Introduction

Replacement of missing teeth using implant–supported prostheses is a widely accepted treatment modality [1–5]. Although survival rates of greater than 90–95% have been for dental implants [1–5], the survival of implants is not equal to a treatment success [6, 7]. Rather, the long‐term success of the therapy depends on several factors that affect the stability of the implant–prosthetic complex such as health and stability of peri‐implant soft and hard tissues [6–10]. One of the key elements in maintaining the stability of peri‐implant tissue is early detection of any peri‐implant soft and hard tissue changes [11, 12]. Long‐term and regular maintenance care has been shown to be essential for maintaining the health and stability of peri‐implant soft and hard tissues [13–16]. Radiographs are used to evaluate and monitor the hard‐tissue levels around implants at regular maintenance visits. In this chapter, the applications of radiographs in the maintenance of health and stability of peri‐implant tissues are outlined. In this regard, the factors affecting marginal bone levels as well as type and frequency of radiographs for monitoring the health and stability of peri‐implant tissues are discussed.

Peri‐implant Bone Levels

Stability of marginal peri‐implant bone levels is crucial for successful long‐term treatment outcomes [17, 18], and continuous crestal bone loss results in the failure of implant therapy [19–21]. The reasons for crestal bone loss around dental implants are still debated, but in general, bone loss can occur due to several reasons, such as lack of osseointegration, trauma from surgery, bone remodeling following loading, or peri‐implantitis [21–25].

Lack of osseointegration results in early implant failure that occurs during the healing period prior to the implant loading. Several factors, such as infection, poor primary stability, or impaired wound healing can lead to the early implant failure [26–30]. On radiographs, lack of osseointegration can be diagnosed by the presence of continuous radiolucency around the implant (Figure 3.1). To rule out early implant failure, it is recommended to obtain a periapical radiograph prior to the second‐stage surgery or prior to final impression for one‐stage implants. The treatment for the early implant failure is the removal of failed implant.

Trauma from the surgery can result in crestal bone loss or lack of osseointegration [19, 22, 28, 31]. The trauma can be a result of overheating of bone during the surgery [32–34] or excessive insertion torque [35–37]. The excessive heat generated at the time of surgery causes a certain degree of bone necrosis [33, 38]. Poor irrigation or lack of irrigation during the implant surgery can cause thermally induced bone necrosis. Hence, the bone temperature must not exceed 44–47 °C during the site preparation [33]. In addition, excessive insertion torque can also lead to bone necrosis and result in peri‐implant crestal bone loss [35–37]. Bone necrosis as a result of surgical trauma can be detected on radiographs as peri‐implant bone loss of greater than 2 mm before the loading of the implant (Figure 3.2). The treatment for these lesions depends on the degree of the bone loss and shape of the defect, and it can be implanting removal or bone grafting around the implant.

Bone remodeling occurs following the loading of implants, and it can result in some crestal bone loss [39–42]. It has been shown that the amount of crestal bone loss following the loading depends on several factors such as implant design [43–45], implant positioning [46–49], and location of the implant–abutment interface (microcap) [50–52]. Hence, the amount of crestal bone loss due to remodeling varies between implant different brands/systems and implant–abutment connections [42]. This bone remodeling mainly occurs during the first year following the loading (Figure 3.3) and most implants experience less than 1–2 mm of bone loss during this period [53–55].

Bone loss of greater than 2 mm following the loading is considered pathologic, [1456–58] and it is a result of peri‐implant diseases such as peri‐implantitis (Figure 3.4), which is the main cause of implant failure after osseointegration [55, 59, 60]. Peri‐implantitis is diagnosed based on the presence of bleeding on probing and/or suppuration, increased probing depths, radiographic bone loss beyond bone level changes resulting from the initial bone remodeling following the loading [14, 58]. It has been suggested that, in clinical situations where baseline radiographs are not available, the diagnosis of peri‐implantitis can be made based on the presence of bleeding on probing and/or suppuration, pocket depth of 6 mm or greater, and alveolar bone loss of 3 mm or greater from implant shoulder [14, 58]. Several treatment approaches have been used for the treatment of peri‐implantitis [11, 55,59–66]. In general, non‐surgical mechanical treatment alone seems to be ineffective in the treatment of peri‐implantitis [67–69]. A surgical approach that includes open flap debridement and surface decontamination has been shown to be more effective than non‐surgical approaches for the treatment of peri‐implantitis [70, 71]. The decision on utilizing resective or regenerative approach following the open flap debridement is based on the morphology of peri‐implant defects [72–74]. Contained three‐wall and four‐wall defects can be treated with regenerative approach using a combination of bone grafting materials, a barrier membrane, and/or biological factors.

Type of Radiographs

Monitoring the hard and soft tissues around dental implants is vital during maintenance care [25]. Unlike around teeth, there is no defined range of probing depth associated with peri‐implant health [42, 75, 76]. However, peri‐implant bone levels can be readily assessed using radiographs. Hence, radiographic evaluations are crucial not only for early diagnosis of peri‐implantitis, but also in determining the therapeutic approach for treatment of peri‐implantitis defects.

Parallel periapical radiographs are routinely used to monitor peri‐implant hard tissue levels due to their accuracy, low radiation exposure, and cost‐effectiveness [25, 77]. Nevertheless, periapical radiographs have some limitations such as two‐dimensional projection of three‐dimensional structures, low spatial resolution, and inability to represent the bone around buccal and lingual areas of implants (Figure 3.5) [25, 77]. In addition, periapical radiographs have been associated with relatively low sensitivity and high portion of false negative in early changes in peri‐implant bone levels [25,78–80]. Hence, the application of three‐dimensional (3D) imaging such as cone‐beam computed tomography (CBCT) has been advocated to monitor implants during maintenance care [81–85].

Although CBCT images provide valuable 3D volumetric data for planning the surgical placement of dental implants, application of CBCT for monitoring peri‐implant hard tissue level during maintenance care is still questionable [25, 86]. The challenges for the application of CBCT for this purpose are high radiation dose and imaging artifacts that significantly affect the image quality and diagnostic value of these scans [87, 88]. High‐density objects such as titanium implants and other metallic objects in the field of view result in noise and beam‐hardening artifacts [88, 89]. These artifacts can mask bony defects around implants and limit visualization of buccal and lingual/palatal plates as well as bone‐implant interface [25, 86].

The accuracy of periapical digital radiographs and CBCT images has been compared by several groups [77, 90, 91