Shaima’a Ahmed Radwan

2- Implant related:

a)IMPLANT MACROGEOMETRY

The shape of the implant determines the surface area available for stress transfer and governs the initial stability of the implant.

Fix

ture

Re

gio

ns

Crest module

Apex

Body

Smooth sided cylindrical implants provide ease in surgical placement, however the bone to implant interface is subjected to significantly larger shear conditions.

Implant shape

As a consequence, cylinder implants require a coating to manage the shear stress at the interface through a more uniform bone attachment along the implant length

Threaded implants with circular cross sections provide for ease of surgical placement and allow for greater functional surface area optimization to transmit compressive loads to bone implant interface

Implant shape

-Manufacturers describe root form implant in dimension of length -corresponds to bone height- and diameter -corresponds to bone width and length. -Some manufacturers propose implants with a crest module wider than body dimension

Implant diameter and length

Implant Diameter

-Increase in surface area depends on implant diameter more than implant length.

Wider root form designs exhibit a greater area of bone contact than narrow implants of similar design because of an increase in circumferential bone contact

1 mm increase in diameter 20% - 30% increase in surface area.

Length of implants:

3 mm increase in length 10% increase in surface area. • Implant length is a more relevant factor in case of

immediate loading, especially in case of softer bone

(Implant neck (crest module/implant collar

Smooth parallel sided may result in a shear stress in the

crestal region

Crest module of an implant body is the transosteal region from the implant body and characterized as a region of highly concentrated mechanical stress

an angled crest module of more than 20 0 with a surface texture which increases the bone implant contact, might impose a slight beneficial compressive and tensile component to the contiguous bone, and decrease the risk of bone loss.

Crest module seats fully over the implant body osteotomy , deterrent to ingress of bacteria & fibrous tissue ,provides greater initial stability of the implant surface area .

(Implant neck (crest module/implant collar

THREAD GEOMETRY Threads are designed to maximize initial contact enhance surface area and facilitate dissipation of stresses at the bone- implant interface. Functional surface area per unit length of the implant may be modified by varying three thread geometry parameters

1.thread pitch, 2,thread shape and 3. thread depth.

b)IMPLANT MICROGEOMETRY

1.thread pitch

Thread pitch refers to the distance from the center of the thread to the center of the next thread.

Implants with more threads (i.e. smaller pitch) were found to have a higher percentage of BIC(bone implant contact) and increase resistance to vertical forces.

2,thread shape

Square , V shape, buttress

V-shaped 10 times greater shear Caution in D3 and D4 bone Failure .

Greater the thread depth , greater the surface area of the implant

c) Number, distribution and inclination of supporting implants:

Increasing the number of supporting implants increases the functional surface area upon which dissipation of forces occurs.

The maximum compressive stresses, generated in an

Osseo integrated implant, increase as the inclination of the implant towards the load direction increases.

Thus, for a long term favorable prognosis, it is

necessary to take into consideration the antagonistic teeth and the positioning of the implants when designing the prosthetic appliances.

Shaima’a Ahmed Radwan

3- Bone Related

A) Bone Quality (Density): In 1970 Linkow classified bone into three categories :

1) Class I consist of even spaced trabeculae with small cancellated spaces. 2) Class II consist of less uniform spaced trabeculae with larger cancellated spaces. 3) Class III consist of large marrow spaces in less uniform trabeculae.

In 1985 Zarb classified bone into four categories : - Quality 1 composed of homogenous compact bone. - Quality 2 composed of thick compact bone surrounding core of dense trabecular bone.

- Quality 3 composed of thin compact bone surrounding core of dense trabecular bone

- Quality 4 composed of thin compact bone surrounding core of low density trabecular bone

In 1988 Misch classified bone into four categories : - D1 dense cortical Ex: Anterior mandible - D2 porous cortical and course trabecular Ex: Posterior mandible

- D3 porous thin cortical and fine trabecular. Ex: Anterior maxilla. - D4 fine trabecular (Heals 50% faster than D1 bone). Ex: Posterior maxilla

olume):V(Quantity B)Bone

1985 Carl E. Misch proposed four basic divisions. The divisions are: 1) Division A 2) Division B 3) Division C 4) Division E

These divisions are based on bone height, width,

length and angulation.

A) Bone height: - Measured from the crest of remaining ridge to the opposing land mark.

B) Bone Width:

- Bucco-lingual dimension of bone around implant. - Minimum 0.5 mm of bone is needed.

C) Bone length: - Mesio-distal length of bone around implant. - Implant should be at least 1.5 mm from adjacent tooth \ implant to allow an adequate blood supply for the bone.

