Direct RetainersDirect Retainers

Infra Bulge Direct RetainersInfra Bulge Direct Retainers

Dr.Mohammad Al SayedDr.Mohammad Al Sayed26/4/200826/4/2008

Infra Bulge Retainers:Infra Bulge Retainers:Bar clasp:Bar clasp: (Roach) (Roach)

Bar clasp originate from denture Bar clasp originate from denture framework or a metal base and framework or a metal base and approaches the retentive undercut approaches the retentive undercut from a gingival directionfrom a gingival direction..

* *Other bar clasps e.g. T bar or modified T Other bar clasps e.g. T bar or modified T bar do not have a tripping action since bar do not have a tripping action since the retentive terminal engages the the retentive terminal engages the

undercut from an occlusal directionundercut from an occlusal direction . .

* *The push type retention of bar clasps is The push type retention of bar clasps is more effective than the pull retention of more effective than the pull retention of

a circumferential claspa circumferential clasp..

Types of bar claspsTypes of bar clasps::

* *The bar clasp arm is classified by the The bar clasp arm is classified by the shape of the retentive terminal into: T, shape of the retentive terminal into: T, modified T, I, Y or any letter clasp armmodified T, I, Y or any letter clasp arm..

* *Bar clasp arms generally are used on the Bar clasp arms generally are used on the buccal surfaces of teeth in combination buccal surfaces of teeth in combination with lingual circumferential clasp armswith lingual circumferential clasp arms..

Some types of bar clasps e.g. “I” bar are Some types of bar clasps e.g. “I” bar are “Push” type having a tripping action “Push” type having a tripping action

Tripping ActionTripping Action:: Is caused by a clasp arm that engages the Is caused by a clasp arm that engages the

undercut directly from a gingival undercut directly from a gingival directiondirection . .

Rules applied to bar type claspRules applied to bar type clasp::

11..The approach arm of a bar clasp must The approach arm of a bar clasp must never impinge on soft tissues. never impinge on soft tissues. Adequate relief must be applied under Adequate relief must be applied under

the armthe arm . .22..The approach arm must always taper The approach arm must always taper

uniformly from its attachment at the uniformly from its attachment at the frame to the claspframe to the clasp . .

33..The approach arm must never cross a The approach arm must never cross a deep soft tissue undercut requiring a deep soft tissue undercut requiring a great deal of relief. This will result in a great deal of relief. This will result in a food trap or lead to injury of the food trap or lead to injury of the

mucosa of the lip or cheekmucosa of the lip or cheek . .

44..A bar clasp usually engages .02 inch A bar clasp usually engages .02 inch undercut except for the “I” bar which undercut except for the “I” bar which engages .01 inchengages .01 inch..

55..The occlusal rest of the clasp assembly The occlusal rest of the clasp assembly must be thick enough to provide must be thick enough to provide adequate support without breaking and adequate support without breaking and to avoid impinging of the soft tissue due to avoid impinging of the soft tissue due

to settling of the approach armto settling of the approach arm . .66..The minor connector (proximal plate) The minor connector (proximal plate)

should be rigid and strong to provide should be rigid and strong to provide some bracing to the partial denturesome bracing to the partial denture..

77..The Approach arm should cross the The Approach arm should cross the gingival margin at 90° angle to avoid gingival margin at 90° angle to avoid

irritationirritation . .

88..The distance between the vertical The distance between the vertical projection arm and other vertical projection arm and other vertical component should be at least 5mmcomponent should be at least 5mm..

99..The retentive terminal of a bar clasp The retentive terminal of a bar clasp should point toward the occlusal surface should point toward the occlusal surface never towards the gingivanever towards the gingiva..

* * It must be kept as low as possible on the It must be kept as low as possible on the tooth to reduce leverage tooth to reduce leverage . .

