B2B1- Prosthodontics Flashcards
Rational for provisionals
- Protect pulp
- Protect teeth for sensitivity
- Improve aesthetics
- Provide comfort and function
- Evaluate reduction of preps
- Immediate replacement of missing teeth
- Precent migration/overeruption
- Provide environment conducive to perio health
- Aid in developing occlusal scheme for before definitive treatment
- Allow evaluation of vertical dimentsion, phonetics and mastication
- Determine prognosis of questionable abutments
Why are provisionals helpful in treatment planning?
- They resembe final form/function of planned tx
- Good tool for pt management to discuss tx outcomes and limitations
- Assess potentual long term consequences from change in OVD
- Plan and assess changes in occlusal scheme
Technical requirements for provisions?
- Good marginal adaptation
- Adequate retention and resistance to dislodgement during function
- Strong, durable, hard
- Dimensionally stable
- Comfortable
- Aesthetically acceptable
- Stable shade
- Ease of mix, short setting time
- Highly polishable
- Easy to remove, re-cement, non-allergic
What are advantages of polymethyl methacrylate (PMMA)?
- PMMA’s can be added to (clean surface wetted by monomer)
- Colour stability
- Good marginal fit
- Durable
- Polishable
What are disadvantages of polymethyl methacrylate (PMMA)?
- Low abrasion resistance
- High exothermic reaction
- Strong odour
- Pulp irritation
What are advantages of polyethyl methacrylates (PEMA)?
- PEMA’s can be added to (clean surface wetted by monomer)
- Low exothermic reaction
- Kinder to pulp
- Lower setting shrinkage
- Good handling
- Polishable
- Less odour
- Better suited when provisional needs to remain for longer periods.
What are disadvantages of polyethyl methacrylates (PEMA)?
- Low tensile strength
- Poor surface hardness and wear resistance
- Poor durability
- Poor colour stability
*
What are advantages of composite resins for provisionals?
- Low exothermic reaction
- Low shrinkage
- Good marginal fit
- Good wear resistance
- Improved aesthetics
- Easy to use
- No damage to pulp
What are disadvantages of composite resins for provisionals?
- More expensive
- More brittle
- Poor stain resistance
- Poor surface hardness
- Not good for splinting
What are differences between bis-acryl resins and bis-GMA resins?
Bis-GMA resins are less brittle, can be easily repaired with flowable CR and have more shades available
What are the different techniques for temporaries?
- Matrix or copy techniqe
- Shell or direct/indirect technique
- Indirect technique
What is the matrix or copy technique for fabricating provisionals?
- Matrix made from alginate/silicone putty either directly or indirectly from tooth/wax up
- Matrix is loaded with temporary material and placed over prepared tooth
- Provisional is trimmed, polished and cemented
Why is it better to make matrix based on wax up rather than the original tooth?
Xax up is best as it shows the ideal contour, occlusion and margins (for perio health). If you made temp crowns based on current crowns, the final temporaries will have same defects.
What is the shell or direct/indirect technique?
- Technician builds hollowed out shell and seating jig on study casts
- Dentist does tooth preparation
- Shell fit is checked by placing PVS and seating
- Once complete seating of shell ensured, it is relined with acrylic and seated.
- Shell is lifted up/down during polymerisation to avoid locking onto tooth.
- Shell temp is then trimmed, polished and cemented
When is shell technique favourable to use?
Multiple anterior teeth in highly aesthetically demanding cases
What is indirect technique for provisionals?
- A matrix is made either directly on unprepared teeth or wax up
- After preps, impression of preps is taken and poured up
- Provisionals are made extra-orally
- Temporaries are trimmed and cemented onto teeth.
What are preformed materials for provisionals?
- Tooth shaped shells of plastic, cellulose or metal that is relined with acrylic resin to provide custom fit.
- Commercially available in various tooth sizes
- Fast method
- May lead to improper fit, contour or occlusal contact
What are polycarbonate resin preformed crowns?
- Select size, trim margins, proximal walls and height
- Fill with acrylic and seat on prep
- Trim excess, adjust occlusion
- Cement in place
What are characteristics of aluminium metal provisionals?
- Unaesthetic
- Quick adaption
- Suffers rapid wear
- Can lead to extrusion of tooth
- Unpleasant taste sometimes
What are advantages of splinting adjacent temporaries?
- Enhanced stability & retention
- Convenience for easy removal and recementatoin
- Unification helps prevent drifting/overeruption
What are disadvantages of splinting adjacent temporaries?
