Lecture 8: Design For Tissue Support 2

It can be difficult to achieve, but an accurate fit of your metal framework on is essential for prosthodontic success. Why is a "near fit" RPD inadequate?

"nearly fitting" frameworks can be as damaging to the oral structures as poorly fitting frameworks. An RPD that is not quite seated can produce discomfort and destruction beyond what might be expected

You are designing an RPD. Your pt's mandibular arch includes teeth #18, #19, all six anteriors, and #29. You want to avoid having a pier abutment for a distal extension RPD. Of your 4 choices (bridge, implant, ignore, and extract), you and your patient choose a bridge. Which teeth #s will the bridge include?

#27-29 with #28 as pontic

Teeth present in mandibular arch include all anteriors, #29, and #31 Which tooth is the pier abutment?

#29 (lone standing premolar)

You are designing an RPD. Your pt's mandibular arch includes teeth #18, #19, all six anteriors, and #29. You want to avoid having a pier abutment for a distal extension RPD. Of your 4 choices (bridge, implant, ignore, and extract), you and your pt choose to extract. Which tooth/teeth will be extracted to solve your pier abutment problem?

#29 (make it a distal extension with #27 as free-end abutment)

1) T/F: A lone-standing premolar can successfully serve as a free-end/terminal abutment for a distal-extension RPD 2) T/F: Pier abutments have a very poor prognosis

1) false--"pier abutments" have a very poor prognosis when they are 2) false -- prognosis is poor only when they are free-end/terminal abutments for distal extension RPDs

1) ____ is the first and most important requirement of a major connector a) flexibility b) rigidity c) retention d) placement 2) How can you test this (^) when trying on metal framework?

1) rigidity (note: ack of rigidity can result in the localization of destructive forces and may cause traumatic injury to the teeth, soft tissues, and underlying bone) 2) apply light-to-moderate finger pressure to both sides of the framework simultaneously (arrows in image). The framework should be rigid enough to resist flexure.

Treatment planning includes a tentative design: 1. Rests are placed on the ____ surfaces of abutments adjacent to the distal extension bases 2. ____ are placed adjacent to modification spaces. 3. Reciprocation for distal extension applications is provided by long _____ _____ and properly positioned ____ (major/minor?) connectors. 4. Reciprocation for tooth-bounded applications may be provided by ____

1. MO 2. rests 3. guiding planes; minor 4. lingual plating (as depicted on the canine and molar)

advantages of the I-bar configuration include: 1. Food accumulation is minimized because tooth contours ____ (are/are not?) significantly altered. 2. ____ disengages from the tooth when an occlusal load is applied to the adjacent distal extension base. 3. Because the approach arm does not contact the abutment, ____ forces are minimized.

1. are not 2. clasp terminus 3. lateral

4 possible solutions for a "Pier abutment" aka a lone-standing premolar

1. extract 2. bridge 3. implant 4. ignore/skip over memory trick: BIIE (like byyyye Pier abutment) note: image shows pier abutment that is ignored/skipped over

Maxillary or mandibular major connector ? 1. should be placed on unattached mucosa 2. should be positioned at least 6 mm away from gingival margins 3. should be positioned at least 3 mm away from gingival margins 4. an AP strap is most recommended 5. a lingual bar is most recommended

1. mandibular 2. maxillary 3. mandibular 4. maxillary 5. mandibular (unless lingual tori are present or lingual sulcus is shallow, then use lingual plate)

list a convenient/common location to place a rest for indirect retention: 1. in mandibular arch 2. in maxillary arch

1. mandibular: occlusal rest in mesial fossa of first premolar 2. maxillary: cingulum rest on canine

(historically) 2 most commonly cited causes for abutment loss

1. overloading 2. perio disease (b/c overloading is related to RPD design and could be prevented, Kratochvil introduced I-bar design philosophy in 1963) from book, dont need to know name/year

2 most common areas of interference when adjusting fit of metal framework (i.e. areas of metal show-through on disclosing wax)

1. shoulders of circumferential clasps 2. interproximal extensions of lingual plating

1. 2 solutions for a tipped abutment tooth that results in an excessive undercut? a) ____ to reduce the undercut b) placement of a ____ 2. 2 solutions for a tipped abutment tooth that results in an inadequate undercut? a) preparation of a(n) ____ via enameloplasty b) use of an existing undercut on the ____ surface

