BDS5 content + exam Qs Flashcards
What things do you need to consider and check prior to selecting an RBB?
10 (5+5)
- Is the abutment tooth…
…long enough to have a metal cantilever?
…have enough enamel surface area for bonding with the adhesive resin based cement?
….translucent? If enamel surface is too translucent, tooth can appear darker
…restored / heavily restored?
….periodontally sound?
- Is spacing & alignment of natural teeth favourable?
- How large is the pontic span? Will abutments support this span length
- smile line
- Any parafunctional habits / tooth wear, angulation, crowding & rotations?
What are the occlusal considerations for RBB design?
Pontic should have…
…no contact on dynamic occlusion (lateral excursions) &
…very light contact on static occlusion (ICP)
What are the types of forces experienced by the teeth?
Oblique forces for anterior teeth
Posterior forces for posterior teeth
What material are RBBs made of?
Porcelain fused to non-precious metal alloy wing
Wing: Non-precious metal alloy (Ni-Cr or CoCr), recently zirconia wings
- Thin section 0.7m - 1mm
- max surface area
(Anterior RBB –> cover most of the palate aspect
Posterior RBB –> cover most of occlusal surface & all of palatal/lingual surface)
Connector:
- 180o “wraparound”
- 3mm connector height
Crown: non-precious alloy covered by layer of porcelain
- modified ridge lap shape (ideal)
- ovate (for immediate rbb)
What is a major contraindications for RBBs?
Class 3 malocclusion
Heavily restored abutment teeth
Bruxism & parafunctional habits
Teeth with extensive bone loss
Lack of clinical crown height in the abutment teeth (reduced surface area increasing failure risk)
Advantages of RBBs
- Preserve tooth tissue (minimal or no prep)
- Less risk to pulpal tissues due to no drilling
- Less time required as minimal or no prep
- If it fails, it’s not catastrophic
- Good intermin solution (temporary whilst pt is saving for a c)
- Cheaper tx option
- Relatively reversible
Disadvantages of RBBs
- Debonding
- Longevity - Don’t last as long as conventional bridge (mean 7 years)
- Aesthetics - Metal shine through
- Can’t chew on very crunchy / hard foods
- If pt has a diastema (can’t do this as the tooth needs to be touching an adjacent tooth)
Reasons RBBs fail
- heavy contact on pontic
- lack of seal
- poor cementation technique (lack of moisture control)
Stages of RBB cementation
- fit & show pt (use gauze protect airway)
- assess fit & contacts
- isolate with rubber dam
- re-sandblast metal wing & abutment surface prior to cementation
- use adhesive resin based cements (Panavia)
- etch, prime & bond abutment
- mix panavia & cement RBB
- remove excess with microbrush while cement is setting
- apply oxyguard for 4 mins to create O2 free environment for setting
What is the ideal RBB design & why?
- modified ridge lap pontic design shape
- mesial cantilever
- abutment to be tooth with longest root (PDL support)
- 3mm connector height
What happens if RBB is too high?
- Tooth not prepped so no space for wing
○ Eg if all teeth touching on ICP, then when placing the 0.7mm wing, everything else will dis-occlude & the only contact- But because of Dahl, there is an axial movement so some teeth will extrude & intrude, making the teeth touch (-> reasonable recalibration of bite to re-establish all those contacts)
Options for RBB placement if there is limited space?
- Place RBB & dahl teeth into occlusion
- Prepare the teeth, consent to prep, place rbb (if prep is in dentine, pt may post-op experience sensitivity & use prep guides to help)
- Create space for wing w/out prepping (by placing GIC stop at surface where wing would be, ie the palatal surface/incisal edge or occlusal aspect for post teeth), open up bite so when in contact, teeth only bite on GIC, monitor every week to see if rest of teeth
What is the dahl concept?
Axial migration of teeth in their natural state in order to re-establish ICP contacts over a period of time when you fit a resto high in occlusion
Effect works by a combination of:
1. Eruption (60%) of the unopposed (not in contact) posterior teeth
2. Intrusion (40%) of the anterior teeth in contact w the appliance
3:1 difference from front to back
What are the considerations for replacing the space of a missing 1st premolar with a RBB?
