Introduction

Implant dentistry has revolutionized the field of oral rehabilitation, offering patients restored function and esthetics with highly predictable outcomes. Among the myriad factors influencing the success of dental implants, understanding the intricate details of radiographic and anatomical considerations is paramount. This chapter delves into the essential aspects of immediate anterior and premolar implants in both jaws, highlighting the critical role of imaging techniques and anatomical landmarks in treatment planning and execution.

Radiographic evaluation forms the cornerstone of accurate implant placement, guiding clinicians in navigating the complex anatomical landscape of the oral cavity. From the initial assessment using two‐dimensional (2D) imaging modalities to the advanced capabilities of three‐dimensional (3D) imaging provided by cone beam computed tomography (CBCT), each technique offers unique benefits and insights. The evolution of dental imaging has significantly enhanced the precision of implant placement, reduced risk of complications and improved patient outcomes. In this chapter, we explore various radiographic techniques and their application in evaluating potential implant sites. We discuss the fundamental anatomic considerations for immediate implant placement in anterior and premolar regions, emphasizing the importance of individualized radiologic analysis. By understanding the unique anatomical variations and potential challenges associated with each patient, clinicians can optimize treatment plans, ensuring the highest standards of care and successful implant integration.

Imaging Techniques

Dental imaging techniques are invaluable tools when conducting a comprehensive anatomic assessment of any proposed implant site. Although a diverse range of imaging modalities are used, three fundamental techniques act as pillars for the modern dentist: plain film, panoramic, and CBCT imaging.

Two‐dimensional imaging has been and continues to be routinely used today as the initial imaging modality of choice for the evaluation of all contemplated implant sites. Plain film imaging, including periapical and bitewing images are intraoral techniques where the imaging sensor is placed within the oral cavity and lies lingual to the alveolar process. This radiographic geometric relationship allows for the acquisition of high‐resolution images at a low dose of radiation. Since these sensors are placed intraorally, there is an intrinsic limitation to the size of the image detectors and consequently, plain film images have smaller fields of view. A typical periapical image can adequately image up to four teeth only.

Panoramic imaging is an extraoral technique, which provides a broad overview of the entire dentition and supporting osseous structures. This larger field of view allows for visualization of distant implant sites and, most importantly, the visualization of critical anatomic structures that may not be predictably seen on plain film images. However, since the imaging sensor lies outside of the oral cavity, these images tend to have lower spatial resolution and are more susceptible to artifacts such as ghosting and movement. Currently, the position of the American Academy of Oral and Maxillofacial Radiologists is that 2D imaging should remain the initial imaging modalities of choice when evaluating potential implant sites and for routine follow‐ups [1]. Only once these have been acquired, should 3D imaging (such as CBCT) be considered.

Cone Beam Computed Tomography

Cone beam computed tomographic imaging has revolutionized dental implantology by providing detailed, three‐dimensional images of targeted dentoalveolar regions with minimal radiation exposure. In contrast to conventional 2D imaging, CBCT offers clinicians an unparalleled and unobstructed view of patient anatomy, allowing for precise planning and implant placement. With CBCT imaging, dentists can assess the trabecular bone pattern, bone quantity and morphology, as well as the precise location of critical anatomic structures, to determine the feasibility of implant placement. The primary advantage of CBCT for dental implant placement is its ability to visualize anatomical structures in three dimensions. This capability enables clinicians to identify vital structures such as bony concavities, neurovascular canals, and the maxillary sinuses, anticipating and thereby minimizing the risk of surgical complications. Additionally, CBCT allows virtual implant placement during treatment planning including digital simulation of optimal implant positions and angulations relative to surrounding anatomical landmarks. This preoperative planning enhances the predictability of implant placement and helps optimize the surgical procedure for each patient’s unique anatomy. Moreover, CBCT imaging facilitates the evaluation of bone volume and trabecular density, which are essential considerations for implant success. By accurately assessing these factors, clinicians can determine the optimal implant size, length, and positioning to achieve good primary stability and successful osseointegration.

Radiographic Evaluation for Immediate Implant Placement

There are numerous osseous anatomic landmarks that must be considered during implant treatment planning, and investigators have published their analyses creating size distributions and anatomic categories to guide clinicians. However, these generalized metrics can be of limited value in real‐life clinical dentistry. Using individualized radiologic techniques, especially CBCT, offers significant advantages over relying on published statistical averages regarding vital structures as it is based on each specific patient’s anatomy. Anatomic structures are unique for each patient including variations in bone morphology, density, and the spatial relationship of critical structures. This individualized information enhances the accuracy of implant placement, reduces the risk of complications, and improves the predictability of achieving optimal esthetic and functional results. By tailoring the treatment plan to the specific anatomical nuances of each patient, clinicians can ensure a higher standard of care, fostering better patient outcomes and satisfaction.

