Dental fear is the most common reason for patients to avoid visiting the dentist. Dental fear can occur for a variety of reasons, including noise and vibration from tooth-cutting devices such as dental handpieces, smell of drugs or materials used in dentistry, pain during dental treatment, and irrational fear of local anesthesia [1]. Because dental treatments may be painful, appropriate local anesthesia is necessary to reduce pain during such treatments. However, paradoxically, patients often fear pain caused by anesthetic injections more than pain from dental treatment itself [2].

Despite careful anesthetic procedures, dental local anesthesia can cause pain for various reasons, including soft tissue damage during penetration of the oral mucosa, pressure from the spread of the anesthetic solution, temperature of anesthetic solution, low pH of anesthetic solution, and pain from the characteristics of the drug. In order to reduce pain during local anesthesia, swabbing anesthesia is often performed on the injection point; similarly, local anesthetic techniques that can anatomically reduce pain, such as infiltration anesthesia, should be used rather than subperiosteal or intraosseous injections that can cause pain. In addition, the anesthetic ampoule must be used administered at a temperature similar to body temperature; sterile local anesthesia should be used; and effort should be made to slow the injection speed [3]. Although reducing the injection speed is the most effective method of reducing pain, controlling and maintaining the amount or speed of injection in actual clinical settings is difficult.

Many devices have been introduced that can inject local anesthetic into the tissues at a set speed. Collectively, these "painless anesthetic devices", are termed "computer-controlled local anesthetic delivery" (CCLAD) devices. CCLAD also collectively refers to devices that not only slow and maintain the injection speed, but also maintain a constant speed while taking into account the anatomical characteristics of the tissues being injected [45]. The most widely known devices of this type include the Wand® (Milestone Scientific, Livingstone, NJ), Comfort Control Syringe (CCS; Dentsply, USA), QuickSleeper (Dental HiTec, France), and iCT (Dentium, Seoul, Korea).

The purpose of this review was to review published clinical trial papers on CCLAD in adults and children in order to share the latest knowledge and current state of CCLAD. Two authors (Kwak and Park) conducted a literature search of the National Center for Biotechnology Information (NCBI) Pubmed database for papers published between January 2001 and May 2016. The papers were limited to those published in the English language only using the CCLAD-related keywords "computer local anesthesia," "Wand," "Comfort Control Syringe," and "Quicksleeper." After the initial search, the original papers were assessed to identify those related to clinical trials, those that included dental local anesthesia and human subjects, and those that included comparison results. A total of 27 papers met these search criteria. These papers were then divided into those on adults and children.

CCLAD can reduce pain by controlling anesthetic injection speed, which permits continuous administration of a small amount of anesthetic at a slow speed, which can reduce pain not only from resistance felt in the tissues, but also from anesthesia taking effect simultaneously with injection, which in turn allows the anesthetic to be injected into tissue that has already been anesthetized. Thus, owing to this series of processes, the patient feels less pain.

The design points to consider when evaluating CCLAD devices include whether the anesthetic cartridge is included in the main unit, speed and mode of drug injection, possibility of aspiration, weight, and ease of infection management. Milestone Scientific (Piscataway, NJ, USA) first introduced the Wand® in 1997; since then, several companies have also developed the computer-based, speed-controlled local anesthetic devices used today, including the Quicksleeper® and Comfort Control Syringe (CCS®) in use overseas; and the Comfort-in®, Deninjection®, iCT injection®, No Pain III®, Meg-inject®, and Smartject® devices used in South Korea. Because these devices have varying characteristics, such as design, injection speed, shape, weight, and possibility of aspiration, it is important to choose the appropriate product based on operator preference.

The Wand®, has been on the market for the longest period of time, and is known for its ease in operation due to its light weight and a circumference that is about half that of traditional anesthetic syringes. In contrast, the Quicksleeper® and CCS® have are about three times size and weight of traditional anesthetic syringes, which can present difficulties in handling for operators with small hands. This difference is because the syringe is contained within the main unit of the Wand®, whereas the Quicksleeper® and CCS® have the syringes and motors in the hand piece. The Korean products include a gun-type, such as the DenInjection®, as well as ergonomically designed products for better grip, such as the iCT injection® and Smartject®. Recently, various devices have been developed to enhance operator convenience. The Comfort-in® is an anesthetic device that utilizes a jet injection method and applies pressure with a needle, and thus has the advantage of being able to inject the anesthetic solution within a short period of time. However, it is difficult to consider it a speed-controlling CCLAD, and because this does not have a syringe needle, it is difficult to use this on posterior teeth; thus, this device is considered most suitable for use in treatment of children's anterior teeth or as a preliminary anesthesia method.

