Ceph Superimposition
3 reasons you might superimpose ceps
1) Assess/monitor growth of mandible and maxilla relative to cranial base 2) Assess treatment changes § Dentition to eachother and bases § Skeletal § Soft tissue 3) Assess post treatment changes § Relapse § Further growth/change
What is the ABO colour coding for ceph superimposition?
1) Black Pre Treatment 2) Blue progress/Mid treatment 3) Orange end of treatment 4) Green end of retention
What 3 things can we evaluate by superimposing cephs?
1) Changes in facial skeleton relative to cranial base 2) Maxillary growth and dentoalveolar change 3) Mandibular growth and dentoalveolar change
What are the structural landmarks used by Bjork to superimpose on the mandible?
1. Anterior contour of chin 2. Inner contour of cortical plate at lower border of symphysis 3. Trabecular structure in symphysis 4. Contour of mandibular canal 5. Contour of mineralised molar tooth germ before root development
What are the Bjork landmarks for superimposition on the cranial base? 7 things.
1. Inner anterior wall of sella (5-6 years old) 2. Intersection of the lower contours of the anterior clinoid process and the anterior wall of sella (5-6 years) 3. Anterior contours of the middle cranial fossa (12-14 years) 4. Contour of the cribiform plate (4 years) 5. Trabecular system in the anterior cranial base (4 years) 6. Contours of the bilateral fronto-ethmoidal crests (4 years) 7. Cerebral surfaces of orbital roof (5-6 years)
Within what range should the focus to film distance be for ceps to minimise magnification effects?
1.5-1.8m
Describe the Pancherz analysis
A reference line constructed perpendicular to the occlusal plane with radiographs superimposed on SN, registered at S.
For Rickett's method (nasion to basin) of superimposing on cranial base where do you register for mandible and maxillary changes?
Mandibular - CC point, intersection of a line from PT to gnathion Maxillary - Nasion
Give 2 methods of superimposing on the mandible
Mandibular plane Structural method of bjork
Is the magnification constant across the film?
No it is slightly different due to shape of beam
When superimposing for maxillary structures using the structural method of Bjork, how do you orientate your second radiograph with regards to the nasal floor and orbital floor?
Orientate second rad so that resorptive lowering of nasal floor is slightly less than apposition at the orbital floor, approx. 2/5 nasal floor compared to 3/5 at orbital floor. Floor of the orbit should go up slightly more than the nasal floor comes down
Give 3 methods of superimposing maxilla
Palatal plane (ANS-PNS) Best fit Structural method of Bjork
Which ceph analysis used in the O'Brien twin block studies?
Pancherz
Give 4 methods of superimposing on cranial base
SN De-Coster's line Rickett's (Nasion-Basion) Bjork's structural method
What is purpose of the ear rods?
To maintain a standardised distance between the mid-sagittal plane of the head, the X-ray source and the film (this keeps magnification constant for every radiograph taken with that apparatus). To limit head movement (to achieve a sharp image). To allow the radiographer to position the head so that all important structures will appear on the image.
Difference between validity and reliability in ceph analysis
Valid: represents accurately the structure of interest reproducible: repeatedly identifiable with good level of accuracy
Difference between random and systematic error in cephalometry
random error: error which is wholy due to chance and does not reoccur systematic error: error which does not occur by chance but occurs due to an innacuracy in the system
Where is registration of a palatal plane superimposition?
§ ANS - Ricketts, McNamara, Broadbent § Pterygomandibular Fissure - Moore
Which structures make up De-Coster's line?
§ Anterior lip of sella § Spenoethmoid suture § Planum sphenoidale § Roof of ethmoid § Cranial side of frontal bone
Which structure do you superimpose maxilla on using structural method of Bjork?
§ anterior surface of zygomatic process of maxilla
