1
Q
Tooth loss would result in: [4]
A
- Loss of appearance and clear speech: affected by loss of upper anterior teeth
- Loss of masticatory function: need sufficient teeth to masticate food stuffs with ease
- Tooth Drifting and over-eruption:
- Loss of occlusion: normal relationship between maxilla and mandible determined by ICP can become less distinct and eventually lost
2
Q
Harmful effects of denture wearing [5]
A
- Plaque accumulation –> PD
- Direct trauma from components
- Transmission of excessive functional forces (increase mobility if excessive force to a tooth, incisal rest transmits a more favourable vertical load)
- Occlusal error:
- Premature contact on natural tooth –> damage to tooth/PDL
- Localised mucosal inflammation and resorption of underlying bone
- Abnormal closing pattern –> increased demand on muscle of mastication –> facial pain - Damage to periodontium (Excessive force–> destruction of periodontal support of abutment teeth + mobility)
3
Q
Advantages of fixed prosthesis [4]
A
- Reported clinical complication frequencies are lower ( Better patient acceptance and tolerance+ Interferes less with plaque removal)
- Median life of conventional FPs has been reported to be in the region of 20 years, whereas RPDs have a service life of around 10 years
- More retention and stability
- More aesthetically acceptable
4
Q
Advantages of RPD [6]
A
- Non-invasive: Do not require extensive modification of abutment teeth
- Versatile: Applicable to wide variety of clinical situation
- Removable to assist cleaning
- Treatment of extensive tooth loss (FPs at an increased risk if abutment teeth have undergone endodontic treatment (fracture))
- Necessary adjustments and repairs are much easier to carry out
- Initial cost of RPD is lower than that of FP
5
Q
what is a major connector and what are its functions
A
The unit of a RPD that connects the parts of one side of the dental arch to those of the other side.
Functions:
1. To provide unification
2. To provide rigidity to the denture
6
Q
what is a minor connector and what are its functions
A
A unite of a RPD that connects other components (i.e. direct retainers, indirect retainers, denture base, etc.) to the major connector.
Functions:
1. To provide unification
2. To provide rigidity to the denture
7
Q
what is a minor connector and what are its functions
A
A unit of a RPD that connects other components (i.e. direct retainers, indirect retainers, denture base, etc.) to the major connector.
Functions:
1. To provide unification
2. To provide rigidity to the denture
8
Q
Direct retainers
A
A unit of a RPD that provides retention against dislodging forces. Commonly called a "clasp". It is composed of 4 elements: 1. Rest 2. Retentive arm 3. Reciprocal arm 4. Minor connector
9
Q
Indirect retainers
A
A unit of a Class I or II RPD that prevents or resists movement or rotation of the base away from the residual ridge (Residual ridge is a term used to describe the shape of the clinical alveolar ridge after healing of bone and soft tissues after tooth extractions. ). It is usually composed of 1 element which is called a rest.
