RPI SYSTEM

INTRODUCTION –

• The current concept of increasing the retention & stability of RPD by changing the fulcrum location is known as RPI system. Here “R” stands for mesio-occlusal rest, “P” stands for proximal plate, & “T” stands for “I” bar of clasp assembly.

OBJECTIVE-

• Distal extension of RPD acts as a long effort arm across the distal rest fulcrum to cause the clasp tip resistance arm to engage the tooth undercut. This results in a harmful tipping or torquing of tooth & is greater with stiff clasp & more denture base area causing poor retention & stability of RPD. To improve these problems changing the fulcrum location & increasing the resistance arm engaging effect can be brought by RPI system.

INDICATION-

• 1) In kennedy class 1 cases where denture retention depends on tissue borne saddle.

• 2) In kennedy class II cases where both tooth & tissue borne retention is needed.

• 3) In kennedy class II, modification cases.• 4) In case of long effort arm where fulcrum

line is needed to be changed & resistance arm is to be increased.

CONTRA-INDICATION-

• When the abutment tooth is inclined lingually or buccaly.

• In severe undercut areas.

• Where sulcus depth is insufficient.

• In those cases where distal abutments teeth are distally tilted.

Disadvantage-

• Gingivally approaching “I” bar causing food impaction & resulting in periodontal problem.

The components of this

clasp assembly are:• "R" - rest (always

mesial)• "P" - proximal plate• "I" - I-bar (retentive

arm)

The rest is located on the mesio-occlusal surface of a premolar or mesiolingual surface of a canine. The minor connector is located in the mesio-lingual embrasure but is not in contact with the adjacent tooth (prevents wedging).

• The proximal plate (essentially a wide minor connector) is located on a guide plane on the

distal surface of the tooth. The superior edge of the proximal plate is located at the bottom

of the guide plane (at approximately the junction of the occlusal and middle third of the

guide plane). The proximal plate extends lingually so that the distance between the minor

connector and the proximal plate is less than the mesio-distal width of the tooth. The

plate is approximately l mm. thick and joins the framework at a right angle.

• The I-bar clasp is located on the buccal surface of the premolar and on the mesio-buccal

surface of the canine. The I-bar originates at the gridwork and approaches the tooth from

the gingival direction. The bend in the I-bar should be located at least 3 mm. from the

gingival margin. This distance will prevent food entrapment and provide the length for the

necessary flexibility in the clasp arm. The clasp is usually cast and is placed just below the

height of contour line.

• On premolars, the proximal plate should extend lingually so that the distance between

the proximal plate and the mesio-occlusal rest is less than the mesio-distal width of

the tooth. The proximal plate in conjunction with the mesial rest (and minor connector)

acts as the reciprocating element of the clasp and prevents the lingual migration of the tooth

when the clasp arm moves over the height of contour.

• On cuspids, the minor connector cannot be used for reciprocation since it does not contact

the tooth until after the retentive element has passed across the height of contour and the

partial denture is seated. This is because the mesio-lingual rest is located fairly low on the

cingulum of the tooth. Therefore, the I-bar is located in the mesio-buccal undercut and

is reciprocated directly by the proximal plate.

• The guiding plane is a parallel surface prepared on the occlusal one third of the distal

surface of the tooth. The guiding plane extends lingually enough so that, along with the

mesial rest, it can prevent lingual migration of the tooth. It is approximately 2 to 3 mm in

height.