This study was funded by grants from National Natural Science Foundation of China U21A20368 (L. Y.), 82101000 (H. W.), and 82100982 (F. L.), and by Sichuan Science and Technology Program 2023NSFSC1499 (H. W.). All the original data and images are included in this paper.

The experimental procedures in this study were approved by the ethical committee of the West China School of Stomatology, Sichuan University (WCHSIRB-D-2021-125). Adult C57BL/6 mice were obtained from Gempharmatech Experimental Animals Company, Chengdu, China. The whole crown of the maxillary first molar erupts 21 days after birth. Mice for surgery should be older than 21 days with normal vitality11. Here, 6 to 8-week-old mice were used for modeling. Figure 1 is a flo...

Creating a Pulp Inflammation Mouse Model Using a Novel Mouth-Gag 

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	<li>Kleinert, A., Kleinert, L., Ozimirska, M., Cha&#322;as, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endodontium+-+together+or+separately.">Endodontium - together or separately.</a> Folia Morphol. 77 (3), 409-415 (2018).</li><li>Dhillon, H., Kaushik, M., Sharma, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regenerative+endodontics-Creating+new+horizons.">Regenerative endodontics-Creating new horizons.</a> J Biomed Mater Res B Appl Biomater. 104 (4), 676-685 (2016).</li><li>Prati, C., Pirani, C., Zamparini, F., Gatto, M. R., Gandolfi, M. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regenerative+endodontics:+a+review+of+current+status+and+a+call+for+action.">Regenerative endodontics: a review of current status and a call for action.</a> J Endod. 33 (4), 377-390 (2007).</li><li>Arora, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+application+of+immunotherapy+for+modulation+of+pulp+inflammation:+opportunities+for+vital+pulp+treatment.">Potential application of immunotherapy for modulation of pulp inflammation: opportunities for vital pulp treatment.</a> Int Endod J. 54 (8), 1263-1274 (2021).</li><li>Eramo, S., Natali, A., Pinna, R., Milia, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dental+pulp+regeneration+via+cell+homing.">Dental pulp regeneration via cell homing.</a> Int Endod J. 51 (4), 405-419 (2018).</li><li>Hasan, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+Toll-like+receptor+2,+Dectin-1,+and+Osteopontin+in+murine+model+of+pulpitis.">Expression of Toll-like receptor 2, Dectin-1, and Osteopontin in murine model of pulpitis.</a> Clin Oral Investig. 27 (3), 1177-1192 (2023).</li><li>Wang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DDIT3+aggravates+pulpitis+by+modulating+M1+polarization+through+EGR1+in+macrophages.">DDIT3 aggravates pulpitis by modulating M1 polarization through EGR1 in macrophages.</a> Int Immunopharmacol. 120, 110328 (2023).</li><li>Richert, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+critical+analysis+of+research+methods+and+experimental+models+to+study+pulpitis.">A critical analysis of research methods and experimental models to study pulpitis.</a> Int Endod J. 55 (Suppl 1), 14-36 (2022).</li><li>Huang, X. 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N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+biomarkers+for+objective+assessment+of+symptomatic+pulpitis:+A+systematic+review+and+meta-analysis.">Molecular biomarkers for objective assessment of symptomatic pulpitis: A systematic review and meta-analysis.</a> Int Endod J. 56 (10), 1160-1177 (2023).</li><li>Goldman, E., Reich, E., Abramovitz, I., Klutstein, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inducing+apical+periodontitis+in+mice.">Inducing apical periodontitis in mice.</a> J Vis Exp. (150), e59521 (2019).</li><li>Duncan, H. 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Authors declare no conflict of interest.

As the solitary soft tissue within teeth, dental pulp fulfills a crucial role in maintaining bioactivity of tooth but remains highly sensitive. The preservation of this vital pulp has become the preferred initial approach in recent endodontic treatments, necessitating a comprehensive understanding of the inflammatory mechanisms of dental pulp16. The spatiotemporal fluctuation of the inflammatory microenvironment and interactions between resident cell types in pulpitis complicates its investigation...

