CLASS II DEEP SUBGINGIVAL BOX
Sometimes the proximal box extends so far subgingivally that you can’t reach the gingival floor with normal-length burs. Additionally, the tissue is these cases is often very inflamed, hypertrophic, and hyperemic, making visibility short-lived.
Then matrixing becomes more difficult, perhaps problematic. Under these circumstances, ultimate success with a light-cured restoration can start to seem chancy.
Can we still succeed? The answer is yes, and the strategy, as always is to reduce the difficult job to an easy one that we are familiar with. How to normalize this beast,and make it into a ho-hum MOD?
The first obstacle to overcome is to prepare a proximal box that is outside the reach of normal length burs.
- Extra- long friction grip burs are available – OS 1557 or OS 1558, oral surgery -length high-speed burs . These are 26mm long, 6mm longer than standard dental burs. and will reach nicely. This oral surgery bur is a special order bur from many supply houses, so allow lead time in ordering.
Ideally, a bur without crosscuts would be used, however, no such animal exists. To improve the cavosurface finish of box walls, use a 284K.018 spiral-cut crown prep finishing bur, a long, spiral-cut crown finishing carbide,made by Brasseler to finish gingival margins, to polish the box walls smooth. See Brasseler 284k.018 finishing burs
The floor of the box, however, will be adequately smooth because the end of the 1558 bur is not crosscut.
- For caries removal, use extra long slow speed burs; oral surgery (25.5mm) #4 and #6. These are often special order also. Note: that these are not endodontic-length burs, which are only 21mm in length and therefore have inadequate reach.
Sometimes the handpiece head impinges on the cusp, even using an over-length bur, and this impingement prevents reaching the floor of a deep gingival box. A practical solution is to reduce and subsequently shoe the interfering cusps.
With an attitude of conservatism and a Minimally Invasive Dentistry outlook, we may need to ease our conscience about this elective removal of crown structure. It may help to bear in mind that when you follow this strategy you are still removing much less tooth structure than would be required to prepare the tooth for a crown. Equally, a crown could prove impossible to prepare when the dental crown is that long, as in periodontally involved teeth. As well, in mouths with such extensive breakdown, are crowns indicated?
Also, restoring a cusp is no big deal, whereas a defective gingival margin is a very big deal. Go for a clean, caries-free, well-instrumented margin, and take off adjacent cusps if that is what is needed.
STRATEGY FOR MAXIMIZING VISIBILITY
- Unavoidably tissue will be traumatized as the subgingival areas are prepared. To maximize the duration of good visibility, finish the internal aspects of the preparation, including caries removal, before tackling this sub-tissue margin. Wedges can be helpful to compress the tissue interproximally,as one completes the internal form. If wedges do not control bleeding, place cord,or work inside a band while prepping the internal form.
- Finish the gingival margin. Eliminate weak and irregular cementum to produce a clean gingival floor and rounded box corners. In a cementum margin, because this margin is not enamel, you do not have to produce a 95-degree margin –in can range from 80 to 100 degrees, for instance, provided it is sound, regular, and clean.
- Design margins for optimum final finishing. It is better to “overcut” to the facial and lingual if over-extension allows you to better access and finish margins. This is GV Black Convenience Form in the composite era. A wider box makes a margin that the patient can also easily access with a toothbrush. The extensive and deep box seems to be one place where GV Black “Extension for Prevention” and “Convenience Form” are still very applicable.
- Prepare the matrix. If it will not seat due to impingement on lingual or facial tissue line (elsewhere than the box), carefully cut those impinging portions of the band away, using un-serrated crown-and-collar scissors. This is painstaking work – following a tissue line and trimming the band to suit. Sometimes we may need to do two matrixes, the first one being a trial run that becomes the template for a second, successful one.
- The Waterpik #2 Tofflemire matrix band, (the one with wings) is the one of choice. They are available tempered, .0015 or .002thick, or dead-soft, .001 thick. This Handbook recommends the .0015 tempered for contouring with the Bandbender Matrix system
In difficult boxes of any type, tempered bands are almost always preferable, because stiffness helps in guiding and placing the band. Stiffer bands resist deformation by probes or other instruments used to guide the band into place, and also wedges.
- In extreme situations, if the band does not achieve proximal contact, don’t worry. The primary goal is to emerge from the sulcus with a perfectly adapted band and perfectly restored gingival margin.
