Supplementary File 1.Procedures: anesthesia and electrogustometry

1. Anesthesia

a. Mandibular block nerve (MdN group)

After local anesthetic infiltration of the buccal nerve suppressing the sensitivity of the buccal gingiva, removing the sensitivity of the half-dental arch was obtained by anesthetic infiltration of the MdN at the mandibular foramen1, with a syringe and a 30-gauge needle (Soficoncept®, Septodont). The anesthetic solution was composed of 2% lidocaine and epinephrine 1/100.000 contained in 1.8 ml carpules (lignospan® 2%, Septodont). This classic and well standardized technique lead to anesthesia of the oral mucosa and all the lower teeth of the quadrant, as well as the ipsilateral half lower lip and chin and part of the somatosensory of the tongue. In order to avoid any lateralization effect, procedures were further divided in two groups: left and right side.

  1. Anesthesia of the inferior alveolar nerve (IAN group)

The anesthetic solution was directly brought through the cortical bone into the medullary bone, close to the mandibular canal containing the IAN, by means of a removable single-use device (X-Tip device, Dentsply). Selective anesthesia of the IAN quickly removes the sensitivity in non-inflammatory posterior mandibular teeth pulp.2-3 The X-tip intraosseous injection was done according to the manufacturer's instructions: After evaluating root proximity by radiography, perforation site was located in alveolar mucosa at the distal site of the first molars or at the mesial site of the second molars. A volume of 0.1 ml of 2% lidocaine with 1:100.000 epinephrine (lignospan® 2%, Septodont) was infiltrated through a 30-gauge needle at the perforation site before intraosseous injection.2 The perforator drill position was at an angle of 90° to the cortical bone, and the slow-speed handpiece was activated in a series of short bursts, using light pressure until 2-5 seconds had passed. The needle was then engaged in a pen-gripping fashion and 1.8 ml of 2% lidocaine with 1:100.000 epinephrine (lignospan® 2%,Septodont) was injected slowly during 60 seconds.Before inserting the 27-gauge ultrashort X-tip needle into the guide sleeve, the needle was bent at a 60-80° angle to allow easy insertion. The perforator was pushed through the alveolar mucosa until the X-tip faced bone.3

c.Anesthesia of the maxillary afferents (MxN group)

Anesthesia of maxillary afferents was performed according to two techniques depending on the type of teeth to be anesthetized.1

Retro-tuberosity anesthesiawhich ensures block of the posterior superior alveolar nerve was done for the treatment of one or more ipsilateral maxillary molars.The needle was inserted at the buccal side of the 2nd upper molar. The syringe as held with an 45° axis,in both anteroposterior and vertical directions, and the needle entered 15 à 20 mm deep without osseous contact after deposition of 0.2 ml in the mucosa, Avolume of 1.8 ml of anesthetic solution (2% lidocaine with 1:100.000 epinephrine (lignospan® 2%, Septodont, France) in 30-60s was injected after aspiration test to avoid intravascular injection.

Palatal anesthesiawasperformed when dental treatments on premolars were needed. The anatomical target for the deposition of the solution consists of palatine channels that allow diffusion to the upper and middle alveolarnerves which are located halfway up the alveolar wall between the two premolars. Avolume of 1.8 ml of anesthetic solution (2% lidocaine with 1:100.000 epinephrine (lignospan® 2%, Septodont, France) in 30-60s was injected at a rate of about 0.5 ml per minute.

  1. Electrogustometry

A custom-made electrogustometer delivering a constant current from 0 to 200 µA through a stainless steel ball electrode (5 mm diameter), which provided an electrode-tongue contact of approximately 40 mm² was used by a trained investigatorwho performed multiple sessions in order to limit intraindividual variations. A reference electrode was placed at the subject's wrist with KCl gel to improve electrical contact. All the patients were explained the procedure beforehand. They were told that the gustometer will not test chemical taste i.e. sweet, salt, bitter, acid or umami, but deliver a non-noxious electrical current eliciting a faint sensation comparable to that produced by the contact of the tongue with a low voltage battery.

An EGM session comprised 9 recordings. All loci were successively tested according to the following sequence: at the tip of the tongue where the density of fungiform papillae is the highest(T, Tr, Tl), at the edge of the tongue where foliate papillae are located (Er, El), at the surface of the dorsal tongue where the density of fungiform papillae is lower (Dr, Dl), and at the posterior tongue near the circumvallate papillae (Pr, Pl). For each threshold evaluation, the electrode was put on the tongue and after an adaptation period to the tactile stimulation, current was applied for about 1 second.4 The subject answered "yes" or "no", if he/she perceived any taste sensation. The subject was kept unaware whether the current was applied (blind procedure) or not and no feedback was ever given to the subject. The test included successive applications of current in a staircase procedure with increasing and decreasing 10µA steps, then 2µA steps when nearing the threshold value. Trials without current application were intermingled within the staircase procedure and subjects who answered positively to such control tests without current were discarded. The EGMt detection threshold was taken as the lowest current intensity perceived by the subject (100% detection threshold).

References

  1. Malamed SF. Handbook of Local Anesthesia. 5th ed. St. Louis, Mo: Mosby. 2004; pp: 208–209.
  2. Nusstein J, Reader A, Nist R, Beck M, Meyers WJ. 1998. Anesthetic efficacy of the supplemental intraosseous injection of 2% lidocaine with 1:100.000 epinephrine in irreversible pulpitis. J Endod.24:487–491.
  3. Razavian H, Kazemi S, Khazaei S, Jahromi MZ. 2013. X-tip intraosseous injection system as a primary anesthesia for irreversible pulpitis of posterior mandibular teeth: A randomized clinical trial. Dent Res J.10(2): 210–213.
  4. Boucher Y, Berteretche MV, Farhang F, Arvy MP, Azérad J, and Faurion A. 2006. Taste deficits related to dental deafferentation: an electrogustometric study in man. Eur J Oral Sci. 114(6):456-464.