Oro-facial implants

By Dr. Hassan M. Abouelkheir

BDS, MSC, PhD.

Ideal image casting:• The ability to visualize implant site

buccolingually, mesio-distally & superio-inferiorly.

• The ability to allow reliable accurate measurements.

• The capacity to evaluate trabecular density & cortical thickness.

• The capacity to correlate the imaged site with clinical site.

• Reasonable access & cost to patient. • Low radiation dose.

Intra-oral Radiography

• 1- Periapical Radiographs: • It Provide superior resolution

and sharpness. • Parallel technique is used to

decrease geometric errors. • They determine vertical

height, architecture and bone quality (bone density, amount of cortical & trabecular bone.

!

Intra-oral Radiography (continue):

• Geometric & anatomical limitations:

• Foreshortening & elongation of radiographic alveolar height.

• Positioning of film may miss anatomical structures.

• Unable to provide any cross- sectional information.

2- Occlusal radiographs: • Although it gives a clue about facio-

lingual dimension of mandibular alveolar ridge .

• It records the widest portion of the mandible which is below the alveolar ridge .

• It is not suitable for maxilary arch due to anatomical limitations.

Intra-oral Radiography (continue):

Extra-oral radiographs:

• 1- Lateral & Lateral-oblique cephalometric radiography:

!• Lateral cephalometric: has 7% to 12% magnification

It gives the axial tooth inclination and dento - alveolar relationships as well as cross section at midline only due to over projection of the lateral areas of the jaw.

Extra-oral radiographs (continue)

2-Oblique Lateral Cephalometric Radiographs (OLCR)

• One side of the body of the mandible positioned parallel to the film cassette.

• A cephalostat with earplugs and a nasion support was used to position the head with the porion-subnasal plane in a horizontal position. A light beam was used to position the mandibular lower border with an inclination of 20 degrees.

• Measurements from this image are not reliable.

Extra-oral radiographs (continue):

!3- Panoramic radiography: • It is important for broad visualization

of the jaws and anatomical structures. • It is useful for preliminary estimations

of crestal alveolar bone and cortical boundaries of ID canal, max. s. & nasal fossa.

Limitations of panoramic radiography:

1- angular measurements are accurate but horizontal ones are not.

2 - Magnification (size distortion) varies among films from different panoramic unites and also at different areas on the same film.

3- Foreshortening and elongation of vertical measurements.

4- Overestimation of vertical bone heights. 5- Magnification of horizontal image measurements

as a result focal trough area constructed on average population (0.70 to 2.2 times actual size) .

4- conventional tomography:

• This technique produces a cross –sectional , flat-plane image layer that is perpendicular to the x-ray beam.

• The complex (multidirectional) tube motion of current conventional tomographic units minimizes image superimposition & provide fixed uniform image magnification for accurate measurements.

• Radiographic stents are used to determine the width and height of pre-planned implants after correction with magnification factor as in case of using scanora integrated imaging system.

• Two or three cross-sectional tomographic slices are required to preplan each intended implant site.

5- Reformatted computed Tomography:

It is indicated for : 1- Edentulous pts. 2- Multiple implants. 3- Augmentation procedures. 30 axial images are required per jaw

(1-2mm). These sequential axis images can be

manipulated by process called multiplannar reformatting (MPR) to produce multiple two dimensional images in various planes.

Reformatted computed Tomography (cont.)• The CT analysis comes from 3 basic

image types: • Axial images. • Reformatted cross-sectional

images. • Panoramic like images. • The computer places a series of

sequential dots on selected scan then connect them to construct a customized arch .

• Then it places a series of lines at constant intervals (1-2mm) on axial image to indicate the position at which each cross sectional slice will be reconstructed.

Reformatted computed Tomography (cont.)• These reformatted images

provide the clinician with two-dimensional diagnostic information in all three dimensions.

• It gives information on; 1- amount of cortical bone and

residual bone. 2- location of vital structures. 3- contour of soft tissues. 4- 3D reformations for

augmentation as in maxillary sinus lifting.

Pre-operative planning:• Diagnostic image can give 3D information

about quality and quantity of alveolar bone. Quality: • 1- the thicker the cortical bone the best

withstand for functional load. • 2- A greater number of internal trabeculae

per unit area is advantageous.

Pre-operative planning (cont.):Quantity: 1- Height . 2- Width of alveolar

bone. 3- Morphology of ridge. Cross –sectional image

to determine facio-lingual width and height , along with inclination of bone contour.

Pre-operative planning (cont.): • Pre-planning

measurements in different technique shows variable magnification factor (MF).

• Radiographic image / MF to correct measurements.

• (Pan, Periapical).

Pre-operative planning (cont.):• If MF is constant a

plastic overlay with 1mm grids or diagrams of available implant sizes can be used directly on image.

• Specialized reformatted CT implant programs can perform image without magnification. It can be printed life size.

Imaging stent

• Pre-surgical imaging can be enhanced by radiographic stent to locate the position of pre-surgical site for end osseous implant.

• The intended implant sites are identified by radiopaque spheres or rods (metal, composite resin or Gutta percha).

Interactive Diagnostic software: several interactive

software packages (e.g. Sim-plant ) allow presurgical simulation of implant orientation and placement.

Interactive Diagnostic software:• There are 3 basic views available

on the Sim/Plant™ screen: • The Panoramic view is similar to

a normal two dimensional panoramic view.

• The axial view offers a perspective from a coronal/apical direction.

• There is a cross sectional view that allows a mesial /distal cross sectional perspective of the arch.

Selecting diagnostic imaging for pre-operative planning:

1- panoramic view. 2- intraoral periapical films for particular

region of interest. 3- CT if entire maxilla or/and mandible is

required. 4- conventional tomography for few selected

regions.

Intra-operative & postoperative assessments:1- panoramic view. 2- intraoral radiographs. • Intra- operative films may be required for

confirmation of correct implant placement or to locate a lost implant.

• Inspection includes; 1- alveolar bone height around implant. 2- the appearance of bone around and

adjacent to implant.

Intra-operative & postoperative assessments• Angulations of x-ray beam

must be within 9 degrees of long axis of the fixture to see the sharp image of threads of fixuture .

• Otherwise angular deviation of 13 degrees or more result in complete overlap to the threads.

Intra-operative & postoperative assessments• Longitudinal assessment of

implant by serial standardized periapical films using XCP- film holder with rubber base impression material to measure;

1- Mesial & Distal bone height from standard landmark at the collar of implant.

2- or interthread measurements compared to bone levels on serial radiographs.

Intra-operative & postoperative assessments

• There is initial circumscribed resorptive osseous changes around cervical area of fixture during 1st 6 months after surgery.

• It was estimated that there was marginal bone loss 1.2mm in the 1st year then 0.1mm in succeeding years.

Intra-operative & postoperative assessments

• If any resorptive changes are present , they evidenced by apical migration of the alveolar bone or indistinct osseous margins.

• Density can be measured in intraoral digital radiographs to measure bone resorption .

Intra-operative & postoperative assessments

• Digital subtraction radiography requires image geometry reproduction between radiographic examinations.

• The success of implant can be evaluated by normal bone surrounding and up to the surface of the implant .

• No clinical mobility.

Radiographic signs of failing endosseous implants:

• Thin radiolucent area surrounding the entire implant.

• Crestal bone loss around the coronal portion of the implant.

• Apical migration of alveolar bone on one side of the implant.

• Widening of PDL space of nearest natural Tooth (abutment).

• Fracture of implant fixture.