Fixed Prosthesis Flashcards
What is the defintion of an extra-coronal restoration?
Is a restoration that which is outsaide or external to the crown portion of a natural tooth. (sits over remaining tooth structure)
Name 3 different types of extra-coronal restorations?
Veneer
Only
Crown (partial or full)
Name the 3 main indications for extra-coronal restorations?
Support for remaning broken down teeth
Prevention of microleakage
Aesthetics
In what order should treatment be planned?
Relief of pain/emergency Cause related therapy Intial reassessment Basic operative care Reassessment Reconstructive therapy Recall and maintance
Name the 5 main risks of extra-coronal restorations?
Pulpal inflammation Periapical periodontitis Poor plaqie contraal Restoration loss if poor occlusal management Loss of occlusal stability
Name the 3 main factors when deciding whether a patient is suitable for an extra-coronal restoration?
Patient expectations
Tolerate the procedure
Maintain their mouth for the foreseeable future
What are the 4 guiding principles for preparing an extra-coronal restoration?
Plan resto that maintains structural integrity of remaining tooth tissue
Least invasive option
Consider effect on pulp
For endo teeth provide best coronal seal and support weakened teeth
What are the alternbatives to extra-coronal restorations?
Direct resto bonding
Excellent marginal adaptation and bonding systems
Bleaching
Micro-abrasion
What are the 6 key principles of extra-coronal restoration tooth preparation?
Preservation of tooth structure Retention and resistance form Structual durability of resto Mariginal integrity Periodontal health Aesthetics
What are the principles to follow when preserving tooth structure?
Conservative preparations
Minimise pulpal damage
Restoraton should protect remaning tooth structure
Name the 9 factors in which crown preparations effect the pulp-dentine complex?
Dentinal fluid flow Smear layer Pre-exitising pulapl condition Thermal trauma LA Material irrigation Micro-leakage Luting Dehydration
How can exisiting pulpal condition affect the sucess of a future extra-coronal restoration?
Restorative procedures are injurious to the pulp
Can result in fibrosis, reduced vascualrity and tertiary dentine
Pulp less able to recover from further injury
Effect of pulp damage is cumulatiev
Can elad to pulapl necrosis
How can theraml trauma affect the sucess of a future extra-coronal restoration?
From previous light-cure or exothermic materials
Pulpal temperature is rasied during crown preps
Can reach a fatal level if inadequeatly cooled air-rota
Sub-lethal temperature can still lead to scarring, fibrosis and reduced vascualrity
How can microleakage affect the sucess of a future extra-coronal restoration?
Following tooth prep tubules are exposed
Must be adequately sealed or it will be permeable
This can cause hypersensivitiy, bacterial invasion and dehydration
How can luting affect plaque control for extra-coronal restorations?
All cements are soluble
Good marginal integrity is essential for plaque contrl and aesthetics
Good mechnical form of prep and well manaufactures corwn required to protect cement lute
How can dehydration of dentine affect the sucess of a future extra-coronal restoration?
Excessive use of the 3in1
Delays in preparation stages
Name the 9 main precaustion to preotect the long-term vitality of the pulp?
Evaluate pulp health pre-op
Lots of water spray during tooth prep
Use light and intermittent cutting forces
Sharp brus
Ensure the suction doesn’t suck the cooling water away
Avoid dehydrationg the denture tubules
Ensure good mechanical form of prep
Seal dentine ASAP
Wait 2 weeks between cutting corwn and placing final restoration
What is the defintion of resistance form?
The features of a tooth prep that enhance the stability of a restoration and resist dislogment along an axis other than the path of displacement (apically or obliquely)
What is the defintiion of retention form?
Quality inherent in the dental prostheiss acting to resist the forces of dislogment along the path of insertion (direct and indirect retention)
The more parallel the opposing wall the greater the retention
What can be done to increase retention and resistance form?
Degree of taper Grooves Boxes Pins Larger SA for luting Prep of occluso-gingival height and bucco-lingual width
What is the optimal taper for a crown prep?
