Modified Mylohyoid Nerve Anesthesia/Block With 4% Articaine and Dexamethasone Versus Halstead’s IANB With 2% Lidocaine in Mandibular Molar Surgery: A Comparative Analysis of Efficacy and Safety Outcomes

Introduction

Achieving profound anesthesia and effective pain control is essential for successful mandibular molar surgery. The most commonly used technique for anesthetizing the inferior alveolar nerve is the direct mandibular anesthesia according to Halstead (DMAH) [1,2]. This technique involves advancing the needle through the pterygomandibular space toward the medial surface of the mandibular ramus, where the anesthetic solution is deposited to block the inferior alveolar nerve. During withdrawal of the needle, the lingual nerve can also be anesthetized [3].

Despite its widespread use, the success rate of the conventional inferior alveolar nerve block (IANB) is not always predictable. One important reason for failure is accessory innervation of the mandibular teeth, particularly through the mylohyoid nerve. Anatomical studies have shown that the mylohyoid nerve can provide sensory innervation to mandibular teeth through small foramina on the lingual surface of the mandible, which can result in incomplete pulpal anesthesia when conventional IANB is used [4,5]. This anatomical variation has led to the exploration of alternative or supplementary anesthetic techniques targeting the mylohyoid nerve.

The mylohyoid nerve typically branches from the inferior alveolar nerve just before it enters the mandibular foramen and courses along the mylohyoid groove toward the mylohyoid and anterior digastric muscles [6–9]. Although traditionally considered a motor nerve, several studies have demonstrated that it can also provide sensory innervation to mandibular teeth, including the first molar and, in some cases, premolars, canines, and incisors [9,10]. This accessory sensory supply can contribute to the failure of conventional IANB in certain patients.

Local anesthetic selection can also influence the success of mandibular anesthesia. Lidocaine 2% with epinephrine (1: 100 000) is widely regarded as the gold standard due to its reliability and moderate duration of action in soft tissues, typically lasting approximately 190 min [11]. Articaine hydrochloride, an amide-type anesthetic with an additional ester group and a thiophene ring, demonstrates greater lipid solubility compared with other local anesthetics, allowing improved diffusion through nerve membranes and surrounding tissues, including bone [12–17].

Adjunctive agents can further enhance anesthetic efficacy. Dexamethasone, a potent long-acting corticosteroid, has been shown to prolong the duration and improve the quality of peripheral nerve blocks when used in combination with local anesthetics in both general and oral surgical procedures [18–20].

Previous studies evaluating mylohyoid nerve anesthesia (MNA) have reported variable success rates. Limited pulpal anesthesia was observed in 21% of patients when 1.8 mL of 3% prilocaine with felypressin was administered [21]. Similarly, Clark et al [4] reported anesthetic success rates of only 7% for the first molar and 17% for the second molar using 1.8 mL of 2% lidocaine. However, other studies have demonstrated improved outcomes when modified mylohyoid anesthesia (MMA) was used as a primary technique, achieving painless bone drilling during posterior mandibular implant placement in 54.2% of patients [22,23]. More recent evidence suggests that MMA can provide anesthetic success comparable to the conventional Halstead IANB technique [9].

Based on these findings and the results of our pilot study indicating comparable effectiveness between MMA and the conventional Halstead technique [17], the present study aimed to evaluate and compare anesthetic efficacy during mandibular dentoalveolar surgery using modified mylohyoid anesthesia with 4% articaine and epinephrine, with or without dexamethasone, versus the conventional Halstead inferior alveolar nerve block with 2% lidocaine and epinephrine. The null hypothesis was that MMA would not provide anesthetic efficacy comparable to that achieved with the Halstead technique using the selected anesthetic solutions.

Material and Methods

SELECTION OF PATIENTS:

This prospective randomized clinical study included patients scheduled for mandibular dentoalveolar surgery under local anesthesia. Participants were recruited from among patients treated on an outpatient basis and were classified according to the American Society of Anesthesiologists (ASA) physical status classification system as ASA 0 or ASA I [24]. All participants were adults of both sexes who required mandibular anesthesia for surgical treatment of mandibular molars.

The exclusion criteria were: allergies to any of the drugs or materials used in this study, acute infections around the mandibular molars, contraindicated cardiovascular, hematological, and endocrine diseases, uncontrolled hypertension, pregnancy, uncontrolled kidney diseases, osteoporosis, psychiatric disorders, blood clotting disorders, cataracts, or patients using long-term non-steroidal anti-inflammatory drugs, as well as uncooperative patients.

