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BDS2 CDS Prosthodontics > Partial denture system of design > Flashcards

Partial denture system of design Flashcards

ILO 2.6a: be familiar with the design and choice of materials used in the production of partial dentures, along with the knowledge of laboratory procedures

1
Q

what are the alternative treatments to getting dentures?

A
  • no treatment
  • fixed prosthesis - conventional, resin bonded
  • implant retained prosthesis
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2
Q

what are the key principles of partial denture design?

A
  • replace lost teeth and tissues, restoring function, speech and aesthetics
  • minimise damage to adjacent teeth, restorations and tissues
  • designed with periodontal health in mind
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3
Q

why do clinicians design the denture not the technicians?

A

clinicians have seen the patient so understand:
* patient story and expectations
* condition of teeth and periodontium/oral health
* assessment of current dentures
* assessment of occlusion
* more complete understanding of alternatives
* to give clear cost information

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4
Q

what is the order of designing partial dentures?

A
  1. case assessment
  2. determine saddles
  3. choose denture base material
  4. choose path of insertion and delineate undercuts (survey)
  5. design support
  6. design retention
  7. design bracing/reciprocation
  8. connect saddles together
  9. indirect retention
  10. simplification
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5
Q

what is a saddle?

A

an area of oral mucosa where teeth are being replaced

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6
Q

what is Craddock classification? what does each classification represent?

A

classifies how the saddle is loaded
* class I: tooth borne
* class II: mucosa borne
* class III: tooth and mucosa borne
* class IV: implant borne
* class V: implant and mucosa borne

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7
Q

what is Kennedy classification? what does each classification represent?

A

classifies the position of the saddles
* class I: bilateral free end saddle
* class II: unilateral free end saddle
* class III: single bounded saddle not crossing the midline
* class IV: single bounded saddle crossing the midline

if there is more than one saddle, modifications are used but the most posterior saddle is the main classification

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8
Q

what KEnnedy classification is this?

A

Kennedy class II modification 2

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9
Q

what is the definition of support?

A

the resistance of a denture to occlusally directed load

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10
Q

what component of a denture provides support?

A

rests

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11
Q

what kinds of rests are there?

A
  • incisal rest
  • cingulum rest
  • occlusal rest
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12
Q

what is the difference between tooth support and mucosa support?

A

tooth support
* prevents/resists movement and directs load through PDL of abutment teeth then to alveolar bone
* allows the supported denture base feel like the natural dentition
* more comfortable for the patient
* protects soft tissue from trauma
* likely to stay in close contact with its supporting structures over time
mucosa support
* requires a large surface area to distribute load to the alveolar bone
* allows the denture base to move slightly as it is compressible
* can cause possible damage to adjacent gingival margins

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13
Q

what is the order of teeth with the highest to lowest crown to root ratio? how much can a healthy tooth carry?

A
  • molars
  • canines
  • premolars
  • upper central incisors
  • upper lateral incisors
  • lower incisors
  • a healthy tooth can potentially carry its own weight plus one and a half of similar teeth (x1.5)
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14
Q

how far should mucosal support be away from the gingival margin?

A

3mm as it will place pressure at the gingival margin

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15
Q

where is the primary and secondary support of the maxillary and mandibular arch?

A
  • primary support - hard palate (maxillary), residual ridge/buccal shelf to the buccal sulcus (mandibular)
  • secondary support - anterior hard palate, residual ridge (maxillary), residual ridge to the lingual sulcus (mandibular)
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16
Q

why should occlusal rests be large?

A
  • they apply large forces per unit area
  • large rests direct force down the long axis of the tooth to the PDL and alveolar bone
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17
Q

what are the disadvantages of incisal rests?

A
  • poor aesthetic appearance
  • may interfere with incisal occlusion
  • not recommended on wear facets
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18
Q

what are the advantages of cingulum rests?

A
  • aesthetically superior to incisal rests
  • apply stress at lower level so less rotational forces
  • less likely to break
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19
Q

what are the advantages of occllusal rests?

