This was a cross-sectional study that aimed to translate and validate the OFI-8-PT in a sample of patients aged 60 years older from the Egas Moniz Dental Clinic (Almada, Portugal).

To be eligible, participants needed to be aged 60 years or older; be fluent in Portuguese; and consent to participate. The recruitment was carried out between December 30, 2022, and February 17, 2023, which corresponds to a total period of approximately 7 weeks. The recruitment procedure and sampling method consisted of a consecutive convenience sample of participants eligible for participation that presented at the Egas Moniz Dental Clinic for a first dental appointment.

To achieve the proposed aim, we calculated a minimum sample size based on the rules of thumb from Terwee et al [14] (between 4 and 10 participants per variable), with a minimum of 10 individuals per questionnaire item. As such, considering an 8-item questionnaire with a dichotomous nature, we estimated a minimum number of 80 participants to ensure the stability of the variance-covariance matrix when performing confirmatory factor analysis (CFA).

The original OFI-8 questionnaire measures the oral frailty using 8 dichotomous items, representing the number of natural teeth, masticatory performance, maximum tongue pressure, articulatory oral motor skill, subjective difficulties in eating tough food, and subjective swallowing difficulties.

Each question is assigned a score that is then added together to obtain the total score of the questionnaire, resulting in a numerical scale that ranges from 0 to 11 points; higher scores indicate a greater degree of oral frailty, which in turn has other implications previously described, such as physical frailty, dependence, and mortality [5]. For questions 1, 2, and 3, a response of “Yes” was allocated 2 points, while for questions 4 and 5, a response of “Yes” was allocated 1 point. In contrast, a “No” response was awarded 0 points. Conversely, for questions 6, 7, and 8, a response of “No” was given 1 point, while a response of “Yes” was not awarded any points [10].

Two independent, bilingual individuals fluent in both Portuguese and English translated the original English version of the OFI-8 into Portuguese (VM and JB) in a “double-blind” process. Because no disagreements were recorded, a final version of the questionnaire was named OFI-8-PT. After back-translation to English and comparing with the original to identify discrepancies, no ambiguous wording or cultural nuances were identified. The semantic and conceptual equivalence was attested (Table 1).

The dependent variable in this study was the older adults’ self-perception of their own oral health (oral frailty score), which occurs as a result of the independent variable. The way in which participants define their oral health condition is used as an indicator for the oral frailty score.

Some parameters of the participants in this study, such as age and sex, were considered independent variables of the study. These variables can be used to determine if there is any relationship with the oral frailty score of the individuals.

The statistical analysis was conducted in the R plyr package (R Foundation for Statistical Computing).

The data collection was performed electronically, ensuring the confidentiality and anonymity of the participants’ data through a cloud-based system [24]. The study was conducted in accordance with the regulations applicable to research and was approved by the Ethics Committee of the Egas Moniz (ID: 1140/2022). Informed consent was obtained from each participant before their inclusion in the study. Participants entered into this research voluntarily, fully aware of their right to withdraw from the study at any point without the need for justification. The informed consent process ensured that participants had a clear understanding of the study’s purpose, procedures, and the voluntary nature of their involvement. Patients received compensation in the form of free diagnosis and treatment without costs.

A total of 159 participants completed the OFI-8-PT, with an average age of 73.9 (SD 9.4; range 60-99) years (mean 74.8, SD 9.7 years and mean 73.1, SD 9.0 years for female and male participants, respectively), and the group was equally composed by female and male participants (n=80, 50.3% female vs n=79, 49.7% male).

To test the reliability of the OFI-8-PT, 16 participants answered the translated tool 2 times (baseline and 2 weeks after). Of these participants, 6 (38%) were female and 10 (62%) were male, with similar age intervals (female: mean 70.8, SD 4.7 years vs male: mean 71.7, SD 9.2 years). The median total score of the instrument was 3 (range 0-7).

The overall internal consistency through Kuder-Richardson formula 20 was 0.69, thus considered to be a good reliability score. Nominally, each question had excellent reliability (Multimedia Appendix 1).

The OFI-8-PT exhibited an adequate reliability (with a Cronbach α coefficient of 0.95) and an adequate psychometric feature.

The CFA analysis attested the unifactorial structure of the OFI-8-PT. The first-order unifactorial model resulted in an adequate model fit (GFI=0.96; CFI=0.85; and RMSEA=0.05, 90% CI 0.00-0.09; Table 2).

A multigroup CFA assessed the invariance across sex groups in the OFI-8-PT (Table 1). Accordingly, there was invariance for sex groups based on the comparisons of CFI, χ², and df values across the unconstrained and constrained models studied.