ASSESSMENT OF STUDY GROUPS AND RANDOMIZATION:

Researchers’ computer-generated random number lists (www.randomizer.org) were used for the random pattern success evaluation of the investigated anesthetic variables, with a permuted block stratified randomization protocol for randomizing the consenting study participants at a 1: 1 ratio, and with a provided random number of study group and anesthesia techniques, in the same manner as successfully used in previous clinical studies [15]. The studied local anesthetic solutions were prepared by nursing staff who were not familiar with this study. Under this protocol, all the included staff in this investigation was not informed of the group assignments. Before the beginning of all the procedures, the patients were instructed on how to answer and complete the research forms.

THE TECHNIQUES OF ANESTHESIA ADMINISTRATION WITH SELECTED ANESTHETICS:

The volume of local anesthetics in this study was uniform at 4 mL for all participants. All the subjects received the same amount of the tested local anesthetic solutions for the techniques determined in the study. Three equal groups of 20 patients were formed for this research. Aseptic protocols were employed for manipulation with syringes, needles, and anesthetic solutions for all the tested drugs and anesthesia techniques. We used 5-mL syringes (Nipro syringe, Shanghai International Holding Corp. GmbH, Eifestrasse 80, 20537, Hamburg, Germany) and 21G×1½′, 0.8×40 mm needles were used for administration of local anesthesia.

In Group 1, 3.5 mL of 4% articaine with 1: 100 000 adrenaline (Artinibsa, 40 mg/ml +0.01mg/ml adrenaline, Inibsa Dental S.L.U., 08185 Lliçà de Vall, Barcelona, Spain) was aspirated into a 5- mL syringe, and directly with an added 0.5 mL/4 mg of dexamethasone, which yielded a 4-mL local anesthetic solution for patient administration by means of modified mylohyoid nerve/block anesthesia [21].

In Group 2, 3.5 mL of 4% articaine with 1: 100 000 adrenaline (Artinibsa, 40 mg/ml +0.01mg/ml adrenaline, Inibsa Dental S.L.U., 08185 Lliçà de Vall, Barcelona, Spain) was aspirated into a 3.5-mL syringe, with the addition of 0.5 mL sterile water, which yielded a 4-mL local anesthetic solution for patient administration by means of modified mylohyoid nerve/block anesthesia.

In Group 3, 4 mL of anesthetic solution was formed from 3.5 mL 2% lidocaine with 1: 100 000 epinephrine, mixed with 0.5 mL of sterile water for injection, for anesthesia administration to the patients with a direct inferior alveolar nerve block according to Halstead [1,2].

MODIFIED MYLOHYOID NERVE ANESTHESIA/BLOCK TECHNIQUE (MMA) WITH 4% ARTICAINE WITH 1: 100 000 ADRENALINE AND 0.5 ML/4 MG DEXAMETHASONE (GROUP 1):

Patients were seated in an operating chair in the supine, slightly back and lower position, with the mouth open. The doctor was located at the right side of the patient. The intervening doctor was positioned close to the patient in order to perform the inspection of the oral cavity, particularly the inner side and retromolar part of the mandible, sublingual groove, and the position of the attachment of the sublingual mucosa on the mandible. The first step is the adjustment of the needle for easier puncture of the lingual mucosa; the doctor first performed a bend of the needle at an angle of ~107° about 20 to 25 mm from the tip of the needle and with a rubber stopper located 15 mm from the needle’s tip, determining the depth of the needle puncture [4]. A syringe barrel with this type of needle is preferably placed parallel to the occlusal surfaces of the teeth and over the frontal teeth. Thereafter, the back part of the tongue was moved to the opposite side with a dental mirror or lingual retractor, with prior instructions to the patient to move the tongue towards the teeth on the opposite side of the mandible in relation to the side where anesthesia is performed.

According to the original technique of the mylohyoid anesthesia [18], the tip of the needle reaches beneath the mylohyoid muscle in the sublingual region behind the distal root of the first molar. When administering MMA with/without dexamethason [4], the needle tip is directed lingually and anterior to the mandibular foramen, down to the mylohyoid groove, at the distance of ~15 to 25 mm from the surface of the mucosa, for the deposition of anesthetics. The index finger palpates the beginning of the medial crus of the trigonum of the retromolar area of the mandible (the retromolar fossa) behind the third molar (Figures 1–3).

