Intraligamentary anaesthesia: a possible alternative for perineural blocks in equine dentistry

doi:10.21203/rs.3.rs-4276992/v1

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Intraligamentary anaesthesia: a possible alternative for perineural blocks in equine dentistry

https://doi.org/10.21203/rs.3.rs-4276992/v1

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Background The injection of a local anaesthetic into the periodontal ligament (PDL) to achieve desensitisation of the pulp, periodontium and adjacent tissues, is a well-established technique in humans, especially in paediatric dentistry. The technique is commonly referred to as intraligamental or intraligamentary anaesthesia (ILA). The aims of the present publication were: (1) to provide a review of the literature, (2) to describe an ILA technique used by the authors in the field of equine dentistry, and (3) to evaluate ILA in a cadaver study in horses.

Results In the clinic, we used a 27G x 35mm disposable dental needle in combination with a long-handled syringe. According to authors’ experience, high pressure is not necessary. 1.8 ml of anaesthetic solution was used. With the help of a crocodile forceps or a needle holder, the needle is directed into the PDL. The needle is inserted into the periodontal ligament until resistance is met (in general after 25–35 mm). The procedure was repeated on the mesiobuccal, mesiolingual (or -palatal), distobuccal and distolingual (or -palatal) side of the teeth.

Four frozen equine cadaver heads and two fresh horse heads were used to evaluate the distribution of a local anaesthetic after an intraligamentary injection. Four cheek teeth were chosen at random on each skull. At each site of the tooth, one cartridge (1.8 ml) of black ink was manually injected.

Conclusion The ILA technique is simple to use in equine dentistry to achieve desensitisation of the pulp, periodontium and adjacent tissues. The supplementary cadaver study showed spreading of the solution around apex of the root. We conclude that ILA may be an interesting alternative for perineural blocks in equine dentistry.

Equine dentistry

ILA

intraligamental anaesthesia

intraligamentary anaesthesia

local anaesthesia

nerve block

regional anaesthesia

The injection of local anaesthesics into the periodontal ligament to achieve desensitisation of the pulp, periodontium and adjacent tissues, is a well-established technique in humans, especially in paediatric dentistry, but also in adult patients. The technique is commonly referred to as “intraligamental/intraligamentary anaesthesia” (ILA), or periodontal ligament injection. In PubMed, there are > 100 publications using these two mesh terms.

In equine dentistry, the technique has not been described in detail. It has however been used by one of the authors (TL) in his clinic for equine dentistry in Sweden for over 30 years. The purpose of the present article was to provide a review of the literature regarding ILA and to describe the technique proposed by the authors in an equine cadaver study.

Equine dentistry has advanced in recent decades because of a better understanding of the anatomo-physiological aspects of the equine oral cavity, the availability of dedicated dental instruments, the inclusion of routine oral examinations and the development and improvement of a variety of oral surgical techniques. In addition, there is a growing interest in minimally invasive procedures in equine dentistry, which are carried out on the standing, sedated horse [1].

For painful interventions, supplementary anaesthesia of the region of interest is often desired and even more frequently a prerequisite. Local anaesthesia is used to desensitize the surgical area, alleviate perioperative pain and to decrease the amount of sedation needed to be able to work safely and efficiently [2]. The potential and safety of nerve blocks was improved with the development of safer and more efficient local anaesthetic agents (novocaine). It was not until 1943 that lidocaine was invented by the Swedes Nils Löfgren and Bengt Lundquist [3]. Besides the development of new drugs, the technique of administration has also been improved. Without the use of a vasoconstrictor, local infiltration anaesthesia had limited potential in the oral region.

In human dentistry, the risk of complications and the relatively high number of failures, especially of the inferior alveolar nerve block (IANB), encouraged dentists to further develop alternative anaesthetic techniques for orofacial procedures [4]. ILA was introduced in human dentistry in the early 20th century [5]. It gained popularity in the 1970s due to the development of a high-pressure dental syringe: Ligmaject and Peripress Pen [6, 7].

In the field of equine dentistry and in oral and facial surgery, perineural nerve blocks are today’s gold standard. The techniques have been extensively described in previous articles [8, 9]. Although perineural nerve blocks are relatively simple and safe techniques, there are some disadvantages. Reported extraoral complications include; hematoma formation, retrobulbar abscess formation, ocular protrusion, corneal ulceration, blindness, neuropraxia, cellulitis and meningitis [8–11]. Within the oral cavity, self-inflicted lingual trauma and oral abscess formation are known complications [12]. Anaesthesia of the maxillary cheek teeth using a perineural nerve block, is associated with a greater possibility of complications [8].

