Predictability in anterior aesthetic implants: assessment, planning and execution

Missing or damaged teeth in the anterior maxilla, the ‘aesthetic zone’, undoubtedly pose a challenge, and there are several treatment options for a patient with one or more missing teeth in this area:

• Do nothing: leave existing space with minimal intervention.
• Removable dentures: metal based or acrylic based denture options
• Fixed bridgework: permanently attaching prosthetic teeth to adjacent teeth to close existing gaps helps to reduce tooth movement.
• Dental implants: permanently filling existing gaps without the need for surgical intervention of adjacent teeth.

Replacement of a single tooth with an implant-supported crown has become a popular treatment of choice. Implant placement in the anterior maxilla has been shown to have success rates comparable to posteriorly placed implants,^1,2 and the aesthetic results of implants in this area are the subject of many studies owing to their complex nature.^3,4,5 Predictable outcomes are undoubtedly more challenging to achieve and sustain, and greater consideration must be given to the precision of implant positioning and restoration in order to achieve both clinical and aesthetic success. Moreover, patient expectations are likely to be higher because there are both functional and aesthetic implications to consider, with emphasis on psychological and social outcomes in addition to physical and functional results.

There are also a number of practical challenges to consider that can impact on the overall aesthetic outcome. For example, limited bone or soft tissue volume can affect the ability to position implants in an ideal aesthetic position for the implant crown or bridge.

Additionally, current or previous infection may affect implant stability and the overall aesthetic result. The pathology and restorative circumstances of adjacent teeth also play a part, with the potential to influence stability and aesthetic outcomes, and a unilateral gap is more aesthetically challenging for matching to a natural comparator.

This article summarizes factors relating to assessment, planning and execution, with emphasis on the strengths and benefits of a Type II approach. These factors can, with appropriate expertise, lead to predictable and stable outcomes for implants in the aesthetic zone.

Defining predictable outcomes

Successful clinical outcomes can be defined as long-term implant survival in the absence of pain, and with stable marginal bone levels (see Figure 1).⁶ Additionally, in the aesthetic zone, the PESWES scoring system can be used as an objective outcome measure. Developed originally as a soft tissue index (Pink Esthetic Score, PES) for anterior implants,⁷ this was further developed and combined with a White Esthetic Score (WES), to give a combined soft tissue and restorative index, PESWES.³ This comprehensive index relies on the presence of a natural comparator tooth, and so is not always applicable. However, given that the most challenging situation is that of matching an implant to a natural tooth, it provides an excellent quantifiable measure of aesthetic success.

There are of course many factors that contribute to implant stability and success.⁸ Patient-related risk factors affecting outcomes include medical history, poor oral hygiene, and smoking. Clinician-related factors apply to elements of the process, such as structured treatment planning, extensive knowledge of treatment options, knowledge of different methods and materials and an overview of current literature. Moreover, in addition to all the above, the ability to recognize appropriate levels of expertise is essential for a predictable and stable outcome.

Structured risk assessment (SAC)

The first ITI Treatment Guide brought together an evidence base for single implant treatment in the aesthetic zone.⁹ Combining guidance and recommendations for a number of clinical situations since its publication in 2006, it was followed by an updated volume in 2017.¹⁰ These guides, alongside numerous publications in the field, have helped to shape and drive the assessment required for aesthetic zone implants, because this is not a viable treatment option for all. A structured risk assessment is vital for planning purposes, identifying challenges, assessing clinician expertise for any individual situation, and ensuring that this is the most appropriate treatment of choice.

There are a number of general risk factors to be considered before any implant placement. Patient-related risk factors, such as any medical history that may compromise bone healing, diabetes, and some medications (e.g. bisphosphonates) should all be considered as increasing the risk of an unfavourable outcome. Alongside these sit other patient factors, such as incidence of periodontal disease, smoking habits, and compliance with oral hygiene. These and more factors form part of the SAC Classification in Implant Dentistry,¹¹ guidelines for combined assessment of the degree of complexity and potential risk, resulting in a classification of whether placement is straightforward, advanced or complex. These guidelines have been shown to be of particular use for the less-experienced practitioner.¹² Hence clinician expertise,¹³ in addition to managing patient expectations, should form part of a risk assessment.