Abutment tooth should ideally be the one with the greatest root surface area & good bone levels:
- if the 2nd premolar has 2 roots, it will have greater root surface area than the canine
- If the 2nd premolar has 1 root, the canine will have a greater surface area, therefore it would be better for the abutment
○ BUT check if there is canine guidance or group function
§ If canine guidance –> do not interfere with it, so no canine abutment
§ If group function –> can use canine as abutment
Special investigations of abutment teeth
Bissu
- PA radiograph (assess PA status, bone levels & root morphology)
- bone support
- PPD at 6 sites of TIQ
- mobility
- TTP & TTPal
- sensibility testing (cold test & EPT)
- occlusal assessment (static & dynamic)
- any cracks
- any caries? / quality of any existing restos (e.g. if abutment has amalgam restoration, replace it with composite, as cement can bond to composite)
Types of crown/bridge failures:
- Biological failure (2o caries, open margin, operator skill, contour, occlusion)
- Aesthetic failures (restoration contour, emergance profile, hue - pure, colour, value - lightness & chroma - saturation)
- Mechanical failures (delamination/fracture of porcelain, bulk fracture, debonding)
Articulating paper thickness
GHM paper –> 20-30 microns
Shimstock aluminium -> 1 micron
Define abrasion
Abrasion = ‘the wearing of tooth substance that results from friction of exogenous material forced over the tooth surface’
But it can also be wear on a restorative material too i.e. a denture tooth.
Abrasion can lead to cervical abrasion cavities/gum recession
Define attrition
Attrition = ‘wear caused by endogenous material such as microfine particles of enamel prisms caught between two opposing tooth surfaces.
This can be tooth to tooth or tooth to dental materials and is made worse with parafunction.
Define acid dissolution (aka ‘erosion’)
Acid dissolution = loss of tooth structure due to a chemical process that does not involve bacteria.
Effects include: Tooth surface not involved in articulation, cupping of incisal edges or cusp tips, smooth rounded polished lesions, restorations can be standing proud of tooth structure. Sources of acid may be intrinsic or extrinsic.
- Intrinsic sources: morning sickness, GORD, binge drinking, competitive swimmers, anorexia, bulimia. - Extrinsic sources: fruit juices, wine, fizzy drinks, sugary drinks
Define abfraction
Abfraction = loss of tooth structure caused by transmission of forces through cusp tips to thin cervical enamel region resulting in fracture of cervical enamel.
Presents as V-shaped craters
What would you do if a pt has a symptomatic cracked tooth with heavy amalgam restoration?
Bissu
- special investigations to rule out any PA path (before you give LA)
- tooth slooth for pain on release, sensibility tests may give exagerated response, TTP, TTPal, mobility, PPD@6 sites & rad to assess PA path
- impressions for study casts &diagnostic wax ups + photographs
- I need to assess if the tooth is saveable or not, remove old amalgam, check for depth of cracks & amount of sound tooth tissue
- use transillumination, methylene blue dye & magnification (loupes) to assess cracks visually
○ if you see a big crack line, it's a red flag (vertical fracture --> XLA) ○ take picture of crack line, enlarge the image & show it to the pt for them to understand the severity of the prognosis
- If it is a horizontal supragingival crack, then drill around it to remove it until you reach sound tooth tissue & then place a temporary resto, like GIC build up (& make it very clear to the pt that this is a temporary resto)
○ assess if the pt is symptomatic at review
○ if symptomatic of cracked tooth pain (no PA path), explain poor prognosis & XLA
○ if asymptomatic, plan for removal of GIC & prep for cuspal coverage (onlay or crown)
What literature can you refer to, to assess the prognosis of a tooth?
Tooth restorability index (2005)
Dental Practicality Index (BDJ, 2024)
Assesses:
- structural integrity
- periodontal tx need
- endodontic tx need
- the ‘context’ (e.g. old vs younger pt, bruxist vs no bruxist, hx of bisphosphonates etc)
Each assessment category is weighted in scores of 0, 1, 2 & 6
Overall DPI score of 6> indicates tx may be impractical
- impractical threshold is decreased to DPI 4> if TIQ is for a bridge abutment
What are the stages of tx planning?
1) Emergency (get them out of pain)
2) Prevention & Stabilisation (make mouth healthy)
3) Restorative & Rehabilitation (make the mouth function & look well)
4) Recall & Maintenance (monitor & protect mouth)
Exam Q:
What factors do you need to consider when making a diagnosis for TSL?
- Age –> distinguish between physiological vs pathological TSL
- MH –> GORD (‘heartburn’), pregnancy, parafucntional habits (TMJ/TMD), psychological disorders (clenching)
- Drugs –> protein pump inhibitors (lansorprazole)/ antacids = GORD | liquid meds can cause wear
- SH –> stress, alcohol, occupation (wine tasting/ swimmers)
- Diet history –> fizzy drinks, fruits, sugar
What are the indications for a fixed-fixed conventional bridge?
- Pt w restored abutment teeth
- where implants are contraindicated
- good OH
- most favourable prognosis: lateral incisor replacement
Why do fixed-fixed conventional bridges fail?
Bissu
Each abutment tooth has different physiological movements in magnitude & in direction. There may have also been an unequal distribution of occlusal forces on the abutment teeth.
