Additive bonding approaches to managing root-filled, cracked or weak teeth

Despite decades of dogma, disagreements and debate, the supposedly ‘ideal restoration’ for root-filled premolar and molar teeth remains controversial.¹ Most ‘authorities’ advocate cuspal coverage of some sort to ‘protect and restore the root-filled tooth to its full form and function’, while usually conforming to the patient's existing intercuspal position (ICP), meaning without altering their existing anterior occlusal vertical dimension.¹ Leaving aside the dubious wisdom of subjecting an already compromised root-filled back tooth to all of those ongoing occlusal, as well as potentially damaging clenching/bruxism forces, some of which might well have been involved in the tooth requiring that root filling in the first place, that traditional dogma nearly always involves the loss of more valuable sound tooth structure in order to create enough space for whatever ‘restorative’ material is deemed to be appropriate for that situation.¹

The proposition offered in this article is that additive direct composite bonding of many other strong teeth is a non-destructive way of getting space over the occlusal aspect of a weak root-filled tooth rather than taking more off its occlusal (and possibly other surfaces) to provide a cuspal coverage restoration with the aim of reducing the risks of a later catastrophic vertical fracture.

If that additive direct bonding is carried out on the other stronger teeth first, then on some occasions, a modified direct composite cuspal-coverage restoration might be all that is then judged to be required, particularly if most of the important marginal ridges of the root-filled tooth are still reasonably intact.

However, if an indirectly fabricated cuspal-coverage restoration is still deemed to be prudent, then quickly cutting down the visibly different-coloured composite on the bonded part of the occlusal aspect of that root-filled (or cracked/very weak) tooth creates most of that desired occlusal space easily and predictably.

The occlusal space that is deemed to be required for any allegedly ‘permanent cuspal-coverage restoration’ varies according to the material chosen. However, in general structural engineering terms, the more load-bearing sound tooth structure that is left at the end of whatever euphemistic ‘preparation’ is done for that chosen material, the better is the likely long-term prognosis for that already structurally compromised root-filled back tooth.

Once the impression has been taken, the occlusal space that was obtained can be maintained predictably between appointments by using different consistencies of polycarboxylate cement alone as the temporary restoration because that material seals and protects the preparation predictably, as will be described later in more detail in one of the cases used to illustrate these pragmatic ideas.

When the indirectly fabricated restoration is ready, the contrasting creamy colour of the polycarboxylate cement means that it is very easy and quick to grind that off with a high-speed drill and then vibrate off the thin last bits with an ultrasonic tip to leave a clean bondable surface.

Once the ‘definitive’ cuspal coverage restoration is cemented in position, the additive direct composite bonding is still left on the other stronger teeth where it continues to load those mainly intact stronger teeth. That wider distribution of potentially destructive loads helps to protect the usually structurally compromised and vulnerable root-filled back tooth from a catastrophic vertical fracture.

While all of this palaver might sound quite tedious to undertake, in practice it is quite quick to do and uses readily available skills and well proven materials. Those protective benefits can be obtained at minimal biological and reasonable financial costs, by using a ‘satisficing’ approach (meaning one that is sufficient to be satisfactory) by using additive direct composite bonding.

Any or all of those directly bonded composite additions can be polished, repaired or renewed at any time, if and when that might be indicated, without damaging the patient's remaining ‘dental capital’ (see below).

Concerns about traditional approaches to managing root-filled weak back teeth

Dentists use the euphemistic term ‘tooth preparation’ when providing a crown or onlay in their preferred ‘restorative’ material. However, in reality, most ‘preparations’ involve reducing the residual sound tooth structure even further (Figures 1 and 2).

In previous decades (and still in some cultures), three-quarter gold crowns (Figure 3), ‘seven-eighths’ or full-coverage metal restorations were the preferred choice for weak back teeth mainly because the tooth ‘preparations’, especially when done on root-filled posterior teeth preserved significantly more of their reduced load-bearing sound tooth structure than did bonded full-coverage crowns.

