Fourth Year Flashcards
Describe the factors associated with edentulousness and tooth loss (5)
Age
Social class
Education
Marital status
Geography
Describe the consequences of edentulism (5)
Psycho-social
Emotional issues
Self Confidence / Behaviour Issues
General health (eating ability)
QoL
Name 4 reasons to make complete dentures
Mastication – quality of experience and aspects of nutritional health
Aesthetics
Appearance
Psychological benefit
Describe the reasons alveolar bone will resorb (8)
Period of edentulousness
Gender
Denture wearing habits
Denture quality: induced-trauma
Systemic influences – osteoporosis, diabetes
Inherent quality/size of ridge
Extraction technique
Periodontal disease
Pressure loading – patient capability, parafunction
Describe the complete denture clinical course (6)
Patient assessment, diagnosis and treatment planning
Preliminary impressions
Master impressions
Recording aesthetics and jaw relationship
Try-in procedures
Insertion/occlusal modification/care and maintenance
Name 3 ways problems that arise through faults in design
Fit surface
Polished surface
Teeth (position and relationship)
Describe the clinical assessment during a complete denture case (5)
Soft tissues
Ridges
Shape (retentive and supportive characteristics)
Nature of denture bearing area – firm or flabby, sensitive or comfortable to finger pressure.
Sensitive or mobile ridges may need a modified impression technique. Sharp ridges may require provision of relief.
Saliva
Previous prostheses - denture design
SIs of hard tissues
Describe implant retained dentures
The McGill Consensus Statement 2002- Canada
(York Consensus 2009 – UK)
indicates that, as a minimal treatment objective, a mandibular two-implant overdenture should be considered as a first-choice standard of care for the edentulous patient
Reissman, Dard, Lamprecht, Struppek, Hevdecke. 2017
Systematic review of OHRQoL in subjects with implant-supported prostheses.
Results: Implant tx is usually related to improvement in OHRQoL.
However, improvement is not necessarily higher than for conventional prosthodontic treatments but depends on patient’s clinical and psychosocial characteristics.
What is stability?
Quality of a denture to resist displacement by functional forces.
Quality of denture to be firm, steady, constant and not subject to change of position when forces are applied – subjective assessment mostly by patient.
What is retention?
Resistance of denture to removal from the denture bearing tissues in a vertical direction – test by pulling down or lifting up anterior teeth with finger and thumb
What is support?
Resistance of a denture to occlusally-directed forces. Determined by the form and consistency of denture-bearing tissues.
Good if there are well formed ridges with good bony support.
Describe 2 broad categories of retentive forces for dentures in detail (9)
Acquired muscular control – mostly applies to lower denture
Control with lips, cheeks and tongue (via the polished surfaces) and by the muscles of mastication (via the occlusal surfaces of the teeth)
Ability of patient to acquire the necessary skill – reduced in elderly or debilitating illness, especially muscular disease e.g. stroke/Parkinson’s
Design of denture
Correct extension
Correctly contoured polished surfaces
Lower teeth placed on top of alveolar ridge (neutral zone)
Level of lower occlusal plane below level of resting tongue
Correct occlusal relationships
Physical forces of retention – mostly applies to upper denture
Dependant on adhesion and cohesion of saliva between mucosa and acrylic producing a negative pressure to cause retention (via the fit surface - *think analogy of 2 glass slides stuck together) and is maximised by a combination of good design/construction regards:
Border peripheral seal
Contact between denture periphery and mucosal tissue at all time: requires correctly border-molded impression (full functional depth and width of sulcus) and effective post-dam.
Greater area of impression surface
Retentive forces directly proportional to area of impression surface: requires correctly extended impression.
Accuracy of fit
Thinner saliva film provides greater retentive forces: requires accurate impression.
Describe 4 displacing forces of dentures
Muscles surrounding oral cavity (lips and cheeks) during normal function – are the teeth in the “neutral zone” (also called “area of minimal conflict”)
Tongue – as above and during excessive movements
Occlusal interference +/- locking cusps/teeth during chewing (lack of balanced articulation/occlusion)
Viscous and sticky foods
Describe the assessment of 3 dentures surfaces
Fit surface – extension giving maximum functional coverage of all U/L denture bearing areas.
