The Unicode Standard has its fair share of mysterious and sometimes unexplained characters. The story of the Farsi symbol (U+262B ☫ farsi symbol) is one of the more well-known ones. Many blocks, especially the “miscellaneous” blocks, have smatterings of rather arbitrary character sets grouped together only by history. One such block is Miscellaneous Technical, which contains completely unrelated groups of characters, including keyboard symbols, APL symbols, electrotechnical symbols, UI symbols, drafting symbols, and of particular interest in this blog post, dentistry notation symbols. Here they are, all 15 of them:

⎾⎿⏀⏁⏂⏃⏄⏅⏆⏇⏈⏉⏊⏋⏌

The first two and last two are part of Palmer notation for denoting human teeth by their position. What are the rest for?

The Unicode Standard, Section 22.7 Technical Symbols, doesn’t have much specific to say about the matter.

Dental Symbols. The set of symbols from U+23BE to U+23CC form a set of symbols from JIS X 0213 for use in dental notation.

Looking at the Miscellaneous Technical code chart, their names describe the appearance of the symbols but not so much their function.

23C0 ⏀ DENTISTRY SYMBOL LIGHT VERTICAL WITH CIRCLE
23C1 ⏁ DENTISTRY SYMBOL LIGHT DOWN AND HORIZONTAL WITH CIRCLE
23C2 ⏂ DENTISTRY SYMBOL LIGHT UP AND HORIZONTAL WITH CIRCLE
23C3 ⏃ DENTISTRY SYMBOL LIGHT VERTICAL WITH TRIANGLE
23C4 ⏄ DENTISTRY SYMBOL LIGHT DOWN AND HORIZONTAL WITH TRIANGLE
23C5 ⏅ DENTISTRY SYMBOL LIGHT UP AND HORIZONTAL WITH TRIANGLE
23C6 ⏆ DENTISTRY SYMBOL LIGHT VERTICAL AND WAVE
23C7 ⏇ DENTISTRY SYMBOL LIGHT DOWN AND HORIZONTAL WITH WAVE
23C8 ⏈ DENTISTRY SYMBOL LIGHT UP AND HORIZONTAL WITH WAVE
23C9 ⏉ DENTISTRY SYMBOL LIGHT DOWN AND HORIZONTAL
23CA ⏊ DENTISTRY SYMBOL LIGHT UP AND HORIZONTAL

The JIS X 0213 is yet another character set encoding standard and doesn’t explain much either. Any technical documents would probably be in Japanese, which I can’t read. Luckily, the Wikipedia page on Miscellaneous Technical keeps a pretty extensive historical record of how its characters were introduced into Unicode. According to the table, the dentistry symbols were introduced in version 3.2 originating from a proposal in 1999. Here’s where we’ll start our hunt for their meaning.

History in Unicode 3.2

The dentistry symbols along with some circled digits were introduced in Addition of medical symbols and enclosed numbers on 13 September 1999. The document doesn’t actually explain what the symbols mean.

There you have it. The earliest references to these symbols that I could find.

The Unicode Technical Committee has the same questions I do. The meeting minutes for a committee meeting over 26–29 October 1999 note:

Twenty Seven Dentist Characters
Consensus 81-C5: The circled characters will considered as part of a general mechanism as documented in 81-C4. Respond to the Shibano-san on the remaining proposed dentist symbols that we need evidence of usage. The UTC is not accepting any of the dentist symbols at this time. [L2/99-238]
Action Item 81-33 for Lisa Moore: Inform Shibano-san that we are not accepting any of the dentist symbol characters, and provide our feedback.

And so in a proposal comment on 23 November 1999, Lisa Moore, chair of the Committee, writes:

6) Twenty Seven Dentist Characters. The UTC will consider the ten double circled numbers as part of the general mechanism to be defined in the future. See 4) above. The remaining seventeen dentist symbols were not accepted due to insufficient evidence of usage. Please provide documents with examples of usage, and explain if any of these characters are combining, or if any extend across other symbols to delineate quadrants of the jaw.

The 17 symbols refer to the 15 dentistry symbols along with U+29FA ⧺ double plus and U+29FB ⧻ triple plus, which are later encoded in Miscellaneous Mathematical Symbols-B. In a proposal revision on 31 January 2000, Professor Kohji Shibano, chairman of the JCS committee, writes:

(c) Evidence of usage
You requested to submit evidence of usage for some characters. We are now preparing the requested document for the following characters with some explanation in English. This document will be sent to you as soon as possible.

This explains nothing.

Finally, in Rationale for non-Kanji characters proposed by JCS committee on 15 March 2000, the dentistry symbols are… “explained”.

(2) Dentist’s symbols
These symbols are used in dentistry when drawing XXX together with some BOX DRAWING characters. The proposal includes two types of characters; those used in single-line drawing and those in triple-line drawing.

What does it mean???

It makes sense that the lines are meant to be used with box-drawing characters in dental notation to illustrate the teeth. But what do the circle, the triangle, and the tilde mean? The Wikipedia article on dental notation doesn’t seem to use these symbols (and nor does the corresponding German article, which is much more comprehensive).

