Implants, Peri-implantitis, and a Regeneration Question

Correct answer: A. They are broadly similar — both are dominated by anaerobic Gram-negative species

• A. CORRECT. The microbial profiles are BROADLY SIMILAR. Both are dominated by anaerobic Gram-negative organisms, including the red complex — Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola — together with Prevotella intermedia and Fusobacterium. In a partially dentate patient, the remaining teeth act as the reservoir from which the implant surface is colonised, which is precisely why untreated periodontitis is such a strong risk factor for peri-implantitis.
• B. There are some differences in peri-implantitis lesions — a higher prevalence of staphylococci, particularly S. aureus, and of some enteric species and Candida — but the dominant picture is the same anaerobic Gram-negative flora, not a more pathogenic one.
• C. There is no basis for regarding periodontal flora as the more pathogenic of the two.
• D. The two are closely related — the shared flora is the mechanism of the shared risk.

Note: The clinical consequence: periodontal disease must be treated and STABILISED before implants are placed, and lifelong maintenance is mandatory. Peri-implantitis differs from periodontitis in its progression — faster, with a larger inflammatory infiltrate extending closer to the bone, because the implant lacks a periodontal ligament and has only a parallel-fibre attachment with no perpendicular Sharpey fibre insertion.

Correct answer: A. A narrow three-walled intrabony defect on the mesial of a canine

• A. CORRECT. NARROW THREE-WALLED intrabony defects give the most predictable regenerative outcome. The reasons are geometric and biological: three surrounding bony walls provide space maintenance and containment for the graft, a large surface area of vascular bone supplying progenitor cells, and mechanical protection for the clot. Narrow, deep defects — with a small angle between the root and the bony wall — regenerate better than wide shallow ones. A single-rooted anterior tooth adds good access.
• B. A Class III (through-and-through) furcation has a very poor regenerative prognosis. Only Class II furcations, particularly mandibular buccal ones, respond predictably.
• C. HORIZONTAL bone loss cannot be regenerated at all. There is no defect to contain a graft — this is the fundamental limitation of regenerative periodontal therapy.
• D. A one-walled defect has almost no containment, minimal cellular contribution and no clot protection. These are usually managed by resective therapy instead.

Note: The hierarchy: three-wall > two-wall > one-wall, and narrow > wide, and deep > shallow. Mandibular Class II furcations respond; Class III does not.

Correct answer: B. 2 mm

• A. 10 mm would preclude posterior mandibular implants in the great majority of patients.
• B. CORRECT. A minimum of 2 mm of vertical clearance is maintained between the implant apex and the superior border of the inferior alveolar canal. This margin absorbs the cumulative error of radiographic magnification, surgical guide fit and drill depth, and protects against the heat generated during osteotomy preparation. Violating it risks permanent paraesthesia or dysaesthesia of the lower lip and chin.
• C. 5 mm is unnecessarily conservative and would exclude implants in many atrophic posterior mandibles where they can be placed safely.
• D. 0.5 mm is well within the combined margin of measurement and surgical error and offers no real protection.

Note: Companion figures to know: 1.5–2 mm from an implant to an adjacent natural TOOTH; 3 mm between two adjacent IMPLANTS; and at least 1 mm of bone circumferentially, preferably 2 mm on the buccal. Use CBCT for posterior mandibular planning — a panoramic film alone is not adequate.

Correct answer: D. 7 mm

• A. 10 mm is generous and comfortable but is not the MINIMUM.
• B. 5 mm would leave only 0.5 mm on each side of a 4 mm implant — insufficient bone, with predictable crestal resorption and papilla loss.
• C. 4 mm is the implant diameter alone with no clearance at all.
• D. CORRECT. Approximately 7 mm. The arithmetic is simple and worth being able to reconstruct: a standard 4 mm diameter implant, plus a minimum of 1.5 mm of bone to the root of each adjacent tooth, gives 4 + 1.5 + 1.5 = 7 mm. That 1.5 mm on each side is what preserves the crestal bone and, with it, the interdental papilla.

Note: Two other dimensions that come up alongside this: the distance from the implant platform to the contact point should be 5 mm or less for reliable papilla fill, and adjacent implants need 3 mm between them (not 1.5) because two implants together produce more crestal resorption than an implant beside a tooth.