Implant therapy began with the primary goal restoring function. For the past several years, dental esthetics has become an important component that is paramount to achieving success in implant therapy. In the esthetic zone, less than optimal results often lead to catastrophic clinical situations leading to implant removal followed by extensive augmentation procedures or compromised treatment outcomes. It is important for the clinician to have a conceptual understanding of the key principals associated with a successful esthetic outcome. Every therapy should include thorough knowledge of the patient's desires, which in most cases is beyond just tooth replacement. To facilitate an esthetic outcome, a team approach using an experienced surgeon, a restorative clinician, and a dental technician is essential.
The decision a surgeon is often faced with is whether or not a gingival flap needs to be raised in a given clinical scenario. If a flap is deemed necessary, the incision and flap design in the esthetic zone are critical in achieving an optimal esthetic outcome. The specific aim of this article is to outline various important factors that influence healing, discuss the advantages/disadvantages of several key incision/flap designs, and to help guide the clinician in treatment planning tooth replacement in the esthetic zone.
Enhancement of Final Esthetic Outcome
Basic Surgical and Wound Healing Principals
In any surgical procedure, incisions are designed based on anatomical location, surgical technique, and desired healing outcome. A flap can be designed according to which tissues are included (full vs partial thickness), the number of incisions used to create them (envelope, papilla sparing, triangular, trapezoidal), or by secondary incisions that dictate the flaps direction (rotating vs coronally vs apically advancing). Irrespective of the design or number of incisions used, a flap by definition retains a portion of the native blood supply to continuously perfuse the tissue.
Vascularization has been shown to be paramount for all healing and regeneration. Each flap design should begin with consideration of the blood supply beginning with the base to the edentulous midcrestal area, inclusion/avoidance of any adjacent papilla, and if necessary the location and termination of any releasing incisions.1,2 Using an animal model, it has been shown that a wider base is necessary to maintain perfusion to reflected tissue.3,4 However, even with a wider base, vessel perfusion was compromised for at least the first 7 days.2,4 It is noteworthy that in the midcrestal region of an edentulous alveolar ridge, there is a 1.0 to 2.0 mm wide avascular zone with no anastomoses or crossing of the alveolar ridge.1,2 Any incision in the midcrestal area of an edentulous space is a safe and predictable location to begin without disruption of the blood supply.
Adding vertical releasing incisions is dependent upon the amount of release and visualization needed for any given procedure. The more pronounced the vertical and horizontal hard and soft tissue loss, the more critical the need to add vertical releasing incision for advancement of flap and tension-free closure. When incorporating vertical releasing incisions into a flap design, whenever possible, priority must be given to locate them outside the esthetic zone, avoid any buccal root prominence, and make them as long as needed but as short as possible.1,2 When indicated, a vertical releasing incision should be made to ensure adequate flap release and tension free closure.5,6 If a site requires hard tissue augmentation, then the vertical release should be extended into the vestibule with scoring of the periosteum to provide proper release and tension-free primary closure.6 If soft tissue grafting is required, then any vertical releasing incisions should extend to the vestibule to be able to coronally position the flap to cover any grafting material, taking care to apply the proper amount of pressure to eliminate dead spaces or hematoma formation.6,7 Any healing of the oral mucosa will occur through the same predictable stages as the rest the of body's tissues.8,9 In general, it has been found that the oral mucosa is less prone to scar formation potentially because of reduced numbers of macrophages in the tissue and the presence of growth factors in saliva.8,9 However, by comparison, in the oral cavity attached keratinized tissue has shown reduced scar formation while the buccal mucosa is slightly more prone to scar formation when incised.10 That being said, studies have shown that flap tension and margin adaptation are increasingly important as tissue shrinkage and wound dehiscence amplify the likelihood of scar formation.3,11
Providing primary closure in such a way so that the incision is not directly over a defect is important for uneventful healing and the survival of any grafted material.3 Preoperative planning that involves radiographic 2 (Peri-Apical, Bitewing, Panoramic) and 3 dimensional imaging (Cone Beam Computed Tomography) can influence incision and flap design but the extent of the defect must also be determined clinically via bone sounding and probing. Incomplete coverage of graft material or wound dehiscence is the most common problem associated with grafting procedures and compromised healing.12 This problem can be exacerbated in the interproximal areas because of surgical technique even if there is apparent tissue approximation and primary closure.12 Therefore, whenever possible, incisions should be designed to be at a distance of at least 3 mm from any boney defect to ensure closure that is well separated from the grafted area and elevated on both sides of the wound margins.3,12
In the literature, there is an association with full-thickness flap elevation and predictable tissue loss (0.5 mm) because of the disruption of the periosteum.6 With regard to vertical bone loss and flap elevation, there is an abundance of contradictory data reported as to which technique is superior.6 However, when a comparison was done between flap elevation with papilla sparing (0–1.0 mm) verses flap elevation with papilla elevation (0–3.5 mm), the amount of interproximal tissue loss was far less on a papilla-sparing flap/incision.6 It is for this reason that if either the papilla preservation technique or a flapless surgical technique can be used, there will be a far more predictable outcome with respect to the interproximal bone loss and healing.6 This becomes even more critical in thin biotypes where any surgical insult to the periosteum and supracrestal gingival fibers may result in more significant interproximal tissue loss.
