RPD Flashcards
Tooth loss would result in: [4]
- 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
Harmful effects of denture wearing [5]
- 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)
Advantages of fixed prosthesis [4]
- 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
Advantages of RPD [6]
- 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
what is a major connector and what are its functions
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
what is a minor connector and what are its functions
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
what is a minor connector and what are its functions
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
Direct retainers
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
Indirect retainers
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.
Denture base
A unit of a RPD that covers the residual ridge and supports the denture teeth
Information that can be obtained from surveying a cast is: [5]
- 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
Analysing rods are for [2]
- Identify undercut areas
2. To determine the parallelism of surfaces (guiding plane) without marking the cast
Function of Graphite Marker [1]
Identify and mark the position of maximum convexity (survey line)
*The tip of the marker should be level with the gingival margin
Function of undercut gauges and their sizes and respective materials [1+3]
- Use to measure the extent of horizontal undercut
- 25mm (Cobalt Chromium)
- 50mm (Stainless Steel)
- 75mm (Gold)
Function of trimming Knife/Wax Knife + how it’s used [4]
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
Path of insertion/withdrawal: [3]
- 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)
Path of displacement [2]
- 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
what are guide planes and their functions? [4]
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)
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]
particular, equally, undercut distribution
What are dead spaces/unwanted undercuts and how can you keep them to a minimum? [3]
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)
Survey line are… [1]
Function of 1st survey line… [1]
Function of 2nd survey line… [1]
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)
Steps in surveying are: [5]
- 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
Requirements of a guide plane are [3]
Which burr should be used for guide plane prep? [1]
- 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
Why is a high survey line unfavourable? [1]
How would you lower a survey line? [2]
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
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
- Build Composite of tooth surface to higher the survey line
- 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?)
The term “support” means [1]
Resistance to vertical force directed towards the mucosa
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
The term “Mucosa-borne” means [1]
Denture rests solely on the mucoperiosteum, force is transmitted through that tissue
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
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
Factors considered in planning support in dentures [3]
- 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 - Extent of the saddles
- The smaller the saddle, the lower the functional force - 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
Functions of rest [7]
- 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 - Provide Bracing function
- Certain shape of rest will transfer some of the horizontal functional force - 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 - 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 - Reciprocation
- Rest provides effective reciprocation for a retentive clasp - Preventing overeruption
- In the absence of an opposing tooth, well-retained occlusal rest is able to prevent overeruption - Providing indirect retention
- Prevent the denture from moving away from the ridge (part of reciprocation)
Why rest on abutment should be placed mesially in free-end saddle? [2]
- Rest placed distally may allow occlusal force to exert a tilting movement on the tooth
- 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)
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]
- Reduce the force to the underlying tissue during mastication as penetration of the food bolus by the teeth is easier
- Increase in space made for tongue that may well have spread laterally following extraction of the natural teeth
Why is it necessary to extend the area of saddle to the maximum? [2]
- Increase the area available for support
2. Reduce the force per unit area falling on the edentulous ridge
Requirements of an occlusal rest seat prep? [4] Which burr(s) should be used? [2]
- Covers 2/3 of marginal ridge and tapers into adjacent fossa
- Deeper in fossa and direct forces along the long axis of the tooth
- Allow >0.5mm thick rest (1.5mm(red book); 1mm (bdj) is necessary for adequate bulk and strength)
- No occlusal interference
Burrs:
- ball shaped diamond/carbide
- Appropriate size: No.6 for molar and No.4 for premolar