The key to profound local anesthesia: neuroanatomy

Mylohyoid Muscle: Current Understanding for Clinical Management-Part I: Anatomy and Embryology

The mylohyoid is one of the suprahyoid muscles, along with the geniohyoid, digastric, and stylohyoid muscles. It lies between the anterior belly of the digastric muscle inferiorly and the geniohyoid superiorly. In Part I, the anatomy and embryology of the mylohyoid muscle will be reviewed in preparation for the clinical discussion in Part II.

The interaction between the nervous system and the stomatognathic system: from development to diseases

The crosstalk between the nerve and stomatognathic systems plays a more important role in organismal health than previously appreciated with the presence of emerging concept of the "brain-oral axis". A deeper understanding of the intricate interaction between the nervous system and the stomatognathic system is warranted, considering their significant developmental homology and anatomical proximity, and the more complex innervation of the jawbone compared to other skeletons. In this review, we provide an in-depth look at studies concerning neurodevelopment, craniofacial development, and congenital anomalies that occur when the two systems develop abnormally. It summarizes the cross-regulation between nerves and jawbones and the effects of various states of the jawbone on intrabony nerve distribution. Diseases closely related to both the nervous system and the stomatognathic system are divided into craniofacial diseases caused by neurological illnesses, and neurological diseases caused by an aberrant stomatognathic system. The two-way relationships between common diseases, such as periodontitis and neurodegenerative disorders, and depression and oral diseases were also discussed. This review provides valuable insights into novel strategies for neuro-skeletal tissue engineering and early prevention and treatment of orofacial and neurological diseases.

Retromolar canal infiltration as a supplement to the inferior alveolar nerve block injection: an uncontrolled clinical trial

OBJECTIVES

This study aimed to determine the success rate of retromolar canal (RMC) infiltration following the failure of inferior alveolar nerve block (IANB) injections for the anesthesia of mandibular first molars with acute irreversible pulpitis.

MATERIALS AND METHODS

An IANB injection was administered for 50 patients with acute irreversible pulpitis. Lip numbness was set as the sign of anesthesia and further evaluated and confirmed with pulp sensibility tests after 10-15 min. Access cavity preparation was commenced unless the patient felt any pain; in this case, an RMC infiltration injection was given. The success rate was determined through the patients' recording of the presence, absence, or reduction of pain severity during access cavity preparation using the Heft-Parker visual analog scale.

RESULTS

Seven patients (14%) did not experience any pain by pulp sensibility tests and during access cavity preparation after IANB injection. Twenty-five (58.1%) of the remaining 43 patients who had the RMC infiltration injection had reduced pain, and four patients (9.3%) experienced no pain after the RMC infiltration. Fourteen patients (32.5%) experienced no change in pain. Chi-squared test results revealed that the percentage of patients with reduced pain was higher than that of other patients (P < 0.001).

CONCLUSIONS

RMC infiltration, along with IANB, significantly reduced the pain felt by patients and increased the success of the anesthetic technique for root canal treatment of mandibular first molars with acute irreversible pulpitis.

CLINICAL RELEVANCE

The administration of RMC infiltration can enhance the success of the IANB technique for anesthetizing mandibular first molars exhibiting acute irreversible pulpitis.

Evaluation of different mandibular blocks for the removal of lower third molars: a meta-analysis of randomised clinical trials

OBJECTIVES

To describe the efficacy and number of side effects for the Gow-Gates mandibular block (GGMB) and Vazirani-Akinosi mandibular block (VAMB) compared to inferior alveolar nerve block (IANB) in patients requiring lower third molar (L3M) extraction.

MATERIALS AND METHODS

A systematic search was performed in three electronic databases and complemented with a manual search. The inclusion criteria were randomised clinical trials in healthy patients who underwent at least one L3M extraction. Screening and article selection were carried out by two independent reviewers. After data extraction, a meta-analysis was performed for the success rate, number of positive aspirations, and onset time outcomes.

