Philips Sonicare DiamondClean Smart 9400 Review: a pricey brush that actually cleans like crazy

I’ve been using electric toothbrushes for years, mostly Oral-B, and I honestly thought spending this much on a toothbrush was a bit stupid. But my dentist kept hinting that a Sonicare might help with my gums, so I picked up the Philips Sonicare DiamondClean Smart 9400 (model HX9917/88) and used it daily for a few weeks. I went in with a pretty skeptical mindset, especially with all the app and “smart” features plastered on the box.

First impression: it’s a strong brush. The first time I turned it on, the vibration felt pretty intense compared to my older Oral-B. It’s not painful or anything, but if you’ve only used manual brushes before, it will feel weird for the first few days. I had that moment where I added toothpaste, switched it on before putting it in my mouth, and yes, toothpaste everywhere. You learn fast not to do that again.

After about three or four days, I got used to the sonic feeling. My teeth did feel smoother, especially around the gumline and between the teeth where I usually miss spots. It’s one of those things where you run your tongue over your teeth and go “ok, that’s cleaner than usual”. But I also started noticing some annoyances, like the app being a bit gimmicky and the handle being slightly slippery when wet.

Overall, the start was a mix: very good cleaning performance, but lots of bells and whistles that feel more like marketing than something I actually need every day. If you’re expecting a toothbrush that changes your life, calm down. If you just want something that cleans very well and you’re ok paying for it, then it starts to make more sense.

Let’s be blunt: this brush is not cheap. You’re paying a serious amount of money for something that essentially does one job – clean your teeth. So the real question is: does the Philips Sonicare DiamondClean Smart 9400 justify its price, or are you just paying for fancy marketing and an app you’ll barely use? After using it for a few weeks, I’d say you’re mainly paying for three things: strong cleaning performance, a nice travel setup, and the Philips brand with all the dentist recommendations behind it.

In terms of cleaning, it’s definitely a step up from a manual brush and also from some lower-end electric brushes I’ve used. My teeth felt smoother, and my gums were less irritated once I stopped pressing too hard. If you’ve had warnings from your dentist about plaque or gum health, this kind of brush can make a difference, as long as you actually use it properly. But you can also get pretty good cleaning from cheaper Sonicare or Oral-B models, so the question is whether the extra modes, glass charger, and app are worth the extra cash for you personally.

Another thing to remember: replacement heads are not cheap either, especially the “Premium” ones like the A3 and G3. You get a year’s worth to start, which softens the blow, but after that you’re looking at a decent recurring cost if you stick to official Philips heads. There are compatible third-party heads, but quality can vary. So long term, this is not a low-cost setup. You’re signing up for a more expensive brushing routine overall.

So value-wise, I’d put it like this: if you really care about your oral health, want a strong sonic brush, travel fairly often, and don’t mind paying extra for a nicer design and a decent app (even if you don’t use it daily), then the price is just about defendable. If you just want clean teeth and don’t care about smart features or a glass charger, you can find cheaper electric brushes that will get the job done for much less. It’s not a rip-off, but it’s definitely not the best price-performance ratio on the market either.

Design-wise, the Sonicare DiamondClean Smart 9400 definitely tries to look like a fancy gadget rather than a boring toothbrush. The white version I used has a clean, minimal look with a matte-ish finish, a simple power button, and a mode/intensity button below it. There are small LEDs for the modes and battery, and the light ring at the bottom that glows when you press too hard. It’s not flashy, but it does look more “upmarket” than a lot of chunky Oral-B handles.

In the hand, it’s fairly slim and not too heavy. You can hold it easily, but one thing I noticed is that when your hand and the handle are both wet, it can feel a bit slippery. There’s no rubberized grip like on some cheaper brushes. It’s fine most of the time, but if you’re the type who brushes in the shower or with very wet hands, you might notice it twisting slightly if you’re not paying attention. Not a big disaster, just something that doesn’t match the price in my opinion.

The charging glass is a nice idea: you just drop the handle in the glass and it charges through the base. It looks good on the sink and doubles as an actual glass to rinse, though I personally don’t love the idea of mixing charging hardware with something I drink from. But from a design point of view, it does stop the brush from toppling over and it looks more tidy than a plastic charging stand. The travel case is also well thought out: it’s solid, holds the handle and heads, and charges via USB so you can plug it into a power bank or laptop when travelling.

