Fixed Prosthodontics Flashcards
What is a fixed prosthesis?
a prosthesis not removable by the patient
Give three examples of fixed prosthesis
crowns, veneers, bridges
What are some indications for fixed prosthesis?
teeth with large multi-surface restorations, fractured teeth, endodontically treated posterior teeth, to replace a missing tooth, as part of a RPD
What are some contraindications for fixed prosthesis?
tooth unrestorable, uncontrolled perio, untreated caries, poor oral hygiene, no interocclusal space, short clinical crown
What must you ensure before commending a crown preparation?
ensure the tooth is restorable
What should you check to determine how restorable a tooth is?
remaining tooth, are there any subgingival restorations, how much remaining enamel, is the perio attachment good, is there any apical pathology, is there RCT, is the tooth important for masitcation, are patients motivated, the tooth restorability index
What is the tooth restorability index?
an index to determine if there is enough remaining sound tooth structure to retain a core or crown
What does a sextant score of 0 mean in the tooth restorability index?
no axial wall of dentine to aid retention or resistance
What does a sextant score of 1 mean in the tooth restorability index?
inadequate coronal dentine distribution to make a predictable contribution to retention or resistance
How thick would the coronal dentine need to be to get a score of 1?
less than 1.5mm
What does a sextant score of 2 mean in the tooth restorability index?
a questionable amount of dentine is present, more than 1 but no predictable contribution to retention and resistance
What does a sextant score of 3 mean in the tooth restorability index?
adequate coronal dentine for retention and resistance
What does a whole tooth score of 12 and greater mean in the tooth restorability index?
restorable
What does a whole tooth score of 9-12 mean in the tooth restorability index?
Acceptable if 2-3 sextants have a comfortable 3 score
What does a whole tooth score of less than 9 mean in the tooth restorability index?
unacceptable to retain a plastic core
What are potential other treatments to consider if the whole tooth score is less than 9 in the tooth restorability index?
crown lengthening, cast post and core
What must you ensure is complete before the patient arrives for their crown prep?
stabilisation of any active disease process, periapical radiograph, assessment of the interocclusal space and occlusion, restorability assessment, know which type of prep you are completing
What must you ensure is done while you complete the crown prep?
ensure you use sharp highspeed burs with copious water irrigation to ensure the tooth doesn’t overheat, ensure the prep is smooth and not undercut, ensure there are adequate retention features
What must you ensure is complete once the crown prep is done?
retraction cord placed and an impression taken of the prep, impression of the opposing arch, take a shade match
What are the five principles of crown prep?
preservation of the tooth structure, retention and resistance form, structural durability, preservation of the periodontium, marginal integrity
What can excessive reduction of the tooth structure lead to?
thermal hypersensitivity, pulpal inflammation, pulpal necrosis, tooth may be over tapered or shortened which may affect its retention and resistance form
What is retention in crown prep?
the ability of the preparation to resist the dislodgement of the crown restoration by forces directed along its path of insertion
What is resistance in crown prep?
the ability of the preparation to resist the dislodgement of the restoration by forces directed horizontally to the restoration
What are the six factors affecting retention and resistance?
taper of the preparation, surface area of the preparation, length and height of the preparation, diameter of the tooth, texture of the preparation, accessory means
What is the convergence angle in regards to the taper of a crown prep?
the angle that is formed between each two opposing axial walls of a tooth prep to receive a crown restoration. It determines the taper of the tooth
What is the ideal overall taper for a crown prep and what does that mean for the ideal taper either side of the tooth?
ideal is 6 degrees, meaning the taper either side of the tooth needs to be 3 degrees in line with the long axis of the tooth
What can the surface area of the crown prep depend upon with regards to retention?
the size of the tooth, the extent of the tooth covered by the restoration, the accessory features
How can the size of the tooth affect the surface area for retention of the crown?
the larger the size of the tooth, the larger the surface area available for bonding, therefore the higher the retention
How can the extent of tooth coverage by the restoration affect the surface area for retention of the crown?
the higher the area covered by the restoration, the higher the retention
How can accessory features such as boxes, grooves, slots within a crown prep affect the surface area for retention of the crown?
increases the surface area for bonding as well as providing mechanical interlocking which increases the retention
How can the length and height of the preparation affect the retention of the crown?
increasing the length of the prep will increase the retention and resistance
How can the diameter of the tooth affect the retention of the crown?
a narrower tooth can have greater resistance to tipping than a wider tooth
How can the texture of the crown prep affect the retention of the crown?
rough surfaces can provide more mechanical interlocking which would increase retention however, we should aim for a smooth prep to give the best fit for the crown
What is structural durability in crown prep?
crown must be rigid enough to not flex, perforate or fracture
What are the two features related to structural durability in regards to crown prep?
occlusal reduction and axial reduction
Why is it important to remove enough tooth structure during occlusal reduction?
so the restoration can be built back to the ideal occlusion and thick enough to prevent wearing or distortion
Why is it importance to remove enough tooth structure during axial reduction?
important to provide enough space so that the restoration can be built with adequate thickness
What are five reasons why we should aim to place the margin of the prep supra-gingivally?