Subsequently, medial displacement of the needle is performed, an imaginary vertical line is drawn downwards, and the syringe barrel (5-mL syringes – Nipro syringe, Shanghai International Holding Corp. GmbH, Eifestrasse 80, 20537 Hamburg, Germany), with a ~107° pre-bent needle tip (21 G×1½ 0.8×40 mm Nipro needle, Nipro Europe N.V., Weihoek 3H, B-1930 Zaventem, Belgium) is inserted sublingually, oriented in the area behind the retromolar fossa, vertically down approximately 15 to 25 mm, attempting to reach the lingual mandibular cortex between the linea obliqua interna, with the mylohyoid line above the border (mylohyoid muscle attachment) (Figure 3), and the sulcus mylohyoideus (ledge for the mylohyoid nerve) as the lower border, depending on the patient’s sex, body weight, and the anthropometric and anatomical characteristics of the oromandibular tissue.

By puncturing the mucosa towards the inner side of the mandible, the anesthesia maneuver continues until contact is made between the lingual side of the mandible and the tip of the needle, targeting an imaginary point beneath the internal oblique line and above the mylohyoid groove, and depositing 3.5 mL of the anesthetic solution (3.5 mL of 4% articaine with 1: 100 000 adrenaline and 0.5 mL/4 mg dexamethasone), sublingually and supraperiosteally (Figure 3).

The remaining 0.5 mL is used for the buccal infiltration in the innervation zone of the buccal nerve. Allowing, through the mandibular lingual cortex, direct anesthetic infiltration of the molar teeth of the mandible with subsequent anesthetic infiltration of the inferior alveolar nerve, mylohyoid nerve, and lingual nerve, lower portion of the mandibular ramus, anterior 2/3 of the tongue, posterior oral floor, and the lingual soft tissue, while the anesthetic deposition is performed for the buccal mucoperiosteal tissue.

MODIFIED MYLOHYOID NERVE ANESTHESIA/BLOCK TECHNIQUE (MMA) WITH 4% ARTICAINE WITH 1: 100 000 EPINEPHRINE (GROUP 2):

The patient is positioned fully reclined in the dental chair with the oral cavity maintained open. The operator stands on the patient’s right side and remains close to ensure clear access to the lingual mandibular region. Examination focuses on the retromolar area, sublingual sulcus, and the mandibular attachment of the sublingual mucosa. To facilitate controlled penetration, the injection needle is pre-angulated to approximately 107° at a point 20 to 25 mm from the tip, and a rubber stopper is placed 15 mm from the tip to limit penetration depth. The syringe is oriented parallel to the occlusal plane and positioned over the anterior teeth. The posterior tongue is displaced contralaterally using a mirror or lingual retractor after instructing the patient to actively move the tongue away from the injection side. Following the principles of mylohyoid anesthesia, the needle is advanced into the sublingual space beneath the mylohyoid muscle, posterior to the distal root of the first mandibular molar. In the modified technique, without dexamethasone, the needle is directed anteriorly and lingually relative to the mandibular foramen and advanced along the mylohyoid groove to a depth of approximately 15 to 25 mm. The retromolar fossa, located posterior to the third molar, is identified by palpation as the primary landmark. From this reference point, the needle is guided medially along an imaginary vertical trajectory. A 5-mL syringe with a pre-bent needle is inserted sublingually behind the retromolar fossa and advanced downward until the lingual cortical plate is contacted. The intended deposition site lies between the internal oblique ridge superiorly and the mylohyoid sulcus inferiorly. Final needle depth is adjusted according to patient-specific anatomical characteristics. Upon contact with the lingual mandibular cortex, 3.5 mL of anesthetic solution (4% articaine with 1: 100 000 epinephrine combined with 0.5 mL saline water) is delivered supraperiosteally into the sublingual space. The rest of 0.5 mL should be administered as a buccal infiltration within the buccal nerve distribution.

DIRECT ALVEOLAR INFERIOR NERVE BLOCK, ACCORDING TO HALSTEAD (GROUP 3):

Halstead’s direct inferior alveolar block anesthesia is performed according to a similar procedure described in the English literature [3]. The formed anesthetic 4-mL solution consisted of 3.5 mL of 2% lidocaine with 1: 100 000 epinephrine (Lidocaine 2% – adrenaline 40 mg/2 mL +0.025 mg/2 mL Galenika a.d., Belgrade) and 0.5 mL of sterile water for injection, which is used for the anesthesia of the inferior alveolar nerve (3 mL), the lingual nerve (0.5 mL), and the buccal nerve (0.5 mL) block.

With these techniques of anesthesia, the following should be anesthetized: the inferior alveolar nerve, lingual nerve, incisor and mental nerves, mandibular teeth to the midline, body of the mandible, lower mandibular ramus, anterior 2/3 of the tongue, oral floor, and the lingual soft tissue; additional anesthetic infiltration is performed for the buccal periosteum, as well as the mucosa up to the premolars [3].

