Operative and endo Flashcards
What is a crown?
A restoration that encompasses coronal tooth tissue, covering remaining tooth substance and restorations
Why do we place crowns?
What pressure is exerted when cutting at low speed?
2-5 lb
n.b. speed is inversely proportional to the pressure
What pressur eis exerted when cutting at higher speed?
1 lb
n.b. speed is inversely proportional to the pressure
What pressure is exerted when cutting at ultra high speed?
1-4 oz
What increases heat production of a treatment?
RPM of instrument
Amount of pressure applied by operator
Area of tooth in contact with the tool
What happens to the pulp at 113 degrees F?
Inflammatory respinse of pulp = Pulpitis
(n.b. this is reversible)
What happens to the pulp at 130 degrees F?
Permanent damage to the pulp
= pulpal necrosis
What are the uses of rotary cutting instruments?
- Intra-coronal tooth preparation
- Excavation of caries
- Finishing cavity walls
- Finishing restorations
- Polishing restorations
- Removing old restorations
- Extra-coronal tooth preparation
- Separating crowns and bridges
- Adjusting acrylic prostheses
What are the 2 different designs of low speed handpieces?
Straight/contrangle
What is the speed range for a slow handpiece?
10,000 to 30,000 rpm
Which direction do slow handpieces turn?
Either clockwise (forward) or anticlockwise (backward)
What are the clinical uses for slow handpieces (5)?
- Cleaning teeth
- Caries excavation
- Finishing and polishing procedures
- Adjustment of porcelein
- Root canal treatment
What are the lab uses for slow handpiece?
Trimming and adjusting of:
Temp crowns
Removable prostheses
Orthodontic appliances
What are the (2) advantages of low speed handpieces?
Better tactile sensation
Less chance of overheating cut surface
What are the (7) disadvantages of low speed handpieces?
- Ineffective compared to high speed
- Time consuming
- Need to apply more pressure
- Vibrations (uncomfortable for patient)
- Slower cavity prep (increased operator fatigue)
- Burs have tendency to roll out of preperation
- Carbide burs = brittle = break at slow speed
What are the uses of high speed handpieces?
Tooth prep & removal of old restorations
What are the (3) advanatges of high speed handpieces?
- Faster
- Less pressure, vibration and heat needed
- Less operator fatigue
What are the (3) disadvantages of fast handpieces?
- Increased temp (without water)
- Less tactile sense (overcutting possible due to water spray)
- Air & water spray impair visibility
What speed do high speed handpieces go?
450,000 to 500,000 rpm
What are the 3 basic parts of rotary instruments?
Shank = fits into handpiece (friction grip/ latch grip)
Neck = connects shank to head
Head - cuts/finishes/polishes
Where do you dispose of fractured/blunt burs?
Sharps bin
What happens to caries hen it reaches the enamel-dentine junction (EDJ)?
Why?
It spreads laterally and deep into dentine
This is because….
Dentine has a lower inorganice mineral content than enamel = softer
In a carious lesion that extends up to half way between the EDJ and the pulp will the superficial dentine caries be hard or soft?
Soft
it will also correspond to the zone of destruction (bacterial invasion) histologically
As a carious lesion in the dentine becomes deeper what happens to its consistency and which areas will it correspond with histologically?
Harder
Regions of demineralisation without bacterail invnsion
What is the consistency of extensive, deep carious lesions which approach the pulp?
They will often be soft throughout
How do we remove caries?
- Gain access using 544 bur to cut through enamel (may be omitted where there is an open cavity and the caries can be seen directly) -> should be large enough so that caries at the EDJ can be seen and removed adequately
What difference can be noted when a 544 bur on a air turbine handpiece comes into contact with caries?
Sound changes
Bur doesn’t really move (just sinks in because its soft!)
What is the length of the cutting head of the 544 bur?
3mm
What do arrested caries feel like?
stained
hard/firmer -> due to remineralisation
How far into the tooth do you first come into contact with dentine caries?
Approx. 2mm
(2/3-3/4 of 544 bur depth)
In which direction should the slow (motor) handpiece be moving to make caries removal easier?
Clockwise
n.b. On the handpiece:
F = forward (clockwise)
R = reverse (anti-clockwise)
Which (3) instruments can we use to detect adequate removal of caries?
