Citation of this Article:
Wita Anggraini,“Somatic Gag Reflex in Dental Treatment Procedures: An Anatomical Perspective”, IJDSIR- August - 2020, Vol. – 3, Issue -4, P. No. 509 – 516.
https://www.ijdsir.com/issue/pagedata/1277/Somatic-Gag-Reflex-in-Dental-Treatment-Procedures--An-Anatomical-Perspective
Abstract
Background: Somatic
gag reflex is a condition that commonly occurs
in dental treatment especially
in prosthodontics procedures and while
taking intraoral periapical radiographs at either maxillary or mandibular posterior teeth.
Patients who are sensitive to foreign matter inserted to
the oral cavity, can generate feeling of gag/nausea or even vomiting, in
sudden. This situation is difficult to be controlled by either the patient or
the dentist. The somatic gag reflex depends on the
integrity of the glossopharyngeal and the vagus nerves. Clinical manifestation of somatic gag reflex varies in
each individual so that the management is different from one another, because
of it has never been a ‘one-size-fits-all
management’. Conclusion: Somatic gag
reflex is a gag reflex triggered by a stimulus
in the "trigger zone" area, namely the posterior 1/3rd of tongue,
palatine tonsils and pharynx. The gag reflex has a sensory limb
from the glossopharyngeal nerve and a motor limb
from the vagus nerve. The
management of somatic gag reflex in some of dental
treatment procedures varies
in each individual.
In
the top of that, the dentist need to minimize the sensory stimulus carried by
the glossopharyngeal nerve.
Keywords: Somatic Gag Reflex, Dental Treatment Procedures, Glossopharyngeal Nerve
Gag
reflex is a normal mechanism under the parasympathetic division of
the autonomic nervous system. [1] As a normal defense,
the gag reflex aims to prevent the foreign matter enter into the trachea.[2] Once gag
reflex has occurred/generated, the contraction of the posterior pharynx leads
to narrowing pharynx wall, in which also referred to pharyngeal reflex.[3&4]
The etiology of the
gag reflex can be categorized as somatic, psychological or a combination of
both. Somatic responses occur in response to intraoral physical stimulation.[5] In somatic gag reflex, there are five areas called
"trigger zones" namely: (1) the palatoglossal arch, (2) the palatopharyngeal arch (3) the posterior 1/3rd of tongue, (4) the palate, (5) the uvula, and (6) the posterior pharynx wall.
Physical stimulation in these zones will trigger to gag reflex as somatic response.[6&7] The somatic gag reflex depends on the integrity of
the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X). In psychological
gag reflex can occur without direct physical contact even it can be induced
through visual, smell or sound of instruments and materials used by dentists. The worst
psychological condition is when a patient has assumed that dental treatment may generate gag.[6&8]
Somatic gag reflex is
a condition which
is commonly found
during dental treatment. Individuals with normal to mild gag reactions can
occasionally gagging in difficult treatments, but generally the gag reflex is
still under patient control. Whereas
some individuals with severe gag reflex tend to endanger dental treatment and create difficulty for patients and
dentists. Thereby,
special measures are required. In this review, we will discuss about the role of the
glossopharyngeal and vagus nerves in the somatic gag reflex and the anatomic
principles for preventing the somatic gag reflex in some of
dental treatment
procedures.
Literature review
Communication of
glossopharyngeal and vagus nerves in somatic gag reflex
The
name glossopharyngeal refers to Latin, glosso (tongue) and pharynx (the
beginning of the digestive tract), this name is given in accordance with the
target function. Vagus, is a Latin adjective which means wandering or roving.
The naming of the vagus nerve is in accordance with its very wide range of afferent
and efferent innervation.[9] The involvement of
these two nerves in the gag reflex needs to be discussed together as they come
out of the medulla oblongata side by side. The vagus nerve fibers are located in between the
glossopharyngeal nerve fibers and the accessory nerve (CN XI), and leaving the cranial cavity
through the nerve parts of the jugular foramen.[10] The glossopharyngeal nerve is a
smaller nerve bundle compared to the vagus nerve, but has a similar functional
and anatomical distribution, and often overlaps peripherally. These nerves are
connected to many of the same brain stem nuclei (nucleus ambiguus, solitary nucleus, spinal nucleus of the
trigeminal) and are often damaged together.[11&12] Nucleus ambiguus is a
long cell column in the medulla oblongata, and is a source of branchiomotor
fibers (special somatic efferent) in
the glossopharyngeal and vagus nerves that serve the speech and swallowing
muscles.[13&14]
The glossopharyngeal nerve
supplies bilaterally and has sensory, parasympathetic, and motoric components.
