Removable Partial Dentures Flashcards
1
Q
What is an RPD
A
- restores partial loss of natural teeth and supporting structures
- supported by natural teeth/ mucosa
- can be removed and replaced in the mouth by patient
2
Q
What are the consequences of tooth loss?
A
- Reduced facial height
- Compromised aesthetics
- Partial or complete loss of function
- Extrusion can lead to ectopic caries
- Bone resorption leads to lose of lip support
- Costly and some can be challenging to replace
- Front teeth can flare if posterior bite collapses
- Collapse dental arch or occlusion
3
Q
What are some of the rationale and indications for an RPD?
A
- Patient desire
- Cost of treatment
- Excessive alveolar bone loss
- No posterior abutment for fixed
- Immediate replacement of extracted teeth
- Lengthy edentulous span cant support fixed prosthesis
- reduced periodontal support of remaining teeth
- Cross-arch stabilization of teeth
4
Q
What is the relevance of RPD’s?
A
- restores chewing and biting efficiency, restores 2/ preserves and improves appearance
- aids speech
- restores health comfort and quality of life
- provides splinting action to weakened teeth
- preserves remaining teeth and supporting structures
- restores integrity of dental arch
5
Q
What is a kennedy Class I?
A
Bilateral edentulous areas located posterior to the remaining natural teeth
6
Q
What is a kennedy Class II?
A
Unilateral edentulous area located posterior to remaining natural teeth
7
Q
What is a kennedy Class III?
A
unilateral edentulous area with natural teeth remaining anterior and posterior to it
8
Q
What is a kennedy Class IV?
A
Single but bilateral (crosses midline) edentulous area located anterior to remaining natural teeth
9
Q
What is a surveyor used for?
A
Determining relative parallelism of two or more surfaces teeth or part of the cast
10
Q
What is a tissue-supported rpd?
A
Tissue supported RPD’s are primarily supported by the tissues (mucosa overlying bone) of the denture foundation area
11
Q
what is a tooth-supported rpd?
A
primarily supported by natural (abutment) teeth, denture retention is derived from direct retainers
12
Q
what are some advantages of polymer based rpds?
A
- good aesthetics
- processing technique is simple
- reduced construction time
- popular and affordable
- PMMA van be easily repaired or relined
- restore the full contour of an edentulous ridge
13
Q
what are some disadvantages of polymer based rpds?
A
- brittle and liable to fracture
- reported biological reactions to oral tissues
- rigid so can be difficult to insert in deep undercut is required for retention
- mainly tissue supported therefore wide and thick designs required for stability
- pressure is transmitted directly to mucosa and underlying tissues
- fitting surface can accumulate mucous deposits and food debris
14
Q
what are some advantages of nylon-based rpds?
A
- easy undercut insertion
- allows movement and tissue simulation
- monomer free reduces tissue reaction
15
Q
what are some disadvantages to nylon-based rpds?
A
- inferior to metal-base dentures
- high water absorption
- possible discolouration
16
Q
what are some advantages to metal rpds?
A
- easy to clean
- mainly tooth or tooth and mucosa supported
- framework can be fabricated with CAD/CAM
- better durability and stability from direct and indirect retainers
17
Q
what are some disadvantages of metal rpds?
A
- difficult to repair
- labour intensive construction
- reported patient allergies
- mechanical retention of denture can fail
18
Q
what are interim rpds?
A
sometimes made prior to making a definitive one and is used to:
1. maintain or enhance appearance
2. maintenance of space
3. reestablishment of occlusal relationships
4. conditioning of teeth and residual ridges
5. interim restoration
6. conditioning the patient for wearing prosthesis
19
Q
Why are rpds used to improve conditions before definitive dentures?
A
tissue conditioning:
- due to papillary hyperplasia (massage, brushing) or acute inflammation (increase tissue adaption and redistribute stress)
implant healing:
- may be necessary for aesthetics or function, a soft liner is placed so that the fixtures can heal
alteration of vertical dimension:
- important use to determine how a patient will react to changes
Surgical splint:
- after removal of palatal tori, etc.
20
Q
what is required on a patient form?
A
patient name, record number, DOB, gender, clinical details, clinician name and contact details, type of restoration, shade, prescription date, due date (including next appointment), items included in prescription (impressions, models, bite registrations)
21
Q
what is an articulator?