RESULTS

Six randomised clinical trials were included out of the 367 potentially eligible papers. No significant differences were found in terms of success rate using GGMB (risk ratio [RR] 1.04; 95% confidence interval [CI] 0.92 to 1.18; P = 0.48) nor VAMB (RR 0.96; 95% CI 0.86 to 1.06; P = 0.41). The VAMB group exhibited a lower number of positive aspirations than the IANB group (RR 0.08; 95% CI 0.01 to 0.55; P = 0.01), but there was no statistically significant difference between the GGMB and IANB groups (RR 1.06; 95% CI 0.13 to 8.78; P = 0.96). The delayed onset was even longer in GGMB (mean difference [MD] 3.32 min; 95% CI 1.98 to 4.66; P < 0.001) and VAMB (MD 0.90 min; 95% CI 0.37 to 1.43; P = 0.0001) than IANB.

CONCLUSIONS

GGMB and VAMB seem to be effective and safe anaesthetic techniques for the removal of L3M, but these blocks exhibited a more delayed onset time than IANB.

CLINICAL RELEVANCE

GGMB and VAMB are safe and effective anaesthetic techniques for the removal of L3M. However, IANB can still be considered the first option since GGMB and VAMB exhibited more delayed onset times and variable buccal nerve anaesthesia.

Clinical anatomy of the nerve to the mylohyoid

The nerve to the mylohyoid (NM) originates from the mandibular division of the trigeminal nerve. The NM provides motor control to the mylohyoid and the anterior belly of the digastric. Its sensory component, as a variation of this nerve, has scantly been described in the literature. We discuss the current clinical implications of the NM based on its anatomical variations of the with the hopes of benefiting patients who are undergoing invasive maxillofacial procedures.

Is Inferior Alveolar Nerve Block Sufficient for Routine Dental Treatment in 4- to 6-year-old Children?

Introduction

Pain control is one of the most important aspects of behavior management in children. The most common way to achieve pain control is by using local anesthetics (LA). Many studies describe that the buccal nerve innervates the buccal gingiva and mucosa of the mandible for a variable extent from the vicinity of the lower third molar to the lower canine. Regarding the importance of appropriate and complete LA in child-behavior control, in this study, we examined the frequency of buccal gingiva anesthesia of primary mandibular molars and canine after inferior alveolar nerve block injection in 4- to 6-year-old children.

Study design

In this descriptive cross-sectional study, 220 4- to 6-year-old children were randomly selected and entered into the study. Inferior alveolar nerve block was injected with the same method and standards for all children, and after ensuring the success of block injection, anesthesia of buccal mucosa of primary molars and canine was examined by stick test and reaction of child using sound, eye, motor (SEM) scale. The data from the study were analyzed using descriptive statistics and statistical software Statistical Package for the Social Sciences (SPSS) version 21.

Results

The area that was the highest nonanesthetized was recorded as in the distobuccal of the second primary molars. The area of the lowest nonanesthesia was also reported in the gingiva of primary canine tooth.

Conclusion

According to this study, in 15 to 30% of cases, after inferior alveolar nerve block injection, the primary mandibular molars’ buccal mucosa is not anesthetized.

How to cite this article: Pourkazemi M, Erfanparast L, Sheykhgermchi S, Ghanizadeh M. Is Inferior Alveolar Nerve Block Sufficient for Routine Dental Treatment in 4- to 6-year-old Children? Int J Clin Pediatr Dent 2017;10(4):369-372.

Cone beam CT findings of retromolar canals: Report of cases and literature review

A retromolar canal is an anatomical variation in the mandible. As it includes the neurovascular bundle, local anesthetic insufficiency can occur, and an injury of the retromolar canal during dental surgery in the mandible may result in excessive bleeding, paresthesia, and traumatic neuroma. Using imaging analysis software, we evaluated the cone-beam computed tomography (CT) images of two Korean patients who presented with retromolar canals. Retromolar canals were detectable on the sagittal and cross-sectional images of cone-beam CT, but not on the panoramic radiographs of the patients. Therefore, the clinician should pay particular attention to the identification of retromolar canals by preoperative radiographic examination, and additional cone beam CT scanning would be recommended.

Number of accessory or nutrient canals in the human mandible

OBJECTIVES

The aim of the study was to assess the presence, location and the number of accessory or nutrient canals in the body of the mandible by means of cone beam CT images, obtained with the Planmeca ProMax® 3D Max device.