The sensory fibers, originating from the solitary nucleus, receive impulses from the
posterior 1/3rd of tongue, palatine tonsils, pharynx, middle ear, carotid body, carotid sinus and their afferent
taste/gustatory
fibers receive impulses from the posterior 1/3rd of tongue. The parasympathetic fibers are derived from the
inferior salivatory nucleus, supplies secretomotor innervation to the parotid gland. The
branchiomotor fibers of glossopharyngeal nerve innervates the stylopharyngeus muscle. [15&16]
The vagus nerve has the
same components as the glossopharyngeal nerve. In the gag reflex, the vagus
nerve has 3 bilateral motor innervation from the ambiguus nucleus, namely: (1)
pharyngeal branch, which innervates the soft palate muscles (muscles of the
palatopharyngeal, palatoglossal, uvula) and pharyngeal constrictor muscles, (2) the superior
laryngeal nerve, which innervates the inferior pharyngeal constrictor muscle and the
cricothyroid muscle of the larynx, and (3) the recurrent laryngeal nerve branch innervates the other
intrinsic larynx muscles. [15&16]
The pharyngeal branch (sensory) of the glossopharyngeal nerve communicate and
join with the pharyngeal
branch (motor) of the vagus nerve, and they form the pharyngeal plexus together with
the sympathetic
fibers
(vasomotor) of the superior cervical
ganglion. Through the pharyngeal plexus, the glossopharyngeal nerve receive sensory information from the nasopharynx and oropharynx mucosa
and the vagus nerve provides motor innervation to the soft palate muscles and
pharynx muscles.[17] Because of the mixing of the two cranial
nerve fibers mentioned above in the pharyngeal plexus, it is difficult to determine a
pure lesion of the glossopharyngeal nerve.
Damage to the glossopharyngeal nerve
often occur together with damage to the vagus nerve and radix of the accessory nerves in the jugular foramen.[18] Single damage of the
glossopharyngeal nerve is very rare.[19] Lesions of the glossopharyngeal nerve will induce: (1) sensitivity
reduction
of taste over the posterior 1/3rd of
tongue, (2) loss of gag and palatal reflexes, (3) impaired sensation over the
posterior 1/3rd of tongue, upper pharynx, tonsils (4) mild difficulty in swallowing, (5) parotid gland
dysfunction and (6) glossopharyngeal neuralgia. [20] Unilateral damage to the
vagus nerve causes paralysis of the pharynx muscles on the affected side, so that the palate on the affected
side descends which is then followed by the rise of the palate and uvula to the healthy side during
phonation. In addition, homolateral paralysis can occur in the muscles of the larynx
and vocal cords (nasal sounds appear), minor dysphagia, tachycardia and
arrhythmia.
