Pros rpd design features Flashcards
flange
the replacement tissue extending into the vestibular sulcus from the alveolar area
tooth support
directs the masticatory occlusal load through the periodontal ligaments of adjacent teeth
- more natural as it directs the load down the natural central axis which feels better for patients
mucosal support
requires a large surface area to prevent sinking into the mucosa
- can accelerate resorption of underlying tissue if not placed correctly
- spreads the load through the mucosa onto the bone
tooth borne support
craddock class 1 - directs load down the central axis of teeth
- protects the soft tissue from trauma
- more comfortable for the patient as it feels more natural
- directs the load of spaces into the PDL of abutment teeth
mucosal borne support
craddock class 2 - abutment teeth not involved
- load is directed through the residual ridge below the saddles
- large palate to maximise distribution
- reduces the occlusal table
- allows the denture base to move slightly which could cause damage to adjacent teeth
tooth and mucosa support
combination when there are still teeth available for support but not enough to completely support the load or in larger saddle areas
- MUST be used in free end saddle areas
order of teeth in load bearing
- molars
- canines
- premolars
- anteriors
the best teeth for providing tooth support are those with the largest…
root area
- depending on the health of the PD attachment
a tooth can bear
its own occlusal load plus one half of the load of similar teeth
what ratio should be considered when deciding if a tooth is suitable for support
the crown to root ratio
types of rests
- occlusal
- cingulum
- incisal (rarely used)
cutting tooth rests
may need to cut into a healthy tooth tissue to provide area for a rest seat without interfering with the occlusion
- not ideal
- try and seat rests in existing areas
axial tork
tilting and rotation of the tooth if the load is not directed down the central axis of the tooth
- minimised by placing the rest as close to the central axis of the tooth as possible
cingulum rests
placed on prominent cingulums
- can remove tooth tissue or add composite to produce a vertical stop for which the rest can sit on
functions of rests
- prevents RPD moving to soft tissues
- assists in distribution of occlusal load
- prevents over eruption of opposing teeth
- provides bracing to anterior teeth
- determines the acid of rotation on the free end saddles of RPDs
when is crown to root ratio unacceptable for using a tooth for support
all teeth used for support have their ratios added to give a total root area
- this is multiplied by 1.5
- if this exceeds the total of the ratios of the missing teeth then there is insufficient tooth support and mucosal support must be considered
in a bounded saddle, occlusal rests are placed
on either side of the saddle (one mesial one distal)
in a free end saddle, the occlusal rest is placed on the
other side of the tooth to the saddle (mesial side)
centric stop
the point where opposing teeth touch in centric occlusion
- should not place rest seats here as this can interfere with the occlusion and feel unnatural to patients
primary mucosal support comes from
- the hard palate (maxillary)
- the buccal shelf/sulcus and pear shaped pad (mandibular)
- the residual ridges
- the maxillary tuberosity
how far fro the gingival margi should a base place be placed
3mm to prevent bone resorption, pressure causing recession and to allow clearing and flow of saliva (no food traps)
paeriodontium can be displaced by
0.1mm
mucoperiosteum can be compressed by
2mm
if there is no hard tissue support to the mesial of the abutment tooth on a free end saddle, this could result in
DISTAL AXIAL TORQUE
- the denture sinks into the compressible mucoperiosteum over time
retention
the resistance of a denture to lifting away from the tissues
means of achieving retention
mechanical, frictional, muscular or physical means
denture features which aid retention
- altering the path of insertion
- clasps
- frictional contacts (guide planes)
achieving mechanical retention
- from a clasp
2. the clasp engages the undercut of the tooth under the maximum bulbosity
muscular faces in retention
comes through time once the patient is used to the denture
- over time the orofacial muscles will have strengthened around the denture to hold it in place
frictional forces in retention
the use of parallel guide planes helps to retain the base of the denture between two frictional contacts
physical forces in denture retention
adhesion and cohesion
- adhesion from the surface forces between the saliva and mucosa
- cohesion from the forces with the saliva and its viscosity
negative pressure
pressure used to retain the entire base from the saliva suction and peripheral seal in the maxilla
