Evexia’s owner also owns Greco Gum, so take the comparison for what it is. I bought Underbrush, chewed it for a month, and reviewed it on its own terms first.
Both brands’ marketing blurs the same thing, Greco’s included: Underbrush and mastic gum barely compete. They’re built for different jobs, and once that clicks the choice gets a lot simpler.
Underbrush is a hydroxyapatite “remineralizing” gum, an oral-care product aimed at your enamel. Greco is a pure mastic chew: one ingredient, aimed at your jaw, gut, and breath. Underbrush works fine as a sugar-free chew, though its headline remineralization claim rests on studies of toothpaste, not gum. And despite the “mastic” on its label, it isn’t a mastic gum. Which one is “better” depends entirely on which of those two jobs you’re buying for.
They’re not the same kind of gum
Underbrush is built around hydroxyapatite (the mineral tooth enamel is actually made of) on a soft, sugar-free, flavored base. Its whole pitch is your teeth. Greco is pure mastic gum: the hardened resin of the Chios mastic tree, one ingredient, firm, nothing added. Its whole pitch is the chew. Comparing the two head to head is a bit like comparing mouthwash to an apple. Both go in your mouth, both are “good for you,” and you don’t really choose between them.
Underbrush leans into that confusion, so it spreads. “Mastic” sits right in the name of its lead flavor, Mastic Mint, and the brand’s own blog files Underbrush under mastic with posts on the best mastic gums and on mastic’s benefits, nudging shoppers to shelve it next to the real thing.
They even feel different in the mouth. Underbrush is soft and sweet, and, like most flavored gum, its taste is largely gone within a minute or two. Greco is firm and resinous, a slow, substantial chew with a subtle flavor that was never really the point. One is a quick mint; the other is something you settle in with for twenty minutes and feel in your jaw afterward.
Side by side
| Greco (mastic gum) | Underbrush (hydroxyapatite gum) | |
|---|---|---|
| What it is | Pure Chios mastic resin | A hydroxyapatite remineralizing gum |
| Ingredients | One (100% Chios mastiha) | Hydroxyapatite + a five-resin base, xylitol/erythritol, flavor, minerals |
| The point | A clean, firm mastic chew | Remineralize / whiten teeth |
| Mastic content | 100% | One of five base resins, % undisclosed |
| Sugar | None | None (xylitol/erythritol) |
| Texture | Firm resin, real resistance | Soft and sweet; flavor fades fast |
| Best evidence | Eases indigestion (RCT); builds bite force | Hydroxyapatite remineralizes, but in toothpaste |
| Price | Premium (~$0.9/g) | ~$30 a pack |
| Best for | Jaw, gut, a clean single-ingredient chew | Chasing enamel remineralization |
What’s actually in each
Greco’s ingredient list is one line: 100% Chios mastiha, refined and third-party tested, and nothing else.[8]
Underbrush’s is longer, and genuinely thoughtful; I’m not knocking the formula. Hydroxyapatite is the active ingredient, sitting on a base of five tree resins (chicle, mastic, spruce, myrrh, and acacia),[7] plus xylitol, erythritol, flavor, a little bentonite clay and minerals. It’s clean, it’s plastic-free, and the sweeteners are the good kind.
There’s a catch if you came for the mastic specifically: Underbrush never says what share of that five-resin base is actually mastic. It’s one resin of five, the percentage isn’t published anywhere I could find,[7] and neither is the hydroxyapatite dose. So if you’re chewing Underbrush for the mastic, as plenty of people apparently are, you can’t tell whether you’re getting a meaningful amount or a trace. With a plain mastic gum there’s nothing to work out: it’s all mastic.
Does Underbrush gum work?
It depends what you’re asking. As a pleasant, sugar-free chew, yes. As the enamel-rebuilding treatment the ads imply, it’s not proven for a gum.
Hydroxyapatite is a real ingredient with real science behind it, in toothpaste, where it remineralizes early enamel about as well as fluoride, though even there the evidence isn’t fully conclusive.[1] Gum is a different delivery system, and for hydroxyapatite delivered by chewing gum the evidence is essentially a single small study.[2] Underbrush’s own dentist-reviewed content concedes that no peer-reviewed trial has tested the gum itself.
The clean, just-polished feeling people rave about comes from any sugar-free gum: it’s the saliva and the xylitol at work, not evidence that the hydroxyapatite did anything. Hydroxyapatite itself is perfectly safe, the mineral your teeth are already built from, so no one is getting hurt. The trouble is narrower than safety: a genuine ingredient is carrying a promise the gum format hasn’t backed up.
That doesn’t make it a scam, just a nice gum sold under a headline the category can’t support yet. I go into the detail in my full Underbrush review. If enamel really is your goal, a ten-dollar hydroxyapatite toothpaste beats both of these gums on the evidence, and I’d rather tell you that than sell around it.
What mastic gum is good for
Everything mastic is credited with was studied on pure resin, the single-ingredient Chios PDO stuff,[6] at the doses the trials used, which is what a mastic gum delivers and a five-resin blend with an undisclosed mastic fraction does not.