As a result, one of the abutments may have debonded (+ develop caries) while the other remained cemented
How to remove ceramic-metal crown:
Bissu
- rubber dam (split dam)
- Use narrow diamond bur (or new pear shaped one) for porcelain element of crown
- Use narrow tungsten carbide pear shaped bur to section metal
- Always stop at cement layer
- Keep cutting groove narrow & in midline of crown (easier to remove w/ flat plastic)
- Make sure all of the metal is cut on buccal, occlusal & palatal aspects
- consider ultrasonic o remove old cement debris from tooth surface
List the different metal & ceramic crown materials:
Bissu
Metal types:
1) High noble metal alloys (Au-Pd-Ag)
2) Noble metal alloys (Pd-Ag)
3) Basic metal alloy (Ni-Cr, Co-Cr,Ti)
Ceramic types:
1) synthetic GLASS-MATRIX ceramic, e.g. lithium disilicate (E-MAX - has more translucency/aesthetics & is etching)
2) glass-infiltrated GLASS-MATRIX ceramic, e.g. alumina
3) feldspathic GLASS-MATRIX ceramic
4) POLYCRYSTALLINE (oxide) ceramic, e.g. zirconia or alumina toughened zirconia (stronger, more opaque/slightly less aesthetic)
5) RESIN-MATRIX (hybrid) cermaic, e.g. resin nanoceramic (ideal for CAD/CAM)
Preparation for crown prep
- Metal :
○ Margin = 0.5mm
○ Non-functional occlusal reduction = 1mm
○ Functional occlusal reduction = 1.5mm- Metal-ceramic: need to add approx 0.5mm to where you will add ceramic:
○ Labial/Buccal margin = 1mm (to max 1.5mm if incisor)
- Metal-ceramic: need to add approx 0.5mm to where you will add ceramic:
Exam Q:
Briefly describe the mechanisms involved in possible causes of non-carious tooth tissue loss
Attrition: this is due to enamel contact between tooth and tooth or tooth and dental material (restoration). Worsened by parafunction (TMJ/ TMD problems)
Erosion: acid dissolution due to a chemical process. Intrinsic acid –> morning sickness, GORD, binge drinking, swimmers, anorexia + bulimia | extrinsic acid –> fruit juices, wine, fizzy drinks, sugary drinks, polypharmacy
Abrasion: TSL is due to friction with exogenous material forced over the tooth surface, mainly due to aggressive brushing.
Abfraction: TSL presents as V-shaped crevices on the tooth cervical. This is due to transmission of forces from cusp tips to thin cervical enamel.
Exam Q - If a temporary crown keeps de-cementing, list the possible reasons
(5 marks)
- Over-impression not accurate
- Moisture control poor
- Preparation not retentive - over tapered &/or inadequate reductions and does not follow contour of tooth
- Cement not mixed properly and/or too thick
- Margins not accurate - overextension, underextension, overcontoured or open margins
- Occlusion incorrect – excessive loading e.g. interferences during lateral excursion, premature contacts
Exam Q: What are the different types of temporary cement?
Zinc-oxide Eugenol (e.g. Temp Bond, self-curing but don’t use straight after comp resto as eugenol inhibits cure of composite)
Non-eugenol cements (e.g. Temp Bond NE, a ZnO & nonanoic acid like clove oil so contraindicated in clove oil allergy)
Exam Q:
A patient’s tooth is prepared for a crown. The patient attends for cementation of the permanent crown but complains that the temporary fell off two weeks ago and has not been replaced.
How will loss of the temporary crown affect the tooth and how could this stop the permanent crown from fitting? (4 marks)
- Loss of interdental space and contacts e.g., tilting of adjacent teeth, which may obstruct the seating of the permanent crown
- Changes in the occlusal relationship: e.g., over-eruption of opposing tooth, which can result in premature contacts when fitting the permanent crown
- Gingival hyperplasia at the margins and deterioration of gingival health: e.g., gingival overgrowth may make margins not visible or subgingival
- Exposure of dentinal tubules, which can damage the pulp of the tooth or compromise the seal of an RCT tooth
Exam Q:
If a patient’s temporary crown fell off 2 weeks ago, why will a new temporary not fit easily and how can you adjust it to ensure it does? (4 marks)
- Retained temporary cement or trapped gingival tissue – check to make sure neither of these are present. If residual temporary cement is present, then clean the preparation of it and remove any debris
- Tight proximal contacts – check and adjust tight proximal contacts, and also check the original cast for damage to the stone in these contact areas. Conversely, open contacts need to be modified in the laboratory (gold solder or addition of ceramic)
- Laboratory errors e.g., casting blebs, damaged or shipped dies or over/under-extended margins. Casting blebs can be removed with a bur. Over-extended margins can be adjusted from the axial surface using softlex discs.