Overall, the design is clean and modern, but not perfect. I like the slim profile, the light ring, and the travel case. I’m less convinced by the smooth finish with no real grip, and the glass charger is more of a “nice to look at” thing than something that changes daily use. If you care about looks on your bathroom counter, you’ll probably like it. If you only care about pure practicality, some simpler models do the job just as well.

Battery life on the Sonicare DiamondClean Smart 9400 is pretty solid, but don’t expect miracles. Philips doesn’t plaster a big number in the description, but in my actual use (twice a day, 2 minutes each, mostly Clean mode, medium intensity), I was getting around 2 to 2.5 weeks on a full charge before the battery indicator started blinking. That lines up with what other users mention: you’re not charging it every few days, but it’s also not one of those brushes that lasts a full month without touching the charger.

Charging is easy enough. You can drop it into the glass that sits on top of the charging puck, or use the USB travel case when you’re on the go. The glass solution looks nice on the sink and avoids dealing with a loose handle lying around. I usually just kept it on the glass when at home, so the battery never really went fully flat. When I did test draining it and then recharging, it took a couple of hours to get back to full, which is pretty normal for this type of toothbrush.

The USB travel case is actually one of the more practical bits of the whole kit. You plug a USB cable into the case, and it charges the handle inside. This is handy if you travel with a power bank or don’t have a shaver socket in a hotel bathroom. It’s not ultra-fast charging, but it’s good enough. The case itself is quite sturdy and doesn’t feel cheap, so you can throw it in a bag without worrying about breaking it.

Overall, the battery situation is “good enough” for the price, but not outstanding. There are cheaper electric brushes now that claim longer battery life. But in daily life, charging every couple of weeks or just leaving it on the glass charger isn’t really a big issue. If you’re looking for something you can take on a 3-week trip without a charger, this might fall a bit short, but for normal home use plus occasional travel, it’s fine.

The packaging for the Sonicare DiamondClean Smart 9400 is clearly designed to make you feel like you bought something high-end. The box is fairly large for a toothbrush, with the usual glossy photos and long lists of features. Inside, everything is nicely laid out in separate compartments: handle, heads, glass, charging base, and travel case all have their own spots. It looks tidy and organised, and you don’t feel like you’re unboxing a cheap gadget.

From a practical point of view, it’s a bit much. There’s quite a bit of cardboard and printed material for what is basically a brush, a stand, and a case. One Amazon review mentioned the outer shipping box arriving damaged, but the product inside was fine. That doesn’t surprise me; the internal packaging is pretty rigid, so it protects the contents well. But if you care about waste, this is not exactly minimal packaging. Most of it is recyclable cardboard though, so at least you’re not dealing with tons of foam.

Documentation is clear enough. You get a quick start guide that actually helps, and a thicker booklet with all the modes, app instructions, and warranty info. Honestly, you only need about 10% of what’s written there to start using it. I ended up scanning the mode list once, pairing the app one time, and then ignoring the rest. It’s not confusing, just more text than you realistically need.

Once everything is out of the box and set up in the bathroom, you’ll probably never touch the packaging again. It does its job of protecting the product during shipping and giving that “premium” feeling at first, but it’s definitely not a selling point by itself. If anything, I’d say it’s slightly overkill. Still, nothing was missing, nothing was scratched, and everything worked right away, so in terms of basic expectations, it ticks the boxes.

In terms of build, the Sonicare DiamondClean Smart 9400 feels more premium than a lot of cheaper brushes, but there are a few things that make me a bit cautious about long-term durability. The handle is solid plastic, with a good finish, and doesn’t creak or flex when you press on it. The brush heads click on firmly and don’t wobble. After a few weeks of twice-daily use, there was no visible wear on the handle, and the motor strength felt exactly the same as day one.

However, reading other user reviews, there are some red flags. One user mentioned the bottom button sticking in, and that they had the same issue on a previous Philips toothbrush. That lines up with what I’ve seen in the past too: Philips handles can develop button problems or internal moisture issues after a year or two, especially if they get knocked around or not dried properly. I didn’t have that issue yet with this model, but it’s something I’d keep in mind if you’re planning to use it for many years.