Polished surface – form correct - B=convex and L/P=concave
Teeth
Aesthetics – upper anteriors
B-L placement of lower teeth – are they on top of the alveolar ridge?
Lower occlusal plane below resting level of the tongue?
Occlusion. ICP = RCP, and contact position at the correct OVD.
The “neutral zone”, or “zone of minimal conflict”, or “denture space”
The position of the mandibular prosthetic teeth and allows for muscular balance.
“The potential space between the lips and the cheeks on one side and the tongue on the other. That area or position where the forces between the tongue and cheeks or lips are equal.”
Describe the requirements of a complete denture impression (5)
Should cover max. possible denture-supporting area.
Impression surface should achieve closest possible contact (fit) with underlying mucosa compatible with its tolerance.
The border form of the prosthesis should establish a peripheral seal and, further, help support the lips and cheeks in a functionally and aesthetically correct manner.
Describe the factors governing the extension of C/- (5)
Correctly muscled molded functional impression extending over the maximum denture bearing area.
Extension distally should cover tuberosities into hamular notch
Record the full functional depth and width of buccal and labial sulci
Posteriorly to non-moving junction of hard and soft palate
Muscles and anatomical features influencing border: buccinator, masseter, levator anguli oris, incisivus labii superioris, orbicularis oris.
Requires a correct preliminary impression in composition. Followed by an individual tray border molded for sulcular width and depth using an impression material which will not distort the tissues.
Describe the factors governing the extension of -/C (5)
Correctly muscled molded functional impression extending over the maximum denture bearing area.
Extension distally should cover at least 2/3 of retromolar pad
Record the full functional depth and width of buccal, labial and lingual sulci
Muscles and anatomical features influencing border: Mylohyoid, genioglossus, palatoglossus, masseter, buccinator, modiolus, orbicularis oris, sub-lingual salivary gland, genial tubercles.
Describe how preliminary impressions are taken for complete dentures (4)
Taken in compound stock tray – limited range of shapes and sizes so usually poor fit
Taken in red compound (heated to 55-57°)
Used to make plaster cast for special tray to take master impressions
Describe the impression compound properties when taking complete denture preliminary impressions (6)
Mucocompressive – but doesn’t distort the tissues
Rigid
Poor surface detail
High coefficient of thermal expansion
Shrinkage 1.5%
Has the viscosity to support itself beyond the tray confines to record the maximum denture area
Describe the properties of a custom tray used for master impressions (8)
Clean and smooth
Rigid and dimensionally stable
Allow correct uniform thickness for material to be used
Handle (intraoral/extraoral) must not interfere with lip
Finger rests for lowers – to avoid displacing cheeks
Extended to 2mm short of maximum denture bearing area as delineated from preliminary cast and 1mm short of reflection of sulci.
What is the wax spacer used for ZnO/Eugenol, PVS and Alginate
0.5mm ZnO/Eugenol
1..5mm PVS medium viscosity
3mm alginate
Describe the properties of ZnO/Eugenol (6)
Gradual set – amenable to border moulding
Readily adapts to soft tissues
Good surface detail
Rigid
Dimensionally stable
Burning sensation
Adherent to skin
Name 3 reasons to use PVS for a master impression in complete denture cases
Mucosal problems e.g. LP
Large undercuts e.g. tori, prominent tuberosity
Pt cannot withstand “burning sensation” of ZnO/eugenol
Describe the technique used for a grossly resorbed lower when preliminary imp is poor (3)
Take impression with red compound/green compound mixture (50:50) in special tray
Carefully border mould and remove overextension
Take a “wash” impression using paste or PVS
Describe the technique used for a upper anterior flabby ridge when support is poor (4)
Take preliminary impression in mucostatic impression plaster or “sloppy alginate”
Cut window from flabby area and border mould
First impression in paste of non-flabby area
The take flabby area impression with fluid material
Produces a cast of denture bearing tissues undisplaced at rest and therefore best possible retention
Describe the management of gagging during impression taking (6)
Relaxation techniques
Distraction
Hypnosis
Sedation
Local anaesthesia
Desensitisation – give trays home with patient, provision of palatal training plates
Describe possible denture faults due to gagging (5)
Under extension at post dam – common!