However, owing to a variety of fashion, social media and consumer changes in some societies, there can be an over-emphasis now on the appearance of often barely visible heavily compromised back teeth.² Many self-anointing ‘cosmetic’ dentists now accede quickly, and often without serious questioning, to any patient's demands for a ‘white crown’ for their root-filled back tooth. In many cases, that is a very understandable patient request, but when making it, many patients will not be in possession of the balancing facts about the structural risks that they might be incurring to get that questionable ‘cosmetic’ benefit. Many of them will probably not understand fully that what dentists refer to as the required tooth ‘preparation’ (spelled ‘mutilation’) for a full-coverage all-ceramic crown, or for a full-coverage porcelain bonded-to-metal crown (‘PBM’) on a posterior tooth, has been reported to remove about two-thirds (63%) to three-quarters (72%) of the tooth structure (Figure 4).³

Incidentally, the manufacturer's instructions for ‘preparation’ for a ceramic-veneered zirconia crown, when this is to be ‘scanned’ for digital dentistry, mandate the removal of probably more than the two-thirds of the crown's sound tooth structure that is required for a PBM crown. Worryingly, given the fashion for many dentists and technicians adopting CAD/CAM and scanner technology unquestioningly, seemingly in order to fabricate full-coverage crowns quickly and relatively inexpensively, the manufacturer's instructions stipulate the need to produce a 1-mm wide cervical chamfer, or a rounded internal shoulder, all around the tooth so that the scanner can sight down that more tapering preparation to record the full details at the cervical margins. In other words, rather than having just a minor chamfer on the lingual or palatal of the ‘preparation’ that is indicated for a traditional PBM crown, even more of the remaining sound structure on the lingual/palatal now needs to destroyed because of the serious limitations of current scanners when undertaking ‘digital dentistry’ on natural back teeth, thereby resulting in stupid and unnecessary destruction of already compromised teeth (Figure 5).^4,5

That is ethically highly dubious and engineering madness.

Consent issues

Carefully, or casually, noting that the patient ‘demands a white crown’, while choosing not to advise that possibly semi-informed patient clearly of the ‘material risks’ that are inherent in their understandable request, has serious consent implications, particularly following the 2015 Montgomery ruling in the Supreme Court.⁶ Bearing in mind that many such patients will have already spent significant time, effort (and usually money) in having the root filling undertaken in order to try to keep their back tooth, it is probably reasonable to suggest that if they really understood that before choosing to lose much more of the residual structure of their precious, newly root-filled tooth electively in order to have an indirect ceramic-covered restoration placed on their back tooth, which is often barely visible during normal activities, that they might well wish to know more about any other viable options (including minimal treatment) that could ‘satisfice’ for them. Incidentally, ‘satisfice’, in this context, means that it would be ‘sufficient for it to be satisfactory’ for them.^7,8,9,10

This article now explores some concepts about ‘dental capital’ that have significant implications for validity of consent. It goes on to outline in more detail a biologically sensible and practical option for maintaining ‘dental capital’ when managing root-filled, or cracked, or just very weak premolar or molar teeth. Essentially, that approach involves firstly bonding direct resin composite pragmatically to other sounder teeth to create enough occlusal clearance over the root-filled premolar or molar tooth to provide a cuspal-protection restoration without reducing significantly the residual sound tooth structure to provide that restoration. Furthermore, the consequential spreading of potentially destructive forces more widely on to many other sounder teeth reduces the longer term dangers of catastrophic fracture of that root-treated, cracked or otherwise compromised, tooth/teeth (Figures 1 and 2).

Consent and communication issues: helping patients understand the concepts of ‘dental capital’, ‘self–preservation’, self-improvement’ and ‘self-destruction’.^6,7,8,9,10

It is important that patients (and some dentists) understand what the concept of ‘dental capital’ means. It refers to the total of a patient's existing healthy enamel, their sound dentine, their periodontal and their pulpal health (or their now reasonably root-treated tooth/teeth). In this context, an extraction depletes the ‘dental capital’ rapidly and irreversibly, while a root filling aims to preserve as much as possible of their ‘existing dental capital’ (Figure 6).

• ‘Self-preservation’ in dentistry means trying to keep as much as possible of one's ‘dental capital’. Although not necessarily described exactly that way, nor using those precise words, that is usually a key goal for most endodontic treatments, and indeed for most of preventive and routine decent dentistry. It is rather akin to keeping one's good health, or maintaining one's existing financial assets, without taking unnecessary risks of losing them.
• ‘Self-improvement’ could describe things like bleaching and/or direct composite bonding to improve the appearance and/or function of the existing teeth. It could describe ‘self-preservative orthodontics’, which means orthodontics that avoids unnecessary extractions, or having extensive interproximal stripping, or speculative orthodontics that involves risking tooth instability, or serious root resorption, or relapse, or longer-term periodontal maintenance issues caused by fixed wire retainers. One could regard someone having dental implants placed to hold replacement teeth as being ‘self-improvement’ by adding to their existing dental capital. In truth, the main advantage of having appropriately placed dental implants restored properly is that it solves many patients' perceived problems about their missing teeth by having something that is fixed in their mouth, but without depleting further their remaining dental capital.
• ‘Self-destruction’ means destroying one or more bits of the dental capital, e.g. by an extraction, or by undertaking unnecessarily destructive full-coverage ceramic crowns on moderately worn teeth.^9,10

