Keys to Achieving Predictable Single-Unit Implant Esthetics in the Smile Zone

For a single-unit implant in the smile zone, oftentimes the most important factor for patients is the esthetic outcome.¹ Historically, implants have been evaluated on the basis of osseointegration to determine their success. The evolution of implant dentistry has been such that healed bone around an implant is now just part of what constitutes success; judgment is also based on an esthetic restoration consisting of a harmoniously scalloped gingival line, lack of abrupt changes in clinical crown lengths between adjacent teeth, a convex buccal mucosa with sufficient thickness, and distinct papilla.²

Regarding single-unit implants in the smile zone, esthetic failures are far more common than mechanical failures.³ Most often, these esthetic failures result from the clinician neglecting to recognize risk factors such as unrealistic patient expectations, high smile line, poor gingival architecture, poor interproximal papilla, and/or inadequate bone height during the diagnostic and planning phase of implant placement in the smile zone.⁴ Proper diagnosis and planning along with coordination and mutual understanding among the clinicians, both surgical and restorative, and the patient can reduce incidence of esthetic failures and highlight potential complications, allowing for better patient education regarding expectations and options.

Diagnosis and planning are the keys to predictable esthetic implant success in the smile zone and are best attained when directed by the restoring clinician. These steps address such factors as why an implant is being considered, evaluation of hard and soft tissue present, implant position, immediate versus delayed placement, temporization, surgical success, esthetic success, and patient expectations. If in the diagnostic and planning phases any factor is determined to be inadequate, the implant site should be developed to address the inadequacy. Ridge augmentation, orthodontics, and/or soft-tissue augmentation can be used to idealize the site in order to achieve predictable esthetic results.⁵ Recognizing and addressing potential inadequacies helps to inform patients regarding their unique treatment recommendations and aids in establishing mutually agreed upon expectations and reducing risk of esthetic failure.

The restoring clinician and surgical clinician must evaluate the planned implant site to ensure adequate bone volume and contours (vertical and horizontal) as well as ideal position (mesio-distal/buccal-lingual/coronal-apical). Placement of the implant in the bone will affect the marginal bone height in the area, which, in turn, will have a direct effect on the soft-tissue contours.⁶ The degree of this soft-tissue effect is dependent on proper diagnosis of the gingival biotype, thick versus thin. A thick gingival biotype implies more fibrotic tissue, increased vascularization, and thicker underlying hard tissue, which, in turn, is more resistant to recession.⁷ Thin gingival biotype has less underlying osseous support and less blood supply, which predisposes the site to recession after tooth extraction.⁷ Early identification of the patient's biotype is an important clinical indicator that can be used to educate patients about esthetic success in both the short term and long term as it relates to gingival architecture and balance between white (tooth) and pink (gingiva).

Advances in radiology, most notably 3-dimen-sional (3D) radiology, have in recent years rapidly enhanced the assessment of implant conditions and placement. Cone-beam computed tomography (CBCT) allows the clinician to generate a 3D image of the oral structures, soft-tissue lines, nerve canals, and craniofacial bones and permits evaluation of implant position and placement before surgery occurs. Additionally, current CBCT has the advantage of significantly reducing radiation exposure to the patient through collimation of the primary x-ray beam and focused target. These advances in CBCT have been shown to reduce radiation exposure by as much as 98% compared to conventional fan-beam CT all while providing invaluable information to the clinician.⁸

CBCT analysis affords the surgical and restoring clinicians an opportunity to simulate implant position, allowing decisions to be made regarding ideal diameter and length of the implant well in advance. The implant diameter should be no larger than the diameter of the natural tooth it is replacing 2 mm below the cementoenamel junction (CEJ).⁹ The initial level of bone support around the implant has been shown to be a key indicator in both short-term and long-term implant success.¹⁰ To accomplish bone support and preserve surrounding bone, the minimum distance mesial-distal between an implant and a natural tooth should be 1 mm to 1.5 mm to ensure proper osseointegration of the implant and decrease potential damage to adjacent natural teeth.¹¹ Bucco-lingually, the implant should be placed to allow facial bone thickness of at least 2 mm to avoid crestal bone loss and soft-tissue recession.¹² Apico-coronally, the implant should be positioned 2 mm to 3 mm below the CEJs of the adjacent natural teeth to allow creation of ideal emergence profile.¹³

Additionally, CBCT analysis plays a key role in helping to determine whether immediate implant placement or delayed implant placement is indicated. Historically, implants were primarily placed in healed alveolar ridges, a delayed placement technique. In the 1990s, clinicians began placing implants in fresh extraction sites, predominantly in the smile zone, ie, immediate placement technique.¹⁴ Immediate placement of an implant has the advantage of reduced resorption of the alveolar process following extraction, which typically results in better long-term function and esthetics.^15,16 Also, the patient's total healing time is shortened due to the elimination of a second surgery; this typically reduces psychological stress and leads to higher patient acceptance.¹⁷

Immediate implant placement indications include nonrestorable fractured teeth, nonrestorable carious teeth, endodontic failures, root fractures, and replacement of deciduous teeth as long as intact alveolar bone is present and primary stability is achievable.¹⁷ In order to achieve primary stability, the apical portion of the implant must be engaged in a minimum of 3 mm to 5 mm of host bone (Figure 1).¹⁸ If the tooth being replaced has an active infection or is periodontally compromised without intact alveolus or adequate support to achieve primary stability, the site should be idealized before proceeding and immediate implant placement should be avoided.¹⁹

