2.1 Introduction

The definition of a “successful implant” has evolved over the years to include, beyond functional utility, high esthetic outcomes. Nowadays, a definition of a successful dental implant includes, among others, the patient’s and clinician’s esthetic satisfaction, which is achieved by a restoration that is in harmony with the surrounding teeth and tissues [1]. The final restoration should match the size, form, and color of the adjacent teeth and be framed by soft tissues consistent in color, shape, and texture [2] (Fig. 2.1).

The harmonization of peri-implant structures may depend on several clinical parameters such as bone and soft tissue volume, precise implant placement, and the quality of the prosthetic restoration. Appropriate diagnosis and treatment planning is imperative to achieve a successful outcome.

Lack of keratinized mucosa, inadequate soft tissue volume, and peri-implant tissue recession may all result from inappropriate treatment planning and execution. Peri-implant soft tissue plastic surgery has been used to prevent and correct such tissue deficiencies. In this chapter both preventive and treatment strategies will be reviewed.

2.1.1 Etiology

2.1.1.1 Inadequate Keratinized Tissue

The need for keratinized mucosa around dental implants has been controversial. While some systematic reviews have shown no significant difference in long-term peri-implant health and stability, others have disputed this conclusion. Wennström et al. examined the importance of keratinized tissue in maintaining peri-implant health and tissue stability. They concluded that there was limited evidence that keratinized tissue was necessary if plaque control was adequate. Appropriate width of keratinized tissue was defined as >2 mm [4]. However, recent evidence has shown a stronger correlation between the lack of keratinized tissue around dental implants and worse peri-implant parameters, including more pronounced gingival recession [5] (Fig. 2.2). Despite the controversy existing in the literature, on the need for keratinized tissue around dental implants, soft tissue augmentation may be advantageous for the maintenance of peri-implant soft tissue health [6]. Furthermore, an increased width of keratinized tissue may facilitate more effective oral hygiene and improve peri-implant soft tissue health, as well as long-term soft tissue stability [7].

2.1.1.2 Soft Tissue Volume/Mucosal Thickness

There is no general consensus on the amount of soft tissue needed around dental implants in order to maintain soft tissue architecture. Zigdon and Machtei found that thin mucosa (<1 mm) was associated with two times greater recession than thick (>1 mm) [8]. In addition, a narrow mucosal band (<1 mm) was associated with three times greater mucosal recession and more peri-implant attachment loss.

It has been recommended that the optimal thickness of the peri-implant tissue be around 2 mm [9, 10]. Evidence suggests that when the tissue volume is less than 2 mm, the restorative material may affect the esthetic outcome [11, 12]. Thus, all ceramic abutments/restorations should be used in order to achieve optimal esthetics. On the other hand, when the soft tissue volume is more than 2 mm, more options for the restorative materials are available, as the esthetic outcome does not seem to be compromised [13, 14] (Fig. 2.3).

There is evidence that soft tissue volume may facilitate hard tissue stability. A prospective controlled clinical trial found that significantly less bone loss occurred around bone-level implants placed in naturally thick buccal mucosa when compared to ones surrounded by thin soft tissue [15]. However, at this point in time, Akcali et al., in a systematic review, found that there is insufficient evidence that soft tissue thickness impacts crestal bone loss [16]. Unfortunately, a critical soft tissue dimension that would offer long-term peri-implant soft tissue stability has not yet been universally accepted [17].

2.1.1.3 Periodontal Biotype

Periodontal biotype plays a critical role in the predictability of the outcome and long-term stability of peri-implant soft tissues. Multiple studies have subdivided periodontal tissues into thin, scalloped, and thick, flat periodontium [18, 19]. Each periodontal biotype responds differently and has its own characteristics that may affect the final surgical outcome [20, 21] (Table 2.2). One of the difficulties in evaluating the data that attempts to link peri-implant biotype to mucosal recession is that current studies have limited sample size and lack of consensus as to what is considered a thin or thick biotype. In some studies thin biotype is defined as “probe seen through the labial tissue,” while in others 1mm or less soft tissue thickness is used as a criterion. There are, however, some studies that have shown an increased risk of mucosal recession around dental implants, in patients with thin soft tissue biotype [22–24]. In general, periodontal biotype should be taken into consideration during treatment planning, keeping in mind that a thick periodontal biotype is typically more predictable in preserving the gingival architecture when compared to a thin biotype. In patients with a thin biotype, a more sophisticated treatment protocol should be selected in order to achieve the desired outcome (Figs. 2.4 and 2.5).