10
Q
Denture base
A
A unit of a RPD that covers the residual ridge and supports the denture teeth
11
Q
Information that can be obtained from surveying a cast is: [5]
A
- Selection of path of insertion
- Selection of guiding planes
- Mark out wanted and unwanted undercuts
- Indicate tooth preparation
- Show where potential sources of retention are located
12
Q
Analysing rods are for [2]
A
- Identify undercut areas
2. To determine the parallelism of surfaces (guiding plane) without marking the cast
13
Q
Function of Graphite Marker [1]
A
Identify and mark the position of maximum convexity (survey line)
*The tip of the marker should be level with the gingival margin
14
Q
Function of undercut gauges and their sizes and respective materials [1+3]
A
- Use to measure the extent of horizontal undercut
- 25mm (Cobalt Chromium)
- 50mm (Stainless Steel)
- 75mm (Gold)
15
Q
Function of trimming Knife/Wax Knife + how it’s used [4]
A
Used to eliminate unwanted undercuts on Master Cast
1. Wax is added to “block out” the undercut
2. Excess is removed with the trimmer
3. Modified surfaces are parallel to the chosen path of
insertion
16
Q
Path of insertion/withdrawal: [3]
A
- Path followed by the denture from its first contact with the teeth until it is fully seated
- Coincide with the path of withdrawal, may or may not coincide with path of displacement
- Occasionally a rotational path of insertion can be used (Class IV)
17
Q
Path of displacement [2]
A
- Direction in which the denture tends to be displaced in function
- Path is variable but is assumed to be at right angles to the occlusal plane
18
Q
what are guide planes and their functions? [4]
A
Two or more parallel tooth surfaces which determine the path of insertion and withdrawal of a partial denture
Functions:
1. Limit Path of insertion and make clasp effective (resist displacement of the denture in directions other than POW)
2.Reduce dead spaces (Permits an intimate contact between saddle and tooth which allows the one to blend with the other)
3. Provide frictional retention and make clasp effective
(Allow reciprocating component to maintain continuous contact with a tooth when denture is displaced occlusally, retentive arm is forced to flex –> clasp’s elastic deformation creates retentive force)
19
Q
Undercut only exists in relation to ______ path of insertion and withdrawal and should be distributed ____. The final design of the clasps should be deferred until the retentive ____ ____ has been revealed [3]
A
particular, equally, undercut distribution
20
Q
What are dead spaces/unwanted undercuts and how can you keep them to a minimum? [3]
A
Any undercut area beneath the survey line of the abutment teeth, adjacent to the framework or other teeth enclosed by the framework is called a dead space where food debris can stagnate
Keep them at a minimum by
1. Averaging them (tilting the cast)
2. Removing tooth substance (creating guide planes)
21
Q
Survey line are… [1]
Function of 1st survey line… [1]
Function of 2nd survey line… [1]
A
Lines on a cast indicating the maximum convexity of a tooth or the alveolar process in relation to a planned path of insertion
Functions of 1st survey line:
1. find undercuts which can be used to resist movement in the path of displacement
Functions of 2nd survey line:
1. Aesthetic (could be eliminating dead spaces anteriorly)
22
Q
Steps in surveying are: [5]
A
- Mark tripod and reference point on the cast
- POI and Position of guiding plane established (analyzing rod)
- 1st survey line and 2nd survey line (tilt the cast) only if needed
- Mark position of guide plane
- Use undercut gauge to measure depths of undercuts
required by clasp
23
Q
Requirements of a guide plane are [3]
Which burr should be used for guide plane prep? [1]
A
- Curved buccolingually, straight occlusogingivally
- Width 2/3 of buccal/lingual cusp (buccal-lingually)
- Depth 2-3mm (vertically)
Preparation of guiding plane is achieved using a cylindrical diamond
24
Q
Why is a high survey line unfavourable? [1]
How would you lower a survey line? [2]
A
Clasp placed too close to the occlusal surface may create and occlusal interference –> result in deformation of the clasp, High clasp arm is noticeable to patient and may interfere with mastication
Method
- Similar procedure to that of preparing guiding plane, differing in only in that a slight shift in angulations of the diamond is made towards the central long axis of tooth
- Maintaining this small deviation toward long axis of tooth, tooth structure is removed until the gingival part of the preparation occupies the desired position
25
Why is a low survey line unfavourable? [1]
| How would you higher a survey line? [2]
Unfavourable because:
- Clasp cannot be place of the tooth since no retentive/undercut area
- Clasp placed too close to gingival surface may promote plaque accumulation/trap food easily --> PD
1. Build Composite of tooth surface to higher the survey line
2. composite should look similar to guild plane, broad area of attachment is desirable (Reduce the chance of restoration being displaced; produce a contour suitable for clasping) (And more surface to bond to therefore stronger?)
