Removable Prosthetics Flashcards
1
Q
What is support?
A
Resistance of vertical movements towards tissues. Obtained from; - rest seats - tooth supported - ridges - mucosa supported - palate - mucosa supported
2
Q
What are the consequences of poor RPD support (generally)?
A
- Compromised function
- Poor occlusal stability
- Ulceration
- residual ridge resorption
- Limited teeth stability
- Limited aesthetics
3
Q
What anatomical structure provides tooth support?
A
Periodontal ligament
- specialised to receive vertical forces
- sensory perception
4
Q
What is an RPD rest?
A
A rigid component of RPD which fits in a recessed preparation (rest seat) on the occlusal, lingual or incisal surface of a tooth to provide vertical support for the denture
5
Q
What is an RPD rest seat?
A
A portion of a tooth selected and prepared to receive an occlusal, incisal or lingual rest
Types include; occlusal, cingulum, incisal, overlay and precision.
6
Q
What is the function of RPD rests?
A
- Directs the forces along the long axis of the abutment tooth.
- Prevents the denture base from moving cervically and impinging on gingival tissues
- Maintain clasp-tooth relationship
- Prevent extrusion of abutment teeth
- Provides positive reference seats in rebase and reline impression
- Serves as an indirect retainer by preventing rotation of the partial denture
6
Q
What is the function of RPD rests?
A
Directs the forced along the long axis of the abutment tooth.
Prevent the denture base from moving cervically and impinging gingival tissues.
7
Q
What is an occlusal rest?
A
A rest placed on the occlusal surface of premolar or molar.
It has a characteristic design that looks like a spoon - with a rounded triangular shape with its apex nearest to the centre of the tooth. The base of the triangular shape is at the marginal ridge and should be 1/3 the bucco-lingual width of the tooth. The marginal ridge must be lowered and rounded to allow sufficient bulk of metal (1-1.5mm). The floor of the rest seat should be inclined towards the centre of the, the angle formed by the rest and minor connector should be less than 90 degrees - ensuring that the material will stay.
8
Q
What is a cingulum rest?
A
A rest placed on the cingulum of an anterior tooth - usually a canine.
- More suitable for maxillary canines as they have an exaggerated cingulum.
9
Q
What are the types of cingulum rests?
A
- Inverted V shape
2. Round form
10
Q
What is an incisal rest?
A
A rest placed on an anterior tooth at the incisal edge.
- Significantly affects the aesthetics
11
Q
What is an overlay?
A
Coverage of all the occlusal surface of molar or premolar.
- Ideal of occlusal alteration and changing vertical dimension
12
Q
Intracoronal (precision) rest
A
A rest consisting of precision manufactured attachments that are placed within the coronal contours of a crown or retainer.
13
Q
Disadvantage of ridges
A
- More limited and less specialised than teeth
- Compromised substitute for PDL
- Limited tolerance and adaptability
- Unsuitable for load bearing
- Can results in tipping or RPD during function - due to uneven distribution of functional forces over the edentulous area (one side is supported by teeth (hard tissue), while the other is supported by soft tissues). Maximal mucosal coverage can enhance support - needs to be fully extended to sulcus depth.
- Further bone resorption affects the RPD fit
14
Q
What are maxillary primary support areas that resist occlusal loading?
A
1 - Hard palate
2 - Buccal shelves
15
Q
What are the mandibular support areas that are more ideal to resisting occlusal loading?
A
- Retromolar pads
2. Buccal shelves
16
Q
Examples of compromised edentulous areas
A
- Severely resorbed ridge
- increased tenderness on function
- Hyperplastic or flabby ridges
- compromised RPD support
- loss of occlusal contacts
17
Q
Management of compromised edentulous areas
A
Modified impression techniques
- Muco-compressive impression technique - recording soft tissues under some loading
- Altered cast technique - Distributing the loads to maximal area possible
18
Q
What is the muco-compressive impression technique?
A
Mucocompressive means that the impression is taken when the mucosa is subject to compression.
These impressions will generally lead to a denture that is most stable during function but not at rest.
19
Q
What is the altered cast technique?