A
mechanical device that simulates the movements of the mandible in relation to maxillary arch
22
Q
why use an articulator?
A
- maintain or re-establish healthy occlusion
- enhance efficiency and precision
- construction with articulator will suit better
- communication between dentist and technician
- minimize major occlusal adjustments
23
Q
what is occlusion?
A
the static contact relationship between the incising or masticating surfaces of maxillary and mandibular teeth
24
Q
what are the types of denture processing techniques?
A
- compression moulding
- injection moulding
- pouring (fluid resin)
- light activated
25
what are the components of an RPD?
1. saddle
2. major connectors
3. minor connectors
4. rests
5. direct retainers
6. stabilizing components
7. indirect retainers
8. denture base
26
what is the saddle?
a saddle is the part of the denture that replaces lost alveolar tissue and carries artificial teeth - bounded or free-end
27
what are major connectors?
join components on both sides of a dental arch together to effectively distribute forces throughout the arch and reduce the load
28
what are types of maxillary major connectors?
1. single palatal strap
2. anterior-posterior palatal strap
3. palatal plate
4. u-shaped palatal
5. single palatal bar
6. anterio-posterior palatal bar
29
what is a single palatal strap?
bilateral bounded saddles for kennedy class II and III cases
30
what class is a anterior-posterior palatal strap type used for?
ideal for all classes (mostly II and IV)
31
Why are single palatal bar and antero-posterior palatal bars used?
for cross-arch distribution of stress
32
what is a palatal plate-type connector?
a full palatal plate that is indicated when maximum tissue support is required. ideal for long distal extension cases when theres 6 or less anterior teeth remaining
33
what is a u-shaped palatal connector?
least favourable design due to lack of rigidity, and only used in situations when inoperable tori extends to the posterior limit of the hard palate
34
what are the types of mandibular major connectors?
1. lingual bar
2. linguoplate
3. sublingual bar
4. lingual bar with cingulum bar
5. cingulum bar
6. labial bar
35
what is a lingual bar?
used when enough space (>8mm) exists between the slightly elevated alveolar lingual sulcus and gingival tissue
36
what is a sublingual bar?
used when the height of the floor of the mouth in relation to free gingiva margins are <6mm.
37
what is a lingual plate?
used when there is insufficient space for a lingual bar, class I arches with highly resorbed residual ridges, for splinting
38
what is a labial bar?
when severe lingual tori cant be removed and prevents the use of a lingual bar or plate
39
what are the functions of a minor connector?
1. connects major connector to other components (such as clasps, rests or indirect retainers)
2. transfers functional stress to abutment teeth
3. transfers the effect of retainers, rests and stabilising components through prosthesis
40
what are important things to consider with minor connectors?
1. have adequate relief
2. at a right angle to the major connector
3. should not be located on a convex surface
4. should be least noticeable
5. tapered, no sharp edges or spaces for food debris
41
what are direct retainers - precision attachments?
direct retainers engage the vertical walls built into or around the crown of the abutment tooth to create frictional resistance for removal
42
what are direct retainers - clasps?
engage the external surface of abutment teeth in natural undercut or prepared depression and are either occlusally approaching or gingivally approaching.
43
what is the undercut for a g-clasp?
0.25 - 0.35mm
44
what is the undercut for a e-clasp?
0.20 - 0.35mm
45
what is the undercut for a ring clasp?
0.30 - 0.50mm
46
what is the undercut for a bonwill clasp?
0.20 - 0.35mm
47
what is an e-clasp?
on a bounded saddle (class II, III and IV (sometimes))
48
advantages of a e-clasp (akers)?
1. has 1 or 2 retentive clasp arms
2. path of insertion easy to define
3. reliable retention close to saddle
4. excellent bracing qualities
5. less potential for food accumulation
6. easy to design, construct and activate
49
disadvantages of e-clasp (akers)?
1. more tooth coverage
2. more metal is displayed
3. adjustments are difficult or impossible
4. low undercut depth
50
what class is a g-type clasp used for?
kennedy class I, II and III
51
what are some advantages for a g-clasp?
1. mesial rest support acts indirectly to elongate the saddle
2. minor connector is away from saddle (periodontally hygienic)
3. passible clasp arm leads and stabilises denture
52
what are disadvantages of a g-clasp?