No. 18 probe
(listen - scrape = enamel, no sound = caries)
Excavators = Discoid or spoon
Which senses do we use to determine if caries has been removed?
Sight
Tactile (touch)
Sound (scraping)
Which instruments best remove caries?
Rosehead burs (problem will stil cut healthy enamel and dentine)
Excavator (preferrable near pulp because wont remove hard tissue)
What is the cavo-surface angle?
What is the ideal cavo-surface angle?
90 +/- 20 degrees
= 70-110 degrees
Which cusp is functional in the upper molars and premolars?
Palatal cusp
Which cusp is functional in the lower molars and premolars?
Buccal
What are the 3 different marginal finishes for crown preps?
- Knife edge
- Champfer
- Shoulder
What is a knife edge finishing line?
Approx 180 degrees
= difficult to see & casting may be distorted during finishing
but close adaptation to the tooth surface
What is a butt joint/shoulder finish?
Approx 90 degrees
= seen clearly, not distorted by casting
= GOLD ALLOY DOES NOT CAST WELL TO IT!
What is a chamfer finish?
Approx 135 degrees
= good compromise between knife edge and shoulder
= seen readily and resists distortion
= reasonable adaptation to the finish line at the tooth margin
Depth = approx 1/2 bur width (0.7mm)
What is Supra-gingival?
Above the gingival margin
What is sub-gingival?
Below the gingival margin
What is equagingival?
Within the gum level (uses a retraction cord to push the gum away)
This is used more for anterior crown preparations
What are the (2) disadvantages of getting lining on the walls of a cavity?
- With time the lining will dissolve = microscopic gap between filling an tooth = microleakage & secondary caries
- Important not to eliminate any undecuts needed for retention of the filling material
When excess amalgam is safely disposed which four things should it be kept under?
Water
OR
Old x-ray fixer
OR
Potassium permanganate solution
OR
A container with a ‘vapour lock chemical’
What is the problem with having extra holes in a rubber dam?
Seepage of saliva and materials through the dam
What is the problem with having inappropriate positioning of holes in a rubber dam?
Seepage due to overstretching of the dam
Discuss good and bad points of operator posture
What is the normal focussing distance of the dental light?
30cm
Why should the light not be too close to the patients mouth?
Impede operator access
Transmit too much heat to patient
Loose effective lighting in middle of field (black square)
In which two ways can light be used?
Directly
Reflected onto work surface using mouth mirror
Which two materials may be used to line a composite restoration?
A setting calcium hydroxide cement
Light cured GIC
Why should Eugenol containing aterials never be used to line a composite restoration?
The eugenol would plasticise the resin base
What is the consequence of over-etching the dentine?
Pulpal inflammation and pain
Which wavelength of light is used to cure composites?
470nm
What is the maximum depth for an increment in a composite restoration?
3mm (2mm to be on the safe side!)
What is Oblique incremental curing?
And what does it avoid?
Building up a composite in 2mm increments
Avoids tension on a cavity = shrinkage at the margins = microleakage
What possible problem has recent research indicated following light curing of composite resin?
Damaging temperature rises of the pulp
What is the benefit of using a teflon coated instrument for composite?
Composite resin does not adhere so greatly to the instrument
At what stage can we start to see occlusal caries on a bitewing xray?
When it has gone into dentine
When is a class II cavity required?
What does close adaptation of an amalgam fillin minimise (3)?
- Marginal leakage
- Secondary caries
- Post-operative sensitivity
Compared to adjacent teeth what level do marginal ridges normally lie?
Similar level
(unless teeth are tilted following extraction of a tooth more mesial in the quadrant or if the tooth has over-erupted after the loss of an opposing tooth)
What are the advantages of pre-wedging (2)?
Protects the rubber dam from damage by the bur
Increases the space between the teeth before the restoration (can overbuild contact = tighter meeting after the restoration has been placed and the wedge removed)
Why can we not use a matrix band for Class II composite restorations?
We cannot condense composite = would not have as good a finish
In which two ways can we protect adjacent teeth from damage when drilling a class II cavity?
- Apply a matrix band (only protects from light damage with the bur)
- Carefully removing the tooth structure att he contact point without rotary instruments (fracture out the surface with fgingival margin trimmer) = best way
When is a matrix required?