Patients need to be made very aware that their dental capital is finite and that it can be depleted casually and quickly as a precursor to them obtaining their perceived ‘self-improvement’ in appearance, for example by them electing to have multiple ceramic ‘extended’ veneer restorations, or full-coverage ceramic crowns (Figures 4, 5 and 7). Unfortunately, many supposedly ‘just cosmetic’ outcomes come at serious long-term biological and/or structural risks and the benefits, if any, can be subjective, temporary or illusory.^{2,3, 9,10}

When people evaluate options and risks, losses loom larger than gains

The Nobel Prize winner, Daniel Kahneman, described how most rational people are ‘loss averse’, meaning they dislike losing things much more than they value potential gains. Kahneman and Tversky described how ‘losses loom larger than gains’ when people are considering their available options carefully before making their decisions.¹¹ That particular expression has been used in relation to the options comparing the dental destruction electively undertaken to produce multiple full-coverage pressed-ceramic crowns for managing moderate tooth wear problems, as compared to the minimal ‘dental capital losses’ incurred by using additive direct composite in order to help to manage those problems.^9,10,11,12

Although it is not usually described in those exact words, the general concept of avoiding losses of their ‘dental capital’ is probably reflected in the very substantial volume of dental literature, now readily available from multiple sources, all reporting that patients adapt readily to various localized occlusal changes where direct composite has solved their perceived problems, regardless of whether these were caused by their tooth surface loss, their missing teeth, their bulimia, or open bites, and all without losing more of their remaining ‘dental capital’, i.e. sound tooth structure in those pragmatic processes.^{10,13,14,15,16,17,18,19,20}

Communication and consent issues

Requirements for patient adaptation to ‘additive bonding’ restorations

When discussing possible elective treatments to help protect their root-filled (or very weak posterior teeth), it is important to be absolutely frank with any potential patient about some provisos and limitations before allowing them to possibly choose to have additive composite bonding done on their other sounder teeth, which will change their existing intercuspal occlusion and their anterior vertical dimension.^{13,14,15,16,17,18}

Provisos

• The patient must understand the reasons why this elective additive bonding treatment might be undertaken in that way for them, as well as their other viable options, including doing nothing.
• They need to accept in advance (and preferably in writing) that significant adaptation will be required by them to that additive bonding to their other teeth, if the ultimate outcome of protecting their very weak/root-filled back teeth is likely to be beneficial for them.
• The patient must have enough sounder teeth in that arch with most of their marginal ridges still intact, and those stronger teeth must be opposed by similarly reasonably sound teeth. In practical terms, that means that it is important to avoid the elective additive bonding being opposed by all-ceramic or PBM full crowns, and especially not post-crowned teeth, because those teeth will have lost their load-bearing marginal ridges and most of their coronal structure.
• The sounder teeth chosen for elective bonding need to be periodontally stable and be capable of independent movement in their periodontal ligaments. The feedback mechanisms of the periodontal ligament mechanoreceptors play a vital role in patient adaptation to occlusal changes. It is important, therefore, to avoid implant-retained crown/bridges and fixed/fixed bridgework, mainly because no independent adaptive movement is feasible in those situations. In assessing such things, all-metal crowns usually have much more sound structure left underneath them than PBM crowns. Cantilever bridges or fixed-movable bridges can be considered, but sensible caution is advised.
• The improvement in their appearance needs to be at least as good (and preferably better) than they were promised by them having a realistic, but reversible, composite ‘diagnostic mock-up’ performed on their dried (NOT ETCHED) visible teeth to assess their reaction to those proposed appearance changes before committing either the patient, or the treating dentist, to doing that elective additive direct bonding. If, on assessing that composite mock-up in a full-face mirror, the patient appears to be ‘underwhelmed’ by that proposed aesthetic outcome, then serious caution is advised because this ‘additive composite approach’ is elective.
• The patient needs to realize and accept that nothing is ‘perfect’ or ‘permanent’ in dentistry (or in life) and that some polishing or resurfacing or replacement of the composite will be required at some stage, but they will have all their remaining ‘dental capital’ left underneath that composite, and that composite is an intentionally recyclable sacrificial material, unlike their remaining sound tooth structure.