The dental pulp, an integral part of the tooth, is responsible for multiple essential functions such as nutrient supply, dentin formation, sensory function, and defense reactions1. Nevertheless, the dental pulp, surrounded by hard tissue, is susceptible to injuries and damages from deep caries, pulpitis, trauma, or subsequent therapies2,3. The absence of functional dental pulp increases the risk of tooth fragility4. Moreover, the loss of pulp vitality in young permanent teeth can adversely affect tooth maturation, and current denture techniques fail to restore the neural feedback offered by healthy pulp4. This situation has led researchers to explore alternative solutions for managing inflamed pulp beyond mere removal.
In 2007, Murray et al. initiated the application of tissue engineering in regenerative endodontics, thereby sparking increased interest in pulp preservation and regeneration5. However, inflamed pulp tissue poses a challenge as cells release inflammatory factors such as IL-6, which recruit inflammatory cells and results in cell necrosis, loss of pulp vitality, and complications in functional recovery6,7. Understanding inflammation and the associated cell death is, therefore, crucial for advancements in the preservation of vital pulp. There are a number of experiments that have been conducted to explore the molecular biology of the inflame pulp in vivo or in vitro8,9. Though in vitro&#160;experiments like 2D or 3D cell cultures have been developed for years and are becoming mature and widely used to test reactions of pulp cells to inflammatory factors, these experiments cannot reflect the interaction between pulp tissue and the systemic immune system10. If the phenomenon being studied is derived from cells of other tissue origin like immune, vascular and nervous system, then pure pulp cell culture will lead to a dead end. Therefore, in vivo experiments are very necessary and referential.
Mice have increasingly become a common choice in inflammation research in vivo&#160;due to their cost-effectiveness, high fertility, and vitality. However, a comprehensive protocol for mice pulpitis model is currently absent, which can serve as a reference. The small size of mice and their sensitivity to stimulation pose significant challenges during experimental procedures. Observing the minuscule teeth concealed deep within the mouse mouth often necessitates the use of a cantilever microscope, notwithstanding the more common presence of desktop microscopes in laboratories. The absence of a mouth opener requires assistance from others. To address this, the group has devised a mouth-gag using readily available materials which aims to provide a standardized and reproducible protocol for constructing the mice pulpitis model. This article details the procedure, covering preoperative preparation, immobilization, pulp exposure surgery, and sample collection on C57 mice. This protocol recommends the use of the mouth-gag, providing information on its structure, production, and application to facilitate other researchers in replicating the procedure.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Animal</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>C57/B6J mice</td>
			<td>Gempharmatech Experimental Animals Company</td>
			<td>C57/B6J</td>
			<td>For the establishment of pulp exposure</td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL syringe</td>
			<td>Chengdu Xinjin Shifeng Medical Apparatus &#38; Instruments Co. LTD.</td>
			<td>SB1-074(IV)</td>
			<td>Apply in drug injection.</td>
		</tr>
		<tr>
			<td>8# C+ file</td>
			<td>Readysteel</td>
			<td>0010047</td>
			<td>Apply in exposing the roof of pulp chamber.</td>
		</tr>
		<tr>
			<td>Anesthesia Mix solution</td>
			<td></td>
			<td></td>
			<td>10% ketamine hydrochloride+ 5% xylazine + 85% sterile isotonic saline.&#160;</td>
		</tr>
		<tr>
			<td>DAPI Staining Solution</td>
			<td>Beyotime</td>
			<td>C1005</td>
			<td>Apply in immunofluorescence staining for counter-staining of nucleus.</td>
		</tr>
		<tr>
			<td>Dental high-speed dental handpiece</td>
			<td>Jing yuan electronic commerce technology</td>
			<td>WJ-422</td>
			<td>Apply in pulp exposure.</td>
		</tr>
		<tr>
			<td>Heavy wire cutter</td>
			<td>Jirui Medical Instrument Co., Ltd.</td>
			<td>none</td>
			<td>Apply inarc cutting.</td>
		</tr>
		<tr>
			<td>Hematoxylin and Eosin Stain kit</td>
			<td>Biosharp</td>
			<td>BL700B</td>
			<td>For the histological analysis of the slides.</td>
		</tr>
		<tr>
			<td>IL-6 antibody</td>
			<td>Novus</td>
			<td>NBP2-89149</td>
			<td>Apply in immunofluorescence staining to detect the inflammation of the dental pulp.</td>
		</tr>
		<tr>
			<td>Ketamine(Ketamine hydrochloride)</td>
			<td>Vet One, Boise, Idaho, USA</td>
			<td>C3N VT1</td>
			<td>100mg/kg, IP. Apply in nesthetization.</td>
		</tr>
		<tr>
			<td>Medical tap</td>
			<td>3M</td>
			<td>1530</td>
			<td>Apply in mice immobilization.</td>
		</tr>
		<tr>
			<td>Orthodontic arch wire&#160;</td>
			<td>Shanghai Wei Rong Medical Apparatus Co. LTD.</td>
			<td>K417</td>
			<td>Diameter of 8&#181;m</td>
		</tr>
		<tr>
			<td>Round dental burr (0.6 mm)</td>
			<td>Shofu global</td>
			<td>072208</td>
			<td>Apply in removing enamel and shallow layer of dentin.</td>
		</tr>
		<tr>
			<td>Young loop bending plier</td>
			<td>Jirui Medical Instrument Co., Ltd.</td>
			<td>none</td>
			<td>Apply in arc bending.</td>
		</tr>
	</tbody>
</table>