- Gingival embrases need to be freed to ensure gum health
- IMpinged papilla can become inflamed
- Trimming embrasures leads to small contact areas that can fracture (best to use acrylic resin)
What are spot etch provisional veneers?
- Diagnostic Wax-up
- Alginate index of the wax-up
- Removal of old veneers
- Spot etch
- Index loaded with Protemp and seated over preparations
- Excess of Protemp removed and
- polished
Why do provisionals need to be polished to smooth shiny surface?
- Resist plaque/staining
- Promote good soft tissue health
What are lab made provisionals?
Made in dental lab from impressions of preparations. May need to do chairside provisionals in meantime.
What are characteristics of lab made provisionals?
- Stronger, more aesthetic than chairside temps
- Require no/minimal adjsutment
- Functional/aesthetic blueprint of final restorations
When to use lab made provisionals?
- Aesthetically demanding cases
- Changes in OVD or changing occlusal scheme
- Multiple teeth
- Cases requiring long term temporisation such as implant healing
- To create optimum tissue health around preps prior to definative impression
When should we avoid canine guidance?
If canine is the pontic, RCT’d, heavily restored, crowned or implant. We would want group function instead to avoid overloading the canine.
What tooth should we avoid placing heavy contact/pressure on?
Lateral incisors. Avoid as bridge abutment or denture support
What does loss of temporary lead to?
- Pain
- Overeruption/space loss
- Drifting of proximal teeth
- Damage to core preparations
What can be used for temporary cements?
- ZOE
- Non-eugenol pastes
When should ZOE be avoided as temp cement?
If using resin cement for final cementation make sure you use non-eugenol paste. Eugenol interferes with bonding.
How should bridge pontic be in occlusion once cemented?
Ensure pontic is not loaded in excursions and protusive movements. Fine to lightly contact in group function but should not guide occlusion
What is biomimetic?
Study of structure, function and biology of tooth organ as a model for design and engineering of materials, techniques and equipment to restore or replace teeth.
What happens with enamel ageing?
- Progressive thinning of enamel
- Increased crown felxibility
- Higher enamel surface stains
What is the benefit of additive wax up for veneers?
Allows tooth preps that are both more accurate and conservative compared to conventional methods
Why should you cut away matrix around gingival margin?
Prevents build up of excess protemp material at gingival margin. It flow into area where the alginate was cut.
How to do guided preps (working from final form)?
Use of differential depth cutters in combination with an additive
mock-up should maintain most of the enamel
- The shank of the bur must always stay in contact with mock-up
- The large round bur is used to create a groove at the junction
between the middle and incisal thirds of the facial surfaces. - The small round bur is used to create a slightly scalloped groove at
the junction between middle and cervical thirds of tooth - Both grooves are then marked with pencil
- Round-ended, tapered burs are used for preparation/margins
- Sufficient space for the porcelain is created when the pencil marks
disappear - Horizontally sectioned silicon index from wax up is used to check facial clearance
What factors influence enamel bonding?
- Water: higher water content = poorer adhesion
- Wetting, which depends on:
- Cleanliness of adherend (cleaner surface = greater adhesion)
- Surface energy of adherand (greater surface energy = greater adhesion)
Describe contact angles in terms of adhesion?
Angle formed between surface of liquid drop and adherent surface.
* Stronger adhesion = smaller contact angle and good wetting
Describe composition of dentine
Detine has 50% inorganic hydroxyapatite by volume and contains more water than enamel
What factors influence dentine bonding?
- Presence of smear layer
- Difference in number/diameter/size of dentinal tubules
- Dentin permeability is more in coronal dentune than root dentine
- Bonding less effective in deeper dentine
- Amount of collagen (decreases with age which decreases number of dentinal tubules)
What does dentine etching with 37% phosphoric acid cause?
Removes smear layer and exposes microporous collagen network/fibrils into which resin monomer penetrates.
Why should conditioned dentine be maintained in moist state?
Present collapse of unsupported collagen fibres. Interfibrillar water acts as a plasticizer and keeps fibres open
What are reasons for failure of dentine bonding?
- Variable structure of dentine
- Contamination of dentune with sulcular fluid or saliva
- Structural changes close to pulp making it difficult to bond
- Thickening of bonding agent bc of evaporation of solvent which reduces penetration
What is immediate dentine sealing?
Application of a dentin bonding agent to freshly cut dentin when it is exposed during tooth preparation for indirect restorations
* Freshly cut dentine is uncontaminated and clean, thus more easily capable of resin infiltration.