Case reports illustrating additive composite bonding of other sounder teeth as part of a pragmatic approach for managing root filled, cracked, or very weak molar teeth

Case report 1

A 53-year-old male patient had very weak molar teeth with arrested decay and fractured lingual walls (Figure 8). There was also grey incisal translucency, that was largely a result of erosive tooth surface loss, but with some attrition (Figure 9). The additive anterior bonding (Figure 10) and the cores in the back teeth were left for a month to ensure that the patient had adapted without any symptoms before then preparing the molar teeth (one side at a time) for three-quarter gold crowns (Figure 11). Preparations were quick and simple to do because the cores and the residual tooth structure were very easy to identify, thereby enabling most of the remaining load-bearing buccal walls to be left intact.

The use of cemented self-threading pins

The technique and justification for using cemented self-threading pins placed very slowly in the bulk of the remaining dentine, rather than just using a standard mixture of glass ionomer cement as the core, is described below.

In this case, there was a massive amount of very unpredictable dentine left relative to the remaining enamel (Figure 8). A useful way to think about achieving predicable adhesion to sclerosed, chronically decayed and eburnated dentine is that it can behave a bit like an unreliable boyfriend. Consequently, it is sensible not to expect too much from it. In view of that, it was decided that some self-threaded dentine pins would help to secure a core more predictably.

The variation on the traditional titanium pin placement used here was to cement them with radiopaque glass ionomer cement, which would then become part of the core. The conventional radiopaque glass ionomer cement (Ketac Cem Radiopaque, 3M Espe, solventum.com) was used in two consistencies. It was first mixed to a double cream consistency to flow, and thereby to ‘wet’ the pins when they were being inserted very slowly and also flow over all the cleaned dentine.

As the pins were being placed, a lot more of the GIC powder was then mixed in quickly to the remainder of that double cream mixture to form a ‘doughy consistency’, which was then picked up on a flat plastic (using some GIC powder acting as a separator) and the dough was inserted to displace the double cream mixture and thereby producing a very tough pin-retained and bonded core material.

The use of any small titanium dentine pins in dentistry is deprecated by many who are inexperienced in their use. The present authors recognize this, and only use them very selectively, and then by following this protocol carefully, which directly addresses known concerns about stresses and heat generation.

The dentine pin placement protocol used here was as follows.

• The pin holes were drilled very slowly with a brand-new drill, and water coolant, in order not to raise the critical temperature within the tooth. It is known that the ‘critical bone temperature’ when placing dental implants is 45°C, i.e. 8°C above body temperature. As dentine and bone are similar in many ways, it is not unreasonable to suggest that it would be sensible to cross fertilize that well-known fact about ‘critical bone temperature’ for titanium implants when using small titanium pins.
• The pins were sited 1 mm inside the amelo-dentinal junction and parallel to the external aspect of the tooth in that area.
• Prior to cementation of the pins, each pin was pre-stressed by bending it at 45° at the join between the pin and the plastic pin holder once. The pin was then bent back so that it was parallel again with the pin-holding shank. The reason for doing that first is that it caused the pin to shear off very easily at the chosen depth, which was ‘just as soon as resistance was felt’ rather than ‘bottoming out’ at the end of the pin channel, and possibly causing stresses there.
• The conventional GIC (Ketac Cem radiopaque 3M Espe) was hand-mixed to a double cream consistency. The pre-stressed pin tip picked up some of that flowable cement and (without using any water) was gently and slowly cemented into the pin hole using minimal pressure to minimize heat and stresses being produced within the tooth.
• Just as soon as resistance was felt, the handpiece rotations were stopped immediately, and the pin was then bent at 45° to shear it from off the pin holder, leaving the pin cemented with half of it projecting upwards from the tooth. The net result was minimal stress to the residual tooth structure, while minimizing the risk to the well retreated pulp. The idea of using the conventional glass ionomer cement on the pins was to stop any potential microleakage, as well as acting as a lubricant for the small titanium pins.
• Once the cement had set, the pins were bent inwards to the centre of the tooth using a pin bender (Whaledent, Altstätten, Switzerland), thereby taking the pins away from any danger of being hit during the crown preparation itself. The excess cement escaping from the pin holes on cementation of the pins remained, and the whole of the exposed dentine was then covered with more double-cream consistency GIC cement to wet all the cleaned dentine and etched enamel remaining.
• The core for a crown was built immediately using radiopaque glass ionomer cement. The initial double cream thickness was used so that it flowed and thereby ‘wetted’ the dentine and the pins. Subsequently, that glass ionomer cement on the mixing pad was thickened quickly by the addition of enough GIC powder to produce a doughy consistency. That was picked up on a flat plastic using some GIC powder as a separating medium. That thicker dough was inserted and used to displace most of the double cream thickness GIC material, and it was then shaped, prior to setting, to provide a very tough bonded and pinned core.

