The need for keratinized tissue around implants remains a controversial topic. However, reconstruction of keratinized mucosa may be needed to facilitate restorative procedures, improve aesthetics, and control plaque during oral hygiene. Free gingival grafts, connective tissue grafts, allogenic/xenograft materials, and apically positioned flaps have been used to augment soft tissue around implants. Four different timing protocols have been explored with regard to soft-tissue augmentation: before and during implant placement, during the second-stage surgery, or after restoration. The timing and technique of soft-tissue augmentation remain controversial and lack support from literature. Long-term clinical studies to establish clear guidelines are warranted.
Key points
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The effect of peri-implant mucosa thickness and keratinization on the long-term health of implants remains controversial.
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Peri-implant mucosa characteristics have an effect on the aesthetic outcome of implants.
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Implant placement position and macrostructure design play an important role in the final soft-tissue status.
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The surgical technique and timing of soft-tissue augmentation are determined according to peri-implant soft-tissue condition, objective of the procedure, and desired final aesthetic outcome.
Introduction
Teeth and implants have comparable surrounding soft-tissue configurations including elements of connective tissue and epithelium. However, they have several structural differences. The junctional epithelium around teeth attaches to the enamel surface via desmosomes and internal basal lamina along the length of the junctional epithelium, whereas in implants the junctional epithelium attach to implant surface via hemi-desmosomes. Peri-implant tissues lack cementum and periodontal ligament (with direct contact between alveolar bone and implant surface), and have less vascular supply and fewer fibroblasts with parallel rather than perpendicular orientation of supracrestal connective tissue ( Table 1 ).
| Clinical Characteristics | Tooth | Implant |
|---|---|---|
| Connection | Cementum, bone, PDL | Osseointegration Ankylosis |
| Junctional epithelium | Desmosome Internal basal lamina |
Hemidesmosome |
| Connective tissue | Perpendicular fibers | Parallel/oblique fibers |
| Vascularity | More | Less |
| Probing depth | ≤3 mm | 3–4 mm |
The transmucosal attachment around implants is formed after adaptation of the mucosal wound edges to the transmucosal part of the implant. Therefore, following surgical intervention the soft-tissue attachment around the implant develops whereby the development of the periodontium around teeth takes place simultaneously and remains structurally continuous with the surrounding tissues.
There has always been debate surrounding the significance of soft tissue at implant sites on aesthetic outcome and long-term stability of dental implants. The objective of this article is to discuss the controversy of this importance and illustrate suggested surgical techniques and timings for soft-tissue augmentation around implants.
Factors influencing the peri-implant mucosal barrier
Supracrestal Attached Tissues Around Implant “Biological Width”
The term supracrestal attached tissues, previously known as “biological width,” refers to the vertical dimension extending from the coronal portion of the junctional epithelium to the apical aspect of the connective tissue attachment. The supracrestal attached tissues provide a biological protective seal around the implant or tooth against any external or biological impingement. Gargiulo and Arrocha and Vacek and colleagues studied the supracrestal attached tissue dimensions in natural dentition in humans. The former study reported that the supracrestal attached tissues’ “biological width” consists of a gingival sulcus (average 0.69 mm), an epithelial attachment (average 0.97 mm), and a connective tissue attachment (average 1.07 mm). The latter study confirmed the results of the earlier study, reporting average values of epithelial attachment as 1.14 mm and connective tissue attachment as 0.77 mm. The authors of both studies concluded that the most consistent value between individuals was the dimension of the connective tissue attachment.
In peri-implant mucosa, early studies have shown that the supracrestal attached tissues’ “biological width” around dental implants consists of a sulcular epithelium width ranging between 1.5 and 2 mm and connective tissue width ranging between 1 and 2 mm. Therefore, dental implants have longer supracrestal attached tissues (2.5–4 mm) in comparison with natural tooth (2–3 mm).
It is important to mention that there are several factors that may influence the dimension of the supracrestal attached tissues around an implant, such as different designs and surface characteristics of different commercially available implant systems, and various placement and surgical protocols. Many studies noted similar mucosal attachment formation around various titanium implant systems and around intentionally submerged and intentionally nonsubmerged implants. The peri-implant junctional epithelium was significantly longer in initially submerged implants to which an abutment was connected later than in intentionally nonsubmerged implants.
Regarding the design of macrostructure topography, the use of 1-piece or 2-piece implants has been the most relevant factor in determining the vertical dimension of the supracrestal attached tissues. There is an absence of a gap (implant-abutment interface) at crestal bone level when 1-piece (tissue level) dental implants are used, whereas 2-piece (bone level) dental implants have a gap at this region. Herman and colleagues revealed that 1-piece implants showed soft-tissue dimension relatively smaller than that of 2-piece implants, and the supracrestal attached tissues of the 1-piece implant more closely resembled that of the natural dentition.