1. extensive tooth coverage
2. rest being distant to saddle
53
what class are back-action clasps used for?
ALL - kennedy class I, II, III and IV
54
what are some advantages of a back-action clasp?
1. large retention field due to long retentive arm
2. minor connector stabilises support
3. aesthetically favourable
55
what are some disadvantages of a back-action clasp?
1. space between minor connector and saddle
2. extensive tooth coverage
56
what class are ring clasps used for?
only lingually shifted molars in kennedy II, III and IV
57
what are some advantages of a ring clasp?
1. retention adjacent to saddle prevents displacement
2. protection against distal drifting
3. long retentive arm implies high ability of retention
4. allows for use of available undercut adjacent to edentulous area
58
what are some disadvantages of a ring clasp?
1. extensive tooth coverage
2. long clasp arm can deform
3. covered distal area of posterior teeth
4. very difficult to adjust
5. lower bracing arm should be at least 1mm from free gingival margin to prevent impingement of gingival tissues
59
what class is a bonwill (double akers) clasp used for?
kennedy II, III and IV
60
what are some advantages of a bonwill clasp?
1. allows placement of direct retainer where none can be placed
2. maximised retention
3. retentive forces distributed
4. provides splinting effect
61
what are some disadvantages of a bonwill (double akers) clasp?
1. extensive tooth coverage
2. bulky minor connector
3. clasp arm can impede occlusion
4. extensive interproximal reduction required
62
what are some advantages to a bar (or roach) clasp?
1. easy insertion
2. extreme undercut depth
3. minimum tooth coverage
63
what are some disadvantages of a bar (roach) clasp?
1. often unstable
2. risk of labial tooth tilting
3. hygienically unfavourable
64
what are the contraindications of a bar (roach) clasp?
1. deep cervical undercuts (food trap)
2. severe soft tissue or bony undercuts (food trap)
65
what are wrought circumferential clasps?
wrought wire clasps are fabricated by using metal that is made from a wire
66
what are some disadvantages of precision attachments?
1. expensive and complex procedures
2. require prepared abutment for fixed restorations
3. wear with progressive loss of frictional resistance
4. difficult to repair
5. less effective on short teeth
6. difficult to place within circumference of abutment tooth due to pulp size
67
what are some advantages to precision attachments?
1. eliminates visible retentive and support components
2. provide better vertical support
68
what is the function of a clasp?
1. retention against vertical dislodgement
2. vertical support
3. bracing
3. reciprocation
4. encirclement
5. passivity
69
what is retention?
prevents vertical dislodgement of a partial denture
premolar retention: 1/2 of the clasp arm is active
molar retention: 1/3 of clasp arm is active
70
what is vertical support?
support provided by rest and prevents tissue ward movement of RPD
types include incisal rests, occlusal rests and cingulum rests
71
what is bracing?
prevents lateral displacement or horizontal shifting of a partial denture
72
what is reciprocation?
stabilises horizontal movement or prevents tooth movement lingually or palatally
73
what is encirclement?
the degree the clasp encircles the tooth, should be at least 180 degrees, but is better with 270 degrees
74
what is passivity?
direct retainers should not exert forces against a tooth until a dislodging force is applied
75
what are indirect retainers?
prevents rotational displacement of the denture such as rests
76
what are rests?
rests are located anterior to a retentive arm on the distal extension to prevent downward movement of the anterior portion of the rpd
77
what is the finishing line?
the finishing line minimizes the bulk of acrylic attached to the artificial teeth
78
what are tissue stops?
integral parts of minor connectors that are designed for the retention of acrylic-resin bases and provide stability to the framework, prevent distortion during the acrylic-resin processing and engage buccal and lingual slopes of the residual ridge for stability
79
how to reduce torque in rpds?
1. extend denture base in free-end saddle
2. arrange indirect retainers away from saddle
3. arrangement of compensating elements (additional clasps, rests)
4. consider expected pressure load on masticatory function
80
what is the lost-wax technique?
a process whereby molten alloys are caused to flow into heated hollow moulds formed by burnt-out wax patterns
81
what is a sprue?
the channel in the investment mould which a molten alloy flows to reach the hollow mould formed after burnout of wax patterns. they should be round and smooth
82
what are the requirements of investment materials?
