bone density for dental implant

welcome

Presenter Name: Dr.Riad Mahmud

Resident ofProsthodontics,

BSMMU

Date:15: 11: 2016

BONE DENSITY: A KEY DETERMINANT FOR IMPLANT PLANNING

JAW BONESThe external and internal architecture of bone controls virtually every facet of the practice of implant dentistry.

The density of available bone in an edentulous site is a determining factor in

Treatment planning,

Implant design,

Surgical approach,

Healing time, and

Initial progressive bone loading during prosthetic

reconstruction..

INFLUENCE OF BONE DENSITY ON IMPLANT SUCCESS RATES

The quality of bone is often dependent upon the arch position.

The most dense bone is usually observed in

the anterior mandible, followed by

the anterior maxilla

posterior mandible, and the least dense bone is typically

found in

the posterior maxilla.

INFLUENCE OF BONE DENSITY ON IMPLANT SUCCESS RATES

Following a standard surgical and prosthetic protocol, Adell et al.reported an approximately 10% greater success rate in the anterior mandible

as compared with the anterior maxilla.

Schnitman et al. also noted lower success rates in the posterior mandible as compared with the anterior mandible

when the same protocol was followed.

The highest clinical failure rates have been reported in the posterior maxilla, where the force magnitude is greater and the

bone density is poorer.

ETIOLOGY OF VARIABLE BONE DENSITY

Bone is an organ that is able to change in relation to a number of factors, hormones, vitamins, and mechanical influences.

Biomechanical parameters duration of edentulous state.

Control Factors for Bone Modeling

ENDOCRINEBone metabolic hormones: PTH, Vitamin D, Calcitonin Growth hormones: Somatotropin, IGF-I, IGF-II Sex steroids: testosterone, estrogenPARACRINE AND AUTOCRINEWIDE VARIETY OF LOCAL AGENTS

Control Factors for Bone Modeling

FACTORS: PEAK LOAD IN MICROSTRAIN

Mechanical†Disuse atrophy <200 Bone maintenance 200 to 2500 Physiologic hypertrophy 2500 to 4000 Pathologic overload >4000

*me = percent deformation μ10–4. †

Frost’s mechanostat theory Frost proposed a model of four histologic patterns for compact bone as it relates to mechanical adaptation to strain. The pathologic overload zone, Mild overload zone, Adapted window, and Acute disuse window

Density of alveolar bone evolves as a result of mechanical deformation from microstrain. (The greater the magnitude of stress applied to the bone, the greater the strain observed in the bone)

Frost’s mechanostat theory Four zones for bone related to mechanical adaption to strain before spontaneous fracture. The acute disuse window is the lowest microstrain amount. The adapted window is an ideal physiologic loading zone. The mild overload zone causes microfracture and triggers an increase in bone remodeling, which produces more woven bone. The pathologic overload zone causes increase in fatigue fractures, remodeling, and bone resorption.

Frost’s mechanostat theory Four zones for bone related to mechanical adaption to strain before spontaneous fracture.

THE ACUTE DISUSE WINDOW Lowest microstrain amount.

THE ADAPTED WINDOW Ideal physiologic loading zone.

THE MILD OVERLOAD ZONE Causes microfracture and triggers an increase in bone

remodeling, which produces more woven bone. THE PATHOLOGIC OVERLOAD ZONE

Causes increase in fatigue fractures, remodeling, and bone resorption.

THE MAXILLA IS A FORCE DISTRIBUTION UNIT, AND THE MANDIBLE

IS A FORCE ABSORPTION UNIT.

The trabecular bone in a dentate mandible is more coarse.The mandible a independent structure, is a force-absorbing element.

THE MANDIBLE

BONE CHANGES IN RELATION TO FUNCTION

Biomechanical functions

THE MANDIBLE An independent structure, A FORCE-ABSORPTION UNIT.

When teeth are present, Outer cortical bone is denser and thicker and Trabecular bone is more coarse and dense.

BONE CHANGES IN RELATION TO FUNCTION

The trabecular bone of each jaw has structural variations.The trabecular bone is most dense next to the teeth, where it forms the cribriform plate. Between the teeth, the bone is usually most dense near the crest and least dense at the apex.