* IDS protects the tooth from contamination, bacterial leakage and temp cement remnants and provides a sealed an clean dentin surface optimal for adhesion
What is biological rational for IDS?
- Creates hybrid layer mimicking the DEJ
- Gives significant thickness to hybrid layer, preventing collagen collapse during imps/cementation
- Allows maturation of hybrid layer during provisionalisation
- Reduces hydrodynamic water movement in dentinal tubules, minimising sensitivity
What is clinical rationale for IDS?
- Max tooth structure can be preserved
- Pt comfort with reduced post-op sensitivity and reduced need for anaesthesia at cementation
- Capturing hybrid layer into impression avoids gap formation and ill-fitting restos
- IDS combined with resin cements is expecially useful for short clinical crowns/tapered preps
- More durable bond at cementation appt
What are problems with uncured DBA when seating indirect restorations? What is a solution?
- Outward flow of dentinal fluid dilutes bonding agent and blocks micro-porosities
- Pressure of luting material during seating leads to collapse of collagen fibres
-> IDS after completion of tooth prep can resolve uncured DBA issues.
OR dual cured DBA can be used but it has high levels of polymerisation and colour instability
Why should DBA not be light cured before placement of indirect restroation?
Can interfere with complete seating
Why is a marked chamfer recommended if margins terminate in dentine?
Provide adequate margin definition and enough space for adhesive and overlaying restoration.
Shallow chamfer would cause adhesive resin to pull over margin and compromis margin definition and porcelain thickness.
Gingival margin should be revisted with ultrafine chamfer bur to remove bonding agent
Why should glycerine jelly be palced when curing DBA for IDS?
Polymerises oxygen inhibition layer and prevents interaction of dentin advesibe with impression material
What are the steps of IDS?
- Etch freshly cut dentine with phosphoric acid
- Rinse and remove excess water with suction
- Application of primer, wait to evaporate
- Application of DBA, suction excess. LC
- Air blocking by layer of glycerine jelly adn additional LC
What is issue with IDS when fabricating temps? How to overcome this?
Sealed dentine surface has potential to bond to resin based provisionals and cemets, making removal difficult.
* Isolate tooth preps with petrolium jelly during temp fabrication
* Avoid use of resin pased provision cements
* Try to achive mechanical retention instead (shrink fit)
* Recommended to keep provisionalisation period reduced to max of 2 weeks.
How are ceramic restorations bonded onto tooth?
- Ceramic resto tried in on clean tooth and fit checked
- Ceramic is etched using HF (9.5%) acid
- Fit surface is re etched with Phosphoric acid
- Silane applied and allowed to evaporate
- Tooth cleaned with pumice/AlO blasting/coarse diamond bur at slow speed
- Tooth enamel re-etched
- Adhesive aplied to tooth and restoration but not LC
- Resin cement is applied to fit surface, crown seated and excess removed, LC.
- Glycerine applied to margins and re-cured
When is emax indicated?
- Crowns and veneers in anterior region
- Can be a good choice for anterior short span bridges
What are advantages of Emax?
- Great aesthetics
- Durable
- Ability to be milled
- Conservation of tooth structure
- Versatility
Why is Emax so aesthetic?
- Closest match to natural teeth due to translucency
- Lacks metal (no grey line at gum line)
- Improves light transmission
What are disadvantages of emax?
- Expensive
- Not ideal for posterior due to higher fracture rate
- Not ideal for darker teeth
- Not suitable for long span/posterior bridges
What material should be used to crown darker tooth?
Zirconia as it is less translucent than emax
What is the general treatment plan for patient wanting veneers/crowns?
Immediate:
* Address active periodontal disease/eliminate the cause
Transitional
* Evaluation outcome of the periodontal tx
* If satisfactory, consider options for replacement. If not, reinforce OHI and re-evaluate.
* Prescription of a diagnostic wax-up
* Aesthetic evaluation of the wax up via mock-up in the mouth.
* Direct provisional restorations.
Reconstruction
* Silicone impression
* Provision of lithium disilicate E-max veneers.
* Provision of occlusal splint
Maintenance
* + history of parafunction needs to wears occlusal splint to protect the new restorations.
* OH reinforced to avoid further perio/recession.
* 6 monthly review.
What margin finish for veneers increases mechanical resistance to fracture?
Incisal overlap (consider for bruxist patients)
What are limitations of ceramic veneers?
- Lack of enamel
- Colour change
When are emax onlays indicated?
- Compromised posterior teeth with intact buccal and lingual walls
- Large MOD amalgam
How should emax onlays be prepared?
