Prosthetics Flashcards
what are the causes of tooth loss ?
caries,
periodontal disease,
trauma,
planned orthodontic extractions
what are the consequences of tooth loss ?
anatomical,
aesthetics,
functional,
psychological
what are the anatomical consequences of tooth loss ?
bone loss,
lip support,
tooth movement,
TMJ
what are the options for replacing missing teeth ?
nothing,
conventional or resin retained bridges,
dentures,
implant retained prostheses
what is meant by the ‘shortened dental arch concept’?
able to function well with 5-5
in what case are people with missing teeth unlikely to have removal partial dentures ?
when they still have 21 remaining natural teeth
what are the advantages of fixed bridges ?
better patient acceptance,
better tolerance,
easier to keep clean,
less plaque accumulation
what are the disadvantages of fixed bridges ?
cost,
invasive (conventional)
operator sensitive,
more technically demanding
what are the advantages of removable dentures ?
non invasive, reversible, young people, can be added to following further tooth loss, atraumatic, restore long spans, less expensive, can be modified
what are the disadvantages of removable dentures ?
psychological,
removable,
less acceptable,
damaging effects
what are the possible damaging effects of removable dentures ?
decalcification, caries, inflammation of gingival tissues, inflammation of mucous membrane, plaque, direct trauma from components e.g. clasps
what are the advantages of implants ?
good success rate,
excellent stability and retention
what are the disadvantages of implants ?
cost,
operator sensitive,
cannot restore alveolar bone
what factors need to be considered for partial dentures ?
number and distribution of missing teeth, stats of abutment teeth, soft tissue loss, anterior tooth spacing, restoration of occlusal face height, patient preference and cost, interim replacement
what are the hygienic principles of RPD design ?
avoid unnecessary coverage of gingival tissues,
RPD components 3 mm from gingival margins,
create space for natural cleansing and OH measures
how do indirect restorations affect RPD design ?
should be planned in conjunction with RPD,
rest seats, undercuts and milled guide planes can be incorporated,
improved fit, retention and reduced bulk of RPD for the patient,
cast restorations should not be construed without a final denture design
what is the process of design for an RPD ?
logical sequence of 6 core elements
- saddels
- support
- retention
- reciprocation
- indirect retention/anti-rotation
- major connector
define support
resistance of movement towards the mucosa
what are the 3 types of denture support ?
tooth,
tooth and mucosa,
mucosa
what are the 3 types of tooth rest ?
cingulum,
occlusal,
incisal
what is required for a mucosally supported denture ?
maximum extension -
hamular notch, tuberosities,
retromolar pad
define retention
resistance away from the tissues
how is direct retention achieved ?
mechanical eg clasps and precision attachments,
path of insertion,
physical
what are the key points of RPD design ?
avoid unnecessary gingival coverage,
use tooth support where possible,
wide extension of mucosally supported saddles,
only two retainers per denture if possible,
rigid connectors
bilateral, even occlusal contacts
what are the advantages of acrylic dentures ?
cheap,
easy to construct,
easy to modify
what are the disadvantages of acrylic dentures ?
weak,
non rigid,
require bulk for strength,
potential soft tissue damage
what are Every’s principles ?
point contact between adjacent standing and artificial teeth,
wide embrasures,
no occlusal interferences,
3 mm gingival clearance,
correct denture extension with accurate fit and the polished surfaces to assist muscular control,
distal stop
acrylic
how are dentures classified ?
kennedy's classification (saddles) Craddock classification (support)
describe Kennedy’s classification
I - bilateral free end saddle
II - unilateral free end saddle
III - bounded saddle
IV - anterior bounded saddle that crosses the midline
what are the advantages of mucosal borne dentures ?
cheap, can be added to, preparation for complete dentures, periodontal disease, young children
what are the advantages of tooth borne dentures ?
forces are directed through the periodontal ligament,
no damage to denture foundation if designed correctly,
well tolerated
what is the purpose of surveying ?
determine the path of insertion,
identify wanted and unwanted undercuts
what factors influence the path of insertion ?
retention,
guide surfaces,
aesthetics,
dead space interferences
what are guide surfaces ?
a series of surfaces parallel to each other and the path of insertion,
ensures that dentures can be inserted and withdrawn along the path of insertion
2-3 mm long
frictional contact may assist overall retention
reduces dead space
what are the objectives of design ?
easily inserted and removed, resist dislodging forces, aesthetically pleasing, avoid food traps, minimise plaque retention
what is a saddle ?
part of the denture that rests on and covers the tissues of the alveolar ridge
where should the polished surface of the saddle lie ?