1. precisely reproduce the detailed form of the wax pattern
2. provide sufficient strength to withstand the heat burnout and casting of molten alloy
3. expand sufficiently to compensate for solidification shrinkage of alloy
83
what are gypsum bonded investment?
compounds are usually mixed with water and are suitable and limited to alloys heated up to 1040 degrees C
84
what are advantages of gypsum bonded investment?
1. easy to divest
2. easy sandblasting due to low oxide adhesion
3. expansion controlled by changing liquid proportion
4. high cristobalite content produces smooth surfaces
85
What are phosphate bonded investment materials?
quartz, cristobalite, MgO (magnesium oxide), ammonium dihydrogen phosphate are homogenously mixed. Silica sol is mainly used as the investment liquid to increase crystallisation effect and expansion.
86
what are some advantages of phosphate bonded investment materials?
1. suitable for any material and technique
2. broad expansion range control
3. high precision
4. longer shelf life
87
what are some disadvantages of phosphate bonded investment materials?
1. harder and relatively difficult to divest and sandblast due to strong adhesion and oxide formation
2. sensitive to light and heat
88
what are ethyl silicate and hydrochloric acid investment materials?
ethyl silicate binds investment during the crystallisation process
89
what are some advantages to ethyl silicate investment?
1. cost efficient
2. easy to divest
3. ideal for base metal alloys heated to 1780 degrees C
90
what are the mechanisms of investment mold expansion?
setting expansion:
- due to crystal growth
hygroscopic expansion:
- if investment is employed to set in the presence of water
wax pattern expansion:
- when investment is still fluid and wax is warmed
thermal expansion of investment:
- occurs in burnout furnace
91
what are high noble alloys?
noble metal content >60%
92
what are noble alloys?
noble metal content >25%
93
what are predominantly base alloys?
noble metal content <25%
94
what are the casting systems?
1. flame
2. induction melting (centrifugal, pressure, vacuum or pressure-vacuum)
3. electrical melting
95
what is induction melting?
harnesses the power of electromagnetism to heat conductive metals and uses a high density electric current to pass through the copper coils to produce a magnetic field around the crucible.
96
what is devesting and air abrasion?
1. allow moulds to cool down until they are warm to touch
2. avoid silica dust by immersing mould in water for at least 3min
3. devest with a small devesting chisel or hammer
4. sandblast excess investment material away
97
what is electrolytic polishing (electrobrightening)
the framework is held at the anode (+) using an alligator clip. the current flows through the framework and metal ions detach themselves from the surface of the framework and migrate to the cathode (-). The cations (+ve ions) from rough surface are removed.
98
what is the electrolytic solution?
ethylene gylcol (70-80%), sulfuric acid H2SO4 (10-15%) and water (5-20%)
99
what causes investment material setting too quickly?
1. soiled mixing or measuring beaker
2. temperature (of room, powder or liquid) too high
3. inaccurate ratio of powder to liquid
4. mixing time too long
100
what causes investment material setting too slow?
1. temperature (of room, powder, liquid) too low
2. inaccurate ratio of powder to fluid
3. soiled mixing or measuring beaker (foreign material, soap)
4. investment material too old
101
what causes bubbles in mixed investment material?
insufficient vacuum
102
what causes soft surface of duplicate model?
1. premature removal from mould
2. mixing ratio or time not correct
3. duplicating mould damp
4. duplicating material too old or watery
5. investment too old
6. insufficient mixing of investment material
7. duplicating mould too cold
8. setting time of investment too long
103
what causes formation of crystals on duplicating model?
time between removal from agar and drying too long
104
what causes the investment material to adhere to duplicating material?
1. mixing ratio too thin
2. damp duplication mould
3. premature removal of model
4. duplication mould too cold
5. setting time of investment material too long
105
what causes bubbles on duplicating model
1. pouring of investment too fast
2. inadequate vibration
3. vacuum too poor while mixing
106
what causes the surface of refractory models to be too soft after hardening?
1. drying temperatures too high
2. time in furnace too long
3. hardener left on for too long
107
what causes the hardener to not be absorbed?
1. very dense surface due to silicone duplication
2. hardener thickened
3. temperature of drying cabinet too low
4. immersion time too long
108
what causes cracking of the ring during pre-heating?