Anatomical Factors and Considerations
It is essential for the clinician to have an in-depth knowledge of ridge anatomy for site analysis that provides the basis for successful implant planning and placement. This starts with an esthetic risk assessment, introduced by Levine and Martin and was adapted from the International Team for Implantology's straightforward, advanced, complex Classification of Implant Dentistry.13,14 This assessment is to be used before treatment commences and weighs the individual's risk factors involved in the esthetic zone.14 These risk factors should be made known to the patient before treatment starts to avoid any misunderstanding with expectations.
The clinician should begin with an extraoral assessment and includes the patient's smile line. As expected, a patient with a high smile line will require the most attention to detail throughout the different phases of treatment. However, even in patients with a low gingival smile line, it was shown that the interdental papilla is displayed in 87% of patients.15 No gender differences exist in anterior tooth display during smiling, however, females tend to show more maxillary gingiva.16 Another consideration is whether or not there is restorative commitment from the patient to address the whole smile. The restorative status of the adjacent teeth also plays a role, whether they have been restored previously or are virgin teeth. The width of the edentulous area is a factor, whether it is a single tooth replacement or if it adjacent implants are to be placed. Features and determination of the gingival biotype play an important role in planning for esthetic implant placement. Extreme caution should be taken with patients that present with a thin biotype as they will often have existing gingival recession around teeth and implants.17 A thin biotype with prominently scalloped tissue will require soft tissue augmentation to add thickness to cover any titanium show through. Crestal bone height and width plays tremendous importance in the development and long-term stability associated with a successful esthetic outcome. Many times, potential implant patients present with a bony crest that is deficient in height and width because of the various causes of tooth loss and extraction techniques. Any attempt to place implants in sites with significant bone defects and no attempts at reconstruction will frequently end up with gingival recession. Areas with deficiencies in the buccal plate should be corrected surgically by using a barrier membrane and bone grafts/substitutes. Crestal bone height also plays a significant role in the presence or absence of a papilla. A clinical study on the evaluation of papilla level adjacent to single-tooth implants showed almost 100% papilla fill when the distance from the contact point to the crest of bone was 5 mm or less.18 Another clinical study evaluated the height of the papilla compared to crestal bone in adjacently placed implants and showed an average of 3.4 mm of papilla height measured from the interimplant bone crest.19
Guidelines for implant placement can be generally summarized stating that the implant–abutment interface at the alveolar bone crest should be 3 mm apical and 2 mm palatal to the gingival zenith.20 These guidelines take into consideration our understanding of the biologic width along the abutment and the stability of thicker tissue buccal to a newly placed implant. In surgery, a flapless approach is often preferred to preserve the soft tissue esthetics. Single implants placed with a flapless approach showed less soft tissue recession when compared with a flap approach.21 Maintenance of supracrestal gingival fibers has been shown to predict postsurgical attachment levels.22 There is a clearly defined relationship between crestal bone height and the stability of soft tissue determinants of esthetic success.20,23 A direct relationship is found between the most coronal position of the interproximal bone height and the consistent development of an esthetic soft tissue profile.24 Here, for predictable soft tissue esthetics, a crestal bone height of 5.0 mm or less is necessary.17 It has been shown that resorption of the buccal bone after extraction results in substantial vertical reduction of the buccal crest.25 Immediate implants placed with the flapless technique do not prevent alveolar bone resorption and have no effect in the dimensional changes of the extraction socket over time when compared with immediate implants placed with a flap.26 Both flapless and flap implant placement techniques result in high success rates, however, a flapless protocol avoiding potential scars and trauma to the supracrestal gingival fibers may provide a better esthetic outcome in certain clinic scenarios.27 The different flap and incision design applicable to each scenario are critical to understand and will be discussed in the following section.
