Fixed and Removable Prosthodontics Flashcards
What is the aetiology of denture stomatitis?
* Poor denture hygiene.
* Dentures worn at night.
* Patient is immunocompromised
What does RPI stand for?
Rest on mesial surface. Proximal plate on distal surface. Gingivally approaching I-bar
What is the mechanism of action for an RPI design?
Rest mesially acts as axis of rotation. As the proximal plate and I-bar rotate downwards and mesially around the axis of rotation during occlusal load. The I-bar and proximal plate disengage from the tooth/undercuts. Therefore potential traumatic torque is avoided.
A patient with a full lower denture has an unerupted premolar which is now causing discomfort. It has been decided to leave the premolar in situ. Describe the design of a new lower denture.
Retention (resistance to vertical displacement), support, stability, extension, occlusion (FWS, OVD, RVD), occlusal plane, appearance (design, tooth shape, shade), neutral zone, relief from unerupted tooth, soft lining.
What measurements are required for a lingual bar?
8mm depth. 4mm height of bar, 3mm from the gingival margin. 1mm from the depth of the functional sulcus of floor of mouth
What should be checked at the try in stage of constructing a new denture?
Midline. Occlusion. Extension. Lip support. Canine line. Incisal level. Buccal corridors. Position of teeth, shade/mould of teeth.
After discussion with an oral surgeon, it has been decided to leave a partially erupted premolar in situ while designing a -/F for an elderly patient. Outline your approach to the design of the new denture that would be stable and comfortable in function.
Retention; resistance to vertical displacement, support, stability, extension, occlusion (FWS, OVD, RVD, occlusal plane), appearance (design, tooth shape), neutral zone, releif from PE tooth, soft lining.
In prosthodontics, what measurements are required for a lingual bar?
8mm depth, 4mm height of bar, 1mm depth from functional sulcus of floor of mouth.
In prosthodontics, what needs to be checked at the try in stage?
Centre line, occlusion, extension, lip support, canine line, incisal level, buccal corridors, position of teeth, colour and mould of teeth
Label this diagram
Label this diagram
What is the definition of retention?
Resistance to displacement forces (vertical, horizontal)
What is the definition of stability?
Resistance to lateral displacement
Name 3 ways in which an upper complete denture is retained.
Muscular. Extension to buccal sulcus and peripheral seal. Adhesion/cohesion. Post dam
What is the biometric guidance in setting upper and lower teeth in dentures?
Aim to place teeth in pre extraction sites. Maxillary teeth placed buccally to the ridge promotes lower denture stability. Mandibular teeth placed over the ridgeso the palatal cusps of uppers occlude with fossa of lowers and the forces are appropriately directed. Positioning lower teeth over the ridge reduces tongue restriction.
Name the three components of the RPI system
Mesio-occlusal rest.
Proximal plate.
I-bar clasp
A lingual bar has been chosen as the major connector. State two reasons for the choice ans state the choice of material.
Colbalt chrome.
Structurally rigid.
There is at lease 7mm of vertical space between the floor of the mouth and the margins of the gingivae
How is Craddock clasification identified?
Work from the back of the mouth to identify which kennedy class the patient fufils first. Once this is determined, any additional gaps = modification
In denture design, describe retention and how it’s achieved
Restists movement away from the soft tissues (prevents denture being disloged).
Optimum = resistance along path of displacement and withdrawal.
Retention can be muscular (held in by the function of cheeks and soft tissues) or mechanical.
It can also be adhesive forces eg forces of saliva seal
What alloys can be used for denture clasps and what are their size requirements?
Cobalt Chrome; 0.25mm diameter and 15mm minimum length.
Wrougt wires (SS or gold); 0.5mm diameter, 7mm minimum length
What are the two broad types of denture clasps?
Occlusally approaching and gingivally approaching
In denture design, what are the two types of occlusally approaching clasp and when are they used?
C clasp and ring clasp used for premolars and molars.
Ring clasp is selected when the undercut is not an easy area for the c clasp to engage. A ring clasp should have a rest mesially and distally.
In denture design, what are the 3 options for gingivally approaching clasps?
I-bar, T-bar, L-bar
What is reciprocation?
