Metapex vs. Metapaste: Unpacking the Differences & When to Use Each

We’ve all been there: midway through an endo session, dealing with a necrotic case, and needing to close things up temporarily before the next appointment. That’s when the perpetually puzzling question pops up: “What exactly should I put inside this canal?” In the market, there are two major players whose names and appearances are remarkably similar, often causing confusion: Metapex and Metapaste.

They look alike. Their names sound alike. Even their primary active ingredient is the same. Yet, the truth is, they are almost entirely distinct in nearly every aspect—from their composition and mechanism of action to their clinical applications. Misusing one in place of the other isn’t just a potential setback for the case; it could genuinely create issues you’d rather avoid.

In this article, we’re going to set the record straight. We’ll provide a highly practical comparison so you can confidently make the right choice, every single time.

1. The Manufacturer’s Distinction: Chemical Composition

To truly grasp the full picture, we need to start at the very beginning: what’s actually inside each syringe?

Metapaste:

This one is your go-to for straightforward, effective work.

• Color: It appears white in the clinic and shows up as a light white on radiographs.

• Components: Just two essential ingredients:

  • Calcium Hydroxide: This is our star player. Its job is to create a highly alkaline, high-pH environment that’s lethal to bacteria and actively encourages tissue healing.

  • Barium Sulfate: This material has absolutely no therapeutic role. Its sole purpose is to serve as a Radiopaque agent, allowing you to clearly visualize it on an X-ray film.

Metapex:

Now, this one is for those special missions; it comes with an extra weapon.

• Color: It appears yellow, both in the clinic and on radiographs.

• Components:

  • Calcium Hydroxide: Our primary hero is present here too.

  • Iodoform: This is the crucial extra weapon and the fundamental difference. Iodoform is a potent Antiseptic and Antibacterial compound, and it’s what gives Metapex its distinctive yellow color and unique scent.

The Bottom Line: So, the entire crux lies in the Iodoform found in Metapex, which grants it significant additional disinfecting power.

2. Ease of Use: Solubility and Removal

This might just be the most practical point that will truly make a difference in your day-to-day practice.

Metapaste:

This is your easy-going friend; it won’t give you a headache. It’s a Water-Soluble material. What does that mean for you? When it’s time to remove it during the next session, the process becomes incredibly simple. A bit of irrigation with sodium hypochlorite or saline, combined with a gentle file, and you’ll find the canal perfectly clean again.

Metapex:

Now, this one can make you tear your hair out if used incorrectly. It’s an Oil-Based material, meaning it absolutely does not dissolve in water. This characteristic makes its removal extremely challenging. If you attempt to remove it with irrigation alone, you’ll likely find a sticky, oily layer stubbornly clinging to the canal walls, refusing to budge. That persistent layer then acts as a barrier, preventing your Sealer from properly adhering to the final obturation.

3. When to Use Each: Clinical Indications

Based on the differences we’ve just discussed, each product has its specific “playground” where it truly excels, and where the other simply shouldn’t trespass.

Metapex: Specifically for Kids

Given its oil-based composition and the presence of Iodoform, Metapex is almost exclusively used in Deciduous Teeth for these particular situations:

• Primary Tooth Pulpectomy (Root Canal Filling in Primary Teeth): Because it’s a Resorbable material, it gradually dissolves over time at a rate similar to the absorption of the primary tooth’s root, thus avoiding any interference with the erupting permanent tooth below.

• Apexification in Primary Teeth.

• Treatment of Internal Resorption in Primary Teeth.

A Clinic-Sized Warning: Never, under any circumstances, use Metapex as an intracanal medicament (temporary filling between sessions) in a Permanent Tooth. Its notorious difficulty of removal could jeopardize your entire final obturation.

Metapaste: The Expert for Permanent Teeth

Metapaste, with its water-based formulation and ease of removal, stands as your primary and essential choice for Permanent Teeth in these cases:

• Intracanal Medicament (Temporary Filling Between Sessions): This is its core function. You place it to ensure the canal remains sterilized between appointments.

• Exudate/Weeping Canals: If you’re dealing with a canal that persistently refuses to dry, calcium hydroxide is incredibly effective at promoting desiccation.

• Treatment of Internal and External Root Resorption: The alkaline environment it creates can effectively halt the activity of cells responsible for root destruction (1).

• Apexification in Permanent Teeth: It remains the classic material used to create a solid apical barrier in teeth with open apices.

4. The Metapex Removal Trick (If You’re Forced To)

Since Metapex is notoriously difficult to remove, there’s a simple trick we employ to make the process considerably easier.

Don’t Go All the Way: During your initial cleaning and shaping session, do not reach your Master Apical File (MAF). Instead, stop at the size before it—your Second to Last File.

• Inject the Metapex and seal the access.

• In the Second Session: All you’ll need to do is advance your actual Master Apical File. The idea here is that you’re using this final file as a “scraper,” both enlarging the canal to its definitive size and simultaneously dislodging the Metapex remnants that were adhering to the walls.

5. Why Two Sessions Anyway? (The Rationale for Multiple Visits)

Many of us prefer to perform root canal treatments in two sessions, especially for necrotic cases. The underlying principle is that in the first session, you mechanically clean the canal with files and irrigation. However, some bacteria invariably remain hidden within the microscopic Dentinal tubules.

Placing Calcium Hydroxide between sessions acts as a long-acting “chemical disinfection,” effectively eliminating these lingering bacteria. A significant study published in the Journal of Endodontics in 2012 demonstrated that using calcium hydroxide between appointments markedly improves the canal’s condition and significantly reduces bacterial counts (2).

6. Metapaste’s Limited Time in the Canal (Metapaste’s Limited Effectiveness)

Because Metapaste is water-soluble, it also tends to dissolve in the tissue fluids present in the periapical region. Consequently, its effectiveness typically lasts for only about 7 days. After this period, it will have largely dissolved and will no longer exert its therapeutic effect.

If you leave it in for much longer than a week or ten days, there’s a risk of Re-infection of the canal. This can even manifest on radiographs as a “Hollow Canal Effect” (3).

The Bottom Line: You absolutely should not leave Metapaste in the canal for more than a week to ten days at most. If the patient expects delays, the wiser choice is to bring them back, remove the old paste, and place fresh material.

7. Why Does Metapex Last Longer?

As we mentioned, Metapex is an oil-based material. This property results in a significantly slower release of Calcium Ions compared to the water-based Metapaste. Therefore, it requires a longer duration within the canal to exert its full effect, a period that can extend to 14 days or even beyond.

The Cheat Sheet: Quick Comparison