26
The term "support" means [1]
Resistance to vertical force directed towards the mucosa
27
The term "Tooth-borne" means [1]
Denture is supported on adjacent teeth by components such as occlusal rests, force is transmitted to the bone via teeth and periodontal ligaments
28
The term "Mucosa-borne" means [1]
Denture rests solely on the mucoperiosteum, force is transmitted through that tissue
29
It is generally accepted that each healthy standing tooth has enough spare capacity not only ts own loading but that of _______ similar teeth [1]
one and a half
30
Mucosa-borne denture is likely to be _______ in the maxillary jaw than in the mandibular as _______ ensures more effective support [2]
more successful, palatal coverage
31
Factors considered in planning support in dentures [3]
1. Root area of the abutment teeth
- Most of the vertical force will be transmitted by the oblique fibres of the periodontal ligaments (wont function effectively if tooth is tilted)
- Governed by the type of tooth and its periodontal health
2. Extent of the saddles
- The smaller the saddle, the lower the functional force
3. Expected force on the saddle
- As the artificial occlusal surface increases in area, the magnitude of force increases
- Functional force created by opposing denture will be less than that arising from several natural teeth
32
Functions of rest [7]
1. Provide tooth-borne support for the denture
- Placed on the teeth in a way that force of occlusion is directed along the long axis of the tooth
2. Provide Bracing function
- Certain shape of rest will transfer some of the horizontal functional force
3. Maintaining components in their correct position
- Components will not sink into underlying tissue thus holding various component in the position. i.e. clasps
- Improve the efficiency of a retentive clasp and keeping it clear of the gingival margin, avoiding trauma to the mucosa
4. Protecting the denture/abutment tooth junction
- Provide an effective roof to the space between saddle and abutment tooth --> protect the gingival tissues from food being forcibly pushed down by masticatory forces
5. Reciprocation
- Rest provides effective reciprocation for a retentive clasp
6. Preventing overeruption
- In the absence of an opposing tooth, well-retained occlusal rest is able to prevent overeruption
7. Providing indirect retention
- Prevent the denture from moving away from the ridge (part of reciprocation)
33
Why rest on abutment should be placed mesially in free-end saddle? [2]
1. Rest placed distally may allow occlusal force to exert a tilting movement on the tooth
2. Mesial rest resist the tilting force by splinting effect of the teeth more anterior in the arch (if there is a tooth anterior to abutment)
34
Reduction in the area of the occlusal table of posterior artificial teeth is likely to play an important part in the success of a mandibular RPD, why? [2]
1. Reduce the force to the underlying tissue during mastication as penetration of the food bolus by the teeth is easier
2. Increase in space made for tongue that may well have spread laterally following extraction of the natural teeth
35
Why is it necessary to extend the area of saddle to the maximum? [2]
1. Increase the area available for support
| 2. Reduce the force per unit area falling on the edentulous ridge
36
```
Requirements of an occlusal rest seat prep? [4]
Which burr(s) should be used? [2]
```
1. Covers 2/3 of marginal ridge and tapers into adjacent fossa
2. Deeper in fossa and direct forces along the long axis of the tooth
3. Allow >0.5mm thick rest (1.5mm(red book); 1mm (bdj) is necessary for adequate bulk and strength)
4. No occlusal interference
Burrs:
1. ball shaped diamond/carbide
2. Appropriate size: No.6 for molar and No.4 for premolar
37
Requirements of an cingulum rest seat prep? [4]
| Which burrs should be used? [2]
1. Cover at least half of the tooth
2. Cutting into a half moon groove such that the rounded groove is lowest at the marginal ridge
3. Placed in the lingual enamel just incisal to the cingulum
4. Deeper toward the centre of the tooth than the cingulum to provide positive seat
Burrs:
1. Started with a suitable round diamond bur (no.2) by cutting a half moon groove (opened proximally first)
2. Labial wall should blended into original lingual slope with a small cylindrical diamond
38
Requirements of an incisal rest seat prep? [4]
| Which burrs should be used? [2]
1. Prepared in the form of a rounded notch at an incisal angle with deepest portion of the preparation towards the centre of the tooth
2. Notch levelled in both lingually and labially
Burrs:
1. Cylindrical and round diamond (red book),
2. Tapered diamond (bdj)
39
Problems with incisal rests?
| Why should one prepare incisal rests?
1. Inferior appearance
Because lingual surface of mandibular anterior tooth is usually too vertical and cingulum is too poorly developed to allow preparation of cingulum rest seat
40
What are the different upper jaw connectors? [3]
1. Palatal Plate
2. Palatal Bar
3. Ring connector
41
Advantages and disadvantages of palatal Plate?