Table 2.2

Characteristics of tissue biotypes, their association to tooth morphology, and the reaction of each biotype to inflammation, surgery, and tooth extraction

Periodontal biotypes	Thin, scalloped biotype	Thick, flat biotype
Anatomy and anatomical variations	Scalloped gingiva	Flat soft tissue
	Scalloped bone	Flat bony architecture
	Pointed papillae	Short papillae
	Thin buccal plate	Thick buccal plate
	Increased prevalence of fenestration and dehiscence defects	Dehiscence and fenestration defects are rare
Tooth morphology	Narrow teeth (tapered) Tooth proportions of 50–60%	Wide teeth (square) Tooth proportions of 80–90%
Inflammation	Responds to inflammation by recession and loss of the thin alveolar bone	Responds to insult by pocket formation, and infra-bony defects
Surgery	Delicate tissues, unpredictable healing (recession, tissue dehiscence)	Predictable hard and soft tissue healing
Tooth extraction	Extensive ridge resorption	Minimal ridge resorption

Sourced from: Olsson M and Lindhe J: Periodontal characteristics in individuals with varying form of the upper central incisors. J Clin Periodontol 1991; 18: 78-82, Becker W, Ochsenbein C, Tibbetts L, Becker BE. Alveolar bone anatomic profiles as measured from dry skulls. J Clin Periodontol 24:727-731,1997 Kao, R. T., Fagan, M. C. & Conte, G. J. (2008) Thick vs. thin gingival biotypes: a key determinant in treatment planning for dental implants. Journal of the California Dental Association 36, 193–198. De Rouck T, Eghbali R, Collys K, De Bruyn H, Cosyn J. The gingival biotype revisited: transparency of the periodontal probe through the gingival margin as a method to discriminate thin from thick gingiva. J Clin Periodontol 2009; 36: 428–433

2.1.1.4 Dental Implant Position

Implant position in relation to the buccolingual, apico-coronal, and mesiodistal dimensions of the alveolar ridge is a factor that influences the degree of bone remodeling following implant placement [25]. Bone remodeling may have a negative impact on the soft tissue position around dental implants and could lead to unfavorable esthetic outcomes.

Buccolingual

A recent systematic review identified buccal implant positioning as one of the factors that can lead to resorption of the buccal plate and mucosal recession [26]. This finding was supported by another systematic review that reported that immediately placed implants that were buccally malpositioned in extraction sockets had a three times greater chance of recession when compared to more palatally placed implants [27] (Fig. 2.6).

Apico-coronal

Some clinical guidelines have been proposed regarding the ideal dental implant positioning. Funato et al. described the ideal position as a restoration-driven 3D implant placement [28]. The author also suggested that the platform of the implant should be placed 2–4 mm below the mid-buccal aspect of the future gingival margin. Buser described the concept of “comfort zone and danger zone,” when dental implants are placed in the esthetic zone, where the position of the dental implant shoulder should be at the ideal point of emergence [29]. He also suggested that the implant shoulder should be placed as shallow as possible and as deep as necessary, as a compromise between biological principles and esthetics.

Mesiodistal

The distance between an implant and a tooth or among two implants can affect papillary height.

When considering implant placement adjacent to a tooth, the papilla fill depends mostly on the clinical attachment level of the adjacent tooth and more specifically on the apico-coronal distance from the alveolar bone crest to the contact point. Choquet et al. reported that when the distance from the alveolar crest to the contact point is 5 mm or less, the papilla was present in almost 100% of the cases, whereas when the distance increased to 6 mm or more, the papilla was present in only 50% or less of the cases [30]. The greater the distance from the bone crest to the contact point, the higher the risk for incomplete papilla fill. There is no current agreement in the literature on an absolute number that will result in a predictable papilla fill [9].

Buser et al. suggested that the mesiodistal distance between a tooth and an implant should not be less than 1.5 mm and between two implants should be 3 mm or more [29]. Therefore if this distance is not respected, there is a risk of bone loss resulting in loss of interproximal papilla.