The bright white colour of the very thick GIC core contrasted markedly with the residual tooth structure, which meant that during the subsequent crown preparation, a month later, a minimal amount of tooth structure had then to be removed to provide the retention/resistance form for the crown (Figure 10b, Figure 11a).

It is the present authors' contention that drilling the small titanium dentine pins slowly and carefully in the maximum bulk of the remaining dentine and cementing them with glass ionomer cement using the protocol above very carefully overcomes many of the traditional academic arguments about ‘never using small titanium pins under any circumstances’.

One author (MGK) remains sceptical about laboratory studies of pre-dosed resin-modified glass ionomer cements for use as cores in similar situations to Figure 8.

Case report 2

A 27-year-old female patient cracked a first molar tooth, which then developed irreversible pulpitis and required an emergency root filling (Figure 12). She was insistent on having a ‘white restoration’ even when it was explained clearly that this would require more occlusal space than would metal. However, after discussion of her available options, she chose to have composite bonded on to her other teeth to create space for the ceramic occlusal on her weak lower first molar and, partly, to try to reduce the risks of her cracking other teeth. The upper teeth were bonded freehand using chilled direct composite to create enough occlusal space for a ceramic cuspal-coverage restoration to be bonded to the residual tooth structure left at the cracked and root-filled lower left first molar without doing significant tooth reduction there (Figure 12).

That additive composite bonding was kept within the existing occlusal tables of the back teeth to load them mainly in compression and to reduce the chances of the composite being subjected to serious shear or tensile stresses. The main occlusal aim was to provide a pragmatic landing zone for the opposing mandibular teeth and provide simple canine guidance during lateral movements. The flatter occlusal surfaces on the molars reduced the wedging effects of the previous steep intercuspation of her back teeth, which can sometimes be involved in centric clenchers cracking their posterior teeth vertically.

That pragmatically bonded arrangement meant that the sounder teeth shared the occlusal loads much more widely and the composite was being loaded in compression. The canine guidance prevented lateral shearing forces being applied to the vulnerable root-filled mandibular first molar.

As an aside, the bonded composite on the sounder maxillary teeth acted a bit like a fixed variation of a ‘Michigan occlusal splint’ by having ‘posterior stability, anterior guidance with the canine guidance ensuring that there were no non-working interferences’. Because that composite was present 24/7, that should, in theory at least, reduce the potential for further cracked teeth.²¹ One advantage of the composite material being bonded to other ‘vulnerable to cracking’ teeth is that, unlike a conventional Michigan or other occlusal device, it does not rely on the patient being compliant with wearing their removable occlusal device at the critical, but unpredictable, very stressful times that can cause such patients to clench or grind their teeth, and thereby crack either their teeth or their restorations.

Case report 3

This 64-year-old female patient (who had recently married a dentist) had broken multiple teeth and restorations and had acquired three root fillings at various stages in the past. The lower left second molar had cracked catastrophically and been removed surgically the previous year. The left canines were in crossbite (Figure 13). After prolonged ‘BRAN’ discussions (an acronym meaning discussing with the patient the various benefits, risks and nothing), direct composite was bonded freehand to the available stronger teeth (Figure 13) to create enough occlusal space so that a minimal amount of her remaining ‘dental capital’ would need to be removed to place multiple partial veneer internally and externally sandblasted gold crowns.

That pragmatic bonding created space over the occlusal aspects of the root-filled and very weak teeth, and then the last tooth in the arch on each side was bonded on the strongest part of its occlusal surface with a contrasting-coloured composite material to stop the condyles going upwards and backwards and thereby losing the occlusal space that had just been gained over those very weak teeth.

The patient was given 2 months to adapt to her new occlusion, which she did with no discomfort or complaints at all. Partial veneer (‘three quarter’) gold crowns were completed on the right-hand side molar teeth first, and the space at the lower left remaining molar was kept by leaving the contrasting-coloured composite on its occlusal aspect throughout. A few weeks later, when the three-quarter gold crowns were returned from the laboratory, the right-hand side crowns were fitted on to those root-filled teeth. The occlusal space at the lower left remaining molar left was still maintained throughout that time by the contrasting coloured composite bonded to it until it, too, was prepared for a partial veneer gold crown. Some months later, the lower left first molar was prepared for a three-quarter gold crown and an impression taken.