Different devices utilize different methods of changing the cartridge. The Wand® has the cartridge installed in the main unit, which allows the assistant to change the cartridge during anesthesia. However, 0.3–0.4 mL of anesthetic solution inside the tube is lost with this change; in addition, there are many types of components, and a standard syringe needle cannot be used in this device. Having the cartridge on the outside of the main unit, as in the iCT injection device, allows the local anesthesia cartridge to be changed in a similar manner as conventional local anesthesia syringes, but because the cartridge needs to be sterilized during this process for infection management, it is recommended to choose a device designed with these aspects in mind. Ultimately, design aspects such as the position of the main unit and cartridge are related to the product's weight. CCLAD devices must be held stationary for long periods of time in order to ensure safe administration of anesthesia. If the device is too heavy, operation is difficult, and may lead to chance movement while the needle is inside the tissue, which may cause the needle to break. Therefore, it is important to select the right product with appropriate weight. Recently introduced products offer lightweight designs, and further technical advances are expected to lead to development of much lighter CCLAD devices.

With respect to anesthetic solution injection speed, the Wand®, Quicksleeper®, and CCS® have injection speed controls of three, four, and five stages, respectively, meaning that the CCS® offers the most diverse injection speed control, and all three products offer periodontal ligament anesthesia to block anesthesia. The iCT® device also allows three-stage injection, with speed controlled to allow a full cartridge to be injected within 250, 120, and 50 sec. Devices such as the No Pain III® control injection speed using Foot Software.

A point to consider in CCLAD is the potential for aspiration, as aspiration can also be used for block anesthesia. Aspiration is possible in devices such as the Wand®, CCS®, and Smartject®, and although 5 sec of aspiration time in the newly developed Wand PLUS® is an improvement over the 14 sec required for the original Wand® device, it is still relatively long. However, because infiltration anesthesia more often leads to pain in the maxillary palatal side than block anesthesia, aspiration is not a mandatory criterion for selecting a CCLAD device.

The findings from studies on children for comparison of CCLAD and local anesthesia using conventional syringes are shown in Table 1 [6789101112131415161718]. Among 13 studies that assessed pain, six reported similar measured values, while seven determined CCLAD to be more effective in that it caused less pain and allowed behavioral control. The papers that reported CCLAD to be more effective were mostly those that were published relatively recently. The method most often used to assess the effects of anesthesia was visual analog scale (VAS), as well as indices that assess facial or bodily responses, such as sound, eye, motor scale (SEM), face legs activity cry consolability (FLACC), facial image scale (FIS), and faces pain rating scale (FRS). With respect to devices, the Wand® and CCS® were used; the Wand® assessed in 12 of 13 total studies, excluding 1 study. Among papers that reported CCLAD to be effective, three compared infiltration anesthesia on buccal and palatal sides, of which papers by Feda, et al. and Mittal, et al. reported that, in comparison to conventional anesthesia, there were no significant differences on buccal side; however, CCLAD on the palatal side resulted in less pain [68]. Compared to the buccal mucosa, with relatively fluid mucosa, dense palatal mucosa is put under significant pressure during administration of anesthetic solutions; thus, CCLAD offers advantages. Moreover, among three papers that compared the use of CCLAD for local anesthesia to the inferior alveolar nerve (IAN), two (by Baghlaf, et al. and Alamoudi, et al.) reported CCLAD to be more effective than conventional IAN block anesthesia [1011].

Among studies that compared anxiety during local anesthesia, Tahmassebi, et al. and Versloot et al. reported no differences between using CCLAD and conventional local anesthesia with a syringe [1314]. However, Versloot, et al. noted a positive correlation between patients who were more anxious and their perceived pain [14]. Therefore, pain during local anesthesia may be affected by intrinsic factors based the characteristics of children with fears of needles, rather than extrinsic factors associated with differences between using CCLAD versus conventional method using a syringe. In the studies described above, there were no differences in results based on the age of the children and it could not be concluded that there were significant differences based on anesthesia method, anesthesia site, or dental procedure used. However, most of the assessment tools used on children were subjective assessments of patient response and behavior. While the assessments were repeated by the operator, patient, third party, or other expert group to promote objectivity, these methods were still subjective. Moreover, children are more afraid than adults are of receiving an injection, regardless of using CCLAD or conventional local anesthesia-use syringe device. Therefore, there are limitations in the objective assessment of the potential correlations between local anesthesia effects and pain in children.