Unilateral vagus nerve disorders usually does not result in swallowing
disorders. However,
bilateral lesions may cause dysphagia and regurgitation fluid from the nose. [20&21]
Gag reflex mechanism
The
characteristics of reflex is an involuntary rapid response, while the reflex arc is the shortest path of
reflex motion. The gag reflex is protective and is
equipped with three of the motor response, namely: elevation of the soft palate
to close the nasopharynx, glottic closure to protect the airway, and constriction of the pharynx to prevent
the foreign matter enter the pharynx.[22] The glossopharyngeal nerve and vagus nerve control the gag
reflex which have function
as sensory limb (afferent) and motor limb (efferent) within the reflex arch, respectively (Figure 1). Sensory
stimulus from the posterior pharynx wall, palatine tonsils, or posterior third of the tongue carried by the sensory limb (glossopharyngeal
nerve) to the ipsilateral of the solitary nucleus after synchronizing in the superior ganglion
inside of the
jugular foramen. After that, this nucleus sends fibers to the nucleus ambiguus inside of the superior
(rostral)
medulla. Then from
the nucleus ambiguus,
the motor limb (vagus nerve) transmits the motor stimulus to the pharyngeal
constrictor muscles. As a motor response, it stimulates the oropharynx to narrow and
elevate leading to the elevation of the midline of the palatine raphe and uvula, followed by the constriction of the pharyngeal constrictor muscles.[23&24]
Some
literatures
distinguish the pharyngeal reflex (gag reflex) from the palatal reflex. The
pharyngeal reflex can be observed by touching the posterior wall of the pharynx
using a tongue blade, applicator or other similar blunt object. Whereas, the
palatal
reflex can be stimulated by touching one side of the soft palate or uvula. The pharyngeal reflex is more
active than the palatal reflex.[25&26] Soft palate stimulation can
trigger a similar gag reflex. But in this case, the sensory limb originates from the trigeminal nerve (CN V) which transmit the sensory
stimulus from the soft palate through the spinal nucleus of the trigeminal
nerve. [24]
The
gag reflex is a superficial and simple reflex which may happen in normal individual. Based on this,
the gag reflex can be used for assessing the damage to the glossopharyngeal nerve
and vagus nerve. Both nerves are normally examined at the same time due to
difficulty when testing separately.[27] The operator need to clearly explain the examination procedure to
the patient, because it will cause an uncomfortable reaction. Touching the
posterior pharynx wall on one side, gentlely, using the tongue blade while
opening the mouth induces the sensory limb on the pharynx to send a sensory
stimulus which then generate a gag reflex. Normally, patient generates a gag
reflex. Nevertheless, the severity level is various among normal individual
which may exhibit hyperactive effect or even severe vomiting.[28&29]
Gag
reflex during dental treatment is
very disruptive to the patient and hinder the work of the dentist. Patients who
are sensitive to foreign matter inserted to the oral cavity, can generate
feeling of gag/nausea or even vomiting, in sudden. This situation is difficult
to be controlled by either the patient or the dentist. The assessment of the gag reflex
severity can be measured using the Gagging Severity Index (GPI)[30,31] (presented in Table 1).
Saravanan et
al., have treated a 38-year-old female patient
with a chief complaint of gag sensation after wearing a full maxillary denture.[32] Murthy et al., have treated a 30-years-old patient who could not be treated by a dentist before, because of suffering from severe gagging.[33] Another case report has been
presented by Hotta about a 60-year-old male patient who comes with a chief
complaint of inability in inserting his dentures due to a hyperactive gag
reflex. Because of patient has been tending to has a feeling of gag while
brushing his teeth since childhood, he rarely went to see a dentist. As a
result, he has suffered from a lot of tooth decay and required an tooth
extraction treatment, when he was 20 years old.[34] Moreover, Singh and
Gupta,
reported that a 55-year-old man had experienced severe gag reflex, resulting in
difficulty in inserting his denture inside his mouth.[35]
Discussion
Gag reflex can be used as a simple
assessment method to evaluate glossopharyngeal nerve and vagus nerve function.
If there is a sensory disturbance in the glossopharyngeal nerve, touch on the
damaged side will not give a motor response. A damaged vagus nerve resulted in
the elevation of soft palate toward the normal side, regardless of the side of
the pharynx that is touched. Whilst, if unilateral damage occurs to both nerves
at once, the vomiting reflex examination shows a unilateral response
accompanied by soft palate deviation, being pulled toward the normal side when
touched. In contrast, the touch on the damaged side does not produce any
response at all. [11,18]
Somatic gag reflex can
occur in the presence of a trigger on trigger zone for initiating the gag
reflex. Somatic gag reflex, can be distinguished one from the other. Therefore,
gag reflex management among patient is different, because there has never been
a ‘one-size-fits-all management’.[39] Gag reflex most commonly occurs in
prosthodontics procedures.
[40&41] and intraoral
periapical radiographs-taking in the maxillary and mandibular posterior teeth. [37]
Saravanan et al., have
modified the maxillary impression technique using the mandibular edentulous
trays.
During the impression procedure, the patient is given acupressure at the
Yintang point which is located in the middle of the medial end of the eyebrow.
