2024 Volume 66 Issue 3 Pages 198-201
Characterization of materials used in dental restorations and fixed prostheses is useful for personal identification. This study investigated the dental treatment trends and use of metal materials among non-Japanese Asian temporary residents and Japanese individuals aged from 20 to 40 years living in a city in Japan. Analysis of 38 participants from different Asian countries showed prominent use of resin fillings, with metal element analysis revealing nickel-chromium (Ni-Cr) or cobalt-chromium (Co-Cr) alloys. Among five Japanese participants of the same age with dental metal treatment scars, resin fillings and silver-palladium-copper-gold (Ag-Pd-Cu-Au) or silver-indium (Ag-In) alloys were observed. This study suggested some regional differences in dental material choices in Asia.
Various materials are used for dental treatment, and the choice of dental material depends on each country's medical system. For instance, composite resins, metals, and mixed materials with specific components are commonly used for dental treatment in Japan because these materials are covered by Japan’s universal health insurance system. Metal alloys have long been used for dental treatment in Japan, and silver-palladium-copper-gold (Ag-Pd-Cu-Au) alloys are the most frequently used metals for dental restorations and fixed prostheses in the oral cavities of Japanese adults aged 55 years or older [1].
For personal identification, the characteristics of dental materials may help to identify the geographic region in which a person lives. Particularly among people of similar racial or ethnic backgrounds, identifying the country or place of residence based on dental treatment scars could be valuable for personal identification. In Japan, individuals in their 20s to early 40s comprise the greatest number of foreign visitors and residents, with more than 250,000 individuals in this age category in 2023. Furthermore, most of the foreign visitors and temporary residents living in Japan are from other Asian countries.
However, information on dental materials used in Asian countries is not easily accessible because of language barriers and legal differences. This study aimed to report the dental treatment and metal materials used for dental restorations and fixed prostheses among young, temporary Asian residents in a city in Japan. This study also aimed to compare dental metal materials used with case data of Japanese individuals of a similar age living in the same city.
Data for Asian temporary residents in Japan were collected by recruiting non-Japanese Asian participants aged from their 20s to early 40s with no history of metal allergies. The participants had previously received dental treatment in their hometowns. Recruitment was conducted between December 2020 and November 2022, with international students and staff attending or working at Hiroshima University. A total of 38 Asian participants from Bangladesh, PR China, Indonesia, Taiwan, ROC, and Vietnam, where four or more participants were recruited, were included in the analysis. The distributions of the participants’ ages and hometowns are shown in Table 1. Dental examinations had been carried out by licensed dentists. One participant from Taiwan, ROC had a dental restoration that had been treated in Japan, so the restoration was excluded from the tally. The mean age of the 38 participants was 27.0 ± 6.4 years, 28 of whom had dental treatment scars with remaining dental material (Tables 2, 3).
Japanese participants of the same age with metal treatment scars in their oral cavities were recruited from the same university for comparison with metal materials used among the Asian participants, between June 2023 and December 2023. Five Japanese participants, with a mean age of 33.0 ± 7.8 years (two in their 20s, one in their 30s, and two in their early 40s), participated in the study (Table 2).
| Age | Bangladesh | PR China | Indonesia | Taiwan, ROC | Vietnam | Total |
|---|---|---|---|---|---|---|
| 20-29 (n = 26) | 1 | 6 | 5 | 3 | 11 | 26 |
| 30-40 (n = 10) | 3 | 0 | 2 | 2 | 3 | 10 |
| 40-50 (n = 2) | 0 | 0 | 2 | 0 | 0 | 2 |
| Total | 4 | 6 | 9 | 5 | 14 | 38 |
| Hometown | No. | Age | Remaining teeth | Total number of restorations and fixed prostheses | Non-metal | Metal | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| composite resin filling | ceramic inlay | amalgam filling | complete metal crown | porcelain fused-to-metal restoration | metal onlay | metal inlay | |||||
