Quan Jing, Kuo Wan*, Xiao-jun Wang, and Lin Ma

1Department of Dentistry, 2Department of Plastic Surgery, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100730, China

IRREVERSIBLE pulpitis could be caused by caries, non-caries lesions, and combined periodontal-pulpal lesions. The clinical strategy of treating irreversible pulpitis is mainly pulp extirpation. Because the dental nerve is still sensitive to mechanical or thermal stimulation at this stage, it is necessary to adopt local anesthesia during endodontic access. The most common method in treating mandibular molars is inferior alveolar nerve block (IANB), but there are some inherent drawbacks in IANB due to multiple factors.1-3

The periodontal ligament (PDL) injection as a local anesthetic technique was developed a century ago.4The mechanism used in this technique is similar to that in intraosseous anesthesia:5(1) the anesthetic solution is forced through the cribriform plate into the marrow spaces and the vasculature in and around the tooth； (2) the primary route is not the periodontal ligament；6,7and (3) the mechanism of the action is not related to the direct pressure on the nerves.8Due to the difficulties in sensing the “back-pressure” to ensure that the needle is inside the PDL and maintaining adequate pressure (the pressure needed in PDL injection may be 4-5 times of that in palatal injections9), the application of PDL injection is still confined to supplemental anesthesia in recent years.10,11With the introduction of computer-controlled local anesthetic delivery (C-CLAD) systems in the 1980s, the success rate of PDL injection as a primary anesthetic technique in mandibular teeth was improved, yet still lower than that of IANB.12When it was used as a supplemental anesthetic method when IANB failed, the success rate was 56%.13In 2006, the newly developed C-CLAD system offered continuous and real-time identification of tissues with different densities (e.g. free gingiva, attached gingiva, and periodontal ligament) and presented feedback to the operator once it was brought into dental procedures. Owing to its multiple improvements in design, this device provides the possibility of applying PDL injection as a primary anesthetic technique.14Up to now, however, there have been few studies on the evaluation of this device in terms of its efficacy and safety.

This study aimed to assess the effectiveness and safety of PDL injection delivered by the C-CLAD system, which was employed as the primary technique for endodontic access to mandibular posterior teeth in patients with irreversible pulpitis.

PATIENTS AND METHODS

Patients

This clinical study was carried out in outpatients at the Department of Dentistry, Peking Union Medical College Hospital from August 2010 to August 2012. The study protocol was approved by the Institutional Review Board of the Hospital and signed informed consents were obtained from the selected patients.

All the included patients had been clinically diagnosed as irreversible pulpitis in mandibular premolars or 1st/2nd molars. The exclusion criteria were: American Society of Anesthesiologists (ASA) physical status classification ＞2； abnormal perception or cognition； severe dental phobia； acute periodontal infection or inflammation (or tooth movement ＞2°) in the affected teeth； analgesics taken within 12 hours； previous mandibular operations； severe traumas or bone lesions； trigeminal nerve abnormalities and previous adverse reactions to amides of local anesthetic agents. The patients were then trained to grade the intensity of pain with the Visual Analogue Scale (VAS): from 0 meaning no pain to 10 meaning the worst pain.

Computer-controlled PDL injection

A radiographic assessment of the affected tooth was performed. The periodontal condition of the injection site, described as modified gingival index, was evaluated by a periodontist to exclude any acute inflammation or ulceration and recorded as the baseline. Large pieces of plaque and calculus were removed manually. The tooth was then anesthetized using a C-CLAD system (Single Tooth Anesthesia, STA, Milestone Scientific, Livingston, NJ, USA) with PDL injection. A 30-gauge needle was inserted at the site, the STA was set in the “ControlFlo” mode (1 ml/207 seconds), and the needle penetrated the periodontal ligament slowly. After the yellow light was up on the front panel, 0.5 ml of 4% articaine with 1∶100 000 epinephrine (Primacaine Adrenaline, Pierre Rolland, France) was injected. The injection was terminated when the pressure reached the preset limit in the device. Two sites of injection, one disto-lingual and the other mesio-buccal, were selected for each tooth. Two minutes after the injection, decay removal and pulp access was initiated. The patients were informed that if the pain during the procedure was ≥ 5 in the VAS, or if they were unable to complete the procedure and required a supplemental injection to achieve profound anesthesia, they should let the dentist know immediately to stop the procedure, which would be recorded as failures. If the pain was rated ＜ 5 during the entire process, the cases were recorded as successes. All the teeth were divided into 3 groups: premolar group (PM), first molar group (FM), and second molar group (SM).

Local soft tissue changes after injection at the injection sites, such as acute inflammation, erosion, ulceration, and localized gingival necrosis were evaluated and compared with the baseline data by the same periodontist afte 3-8 days and 3 weeks.