- No bevels/retentive features required
- Min 1.5mm reduction on non-working cusp
- Min 2mm reduction working cusp
- Circular shoulder with rounded inner edges or chamfer at an angle of approx 20-30 degrees
- Min 2mm chamfer margins
How to do cuspal coverage?
- Cuspal coverage required in all onlay design for protection of working cusps
- Need cuspal coverage for RCT teeth due to loss of tooth integrity
- Ensure there are no contacts on margins
How to do cuspal coverage?
- Cuspal coverage required in all onlay design for protection of working cusps
- Need cuspal coverage for RCT teeth due to loss of tooth integrity
- Ensure there are no contacts on margins
What distance should remain between restoration margin and alveolar bone to prevent violation of biological width?
3mm
What should you do if you have subgingival defects?
Deep margin elevation
What is deep margin elevation?
Involves building deepest parts of proximal box in CR to relocate the cervical margin to supragingicval level.
* DME facilitates isolation and improves impression taking and adhesive cementation
* Can be considered non-invasive alternative to surgical crown lengthening
Why are conservative onlays better than conventional preps?
- Increased fracture resistance
- Reduced stress concentration (homogenous thickness promotes better stress distribution)
- More favourable fracture modes
What are characteristics of single unit, fixed-cantilevered bridge?
- Design of choice
- Pontic is allowed to move with abutment
- Reduced shear forces on pontic
- Debond leads to cleansible surfaces
- Risk of caries eliminated
What are these bridge designs?
- Resin bonded bridge (used today)
- Maryland bridge (2 wings and not recomended)
- Rochette bridge (not used anymore)
How thick should retainers be?
0.7mm min
When should joint retainer be used?
If there is increased occlusal force
How to improve bonding of RBB?
- Maximum enamel bonding
- Extension of metal framework as far occluso-gingivally and circumferentially as possible without breaking contact or having incisal show-through
What are tooth preparation general principles for RBB?
- Keep to absolute minimum
- Anterior teeth better to not prepare at all if possible
- Posterior abutments have axial guide plane prep like wraparound
- Occlusal rest seats sometimes
- May need to modify/replace old restos
- Consider IDS on freshly prepared abutments
What are pros and cons of no preparation for RBB?
Pros:
* No tooth tissue loss
* Plenty of enamel to bond to
* No sensitivity
* If teeth aren’t in occlusion question need for cingulum rest
Cons:
* A lot of load on luting cement if teeth are in occlusion
* May be difficult to locate wing during cementation- (Ask for a locating tag to help with cementation)
What should you do if you want molar with MOD amalgam as abutment?
- After assessing tooth and taking IOPA, remove MOD amalgam
- Build tooth back into function in occlusion
- Need to look at occlusal contacts and from there can prep tooth for bridge
What are pros and cons of cervical chamfer prep for RBB?
Pros:
* Reduces the potential for an overhang of the cervical margin
* Can help with positioning of wing during cementation
Cons:
* Reduces enamel load
* Potential for dentine exposure and sensitivity
What are advantages of grooves in preparations for RBB?
- Inc resistance to lateral displacement
- Inc retention form
- Inc structural rigidity of framework
- Inc resistance to deobonding forces
What is the function of cingulum rest?
Dissipate stress along long axis of tooth (only prepare cingulum rest if tooth is already restored in that area)
What are the characteristics of occlusal rest seats?
- Transmission of O forces along long axis of tooth
- Should be minimal with no real loss of enamel
- Reduces potential sheer stressors within luting cement
- Helps locate wing during cementation
What are functions of intracoronal preparations for RBB?
- Joining of MD of retainer over O surface to improve rigidity
- Enhances resistance to deformation, resistance form, surface area to bond
What are considerations for canines as abutments?
- Good for abutments
- Problem is that their bulbosity may limit space for connector leading to fragile framework. Can impede aesthetics
- Guide plane preparation can overcome these issues
What is the issue with central incisors as abutments?
- Metal can shine through
- Consider using opaque luting cement
What are poor abutments?
- Mx lat incisors
- Tilted incisor teeth (unfavourable pulp chamber morphology)
- Root filled teeth
- Teeth with large restos (>3/4)
- Perio compromised teeth with bone loss
Why should we avoid double abutments?
Physiological movement of teeth are diferent. One abutment will move more than the other leading to stress in cement and debonding. Pt won’t notice and food/bacteria can go underneath wing causing caries
What are advantages and disadvantages of RBB?