6 degrees (16 more realisitc)
3 degree of inclination on each opposing wall
Less than 6 can make it hard for the lute and technician
How do grooves, boxes and pins increase resistance form?
Decrease the rotational arc of displacment
Placement of auxillary features must be parallel to the path of insertion to the crown
What are the mechanical requirement for a extra-coronal restoration? (diagram)
Small space between tooth and resto - filled with cement
Higher resistance reduces rotational arc compared to higher retention
Increased OG- height and narrow BL-width = smaller rotational arc of dispalcement (higher resistance)
Decreased OG-height and wider BL-width = larger rotational arc of displacement
For anterior teeth for resistance form what is most important?
Bucco-lingually
Limited opportunity for long parallel walls
Cut palatal wall so it is long and parallel
For posterior teeth for resistance form what is most important?
BL is parallel
MD is more limited*
How to plan path of insertion for extra-coronal teeth?
Along long axis of tooth and parallel to adjacent proximal contacts
How to balance structiral durability of an extra-coronal restoration?
Dentine removal and risk to pulp and strcutural integrity
Ensure enough space for material
Thickness for functional cusp size?
1.5mm
Thickness of extra-coronal resto?
1mm
What are the consequences for inadequate preparation?
Weak crown
Poor aestehtics
Compromised gingival and periodontal health
What are the consequences for excessive preparation?
Crown strong Good aestehtics Good perio and gingival health Tooth weak Pulpal problems
What is the defintion of a margin?
The outer edge of a crown, inlay, only or other resto, a boundary surface of a tooth prep is termed the finish line or curve.
Finisgh on sound tooth structure
Adequate sixe and thickness
Name 6 forms of finishing margins?
90 degree shoulder Deep chamfer Radial shoulder Shoulder plus bevel Knife edge Chamfer margin
What is the defintiion of the bioloigcal width
Distance from the depth of the crevice to the alveolar crest
~2mm
What are the 4 consequences of impinging on biologic width and the practical aspects?
Gingival inflamamtion Pocket formation Recession Loss of alveolar crest height (consider crown lengthining)
Practical aspects:
- difficult soft tissue management for impressions
- gingival inflammation
Why do we need a core for an extra-coronal restoration?
Provide retention and resistance form
Restoration of coronal tissue
Durable coronal seal
How can we achieve increased retention and resistance form for the crown?
Use of ferrule
Use of adhesive materials to bong to tooth tissues
How can we achieve increased retention and resistance form for the core?
Use of undercuts and grooves in remaining tooth tissue
Why are dentine pins bad?
They increase stress on tooth
Increased risk of periodontal ligament damage
Predispose tooth to fracture
What is the definition of a ferrule?
A band of iron
2mm from crown margin
1mm thick
What 4 questions shoould you think about when assessing the need for a core?
- Can the tooth provuide retentuion for its extra-coronal resto without additional material being added
- Do we need to add amterial that will aid resistance and retention, or der we just need to block out irregs
- is there sufficient remaining tooth tissue to retair and support a core?
- Can a ferrule be achieved?
What is the prognosis for an extra-coornal that extends subgingivally? Can it be improved?
Poor prognosis
Crown lengthing surgery
Electrocauterisation
What can be done to improve the chance of creating a successful ferrule?
Crown lengthing surgery
What does a coronal seal provide to a vital tooth?
Increased pulpal protection
Prevents caries at and beneath the restoration margin
What does a coronal seal provide to a non-vital tooth?
Additional luine of defense to endodontic seal
Prevents caries at and beneath the restoration margin
What are the advanatages and diadvanatges for amalgam as a core material?
Adv:
- not technique sensitive
- strong in bulk
- sealed by corrosin products
- bonded into place with cemments and resins
Dis:
- Needs 24 hour seeting before tooth prep
- weak when thin
- electrolytic action bvetween core and crown
- not intrinsucally adhaesive
- poor aesethics under ceramic restos
Indications for amalgam as a core material?