An extension to the SAC classification system is the Esthetic Risk Assessment, (ERA),^10,14 with a checklist for identifying factors posing a risk to a predictable aesthetic outcome. For example, smoking can adversely affect wound healing and soft tissue augmentation, as well as it being a risk factor for periodontal health in the future. With guided bone regeneration (GBR) forming an integral part of many procedures in the anterior maxilla, smoking can be considered a significant contraindication owing to the risk of a poor aesthetic outcome created by poor bone graft healing.

Digital workflow

Complications resulting from positioning errors in implant placement can contribute significantly to aesthetic outcomes.¹⁵ Precise planning can help to eliminate this risk factor. Digital technologies have been introduced to offer practical solutions to implant workflow (Figure 2). A 2015 study compared economic parameters of digital and traditional workflows for posterior implant placement, finding the digital workflow more streamlined and economically efficient for both patient and clinician.¹⁶ With this in mind, it is particularly important to evaluate the success of these digital methodologies when applied to implants in the challenging aesthetic zone. Short-term work shows reliable results (no biological or functional problems) for single implant outcomes in the posterior maxilla with fully digital workflow,¹⁷ but with limited (6 month) follow-up. In addition, there have been favourable clinical outcomes from using some digital technologies (e.g. s-CAIS) in anterior implant placement.^18,19 Merging of CBCTs with intra-oral scans allow a 3D analysis of the proposed implant site and associated anatomy, which in turn facilitates detailed planning, including identifying the most suitable implant type and position for the proposed restoration (Figure 3). Simultaneous visualization of soft and hard tissue provide additional means to identify and mitigate risk. This methodology also allows for better patient communication by visualizing proposed outcomes, sharing expectations, with clinician and patient reviewing planned outcomes together ahead of treatment.

Timing of implant placement

The timing of implant placement plays an essential role in determining clinical outcomes. Implants in the aesthetic zone are typically placed either immediately (Type I) or early (Type II or Type III). These timings refer specifically to implant placement in relation to tooth extraction, with definitions as follows:

• Type I (immediate): the implant is placed on the same day as the tooth is extracted;
• Type II (early): the implant is placed after a period (usually 4–8 weeks) of soft tissue healing around the extraction socket;
• Type III (early): the implant is placed after a period (12–16 weeks) of soft tissue healing and partial bone healing

Immediate (Type I) dental implants can seem like an attractive treatment option in the aesthetic zone, with less surgical time and an immediate solution, and precluding the requirement for a temporary bonded or removable prosthesis.²⁰ Using GBR, satisfactory clinical outcomes can be achieved with this technique; however, this is a complex procedure with the risk of mucosal recession impacting on aesthetic predictability.^21,22 Inability to predict hard and soft tissue outcomes and a paucity of significant data for long-term predictability make it difficult to favour this over Type II. Type III (early implant placement with partial bone healing) is a less common approach, used predominantly in cases with bone lesions that require a prolonged healing period in order to give sufficient primary stability at implant placement. However, its extended treatment time and increased chance of bone resorption mean it is also less favourable than Type II.

Strengths and benefits of Type II

The two-stage procedure of a Type II/early implant protocol involves implant placement with simultaneous GBR, at 4–8 weeks following tooth extraction. This allows for a period of soft tissue healing and thickening in the extraction socket, providing a highly vascular environment with good healing potential. This then provides a stable environment for bone regeneration. Early implant placement has been well documented, and there are many clinical studies evaluating treatment outcomes. Studies indicate low risk of complications with successful and stable aesthetic outcomes.^3,23 Additionally, this two-stage process allows time for resolution of infections that may have been present at time of tooth extraction.

Owing to the physiological nature of bone remodelling following tooth loss, a reduction in alveolar bone volume can often be anticipated. When considering implant placement (and particularly in the anterior aesthetic zone) deficient bone levels must be addressed to ensure the ability to place an implant in the appropriate position to provide an excellent aesthetic outcome, as well as long-term stability of the implant and surrounding soft tissues.

