Unlocking the Biology of TMJ Pain: A National Effort for Non-Opioid Treatments
A five-year, $9 million study funded by the National Institutes of Health is investigating the biological mechanisms of temporomandibular joint (TMJ) disorders. Led by UT Health San Antonio, the research aims to develop targeted, non-opioid treatments for chronic pain associated with muscle and joint dysfunction. This project is part of a national consortium of five institutions collaborating to understand how facial pain originates and transitions to chronic conditions.
Led by UT Health San Antonio, the research aims to develop targeted, non-opioid treatments for chronic pain associated with muscle and joint dysfunction.
The Widespread Impact of Chronic Pain
Chronic pain is a widespread health condition globally. Back pain is frequently reported, with head and face pain linked to TMJ disorder following as a common type. TMJ disorder can affect mobility, vocational options, and daily activities. Facial joint and muscle pain can disrupt eating and speaking.
Chronic pain has also been associated with reduced quality of life and functional lifespan, with some reports indicating a potential reduction of up to 10 years due to decreased physical activity and general health decline.
The NIH-Funded TMJ Study
The $9 million study, funded by the National Institute of Neurological Disorders and Stroke, began in 2022 and has received approval to continue its work. UT Health San Antonio, under the leadership of Armen N. Akopian, PhD, is a key participant in a national consortium of five institutions conducting complementary studies. The continued NIH investment is intended to bolster UT Health San Antonio's research capabilities and recognition in the field of pain research.
Mapping the Biology of Facial Pain
The current phase of the project at UT Health San Antonio focuses on identifying and characterizing trigeminal neurons that innervate facial muscle and TMJ tissues. Researchers are documenting differences among male, female, and older mice, both with and without TMJ disorder.
Detailed maps of afferent neurites—projections from a neuron's cell body—are being developed to define their location, plasticity, and phenotype in mice and non-human primates. These maps are designed to provide insights into how pain originates and travels.
The research also includes human studies, examining and cataloging nerve and cellular plasticity in tissues from patients diagnosed with myalgia and TMJ disorders.
A central aspect of this research is neuronal excitability. Pain is understood to begin when sensory neurons become sensitized and hyperexcitable, a process influenced by interactions between neurons and non-neuronal cells in muscles and joints.
From Sensitization to Chronic Pain
Following neuronal sensitization, stimuli that were previously harmless may induce pain (allodynia), and painful stimuli may elicit a disproportionately severe response (hyperalgesia). Dr. Akopian's team investigates pain at various levels, including:
- Patient-reported experiences
- Neuronal firing patterns
- Gene expression changes that control excitability
- Signaling from non-neuronal cells in affected tissue
This multi-level data collection aims to identify biologically specific targets for chronic pain treatment. Reductions in pain, even modest ones such as a 25% decrease on a 10-point scale, are noted to significantly improve a patient's experience.
Advanced Transcriptomic Discoveries
Transcriptomic profiling, which analyzes gene expression, is a significant tool in the study. Since 2015, Dr. Akopian and his team have conducted numerous studies analyzing neurons from the trigeminal and dorsal root ganglia.
Their work, alongside a parallel NIH consortium known as Precision U19, indicates that trigeminal neurons possess a higher degree of specialization than previously recognized.
Neurons that innervate facial skin have been found to be distinct from those innervating muscles, joints, the tongue, or the dura mater, which is involved in headaches. The team is nearing completion of a comprehensive map of neurons that innervate key facial muscles involved in chewing and speech, as well as the temporomandibular joint itself. Each neuron type identified exhibits distinct gene expression and functional properties, contributing to the understanding of facial pain biology.
Building Shared Data Resources
The consortium plans to contribute transcriptomic and clinical data, including patient questionnaires and molecular datasets, to NIH repositories.
These centralized and harmonized datasets are intended to facilitate high-quality meta-analyses, ensuring data validation and accessibility for qualified investigators while maintaining patient privacy and data integrity.
Toward Non-Opioid Solutions for Chronic Pain
The detailed mapping and mechanistic understanding of TMJ pain are intended to establish a framework for discovering novel, non-opioid pain therapies.
The long-term objective is to develop treatments specifically designed for chronic pain, rather than therapies solely focused on acute pain.
Many existing pain medications temporarily suppress symptoms but do not prevent pain from becoming chronic. Some medications, such as opioids, carry risks of tolerance, dependence, and addiction. The research aims to identify the transition points from acute to chronic pain and, for existing chronic pain, to actively resolve it by targeting the biological mechanisms that sustain it.