Advantages:
1. Forces can be shared between teeth and mucosa by utilizing a larger connector that extends posterior to the junction of hard and soft palates
Disadvantages
1. Weight of large metal connector can contribute to displacement of the prosthesis
2. Position of the post-dam(a posterior extension of a full denture to accomplish a complete seal between denture and tissues) cannot be altered should it prove to be poorly tolerated by the patient
42
Palatal bar features: [3]
1. Narrow anterio-posteriorly
2. Thick occluso-gingivally
3. Palatal bar can be bulky
43
when is ring connector used? [2]
1. Used in cases where multiple saddles widely distributed around the arch
2. Used when prominent palatal torus would contraindicate a mid-palatal plate/bar
**If selected, the anterior bar must be carefully positioned and shaped to blend with the contours of the palatal rugae
44
Main anatomical constraint for lower jaw connector design is...? [1]
The relatively small distance between the lingual gingival margin and the functional depth of the floor of the mouth
45
Anatomical Constraints that prevent the use of lingual/sublingual bar [3]
1. Lack of space between gingival margin and floor of mouth
2. Prominent lingual fraenum may compound the problem
3. Presence of Mandibular torus
46
Lingual Bar features [4]
1. Bar must clear the gingival margins by at least 3.5mm (red book), bar itself is normally 4mm(Dyson) and must be clear of the reflected sulcus, thus at least 7mm (red book) between the sulcus reflexion at its highest point
* So need to have 7mm of space between gingival margin and floor of mouth
2. Placed as low as the functional depth of the lingual sulcus will allow
3. Maximum cross-sectional dimension of the connector is oriented vertically (As supposed to horizontally for sublingual bar)
4. Any downward movement of the bar would traumatize the underlying tissue, therefore not recommended if there are no occlusal rest
47
Sublingual bar features [2]
1. Can be used in shallow lingual sulci and be kept further away from the gingival margin
2. Its dimension are determined by a specialized master impression technique that accurately records the functional depth and width of the lingual sulcus --> dimensions are retained on the master cast, waxes up and fill the width at its maximum functional depth --> results in a bar whose maximum cross sectional dimension is oriented horizontally
48
what does a lingual plate do? and When is it used? [2]
| What is the disadvantage? [1]
1. Covers most of the lingual aspects of the teeth, the gingival margin and the lingual aspect of the ridge, it terminates inferiorly at the functional depth of the sulcus
2. Used when there is insufficient room for a lingual bar, or if indirect retainer is required
Disad: Tendency to encourage plaque formation
49
what does a dental bar do? and When is it used? [2]
| Disadvantages? [2]
1. Covers lingual aspects of teeth, does not cover gingival margins
2. Used when there’s insufficient room between gingival margin and floor of mouth
3. Clinical crowns are long enough, lies on the teeth so avoiding gingival damage
Disad:
1. Pt tolerance places some restriction on the cross-sectional area of this connector and thus reduction in rigidity
2. Metal will show through gaps if there’re spaces between incisors
50
what does a buccal/labial do? and When is it used? [2]
| Disadvantages? [2]
Buccal bar lies on the mucosa on the outside of the alveolus and the denture must be stable to avoid trauma to the soft tissue
Used when lower anterior teeth are inclined lingually
Can also be used in upper denture (more common in lower)
51
What are the different lower major connectors? [5]
1. Lingual Bar
2. Sublingual bar
3. Lingual Plate
4. Dental Bar
5. Buccal/Labial Bar
52
Advantages of acrylic dentures? [2]
| Disadvantages? [4]
Adv.
1. Relatively low cost
2. Easy to modify
Disadv.