Issues with temporizing terminal molar teeth after preparations for crowns

Experienced dentists know that whenever one is preparing a crown on the last remaining molar on that side that, if the occlusal space is not maintained properly while the definitive crown is being made in the laboratory, then, during that time, the condyle on that side can go upwards and backwards in the glenoid fossa and thereby the space required for the ‘definitive’ restoration will be lost. Unfortunately, that happens frequently if the temporary restoration is not robust enough to stay in position, and that happens more often when using commercial plastic materials to temporize last molar teeth that have been conservatively prepared to receive an all-metal crown. That is particularly likely if a flimsy plastic temporary crown is then cemented with a weak ‘temporary cement’, which is sometimes chosen because it enables easier removal before quickly cementing the definitive restoration. In the scenario when that plastic temporary comes off a terminal molar, thereby exposing the vulnerable prepared structure any time before the definitive crown is ready to be fitted, the result is that when that crown is tried in it often appears to be ‘embarrassingly high’ and then suddenly requires rapid (and often completely concealed from the patient) gross occlusal reduction to get the patient even vaguely close to their previous intercuspal position before it can be cemented, and even then often also once it has been cemented. Confronted with that exasperating occlusal discrepancy, some cavalier clinicians tell the patient to ‘just to get used to it’ or perhaps even more dubiously, tell them that ‘it will Dahl in’. (As yet another aside, Bjorn Dahl never described doing anything as clumsy as doing that on a last molar tooth. His removable device was used for gaining space over worn anterior teeth only… before then partially crowning them.)

Most experienced clinicians realize that the closer to the condyles that the crown's occlusal discrepancy is, then the greater is the hinge or ‘nutcracker effect’ producing a separation effect much further forward in the incisor region.

To avoid that scenario the occlusal space, which had been created by drilling off the contrasting-coloured composite to create just enough occlusal space for the metal crown, was maintained in this case by using polycarboxylate cement alone as the temporary restoration with the following protocol (Figure 13e,f).

The clinical protocol used here to make the ‘temporary’ polycarboxylate cement restoration was as follows (Figure 13f):

• The polycarboxylate powder and liquid was mixed to a ‘double cream’ initial consistency and applied to the cleaned and dried terminal molar tooth.
• That was followed immediately by the dental nurse mixing in more powder rapidly to produce a ‘doughy consistency’.
• That doughy mixture was picked up by a polycarboxylate-powder covered flat plastic and then pushed on to the prepared molar tooth thereby displacing most of the more flowable (and therefore ‘better wetting) double-cream consistency polycarboxylate cement.
• That doughy mixture was immediately covered with Vaseline and a version of a ‘functionally generated path’ approach was used (as described by Meyer in 1959.)²²
• The patient bit into the Vaseline-covered doughy polycarboxylate cement just as it began setting and then moved her jaw around in all movements continuously while the polycarboxylate cement set and thereby inscribed the anatomy of the opposing teeth into it (Figure 13f).
• Once set, the Vaseline separating material stopped the cement from being pulled off by the opposing teeth when she opened her mouth. That was just tidied up, and that simple technique produced a very well sealing and highly durable temporary restoration requiring minimal finishing or occlusal adjustment.

Once the gold crown was returned from the laboratory, the creamy-coloured polycarboxylate was easy to see and therefore very simple to remove with a high-speed drill and some gentle ultrasonics without damaging the preparation prior to then cementing the three-quarter crown quickly and without any need for any occlusal adjustment (Figure 13f). In busy clinical practice that ‘polycarboxylate cement temporizing approach’ for barely visible back teeth saves a lot of time and is a much more sensible and practical approach than using a flimsy plastic temporary material with a soft temporary cement which nearly always comes off, particularly if it is in thin section on a terminal molar that has been prepared for a ‘dental-capital self-preserving’ partial veneer metal crown.

Case 4

A 20-year-old case showing the durability of additive composite in a case of a mainly erosive tooth surface loss prior to placing an internally alumina-blasted ‘gold hat’ on a dead, root-filled molar (Figure 14a). There are multiple reports in peer reviewed journals of the good medium-term results when using composite for managing extensive tooth surface loss (about 6 years on average) with an excellent fallback position of the composite being able to be repaired or replaced but no reports of any pulpal deaths).^13,14,15,16 There is no logical reason why similar results should not be expected when this concept is applied for helping to manage root filled or cracked- or just very weak posterior teeth (Figure 14b).

