Article
Restoration provision, at the basic level, is the management of missing tooth tissue to reinstate form and function to a standard that is predictable, while designing features that will mitigate against failure. Realizing the future, or indeed inevitable, need for the management of ‘failure’ is an integral piece of the ‘restorative jigsaw’ for the clinician to consider. Different pieces illustrate different aspects, all of which contribute in different ways. The avenues for failure are multiple, although they can be distilled into three aspects (Figure 1).
Mitigating these pathways may result in a more successful restoration, or one that is less likely to fail or deteriorate prematurely.
Marginal interface
The marginal interface is a weak point for failure of restorations. This can manifest in a variety of different ways and may be the measure of a clinician's abilities in achieving optimal outcomes. The interface between restoration and the tooth is the barrier protecting the weak point of the tooth from biofilm ingress.
Well-defined preparations for indirect restorations, captured in detail digitally or in analogue, temporized to maintain gingival health and occlusal stability, subsequently cemented under conditions that are moisture free, resulting in as seamless an interface as possible is a process that requires a broadness of knowledge and skill.
Each process is interlinked, resulting in a cascade of issues if one step is not as optimal as the other. Clearly an ill-defined preparation or poorly captured margin, inadequately constructed restoration, sub-optimal cementation, which is either overflowing into the gingival crevice or there is a lack of moisture control, can manifest as gingival inflammation or leakage, compromising integrity of the cement lute, and potentially further prosthodontic, endodontic or periodontal complications.
The delivery of direct resin ‘bonding’ restorations can also develop marginal issues. Although minimally invasive, the aspect of marginal design plays a role where the tooth is made wider additively, bucco-palatally, resulting in a steeper cervical emergence and interproximal contact area that can be significantly more plaque retentive, potentially resulting in gingivitis. In other scenarios, composite resin or bond ingress into the crevice, or overlaying it, can exacerbate gingival inflammation.
The coronal seal of endodontically treated teeth has long been cited as a significant factor in the outcome of either de novo or root canal re-treatment. Further, marginal seal is also applicable to the apical zone, where obturation that is well compacted, prevents ingress of tissue fluid that could potentially maintain the viability of bacteria remaining in the apical anatomy post obturation, and so perpetuating inflammation.
Counterintuitively, implants also suffer with marginal interfaces that are weak points in their prospective success and failure. The restorative stack on top of the implant can present with avenues for leakage where there is a lack of accuracy in the fit surface of the screw-retained crown, allowing ingress into the screw chamber. This can result in a cesspool of bacteria, saliva and breakdown products festering in the implant, potentially compromising bone encircling the implant margin, and resulting in bone loss. The need to ensure accuracy of fit and mechanical harmony between the restoration and the fixture can be overlooked, but is vital for success.
Magnitude of occlusal force
Accommodating mechanical impact through chewing food is an expected function of the masticatory system, where our teeth and the periodontal supporting structures have evolved to manage axial and non-axial forces. Overloading any system outwith its capabilities by way of prolonged grinding or clenching unsurprisingly can result in mechanical breakdown through cracks or fractures. In contrast, where heavily restored units reside in the absence of parafunction, avenues for catastrophic fracture under normal function can occur owing to propagation of acute forces through the tooth, cleaving their way through the weakest planes of the unit. Teeth bend and flex under loading, if marginal integrity is poor, further avenues for leakage will develop as the tooth deforms towards and away from the restoration. In this respect the interaction of the margin and occlusal force can determine the tooth's outcome.
Planning how load interacts with the restoration, statically and dynamically, requires foresight and the perception of where force is best dissipated, as evenly and as passively as possible, to the periodontal ligament and surrounding alveolus. Such occlusal ‘harmony’ has consistently been the aim of our profession, and contemplated by all. The occlusal contact should be designed to maintain the three dimensional position of the tooth, preventing overeruption where non-existent, or intrusion where too heavy. Equally the nature of static and dynamic contact should mitigate against propagating loads that could create sheer forces, as opposed to compression, which is better tolerated by dental materials. Clearly, occlusal adjustment of direct or indirect restorations requires the acknowledgment that mandibular teeth move against maxillary teeth dynamically, and that this should be incorporated into the shape and design of the restoration. Flat surfaces with steady inclines or topography are much better tolerated than those with steep inclines, or haphazard adjustments creating indentations and divots where the tooth cannot amicably move or manoeuvre.
Where teeth have been debilitated by caries, tooth surface loss or pulpal disease, the need for cuspal coverage ensures the absence of tooth–restoration marginal interface on the occluding portion of the tooth, hence mitigating against this interface, where damaging non-axial or vertical forces may result in tooth disintegration. Knowing the strengths of your restorative material provides greater scope for success, where for example, gold requires less thickness than resin in managing the same load.
Occlusion is a ‘team’ game where loading that is shared among units, protecting those weaker and more debilitated teeth, can result in their retention in the long term despite their compromised strength and volume. Patients need to understand that teeth, root-canal treated or heavily restored, cannot perform in the same manner as those that are unrestored. Equally implant restorations, owing to the absence of a periodontal ligament, are inherently less likely to be able to manage differential and dynamic loads. The implant unit is more likely to rely on adjacent teeth for their proprioception in avoiding damaging load forces in function, and parafunction.
The past is a great predictor of the future. If a tooth has failed and has been extracted due to parafunction, then we should be cognizant that any future prosthetic replacement will similarly need to manage these loads. Patient education and understanding of the scope of restorations or implants, in that their roles are not to ‘replace’ teeth, but rather, are a distant substitute that can achieve an acceptable, although more medial outcome, is likely to help patient understanding in the capabilities of their clinician, and dentistry in general.
