Why isn’t iontophoresis more commonly used in dentistry?

I happened to find a bunch of articles that suggest iontophoresis could revolutionize dentistry through allowing needle-free delivery of local anaesthetic, or even an alternative to drill-and-fill.

Primary article source: "Alternative practices of achieving anaesthesia for dental procedures: a review" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5932994/

The above article compares various anesthetic practices for various dental procedures.

The 4 alternatives to a regular anesthetic injection in scope of the question and covered by the article are:

• Electronic dental anesthesia. Uses electric currents to interfere with pain signaling.
• Jet injectors: pressurized anesthetic delivered as a fast-moving liquid shot with no needles.
• Iontophoresis: Applies an electric potential to the target tissue, facilitating absorption of ionized molecules.
• Computer-controlled anesthesia: A special case of regular anesthetic injections where a computer dictates a slow drip of liquid to minimize injection pain.

Metrics and parameters of the question:

• This question will focus on anesthetic for restorations, or viable alternatives to drill-and-fill.
• Any discussion on topical anesthetics that don't numb teeth in preparation for a drill-and-fill or crown installation is out of scope of the question, except regarding the use of topicals to eliminate the pain of a regular local anesthetic injection.
• The goal: Pain-free anesthetic delivery. This could be done through the use of a novel topical that completely eliminates local anesthetic injection pain, or a completely new local anesthetic procedure that ditches the needle completely into the nearest sharps bin.

Some anecdotal background information:

• IMPORTANT NOTE: While these anecdotes are from my personal experience, they are only intended as background info and motivational framework. This question is NOT specifically about personal health, which would be off-topic and closed on sight. The question is about iontophoresis.
• As far as dentistry in the U.S. goes, I've only ever seen dental anesthetic delivered through a needle – computer-controlled or manual. I have no idea if other countries are faster at adopting new technology (several searches on the topic proved inconclusive, which will be mentioned later).
• The standard practice in the U.S. for anesthetic restoration prep appears to be: topical anesthetic designed to minimize injection pain, followed by a local anesthetic injection. In my experience, the topical anesthetic is generally insufficient or only partially effective in eliminating injection pain.

Going back to the original topic, most of the alternative procedures outlined in https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5932994/ have some serious problems:

• Topical anesthesia: Only useful for "minimally invasive" procedures; insufficient for drilling.
• Electronic dental anesthesia: Truly minimally invasive, but the article's linked source #34 indicates that this approach isn't as effective as traditional local anesthetic. Source #35 linked in the article also concluded that it isn't an appropriate replacement for local anesthetic.
• Computer-controlled anesthesia: Despite the fancy name, it still involves a needle and is therefore going to be somewhat painful without a novel topical anesthetic that properly mutes the pain.

The 2 most promising approaches outlined in the article appear to be jet injectors and iontophoresis. Iontophoresis seems more promising, since jet injectors (according to Table 1 in the article) have a "high overhead cost" and "possibly cause haematoma of soft tissues".

With that in mind, it's time to take a deep dive into applications of iontophoresis, starting with "Selected Medicines Used in Iontophoresis" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6320882/

Of particular interest is section 2 (Local Anesthetics). Iontophoresis can allow a specific anesthetic preparation to travel through enamel and dentin. The approach outlined delivers the anesthetic into the tooth (instead of the traditional approach of injecting anesthetic into a place that intercepts the tooth's nerve connection).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6161066/ offers an even more focused on-topic deep dive into iontophoresis.

Section 6 is of interest, covering the topic of iontophoresis as a possibly viable alternative to needles for local anesthetic delivery.

Section 8 (Iontophoresis on Enamel and Dentin) covers a "thinking outside the box" application: using iontophoresis to deliver fluoride remineralization into a tooth. Figure 5 indicates improved fluoride uptake and reduced depth of decalcification compared to traditional diffusion.

The article (from 2018) indicates there is no current FDA approved iontophoretic delivery system for oral diseases, both for at-home treatment and in the dentist's office. That's no surprise; the U.S. regulatory apparatus has always dragged its feet on anything that could spell the end of painful injections and "drill and fill". (Don't even get me started on the topic of Novamin restorative toothpaste and why it's so tightly restricted in the U.S. when it's readily available OTC in other countries, see https://arstechnica.com/civis/viewtopic.php?f=23&t=1372067 ). So obviously, the best answers will come from other developed nations, and perhaps the primary focus could be Japan and western Europe.

In keeping with the theme of looking for answers outside the U.S., King's College London Dental Institute seeks to revolutionize restorative dentistry with new technology and minimal pain. They spun off a company named Reminova LTD. Academic article link is at https://www.ncbi.nlm.nih.gov/pubmed/29355417 and you can read further by searching "reminova ltd" in Google. Or skip straight to https://www.dailymail.co.uk/health/article-7464373/The-incredible-innovations-mean-no-drilling-dentist.html and read about the genius for yourself.

So, the question: If iontophoresis happens to be so promising dentistry, why do I only see significant progress coming from 1 research institution in the UK? Regulatory barriers in other countries? Cost barriers? Not enough research?

And while I mentioned above that this question is not specifically about personal health, I'd finish by saying that this article makes me almost want to live in the UK where advances like this have a better chance of being deployed.