Klein, et al. reported that CCLAD caused less pain when the local anesthesia needle was inserted, but CCLAD was used for infiltration anesthesia, whereas local anesthesia using conventional syringe is typically used for periodontal ligament anesthesia. Because the difference in pain based on anesthesia injection site cannot be disregarded, accurate comparison is difficult [16]. Moreover, Ram, et al.; Versloot, et al.; Langthasa, et al.; and Thoppe-Dhamodhara, et al. also compared all of cases, without distinguishing maxillary versus mandibular sites. In addition, the reliability of their results was also low [791418]. Finally, pain based on dental treatment procedure must also be considered; however, Klein, et al.; Al Amoudi, et al.; Versloot, et al.; Tahmassebi, et al.; Feda, et al.; Langthasa, et al.; and Thoppe-Dhamodhara, et al. did not specify dental treatment procedures or did not include all dental treatments, which makes equivalent line of comparison difficult [67913141516].

The findings from studies on adults for comparison of CCLAD and local anesthesia using conventional syringes are shown in Table 2 [419202122232425262728293031]. A total of 14 papers assessed pain, concluding that CCLAD resulted in less pain or higher anesthesia success rates. The method most often used to assess these factors was the VAS, just as in children; the other methods used included electric pulp tester (EPT), verbal rating score (VRS), pain rating scale (PRS), dental anxiety scale (DAS), and perceived stress scale (PSS). Studies by Nusstein, et al.; Shah, et al.; Yenisey, et al.; Singh, et al.; and Chang, et al., conducted palatal anesthesia for anterior middle superior alveolar (AMSA) block, reporting less pain from CCLAD [21]; similarly, studies by Sumer, et al.; Yesilyurt, et al.; Ozer, et al.; and Kammerer, et al., also reported less pain in mandibular block anesthesia [19262829]. Based on these findings, CCLAD appears to be superior to conventional methods for maxillary and mandibular infiltration and block anesthesia.

Sumer, et al. and Yenisey, et al. reported that CCLAD showed superior results for both syringe needle insertion and injection [2729]. In contrast, Nusstein, et al. and Kammerer, et al. reported that pain was similar when syringe needle was inserted, but less pain for CCLAD with spreading anesthesia [1930]. These results support the hypothesis that CCLAD can reduce pressure generated when anesthetic solution spreads owing to the ability to control injection speed. Moreover, Loomer, et al. showed more significant differences during anesthesia of the greater palatine and nasopalatine nerves, as compared to other maxillary nerves. Thus CCLAD, which can better control speed and pressure during anesthesia, was more advantageous for anesthesia for palatal regions with thick mucosa [24].

Except for studies by Saloum, et al.; Lee, et al.; and Beneito-Brotons, et al., the remaining 11 studies on adults described the range of dental treatments applied; as such, they offered a fairer comparison than that of the studies in children [1920212425262728293031]. All papers except for those by Saloum, et al. and Rossengerg, et al. defined the anesthesia site, which allowed assessment of CCLAD efficacy [192021222324252627282930].

Two papers that assessed anxiety in CCLAD (Sumer, et al. and Chang, et al.) reported similar or increased levels of anxiety [2129]. Due the size of the devices, CCLAD may have acted as anxiety and stress factor that induced fear in the patients in these studies.

Lee et al. assessed CCLAD for local anesthesia on anterior and middle superior alveolar nerves, revealing showed no significant differences in onset and duration times between CCLAD and conventional local anesthesia; however, CCLAD mostly showed higher efficacy with respect to anesthesia success rates [23]. In studies by Loomer, et al, Shah, et al., and Chang, et al., infiltration anesthesia for periodontal treatment did not show significant differences in either surgical and non-surgical treatments [212425]. Both Sumer, et al. and Ozer, et al. reported less pain with CCLAD compared to conventional local anesthesia [2629], which also proved the efficacy of CCLAD for extraction procedures, which are considered relatively invasive dental treatments.

Ozer, et al., compared IAN block anesthesia (the conventional anesthesia method) to intraosseous anesthesia by CCLAD in mandibular molar extraction cases, revealing that CCLAD showed superior pain control compare to conventional methods [26]. However, intraosseous anesthesia requires longer injection time, the syringe needle may become blocked during anesthesia, and has shorter anesthesia time than IAN block anesthesia; therefore, it was considered unfit for procedures that require long periods of time to complete.

CCLAD devices control the speed of anesthetic injected into tissue and are used to reduce pain during local anesthesia for dental treatments. The results of this review indicate that using CCLAD resulted in less pain and more effective anesthesia in adults than in children. However, differences in shape, weight, and injection speed should be considered when selecting choosing a device. Recent advances in CCLAD have led to the introduction of products that are lighter and easier to use. Establishment of assessment indices and methods for pain and anxiety, as well as additional clinical studies can further evidence are necessary for more effective use of CCLAD in dental treatments.