Types of clasp assemblies:
أنواع تجميعات المشبك:

They are of two types:-
هم من نوعين: -

1. Clasps designed without movement accommodation.
1. المشابك المصممة بدون إقامة الحركة.

2. Clasps designed to accommodate distal extension functional movement.
   مشابك مصممة لاستيعاب الحركة الوظيفية للتمديد البعيد.

Clasps for tooth-borne partial dentures (Class III and IV) have one function ( to prevent dislodgment of the prosthesis without damage to the abutment teeth). Since there is little or no rotation caused by tissue ward movement of the edentulous area (as happens in distal extension cases) stress releasing properties are usually not required. These clasps can also be used in modification spaces for tooth and tissue supported removable partial dentures (Class I and II). 

Circumferential (Circle or Akers) clasp: 

• The circumferential clasp will be considered first as an all-cast clasp and it is the simplest one. 
• The basic form of the circumferential clasp is a buccal and lingual arm originating from a common body (principle occlusal rest and minor connector). 
• The circumferential clasp has only one retentive clasp arm, opposed by a non-retentive reciprocal arm on the opposite side. 
• It approaches the undercut area from an occlusal direction so it is called (occlusally approaching clasp) since it is coming to the undercut area from above the bulge area socalled (supra-bulge clasp) and since it is pulling the tooth during action also called (pull clasp and also called Aker clasp. 
• The retentive arm begins above the height of contour, and curves and tapers to its terminal tip, in the gingival $1/3$$1/3$1//31 / 3 of the tooth, well away from the gingiva. 
• The bracing (non-retentive reciprocal) arm is in the middle $1/3$$1/3$1//31 / 3 of the tooth, and is broader occlusal - gingivally, does not taper and is either entirely above the height of 
  contour or completely on a prepared guiding plane - it should never be designed into an undercut, as it is a rigid element. 
• Support is provided by occlusal rest; stabilization is provided by occlusal rest, proximal minor connector, lingual clasp arm and rigid portion of buccal retentive clasp arm occlusal to the height of contour; retention is realized by the retentive terminal of buccal clasp arm; reciprocation is provided by nonflexible lingual clasp arm. Clasp Assembly engages more than 180 degrees of abutment tooth’s circumferences. 
  

  

Indications:  مؤشرات:

• It is a most logical clasp to use with all tooth-supported partial dentures because of its retentive and stabilizing ability.
  إنه المشبك الأكثر منطقية للاستخدام مع جميع أطقم الأسنان الجزئية المدعومة بالأسنان بسبب قدرته على الاحتفاظ والتثبيت.
• On free end extension when minimal undercut is utilized.
  على تمديد الطرف الحر عند استخدام الحد الأدنى من التقويض.

Contraindication:  موانع الاستعمال:

• When the retentive undercut may be approached better with a bar clasp arm.
  عندما يمكن الاقتراب من القطع المحتجزة بشكل أفضل باستخدام ذراع مشبك الشريط.
• When esthetics will be enhanced by using bar clasp arm. 

Advantages: 

• Excellent bracing qualities.
  صفات تستعد ممتازة.
• Easy to design and construct.
  سهل التصميم والبناء.
• Less potential for food accumulation below the clasp compared to bar clasps. 

Disadvantages: 

• More tooth surface is covered than with a bar clasp arm because of its occlusal origin.
• On some tooth surfaces, particularly the buccal surface of mandibular teeth and the lingual surfaces of maxillary teeth, its occlusal approach may increase the width of the occlusal surface of the tooth (occlusal table).
• In the mandibular arch, more metal may be displayed than with the bar clasp arm.
• Its half-round form prevents adjustment to increase or decrease retention. True adjustment is impossible with most cast clasps.

The circumferential type of clasp may be used in several forms:

1. Ring-type clasp:

• Ring clasp, which encircles nearly all of a tooth from its point of origin.
• Usually used with mesially and lingually tilted mandibular molars or the undercut is on the same side as the rest seat (i.e. adjacent to edentulous span).
• The clasp should never be used as an unsupported ring because if it is free to open and close as a ring, it cannot provide either reciprocation or stabilization. Instead, the ring type clasp should always be used with a supporting strut on the non-retentive side, with or without an auxiliary occlusal rest on the opposite marginal ridge.
  

  

• The advantage of an auxiliary rest is that further movement of a mesially inclined tooth is prevented by the presence of a distal rest. In any event, the supporting strut should be regarded as being a minor connector from which the flexible retentive arm originates.
• Reciprocation comes from the rigid portion of the clasp lying between the supporting strut and the principal occlusal rest.
• The ring-type clasp should be used on protected abutments whenever possible because it covers such a large area of the tooth surface.