1a) enameloplasty 1b) cast restoration (to provide improved abutment contours) 2a) undercut 2b) opposite (i.e. lingual vs. buccal)

How much relief is provided between denture base connectors and the dental cast? a) 1 mm b) 3 mm c) 5 mm d) NO relief provided

A (allows acrylic to encompass the connectors, thereby providing strong mechanical attachment)

Which of the following disclosing medias is recommended for intraoral fitting procedures? a) disclosing wax b) disclosing spray i.e. Occlude

A (sprays are messy/difficult to control in moisture)

Rests: a) provide vertical support against occlusal forces b) control vertical relationship between prosthesis and supporting structures c) control horizontal relationship between prosthesis and supporting structures c) A and B only d) all of the above

A and B only

Which of the following interfere with placement of infrabulge retentive elements? (select all that apply): a) frena b) high muscle attachments c) lack of attached gingiva d) lack of unattached gingiva e) tissue undercuts f) lingual tori

A, B, C, E

A cingulum rest seat: (select all that apply) a) can be prepared in enamel if abutment is large enough b) provides a positive seat c) provides a negative seat d) is rounded mesiodistally e) is straight mesiodistally f) can be prepared in maxillary central incisors

A, B, D, F *note: for F, can be prepared in bulky canines and maxillary central incisors (but mand ant teeth usually dont have enough enamel -- use incisal rest)

If the mandibular lingual sulcus is too SHALLOW, what major connector should be used? a) lingual bar b) lingual plate c) double lingual bar d) AP strap

B (lingual bar is first choice but requires >7mm depth of sulcus from gingival margin)

You are designing an RPD. Your pt's mandibular arch includes teeth #18, #19, all six anteriors, and #29. You want to avoid having a pier abutment for a distal extension RPD. Of your 4 choices (bridge, implant, ignore, and extract), you and your pt choose to have an implant placed. Listed below are different locations for the implant/crown. Pick the 3 options that would solve your pier abutment problem a) in place of #21 b) in place of #28 c) in place of #30 d) in place of #31 e) in place of #20

B, C, and D

In the passive state: a) rests make full contact with rest preparations b) extension bases are closely adapted to the soft tissues c) A and B d) none of the above

C

A lingual plate major connector is advocated when: a) space is inadequate for a lingual bar b) tooth or soft tissue contours promote food impaction c) A and B d) A and/or B

D

Incisal rests may be used: a) on mandibular anterior teeth when esthetics permit b) as a splint for periodontally weakened teeth c) on bulky maxillary canines d) A and B only e) B and C only f) all of the above

D (A and B only)

____ should be considered if adequate preparation of the guiding plane risks pulpal exposure.

Endodontic therapy

Which of the following are true regarding minor connectors? a) they join rests, proximal plates, and retainers to the major connector b) help provide horizontal stability c) are usually located in lingual embrasures d) they are designed to cross gingival margins at acute angles to minimize food impaction e) tooth contours are not altered where minor connectors will be placed f) A and B only g) A, B, and C only h) all of the above

G (note: not D b/c it should read 90 degrees instead of acute angles; not E b/c tooth contours ARE altered by eliminating gross undercuts to allow room for thick metal/improved strength)

Which of the following is desired when examining internal and external finish lines of metal framework? a) smooth and sharply defined b) slightly undercut to improve retention of acrylic denture base c) metal is thin between internal and external finish lines d) staggered placement (internal vs external)

all except C note: excessive thinning sometimes occurs here b/c of the staggered placement of int/ext finish lines. want framework to be thick (thick enough to resist fracture) *note: arrow in image shows internal finish lines

When checking the metal framework you received from the lab on the master cast, which of the following should be in intimate contact with tooth surfaces? a) reciprocal clasp arms b) lingual plating c) tissue stops d) rests (into rest seats)

all except C (note: tissue stops touch tissue not tooth) note: intimate contact is important b/c space --> debris collection --> decalcification of teeth/inflammation of soft tissues note: image shows lingual plating closely adapted to tooth surfaces