A
The altered cast technique allows the ridge, recorded in functional form, to be related to the teeth so that when the prosthesis is seated, it derives support simultaneously from the teeth and the denture base.
20
Q
Why is palatal coverage important?
A
- Provides maximal coverage for support - especially when there are less teeth
- Significantly enhances the performance of Kennedy Class I and II maxillary RPD.
21
Q
What is RPD retention?
A
Resistance of dislodging forces during function
22
Q
Direct retention examples
A
- Retentive clasp
23
Q
Indirect retention examples
A
- Specific rest seats
24
How to achieve mechanical retention?
1. Clasps engaging undercuts
2. Frictional retention
3. Dislodging force direction should be relative/similar to the path of placement
25
Retention via patient muscular control
Muscles action against polished surface of the denture
| Concave flanges are preferred to help with this.
26
Inherant physical forces of retention
1. Enhanced palatal coverage
| - adhesion, cohesion, interfacial surface tension and atmospheric pressure.
27
How is mechanical retention provided via clasps?
The clasping unit engages with an abutment tooth as to resist displacement of the prosthesis away from the basal seat tissues
28
Requirements of the clasping unit
1. Support - resistance to gingival displacement (occlusal rest)
2. Reciprocity - resistance to orthodontic movement of teeth (reciprocal arm, minor connector)
3. Stability - resistance to lateral movement (reciprocal arm, minor connector)
4. Retention - resistance to dislodging forces of the abutment (retentive arm)
5. Encirclement of greater than 180 degree of abutment tooth
6. Passivity
29
What are the determining factors for clasp selection?
1. Flexibility
2. Position of the undercut
3. Health of PDL
4. Shape of the sulcus
5. Aesthetics
6. Occlusion
30
Factors influencing flexibility
1. Section: a round section claps will flex equally in all directions. Half-round clasps will flex more horizontally than vertically.
2. Thickness: thickness significantly effects flexibility. Reducing the thickness by half, results in flexibility increasing by a factor of 8.
3. Length: the longer the clasp arm the more flexible it is.
4. Metal: chromium has high stiffness (modulus of elasticity), twice the stiffness of gold
31
What are the types of oclusally approaching clasps?
1. Circumferential (Aker's)
2. Ring
3. Embrasure (double Aker's)
4. C-clasp
32
Circumferential (Aker's) clasp
1. Most simple and versatile claps
2. The retentive arm begins above the height of contour and curves and tapers to its terminal tip
3. The distal 1/3 of the arm engages the undercut
33
Advantages of Aker's clasp
1. Excellent bracing qualities
2. Easy to design and construct
3. Less potential for food accumulation below the clasp
34
Disadvantages of the Aker's clasp
1. More tooth coverage
| 2. Metal display
35
Ring clasp
1. Encircles the entire abutment tooth
2. Commonly used for tilted molars
3. Undercut is next to the edentulous area
4. Supporting strut on the non-retentive side
5. Auxiliary rest seat on opposite side
36
Advantages of the ring clasp
1. Excellent bracing
| 2. Uses available undercut adjacent to edentulous areas
37
Disadvantages of ring clasp
1. Covers large area of tooth surface
2. Needs an additional rest
3. Difficult to adjust
38
Embrasure (double Aker's) clasp
1. Used in quadrant when no edentulous areas exists
2. Composed of 2 rests, 2 retentive arms and 2 bracing arms
3. Double rests are required to prevent weakening of clasp arms
4. Buccal and lingual occlusal proximal areas must be reduced to provide room and avoid occlusal interferences
5. Should be used with discretion
39
Advantages of embrasure clasp
1. Allows for direct retainer placement
40
Disadvantages of embrasure clasp
1. Extensive inter-proximal reduction
| 2. Covers a large area of tooth surface
40
C-clasp clamp (reverse action clamp)
1. The retentive area is adjacent to the occlusal rest (ring clasp has a retentive area opposite to rest)
2. Alternative to ring clasp
41
Advantages of the C-clasp
Uses the undercut adjacent to edentulous space
42
Disadvantage of C-clasp
1. Difficult to adjust
2. Not aesthetic
3. Difficult to make
4. Covers extensive tooth surface
5. Food trapping
6. Limited flexibility
43
Gingivally approaching clasps
- Contacts the tooth at its tip
- Approaches from the gingiva
- There should be no anatomical obstacles
- Influences by the shape of the sulcus
44
Advantages of gingivally-approaching clasp
Less influence on occlusion
| More aesthetic
45
Disadvantages of gingivally approaching clasp
Less hygienic
Deep sulcus
No hard tissue undercuts
46
Gingivally-approaching clasp variations
1. I-bar
2. L-bar
3. T-bar
47
What is the RPI system?