In order to learn the agreement level of OFI-8-PT components, we analyzed the correlation between the items using Spearman rank correlation coefficient. There was a low number of significant correlations (4/28, 14% of all correlations; Table 3).

When correlating the overall OFI-8-PT score, age was significantly correlated (ρ=0.259; P<.001), whereas sex was not (ρ=–0.035; P=.66), confirming as well the absence of sex invariance.

This study demonstrated the psychometric validity of the OFI-8-PT to depict individuals at risk of oral frailty and functional disability in this Portuguese sample. In addition, we found an adequate internal consistency and reliability of this questionnaire.

The assessment of oral frailty in older adult individuals through a comprehensive scale holds great clinical significance due to its potential influence on geriatric care and the overall health outcomes of these individuals. Older adults typically face a variety of oral health challenges, such as tooth loss, periodontal disease, and dry mouth, which can significantly impact their quality of life and general well-being [25,26]. Despite the prevalence of oral health problems in the older adult population, there is a scarcity of specialized tools designed to assess oral frailty, which encompasses the functional and structural vulnerabilities of the oral cavity [27,28].

Expanding the usability of the OFI-8 to other languages could help health care professionals detect, intervene, and track oral health in older adults, potentially improving their quality of life through preventive care and tailored hygiene. Moreover, incorporating oral frailty assessment into routine geriatric assessments can facilitate comprehensive care planning and interdisciplinary collaboration among health care providers [29]. By addressing the clinical need for a validated scale to assess oral frailty in older adults, this study contributes to enhancing the holistic approach to geriatric health care and underscores the importance of oral health in promoting healthy aging.

The GFI indicated that the observed covariance matrix of the data fitted the covariance matrix implied by the model, revealing a very good fit. The CFI, however, suggested a reasonable fit with room for improvement when compared to a null model. The RMSEA also revealed a good fit with a value of 0.05. These results support the validity of the OFI-8-PT, although they cannot be directly compared with the original study by Tanaka et al [5] due to differences in methodology. Additionally, this is the first study to validate the OFI-8 in a language other than Japanese, which may contribute to future comparability with other validations and cultural adaptations.

With the introduction of the OFI-8-PT, health professionals and researchers will have a valuable tool for assessing oral frailty in older adults in Portugal. This standardized and validated questionnaire will enable early detection of oral frailty, allowing for targeted interventions and preventive strategies. With the current aging population, understanding and managing oral frailty is becoming increasingly important to promote healthy aging and improve overall well-being. By identifying individuals at risk, the OFI-8-PT can facilitate appropriate oral health services, ultimately contributing to improved oral health outcomes and quality of life.

The OFI-8-PT questionnaire offers several advantages that make it a valuable tool for assessing oral frailty in older adults in Portugal. Its standardized and validated nature ensures reliable and consistent assessment, while its ease of administration and scoring facilitates its incorporation into routine assessments. Implementation of the OFI-8-PT also allows for data collection on oral frailty in the Portuguese population, contributing to a better understanding of its prevalence and impact on health outcomes. However, it is important to acknowledge potential drawbacks, such as its primary focus on oral health aspects and its reliance on self-reporting, which may introduce bias or inaccuracy. Addressing these limitations and ensuring proper training and awareness of participants will be critical to maximizing the benefits of the OFI-8-PT questionnaire.

Overall, the study provides valuable insights into the psychometric validity of the OFI-8-PT questionnaire in the Portuguese population. However, there are some important limitations worth discussing that should be considered when interpreting the results.

First, the sample size used in the study was relatively small, which may limit the generalizability of the findings to a larger population. Yet, this shortcoming is limited as the OFI-8 is a 1-factor scale and we followed a previous validated strategy. Additionally, the study relied solely on self-report measures, based on self-perception of oral health, which could result in bias or social desirability effects. Furthermore, the study was conducted in a specific population from a university clinic, consisting solely of patients who visited the dental clinic, and therefore, findings may not be generalizable to the entire Portuguese population or other populations in different geographical locations. Nevertheless, these participants live in the largest metropolitan area in Portugal and may provide a considerable percentage of representation. Moreover, the presence of confounding variables, such as chronic diseases and medications, could influence the oral frailty score of individuals. Although these variables were acknowledged, the study did not extensively analyze their impact or control for their effects, and the study could not assess longitudinal effects due to its design.

Accordingly, conducting further research with larger and more diverse samples is recommended to address these limitations and strengthen the validity of the findings.

In conclusion, the OFI-8-PT was shown to have psychometric validity and reliability in the population under study, providing a snapshot of its oral frailty and functional disability. This consistency and ease of use may contribute to better screening and monitoring oral frailty prevalence and its impact on health outcomes. It may have an impact on future public health strategies to address oral frailty.