Bridges

Question 1

Resin retained bridges

Answer 1

It is minimal or no tooth preparation
High quality framework - good mechanical properties, fit the abutment really well- cast non precious alloys (nickel chrome- not so often as contains barillium - when grinded is associated with carcinogens or chrome cobalt- more often)
High prosthodontic standards
Controlled adhesive techniques - depends on adhesives

Question 2

Role of Torsion and bending in fixed prosthodontics

Answer 2

Mechanical principles needed to make a bridge:

Area of coverage- of the abutments

Thickness of retainers- to have rigidity

Control of the occlusion- controlling the load on the prosthesis

Question 3

Three designs of fixed prosthesis requiring minimal or no tooth preparation

Answer 3

1. Cantilever- one abutment supports one pontic
2. fixed- fixed- retainer at each end of the spam- can carry more than one pontic
3. Hybrid designs- one retainer is a crown and other retainer is resin bonded retainer

Simpler the design- better success
If only one abutment can hold the pontic- that is the best solution ( for resin retained bridges)
highest success rate- replacement of a single missing anterior tooth with only one abutment

Question 4

Anterior cantilever bridge

Answer 4

Indications:
Short spans generally anterior
Using canine or central as abutment to replace lateral

Can be metal or all ceramic resin retained bridges - risk of fracture, ceramic is brittle ( higher connector height is needed, 3-4 mm)

Cantilever can be used in posterior teeth but in limited way- if occlusal load is okay ( premolar with molar) but not to cantilever molar to a molar due to increased occlusal loads on molars compared to anterior teeth ( length of the pontic span in molars in much more so should be avoided)

Question 5

Fixed- fixed- resin retained bridge

Answer 5

Should be avoided

Yes if more pontics

Framework design- large coverage area
Retainer thickens of 0.7 mm , minimum needed
Good connector height - needed to keep the prosthesis rigid -2 mm
Control of the occlusion/occlusal contacts

Question 6

Tooth preparation

Answer 6

No evidence that improves outcomes!
Only to prepare guide planes! For proximal coverage - need to be parallel as they contribute as resistance form of the bridge

Question 7

Framework coverage

Answer 7

Coverage from incisal edge up to the wall apical to cingulum
Extension into the approximal areas adjacent to the pontic to give connector height
Maximum mesio-distal wrap-around
Minimum thickness of 0.7 mm

Question 8

Post orthodontic retention

Answer 8

In adult teeth- fixed- fixed- is the choice as they have a memory and might go back to their original position if only cantilever is used( cantilever not stable)

Need:
Fixed-fixed design
Maximal coverage

Question 9

Posterior tooth replacement

Answer 9

Classical design is 180 degree axial coverage
Rest seats adjacent to the pontic area
Good connector height
Control of occlusion

As aesthetics is not crucial, wings can be extended occlusal so that increased coverage gives increased security

Question 10

Bridge is

Answer 10

Prosthetic tooth replacement that is fixed to at least one natural tooth or dental implant

Component parts ( fixed-fixed conventional bridge)- abutment tooth, retainer- means by which the bridge is attached to the abutment, connector-components of the bridge that attach the pontic to the retainer and pontic - prosthetic tooth

Question 11

Tooth replacement options

Answer 11

Implants
RRB
Conventional bridge
Partial denture (acrylic-more as temorary, cocr)
Nothing (SDA)

Question 12

Resin retained bridge

Answer 12

Retainer is metal wingrather than full coverage crown
Fixed (bonded to abutments)
Unremovable

Question 13

Conventional bridge

Answer 13

Abutments are usually full coverage crowns (pontic is connected to 2 retainers)
Not conservative
Less torque compared with cantilever
Better for longer spans and where relatively heavy occlusal loads
There is significant biomechanical and biological issue

All joints are soldered or cast in one piece to rigidly connect all abutment teeth
Requires good retention at either end of the span
Preparation must be parallel with a single path of insertion/withdrawal

Question 14

Contra indications for fixed prosthesis

Answer 14

Poor tooth prognosis
Young/growing PT due to large pulp horn and risk of pulp exposure on preparation
PT playing contact sports
Gross alveolar bone loss/resorption
Compromised teeth on either side of the bridge
Midline diastema (it will result in asymmetric pontic)
Pt compliance/motivation

Question 15

Reasons for fixed rather than removable prosthetis

Answer 15

More acceptable to PT
No covering of gingival margin
Directs forces axially (non axial forces can cause occlusal trauma causing pain, mobility and pulp death)
Restores the occlusal anatomy
Orthodontic retention/ periodontal splinting

Question 16

Conventional bridge fixed designs

Answer 16

Cantilever - single or double abutment, spring

Fixed-fixed
Fixed-movable
Hybrid

Question 17

Conventional cantilever

Answer 17

Pontic is connected to the retainer at one end only.single retainer more conservative than 2