- Internal discrepancies or areas of interference – can be located by applying a dry aerosol indicator (Occlude), disclosing wax or impression-type materials (light-bodied silicone). Any imperfections can be ground with a bur or stone.
Exam Q:
Why use a temporary cement for a temporary crown? (2 marks)
Temporary crowns are usually cemented using soft cements.
These cements allow: easy removal of the temporary restorations (from more retentive preparations).
This is important as temporary crowns are not to a long-term treatment and are to be replaced.
Exam Q:
The new impression was taken using light and medium-body silicone material - what do you need to do to ensure the wellbeing of the laboratory staff? (6 marks)
- Complete laboratory prescription and indicate that impression has been disinfected. This prescription must also be signed by the prescribing clinician at each stage of laboratory. It is a legal requirement that work entering the laboratory is accompanied by a written prescription from a qualified professional user.
- Ensure any sharp areas of impression tray/any potential sharps are properly packaged/rounded-off to avoid sharps injury
- Disinfection of the impression:
o Rinse the impression under running water to remove saliva and blood
o Shake off water over sink
o Immerse impression in disinfection bath containing ‘Perform’ for 10 minutes
o Rinse thoroughly under running water
o Place impression in plastic bag and label
Exam Q:
What FOUR things would you ask pt in the medical & social history to establish the cause of erosion?
- Do they ever experience ‘Heartburn’, if so how often?
- What does your daily diet typically consist of? do you consume fizzy drinks, fruit juices, herbal and fruit teas?
- What is you occupation? do you ever feel stressed?
- Are you currently taking any medications?
- Do you have suffer from any medical conditions such as Gastro-oesophageal reflux, Anorexia nervosa, Bulimia nervosa? “
Exam Q:
What would you see clinically with erosion?
- Intrinsic causes: wear of palatal surfaces of upper anteriors and occlusal surfaces of posteriors
- Extrinsic causes: Buccal surfaces of upper anteriors worn, occlusal and palatal surfaces of posteriors
- Smooth, rounded polished and often shiny lesions
- Rim of enamel around tooth (in anteriors) - perimylosis
- Restorations can be standing proud of tooth structure”
Exam Q:
Prevention and stabilisation has been carried out. How would you restore the palatal surfaces of these worn teeth? List the steps you would take.
- Take impression and jaw registration in RCP
- Cast up in dental laboratory and mount in RCP
- Build up teeth in wax, and show the patient - ensure they are satisfied
- Take putty impression of wax build ups
- Isolate tooth/teeth with rubber dam
- Using putty impression build up palatal surface of tooth in composite. Putty index acts as a guide to build up to. Make sure margins are flush and smooth.
- May require to build up prominent cingulum on upper central incisors to act as a occlusal stop for lower centrals.
- Adjust occlusion, and ensure patient is comfortable and satisfied with result
Following restoration:
* Medical referral if required to treat systemic conditions such as GORD
* Dietary advice and post-op instructions
* Monitor patient’s tolerance to increase in OVD”
Exam Q:
What other extra-oral signs would you look for to help establish the cause of erosion?
- Weight – if patient is severely underweight (sign of anorexia nervosa) or of a normal weight (e.g., in Bulimia nervosa)
- Hands – Russell’s sign (calluses on knuckles/hands) as with Bulimia nervosa
- Enlarged salivary glands - Puffy cheeks (caused by repeated vomiting)
- Dry eyes/skin
- Hair – thin and brittle
- Angular cheilitis
- Reduction in OVD
Exam Q:
What post-restorative complications may arise from changing their OVD with composites and describe them? (4 marks)
- Composite build ups may chip off (if RCP is not equal to ICP)
- Debonding and wear of composite (esp if bonding to dentine, where bond strength of composite is weaker than bonding to enamel)
- Staining of composite
- Erosion may resume the cause has not been addressed e.g. GORD
Others:
* If we are increasing the OVD the patient may struggle to cope with the change (it is generally advised that OVD should be raised no more than 5mm or leaving a minimum of 2mm of freeway space. The greater the change the more difficult it can be for the patient to adapt)
* If give patient a splint but habits continue, acid may get under splint and cause rapid erosion of build ups and teeth as no saliva to buffer and acid is contained”
Exam Q:
What are features of a good crown preparation on a tooth with good periodontal health? (4 marks)”
- Conservative preparation that satisfies retention and resistance form requirements: ideally 3% taper, 6% convergence angle, sufficient height
- Structural durability - sufficient bulk to withstand occlusal forces
- Ferrule effect
- Well defined, supragingival margins (ideally if possible)
- Does not invade biologic width
Exam Q:
What are the ideal measurements for crown reduction for the following (9 marks):
i. Incisor (full ceramic)
ii. Premolar (CMC)
iii. Molar (full gold)
During occlusal reduction, follow the natural anatomy of the tooth.