Pros
* Conservative prep/no prep
* Fixed replacment for missing teeth without compromising abutment
* Less endo compliations from extensive tooth preps
* Shorter total tx time
* Less expensive
Cons:
* Technique sensitive in design, prep and cementation
* Aesthetic issues due to metal wing showing
* Debonding can happen
* Lack of randomised control trials
If there is insufficient interocclusal for wing of RBB what can you do?
- Prepare tooth to accomodate retainer
- Bridge can be cemeted high (Dahl principle)
How to avoid greyness of metal from RBB?
- Opaque cement
- Avoid extending metal to within 1-2mm of incisal edge
- Reconsider choice of abutment tooth
- Place composite veneer
Why do anterior fixed-fixed RBB’s work?
- Less occlusal loading during mastication
Canine is a good abutment in terms of : - Surface area for bonding
- Crown:root ratio
- Similar movement characteristics of abutment teeth
- Greying effect can be masked by opaque panavia
What is the wing design on posteriors for RBB?
- 180 degree wraparound retainer
- May extend to cover palatal/lingual cusps
Describe occlusion in RBB?
- Pre-op assessment of ICP and dynamic excursions to assess room for a functional and aesthetic RBB
- Light contact of pontic in ICP
- No involvement of pontic in guidance
- ICP contact should be kept away from margin of retainer
- If limited space available for metal framework, it can be cemented high
What is the mean survival for fixed-fixed vs cantilever bridges?
F-F: 7.8 years
Cantilever: 9.8 years
What are considerations for design of F-F bridge?
- Length of span
- Is F-F more suitable than centilever?
- Is there sufficient intra-occlusal space
- Shape of ridge, any defects
- Do we need surgical ridge augmentation or other tx plan to replace teh missing white and pink?
How can we assess abutment teeth?
- Perio: PPD, plaque, mobility, past perio
- Periapical: presence of PA pathology, bone levels, crown:root ratio
- Coronal tooth strucure, restos and oclusion
- Root configuration (conical roots more suitable for short spans)
What are pros and cons of fixed-fixed bridges?
Pros:
* Alternative for implants when bone quantity/quality suboptimal
* Predicatable aesthetic results with good planning
* Allow stressors to disrtibute more evenly
* Various designs
* Can be used in ant/post long spans/perio splinting
Cons:
* Destruction of tooth structure
* Meticulous planning and design
* Pulp death common in abutments
* After RCT, remake usually needed
* Expensive
* Requires excellent OH
What are pros and cons of hybrid bridges?
Pros:
* No/minimal prep on one abutment
* Good for transitional phase to keep space and avoid loss of interocclusal space
* Can be bonded
* Good pt satisfaction
Cons:
* Higher probability of debonding of metal retainer
* Can lead to caries under debonded retainer
* Technique sensitive
* Needs regular check ups to evaluate retainers and thier bond
* Not enough clinical evidence
What are pros and cons of cantilevered bridges?
Pros
* Good aesthetics
* More conservative
* Less comlpications
* Less chance of developing caries under retainer
* Good option for single tooth replacement
* Mostly non-catastrophic failure
Cons:
* Risk of debonding and failire esp on RCT teeth
* Metal base can make tooth look darker
* Pulpal death of abutment tooth can happen
* Not ideal for lead bearing area
What are pros and cons of fixed-moveable bridges?
Pros:
* Allows for flexure of bridge, reduced load on weaker retainer
* Allows for partial coverage of retainers and less prep
* Compensates for abutment misalignment
* Alls individual movement of sections during function
* Units should be cemented as individual sections in right order
Cons
* Destructive tooth structure as room for dove tail joint needs to be created
* Metal may show on site of moveable joint
* Wear and mechanical failure of joint can happen
* Try in and cementation can be challenging
* Technicially challenging for technician
What is intracoronal precision attachment?
Dovetail attachments are incorporated within contour of crown.
What are pros and cons of intracoronal precision attachments?
Pros: reduced stress on abutment teeth, stress is directed along long axis of tooth, allows for individual movement of abutment teeth
Cons: extra prep to create room for dovetail joint, attachment is subject to wear
What are the 3 types of stresses in a fixed bridge?
- Tensile stress: internal induced force that opposes elongation of material parallel to direction of stress (when structures are flexed).
- Compressive stress: internal induced force that opposes shortening of material parallel to direction of the stress. Can
- Shearing stress: internal induced force that opposes sliding of one plane of material on adjacent plane in direction parallel to stress
What stresses should be minimised in bridges?
