Critical factors for esthetic central incisor implant restorations

Clinicians must understand the critical factors to achieve an esthetic implant restoration. These principles can be demonstrated using the central incisor tooth as the example, with applications to other teeth.

The central incisor is the dominant tooth in the smile (Figure 9-1). Gingival problems, such as recession of the facial gingival margin, clefts, scars from vertical incisions, lack of papilla, discontinuous bands of keratinized gingiva (KG), and changes in gingival thickness all have a major effect on the final esthetic restoration. These problems must be prevented or compensated for to provide the patient with an esthetic tooth rather than simply a crown on an implant.

Six related areas must be evaluated preoperatively for implant restoration of the single central incisor, as follows (Figure 9-2):

Bone and soft tissue

Four walls of bone surround the implant. Palatal bone is often present and minimally prone to resorption after tooth extraction. If lost from caries or trauma or palatally located external tooth resorption below the alveolar crest, vertical bone deficiency may need to be reconstructed with interpositional grafting or other methods. However, palatal bone defects in the presence of adequate interdental and labial bone may need less grafting to achieve a healthy long-term solution.

If the mesial or distal interproximal bone has been lost on the adjacent tooth, loss of papilla results from loss of bone support. To correct this problem, the adjacent tooth may need to be extruded with orthodontics to reposition the soft tissue and may require tooth removal and additional crestal grafting to allow for an esthetic result.

A periapical radiograph can be used to assess the crestal level of bone on the adjacent teeth. If the bone is at the level or within 1 mm of the cementoenamel junction (CEJ) of the adjacent teeth, papilla support is expected. Ryser et al.³ found that the most critical factor for predicting papilla in the final restoration was the distance of bone from the contact point of the teeth to the level of bone on the adjacent teeth. Thus, a periapical radiograph combined with the observation of adequate papilla before tooth extraction is often the basis for predicting the esthetic quality of the final restoration (Figures 9-3 to 9-8).

Loss of bone occurs most often on the labial surface (see Figures 9-5 and 9-6). If labial bone loss is limited to 3 mm from the planned gingival margin, the implant can be placed at the level of the remaining bone with minimal esthetic compromise as long as the original position before tooth extraction of the facial gingival margin is appropriate and the gingiva has adequate thickness. If gingival recession is present, extrusion of the tooth may be necessary to reposition the facial gingiva.

Loss of greater than 3 to 6 mm of bone

Labial bone defects may be small, narrow, linear bone clefts, wide U-shaped defects, or loss of the entire labial surface. If the defect is narrow and linear in nature, an implant can be placed and the gap and narrow defect grafted with either allograft alone, sintered xenograft alone, or allograft within the socket with xenograft onlayed.

Loss of all of the labial bone

This situation requires grafting to reconstruct the missing labial bone to allow for future implant placement in the correct position. At the time of tooth extraction, a particulate graft is placed within the socket to promote bone formation, which will be essential to achieve implant integration. When there is a large labial bone defect, the allograft within the socket is covered with a thin layer of sintered xenograft to augment the ridge contour.

The patient with thick gingiva may have significant labial bone loss without gingival recession. The facial gingival margin is ideal even though labial bone loss exists. These patients have an excellent prognosis for a great result. If labial bone loss from chronic disease is present in a patient with thin gingiva and if gingival recession is present, the prognosis is guarded. These cases may require connective tissue grafts to convert thin to thick tissue. If not properly treated, the final result is compromised with a “long” tooth. Adjunctive procedures on the adjacent tooth such as crown lengthening may be necessary to achieve esthetic symmetry.

Labial orientation of the implant results in gingival recession because of the labial position of the implant (see Figure 9-7, A and B). When a crown is placed on a labially positioned implant in the esthetic zone, excessive gingival contour results in apical migration of the gingiva. This situation often requires removal of the malposed implant to gain a final esthetic result.

Prognostic factors

Factors to consider in determining whether a single-implant restoration will be esthetic include the gingival margin, loss of labial bone, and implant positioning.

