Several factors influence the success of implant treatment. These include basic requirements to the surgical aspect of implant therapy. This module will focus on basic principles of flap design for oral surgery in general and for surgical implant procedures. The aim is to ensure that the surgery can be performed as atraumatically as possible with adequate visibility and access to the surgical area.

After completing this ITI Academy Module, you should be able to: describe flap designs in general, describe flap designs for implant surgery and indicate flap designs for specific situations in implant surgery.

Surgical flaps are prepared to gain surgical access to an area or to move tissue from one place to another. In order to achieve these goals, several basic principles of flap design must be followed to ensure adequate visualization of the surgical field and to prevent possible complications such as necrosis, dehiscence or tearing of the flap. These complications will compromise the blood supply, which may lead to delayed healing, scarring of the soft tissue and even failure of the treatment.

To open a surgical flap, incisions are made into the mucosa. The first incision is the horizontal incision which is made at the crest of the ridge and is therefore also referred to as the crestal incision. When this incision is extended into the gingival sulcus of the adjacent teeth, a limited flap can be elevated as depicted in this diagram.

Vertical incisions are made to allow wider elevation of the flaps to improve visibility and access. One or 2 vertical incisions can be placed depending on the clinical situation and the surgical access required.

To prevent flap necrosis, four basic flap-design principles must be met. The base of the flap should always be wider than the apex, unless a major artery is present in the base. The flaps should have sides that run parallel to each other or converge moving from the base to the apex of the flap. The length of the flap should be shorter than the base. Whenever possible, axial blood supply should be included in the base of the flap. Finally the base of the flap should not be excessively twisted, stretched or grasped since this may damage the blood vessels supplying the flap. Blood supply may be compromised as a consequence of such damage, resulting in flap necrosis and delayed healing.

Flap dehiscences expose the underlying bone, implants and bone augmentation material. They may result in pain, bone loss, loss of augmentation material, delayed healing, increased scarring and potential failure of the treatment.

To prevent flap dehiscences, the initial incision must be placed over healthy bone. After the surgery is completed, the edges of the flap must be approximated again over healthy bone. The edges of the flap have to be handled with care and the flap must not be placed under tension. Hematoma formation must be minimized to ensure close flap adaptation to the underlying bone. The edges of the flap should lie passively close to each other just before suturing. Suturing must be performed with connective tissue opposed to connective tissue to ensure primary closure. No significant force should be used to make the edges line up with each other.

If the edges do not line up, the flap must be mobilized by preparing a horizontal periosteal releasing incision. This incision is made at the base of the flap apical to the mucogingival junction. Care must be taken not to perforate the flap with this procedure. Once the periosteum has been released, the flap can be mobilized and moved coronally.

Tearing of the flap is a common complication when the prepared flap is not large enough for the surgeon to inspect the surgical area. A surgical area that is too small may result in the application of unnecessary force with the tissue retractor and other instruments in order to be able to perform the surgery. A horizontal or one-sided flap along the marginal gingiva of the teeth is usually not sufficient to gain access to a surgical area. Access can be improved by a vertical releasing incision to convert the flap to a two-sided design. As a fundamental rule a vertical releasing incision must not compromise the blood supply of the flap and in general, it is therefore placed anteriorly and at an angle that ensures a broad base to the flap. This can be seen in the diagram as a blue line By contrast an incision parallel to the red dotted line, could cut important vessels and thereby compromise blood supply. For larger surgeries, a three-sided flap may be raised. As demonstrated in the diagram both the vertical releasing incisions are angled to give the flap a broad base to maximize the blood supply.

General Flap Designs, Key Learning Points: Flaps must be raised to ensure maximal visibility of the surgical area. Flaps must be raised without compromising the blood supply of the flap. The flaps can be horizontal, two-sided or three-sided. Horizontal flaps do not usually allow sufficient access to the surgical area.

Raising flaps in implant surgery must be performed in the same way as for any other oral surgical procedure. There are, however, some important conditions that have to be considered. The surgeon must be able to visualize the local anatomical structures. To give an example, an implant must be placed no closer than 1.5-2mm to the mental foramen. For correct implant placement, the mental foramen must be visible in the surgical field during the osteotomy.

The incisive canal and local buccal and lingual bone concavities are other structures that have to be visualized to correctly insert the implant. Radiographic examination may reveal local anatomical variations or pathologies. This information, however, must be confirmed clinically by raising a flap large enough to inspect the area in question. Another reason for raising a proper flap is to prevent damaging neighboring roots during the implant osteotomy. In this clinical example, a well reflected and retracted flap reveals the alignment of the roots of adjacent teeth.

