NA0D – The new Traumatic Dental Injury classification of the World Health Organization

Abstract An accurate, clear, and easy‐to‐use traumatic dental injury (TDI) classification and definition system is a prerequisite for proper diagnosis, study, and treatment. However, more than 50 classifications have been used in the past. The ideal solution would be that TDIs are adequately classified within the International Classification of Diseases (ICD), endorsed by the World Health Organization (WHO). TDI classification provided by the 11th Revision of the ICD (ICD‐11), released in 2018, and previous Revisions, failed to classify TDIs satisfactorily. Therefore, in December 2018, a proposal was submitted by Dr's Stefano Petti, Jens Ove Andreasen, Ulf Glendor, and Lars Andersson, to the ICD‐11, asking for a change of the existing TDI classification. Proposal #2130 highlighted the TDI paradox, the fifth most frequent disease/condition neglected by most public health agencies in the world, and the limits of ICD‐11 classification. Namely, injuries of teeth and periodontal tissues were located in two separate blocks that did not mention dental/periodontal tissues; infraction, concussion, and subluxation were not coded; most TDIs lacked description; and tooth fractures were described through bone fracture descriptions (e.g., comminuted, compression, and fissured fractures). These limitations led to TDI mis‐reporting, under‐reporting, and non‐specific reporting by untrained non‐dental healthcare providers. In addition, no scientific articles on TDIs, present in PubMed, Scopus, and Web‐of‐Science, used the ICD classification. Proposal #2130 suggested to adopt the Andreasen classification, the most widely acknowledged classification used in dental traumatology. The Proposal was reviewed by two WHO teams, two scientific Committees, one WHO Collaborating Center, and the Department of Non‐Communicable Disease Prevention at WHO headquarters, and it underwent two voting sessions. In March 2022, the Andreasen classification was accepted integrally. A new entity was generated, called NA0D, “Injury of teeth or supporting structures” (https://icd.who.int/browse11/l‐m/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f1413338122). Hopefully, this will contribute to increasing the public awareness, and the dental profession's management, of TDIs.


| THE WHO INTERNATIONAL CL A SS IFIC ATION OF DIS E A S E S AND TR AUMATIC DENTAL INJ URIE S
In 1891, the International Statistical Institute designed the socalled Classification of Causes of Death, presented two years later, that received general approval and was adopted by several countries worldwide. The classification was updated periodically, and the 6th revision, called the International Classification of Diseases, Injuries, and Causes of Death, was endorsed by the World Health Organization (WHO) at the first World Health Assembly in 1948. 1 The aim of the International Classification of Diseases (ICD) system was to provide a universally acknowledged tool for epidemiologic, health management, and clinical purposes.
To be able to diagnose, study, and treat injuries, a prerequisite is to use an accurate definition of the injury. Traumatic dental injuries (TDIs) have over the years been diagnosed and reported according to a variety of factors such as anatomy, etiology, pathology, therapeutic consideration, and degree of severity. The variety of diagnostic methods used has complicated accurate documentation of TDIs and interfered with the development of systematic comparisons between different studies and meta-analyses of larger materials have been hindered. 2 Such uncertainty could be responsible for the low awareness among non-dental healthcare workers worldwide, which is a serious problem because TDI mis-management could lead to serious sequelae, medico-legal problems, and reduced quality of life for the patients. 3 More than 50 TDI classification systems have been used in the past in the literature. 4 The most commonly used classification was developed by Dr Jens Ove Andreasen in 1970 5 with further modifications. This classification served as the basis for the TDI codification of the "Application of the International Classification of Diseases in Dentistry and Stomatology" (ICD-DA), released by the WHO in 1995, 6 an oral health related branch of the 10th Revision of the ICD (ICD-10), endorsed at the 43rd World Health Assembly in 1990, and used by member states since 1994. However, the WHO classification was in many ways incomplete, and Dr Andreasen suggested certain entities to be added that were not included in the WHO system. The Andreasen classification has over the years become a global standard for clinicians and researchers, because of its appropriateness to be used in modern clinical practice and for comparing results from different studies. The strength of the Andreasen system is that it is very closely related to the specific tissue injuries, treatment methods, and later complications of dental injuries.
Despite becoming the global standard for the clinic and research worldwide, the Andreasen classification was not completely taken into consideration for TDI classification in further ICD-10 revisions.
In 2018, 28 years after the launching of the ICD-10, the WHO released the 11th Revision of the ICD (ICD-11) to allow the member states to start planning. ICD-11 is a more modern digitized classification system that contains around 17,000 unique codes, more than 120,000 codable terms in a smart coding tool and it is entirely digital. By March 2022, 35 countries had already adopted ICD-11.
The ICD provides a common language that allows health professionals to share standardized information across the world. For this reason, it was important to correct the ICD-11 according to the Andreasen classification system. Therefore, Dr's Stefano Petti, Jens Ove Andreasen, Ulf Glendor, and Lars Andersson decided to submit a proposal to modify the existing TDI classification that was present in ICD-11.
The urge to re-classify TDIs within the ICD system, based on solid public health, healthcare policy, and scientific motivations, was acknowledged internationally thanks to a Lancet Global Health publication in 2018, 7