R: Occlusal Rest
P: Distal guide Plate
I: Gingivally approaching I bar
Provides all the function of the clasping unit.
Not used unless there are no posterior teeth.
Used on premolar mandibular teeth.
48
Principles of the RPI system
The distal guide plate is located at the gingival third of the guiding plane.
The RPI system allows vertical rotation of the distal extension saddle into the denture bearing mucosa under occlusal loading without disengaging the supporting structure of the abutment tooth.
As the saddle is pressed into the mucosa, the denture rotates around the point close to the mesial rest seat
The plate and the I bar disengage the tooth, eliminating the potentially harmful torque on the abutment tooth
49
Indications of the RPI system
1. Free-end saddle area - Class I/II
2. Premolars
3. Presence of buccal or mesio-buccal undercut
4. Compromised abutment tooth
50
Contraindications of RPI
1. Insufficient vestibular depth (4mm from gingival margin)
2. No labial or buccal undercut on the abutment
3. Severe soft tissue undercut
4. Distobuccal undercut
51
What is the RPA system?
Same system as RPI but with Aker's clasp
52
What is a combination clasp?
A combination clasp is a circumferential retainer for a removable dental prosthesis that has a cast reciprocal arm and a round wrought wire retentive clasp.
53
Advantages of Combination clasp
1. Better aesthetics
2. Can be placed in deeper undercuts
3. Round wrought wire is more flexible
54
What is indirect retention?
A feature of RPD that reduced the tendency of a denture base to move in an occlusal direction while rotating about the clasp axis line - usually relieved by placing a rest on a more anterior tooth. Dislodging forces include; gravity and food
The rest become the fulcrum of movement causing the clasp to remain in the undercut and preventing the denture from pivoting
Indirect retainers are placed opposite to saddles, parallel to the clasp axis.
55
What is a clasp axis?
A line formed from the retentive tips of a pair of clasps on opposite sides of the arch.
If there is more than one clasp axis, then the one close to the saddle contributes more to indirect retention.
56
Forms of indirect retainers
1. Rests
2. Palatal coverage
3. Lingual plate
57
What is bracing?
Resistance to horizontal forces being applied on the denture during function
- anterior, posterior and lateral
58
What elements can help provide bracing?
On teeth: plates, reciprocating arms and minor connectors
On ridges: major connectors, flanges
59
What is reciprocation?
Bracing element of a clasping unit that is in contact with the side of the tooth opposite the retentive clasp arm
60
What is a connector?