As in human dentistry, veterinarians further develop anaesthetic techniques to reduce the complications and improve the accuracy of the local anaesthetics. Ultrasound-guided local techniques can be used [13]. The ILA-technique might be a valuable alternative to nerve blocks in the equine patient. In human dentistry, ILA is a widely used, efficient and clinically-safe anaesthetic technique [14–16]. To the authors’ knowledge, the technique has not been thoroughly described in horses, probably due to the more difficult approach and the enormous length of the equine periodontal space.

Equipment and technique

Intraligamentary injections in human dentistry are usually made with a 30-gauge short disposable needle. A high-pressure dental syringe has been developed, which accommodates a cartridge that contains 1.8 ml of anaesthetic solution [17]. The use of computer-assisted devices to administer a local anaesthetic at a set speed and pressure further decreases the discomfort during the injection [18]. The devices inject local anaesthesia over a period of 1–3 minutes.

The needle is inserted via the gingival sulcus into the PDL. The bevel of the needle faces the alveolar wall. Classically four injection sites are chosen: mesiobuccal, mesiolingual (or -palatal), distobuccal and distolingual (or -palatal). The needle is inserted until resistance is met (2-3mm) [17]. At each injection site 0.2 ml of local anaesthetic is delivered. The total amount of anaesthetic varies between 0.2–1.8 ml depending on the number of injections, the specific tooth and the type of procedure. The anaesthetic solution is delivered slowly with a manual dental pressure syringe or via a computerised syringe.

In the equine patient, a longer 27G x 35mm dental needle is used in combination with a long-handled syringe [40 cm Extended Intra-Oral LA Syringe, Equine Blades Direct Ltd, Wedmore, United Kingdom]. For ILA of incisors, wolf teeth, canine teeth or second premolars, a dental pressure syringe [Ligmaject©, Henke Sass Wolf GmbH, Tuttlingen, Germany] can be used (Fig. 1). This provides a higher pressure, which can be useful to achieve a more profound diffusion around the tooth. In the authors’ experience, the high pressure is not necessary for a clinical satisfactory anaesthesia. The long-handled syringe and the pressure syringe both accommodate a cartridge that contains 1.8 ml of anaesthetic solution. Similar to the regional nerve block, supplementary submucosal anaesthesia is administered on the buccal and lingual or palatal side of the tooth. In general, one cartridge (1.8 ml) is administered on each side to desensitize the surrounding gingiva.

With the help of a crocodile forceps or a long needle holder, the needle is directed into the PDL (Fig. 2). The needle is inserted into the periodontal ligament until resistance is met (in general after 25–35 mm). Although the purpose is not to advance a needle to the apical area, it is often possible to introduce the entire 35-mm needle into the PDL (Fig. 3). The procedure is repeated on the mesiobuccal, mesiolingual (or -palatal), distobuccal and distolingual (or -palatal) side (Fig. 4). One cartridge of anaesthetic solution is administered at each of the four injection sites. Where this is not possible, molar spreader forceps may be used very gently to create more space to allow correct needle placement. In the authors’ experience, this is only necessary on rare occasions with a higher prevalence in older horses, due to the more rigid organisation of the PDL.

Cadaver study

Four frozen equine cadaver heads and two fresh equine heads were used to evaluate the distribution of local anaesthetic after intraligamentary injection. Four cheek teeth were chosen at random on each skull. The injections were performed at the four sites as described above. At each site, one cartridge (1.8 ml) of black ink was manually injected. Half of the injections were performed with a dental pressure syringe, the other half with a long-handled syringe.

Although the ink was injected into the PDL, the fluid did not stay within this structure. Ink was seen in the PDL as well as in the surrounding alveolar bone (Fig. 5). It seems that fenestrations in the alveolar bone wall are the port of entrance for the solution from the PDL [19]. The injected solution was found pooling around the apex of the tooth, but did spread much further than presumed. In all sections that were made, ink was found around the apices of neighbouring teeth. Garfunkel et al. [19] stated that the spread of the solution was noticed apically through the alveolar bone crest. The spread was noticed through the bone marrow spaces, avoiding the PDL route. Our observations concur with this route of distribution, although in most sections that were made, ink was also found in the PDL surrounding the teeth. Therefore, in horses, the spread of the injected solution is most likely a combination of the PDL route and the bone marrow route.

