Jaw Functional Limitation Scale: Guide to JFLS-20 and JFLS-8 Assessment

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Accurately measuring jaw functional limitations is crucial for effective diagnosis and treatment of orofacial conditions. The jaw functional limitation scale provides clinicians and researchers with standardized tools to quantify restrictions in mandibular movement and function. Developed through rigorous methodological processes, this assessment instrument has become essential in temporomandibular disorder management and research.

The JFLS exists in two validated versions—the comprehensive JFLS-20 and the abbreviated JFLS-8. Both versions offer reliable functional limitation assessment across three key domains: mastication, vertical jaw mobility, and emotional/verbal expression. Furthermore, these instruments demonstrate strong psychometric properties, making them valuable for TMJ assessment and monitoring treatment outcomes for patients with orofacial pain. The standardized scoring system allows for consistent interpretation of results and facilitates meaningful comparisons across different clinical populations.

This article examines the development, structure, and application of the Jaw Functional Limitation Scale. Additionally, it provides detailed guidance on proper administration, scoring, and interpretation of both the JFLS-20 and JFLS-8. Finally, we explore the clinical utility of these instruments in various settings and their contribution to evidence-based practice in orofacial pain management.

Development of the JFLS Instrument

The Jaw Functional Limitation Scale (JFLS) emerged from a need to resolve shortcomings in previous measures of jaw limitation. These earlier instruments often suffered from insufficient item definitions and overlapping functional and psychosocial domains. The development process was methodical, beginning with existing validated instruments and progressing through several scientific validation phases.

Item pool generation from 52 candidate behaviors

The JFLS was derived from two established instruments: the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) checklist and the Mandibular Functional Impairment Questionnaire (MFIQ). The initial development involved a consensus panel of five expert clinicians and researchers specializing in orofacial pain, oral medicine, and prosthodontics. This panel identified a comprehensive pool of 52 candidate items representing a broad spectrum of jaw functions.

The item pool was intentionally designed with overlapping content since panel members had varying interpretations of how to best describe specific jaw behaviors. These items covered four primary domains:

• Mastication (20 items) including activities like chewing various foods
• Vertical jaw mobility (9 items) such as opening wide enough to talk
• Verbal and emotional expression (14 items) including smiling and talking
• Miscellaneous functions (9 items) like swallowing and yawning

Each behavior was assessed on a 0-10 numeric rating scale (NRS), with endpoints anchored by “no limitation” and “extreme limitation”. This initial 52-item pool provided the foundation for subsequent refinement through statistical modeling.

Rasch modeling for item reduction and fit analysis

Rasch methodology served as the primary analytical approach for item reduction and assessment of model fit. This probabilistic model simultaneously estimates item difficulty and subject ability, producing a scale where both items and subjects are mapped commensurately.

The development study included 132 consecutive patients from five diagnostic groups: temporomandibular disorders (TMD), primary Sjögren syndrome, burning mouth syndrome, skeletal malocclusion, and healthy controls. This diverse sample participated in a known-groups validity design to ensure the instrument’s generalizability across different clinical populations.

During analysis, the graded response model of the Rasch method was selected for the 0-to-10 response format data. To reduce statistical noise, the data were recoded from the 0-to-10 scale to a 0-to-3 scale. Through iterative Rasch modeling, the researchers identified three distinct constructs comprising a total of 20 items, forming the JFLS-20. Concurrently, they developed a shorter 8-item form (JFLS-8) for assessing global functional jaw limitation.