Resistance to lateral forces.
Reciprocation is placed opposite to retentive clasps to assist in preventing unwanted movements/stresses of abutment teeth.
*Reciprocating arms provide some resistence but also allow flexure so that the retentive arm does not get put under too mujch pressure and break.
* Reciprocating clasps still need to engage undercut
* Try to encircle the tooth by 180 degrees
What is the purpose of the RPI system in prosthodontics?
Minor connector on mesial rest of tooth prevents excessive distal movement
In removable prosthodontics, describe bracing.
In the maxilla, the palate and alveolar ridge can be taken advantage of.
Flatter ridge = more movement.
Major connector and flanges can be useful to help with bracing, this should be incorporated into the design.
In removable prosthodontics what is the fulcrum axis?
The line of rotation - it is an imaginary line between the most posterior rest seats on the end of each arch
In removable prosthodontics, what is the clasp axis?
Imaginary line between clasps on opposite sides of the arch. When there are multiple clasp axes, use the one closest to the saddle.
In removable prosthodontics, what are the principles of indirect retention?
This resists rotation around a fulcrum axis.
Providing indirect retention moves the fulcrum of movement.
Principles; Retentive clasps should always be between the saddle and indirect retainer. Retentive clasps should be as close to saddle as possible, whilst the indirect retainer is as far away from the saddle as possible. Try not to have movements that will force pressure on a tooth.
What components are there of the RPI system and describe what it is.
* Occlusal rest, distal guide plane, gingivally approaching I-bar.
* Used to prevent distal movement/tipping of abutment tooth to a free-end saddle.
* Allows the free end saddle to rotate slightly without damaging the soft tissues or abutment tooth. As the denture is pushed into the tissues, it rotates around the mesial rest - the plane and I-bar disengage from the tooth and remove any harmful torque forces. Need this flexibility and adaptability of this system so that the saddle does not apply unwanted/unfavourable force to the tooth.
* Naroow occlusal table reduces load on tissue. Useful in free end saddles.
In removable prosthodontics, what is a guide plane?
Parallel surfaces on abutment teeth which are used to control the path of insertion and add stability. These can be prepared if required.
what is the ideal crown to root ratio when considering fixed prosthodontics?
Ideal 1:2
Realistic 2:3
Minimum 1:1
Poor 2:1
When providing a bridge, describe Ante’s law
The PDL surface area of the abutment teeth should be equal to or greater than the imaginary PDL surface area of the missing teeth.
DMS. What is alginate?
An irreversible hydrololloid.
The material of choice for diagnostic casts.
Sodium or potassium salts of alginic acid which react chemically with calcium sulfate to produce insoluble calcium alginare.
Diatomaceous earth adds strength.
Tisodium phosphate controls the setting rate.
More bulk means less susceptibility to unwanted dimensional changes.
What is RCP?
The position in which condyles articulate with the thinnest avascular portion of their respective discs in the most anterior-superior position against the articular emineses. Independent of teeth
What is ICP?
Complete interdigitation of the teeth.
Independent of condylar position.
Describe RCP vs ICP
RCP and ICP coincide in only 10% of the population.
Casts are mounted in ICP when ICP can be maintained (single fixed procedure).
Casts are mounted in RCP when ICP is impossible to maintain (complete dentures, multiple teeth being restored).
Descripe how to use bimanual manipulation to acheive RCP
One of the most accurate methods to obtain accurate RCP interocclusal records.
With the patient lying back, support the posterior mandible with fingers and the chin with thumbs.
Deprogram the jaw.
Identify first CCP tooth contact and repeat until you identify a consistent first tooth contact.
Keep anterior teeth slightly apart in RCP with acrylic resin jig.
Take interocclusal record of posterior teeth with PVS.
What is a facebow record?
The objective is to duplicate on the articulator the relationship of the maxillary arch to the skull and the mandible to the rotational centre of the TMJs that exists for that particular patient.
What are the bite materials of choice when mounting casts?
Casts poured from alginate are more accurately mounted with a wax bite.
