foundations of fixed pros Flashcards
Crown
An artificial replacement that restores missing tooth structure by surrounding part/all of the remaining structure with a material.
Name 5 examples of materials that can be used for crowns.
- cast metal alloy
- metal-ceramics
- ceramics
- resin
- combination of materials
Onlay
partial coverage restoration that restores 1 or more cusps and adjoining occlusal surfaces* or an entire occlusal surface and is retained by mechanical or adhesive means.
Laminate Veneer
a thin bonded ceramic or composite restoration that restores the labial, incisal and part of the proximal surfaces of teeth.
Bridge
any prosthesis that is luted, screwed or mechanically attached to natural teeth, tooth roots and/or dental implants/abutments.
What is the aim of a bridge?
to furnish the primary support for the dental prosthesis and restore teeth in a partially edentulous arch.
Long Axis
a theoretical line passing lengthwise through the centre of a tooth.
Where are indirect restorations fabricated?
outside of the mouth -
typically in a dental lab but can also be chairside.
Which 3 things does an indirect restoration aim to restore?
- function
- aesthetics
- comfort
Stages of indirect restoration delivery:
- tooth prep
- impression of the area
- impression cast and restoration fabricated
- cementation
Clinical stages of an indirect restoration:
- preoperative records and justification for this type of restoration.
- shade selection
- tooth prep
———————————————————————————— - temporary restoration construction
- impression
- fit temp
———————————————————————————— - removal of temp and cement
- assess definitive restoration
- cementation / bonding of definitive restoration
What are the ideal components indicating ‘A Healthy Start’ before starting fixed pros?
- risk assessment
- prevention
- caries management (limit caries risk)
- periodontal considerations
- endodontic considerations (confidence in pulpal stability)
- tooth surface loss
- parafunction, TMJ
What 4 preoperative records must you have before providing any indirect restoration?
- recent PA
- vitality / sensibility testing to confirm pulpal status
- study models from pre-op impressions
- occlusal assessment
Types of Partial Coverage Indirect Restoration
- laminate veneer
- inlay
- onlay
- 3/4 crowns
- resin bonded bridgework (‘adhesive’ or ‘minimally invasive’ bridgework)
Types of Full Coverage Indirect Restoration
- gold shell crown
- metal ceramic crown
- all ceramic crown
- conventional bridgework
- implant crowns / bridges
7 General Indications for Fixed Pros
- badly broken down teeth (e.g: caries, toothwear, hypoplastia)
- restore function and aesthetics following trauma
- alter size or shape of teeth
- improve appearance of non-vital anteriors
- restore root filled teeth
- fixed replacement of missing teeth
Which percentage of coronal tooth tissue is removed during anterior full coverage crown preparation?
between 63 and 72%
How much sound tissue may be removed for an extended veneer preparation?
Up to 30%
When ensuring you have informed consent, what statistic should you quote when referring to the death of crowned teeth?
20% - 1 in 5 crowned teeth die due to pulpal death within 10 years
How does pulpal death occur in a crowned tooth?
Due to exposure of dentinal tubules and bacterial ingress.
(diameter increases closer to the pulp)
What are the benefits of Immediate Dentine Sealing?
- improved bond strength (important for adhesively retained restorations)
- reduced micro-gaps and marginal leakage
- reduced post-op sensitivity
When should dentine bonding agent be applied for immediate dentine sealing?
At the time of preparation to freshly cut dentine, before recording impression.
Which 2 factors need to be balanced and considered when looking at the structural durability of the restoration?
- sufficient clearance for the construction of a durable restoration
- preservation of tooth structure
(in other words, does the restoration have sufficient bulk of material to withstand occlusal forces?)
What does the amount of occlusal clearance depend on?
The choice of material.
In general, what level of occlusal clearance is needed for metal?
1.0mm
What is an Iverson Gauge used for?
To check the thickness of an indirect restoration.
(also useful for adjusting a high restoration)
If occlusal clearance is inadequate, what will this result in?
Perforation or fracture of the restoration +/- underlying tooth.
What is a functional cusp?
Cusps which occlude with the opposing teeth in intercuspal position (centric occlusion).
Which cusps are classed as functional cusps?
palatal cusps of upper posterior teeth
and
buccal cusps of lower posterior teeth
(if the teeth are in crossbite, the opposite would be true)
Although a functional bevel is not advocated anymore, which cusps would this be placed on?
- palatal slope of maxillary palatal cusp
- buccal slope of the mandibular buccal cusp
On most posterior teeth, what angle should the functional cusp bevel be placed at?
45º to the long axis of the tooth.
When adding a functional bevel, how much more of the tooth should be taken away ON TOP OF the occlusal clearance.
0.5mm
(final width of 1.5-2mm)
Retention Form
the features of a tooth preparation that prevent the restoration from being dislodged by forces along the path of insertion and withdrawal.
Which 2 factors does adequate retention depend on?
- geometry of the tooth preparation
- roughness of fitting surface of restoration
Ideally, what should the path of insertion be coincident with?
The Long Axis of the Tooth
Why is the long axis of the tooth important to consider during indirect preparations?
- preparing along the long axis helps to conserve tooth structure.
- occlusal forces are parallel to the long axis so then are easily dissipated by the periodontium.
How many degrees and in which direction are molar teeth typically inclined?
9-14º lingually
Taper
The convergence of 2 opposite facing walls of a crown preparation.