Translation and cross-cultural adaptation process

The translation and cross-cultural adaptation of the JFLS followed standardized guidelines to ensure semantic and cultural equivalence across languages. This process typically involved multiple steps:

1. Initial forward translation by bilingual translators whose native language was the target language
2. Synthesis of translated versions into a common translation
3. Back-translation by translators blind to the original version
4. Expert committee review of all translations
5. Testing of pre-final versions with target populations
6. Submission of documentation to coordinating committees for final approval

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For example, the Brazilian Portuguese adaptation process included 117 participants with TMD assessed on two separate days. The validation research confirmed excellent reliability over time with intraclass correlation coefficients exceeding 0.85 and adequate internal consistency with Cronbach’s alpha values above 0.77. Similarly, the Malay version underwent rigorous translation involving three forward translators and two back-translators, followed by expert panel reviews and pre-testing with 10 subjects.

Through these methodical development and adaptation processes, the JFLS has evolved into a psychometrically sound instrument capable of assessing jaw functional limitations across diverse patient populations and cultural contexts.

Structure and Constructs of the JFLS-20

The JFLS-20 consists of three distinct constructs, each measuring different aspects of jaw function. These three domains—mastication, vertical jaw mobility, and emotional and verbal expression—comprise a total of 20 items that collectively provide a thorough assessment of mandibular functional limitations. Each construct demonstrates excellent psychometric properties with respect to modeled variance, item fit, reliability, and internal consistency.

Mastication: Chewing and biting item hierarchy

The mastication construct encompasses items 1 through 6 of the JFLS-20, focusing on eating behaviors of varying difficulty. These items include:

1. Chewing tough food
2. Chewing hard bread
3. Chewing chicken
4. Chewing crackers
5. Chewing soft food
6. Eating soft food requiring no chewing

The selection of these specific items resulted from analysis of many food types, where redundant information was eliminated through successive iterations while considering fit and clinical meaningfulness. The final items were determined based on suitable spread of item difficulty measures, creating a hierarchy where chewing tough food presents the greatest challenge while eating soft food represents minimal difficulty.

According to research findings, this hierarchy is validated by effect sizes that range from 1.0 for chewing tough food to less than 0.1 for eating soft food. The means of these items were only one standard deviation greater than the mean of the subjects, indicating reasonable fit where many persons were functioning relatively well. Notably, ceiling effects were essentially absent, with only two subjects reporting limitation levels greater than the highest rated item.

Vertical jaw mobility: Range of motion indicators

Items 7 through 10 constitute the vertical jaw mobility construct, assessing the range of motion necessary for various daily activities:

1. Biting from a whole apple
2. Biting into a sandwich
3. Opening wide enough to talk
4. Opening wide enough to drink

These mobility items inherently fit less well than mastication items, primarily because the patient sample demonstrated far less overall limitation in mobility compared to mastication. Nevertheless, the item reliability remained equivalent. Effect sizes across these four items demonstrated a hierarchical pattern (0.6, 0.5, 0.4, and 0.2 respectively), confirming the validity of the construct.

The observed findings regarding model fit within each diagnosis met expectations, although no statistics could be computed for the recall group because too many patients reported values at the floor of the instrument.

Emotional and verbal expression: Social and affective behaviors

The emotional and verbal expression construct comprises items 11 through 20, representing a wide spectrum of social and communicative behaviors:

1. Swallowing
2. Yawning
3. Talking
4. Singing
5. Putting on a happy face
6. Putting on an angry face
7. Frowning
8. Kissing
9. Smiling
10. Laughing

The selection of these items involved balancing efficiency (item reduction) with maintaining suitable representation of the wide range of verbal and emotional behaviors for which the masticatory muscles and associated facial muscles are essential. This approach allows the scale to function as a checklist for monitoring specific behaviors that individuals might regard as important.

Although there was evidence of poor outfit in the PSS group, infit remained excellent for all groups. The wide range of oral behaviors used for verbal and emotional expression exhibited uniformly high Cronbach’s alpha values, suggesting these items might be related more to a traditional factor. However, inspection of the residual factor plot revealed no significant clustering, and variance accounted for by Rasch scaling (73% to 93%) was comparable to that of the mastication items.