Casts poured from elastomeric materials are more accurately mounted with elastomeric materials (PVS)
Describe condylar guidance
*Slope of articular eminence
*Represented by horizonal condylar inclination on articulator
*Posterior determinant of occlusion
Describe incisal guidance
*Incisal edges of lower incisors against lingual slopes of upper incisors.
*Represented by pin and guide table on articulator.
*Anterior determinant of occlusion.
Describe canine guidance
When in lateral movements all posterior teeth are immediately discluded as contact occurs soley between upper and lower canine on the working side.
Describe anterior guidance
Refers to both incisal and canine guidance.
During protrusive, incisal and condylar guidance provide clearance for all posterio teeth.
During lateral, canines on working side and condyle on balancing side provide clearance for posterior teeth on balancing side.
In prosthodontics, describe mutual protection
Front teeth protect back teeth - front teeth disclude posterio teeth during protrusive and lateral movements.
Back teeth protect front teeth. Back teeth have flat occlusal surfaces and strong roots to help protect anterior teeth from bite forces/
How is denture stomatitis managed?
* Denture hygiene instructions.
* Tissue conditioner.
* Chlorhexidine mouthwash.
* Script for antifungal agent.
* New dentures when health restored
How do you restore free-way space in very worn dentures?
Occlusal pivots or restore occlusal surface with provisional acrylic resin
What problem can occur with F/P?
Combination syndrome resulting in a flabby ridge
Why does a flabby ridge occur with F/P?
Forces are directed anteriorly and the upper denture is displaced, resulting in excessive and rapid bone loss of maxillary alveolar ridge. This is replaced by excess fibrous tissue.
How is a flabby ridge managed when taking an impression?
Take a mucostatic impression so the tissues are recorded at rest.
Use a 2 stage impression with a medium body first. Then cut out impression material to make a window over the flabby ridge before taking the second impression with light body material.
Or use the window technique where relief holes are cut into the special tray to allow flow of impression material and leave tissues undisplaced. Use a low viscocity impression material.
What is a system of design used for designing partial dentures?
Outline saddle area, support, retention, stability and reciprocation, connector.
Give 2 maxillary and 2 mandibular connectors with advantages and disadvantages
MAXILLA; Plate - thin but covers palate. Bar - thicker but offers less coverage
MANDIBLE; lingual bar - gingiva clear but less well tolerated. Plate - well tolerated as it’s thin but difficult to keep clean.
Define support
Resistance to occlusally directed loads. ie rest seats
Define retention
Resistance to vertical displacement forces. Can be mechanical eg clasps/guide planes, muscular eg buccinator/orbicularis oris or physical eg adhesion and cohesion
Define stability
resistance to horizontal displacement forces in function eg keep denture in neutral zone
Define indirect retention
Resistance to rotational displacemtn forces. It’s provided by supporting comonents eg a rest preventing disto-vertical rotational displacement of a saddle. Should ideally be 90 degrees to the axis of rotation. Should be on the opposite side of the axis of rotation to the displacing force. Mainly used in fee end saddles.
What instuctions would you give to the lab for an upper special tray for a new f/-
Please construct upper special tray with 2mm wax spacer, intraoral handles, non perforated, intraoral finger rests in light cured PMMA
What two instructions should be given to a patient who wears a denture?
*Remove denture at night and store in water
*Denture hygiene, remove to clean with soapy water and brush daily
*Rinse after eating
*Use denture cleaner once weekly
*Clean palate and gums with soft toothbrush
The RPI system is designed to allow vertical rotation of a distal-extension saddle into the denture bearing mucosa without damaging the periodontium of the abutment tooth. Briefly describe how this is achieved.
As the saddle sinks into the denture bearing mucosa, there is rotation of the denture about the mesial rest. Both the distal guide plate and Ibar rotate downwards and mesially and disengage from the tooth. Potentially damaging torque is avoided.
From the photograph, what difficulty may arise with regard to the aesthetics of a prosthesis to replace 22 and 23?
* Space is too narrow mesial-distally for two full units but is wider than one single unit
What difficulty may arise with regard to the function of a prosthesis to replace 22 and 23?
The canine is likely to be involved in guidance.
The lower canine appears to be over erupted.
