1. INTRODUCTION

There is a significant concern with implant placement in the socket and tissue thickness in the anterior region. There is an association with the occurrence of prosthetic and biologic complications¹. One of the goals of performing immediate implant placement is to shorten treatment time and surgical procedures. The success of the technique is based on the ideal three-dimensional (3D) position of the implant². This position is the most challenging aspect of the technique. If the implant is installed in an inappropriate position, treatment may become more complicated and time-consuming than conventional treatment. The chosen technique must be performed by experienced professionals, with appropriate theoretical and psychomotor training³.

Both immediate (type I) and early (type II) implant placement present the challenge of preparing and positioning the implant since there is not enough time for the newly formed bone to fill the socket. If it is not possible to heal an infection associated with the tooth to be extracted or if the bone defect present in the socket is too extensive, early implant placement is recommended. It will take 4–8 weeks for soft tissue healingof the socket. Subsequently, surgery is performed with a large flap to allow bone and gingival grafting along with implant installation.

Minimally invasive procedures without flap elevation make it difficult to visualize the alveolar bone; however, it is a current approach and should, whenever possible, be applied to fresh sockets⁴. Flapless immediate implant placement is advantageous because it avoids scarring and keloid scarring, reduces buccal bone loss, surgical morbidity, and the number of sutures but requires absolute knowledge of the anatomy of the region^5–10.

OBJECTIVES

At the end of this chapter the reader should be able to:

• Identify the anatomy of the socket before implant placement.

• Select the ideal implant to be installed immediately after extraction.

• Avoid implant positioning errors in fresh sockets.

2. SCIENTIFIC BACKGROUND

2.1. ALVEOLAR BONE ANATOMY IN THE ANTERIOR REGION

The possibility of immediate implant placement depends on the anatomy of the socket and the bone remnant. Tomographic evaluation allows us to verify the position of the root and its relationship with the maxillary bone ridge (Figs 01A–D). This relationship has been classified into four distinct classes¹¹:

• Class I: The root is positioned in contact with the buccal cortical bone. Prevalence of 81.1%.

• Class II: The root is centered on the ridge, not maintaining contact with the buccal or lingual bone. Prevalence of 6.5%.

• Class III: The root is in contact with the lingual bone. Prevalence of 0.7%.

• Class IV: At least two-thirds of the root are in contact with the buccal and lingual bone. Prevalence of 11.7%.

The class IV type of defect is the least favorable for placement of immediate implants. It can often make it unfeasible to properly place the implant in the ideal 3D position. Immediate implant placement after extraction requires the presence of lingual/palatine bone and at least 3 mm of bone apical to the bottom of the socket to provide adequate stability and lock in the implant¹² (Figs 02A–D).

The challenge in immediate implant placement in anterior teeth is due to the characteristics of the area. The palatal bone wall should be prepared to place the implant from 2 mm to 3 mm away from the facial bone wall, creating a gap for the grafting biomaterials. In sockets without the facial bone wall, this distance should be 3–4 mm to the facial gingiva^13,14. Preparation of the palatal wall, however, is hindered by the depth and inclination of the socket. Burs tend to escape toward the bottom of the socket, which may tilt the preparation toward the buccal side^15–17. During surgical preparation, it is necessary to use a bur protractor, have a stable fulcrum for the handpiece, and place the implant with pressure toward the palatal bone wall. Several techniques have been described to facilitate the preparation of the socket; however, the procedure is still sensitive and maximum precision must be aimed for.

2.2. SOCKET PREPARATION FOR THE IMPLANT

Before the use of helicoidal burs, preparation of the palatal bone wall was performed with a 2 mm diameter round bur to smooth the bone in the apical-coronal and buccolingual (BL)¹⁵ direction (Figs 03A–F). A flat area is created in the socket, where other burs are used to prepare the bone accurately. The use of a long side-cut bur may also be recommended to rectify the socket walls. The use of a lance pilot bur angled to the face is another option; as the bur is introduced, its angulation is corrected, directing it to the palate (Figs 04A–F). In both techniques, knowledge of the socket and bone topography is necessary. Thus, tomographic evaluation before the surgical procedure is crucial (Figs 05A–J). Depending on the length of the socket, the presence of apical lesions, and the anatomy of the remaining bone, immediate implant placement may not be indicated.