Posterior teeth
Interim resto for posterior teeth
Substitiute for dentine pin
What are the advanatages and diadvanatges for composite as a core material?
Adv: - strong - stonger than amalgam in thin sections - fast setting - no need for matrix placment Dis: - technique sensitive - essential isolation - dentine bond can be ruptured by polymerisation contraction - hard to distingish between tooth and core during prep
Indications for composite as a core material?
Build-up material for posteruiior and anterior teeth if isolation is insured
Aesthetic interim resto - longer than amalgam
What are the advanatages and diadvanatges for GIC as a core material?
Adv: - intrinsucally adhesive - fluoride release Dis: - too weak - crack - radiolucent
Indications for GIC as a core material?
Excellent filler for inlays but needs sufficient dentine to support crown
No strong enough to be a core
Exisiting crown with caries, remove the caries then fill the area with GIC
Why is it advised to remove the exisiting restoration before an extra-coronal restoration is to be placed?
Assess tooth strcutral integrity
Pulpal expopsure
Underlying caries
Unless an interim has been placed (by you)
What are the advantages and disadvanatges of using the Nayyar core technique? (endo)
Placed immediatalu after endo - reduing risk of coronal leakage
Utilises coronal tooth structure to increase retention
Reduces stressess created byt post placememnt
Easily retrievable
What is the Nayyar core technique? (endo)
Amalgam dervied, using the pulp horns and chamber for retention
Retention from coronal and radicular tooth tissue
How to plan to minimise the risk of failure for extra-coronal restorations?
Treatment planning perfect
Pt shows good OH, diet and protected occlusion
Perfect preps and impressions
Perfect lab work
Plan for failure - least invasive
Explain that the restoration will fail in time
What 3 questions to think about when a restoration has failed?
- Possible causes of the failure of the EC restoration
- How can it be prevented in the future
- Suitable strategies to remedy the situation
Name the 7 objectives to be acheived when trying to have a successful EC restoration?
- Miminaml intervention to secure patient’s OH
- Careful case selection (treat tooth with context - remaining dentition, occlusal facros, age, dexterity, diet, maintenace and expectations)
- Excellet assessment and planning (plan instages)
- Textbook standard prep and impression
- Perfectly fitting temporary
- Careful cememntation of crown
- Regular maintenance
Name the 7 main reasons for EC restoration failure?
Loss of retention Mechanical failure Caries Periodontal Endodontic Aesthetic Damage to opposing tooth
How does the loss of retention lead to EC restoration failure?
Lack of ferrule or poor retention of the core
Poor retention between core and undercuts, pits and grooves
Occulsion - axial forces only on molars, canine guidance and no deflective contacts)
How does mechanical failure lead to EC restoration failure?
Due to lack of ferrule
Forces focussed on apical terminus of post
What is the main reasons for why ceramic crowns fail?
Secondary caries Chipping due to: - metal coping too thin and flexure - oxide layer not good enough to bond to ceramic - poor occlusal planning
How can you resolve a mechanical failure in ceramic crowns?
Replace - risk iatrogenic weaking of tooth, loss vitality, cost and time Repair kit (etched with HF - very corrosive)
How can caries lead to EC restoration failure?
Aetiological factors can’t be controlled
Loss of tooth tissue and structure/integrity
Usually unrestorable
At crown margins
How can periodontal failure lead to EC restoration failure?
Poor emergence profile - poor crown contouring
Ledges at the margin - PRFs
Encroaching on biologic wifth - inflamm, PPD, recession and bone loss
Perio not controlled before crown
Plan the simpliest and least invasive option to allow more room for resolution in the future
How can endodontic failure lead to EC restoration failure?
Marginal breakdown - caries - loss vitality - root infection - apical periodontitis
Questionable marginal fit and patients OH
Failure of coronal seal leading to reinfection of RCS (remove GP to CEJ and fill with GIC for isolation)
How can aesthetic failure lead to EC restoration failure?
