References
Soft tissue profile around dental implants placed in the aesthetic zone — a biological update
From Volume 45, Issue 3, March 2018 | Pages 247-252
Article
Rehabilitation of missing natural teeth by osseointegrated implants has signified a new advent in restorative dentistry. In the past decade, much of the focus was on achieving good bone to implant contact for the survival and success of implants. Recently, implant dentistry has seen a paradigm shift from focusing on functional restoration to aesthetic integration of tissues.
Regardless of high success rates attained with osseointegrated implants, the peri-implant mucosal response is still not stated clearly.1 For a clinician, restoration in the aesthetic zone has become a complex and challenging task, particularly in sites with deficiencies of soft tissue or bone and, at the same time, maintenance of it has become equally demanding. Simultaneous removal of multiple teeth may often result in flattening of the interproximal osseous scallop and subsequent collapse of interproximal papillae. Hence, management of soft tissues in cases of multiple implant placement becomes more critical. Therefore, for a clinician it is a prerequisite to have a clear vision and understanding of the three-dimensional envelope of soft tissue and bone surrounding the implant to aid in selection of a proper treatment approach.
To date there are neither clearly stated aesthetic parameters in the literature nor does a consensus exist on the most suitable method to use in any particular case. The purpose of this article is to look at various biological factors accountable for the maintenance of adequate soft tissue profile around implants placed in aesthetic zones, that need to be evaluated for a predictable outcome. The final aesthetic outcome is dependent on many variables, including but not limited to, the following:
1. Bony framework
It is well documented in the literature that soft tissues follow hard tissues. Holmes noticed the collapse of interdental papillae following the loss of its osseous support.2 Clinicians may overlook the minimum amount of bone support needed around implant-supported restorations for adequate soft tissue profile. Tarnow et al in his study established the significance of a vertical distance from the base of the contact area to the crest of the bone.3 It was observed that, when the distance was 5 mm, the papilla was present 98% of the time. However, as the distance increased to 6 mm, in 56% of cases the papilla existed and, at 7 mm, the papilla was seen only 27% of the time. A similar study performed by Gastaldo et al correlated the vertical and horizontal parameters between adjacent implants and between a tooth and an implant.4 It was reported that, at a vertical distance of 3 mm, in 100% of cases the papilla was present and, when the distance increased to 8−10 mm, the papilla was absent 60−75% of the time. The author recommended the maintenance of a minimum amount of 3−4 mm of horizontal distance between two adjacent implants (Figure 1a). Thus, it can be concluded that, as there is an increase in distance from the base of the contact area to the crest of the bone, there is a reduced amount of papillary fill, leading to the formation of black triangles and creating an aesthetically compromised result. Studies have reported an average crestal bone loss of 1.04 mm when the inter-implant distance is 3 mm or less, as compared to 0.45 mm crestal bone loss when the distance is greater than 3 mm.5,6 Hence, a minimum of 1.5 to 2 mm of distance is recommended between a natural tooth and dental implant for the stability of peri-implant soft tissues (Figure 1).
2. Biologic width
One of the biological factors that should not be neglected is the biologic width. It is important to understand that soft tissues around an implant behave differently from those around a natural tooth.7,8 Multiple animal and human studies have demonstrated that biologic width around implants is 1 mm longer than for natural teeth.9,10,11,12
The basic difference between natural teeth and implants is the orientation of periodontal fibres. In addition, biologic width around natural tooth is supracrestal as compared to subcrestal formation in an implant. It has been postulated that the formation of the biologic width around dental implants serves as a defence mechanism against bacterial invasion. Tarnow et al have demonstrated that biologic width has both horizontal and vertical components that affect both interproximal bone and facial bone.13 Berglundh and Lindhe have demonstrated that surgically reducing the thickness of a gingival flap prior to suturing would allow for a corresponding remodelling to occur, permitting re-establishment of the biologic width of peri-implant soft tissue to its original dimension at the expense of reduced crestal bone height.14 Henceforth, it is important to maintain the crest in order to support overlying soft tissues. The establishment of a stable biological dimension around implant-supported restorations may contribute to papillary fill and encroachment of this space may lead to bone loss.
3. Keratinized mucosa
It has always been a debatable issue whether the presence of a sufficient band of keratinized mucosa around an oral implant is imperative to maintain longterm tissue health.1,15 Lang and Loe have advocated the presence of a minimum of 2 mm of keratinized gingiva and 1 mm of attached gingiva to sustain healthy gingiva around a natural tooth.16 Some authors believe that the keratinized tissues are more resistant to abrasion and incur less recession, therefore reducing the likelihood for implant failure. In addition, mobile mucosa can result in disruption of the implant epithelial attachment, contributing to the increased risk of inflammation subsequent to plaque accumulation.17,18 In contrast, Wennstrom et al validated that the paucity of attached masticatory mucosa did not jeopardize the long-term health of soft tissues, assuming that good oral hygiene is maintained.19 However, from the available literature, an adequate amount of keratinized mucosal band has been recommended for the maintenance of soft tissue health based on anatomic characteristics and clinical experience.20,21 Thus, 2−3 mm of keratinized mucosa width has been considered as desirable for adequate soft tissue seal around implants.22
4. Biotype of periodontium
Different gingival biotypes respond differently to clinical situations. The periodontal biotype could be categorized into flat-thick and scalloped-thin based on buccolingual thickness.23 Claffey and Shanley defined gingival thickness of 2 mm or more as thick biotype and gingival thickness of not more than 1.5 mm as thin biotype.24
The thick periodontium comprises a thick band of keratinized mucosa, more resistant to inflammation and trauma,25 though it is more prone to pocket formation, but better at concealing metal implant margins.26 In addition, the vascularity is maintained even after surgery and prognosis becomes more predictable as primary closure can be achieved easily. In contrast, thin biotype tissue exhibits compromised soft tissue healing following surgical and restorative treatment and higher susceptibility to resorption of underlying bone.27 Several authors have reported increased incidence of bony dehiscences and fenestrations with thin biotype tissue (Figure 2).28 In some instances, the greyish hue of the implant fixture or overlying superstructure is visible through the mucosa. When confronted with thin biotype, the clinician should consider converting it into thick biotype with gingival grafting prior to implant placement for a more favourable outcome.