- Should minimise tensile and shear stresses
- Dental procelain is weak in tesnion but strong in compression
- Weakest part in posterior fixed bridges is fixed joint due to high concentration of tensile and shear stresses
What are characteristics of PFM for F-F bridge?
- Strong metal substructure but not aesthetic for anterior
- Good for posterior edentulous space
- Well documented long term clinical performance
- Good for bruxists
- Can be designed to save more tooth strucutre
- Incorporation of attachments.moveable joint
What are characteristics of layered zirconia?
- More aesthetic (masks discolouration)
- Strong framework but new materual
- Lacks long term clinical evidence
- Not ideal for bruxists
- Problems with chipping/breaking of laminating procelain
- Cannot be modified for moveable joint
What are disadvantages of pier abutments?
- Tooth movements vary across dental arch and due to shape of arch, movements are in different directions
- Unfavourable forces put constant stress on restoration and luting material
- Abutment fails at weakest interface and will lead to caries
When can a pier abutment be beneficial?
Long span splinting in periodontally compromised teeth with some degree of mobility
What are tooth preparation general principles for bridges?
- Diagnostic wax up
- Conservative tooth prep with putty index
- Parallel tooth preps
- Max resistance, retention form
- Supragingival finish line
- Need to modify/replace old restos
- IDS
Why do pts with oligodontia have extensive wear?
Poor quality enamel
How to treat missing 4 lower incisors?
Can replace with fixed-fixed RBB bridge from 33-43. The movement of 33 and 43 is the same so there is less flexure and chance of bridge debonding
What depth of connector is requried for bridge?
At least 2.5mm occluso-gingivially and bucco-lingually
What are considerations when choosing pontic design?
- Ease of cleaning (lesser soft tissue pontic contact=better OH maintenance
- Aesthetics
- Abutment height (taller abutments allow for desired connector dimensions)
What are pros and cons with ridgelap pontic?
Pros:
* Aesthetic
* Good pt adaptability as it feels similar to original tooth
Cons:
* Extremely difficult to clean and remove excess cement under pontic
* High possibility of inflammation at pontic soft tissue contact areas
* Food impingement under pontic
* Gingival recession can occur following gingival inflammation
What are pros and cons of modified ridge lap pontics?
Pros:
* Good aesthetics (labial crest overlap)
* Easy to remove excess cement
* Can be maintained clean
* Most routinely used pontic
* Can replace any missing tooth in oral cavity
Cons:
* Requires pt adaptation as undersurface partially hollowed out
* Pontic may be unusually long if there is excessive ridge loss
* Air/saliva may peroclate through embrasures, esp while speaking
What are pros and cons of sanitary pontics?
Pros
* Ideal for OH
* Easy to remove excess cement
Cons
* Requires initial adaptation by tongue
* Lacks aesthetics so good for posterior teeth
What are pros and cons of ovate pontics?
Pros:
* Most aestheics
* Can be maintained by pt using correct flossnig technique
* Ideal in aesthetic zone, esp in pts with high lip line
Cons:
* Requires additional effort to mould soft tissue
* Requires multiple appts
When are ovate pontics used?
Aesthetics anterior cases. In immediate extraction, the socket needs to be preserved with a provisional prosthesis that has been designed with an ovate pontic bed. Sometimes need to do microsurgery to create room for ovate pontics.
What pontics should be used for different areas in mouth?
What is shortened dental arch?
Dentition of no more than twenty teeth with an intact anterior region but a reduced number of occluding pairs of posterior teeth.
What is the most common type of failure for fixed bridges?
Caries
(then need for RCT, loss of retention and aesthetics)
Why are zirconia bridges more prone to caries than PFM?
More extensive tooth preps
What are the most common failures of cantilevered bridges?
Debonding
(then fractured metal)
What are the 2 determinents of occlusion?
Anteriorly: teeth
Posteriorly: TMJ
CNS plays crucial role in regulating these and muscles, ligaments and tendons
What is the issue with RCT’d teeth being last in the arch?
RCT’d teeth that are last in arch fail more frequently as they don’t have distal tooth to regulate load they receive. They become overloaded and can fracture. (RCT’s teeth lack proprioception). Usually if RCT’d tooth is surrounded by vital teeth, they can regulate force applied.
Where should B and P cusps contact?
- P cusp of uppers should contact contral fossa and marginal ridges of lower teeth
- B cusp of lowers should contact central fossa and marginal ridges of upper teeth
What is balanced occlusion? Which case is this occlusion required?
.