Gingival recession leading to expoure of unsightly margins:
- taruma to soft tissues during crown prep or insertion of retraction cord
- inflamm due to poor fitting temo; enchroaching on biologic width - uncontrolled perio disease
Poor shade matching
Need to think if crowns were neccesary rather than composite veneers
How can damage to opposing teeth lead to EC restoration failure?
Poor occlusion understanding
Damage/wear to other teeth - poor aestehtics
Porcelain is abrasive when unglazed
What are the 7 key ideas when trying to minimise failure for EC restorations?
Careful case selection - motavation, OH and appropriuateness of tooth
Excellent assessment and planning
Planning: - pulp, occlusion, periodontal support, remaining tooth structure and aesthetics
Well executed prep and impression
Well fitting temporary - to stop movememnt and inflamm
Appropriate cemment selection for specific crown
Maintenance - remediation could be necessary
What are the advanatages and disadvanatges for RMGIC for ECRs?
Adv:
- command set
- seal tubules
- bond to tooth
- variable colour
Dis:
- moisture senitive
- weak
- contains HEMA
What is the definition of temporisation?
Restores form and function to the tooth while the
definitive restoration is being constructed
What are the advantages of a good temporisation?
Facilitates subsequent stages of the procedure
Produces a better definitive restoration
Can be useful to glean information from
temporaries
What are the requirements of a good temporisation restoration?
Retained for the period of time between fitting and
placement of the definitive restoration
Removed easily at the fit appointment without damage to the preparation
Good retention for this period and ease of removal
What is the most satisfactory combination of a temporisation?
Well-prepared (mechanically retentive)
preparation with a well-constructed temporary
restoration grouted by a soft luting cement
Name 4 types of temporary restorations?
Acrylate-based materials
Dimethacrylate composites
Light-cured temporary materials
Putties
What is suggested for long term temporisation?
Indirect temporary restoration
What are preformed crowns made from?
Polycarbonate
Cellulose acetate
Aluminium
Stainless steel
What are the mechanical properties of polycarbonate crown forms?
High impact resistant polymer
Sufficiently strong to withstand occlusal forces
Linked by a variety of chemical groups (bis-GMA)
What is the clinical technique to place a polycarbonate crown?
Crown form of the approximate size selected
Acrylic bur used to adjust its size and shape
Roughen interior of the polycarbonate crown
Refined with another material (usually an acrylate)
Can trim through the polycarbonate ‘shell’ to
accommodate, if occlusion dictates
Acrylic can withstand occlusal forces if at least c1 mm
thick
Often too broad buccolingually and so require thinning
to achieve a satisfactory contour gingivally
Describe a cellulose acetate crown form?
Transparent
Packed with another material matching in shade to the
surrounding teeth (resin-based composite)
What are the disadvantages of cellulose acetate crown form?
Merely act as a matrix - must be removed after
Thickness of the crown reduces by about 0.2 mm
when removed
Leads to instability in the occlusion and movement of
adjacent teeth
Refining material may lock into undercuts
Compromises removal of the crown and the patient’s
ability to keep the (gingival) area clean
What is the main indication for cellulose acetate crowns?
Matrix to build up teeth using resin based composite
What is the main indication for metal crown forms?
Posterior teeth
Name the 2 materials avalaibale for metal crown forms?
Aluminium
Stainless Steel
What are the advantages and disadvantages of using aluminium metal crowns?
Easy to manipulate - malleable and ductile
Corrode with time as saliva can react with them
Risk of galvanism if placed adjacent to another
metal
How are aluminium metal crowns prepared?
Cut to approximate size of the preparation using
crown shears
Ability of the aluminium to be worked and shaped lends itself to this process
What are the disadvantages of aluminium corwn if the form is not refined?
Not possible to perforate the metal shell should the
occlusion dictate it
No other information gained
Wear may lead to temporary cement being exposed
with the restoration failing
Why are acrylic materials used with temporary crowns?
Enhance the fit between their internal surface and the preparation
Closeness of the fit enhances retention
What are the disadvantages of using methylmethaycrylate/polymethlymethacrylate with temporary crowns?