D) Bone angulations:

• Angled abutments are used to improve esthetics or the path of insertion of a restoration, not to determine the direction of load. • Angled abutments also result in development of dangerous transverse force components under occlusal loads in the direction of the angled abutment. 15 degrees = 25.9% force 30 degrees = 50% force

)1 ):Division A (abundant bone

≥ 5 mm width ≥ 12 mm height ≥ 7 mm length Up to 30o angulations

) Division B: 2

B+ 4-5 mm width ≥ 12 mm height ≥ 6mm length Up to 20o angulations

B-w • 2.5-4 mm width • ≥ 12 mm height • ≥ 6 mm length • Up to 20o

angulations

) Division C:3

C-w 0-2.5 mm width ≥ 12 mm height ≥ 6mm length Up to 20o angulations

C-h • 4-5 mm width • < 12 mm height • ≥ 6mm length • Up to 20o

angulations

) Division D:4 Severe atrophy Basal bone loss

Shaima’a Ahmed Radwan

4- Mechanical properties of the bone-implant interface:

FUNCTIONAL SURFACE AREA:

as the area that actively serves to dissipate compressive and tensile non shear bonds through the implant to bone interface and provides initial stability of the implant following surgical placement.

D1 bone, is the densest bone found in the jaws is also the strongest bone and provides an intimate contact with a threaded root form implant at initial implant loading.

D4 bone has the weakest biomechanical strength and the lowest contact area to dissipate the load at the implant to bone interface.

Osseointegration A direct functional and structural connection

between ordered living bone and the surface of a load-bearing implant. “Branemark 1985”

Osseointegration (biologic processes) Blood clot

formation

Angiogenesis

Osteoprogenito

r

Deposition of bone

A) Bonding-Osseointegration: - This type of Osteointegration occurs in bio-active implants such as those hydroxy apatite coated or Plasma sprayed.

B) Contact-Osteointegration:

- This type of interface occurs in bio-inert implants made of titanium with no coating.

C) Distant-Osteointegration: - Fibro integration is the weakest type of interface and it

can be seen around stainless steel or cobalt chromium implants.

Wolff’s law would suggest that implants reach their optimal integration only after being placed in function due to bone remodeling (Deposition and Resorption) that occurs around the implant as a consequence of loads applied.

5- Loading related:

Timing of loading: A) Immediate ( On the same day of first surgery up to 48 hours ). B) Early ( 2 to 3 weeks after first surgery ). C) Late ( 3 to 8 months after first surgery ).

Elements of Progressive loading: 1) Time interval (3 to 8 months acc. To type of bone). 2) Diet (Soft diet). 3) Occlusal material and occlusal contact. 4) Prosthesis design (Avoid Cantilevers and wide occlusal tables).

6- Superstructure related:

a) Implant abutment connection

The misfit at abutment-implant interface and the missing of a passive adaptation between the prosthesis and the -abutment can lead prosthesis components, abutment screw or implants to fracture

a) Implant abutment connection

.

Functionally, this misfit can cause overload at the abutment and distribute non-axial load along implant and marginal bone. The gap generated bacteria colonization, which might cause inflammatory reactions in the per implant soft tissues

Implant abutment interface:

External hex connection:

the two stage

method, an antirotational

mechanism retrievability

disadvantages :micro movements because of

the size of the hex, higher center of rotation that leads to lower resistance for rotational and micro gap leading to bone resorption.

butt-joint interface have shown an incidence of abutment screw loosening of up to 38%.

Internal hex connection : distribute intraoral forces deeper within the implant to

protect the retention screw from excess loading and to reduce the potential of microleakage

Internally connected implants also provide superior strength for the implant/abutment connection.

Morse taper connection abutment post is inserted

into the non-threaded shaft of a dental implant with the same taper.

vertical positioning and self-locking characteristics enhances ability to resist bending forces, abutment loosen in micro-movement and micro pump formation.

internal morse taper design is such that an essentially “cold weld” is produced when the precision fit tapered abutment

Internal hex connection :

.

Joint clamping forces (preload)

the screw joint as 2 parts tightened together by a screw, such as an abutment and implant tightening together by a screw

Joint Separating forcers : Opposing the clamping force is a joint-separating force, which attempts to separate the screw joint. Screw loose occurs when the joint-separating forces acting on the loosening are greater than the clamping forces holding screw unit together.

Joint Separating forcers : separating forces may include: 1. off-axis occlusal contacts, 2. lateral excursive contacts, interproximal contacts

between natural teeth and implant restorations, protrusive contacts,

3. parafunctional forces and 4. non-passive frameworks that attach to the implants .

b) Artificial teeth cuspal inclination:

The greater cusp angles may incise food more

easily and efficiently yet the occlusal contact

along an angled cusp results in an angled load

to the crestal bone.

The magnitude of the force is minimized when the

angled occlusal contact is not a premature contact

but instead is a uniform load over several teeth or

implants.

This position usually is accomplished by: 1- Increasing the width of the central groove to 2 to 3 mm in posterior implant crowns, which are positioned over the middle of the implant abutment. 2- The opposing cusp is recontoured to occlude the central fossa directly over the implant body.