easily prepared and finished by the operator, provides good vision for the operator, patient can keep the area clean easier, mostly on enamel, less destructive to the periodontium
What does equi-gingivally mean?
with the level of the gingiva
What are four situations which require sub-gingival placement of the finishing line?
aesthetics, when we need extra retention in teeth with short crowns, when there is caries or restoration at the area of the finish line, margin should be placed on sound tooth structure
What should a crown preparation never involve?
the biological width
What is the biological width?
the band of tissue attached to your tooth until it meets the alveolar bone - approx 2mm
What will impinging on the biological width lead to?
attachment loss, gingival inflammation, difficulty cleaning, crestal bone loss
What are the three requirements of a restoration margin?
it must fit as closely as possible against the finishing line of the prep, it must have sufficient strength, it should be placed in an area the dentist can finish
What are the 6 factors to consider when choosing an indirect restoration?
location of the tooth, amount of tooth structure available, remaining dentition and occlusion, parafunctional habits, underlying tooth colour, what cement can be used to bond the crown based on the material
Which types of cements can be used to cement metal crowns?
a wide range
Which types of cements can be used to cement ceramic crowns?
resin-based
What should you not cement a temporary crown with if you aim to use a resin-based cement for the permanent crown? why?
a eugenol based temporary cement as it inhibits polymerization
What is needed for glass based ceramic crowns to have a strong bond?
sufficient enamel to bond to
Where can you not use a resin-based cement?
sub-gingival finish lines
What are the four types of crown available?
metal based, PFM, ceramic, zirconia monolithic
What should the occlusal reduction be for metal based crowns?
1mm
What should the axial reduction be for metal based crowns?
0.5mm
What should the function cusp bevel reduction be for all crowns?
0.5mm
What should the occlusal reduction be for PFM crowns?
1.5mm
What should the axial reduction be for the porcelain sections of the PFM prep?
1.2-1.5mm
What should the axial reduction be for the metal sections of the PFM prep?
0.5mm
What should the occlusal reduction be for ceramic crowns?
1.5mm
What should the axial reduction be for ceramic crowns?
1mm
What should the occlusal reduction be for zirconia monolithic crowns?
1mm
What should the axial reduction be for zirconia monolithic crowns?
0.5mm
Should the finishing lines for metal based crowns be champfer or shoulder?
champfer
Should the finishing lines for the porcelain sections of PFM crowns be champfer or shoulder?
shoulder
Should the finishing lines for the metal sections of PFM crowns be champfer or shoulder?
champfer
Should the finishing lines for ceramic crowns be champfer or shoulder?
champfer
Should the finishing lines for zircoina monolithic crowns be champfer or shoulder?
champfer
What are some indications for the use of metal crowns?
minimal prep required, patient request, bruxism, subgingival margin
What are some indications for the use of PFM crowns?
aesthetics, bruxism, metal sub structure required to block out discolouration, insufficient enamel for ceramic crown, subgingival margin
What are some indications for the use of ceramic crowns?
aesthetics and sufficient enamel for bonding
What are some indications for the use of zirconia monolithic crowns?
compromise between minimal prep and aesthetics, non-metal crown in a posterior region
How can high speed handpieces affect the pulp complex?
can cause localised inflammation and changes in odontoblast nuclei
How can drying the dentine affect the pulp complex?
can cause aspiration of the odontoblastic nuclei and pulpal inflammation
How can opening the dentinal tubules affect the pulp complex?
increases the chance of bacterial contamination of the pulp
How can cementing uncured resin components affect the pulp complex?
been shown to inflict localized pulpal inflammation when in close proximity to pulp tissues
How can inadequate cementation of the crown and inadequate marginal fit affect the pulp complex?
can lead to microleakage and subsequent inflammation of the pulp
What issues can under-preparing the crown prep result in?
compromised structural durability of the crown, knife edge crown margins which can splay or fracture, lack of inter-occlusal clearance, damage to opposing teeth, bulky restorations, poor aesthetics
What issues can occur if a sub-gingival margin is used?
localised gingival inflammation, plaque accumulation, increased pathogenicity of subgingival plaque, violation of the biological width, attachment loss
What issues can occur if there are poorly defined or poorly captured crown margins?
the technician may struggle to determine the margins which will result in overhanging or open crown margins leading to perio issues
What is retraction cord used for?
to temporarily displace the gingivae so an accurate impression can be taken of the finish line to allow the use of hydrophobic impression materials
If the retraction cord is used too aggresively, what can occur?
gingival bleeding, patient discomfort, damage to epithelium attachment, gingival recession
Can crowns be used alongside RPD?
yes, the crowns can be incorporated into the design
What does hue mean regarding shade selection?
colour tone such as red or blue or yellow
What does value mean regarding shade selection?
intensity or saturation of the hue such as light blue or dark blue
What does chroma mean regarding shade selection?
the relative brightness or darkness of the hue
What does an A grade mean on the vita shade guide?
red-yellow hue
What does a B mean on the vita shade guide?
yellow hue
What does a C grade mean on the vita shade guide?
grey hue
What does a D grade mean on the vita shade guide?
brown hue
What does the number for each grade on the vita shade guide mean?
the chroma of each tooth
Does every area of the tooth need to have the same shade selection?
no