Although the remaining sections of this chapter present aggregated statistics for reference purposes, the authors believe that individualized clinical and radiographic analyses should be conducted, whenever possible.

General Osseous Considerations

Varied terminologies for anatomical surfaces have been used in the literature, so that some confusion may arise when comparing studies. Therefore, for reader ease in this chapter, the following terms and definitions are used. The term “oral vestibule” refers to the space situated between the teeth (along with the gingiva) and the cheek and lips, while “oral cavity proper” denotes the inner aspects (lingual/palatal) of the dental arches. Throughout this chapter, the term “vestibular” is used to describe the buccal or labial aspects of the dental arches. “Palatal” refers to the inner aspect of the maxillary dental arch, and “lingual” denotes the inner aspect of the mandibular dental arch.

Alveolar Bone Thickness

The vestibular bone of alveolar processes in anterior regions of both jaws is of minimal thickness and generally thinner than that of the lingual/palatal plates, especially at maxillary incisor sites. This thickness ranges on average from 0.4 mm at the crest to 1.9 mm apically [2]. In a 2021 systematic review, Heimes et al. [3] evaluated vestibular alveolar bone thickness in 4324 healthy individuals of various ethnic backgrounds using CBCT images. A total of 25 452 maxillary and mandibular teeth were included, and the study revealed that the thickness of vestibular bone (up to 9 mm from the alveolar crest) for both maxillary and mandibular incisors and canines averaged less than 1 mm (Table 2.1).

The data in Table 2.2 present average bone thicknesses overlying the apices of the maxillary and mandibular anterior teeth and premolars. Measurements were obtained from the center of apical foramina to the vestibular and lingual/palatal bone cortices, using CBCT images of 1400 maxillary and mandibular teeth [4]. It is important to acknowledge that root angulations of the analyzed teeth could have influenced these measurements, resulting in variations among individuals.

Variations in Trabecular Bone Density

Sclerosis, a reactive inflammatory response, is frequently observed around planned immediate implant sites. Sclerotic bone is characterized by dense trabeculation and decreased vascularity, and its presence at a potential implant site is an important surgical and biological consideration. The increased density can complicate the osteotomy drilling process, including drill deflections. Moreover, the reduced blood supply in sclerotic bone can hinder healing and even long‐term success of the implant. Early studies suggest that sclerotic bone may pose a risk factor for late implant failure [5]. Dense bone islands, like sclerotic bone, exhibit increased radiopacity and are characterized by densely packed trabeculae (Figure 2.1). Although no scientific evidence links dense bone islands to increased implant failures, their similar biology to sclerosis would suggest the likelihood of similar outcomes.

Nasopalatine Canal and Foramen

The nasopalatine canal (NPC), also known as the incisive canal (Figure 2.2), is a critical anatomical structure to consider during immediate implant placement in anterior maxilla. This canal lies at the maxillary midline, connecting the nasal cavity with the oral cavity via the nasopalatine (or incisive) foramen, and contains the nasopalatine nerve and vessels. Its varied anatomy has been well documented, including differences in size, shape (cylindrical, funnel‐shaped, hourglass‐shaped, or spindle‐shape), angulation, number of nasal foramina, intracanal septations, and supplemental canals [6]. However, when treatment planning implant placement, the most critical anatomic consideration is the amount of available alveolar bone. When measured on a sagittal CBCT cuts, the buccopalatal dimension of the maxillary alveolar process (as measured from the vestibular cortex to the anterior cortex of the NPC) measures 6.74 ± 1.60 mm, 6.73 ± 1.50 mm, and 7.48 ± 1.61 mm (mean ± standard deviation) at its inferior border, mid point, and superior borders in a non‐resorbed ridge.

Another important consideration when planning for immediate implants is the amount of trabecular bone between the palatal surface of maxillary central incisors and the NPC; this distance measures 2.93 ± 1.33 mm at its closest point on an axial cut. During immediate implant placement, careful planning is necessary to avoid encroaching upon the NPC. Inadvertent perforation of the canal can lead to several complications, including sensory disturbances due to damage to the nasopalatine nerve, hemorrhage from injury to the nasopalatine vessels, and potential infection risks [7].