1. Material is weaker and less rigid than metal alloy --> more likely to flex or fracture during function
2. Acrylic is radiolucent so that location of the prosthesis can prove difficult if swallowed or inhaled
3. Have high potential for damage to the periodontal tissue and edentulous ridge because of the difficulty to provide adequate support
4. Plaque retentive and may cause other complications
53
Indications for acrylic dentures [4]
1. Denture is required during the phase of rapid bone resorption following tooth loss
2. Remaining teeth have a poor prognosis and their extraction and subsequent addition to the denture is anticipated
3. Required the use of diagnostic denture (eg. To determine whether the pt can tolerate increase OVD)
4. Denture provided for a young patient where growth of the jaws and development of the dentition
are still proceeding
54
Spoon Denture [2]
Ad [1]
Disad[1]
1. Popular for the replacement of one or two anterior teeth
2. Relies on the forces of adhesion and cohesion for retention and must have labial flange to prevent displacement palatally and rotation under occlusal load
Adv - Reduces gingival margin coverage to a minimum
Disadv – risk of inhalation or ingestion
55
When is "Every denture" used? [1]
| Features [5]
Used for restoring multiple bounded edentulous area
1. Retention is gained by using opposing undercuts
2. Connector borders are at least 3mm from the gingival margin
3. Point contacts between artificial and abutment teeth are established to reduce lateral stress
4. Posterior wire stops (lie on survey line) are included to prevent distal drift of the posterior teeth
5. Flanges are included to assist the bracing of the denture
56
what is "Overlay denture"? [1]
What are the 2 types? [2]
When are they used?
Type of partial denture which covers the occlusal surfaces of one or more teeth
Temporary:
1. Used for treatement of the temporomandibular pain dysfunction syndrome / patients with severe toothwear and with reduction of OVD --> helps re-establishing OVD prior to fixed restorations
2. Used to overcome occlusal disharmony until the symptoms have ceased and more permanent treatment instituted
3. Provides an even occlusal plane
4. Allow a smooth movement between eccentric positions and centric occlusion
Permanent:
1. Used to make the occlusal plane even, usually requires coverage of a few teeth
2. Uneven occlusal plane makes proper arrangement of eccentric occlusions difficult, premature contact on the non-working side in lateral occlusion and posteriorly in protrusive occlusion are difficult to eliminate
57
Revise comparison between Co-Cr and acrylic resin based dentures.
Go revise
58
Retention is
Resistance to movement away from tissues provided by clasps/attachments placed close to the saddle
59
Retention of RPD can be achieved by...[4]
1. Use of mechanical means such as clasps by engaging undercuts on the tooth surface
2. Use of mechanical means by selecting a path of insertion which permits rigid components to enter undercut areas on teeth or on ridges
3. Harnessing the patient’s muscular control - acting through the polished surface of the denture ( Cover mreo of the palate in order to harness the physical force of retention)
4. Using the inherent physical forces – arise from coverage of the mucosa by the denture (Important in Class I cases, as there is tendency for retentive clasps to lose some of their efficiency with the passage of time, retention become more dependent upon physical forces
and muscular control in long terms)
60
The 2 types of clasps are [2]
Occlusally approaching clasps – those which enter the undercut from the occlusal area of the tooth
Gingivally approaching clasps – those which enter the undercut by crossing the gingival margin
61
Flexibility of clasp is dependent on...? [5]
1. Cross- Section – Round cross section clasp will flex equally in all directions, whereas a half round clasp will flex more readily in the horizontal than in the vertical plane
2. Length – the longer the clasp arm, the more flexible it is
3. Thickness – If thickness is reduced by half the flexibility is increased by a factor of eight
4. Curvature – clasp curved in two planes increases flexibility of the clasp arm
5. Alloy used – force required to deflect the Co-Cr over the bulbosity of tooth is twice that of Au clasp
62
Why is I-bar preferred on premolars? [1]
Co-Cr clasp is likely to distort if the arm is too short on a premolar. A shorter clasp is less flexible
63
Comparison of occlusally and gingivally approaching clasp [3]
1. Appearnace
- Gingivally approaching clasp has more potential being hidden in the DB aspect of tooth provided that there is suitable undercut area for the clasp
2. Retention
