AVAILABLE BONE

CONTENTS

INTRODUCTIONAVAILABLE BONEBONE HEIGHTBONE WIDTHBONE LENGTHBONE ANGULATIONCROWN HEIGHT SPACEDIVISION OF BONESUMMARY

Introduction

Long term success in implant dentistry requires certain important criteria .There are more than 50 criteria that are required in treatment planning.

Once the prosthodontic needs of the patient have been determined,the most important criteria is the available bone.

AVAILABLE BONE

Describes the external architecture or the quantity of bone present in edentulous area considered for implants

AVAILABLE BONE

1.5-2mm-Surgical error.

Root form implants-width Diameter and Mesiodistal length of available bone

length of implant Height of bone available

Implant width S=F/A 0.25mm increase in diameter,5-8% surface area

increases. Increase in dia-less stress at crestal bone

implant interface.

Implant Height Also affects total surface area. 3mm longer implant 20-30% increase in surface

area. Initial stability of implant

It is measured in terms of Bone height Bone width Bone length Bone angulation Crown-height space

Available bone height

Radiographic Evaluation-OPG

Anterior regions of jaws-greatest height

Maximum height-Maxilla and mandible-sites

The minimum bone height for a predictable long term endosteal implant survival is 12 mm.

Skeletal relationships-Class 2 and class 3

Posterior jaws –more limiting for implant height

Suggested bone height -12mm

Available bone height

Dense bone may accommodate shorter implant but a porous bone may require longer implant.

More imp.as affects implant length and crown height.

Once the minimum bone height is established width is more important than additional height.

Available bone width

Measured between the facial and lingual plates at the crest .

The crest is supported by a wider base.

Osteoplasty Exception-ant maxilla

Available bone width

Minimum bone width for a 4mm root form implant is more than 6 mm.

Reduced width -narrower diameter implant.

Initial width of available bone is related to crestal bone loss,after loading.

Available bone length

The mesiodistal length of bone in an edentulous area is limited by adjacent teeth or implant.

Implant - 1.5 mm adjacent tooth and

3mm from adjacent implant

-For a bone width of 5mm the minimum length is 8mm.

Ideal implant width for single tooth or multiple implants.

Natural tooth being replaced

Available bone angulation

It represents the root trajectory in relation to occlusal plane.

Acceptable bone angulation depends on the width of the ridge.

For wider ridges bone angulation can be as much as 25 degrees .

For narrower ridges acceptable angulation is 20 degrees

Ideally,angulation is:

1.Perpendicular to occlusal forces.

2.Aligned with forces of occlusion

3.Parallel to long axis of prosthodontic restoration.

Rarely bone angulation remains ideal.

Mandibular Teeth: lingually inclined in posterior region and labial inclination in anterior region.

Anterior region in both jaws is usually deficient in bone

Posterior mandible –submandibular fossa dictates angulation

Crown-Height space

Vertical distance from the crest of the ridge to the occlusal plane.

Affects appearance , amount of moment of

force on the implant and surrounding crestal bone.

Considered as a vertical cantilever.

Greater the CHS,greater the moment of force,or lever arm.

Ideally,CHS should be =,< 15mm.

LEKHOLM and ZARB (1985)

TYPE 1TYPE2TYPE3TYPE4

Classification of available bone

DIVISION ADIVISION BDIVISION CDIVISION D

Misch and Judy in 1985

DIVISION A BONE

Consists of abundant bone in all directions

DimensionsWidth>6mm

Height>12mm

Length>7mm

Angulations<25 degrees

CHS < or =15mm

DIVISION A BONE

Treatment options Division A root forms or wider implants .

All prosthetic options.

Limited inter arch space. (High profile O-ring)

Osteoplasty .

Fixed Prosthetic options

FP-1

FP-2

FP-3 restoration in Div A bone

Removable prosthesis

DIVISION B BONE

Barely sufficient bone.

Ridge width is reduced.

M-D width of bone is less…so 3mm implants.

DIVISION B BONE

Dimensions Width 2.5mm-6mm

B+ :4-6mm B-w:2.5-4mm

Height> 12mm Length> 6mm Angulations <20 degrees CHS <15mm

Treatment options

3 Rx:-

1) Modify the narrower div B bone to div A by osteoplasty However after

osteoplasty the ridge height should not become <10 mm

And place division A root form

2) Narrow diameter division B root form angulation <20 available bone length

atleast 12mm to ensure adequate surface area for narrow diameter implants

The design of prosthesis also changes with osteoplasty procedures.

3) Ridge augmentation In cases where

osteoplasty will result in ridge height less than 10mm, ridge augmentation instead should be done.

Bone spreader-an alternative

DIVISION C(COMPROMISED BONE)

Deficient in one or more dimensions

Resorption first occurs in width .The bone is called C-w

Then in height. The bone is called C-h

Posterior maxilla VS Anterior maxilla

Posterior mandible VS anterior mandible.

Inform patient about bone loss

Dimensionsunfavorable in Width (c-w) :0 to 2.5mm Height(c-h)-<12mm Angulation (c-a)>30 degrees CHS > 15mm

Uncommon sub category C-a Avbl bone adequate in

height and width Angulation greater

than 30 degree

Treatment options

1)C-w ridge

a) Osteoplasty which converts it to C-h ridge type with adequate width

b) Bone augmentation can be done

Treatment options

2)C-h ridge can be treated with a) Greater no of endosteal implants of reduced height. b) Ridge augmentationton to upgrade div C to div A c) Subperiosteal –Circumfrential and unilateral. Disk design implants

DIVISION D (DEFICIENT BONE)

Characterized by severe atrophy of alveolar process as well as basal bone

Basal bone loss: Flat maxilla Pencil-thin mandible

CHS>20mm

Treatment options

Ridge augmentation is the treatment of choice.

Complete implant supported dentures indicated

Fixed restorations X

RP-5 not suggested.

90 percent of autogenous graft resorbs in 5 years-so not intended for denture support.

Chances of dental cripple.

Subperiosteal implants-the myth.

If adequate bone present in mandibular anteriors with D bone in posteriors- Root form implants. Tripodal sub-periosteal implants. Mandibular staple implants Ramus frame implants

Summary

In implant dentistry prosthesis is designed at onset of treatment to satisfy patients needs and desires.

Bone is THE most critical criteria indetermining the success.

References

Misch 3rd editionBabbush:art and science