GBR is often used in such circumstances to provide contour and bone volume, usually using a combination of grafting materials and barrier membranes at the site of the bone defect.²⁴ This can be carried out either during implant placement or prior to implant placement to facilitate site development. Simultaneous GBR is preferable, performed at the same time as implant surgery. However, in some cases morphology does not favour this approach, and staged GBR must be undertaken.

Type II protocol and clinician expertise

For many years at the authors' practice, the principle has been adopted that Type II implant placement in the anterior aesthetic zone is an essential skill and appropriate protocol for competent (as opposed to exceptional) dentists. One of the main reasons for this approach is that dentists are not always the best at deciding whether they are competent or exceptional. This has an impact on their choice of the most appropriate course of treatment according to their expertise. This relates directly to the principles described by Dunning and Kruger in the Journal of Personality and Social Psychology around being unskilled and unaware of it, where those with a lower level of competence are more likely to overestimate their ability.^25,26

With respect to aesthetic implant placement, it is a broad estimate that 80% of practitioners practice in the competent zone, and thus it is not a far stretch from this to suggest that Type II implant placement is the safest and most predictable anterior aesthetic protocol for most practitioners. While there are more advanced and more exciting protocols, and Type I may seem attractive to both patient and clinician owing to its immediate result, research suggests that Type I implant placement is only suitable for experienced and advanced practitioners, and even then, only in carefully selected cases.^27,28 The Type I approach's classification as a complex procedure in the SAC structured risk assessment, which should only be performed when anatomical conditions are ideal, reinforces this.^27,29

The protocol in the authors' practice is for all clinicians to provide Type II implant placements in the majority of cases. This involves a suite of complete diagnostics including CBCT/IOS scan, digital wax-up and a guided-surgery guide produced in-house, and this is carried out for every anterior aesthetic case. In extraction cases, removal of the remaining tooth is followed by a wait of approximately 6–8 weeks to allow soft tissue coverage.²⁷

In the majority of these cases, an anterior GBR will be required, such as a composite GBR graft protocol described by Buser et al.²⁷ Using GBR in a Type II implant placement can provide predictable results in a structured treatment format. A mixture of freshly harvested autologous bone chips (harvested by a bone scraper) and deproteinized bovine bone mineral (DBBM) is used to cover the exposed implant, and this is then covered with a non-cross-linked collagen membrane that provides a framework for vascularization, and promotes tissue integration and bone formation (Figure 4). This procedure requires tension-free primary closure, which is why a 6–8-week period of healing is required following extraction of the tooth. This ensures soft tissue healing, and primary closure is much more straightforward for competent practitioners (Figure 5).

Following appropriate implant placement and contour GBR, the area heals for approximately 12 weeks prior to exposure of the site under local anaesthetic (Figure 6). A further 2 weeks is left for the exposure site to mature, after which a digital impression is taken (Figure 7) to provide a provisional crown, which is used to optimise soft tissue formation.³⁰ This provisional crown is then used over a timeframe deemed appropriate by the clinician (usually anywhere from 1 to 6 months), to shape the gingival architecture prior to completion of the case with a ceramic crown, usually as a single-piece construction (Figure 8).

Using this protocol, a long-running service evaluation has demonstrated the stability of aesthetic results from a Type II placement protocol using analogue workflow, prior to a move to digital processes (unpublished data). This data uses the PESWES scoring system³ to assess long-term stability of pink tissue, with PESWES scores remaining predominantly unchanged at 2- and 5-years post implant placement (average PES 7.95/10), indicative of long-term stable aesthetic outcomes using a Type II protocol (Figure 9). This method of in-house assessment provides a useful guide to effective practice and long-term outcomes.

Summary

The authors would recommend this protocol to the large proportion of practitioners, whose competency is not yet accompanied by the experience that classifies them as exceptional clinicians, for predictable outcomes in anterior implant reconstructions in the vast majority of cases.