DS5101 - RBB Flashcards
1
Q
Rationale for resin-bonded bridges (RBB)
A
- minimally invasive to replace missing teeth
- relies on resin cements for retention
- altering surface of metal retainer enhanced micromechanical retention
- resin cements bond to tooth and metal alloy
- good survical rate, predictable mid to long term outcome
- good pt satisfaction
- cheap and fast solution for mid to long-term
- ideal for hypodontia
2
Q
Types of bridges
A
- adhesive aka RBB
- maryland bridges (wings on 2 abutments, not good)
- rochette bridge (perforations in wings, not good)
3
Q
Retentive elements (2)
A
- full coverage crowns on abutment
- adhesive retainers - minimal prep on abutment and involves only palatal or proximal surfaces
4
Q
Design considerations for adhesive bridge (8)
A
- periodontal support
- occlusal loading (magnitude and direction of force vectors)
- conservation of tooth tissue
- cleansability
- appearance
- rigidity
- quality of abutments
- number of abutments
- choice of adhesive lute
5
Q
Pros of single unit, fixed-cantilevered (4)
A
- best design
1. pontic allowed to move w abutment
2. reduces shear forces on pontic
3. debond leads to cleansable surfaces
4. risk of caries eliminated
6
Q
Framework Design - adhesive bridge
A
- Retainer thickness
- atleast 0.7mm thick
- greater if not joined over O surface - Bonding area
- maximum enamel bonding
- extension of metal work as far occlusogingivally and circumferentially around tooth as possible - Wrap-around
- maximum: 180 degrees
(don’t go through contact - unaesthetic) - occlusal extension of metalwork
- full P coverage w no tooth prep (ideal)
- reduced P coverage w tooth prep (finish 1-2mm short of incisal edge) - Posterior Occlusal Coverage - only partial not full O coverage needed (ML)
- Connector design
7
Q
Why is posterior occlusal coverage used in adhesive bridges (3)
A
- resistance of apical and lateral **displacement **
- increased** ridigity** of framework
- greater SA for bonding
8
Q
Requirements for connector design of adhesive bridge (3)
A
- signficant **width and height **required
- need to resist bending of alloy
- must **avoid putting adhesive lute under tensile loading **
9
Q
Tooth preparation general principles for adhesive bridges (6)
A
- keep tooth prep to absolute **minimum **
- anterior: better not to prepare at all
- posterior: axial guide plane prep like wraparound
- occlusal rest seats/extensive occlusal coverage sometimes
- need to modify/replace old restorations for better bonding
- consider IDS on freshly prepared abutments to achieve better bonding
10
Q
Tooth with old MOD amalgam and broken M cusp. How to prep as abutment for adhesive bridge?
A
- take PA, assess symptoms
- remove amalgam, restore w CR to build tooth back into occlusion/function (don’t straight away prep for bridge)
- look at O contacts: RCP etc
- then reduce for bridge
11
Q
Advantages of not preparing teeth for adhesive bridges (3)
A
- no tooth tissue loss, plenty of enamel to bond
- no sensitivity
- if teeth arent in occlusion, question the need for cingulum rest
12
Q
Disadvantages of not preparing teeth for adhesive bridges (2) One way of helping (1)
A
- alot of load on luting cement if teeth are in occlusion
- may be difficult to locate the wing during cementation
- ask for locating tag to help with cementation
13
Q
2 advantages and 2 disadvantages of cervical chamfer for adhesive bridges
A
- reduces potential for **overhang at cervical margin **
- helps position wing during cementation
~ reduces enamel bond
~ potential for dentine exposure and sensitivity
14
Q
What does axial tooth preparation do in adhesive bridges?
A
- increases the area for bonding, resistance and retention form
15
Q
4 advantages of grooves in adhesive bridges
A
- increased resistance to **lateral displacement **
- may help increase **retention form **
- increase the **structural rigidity **of framework
- increases resistance to debonding forces
16
Q
3 advantages of occlusal rest seats for adhesive bridges. (3) And one requirement (1)
A
- transmission of **occlusal forces along long axis of tooth **
- reduces potential sheer stresses within luting cement
- helps locate the wing in the correct place during cementation
- should be minimal w no real loss of enamel so wont reduce bond strength
17
Q
What is intracoronal preparation in adhesive bridges? and 1 advantage
A
Joining of MD of retainer over the O surface to improve rigidity
- enhances resistance to deformation, resistance form, SA to bond
18
Q
2 disadvantages of canines as abutments in adhesive bridge. 1 way to overcome these issues.