An RPD feature that joins the components of the RPD
61
Functions of major connectors
1. Unification: uniting all the components of the partial denture
2. Stress distribution: even distribution of forces on all the abutments
3. Cross-arch stabilisation
62
Requirements of major connectors
1. Rigidity
2. No interference with soft tissues
3. Prevent food impaction
4. Unobtrusive
63
Features of maxillary major connectors
1. At least 6mm from gingival margins
2. Tapered borders
3. Smoothly curved outlines
4. The posterior border should not extend to the soft palate
5. The borders should be beaded
6. The anterior border should merge with rugae region
7. Should maintain peripheral seal
64
Advantages of maxillary major connector plates over bars
1. More coverage
2. Thinner
3. Provides mucosal support
4. Can blend with palatal mucosa
5. More comfortable
65
Disadvantage of maxillary major connector bars
1. Less coverage
2. Thicker (2-3mm)
3. Minimal contribution to support
4. Noticeable
5. Rarely used
66
Advantages of the mid-palatal plate
1. Simple
2. Uncovering all gingival margin
3. Rigid
4. Simple outline
5. Well tolerated
67
Features of a palatal plate
1. Maximal support
2. Uncovered gingival margins
3. Long distal extension
4. 6 or less anterior teeth remaining
5. Flabby ridges
6. Shallow palate
68
Features of the anterior palatal strap
1. Kennedy IV
2. Lack of palatal support
3. Rigidity might be compromised
4. Hygiene may be compromised when gingival tissues are covered
69
Features of the ring connector
1. Multiple saddles
2. Provides relief to palatal torus
3. Kennedy IV
4. Tolerance may be compromised
70
Features of a mandibular major connector
1. The borders should be at least 3mm from the gingival margin
2. Relief is require to prevent impingement at rest and function
3. Limited by the floor of the mouth and depth
71
Features of a lingual bar
1. Flat on tissue side
2. Convex on lingual side
3. Hygienic
4. Rigid
5. Well tolerated
6. 4mm height and 2mm width
72
Features of a sublingual bar
1. Hygienic
2. Rigid
3. Well tolerated
4. Indicated if the floor of the mouth is hight
5. 2mm height, 3-4mm width
73
Indications for a lingual plate
1. Severe ridge resorption
| 2. Few teeth present
74
Features of a lingual plate
1. Unhygienic
2. Rigid
3. Well tolerated
4. Contributes to support
5. Provides indirect retention
6. Enhances support for compromised situations
7. Indicated for people with shallow floor of the mouth or shallow sulcus
75
Indications for a dental bar
1. Lack of room between gingival margin and floor of the mouth
2. Useful for long clinical crowns
3. Affects aesthetics
4. Compromised rigidity and tolerance
76
Features of a continuous bar
1. Combination of lingual and dental bar
2. Not well tolerated
3. Potentially unaesthetic
77
Indications for a lingual bar
1. Indicated for lingually inclined teeth
| 2. Rarely indicated as it has compromised rigidity and tolerance
78
Function of minor connectors
1. Unification and rigidity
2. Facilitate stress distribution within the RPD and abutment teeth
3. Act as bracing element
4. Maintain path of insertion
79
Requirements of minor connectors
1. Triangular cross section
2. Join the major connector at right angle
3. Should cover as minimal tissue as possible
4. Should fill the embrasure space
5. Should be smooth on the tongue
6. Passively fitting against the abutments
80
What is a proximal plate?
The proximal plate originates from the resin retention component on the edentulous area.
The plate is shifted slightly towards the lingual to increase rigidity, enhance reciprocation and improve aesthetics.
81
Components of RPD that connect the metal framework to acrylic resin.
1. Mesh retention
2. Open lattice retention
3. Metal base with retentive pins
4. Metal backing
82
Features of mesh retention and open lattice retention?
1. Used for wide edentulous area
2. Acrylic labial/buccal flanges are needed
3. Not used for single tooth replacement
83
Principles of resin mesh and lattice retention
1. Relief under the grid work should begin 1.5-2mm from the abutment tooth
2. Facilitates metal to tissue contact immediately adjacent to the tooth
3. More resistant to wear
4. More hygienic
5. The junction of the metal to the major connector should be in the form of a butt joint with a slight undercut in the metal - enhances the resin retention
84
Resin retention on mandible
The resin retention on a mandibular distal extension should extend 2.3 of the way from the abutment tooth to the retromolar pad.
The mandibular resin retention should have a tissue stop at their posterior limit to provide direct contact with the ridge.
85
Resin retention on maxilla
Maxillary distal extension resin retention should extend at least 2/3 of the length of the ridge to the hamular notch
The finishing line of the maxillary major connector should be fully extending to the hamular notch
86
Indications of metal base with retentive pins
1. Few teeth replacement
2. Stable ridge
3. Suitable for flangeless design
87
Indications for metal backing
1. Single tooth replacement
2. Stable ridge
3. Flangeless design
88
Indications of flanged design
1. Indicated where there is significant loss of residual ridge
2. Ideal for soft tissue support
3. Ideal for long edentulous span
4. Less hygienic
89
Indications for flangeless design
1. Indicated where there is minimal loss of residual ridge
2. Ideal for short edentulous span
3. More hygienic
4. Mimics fixed partial denture pontic
90
What is a partial denture?
