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虫歯の悪化が顎の骨を腐らせ顔面神経痛を引き起こす（ＮＩＣＯ）

今回は神経痛の原因として医歯学界で注目されているＮＩＣＯについてお話したいと思います。
上の図の白い部分は顎の骨が腐敗した部分です。これを腐骨といいます。

NICO

NEURALGIA-INDUCING CAVITATIONAL OSTEONECROSIS

空洞化骨壊死を原因とする神経痛

補足：主に根尖病巣を伴う虫歯より保存不可能となり抜歯をされた場合に、骨がスカスカになって再生していきます。その後壊死を起こして神経痛を引き起こすことをここでは報告していおります。

Description
Neuralgia-inducing Cavitational Osteonecrosis described in medical literature since 1976, is known under a number of names including, Ratner bone cavities, alveolar cavitational osteopathosis, Roberts bone cavity, trigger point bone cavity, interference field, and most commonly, NICO.  In NICO, it is claimed that small areas of bone in the upper or lower jaw become infected or inflamed and die, producing neuralgia-like pain.  Most often, no sign of inflammation appears on x-ray.  NICO is said to appear after tooth extraction, jaw surgery, endodontic therapy or crown preparation and is speculated to be the result of a long-standing low-grade infection.

要約：上下顎の歯槽骨に細菌感染が起きたり（主に虫歯が原因）、外傷を受けたりすると顎の骨が壊死を起こし神経痛を起こすことがあります。これをＮＩＣＯと称しています。しばしばレントゲンでは診断することができません。発症のきっかけとしては長期間に及ぶ慢性炎症を起こした抜歯、顎の手術、歯の根の治療などがあります。

Symptoms
The pain felt is constant and is often burning and cramping, much like atypical facial pain symptoms.  Usually there are trigger points immediately over the areas of infected jawbone that will produce pain when pressed. NICO can cause “referred pain” in that the neuralgia-like symptoms are “referred” to other parts of the face, intraoral cavity and head.

症状：灼熱感を伴う顔面神経痛、口腔内や頭部への関連痛

Possible Causes
Some cases of NICO appear to be caused or aggravated by infection. Others speculate that minor trauma from extractions, root canal and other dental procedures are common initiators of NICO but  believe this only happens in people already susceptible because of a pre-existing blood clotting disorder.  Some believe that NICO can develop when blood vessels are injured in the area, resulting in poor circulation which in turn can lead to bone death.

原因：歯の根の慢性炎症、抜歯に伴う軽度な外傷、歯肉の血流障害など

Diagnosis
It is  difficult to diagnose this problem as the pain symptoms often are similar to other conditions such as Myofascial Pain Disorder (MPD), Temporal Mandibular Joint (TMJ) problems, atypical facial pain, trigeminal neuralgia, phantom toothache, or headache.    X-rays of the jawbone most often appear normal. However, a bone biopsy of the affected area can show positive signs of jawbone inflammation.

診断：診断は概して難しい。顎顔面痛症候群、顎関節症と、三叉神経痛、不定愁訴と誤診することも多い。確定診断には生検により行われる。

Discussion
NICO is not generally accepted as a cause of Trigeminal Neuralgia by most medical and dental professionals. It is possible that NICO is involved in some cases of facial neuralgia [1], especially atypical facial pain. One long-term study (of nearly 5 years) has reported considerably or totally reduced pain in 74% of facial neuralgia patients who had jawbone curettage. However, the pain returned for about 30% of these patients of whom most had been diagnosed with either TN or atypical facial pain -2.

In dental circles, there appears to be two distinct “schools of thought” on NICO.  Some medical and dental  professionals consider NICO a controversial diagnosis.  Not only do they not consider it  a possible cause of trigeminal neuralgia or other facial neuralgias, they doubt the condition exists as a disorder.  They point to data suggesting bone cavitations are found routinely in cadaver jawbones, casting doubt on the theory that bone cavities cause facial neuralgias.

Another group of dentists believe NICO is the culprit in many facial pain syndromes and that these painful conditions can be cured by jawbone curettage (scraping and removing infected tissue).  They point to studies that show a high success rate for  jawbone curettage. Some dentists in this group believe that root canals and mercury fillings are partly responsible for NICO.

総括：ＮＩＣＯはまだ一般的に認識されている疾患ではない。顔面神経痛に誤診されていることが多い。5年間に及ぶ追跡調査では顔面神経痛をもつ患者の74％が腐骨除去手術により症状が改善している。あるグループの歯科医師は腐骨除去の必要性を強調している。また、アマルガム充填（銀歯の一種）もＮＩＣＯの原因と主張する歯科医師もいる。
歯科を取り巻く環境では現在、ＮＩＣOの概念はあまりとりいれられてはいない、しかし解剖学の研究の成果により少しずつ認識されようとしている。

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