- Only terminal third of an occlusally-approaching clasp should cross the survey line and enter the undercut area. If too much of clasp arm engages the undercut --> high force required to move it over the maximum bulbosity --> put considerable strain on the fibres of PDL - exceed proportional limit and distort the clasp
- Gingivally approaching clasp contacts the tooth surface only at
its tip, the remainder is free of contact with the mucosa of the sulcus and gingival margin; Length of the gingivally approaching clasp arm can be increased to give greater flexibility which can be a positive advantage
3. Bracing
- Occlusally approaching clasp is more rigid --> capable of transmitting more horizontal force to the tooth and is a more efficient bracing component as a result
64
Factors affecting the choice of retentive clasp [6]
1. Position of the undercut
2. Health of the PDL
3. Shape of the sulcus
4. Length of clasp
5. Appearance
6. Occlusion
65
what is the RPI system? [2]
Rest,proximal plate, i-bar
1. Allow vertical rotation of a distal extension saddle into the denture-bearing mucosa under occlusal loading without damaging the supporting structures of the abutment
2. I-bar moves Mesial-buccally (further into undercut); plate swings mesially
66
What can one do if there's no undercut at all? [3]
1. Recontour part of the tooth with composite resin
2. Grind a depression in the enamel
3. Fit an inlay with a dimple or groove on the surface for a ball or ordinary arm to engage
67
Reciprocation is....[1]
Any component of a partial denture which prevent displacement of a tooth
68
Why is reciprocation needed? [1]
As tip of a clasp passes into, or resists removal from an undercut, it exerts a sideway force on a tooth (PDL can be damaged by this action) so a balancing or reciprocal action is needed to counteract
i.e. provided by a guide plane or a reciprocal arm, gives balancing force with no retention
69
Bracing is...[1]
resistance to horizontal components of force applied to denture as a whole
70
How can a denture be displaced? [1]
Horizontal force are generated during function by occlusal contact and by the oral musculature surrounding the denture --> forces may displace denture in both antero-posterior and lateral directions
71
Bracing can be achieved by [4]
1. Rigid portions of clasp arms
2. Rigid portions of plates
3. Maxilla - By major connectors and flange (prevent posterior displacement in Class IV)
4. Mandible – By coverage of the pear-shaped pad and by minor connector which contacts the ML surface of the premolar tooth
** Horizontal forces are resisted by placing rigid components of the denture (bracing components) against suitable vertical surfaces on the teeth and residual ridges
72
Indirect retention is [1]
| Which types of denture need indirect retention the most?
the resistance to movement away from the tissues provided by supporting components placed distant to the saddle on the opposite side of the potential axis of rotation
Indirect retention relates to saddles that cannot have a retainer at each end (Class I/II) or do not have pontics in a straight line between the abutment teeth (Class IV)
73
How can one achieve indirect retention? [2]
1. Rest in anterior teeth
2. Major connectors (eg. Lingual plate; extension of acrylic base around the anterior teeth; backward extension of the denture base)
Fulcrum is on the teeth (which do not move) and the effort is the tip of the clasps (which can move)
i.e. clasps placed close to saddles and rests placed distant to saddles
74
Factors influencing the effectiveness of indirect restoration [5]
1. Mechanical disadvantage of the denture design
2. Clasp axis should be placed as close as possible to the saddle and placing the indirect retainers as far as possible from the saddle
3. Support of the indirect retainers
4. Should cover a sufficiently wide area to spread the load and avoid mucosal injury (maxillary case)
5. When possible, indirect retainer should rest on a surface at right angles to its potential path of movement, otherwise, loss of support may occur due to movement of tooth by horizontal force
75
Problems with Kennedy Class III denture designs? [3]
1. Need to prepare the teeth
2. If abutment teeth lost periodontal support, maybe necessary to find other adjacent tooth
3. Long saddle might overload the supporting teeth
76
Problems of Support in Kennedy Class I/II dentures?
| Solutions?
1. Stress on mucosa --> pain, ulcer, bone resorption
- Extend the base widely so that load per unit area falling on the ridge is reduced
- Rest on teeth
- Teeth with small bucco-lingual width and small occlusal area should be used
- Support from edentulous ridge should be maximized by Mucodisplacing impression
2. Stress on abutment--> tending to lever the tooth distally --> weaken periodontal support --> torque
- Mesial rest
- RPI/RPA
- Splint the teeth
- Stress breakers
77
Problems of retention in Kennedy Class I/II dentures?
| Solutions?