A
  • prevent movement of the RPD to the mucosa
  • assists the distribution of occlusal load
  • prevents over-eruption of unopposed teeth
  • helps determine the axis of rotation for free-end saddle PRDs
  • can provide indirect retention
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20
Q

what is the default position of rests with a bounded saddle?

A

immediately adjacent to the saddle - distal side of mesial tooth and mesial side of distal tooth

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21
Q

what is the default position of rests with a free end saddle?

A

not immediately adjacent to the saddle - mesially on the abutment tooth so the tooth does not rotate towards the tissue (torque)

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22
Q

what are rest seats? what are their disadvantages?

A

when occluding teeth are close together and a rest seat needs to be placed, a rest seat can be made
* loss of occlusal stop when denture is not worn
* destruction of tooth surface
* exposure of dentine

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23
Q

what is the definition of retention?

A

the resistance of a denture to lifting away from the tissues (vertical dislodging forces)

24
Q

what are methods of retention?

A
  • clasps
  • soft tissue undercuts
  • adhesion (maxillary plates)
  • friction (guide planes)
  • path of insertion
  • precision attachments/implants
25
what are the three ways that retention can be achieved?
* **mechanical** - clasps * **muscular** - shape of denture * **physical** - coverage of mucosa (adhesion, cohesion, atmospheric pressure (saliva))
26
what are guide planes? what do they do?
* **parallel proximal surfaces** of teeth that are **close to the base** * provides **supplementary retention** in the form of **friction** * can adjust proximal surfaces of teeth to make them parallel
27
what is a common path of insertion?
a **single, defined direction** in which a removable partial denture is designed to be **inserted and removed** from the mouth
28
why may you need to alter a path of insertion?
* to get a **closer fitting denture** to the abutment teeth * to get the **acrylic closer to the vestibular sulcus** * better **aesthetics** * better **localised retention**
29
describe the principal method of providing retention
***clasps*** - metal arm that is placed below the bulbous part of a tooth in an **undercut** and **contacts** the tooth to **prevent removal** of hte denture base
30
what does surveying casts help you to do?
* helps choose retentive elements (clasps) by **identifying undercuts** * helps find **path of insertion and removal** of denture
31
what are the two types of clasps?
* **occlusally approaching** - approaches from above the survey line into the undercut * **gingivally approaching** - approaches from the gingival sulcus
32
what clasp is this?
I-bar clasp (gingivally approaching)
33
what clasp is this?
self reciprocating clasp / ring clasp / circumferential clasp (occlusally appraoching)
34
what clasp is this?
single arm clasp with a reciprocal arm / C-clasp (occlusally apporaching)
35
what is reciprocation?
* an element on an occlusally appraoching clasp that opposes a retentive arm * the retentive arm applies a **horizontal force** onto the tooth when it comes into contact with it * the reciprical arm also contacts the tooth, **counteracting the horizontal force** and **preventing tooth movement**
36
what is the optimal pattern of retention?
triangular (as big as posible)
37
describe why indirect retention is needed in dentures with free end saddles
* when a **dislodging force** (i.e. sticky foods) is applied to a free end saddle, it can lift up and dislodge the whole denture * the **rests** on the denture act as **pivot points/fulcrum** and there is **resistance** from the **clasp** by the saddle * when the distance between the fulcrum and resistance is **greater**, it is **more effective** at resisting the dislodging forces
38
what other components can provide indirect retention?
* major connectors * minor connectors * rests * saddles * denture base
39
what are some denture base materials?
* CoCr * acrylic * PEEK - poly ether ether ketone * gold
40
what is the difference between a major and minor connector?
* major connector connects **all the components** together * minor connector connects, **rests, clasps and bracing arms** to the major connector
41
what are some common mandibular major connectors?
* lingual bar * lingual plate * acrylic plate * dental bar * sub-lingual bar * combination of plate and bar
42
what are some common maxillary major connectors?