BONE CHANGES IN RELATION TO FUNCTION

Biomechanical functions THE MAXILLA FORCE- DISTRIBUTION UNIT.

(Any strain to the maxilla is transferred by the zygomatic arch and palate away from the brain and orbit ).

Has a thin cortical plate and fine trabecular bone supporting the teeth.

most dense around the teeth (cribriform plate) and more dense around the teeth at the crest, compared with the

regions around the apices

BONE CHANGES IN RELATION TO FUNCTION

The dentate maxilla has a finer trabecular pattern compared with the mandible. The maxilla is a force distribution unit and is designed to protect the orbit and brain.

BONE CLASSIFICATION SCHEMES RELATED TO IMPLANT DENTISTRY

Linkow, in 1970, classified bone density into three categories:CLASS I BONE STRUCTURE:

This ideal bone type consists of evenly spaced trabeculae with small cancellated spaces.

CLASS II BONE STRUCTURE: The bone has slightly larger cancellated spaces with less

uniformity of the osseous pattern.CLASS III BONE STRUCTURE:

Large marrow-filled spaces exist between bone trabeculae.

BONE CLASSIFICATION SCHEMES RELATED TO IMPLANT DENTISTRY

LINKOW STATED

Class III bone results in a loose-fitting implant

Class II bone was satisfactory for implants

Class I bone was the most ideal foundation for implant

prostheses.

BONE CLASSIFICATION SCHEMES RELATED TO IMPLANT DENTISTRY

In 1985, Lekholm and Zarb listed Four bone qualities for the anterior

region of the jaws.

QUALITY 1 is composed of homogenous compact bone.

QUALITY 2 has a thick layer of cortical bone surrounding dense

trabecular bone.

QUALITY 3 has a thin layer of cortical bone surrounding dense

trabecular bone of favorable strength.

QUALITY 4 has a thin layer of cortical bone surrounding a core of low-

density trabecular bone.

BONE CLASSIFICATION SCHEMES RELATED TO IMPLANT DENTISTRY

In 1988, Misch proposed four bone density groups Independent of the regions of the jaws. Based on macroscopic cortical and trabecular bone characteristics.

MISCH BONE DENSITY CLASSIFI CATION SCHEME

BONE DENSITY DESCRIPTION TACTILE ANALOG TYPICAL ANATOMICAL

LOCATION

D1 Dense cortical Oak or maple wood Anterior mandible.

D2 Posterior mandible White pine or spruce wood

Anterior mandible Posterior mandible

Anterior maxilla

D3Porous cortical (thin)and fine

trabecular

Balsa wood Anterior maxillaPosterior maxilla

Posterior mandible

D4Fine trabecular Styrofoam Posteriormaxilla.

USUAL ANATOMIC LOCATION OF BONE DENSITY TYPES (% OCCURRENCE)

BONE ANTERIOR MAXILLA

POSTERIOR MAXILL

ANTERIOR MANDIBLE

POSTERIOR MANDIBLE

D1 0 0 6 3

D2 25 10 66 50

D3 65 50 25 46

D4 10 40 3 1

BONE DENSITY AND STRESS TRANSFER

The four macroscopic bone qualities are, from left to right, D1, D2, D3, and D4.

The four macroscopic bone qualities are, from left to right, D1, D2, D3, and D4.

The four macroscopic bone qualities are, from left to right, D1, D2, D3, and D4.

The four macroscopic bone qualities are, from left to right, D1, D2, D3, and D4.

The four macroscopic bone qualities are, from left to right, D1, D2, D3, and D4.

D1 bone density has the greatest amount of bone-implant contact. Because stress equals force divided by area, the increase in the area of

contact results in a decreased amount of stress.

A cross section of a D2 mandible in the region of the mental foramen. A thick cortical plate exists on the crest and a coarse trabecular bone pattern exists within.

A posterior maxilla demonstrating D3 bone with a thinporous cortical plate on the crest with fine trabecular bone underneath.

In a D4 posterior maxilla, the posterior crestal region has little to no cortical bone on the crest and is composed primarily of fine trabecular bone.

FINITE ELEMENT ANALYSIS STUDY OF BONE

A, In a finite element analysis study of D1 and D2 bone with a Division

A, B, or C bone volume predicted no implant failure.

