1. Direct retainers (general considerations) &
Suprabulge direct retainers

2. Retention
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 ?

3. Direct Retainers
Direct retainer is any unit of a removable dental prosthesis that engages an abutment tooth to resist displacement of the prosthesis away from basal seat tissue.

4. 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

5. Types of Directs Rerainers
Intra-coronal retainer
extra-coronal retainer

6. Intracoronal retainer consists of a key and keyway

7. Intracoronal retainer
Advantages
Disadvantages
Esthetics
Better support
More abutment prep
Complicated
Difficult to repair
Cost
Least effective on short teeth
Size of the pulp of abutment teeth

8. Extracornnal direct retainers (clasp retainers )
Basic Requirements of clasp :
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

9. Extracornnal direct retainers (clasp retainers )
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

10. Factors Determining the Amount of Clasp Retention

11. Angle of cervical convergence
Depth of undercut engaged
Flexibility
Length
Tapered
Diameter
Cross-sectional form
Material

12. Functions of a Reciprocal Arm
Provides reciprocation against the action of retentive arm
Provided stability against horizontal forces
May acts as an indirect retainer

13. Classification of Extra coronal Direct Retainers

14. A. supra-bulge or circumferential clasp
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 .

15. B- Infra-bulge or Bar 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

16. Supra-bulge direct retainers

17. 1-circlet 2-multiple clasp 3-embrasure clasp 4- ring clasp 5- reverse action 6- combination clasp 7- half &half clasp

18. Circlet clasp

19. Ring clasp

20. 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 entirely
Unmodified class II or class III

22. 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 denture
Multiple clasping when a partial denture replace an entire half of the dental arch
Two embrasure approaches disadvantage

23. Multiple clasp

24. Half & Half clasp Consists of a circumferential retentive arm arising
from one direction and a reciprocal arm arising
from another
Rare
Unilateral partial denture

25. Reverse action / Hairpin clasp
Indications
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
Disadvantages

27. Combination clasp Advantages
Its consist of a wrought wire retentive arm and cast reciprocal arm
Flexibility
Adjustable
Minimum tooth surface coverage
Less likely occur fatigue failure
Advantages

29. Disadvantages 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.

30. 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

31. Thank You
The End