5. Existing tooth position
The present gingival silhouette is significantly influenced by the existing tooth position, which should be evaluated in the three planes listed below to ensure predictability and definitive outcome.
1. Vertical or apico-coronal plane
There are studies showing between 1−2 mm of gingival recession in the mid facial aspect subsequent to extraction and immediate implant placement.29,30 If a tooth is already positioned apically compared to its counterpart, extraction of the same would result in long clinical crowns or visible metal margins, resulting in an aesthetic compromise (Figure 4). In such cases, the hopeless teeth with free gingival margin positioned 1−2 mm more coronal to their existing position would be in a more favourable situation for an aesthetically pleasing outcome. Therefore, orthodontic forced eruption before extraction to attain a harmonious gingival level should be delineated.31,32
2. Faciopalatal plane
One study has established a minimum requirement of 1 mm of bone to be remaining on the buccal and palatal aspects following implant placement to reduce the risk of failure.33 Nevertheless, the potential for bone loss decreases when 1.8 mm of bone thickness is maintained on the facial aspect.34 A tooth positioned too far facially will often result in thin or non-existent bone labially.
Moreover, extraction in such instances could result in vertical bone loss with collapse of soft and hard tissues (Figure 2). Since such cases hold a poor prognosis for orthodontic extrusion, bone augmentation and socket preservation procedures would be a better treatment option prior to the implant placement.
3. Mesio-distal plane
The proximity of the adjacent teeth essential for optimal proximal support and volume of the interdental papilla should be assessed by the clinician prior to the commencement of treatment. The mesiodistal width should be equal to its contralateral tooth. Excessive or deficient space should be corrected with the use of orthodontics, enameloplasty or restorations.
In addition to proximity of the crown structure, the root proximity is also influencing papilla volume. Roots positioned in close proximity possess thin interproximal bone, which increases the risk of lateral resorption resulting in reduced vertical height of the papilla following extraction or implant placement. Nevertheless, maintenance of 1.5 mm of interproximal bone width at the crest can prevent the violation of biologic width.35
6. Form of periodontium
The gingival scallop could be categorized into high, normal and flat forms.36 In health, the underlying bone crest remains 2 mm apical to the cemento-enamel junction and trails the scallop of the gingival margin.37 The higher the scallop of the gingival margin, the gingival loss is likely to be greater following tooth extraction. In instances where the scallop is flat, post extraction changes in contour are reduced.37
7. Tooth shape
Tooth shape is another factor influencing peri-implant aesthetics. Square, ovoid and triangular forms are the three basic tooth shapes. It must be emphasized that tooth form affects soft tissue profile, both coronal and apical to the free gingival margin. The volume and height of the gingival embrasure will affect the coronal aspect. The proximity of the roots and support of gingival tissues, both facially and intrproximally, would be influenced by the apical aspect.35
It is interesting to note that a square form would present the most favourable clinical situation as the proximal contacts are longer, therefore the tooth portion would occupy the majority of the interdental area, leaving little room for the papillary fill, thus reducing the probability of a black triangle appearance. In contrast, the triangular form presents the highest risk for an aesthetic compromise since the proximal contact point is positioned more incisally and would necessitate a greater volume of tissue to fill the interdental area. Therefore, even the slightest deficiency would produce a compromise.
In addition, triangular tooth shapes allow roots to be positioned further apart, providing thicker interproximal bone, and aid in minimizing vertical bone loss. In contrast, square and ovoid tooth forms are at greater risk of bone loss as the osseous crest is thinner. In summary, square tooth forms pose less aesthetic risk compared to triangular tooth forms.
8. Smile line
The fabrication of implant-supported restorations for cases with a high smile line in the maxillary anterior region is a formidable task, since the gingival tissues are completely exposed (Figure 3). In such situations, maintenance of peri-implant soft tissues during the surgical, provisional and restorative phases is demanding. In contrast, the patients exhibiting low smile lines is less of a concern for the clinician since the upper lip would hide the interface present between the restoration and soft tissues. Some patients with high aesthetic demands will lift their lip up to inspect the work.
Summary
An unaesthetic yet functionally acceptable result is not desirable but may be acceptable for some patients. Even the slightest lack of planning can result in severe cosmetic deficiency. The final aesthetic outcome depends on multiple variables that include biological, surgical, implant design and surfaces and prosthetic factors. However, compared to other variables influencing soft tissue profile, biological factors that are closely interrelated to each other are the most difficult to manipulate. Attention to detail in the assessment and provision of implant treatment is important to avoid an aesthetic compromise. Some biological factors are not under the control of the clinician. Any likely compromise should be explained to the patient in advance of treatment. Commendable research has been carried out in this field. Therefore, it is a prerequisite for a clinician to keep updated for the delivery of the best possible patient care.