Establishment of a Murine Pulp Exposure Model with a Novel Mouth-Gag for Pulpitis Research

Individual experiments, like 2D or 3D cell cultures, have been widely used to test the reactions of dental pulp cells. These experiments cannot reflect the interaction between pulp tissue and the systemic immune system. Therefore, in vivo experiments are becoming increasingly popular in endodontic research.

C57 mice have increasingly become a common choice in inflammation research on dental pulp due to their cost-effectiveness, high fatality, and vitality. However, the small size of mice and the lack of coordination pose significant challenges during experimental procedures. The fixation process is an important factor that higher the technical threshold.

We devised a novel mouth gag using readily available materials and simple assemblies to assist researchers in pulp exposure surgery. According to our research, this mouth gag can significantly shorten the time required for beginners to immobilize the mouth and expose the maxillary first molar of mice. To begin, straighten an eight-micron-thick orthodontic arch wire with your left hand, while keeping the right hand slightly bent against the wire arch.

Use a Young loop-bending plier to bend the top edge of the trapezoid about eight millimeters at the midpoint of the bow wire. Ensure that point a is on the edge of the plier beak. Now, hold the plier with the left hand, clamp the free end of the bow wire with the right thumb and forefinger.

Then bend the bow wire from point a to make a 120 degree angle. Place the arch wire on a horizontal table to check if it is on a single plane. Leave about nine millimeters on each side of the wire, and use pliers to bend the free end to a 75-degree angle.

Now locate point c, which is about five millimeters from point b. Bend the wire at point c to make a 105-degree angle. Similarly, bend the wire at points d and e.

Clamp the ik and kj parts simultaneously. Duplicate the a, b, c bending at points l, j, and k. Then, bend the free end at point j to make it vertical to the ikj plane.

Bend an extra tongue depressor for the mandibular part. Clamp point i five millimeters from point j, and bend the free end to make it parallel to both the ikj plane and the cd part. Next, leave a five millimeter gap from point i.

And at point h, bend the arch vertically to the ih and jih planes. Locate point g five millimeters from h and clamp the jihg lane. Then, bend the arch at point g.

Now, bend the free end symmetrical to the kj plane. The free end after point f should be symmetrical to the free end at point e. Finally, place rubber caps on the free ends.

To begin, fix an anesthetized mouse in a supine position on a fixation plate. Secure the limbs with skin tape. Compress the free ends of a prepared mouth gag with the thumb and the index finger.

Fix the mouse's front incisors in the trapezoidal groove between the two arms of the mouth gag. Ensure the arm with the tongue depressor is placed on the mandibula. Check the maxillary first molar to ensure it is free of dental caries, trauma, and odontogenesis.

Assess the surrounding gingiva to ensure absence of redness, swelling, or fistula. Then, check the health of the opposite teeth. Next, with a dental burr, drill the occlusal side of the maxillary first molar at 20, 000 RPM.

Remove the enamel. With a syringe, drop normal saline every three minutes over the tooth to prevent overheating. Put a number 8 C-plus file on the lowest position of the drilled pit and pierce the last dentine to expose the pulp chamber.

Clean the fragments around the tooth, then remove the mouth gag. The time taken to fix the mouth with the mouth gag and to find the maxillary first molar was significantly shortened relative to the traditional method. The pulp exposure was confirmed through micro-CT and reconstruction modeling.

At 24 hours post-surgery, most of the pulp tissue retained its morphology.