- Scribe the band, remove it, shape it with the Bandbender, and re-insert.
- If the band is too low to achieve proximal contact, restore the gingival portions and then raise it up and re-wedge.
- Alternatively, place the gingival portion with an uncontoured band to bring the gingival margin supragingival. The place, a second band, modified on the Bandbender to proper proximal contact. In essence, restore the deep box, and then treat the tooth as if it was just a normal MOD, except that there is now a restored composite box where you normally have tooth structure. The reader can see in this strategy that a sound gingival seal is the first and critical priority. Other clinicians have given this strategy the name “Margin Elevation”
- There is almost no opportunity to finish a subgingival margin. Plan to leave it primarily as is, once cured against the band. This maximizes the integrity of the margin and the smoothness of the resulting surface. Finishing near cementum must be approached with great discretion. A root surface that has been gouged, roughened, or beaten up by ill-advised attempts at finishing will fail early. The cementum, in an abrasive showdown, being so much softer than composite, will be sacrificed first and more finishing will only worsen the defect. The only viable approach is to place the rotary bur on the composite surface and work that surface down until it closely approximates the cementum, and then quit. Be always sure that the bur runs over the composite at an oblique angle to the cementum/restoration margin, so the bur cannot drop off the composite and bury itself into the cementum, i.e., the bur is always supported by the harder material.
- Custom wedges can be made from tongue depressors, wooden topical applicator sticks, or by piggybacking several wedges. Fast-cure rigid PVS bite registration material can be introduced in the gingival embrasure and then used as a buttress to wedge against. The goals are hemostasis, isolation, band adaptation, and controlling the emergence form. Don’t fret about the final form of the restoration at this point. Get the restoration up from under the tissue line with perfection, and then go from there.
RESTORING THE DEEP BOX; STARFILL 2B; PHOTOCORE
The rule of thumb in this Handbook is that boxes deeper than 6 mm. must be restored with dual cure resin. Attempting to place LC resins deeper than 6mm is pure folly see Curing resins
Once the box is properly matrixed, and perfectly isolated, it can be bonded and restored.
Here is a situation where the bond sequence of this Handbook, with liquid etch, primer, and dual-cure adhesive, currently Photobond (Kuraray)or All-Bond 3 (Bisco) really shines. The liquid etch debrides the preparation quickly, simultaneously and beautifully. Residual bleeding can almost always be controlled by using hemostatic etch, see Hemostatic etch
Microprime B on a Voco #1 Pele Tim pellet follows etch and rinse into all parts of the prep efficiently, copiously and quickly, sealing up any potentially sensitive post-operatively dentin in these large and deep preps with the least probability of tissue burns. Rapid deployment with low viscosity materials in all of the steps ensures consistent and quick results.
Photobond and All Bond III are dual-cure bonding agent. This is critical to deep boxes to assure proper adhesion when light activation is questionable. As a rule of thumb, also double the light exposure time to the bonding agent if the box is deeper than 6mm.
STARFILL 2B DUAL CURE FLOWABLE
Instead of Starflow or other LC flowable use Starfill 2B (Danville Dental), a dual-cure flowable, as the initial flowable increment. It is very strong, aesthetic, and smooth finishing, unlike its competitor, Bisfill 2B, which is a rough-finishing macro, and it is chemical cure only. See Dual-Cure adhesives and Dual cure Flowables
Starfill 2B is supplied in a dual-barrel auto-mix syringe with a small tip angled about 30 degrees off the shaft axis. Fill up the prep to normal gingival height and light cure. Full set will be achieved at 2.5 minutes.
However, if the tissue is oozing around the band, and isolation looks like it will be short-lived, despite everything you’ve done, then follow this approach: place a small initial increment of Starfill 2B, adapt it to the gingival margin with a perio probe, and immediately light cure.
Then place the remaining Starfill 2B. In all cases limit the overall increment thickness of Starfill 2B to 2.5mm for best subsequent top-up of polymerization by secondary light cure, and extend cure times as appropriate with greater tip to tooth distances. Never take a chance on under-cure.
In the attempt to save time in these large and difficult restorations, manufacturers have introduced bulk fill resins, with claims of 5 mm increments and a 40 second cure. See Bulk Fill Resins for the reasons that this is not generally a viable approach.