| Non-Japanese Asian participants | |||||||||||
| Bangladesh | 1 | 26 | 28 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2 | 30 | 32 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 3 | 31 | 32 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 4 | 36 | 28 | 5 | 1 | 0 | 4 | 0 | 0 | 0 | 0 | |
| PR China | 5 | 22 | 28 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 |
| 6 | 23 | 31 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 7 | 24 | 26 | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 8 | 25 | 32 | 5 | 5 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 9 | 25 | 31 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 10 | 26 | 28 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| Indonesia | 11 | 20 | 29 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 12 | 21 | 29 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 13 | 22 | 32 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 14 | 26 | 32 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 15 | 28 | 32 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 16 | 34 | 27 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 17 | 35 | 26 | 3 | 0 | 0 | 3 | 0 | 0 | 0 | 0 | |
| 18 | 41 | 25 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 19 | 42 | 32 | 4 | 0 | 0 | 3 | 0 | 1 | 0 | 0 | |
| Taiwan, ROC | 20 | 24 | 29 | 3 | 2 | 0 | 0 | 0 | 1 | 0 | 0 |
| 21 | 27 | 24 | 11 | 10* | 0 | 1 | 0 | 0 | 0 | 0 | |
| 22 | 27 | 30 | 15 | 15* | 0 | 0 | 0 | 0 | 0 | 0 | |
| 23 | 31 | 28 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 24 | 37 | 28 | 8 | 0 | 0 | 8 | 0 | 0 | 0 | 0 | |
| Vietnam | 25 | 20 | 29 | 3 | 3 | 0 | 0 | 0 | 0 | 0 | 0 |
| 26 | 20 | 28 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 27 | 20 | 28 | 7 | 7 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 28 | 21 | 25 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 29 | 21 | 28 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 30 | 21 | 32 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 31 | 21 | 32 | 7 | 7 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 32 | 22 | 30 | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 33 | 22 | 25 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 34 | 23 | 28 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 35 | 28 | 24 | 4 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 36 | 31 | 31 | 9 | 6 | 0 | 0 | 1 | 2 | 0 | 0 | |
| 37 | 36 | 28 | 5 | 3 | 0 | 1 | 1 | 0 | 0 | 0 | |
| 38 | 38 | 28 | 9 | 9 | 0 | 0 | 0 | 0 | 0 | 0 | |
| Total | 123 | 97 | 0 | 20 | 2 | 4 | 0 | 0 | |||
| Japanese participants | |||||||||||
| Japan | 39 | 32 | 28 | 10 | 9 | 0 | 0 | 0 | 0 | 0 | 1 |
| 40 | 26 | 30 | 8 | 2 | 0 | 0 | 0 | 0 | 2 | 4 | |
| 41 | 25 | 28 | 8 | 5 | 1 | 0 | 0 | 0 | 0 | 2 | |
| 42 | 42 | 28 | 3 | 2* | 0 | 0 | 0 | 0 | 0 | 1 | |
| 43 | 40 | 24 | 4 | 2 | 0 | 0 | 0 | 0 | 0 | 2 | |
| Total | 33 | 18 | 1 | 0 | 0 | 0 | 2 | 8 | |||
*Includes composite resin fillings replaced with amalgam fillings
| Age | Non-metal | Metal | ||
|---|---|---|---|---|
| composite resin filling | amalgam filling | complete metal crown | porcelain-fused-to- metal restoration | |
| 20-29 n = 26 (%) |
19 (73.1) |
1 (3.8) |
0 (0.0) |
1 (3.8) |
| 30-40 n = 10 (%) |
5 (50.0) |
4 (40.0) |
2 (20.0) |
1 (10.0) |
| 40-50 n = 2 (%) |
1 (50.0) |
1 (50.0) |
0 (0.0) |
1 (50.0) |
| Total n = 38 (%) |
25 (65.8) |
6 (15.8) |
2 (5.3) |
3 (7.9) |
Metal elements were analyzed in the dental restorations and fixed prostheses of the Asian participants. Amalgam fillings and two porcelain-fused-to-metal restorations whose metallic parts were located below the gingival margins, were excluded. In addition, metal elements were analyzed in twelve metal inlays and onlays, all of which were metal dental treatments of the Japanese participants. The analytical protocol was consistent with a previously reported methodology [1].
Among the 38 Asian participants from Bangladesh, PR China, Indonesia, Taiwan, ROC, and Vietnam in this study, a total of 123 dental restorations and fixed prostheses were found (Table 2). Of the 38 Asian participants, 25 (73.7%) had treatment scars with remaining dental materials. Of the 38 Asian participants, 65.8% had composite resin fillings, 15.8% had amalgam fillings, 5.3% had complete metal crowns, and 7.9% had porcelain-fused-to-metal restorations (Tables 2, 3).
The metals in two complete metal crowns and two porcelain-fused-to-metal restorations were analyzed; the metal element components were nickel-chromium (Ni-Cr) or cobalt-chromium (Co-Cr) (Table 4).