Hermann and colleagues also demonstrated that in 2-part implant systems, bone remodeling occurred 2 mm apical to the micro gap, regardless of the positioning of the implant relative to the bone crest (ie, depth of placement). The investigators postulated that the microbial contamination (or leakage) from the micro gap after the abutment connection could be the cause of the greater apical extension of epithelial attachment in submerged 2-part implants.
Platform switching has been developed to overcome crestal bone loss resulting from the re-establishment of supracrestal attached tissues apical to the implant-abutment interface, where there is a horizontal mismatch between the diameter of the implant and the abutment. The rationale for this development is that the internal repositioning of the implant-abutment interface would shift the inflammatory cell infiltrate (formed at this interface) away from the crestal bone. This results in re-establishment of the supracrestal attached tissues in a predominantly horizontal rather than vertical dimension. Furthermore, it would minimize the vertical bone resorption that occurs as a result of physiologic remodeling associated with biological width formation. In addition, it has been postulated that platform shifting has a biomechanical advantage by moving stress concentration from the outer edges of the implant.
Papilla height
Papilla height next to dental implants is one of the most significant factors that can affect the aesthetic outcome around an implant. Clinical studies were conducted to evaluate the presence or absence of the papilla between implants and teeth. The presence of the papilla between an implant and adjacent tooth was demonstrated to depend on the vertical position of the periodontal attachment of the neighboring tooth. In cases with a vertical distance between the contact point and the bone crest of 5 mm, complete papilla fill is anticipated. When the distance was greater than 5 mm, the presence of the papilla was reduced to a frequency of 50%. In a clinical study, the mean papilla height between 2 adjacent implants was 3.4 mm, which is 1.5 mm less than between an implant and a natural tooth. Compared with natural teeth, the papilla at implant sites are reported to be significantly shorter.
In addition to the vertical position, the horizontal distance between the implant and the adjacent tooth needs to be considered. It was suggested that a minimal distance of 1.5 mm would be necessary to compensate for remodeling processes following establishment of the biological width. Tarnow and colleagues evaluated the horizontal distance of bone between 2 adjacent implants and the respective presence of the papilla. When the measurement of interimplant distance was ≤3 mm, the amount of crestal bone loss was 1.04 mm, whereas 0.45 mm of bone loss was noted with an interimplant distance of greater than 3 mm. These findings indicate the need for a minimum distance of 3 mm between 2 adjacent implants for the presence of a normal papilla. These distances may have to be reconsidered in the future following the introduction of dental implants with platform-shifting modifications. Such implants have been shown to result in less peri-implant bone loss compared with the standard types of implant.
Mucosal phenotype
Mucosal thickness of soft tissue around implants is of clinical importance because of the influence on the aesthetic outcome and implant health. In addition, it may partly compensate for missing bone on the buccal side of dental implants.
At implant restorations, the gingival phenotype has been described as one of the key elements that lead to a successful treatment outcome. In particular, papilla between immediate single-tooth implant and adjacent teeth was significantly correlated with a thick-flat phenotype. According to Evans and Chen, mucosal recession increases in patients with thin gingiva immediately after single-implant restorations. Implant sites with thin mucosa were vulnerable to angular bone defects, and implants with thick mucosa have shown a stability in crestal bone dimension. In addition, patients with thick-flat mucosa had the ability of retaining the implant papilla height, resisting recession, concealing titanium, and an overall better aesthetic outcome that is more amenable to various implant positions. Therefore, thick soft-tissue phenotype around dental implants is more favorable to thin phenotype.
The critical soft-tissue thickness on the buccal aspect of implants has been demonstrated to be 2 mm. In cases where the buccal soft-tissue volume is <2 mm, when the choice of the soft-tissue augmentation material can significantly influence the aesthetic outcome at the implant site, the results of all-ceramic restorations were superior than metal-ceramic restorations. In another study, the presence of >1 mm of thick mucosa around dental implants had lower gingival recession than <1 mm of thin mucosa.
Keratinized mucosa
The influence of keratinized mucosa (KM) dimension around implants on the maintenance of soft and hard tissue is a controversial topic, as is the need to augment the keratinized tissue around implants in patients with lack of width or reduced width. Preserving healthy peri-implant tissue around a dental implant might be related to presence of an adequate amount of attached mucosal tissue. According to a study conducted by Adibrad and colleagues in 2009, a significant association exists between a limited zone of keratinized mucosa around dental implants and increased plaque accumulation, mucosal inflammation, bleeding on probing, recession, alveolar bone loss, and probing depth.