Tipped teeth may require endodontic therapy and cast restorations to provide appropriate guiding planes. If this is not possible, the practitioner should ensure that guide planes are restricted to the ____ (enamel/dentin?). Proximal plating should be kept _____ (away from/close to?) the marginal tissues to reduce food impaction

enamel away from

T/F: An I-bar cannot be placed in an area where it contacts a frenum

false -- it can be placed IF frenum attachment is loose enough to allow the vertical portion of the I-bar to be at least 5mm long (for flexure and hygiene)

T/F: When clinically testing framework fit with disclosing wax, pressure should be applied over distal extension areas to examine for metal show-through that will guide your adjustments

false -- no pressure on distal extension areas! finger pressure is applied to rests in planned POI

T/F: The tissue surface of the metal framework should be polished by the practitioner once it comes back from the lab to take it from a fine matte texture to a smooth, high-shine

false -- tissue surface should be finished to fine matte texture when you receive it from lab and you shouldnt touch it after that. any further polishing would negatively affect the fit *note: EXTERNAL surface of framework should be polished to high shine when it comes back from lab

A lingual I-bar with and a buccal rest extension is NOT an adequate alternative to placement of a buccal I-bar

false-- it is (lingual I-bar = retention, buccal rest extension = reciprocation)

T/F: It is likely that teeth will have moved by the time you get to the framework try-in appt

false-- not likely (unless there is a LONG delay between impression appt and fitting appt) *note: perio therapy and extractions adjacent to abutment teeth may increase likelihood of tooth migration/should be considered when treatment planning

T/F: Most RPDs fit well on the day of insertion if properly designed

false--as many as 75% of RPDs do not fit on the day of insertion (improper fit may be primary reason RPDs are not worn; contributes to movement of teeth and results in discomfort)

T/F: Mesiodistal tipping does not the resistance and retention provided by opposing guiding planes.

false--does

T/F: Irregularities (nodules, pits, scratches, etc) found on the framework should be eliminated from the internal surface only (leave external surface irregularities as is)

false--eliminated from both internal and external suraces (arrow in image shows nodule)

Relief ____ (is/is not) provided at the intaglio surface of a major connector

is not (close adaptation is needed to prevent soft tissue hypertrophy and food impaction) note: Tissue impingement is minimized by providing adequate vertical support for the major connector

I-bar clasp assembly: Occlusal force on the distal extension base causes rotation about the ____ (mesial/distal?) rest. The retentive terminus ____ (engages/disengages?) into the mesial undercut, minimizing torque at the abutment

mesial disengages

An I-bar clasp terminus engages an undercut at the height of mesiodistal contour or slightly ____ (mesial/distal?) to it. This allows the clasp terminus to move passively toward the ____ (mesial/distal?) embrasure space when a load is applied to the denture base

mesial mesial

Disclosing wax is applied to the _____ (metal framework/denture base?) prior to seating in the oral cavity to indicate areas that bind as a result of functional loading

metal framework (note: moderately heavy finger pressure is placed on the latticework of extension bases when framework is seated in mouth. Then the framework is removed/inspected, and areas of binding are relieved. Repeat process until framework moves freely under moderately heavy pressure)

Pt states that their abutment tooth is sore. Radiographs reveal crestal bone loss and widened PDL space around that tooth. This could be caused by what error in the fit of a retentive clasp?

tip that doesnt reach the undercut (b/c it wont sit passively and will apply lateral forces)

T/F: Severe tipping is most effectively controlled with cast restorations

true

T/F: It is okay to alter your RPD framework design to avoid using a tipped tooth

true (as long as the tooth in question is not critical to RPD function) -- especially true if adequate retention can be obtained from other retentive elements

T/F: A cingulum rest seat can be incorporated into a surveyed crown (fixed restoration)

true (helpful when when the abutment tooth lacks appropriate contours or sufficient enamel)

T/F: Underprepared guiding planes compromise the stability and function of the prosthesis

true (long guiding planes are better but many dentists are hesitant to make the tooth reductions required)

T/F: Mandibular anterior teeth generally lack sufficient enamel for appropriate preparation of cingulum rest seats.

true (therefore, incisal rest seats should be used on mandibular anterior teeth when esthetics permit)

T/F: An I-bar can be placed to provide indirect retention (on opposite side of fulcrum line) for a distal extension RPD and IS NOT placed in a retentive undercut

true provides frictional retention and horizontal stabilization (C in pic above)