Disadvantage: High polymerisation shrinkage Poor mechanical strength Highly exothermic setting reaction High level of monomer release Poor wear resistance Poor aesthetics Chemical interaction with eugenol
What are the clinical impact of using methylmethaycrylate/polymethlymethacrylate with temporary crowns?
Clinical impact: Unsatisfactory fit Breakage during function Thermal trauma to the pulp Significant pulpal irritation Undesirable wear during function leading to perforation or fracture of the temporary leading to occlusal instability Unsightly restoration Non-eugenol-containing products should be used
What are the physical properties of higher methacrylates?
Lower glass transition temperature
Poly(butylmethacrylate) then distortion seen at mouth temperature
Combo no distortion at mouth temp
Tough and less brittle
Morphology changes on hot foods and liquids
Describe methylmethacrylate?
MMA monomer and PMMA polymer
Benzoyl peroxide/tertiary amine, initiator/activator curing system
Presence of a tertiary amine results in yellowing
after setting
Especially in sunlight as the solar ultraviolet
breaks down the amine
What are the properties of methylmethacrylate?
Monomer has a distinctive, unpleasant smell Relatively inexpensive Good marginal fit Good transverse strength Good polishability Durable
What are the indications for methylmethacrylates?
Inlays and Onlays
Prevents overeruption
Affords increased fracture resistance
Explain the clinical technique when refining a preformed crown with an acrylic material?
- Complete the preparation
- Select a crown form that approximately corresponds to the
tooth being temporised - Trim this crown form (using an acrylic bur for a
polycarbonate crown form and crown shears for a metal crown
form) so that the margins approximate those of the
preparation. Roughen the internal surfaces of the
polycarbonate crowns - Mix the acrylic material to the consistency of wet sand
- Fill the crown form by running the material down the sides to
ensure no air bubbles are incorporated inside the crown form - Allow the excess monomer to evaporate and watch the
surface until it turns from a shiny to matt finish - At this point fully seat the temporary crown onto the moist
preparation and remove the obvious excess using a probe or flat
plastic to prevent it setting into the undercuts so that the crown
can be removed easily later - Remove and reseat the crown several times to reduce the
effect of polymerisation shrinkage
(9. Place in hot water to accelerate the setting reaction) - Trim the margins using an acrylic bur and reseat on the
preparation to verify the margins - Check the occlusion and adjust if necessary
- Polish if necessary
- Lute the crown using a temporary luting cement
What alternative clinical technique for preformed crown with an acrylic material?
Blowdown splint made of thermoplastic resin
may also be used
Wax temporary prosthesis on a study cast
Vacuum-formed splint constructed from this
Splint filled with a methacrylate material and
inserted intraorally once the preparation has
been done
Name the 2 types of resin composite based materials for temporary restorations?
Some form of dimethacrylate resin (frequently bis-GMA and triethylene glycol dimethacrylate)
Composite-type technology which is based on the
ethylene imine derivative of bisphenol-A
Describe dimethacrylate resin?
Frequently bis-GMA and triethylene glycol
dimethacrylate
+ filler (usually inorganic and containing zirconia
and silicon dioxide)
Filler forms only 40% by weight
Describe Ethylene Imine Derivative Of Bisphenol-A?
Catalysed by an aromatic sulphonated ester
Filler is added to increase strength
Multifunctional methacrylates produce a
relatively high cross-link density early on in the
setting reaction
Rubbery stage is achieved allowing the partially
set restoration to be removed without distortion
or damage
What are the properties of Ethylene Imine Derivative Of Bisphenol-A?
Presence of filler reduces polymerisation shrinkage
As the resin monomer volume is reduced,
shrinkage is reduced in proportion
Catalyst and base
What are the advantages of dimethacrylate resins?
Good aesthetics Good colour stability Available in a range of shades including a bleach shade Good flexural strength Hard Moderately good wear resistance Moderately low exothermic reaction Polishable due to small filler particles Good tissue biocompatibility Non-irritant to the soft and hard tissues Generally radiopaque Replicates occlusal surface May be repaired Minimal shrinkage
What are the disadvantages of dimethacrylate resins?