Incisor full ceramic reductions:
- incisal surface: 1.5 mm
- buccal surface: 1 mm in 2-3 planes following the contour of the tooth
- palatal and cingulum: 1 mm
- shoulder margin: 1 mm wide all around the preparation
Premolar CMC reductions: occlusal:
- non-functional occlusal: 1 mm
- functional occlusal: 1.5 mm
- functional cusp bevel: 0.5 mm
- buccal surface: 1-1.2 mm (metal-ceramic side) with a 1 mm shoulder margin
- lingual surface: 0.5 mm (metal side) with 0.5 mm chamfer margin
Molar (full gold) reductions:
- non-functional occlusal 1 mm
- functional occlusal: 1.5 mm
- functional cusp bevel: 0.5 mm
- lingual/palatal & buccal axial wall margins: 0.5 mm (chamfer margin)
Exam Q:
What features of an impression material are desirable for crown preparations? (2 marks)
- Cheap & easy to use
- Be able to record fine detail providing an accurate replica of the crown preparation (good surface detail and flows into small spaces accurately capturing crown margins)
- Confer a degree of wettability (hydrophilic)
- Dimensional stability (e.g. in transport)
- Good elasticity & tear strength
- biocompatibiloty w mucosal tissues
Exam Q:
What are possible problems of inadequate reduction of the crown preparation? (3 marks)
- Inadequate structural durability: crown may not be able to withstand occlusal forces
- Metal or ceramic layer may be too thin, and therefore have a higher propensity to fracturing
- Occlusal interferences e.g. premature contact with opposing teeth
Exam Q;
What other information would you send to the laboratory staff on the lab card? (2 marks)
- Tooth shade
- What material to use and return date
- Patient details (identification number) and dentist details
- The actual prescription
List 3 problems w old crowns:
- Stained or worn down / fractured
- Microleakage / caries growing underneath
- Natural dentition has aged & changed colour
Exam Q:
Importance/advantages of a temp (8 marks)
- Protects the prep (& tooth from sensitivity, microleakage or caries)
- Maintains appearance / aesthetics
- Maintain occlusal relationship & stops opposing tooth from over erupting
- Maintain the interdental space & contacts
- Maintain function (speech & mastication)
- Confirm that tooth prep is adequate (taper & reductions)
- To prevent gingival hyperplasia at the margins and maintain gingival health
- To protect dentinal tubules from microleakage (even in RCT tooth)
List the preparation criteria for all-ceramic indirect restorations (5 marks)
Bissu
- Preservation of tooth structure
- Cusp coverage (cover compromised w the onlay to protect them form fracture)
- Occlusal reduction: 1-1.5mm
- Axial wall taper: 6-10 degree taper
- Margin design: butt joints, 45 degree bevel w 1-1.5mm length & 1mm shoulder
Indications of partial coverage indirect restorations (6 marks)
Bissu
- Medium-large cavities where one or more cusps are missing
- Cavities where coverage of one or more cusps is advisable to improve the prognosis of the complex restoration
- Morphological modification &/or raising the posterior OVD
- Cracked tooth syndrome
- Multiple medium - large sized cavities in the same quadrant
- Endodontically treated tooth
Define inlay
a fixed intracoronal restoration
a dental restoration made outside of the tooth to correspond to the form of the prepared cavity, which is then luted into the tooth
(Journal of Prosthodontic Dentistry, 2017)
Define onlay
a partial coverage restoration that restores one or more cusps and adjoining occlusal surfaces or the entire occlusal surface & is retained by mechanical or adhesive means
(Journal of Prosthodontic Dentistry, 2017)
Note: when you cover all the cusps, it’s called an ‘overlay’
What are the different core materials?
Bissu
- Amalgam (‘Nayyar core for multi-rooted teeth’) – fast setting & can prepare the tooth shortly after
- Composite – placed under rubber dam for moisture control
- GIC – only as space fillers, not to build up entire core
Other considerations:
* Build the core to full anatomy – will help with putty index etc
* Ideally build the core once you have completed the RCT & same appointment under rubber dam
* Use the automatrix if only one tooth
What is the function of a post?
Nehete
To retain a core (they don’t reinforce teeth)
What are the different post materials?
Nehete
DIRECT POSTS (no casting or impression required)
1) Wrought pre-fabricated posts:
- Gold
- Titanium
- Stainless steel
- Aluminium
2) Fibre posts
INDIRECT POSTS (casting & impression required, duralay technique or direct technique)
1) type 3 alloy (noble gold alloy)
2) Basic metal alloy (Ni-Cr, Co-Cr,Ti)
For an upper 1st premlar with 2 canals, which one will you put your post in?
