Prosthodontics Flashcards
what are some adv and disadv of RPD over other restorations
adv - cheaper, removal for hygiene, minimally invasive
disadv - may be bulky and less aesthetic, less retention and stability
what is an occlusal unit and how many should we aim to have
an opposing molar or premolar - should aim to have 3-5, molar is 2 units, premolar is 1
what are some anatomical consequences of missing teeth
mandibular and alveolar bone resorption, decreased chin to nose distance as chin protrudes, tooth movement - over eruption or drifting
what are some other consequences of missing teeth
aesthetics, functional - eating and speaking, may result in malabsorption and weight loss, psychological
what is the denture flange
where it extends into vestibular sulcus
what are the kennedy classifications
class I - bilateral free end saddle class II - unilateral free end saddle class III - unilateral bounded saddle class IV - bounded saddle crossing the midline
what are saddles classified on and when can they be modified
classified on most posterior saddle, any additional anterior saddles are a modification
what is denture support defined as
resistance of denture to occlusally directed load
how can support be classified
craddock classification
1 - tooth only, 2 - mucosa only, 3 - tooth and mucosa
how should the force be distributed if using rest seats on abutment teeth
down the long axis of the tooth, through periodontal ligament to alveolar bone, if bounded saddle adjacent to saddle, if free end, should be on the other side
what should be avoided when using abutment teeth for support
distal axial torque of the abutment tooth, when the force is not down the long axis
what determines the force a tooth can withstand
the surface area of the root - molars, canines, premolars then incisors in order of most force
why is mucosa borne support not ideal
transmits force directly through to alveolar bone, which can increase bone resorption, need a large area to reduce resorption. soft tissue is also more compressible so more movement of denture
how much occlusal space is required for a rest seat
0.5mm
what is blocking out
using wax to remove any unwanted or unused undercuts between high and low survey line
why do casts need to be blocked out
if undercuts are not removed, acrylic will be produced that goes into this undercut, the denture then wont be able to fit over the most bulbous part of the tooth, dentist will have problems trying to seat the denture
how are casts blocked out
wax put over cast then chisel on surveyor to remove excess wax, can also use plaster
why are casts duplicated
to have a working cast and a master cast
how are cast duplicated
use an investment material and place cast inside, either hydrocolloid or sillicone is poured into this investment material, basically takes another set of impressions. the cast is then removed, impression left and stone is poured in, produce another cast
what is the duplicated cast used for
for producing a wax design
why is a refractory cast required
when producing cocr in an investment material, a cast is required to withstand temperatures of 1000 degrees, stone and plaster cannot so another cast is required made of material that will
what is a post dam
adhesion at posterior periphery of upper denture in palate, before palatine fovea
what is a pin dam
anteriorly at gingival margin, ensures food and plaque cannot get underneath the denture - flush fitting
what is retention
resistance to vertical displacement of denture
what are the mechanisms of retention
mechanical - clasps around abutment teeth
physical - coverage of mucosa, saliva
muscular - buccinator, lips and tongue muscle keeping it in
what are guide planes
proximal surface is parallel to path of insertion, no distortion on insertion and removal
what are the dimensions for a cobalt chrome clasp
length - 50mm, in an undercut of 0.25mm, ensure undercut isnt 1mm within gingival margin
where are undercuts commonly found on upper and lower molars
upper - buccal normally distal
lower - lingual normally mesial
what is reciprocation
preventing horizontal displacement of tooth caused by clasps
are there any dimensions for reciprocal arms
do not engage undercuts but must have sufficient space from occlusal surface without being in undercut
what is the pattern of retention
should have 3 points of retention on 1 arch - the bigger the triangle the more stable the retention
how can the path of insertion be altered for retention
if undercuts present anteriorly at common path of displacement, altering the path of insertion can remove these undercuts, allows for resin to flow into here and provide retention.