Gingival margin of the tooth before extraction or after healing

A key clinical sign used to predict the final esthetic result is the position of the facial gingival margin as it appears before extraction of the tooth. If the gingiva is not healthy or appears hyperemic, with evidence of granulation tissue, healthy gingival levels after implantation may result with the facial gingival margin apical to the ideal location. In this clinical situation, the tooth to be extracted should be treated prophylactically to allow the gingiva to heal and achieve health, if possible. A healthy gingiva can be used to predict the final position of the facial gingival margin at the conclusion of the implant restoration.

If the gingival position is 1 to 2 mm apical to the adjacent tooth, the final gingival position will most likely be no better than 1 to 2 mm apical to the gingiva on the adjacent tooth unless specific procedures are followed, which are illustrated in this chapter. To correct this problem, the tooth to be extracted may need to be orthodontically extruded, the tooth and bone moved coronally by an osteotomy, or the site grafted around a healing abutment with a concave subgingival contour. Orthodontic force eruption of a tooth can move bone coronally, and the gingiva will move coronally as well. Grafting the gap between the implant and labial bone at the time of implant placement with sintered xenograft and the use of abutments with a subgingival concave shape will facilitate soft tissue thickening and genesis.

Many patients choose to avoid orthodontic therapy because of the cost, esthetics, and time factors. Patients also may choose to avoid interpositional osteotomies because of the extent of the surgery. Patients would rather adjust the adjacent tooth by using a simple and predictable crown-lengthening procedure, with or without a prosthetic procedure (e.g., laminate). The severity of the problem from one patient to another determines the recommended therapy.

The observation that pre-extraction gingival levels are predictors of the final gingival position holds true even with extensive labial bone loss in the presence of a thick gingival biotype. As long as (1) the surgical procedures are performed with minimal trauma and avoid excessive tension on closure, (2) the restorations—temporary and final—are not overcontoured at the cervical margin, and (3) the implant is positioned 2 mm palatal to the labial emergence of the restoration, an esthetic restoration can be achieved. In contrast, if the surgery traumatizes the gingival margin by laceration, excessive tension on closure, the use of too many sutures, the use of numerous simultaneous procedures, overcontouring of the implant, or malpositioning of the implant, a poor esthetic result occurs.

Loss of labial bone

When a tooth is removed, a labial bone defect may exist. The ideal graft result is a ridge that has a convex profile that simulates an underlying tooth root, such as the root prominence. As a labial bone defect increases in dimension and shape, the final bone graft bulk may result in a flat, rather than a convex, root prominence. Therefore, soft tissue augmentation or further hard tissue augmentation with a nonresorbable material may be needed. If the ridge crest is exposed and found to be flat but sufficient for implant placement, the establishment of a root prominence is essential because of the smile line. In this situation, sintered xenograft can be placed over the ridge to “plump” the ridge form, establishing a root prominence (see Figure 9-8).

When the single-tooth edentulous site in the central incisor region is examined, four surfaces of bone need to be evaluated. The mesial and distal interproximal crestal bone surfaces on the adjacent teeth determine the bone support for the papilla. The interproximal bone level on the adjacent tooth is the most critical bone determinant of papilla support³ (Figure 9-9).

The level of the palatal bone is important in predicting success in restoring the horizontal width of the ridge. If the palatal bone height is compromised, the resultant vertical height deficiency may be difficult to restore. In this situation, options include routine crown and bridge restorations with soft tissue grafts to augment the ridge under a pontic, placement of an onlay bone graft, or an interpositional osteotomy with either immediate or distraction osteogenesis to achieve vertical ridge augmentation.

The labial bone that supports the facial gingival margin of the tooth must be restored to provide bone support for the final restoration. Labial bone loss is common because the labial bone thickness over an anterior tooth is very thin. This thin bone is lost secondary to periodontal disease, caries, fracture of the tooth, and recession by attrition. If the tooth is extracted and the site is not grafted, labial bone resorption results in a less-than-ideal ridge width.

