Major connector of RPD l Removable partial denture MCQs

Major connector of RPD l Removable partial denture MCQs (multiple choice question) for dental students

 

Maxillary major connectors

Single palatal strap

• Used in cases of bilateral, short span, tooth borne restorations

• Disadvantage :

1. not very rigid – to make it rigid it will become bulky

• It should be as wide as the max PM and 1st molar

U shaped palatal connector

• Least desirable of all max connectors
• Used in cases of inoperable tori [ located more posteriorly] or if Several anterior teeth need to be replaced
• Anterior border should be 6 mm away from teeth – if it touches teeth it should be supported by rests
• Any part of the connector that extends anteriorly from the principle occlusal rests should be supported by indirect retainers

• Disadvantage : 

1. not very rigid – to make it rigid it will become bulky

Combination anterior & posterior palatal strap like connector MOST RIGID TYPE

Used in cases of :

• Class 1 and class 2 arches with good abutments
• Long edentulous span [ class I and II ]
• Class III where ant teeth need replacing
• Inoperable palatal tori [ located in the cneter]

1. Can be : square, pallaleogram, rectangle
2. Ant and post strap = 6-9 mm longitudinal strap = 5-6 mm
3. Posterior strap is located at the junction of movable and immovable parts of the palate
4. Needs 6 mm relief from the gingiva

Palatal plate

• Thin contoured plate covering ½ or more of the palate

Used in cases of:

1. Class 1 with minimal ridge resorption
2. V or U shaped palates
3. No tori
4. More than the 6 anteriors remaining

• Does not extend anterior to the occlusal rests or indirect retainers
• Post border is slightly ant to the PSA but borders are extended to the hamular notches
• Can be ½ coverage or full coverage- full metal or ½ metal and ½ acrylic
• Casting anteriorly with retention posteriorly for acrylic → easier to reline and rebase + easier to make post seal

Indicated in:

1. Class 1 with one or more premolars + all anterior teeth
2. Class 2 with some missing anterior teeth
3. Full cast extending to PSA → expensive but more preferred by patient
4. Single palatal bar or anterior post palatal bar

Palatal bar

1. less than 8 mm width
2. Can be very thin and flexible or very bulky
3. Irritating to the tongue

 

N.B :

• Any part of the connector that touches teeth should be supported by rests
• rests should be anterior to the major connector ALWAYS

Mandibular major connectors

Lingual bar

• Used in cases where there is sufficient space between elevated alveolar lingual sulcus and lingual gingival tissues
• 4 mm from GM to the bar + 4 mm thickness of the bar + few mm below = 9-10 mm at least
• Superior border should be at least 4 mm away from gingival margin and should be tapered to the soft tissue without a step
• Inferior border at the height of the alveolar sulcus when the tongue is slightly elevated
• Disadvantage : traps food

 

Sublingual bar

• Used in cases that don’t have enough height of the floor of the mouth
• The bar is narrower than the lingual bar → more flexible → you need to use retainer on top of it.
• More uncomfortable to the patient

 

Lingual bar with continuous bar retainer

• Used in cases the axial alignment of teeth requires excessive block out of interproximal undercuts or if bar needs to be placed close to the gingival margin to obtain enough rigidity
• Located slightly above the cingulums of anterior teeth & extends to interproximal contact points MUST be supported by rests

 

Labial bar

Used in cases :

• Extreme lingual inclination of lower incisors and premolars
• Inoperable mand tori
• Lingually inclined teeth can be adjusted by disking, crowns , block out

 

Linguoplate

Used in cases:

1. The lingual frenum is high or there is no space for lingual bar
2. For stabilizing periodontally weakened teeth
3. In class 1 where the ridge had severe vertical bone resorption
4. If you expect one or more incisor teeth will be lost later → you can add artificial teeth by retention loops

• A thin metal apron extends superiorly to contact the cingula of anterior teeth and the lingual surfaces of post teeth up to the height of contour
• it extends inferiorly to the height of the alveolingual sulcus
• extends interproximally to the contact points

 

Q: how can you determine the height of the floor of the mouth?

1. By perioprobe and asking the pt to touch with their tongue the vermillion border of the upper lip ( from GM to floor of the mouth)
2. On the cast – make the special tray 3 mm short then during border molding ask the pt to lick their lips → inferior border is located on the cast

Indirect retainers: only in tooth tissue support

• Rest + minor connector located anterior to the fulcrum line
• Fulcrum line = an imaginary line that passes through the most posterior clasp assembly – indicates the line around which the denture will rotate during function

 

Types of indirect retainer:

• Occlusal rests
• Canine rests
• Canine extensions from occlusal rests

 

Cingulum bars ( continuous bars) + linguoplates act as indirect retainers

 

• In class 1 → ideal indirect retainer would be a mesial occlusal rest on the premolars or 2 cingulum rests
• In class 4 → embrasure clasps will act as indirect retainers
• In tooth supported RPD the occlusal stresses are transferred to the bone by the PDL ( PDL displaced only 0.25 mm)

• In tooth tissue supported RPD the occlusal stresses are transferred to the bone by PDL + mucoperiostum ( mucoperiosteum displacement = 2 mm)