A prosthesis that replaces one or more teeth, but not all of the natural teeth and supporting structures.
It is supported by teeth and/or mucosa. It may be fixed or removable.
91
What is a clasping unit?
A unit of RPD that engages an abutment tooth as to resist displacement of the prosthesis from the basal seat tissues.
Includes; retentive arm, reciprocal arm, rest and minor connector
92
Clinical protocol of RPD design
1. Assessment
2. Primary impression
3. RPD design
4. Teeth preparation
5. Definitive impression
6. Framework casting
7. Framework try-in
8. Occlusal record
9. Teeth set up
10. Try in
11. RPD processing
12. Insertion
13. Review
93
Consequences of partial edentulism
1. Compromised function and comfort
2. Tooth movement
3, Aesthetic limitations
4, Compromised phonetics
5. Increased risk of tooth wear
6. Further loss of residual ridge 7. Overloading of the remaining teeth
8. Deficient mastication
94
What are the benefits of RPD?
1. Functional improvements
2. Aesthetics restoration
3. Phonetics restoration
4. Stability of the arch
5. As preparation for complete dentures
6. Psycho-social improvements
95
What are the consequences of RPD?
1. Plaque accumulation and oral hygiene
2. Mucosal inflammation
3. Ulceration
4. Trauma from RPD components
5. Maintenance
96
What is the likelihood of caries with RPD?
There is a 6 times increase in caries rate with RPD
97
Why is metal RPD preferred over acrylic?
1. Less bulk
2. Natural transmission of heat
3. Hygienic - less plaque
4. Support
5. Stability
6. Patient comfort
98
Alternative RPD treatments
1. Fixed prosthesis
2. Implant prosthesis
3. Shortened dental arch
4. Complete denture
99
What are the stats for an average smile line?
Found in 70% of the population
75-100% display of maxillary incisors
100
What are the stats for a low smile line?
20% of the population
Less than 75% display of maxillary incisors
101
What are the stats for a high smile line?
Found in 10% of the population
Complete display of dental tissues and associated gingival band
102
What is the purpose of diagnostic casts?
1. Partial denture design
2. Occlusal assessment
3. Trial treatment
- occlusal adjustment
- diagnostic wax-up
- diagnostic set-up
- provisional denture
103
Classification of patients
1. Adaptive/philosophic
2. Exacting
3. Indifferent
4. Maladaptive
104
Traits of an adaptive/philosophic patient
1. Highly motivated
2. Sensible
3. Calm
4. Rational
5. Confident about dentists abilities
Good prognosis for patient
105
Traits of an exacting patient
1. Precise
2. Hard to please
3. Overly concerned about aesthetics and function
4. Dictates treatment
5. Expects repeated effort from the patients
Prognosis depends on the dentists abilities to address patient's concerns
106
Traits of an indifferent patient
1. Unconcerned about aesthetics and function
2. Not willing to persevere with dentures
3. Often persuaded by someone else
Prognosis is generally unfavourable, unless instructions and education are effective and successful
107
Traits of a maladaptive patient
1. Poor health and neglected dental condition
2. Emotionally unstable
3. Feeling of guilt and insecurity
4. Often blame the dentist
5. Feels that no-one can help them
Unfavourable prognosis and referral is indicated
108
Treatment steps
1. Present treatment options
2. Phase 1: Pre-prosthetic management
3. Prosthetic phase
4. Recall/Review and maintenance
109
What is stabilisation in the pre-prosthetic phase of management?
Dental procedures that need to be undertaken before prosthodontics treatment can be commenced. Especially caries control and periodontal health - as these are required for oral health stabilisation.
110
Available treatment options
1. No treatment
2. Shortened dental arch
3. Orthodontic treatment
4. Fixed partial denture
5. Removal partial denture
6. Complete denture
7. Implant supported prosthesis
111
When is no treatment indicated?