The best approach to cure is to use a fast-cure light. In large restorations, where there may be 20 or more increments, this really pays off. In this writer’s practice, the Sapphire plasma-arc curing light (Denmat) is the instrument of choice. While the manufacturer claims 3 second cure, test discs of 2mm and 3,5 mm thickness chairside have shown that 5 seconds is the more realistic time. While an older light, reminiscent of the 80s and 90s, with a fiber optic cable and a somewhat noisy fan, it registers 2200 Mw. It reduces placement time in large MODXYZs by many minutes, not to mention reduced frustration when long periods of curing interrupt forward movement of the procedure. Some of the worries from its inception- pulpal overheating, or crazing of tooth structure, have failed to materialize clinically.
Other fast-cure lights claiming a five second cure have failed to demonstrate this capability when reviewed independently by Reality Research. False claims of curing efficacy are unethical and dangerous for both public and practitioner. Perhaps with shade A1 close to the surface, one may reach the criteria of 80% photoconversion. But manufacturers never specify in scientific or legally binding terms what a 5 second cure objectively means- what resins, what distance, what percent of photoconversion – so we are in a swamp of marketing hogwash and indefensible claims when it comes to the always invisible subject of “cure”. See to see what one can do to improve the odds of success under these circumstances at Curing Resins
Once up to ideal depth, finish with a final resin as usual. A smooth-finishing small-particle hybrid or nano-hybrid with flexural strength exceeding 150 Mpa is desired. This limits the choices to a minority of resins, because the majority of resins are well below 150 MPa.
RECOMMENDED RESINS FOR LARGE COMPLEX RESTORATIONS
See Class II Resins 2019
Filtek Supreme Plus,(3MEspe) or Venus Diamond,(Hereaus Kulzer) or HNA ERI(Mycerium) or Grandioso (Voco)are all above 150 MPa in flexural Strength and are recommended.
An older-generation macrofill core buildup material, Photocore (Kuraray) performed well for many years, as it claims to achieve (and has been tested to achieve) a cure depth of 9 mm. This amazing finding is achieved at the expense of esthetic appeal- it is extremely transparent and cosmetically downright ugly. But no other resin has the cure-ability of Photocore. It stands alone in the resin world. More attractive, better wearing resins with less contraction have largely supplanted it, but it earns a historical nod in the author’s practice at a time when nothing else was standing up in heavy-function, enormous posterior composites.
KEEPING YOUR COOL AT THE OUTER LIMITS; FEES; PROGNOSIS
- Don’t forget that your MODXYZ fee needs to be comparable to the time and challenge presenting.When you enter deeply subgingival preps, it represents a time factor of at least one or two additional surface. A deep MO becomes a MOD in terms of fee, and a MODBL is surcharged proportionately to the time taken to place it.
- Don’t forget you are saving a tooth that somebody else has destroyed – either the patient or another dentist. Feel good, even though it is hard work, and departs from conventional wisdoms about treatability. Balderdash to the norms- this approach works.
- Realize that every difficult case you do will make the next one easier and will improve your skills. So embrace the learning potential. Your achievable mission is to hold back the patient’s progress to edentulism. Surprising longevity is possible.
- Balance confidence with caution: guard against unrealistic expectations; chart the case as guarded prognosis, note if you feel that it is last time it can be treated, and inform the patient of its expected lifespan. Believe me when I say that the tooth restored to the above protocol will not fail structurally, but rather because of the same causative factors that led to its initial breakdown-plaque and neglect,and a high caries rate.
Margin failure is its likely demise, for several reasons. Firstly, it is a cementum/ composite bond, purportedly shorter-lived than an enamel/composite bond, although this has not been consistently true in this writer’s clinical experience.
Secondly,and applying to all restorative materials: the restoration is unfavorably located – beyond the reach of normal hygiene.
In most cases with a deep box there is reverse bony architecture, so that a large gingival embrasure exists over top of an infrabony defect. This is a natural food trap. This whole negative structural form is superimposed on the poor oral care and diet patterns that initiated the previous carious breakdown.
- Periodontal failure can be another mode of failure, as often in the maxillary arch the deep proximal box opens up access to the trifurcation area. Nonetheless, time moves along slowly for teeth that are definitively restored with skill, following sound basic principles, and maintained with diligence by the patient.