B, In a finite element analysis study of D3 bone of one third the

strength, no failure was predicted in Division A bone.

C, In a finite element analysis study, D4 bone was inadequate in strength

for implant success, even in Division A bone volume.

Division A, D1/D2 100% DensityUltimate compression strength: 22.5 MpaNo failure predicted

Division B, D3 50% DensityUltimate compression strength: 7.5 MPaNo failure predicted

Division C, D4 25% DensityUltimate compression strength 3.5 MPaFailure predicted

BONE DENSITY AND STRESS TRANSFER

A range of bone loss has been observed in implants with similar load conditions. The magnitude of a prosthetic load may remain similar and give one of the following three different clinical situations at the bone-implant interface, based on bone density: (1) Physiologic bone loads in the adapted window zone and no marginal bone loss, (2) Mild overload to pathologic overload bone loads and crestal bone loss, or (3) Generalized pathologic overload and implant failure.

Therefore, to obtain a similar clinical result in each implant prosthesis, the variables in each patient must be either eliminated or accounted for in the treatment plan.

RADIOGRAPHIC BONE DENSITYPeriapical or panoramic radiographs are not very beneficial to determine bone density.

Bone density may be more precisely determined by Tomographic radiographs.Especially computerized tomogram. CT produces axial images of the patient’s anatomy, perpendicular to the long axis of the body.

Each CT axial image has 260,000 pixels, and each pixel has a CT number (Hounsfield unit) related to the density of the tissues within the pixel. In general, the higher the CT number, the denser the tissue.

MODERN CT

Modern CT scanners can resolve objects less than 0.5 mm apart. Software is available to electronically position the implant on the CT scan and evaluate to Hounsfield numbers in contact with the implant.

The Misch bone density classification may be evaluated on the CT images by correlating Hounsfield units ranges.

The very soft bone observed after some immaterialized bone grafts may be 50 to 200 units.

CT DETERMINATION OF BONE DENSITY

D1: >1250 Hounsfield units D2: 850 to 1250 Hounsfield units D3: 350 to 850 Hounsfield units D4: 150 to 350 Hounsfield unitsD5: <150 Hounsfield units.

TREATMENT PLANNING

The patient is first examined, Most common radiographic evaluation

A panoramic radiograph.

The initial treatment plan is presented to the patient using the anatomical location as an index of the bone density:

Anterior mandible and single tooth replacement is D2, Anterior maxilla and posterior mandible is D3, and Posterior maxilla is D4.

TREATMENT PLANNING

Bone density/Treatment plan Stress = Force/AreaDecreased Bone density = Increase Implant area by -

Implant number Implant width Implant length Implant design Implant surface condition

TREATMENT PLANNING

Scientific rationale of strength, Modulus of elasticity, Bone-implant contact percent, and Stress transfer difference related to bone density has to

be addressed.

GENERALIZATIONS FOR TREATMENT PLANNING CAN BASED ON LOCATION.

The bone density by location method is the first way the dentist can estimate the bone density in the implant sites to develop an initial treatment plan.

Therefore the initial treatment plan before computed tomographic (CT) radiographic scans or surgery suggests

o The anterior maxilla is treated as D3 bone,o The posterior maxilla as D4 bone, o The anterior mandible as D2 bone, and o The posterior mandible as D3 bone.

A more accurate determination of bone density is made with computerized tomograms before surgery or tactilely during implant surgery.

WHEN THE IMPLANT IS INITIALLY INTEGRATED WITH THE BONE

The bone-loading process from occlusal forces becomes a

critical factor in long-term implant survival. The bone density under load is directly related to the bone

strength and is therefore a critical parameter for long-term

survival.

THE OCCLUSAL STRESSES APPLIED THROUGH THE IMPLANT TO THE BONE

Must remain within the physiologic to mild overload zone; otherwise, Pathologic overload With

Associated bone loss and Micro fracture, and Implant mobility may occur.

THREE REQUIREMENTS NECESSARY FOR INITIAL RIGID FIXATION

Atraumatic bone preparation,

Close approximation of living bone to the biocompatible implant surface, and

Absence of movement at the interface during healing.

•Thank you