in the neutral zone (area of minimum conflict)
what are saddles almost always made of ?
acrylic
how does the type of denture support affect the design of the occlusal surface ?
if tooth and mucosal or mucosal borne the number and size of the occlusal surface is reduced to decrease the force on underlying mucosa during mastication
what are the functions of rests ?
support,
indirect retention,
deflection of food from saddle abutment junction,
ipmroved occlusal contacts when used as an onlay
what are the essential features of a rest ?
rigid,
non interference with existing occlusion
where should a rest always be placed on a free end saddle ?
mesially
what are retainers ?
components that prevent movement of the RPD away from the tissue
what are the essential design criteria for effective clasps ?
flexible retentive arm,
reciprocation,
encirclement,
passivity
what factors affect clasp retention ?
material of clasp, cross section, length, depth of undercut, clasp design
what determines the type of clasp ?
position of undercut,
amount of bone support,
length of clasp,
appearance
what other mechanical devices are available to aid retention ?
magnets, precision attachments, implants
when are indirect retainers required ?
in free end saddles where displacement occurs as a rotation of the saddles away from the tissues
what is bracing ?
resistance to horizontal or lateral forces when denture is fully seated
what is the definition of a connector ?
links the saddle components of the partial denture together
define major connector
links the saddles to the denture
define minor connector
joins the components such as rest and clasps to the saddles and major connector
what are the properties of a good major connector ?
rigid to prevent flexion and distortion, vertical support, soft tissue protection, indirect retention, patient comfort, link saddle areas
list the major connectors in the maxilla
ring, horse shoe, palatal strap, palatal bar, palatal coverage
when is it suitable to use a ring ?
multiple bounded saddles
what are the advantages of a horseshoe connector ?
strong,
useful for missing anterior teeth,
relieves palate,
gains some support from tissues
what are the disadvantages of a horseshoe as major connector ?
can deflect and distort in free end saddle cases,
bulk of metal on anterior border can be unacceptable to some patients
what are the advantages of a palatal strap as a major connector ?
thin and versatile,
can be in 2 planes increasing rigidity,
well tolerated,
good tissue support due to increased surface area
what are the disadvantages of the palatal strap as a major connector ?
must be at least 8mm in width for strength,
patients can be sensitive to position of strap border
what are the disadvantages of the palatal bar ?
bulky,
narrow with little support from palatal tissues,
may impede speech if anterior to second premolar region
what are the advantages of complete palate coverage ?
very rigid and supportive,
most comfortable
what are the disadvantages of complete palate coverage ?
extensive coverage of tissues,
oral and denture hygiene issues
what should be considered with maxillary major connectors ?
borders must be 3mm from gingiva,
borders should bend with anatomy,
thickness of metal should be uniform,
all borders in contact with soft tissues should be beaded,
beaded lines should be less distinct as they approach the gingiva,
if perio support is poor a connector which gains more tissue support should deb used,
if perio support good a palatal strap/bar may be used,
when anterior teeth are to be replaced a ring, complete palate or horseshoe can be used,
palatal bar is rarely indicated
what are the options for the major connector in the mandible ?
lingual bar, sublingual bar, dental bar, kennedy bar, lingal plate, labial bar
what are the advantages of the lingual bar ?
minimal contact with tissues,
simple design and construction,
beneficial for oral hygiene
what are the disadvantages of the lingual bar ?
rigidity can be an issue,
8mm of clearance required from gingiva to floor of mouth,
if tori ar present bar construction is difficult
what are the advantages of the lingual palate ?
can be used where space does not allow a lingual bar,
useful with compromised anterior teeth,
good indirect retention,
very rigid
what are the disadvantages of the lingual plate ?
OH, caries, perio issues
what are the advantages of the kennedy bar ?
excellent indirect retention,
advantages of lingual plate with better OH access
what are the disadvantages of the kennedy bar ?
debris trap,
crowding makes adaptation difficult,
may irritate tongue
what are the advantages of the labial bar ?
can be used for lingually inclined teeth
what are the disadvantages of the labial bar ?
poorly tolerated,
bulky,
requires sufficient sulcus depth
what should be considered with mandible major connectors ?
for a tooth supported RPD a lingual bar is the connector of choice,
when space insufficient lingual plate should be used,
when anterior teeth have reduced support lingual plate can be used,
with anterior saves and good perio support a notched play or kennedy bar can be used,
labial bar rarely indicated
what are the main reasons for changing the path of insertion ?
aesthetics,
maximise retention of a free end saddle