Nehete
Use the larger palatal canal to create the hole for the post
Where is the functional cusps on the upper & lower posterior teeth?
Lower teeth: BUCCAL functional cusp
Upper teeth: PALATAL functional cusp
Crown cementation choice for ceramic
Adhesive resin based cements
- self-curing (panavia)
- dual-curing
Crown cementation choice for metal
Conventional luting cement
- Zn phosphate
- RMGIC
- GIC (e.g. aquacem)
Checklist to do in fixed pros
- Photographs
- Full mouth radiographs
- Sensibility testing (repeat on multiple occasions)
- Articulated study casts
- Duplicate casts
- Diagnostic wax ups
- Mock up
- Review wax up
- Trays selected and adhesive prepared
- Lab card written
Define the 4 different types of marginal defects
- Under-extended margin = crown lies short of finish line of prepared tooth
- Over-extended margin = overhang, margin of crown resto lies beyond finish line of prepared tooth
- Open margin = margin w/in the finish line but there is space between the rest of margin & prepared tooth
- Over-contoured margin = w/in finish line but contour of gingival 3rd show excessive bulk
Poor fitting margins lead to… (3 marks)
- Cement dissolution
- Plaque retention & affect the health of gingiva
- Recurrent caries
How do you identify & correct a heavy proximal contact of crown prior to cementation?
Identity w dental floss, it wouldn’t pass through & therefore must be reduced
○ Correct by:
§ Unglazed porcelain is easily adjust w cylindrical stone
§ Glazed porcelain adjusted w/ diamond impregnated silicone points or diamond polishing paste
How do you identify & correct an open proximal contact prior to cementation
Identity w dental floss, it would pass through too easily with no resistance (cotact point area would appear deficient & under-contoured)
○ Correct by:
§ repeat impression & adding solder to that area / adding porcelain (in lab)
What can you do to ensure you have enough clearance on your functional cusp bevel?
Bissu
Use futar-d and measure clearance with callipers
or, go below the contact points with your margins even if it feels destructive
How can you guarantee cuspal protection in your onlay preparation?
Bissu
- Always take your preparation over the cusp tip & onto the axial wall but reduced length
- Try and avoid finishing your preparation on cusp tip
What can happen if your onlay preparation if finished on the cusp tip?
Bissu
Risk of fracture of that axial wall during lateral excursions/chewing
Tips for crown prep
- If bleeding as subgingival prep, aim for at least completing prep and perfectly adapted provisional
- Make your temp first, make sure margins & occlusion is well & then take your impressions for the lab & then cement your temp
- Use sectional tray or lower tray on uppers & lowers to help avoiding drags in the putty
Ferrule fact
- Ferrule: amount of sound tooth tissue to distribute occlusal forces from post to tooth too
- If you can’t get ferrule, you can do surgical crown lengthening, lasers, electrosurgery
Exam Q:
What are the contents of Panavia and how is it different to other cements in the same category, why is this useful? (3)
- Panavia is a resin-based cement used for definitive cementation of restorations such as permanent crowns
- There are different types of Panavia systems, distinguished from one another by their curing mechanism.
- For example, Panavia 21 is a self-cure system, whereas Panavia F 2.0 is a dual cure system – a bi-cure system that cures both chemically and via light activation
A distinguishing feature of all Panavia systems is the presence of resins with a phosphate group (MDP) and a carboxyl group (4-META) that promote bonding to the Ca2+ in the tooth and metal oxide in ceramic or metal-alloy restoration (but no direct bond to precious metals) i.e., Panavia bonds tooth to metal
* This molecular adhesion of the tooth and crown material results in a high compressive and tensile strength, useful for retention of the restorative material
* Other contents may include, but are not limited to: Bis GMA, camphorquinone, DMPT, phosphorylated methacrylate molecule.
Exam Q:
What you need to do before using Panavia (2)
- For base metals e.g., NiCr you can simply etch the metal surface with hydrofluoric acid and this leaves an oxide layer for Panavia to bond to
- For precious metals, this oxide layer doesn’t occur so they must be grit blasted with Al2O3 and SiO2 (sandblast). Then a metal primer is added to the metal surface and a silane coupling agent.
Exam Q:
List FIVE alternatives to dentine pins? (5 marks)
1) Undercuts in the remaining tooth tissue - undercuts in preparation help to retain cores.
2) Slots - slots are placed in the base of the cavity in horizontal direction and grooves are placed parallel to the long axis of the tooth
3) Grooves - provide retention by limiting path of insertion and by preventing the rotation of restoration
4) Adhesives - e.g. Panavia – core is retained using adhesive. Main disadvantage is that it cant be used in conjunction with pins, amalgapins, slots or grooves. They also do not bond to well to wet substances e.g. dentine
5) Cores (e.g., Nayyar core): amalgam (usually 1st choice) or composite”
Exam Q:
List FIVE properties of an ideal post on an anterior tooth (5)
- Fill over 50% of canal length
- Leave 4mm of GP at apex. (minimum length of 4-5 mm of GP). No space between post and GP.