All three constructs of the JFLS-20 utilize an 11-point numerical rating scale ranging from 0 (“no limitation”) to 10 (“severe limitation”). For analytical purposes, researchers sometimes recode responses to a 0-3 or 0-4 scale to address low frequencies in some response categories. Together, these constructs provide clinicians with a comprehensive assessment tool for evaluating jaw functional limitations across different domains of daily activities.

Scoring and Interpretation of JFLS-20 and JFLS-8

Proper administration and scoring of the jaw functional limitation scale instruments ensure consistent evaluation across diverse patient populations. Both versions employ standardized methodologies that maintain psychometric integrity while facilitating practical clinical use.

0–10 Numeric Rating Scale and recoding to 0–3

The JFLS utilizes an 11-point numeric rating scale (NRS) where patients rate each functional limitation from 0 (“no limitation”) to 10 (“extreme limitation”). This scale captures nuanced differences in limitation severity while remaining intuitive for patients to complete. For participants from general dental populations, an “NA” (not applicable) response option may be provided when difficulties with jaw function do not apply to their condition, though these responses are typically excluded from analysis.

Despite the original scale’s 0-10 format, researchers sometimes recode responses to simplify analysis. The most common recoding scheme converts the 11-point scale to a 4-point scale (0-3) using the following pattern: 0=0; 1-3=1; 4-7=2; 8-10=3. This recoding improves person reliability from 0.67 (in the 0-10 scale) to 0.82 (in the 0-3 scale) while maintaining item reliability between 0.94-0.96 regardless of category count. Alternatively, some studies employ a 5-point (0-4) recoding scheme: 0=0; 1-3=1; 4-6=2; 7-9=3; 10=4.

Summary score calculation for each construct

The JFLS-20 yields scores for three distinct functional domains. Each construct score is calculated as the mean of its constituent items:

• Mastication: mean of items 1-6
• Mobility: mean of items 7-10
• Verbal and non-verbal communication: mean of items 13-20

When handling missing data, scores can still be computed with specific limitations: mastication allows up to 2 missing items; mobility permits 1 missing item; and communication accommodates up to 2 missing responses. Score calculation with missing items is adjusted by dividing by the number of items present.

Global score derivation in JFLS-8

The JFLS-8 provides a concise assessment of global jaw functional limitation. This shortened version includes items 1, 3, 6, 10, 11, 12, 13, and 19 from the full instrument. The global score is calculated as the mean of all available items, with no more than two missing responses permitted.

Importantly, the JFLS-20 can also yield a global score through two distinct methods. First, by computing the mean of all 20 items; second, by calculating the mean of the three construct scores. Both versions demonstrate exceptional correlation—research indicates a 0.98 correlation between the original 8-item and new 8-item global measures.

Internal consistency measurements underscore the instruments’ reliability, with Cronbach’s alpha of 0.87 for JFLS-8 and 0.95 for JFLS-20. This strong psychometric foundation makes both versions suitable for longitudinal monitoring, where the comprehensive JFLS-20 might be used at baseline (providing all three subscales plus global score), while the more efficient JFLS-8 can be employed for follow-up assessments.

Psychometric Properties and Validation Results

Extensive validation testing confirms the robust measurement properties of the jaw functional limitation scale across diverse populations. Rigorous psychometric evaluation ensures both versions provide reliable and valid assessments for clinical and research applications.

Internal consistency: Cronbach’s alpha across constructs

The JFLS demonstrates exceptional internal consistency with Cronbach’s alpha values ranging from 0.91 to 0.93 for the full instrument. Each construct maintains impressive reliability metrics, with the mastication domain showing particularly strong values. Even in shortened formats, reliability remains excellent—the JFLS-8 maintains a Cronbach’s alpha of 0.91, whereas the recently validated JFLS-4 demonstrates good reliability with a Cronbach’s alpha of 0.714. In corrected item-total correlations, each item’s coefficient varies between 0.74 and 0.87, confirming robust associations between individual items and total scores.