When implant treatment is performed as a one-stage procedure, the implant and the healing abutment are placed in the same surgical intervention leaving the healing abutment exposed. This means the implant is non-submerged during the healing period. In a two-stage procedure the implant is submerged. The two-stage procedure requires primary wound closure to protect the implant and - if needed - the bone augmentation material against bacterial contamination. After a healing period, it is exposed again to place the healing abutment.

Flaps must be raised not only for implant placement but also for bone augmentation procedures. Flaps for bone augmentation are normally larger than the ones prepared for a single implant without simultaneous bone augmentation. This is because the bone augmentation material needs more space and a proper primary flap closure must be ensured. The flap must be raised and mobilized by preparing horizontal releasing incisions of the periosteum.

Cases requiring implant placement in the esthetic zone are classified as Advanced or Complex according to the SAC Classification. SAC stands for Straightforward, Advanced and Complex. Advanced and Complex cases require great care to be taken of the soft tissue. The smallest mistake or unsuitable incision will result in scarring of the soft tissue, which may compromise the esthetic outcome as seen in this clinical image. Damage to the papilla, particularly if there is resorption of the underlying proximal bone on the adjacent teeth, will result in tissue recession leaving black triangles between the neighboring teeth and the implant crown. Any excessive mobilization of the flap may induce a movement of the mucogingival border in a coronal direction as seen in this patient. A large flap was mobilized in a palatal direction during a previous bone augmentation procedure. In patients with a very distinct border between the keratinized and non-keratinized mucosa, in particular, the esthetic outcome may be unsatisfactory. So great care must be taken to preserve the soft tissue at the adjacent teeth.

Flap Design in Implant Surgery, Key Learning Points: Local anatomic structures that are important to the implant surgery must be visible. The flap must be designed to provide adequate access for the planned implant procedure including bone augmentation procedures. The flap must allow for proper wound closure especially with bone augmentation procedures and for implants to be submerged during healing. The soft tissue at adjacent teeth should be preserved as far as possible to obtain a satisfactory esthetic result.

The choice of flap design for implant therapy depends on the treatment plan. It is important to select the appropriate design in advance. It is usually not possible to change the flap design during the surgery if the conditions of the anatomical structures, the amount of bone and/or the amount of soft tissue are not as expected. Therefore the selection of the appropriate flap design depends on thorough treatment planning. The flap design must take into consideration the number and location of implants required to replace the missing teeth, and whether the implants are to be inserted in a one-stage or a two-stage procedure. The amount of bone should be assessed clinically and radiographically to decide if the implant can be placed with or without simultaneous bone augmentation or if bone augmentation should be performed as a separate surgical procedure. A special esthetic risk assessment should be done before placing implants in the esthetic zone to determine if the flap design needs to be varied to minimize esthetic complications.

There are many variations in the design of surgical flaps for dental implant surgery, often with subtle differences according to the clinical conditions and preference of the clinician. Although it is not possible to cover every variation, there are certain situations where specific flap designs can be considered. Horizontal incisions, also referred to as crestal incisions, are usually made in the median position of the ridge. This incision can also be made in a paramedian position, either buccally and lingually to the mid-crest. In this example, a paramedian incision has been made on the lingual side of the ridge.

In this clinical example, there has been significant resorption of the posterior mandibular ridge from the buccal aspect. There is also minimal keratinised mucosa remaining at the crest of the ridge. A horizontal incision placed at the median part of the ridge would result in the incision being made into non-keratinised mucosa. In order to maintain keratinised tissue at the edges of the buccal and lingual flaps, the horizontal incision needs to be made in a lingual position. On flap closure, a region of keratinised tissue is maintained on both the buccal and lingual sides of the implants.

For implant surgery in the anterior maxilla where esthetic outcomes are important, paramedian incisions are made on the palatal side of the crest to increase the volume of soft tissue on the buccal aspect of the implant. Paramedian incisions are also used when bone augmentation procedures are being considered to facilitate closure of the flaps.

A crestal incision, extending intrasulcularly around the neighboring teeth, can be combined with an anterior vertical releasing incision, as seen on these images. This flap design usually provides sufficient visualization of the surgical field in sites with sufficient bone volume, or only minor bone augmentation is required in conjunction with implant placement. It is possible to treat minor residual peri-implant defects and still ensure tension free adaptation incision of the flap with this design.

If the surgeon expects peri-implant fenestration or dehiscence defects that require simultaneous bone augmentation, the flap should be raised using a crestal incision that is combined with intrasulcular incisions on the neighboring teeth with at least one and sometimes two vertical releasing incisions. The aim is to expose the whole surgical area to provide access for implant placement and bone augmentation, and to be able to mobilize the flap for primary closure using horizontal periosteal releasing incisions. In the first example, a 2 sided flap is shown. This consists of a horizontal incision over the edentulous ridge which extends posteriorly by 2 or more teeth, in this case involving the right central and lateral incisors. The flap is then supplemented by a vertical releasing incision on the left lateral incisor. Alternatively, a 3 sided or trapezoid flap can be raised which combines a horizontal incision with mesial and distal releasing incisions.

