprocal arm

• Flexibility• Adjustable • Minimum tooth surface coverage • Less likely occur fatigue failure

Combination clasp

Advantages

It involves extra steps in fabrication It may be distorted by careless handling on

the part of the patient It may be less accurately adapted to the tooth It may distort with function and not engage

the tooth.

Disadvantages

Indications

• It is used when maximum flexibility is desirable, such as on an abutment

• tooth adjacent to a distal extension base or on a weak abutment when a bar-type direct retainer is contraindicated

The End

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