Mouth gags have been in use since 1220 as a solution to the cumbersome limitations encountered when visibility and access to the oral cavity, pharynx, and larynx are needed. The instruments being used today range from the simple but effective design of the bite block to the sophisticated and intricate design of the Feyh-Kastenbauer. This article highlights the most frequently used well-designed mouth gags and the applications for which they provide the most benefit. Disadvantages and risks of their use are explored, especially those that clinicians should be aware of for patient and operator safety.
Key points
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This article serves as a review of the history and motivation behind invention of mouth gags.
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This review should enable readers to gain an appreciation for the various types of mouth gags available for simple and complex surgical procedures.
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This article should help the reader to select the appropriate mouth gag based on the setting, surgical procedure and needs of the operator.
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The reader should be able to understand the benefits and limitations of the popular mouth gags in use today.
Introduction
With maximum opening of the oral cavity limited to 40 to 50 mm, access and visibility for manipulation of intraoral and pharyngeal structures tends to be insufficient. Compounded with behavioral challenges, such as those encountered in the pediatric or developmentally delayed population, and physiologic or structural limitations such as tetanus or temporomandibular joint (TMJ) disorders, access can be quite frustrating. Mouth gags are fundamental in a provider’s armamentarium as a solution to this spatial dilemma. In use since 1220 AD, mouth gags can be defined as instruments with levers that are used to separate the maxillary and mandibular arch and maintain the mouth in an open position. To date, there are more than 36 subtypes of mouth gags ( Table 1 ) that provide a wide variation in design and modification of function for providing transoral access for examination, surgical intervention, and general dental care.
| Crowe- Davis | Lane |
| McIvor | Rose |
| Schmid | Roser-König |
| Dingman | French |
| Feyh-Kastenbaeur | Mahu |
| Laryngeal Advanced Retractor System | Buxton |
| Molt Side-Action | Buxton–Ackland |
| Molt-Doyen | Collin |
| Bite Block | Davis |
| Dott | Colt |
| Kilner | Doyen |
| Kilner-Doughty | Doyen-Jensen |
| Thomas Smith | Doyen-Collin |
| Mouth gag with ratchet and pinion adjustment and ebony handle | Sklar-Doyen-Jansen (Sklar molt) |
| Sluder-Jansen | Feathersone |
| Whitehead’s gag | Geffer |
| Black’s gag with sheet spring and a ring type retention system | Heister |
| Fergusson | Mason |
| Fergusson-Ackland | Mason-Ackland |
| Coleman | Mickesson |
| Hewitt’s | Boyle-Davis |
Mouth gags have the added benefit of decreasing the incidence of perioperative and postoperative TMJ pain, dysfunction, and muscle stiffness during lengthy procedures. From the operator’s perspective, the mouth gag enables efficient completion of time and technique-sensitive procedures that rely on patients keeping their mouth open consistently. Furthermore, mouth gags are safe and protective for the patient and operator while having the desired maximal incisal opening that allows for better exposure and visualization of the operative field for the procedure. This article highlights the most frequently used well-designed mouth gags and the applications for which they provide the most benefit. We also explore the disadvantages and risks of their use, especially those that clinicians should be aware of for patient and operator safety.
Content
Mouth opening is facilitated by the muscles of mastication and the TMJ. The TMJ is a compound, diarthrodial joint that is divided into a superior and inferior compartment by the articular disk. The inferior compartment permits a ginglymus (hinging) motion that results in mouth opening up to 20 mm. After this point, further opening must occur via an arthrodial (sliding) mechanism within the superior compartment, usually up to 40 to 50 mm. Dislocation or derangement of the articular disk and mandible is prevented by the functional ligaments surrounding the joint: the collateral (discal), capsular and temporomandibular ligament. Dislocation of the mandible with maximal opening is prevented by the temporomandibular ligament while anterior dislodgement of the articular disk is prevented by the superior retrodiscal lamina. The superior retrodiscal lamina consists of elastic fibers that attach to the tympanic plate and function as a restraint to disk movement in extreme translatory movements. In addition, there are also the sphenomandibular and stylomandibular accessory ligaments that serve, to some degree, as passive restraints on mandibular motion.
Prolonged near maximal mouth opening has been shown to result in TMJ arthralgia, open lock jaw, trismus, and/or myalgia of the masseter for up to 14 days due to activation and prolonged sensitization of nociceptive neurons in the trigeminal ganglion and nucleus. Activation of the neurons in the trigeminal ganglion is initiated by nociceptive input from the efferent limb of somatic axons that provide sensory innervation of the TMJ, muscles, ligaments, and tendons associated with mastication. , If the muscles, ligaments, or tendons are stretched for long periods of time, or if excessive force is applied with opening, the muscles will fatigue and there is a release of inflammatory agents at the peripheral terminals of the axons. This results in peripheral sensitization and a lower threshold for the primary nociceptor. This concern can be mitigated with the use of mouth gags, because they provide support to the TMJ and muscles of mastication as patients have less activation of the muscles and stress on the joint while biting on a mouth gag. The mouth is kept open in a less than maximal opening position. The caveat is that mouth gags can cause dislocation of the TMJ if not used appropriately or if the mouth is kept open for too long, albeit the level of discomfort is less. Mouth gags with the most utility today are the bite block, Molt Side-Action, Isodry System and its variations, Mr. Thirsty, DryShield, Crowe-Davis (CD), Feyh-Kastenbauer (FH), McIvor, Dingman-Grabb (DG), the Denhardt and most recently, the Laryngeal Advanced Retractor System (LARS).
The bite block is arguably one of the most ubiquitous instruments in use by providers who seek access to the oral cavity. The bite block assumes a trapezoid shape, is typically made of silicone and is re-useable by sterilization ( Fig. 1 ). The trapezoid shape mimics the alignment of the maxillary and mandibular arch with the shorter base inserted posteriorly and the widest base facing anteriorly. Bite blocks feature multiple sizes: pediatric, medium, and large for edentulous ridges. Bite blocks are relatively atraumatic, as they have no sharp edges, are made of soft but resilient material, and if the appropriate size is used based on a patient’s opening ability, are safe and protective to the TMJ and muscles of mastication. Bite blocks are simple to use. The awake patient is asked to open their mouth and the prop is inserted into the nonoperative side of the jaws and then the patient is asked to bite down on the block for comfort and retention. In the sedated or intubated patient, the mouth is opened judiciously by the operator using their thumb and index finger and the bite block is placed. The utility of the bite block diminishes in cases in which patients have trismus, as the provider would find it almost impossible to open the mouth wide enough for insertion. Another disadvantage lies in the ease of dislodging the bite block from the patient’s mouth by movements of the tongue or jaw, which can be harmful to the patient or operator.
The molt side-action mouth prop ( Fig. 2 ) is classically and most commonly used when patients are unable to cooperate, whether in pediatric or intellectually delayed patients, in patients who are deeply sedated, or in cases of mild trismus. The levers of the mouth prop can be used to open the mouth wider due to a ratchet-type action as the handle is closed. The disadvantage of the molt lies within the potential damage that may be imparted on the teeth and TMJ if inappropriate pressure is applied to open the mouth. Opening the mouth too wide can result in a stretch injury to the joint that may, in some cases, necessitate treatment and leave the patient with discomfort and potentially trismus for up to 2 or more weeks.