Types of Incisions and Techniques
If there is an abundance of bone, adequate keratinized tissue, and acceptable osseous contour, a flapless technique can be used. However, there is inherent risk associated with not being able to visualize the underlying buccal and palatal osseous architecture. Flapless surgery utilizes most commonly a tissue punch device of varying diameters (3.0–6.0 mm) but in less than ideal situations a scalpel can be used to minimize any loss of keratinized gingiva as well as maximize tissue volume for better emergence profile (Fig. 1A). This is done to gain access to the alveolar ridge.1,11 Similar to an atraumatic extraction with immediate implant placement, there should be minimal disruption of any of the gingival tissues, in particular the gingival fibers and blood supply.
In the edentulous site, the tissue punch is directed through the mucosa and the gingival tissue removed only in the area where the osteotomy will occur and the implant is to be placed. This has been associated with some perceived advantages, most importantly the preservation of the blood flow to the papilla and surrounding soft tissues as well as increased postoperative patient comfort and recuperation.11 There are several noteworthy disadvantages for the surgeon. The lack of visibility of any underlying anatomical structures or defects coupled with the inability to manipulate soft tissue is the obvious complications to the flapless surgical approach.11 In addition, this minimally invasive approach leads to the reduced ability to contour osseous architecture either through an additive or subtractive measures, increased risk for malposition of the implant, and increased risk of thermal damage to the underlying bone.11 This approach should not be taken unless the experienced surgeon is fully confident in executing implant surgery and potential complications that may arise using this approach.11
Although several minimally invasive techniques have been reported and developed over the years, such as the linear flap or semilunar flap,28 a recent technique that allows preservation of interproximal tissue and allows access for buccal ridge contouring and soft tissue grafting is the vestibular incision technique.29 The vestibular incision technique is another minimally invasive flap one can use during implant placement (Fig. 1B). One recent version of this, known as subperiosteal minimally invasive aesthetic ridge augmentation technique, avoids traditional flap elevation, the use of a membrane, and tenting screws.30 The technique involves one or more full-thickness vertical incisions in the vestibule kept away from the gingival margin and sulcus. These incisions are typically located at the midline in mucosa where the most coronal portion of the incision is terminated well above the high smile line (Photo 1). Therefore, any scarring afterwards from the incision is kept above the smile line (Photo 2, A and B). The number of incisions used depends on the extent of the area the graft is planning to augment. After elevation, a subperiosteal pouch was created to accommodate the bone graft. This technique is associated with some limitations, which include lack of visualization of the underlying osseous structure as well as difficulty in predictably manipulating biomaterials under the pouch, especially if greater amount of bone is missing and planned to be augmented. However, the avoidance of soft tissue complications/disfigurements as compared with flap techniques and the avoidance of disruption of blood supply, use of membranes or tenting screws are but a few of the perceived advantages (Table 1).
A full-thickness flap is indicated when the surgeon's access must accommodate grafting of any existing defects or osseous recontouring. There are many slight variations to this technique based on different factors such as the width of keratinized gingiva present on the buccal flap margin, the vestibular depth, the extent/type of the defect, and the number of implants placed.11 Resective contouring or crown lengthening may be indicated based on preoperative or intraoperative esthetic evaluations. These can only be accomplished with a full-thickness flap that may incorporate one or more releasing incisions.
