It depends on how you want to cast it.
Unless you are targeting a specific spell the roll for dispel magic is compared to the spell with the highest caster level first. If you don’t dispel that spell it is compared to the spell with the next highest caster level. You keep going until you dispel a spell or fail to dispel any of the target's spells. When using this option, you don’t choose which spell is dispelled. You use the same roll for every spell and don’t get to roll each check separately.
I you target a particular spell you only check vs that spell. If you fail the roll, there is no further checks for other spells. If you use this option, you can target whichever spell you want. If you dispel the Permanency and the normal duration of the spell has expired, it will also stop working. If the other spell still has any duration left it will continue to function
The first option gives you more than one chance to end the spell but has a chance of ending a different spell. Let’s say the target had the spell Magic Aura cast by a 12th level wizard in addition to the spells listed. You roll your dispel magic check and it is not high enough to end the magic fang, but is high enough to end the Magic Aura, it would end that and not even check for the Permanency.
It is as MS said above…
But to answer the original question… Magic Fang would still be caster level 14. Permanency, on the otherhand, is CL 10.
When a spell is permanencied you are left with two active spell effects. The original spell cast and permanency. When dispel is cast it needs only dispel one of the two spells. Remember permanency has a duration of permanent, not instantaneous. It remains in effect after cast.
A level 14 druid casts greater magic fang on a level 10 wizard. The wizard then casts permancy on the greater magic fang effect. Tomorrow an enemy casts dispel magic. What is the relevant caster level for greater magic fang, 10 or 14? 10 right?
A little nitpick: to make Magic Fang, Greater permanent you need an 11th level caster.
Some permanent spells require a Dispel Magic with a CL higher than the caster of permanency to cancel them, but only those that are cast on the caster of permanency:
You can make the following spells permanent in regard to yourself.
Spell Minimum Caster Level GP Cost
Arcane sight 11th 7,500 gp
Comprehend languages 9th 2,500 gp
Darkvision 10th 5,000 gp
Detect magic 9th 2,500 gp
Read magic 9th 2,500 gp
See invisibility 10th 5,000 gp
Tongues 11th 7,500 gp
You cannot cast these spells on other creatures. This application of permanency can be dispelled only by a caster of higher level than you were when you cast the spell.
Spells cast on other targets are vulnerable to dispel magic as normal. The GM may allow other spells to be made permanent.
The wording is somewhat awkward, as verbatim, if you cast a spell that isn't in the first list but is in the second list on yourself and make it permanent, it doesn't fall under the first condition, nor under the second, there is no instruction on how it works.
As I read it, the RAI is that permanency on all the spells that aren't in the first list can be Dispelled even by a lower CL caster.