Mouth Preparation

Lecture given 1/7/2026

when preparing a mouth for RPD, what are some reasons extractions may need to be done?

periodontally hopeless teeth, residual roots, teeth detrimental to the design of RPD, impacted teeth (if detrimental)

what can be done about too little interarch space?

osteotomy

t/f bony exostoses or tori do not ever have to be removed when preparing a mouth for RPD

false- sometimes surgery to remove them should be considered

what soft tissue factors may need to be surgically altered before designing an RPD?

movable soft tissue, muscle and freni attachments, or a need for increased vestibular depth

what are all of the surgical considerations for mouth preparation for RPDs?

extractions, osteotomy, bony exostoses or tori, movable soft tissue, knife edge residual ridge, muscle and freni attachments, vestibular depth, implant placement, severely malposed or extruded teeth

what can be done about severely malposed or extruded teeth?

extraction or orthodontic correction

what periodontal considerations need to be made when planning for RPD?

optimal periodontal conditions should be present before RPD treatment is considered, good plaque control and home care are essential

what restorative considerations need to be made when planning for RPD?

removal of caries, replacement of defective restorations, restorations of structurally compromised teeth, occlusal plane evaluation, condition of natural teeth

what should be considered when examining the condition of natural teeth?

splinting, full coverage restorations, RPD design modifications

t/f you should expose dentin when you are preparing teeth for RPD

false- exposing dentin during preparation can lead to sensitivity and increased caries susceptibility

what are the objectives of mouth preparation?

create acceptable path of insertion, optimize esthetics, ensure comfort/retention/stability/support

what is the sequence in which mouth preparation should be performed?

guiding planes, heigh of contour adjustment, retentive grooves or depressions, rest seats

what are the 2 methods of transferring the position on the cast into the mouth?

making a tray similar to a cast for a full denture with burs in it

make a guide with acrylic

guiding planes

tooth surfaces where minor connectors (guide plates) will be placed

where should guiding planes be located?

occlusal to middle third, 2-4mm long

remember to blend the proximal area facio-lingually

t/f when creating guiding planes, lingual surfaces may need adjustment to optimize reciprocal arm contact

true

t/f guide plane creation on anterior teeth can help to re-establish needed space and/or reduce the black triangle that may be visible

true

what is the purpose of adjustment of the height of contour?

allows the proper placement of the retentive arm above the height of contour

t/f retentive dimples should have sharp edges to make sure it is retentive

false- should not be sharp, should be rounded and care should be taken to minimize the risk of enamel perforation or creation of excessive undercuts

what are the important measurements to know for rest seat preparation?

1.5mm reduction at the marginal ridge, 0.5mm deeper at the deepest portion, less than 90 degrees

what are the important properties to know for rest seat preparation?

rounded line angles, 1/3 to 1/2 of the mesio-distal length, 1/2 of the inter-cuspal distance

embrasure occlusal rest seats

two conjoined rest seats facing each other, additional reduction on buccal and lingual areas (channels) are needed to allow for metal thickness

what are the important properties of cingulum rest seats?

should have rounded internal angles, extend from marginal ridge to marginal ridge

mesio-distal width of 2.5-3mm

facio-lingual width of 2mm

inciso-gingival depth of 1.5mm

t/f the axial wall of a cingulum rest seat should be parallel to the path of insertion

true

mesio-lingual rest

located at the middle 1/3, requires marginal ridge reduction

t/f it is fine to have rest seat margins at the junction between restorative material and tooth structure

false- you should avoid doing this

extensive restorations may require…

the placement of full coverage restorations (AKA surveyed crowns) to protect the abutment tooth

surveyed crown

a crown made to ideal form…

ideal retetive contour, ideal guide plane, ideal rest, ideal reciprocation

slight adjustment on preparation is needed to account for the location of the rest seat