lect 7 - bar type precision attachments

splint bar indications

anterior teeth severe resorption of residual ridge

too much vertical space prevents the use of a FPD

esthetic requirements

smooth contoured bar resting lightly on the gingival tissues to support the RPD

lower incisors splint together with a splint bar to enhance longevity

tissue surfaces are minimally contacted by the rounded form

floss to clean inferior portion of splint

connecting bar

• cast of rigid alloy

• soldering not recommended as weaker

• available in plastic can be customised for length and cast in metal alloy

• internal clip attachements commercially available

cross-section and appearance

Gilmore - oval

Reichenbach - rectangular

Dolder - egg-shaped

diameter shouldn’t exceed 2.35mm

egg-shaped most favourable because it allows the saving of the abutment teeth and retention

most common dimensions :

height - 3mm

width - 2mm

OR

height - 2.2mm

width - 1.46mm

Dolder dimensions

height : 3mm or 2.2mm

width : 2mm or 1.46mm

widest part of the egg shape used in the upper 3rd so the retention minimum 2/3rd is used

clip attachment

longer = better retention

resembles the shape and cross section of the bar, opened from the bottom side and distance between edges is smaller then the widest part of the bar element

can be easily replaced to compensate the subsiding of the denture and facilitate abutments

Wirz

elongating clip attachment x1.5 can double the retentional force

Popoy & Manchev

splint bar made of plastic (polyethene, polypropylene) using element + many chewing cycles friction is increased and can be easily replaced to compensate subsiding of dentur

clip attachment

1. resilient - withstands from the bar on a distance that is more than the mucosal resilience

2. rigid - clip attachment in contact with the bar

3. PD physiologically engages abutment teeth pathophysiologically by bone

3 types of movements of the denture over the egg shaped splint bar

1. vertical translation

2. sagittal rotation

3. frontal rotation

constructional principles

1. bar must withstand from the gingiva 1-2mm ( to allow flossing)

2. bar must connect abutments in a straight line

3. bar must be perpendicular towards the rotational movements

4. if 2 bars used they must never be bigger than 30o angle one towards another

5. vestibular flange of denture should be as short as possible (if there is a vacuum here there will be a hypertrophia of the soft tissue under the bar closing the 1-2mm gap under the gingiva)

telescopic crowns

• consist of inner and outer telescope or primary/secondary

• firmly attached to one another caps

• can’t be prefabricated

• can be made cylindrical or conical

Bottger

need as much contact between the inner and outer telescope for better retention

Korber

conical telescopic crown

4-8o optimal for friction force of 5-9N

opened telescopic crowns/ring

in cases where the occlusal surface cannot be prepared properly

restricts subsiding of secondary crown

indication for RPD with precision attachments

1. attachment with 1 direction of movement - rectangular bar

2. attachments with 2 directions of movement class III and IV

3. attachments with 3 directions of movement class I and II

contraindication for RPD with precision attachments

1. abutments with short clinical crowns

2. parallelism among abutments can’t be achieved

3. retentive alvolar ridges

4. abutments with peripheral lesions

5. abutments with perodontophathia gr. II and III