MATERIAL AND METHODS

Seventy-four cone beam images of the mandible from adult patients (37 males and 37 females) who were imaged for dental implantology planning or third molar extraction were used to assess the number and location of accessory or nutrient canals. All images were taken with the same machine (Planmeca® ProMax 3D Max) at 200-, 400- or 600-μm resolution. Distinction was made between canals entering or exiting the mandible superior or inferior of the inferior alveolar canal and between similar canals superior or inferior of the genial tubercula.

RESULTS

The number of accessory canals varied between nil to 11. No statistical significant difference between males and females was found with regard to the number or location of accessory canals in the mandible. Only 5.4% of patients had no accessory canals. One to five accessory canals were found in 71.6%, and 23% of patients had more than five accessory canals. The majority (81%) of patients had between two and six accessory canals.

CONCLUSION

It seems that subjects showing no accessory canals whatsoever should be considered exceptional as more subjects with than without accessory canals in the body of the mandible were found.

CLINICAL RELEVANCE

These results are clinically relevant for mandibular surgery and mandibular local anaesthesia.

Pharmacology of local anesthetics used in oral surgery

This article provides a comprehensive review of the pharmacology of local anesthetics as a class, and provides details of the individual drugs available in dental cartridges. Maximum recommended doses of local anesthetics and vasoconstrictors are presented for healthy adult and pediatric patients, and for patients with cardiovascular system impairments. Various complications and reasons for failure of local anesthesia effectiveness are discussed, and current and future trends in local anesthesia are presented to provide an overview of current research in local anesthesia.

A recurrent variant branch of the inferior alveolar nerve: is it unique?

The only named branch of the inferior alveolar nerve (IAN) before it enters the mandibular foramen is the mylohyoid nerve. However, several variations have been reported in the literature. In this study, a recurrent variant branch of the IAN arising just below the origin of the mylohyoid nerve was investigated in adult Indian cadavers allotted for dissection to the first year dental students of Government Dental College, Ahmedabad (India). The dissection was performed by the lateral approach to the infratemporal fossa. The nerve was found in 12 of 35 sides (34.3%) and 8 of 18 cadavers (44.4%). Thus, in our study it was not a rare variation of the IAN, where in most cases it innervated the lateral pterygoid muscle. In some cases, it terminated in the lateral pterygoid muscle. In others, it penetrated the muscle to join the anterior or posterior division of the mandibular nerve or its branches; thus, the variant nerve in such cases might be regarded as an additional root of the IAN. Because the concerned primordia of the nerves and muscles migrate extensively during development and growth, alternative routes of migration may bring about variants like the one under study. The variant appeared to be unique in some of its features. It may be a source of neuropathic and referred pain. Failure of the conventional inferior alveolar nerve block anesthesia and the peripheral neurectomy used for the treatment of trigeminal neuralgia may be partly due to the presence of this variation.

Radiographic study of the mandibular retromolar canal: an anatomic structure with clinical importance

INTRODUCTION

The retromolar canal is an anatomic structure of the mandible with clinical importance. This canal branches off from the mandibular canal behind the third molar and travels to the retromolar foramen in the retromolar fossa. The retromolar canal might conduct accessory innervation to the mandibular molars or contain an aberrant buccal nerve.

METHODS

Patients referred for panoramic radiography were consecutively enrolled, provided a limited cone-beam computed tomography (CBCT) scan had also been taken in the area of interest. Radiographs were retrospectively screened for the presence of a retromolar canal, and linear measurements (distance to second molar, height, width) were taken.

RESULTS

One hundred twenty-one sides in 100 patients were evaluated (100 unilateral and 21 bilateral cases). A total of 31 retromolar canals were identified with CBCT (25.6%). Only 7 of these canals were also seen on the corresponding panoramic radiographs. The existence of a retromolar canal was not statistically related to gender or side. With regard to the linear measurements, the mean distance from the retromolar canal to the second molar was 15.16 mm (±2.39 mm), the mean height of the canal was 11.34 mm (±2.36 mm), and the mean width was 0.99 mm (±0.31 mm).

CONCLUSIONS

This radiographic study documents a frequency of 25% for the presence of a retromolar canal. The clinician is advised to preserve this anatomic variation when performing surgery in the retromolar area and to consider additional locoregional anesthesia in the case of failed mandibular block anesthesia.