Assuming there is no relevant medical history; suggest three general factors which need to be considered before referring a patient for consideration for implants?
* Oral health and hygiene.
* Patient understands what is involved and willing to comply
* Smoking satus
* Cost
* Perio history
* Does the patient play contact sports
List 3 factors local to site 22, 23 of the proposed implants, which will be assessed for the implant treatment planning
* Bone height
* Bone width
* Root position of 21 and 24
* Soft tissue adequacy
* Smile line
* Local perio health/plaque control
What is meant by the term shortened dental arch?
A dentition in which the posterior teeth have been lost. It usually consists of 6 anteriors and 4 premolars in each arch. 20 teeth in total.
Identify 3 aspects of oral function that are regarded by proponents of the shortened dental arch as acceptable in older patients?
* Ability to chew food efficiently
* Acceptable aesthetics
* Can be maintained in a healthy state by the patient
List four factors that could cause a bridge to debond
Poor OH
Poor moisture control during cementation
Unfavourable occlusion
Parafunction
Trauma to face
List tooth borne support for a co/cr
Occlusal rests
Cingulum rests
Full coverage rests
What should be the extension of the co/cr denture base?
2mm short of palatine fovea
There is a rest seat on tooth 21 for a co/cr, what is its purpose
Indirect retention
There is a rest seat on tooth 16 for a co/cr what is it for?
Bracing and reciprocation
Give two criteria to obtain valid consent
Informed
Voluntary
Not manipulated
Not coerced
With capacity
What 6 things should be explained to the patient to obtain consent?
The treatment and what it involves
The risk of treatment
The benefits of treatment
The likely outcome of treatment
The risk of no treatment
Alternative treatments
Cost
Fractured 26 MOD amalgam with RCT. Treatment options
MCC.
Full cuspal coverage onlay
What are the features of Nayyer core?
An amalgam core.
Retention obtained from undercuts in divergent canals and pulp chamber.
2-4mm of GP removed from the canal and replaced with amalgam.
Immediate placement and coronal preparation can be done at same appointment
Name two restorative materials that can bond amalgam to a tooth
RMGI
GIC
Name 3 ways a tooth can be desensitised?
Seal and protect
Duraphat
Sensitive toothpaste
Tooth mousse
What is the DAHL technique?
Localised appliance or restorations to increase the interocclusal space available for restorations
Describe how the DAHL technique works
Composite platforms are added to palatal aspect of upper incisors, left for 3-6 months to allow dentoalveolar compensation, then provide definitive restorations
List four contraindications for use of the DAHL appliance
MRONJ
Active periodontal disease
Ankylosis
Implant
Name four constituents of composite and give an example of each
Resin - Bis-GMA
Glass particles; Silica or quartz
Low weight dimethacrylate; TEGDMA
Light activator; camphorquinone
Silane coupling agent; bifunctional molecule binding resin and filler
Why would you use RMGI instead of composite for a buccal abraision cavity?
Less polymerisation shrinkage
Moisture control
You are carrying out root canal preparation of an upper right canine under local anaesthetic. You are irrigating the canal with a dilute solution of sodium hypochlorite when the patient suddenly feels intense pain. Within minutes you notice a marked facial swelling in the area and profuse bleeding into the root canal from the periradicular tissues.
What is the most likely cause for these signs and symptoms and why?
Extrusion of sodium hypochlorite through root apex.
Due to high pressure injection, injecting too deep, locking syringe in canal.
Accute inflammatory reaction which can be oedematous and/or haemorrhagic.
Can lead to significant tissue necrosis
What would be your immediate action following a hypochlorite accident?
Local anaesthetic for pain relief.
Copious irrigation with physiologic saline
Reassure patient that this is a complication that can be controlled
Dress tooth with non setting calcium hydroxide
After immediate steps taken following a hypochlorite accident, what action should be taken?
Priority must be given to pain relief, reduction of swelling, and prevention of secondary infection.
Cold compress during the first few days, warm compresses for resolution of soft tissue swelling and elimination of the haematoma
Analgesics; ibuprofen 400-600mg 4 x daily, paracetamol 1g 4 x daily
Review after 24 hours
Script for ABs case specific
Refer if severe
