Pros Paper 2021 Flashcards
List the 5 possible benefits to patients of replacing missing teeth (5 marks)
- Aesthetic
- Speech
- Mastication
- Maintenance of dental health
- Psychological
Explain with examples how the provision of removable partial dentures helps maintain oral health (5 marks)
- Maintain stability of remaining dentition to prevent over eruption and drifting which can lead to periodontitis and caries risk factors.
- Prevention of wear of anterior teeth through loss of posterior support.
- RPDs fixes unstable mastication from missing posteriors which would result in TMJD
- If an upper tooth doesn’t have an occluding lower tooth it will continue to erupt causing furcation exposure leading to periodontal issues and damage to the gingiva below.
- If an anterior tooth is missing mesial drift can take place leaving a food trap which results in plaque and then caries.
Which structures/anatomic features should you record in the preliminary impression for a patient with a partially dentate upper arch with only the anterior teeth remaining? (5 marks)
- Tooth surfaces
- Border extension, alveolar ridge, and full functional depth of buccal, palatal and labial sulci.
- Anatomical landmarks such as hard palate and distal extension extended back to the hamular notch
- Surface detail (check for voids/complete capture of finish line)
Describe how you would make the impression (upper prelim) (5 marks)
- Select stock tray from s/m/l, adapt trays if needed with red composition to improve extension/fit (the palatal vault).
- Apply adhesive to the tray and composition and allow to dry
- Mix the alginate and load the tray filling the box section
- Insert the tray firmly up at the posterior at first and then rotate up into position, ensuring the tray seats fully up into the labial sulcus with the tray aligned centrally with the arch and midline
- Mold cheeks and lip firmly against the tray and have the patient open and close a few times and then move their lower jaw from side to side
- Leave to set, remove tray, rinse it, and wrap It in one sheet of damp gauze and disinfect in preform for 10mins then rinse and bag and label
Describe the jaw relationship to which you would restore a patient requiring a partial denture when using the conformative approach to occlusal rehabilitation (3 marks)
- If a patient has an ICP: then reproduce this and set teeth to harmonise with the existing occlusion, (confirmative approach)
- ICP is the relation of the upper and lower jaws when the teeth are in maximum intercuspation
- This is the most comfortable position to bite hard and a good start position to assess occlusal relationships
Describe how wax occlusal registration rims are modified to record this relationship (7 marks)
- Try in wax occlusal registration rims, looking for overextension of borders and reduce if required.
- Have patient close into maximum intercuspation with one of the wax rims in position. Trim rim until no contacts (2mm space apparent) remain between wax and opposing teeth
- Repeat for the other wax rim. Trim with a wax knife over a Bunsen burner
- Place both rims in the mouth. Eliminate contacts between rims to allow maximum intercuspation of the teeth
- Record position of maximum intercuspation using Zinc oxide – Eugenol impression paste
- Place the rims on the models and check recorded position – if they do not meet the same, it’s inaccurate
What is the main purpose of preparing occlusal rest seats? (2 marks)
- An occlusal rest is a metal projection attached to an RPD that extends over and bears on the occlusal or prepared surface of a tooth
- Its main purpose is to transmit load vertically preferably along the long axis of the tooth
Describe how you would prepare a mesial rest seat on a lower molar tooth (5 marks)
- Using the drill make a rounded outline in enamel/ restoration, prepare through the marginal ridge, taper towards mid-occlusal surface (correct prep helps avoid premature occlusal contacts and plaque retention)
- Dimensions of occlusal rests are about one half of the bucco-lingual cusp width and about one third of the mesiodistal width of the tooth
- The aim of it is to provide more suitably inclined bearing surface for the occlusal rest than those existing on the natural teeth and to provide a shape of surface giving a desirable amount of bracing (saucer-shaped without sharp angles)
Guide planes are often prescribed when constructing partial dentures. Describe how and where you would prepare a guide plane on a premolar tooth when using a vertical POI. (3 marks)
- Guide planes provide a definite path of insertion
- To prepare you require two or more vertical parallel surfaces, using a straight bur at maximum bulbosity of the survey line
- In this case, survey the premolar and take a 2mm square vertical to the parallel surfaces at the maximum bulbosity using a straight bur
Having taken upper and lower master impressions for removable cast partial dentures what would you assess when considering are they fit for purpose (8 marks)
- Check the tooth surfaces, border extension and rolled borders for sulci, anatomical landmarks – hard palate, distal extension saddle limits, surface detail
- Check fit of castings on masters’ casts, has the prescription been followed?
- Check model for damage caused by fitting down the casting. If you can see where the casting damaged the model you can see where the problems will arise in the mouth
- Try framework in the mouth. Do not force it into position – it might never come out again and if it hurts it’s not right. (it is not necessary that the castings be retentive at this stage)
- Note where the casting is binding. Paint a thin layer of pressure indicating paste or spray a thin layer of “occlude” on the areas where the framework touches teeth and reinsert. Heavy contacts show areas of bare metal. Adjust all of these except on clasp tips
- If gingivally approaching clasps impinge on soft tissues adjust them
- If the framework does not clearly fi well or continues to rock when it has been fully fitted down you may need to make new impressions
What is your preferred choice of impression material and why? (2 marks)
PVS as it viscous, biocompatible, hydrophilic and it is more accurate than alginate.
What is the minimum space required to allow prescription of a cast lower lingual bar connector and how is the space distributed? (4 marks)
- The lingual bar lies against the alveolus
- Minimum of 8mm space required from the lingual gingival margins to floor of the mouth – 2mm clear of the gingival margin, 4mm width of the bar, 2mm clear of the floor of mouth
- If more than 8mm space available, make bar broader not thicker for better rigidity
Comment on the positive and negative aspects of such a connector (6 marks)
Positives
• Covers minimum surface area of teeth and tissue therefore potential for caries, periodontal problems caused by plaque being held in contact with teeth and tissue is minimal.
• It is relatively small, inconspicuously located and minimally interfere with functions
Negatives
• Not as rigid as the lingual plate or sublingual bar
• Difficult to add additional prosthetic teeth to framework.
• Framework goes from thick (at the minor connectors) to thin (at the bar) to thick again which is metallurgically and structurally complicated. The result may be weak areas in the casting with the potential to fracture.
Give a general definition of ‘support’ as regards removable partial dentures. (2 marks)
• Defined as the resistance to the vertical load applied to the prosthesis during function
In what way is ‘tooth support’ different from ‘mucosal support’? (6 marks)
- Tooth support – via periodontal ligament and is a tensile force and perceived as “healthy”. It is classified as Craddock 1 and the occlusal load is transferred indirectly to the alveolar bone via occlusal rests placed on the natural teeth
- Mucosal support – is directly to the alveolar bone via the saddles and mucosa which is compressive and perceived as unhealthy.
