**2. Peri-implant tissue**

The periodontium is known as a tooth-supporting structure while the peri-implant mucosa is the structure and function of the mucosa that surrounds the abutment of a dental implant. Clinically, both tooth and prosthesis of the dental implant will emerge from the gingival tissue with tight gingival cuff. **Figure 1** features the clinical pictures of healing abutment in situ and the appearance of peri-implant mucosa following removal of the healing abutment. The mucosa surrounding the dental implant formed tight gingival cuff consists of epithelium and connective tissues established during healing after the surgery. Many studies provide information on similarities and differences between peri-implant soft tissue and tissue at the dento-gingival junction. The similarities and differences of both periodontium and periimplant mucosa are depicted in **Table 1**.

**Figure 1.** The clinical pictures of healing abutment in situ and mucosa at the implant neck. (Courtesy of Dr. Masfueh Razali).


**Table 1.** Comparison of periodontium and peri-implant tissue.

These studies range from clinical [1, 2] to molecular levels [3], and from animal model [4, 5] to human biopsies [6, 7]. In all studies, the bone appears to be in direct contact with implant without the presence of any connective tissue or fibrous tissue encapsulating the implant.

The extensive and well-established researches on bone-implant interface have led to the wide acceptance of the concept of osseointegration. Presently, more focuses are placed on under‐ standing and improving the implant-soft tissue interface. The biological seal of the soft tissueimplant interface is created by epithelium and connective tissue. The presence of keratinized mucosa surrounding an implant is thought to be one of the important factors in maintaining peri-implant soft tissue health. Moreover, materials and surface topography of implant abutment materials may also influence the biological seal formed at the implant-soft tissue interface. The available data from animal studies and emerging information from human investigations suggest that different material with different surface energy and enhanced surface topography is associated with increased soft tissue-to-implant contact [8, 9]. The nature of soft tissue-implant against normal periodontium is compared in the subsequent paragraph. By understanding the tissue around transmucosal region, the factors influencing this biological

The periodontium is known as a tooth-supporting structure while the peri-implant mucosa is the structure and function of the mucosa that surrounds the abutment of a dental implant. Clinically, both tooth and prosthesis of the dental implant will emerge from the gingival tissue with tight gingival cuff. **Figure 1** features the clinical pictures of healing abutment in situ and the appearance of peri-implant mucosa following removal of the healing abutment. The mucosa surrounding the dental implant formed tight gingival cuff consists of epithelium and connective tissues established during healing after the surgery. Many studies provide information on similarities and differences between peri-implant soft tissue and tissue at the dento-gingival junction. The similarities and differences of both periodontium and peri-

**Figure 1.** The clinical pictures of healing abutment in situ and mucosa at the implant neck. (Courtesy of Dr. Masfueh

seal will be better appreciated.

40 Dental Implantology and Biomaterial

**2. Peri-implant tissue**

implant mucosa are depicted in **Table 1**.

Razali).

**Figure 2.** A schematic drawing of similarities and differences between dentogingival tissue and peri‐implant mucosa (Prepared by Dr. Masfueh Razali).

Macroscopically, a tooth-supporting structure comprises the gingiva, connective tissues and periodontal ligament, which connects tooth to bone via cementum. There are three types of gingival epithelium covering the underlying connective tissue of a tooth. These are junctional epithelium, which provides the contact between the gingiva and the tooth; sulcular epithelium, which faces the tooth surfaces without any contact being made with the tooth surface; and lastly, oral epithelium, which faces the oral cavity. The oral epithelium is a keratinized, stratified squamous epithelium. The junctional epithelium, which is structurally different, is formed from the reduced enamel epithelium during tooth eruption and from dividing basal cells of the oral epithelium. The junctional epithelium forms a collar around the tooth and is about 2 mm high and 100 μm thick. It is composed of only two cell layers, namely a basal layer and a supra basal layer. The inner cells of the junctional epithelium form and maintain a tight seal against the tooth surface. The connective tissue is composed of gingival fibres, which runs in many directions, from tooth and/or bone to gingival tissues. Similarly, the supporting structures of dental implant also consist of gingival epithelium and connective tissue attach‐ ment but without periodontal ligament. The epithelial part resembles the junctional epithelium around natural teeth [10, 12, 18, 19]. The features of both normal periodontium surrounding teeth and peri-implant tissue are illustrated in **Figure 2**.