More expensive
May be insufficient thickness for strength interocclusally
Can stain with certain foodstuffs
What are the indications for dimethacrylate composirte materials?
Temporary inlays
Temporary onlays
Temporary veneers
Temporary crowns
As a refining material for temporary crown forms
Short temporary bridges (three units maximum)
Give 1 comerically avaliable example of dimethacrylate composite material?
Protemp 4 - 3M ESPE
Descirbe the step-by-step process of the resin-replica technique?
. Preoperative impression
• Include at least one tooth on either side of the tooth
to be prepared made either in the mouth or on a
study cast
• +/- modify the shape of the crown to be temporised
prior to impression taking (e.g. thickening it to
increase the strength of the temporary crown)
• Putty v alginate
• Impression may be adjusted using a scalpel blade to
open up the interproximal areas to increase the bulk
of material and hence its strength
2. Select the shade of the temporary material to be
used (if applicable)
3. Carry out the tooth preparation
4. Syringe the first portion of material mixed on the
bracket table
5. Syringe the mixed material into the matrix keeping
the nozzle within the body of the expressed material
6. Reseat the matrix on the preparation
7. Monitor the setting material (on the bracket table)
• Remove it when it has reached a rubber stage (usually 30–90
seconds depending on the material and mouth temperature
and humidity)
• Do not delay any longer or the set material will lock into any
undercuts
8. Remove the matrix impression
• Allow the temporary restoration to self-cure for 4–5 minutes
(may be accelerated by placing it in hot water)
• Remove it from the impression
9. Trim the flash
• Use tungsten carbide or diamond burs
• Reseat on the prep(s)
10. Check the occlusion and adjust if necessary
11. Wipe the surface with a cotton wool roll to
remove the oxygen inhibition layer
12. Polish the completed restoration using
polishing instruments (e.g. discs, burs, etc.)
13. Lute the crown using a temporary luting
cement
How to repair a dimethacrylate composite material?
Resin based composite materials can bond to the dimethacrylate composite Flowable resin composite may be used to: • Repair small non-load-bearing defects • Fill voids • Refine margins • Improve contacts For newly placed material: • Remove any contamination (e.g. saliva or dust) with water • Air dry • Add the flowable composite and cure in no more than 1 mm increments
Describe light cured temporary resin materials?
Used to temporise intracoronal preparations
Rubbery in consistency
Retained in the cavity mechanically
No bonding to the cavity walls which facilitates
their subsequent removal
Reasonably easily removed at the fit appointment using an excavator
Only suitable for short term use (no more than a month)
because it slowly degrades and wears
Tend to develop a malodour due to bacterial activity over time
What is the function of CaSO4 in light cured temporary resin materials?
Harden in presence of moisture
What is the setting reaction for light cured temporary resin materials?
Primarily by light curing
Shrinking by 1.6–3%
Prepolymers added to them to decrease polymerisation shrinkage
Shrinkage is relatively low so formation of marginal
gaps, microleakage and discolouration of the
material is reduced
Depth of cure <4mm
Tend to discolour with use
Which light cured temporary resin materials is indicated for inlays?
Low-viscosity materials
Which light cured temporary resin materials is indicated for onlays?
Rigid ones are designed for onlayswhere the cavity size is larger
What are the properties of light cured temporary resin materials?
More difficult to manipulate
Place material into the cavity and the gross remove
excess prior to light curing
Surface can be finished using rotary instrumentation
If necessary
Stiffer materials offer higher strength and reduce
drifting of adjacent and opposing teeth
Easier to manipulate into the cavity as they can be
condensed into place
Radiopaque
How to manipulate light cured temporary resin materials?
Do not need to be cemented
With a temporary luting cement
Applied to the preparation walls prior to placement
of the temporary material to seal the cut dentinal
tubules
What are the indications for light cured temporary resin materials?