1. Long standing space between teeth with no drifting or over-eruption
2. No aesthetic implications
3. No functional limitations
4. Replacement of missing teeth
112
What is shortened dental arch?
Occlusion with no molars.
- Requires a minimum of 4 occluding units
- No implications on masticatory efficiency, oral comfort or signs/symptoms of mandibular dysfunction
- Most patients can function with shortened dental arch
113
When are fixed partial dentures used (bridge)?
1. For few teeth replacement
2. When there are sound abutments at both ends of an edentulous area
3. Adequate ridge and bone level in the edentulous area
4. Usually indicated when the abutment teeth are restored
5. More hygienic than RPD
114
Disadvantages of FPD over RPD?
1. More expensive
| 2. Invasive to teeth - prep adjacent teeth
115
Reasons for choosing FPD and RPD
FPD - for short space
| RPD - for long span
116
Indications of implant prosthesis
1. Indicated if adjacent teeth are not restored or minimally restored
2. Suitable if there is no distal abutment
3. Closest replacement to natural teeth
4. Very expensive
117
Indications for complete dentures
1. Very few teeth remaining
2. Remaining teeth are in compromised situation
3. Uncontrolled caries and periodontal issues
118
Indications for removable partial denture
1. Lengthy edentulous span (loss of >2 posterior teeth, > 4 incisors, one canine and 2 other contiguous teeth)
2. No posterior abutment for FPD
3. Bilateral edentulous area
4. Excessive alveolar bone loss
5. When complete denture can be postponed
6. Immediate tooth replacement
7. Patients with financial limitations
119
Principles of RPD design
1. Simplicity
2. Hygienic
3. Conservative
4. Strategic
5. Aesthetic
120
What is "simplicity" for RPD design?
1. Repairable
2. Maintainable by the patient
3. Easily handled by the patient
4. Cleansable
121
What is "conservative" for RPD design?
1. Ensure the right RPD treatment for the patient
2. Less coverage and bulk
3. Minima interference with occlusion
122
What is "strategic" for RPD design?
1. Should accommodate future modifications
123
What is "hygienic for RPD design?
1. Plaque accumulation
2. Mucosal inflammation
3. Trauma from RPD components
4. Maintenance
5. Occlusal stability and potential for wear
124
How do you enhance oral hygiene with RPD?
1. Minimise tooth and free gingiva coverage
2. Soft tissue coverage should be on the palate and residual ridge (at least 3mm from the free gingival margin)
3. Flangeless design is preferred
4. Gingival relief to minimise risk of injury, irritation and plaque accumulation
125
What is the sequence of RPD design?
1. Classification
2. Path of insertion and surveying
3. Support
4. Retention (direct and indirect)
5. Bracing and reciprocation
6. Connectors (major and minor)
7. Resin retention
126
What is the Kennedy classification?
Kennedy classification is the most widely accepted classification for partial edentulism.
127
What is the Kennedy Class I classification?
Bilateral edentulous areas located posterior to the remaining natural teeth
128
What is the Kennedy Class II classification?
Unilateral edentulous area located posterior to the remaining natural teeth
129
What is the Kennedy Class III classification?
Unilateral edentulous area with natural teeth at both ends
130
What is the Kennedy Class IV classification?
Single bilateral anterior edentulous area crossing the midline
131
Applegate's rules for applying the Kennedy classification
1. Classification should follow extraction
2. If the 3rd molar is missing and is not replaced, it is not considered in classification
3. If the 3rd molar is present and to be used as an abutment tooth, then it is considered in the classification
4. If the second molar is missing and not to be replaced, it is not considered in the classification
5. The most posterior edentulous area determines the classification
6. edentulous areas other than those that determine classification and known as modification spaces
7. The extent of the modifications is not considered, only the number of modifications is noted
8. There is no modification space for class IV
132
How is the path of insertion determined?
On a surveyor
133
What is support obtained from?
Support is resistant to vertical forces towards the gingival tissues.
Support is obtained from rest seats, ridges and the palate.
134
What is retention obtained from?
Retention is resistance to removal of the RPD during function.