Case 5

In this case, additive bonding was carried out prior to placing an adhesive three-quarter crown style restoration on a recently root-filled upper right first molar (Figure 15).

Discussion

How does adaptation to additive occlusal changes work?

Once the minimally destructive (Note: not the often lazily parroted ‘minimally invasive’) pragmatic composite bonding has been carried out on the outsides of various other stronger teeth, the adaptive processes to those occlusal changes appear to be programmed mainly by the mechanoreceptors of the periodontal ligaments, but there are other receptors in the face also involved.²³ Positional changes happen quickly in healthy temporomandibular joints, as well as during various relative axial movements of different teeth occurring over time with some minor eruption or intrusion of some teeth. The most obvious clinical evidence of ready adaptation by most patients to expected occlusal changes is the success of various types of orthodontics and orthognathic surgery, as well as the widely reported successes of additive bonded composite approaches for managing wear and solving other dental problems.^{13,14,15,16,17,18,19,20} However, patients do need to be involved fully in detailed discussions beforehand about their various viable options (including not doing any bonding) for their consent to be valid (see earlier). That said, once matters are explained fairly to them, many patients who have undergone the dubious delights of a root filling, often wish to minimize further sound tooth destruction to preserve their existing ‘dental capital’, particularly if it means them getting a ‘satisficing’ outcome (meaning a result that is sufficient for it to be satisfactory for them).^7,8

The variations on the additive bonding theme being proposed here is to use those proven additive composite ideas²⁴ to provide a pragmatic, but protective, occlusal scheme that creates interocclusal space for a protective cuspal coverage restoration without the need to reduce the patient's ‘dental capital’ further.

Using direct resin composite bonding as an additive procedure ensures that the stronger sounder other teeth continue to protect the still weak root-filled teeth in the longer term (Figure 13c,d). In this ‘protective and preservative composite philosophy’, the now supposedly ‘definitively restored’ root-filled (or other very weak) tooth should not be expected to take more than a fair share of occlusal load in the patients new ICP, and certainly no heavy lateral loads. That pragmatic approach seems clinically sensible, all depending on the estimated reduction in the tooth's ring integrity and load-bearing structure caused by the previous caries, or tooth fracture/trauma and which might well have necessitated the root filling in the first place.

OK. Any other points?

The one thing that even the most expert endodontist cannot do is regrow more sound tooth structure in even their most elegantly root-filled tooth. However, endodontists can avoid depleting that patient's valuable load-bearing ‘dental capital’ themselves (Figure 6), as well as encouraging others, including their referring practitioners, not to default to doing easy and quick, but unnecessarily destructive, preparations for full-coverage ceramic or ceramic bonded to zirconia or other unproven, but heavily promoted CAD/CAM materials to produce a potentially misleading ‘permanent’ crown on a natural tooth.^5,9,10,11,12

One practical tip is that chilling hybrid composite reduces its slumping. Doing that first makes it very easy indeed to keep the material within the palatal surfaces of the sound incisor and canine teeth and also confine it within the occlusal tables of the other sounder premolar or molar teeth with no real attempt being made initially to produce ‘fancy anatomy’ (Figure 16).

That is simple to do if a chilled wine or beer cooling sleeve (kept until required in the freezer compartment of any fridge) is placed over the required amount of composite once it has been extruded from the composite tube on to a pad and covered with an opaque light-proof Dappens pot until it is required. (Note: please don't put the tube or compule inside the cooling sleeve because doing that would stop it flowing).

Summary

The main purpose of bonding the additive composite early is to separate the occlusal surface of the root-filled (or other weak target tooth) from its opponents in all jaw excursions.

The occlusal adaptation that is programmed, mainly by the periodontal ligament mechanoreceptors, has been termed ‘the gifts from the lovely ladies in the ligaments’.^17,18

Composite, when loaded in compression and placed in thick section, performs very well. It is only when composite is placed in thin section and/or subjected to shear or tensile stresses that it performs poorly. In many ways the composite is an intentionally sacrificial material that can be polished, re-surfaced or replaced at any point and leaves the remaining ‘dental capital’ intact.^17,18

Once that has been achieved then, immediately afterwards, the root-filled back tooth (or other cracked or weak tooth) gets bonded immediately on the soundest part of its occlusal surface to produce a simple ‘occlusal stop’ using an obvious contrasting-coloured composite (or, if really preferred, with a fast-setting contrasting-coloured GIC).