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Temporal stability: Concordance correlation coefficients

Temporal stability represents the instrument’s consistency over time. The JFLS demonstrates satisfactory temporal stability, with Lin’s concordance correlation coefficient (CCC) serving as the primary metric. This coefficient measures both precision and accuracy, ranging from 0 to ±1. For the JFLS constructs, CCC values demonstrate excellent stability: 0.87 for limitations in mastication and 0.94 for limitations in vertical jaw mobility. Verbal/emotional expression shows moderate stability at 0.56. Test-retest reliability for the JFLS-8 reveals an intraclass correlation coefficient (ICC) of 0.93, confirming excellent temporal stability. The JFLS-20 demonstrates similarly impressive test-retest reliability with ICC values between 0.91 and 0.95.

Clinical and Research Applications of JFLS

The jaw functional limitation scale serves as a cornerstone assessment tool in various clinical settings. Its practical applications span multiple specialties within dentistry and pain management.

Use in temporomandibular disorder (TMD) assessment

The JFLS-8 functions as a self-administered questionnaire for evaluating the functional status of the masticatory system in TMD patients. This abbreviated version is officially recommended by the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) protocol. Research confirms that patients with more TMD symptoms report significantly higher levels of functional limitations. Interestingly, female adolescents experience TMD pain more commonly than males yet show similar patterns of jaw functional limitations. The OPPERA study utilized the JFLS to characterize jaw function in 185 patients with chronic TMD.

Suitability for prosthodontic and Sjögren syndrome patients

Beyond TMD applications, the JFLS effectively assesses functional limitations in patients undergoing major prosthetic rehabilitation. For Sjögren syndrome patients, even those with preserved salivary flow rates (≥0.1 mL/min) often report oral dryness and demonstrate significantly higher oral health impact scores compared to non-Sjögren controls (13.6 vs. 7.1, p=0.029). These patients particularly struggle with being self-conscious, finding their diet unsatisfactory, and feeling life less satisfying.

Integration into outcome tracking and treatment planning

The JFLS demonstrates excellent utility as an outcome measure in intervention studies. Recent research showed significant improvements in JFLS-20 scores with large effect sizes following therapeutic exercises. A simplified 4-item version (JFLS-4) maintains good reliability (Cronbach’s alpha 0.714), potentially streamlining clinical evaluation processes. Practitioners frequently use JFLS alongside other instruments like the Oral Behaviors Checklist (OBC) to comprehensively evaluate jaw function.

Conclusion

The Jaw Functional Limitation Scale stands as a vital instrument in orofacial pain assessment and management. Throughout this article, we examined the comprehensive development, structure, and practical applications of both the JFLS-20 and JFLS-8 versions. These validated assessment tools effectively quantify functional limitations across three essential domains: mastication, vertical jaw mobility, and emotional/verbal expression.

The methodical development process, beginning with a 52-item pool and refined through Rasch modeling, resulted in psychometrically sound instruments applicable across diverse clinical populations. Additionally, the standardized scoring system—utilizing a 0-10 numeric rating scale—ensures consistent evaluation and interpretation of jaw functional limitations.

Both versions demonstrate exceptional psychometric properties. The JFLS-20 offers comprehensive assessment through three distinct constructs, while the JFLS-8 provides an efficient global measure suitable for follow-up evaluations. Their strong internal consistency, temporal stability, and known-groups validity confirm their reliability as clinical and research tools.

Beyond temporomandibular disorders, these instruments prove valuable for patients with Sjögren syndrome, those undergoing prosthodontic rehabilitation, and various other orofacial conditions. The ability to track functional limitations objectively makes the JFLS particularly useful for monitoring treatment progress and outcomes.

Clinicians should therefore consider incorporating either the JFLS-20 or JFLS-8 into their assessment protocols, depending on their specific needs and time constraints. These standardized measures ultimately enhance clinical decision-making and contribute significantly to evidence-based practice in orofacial pain management.