Leverage imposed on abutment teeth
Suitable for limited span length only

For short spans, mainly anterior
Not to be used with heavy occlusal forces on pontic

Question 18

Double abutment cantilever

Answer 18

When pontic flexes, secondary abutments are in tension and may debond
Resistance is compromised and extra flexion of the bridge metal work when placed under load

Tensile forces are transmitted to distal retainer so cement failure can happen- risk of secondary caries as it is not possible to assess clinically the distal abutment (whereas mesial abutment stays cemented but not strong enough to take all the forces)

Question 19

What records do you need to study and plan rehabilitation of this pt occlusion

Answer 19

Study models-to reproduce the articulating surface of teeth

Facebow- to locate maxillary study model to the condaylar component of the articulator such that it reproduces patients condylar movements

Interoclusal record in RCP - to relate maxillary to mandibular study model in precentric, this makes it possible to plan a reorganised occlusion should be required to for example if there is insufficient space for the aeshetic pontic

Question 20

Appointment one-lab prescription

Answer 20

Pour the impressions in dental stone
And trim to study models
Please return metal stock trays
Mount the maxillary model on a Dinar semi adjustable articular using the facebow transfer jig provided. Locate the mandibular model to the maxillary model using the precentric occlusal beauty wax record.
Return the mounted model on the articulator in advance of the patients next appointments

Question 21

Fixed prosthesis- biomechanical challenges

Answer 21

Conventional fixed movable bridge
- conventional because both abutments are heavily restored
-to distribute the relatively high occlusal loads between 2 abutments ( in contrast to doing a cantilever)
- If distal abutment is inclined, meaning a conventional fixed fixed bridge would require a lot of tooth reduction to allow for a single path of insertion

Hybrid fixed-fixed bridge
- if one tooth is unrestored- to preserve the tooth tissue placing only a wing and other tooth as conventional crown if it is heavily restored already
- better than cantilever so it can distribute relatively high occlusal loads between 2 abutments

Question 22

Recall intervals for bridges

Answer 22

NICE- dental checks: intervals between oral health reviews

SDCEP- oral health assessment and review dental clinical guidance

Discussing protective and modifying factors ( periodontal, caries, periapical, diet, no interdental cleaning, regular attendee)
Determining risk for oral disease
Stating the advised recall period should not exceed 6months

Question 23

What hard can restoration do

Answer 23

Impact on periodontal health (poor emergence profile, impingement on biological width)
Destruction of tooth tissue
Opens dentinal tubules (compromises pulp-dentine complex)
Starts restoration cycle

Question 24

Spring cantilever bridge

Answer 24

Little support to pontic, covers gingival margin
It was used to manage midline diastema
Used when adjacent teeth are not suitable abutments to farther teeth are used as abutments

Long connector is under more flexion

Question 25

Conventional fixed fixed bridge

Answer 25

Pontic is connected to 2 retainers Not conservative Less torque compared to cantilever Better for long span Can be used where relatively heavy occlusal loads They are single rid entity so preparation needs a single path of insertion for both abutments (retainer preparation must be parallel to eachother, no undercuts) Increase in taper- decreased resistance force and increased stress on cement)

Question 26

Occlusal forces

Answer 26

Direction of occlusal forces is dependent on position in the arch Distance and direction of tooth movement during function translates to stress on lute In fixed-fixed designs each abutment should provide equivalence of retention - addition of axillary features in weaker abutments - way to manage the load on weaker abutment

Question 27

Risks with fixed-fixed designs

Answer 27

1. Biological consequences of tooth preparation 2. Debonding of the weaker abutment

Question 28

Fixed movable design

Answer 28

For short span To help with alignment of abutments Depends on quality of abutments And where abutments have independent mobility For tilted teeth/abutments, different path of insertion There is a fixed element of the bridge and the movable connector/joint between the two

Question 29

Golden proportional for the aesthetics/width of the tooth

Answer 29

It is what is seen when looking the pt from the frontz not actual width If centrals are 100% Laterals should be 65% of the width of the centrals Canines shout be 85% of the width of the laterals

Question 30

Colour of the indirect restoration/matching

Answer 30

Hue-way to distinguish one colour from another Chroma- amount of saturation in a given hue/ saturation of the colour Value-most important, it determines the accuracy of colour matching

Question 31

What is metamerism

Answer 31

When a colour appears different under a different source of light

Question 32

Resin retained bridgework

Answer 32

Ideally: Minimal, preferably no tooth preparation High quality framework- good mechanical properties and fit the abutment well High prosthodontic standards Controlled adhesive techniqiet

