Stabilization and enhancement of soft and hard tissues around dental implants: a surgical perspective

Tissue biotype

Knowledge of tissue biotype prior to implant placement is an important factor. The gingival biotype can be divided into thick-flat and thin-scalloped.²⁴ Placing a periodontal probe within the gingival sulcus is a simple way to check the biotype. The probe is visible through the free gingiva in thin biotype. The gingival biotype influences the design of surgical flaps during implant placement and the provision of soft and hard tissue grafting. Some studies have indicated that thick gingival biotype is more predictable for reducing post-surgical recession.^24–26

Thick gingival biotype has a flat contour with a thickness of more than 2 mm of keratinized mucosa over thick underlying bone architecture. In contrast, thin biotype has a scalloped contour with a thickness of less than 1.5 mm with a narrow band of keratinized mucosa over the thin underlying bone. Thick-flat biotype has short papillae and squared teeth compared with thin-scalloped biotype, which is associated with long interdental papillae and triangular teeth (Figure 1).²⁴

Therefore, definitive implant restorations might not always show full papilla infill where there is a thin gingival biotype, and crowns might need to be rectangular in shape with longer contact surfaces to reduce the size of interdental black triangles, especially when multiple teeth are being replaced. Thin gingival biotype and buccally placed implants are high risk factors for bony dehiscence and gingival recession especially in the aesthetic zone.^27–28

The average thickness of the buccal plate in the aesthetic zone is about 0.94 mm (0.92 mm in centrals, 0.94 mm in laterals and 0.97 mm in canines). Following dental extractions, buccal plate (bundle bone) will be lost, and sockets lose about 25% of their width and shrink by about 4 mm vertically in the first year. Ridge volume reduces by approximately 40–60% in 3 years if left untreated.²⁹ It is important to preserve the socket space by some form of socket preservation, or use of an immediately placed implant to avoid the collapse of socket volume and lack of soft tissue support. Araújo et al demonstrated that approximately 2.2 mm of vertical buccal height is lost 4 weeks after dental extraction compared with the lingual plate (Figure 2).²⁹ Therefore, it is advantageous to reduce the potential resorption of the buccal plate, dehiscence, and gingival recession in this area.^29–31

Elian et al³¹ suggested a simple classification for socket healing after dental extraction (Table 1, Figure 3):

A few clinical protocols were suggested in the literature to deal with potential loss or resorption of buccal plates, immediate implant placement with provisional restorations (Figure 4), contouring GBR with or without connective tissue grafts, and socket-shielding techniques.^33–35

Immediate implant placement with provisional restoration is an effective method for the maintenance of the buccal plate around the area. However, there is some concern that the buccal plate would still be subject to resorption, regardless of the placement protocol, if no ridge preservation procedures were carried out simultaneously. Ridge preservation with some biomaterials, such as xenografts, seems to minimize the risk of buccal plate resorption and soft tissue recession.^33–38

Socket shielding, which has been described in the literature, is a technique by which part of the root dentine is left inside the socket between the buccal plate and implant surface.³⁹ There is limited evidence to support this approach. However, this technique showed some positive results in preserving the buccal plate if augmented with GBR.³⁹

Clinical studies indicated the effectiveness of contouring augmentation in early implant placement with GBR to reduce the risk of buccal plate resorption.^41,42 Stable buccal bone reduces the risks of mucosal recession; however, some studies indicated that pre-operative thickness of soft tissues and width of adjacent crestal bone are key factors for success.^41–43 A prospective cross-sectional study showed stable peri-implant soft and hard tissues in 41 implants along with satisfactory aesthetic outcomes with 5–9 years' follow-up. However, it was highlighted that there was a risk for mucosal recession in early implant placement protocols. Contour augmentation with GBR was adequate to maintain the buccal bone wall in 95% of patients.⁴⁰ Notably, GBR procedures are still being practised in almost 90% of implants placed in the aesthetic zone (Figure 5).^41–43

Surgical implant position

The surgical positioning of dental implants is key for both aesthetic and functional outcomes and long-term maintenance of soft and hard tissues. The horizontal position of implants should have at least 2-mm buccal bone thickness and be at least 1.5 mm away from the adjacent teeth. If two implants are placed next to each other, 3 mm space should be maintained between adjacent fixtures (Figure 6). Maintaining enough space between implants and adjacent teeth is important to avoid the risk of reduced vascularization, bone necrosis and subsequent bone and soft tissue loss, which might cause implant failure (Figure 7).