Initially, the gag reflex level showed at grade III (moderate) based on the
Gagging Severity Index (GSI) but after combining with acupuncture, it
facilitated a reduction of gag reflex from grade III to grade II (based on GSI)
meaning that acupuncture provides effective therapeutic effect in controlling
gag reflex and may act as an additional therapy for
achieving satisfactory during dental treatment.[32]
In another study, Murthy et al.,
gave an anesthetic block injection of the glossopharyngeal nerve in the
palatopharyngeal arch with a 2%
lignocaine solution containing 1: 200000 epinephrine. It facilitates a successful in the tooth
preparation procedure for fixed partial denture and jaw impression and gives a
comfortable feeling in dental patient.[33] Hotta, reduced the plate area of
removable denture to be smaller than usual in order to lowering the intensity
of the severe gag
reflex. The palatal area of denture is made only till the premolar area, in
order to reduce physiological contact which subsequently reduce contact between
the acrylic denture plate and the palate. He also instructed the patient to
stimulate his oral mucosa so that a gradual adaptation between denture and oral
mucosa was obtained.[34]
Singh and Gupta, create a modification of the dentures in
the form of a palateless bar supported overdenture. This modification was successfully
accepted by patients with severe gag reflex triggered while using old prostheses made of acrylic
resin.[35] Malkoc, et al., found difficulty when taking impression on his
patient, so that he gave 2.5 mg of intranasal midazolam which was applied
gradually in both nostrils. Within five minutes, the patient did not showed any
gag reflex symptom anymore, and has no side effects afterwards. The advantages
of anesthetic application through nasal is to facilitate a quick absorption and
rapid effect to the systemic circulation system.[36]
The other study,
Choudhary et al., devised an alternative technique for taking up periapical
radiographs of the maxillary and mandibular third molars. The intraoral
periapical film is placed parallel to the occlusal plane, as the same as making
an occlusal radiograph with the protruded dot side facing towards the desired
tooth.
This method resulting in good quality of radiographic image of the whole third
molar without stimulating the gag reflex which is subsequently provide
satisfactory for either dentist and patient.[37] Silva et al.,
achieved a deal with patients who are intolerant of intraoral periapical films.
He modified an extraoral radiographic techniques as an alternative approach
during root canal therapy in patients with severe gag reflex.[38] Moreover, Reshetnikov et al., reported a successful outcome in
eliminating excessive gag reflex, through performing intravenous regional
anesthesia with dexmedetomidine sedation in dental patient who exhibits
psychological factor such as anxiety and fear (grade IV, GSI).[42]
All reported cases of gag
reflexes in patients during dental treatment that have been discussed above,
mostly included in somatic gag reflexes which are in Grade I, II and III of
GSI. In cases of hypersensitive (Grade III, GSI) gag reflex can be triggered by
very strong motor response to touch stimulation, or by very high sensitivity to
sensory stimuli in trigger zone leading to the gag reflex. Somatic gag reflex
control requires management strategies that vary among dental patient. Based on
this, the anatomical principle for preventing gag reflex is required to
minimize sensory stimulus to the glossopharyngeal nerve, by designing various
modification in dental treatment.
Conclusion
Somatic gag
reflex is a gag reflex caused by a stimulus in the "trigger zone"
area, namely the posterior 1/3rd of tongue, palatine tonsils and pharynx. The
gag reflex has supplied by sensory limb from the glossopharyngeal nerve and motor limb from the vagus nerve. The management of somatic gag reflex
in dental treatment procedures varies from one another. In the top
of that, the dentist need to minimize the sensory stimulus carried by the
glossopharyngeal nerve.
 |
| Figure 1. Gag reflex pathway |
Table 1. Gagging Severity Index (GSI)[30]
|
Grade
I |
Normal Gagging
Reflex
which occurs very occasionally,
and are under the patient's control |
|
Grade
II |
Mild Gagging Reflex which
occurs occasionally, and still can be controlled again by the patient, may
require assistance and vigilance dentists and dental nurses |
|
Grade
III |
Moderate Gagging Reflex which occurs routinely and
consistently, especially if physical touch is applied to the high-risk
trigger area. It is difficult for patients to control it without stopping
dental treatment procedures. |
|
Grade
IV |
Severe Gagging Reflex which occurs with all types of dental treatment procedures including
regular visual inspection, dental treatment procedures is not possible without special care to
control the problem of gagging. |
|
Grade
V |
Very Severe Gagging Reflex which occurs easily even without any physical
intervention, dental treatment procedures is not possible without special care to
control the problem of gagging. |