establishment of a murine pulp exposure model with a novel mouth-gag for pulpitis research

Pulpitis, a common cause of natural tooth loss, leads to necrosis and loss of bioactivity in the inflamed dental pulp. Unraveling the mechanisms underlying pulpitis and its efficient treatment is an ongoing focus of endodontic research. Therefore, understanding the inflammatory process within the dental pulp is vital for improving pulp preservation. Compared to other in vitro experiments, a murine pulpitis model offers a more authentic and genetically diverse context to observe the pathological progression of pulpitis. However, using mice, despite their cost-effectiveness and accessibility, poses difficulties due to their small size, poor coordination, and low tolerance, complicating intraoral and dental procedures. This protocol introduces a novel design and application of a mouth-gag to expose mouse pulp, facilitating more efficient intraoral procedures. The mouth-gag, comprised of a dental arch readily available to most dentists and can significantly expedite surgical preparation, even for first-time procedures. Micro-CT, hematoxylin-eosin (HE) staining, and immunofluorescence staining were used to identify changes in morphology and cell expression. The aim of this article is to help researchers establish a more reproducible and less demanding procedure for creating a pulp inflammation model using this novel mouth-gag.

Author Spotlight: Enhancing Dental Pulp Research with Improved Mouse Models

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 fertility and vitality. However, the small size of mice and lack of coordination posed 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.

The procedure described above was performed on the right maxillary first molar of 3, 6-8 weeks old C57BL/6 mice, while the left maxillary first molars were preserved as control. Histology and immunofluorescence results from blank control, 12 h pulpitis and 24 h pulpitis samples were utilized for demonstration.
Following protocol of CT analysis from Goldman et al.15, pulp exposure was confirmed through micro-CT and reconstruction modeling in Figure 4...

Watch this Scientific Journal Video about Establishment of a Murine Pulp Exposure Model with a Novel Mouth-Gag for Pulpitis Research at JoVE.com

This article presents a streamlined protocol for establishing a pulpitis model in mice using an innovative mouth-gag, followed by subsequent histological analysis.

Pulpitis, a common cause of natural tooth loss, leads to necrosis and loss of bioactivity in the inflamed dental pulp. Unraveling the mechanisms ...

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Research

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Medicine

Preparation of the Mouth Gag for a Mouse Pulpitis Model

To begin, straighten an 8 micron thick orthodontic arch wire with your left hand while keeping the right hand slightly bent against the wire arc. 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.

Using A Mouth Gag for Pulpitis Assessment in Mice

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+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.

589 Views.  Sichuan University.  This article presents a streamlined protocol for establishing a pulpitis model in mice using an innovative mouth-gag, followed by subsequent histological analysis.

Creating a Pulp Inflammation Mouse Model Using a Novel Mouth-Gag

Summary