Question 33

Survival rate of RRB

Answer 33

65% at 10 years 69% at 13 years 88 % at 5 years 77% at 10 years 80% at 10 years

Question 34

Hybrid designs

Answer 34

Not common Useful alternative when there is one tooth that already has a crown/a tooth that needs a crown and one that has efficient enamel to be used as resin bonded retainer It is not made in one piece Resin retained bridge must be serviceable as if anything happens, it will be resin retained portion that will become uncemented It has a movable connector that should always go to the distal surface of the minor abutment tooth( which is always more anterior) They work better when the crown is more mesial rather than distal of the retainers and better Producing parallelism in the gingival part of the crown prep is crucial/more important than in incisal portion

Question 35

Fitting surfaces of non precious metal for bridgework

Answer 35

Ceramic will bond to non precious metal but not other way around Surface roughness can help with bonding but not enough Sandblasting is needed just before cementation because non precious alloy is highly reactive and starts to produce oxide rapidly so there can be a layer of that risking the cohesive failure of the bond

Question 36

Harm restoration can do

Answer 36

Impact on periodontal health Destruction of tooth tissue Opening dentinal tubules Starting restoration cycle

Question 37

Occlusal forces in bridges

Answer 37

The direction of occlusal forces is dependent on position in the arch Distance and direction of tooth movement during function translates to stress on lute In fixed-fixed designs each abutment should provide "equivalence of retention"

Question 38

Fixed-movable bridge

Answer 38

It is a stress breaker ( to allow a degree of differential vertical movement Between the pontic and the retainer)- reducing the forces applied on the weaker abutment For angled abutments (different path of insertion) Provision for failure It is for: Short span Independent mobility of teeth

Question 39

Types of retainers

Answer 39

3/4 gold crown Full veneer crown: Gold MCC Ceramic

Question 40

Inlays as a retainer

Answer 40

Should be absolutely avoided It is conservative but no cusp protection Retention and resistance is much less than full coverage crown Poor durability Minimal impact of periodontium which is a good side

Question 41

3/4 gold crown as a retainer

Answer 41

More conservative than full coverage crown Retention and resistance is poorer than full crown Structurally weaker due to open face Chamfer margin and modest occlusal reduction for gold is advantageous Long margin can lead to failure- longer interface so leakage is possible Supragingival margins are good for periodontal health Poor/good aesthetics

Question 42

Full veneer gold crown as a retainer

Answer 42

Requires preparation of all coronal tooth tissue- relatively destructive Very good retention and resistance Structurally strong Minimal prep for the gold Can burnish margins to achieve good adaptation Preservation of periodontium depends on margins and contour Poor aesthetics

Question 43

Metal ceramic retainer

Answer 43

Requires preparation of all coronal tissue Very good retention and resistance form Structurally strong Destructive prep Preservation of periodontium depends on margins and contour if supragingival and well adapted Good aesthetics

Question 44

All ceramic retainer/bridgework

Answer 44

Abutments need heavy preparation to give greater taper and thicker ceramic layer Good resistance and retention Questionable structural durability Very aesthetic

Question 45

Abutment selection

Answer 45

Factors affecting the selection of abutment teeth: Suitability of the pt (MH, DH - previous treatment, managing long appts..., SH - attendance, pafinance, consent, smoking, diet) Suitability of oral environment (full dental charting, perio assessment - plaque, PPD, BoP, mobility, parafunctional habits, occlusion-occlusal scheme, toothwear) Suitability of position of abutment Suitability of tooth and supporting structures

Question 46

Assessing the suitability of the position of the tooth

Answer 46

Length of span-Ante's law ( ideally, no more than 2 pontics for fixed-fixed and 1 for cantilever) Curvature of span ( pontics lying outside of the inter -abutment axis will act as a lever) Angulation of span (to achieve parallelism preps must be very heavy- unless fixed-movable design; non-axial loading of teeth-can cause occlusal trauma) For fixed-fixed relative retention of individual abutments Position of span in the arch

Question 47

Long span

Answer 47

Avoid due: Flexing- stress to abutments and cement lute Places increased load on PDL Produce more torque on abutments

Question 48

Support of abutment teeth

Answer 48

Depends on: Root configuration Surface area Length of clinical crown Crown: root ratio( ideally 1:2, okay if 2:3 and could be acceptable 1:1)

Question 49

Ideal occlusion for a bridge

Answer 49

Posterior stability Incisal/canine guidance Absence of posterior interfaces on mandibular movements No guidance on pontic for cantilever bridge- contact in ICP only (so the opposing tooth does not super erupt)

Question 50

Pontic design

Answer 50

Ridge lap Modified ridge lap Bullet Ovate Hygienic Pontics are not an anatomical reproduction of the missing tooth but they should be: Aesthetic Functional Cleanable Compatible with mucosal health Comfortable *Pontic is an artificial tooth fixed on a bridge/partial denture replacing the missing tooth, restores its function and restores the space previous occupied by the clinical crown

Question 51

Consent info regarding RRB

Answer 51

Can debond (around 20% over 5 years) Approx 90% survival over 5 years Can be re cemented or may need to be remade