Bone can be restored to the width of the bone at the mesial or distal surfaces facing the adjacent teeth. It is difficult to establish long-term maintenance of the convex ridge profile after this bone has been lost. In the thick gingival biotype, this is less of a problem (Figure 9-10). In the thin biotype, however, it is a significant problem. The lip line must be assessed. Often the problem can be solved by using carefully designed crown contours. The use of temporary prostheses is critical in these patients to develop optimal gingival architecture.

Orthodontic extrusion of a tooth before its extraction can move the gingival margin from an unaesthetic apical position to an ideal position. When the tooth is extruded, if the tooth movement is directed labially, labial bone loss occurs. At the time of tooth extraction, the facial gingival margin will be excellent, but a labial defect will be present and will require grafting. Because the gingival margin has been corrected, the case has a very good esthetic prognosis because when the gingival margin is at an ideal location before extraction, the implant restoration has an excellent prognosis to achieve excellent esthetics.

Crestal bone remodeling around an implant may result in apical migration of the facial gingival margin. When an implant has a flush abutment–implant interface or a smooth collar, bone remodels to approximately 2 mm from the interface. Gingival migration may occur with movement of the facial gingival margin up to 2 mm. Implant designs that medialize the abutment implant interface and use a rough surface at the location of the crestal bone are purported to preserve crestal bone, with less chance of gingival margin migration because facial bone is preserved. Even with a medialized interface, space juxtaposed to the medialized interface must be present to develop adequate thick gingiva around the implant.

Implant positioning

For a single-tooth replacement, two considerations are important when positioning the implant. First, the implant should be placed equidistant from the adjacent teeth. This allows for symmetry of the final restoration. If the space is excessive, a diagnostic setup determines the specific location of the implant.

Second, the position of the implant labial to palatal is critical to achieve an ideal restoration. If the implant is labially positioned, the gingival margin around the restoration will be apical to the planned restoration. A labially positioned implant also is prone to labial bone loss or bone dehiscence. From the implant’s shoulder, the abutment emerges labially, and the crown also emerges labially. The implant’s labial edge needs to be positioned approximately 2 to 3 mm palatal to the labial edge of the planned restoration. If the clinician draws a line connecting the labial surfaces of the adjacent teeth, the labial edge of the implant is placed 2 to 3 mm palatal to this line.

Diagnosis, treatment planning, and surgical techniques

To establish the treatment plan, the surgeon and restorative dentist initiate a diagnostic phase at the patient’s first visit. Articulated models are used to create an esthetic diagnostic tooth setup using wax or denture teeth to determine the extent of missing hard and soft tissues. The planned restoration is used to determine the need for hard and soft tissue grafting.6–12 The use of virtual tooth setups can be used to simulate tooth positions, eliminating the need for study models and wax setups. The virtual plan can be milled into a mask and tried in the patient’s mouth. In the future, the use of digital methods rather than laboratory models will dominate the market.

In a series of 100 consecutive cases of single anterior maxillary implants treated with a traditional two-stage technique, fewer than 20% of patients had adequate bone and soft tissue with no need for hard or soft tissue grafts. Another 20% of the single anterior maxillary implant sites appeared to have adequate bone, but soft tissue thickness was deficient, requiring only an adjunctive soft tissue procedure after implant placement. The most common finding for esthetic implant sites was inadequate bone and soft tissue, requiring both bone and soft tissue augmentation.¹³

Patients have either a tooth in need of extraction or an edentulous space from a prior extraction. When extracting a tooth with plans for its replacement with an implant, the clinician must decide whether to perform an immediate implant placement or a delayed placement.^10,14–18 Implants are not placed at the time of extraction when signs of infection are present. These signs include severe pain, the presence of granulation tissue, hyperplastic and hyperemic gingiva, periapical radiolucency, serous or purulent exudate, and lack of adequate bone for the restoration. If an infection occurs after placement of an implant in the esthetic zone, severe gingival compromise results, and an ideal esthetic restoration is difficult to achieve. Therefore, delaying implant placement for a short period time to allow for resolution of the infection after tooth extraction is the safest method for esthetic implant restoration. However, delaying implantation may result in loss of labial bone. Careful clinical judgment needs to be used in these cases.