Generally, the macroscopic and microscopic features of peri-implant mucosa are almost similar to the tooth-supporting tissue (at the dento-gingival junction) with few exceptions.


**Figure 3.** Transmucosal region of peri-implant mucosa demonstrating fibres of gingival connective tissue, no attach‐ ment of fibres on implant surface. (Reproduced with permission from [15])

So far, the structure, dimensions and the composition of gingival and implant transmucosal regions have been investigated by many researchers. These include early animal models studies in dogs [10, 11, 14] and in human [20, 21]. From those studies, a few conclusions have been made which included:

and a supra basal layer. The inner cells of the junctional epithelium form and maintain a tight seal against the tooth surface. The connective tissue is composed of gingival fibres, which runs in many directions, from tooth and/or bone to gingival tissues. Similarly, the supporting structures of dental implant also consist of gingival epithelium and connective tissue attach‐ ment but without periodontal ligament. The epithelial part resembles the junctional epithelium around natural teeth [10, 12, 18, 19]. The features of both normal periodontium surrounding

Generally, the macroscopic and microscopic features of peri-implant mucosa are almost similar to the tooth-supporting tissue (at the dento-gingival junction) with few exceptions.

**1.** The junctional epithelium: the junctional epithelium faces the implant smooth surfaces or abutment of an implant is less thick, and consists of only a few cell layers especially at the

**2.** Biologic width: both consist of junctional epithelium and connective tissue attachment, but the junctional epithelium of an implant is longer [10, 14, 17] than that around teeth. Variation in height of these two attachments is noted between human and animal studies.

**3.** The gingival fibres connecting the periosteum to bone run parallel to the long axis of the implant, as compared with those around a tooth, where the gingival fibres consists of complexes arrays running from many direction including from tooth to gingival tissues, some of which perpendicular to the tooth. There were also fibres running circumferen‐ tially as shown by [15]. The arrangement of the fibres is schematically illustrated in **Figure 2**. The histological sections of transmucosal region of peri-implant soft tissue are shown in **Figure 3**. Note that there was a cell-free area adjacent to implant, and fibres appear

**Figure 3.** Transmucosal region of peri-implant mucosa demonstrating fibres of gingival connective tissue, no attach‐

teeth and peri-implant tissue are illustrated in **Figure 2**.

running parallel to long axis of implant.

**4.** No periodontal ligament—bone is present.

ment of fibres on implant surface. (Reproduced with permission from [15])

apical region.

42 Dental Implantology and Biomaterial


A qualitative analysis of the subepithelial connective tissue showed a cell-rich, wellvascularized outer zone with fibres running in many different directions and a poorly vascularized inner zone consisting of numerous dense collagen fibres running close to the implant surface, predominantly in a parallel direction [14, 15, 22]. The inner zone is in direct contact with the implant/abutment surface and is 50–100 mm thick. It is rich in fibres, with few scattered fibroblasts that appear to be in close contact with the transmucosal component. The peri-implant mucosa generally resembles and is recognized as a scar tissue, exhibiting an impaired resistance towards bacterial colonization [13, 16]. As a consequence, the connective tissue adhesion at implant has a poor mechanical resistance as compared to that of natural teeth.

As suggested by some studies mentioned earlier, the biological seal of the peri-implant tissue formed by both epithelial and connective tissue attachments is weak and poor in mechanical resistance [13, 16]. Hence, this area is subjected to increased risk of peri-implant diseases, as the bacterial assault begins in this area. It is important to understand the nature of both attachments as it may lead to an enhancement this biological seal. Various models been used to evaluate the implant-soft tissue interface. These models are reviewed in the next section.
