Role of available bone in dental implants

Fig 6.1 (A) Panoramic view of the edentulous mandibular molar site showing adequate bone length availability (15 mm) to place widest implant of any system (B) but the cross-sectional view of the same edentulous region shows inadequate bone availability at the ridge crest (5 mm), which cannot allow placement of even the narrowest implant of any system. The height of the bone above the mandibular canal is adequate (16.83 mm) to place an adequately long implant (14–15 mm long). (C) The implant with 4 mm x 15 mm dimensions can be placed with its platform at the crest level with simultaneous lateral bone augmentation to cover the facially exposed implant threads near the crest. (D) The shorter length (4 mm x 12 mm) implant is placed after 3 mm of osteoplasty, so that the implant platform can be placed at the level of wider subcrestal ridge.

Misch and Judy classification of bone availability

In 1985, Misch and Judy presented a classification of available bone for dental implant insertion, which is similar in both arches (< ?xml:namespace prefix = "mbp" />Fig 6.2A–D). Bone modification procedures, grafting methods, and prosthodontic-related treatments were suggested for each category.

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Fig 6.2 Misch and Judy classification of bone availability (Divisions A, B, C and D): Division A (abundant bone), Division B (barely sufficient bone), Division C (compromised bone), Division D (deficient bone), w (width), h (height).

Division A (abundant bone)

Division A bone is three-dimensionally abundant for the ideal implant insertion (Fig 6.3A and B). According to Misch, bone in this category should be:

a. 5 mm or more in width

b. 12 mm or more in height

c. 7 mm or more in length

d. Less than 30° in angulation

e. 15 mm or less in crown height.

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Fig 6.3 (A and B) Abundant bone in the maxilla and mandible suitable for inserting an implant with ideal dimensions.

Prosthetic options for Division A bone

The Division A bone:

a. is the best bone for any prosthetic option (Fig 6.4A–I).

b. may need osteoplasty for implant overdentures, to achieve more vertical height space and accommodate the implant suprastructures (ball/bar) under the denture.

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Fig 6.4 (A) Panoramic radiograph and (B–I) CT scan showing cross-sectional views of the maxilla and the mandible, showing the Division A bone (adequate bone) for implant placement without any ridge modification or grafting. (J) The implant-supported, full mouth fixed prosthesis can be seen in the radiograph.

Division B (barely adequate) bone

Bone in this category should be:

a. 2.5–5 mm in width (B+: 4–5 mm; B−: 2.5–4 mm)

b. 12 mm or more in height

c. 6 mm or more in length

d. Less than 20° in angulation

e. 15 mm or less in crown height.

Prosthetic options for Division B bone

The bony ridge with Division B bone may be modified to division A bone by osteoplasty to achieve the wide ridge crest required to insert a regular diameter implant (Fig 6.5A–C). Lateral bone augmentation can also be performed before or with implant placement, especially in aesthetic areas where osteoplasty can elongate the clinical crown height (Fig 6.6A–C). This bone may be adequate for any prosthetic option in implant therapy.

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Fig 6.5 (A) Either a narrow diameter implant is inserted or (B) a Division B ridge is converted to Division A bone by vertical ridge osteoplasty or (C) lateral bone augmentation to achieve a wide ridge crest for placement of regular-diameter implant.

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Fig 6.6 (A) Implant placed in the Division B bone, showing implant threads exposed in the crestal region at the facial aspect of ridge. (B and C) Simultaneous lateral bone augmentation is performed to cover the exposed implant threads and also to improve the aesthetic ridge profile.

Division C (compromised bone)

Bone in Division C category should be:

a. 0–2.5 mm in width (C-w bone)

b. Less than 12 mm in height (C-h bone)

c. More than 30° in angulation (C-a bone)

d. More than 15 mm in crown height.

Treatment options

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Apr 12, 2015 | Posted by in Implantology | Comments Off on Role of available bone in dental implants
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