At the time of tooth extraction, the plan should anticipate resorption of the labial plate of bone regardless of the method chosen. When the implant is not being placed at the time of tooth removal, a material, which will turn over to form bone, is placed within the socket. A labial onlay of sintered xenograft will maintain ridge contour and result in less flattening of the grafted site. The sintered xenograft has a very slow turnover rate and hence will maintain ridge contour even when the underlying labial cortex resorbs.

When extracting a tooth in the anterior maxilla, incisions are made within the sulcus but without vertical release. The tooth is minimally subluxed and removed with preservation of the labial bone if present. Gentle curettage is performed to remove granulation tissue from the socket. The walls of the extraction site are gently probed to determine the amount of bone available when the implant is placed. The natural healing response of the extraction site forms woven bone within 8 weeks. If labial bone is missing, grafting within the socket is performed with mineralized bone allograft, with an onlay of sintered xenograft (bovine or equine) to prevent excessive hard tissue grafting 3 to 4 months later (Figure 9-11). Techniques used to replace the missing tooth temporarily include a removable partial prosthesis, bonding a temporary pontic to the adjacent teeth, or the use of a type of Essix device.

The first choice in most cases is to place an esthetic provisional tooth at the time of implant placement. If this cannot be achieved, then it is desirable to place an anatomically correct healing abutment followed by a conventional, subgingival concave healing abutment if an anatomically correct healing abutment is not available.

Most anterior maxillary single-tooth sites have inadequate bone and soft tissue, requiring both bone and soft tissue augmentation. The height of the papilla reflects the underlying crestal bone height on the adjacent teeth.^11,19 Careful assessment of the bone levels on the adjacent teeth enables the surgeon and restorative dentist to inform patients of the realistic expectations of retaining or creating papilla for an esthetic single-tooth restoration. For example, when the level of crestal bone on a central incisor is apical to the CEJ of the incisor and the distance from the crestal bone to the proposed contact of the lateral incisor single-tooth implant restoration is greater than 7 mm, the chances of achieving adequate papilla are low.^19–21 Patients are counseled before surgery concerning the realistic expectations of the papillary prognosis based on the adjacent bone–tooth height relationship. For patients with 7 mm or greater distance from the contact area to the crestal bone, papilla-sparing incisions are used rather than sulcular incisions and an enveloped reflection.

Decisions affecting treatment

The decision tree in Figure 9-12 outlines the major choices the surgeon and restorative dentist face when placing anterior maxillary implants, as well as implants for other sites in the jaws.

The first decision concerns the adequacy of alveolar bone. Is the alveolar bone width satisfactory? Is the alveolar bone height satisfactory? The preoperative physical examination and the diagnostic setup, with appropriate radiographic studies (e.g., panoramic and periapical views and tomograms), should provide the surgeon with an accurate understanding of the anatomy of the surgical site as follows (Figure 9-13):

1. If both the alveolar bone width and the alveolar bone height are satisfactory, the implant can be placed without hard tissue grafting.

2. If a vertical bone defect is present with adequate alveolar bone width, an onlay bone graft or other bone-regenerative process is indicated before placement of the implant.

3. For thin bone, which is slightly less than or greater than the diameter of the implant, the implant can be placed and the area grafted simultaneously as long as the vertical height of bone is adequate. Grafting the labial surface helps form a root eminence, which enhances the natural appearance of the final restoration.

4. If the vertical alveolar bone height is deficient along with a thin ridge, an onlay graft or other regenerative procedure is indicated before the implant is placed.

5. If the bone is severely thin, preventing implant stability at placement, with or without a vertical defect, an onlay graft or other bone-regenerative procedure is indicated before the implant is placed.

Sufficient bone width and height

In patients with sufficient bone width and height, implants can be placed with minimal surgical incisions, without vertical release incisions, on the facial aspect of the ridge. Avoiding incisions along the facial aspect of the ridge in the esthetic zone increases the potential for an exquisite esthetic restoration of the missing tooth. At the time of implant exposure, a small, semicircular incision can be used to avoid vertical incisions. The resultant restoration then is surrounded by gingivae that show no scars from incisions.