The strongest of those benefits is digestive. A placebo-controlled trial found mastic eased indigestion-type (functional dyspepsia) symptoms in more people than placebo.[3] In a small pilot, pure mastic cleared H. pylori in about a third of people.[4] That result is modest and no substitute for what a doctor would prescribe, but it’s a real clinical signal, well beyond a test-tube curiosity. Because it’s a firm resin, mastic is also a genuine resistance chew that builds bite force,[5] though no gum sculpts a jawline, a point I keep making (see the mewing guide).
None of that evidence carries over to a diluted blend, so the case for chewing mastic is really a case for chewing pure mastic.
A fair word for Underbrush
None of this makes Underbrush a bad product. Its instincts are good: a plastic-free base instead of the synthetic gum base most brands use, sweeteners that are genuinely kind to teeth, and a real, safe active ingredient. It’s a cleaner, more thoughtful gum than almost anything at a checkout counter, and it isn’t a scam. That’s worth saying plainly, because Underbrush has a real counterfeit problem, and a single-ingredient mastic resin is much harder to fake convincingly than a complex branded formula. If what you want is a clean, minty, feel-good chew, Underbrush delivers it. It just isn’t the mastic gum many of its buyers think they’re getting.
Which should you buy?
Buy Underbrush if your specific goal is enamel remineralization and you like the idea of hydroxyapatite in gum form. (And genuinely, try a hydroxyapatite toothpaste first; the evidence is better and it costs less.) Greco has no hydroxyapatite, so I won’t pretend it remineralizes better, because it doesn’t.
Buy Greco if you want a clean, single-ingredient, sugar-free chew, whether for jaw training, the gut and breath reasons, or just a better daily chew than soft flavored gum. It’s firmer, it’s all mastic, it’s third-party tested, and it’s the one with the studied ingredient at the studied dose. If you’d rather weigh it against other mastic brands than against Underbrush, that’s my best mastic gum guide.
If you came here to choose between them, the odds are you want a daily functional chew rather than a tooth treatment, and that points to Greco. If you genuinely want enamel remineralization, Underbrush has the ingredient Greco doesn’t, and that’s the honest answer. Greco Gum shares our owner (Hubert Ventures LLC).
References
Evexia cites primary research and authoritative sources. Claims are traceable; where evidence is limited or mixed, we say so.
- Wierichs et al. — Efficacy of nano-hydroxyapatite on caries prevention: a systematic review & meta-analysis (Clinical Oral Investigations, 2022) · pmc.ncbi.nlm.nih.gov
- Naim & Sen — The remineralizing and desensitizing potential of hydroxyapatite: a narrative review (only one hydroxyapatite-gum study identified) (J Funct Biomater, 2025) · pmc.ncbi.nlm.nih.gov
- Dabos et al. — Mastic gum for functional dyspepsia: a double-blind, placebo-controlled RCT (J Ethnopharmacol, 2010) · pubmed.ncbi.nlm.nih.gov
- Dabos et al. — Is mastic gum effective against H. pylori? A pilot study (Phytomedicine, 2010) · pubmed.ncbi.nlm.nih.gov
- Jung et al. — Gum-chewing raised bite force but did not change masseter thickness or jaw shape (J Oral Rehabil, 2024) · doi.org
- Chios Masticha (Masticha Chiou) — EU Protected Designation of Origin (eAmbrosia GI register) · ec.europa.eu
- Underbrush (Mastic Mint) ingredient list — five-resin base (Healf product listing) · healf.com
- Greco Gum — single-ingredient Chios mastiha, third-party tested · grecogum.com
Frequently asked questions
Is Underbrush the same as mastic gum?
No. Underbrush is a hydroxyapatite remineralizing gum. Mastic is just one of five tree resins in its base (the percentage isn't disclosed), plus the name of its flagship flavor. A mastic gum like Greco is a single ingredient, 100% Chios mastiha, and nothing else.
Does Underbrush gum work?
As a pleasant, sugar-free chew, yes. As the enamel-rebuilding treatment the marketing implies, it's unproven for a gum. Hydroxyapatite's remineralization evidence comes from toothpaste, and Underbrush's own dentist-reviewed content concedes no trial has tested the gum itself. It's not a scam, just a nice gum with an oversold headline.
Does hydroxyapatite gum really remineralize teeth?
Hydroxyapatite remineralizes early enamel in toothpaste about as well as fluoride, though even there the evidence isn't fully conclusive. For hydroxyapatite delivered by chewing gum specifically, there's essentially one small study. If enamel is your goal, a hydroxyapatite toothpaste has far better evidence than either gum.
Which is better, Underbrush or Greco?
They're built for different jobs, so it depends on yours. For enamel remineralization, Underbrush has the relevant ingredient and Greco has none; I won't pretend otherwise. For a clean, single-ingredient, sugar-free chew, jaw training, or the gut and breath reasons, Greco is the better-made pick.
Is mastic gum good for your gut or jaw?
Mastic has real, if modest, human evidence. A placebo-controlled trial found it eased indigestion-type symptoms, and as a firm resin it's a genuine resistance chew that builds bite force (though no gum sculpts a jawline). Those benefits are studied on pure mastic, not a diluted five-resin blend.
Is Underbrush worth the price?
At around $30 a pack with the flavor gone in about a minute, it's expensive for a gum. If you want the clean, plastic-free chew and don't mind paying, fine, but as an enamel treatment a cheaper hydroxyapatite toothpaste is better value.