- better in dentures with larger base and made acrylic
ring clasp
most common type
- starts at the occlusal and goes around the tooth
- terminates in the undercut it engages
- self reciprocating as it goes all the way around the tooth
direct retention
resistance to vertical displacement of the denture
- clasps and oromusculature
indirect retention
resistance to the rotational displacement of the denture
clasps should be
as close to the denture base as possible
guide planes are parallel to
the path of insertion and removal
gingival approaching clasps approach the undercut from
the gingival margin
occlusally approaching clasps approach the undercut from
the occlusal surface
occlusal approaching clasps
15mm or greater in length
- 2.5mm undercut necessary for CoCr
- begin not he occlusal surface and terminate in the undercut
gingival approaching clasp
usually on canines and premolars
- below the lipline so more subtle
- crosses the gingival margin which can be an issue
1. gum stripping
2. plaque retentive factor
clasp elements affecting retention
- flexibility
- depends on material and thickness - placement of the retentive arm
- should be placed to 15mm and engage an undercut but this is not always possible - depth of the undercut
- needs to be sufficient to seat a clasp
reciprocation component
a retentive arm which deflects over the bulbosity of the crown to counteract the forces of the retentive component by using an equal and opposite force
purpose of reciprocation
- stops the tooth from moving when the clasp is engaged
2. prevents pressure from the clasp acting on or damaging the tooth
how much of the clasp sits below the survey line to engage the undercut
01-Mar
how much of the clasp sits above the survey line
02-Mar
once the 1/3 of the clasp is activated, what should happen
it should be passive and no longer exert forces on the tooth
benefits of altering the path of insertion
- more frictional retention
- better aesthetic result
- prevents gaps forming
pattern of retention
needs to be as large a triangle as possible
when can using 2 clasps for the pattern of retention be allowed
when there is bilateral free end saddles
3 parts to the RPI clasp
- rest
- proximal plate
- I-bar clasp
the only part of the RPI clasp which applies pressure to the tooth is the
occlusal rest
the occlusal rest in RPI
must be on the mesial side of the tooth
- rounded to impression on the surface
- the only part of the clasp which put pressure on the tooth
the proximal plate of the RIP system
adjacent to the saddle
- sits in the undercut
- on the proximal surface
- provides bracing and stability of the denture during function and helps to guide during insertion
- slips into the undercut and disengages during function
I-Bar clasp of the RPI system
gingivally approaching
- greatest prominence of the tooth contour is where it site
- when there is loading it moves down and forward away from the tooth
why are RPI systems only used in the lower arch
the upper arch has a plate which restricts movement more than the lower
where is the reciprocation on the RPI system
there is minor connectors on both the mesial and distal of the engaged tooth
- the gap before the tooth to here is narrower to prevent the denture moving lingually
why is the rest to the mesial of a free end saddle
it puts the fulcrum further away from the clasp to allow it to resist the rotational movement
connector
a rigid part of the denture which unites components
minor connectors
join the smaller individual parts of the denture to the major connector
- transfers the function stresses to and from the abutment teeth
ideal characteristics of a minor connector;
- rigid
- finished above the survey lie on the teeth (toward occlusal)
- cross the gingival margins at 90 degrees
- maintains an area of self cleaning
- cross the gingival tissues as little as possible
major connector
the part of the denture than connects components other side of the arch to the other
plates
- horshoe
- ring (anterior/posterior bar)
- full plate with gingival clearance
- lingual plate
bars
- dental bar
- lingual bar
- sublingual bar
dental bar
sits on the cingulum of the teeth to avoid the mucosa
- has to be quite bulky to be rigid enough
thickness of plates
- can be made thinner and still maintain rigidity
- thickness however depends on the shape of the mucosal areas and the amount of coverage
- can be 0.45-0.5mm thin
bars thickness
less mucosal coverage so needs to be ticker
- shoud be 2mm thick
how far must the plate or bar be from the gingival margin
3mm
what amount of space is required for a mandibular plate and why
8mm
- 2mm from gingival margin
- 4mm height of the bar
- 1mm for clearance
every design
open connector design to prevent an of the gingiva being irritated