The charging glass and base feel okay, but they’re not bulletproof. If you drop the glass on tile, I’m pretty sure it’s gone. It’s an actual glass, not plastic. The travel case, on the other hand, is tough. The hinges and closing mechanism feel robust, and I wouldn’t worry about it opening by accident in a suitcase. The brush heads themselves are standard Sonicare quality: the bristles hold up well for the usual 3 months, but you’ll see them flare slightly if you press too hard, which is a good reminder to ease up.

Philips gives a 2-year warranty, which is decent for this type of product. For the price, I would have liked a bit more reassurance about long-term reliability, but at least you’re covered if something goes wrong early on. So, durability-wise: it looks and feels like a high-end product, but there are enough reports of button problems that I wouldn’t call it bulletproof. I’d treat it with care and keep the warranty info handy, just in case.

Let’s talk about how it actually brushes, because that’s the only thing that really matters. The Sonicare DiamondClean Smart 9400 is strong. Philips claims 62,000 “bristle movements” per minute and up to 20x more plaque removal than a manual brush. I can’t measure that exactly, but in day-to-day use, my teeth felt noticeably smoother, especially at the gumline and behind the front teeth where I usually get a bit of buildup. After a week, I could feel less roughness when I ran my tongue across my teeth.

The 4 modes are not just fake labels; they do feel slightly different. Clean is the default and works for most people. White+ feels a bit more intense and slightly more focused on the front surfaces. Gum Health has a gentler pattern with more focus near the gumline. Deep Clean+ runs a bit longer and feels like a stronger cycle. That said, after the “honeymoon” where you try every mode, I ended up using Clean or Gum Health 90% of the time. The 3 intensity levels help if you find it too strong at first; I started on the middle level and only used the highest level once I was fully used to the vibrations.

The pressure sensor is genuinely useful. The light ring at the bottom flashes when you press too hard, and if you use the app, it also shows up there. This actually helped me stop scrubbing like a manual brush and just let the head glide over the teeth. I used to get a bit of gum soreness with cheaper brushes; with this one, once I adjusted my pressure, that basically went away. So from a gum protection point of view, I’d say it does its job.

The app is where it gets a bit “meh”. It tracks your brushing in real time and tells you if you missed spots, moved too fast, or pressed too hard. It’s fun for the first few days, then it becomes a hassle to open your phone every single time you brush. Also, the “coverage” feedback isn’t always accurate. Sometimes it said I missed areas even though I know I went over them carefully. I ended up ignoring it and just relying on the timer and my own routine. So performance in cleaning: very good. Performance of the so-called smart features: decent, but mostly a novelty after the first week.

Out of the box, the Philips Sonicare DiamondClean Smart 9400 looks like a premium kit, but let’s strip away the fancy packaging and look at what’s really there. You get: the handle, 2 brush heads (A3 Premium All-in-One and G3 Premium Gum Care), a charging glass with the charging base, and a USB charging travel case. There’s also the standard UK 2-pin bathroom plug. So you’re basically ready to go for about a year on brush heads if you follow the usual 3-month replacement rule.

The handle has 4 modes: Clean, White+, Gum Health, and Deep Clean+. On top of that, there are 3 intensity levels. In practice, I mostly stayed on Clean or Gum Health at medium intensity. The other modes are there if you like playing with settings, but I’d say 80% of the time you’ll stick to one or two favourites. There’s also a built-in 2-minute timer and a QuadPacer that sort of nudges you every 30 seconds to move to the next quadrant of your mouth.

Philips pushes the whole “smart” side: it connects to the Philips Sonicare app via Bluetooth, it has BrushSync to detect the type of head and remind you to change it, and there’s a light ring pressure sensor that flashes if you press too hard. The pressure light is actually useful; it’s simple and you don’t have to open your phone for it. The app… that’s another story. It works, but you have to have your phone open while you brush, which in real life I stopped doing after a few days.

So in terms of presentation, it’s a full kit with most of what you’d expect from a higher-end brush: multiple modes, pressure sensor, app, travel case with USB charging, and two decent heads. On paper, it’s loaded. In practice, you’ll probably use half of what’s advertised, but at least you’re not missing any key features compared to other top-range electric toothbrushes.