Chiropractic Adjustments Increases Maximal Bite Forces Through Effecting Cortical Changes
By: Mark Studin
William J. Owens
Citation: Studin M., Owens W. (2019) Chiropractic Adjustments Increase Maximal Bite Forces Through Effecting Cortical Changes, American Chiropractor, 41 (1) 12, 14, 16
A report on the scientific literature
Chiropractic has been shown in the literature to affect neural plastic changes. According to Wikipedia, “Neuroplasticity, also known as brain plasticity and neural plasticity, is the ability of the brain to change throughout an individual's life, e.g., brain activity associated with a given function can be transferred to a different location, the proportion of grey matter can change, and synapses may strengthen or weaken over time. Research in the latter half of the 20th century showed that many aspects of the brain can be altered (or are "plastic") even through adulthood. However, the developing brain exhibits a higher degree of plasticity than the adult brain. Neuroplasticity can be observed at multiple scales, from microscopic changes in individual neurons to larger-scale changes such as cortical remapping in response to injury.” (https://en.wikipedia.org/wiki/Neuroplasticity) This article focuses on a specific piece of evidence to demonstrably verify the effects of those neuroplastic changes as sequella to a chiropractic “high velocity-low amplitude spinal adjustment.
Haavik, Ozyurt, Naizi, Holt, Nefergaard, Yilmaz and Turker (2018) reported “It has previously been proposed in the literature that chiropractic spinal manipulation has a central neural effect. This is because multiple studies have shown that spinal manipulation of dysfunctional spinal segments can impact somatosensory processing, sensorimotor integration, and motor control.” (pg. 6) Haavik, Naizi, Jochumsen, Sherwin, Flavel and Turker (2017) supported the previous finding by reporting “The result presented are consistent with previous findings that have suggested increases in strength following spinal manipulation were due to descending cortical drive and could not be explained by changes at the level of the spinal cord. Spinal manipulation may therefore be indicated for the patients who have lost tonus of their muscle and/or are recovering from muscle degrading dysfunctions such as stroke or orthopedic operations and/or may also be of interest to sports performers.” (pg. 12)
Lelic, Niazi, Jochumsen, Dremstrup, Velder, Murphy, Drewes and Haavik (2016) also supported the neural plastic changes of a chiropractic spinal adjustment by reporting their “study resulted in two major findings. Firstly, the study reproduced previous findings of somatosensory evoked potential (SEPs) studies that have shown that chiropractic spinal adjusting of dysfunctional spinal segments alters early sensorimotor integration (SMI) of input from the upper limb. The second major finding of this study was that we were able to show, using dipole source localization, that this change in SMI that occurs after spinal manipulation predominantly happens in the prefrontal cortex. The SEP peak showed multiple neural generators including primary sensory cortex, basal ganglia, thalamus, premotor areas, and primary motor cortex. The frontal N30 peak is therefore thought to reflect early SMI.”
Haavik, Ozyurt, Naizi, Holt, Nefergaard, Yilmaz and Turker (2018) also found “The major finding of this study was that chiropractic spinal manipulation (adjustment) increased maximum bite force immediately after the intervention and the increase in bite force remained at 1-week follow-up. This is the first study to show that a single session of chiropractic spinal manipulation can increase jaw bite strength compared to a sham intervention.
This immediate increase in jaw bit force of 11% post spinal manipulation was unlikely to be due to the placebo effect, as all subjects were naïve to chiropractic, and most of the subjects did not know which intervention was real upon questioning after both interventions. The 2.3% decrease in maximum bite force after the sham intervention may have been due to fatigue from maximum biting on the mold, or simply due to random variations in maximum efforts.
The current study now also suggests that cervical spine function can influence maximal bite force. The effort with which the subject’s bite would also influence maximum bite force, and for this reason the study was conducted in Turkey, where chiropractic is relatively unknown, to enable a more effective sham intervention. As no increase in strength occurred following the sham intervention, the effort is unlikely to have been the reason the subjects’ bite force increased after the spinal manipulation.
Increases in lower limb muscle strength in subjects with subclinical pain following chiropractic spinal manipulation has been reported. An increase in lower limb strength in elite athletes that lasted 30 min post spinal manipulation was shown. Chilibeck, et al. reported that in subjects with imbalances in lower limb muscle strength, spinal manipulation resulted in increased muscle strength of hip abductors in their weak leg. Botelho and Andrade reported increases in grip strength in a group of national level judo athletes following spinal manipulation.”
Haavik et. Al continued, “In two of these previous studies that showed lower limb muscle maximum voluntary strength increases after chiropractic spinal manipulation H-reflex excitability and V-waves were also recorded. Both studies showed increases in maximum plantarflexion force and significant increases in the cortical drive to the plantar flexors (i.e., V-wave) following spinal manipulation, and that both these measures significantly decreased after the control intervention… The increase therefore seen following the spinal manipulations was, therefore, most likely because of the increased cortical drive to the muscle.”
“It has previously been proposed in the literature that chiropractic spinal manipulation has a central neural effect. This is because multiple studies have shown that spinal manipulation of dysfunctional spinal segments can impact somatosensory processing, sensorimotor integration, and motor control as mentioned in the introduction. This current study supports this notion, as spinal manipulation appears to alter maximum biting force in this group of subjects. This study, therefore, supports the growing body of research that suggests chiropractic spinal manipulation’s main effect is neuroplastic in nature that affects cortical excitability.”
“Spinal dysfunction, even mild, recurrent spinal dysfunction, has been shown to be associated with maladaptive neural plastic changes, such as alterations in elbow joint position sense, mental rotation ability, and even multisensory integration, suggesting spinal dysfunction can alter the brains inner body schema and maps of the body and the world around us. This may be because spinal manipulation has been shown to change both cerebellum-M1 processing as well as prefrontal cortex processing. In the current study, the subjects’ mild spinal dysfunction may have altered the somatosensory input from the neck to the brain centers involved in sensorimotor integration and motor control of the jaw, and that adjusting these dysfunctional segments therefore impacted on these same central regions altering the maximum bite force the subjects could perform.”
Haavik et. Al concluded “Knowing that spinal function can have an impact on jaw function has functional implications for patient populations. It is possible that chiropractic spinal manipulation may influence the clinical outcomes for patients with TMJ disorders, as has been suggested by individual case studies.” There are also a significant amount of other applications of maximal bite force in our population that would also benefit from a chiropractic spinal adjustment when clinically indicated.
What’s not to be lost in this reporting of the literature as mentioned previously “multiple studies have shown that spinal manipulation of dysfunctional spinal segments can impact somatosensory processing, sensorimotor integration, and motor control.” There is a myriad of signs, symptoms, conditions and disease process that emanate from the malfunction of those centrally controlled functions in the human body. Although we have proven that a chiropractic spinal adjustment positively affects these functions, we are still at the forefront of fully understanding the full extent of how the adjustment influences a patient’s overall health although these authors have seen evidence clinically for almost four decades and chiropractors since 1895 have been reporting the same.