PRIMARY OUTCOME:

The primary outcome was pain reduction achieved by the tested anesthesia techniques with the anesthetic solutions used for mandibular molar surgery.

Pain is measured perioperatively using visual analog scale (VAS) scoring [25], which represents the patient’s (respondent’s) pain experience during dentoalveolar surgery. The VAS represents the patient’s self-assessment of the pain level, with a handwritten vertical line mark at one point (distance) on a 100 mm (10 cm) straight line, which forms a connection between the 2 ends of the scale’s line, where “no pain” is on the left side of the line (0 mm), and the “worst pain” is on the right side of the line (100 mm). It is considered that successful anesthesia for performed dentoalveolar surgery has been achieved when the planned surgery is undergone with the pain rating of “no pain” (up to 4 mm), or “mild pain” (up to 44 mm) [26–29].

The effectiveness of local anesthesia techniques is also measured as the overall success rate of the achieved anesthesia measured in percentages (% of anesthesia effectiveness, calculated as the number of administered anesthetics/number of injections for successful anesthesia for the patient’s painlessness surgery). If there was insufficient anesthesia, and profound pain occurred during surgery, an additional injection of the tested anesthetics in the amount of 1 carpule was additionally administered and recorded.

The objective measurement of the quality of the achieved local anesthesia is measured through the quality of anesthesia score (QAS) according to Senes et al [29], and Sisk [30], in the following manner:

SECONDARY OUTCOMES: The secondary outcomes included anesthetic variables: onset time, duration of local anesthesia (DLA), and duration of the surgery (DOS). The onset time represents the minute-by-minute measured time, which begins from the moment after the anesthetic deposition of the local anesthetics with the selected technique, up to the beginning of the anesthetic action, evidenced by the numbness of the sublingual region and the lip on the anesthetic side, with a negative reaction from the patient to testing with a pincette stub in the anesthetized region. Buccal infiltration is performed with 0.5 mL of the anesthetic solution in the innervation zone of the buccal nerve. The duration of the local anesthesia (DLA) with the tested local anesthesia techniques was defined as the minute-by-minute measured time from the beginning of the onset time up to the time point when the previous numbness of the tissue ceased. The duration of the surgery (DOS) represents the time (min) from the first incision to the last needed suture [31]. The total success rate of pain intensity suppression using local anesthesia is presented in percentages obtained when the number of successfully administered anesthetics for the patient’s surgery is divided by the number of patients. This calculation was utilized in prior studies [31,32].

Additional secondary parameters monitored both the local and systemic adverse effects associated with the local anesthetics administered and the medications used. Adverse effects and reactions were carefully monitored, including blood syringe aspiration, syncope, hematoma, nausea, tinnitus, heart palpitations, dizziness, and drowsiness, which were all separately recorded if they occurred.

SAMPLE SIZE:

The sample size was calculated based on the expected difference in VAS pain scores between groups. Assuming a significance level of 0.05 and statistical power of 80%, a minimum of 18 participants per group was required. To compensate for potential dropouts, 20 participants were included in each group. Despite pilot data indicating a strong effect (Cohen’s f ≈0.90), a more cautious effect level (f=0.40–0.50) was chosen for this study to avoid overestimation. A total sample size of 60 participants, with 20 in each group, ensures a statistical power of approximately 0.80 to detect moderate to large between–group differences. Smaller effects cannot be reliably detected with this sample size, and this limitation has been acknowledged.

STATISTICAL SATA PROCESSING:

Data are presented as descriptive statistics (mean or median, accompanied by standard deviation or interquartile range [IQR]). The median value and IQR were reported for non-normally distributed data or when this measure provided more intuitive interpretation. The comparison of numerical values was performed using the Kruskal-Wallis test due to non-normally distributed data. Since the Kruskal-Wallis test result did not reach statistical significance, no post hoc pairwise analyses were performed, in accordance with standard procedures.

A comparison of categorical characteristics was performed using the chi-square test or Fisher’s test. The null hypothesis was tested at the P<0.05 significance level. The post hoc power of this study was 0.80 or higher, suggesting that this sample size was sufficient to detect the observed effect with reasonable certainty. With a value of 0.80, the study’s post hoc power analysis indicated that the sample size was sufficient to consistently detect the observed effect with a high degree of confidence. Statistical data processing was performed using the R software package version 4.5.1 (R-devel) [33].