Following confirmation of the patient's adaptation, usually by about 4–8 weeks, then the contrasting-coloured composite material is cut back on the occlusal surface of the root-filled tooth to create just enough space for whatever material is chosen for the allegedly ‘definitive cuspal-coverage restoration’

In most cases, unless the back tooth is highly visible in normal mouth activities, alumina-blasted (‘sandblasted’) metal is still preferable for root-filled back teeth because it has many decades of years of clinical proof, as opposed to often just a few years with various versions of all-ceramic or veneered zirconia, especially when those are used for used for ‘restoring’ root-filled, cracked or otherwise weak back teeth.^25,26

Alumina oxide blasting of the metal restoration internally greatly improves the adhesion of the cement to it. If someone really does not like the occasional possible glint of polished metal when it is actually in position, then alumina oxide blasting of the outside removes the shine quickly and doing that once the metal restoration is normally covered by saliva helps it to conceal it (Figure 15c,d).

The main criticism of the traditional subtractive approaches to ‘restoring’ a root-filled premolar or molar tooth by using a full-coverage ceramic bonded crown, or indeed any indirectly made cuspal-coverage device of some ceramic material, is that the euphemistic ‘preparation’ to get one path of insertion required for it frequently involves the irreversible destruction of much of the occlusal surface and the load bearing marginal ridges, as well as much of the interproximal surfaces in order to obtain that mandatory one path of insertion and to conform to the patient's existing intercuspal position (Figures 1, 2, 4 and 5). Conversely, direct composite can be inserted in various small sections from multiple different paths of insertion, and doing that can really help to preserve any residual ‘dental capital’ still present. Following the reported successes of additive bonding for solving many dental problems,^{7,8,9,10,12,13,14,15,16,17,18,19,20} the traditional thinking about semi-automatically restoring all root-filled molar teeth using the patient's existing intercuspal position by using full-coverage bonded or all-ceramic crowns or CAD/CAM technology ought to be challenged more vigorously now and, in many cases, relegated to being a less desirable structural and biological approach for many (hopefully) properly informed patients.

In saying that, one recognizes that one fierce criticism about adopting any pragmatic minimally destructive approach in dentistry is that there is ‘no strong scientific evidence for doing so’ before making any changes to clinical practice. That is often the case in dentistry. However, most of our trumpeted ‘scientific knowledge’ and/or ‘evidence base’ in dentistry is provisional, and on critical appraisal is frequently found to be flawed owing to multiple confounding factors. For example, many studies involve very careful case selection and exclusion criteria, often undertaken in institutional settings with specialist skills available and no time pressures involved. Additionally, many have multiple biases, such as publication bias, availability bias, confirmation bias or Heisenberg effects, commercial influences, or dodgy statistical manipulation.

In many cases, such as with composite bonding for managing tooth surface loss, the ‘scientific’ evidence supporting it only emerged very many years later²⁴ often well after various pragmatic and practical clinicians had shown that it worked in many cases,^{13,14,15,16,17,18,19,20,21,24} sufficiently well for it to be deemed to ‘satisficing’ (meaning that it was sufficient for it to be satisfactory) by the patients.^7,8

Unfortunately, partly because of traditional occlusionist dogma¹⁷ and ‘narrowcisstic’ (meaning both narrow and narcissistic) thinking about root-filled back teeth, coupled with multiple flaws in the NHS UDA remuneration system, consideration is rarely given in the UK to the merits of possibly bonding additive fixed composite devices pragmatically to the stronger teeth with the aim of creating appropriate occlusal space for a later cuspal coverage restoration to protect the vulnerable back tooth. It is proposed that the variations of approach outlined above are likely to be beneficial in managing the perennial problems posed by root-filled, cracked or very weak molar teeth while maintaining the patients precious ‘dental capital’.

Conclusion

Using direct resin composite bonding as an additive procedure creates occlusal space for cuspal coverage restorations and ensures that the stronger, sounder other teeth will protect the still weak root-filled teeth in the longer term. However, in this ‘preservative protective composite philosophy’ the now cuspal-covered root-filled (or other very weak) tooth should not be expected to take more than a fair share of the occlusal loads in the patients new ICP and no heavy lateral loads. That pragmatic approach seems practical and sensible, all depending on the estimated reduction in load-bearing structure, which was caused by the previous caries, or tooth fracture/trauma, which might well have partially necessitated that root filling in the first place.