* * Flexibility of bar clasps can be Flexibility of bar clasps can be controlled by the taper and length of controlled by the taper and length of the approach arm. The greater the the approach arm. The greater the length and more taper the more length and more taper the more

flexible the clasp will beflexible the clasp will be . .

AdvantagesAdvantages::

11..Greater retention than occlusally Greater retention than occlusally approaching due to the trip actionapproaching due to the trip action . .

22..It is more esthetic than the occlusally It is more esthetic than the occlusally approaching claspsapproaching clasps..

33..The flexibility of the bar clasp arm can be The flexibility of the bar clasp arm can be controlled by its taper and lengthcontrolled by its taper and length . .

44..Covers less tooth structure than the Covers less tooth structure than the occlusally approaching clasp (less caries occlusally approaching clasp (less caries susceptibility)susceptibility)..

DisadvantagesDisadvantages::

11..Greater tendency to collect and hold Greater tendency to collect and hold food debris (more gingival food debris (more gingival

irritation)irritation) . .

22..The retentive arm does not The retentive arm does not contribute to bracing and stabilitycontribute to bracing and stability . .

ContraindicationContraindication::

11..When a deep cervical tooth undercut When a deep cervical tooth undercut exists exists..

22..When a severe tissue undercut When a severe tissue undercut exists exists..

33..When there is a shallow vestibuleWhen there is a shallow vestibule..44..When there is excessive buccal or When there is excessive buccal or

lingual tilt of the tooth lingual tilt of the tooth . .55..When the height of contour is close When the height of contour is close

to the occlusal surface of the to the occlusal surface of the toothtooth . .

Types of the gingivally approaching claspsTypes of the gingivally approaching clasps::

11..Bar Clasp (Roach or vertical Bar Clasp (Roach or vertical projection)projection)

Indications: 1.On abutment for tooth supported or

tooth-mucosa supported RPD when there is distobuccal undercut .

2.In situations in which esthetics is important.

DesignDesign::

11..Component parts: It is usually used as a Component parts: It is usually used as a combination clasp formcombination clasp form..

a) Resta) Rest.. b) Minor connectorb) Minor connector..

c) A cast bar retentive clasp armc) A cast bar retentive clasp arm.. d) A cast circumferential bracing d) A cast circumferential bracing

clasp armclasp arm..22..Provides unilateral bracingProvides unilateral bracing..

33..Engages 0.01 inch undercutEngages 0.01 inch undercut..44..The shape of the retentive terminal as a The shape of the retentive terminal as a

T,Y, or I classify the bar claspT,Y, or I classify the bar clasp

- -The I and Y retentive clasp arm provide The I and Y retentive clasp arm provide tripping action, which is called push type tripping action, which is called push type claspclasp..

- -The T and modified T clasps did not have The T and modified T clasps did not have tripping action since the retentive tripping action since the retentive terminal actually engage the undercut terminal actually engage the undercut from an occlusal direction. One terminal from an occlusal direction. One terminal of the T-bar clasp lies above the survey of the T-bar clasp lies above the survey line for bracing and the other terminal line for bracing and the other terminal below the survey line for retention. The below the survey line for retention. The modified T-bar clasp has only one modified T-bar clasp has only one

terminal below the survey lineterminal below the survey line . .

Lingual view Buccal view

22..RPI ClaspRPI Clasp::

IndicationIndication::Commonly used for tooth mucosa borne partial Commonly used for tooth mucosa borne partial denturesdentures..DesignDesign::

11..It consists ofIt consists of:: a) Mesial resta) Mesial rest..

b) Minor connector; placed into the b) Minor connector; placed into the mesiolingual embrasure, but not contacting mesiolingual embrasure, but not contacting the adjacent tooththe adjacent tooth . .

c) Proximal plate contacts approximately 1 mm of c) Proximal plate contacts approximately 1 mm of the gingival portion of guiding plane the gingival portion of guiding plane..

d) Cast I bar retentive clasp arm located at the d) Cast I bar retentive clasp arm located at the mesiobuccal prominence of the tooth or mesiobuccal prominence of the tooth or

mesial to itmesial to it..