1. preheating times and temperatures not observed
2. defective temperature controls
3. wrong mixing liquid
4. different liquid for model and ring
5. mixing liquid spoilt
6. soiled mixing or measuring beaker
7. ring with funnel upwards in oven
8. temperature in oven too high when loading ring
9. machine oil used as ring isolation
109
what causes casting to not flow correctly?
1. final temperature of pre-heating furnace too low
2. ring has cooled down through excessive melting time in casting unit
3. ring partially cooled
4. ring located too close to oven door
5. wax up too thin
6. incorrect arrangement or size of casting sprues
7. metal quantity too low
8. casting pressure too low
9. casting temperature too low
110
what causes casting flash or closed retentions?
1. not perfectly cleaned
2. excessive hardener on model
3. ring setting time too short
4. preheat ramp and temperature not observed
5. wrong application of fine investment
6. different mixing liquids for model and coat
7. separation of model from ring through mechanical shock before casting
111
what causes strong adhesion of investment material when divesting?
1. melt of alloy is too hot
2. ring heated too long
3. ring temperature heated too high
112
what causes rough structure on fitting surface of cast?
1. melt too hot
2. drying time for duplication models not observed
3. investment breaking away during duplicating process caused by damp mould
4. use of unsuitable model hardeners
5. duplicating model dried too long after immersion
6. preheat temperature of ring too high
113
what causes bubbles on framework or plate surfaces?
1. inadequate waxing during modelling
2. inadequate adaption of waxes and wax patterns to duplicating model
3. wax surface tension reducing agent not used or used incorrectly
4. poor venting of material due to mixing consistency being too thick
114
what causes bubbles on tissue side of framework?
1. investment too thick during model fabrication
2. processing time too short
3. bubbles cant escape
4. vacuum unit not performing correctly
115
what causes porosity in casting?
1. gas absorption through use of already cast material
2. metal overheated
3. old crucible used
4. same crucible used for different alloys
5. incorrect gas setting for torch casting
116
what causes material inclusions in casting?
1. not perfectly clean funnel
2. sharp edges which break off during casting
3. ring preheated in oven with opening upwards
4. fine investment chipped off
5. fine investment applied too thickly
5. too rapid preheating
116
what causes shrinkage in casting?
1. incorrect wax-up or attachment of casting sprues
2. casting sprues too thin
3. spin time too short
117
what causes casting to be too small?
1. mixing ratio not observed
2. duplicating material not suitable for investment
3. old duplicating material (greasy)
4. mixing fluid crystallised
5. model fabricated with water instead of mixing fluid
6. investment heated too quickly
7. shore hardness of duplicating silicone very high
118
what causes a cast to be too large?
1. mixing consistency too thick
2. concentration of mixing liquid too high
119
what causes different fitting accuracy in casting?
1. deformation of duplicating material during removal of master model
2. duplicating material old
3. when using duplicating silicone, incorrect flask system used
4. duplicating silicone has separated from flask
5. struck bottom with hammer during removal of investment
120
what is additive manufacturing?
3d printing by adding layer-by-layer using CAD/CAM
121
what are the types of additive manufacturing?
photopolymerisation and powder bed fusion
122
what is photopolymerisation?
when photopolymers are exposed to light (usually UV) and causes a change in their structural and chemical properties
123
what is stereolithography?
layers of photopolymers are cured/solidified layer-by-;ayer using a UV laser scanner
124
what are advantages of stereolithography?
1. good accuracy, surface finish and details
2. machines with large build volume enables large parts
3. variety of different uses
125
what are some disadvantages of stereolithography?
1. materials are expensive
2. build process is slow
3. only works with photopolymers
4. mechanical properties of parts are unstable over time
5. requires to post-cure
126
what is digital light processing?
when a UV light is applied to the entire surface of the photopolymer resin, curing it in one go
127
what is material jetting?
when photopolymers are selectively squirted through multiple jet heads and then cured with a UV light
128
what are some advantages of material jetting?