Saddle will move away from the ridge
- Resist by clasp on abutment tooth
- Make use of indirect retention (diff major connector, cingulum rest)
Upper – use cingulum rest; palatal coverage
Lower – Use cingulum rest on anterior teeth; use dental bar/lingual plate;
78
Problems of stability in Kennedy Class I/II dentures?
| Solutions?
Saddle will move distally
- Mesial rest and its minor connector
- Mesial buccal undercut
- Mesio-distal grip
79
Problems of aesthetics caused by dead spaces in Kennedy Class IV dentures?
Solutions? [1]
Make use of flange (need to tilt the cast posteriorly in order to use flange)
80
Problems of retention in Kennedy Class IV dentures?
| Solutions?
Clasps cannot be placed on anterior teeth (due to aesthetics)
- Indirect retention on posterior teeth as distally as possible
- Use rotational path of insertion
1. Upward and forward rotation of anterior teeth are resisted by rests on the abutments
2. Rotation of the posterior part of the denture resisted by the clasps and minor connectors
3. Movement of saddle away from the mucosa will be resisted by direct retainer and rigid part of denture engaging the proximal undercut
81
Problems of posterior tilting for class IV dentures? [2]
1. DB undercut and complicated design
| 2. Aesthetic problem – clasp pointing backwards
82
Which landmarks define Frankfort plane? What is the significance of Frankfort plane?
Superior borders of the external auditory meatus (porion) to the left infraorbital notch (orbitale)
It is nearly parallel to the surface of the earth, and also close to the position the head is normal carried in the living subject.
83
What is Bennett Angle?
Angle formed by movement of balancing (non-working) condyle with sagittal plane during lateral jaw movement
84
Name four desirable properties or design of major connector
- Compatible with oral tissue
- Rigid
- Provides cross-arch stability thru the principle of broad distribution of stresses
- Does not interfere with and is not irritating to the tongue
- Does not substantially alter the natural contour of the lingual surface of the mandibular alveolar ridge or of the palatal vault
- Covers no more tissue than is absolutely necessary
- Does not contribute to the retention or trapping of food particles
- Contributes to the support of the prosthesis
85
What are the contraindications of using an I bar? (3 marks)
- Deep cervical undercut
- Bony undercut
- Shallow sulcus
- High frenal attachment
86
What is the purpose of periodic recall of patients treated with removable partial dentures? (3 marks)
- For evaluation of the response of the oral tissues, soft tissue changes
- Maintain oral health
- Evaluation of the acceptance of the prosthesis by the patient
- Evaluate patient oral hygiene
87
Describe the purposes of study casts
- Supplement the oral examination so the dentist can see all views of teeth better
- Allow an analysis of existing occlusion to let dentist plan ahead
- Permit topographic survey
- Communicate with patient and technician
- Fabricate custom trays
- Used as a reference point as treatment goes on
- A duplicate set of casts should be kept for records
- Facilitates design of prosthesis
- Trial preparation of duplicate casts
- Diagnostic wax up
- Indicate mouth preparation requirements
88
What is the problem of preparing an occlusal rest seat BEFORE contouring the guiding planes [1]
Contours of the occlusal rest seats will be altered, adjustements will be needed (Occlusal rest areas should be prepared that will direct occlusal forces along long axis of tooth)
89
What are the most common casuses of interference to the placement of a MANDIBULAR major connector? [2]
- Bony prominences (tori)
| - Lingually inclined premolars
90
Describe how you would disinfect an alginate impression before sending to the laboratory (3 marks)
- Rinse the impression under running water (avoid splashing) and shake off surface water
- Dip the impression in sodium hypochlorite solution. (The impression and tray must be totally immersed in the solution but should be removed within 1-2 seconds) Rinse under running water and shake off surface water.
- Dip again in sodium hypochlorite solution for 1-2 seconds
- Cover the impression with gauze dampened with the sodium hypochlorite and leave for 10 minutes
- Rinse well under running water and shake off surface water
- Hydrocolloid impressions should be covered with gauze dampened with water and placed in a polythene bag
- Attach a label indicating that the impression has been disinfected before dispatch to the laboratory
RPD
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