Ultra-low-frequency Transcutaneous Electric Nerve Stimulation for Recording Functional Impression and Neuromuscular-oriented Centric Relation in a Completely Edentulous Patient: A Case Report

BACKGROUND

A successful complete denture must satisfy the requirements of retention, stability, support, esthetics, phonetics, and comfort. Stability is governed by the relationship of denture base to underlying tissue, external surface, and borders to surrounding musculature and occlusal relationship.^1,2 This depends on the neuromuscular control coordinated by various feedback mechanisms. Centric relation is a learnable, repeatable, and reproducible dynamic maxillomandibular relation at which initiation and termination of the various border and intraborder movements occur.

Various methods have been recommended for recording the optimal extension of borders in harmony with orofacial muscular attachments and centric relation records.^3,4 Transcutaneous electric nerve stimulation (TENS) has been used as a noninvasive procedure for orofacial pain management. The term ultra-low frequency (ULF) is attributed to TENS frequency modulated below frequency of 4 Hz. Cooper and Kleinberg concluded that ULF-TENS applied for 60 minutes allow relaxation of masticatory musculature to facilitate physiologic rest position of jaw.⁵ Ultra-low-frequency TENS can also be used to produce controlled jaw movement, thus giving accurate position of centric relation for successful rehabilitation of completely edentulous patient.

This case report highlights the use of ULF-TENS for border molding and guiding and verification of physiological centric relation in a completely edentulous patient.

CASE DESCRIPTION

A 64-year-old woman reported to the Division of Prosthodontics, Department of Dental Surgery, Armed Forces Medical College, Pune with a chief complaint of difficulty in eating due to complete loss of teeth over 4 years. The patient had not used any prosthesis in the past and desired replacement of missing teeth. Medical history revealed that she was diagnosed with arthritis and was undergoing treatment for the last 06 months. The extraoral examination also revealed that the patient had fair neuromuscular control (House’s class II) (Fig. 1A).⁶ Intraoral examination revealed high frenal attachments in maxillary labial and buccal freni with insufficient vestibular depth. Patient was diagnosed as PDI class III completely edentulous maxillary and mandibular arch (Fig. 1B).⁷ Patient was scheduled for prosthetically guided vestibular deepening (Figs 1C and D). After adequate healing, a conventional complete denture prosthesis using Boucher’s protocol was planned.⁸ Ultra-low frequency-TENS was used for recording of peripheral extensions by fabrication of a custom tray using autopolymerizing resin (DPI, India) with a spacer of 1.3 mm. The extent of the tray was checked for sufficient space of 2–3 mm. A US-FDA approved portable electromyography pain relieving device (BLD T250 Stimulator; Johari Digital Healthcare Ltd.) was used for TENS in which electrodes were attached in posterior triangle region and other in preauricular region, in presence of a trained physiotherapist. The unit was operated at continuous mode with current gradually increased from 0 to 20 mA. Thirty minutes of continuous ULF-TENS therapy were provided to allow physiological contraction of muscle till muscle twitching was achieved. The tray was loaded with putty consistency of polyvinyl siloxane impression material (Zehrmark, Italy) at the border area (Figs 2A and B). It was held in position to record functional trimmed peripheral borders caused due to rhythmic contraction induced by application of ULF-TENS (Figs 2C and D). Functional manipulation was done for recording alveololingual sulcus and posterior palatal seal area. When the material was set, the tray was retrieved and escape holes were made using a round bur of 1.8 mm diameter for final impression using light body consistency of PVS impression material (Zehrmark, Italy) (Figs 2E and F). Casts were fabricated, occlusal rims made, and orientation relation was recorded. It was observed that patient was unable to guide mandible to a repeatable centric reaction position despite regular training. Mandible was manipulated into centric relation and tentative midline was marked based on facial landmarks. To relax the muscles associated with TMJ activity, ULF-TENS of joint and buccal region was performed in a similar manner as earlier. Following this, the patient was asked to open and close the mouth with TENS apparatus set at tolerable settings (Fig. 3A). The discrepancy in centric relation which was noticed earlier was eliminated and patient was able to reproduce same centric relation repeatedly (Figs 3B and C). Teeth arrangement and try-in was carried out to provide balanced occlusion. Denture curing was done as per conventional protocol and finished prosthesis was delivered (Fig. 3D). Post-insertion instructions were given and regular follow-up was done at 01 week, 01 month, and 06 months period. Patient was comfortable and satisfied with the prosthesis.

DISCUSSION

Various methods and materials have been used to record the peripheral borders in optimal harmony with the surrounding musculature including low fusing compound, addition silicone, polyether impression material, using pre-border molded trays, and application of TENS.^9,10

Bulbule et al. demonstrated the use of putty consistency PVS for border molding and light body consistency for making a final impression using muscle twitching produced by the use of TENS.¹¹

Clinically two types of TENS include low-frequency TENS (%3C;10 Hz) and high-frequency TENS (%3E;50 Hz). Ultra-low frequency has been designated to frequency stimulation below 4 Hz. Transcutaneous electric nerve stimulation is a device that emits a small electric current to targeted body parts mainly used for pain relief. According to electromyographic studies, the application of TENS stimulates a change in the biochemical and physiological muscular conditions leading to muscle relaxation.¹² It consists of the application of electrodes on the skin overlying the sigmoid notch near the tragus and along the nuchal line near the midline of the neck just below the hairline. This allows the excitation of certain fibers of the V and VII cranial nerves resulting in guiding the mandible into a physiological rest position. Stimulation of these areas causes relaxation and twitching of orofacial musculature to produce desired effects.¹³ Didier et al. highlighted that with use of ULF-TENS deprogramming of masticatory musculature aided in identifying physiological rest position of the jaw in patients undergoing neuromuscular therapy.¹⁴ In this case report, similar deprogramming of musculature was achieved using ULF-TENS in patient who was unable to reproduce a repeatable CR position.

However, shortcomings with the use of ULF-TENS include clinical areas like alveololingual sulcus area and posterior palatal seal cannot be recorded using ULF-TENS as controlled twitching of muscles causing recording of these areas is not possible. A detailed medical history and specialist supervision are required during the procedure. It cannot be used in patients with conditions like a cardiac pacemaker, history of paralysis, and cardiac arrhythmias in the past.

Though literature reveals the use of TENS to cause deprogramming of muscles and to achieve myocentric relation, is yet to be explored in-depth to be used as an alternative therapeutic option for recording centric relation.¹⁵

CONCLUSION

Ultra-low-frequency TENS can be used as an acceptable clinical modality to obtain a satisfactory outcome in recording border molding to achieve stability in complete denture prosthesis. Its ability to cause controlled excitation of muscles can be used to record physiological extension of borders and to guide condyle to a neuromuscular-oriented centric relation.

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