1. good accuracy and surface finish
2. multi-material and multi-coloured parts
3. support structures can be built with different materials and melted away
4. usually no post-curing required
129
What is selective laser melting?
employs primarily semi-crystalline metal powders, which are preheated close to the melting transition and recrystalization temperature and are sintered by a CO2 laser to fuse the particles
130
what maxillary major connectors are used for Class I?
anterior-posterior palatal strap or palatal plate
131
what mandibular major connectors are used for Class I?
lingual bar, lingual plate or labial bar (not ideal)
132
what clasps are used for Class I?
g-clasp, back-action, bar (roach) or wrought wire
133
what maxillary major connectors are used for class II?
single palatal strap, anterior-posterior palatal strap, palatal plate, anterio-posterior palatal bar or u-shaped (not ideal)
134
what mandibular major connectors are used for class II?
lingual bar, lingual plate, sublingual bar or labial bar (not ideal)
135
what clasps are used for class II?
e-clasp, g-clasp, back-action, ring clasp, bonwill or bar (roach)
136
what maxillary major connectors are used in class III?
single palatal strap, anterior-posterior strap, palatal plate or u-shaped (not ideal)
137
what mandibular major connectors are used in class III?
lingual bar, lingual plate, sublingual bar or labial bar (not ideal)
138
what clasps are used for class III?
e-clasp, g-clasp, ring clasp, bonwill or bar (roach)
139
what maxillary major connectors are used in class IV?
anterior-posterior palatal strap, anterio-posterior palatal bar, palatal bar or u-shaped
140
what mandibular major connectors are used in class IV?
lingual bar, lingual plate or labial bar
141
what clasps are used in class IV?
e-clasp, back-action, ring clasp, bonwill or bar (roach)
142
what is the fulcrum line?
imaginary axis where denture could rotate where pressure/ forces are applied, especially during mastication or speech. it typically passes through rests or abutment teeth closest to the edentulous area.
143
what type of investment material is strictly thermal expansion?
ethyl silicate
144
why is bearing used in a single palatal strap?
used to provide a visible finishing line on cast framework and ensures tissue contact of palatal tissue
145
what does a single palatal bar or anterio-posterior palatal bar need?
necessary rigidity for cross-arch distribution of stress
146
what is the maximum temperature gypsum-bonded investment can be preheated and casted at?
preheated - 670 degrees C
casted - 1040 degrees C
147
what is hygroscopic expansion?
when investment material is set in the presence of water, such as immersing it in water during the setting time.
this increases the expansion of the investment material
148
what is setting expansion?
the expansion that occurs as investment material sets after mixing.
occurs due to crystallisation process from a liquid to a solid crystalline form.
amount of setting expansion can be manipulated with liquid-to-powder ratio
149
what is wax-pattern expansion?
when the investment material is liquid, the wax is heated above the temperature that it was formed.
increase in dimensions of wax-pattern when submerged in investment material and subjected to heat allows for compensation of shrinkage that occurs in metal alloys
150
what is thermal expansion?
occurs during burning out, due to investment material being heated.
when it is heated, the material expands due to increased molecular motion
quartz and cristobalite have different expanding rates depending on temperature, the combination allows for controlled and gradual expansion
151
how much does gold shrink after casting?
around 15%
152
how much does nickel/chromium shrink after casting?
around 2.4%
153
what temperature can ethyl silicate be casted up to?
1780 degrees C
154
what is a tissue stop?
a minor connector that helps with the retention of acrylic-resin bases.
provides stability, prevents distortion during acrylic processing and engages buccal and lingual slopes of residual ridge for stability
155
what clasp is only in class II, III and IV?
e-clasp, ring clasp and bonwill (double akers) clasp
156
what is the change in polarity in the induction casting process?
positive to negative at 1500 khz/s
157
what does the change in polarity in the induction casting process cause?
molecules of the alloy to oscillate and molecular bonds to breakdown
158
what is the chemical makeup of gypsum bonded material?
calcium sulfate hemihydrate (gypsum) + quartz + cristobalite which reacts with water
159
what is the chemical makeup of phosphate bonded materials?
quartz + cristobalite + ammonium dihydrogen phosphate which reacts with silica sol
160
what clasp is not used in class IV?
g-clasp
161
what is the undercut for a back-action clasp?
0.25 - 0.40mm
162
how does the centrifugal induction casting system work?
once melt is molten, the ring is placed in the rotating arm of the system. the lever is pushed which causes the casting arm to spin rapidly produces centrifugal force that drives molten metal out of the crucible into the mould.
163
how does a vacuum-pressure induction system work?
the vacuum chamber is filled with gas to reduce exposure to oxygen.
once metal is molten, pressure pushes the molten metal to flow into the mould.