Retention is provided by mechanical means (clasps), muscular control, and physical forces (surface tension, adhesion forces, cohesion forces, surface adaptation)
135
What is indirect retention?
A feature of RPD that reduces the tendency of a denture base to move in an occlusal direction or rotate about the clasp axis.
136
What is bracing and reciprocationg?
Resistance to horizontal forces applied on the denture during function - reducing trauma to the periodontal ligament
137
What is resin retention?
Component of the RPD framework that connects the metal framework to the acrylic resin (mesh, pins and plates)
138
What are the aims of primary impressions?
1. Diagnostic tool
2. Model survey
3. RPD design
4. Custom tray fabrication
5. Pick-up impression of existing RPD
6. Opposing model
139
What are the requirements of primary impressions?
1. Accurately record teeth and soft tissues
2. Taken with stock tray and alginate impression material
3. Full arch
4. Fully extended
5. Border moulded
6. Free of deficiencies
140
Step in primary impression
1. Prepare the patient
2. Tray selection
3. Tray try-in
4. Tray modification
5. Take impressions
6. Impression evaluation
7. Disinfect and transport impressions
141
Patient preparation
1. Explain the procedure and position the patient.
2. Patient position - upright position to prevent flow backwards.
3. Protection - clothes and eye protection.
142
Tray selection
1. The stock tray should allow adequate thickness of the impression material.
2. A space of 5-7mm is required between the tray and and tissue.
- The tray should be short of the labial vestibule and slightly beyond the vibrating line on the palate.
- The tray should cover all anatomical features
- There must be 3mm space between the borders of the tray and oral structure
143
Tray try-in
1. Retract one cheek with an index finger
2. Push the other cheek gently with the outer-side of the tray
3. Rotate the tray into position above the teeth
4. Seat the tray on teeth and soft tissues
144
Tray modifications
1. For under-extension - add periphery was. For overextension - trim the overextended tray borders
2. Apply alginate adhesive on the tray - to prevent separation of alginate from the tray
3. Make the material - use the mixing bowl to mix powder and water into a creamy mix (in 60s)
4. Load the tray. The mandibular tray should be loaded from each side. The maxillary tray should be loaded from the posterior border and then placed forwards
145
Impression taking
1. Lightly dry the teeth and mucosa
2. Seat the tray carefully in the mouth with correct midline alignment
3. Place pressure evenly with fingers and hold into patients mouth
4. Prior to initial set, manually and functionally activate all the muscles, frenal attachments and tongue
146
Mandibular impression taking
1. Stand to the side and in front of the patient
| 2. Support the lower jaw while the material is setting
147
Maxillary impression taking
1. Stand behind the patient
2. Seat the tray in position
3. Place the posterior tray edge first and press forward
4. Support the patients head while the material is setting
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Impression evaluation
1. Rinse the impression with water and inspect
- The material should be firmly attached to the tray
- No large voids or tears in the impression
- All important anatomy recorded
- Well recorded sulcus
2. Pour the impression with dental stone
149
Why are study models useful?
1. Special tray fabrication
2. Surveying and undercut determination
3. Partial denture design and planning
4. Diagnostic set-up
6. Model duplications
150
What is surveying?
Part of the diagnostic procedure. Surveying is an integral part of RPD design and fabrication.
151
What are the aims of surveying of diagnostic casts?
1. Determines the most suitable path of insertion
2. Identifies parallel surfaces and proximal tooth surfaces that can act as guiding planes
3. Determines soft and hard tissue undercuts
4. Identifies survey lines on abutment teeth
152
What is a guide surface/plane?
Two or more parallel axial surfaces on abutment teeth which can be used to limit the path of insertion and improve stability of the RPD. May need to be prepared.
153
What is the path of insertion?
The path followed by the denture from its first contact with the teeth until it is seated. Coincides with the path of withdrawal and may coincide with the path of displacement.
Single paths of insertion can be established if sufficient parallel guide surfaces are contacted by the denture. Whereas, multiple paths of insertion will exist where parallel guide surfaces are not applied.
154
Why is a single path of insertion desirable?
