True or false: a radiolucent lesion of NON-endodontic origin will remain superimposed over the apex of the suspected tooth regardless of the horizontal cone angulation used.

Correct answer: C. False — a non-endodontic lesion typically shifts away from the apex when the angulation changes

• A. Lesion size does not change the parallax principle; the behaviour depends on the anatomical relationship, not the dimensions.
• B. The parallax effect operates with both paralleling and bisecting-angle techniques.
• C. CORRECT. This is the diagnostic value of the SLOB rule applied to periapical pathology. A lesion of ENDODONTIC origin arises from the apical foramen and therefore stays centred on the apex no matter how the tube head is angled. A lesion of NON-endodontic origin — an incisive canal, a lateral periodontal cyst, a mental foramen, an odontogenic tumour — is a separate anatomical structure, so shifting the horizontal angulation makes it move relative to the root.
• D. This reverses the rule. It is the endodontic lesion that stays anchored to the apex.

Note: SLOB: Same Lingual, Opposite Buccal. Take a second film at a different horizontal angle whenever an apical radiolucency might not be endodontic — and always confirm with pulp testing.