- Extends well below bone crest - ideally at least an equal amount of post below and above the alveolar crest
- Longer than crown height
- Design: Parallel sided (offers more retention than tapered)
- Diameter should leave at least 2mm of surrounding tooth tissue to reduce chance of fracture
- Aesthetic (consider white carbon posts or fibre posts)
- Roughen surface - better retention
Exam Q:
What happens if a post doesn’t extends to the level of crestal bone? (2)
Creates a high fulcrum, which is above the supporting bone.
This leaves the tooth at high risk of horizontal fracture when forces are directed onto it, which could eventually lead to loss of the crown and tooth
Exam Q:
What happens if a tapered screw post is used? (2)
- Tapered screw engages the dentine to gain retention
- Stress is created within the tooth as the taper forces tooth tissue apart leading to tooth fracture”
Exam Q:
What would happen if your crown margins are subgingival? (2 marks)
Crown margins may encroach onto the biologic width (N.B. do not write biological width as this would be incorrect), which may result in:
* Gingival inflammation
* Loss of alveolar bone
* Formation of a periodontal pocket “
Exam Q:
What are the indications for the use of a threaded post?
- When retention is of utmost importance - threaded posts offer best retention
- Smaller tapered roots e.g., lateral incisors
Exam Q:
What are the differences between wrought and cast posts AND what indication would you use a wrought post over a cast post?
- Conventional gold cast not adequate to resist bending (unless in thick sections) - instead use wrought precious metal
- For paraposts < 1.25 mm (red), use wrought post as this gives strength in thin sections “
Exam Q:
Define a resin bonded bridge
A resin bonded bridge (or resin retained bridge or more recently a fixed partial denture) are minimally invasive fixed prostheses used to replace missing teeth. They are luted to tooth structures (primarily enamel), which has been etched to provide micromechanical retention for the resin luting agent (as defined by the glossary of prosthodontic terms).
Exam Q:
What are RBBs bonded with and how do they differ from other cements?
- Resin composite luting cement – usually variants of Panavia
- Panavia is a resin cement with the addition of a phosphonated methacrylate monomer.
- It has a very high strength and offers superior bond strength than other types of cements.
- Longer working time requires oxyguard to prevent oxygen inhibition – anaerobic set”
Exam Q:
Why are long span posterior bridges likely to be less successful?
- Increased occlusal demands (versus anterior spans).
- More load on bridge & bridge framework,
- Surface area coverage of abutments may not be sufficient for dealing with magnitude of forces
- Difficult to keep clean
Exam Q:
What is meant by a ““cantilever bridge”” (2 marks)”
A bridge that has an abutment or abutments at one end only, with the other end of the pontic remaining unattached “
Exam Q:
What are the advantages of cantilever bridges? (4 marks)
- Minimally invasive and easier to clean as it is only fixed to one end
- Less clinical time in comparison to other treatment modalities e.g., implants
- Less expensive (in comparison to implants and removable options)
- Less demanding to fit than all other forms of tooth replacement (although moisture control imperative)
- Aesthetic and predictable restoration
- If fails, complete dislodgement of bridge, which can be recemented
Exam Q:
A tooth has an MOD amalgam and the lingual wall has fractured off
What are THREE causes of fracture?
- Flexure of cavity walls results in flexure fatigue and fracture
- Excessive occlusal forces on restoration e.g., because the restoration is high
- Exogenous agents e.g., hard food during mastication “
Exam Q:
How can you diagnose cracked tooth syndrome?
- Signs and symptoms: pain with hot and cold fluids and on biting and or/release. Sharp pain with short duration. Long history of symptoms, may be difficult to localise tooth
- Examination findings: heavily restored tooth, evidence of parafunction/bruxism habits, may be visible evidence of a fracture e.g., stained enamel fracture (although common not to see fracture thought), may be TTP
- Special investigations:
- Visual inspection with magnification
- Removal of existing restoration (if one is present)
- Tooth slooth/Frac finder – usually will have pain on release of pressure
- Transillumination – uses fibreoptic light which is held against the gingival margin of the tooth to investigate for fractures.
- Dyes
- Sensibility testing – usually positive with an exaggerated response
- Radiographs
Exam Q:
What should a crown preparation have?