Middle Superior Alveolar Canals

The middle superior alveolar canal is an uncommonly reported anatomical structure in the maxilla, specifically involved with the innervation and vascular supply of the canine/premolar region and surrounding tissues (Figure 2.3) [8, 9]. It typically contains branches of the middle superior alveolar nerve and artery, which originate from the infraorbital nerve and artery respectively. The size of the middle superior alveolar canal can vary; in some cases, it can occupy a significant amount of the proposed implant site. The middle superior alveolar foramen typically lies lingual to the maxillary canine or first premolar, at the junction of the alveolar and palatal processes of the maxilla. These anatomic relationships are important to appreciate when placing immediate implants in these regions.

Nasal and Maxillary Sinus Floors

Depending on which tooth is being replaced, the vertical dimension of available bone can be limited by either the nasal or maxillary sinus floor. These structures are important landmarks to identify to avoid complications. Perforation of implants through these structures can cause apical migration of implants, inflammation of mucosal linings, or changes in airflow.

The height of the maxillary alveolar process (as measured from alveolar crest to the nasal/sinus floor) measures 19.23 ± 8.74 mm, 18.29 ± 2.98 mm, 18.21 ± 2.65 mm, 16.58 ± 3.58 mm, and 13.19 ± 3.72 mm (mean ± standard deviation) in the central incisor, lateral incisor, canine, first premolar, and second premolar regions, respectively. A special consideration for immediate implants is the amount of apical bone. When measured along the long axis of the root, the distance between the root apex and the nasal or sinus floor measures 8.82 ± 2.91 mm, 9.65 ± 2.81 mm, and 8.00 ± 4.87 mm (mean ± standard deviation) for the central incisor, lateral incisor, and canine, respectively. These measurements can be drastically reduced when teeth are being extracted due to periapical inflammatory disease, because of the localized bone loss at the root apex.

Mental Foramen

The mental nerve and vessels emerge from the mental foramen as terminal branches of the inferior alveolar nerve and vessels. Their branches supply the vestibular gingiva of mandibular anterior and premolar teeth, and the lower lip and chin. Injury to these structures may cause hemorrhage and neurosensory disturbances to this region. Studies have shown variations in the number (single or multiple), diameter and position of the mental foramen (Figure 2.4).

A 2021 systematic review [10] evaluated the topographical characteristics of the mental foramen using CBCT imaging, including 66 articles and 12,539 patients. The findings revealed that the most common horizontal positions of the mental foramen were in line with the long axis of the second premolar (47.49%) or between the premolars (38.74%). Although the exact prevalence and most common location can vary between studies, the majority agree that these are the two most common locations for the mental foramen [11–14]. Other positions such as distal to the second premolar or mesial/in line with the long axis of the first premolar were less likely. Furthermore, Barbosa et al. [10] identified the most common vertical position for the mental foramen to be below the root apex level (93.2%).

An accurate determination of the mental foramina’s vertical position is important during preoperative planning for immediate implant treatment to avoid injury to the neurovascular bundle. This is especially true when the foramina appear to be located at or coronal to the apices of teeth. Greenstein et al. [15] suggested surgical exposure of the mental foramen when there is concern of its location prior to implant placement. However, the increased usage of advanced imaging techniques, such as CBCT, has reduced the need for these invasive procedures. Besides the location of each mental foramen, another possible anatomical variation pertains to the number of foramina on each side of the jaw. A retrospective study that evaluated CBCT images of 348 patients found that in a Spanish population each hemi‐mandible housed a single mental foramen in 95.97% of patients, while 3.59% had double, and 0.43% had triple mental foramina [13].

Anterior Loop of the Inferior Alveolar Nerve

The inferior alveolar nerve and vessels (IANV) travel along the mandibular canal and supply the pulp of the mandibular molars and second premolar. Near the mental foramen, they give off two terminal branches: the mental nerve and vessels and the incisive nerve and vessels. A frequently observed anatomical variation of the IANV occurs when these structures traverse inferior and mesial to the mental foramen. At this point, the IANV bifurcates with the incisive nerve and vessels extending anteriorly and the mental nerve and vessels curving distally to exit through the mental foramen. This curved path is referred to as the anterior loop of the inferior alveolar nerve.

There has been great variation in reporting on the prevalence and length of the anterior loop of the IANV (Table 2.3), mostly because the methods of identification and measurements of this anatomical structure vary considerably. To our knowledge, the vertical distance between the root apex of mandibular premolars and canine teeth and the anterior loop of the IANV has not been reported. Nevertheless, preoperative awareness and identification of this anatomical variation and its extension is recommended for safe dental implant placement in the mandibular foraminal region to avoid serious surgical complications such as hemorrhage and/or neurosensory disturbances to the lower lip and chin.