The response of the peri-implant mucosa to plaque formation was investigated in human and animal studies. It was observed that plaque formation and soft-tissue response develop in a similar manner around teeth and dental implants. However, with increasing duration of plaque accumulation, the peri-implant mucosa showed less efficiency in encapsulating the inflammatory lesion. Thus, the rate of tissue destruction in peri-implant mucositis is higher than that in periodontal lesions. As a result, having an adequate amount of peri-implant soft tissue that firmly attaches to underlying bone has been suggested as a key factor for long-term success of dental implants.
The existence of an adequate band of KM around dental implants might be imperative for plaque control and plaque-associated mucosal lesions because the potential for plaque control was better for implants with KM for the same patients. Warrer and colleagues reported that tissue breakdown and early loss of attachments is more likely to arise from plaque accumulation in an area with inadequate amount of KM around a dental implant. A higher rate of plaque accumulation and peri-implantitis was expected after placing an implant in an area with no KM implants in comparison with implants placed in an area with KM. This finding is in agreement with other studies that support the significance of KM around dental implants in controlling plaque and maintaining overall health of peri-implant tissues ( Fig. 1 ).
Langer and Langer, Landi and Sabatucci, and Lee and colleagues concluded that a minimum width of 2 mm of KM was needed to maintain peri-implant tissue because it decreased plaque accumulation, bleeding around the implant, and mucosal recession. Zigdon and Machtei reported that the width of KM around implants might be critical in the early identification and diagnosis of mucosal recession. These investigators suggested that patients with less than 2 mm of KM have a significantly higher plaque accumulation associated with peri-implantitis over a period of 3 years.
On the other hand, different systematic reviews dispute that an adequate width of KM around dental implants is critical for the health of the peri-implant mucosa, improved aesthetic outcome, and higher survival rates of dental implants. In their systematic review, Wennstrom and Derks reported that there is no strong evidence with regard to risks/benefits of absence/presence of KM at dental implants. They also stated that proper plaque control is more important than the presence of KM around implants. Another study revealed that the width of keratinized band had no critical impact on the health condition of peri-implant tissue or plaque control.
Although a conclusion cannot be reached on the influence of KM on long-term survival of dental implants, the preservation and/or reconstruction of KM around dental implants may be needed to facilitate restorative procedures, improve aesthetics, and control plaque formation ( Table 2 ).
| Authors, Year | Objective of Research | No. of Studies Included | Conclusion |
|---|---|---|---|
| Lin et al, 2013 | Examination of KM effect on peri-implant health parameters | 11 | Lack of adequate KM around dental implants is associated with more plaque accumulation, tissue inflammation, mucosal recession, and attachment loss |
| Gobbato et al, 2013 | Effect of KM width on clinical parameters of soft-tissue health and stability around dental implants | 8 | Predictive value of KM width was limited, although reduced KM width was associated with inflammation and poor oral hygiene |
| Brito et al, 2014 | Importance of KM around dental implants to maintain proper health of peri-implant tissue | 7 | Adequate zone of KM may be necessary for better peri-implant tissue health, but more randomized controlled trials are needed to support this claim |
| Pranskunas et al, 2016 | Influence of peri-implant soft-tissue condition and plaque accumulation on peri-implantitis | 8 |
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Timing of peri-implant soft-tissue augmentation
At present there is not enough evidence in the literature to allow formulation of a guideline for the most suitable timing and technique for performing soft-tissue augmentation around implants. Soft-tissue management of dental implant sites may be completed before placement, after placement, before prosthetic loading, or even after the prosthetic loading of a dental implant. In a study by Stimmelmayr and colleagues on 70 implants, the amount of shrinkage of free gingival graft (FGG) at the time of implant placement was greater compared with FGG placed at the second-stage surgery. Timing of the most effective surgical techniques with clinical outcomes and drawbacks in the augmentation of soft tissue around implants are summarized in Table 3 .
| Procedure | Timing of Augmentation | Outcome and Predictability | Drawback |
|---|---|---|---|
| Free gingival graft |
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Highly predictable to increase the soft-tissue volume and keratinization | Unaesthetic outcome due to color and texture that differs from those of the recipient side |
| Connective tissue graft |
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Highly predictable with maximum aesthetic results in terms of quantity or quality of tissue support |
|
| Apically positioned flap | Mainly at the time of implant exposure |
|
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