- Resistance and retention form: optimal taper: 3% taper (and 6% convergence angle); and sufficient preparation height (longer preparations have more surface area and therefore more retentive)
- Optimal finish: rounded line angles, smooth finish, no sharp line angles or corners
- Marginal integrity: clear well-defined supragingival margins (where possible) not encroaching onto the biologic width
- Structural durability: enough tooth structure to withstand occlusal forces
- Adequate reduction e.g. occlusally, on functional cusps, buccal, palatal etc
- Aesthetics and preservation of the periodontium
- Preparation should follow natural contour of tooth e.g. occlusal table should be similar to that of tooth prior to preparation, not flat
General consideration: a conservative preparation that satisfies all of the aforementioned attributes
Exam Q:
What materials can be used for a temporary crown (2)
Poly methyl methacrylate (PMMA) - Duralay
Bis acryl composite - Protemp II, Quicktemp
Exam Q:
What is the most likely cause of a distal gingival overgrowth following a crown prep (2)
- Crown margin finish lines may have been placed subgingivally, onto the biologic width
- This results in gingival inflammation, formation of a periodontal pocket and loss of alveolar bone”
Exam Q:
How can you manage a distal gingival overgrowth following a crown prep?
- OHI, PMPR
- Place a new temporary crown which has proper fitting (use retraction cords to aid placement) and ensure that crown is seated such that it not encroach on the biologic width
- Electrosurgery - involves removing the gingival overgrowth surgically
- Crown lengthening - reshapes and recontours the gingivae surgically “
Exam Q:
Name 4 elastomers used to record impressions
- Condensation silicones - poly dimethyl siloxanes
- Addition silicones - poly vinyl dimethyl siloxanes (PVDMS)
- Polyethers
- Polysulphide
Exam Q:
What are the THREE aspects of colour and their definitions
- Hue: quality by which it is possible to distinguish one colour family from another i.e. red from yellow or green. It corresponds to the wavelength of light reflected by the teeth.
- Value: an achromatic measure of the lightness or darkness of a particular colour, ranging from pure black to pure white (best determined by a black & white photo). High value = light shade, low value = dark shade. Value is considered the most important factor in colour determination.
- Chroma: degree of strength or saturation of colour of a particular hue - describes the intensity or vividness of a colour.
Exam Q:
Define Opalescence
Light scattering phenomenon caused by the presence of fine particles (opalizers)
Exam Q:
SIX factors influencing colour in a dental practice
- Lighting conditions - tooth shade may vary under different light conditions. natural light vs. artificial light. If using artificial ideally use colour corrected artificial light source (5500 K)
- Contrasts - value or hue-contrast effects - e.g. tooth may appear brighter in patient with dark coloured lip stick, therefore remove prior to shade match
- Observer - eye fatigue can change the appearance of colours
- Lip position, angle and distance
- Tooth dehydration - e.g. following rubber dam placement. Tooth dehydration makes them appear whiter, therefore shade match before placement i.e. using “wet tooth”
- Tooth preparation may also change its colour
Exam Q:
What do you understand by the term taper and convergence angle (4)
Taper: The angle between one axial wall of the preparation and the long axis of the preparation
Ideal taper = 3 degrees (with 6 degree convergence angle)
Convergence angle: angle is defined as the angle between two opposing axial walls of a preparation and equals the sum of the tapers of two opposing axial walls
Consider drawing a diagram to illustrate these definitions
Effects of tooth loss:
- Aesthetics
- Functional issues
○ Discomfort
○ Reduced chewing ability / speech impairment - Biological
○ Drifting of teeth & over eruption
○ TMD
○ Bone loss
○ Occlusal stability - Pt perception & self image
There is a high incidence of overeruption of unopposed posterior teeth.
What percentage of unopposed teeth are likely to over erupt?
83% of unopposed teeth are likely to overerupt
What percentage of unopposed teeth likely have interferences with RCP or excursive movements?
51.6% of unopposed teeth likely have interferences with RCP or excursive movements.
Questions to ask pts if they have missing tooth
1 - How did they lose their tooth?
2 - When did you lose it?
3 - Is it causing you trouble / functional issues
4 - Is there an aesthetic issue
5 - Check if there is any contact point on the opposing tooth or drifting / overeruption
Over-eruption happens mostly in the first 2-3 years
Options for space replacement:
1 - No tx
2 - Implants
3 - Bridges (RBB or conventional)
4 - Removal partial dentures
Tx planning considerations
1) Benefits
2) Risks
3) Cost
4) Longevity, depends on:
○ Materials used
○ Type of restorative procedure
○ Patient parameters
○ Operator variables
○ Local factors (occlusion etc)
5) Maintenance
What are the pt’s main concerns for tooth replacement options?
- Prolonged tx
- Tx stress & discomfort
- Subsequent problems w abutment teeth
What is the shortened dental arch concept
Oral function was adequate where at least 4 occluding premolar units were left, depending on the age of the patient & preferably in a symmetrical position.