* palatal plate * ring (anterior/posterior bar) * mid palatal plate * anterior palatal bar (horseshoe bar) * anterior palatal plate (horseshoe plate) * palatal bar
43
what is bracing?
the resistance of **lateral movement** of a denture provided by the major connector
44
what is beading?
* a **thin layer of wax** is placed around the **border** of the denture base but stops **3mm from the gingival margin** * facilitates an **intimate contact** between the denture and the tissue so **prevents food ingression**
45
what is the difference between plates and bars?
***plates*** * **thinner** in cross section (0.5mm) and maintains **rigidity** * for **craddock class II** designs (mucosa borne) - less tooth support = greater mucosal support * may cover **gingival margins** ***bars*** * **thicker** in cross section (2mm) * for **craddock class I** designs (tooth borne) * **less mucosal coverage**
46
what is the default choice of connector for the mandibular arch? what are the requirements for this?
* **lingual bar** as there is less space in the mandibular arch * needs **7mm** of space minimum between the **gingival sulcus and the floor of mouth** * 3mm from gingival margin + 4mm for height of bar
47
what are the advantages and disadvantages of a ring bar design?
***advantages*** * little coverage of **gingival tissue** * **rigid** * wide **relief of gingival margins** to prevent **food** impaction ***disadvantages*** * **less support to free end saddles** across the hard palate (narror coverage) * lots of **edges** that some patients may find **uncomfortable** * greater cross-sectional **thickness**
48
what are the advantages and disadvantages of a plate design?
***advantages*** * **thinner** cross section * wide **relief of gingival margins** to prevent **food** impaction * **support for free end saddles** across hard palate * **less edges** that patient may find uncomfortabele * **rigid** ***disadvantages*** * **mucosal tissue is covered** so less natural sensation
49
what are some examples of maxillary PMMA connectors?
always plates and not bars as acrylic is not as strong as metal so if it was narrower, it would have to be thicker and bulkier
50
what is the difference between open and closed saddle designs?
* closed design: **more contact** with **greater retention** due to **guide planes** - can **irritate** the gingival tissues (saliva cannot pass bucally to lingual/palatal) * open design: **no gingival coverage** with **greater clearance** - **less irritation** to gingival tissues (saliva can pass from buccal to ligual/palatal)
51
what can be used with tooth position to ensure they don't debond?
**metal posts** within acrylic teeth and a **metal backing** * **tooth trial** required for correct tooth position and post and backing position * when **occlusal contact** occurs when lower teeth contact the cingulum of the upper anterior teeth, it **applies pressure** which can **debond the teeth** so metal backing prevents this
52
what is the difference between tooth and mucosal support?
there is a **difference in compressibilty** between **periodontium** (tooth within the socket) and the **mucoperiosteum** (mucosa coverign alveolar bone) * periodontium can compress **0.1mm** * mucoperiosteum can compress **2.0mm**
53
what is the RPI system? where is it usually used? what does it consist of?
* the RPI system is a **stress relieving clasp system** commonly used on **mandibular free end saddles** to protect the abutment tooth when occlusal load is applied to the saddle * mesial **R**est * Proximal guide **P**late * gingivally approaching **I**-bar clasp
54
describe how the RPI system works
* **torque** occurs when the occlusal forces are applied to the free end saddle and the rest places **horizontal forces distally** on the abutment tooth, leading to **PDL breakdown** and eventually **extraction** * during **occlusal load**, the proximal plate and the I-bar **moves down and forwards** * the I-bar is **out of contact** with the tooth and the proximal plate sinks down **into the undercut** so the only thing on the tooth is the **mesial rest** * the **proximal plate resists** the horizontal forces distally on the abutment tooth
55
what are the advantages and disadvantages of an RPI system?
***advantages*** * **no torque** on the abutment tooth ***disadvantages*** * **windows** created by minor connector - pts. may not be able to **tolerate** and can be a **plaque trap** * loading on the free end saddle may **accelerate bone resorption**

BDS2 CDS Prosthodontics (14 decks)

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