A review of the mandibular and maxillary nerve supplies and their clinical relevance

Mandibular and maxillary nerve supplies are described in most anatomy textbooks. Nevertheless, several anatomical variations can be found and some of them are clinically relevant. Several studies have described the anatomical variations of the branching pattern of the trigeminal nerve in great detail. The aim of this review is to collect data from the literature and gives a detailed description of the innervation of the mandible and maxilla. We carried out a search of studies published in PubMed up to 2011, including clinical, anatomical and radiological studies. This paper gives an overview of the main anatomical variations of the maxillary and mandibular nerve supplies, describing the anatomical variations that should be considered by the clinicians to understand pathological situations better and to avoid complications associated with anaesthesia and surgical procedures.

Area extent anaesthesia from buccal nerve block

This study investigated the extent of complete anaesthesia from buccal nerve block. 40 healthy Thai patients (20 males; 20 females) requiring buccal nerve block for surgery were studied. After the buccal nerve was blocked, the buccal mucosa was explored using a sharp probe to map out the extent of anaesthesia. The operation was carried out after inferior alveolar and lingual nerve block. The extent of the anaesthesia was mainly from the retromolar area to the second molar, followed by the first molar to the second premolar, whilst the first premolar to the central incisor was the area least affected. An important finding of this study was that the anaesthetized extent of some patients extended to the anterior region on the same quadrant. This study showed the affected areas of buccal nerve anaesthesia extended through the buccal mucosa from the first premolar to the central incisor in some patients. It can serve as another informative indication for lower anterior surgery.

Location of the infraorbital and mental foramen with reference to the soft-tissue landmarks

BACKGROUND

The purpose of the present study was to determine the locations of the infraorbital foramen and mental foramen based on soft-tissue landmarks to facilitate prediction of the locations of these structures during facial surgery.

METHODS

Fifty embalmed cadavers (100 sides) of Koreans were dissected to expose the infraorbital foramen and mental foramen. The distances between the bilateral infraorbital foramina and between the mental foramina and the distances between the alae of the nose and between the corners of the mouth (cheilions) were measured directly on the cadavers, and the vertical and horizontal distances between the infraorbital foramen and mental foramen and the ala of the nose and cheilions, respectively, were measured indirectly on photographs.

RESULTS

The distance between the bilateral infraorbital foramina (54.9 +/- 3.4 mm) was greater than that between the bilateral mental foramina (47.2 +/- 5.5 mm). The infraorbital foramen was located 1.6 +/- 2.7 mm lateral and 14.1 +/- 2.8 mm superior to the ala of the nose. The distance between the ala of the nose and the infraorbital foramen was 15.9 +/- 2.8 mm, and the horizontal angle between these structures was 64.1 +/- 9.9 degrees laterosuperiorly. The mental foramen was located 20.4 +/- 3.9 mm inferior and 3.3 +/- 2.9 mm medial to the cheilions. The distance between the cheilions and mental foramen was 20.9 +/- 3.8 mm, and the vertical angle between these structures was 9.2 +/- 8.1 degrees inferomedially.

CONCLUSIONS

This study provides data that will be useful in predicting the locations of the infraorbital foramen and mental foramen when used together with hard-tissue landmarks. These data may be particularly helpful for facial surgery in patients with missing teeth.

Effectiveness of nasopalatine nerve block for anesthesia of maxillary central incisors after failure of the anterior superior alveolar nerve block technique

The purpose of this study was to assess the effectiveness of nasopalatine nerve block for anesthesia of maxillary central incisors after failure of the anterior superior alveolar nerve (ASAN) block technique. Secondarily, the possible innervation of the maxillary central incisors by the nasopalatine nerve was also investigated. Twenty-seven healthy, young adult volunteers (age: 17-26 years; gender: 9 males and 18 females) were enrolled in this study. All participants were undergraduate dental students of the University of Vale do Rio Verde de Três Corações. The volunteers had the anterior superior alveolar nerves anesthetized and a thermal sensitivity test (cold) was performed on the maxillary central incisors. The volunteers that responded positively to cold stimulus received a nasopalatine nerve block and the thermal sensitivity test was repeated. All participants were anesthetized by a single operator. Three patients presented sensitivity after both types of bilateral blocks and were excluded from the percentage calculations. In the remaining 24 patients, 16 had their maxillary central incisors anesthetized by the anterior superior alveolar block and 8 remained with sensitivity after the ASAN block. All these 8 patients had their maxillary central incisors successfully anesthetized by the nasopalatine block. In this study, 33.3% of the subjects had the innervation of one or both maxillary central incisors derived from the nasopalatine nerve, whilst most subjects (66.7%) had such teeth innervated by the anterior superior alveolar nerve. The nasopalatine nerve block was effective in anesthetizing the maxillary central incisors when the anterior superior alveolar nerve block failed.