1. Equalises retention on all abutments
2. Provides bracing and cross arch stabilisation
3. Allows the denture to be removed without encountering interferences
4. Provides frictional retention from contact surfaces on the teeth
155
What is the path displacement?
The direction in which the denture is displaced during function.
The path of displacement is variable, but is assumed to be at right angle to the occlusal plane.
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What is the surveying procedure?
1. Preliminary visual assessment of study cast
2. Initial survey
3. Analysis
4. Final survey
157
Process of preliminary visual assessment
1. Each cast should be evaluated when the occlusal plane is parallel to the bench
2. Identify soft and hard tissue undercuts
158
Process of initial surveying
1. Position the cast horizontal to the occlusal plane
2. The teeth and ridges are surveyed to identify undercuts
3. Use the undercut gauge to measure the undercut
159
Process of analysing surveying
Analyse;
1. Appearance
2. Interference
3. Retention
4. Path of insertion
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What is the aim of surveying?
Aims to locate and measure the undercut.
- If the vertical path of insertion is decided, the it will be the final surveying
161
RPD construction steps
1. Primary impressions
2. Diagnostic casts
3. Surveying
4. RPD design
5. Tooth preparation
6. Definitive impression
7. Framework casting
8. Framework try-in
9. Jaw relation record
10. Teeth set-up
11. RPD try-in
12. RPD precessing
13. RPD insertion
14. RPD review
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What does tooth preparation involve?
1. Establishment of guide planes
2. Preparation of rest seats
3. Modification of unfavourable survey lines
4. Establishment of retentive areas
163
What is the rationale of tooth preparation?
1. Enhances the performance and acceptance of RPD
| 2. Reduces the negative consequences of wearing the RPD
164
When should tooth preparation be conducted?
1. Should be planned after articulating the study models and RPD design
2. Should be done in 2 stages
a) Teeth preparation on the study model
b) Definitive intraoral preparation
165
Principles of tooth preparation
1. Should be on sound enamel
2. Should be confined to enamel
3. Produced by rotary instruments
4. The rough enamel surface should be smoothed and polished
5. Topical fluoride should be applied following tooth preparation
166
Tooth preparation sequence
1. Guide planes
2. Rest seats
3. Modification of unfavourable survey line
4. Addition of retentive area
5. Evaluation
6. Fluoride application
167
Aims of guide planes
1. Increased stability
2. Reciprocation
3. Improved appearance
4. Enhance retention
168
1. Preparation of guide planes
1. Prepared prior to rest seats
2. Approximated from the study model
3. 2-3mm wide vertically
4. 3-4mm wide horizontally
5. About 0.5mm in the enamel
6. Extended lingually for aesthetics
169
What is the aim of rest seat preparation?
1. Produces favourable tooth surface for support
2. Prevents interferences from occlusion
3. Reduces the prominence of rests
4. Allows for adequate material bulk
170
2. Preparation of rest seats - posterior teeth
1. All rest seats should be less 90 degrees
2. Occlusal surface reduction
3. Spoon shaped morphology
4. Should be 3mm wide
5. At least 1.5mm deep, the centre is the deepest portion
6. The base of the rest seat should be 1/3 the width of the bucco-lingual tooth dimension
7. The length should be 3mm long
8. 1/3 the mesio-distal premolar dimension
9. 1/4 the mesio-distal molar dimension
10. if the rest seat is next to a adjacent tooth, a lingual flare should be included, this provides space for the minor connector
171
Rest seat preparation - anterior teeth
1. Cingulum rest seat - maxillary canines are ideal as they have prominent cingulum
172
Evaluation of the rest seat preparation
1. Verify the occlusal reduction
2. Ask the patient to bite on a piece of softened pink wax
3. Measure the wax thickness
4. Ensure that the occlusal rest is smooth - confirmed with ball burnisher
5. Ensure the rest seat is positive
6. No sharp line angles
7. Polish the rest seats
173
3. Modify unfavourable survey lines
1. High survey lines requires occlusal placement of clasp arms - especially as they can cause occlusal interferences
174
4. Addition of retentive area
1. Addition of retentive areas should be considered if the survey line is missing on abutment tooth
2. The created undercut should follow the retentive arm morphology