| PROP OSAL # 213 0
The authors of the proposal opted for a type called "Complex Hierarchical Changes Proposal," which was preferred over simpler types because of the many limits of the ICD-DA/ICD-10/ICD-11 regarding TDI classification. The proposal was originated on December 3, 2018, and was numbered #2130; the full text is available in Appendix S1. These are the main issues. injuries to periodontal tissues, imprecisely called "Dislocation of tooth," were located in another block called "Dislocation or strain or sprain of joints or ligaments of head." Astonishingly, periodontal tissues were ignored and were assimilated to joints and ligaments. Thus, at first sight, untrained healthcare providers could mistakenly think that TDIs were excluded from the ICD-11 system, thus hampering or even preventing reporting. Some TDIs, namely infraction, concussion, and subluxation, were not coded at all, and, therefore, could not be reported or were reported using non-specific codes. TDI entities were not defined, thus making it impossible their accurate coding by untrained healthcare providers, who could use non-specific codes, such as "Unspecified injury of head," "Injury, unspecified," "Open wound of head, part unspecified." Macroscopic mistakes were also present -such as the description of tooth fracture sub-types, that used the descriptions of bone fracture sub-types, namely buckle, burst, comminuted, compression, dislocated, and fissured fractures.
Definitively, these descriptions did not apply to teeth.

3.
Limited TDI coding associated with inaccurate reporting. Actually, this is a chicken-egg dilemma. Was it the inaccurate TDI classification by the WHO that produced unawareness toward TDIs, or was it the general unawareness toward TDIs that produced inaccurate TDI classification by the WHO? Solving this enigma is probably impossible. However, the two phenomena were associated. One example is the situation in general (i.e., non-dental) Emergency services, where TDI treatment delay occurs almost systematically whenever dental healthcare providers are unavailable, 11 because just a handful of physicians working in Emergency services can assess and treat TDIs appropriately, 12 Table 1).

| ANDRE A S EN CL A SS IFIC ATION INTEG R ALLY IN CLUDED IN THE ICD -11
The different appropriateness of TDI classifications between the Hopefully, the inclusion of the Andreasen classification within the ICD-11 system will help improve the awareness of healthcare providers, policy makers, scientists, and epidemiologists toward TDIs, that could be a little bit less neglected in the future.

CO N FLI C T O F I NTE R E S T
The surviving authors confirm that they have no conflict of interest.

Open Access Funding provided by Universita degli Studi di Roma La
Sapienza within the CRUI-CARE Agreement.

AUTH O R CO NTR I B UTI O N S
SP, JOA, UG, LA designed and drafted the manuscript. SP and LA approved the submitted version and are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. As JOA and UG passed away during the study, they could not approve the submitted version and are no longer accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data reported in Tables are accessible on the ICD-11 Maintenance Platform (available at, https://icd.who.int/dev11/ propo sals/f/icd/ en/Propo salList) typing the name of proposal originator (Petti) to the "Text Search" box.