A
- bulbosity can cause connector to be too fragile (might not be enough space)
- can impede aesthetics
= guide plane in preparation
19
Q
Disadvantage of central incisors as abutments in adhesive bridge
A
- metal can shine through (enamel quite translucent)
- centrals can look grey and dull - consider opaque luting cement
(this will affect shade you choose for pontic)
20
Q
Factors affecting choice of abutments
A
- tooth position
- crown shape
- restorative status
- endodontic status
- periodontal status
- occlusion
21
Q
Poor abutments (5)
A
- mx lateral incisors
- tilted incisors (unfavourable pulp chamber morphology)
- root-filled teeth
- teeth with large restorations (where 1/4 or more tooth lost)
- perio-compromised teeth with bone loss (w exceptions)
22
Q
Fixed-fixed adhesive bridges are generally not recommended but when may it be ok and why?
A
mandibular incisors, where ‘peel dislodgement’ effect is less
23
Q
Why is this not recommended (for understanding)
A
- physiologic movement of premolar and molar are different, pm displaces more freely
- 2 abutments movements are different, one which is faster/more freedom to move will cause stress within cement and cause debonding
- but the other retainer remains and pt/dentist dont notice -> caries under retainer
24
Q
Mechanisms of failure of fixed-fixed adhesive RBB (3)
A
- signficant stress due to differential tooth movements between abutments during functional/parafunctional tooth contacts –> tend to push one of the abutments away from the pontic
- increased tensile stress on cement lute
- debonding of abutment and caries under the retainer
25
Can you use 2 adjacent teeth as abutments for adhesive RBB?
No
e.g. UR5 and UR4 to replace UR3
26
Mesial vs distal cantilever for adhesive RBB and why? (2)
- distal cantilever subject to less forces
- occlusal overloading on distal pontic prevented by periodontal propioceptors
(thus reduced biting force in multi-unit cantilevered pontics)
27
Advantages and disadvantages of adhesive RBB
important
28
Wing design principles on Anterior
- 0.7mm minimum dimension of retainer
- if insufficient interocclusal space, teeth can be reduced to accomodate retainer
- alternatively, RBB can be Dahl, the bridge can be cemented high?
- a locating tag can be extended over the incisal edge (locate the retainer correctly and resist cervical displacement during cementation)
- aesthetics depend on:
-> extent of retainer wing, wax up
-> porcelain work and soft tissue management
29
Main challenge of anterior RBBs and methods to overcome
Metal connectors may shine through translucent incisors causing grey appearance
- opaque cement
- avoid extending metal to within 1-2mm of incisal edge
if cement doesnt work:
- reconsider choice of abutment tooth
- place composite labially as veneer
- take shade in natural light at beginning of appt
- high quality digital photograph of shade will help technician
30
E.g. Diagnose and treat (17yo)
- missing md incisors, mx lateral and 1st pm (mx canines moved to lateral position)
- oligodontia, microdontia, tooth wear (syndrome may cause enamel hypoplasia), gingival recession of 34 and 35
Treatment
- prevention (desentisising tp)
- composite build up of upper centrals and reshape upper canines to look like laterals
- adhesive bridges to replace the missing, monitoring gingival recession
33-43, 13-12 and 23-23 using Panavia F2.0 cement
- fabrication and fitting of immediate upper/lower Essix retainers
- review and maintenance
31
Why anterior fixed-fixed RBBs work? Why are canines specifically good abutments
Less occlusal loading during mastication
Canine is a good abutment tooth in terms of:
- greater SA for bonding
- good crown to root ratio
- similar movement characteristics of abutment teeth
- greying effect can be masked by opaque Panavia
32
Occlusion in RBBs (5)
1. pre-op assessement includes examination of ICP and dynamic excursions to assess room for functional and aesthetic bridge
2. pontic with light contact in ICP prevents axial movement of antagonist (overeruption)
3. pontic should not be involved in guidance, where possible
4. ICP contact should be kept away from margin of retainer
5. if limited space available for metal framework it can be cemented high
33
Aetiology of situations requiring RBB
34