Although single-unit implant restorations approximate nature, they lack the intrinsic properties of natural teeth and are associated with potential concerns and less-than-ideal outcomes and even failures. The most significant difference between implants and natural teeth is the lack of a periodontal ligament (PDL). The PDL provides natural teeth with both a cushioning effect and proprioception. The lack of PDL cushioning and proprioception on implants, though it does not affect the ability to chew, requires special consideration when the implant is restored due to potential adverse implications on long-term implant survival.²⁰

When axial forces are applied to natural teeth, PDLs compress under the load, creating the potential to overload an adjacent implant restoration due to its lack of a PDL.²¹ Failure to account for the compression of axial loading and compression of PDLs on surrounding natural teeth can produce occlusal overload, a major cause of implant failure.²² Upon implant loading, restorations designed slightly out of occlusion have less risk of axial overloading and failure.²³ Great care must be taken when assessing lateral forces on implant restorations due to the difficulty in identifying interferences and their more damaging force compared to axial force.²³

When implant failures occur, they are categorized as early, late, or esthetic. Early failure happens when the implant does not osseointegrate during the initial months after placement and is often linked to impaired healing ability of the bone, a disruption of a weak bone-to-implant interface, or an infection. Late implant failures occur after successful osseointegration and are associated with occlusal overload or peri-implantitis. The most common implant failures in the smile zone are those of esthetics and often are the result of poor case management. Of these failures, loss of papilla and presence of open embrasures is the most common. This problem can be avoided by designing the distance between the interproximal contact point and the crest of the bone to be less than 5 mm, ensuring papilla fill and avoidance of open embrasures 100% of the time (Figure 2). If the distance is more than 5 mm, the occurrence of papilla being present drops to 50%.^24-27

The following two cases are examples of the replacement of failing teeth in the smile zone with single-unit implants. Diagnosis and planning enabled predictable and esthetically pleasing results.

A 23-year-old male patient presented with traumatic fracture of tooth No. 9. Comprehensive examination was completed. The patient's medical and dental histories were unremarkable, and periodontal and oral health were excellent. CBCT revealed fracture extending subcrestal on the lingual (Figure 3). The patient was informed of the findings and options were discussed. The patient elected to proceed with an implant restoration to replace the fractured tooth.

CBCT revealed intact buccal and palatal bone, and measurements were made to select an ideally sized implant for immediate placement. The patient was prepared for surgery and tooth No. 9 was removed atraumatically (Figure 4). The socket was checked to ensure intact alveolar bone after which an osteotomy was completed for implant placement, leaving 2 mm of bone to the facial and 1.5 mm mesial and distal to the adjacent teeth. The platform was submerged 2 mm apical to the CEJs of the adjacent natural teeth. A custom healing abutment was fabricated using an engaging temporary abutment with composite to maintain proper emergence profile and delivered at the time of surgery. A thermoplastic retainer with composite in No. 9 was produced to serve as a temporary.

The patient healed for 5 months prior to digital impressioning for fabrication of a custom abutment and an implant crown (Figure 5 and Figure 6). The alveolar crest was sounded on adjacent teeth and the data given to the ceramist to ensure ideal location of the interproximal contact. One month later, the custom abutment and ceramic crown were delivered. The patient returned 6 weeks later for photographs (Figure 7). This case displays predictable esthetic results with immediate implant placement, which can be achieved with single-unit implants in the smile zone when parameters are followed and patients are compliant.

A 40-year-old male patient presented with a previously treated root canal on tooth No. 9 and stated he had been told the tooth needed to be removed (Figure 8). Comprehensive examination was completed. The patient's medical and dental histories were unremarkable aside from childhood trauma from a bicycle accident that resulted in No. 9 root canal therapy. The patient's periodontal and oral health were excellent. CBCT revealed a mid-root fracture with a large mid-root lesion (Figure 9). The patient was informed of the findings and options were discussed. The patient elected to proceed with an implant restoration to replace the failing tooth.

Immediate placement of the implant was ruled out due to the extent of the lesion present. Tooth No. 9 and the associated lesion were removed, grafting was performed, and healing was allowed for 5 months (Figure 10). New CBCT imaging was acquired and used to select the ideal implant size and position (Figure 11). The surgery was executed as planned achieving excellent primary stability, and the implant was immediately loaded with a custom engaging screw-retained healing abutment and temporary out of occlusion (Figure 12).

After 3 months of healing, final digital impressions were acquired (Figure 13 and Figure 14). The alveolar crest was sounded on adjacent teeth and the data given to the ceramist for interproximal contact design. Four weeks later, the custom abutment and ceramic crown were delivered (Figure 15). This case demonstrates recognition of an inadequate site, the idealization of the site before implant placement, and delayed placement of an implant in a more ideal site and position to achieve the desired esthetic success in the smile zone.

Through proper diagnosis and thorough planning, replacement of failing teeth in the smile zone with single-unit implants can be highly predictable and esthetically successful. The surgical clinician and restoring clinician must work together to acknowledge and manage the specific characteristics of each unique case. The clinician's collaboration with and education of the patient can help address expectations and achieve the desired final esthetic result. Planning the implant position in all dimensions relative to the hard and soft tissue is crucial, and recognizing and addressing inadequacies in the implant site will help to reduce incidence of failures.

Partner, Scripps Center for Dental Care, La Jolla, California; Medical Staff, Scripps Memorial Hospital La Jolla, La Jolla, California; Adjunct Faculty, University of California San Diego School of Medicine, San Diego, California