Bilateral, simulataneous, anterior and posterior occlusal contact of teeth in centric and eccentric positions
Want balanced occlusion in complete denture cases to prevent dispalcement
What is mutually proctected occlusion?
Anterior teeth protect posterior teeth in eccentric movements (canine guides occlusion)
Posterior teeth protect anterior teeth in maximal intercuspation
What is canine ideal for disengaging posterior teeth?
Posterior teeth are closer to hinge axis and therefore are subject to greater occlusal forces. Canine guidance is ideal as the canine is situated further away from the hinge axis and has a long, robust root to disocclude the posterior teeth during lateral function and withstand lateral forces.
Seperation of posterior teeth reduces proprioception, hence less muscle activity in mastication muscles.
Why are posterior teeth ideal for withstanding vertical forces?
- Increased number of roots
- Occlusal table is wider
- Orientation is along long axis
Patients with non-working side interferences can lead to fractures of functional cusps
What is a common cause of fractured functional cusps?
Patients with non-working side interferences can lead to fractures of functional cusps
Describe movement in TMJ
- First 20-25mm involves rotation in glenoid fossa
- When opening wider, condyle and disk will move forward and down articular eminence (translation)
Why should we register jaw relationship in CR when changing vertical dimension?
- More space
- CR is reproducible position
How much can you open bite in reconstructions without causing problems?
20-25mm (amount of opening during rotational movement of TMJ)
What is Posselt’s envelope of movement?
Describes movement of mandible from
* CO > CR > rotation > translation > protrusion > edge to edge
* Max opening and lateral movements
?What is CO (ICP, habitual bite, bite of convenience)
Jaw position that allows greatest interdigitation of teeth
What is CR (retruded axis position, terminal position)?
Most anterior superior position of the condyle in the glenoid fossa
What is retruted contact position?
First point of contact in CR
Where does RCP occur in dentate/partially dentate patients?
In dentate/partially dentate pts, RCP occurs in posterior teeth. Separation of anterior teeth happens and no overlap of upper/lower teeth. This leads to increased OVD.
When to restore in ICP?
- Fuly dentate with no OVD changes
- In partially dentate pts when CR=ICP or if CR≠ICP but bite is stable
When to restore in CR?
- When increasing OVD, fabrication of splint, edentulous patients
- In partially dentate patients when CR≠ICP and bite is unstable (no good contacts, moblilty, lack of posteiror supoprt, attrition/erosion)
- Edentulous posterior saddles in one or both sides
What is anterior guidance?
- Protrusive guidance provided by incisor teeth, causing seperation of posterior teeth during md protrusion
- Canine guidance or group fucntion during lateral excursion
Can you have non-working side contacts that don’t cause interference?
Yes. Only becomes interference when it interferes with function of occlusion.
When is it almost impossible to gain posterior occlusion during anterior guidance?
- Incisal edge-to-edge
- Class III
How can occlusion be recorded?
2D methods: clinical photographs, occlusal sketching diagram, articualting paper.
3D: verified articulated study models using facebow record and bite registration materials.
What is a facebow?
Used to transfer relationship of mx arch to TMJ which enables mounting of mx cast on adjustable articulator
What are the different ways of recording RCP?
Patient guided
Schuyler technique
Myo-monitor
Gothic arch tracing in edentulous pts
Operator guided
Lucia jig
Leaf gauge
Chin-point guidance
Bimanual manipulation
What is Schuyler technique for recording RCP?
Pt places tip of tongue at back of palate and closes into horseshoseshow of softened wax with light pressure.
* Difficult to verify nature of unwanted tooth contact
* Wax may not be uniformly softened, leading to innaccuracies
What is Chin-point guidance method for recording RCP?
- Pt seated upright
- Softened 2 layer wax/silicone is pushed against cusps of mx teeth to achieve indentations
- Registration medium (temp bond) applied to md surface of wax
- Md is guided into a hinge closure by thumb and index finger
- Hinge closure is completed as md teeth just indent the registration material
Condyles may be over retruded
What is bimanual manipulation method for recording RCP?
- Pt seated supine position
- Fifth fingers placed behind angle of md, fourth fingers in front of angle
- This permits condyles to be directed A-P within glenoid fossa
- Third fingers placed on inferior surface of body of mandible and index fingers submentally in midline. Thumbs are lateral to symphysus
- Opening/closing a few times on hinge axis, pt will relax and registration can be made.
What is anterior guidance by a lucia jig?
Deprogrammer device made of cold cure acrylic. Very useful in bruxist patients.