Statistical analysis

SPSS 11.0 software was used to analyze the data. The success rates of the 3 groups of teeth were compared using Chi-square test. P＜0.01 was considered statistically significant.

RESULTS

A total of 162 patients aged 18-51 years were enrolled in the present study. The overall success rate was 76.5% (124/162). Success rates in the three groups (PM, FM, and SM) are displayed in Table 1. There were significant differences in success rates amongst the 3 groups (v=2, χ2=34.3, P＜0.01). Both the PM group and SM group showed higher success rates than that in the FM group (v=1, χ2=16.73, P＜0.01； v=1, χ2=24.5, P＜0.01), while no significant difference in success rate was observed between the PM group and the SM group (v =1, χ2=0.05, P＞0.01).

The post-injection adverse reactions were shown in Table 2. Six patients (3.7%) exhibited localized gingival necrosis, of which 3 had controlled type 2 diabetes. After careful surgical debridement and application with 0.12% chlorhexidine mouthwash, all the lesions completely recovered after 3 weeks (Fig. 1). There was no irreversible damage on the local periodontal tissues compared with the baseline condition after 3 weeks.

Table 1. General conditions and success rates of periodontal ligament (PDL) injection in three groups

Figure 1. A case with type 2 diabetes developed localized gingival necrosis after PDL injection.A. The color of interdental papilla between second premolar and first molar turned gray-white 3 days after injection. Localized gingival necrosis was diagnosed； B. The necrotic gingiva healed completely 3 weeks later after surgical debridement and chlorhexidine mouthwash.

DISCUSSION

The traditional method for anesthesia in the mandibular posterior teeth is IANB, which has been widely used as a primary technique. Due to various reasons, for instance, the anatomical variations of the mandibular nerve and the inferior alveolar nerve, the presence of infection, inflammation, previous trauma or operations, pharmacological or psychological factors, and poor technique, the success rate of IANB is no higher than 80%.15There are also some complications related to this technique, including a relatively high risk of intravascular injection (10%-15%),2which may result in series of adverse reactions. The technique of IANB involves obvious injection pain and discomfort；16post-injection soft tissue tingling or numbness may involve a large area, which could last for hours and cause changes of soft tissue contour, even self-biting wounds. In some rare cases, hematoma, trismus, facial nerve anesthesia or even neuro- sensory disturbance could occur.2,17These complications greatly limit the application of this technique, especially in some medically compromised patients. It is also difficult for beginners to well handle this technique.

The overall success rate of PDL injection in this study was close to that of IANB (76.5% vs. 80%), and for premolars and the second molars, the success rate of PDL injection was even higher (both over 90%). Different success rates of PDL injections have been reported with different tooth positions.18,19The results of this study indicated that PDL injection has better anesthetic effect when applying in the mandibular premolars and the second molars than in the first molars (92.1% vs. 53.0%, 93.1% vs. 53.0%, respectively). The success rates showed such teeth position-related difference possibly because of the difference in the width of periodontal ligament, thickness and density of the bone, and number of the roots of different teeth in mandible. All these factors may affect the depth of the needle tip that could be inserted into the periodontal ligament and the extent that anesthetic solution could spread in the cancellous bones, which needs to be confirmed by further studies. In irreversible pulpitis, the teeth may have necrotic pulp chambers, but there are root canals with vital or inflammatory nerves. Thus, an electric pulp tester might yield a false result,20which explains why we used subjective rating of pain by the patients as the evaluation index.

Clinical and animal studies have demonstrated the safety of PDL injections,21-23and minor local damage is limited to the site of needle penetration, thus the adverse effects of injecting into an area with periodontal disease are impossible.24The newly developed STA delivery system has built-in dynamic pressure-sensing technology to limit the maximum pressure used, which greatly enhances the safety to the periodontium. In the present study, within the 3-8 days following the injection, the most frequent adverse effect was acute periodontal inflammation, and a few patients developed ulcerations or erosions at the injection sites. These adverse effects have also been frequently reported in previous studies.18,25Only six patients experienced localized gingival necrosis, and diabetes may pose a potential risk to the development of this adverse effect. Although localized gingival necrosis should be considered a serious complication, early detection and timely management would produce a good result. Compared with the baseline modified gingival index, no irreversible periodontal damage was detected after 3 weeks, which showed a long-term safety of STA system for soft tissue. The safety to periodontal hard tissue, i.e. the alveolar bone, was not tested in this study.

There are some limitations in this study: a control group of IANB or a group of manually delivered PDL injection was not included； it is necessary to involve more evaluation indicators about the safety for periodontal hard tissues as well as the soft tissues.

In conclusion, according to the results of this study, the success rate of PDL injections delivered by the C-CLAD STA system in endodontic access to mandibular posterior teeth with irreversible pulpitis is comparable to the conventional IANB technique. The success rate varies with teeth positions. The computer-controlled PDL injection causes no irreversible injuries to local soft tissues.

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