The ideal 3D positioning of the implant in the socket resembles that of the edentulous ridges. It may change in the cervical-apical (CA) and BL directions to compensate for bone remodeling. Special care should be taken when installing immediate implants in posterior sockets, especially molars. It is challenging to position the implant in an area with unfavorable anatomy and at risk of damaging noble anatomic structures (Figs 06A–G).

In esthetic areas, to obtain a more significant amount of tissue on the facial surface, the implant should be placed in a more palatal and apical position. For each millimeter that the implant is placed palatally, it should be placed 1 mm deeper in the socket¹⁸. A significant amount of bone formation around the implant and increased initial stability occurs when the implant is installed 1 mm apical to the buccal bone crest¹⁹. When the gingival margin is in the correct position, the implant should be installed 4 mm apically to the soft tissue margin. Even in the presence of a buccal bone defect or in the absence of such a wall, the ideal 3D position should be maintained and the tissue reconstructed¹⁸ (Figs 07A–C).

A study in dogs described the ideal position of narrow implants placed immediately after extraction¹⁹. The control group was treated with implants placed at the bone level and in the center of the socket. The test group was treated with implants with lingual anchorage and positioned 0.8 mm infrabone. The results of this study showed that the implants placed in an infrabony and lingual position presented biologic advantages. The degree of bone thickness and height after healing and osseointegration was higher in the test group. Additionally, infrabony implant placement minimizes the risk of thread exposure and allows for a more appropriate emergence profile^7,9,20.

Success in immediate implant placement is dependent on treatment planning, evaluation of imaging, and the ability of the surgeon. In this surgical technique, it is necessary to select the implant accurately. Individual implant characteristics such as length, diameter, type of prosthetic connection, thread design, and shape will influence osseointegration, post-extraction bone maintenance and reconstruction, implant placement, and primary stability²¹.

2.3. SELECTION OF THE IDEAL IMPLANT

Several authors have previously argued against immediate implant placement in anterior teeth with an intact or defective facial bone wall due to esthetic changes^3,22,23. Initial studies demonstrated that recession of the facial gingival margin of the peri-implant tissue may lead to treatment failure¹. In the 1990s, the recommendation was to place implants with a diameter compatible with the size of the socket. This would maintain the anatomy of the ridge without performing bone grafts. In several cases, large implants were placed in contact with the buccal bone wall to reduce the gap or space between the implant surface and the bone wall. Gingival migration reported in these studies is related to limited tissue thickness, buccal implant placement, and the presence of buccal bone dehiscence²⁴ (Figs 08A–C).

2.3.1. IMPLANT DIAMETER

The diameter of the implant influences the amount of bone around the implant and its primary stability²⁵. Diameter selection should take into account both mesiodistal (MD) and BL distances. A common mistake is to select the implant only by the interproximal space present or the tooth to be rehabilitated. The BL distance from the shoulder and root should be considered to position the implant away from the buccal bone plate and create a gap of at least 2 mm between bone and implant. Bearing in mind that in the cervical region of central incisors the BL distance from the root is around 6 mm²⁶, an immediate implant installed in this region should have a diameter less than or equal to 4 mm. The MD distance should only be used as a reference if it is smaller than the BL distance.

Immediate implants placed close to the buccal bone wall showed bone loss of about 50% after healing²⁷. According to the literature, wide neck implants tend to have a bone loss rate higher than narrow neck implants^19,20. Current clinical studies show that even if the socket is grafted, a small loss of buccal bone, around 1.5 mm, can be expected^28–31.

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