CLASPS IN REMOVABLE ORTHODONTICS

The success of removable orthodontic appliance mainly depends upon good retention of the appliance. Adequate retention of a removable orthodontic appliance is achieved by incorporating certain wire components, called clasp, which engages the undercuts on the teeth. Clasps are the retentive components of removable orthodontic appliances. There are various designs of clasps advocated for various clinical situations. This article presents an overview of various clasp designs with advantages and disadvantages of each type and their uses in particular clinical situations.


Introduction
Clasps are wire components that aid in retention of a removable appliance . [1]These are the retentive components that aid in keeping the appliance in place and resist displacement of the appliance.

Mode of action
Clasps act by engaging constricted areas of the teeth, called undercuts.There are two types of undercuts found in natural dentition.
1. Buccal and Lingual cervical undercuts 2. Mesial and Distal proximal undercuts The mesial and distal undercuts of the teeth begin below the contact points. [2]These undercuts are accessible very soon after a tooth has erupted.The buccal and lingual undercuts are much less extensive and are not accessible until the teeth are fully erupted.Thus, a clasp that makes use of mesial and distal undercuts is more useful and more efficient than a clasp which makes use of buccal and lingual undercuts.

Jackson's clasp
It is also known as Full clasp or 'U' clasp.It was introduced by V H Jackson in 1906.This clasp makes use of bucco-cervical undercut and also the mesial and distal proximal undercuts.

Arrowhead Clasp
This clasp was introduced by A M Schwarz in 1956.This clasp makes use of mesial and distal undercuts.This clasp is made using half round or round stainless steel wire of 0.7 mm diameter.This clasp is made by use of a special plier called 'Tischler's plier'.Arrowheads-should be parallel to each other and should sit in the mesial and distal undercuts.
Retentive arms-continue on the lingual or palatal surface that get embedded into the acrylic.

Adam's clasp with incorporated helix
A helix is incorporated into the bridge of the Adam's clasp.This is also useful in engaging elastics.This modification is preferred on mandibular molars.

Adam's clasp with distal extension
A small extension is incorporated distally in the distal arrowhead.This distal extension helps to engage elastics.

Adam's clasp on incisors and premolars
This clasp is fabricated on incisors and premolars when retention is required in those areas.This clasp can be constructed in such a way that it can span a single tooth or two teeth.

Fig. Adam's clasp on incisors 4.8 Smart Clasp: -A modified Adam's clasp
This clasp was developed for use with magnetic activator device.The upper and lower plates, with incorporated magnets, of the appliance exert attracting or repelling force of about 600 gm. [3]A 2 mm loop on each side of arrowhead is given in the Adam's clasp.

Delta clasp
This clasp was designed by William J. Clark.This clasp is similar to Adam's clasp in principle.It engages interdental undercuts.Adjustment: -hold retentive loop and twist inwards.
-bending towards interdental undercut as it emerges from acrylic.

Triangular Clasp
It has a small triangular shape that engages the proximal undercut of two adjacent teeth.It provides excellent retention.It doesn't cause irritation of gingiva.It is used when additional retention is required.

Ball End Clasp
This clasp is also known as Scheau anchor clasp.This clasp has a ball at the end which engages the proximal undercut between two adjacent teeth (interdental area).Preformed wires having a ball at the end are used for making this clasp.The ball can also be made using silver solder.This clasp is used whenever additional retention is required.A bridge segment extends laterally between the flexible members of the first and second ball clasps. [6]This clasp does not exert any wedging force in the interdental embrasure like the single ball clasp.This clasp provides better retention.

Duyzing Clasp
This clasp has two wires emerging from the plate that cross the occlusion over the anterior and posterior contact point of the tooth clasped.Each wire then goes above the greatest circumference of the tooth to the middle of the tooth and again back below using undercuts.This clasp is used to engage the buccal undercuts of molars.If the situation demands, only half of the clasp can also be made. [5]g.
Duyzing's clasp [12] 13.Eyelet Clasp This clasp can be constructed as a single eyelet or continuous eyelet clasp. [5]An eyelet is made using a Young loop forming plier.Eyelets are placed in the embrasure.Three to four eyelets can be made depending upon the retention requirement.The size of the eyelet depends on the width of the interdental area of both anchor teeth. [9]g. Eyelet clasp

Fig. Circumferential
Fig. Circumferential Clasp Advantages:- Easy to construct  Simple design  Prevent mesial migration of tooth Disadvantage:- It can't be used in partially erupted teeth.

Fig.
Fig. Arrowhead clasp Advantages:- Good retention on partially erupted tooth  Eruption of tooth is not hampered Disadvantages:- Occupies large amount of buccal surface  Requires special plier and adequate skill for construction.

Fig.
Fig. Adam's clasp with J hook

Fig.Adam's clasp with incorporated helix 4 . 4
Fig.Adam's clasp with incorporated helix

Fig. Ball end clasp 9 .
Fig. Ball end clasp

Fig.
Fig. Double boule end clasp

Fig.
Fig. Schwarz clasp This clasp is not routinely used because:- It needs special arrowhead forming pliers. It occupies a large amount of space in the buccal vestibule. The arrowheads can injure the interdental soft tissues. It is difficult and time consuming to fabricate.