A loose upper drop to touch posterior tongue and induces gag reflex
Overextension at post dam – rare! but many pt.’s don’t agree
Excess occlusal vertical dimension
Muscle balance – tongue space encroachment / lower occlusal plane high
Thickness of bases
Describe general jaw movements (5)
Mandible is suspended from the skull by muscles, ligaments, vessels, nerves, soft tissues.
Jaw movement in 3D space – maxilla and movement is limited by muscles, TMJ, teeth
Basic movements
Vertical plane – open and close
Lateral plane – RHS and LHS
Antero-posterior plane – protrusion, retrusion
Functional movement almost always a combination of translation and rotation but may be purely rotational.
Describe why jaw movements are important (6)
Mastication (an intermittent rhythmic act in which the tongue, facial and jaw muscles act in coordination to position the food between the teeth, cut it and prepare it for swallowing)
Speech
Swallowing
Respiration
Emotional expression
Parafunction activities: clenching, grinding, lip/cheek biting, thumb sucking, nail biting
What are the 3 parameters of the jaw movement?
Muscles of mastication
TMJ
Teeth
What is occlusion? (2)
A dynamic concept describing the integrated action of the components of the masticatory system that control tooth contact during function and dysfunction.
Describe occlusion in natural teeth and in complete denture cases
Occlusion in natural teeth:
Independent movement and retained by PDL.
Fine neuromuscular control by proprioception from PDL, TMJ, M.O.M, tongue.
Anterior incising involves separation of the posterior teeth.
Lateral excursions produce WS contacts on canines/premolar/both (canine guidance or group function) and separation of teeth on the non-WS.
Malocclusions – posterior contact during anterior incision or non-WS contact – can cause problems if occlusion not checked during restorations or prosthetics.
Complete denture occlusion:
Teeth are all linked together on a denture base and are easily displaced during function.
Proprioception is much reduced and comes from TMJ, mucosa DBA, muscles of mastication and tongue.
Denture bearing mucosa is compressible and likely to be uneven. Stability during tooth contact is dependent on “balanced occlusion/articulation”.
Describe the functional differences between ND and AD (3)
- Stability
ND teeth are independent and firmly attached to bone.
AD united and rest on mucosa. - Comfort
ND biting force greater (x5) than AD as pain threshold of mucosa easily exceeded. - Chewing efficiency
ND>AD (x6 number of chewing strokes)
What is RVD, OVD and Freeway Space (6)
Rest vertical dimension (rest face height) – the vertical dimension of the lower face with the mandible in the rest position.
Occlusal vertical dimension (occlusal face height) – the vertical dimension of the lower face with the teeth in centric occlusion.
Interocclusal distance (free way space) = RVD – OWD
FWS is a range of 2-4mm at the incisors.
What is RCP?
RCP = relation of the mandible to the maxilla with the mandible in its most retruded position at a prescribed occlusal vertical dimension.
Describe 3 options for occlusal schemes
Bilateral balanced articulation – bilateral simultaneous contact of teeth in RCP and during excursions.
Monoplane (non-anatomical) occlusion – ICP and RCP correspond but no attempt to achieve contact in excursions.
Lingualised occlusion – where the maxillary palatal (lingual) cusps articulate with the mandibular occlusal surfaces in RCP and with cuspal inclines in excursions (upper buccal cusps never touch).
What is balanced occlusion?
The simultaneous even occlusal contact between maxillary and mandibular teeth bilaterally or anteriorly-posteriorly.
What is balanced articulation?
The simultaneous bilateral, or anterior-posterior, occlusal contacts between maxillary and mandibular teeth during the movement from one balanced occlusion (i.e. during function) to another.
Describe why balanced occlusion is ideal (4)
↑ efficiency of the dentures by making them more stable and freed from tipping on unbalanced (retention, stability, masticatory function, generalised satisfaction).
It distributes the occlusal load over the whole denture bearing area and this reduces the risk of alveolar trauma and resorption (occlusal force distribution, comfort).