To contain the restorative material in the area where there is a missing wall of tooth
What is Xeno?
A self etching primer
How does a self-etching primer work?
The acid etches the enamel = releases Ca ions = chelates the acid = neutralised and no longer etches
Which solvent does Xeno contain?
Butanol
What properties does primer have when its solvent is butanol?
Longer working time than other materials (that has acetone as a solvent = more volatile)
What happens to the shade of teeth as they dry out?
Lighten
What is Ceram X mono?
A nano-hybrid comosite resin
= variety of filler particle sizes = varies from 5nm to 7 microns
= heavily filled (= strong, wear resistance, minimal polymerisation shrinkage = 1% by volume)
Why should the oblique layer of a composite restoration not contact the buccal and lingual walls of a cavity simultaneously?
Shrinkage when set = pulls the two wall of the cavity towards each other = cuspal bending (fracture risk)
What is needed to diagnose fissure caries (4)?
Inspection of clean dry tooth surface
Sharp eyes (magnification)
Quality radiograph (only sometimes useful)
Probe to remove plaque from fissures
Which types of caries are radiographs useful to exclude?
Occult caries (large dentine lesions underlying seemingly intact enamel only)
n.b. Enamel over cusps is too thick to see caries through and uneven enamel thickness makes it difficult to see any
Why do we use hand instruments such as excavators to remove caries from the pulpal floor of a cavity?
Slow speed handpieces remove even sound dentine whereas handinstruments only remove carious dentine
= if too much dentine removed = exposed pulp :(
What are the advantages of a GIC liner (3)?
Adhering to the dentine floor
Releasing fluoride
Bonds to overlying resin
Why is it important not to look directly into a light curing light?
Damages the retina
When light curing from the buccal side of the tooth in which direction does composite shrink?
Towards the buccal side of the tooth
What is pit and fissure sealant composed of?
Unfilled Organic resin (UDMA/Bis-GMA + Dilutent resin e.g. TEGMA)
Why can’t you wear rubber gloves when mixing putty?
Rubber plasticizers may inhibit the set
What are the 5 principles governing preparation of a tooth for a crown?
- Preservation of tooth structure
- Retention and resistance form
- Structural durability of the restoration
- Marginal integrity
- Preservation of the periodontium
What is retention?
The ability of the preparation to prevent removal of the restoration along its path of insertion
What is resistance?
The ability of the preparation to prevent dislodgement of the restoration by forces directed in an apical, oblique or functional direction with lateral forces
Why can we not do untapered preparation walls for crowns?
Need to avoid undercuts & allow for complete seating of the restoration during cementation
What is the optimum taper for a crown?
5 to 8 degrees
(n.b. a taper of up to 16 degrees has been proposed as being clinically achievable while affording adequate retention)
How can you ensure that you have removed the right amount of tissue?
Silicone index (i.e. impression of tooth before & cut in half)
Depth marker burs
Where should the upper edge of the rubber dam fall (in single tooth isolation)?
Just above or below the nose
When punching a hole in a rubber dam for a single tooth isolation where should it be placed?
Near the centre of the sheet (adjusted to fall in the appropriate quadrant i.e. for upper left would punch the hole slightly to the upper left side of centre)
When isolating multiple teeth with a rubber dam, where should the stamp be placed?
Upper edge of stamp should be 1.5 cm below the upper border of the rubber dam
Which 3 things determines the size of holes needed to be punched in a rubber dam?
The cervical diameter of the tooth (bigger tooth = bigger hole)
The elasticity of the rubber dam (heavier grades = less elastic = need larger hole)
The method of rubber dam application
What can happen if the hole punched in a rubber dam is too small?
The dam can split
What 3 things does a rubber dam napkin do?
- Prevents marks on skin
- Prevents moisture producing sores on the skin
- Improves patient accepibility of the rubber dam
When is single tooth isolation usually used?
Limited to endodontic treatment
What is diagnosis?
The art and science that results from the synthesis of scientific knowledge, clinical experience, intuition and common sense
What does a caries diagnosis imply?
Deciding whther a lesion is active, progressing rapidly or slowly or whether it is already arrested
What (4) must be present for caries to develop?
- Carbohydrate substrate
- Susceptible tooth
- Bacterial plaque
- Time