Sensory innervation of mandibular teeth by the nerve to the mylohyoid: Implications in local anesthesia

Traditionally, the nerve to the mylohyoid has been considered a motor nerve. However, dissection and clinical studies have challenged this dogma implicating the nerve to the mylohyoid as a nerve of accessory sensory innervation to mandibular teeth. Within the infratemporal fossa, the nerve to the mylohyoid branches from the inferior alveolar nerve and may be anesthetized with an inferior alveolar nerve block. However, because of the variability in location of branching and the potential barriers formed by both the pterygomandibular fascia and the sphenomandibular ligament, the nerve to the mylohyoid may escape anesthesia in an inferior alveolar nerve block. This may prevent profound local anesthesia of the mandibular teeth and may account, at least in part, for the high failure rate of the inferior alveolar nerve block. Alternative local anesthesia procedures may be employed to ensure adequate anesthesia of the nerve to the mylohyoid is achieved. This review provides a background of anatomical and clinical research of the nerve to the mylohyoid and outlines techniques suggested for providing a neural blockade of the nerve to the mylohyoid.

Failure to obtain adequate anaesthesia associated with a bifid mandibular canal: a case report

The inferior alveolar nerve (IAN) block is the most common method for obtaining mandibular anaesthesia in dental practice but it is estimated to have a success rate of only 80 to 85 per cent. Causes of failure include problems with operator technique and anatomical variation between individuals. This case report involves a patient who received IAN blocks on two separate occasions that resulted in only partial anaesthesia of the ipsilateral side of the mandible. Radiographic assessment disclosed the presence of bifid mandibular canals that were present bilaterally and that may have affected the outcomes of the local anaesthetic procedures. Previous studies of bifid mandibular canals are reviewed and suggestions provided that should enable clinicians to differentially diagnose, and then manage, cases where IAN blocks result in inadequate mandibular anaesthesia.

Morphological characteristics of the infraorbital foramen and infraorbital canal using three-dimensional models

Infraorbital nerve blocking through the infraorbital foramen and infraorbital canal is used to anesthetize the lower eyelid, upper lip, lateral nose, upper teeth and related gingivae. For this, it is important to know the position of the infraorbital foramen, structures around the foramen, and the direction of the injecting needle related to the angle of the infraorbital canal. Many reports have described the anatomical location of the infraorbital foramen; however, not many have described the angle of the infraorbital canal and those structures around the infraorbital foramen that help the physician visualize the correct direction of the needle. Dried skulls of 42 Korean subjects (27 male and 15 female) were studied to analyze structures around the infraorbital foramen. The morphology of the infraorbital canal was also investigated using three-dimensional models. Structures around the infraorbital foramen were classified into four types according to the existence of a distinct tuberosity above the infraorbital foramen, and the degree of prominence of the canine fossa. Types I and II have a tuberosity above the infraorbital foramen, whereas types III and IV have no distinct tuberosity. Types I and III have a prominent canine fossa, whereas this is less prominent in types II and IV. We analyzed the skulls based on the angle of the infraorbital canal to the median plane. We compared the left and right sides and analyzed differences between the sexes, the three canal shapes, and the four structure types around the infraorbital foramen. Type IV was the most common in this series (38%). The infraorbital canal could be classified into three morphologies: 'tube-like' (69%), 'funnel' (25%) and 'pinched' (6%). The mean angle of the infraorbital canal relative to the median plane was 12 degrees , and the angle relative to the Frankfurt plane was 44 degrees . The mean angle between the infraorbital canal and the Frankfurt plane was 4 degrees larger in males than in females in this series of Korean subjects. The operator of the infraorbital nerve block should pay attention towards directing the needle upward at an angle of about 44 degrees for avoiding nerve damage and consider the different angles of the canal according to the individual's sex.