At surgery, preoperative photographs are taken before the administration of a local anesthetic. The ridge shape is examined, and the surgical guide is tried in place to allow adjustments, if necessary, while the local anesthetic takes effect. The local anesthesia should extend superiorly into the piriform rim to anesthetize the nasal floor because many anterior implants are placed engaging the nasal floor.

Patients with adequate bone height and width for anterior maxillary implant placement usually have excellent crestal bone levels at the CEJ of the adjacent teeth. In such cases, the distance from the crestal bone to the proposed contact area of the restoration usually is less than 7 mm. This is an excellent prognosticator of papilla preservation and maintenance even after incisions have been made through the papillae and they have been elevated.

Two incisions can be used, depending on the clinician’s preference. One incision is on the crest with palatal release, leaving the labial facial tissue intact. The implant site is prepared without visualizing the facial cortical bone. This preparation requires a cross-section image from a cone-beam scan and fine tactile sense so that the surgeon can determine whether the apical portion of the implant is confined within the cortical bone or fenestrates through the bone.

A second approach uses a crestal incision across the edentulous site combined with sulcular incisions extending at least two to three teeth distal to the surgical site. A full-thickness reflection is accomplished, exposing the labial bone at the implant site to the piriform rim and anterior nasal spine. The advantages of this incision and reflection are that direct visualization is accomplished, and vertical incisions are not made. The disadvantage is that the papillae must be raised and sutured back to their original position. The key to success with this technique is gentle tissue management, avoiding tears in the circumdentate gingivae, and an atraumatic suturing technique to close the incisions. The papillae are closed with vertical mattress sutures, everting the papillae back to their original height. If possible, minimizing incisions and tissue manipulation results in small changes in the soft tissue, which aids in preserving excellent gingival architecture.

For the crestal tissue with elevation, a #15c scalpel blade is used to make the sulcular incision. The blade is directed against the surface of the teeth to the alveolar bone, severing the gingival fiber attachment without removing the inner portion of the gingival sulcus. These incisions must be made without cutting the papillary gingivae, only the attachment deep within the sulcus.

A small, fine periosteal elevator is used to gently reflect the papillae and the circumdentate papillae without placing excessive pressure on the gingival margin tissue as the flap is elevated. The elevation of the flap is less traumatic and easy to achieve if a hydropic dissection with local anesthetic has been performed. In addition, the flap elevation may take several minutes to accomplish to prevent tearing from overaggressive tissue manipulation.

For the palatal-based flap, an incision is made in a semi-circle fashion to outline the labial emergence of the implant. Vertical incisions are made toward the palate to create a broad palatal base of the flap. The flap is elevated to the palatal, leaving the labial tissue completely intact.

After the periosteum has been reflected with the flap, a round bur is used to identify and place the implant site within the center of the alveolar bone crest. The implant site should allow for adequate bone labially and palatally to the implant after it has been placed. The surgeon needs to determine that the distance from the entry site to the facial bone is adequate and will not result in excessively thin bone. After the round bur has been used, the graduating-sized burs are taken to depth using the surgical guide stent. The guide pins should show the implant emerging just palatal to the incisal edge of the planned restoration and positioned apically 3 mm from the planned gingival margin. The implant is then placed. Because many anterior maxillary implants require an angle correction, it is important to align the antirotational features of the implant to ensure that the angled abutments can be placed and angled directly palatal to the implant’s axis. For example, external or internal hex implants should have the flat surface of the hex parallel to the facial cortex.

Thin bone width and sufficient bone height

Ridge shapes can lead to thin bone in the apical, middle, or coronal third of the implant site or any combination of these three areas. Thus, the implant surgeon must be aware of these potentially thin areas, which require grafting to obturate the defect and reduce the possibility of soft tissue invagination along a portion of the implant (Figures 9-14 to 9-16).