Since the reserve crown and roots are much longer in equine patients compared to human patients, the needle is advanced in the PDL as far as possible. In contrast to human dentistry, where this is only possible for a few millimetres, in horses it is often possible to advance the whole needle into the PDL, i.e. 35 mm. After the injection, ink was distributed in all aspects of the periodontal ligament and accumulated in the periapical area.

A different pattern of diffusion was noticed between the upper and lower cheek teeth. Due to the more compact organization of the mandibular bone, the injected ink remained in the surroundings of the tooth. This was not the case for the maxillary teeth, where a wider spread of ink was noticed (Fig. 6).

The aim of the present study was to describe an ILA technique and its possible advantages and disadvantages. A clinical double-blinded study is needed to compare the technique with perineural blocks. Based on the authors' clinical experience and the human literature, there is today enough evidence that the ILA technique has a large potential in equine dentistry (Fig. 7).

The tooth and its surrounding tissues receive their innervation from the sensory branches from the fifth cranial nerve (trigeminal nerve) and the sympathetic fibres from the cervical ganglion [20]. All nerve fibres enter the tooth through the apical foramen. The sensory nerve bundles enter the PDL through several slits in the alveolar bone, located at the bottom and in the lateral wall of the alveolar socket [21].

Beside the dental and periodontal innervation provided by branches of the infraorbital and alveolar inferior nerves, which reach the tooth and its periodontal surrounding via a bony canal, additional nerve branches reach the periodontal space via the gingiva [22]. The nasopalatine nerve and the major palatine nerve provide branches for the palatal sides of the maxillary teeth, the lingual nerve provides branches for the lingual sides of the mandibular teeth. The mentioned nerves are most likely blocked by a perineural block of the maxillary nerve at the maxillary foramen or by a block of the mandibular nerve at the mandibular foramen, respectively. However, the buccal gingiva of the maxillary as well as of the mandibular cheek teeth is reached by branches of the buccal nerve, which cannot be blocked by a perineural block so far. Although no studies exist which evaluated the amount of periodontal sensitivity provided by the buccal nerve, it is assumed that reported remaining sensitivity after classical perineural blocks are provided by branches of the buccal nerve. Therefore, an intraligamentary injection of anaesthetics would at least supplement and complete a perineural block.

The injected local anaesthetic spreads through the PDL and alveolar bone and pools around the apex of the tooth. Data available from human dentistry [23–25] and the clinical experience of the authors confirm that the deposition of a volume of local anaesthetic around the apex of the tooth, injected into the PDL, will desensitize the tooth and its surrounding.

Due to the physical trauma of needle placement and the possible ischemia after injecting a local anaesthetic with a vasopressor, the ILA-technique should not be recommended for tooth-saving procedures without further research. In pigs and monkeys a local, mild and reversible inflammation can be observed within 24 hours after injecting [26]. In most of the specimens all damage disappeared within eight days following injection. At 15 days following injection, all damage was considered healed, but in a very limited amount of samples some granulation tissue was still present in the lamina propria of the gingiva [26, 27]. An osteoclastic reaction and reversible bone resorption occur after injecting fluid under pressure in the PDL of dogs [28]. After 25 days the situation was normalised again. Slight postoperative localized pain due to periodontitis was reported by five human patients out of 187 after ILA. The pain disappeared after two days [17]. This has not been recognised in the equine patient, but further research is needed.

The possible introduction of bacteria originating from the oral flora should be taken into consideration when performing an ILA. In children, 96.6% of the injections led to a transient bacteriemia. By comparison, toothbrushing alone caused a bacteraemia in 38.5% of the occasions [29]. In the equine patient a transient bacteraemia is encountered in 90% of the patients during a tooth extraction [30]. The same authors concluded that although arguments exist for prophylactic antimicrobial drugs administration prior to dental extractions, the use of antimicrobials should be restricted to cases in which it is deemed absolutely necessary [30]. The same principle applies for intraligamentary injections. Removing tartar, dental plaque and disinfection of the injection site with chlorhexidine might reduce the bacteraemia and inflammation post injection.