Angle of Convergence
Extension of the planes to form an angle.
(theoretically 6º but 10-14º is more achievable)
Although a preparation with completely parallel walls would have maximal retention, what are the disadvantages of this?
- some convergence is needed to allow excess cement to escape when seating the crown.
- there would be difficulty in fully seating the restoration.
- undercuts may be present in preps if they are too cylindrical.
For axial reduction, what is required to create the desired taper?
The cervical width (base of prep) must be greater than the occlusal width (top).
What is the relationship between retention and degree of taper?
Retention decreases as the degree of taper increases.
How can axial reduction be achieved?
use the burs parallel to the long axis as the burs have built in taper (don’t try and angle it youreself).
Where is the first plane located?
In the cervical 1/3, parallel to the long axis of the tooth.
Where is the second plane located?
In the mid/incisal part of the tooth, follows the external contour.
In terms of surface area, ___ axial walls are more retentive than those with ____ axial walls.
Crowns for preparations with tall axial walls are more retentive than those with short axial walls.
Why are molar crowns more retentive than premolar crowns of a similar taper?
Due to a larger diameter.
Path of Insertion
An imaginary line along which the restoration will be placed onto or removed from the preparation.
(each restoration should have a unique path of insertion)
Which two methods of creating surface roughness increases retention?
- sandblasting
- acid etching
Which two methods of creating surface roughness increases retention?
- sandblasting
- acid etching
Where is the most common site of retention failure?
At the interface between the luting agent and the restoration.
For adhesively retained restorations, is it better to have a smooth or rough finish to the tooth preparation?
smooth
Which 2 types of crown need mechanical retention?
- gold shell crowns
- metal-ceramic crowns
Why are mechanically retentive crowns able to tolerate subgingival margins?
As moisture control isn’t as imperative.
(like amalgam fillings)
What are adhesive-retained crowns depended on?
- the strength of the cement
- ability to bond to the tooth
- fitting surface (intaglio) of the restoration
Why is a halo of enamel ideal around the preparation margins?
As bonding to enamel is stronger and more predictable.
Name 2 examples of adhesively retained indirects:
- laminate veneers
- resin-bonded bridges
Name 3 examples of adhesive resin cements:
- caliebra universal
- panavia 21
- RelyXUnicem
Resistance Form
Features of a tooth preparation that enhance the stability of a restoration and resists dislodgement along an axis other than the path of insertion.
(usually due to an axis of rotation)
Which 2 factors impact resistance form?
- geometry of the tooth preparation
- magnitude and direction of dislodging forces
In what instance would resistance form be more crucial than retention form?
In patients with habits such as pipe smoking, nail biting, bruxism where the restoration has to withstand large oblique forces.
How does height impact resistance form?
Resistance increases as the height of the preparation increases.
(e.g: tall preparations have a greater resistance to oblique displacement than shorter preparations)
In anterior teeth, on which surfaces is height more available?
Mesio-distal as bucco-lingual / bucco-palatal parallelism is limited.
In posterior teeth, on which surfaces is height more available?
bucco-lingual / bucco-palatal as mesio-distal is more limited
How does width impact resistance?
Resistance decreases as diameter increases.
How does the complexity of the occlusal surface impact the resistance form?
Limits displacement in a horizontal plane so increases resistance form.
On what type of tooth structure should margins be placed?
On sound tooth structure - avoid composite, amalgam or GIC restorations.
(only an exception in deep marginal elevation)
The Perfect Margins:
- clear, distinct and easily identifiable
- smooth
- no lips of unsupported enamel (can be removed with excavator)
- sound tooth structure
Margins which are greater than 50 micrometers are considered as what?
open
What does a contact area need to be for full coverage restorations?
fully separated both vertically and horizontally to allow the technician to section the working model and separate the die.
Margins of Onlay Preparations:
- do not always require the contact area to be broken
- if this is the case, the margin should be placed coronal to the contact area.
- margin can’t be placed at the contact as this is a caries-susceptible area
- if the margin finishes at the contact on posterior teeth, it should be extended to fully break the contact.
Which types of indirects require a chamfer margin?
- metal
- glass-based ceramic with crystalline fillers (e.g: lithium disilicate)
- poly crystalline ceramics (e.g: zirconia)
- feldspathic porcelain for veneers
Which bur is used to create the shoulder margin?
shoulder bur (710)
When is a shoulder margin used?
feldspathic porcelain margin on a metal ceramic margin
Why are feather-edge margins not advised?
Does not provide a clear margin and finish line for the technician to work to.
Undercut
the portion of the surface that is below the height of contour in relation to the path of insertion
undesirable for an indirect restoration as cervical is less than occlusal width.
Which 3 areas can margins be placed in?
- supragingival (ideal for conservation, easy prep and OH)
- equi-gingival (compromise between perio health and aesthetics).
- subgingival (problematic, induce inflammation and recession)
If you were to place a sub-gingival margin, where must it be located?
- remain within the gingival sulcus (~ 0.5mm)
- not impinge on epithelial attachment
- 3mm above alveolar crest
What may supra-crystal attachment invasion present similar to?
(formally biological width invastion)
- presents similar to gingivitis associated with a restoration
Emergence Profile
Describes the restoration contour in relation to the surrounding gingival tissues.
Helps maintain good plaque control and periodontal health.
(important when placing sub-gingival margins and restoring implant-retained restorations)