Results

PARTICIPANTS:

A group of 69 patients was recruited for this study and 9 patients were excluded.

The included 60 patients (32 men, 28 women), were of an average age of 30.8±13.1 years (Min 18, Max 77 years). The groups were uniform according to age and sex (P=0.958 and P=0.625, respectively). Patients did not differ in the examined clinical characteristics (Table 1). There were no local or systemic adverse effects, and no significant differences were found among the tested groups concerning sex, age, and the duration of the local anesthesia in any group. It was found that the patients did not differ in terms of the demographic and examined clinical characteristics.

TYPES OF SURGICAL PROCEDURES:

The surgical procedures performed included dentoalveolar surgeries in the posterior mandible: surgical extraction of impacted third molars, enucleation of residual cysts in the posterior mandible, extraction of residual mandibular molar roots, removal of an impacted second premolar, and tumor extirpation.

The non-standard surgeries were performed were the following: in Group 1, there were 2 patients with 2 pathologies requiring surgery (simultaneous extraction of a wisdom tooth with residual roots of the second molar, and the extraction of the wisdom tooth and bone biopsy); Group 2 had a cystic lesion; in Group 3, a wisdom tooth with 5 roots was extracted. The type of surgical intervention was consistent and very similar across all groups.

ANESTHESIA PARAMETERS:

Anesthesia parameters did not significantly differ between the groups (Table 2). Nearly identical volumes of the tested anesthetic solutions were deposited in both local anesthetic techniques (4 mL). The median onset time was 2.0 min with an interquartile range of 2.0 to 3.0 min in Group 1; 2.5 min with an interquartile range of 2.0 to 3.8 min in Group 2; and 2.5 min with an interquartile range of 2.0 to 3.0 min in Group 3. The anesthetic variables VAS, QAS, and DOS did not significantly differ between the groups (Table 2, Figure 4). DOS was not significantly different between the groups (P=0.398). The number of primary injections was the same across all groups. The highest success was achieved in Group 1, followed by Group 2, and Group 3 (95.20%, 86.90%, and 83.30%, respectively) which is clinically relevant. The average anesthesia quality score did not significantly differ between the examined groups (Group 1: 1.86±0.57 vs Group 2: 1.96±0.77, and Group 3: 2.25±0.79, P =0.160) (Figure 5).

The duration of anesthesia (DOA), quality of anesthesia, and VAS scores distributed by group (Figure 4).

Local and systemic adverse effects and reactions – including blood syringe aspiration, syncope, hematoma, nausea, tinnitus, heart palpitations, dizziness, and drowsiness – were not documented.

Discussion

LIMITATIONS OF THE STUDY:

The present study has several limitations. First, only healthy participants were included (ASA 0–1), which may limit the generalizability of the findings to patients with systemic diseases who also require mandibular surgery. Second, the relatively small sample size (20 patients per group) may have limited the statistical power of the study and may have prevented potentially meaningful differences between groups from reaching statistical significance. Third, the study was blinded as much as possible, but was not fully blinded. Finally, all surgical procedures were performed by the same operator (K.B.), which may introduce operator-related bias. Larger studies involving more diverse patient populations will be necessary to further evaluate the clinical role of the MMA technique in mandibular surgery.

Conclusions

MMA using 4% articaine with epinephrine and an admixture of dexamethasone was shown to be safe and adequate for achieving pain control during mandibular dentoalveolar surgery, demonstrating clinical performance comparable to the conventional Halstead technique using 2% lidocaine with epinephrine. No statistically significant differences were observed among the groups with regard to onset time, intraoperative pain, or the quality of anesthesia score. Although a numerically higher success rate was observed with 4% articaine with epinephrine and dexamethasone (95.20%) compared with 2% lidocaine with epinephrine (83.60%), this difference was not statistically significant and should therefore be interpreted cautiously. These findings suggest that the MMA technique with dexamethasone provides anesthetic effectiveness for mandibular molar surgery comparable to that achieved with the Halstead technique. The needle path used in the MMA technique, which passes through the sublingual soft tissue, was also evaluated in terms of safety. No injuries, local complications, or systemic adverse effects were observed in any of the study groups. Based on the present findings, MMA using 4% articaine with epinephrine and dexamethasone appears to be a feasible alternative approach for mandibular dentoalveolar surgery, either as a primary anesthetic technique or as a supplementary technique when necessary. However, since no statistically significant differences were detected among the groups and considering the relatively small sample size and methodological limitations of this study, definitive clinical recommendations cannot be made. Further studies with larger sample sizes are required to provide a more comprehensive statistical evaluation of this technique.