The trapezoid or the three-sided flap can be recommended for larger bone augmentation procedures such as augmentations using a block graft. In this clinical example a maxillary canine is missing. Due to horizontal bone deficiency on the facial side of the ridge, a bone augmentation procedure with a bone block has to be performed. A crestal incision at the palatal aspect is performed together with two vertical releasing incisions. Reflection of the flap starts anteriorly to gain optimal flap control and overview. The trapezoid flap allows very good visualization of the surgical field. However, more bleeding can be expected because vessels running from the posterior to the anterior jaw region may be cut when the posterior vertical releasing incision is made.

The surgical trauma applied to the soft and hard tissue during implant placement may influence the esthetic outcome of the treatment. To preserve the interdental papillae, a limited flap design may be used. In this type of flap design, Parapapillary incisions are prepared. The interdental papillae are not included in the mucoperiosteal flap but are left attached to the bone at a width of 1 to 2 millimeters. This approach may preserve more of the interproximal crestal bone than a wider flap that includes the interdental papillae. This flap design has drawbacks as the surgical field is small and proper adaptation of the flap can be difficult when simultaneous bone augmentation is performed. This shortcoming could have been overcome by designing a wider flap or incorporating vertical releasing incisions.

Raising very small flaps, especially in the esthetic zones, may be beneficial to the healing of bone and soft tissue. However, the visibility of the surgical area is reduced and will not reveal potential bone concavities or bone fenestrations occurring during implant placement. In addition, simultaneous bone augmentation will be almost impossible to perform. This image shows a clinical example with a missing upper canine. The crestal incision is planned to be performed in a palatal approach as the implant will be submerged during healing. Intrasulcular incisions will be performed on the neighboring teeth. However, after reflection of the flap, it is not possible to get a complete overview of the surgical area as the flap is too small.

Another disadvantage of the limited flap design is the risk of soft tissue scarring, especially if the margins of the flap are not adequately adapted. The visibility of the surgical area is also reduced. This limits the overview of the anatomical structures and of the position and angulation of adjacent roots.

Implants may also be placed without elevation of surgical flaps. This is referred to as flapless surgery and results in reduced morbidity and post-operative pain. However, it is a “blind” procedure and a high level of operator skill and experience is required. Careful planning is necessary with three-dimensional radiographic imaging combined with radiographic and surgical templates. In general, flapless surgical procedures are limited in their indications. In healed sites, there should be sufficient bone volume to allow the implant to be placed in the correct three-dimensional position. A sufficient area of keratinised mucosa must be available to ensure that the soft tissue opening is made entirely within the zone of keratinised tissue.

In extraction sockets, implants may also be placed without elevation of flaps. Prerequisites to perform this approach are intact socket walls and a facial bone wall of at least 1 millimeter in thickness which can be verified at the time of extraction. The soft tissue must be thick and the site must be free of infection. The treatment can only be successful if there is sufficient bone apical and palatal to the socket to allow adequate primary implant stability. According to the SAC risk assessment, immediate implant placement is an advanced to complex procedure. Flapless surgery further increases treatment complexity.

Different Flap Designs, Key Learning Points: Thorough planning is required to choose the adequate flap design. Horizontal incisions are combined with vertical incisions to provide the access necessary to carry out the surgical procedure. Two-sided flaps can be used for implant placement with or without simultaneous bone augmentation. Larger bone augmentation procedures may require preparation of a three-sided flap. Limited flaps may preserve more soft tissue and bone but reduce the visibility of the surgical area. Flapless surgery and immediate implant placement increase treatment complexity and should only be performed by experienced surgeons.

Module Flap Designs, Summary: Flaps must be raised to ensure maximal visibility of the surgical area, but without compromising the blood supply of the flap. Local anatomical structures which are important for implant surgery must be visible. The flap must provide access for bone augmentation procedures. The flap must allow proper wound closure especially for bone augmentation procedures and submerged implant healing. The soft tissue of adjacent teeth must be preserved to obtain an optimal esthetic result.

The choice of flap design for implant surgery depends on the treatment that has been planned. Two-sided flaps can be used for a straightforward implant placement with or without simultaneous bone augmentation. Larger bone augmentation procedures may require a three-sided flap. Limited flaps may preserve more soft tissue and bone but reduce the visibility of the surgical area. Flapless surgery and immediate implant placement increase the complexity of treatment and should only be performed by experienced surgeons.