Of the five Japanese participants with metal treatment scars in their oral cavities, 33 dental restorations and fixed prostheses were found (Table 2). None of the Japanese participants had amalgam fillings, complete metal crowns, or porcelain-fused-to-metal restorations. Two types of metal components were detected from the metal inlays and onlays of the five Japanese participants: Ag-Pd-Cu-Au alloys and silver-indium (Ag-In) alloys without Pd and Au (Table 4).
| No. | Cu | Zn | Pd | Ag | Au | Cr | Co | Ni | In | ||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Non-Japanese Asian participants | |||||||||||
| Complete metal crown (n = 1) | 36 | Vietnam | + | + | |||||||
| Complete metal crown (n = 1) | 37 | Vietnam | + | + | |||||||
| Porcelain-fused-to-metal restoration (n = 1) | 19 | Indonesia | + | + | |||||||
| Porcelain-fused-to-metal restoration (n = 1) | 20 | Taiwan, ROC | + | + | |||||||
| Japanese participants | |||||||||||
| Metal onlay (n = 1) | 40 | Japan | + | + | + | + | + | ||||
| Metal onlay (n = 1) | 40 | Japan | + | + | + | + | |||||
| Metal inlay (n = 7) | 40, 41, 42, 43 | Japan | + | + | + | + | + | ||||
| Metal inlay (n = 1) | 43 | Japan | + | + | + | + | |||||
| Metal inlay (n = 2) | 39, 40 | Japan | + | + | + | + | |||||
In this study, composite resin fillings were the most common dental treatment among non-Japanese Asian and Japanese participants in their 20s to early 40s. Based on the data from the latest Survey of Dental Diseases (SDD, Ministry of Health, Labour and Welfare, Japan, 2022), the percentage of Japanese persons in their 20s to early 40s who had dental carious teeth and had been treated with fillings or crowns ranged from 76.4% to 97.4%. Composite resin fillings account for the highest number of cases among the claims related to fillings and dental restorations in their 20s to early 40s under universal health insurance claims in Japan. Although the number of Japanese who participated in this survey is small, government statistical survey data also suggested that most people in their 20s to early 40s who received dental treatment in Japan had composite resin fillings.
The Minamata Convention on Mercury (2013) addresses products that contain mercury (Hg), including dental amalgam, and proposes nine measures to reduce the use of dental amalgam. The World Health Organization reported that more than 85% of regions were phasing out or completing the phase-out of dental amalgam use by 2021. Therefore, fewer participants in their 20s to early 40s had amalgam fillings than older individuals, as reported in the previous study [1]. However, notably, two Taiwanese and one Japanese participant had replaced some of their amalgam fillings with composite resin fillings. From the viewpoint of personal identification, it was impossible to narrow down the region and age based simply on the presence of amalgam fillings in their oral cavities among these countries in this study.
Complete metal crowns were used only by participants from Vietnam, whereas porcelain-fused-to-metal restorations were used only by participants from Indonesia, Taiwan, ROC, and Vietnam. None of the Asian participants used metal inlays or onlays. Additionally, the metal elements in the dental restorations and fixed prostheses of the Asian participants were Ni-Cr or Co-Cr alloys. In contrast, the Japanese participants used Ag-Pd-Cu-Au or Ag-In alloys without Pd and Au. The differences in materials and treatments between Asians and Japanese people can be attributed to various factors, including insurance coverage and regional preferences. Universal health insurance claims for dental Ag-Pd-Cu-Au alloys (mainly composed of 20% Pd and 12% Au with around 50% Ag) for metal inlays and crowns in private dental clinics in Japan have been the largest in recent decades. As of 2022, the most common claims for dental restorations and crowns under universal health insurance in Japan predominantly utilized dental Ag-Pd-Cu-Au alloys, even for individuals in their 20s to early 40s. However, titanium (Ti) crowns were covered by insurance in 2020 and facing Ti crowns were also included in 2022. Conversely, dental restorations and fixed prostheses with Ni alloys and facing Co-Cr alloy crowns are not currently covered by universal health insurance in Japan. In the future, a more diverse combination of materials newly covered by universal health insurance will be found in the oral cavity of people with a history of treatment in Japan, including various non-metal materials, Ti alloys. In Japan, in any case, the dental record must include the tooth number and treatment material for universal health insurance claims. In cases where it is difficult to identify individuals based solely on the morphology of dental treatment scars, it might be useful to analyze the metal element composition of materials in dental restorations and fixed prostheses and compare the results with information in the candidate's dental records.
In this case study, non-metal dental materials were most commonly used among the 38 non-Japanese Asians and five Japanese participants. Non-metal materials may be preferred as they are cheaper and require shorter treatment periods, and they minimize the risk of dental metal allergies associated with using Pd, Ag, Ni, and zinc (Zn) [2,3,4] and reduce the likelihood of Hg toxicity. With this background, recent developments in computer-assisted design, manufacturing, and adhesive-based materials have contributed to the increasing popularity of non-metallic materials in Asia.