Mindfulness
The definition of mindfulness is ‘the quality or state of being conscious or aware of something’. This factor is counterintuitively more important than we may otherwise appreciate in restorative dentistry. A patient who appreciates that marginal integrity of their restoration improves longevity is more likely to maintain cleanliness and hygiene in this critical zone. Equally, patients who play an active role in reducing their parafunction and bruxism by way of compliance with splint wear, or reducing factors that increase non-axial forces, are at a greater chance of restoration success. It can be a difficult conversation with patients when making them aware that they are a significant factor in success or failure of their treatment, and your restoration. In essence, the pushback should be that patients are delicately, but truthfully, made aware of their role and responsibilities. Unlike the purchase of electronics or clothing, treatment is provided on the basis of health, as well as consumer ‘wants’ and ‘needs’. Where a TV may breakdown, under warranty, and be replaced like for like, this cannot be achieved with a failed implant for example.
The difficult conversations relating to prognosis, failure and success need to take place long before treatment is started, and then reiterated and reinforced, during treatment depending on the complexity of the procedure or the patient's expectations. The old adage of ‘underpromise and overdeliver’ rings true in this aspect. The other aspect is having the difficult conversations about compromised oral health or the prospect for failure of any procedure before treatment is started or instigated. Timing is key: information delivered about pitfalls before the event is foresight, but is an excuse if delivered after.
Treatment involves a journey for the patient, and the destination needs to be clearly communicated as best as possible. If individuals are under the impression that they are flying to Le Mans in France, but arrive in Bolton (both of these towns are twinned in France and England, respectively) the patient may be disgruntled, and understandably so. The clinician plays the role of travel agent, explaining and describing the treatment with brochures and props, the pilot, delivering treatment or transporting from one destination to another, then the host ensuring their expectations, heightened or dampened by the travel agent, are met. Patient understanding of their treatment, and achieving their consent, needs to be facilitated through sound and sensible information. This is becoming increasingly more and more difficult with the internet and social media, resulting in a constant battle with information that is manipulated, misinterpreted, misrepresented or even untrue. Therein lies the issue: patients should pay for our expertise, not the product or the material. This has been succinctly illustrated by the recent dental tourism craze, where patients are keen on getting treatment for ‘cheap’, as the implants or the ceramic is the ‘same’ as that can be ‘purchased’ in the UK; however, it is not necessarily provided with the same expertise or indeed regulation. Whatever our opinions are on cosmetic or implant dentistry, zirconia crowns, porcelain veneers or dental implants ‘purchased’ by patients rather than being ‘provided’ under the correct circumstances, are a source of potential disappointment, more than likely felt by patients long after the suntan has faded.
Being mindful of the patient's trust and perception of the profession may seemingly play a huge role in our decision making and restoration outcomes. With the established litigation culture, clinicians may be forgiven for feeling as though defensive dentistry is the best avenue for treatment. Defensive dentistry, where fear of being sued is an anxiety, can result, consciously or subconsciously, in a greater likelihood of procedures that are inherently less risky, but more predictable, being provided. Unfortunately, this may not coincide with the ideal or optimal oral health. For example, a tooth that is borderline restorable may be more likely to be extracted rather than there being a measured and sensible, albeit seemingly heroic attempt, at saving the unit. The latter should be the aim for treatment, under the right circumstances.
Mindfulness also plays a significant role for the clinician. Doubt and reflection in tandem, ideally before, and if not, during and after the provision of treatment, is a cycle of self-improvement that allows us to instigate change in our practice and our decision making. Astute decision making, weighing up success and failure may be an overriding factor that separates the average clinician from the above average, as opposed to actual clinical skill set and abilities. Alas, deciding on doing the wrong treatment to the highest standard is still the wrong treatment. More often than might be otherwise expected or realized, the ‘success’ of decision making is more important than the ‘success’ of individual procedures. Strangely, research into clinician decision making is scarce, whereas there is a plethora for individual procedures. A clinician who has decided to provide and has placed 10,000 implants with 2000 successes is not necessarily more capable or skilful than an individual who has placed 500 with 450 successes. Further, clinicians honing their own decision making to improve their own outcomes can only come through reflection, with further training built on the basis of continued further knowledge.
Discussion
Distilling factors for failure into simpler terms may help clinicians in processing the root cause of premature restoration loss or tooth removal. Seldom do we have reasons for failure being ‘mono-factorial’, in that the triumvirate of patient, clinician and oral health all contribute to the decline of treatment. In certain cases, one factor may contribute much more and override the others.
Clearly patient mindfulness can mitigate against decisions where treatment choice can expedite the development of failure, despite advice against treatment, as the current vogue of dental tourism is now illustrating. From the clinician perspective, presence of thought, and awareness of pitfalls and their own capabilities, all contribute to outcome.
Clinician mindfulness and insight are also hugely important. We may consider perceiving our own strengths and weaknesses as it relates to the provision of dentistry by considering abilities within technical skill, decision making and communication.
A technically skilful clinician can provide an excellent standard of care through a single unit anterior veneer for example, but the decision to provide this may not be considered sensible. Further, a lack of communication with the patient on the relative risks and benefits, despite the quality of care, can also result in ‘failure’ in the patient's interpretation of the outcome, but not necessarily our own.
Equally a clinician may be more adept at decision making, consistently offering treatments that have the highest chance of success within their own skillset, or indeed, deciding to transfer risk to those who are more capable than themselves through referral, to realize the best outcome.
Lastly, an accomplished communicator will inform and digest complicated clinical concepts to their patient to improve understanding, compliance and consent, to enable patients to appreciate their own health and maintenance, which is more likely to translate to restoration success, or their own acceptance of failure if and when it occurs.