The vertical position of anterior fixtures should be at least 2 mm apical to the cemento-enamel junction (CEJ) of the adjacent teeth. This vertical distance is important to ensure an adequate emergence profile for the implant crowns, and also to allow for papilla infill to take place a short time after restoring the dental implants (Figure 8).^41–43

If, for some reason, anterior dental implants are placed superficially, this could compromise the emergence profile, and the shape of the implant crown will be square. The volume of connective tissue around the implant abutments will also be limited. In contrast, placing implants too deep or more apically to the adjacent teeth, either electively or due to lack bone height, could result in the implant crown being more prosthetically challenging, with a risk of increased clinical crown height. The shape of the implant crown may also appear rectangular and the papilla may not fully develop to fill the interdental spaces (Figure 9).^43,46

There has been much debate on whether axially placed or tilted implants will have an impact on marginal bone loss. A systematic review on this topic indicated that implant angulation has no effect on implant survival or bone loss.⁴⁴ However, platform-switching has attracted some attention in the past 10 years or so, because it was suggested that platform-switched implants are better in reducing marginal bone loss in comparison to platform-matched implants. A recent systematic review found that platform-switched implants showed less marginal bone loss, but no significant difference was found between both designs in terms of implant survival or the stability of soft tissues around dental implants.⁴⁵

Adjacent teeth

The integrity and location of the adjacent teeth play a role in the shape and volume of soft and hard tissues around dental implants. The development and maintenance of soft tissues around dental implants is dependent on a lack of gingival recession, and having a thick gingival biotype along with sufficient keratinized mucosa on the adjacent teeth.

When the adjacent teeth are periodontally involved or successfully treated, marked recession might develop on the adjacent teeth along with a loss of interdental papillae. If the adjacent teeth have also been heavily restored with root canal treatments and crowns, the risk for bone loss may be increased.⁴⁶ Therefore, it is essential to look into all existing prognostic factors and decide on the longevity of existing restorations and prognosis of adjacent teeth before embarking on complex and expensive implant treatments. Periodontal stability of soft and hard tissues will reduce the risk of future implant complications (Figure 10).

Surgical protocol and GBR

The size and design of the flap are important factors in the reduction of healing time and surgical morbidities, most importantly to avoid potential gingival recessions on adjacent teeth and dental implants. However, over 90% of dental implants in the aesthetic zone need some sort of GBR, and therefore the flap should be modified to accommodate the grafting material volume while maintaining sufficient blood supply and tension-free closure for the placed implants and the surrounding structures. The long-term maintenance of the newly generated bone and soft tissues is quite challenging, as bone remodelling might not develop fully in all parts of the grafted area. Some bone grafts, such as autogenous bone, resorb more quickly than xenografts or alloplastic materials because autogenous bone is subject to osteoclast activity (Figures 11 and 12). To prevent the growth of connective tissues into the grafting materials, a barrier membrane, for example non-resorbable PTFE (polytetraflourethyline) or resorbable collagen membrane should be used to encourage osteoblastic activities. In order to maintain thick soft tissues around dental implants, it is essential to follow protocols to provide the ideal environment for GBR in terms of blood supply and stability of grafted materials.^47–49

However, when the defect is quite significant, and there is horizontal and vertical bone loss, it may be difficult to completely regenerate the lost tissues. In such instances, a block bone graft may need to be considered to rebuild the lost bone horizontally and vertically.

Connective tissue grafts

Connective tissue grafts are considered the gold standard for root coverage surgeries and also for dental implants because they are more stable and produce better quality keratinized mucosa around dental implants. Connective tissue grafts are more technique sensitive and more difficult than free gingival grafts (FGG). However, de-epithelialized free gingival grafts could be used as an alternative to connective tissue grafts because they are more dense, collagen-rich, and more robust around dental implants. Some evidence suggests that the dense fibrous layer in the FGG is more stable and produces better collagen quality around dental implants.^48,49

There are other biomaterials that could be used to replace soft tissues as an alternative to connective tissue grafts (Fibrogide, Geistlich Pharma AG, Switzerland; Mucoderm, Botiss Biomaterials GmbH, Germany; and Mucograft, Geistlich Pharma AG) (Figure 13), especially in patients who are not keen or suitable for a second surgery, or due to the large size of the required connective tissue (Figure 14).⁴⁷