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Implants · patient case with 4 questions

Maintenance of a screw-retained implant prosthesis

Patient: Male, 59 years old

Chief Complaint: Attends for review of a screw-retained implant-supported prosthesis placed eighteen months ago.

Background: Non-smoker. Well-controlled hypertension. Good plaque control.

Current Findings: The prosthesis is stable and the peri-implant tissues are healthy, with no bleeding on probing and no radiographic bone loss beyond expected remodelling. He asks what ongoing care the restoration will need.

Question 1

What does routine maintenance of a screw-retained implant prosthesis require?

  1. Daily removal of the prosthesis by the patient for cleaning
  2. Replacement of the prosthesis every five years
  3. Periodic assessment and retightening of the abutment screws to the specified torque
  4. No specific maintenance beyond ordinary brushing
Show answer and explanation

Correct answer: C. Periodic assessment and retightening of the abutment screws to the specified torque

  • A. A screw-retained prosthesis is fixed and is removed only by the clinician. Patient removal describes an overdenture.
  • B. There is no fixed replacement interval. Implant prostheses are replaced when they fail or when the biology demands it, not on a calendar.
  • C. Screw joints undergo settling and preload loss over time. Screw loosening is the commonest mechanical complication of screw-retained restorations, and an undetected loose screw permits micromovement, which leads to screw fracture and to bacterial colonisation of the implant-abutment interface. Periodic assessment and retorquing to the manufacturer's specification is standard maintenance.
  • D. Implant prostheses require MORE maintenance than natural teeth, not less — professional peri-implant assessment, radiographic monitoring and mechanical review.

Note: The retrievability of screw retention is precisely its advantage: no excess cement to leave subgingivally, and the prosthesis can be removed for repair. Its trade-offs are the access hole and greater sensitivity to angulation.

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Question 2

Which factor is MOST important to communicate to the laboratory for long-term implant success?

  1. The patient's preferred tooth shape
  2. The brand of articulator being used
  3. That occlusal forces be directed along the long axis of the implants
  4. The shade of the adjacent natural teeth
Show answer and explanation

Correct answer: C. That occlusal forces be directed along the long axis of the implants

  • A. Tooth form is an aesthetic preference and does not determine long-term success.
  • B. Articulator selection affects the accuracy of occlusal registration but is not the governing factor communicated for longevity.
  • C. CORRECT. Implants have no periodontal ligament. There is no proprioceptive feedback to warn of overload and no physiological mobility to absorb it, so a lateral or off-axis force transmits directly into the bone-implant interface as a concentrated stress. Axial loading distributes force favourably; off-axis loading causes crestal bone loss, screw loosening and component fracture. Everything else on this list is secondary.
  • D. Shade matters for aesthetics but has no bearing on the biomechanical survival of the implant.

Note: Implant occlusal principles: centric contacts directed axially, no working or non-working excursive contacts on implant-supported units, shallow cusp inclines, narrowed occlusal tables, and anterior guidance carried on natural teeth where possible.

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Question 3

Where are bilateral implants optimally placed for an implant-retained MANDIBULAR overdenture?

  1. In the second premolar regions
  2. In the canine regions
  3. In the molar regions
  4. In the central incisor regions
Show answer and explanation

Correct answer: B. In the canine regions

  • A. Second premolar sites sit close to the mental foramina and risk nerve injury, and the anterior ridge remains unsupported.
  • B. CORRECT. The canine regions are the standard sites for a two-implant mandibular overdenture. The bone is dense and adequate in volume there, the sites lie anterior to the mental foramina so the mental nerve is safe, and the inter-implant distance gives a favourable anteroposterior spread for retention and stability while permitting rotation about the interconnecting axis so the posterior ridges continue to share the load.
  • C. The posterior mandible carries the inferior alveolar canal and is often severely resorbed. Posterior implants in an overdenture also create a rigid, cantilevered scheme.
  • D. Implants placed too close together in the incisor region give a very short anteroposterior spread and poor resistance to rotation.

Note: The two-implant mandibular overdenture is widely regarded as the minimum standard of care for the edentulous mandible. Note that a MAXILLARY overdenture generally requires four or more implants because of the poorer bone quality.

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Question 4

What is the minimum mesiodistal space required to place an implant between two natural teeth?

  1. 7 mm
  2. 5 mm
  3. 12 mm
  4. 9 mm
Show answer and explanation

Correct answer: A. 7 mm

  • A. CORRECT. A standard-diameter implant of about 4 mm requires at least 1.5 mm of bone between the implant surface and each adjacent root, giving 4 + 1.5 + 1.5 = 7 mm as the minimum mesiodistal dimension. Less than that risks damaging adjacent roots and compromising the interproximal bone that supports the papilla.
  • B. 5 mm leaves under 1 mm on either side of a standard implant — insufficient bone and a high risk of damage to the adjacent roots.
  • C. 12 mm would accommodate a wide implant or even two implants; it is far more than the minimum requirement.
  • D. 9 mm is comfortable but exceeds the minimum, and the question asks for the minimum.

Note: The related numbers worth carrying: 1.5 mm minimum from implant to adjacent TOOTH, and 3 mm minimum between two adjacent IMPLANTS.

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