* Anterior bite platform which covers centreal incisor to provide anterior reference point
* Lower incisors should occlude at 90d to platform with disclusion of posterior teeth, relaxing and deprogramming muscles.
* Operator can then guide md into its posterior position
* RCP can be taken with PVS with lucia jig in situ to prevent sliding into ICP
What is most common approach to building up OVD?
How
Build new OVD at point of RCP with condyle in CR position. This provides interocclusal space without altering contracted legnth of elevator muscles
(mount cast into CR relationship (there will be gaps in occlusion) > wax up > provisionals)
What opening in anterior is created by 1mm posterior opening?
2-3mm opening. For each 3mm opening, there would be approx 2mm increased overjet
What are the 3 appraoches to building up new OVD with CR?
- Build the new OVD at the point of RCP with condyle in CR position- most common
- Build the new OVD less than the point of RCP with condyle in CR position- mild/moderate tooth wear
- Build new OVD mroe than point of RCP with condyle in CR (increases contracted length of elector muscles)- used for excessive wear and flattened posterior teeth
What are the essential dental portfolio photographs required?
- Frontal rest lip position
- Frontal relaxed smile
- Frontal laughter
- Frontal MI
- Frontal separated teeth
- Right and left lateral view in MI
- Occlusal full arch mx and md view
What is the role of diagnostic wax ups?
- Patient communication tool
- Visual aid for determination of final aesthetics
- Template for minimal tooth preparation
- Guide for occlusal analysis and mock up of projected restos
- Fabrication of well fitting provisionals
What are the phases of treatment for restorative intervention?
- Stage 1: Initial asessment and emergency treatment
- Stage 2: Control of disease and stabilisation of structure
- Stage 3: Evaluate outcomes and review effectiveness of treatment and patients response to managment of disease
- Stage IV: Managing clinical aspects of work and execution of treatment plan
- Stage V: Establishing maintanence program
How can you measure tooth surface loss over 1 year?
Take study cast at first appointment and after one year take another study cast and take silicon key of first cast and cut in half and compare tooth surface loss with second cast
What are indications of successful perio treatment?
Bleeding on probing (main indicator)
Pocket depths
What conditions are associated with periodontitis?
- Leukaemias
- Neutropenia
- Downs syndrome
- Papillon-Lefevre syndrome
How many pairs of teeth are needed for adequate function and appearance?
10 pairs (20 teeth toal)- premolar to premolar is accepatable (shortened dental arch)
What is conformative approach?
Restoration of teeth conforming to patients existing occlusion without major changes to static and dynamic occlusion
What is reorganisation approach?
In cases with tooth wear and reduced interocclusal space
* If RCP and ICP are not coincident, some anterior horizontal space may become available by guiding pt into RCP and restoring teeth at this position.
* Dahl approach can be used create space in localised anteiror tooth wear cases
How can this case be treated?
Crown lengthing for mx
Impressions, wax ups, mock up
Decide whether you leave gaps, make cr-co denture, implant or bridge
CR restorations for lowers
Use PFM as material in bruxism patients
Splint
How can you assess tolerance of patient prior to permanent VD increase?
Fabricate michigan splint to open bite. If pt can tolerate, can do wax ups and mock ups
What patients should you avoid opening VDO?
Pts with TMD, prior orthognathic surgery
Why should you avoid composite resin in posteiror worn dentition?
Composite resin wears rapidly (low survivability)
Use ceramic or PFM if opening bite
What are considerations for crown lengthening?
- Root needs to be healthy
- Good bone levels
- Recession, black traingles, poor emergence profile can happen
What are pros and cons of RPD?
Pros:
* Less expensive
* Minimal tooth prep
* Longer edentulous spans can be restored
* Replacement of missing alveolar ridge tissues is possible
* Can be removed for cleaning and adjustments or repairs
Cons:
* Clasps may be unattractive
* Designs may be bulky, complicated and plaque retentive
* May cause gagging
* Retention and stability may be problematic
What are pros and cons of fixed-fixed bridges compared to RPD?
Pros:
* More natural appearing tooth substitutes
* Feel more natural
* Superior stability with chewing hard foods
* Minimal soft tissue coverage
* Not easily removed
Cons:
* More expensive
* More suitable for short spans
* Extensive tooth prep is usual
* Abutments must be in good alingment and functionally adequate
What vertical distance is required from top of ridge mucosa to opposing teeth?
4mm
Why were these implants positioned in this war and fabricated with pink acrylic?
The ridge defect is too extensive for bone grafting