Temporary dressings for inlay preparations
Temporary restoration of (retentive) cavities
Inter-visit access cavity sealants during an
endodontic procedure
Relining prefabricated temporary crown forms
and bridges made of methacrylates or
polycarbonate
Sealing implant screw access openings
What are the contraindications for light cured temporary resin materials?
Allergy to one of the constituents Large (multisurface) cavities Crown or bridge material Subgingival preparations Should not remain in the mouth for more than 6 weeks
Desribe a putty?
Based on zinc oxide and zinc sulphate
Radiopaque
Placed in their soft unset state
Harden in the presence of moisture from saliva
Expand during setting
Basic setting reaction is the hydration of calcium
sulphate to form a plaster (gypsum)
What are the advantages and disadvantages of putty?
Wear resistance is poor
Create a good seal
Some products are claimed to adhere to dentine
What are the indications for putty?
Seal endodontic access cavities between visits
Temporise inlay cavities
Temporise retentive cavities
Give 1 comerically avaliable product of putty?
Cavit-G 3m ESPE (easy to remove)
What are the advantages of indirect temporary restorations?
Better marginal fit Increased strength Better wear resistance Easier to keep clean Better aesthetics and colour stability Greater occlusal reliability and stability
What are the disadvantages of indirect temporary restorations?
Greater cost implication
Failure to provide a satisfactory temporary
prosthesis may prove to be a false economy
Acrylic, Bis-GMA or acrylic bonded metal
Why do we have to retract gingiva when doing crown impressions?
Gingival tissues must not
obscure the margins of a preparation
Sufficient bulk of impression material is required to give
the impression material adequate strength
Name 1 example of a mechnical means for gingival retraction?
Retraction cord
Name 2 examples of chemical means for gingival retraction?
Astringents
Vasoconstrictor agents
Describe the retraction cord and how it works?
Usually made of cotton and placed into the gingival sulcus
Separates the marginal gingival tissues and the tooth by pushing the gingival tissues so exposing the margin of the preparation
Name the 3 types of retarction cords avaliable?
Twisted Braided Knitted - more effective at retraction as they have a springiness
Why is the knitted cord the most effective mechanical means for gingival retraction?
Hold and carry significantly more haemostatic chemicals than conventional cords
Flavoured to increase patient acceptance
How are retraction cords placed?
Packed around the
preparation using a
special instrument
What is the main fucniton of a retraction cord wetted in haemostatic chemicals?
Generally a haemostatic agent
Controls gingival haemorrhage
Facilitates a clean and dry field
Important with hydrophobic impression materials
Name 3 types of astringent haemostatic retractions chemicals?
Aluminium trichloride
Potassium aluminium sulphate
Ferric sulphate
Name 1 type of vasoconstrictor haemostatic retractions chemical?
Adrenaline hydrochloride
Why must haemostatic retraction chemicals be removed? and give an example?
Many of these chemicals adversely affect the set
of the impression material
Racestyptine (Septodont) + polyether
impression material = Gas → bubble defects in
the surface of the stone die
How do retraction chemical work mechanically? and how to remove it?
Chemicals expand either on their own or in combination with applied pressure
Injected perpendicularly into
the gingival sulcus to fill it
Removed by washing away with water from the three-in-one syringe
Which retraction method is good for implants and why?
Aluminium chloride
Useful for implants as cord may compromise the
gingival cuff around the fixture
Name 1 commercially avaliable gingival retraction material?
Ultrapak
Optident
Knitted cord that can be impregnated with 15.5% ferric sulphate
Name 1 other retraction system, describe it and how its used?
Magic Foam Cord: - addition silicone - bubbles form within material - paste/paste and injected around prep - pressure is then applied by the patient biting on a Comprecap - densely packed cotton wool roll
Name the 6 requirements of an impression tray?
Be rigid and non-flexible under load when taking the
impression
Extend sufficiently to support the impression material in
the region being reproduced
Fit loosely around the dental arch and not touch the soft
tissues
Have adequate means of retaining the impression
material in the tray
Have a robust (integral) handle
Be able to be adequately decontaminated (if not meant for single use)