In Japan, Ministry of Health, Labor, and Welfare controls the approval of the manufacturing and marketing of dental devices and materials, including dental treatment materials, based on the Japanese Industrial Standards (JIS) and International Organization for Standardization (ISO). Since the proportion of main metals contained in those dental materials is also specified, analysis of the percentage of each metal element will further narrow down the countries where the dental treatment was performed. If the analysis of the materials in their real oral cavities matches those approved materials with or without insurance coverage, there is a possibility that the unidentified person has had some dental treatment history in Japan.
This study had several limitations. The primary limitation was the small sample size. However, little information is available concerning the dental conditions of non-Japanese temporary residents and the components of dental metals in actual oral cavities, which contributes significantly to the understanding of oral health in healthy controls.
Second, owing to ethical concerns, samples could not be collected from small-sized amalgam fillings and metallic parts below the healthy gingival margins in living individuals. Nevertheless, the major metal elements in almost all dental metal treatments were successfully detected.
Third, this study did not include Japanese individuals with full metal crowns or metal prostheses that are not covered by universal health insurance. It was mainly because participants in this study were recruited from staff and students in medical and dental fields. Most of their dental restorations and fixed prostheses were small due to their high awareness of oral health. Although the number of remaining teeth aligned with the average reported in the SDD, few Japanese candidates with dental metal materials in their oral cavities were found in the field of this study. However, government statistics show that full metal crowns are still used for people in their 20s to early 40s in Japan, with Ag-Pd-Cu-Au alloy being a common material under universal health insurance treatment.
Fourth, mainly due to language barriers, discussion in this study could not include the official information of Asian governments except Japan on approval of the manufacturing and marketing of dental materials. In personal identification, information on dental materials approved by government agencies in each country also help to identify the geographic region in which a person lives. As another approach, it would be useful to gather information on the percentage of dental metals through dental professionals in each country, or data of marketing distribution of dental metals.
In conclusion, composite resin fillings were the most common dental treatment in this case study among non-Japanese Asian temporary residents and Japanese individuals in their 20s to early 40s living in the same city in Japan. However, even though metallic materials were limited, metal inlays or onlays in the oral cavities differed between the non-Japanese Asian and Japanese participants. In addition, the presence of Ni-Cr or Co-Cr alloys used for exposed metal-type dental fixed prostheses (complete metal crowns) was specific to the participants from Vietnam, which differs from the dental metal materials used for the Japanese participants. Additional information on dental materials in each Asian country would also useful for personal identification and clinical diagnosis.
Ag-In: silver-indium; Ag-Pd-Cu-Au: silver-palladium-copper-gold; Co-Cr: cobalt-chromium; Hg: mercury; ISO: International Organization for Standardization; JIS: Japanese Industrial Standards; Ni-Cr: nickel-chromium; PR China: People's Republic of China; Taiwan, ROC: Taiwan, Republic of China; Ti: titanium; SDD: Survey of Dental Diseases; Zn: zinc
All experimental protocols were approved by the epidemiological research ethics review committee of Hiroshima University (No. E2020-2309). This study was conducted in accordance with the “Ethical Guidelines for Medical and Biological Research Involving Human Subjects (Ministry of Education, Culture, Sports, Science and Technology; Ministry of Health, Labour and Welfare; Ministry of Economy, Trade and Industry, Japan).”
The authors confirm that there are no conflicts of interest.
This study was partially supported by a research grant from Pfizer Health Research Foundation FY 2020.
HO: conceptualization, investigation, methodology, data curation, and writing; NO: data curation, formal analysis, editing; MY: conceptualization, investigation, and writing; NK: conceptualization, methodology, editing, and supervision
1)HO*: okhiroko@hiroshima-u.ac.jp, https://orcid.org/0000-0002-6887-8456
2.3)NO: nami-obys@hiroshima-u.ac.jp, https://orcid.org/0000-0001-5146-9747
4)MY: mineka@hiroshima-u.ac.jp, https://orcid.org/0000-0001-5461-1075
5)NK: kakimoto-n@hiroshima-u.ac.jp, https://orcid.org/0000-0003-1274-8991
The authors are grateful to Dr. Masae Kitagawa (Hiroshima University) for years of collaboration and technical support. The authors would like to thank the staff of the Center of Oral Clinical Examination at Hiroshima University Hospital for their support.
Experimental data generated during the current study are presented in this article.
