Sharptooth/Jaws of the Dragon

[Draidis]

Hi guys,

I'm trying to put together the Jaws of the Dragon wonderous item from the Draconomicon. Here's the description:

This complex metal device is worn in the mouth, fitting over the teeth while allowing them to protrude. A row of metal teeth is set into the jaws of the dragon behind where the dragon’s teeth emerge, increasing the damage dealt by the dragon’s bite. The dragon gains the benefit of the sharptooth spell while the jaws are worn. The device resizes to fit any creature as normal for a magic item, but creatures with no natural bite attack gain no benefit from wearing it.

Here is the description of Sharptooth:

Choose one of your natural weapons (your bite, a single claw, a wing, a crush, a tail slap, or a tail sweep). For the duration of the spell, that natural weapon deals damage as though you were one size larger than your actual size. You cannot gain additional attack forms (such as a tail slap) by using this spell; you can only improve attacks you already possess.
This spell does not stack with itself. This spell’s name derives from a marked preference among dragons for improving their bite attacks with this spell, but it works equally well on claw, wing, tail, and crush attacks.

I have no idea how to go about coding the effects of this spell so that when applied to the item, specifically the natural damage of the bite attack, increases by the above stated amount. Any assistance is appreciated.