The papilla-sparing technique, as described by Greenstein and Tarnow,6 avoids papilla elevation (Table 1), which may help to prevent its loss, which is highly desirable goal in the esthetic zone. Reflection of a full-thickness flap on the palate as well as gentle release of the buccal tissue allows for the inspection of any hard tissue defects as well as augmentation, if indicated, without disruption of the papilla. The papilla-sparing incision (Fig. 2) begins with a horizontal incision along the midcrestal or palatal ridge and terminates 1.0 mm from the adjacent teeth. This 1.0-mm thickness is an arbitrary thickness and it is possible that variable bands in thickness or widths of tissue could be left intact and be successful.6 If there is an indication to try and increase keratinized tissue on the buccal, this horizontal incision can be made more on the palatal aspect of the ridge and repositioning the tissue to the buccal. When this repositioning technique is used, the surgeon must keep in mind where the location of the avascular band of tissue is located and anticipate the potential for tissue necrosis (Photo 4).1 Next, bilateral buccal vertical releasing incisions that extend obliquely at an angle should connect to the horizontal incision (Photo 3). The length of the vertical incision will be extended if any grafting is required. If more access is needed, the option to extend vertical incisions bilaterally on the hard palate can be added.6 An indication for this flap is a patient with a thin gingival biotype, in which preservation of the interproximal tissue level is of utmost importance.
The envelope flap has limited expansion potential to allow for any graft material; however, it can allow for proper visualization of the surgical site. An envelope flap (Fig. 3) is designed with a midcrestal incision over the implant site followed by sulcular incisions on the buccal and palatal that extend at least one tooth to the mesial and distal (Photo 5). A full-thickness flap is reflected using blunt dissection. The scarring from vertical incisions will be avoided with the use of the envelope flap (Photo 6). A distinct advantage of the envelope flap is that upon reflection, if there are any indications of osseous defects or potential implant placement complications, vertical releasing incisions can be added to create a triangular or trapezoidal flap (Table 1). If extensive bone grafting procedures are to be completed during the procedure, the clinician should realize this flap design is contraindicated because of limited access and an increased risk for tension upon closure.
Triangular and Trapezoidal Flap
A triangular (Fig. 4) and a trapezoidal flap (Fig. 5) both begin with the same midcrestal incisions over the implant site and sulcular incisions that continue horizontally to at least one adjacent tooth. A vertical releasing incision is then extended apically above the mucogingival junction.31 These vertical incisions are typically located distal to the canine to help conceal any scaring that may occur during the healing process. Periosteal releasing incisions are then placed to aid in flap advancement to gain tension-free primary closure.31 A distinct advantage in using a triangular of trapezoidal flap is that direct visibility of bone is obtained, which allows for great access to bone recontouring as well as bone grafting and can provide low to no tension on closure (Table 1). A contraindication to both flaps is a patient with thin gingival biotype and space limitations (mesial-distal) because of the interproximal bone loss one can expect as a result of lifting these flaps. These full-thickness flaps should be adapted to obtain circumferential closure around the emerging implant abutment or to gain primary closure in a 2-stage approach.31
Any surgical procedure takes time to properly plan and execute. A multidisciplinary approach with comprehensive treatment planning along with proper case selection for each technique will help to minimize complications. The specific aim of this article highlights the important factors that influence healing leading to predictable esthetic results. The planning and design of any incision in the esthetic zone should be carried with careful consideration and made specifically with the desired end point or esthetic result. Treatment planning with an emphasis on patient driven results can be more easily established with the diagnostic mock up or even an esthetic try-in at initial phases of therapy. Each surgery should be planned using a multidisciplinary approach and based on biologically predictable results. A flapless approach or the vestibular incision technique, when indicated, minimizes surgical procedures and incisions in the anterior maxilla which are critical in achieving predictable esthetic outcomes. Therefore, before any surgical procedure, proper consultation that involves a discussion of the expected outcomes along with all the treatment options should be completed with the patient by the treatment team.
The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
Roles/Contributions by Authors
S. D. Beauchamp: Primary coauthor—helped prepare the first and final draft of the manuscript. L. H. Hutchens: Primary coauthor—helped prepare the first and final draft of the manuscript. S. H. McLeod: Illustrator and advisor—illustrated the flap designs in the manuscript. J. K. Stern: Coauthor and correspondent—helped guide the conception of the manuscript, played an advisory role with regard to the content.
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