When two implants are placed adjacent to each other, there appears to be an additive osseous remodeling effect. A study with adjacent implants found that when implants were placed within 3 mm from each other, they developed 1.04 mm of interproximal bone loss compared to implants placed at a greater than 3.0 mm distance, which lost only 0.45 mm of bone [31]. However a recent systematic review concluded that based on the current level of evidence, it is not possible to determine an absolute number for an optimal inter-implant distance. However, a tendency existed for incomplete papilla fill when adjacent implants were placed closer than 3 mm [32] (Fig. 2.7).

2.1.1.5 Peri-implant Bone Volume

A critical component of treatment planning in dental implant therapy is the amount of available bone. It has been postulated that to maintain stable peri-implant soft tissue levels on the buccal aspect of dental implants, a minimum amount of 1–2 mm of buccal bone needs to be present [33, 34]. While some studies support the concept that a thick buccal plate will support peri-implant soft tissues and prevent recession, others have disputed this claim [35]. Given the fact that no consensus currently exists in the literature, it would seem prudent for the clinician to aim at obtaining a buccal plate thickness of 1–2 mm. This can be accomplished by various ridge augmentation methods. Buser et al. in a 10-year follow-up of 41 implant cases placed in conjunction with GBR found that this technique achieved good dimensional stability over several years [36]. This has been supported by a recent consensus report that stated that “lateral bone augmentation procedures are associated with peri-implant soft tissue stability based on bleeding on probing (BOP), probing depth (PD), and marginal bone levels (mBI) ranging from 1- to 10-year follow-up” [37].

2.1.1.6 Persistent Inflammation

Peri-implant diseases are defined as inflammatory lesions of the surrounding peri-implant tissues and include peri-implant mucositis and peri-implantitis. Both of these peri-implant diseases are infectious in nature and are caused by bacterial biofilms [38].

2.1.1.7 Timing of Implant Placement

2.1.1.8 Immediate Implant Placement

Even though the survival rate of immediately placed dental implants is comparable to early or late placements, the risk of mucosal recession is also elevated [40].

In a long-term follow-up study, the placement of immediate dental implants resulted in an average buccal mucosal recession of 1.13 mm [41]. This might be related to the dimensional changes of the alveolar bone and soft tissue following tooth extraction. Immediate implant placement does not reduce bone remodeling [42]. A history of periodontal disease, trauma, or pathology may also result in hard and soft tissue loss. In a recent systematic review, it was shown that immediate implant placement is associated with greater variability in outcomes and a higher frequency of recession of >1 mm of the mid-buccal mucosa in 9–41% of sites, 1–3 years postoperatively. In comparison, early implant placement exhibited no sites with recession >1 mm [27] (Fig. 2.8). Immediate implant placement is a surgically demanding procedure and requires an experienced skill set. Proper case selection is crucial to achieve the desired outcome.

In a review by Chen and Buser, it was noted that the majority of studies published after 2008 involving immediate implant placement imposed inclusion criteria that included a thick biotype and an intact buccal plate in an effort to reduce mucosal recession [27]. Multiple treatment modalities have been utilized to minimize soft and hard tissue changes following immediate implant placement. Those include flapless surgery, simultaneous placement of connective tissue grafts, the use of bone grafts in the residual socket gap, and immediate provisionalization.

Another recent study demonstrated that the least amount of soft tissue changes occurred when a bone graft was placed in the residual socket gap after immediate implant placement followed by either a custom healing abutment or a provisional restoration [44]. In the same study, sites that received no bone graft or a stock healing abutment showed significant tissue collapse.

2.1.1.9 Early Implant Placement

The concept of a 4–8-week healing period post extraction, to allow for soft tissue healing, is utilized in cases where additional height and thickness of soft tissue are required (Fig. 2.9). In a 3D analysis of alveolar bone changes at 8 weeks post extraction, Chappuis et al. found that most osseous remodeling occurred in the center of the facial plate with minimal changes in the proximal areas [45]. Consequently a two-wall morphology was present at 8 weeks post extraction facilitating osseous grafting and implant placement. Low risk for mucosal recession, good esthetic outcomes, and adequate facial bone thickness have been reported [43].