what can be a consequence of altering path of insertion
altering posterior undercuts, can make them larger
what do the letters stand for in RPI
r - rest, normally an mesial occlusal rest seat
p - proximal plate
i - gingivally approaching i bar clasp
what is indirect retention
preventing rotational displacement of the denture
give an example of indirect retention
rest seats on more anterior teeth - e.g. cingulum on canine or on premolar, lingual plate or continuous clasp
what happens at the first visit of denture patient
examine patient, establish relationship, examine denture - what did they like about it etc, primary impressions, wax waiver
what material is normally used for primary impressions and what can be used in saddle areas
alginate normally used, free end saddles can have compound, better accuracy
where should an impression tray extend to
retromolar pad
what is used for recording occlusion
if casts can be hand articulated - wax waver
if casts cannot be hand articulated - jaw registration wax record blocks - separate visit prior to master impressions
what must be done before master impressions are taken
decide on denture design, prepare rest seats, know what undercuts will be used and if any need prepared, decide on path of insertion
how can special trays be altered if not the correct fit
under extended - at green stick or compound at the end, extend peripheries
over extended - trim with a bur
what impression materials are used for master impressions
silicone - medium bodied, not too runny, good surface reproduction
polyether - not good for undercuts, alginate
what happens at visit 3 or 4 (if wax record block)
framework trial and recording occlusion - first done separately then together once experienced
what is done in framework trial
check good fit on framework, not too tight, can check cast for any marks or damage
why is occlusion recorded at this later time
to ensure correct setting of teeth that it doesnt interfere with occlusion
what instructions must be given to the lab after framework trial and recording occlusion
colour and shape of teeth
what are some reference points for setting anterior teeth
midline, inter-pupillary line, ala-tragal line, curvature of lower lip, smile line
what is done in the visit prior to delivery
tooth trial - wax of final denture, like a dress rehersal, need to make sure patient is fully happy with it before sending it to acrylic
what instructions must be given to patient
how to put it in, how to clean it, make sure they know to expect some discomfort and will need to develop neuromuscular control
if a patient isnt wearing denture at their review what should you do
tell them to not to perservere if too sore, but wear for a couple of days before their next visit so we can see where flanges might be digging in or any areas that are too tight
what is the purpose of a minor connector
to connect all the design components to the major connector
give some examples of a major connector used in upper arch
anterior posterior bar (ring design), mid palatal strap, horseshoe bar
give some examples of major connectors used in lower arch
lingual bar, sublingual bar, lingual plate, dental bar, continuous clasp
what are some adv and disadv of plates and bars
plates - can be thinner, 0.5mm, more comfortable but cover more mucosa so feels less like the patient
bars - have to be much thicker 2mm but covers less mucosa so patient has better sensation
how much space is needed between gingival margin and connector
3-5mm
how much space is required for a lingual bar
from gingival margin to floor of mouth - 8mm
3mm for gingival clearance, 4mm height of bar, 1mm from floor for muscle movement
what stages are involved in restorative treatment plan
immediate - temporary dressing to stop the pain and discomfort, short term solution
hygienic - get the patient into good oral hygiene habits, assess patients motivation - determines treatment
corrective - long term solution, rpd, crown, bridge
maintenance - periodontal scaling, support, required for successful treatment
what are the clinical stages of rpd design
primary impression, jaw registration (if required), tooth prep and master impressions, framework trial and secondary occlusion, tooth trial, delivery, review
what treatments might be done prior to rpd design
periodontal treatment, surgery, orthodontic, endodontic if tooth in radiograph seen to have caries, might not be giving them problems but denture will fail, crowns or bridges, not done until design of rpd decided to encorporate it
what have you got to look at before deciding whether to use an abutment tooth for support
periodontal condition, condition of mucosa, occlusal relationship, aesthetics
briefly describe the lost wax technique
on refractory cast, wax up the cocr design. then place spruces to allow molten metal to flow into the mould, then cover with investment material. then heated up, wax melted, molten cocr introduced and allowed to produce mould