For reasons mentioned above, an increased risk of alveolar bone sequestration after tooth extraction might be a possible complication. However, there was no statistically significant difference in post-extraction dry socket formation in humans between a perineural nerve block and an ILA [31]. The overall negative effect of the intraligamentary injection on the surrounding tissues seems to be mild and limited in time [32]. In the primary dentition, ILA does not increase the risk of developmental disturbances to the underlying dental bud [33].

With increasing age, the collagen fibre bundles of the PDL become thicker, the collagen fibre arrangement becomes denser and the portion of cemento-alveolar fascicles increases [34]. In older horses, the more rigid and dense organization of the PDL influences the needle placement when performing an ILA. On rare occasions, it might be necessary to use interdental molar spreaders to gently create space for the introduction of the needle into the PDL.

The most significant disadvantage of the ILA might be the shorter duration of action. In human dentistry, the technique is specifically used for procedures of less than 30 minutes. The presence of a vasoconstrictor seems to play an important role in the quality and duration of the anaesthesia as indicated by several studies [32, 35]. However, there is insufficient high-quality evidence to prove the superiority of one specific formulation over another as stated by a recent Cochrane review [36]. Increasing the administered volume does increase the success rate in humans [37]. The significantly larger volume used in horses might play a role in the prolonged effect that the authors have observed clinically. The duration of action was in the vast majority of cases sufficient to perform the complete dental procedure. In longer procedures, the anaesthesia can be repeated when a decrease in effect is noticed.

In the cadaver study, a different pattern of diffusion was noticed between the upper and lower cheek teeth, due to the more compact organisation of the mandibular bone. The local anaesthetics will spread much further in the upper jaw than in the lower jaw, if the operator does not pay attention to the pressure while injecting.

In human dentistry ILA is referred to as a ‘single tooth anaesthesia’. This does not apply in sensu stricto to the situation of the horse, considering the spread of ink observed in the cadaver study to the surrounding tissues and neighbouring teeth. However, the anaesthesia is more specific than a perineural nerve block. This has many advantages, including reducing the number of possible types of complications. Particularly for the anaesthesia of a mandibular molar, there is no risk of self-inflicted trauma to the tongue, due to desensitization of the lingual nerve.

The downside of the more specific anaesthesia of ILA is most obvious during the spreading phase of a tooth extraction. Despite a complete desensitization of the PDL of the diseased tooth, the horse might still react when placing molar spreaders in between the teeth. Pressure during spreading is probably felt through the complete arcade and not just on one tooth. Therefore, spreading needs to be done gently and with little pressure.

In human dentistry, ILA is a widely used, efficient and clinically safe anaesthetic technique [38, 39]. Probably due to the length of the equine teeth and the more difficult approach, especially in the caudal region of the mouth, the ILA technique has not been thoroughly described in horses. Even if a clinical study is needed to objectively evaluate the efficacy compared to the widely used perineural nerve blocks, our long-term clinical experience and the results of the cadaver study are encouraging.

Many of the possible complications that can occur with perineural nerve blocks can be avoided with ILA. Important limitations of the ILA technique are the more rigid organisation of the PDL in older horses, and the shorter duration of action. However, the latter has not clinically been noticed by the authors. The possible local inflammation after introducing the needle into the PDL and administering an anaesthetic solution might create a (transient) periodontal inflammation. Without further research, ILA is not recommended for tooth saving procedures, but might be a possible alternative or at least a supplement for perineural nerve blocks for extraction procedures.

Authors’ contributions
Stijn Teysen and Wouter Demey authored the main manuscript text, with Carsten Staszyk, Robert Menzies and Torbjörn Lundström providing manuscript editing and scientific input. Carsten Staszyk provided the stereomicroscopic images. Dowen Birkhed adapted the manuscript to meet the standards for this publication. Torbjörn Lundström initiated and supervised the study and writing process.
All authors have read and approved the final version of the manuscript.

Acknowledgements
Not applicable

Competing interests
The authors declare that they have no competing interests.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Consent for publication

Not applicable.

Ethics approval

This study did not require official or institutional ethical approval. All specimen were commercially obtained from an abattoir.

Prior publication
Data included in this article have previously been published as an abstract in the Proceedings of the annual congress of the Nordic college of equine dentistry, January 16^th -18^th 2020 and the proceedings of the European Veterinary Dental Forum, June 4^th – 5^th 2021.

Funding
This study received no external funding.

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Intraligamentary anaesthesia: a possible alternative for perineural blocks in equine dentistry

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