Apostolakis and Brown [16] are among the most cited authors who have conducted studies with the aim of determining a safe distance anterior to the mental foramina for implant placement when advanced imaging techniques such as CBCT are not available for preoperative planning. Although the anterior extent of the IANV loop in their study was 3 mm or less in 95% of cases, they observed a maximum loop extension of 5.7 mm and proposed a safe distance of at least 6 mm from the anterior border of the mental foramen for implant placement. Chen et al. [12] on the other hand, observed an anterior loop extension of up to 8.41 mm and proposed 9 mm as a safe distance to avoid anterior to the mental foramen. However, owing to the large variability reported in the lengths of the anterior extent of the IANV loops, several studies have emphasized that no safe distance for implant placement anterior to the mental foramen can be determined without excellent, patient specific CBCT imaging (Figure 2.5).

Mandibular Incisive Canal

The incisive nerve and vessels are terminal branches of the IANV, which travel anteriorly through the incisive canal to supply the pulp of the mandibular first premolars, canines, and incisors (Figure 2.6). The incisive canal has an average diameter of 2.1 mm or less [17–19] and its identification in radiographic images prior to dental implant placement is usually not a concern, since the mandibular interforaminal area is considered of low risk for implant placement [15, 20]. However, occasionally patients may present with large incisive nerve and vessels creating risks for surgery, such as brisk hemorrhage [21] or neurosensory disturbances, such as discomfort during osteotomy preparation during and/or after dental implant placement that could require implant removal [22].

Pires et al. [23] compared CBCT and panoramic radiographic images of 89 North American patients and identified the presence of an incisive canal in 83.1% of CBCT images and 11.2% of panoramic radiographic images. They observed the length of the canal to be 7.0 ± 3.8 mm and that it was in closer proximity to the vestibular than the lingual plate (2.2 ± 1.1 mm to the vestibular plate and to 4.7 ± 2.1 mm to the lingual plate) with its terminal location 3.3 ± 1.7 mm from the vestibular plate and 5.2 ± 2 mm from the lingual plate. Similar findings were reported in populations of various ethnicities by others [19, 23]. In addition, its mean distance of 4.6 ± 2.2 mm from the apices of the teeth immediately superior to the origin of the incisive canal was significantly lower than its terminal portion (6.1 ± 3.1 mm).

Lingual Foramina

Severe bleeding into the floor of the mouth due to damage of the sublingual artery, a branch of the lingual artery, can be a critical surgical complication with implant placement in anterior mandible, and may lead to upper airway obstruction [24]. The submental artery, a branch of the facial artery, may also contribute to the local blood supply after it ascends above the mylohyoid muscle.

In a study by Rosano et al. on 60 cadaveric mandibles, it was found that at least one foramen was present at the midline of each specimen. A total of 30% of the specimens had one lingual foramen, while 43% had two and 27% had three. In cases where only a single foramen was present, it was located above the genial spines and had an average diameter of 0.9 ± 0.5 mm. The researchers also noted a vascular perforating branch entering the superior genial foramina. This branch originated from the anastomosis between the two sublingual arteries.

Liang et al. [25] reported findings that were similar to the ones mentioned above observing at least one lingual foramen in 98% (49 of 50) of dissected mandibles. Among these, 62% of the foramina were located either above or at the level of the genial spines, while the remaining 38% were found below the genial spines. The average diameter of these foramina was measured to be 0.8 ± 0.4 mm. In addition to the midline foramina, the authors also noticed the presence of lateral foramina between the midline and canine teeth in 62% of the specimens. A detailed micro‐anatomical dissection revealed that the branches of the lingual artery, vein, and nerve entered the superior genial spinal foramina located at the midline. Furthermore, the mylohyoid nerve along with the submental and/or sublingual artery and vein were found to enter the inferior genial spinal foramina.

Tooth‐Related Complications

Mandibular Canine Bifurcations

Mandibular canine root buccolingual bifurcations are uncommon variations in root morphology (Figure 2.7). According to available published literature, this variation has a prevalence between 0.2% and 12.08% depending on the population studied [8]. This bifurcation results in an interradicular septation, which prudent clinicians should identify and account for prior to implant placement.

Conclusions

Successful placement of immediate anterior and premolar implants in either jaw hinges on a thorough understanding of local anatomy and the use of appropriate radiographic techniques to anticipate and prevent surgical complications. This chapter has focused on the pivotal role of imaging in preoperative planning and subsequent execution of dental implant treatment underscoring the appropriate roles of both 2D and 3D imaging modalities. Combining these imaging technologies allows clinicians to identify critical anatomical structures and assess bone quality and quantity with unparalleled accuracy. While the published literature does provide some helpful information, anatomical nuances demand careful individualized considerations in treatment planning on a per patient basis if optimal and safe implant procedures are to undertake.