It increases the patient’s confidence by making sure that the dentures are re-seated evenly if they become dislodged (stability, comfort, generalised satisfaction).
Uses posterior teeth with cuspal anatomy (masticatory function, aesthetics).
Describe how balanced occlusion is achieved (3)
Record the correct RCP relationship of the jaws and transfer this to an articulator capable of reproducing that patient’s mandibular movements i.e. at registration stage.
By setting the teeth up in balanced articulation, using the factors governing balanced articulation, on the prescribed articulator (usually an AV articulator).
Use and understand those factors (Hanau’s Quintet) influencing tooth position to achieve a set up in balanced articulation.
Name 3 reasons RCP is used to produce balanced occlusion
Reproducible (because it is a border position).
Patients can easily accommodate to it (via neuromuscular feedback from proprioceptors in TMJ, muscles of mastication, denture bearing mucosa).
To set up a balanced articulation occlusion we must record the most posterior position achievable as the average value articulator cannot reproduce ‘backwards’ movements.
Describe how to set up balanced articulation for patients
Record RCP with registration rims
Prescription to technician – “please provide balanced articulation set up on AV articulator for try-in”
Technician completes trial set up
Clinician assesses trial set upon articulator and in the mouth
Describe Hanau’s Quintet
Incisal guidance 10 / 15
Condylar guidance 30 / 35
Cuspal angles (height) 20 / 25
Plane of occlusion ala-tragal plane orientation
Compensating curves Spee / Wilson (change effective cusp height)
Describe compensation curves
Posterior plane surfaces separate on protrusion
(Christensen’s Phenomenon)
Need to introduce a curve to the occlusal plane antero-posteriorly (and laterally) to maintain cuspal contact during excursions.
Describe the aesthetics of an upper registration rim (6)
Lip support: tooth position – up to 1cm ahead of incisal papilla tooth inclination - 90° columella-philtrum angle
Good lip support is achieved by correct anterior placement of incisors – not flange thickness.
Incisal level: at rest and function - show 1 or 2 mms below lip at rest, nearly all the crown when smiling but customise to patient
Anterior and posterior occlusal plane: trim using the Fox’s occlusal plane indicator.
Anterior occlusal plane – parallel to interpupillary plane
Posterior occlusal plane – parallel to ala-tragal line (camper’s plane), through tragus of the ear to lower border of ala of nose
This allows the occlusal forces applied to the dentures to be perpendicular to the alveolar ridges which improves stability
Lower occlusal plane – should be below the resting level of the tongue, runs into the RM pad about halfway up
Width and form of arch: harmonise to patient facial profile, no posterior buccal corridor
Mould and shade: customise to patient
Average mould statistics from 433 subjects on mean age 16years
Make sure to mark the centre line and the premolar area when patient is smiling – midline placed in middle of exposed rim at rest/smile - ignore nose.
Describe the vertical component of occlusion registration (at wax rim stage) (8)
Assessment of lower face height by measurement
Willis gauge or callipers with skin dots (rest vertical dimension minus 2-4 mms to provide an interocclusal rest distance. If using Willis gauge have upper rim/denture in place.
Measure existing dentures OVD as a guide as well.
Assessment of appearance
Insufficient OVD, too much IOD = overclosed. Gives only a poor appearance (“popeye”)
Excessive OVD, too little IOD = overopen. Gives poor appearance and affects the function of the denture.
discomfort in facial musculature as no rest from tooth contact
trauma and pain in denture bearing tissue esp. lower
clicking of teeth during speech
Visual assessment during speech: aim to provide a minimum speaking space of 1 or 2 mms between the incisal edges when pronouncing sibilant sounds i.e. ‘s’sounds – “Mississippi, sixty six”
Assess parallelism of ridges when mounted on articulator at trial stage
Describe the method of recording registration at RCP (5)
Mark centre line (of face!)
Mark premolar guide lines to test reproducibility of RCP
Cut V-shaped wedges in premolar region of upper and Vaseline rim
Place registration paste on lower
At the end of the registration – check the reg rims on the model. Ensuring clearance of the cast and rims i.e. no premature contact in the recorded RCP. For example, premature contact in the RM pad or hamular notch region of rims.
