ADC - Australian Dental Council Prosthodontics and Dental Implants Questions and Answers — Questions and Answers
Question 1: A 55-year-old patient requires a full coverage crown for tooth 25, which has had root canal treatment and a large MOD amalgam restoration. Clinical examination reveals 1.5mm of sound coronal tooth structure above the gingival margin circumferentially. What is the most critical factor for the long-term fracture resistance of the final restoration?
- The type of luting cement used.
- The choice of post and core material.
- Achieving an adequate ferrule effect. (Correct answer)
- The occlusal anatomy of the crown.
Correct answer: Achieving an adequate ferrule effect.
The ferrule effect, which is the 360-degree collar of a crown encircling the parallel walls of sound dentine, is crucial for protecting a root-treated tooth from fracture. A minimum of 1.5-2mm of ferrule height is widely recommended to provide a bracing action that resists functional lever forces and dissipates occlusal stresses. While other factors like cement and post material are important, the ferrule is considered the most critical structural feature for improving fracture resistance and long-term prognosis.
Question 2: When taking a final impression for multiple, non-parallel implants intended for a splinted, screw-retained bridge, which technique is generally considered more accurate for capturing the precise three-dimensional orientation of the implants?
- A dual-arch (triple tray) impression technique.
- Closed-tray impression technique.
- Digital scanning with a standard intraoral scanner.
- Open-tray impression technique. (Correct answer)
Correct answer: Open-tray impression technique.
The open-tray (or pick-up) technique is generally more accurate for multiple, angulated (non-parallel) implants. The impression copings are directly connected to the impression material and are unscrewed from the implants while the tray is still in the mouth. This method minimizes errors from the potential malpositioning of copings when re-seating them into the impression, which is a risk with the closed-tray (transfer) technique, especially where implant angulation prevents a clear path of insertion.
Question 3: A 72-year-old patient received new complete maxillary and mandibular dentures one week ago. They return complaining that the lower denture lifts every time they move their tongue. Which of the following is the most likely cause?
- The mandibular lingual flanges are overextended. (Correct answer)
- The occlusal vertical dimension is too high.
- The posterior palatal seal of the maxillary denture is inadequate.
- The denture teeth are set too far buccally.
Correct answer: The mandibular lingual flanges are overextended.
Overextension of the lingual flanges of a mandibular complete denture will impinge on the mylohyoid muscle and the floor of the mouth. When the patient lifts or moves their tongue, these muscles contract and dislodge the denture. An inadequate posterior palatal seal affects the maxillary denture, and incorrect vertical dimension or tooth position typically causes different issues like muscle fatigue or cheek biting.
Question 4: Which of the following is the primary function of a major connector in a mandibular removable partial denture?
- To provide direct retention for the prosthesis.
- To provide vertical support against occlusal forces.
- To unite all components and distribute forces across the arch. (Correct answer)
- To prevent horizontal movement of the abutment teeth.
Correct answer: To unite all components and distribute forces across the arch.
The primary function of a major connector (e.g., lingual bar or plate) is to provide rigidity and unite all other components of the RPD on one side of the arch with those on the other. This unification allows for the effective distribution of functional stresses to the supporting teeth and tissues, providing cross-arch stability and preventing the overloading of any single area.
Question 5: A 60-year-old patient with an implant-supported crown on tooth 46, placed 5 years ago, presents for a routine check-up. Probing around the implant reveals a 6mm pocket with bleeding on probing. What is the most crucial additional diagnostic information required to differentiate between peri-mucositis and peri-implantitis?
- The presence of suppuration from the pocket.
- The mobility of the implant-supported crown.
- Comparison with a baseline radiograph. (Correct answer)
- The patient's reported level of discomfort.
Correct answer: Comparison with a baseline radiograph.
The key feature that distinguishes peri-implantitis from peri-mucositis is radiographic evidence of progressive bone loss beyond initial remodelling. Peri-mucositis is inflammation confined to the soft tissues without bone loss. While bleeding on probing indicates inflammation (present in both) and suppuration is a strong sign of infection, the definitive diagnosis of peri-implantitis requires confirmation of bone loss by comparing current radiographs to baseline or previous radiographs.
Question 6: A 30-year-old patient requires a single full-coverage crown on tooth 11 and is primarily concerned with achieving the best possible aesthetics. The tooth has sufficient coronal structure, and there are no signs of parafunctional habits. Which all-ceramic material would be the most appropriate choice to primarily meet the patient's aesthetic demands?
- Monolithic high-strength zirconia.
- Lithium disilicate (e.g., IPS e.max). (Correct answer)
- Porcelain-fused-to-metal (PFM).
- A gold alloy.
Correct answer: Lithium disilicate (e.g., IPS e.max).
Lithium disilicate offers an excellent combination of high translucency, strength, and favorable optical properties, making it a superior choice for highly aesthetic single anterior crowns. Monolithic zirconia, while very strong, is typically more opaque and less ideal for single anterior teeth where aesthetics are paramount. PFM and gold crowns do not offer the same level of aesthetics as modern all-ceramic options for the anterior region.
ADC - Australian Dental Council Prosthodontics and Dental Implants Questions and Answers
A 55-year-old patient requires a full coverage crown for tooth 25, which has had root canal treatment and a large MOD amalgam restoration.
Clinical examination reveals 1.5mm of sound coronal tooth structure above the gingival margin circumferentially.
What is the most critical factor for the long-term fracture resistance of the final restoration?