22 . .Engages 0.01 inch undercutEngages 0.01 inch undercut..

33 . .Provide unilateral bracingProvide unilateral bracing..

44 . .The proximal plate and the minor connector The proximal plate and the minor connector provide stabilization and reciprocation provide stabilization and reciprocation..

55 . .During function, proximal plate and I-bar clasp During function, proximal plate and I-bar clasp arm move in a mesiogingival direction- arm move in a mesiogingival direction- disengaging tooth. This distribute more disengaging tooth. This distribute more

functional load to edentulous ridgefunctional load to edentulous ridge . .

Combination claspCombination clasp::

IndicationIndication::Commonly used for tooth mucosa Commonly used for tooth mucosa borne RPD, when there is borne RPD, when there is mesiobuccal undercut on the mesiobuccal undercut on the abutment toothabutment tooth..

DesignDesign::

11..Component parts areComponent parts are::

a) Resta) Rest..

b) Minor connectorb) Minor connector..

c) Wrought wire circumferential c) Wrought wire circumferential retentive clasp arm retentive clasp arm . .

d) Cast circumferential bracing clasp d) Cast circumferential bracing clasp arm arm . .

22..Engages 0.01-0.02 inch undercutEngages 0.01-0.02 inch undercut..

33..Provides bilateral bracing, but less than a Provides bilateral bracing, but less than a cast circumferential clasp cast circumferential clasp . .

AdvantagesAdvantages::

11..Greater flexibilityGreater flexibility..22..It is more esthetically acceptable because It is more esthetically acceptable because

it is placed too much gingival it is placed too much gingival..33..It flex in all directions (round in cross It flex in all directions (round in cross

section), Which allow it to dissipate section), Which allow it to dissipate forces exerted on the abutment toothforces exerted on the abutment tooth..

44..The retentive arm can be adjusted in all The retentive arm can be adjusted in all directions directions..

55..Makes little tooth contact (line contact, Makes little tooth contact (line contact, rather than the surface contact of the rather than the surface contact of the

cast clasp arm)cast clasp arm)

DisadvantagesDisadvantages::

11..It is easily distorted or fractured by It is easily distorted or fractured by careless handling by the patientcareless handling by the patient..

22..It does not possess the bracing and It does not possess the bracing and stabilizing qualities of cast clasp stabilizing qualities of cast clasp armarm..

33..It involves extra step in fabricationIt involves extra step in fabrication . .

Criteria for clasp selectionCriteria for clasp selection::

The selection of the clasp depends The selection of the clasp depends mainly on the type of support, the mainly on the type of support, the presence of undercut areas, and presence of undercut areas, and estheticsesthetics..

11..For bounded saddle; the retentive For bounded saddle; the retentive undercut present is used with any undercut present is used with any acceptable clasp type (clasping for acceptable clasp type (clasping for convenience)convenience)..

22..For distal extension base; a stress For distal extension base; a stress releasing clasp that equitably distribute releasing clasp that equitably distribute the force between the abutment and the the force between the abutment and the ridge is usedridge is used . .

a) If a mesiobuccal undercut is available a) If a mesiobuccal undercut is available on the terminal abutment, a on the terminal abutment, a

combination clasp with the wrought combination clasp with the wrought wire, RPI, or RPA clasps are used wire, RPI, or RPA clasps are used . .

b) If the retentive undercut is located on b) If the retentive undercut is located on the distobuccal surface, a bar clasp, the distobuccal surface, a bar clasp, reverse circlet (the minor connector reverse circlet (the minor connector and the occlusal rests are placed and the occlusal rests are placed

mesially) and the C-clasp are usedmesially) and the C-clasp are used . . c) If mesiolingual undercut is present a c) If mesiolingual undercut is present a

wrought wire clasp is used wrought wire clasp is used . .