Early implant placement with partial bone healing is another dental implant placement protocol in the esthetic zone. This placement protocol has been advocated when a periapical bone lesion is present and hard tissue healing is desired to assist in appropriate implant position and primary stability [43].

2.1.1.10 Late Implant Placement

Late implant placement is advocated more than 16 weeks following osseous healing. A randomized clinical trial compared soft tissue stability following immediate and delayed dental implant placement at 3 and 6 months. This study found no significant differences in the soft tissue changes. Authors agree that both immediate and delayed implant placement approaches are appropriate and that the preferred treatment approach should be based on other factors such as bone dimension, dehiscence, and fenestrations [46]. In another multicenter randomized controlled clinical trial, the esthetic outcome for both immediately and delayed single implants in the anterior maxilla was compared 1-year postoperatively. The authors reported that patients of both groups were equally satisfied at 4 months and 1 year after loading [47] (Fig. 2.10).

2.1.1.11 Prosthesis Design and Contour

In order to enhance the esthetic outcomes and healing around dental implants placed in an ideal position, it is critical to have a proper emergence profile of the restoration. A transition from the circumferential design of the dental implant platform to the correct cervical tooth anatomy is required for an appropriate restoration contour. The facial contour of the dental implant restorations could be flat, concave, or convex. Each contour has a different effect on the facial soft tissue healing and stability [48].

A recent study attempted to determine the effect of abutment contour on the peri-implant soft tissue around restored dental implants. This paper identified two distinct zones within the implant abutment and crown, defined as critical and subcritical contours. The critical contour is located immediately apical to the mucosal margin (1.5 mm); it could be on the crown, abutment, or both, whereas the subcritical contour is the area located apical to the critical contour from the dental implant neck to the gingival margin [48]. Changes in the critical contour have a major influence on the stability of the mucosal margin around dental implants, while alterations in the subcritical contour have a minor effect. The concave or flat contour is often preferred in order to avoid pressure on the buccal tissue, while over-contoured restorations may cause contraction of the buccal tissue and recession [48] (Fig. 2.11).

The type of abutment used could also influence the stability of the mucosal margin around dental implants. In a 2-year prospective multicenter cohort study, 72 patients with single dental implants in the anterior area were examined [49]. In this study the authors concluded that zirconia and titanium cad-cam abutments had better mucosal margin stability when compared to the stock counterparts.

2.2 Diagnosis

Peri-implant tissue deficiencies may have an impact on the esthetic appearance of implant-supported restorations, as well as on the health status of the peri-implant tissues. Such deficiencies may refer to lack of keratinized tissue, and/or insufficient tissue volume, which includes thin peri-implant tissue and/or peri-implant tissue recession (Figs. 2.12, 2.13). To date, widely accepted definitions on peri-implant tissue deficiencies do not exist. No threshold has been defined, in regard to the lack of peri-implant keratinized tissue. Most studies, though, have identified that a band of peri-implant keratinized tissue of 1.5–2.0 mm may be advantageous for the maintenance of peri-implant health and stability of the peri-implant tissues. Furthermore, the term peri-implant tissue recession is unclear and confusing. Based on the glossary of periodontal terms, peri-implant tissue recession is the migration of the peri-implant mucosa, apical to the implant platform [50]. Although this definition may address the lack of tissue quantity, it does not address the presence or absence of keratinized tissue or the esthetic appearance of the implant restoration.

More recently, a pilot study attempted to validate another index for the objective esthetic assessment of implant-supported restorations, the implant crown esthetic index [54]. This index takes into consideration nine parameters, which assess the color, form, and surface characteristics of the restoration and the peri-implant tissues. The clinician assigns penalty points, on a 5-point or a 3-point rating scale (depending on the parameter examined). The points are assigned based on the amount of mismatch or discrepancy that any of those nine parameters may have, with the adjacent and contralateral teeth and tissues (Table 2.7). Based on the number of points accumulated, the esthetic result is deemed “excellent” (0 penalty points) or “poor” (5 points or more). However, if any major discrepancy or mismatch is noted, the esthetic result is automatically deemed poor. This study concluded that the implant crown esthetic index is a useful tool to objectively rate the esthetics of implant-supported single crowns. Nevertheless, its practical use needs to be determined with larger-scale clinical trials.

Table 2.7

Implant crown esthetic index

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