The committees, on the other hand, seem satisfied with this explanation. The meeting minutes for an ISO/IEC subcommittee meeting over 21–24 March 2000 note a comment (Section 8.20, page 44) by Dr. Ken Whistler of Sybase, Inc.:

ii) The Dental symbols are sufficiently explained - these are box-drawing characters overlaid in specific manner.

The meeting minutes for a Unicode Technical Committee meeting on 28 April 2000 read:

[83-M3] Motion: Accept the twenty five characters documented in the report on the Beijing meeting, sections E 1, 2, 3, 5, 6, 7, 8, 9 [L2/00-108]:
⚬ Double plus sign and triple plus sign
⚬ 15 dentist symbols

So there aren’t any more explanations we can expect to see from these documents. Subsequent meeting minutes only discuss technical details. From 19–22 September 2000 (Section 7.21, page 40):

Action Items: Messrs. Michael Everson and Takayuki Sato - will provide better glyphs for the DENTIST Symbols (from document N2093). The amendment text is to be prepared by the editor.

From 9 March 2001 (Irish comments, page 5):

Table 63 (67) - Row 23: Miscellaneous Technical
The Japanese remarked in Athens that the glyphs for the dentistry symbols 23C0-23CC should fill a notional square. We have provided the editor with corrected glyphs.

And from 2–5 April 2001, more remarks on the shape of the characters (Section 7.1, page 21), and the proposed character names are changed from DENTIST to DENTISTRY (Section 7.1, page 22):

Comment 14: Shapes of JIS X0213 characters – Accepted.
Japan will supply suitable fonts. Kana has to cover all existing Kana characters also. As to the Dentist symbols, glyphs do not seem to look square. We need to know why current glyphs are not acceptable. A single font is needed for a range.

SE6: […] Rename DENTIST to DENTISTRY symbols … should it be DENTAL? Accept DENTISTRY.

On 27 March 2002, Unicode 3.2 is released. The current blurb on dentistry symbols is added as part of the Unicode Standard Annex #28; the new code points are highlighted in this code chart.

Let’s Ask the Internet

I don’t have any dentistry friends, but surely someone knows, so I asked around. I asked the Medical Sciences Stack Exchange, I asked on the Unicode mailing list, and I even threw the question out there on Twitter. In the end, though, someone I knew found it with a method so simple it never occurred to me.

I can't believe I didn't think of that.

And indeed, an explanation can be found right there in Dental Computing and Applications: Advanced Techniques for Clinical Dentistry by Andriani Daskalaki, published in 2009. In fact, a simple “dentistry unicode” search on Google Books takes me right there.

Of course, this isn’t the origin of the symbols, but it does explain what they mean. According to Chapter XVII on Unicode Characters for Human Dentition^†, the notation comes from Japan’s dental insurance claim system.

Although these signs are not specific to dentistry, we assigned a specific meaning to these modified numerical symbols in accordance with the dental insurance claim system in Japan.
…
Figure 4 shows nine characters in three groups denoting artificial teeth, supernumerary teeth and an abbreviation for a group of teeth respectively. A triangle with a bar indicates an artificial spacer, especially on a denture, a circle with a bar indicates a supernumerary tooth, and a tilde with a bar indicates an abbreviation for a group of teeth.

Now this would've been useful in the Rationale document.

So that’s the end of the mystery. I should go update all the places I’ve asked with this discovery now.

Updates from the Unicode Mailing List

Since the original publication of this post I’ve received some replies to my question posted to the Unicode mailing list, in particular Ryusei Yamaguchi’s response. Some of the sources cited agree with the above: 歯式の記載について on dental notation lists using ⏈ for describing a span of upper teeth and ⏇ for describing a span of lower teeth.

⏈: この記号の両端の歯の間に存在する全ての歯（上顎用で正中を越える）
[DeepL translation: “All teeth present between the teeth on either side of this sign (for maxillary and beyond the median)”]
⏇: この記号の両端の歯の間に存在する全ての歯（下顎用で正中を越える）
[DeepL translation: “All teeth present between the teeth on either side of this sign (for mandible and beyond the midline)”]

On the other hand, 電子レセプトの作成手引き on filing electronic dental insurance claims uses △ to indicate 「部近心隙」 (page 25), which seems to mean a diastema, or a tooth gap, so that ⏅⏃⏄ are used to indicate a gap between the front teeth, rather than artificial teeth as previously suggested. This usage is further backed up by the 歯式メーカー app, which describes using △ to indicate a gap.

△で隙を入力します。選択した歯の近心の隙を入力します。
[Google Translate: “Enter the gap with △. Enter the mesial gap of the selected tooth.”]

Finally, there doesn’t seem to be any other explanation of the circle and the usage of ⏂⏀⏁. Circled numbers indicate dental implants at the given tooth position, so it doesn’t make sense in that case for the circle to go in between teeth. It’s likely, then, that they are indeed for indicating supernumary teeth, and in particular the mesiodentes that occur between the two front teeth.

^†This does require access to IGI Global’s resources, but you can just find the entire book here.