BEGINNINGS: THE FAILURE OF PREP-LESS RESTORATION
Twenty years ago I began placing composite in unprepared attrition defects. Many lecturers recommended this approach at the time, and some still do. However, it has proven to be a short-lived technique. Despite an appeal to our conservative instincts, being a reversible procedure, requiring no reduction, it is unfortunately doomed to a short lifespan, and for good reasons. Let us look at these reasons….
- There is usually insufficient and inconsistent depth for load dissipation into the dentin. We all know that composite, when used in thin layers, is prone to flaking and disintegration.
- Because there is not a consistent depth to the preparations, and darkened sclerotic dentin is not removed, inconsistent aesthetic results are seen
- The enamel is unprepared, compromising bond strength When there is no preparation, bond strengths are poor, due to the etch-resistance of older, highly fluoridated enamel. As well, the enamel surface consists of amorphous, remineralized enamel that is not cohesive with the underlying enamel rods. To properly fuse resin and enamel together, we want to gain access to the structural rods which underlie this layer.See Enamel axioms to understand the method recommended in this Handbook for all composite preparatios.
- Dentin bonding is compromised There is no removal of sclerotic dentin, smear layer, plaque or pellicle that is on the dentin surface. Dentin bonding may therefore be contaminated by biofilm. Additionally, sclerotic dentin rather than fresh-cut dentin presents as the bonding substrate; research demonstrates more variability in bond strength to sclerotic dentin than fresh-cut dentin.Finally, a dentin smear layer covers the dentin when there is no prior preparation, and, depending on the bonding agent in use, this may in fact be incorporated into the bonded interface, sacrificing additional bond strength into the hybrid layer and into tubules.
- Finally, the prep form created by natural attrition is usually saucer-shaped. In GV Black terms, this offers poor resistance form. promoting rotation of the material under load. This lack of resistance form translates into adhesive strain, because shear forces between the composite and the tooth structure are being resisted by the adhesive alone, with no relief from resistance form . Resistance form changes the adhesive loads into compression and tension loads along the interface, where apposing walls meet.
This illustrates an important point: in bonded composite restorations, you can often succeed with reduced classic retention form. But you cannot ignore it altogether. We still have to engineer the case. Alternative streams of retention i.e. sufficient area, sufficient depth, efficient dentin interlocks and preparation form are needed to ensure success. Adhesion works best when combined with classic extra-coronal or intra-coronal retention form.
I call the prep designs in this Handbook a “belts and suspenders preparation”, because some GV Black thinking is still necessary.
Over time, some early prep-less cases survived, more by chance rather than by intention. Overall lifespan was still short because the teeth would continue to wear, and before long the shallow increments of composite at the enamel interface would wear away, leaving an island of composite surrounded by a rim of enamel, or possibly dentin. The enamel rim, no longer bonded to composite and thereby supported, resumed disintegrating as before.
THE EUREKA CASE
After a few years of this futility I was faced with a challenge case. It opened the door to a better technique.
A new patient, a big and muscular man, presented with a desperate situation. His small teeth showed extreme attrition. Functionally, his dentition was exposed to very high load, imposed upon his very small teeth, which were separated by diastemas throughout the mouth. It was a disastrous combination. The anterior occlusion was entirely in dentin by this time, and coronal loss was at a staggering 50% level. The teeth were melting like snowballs in July.
Obviously he was bruxing. Looking at this case with hindsight, it becomes clear that sleep apnea was the most likely etiology, and in fact, this patient did go on to have a stroke and to fitted with an apnea correction device. Apnea was not on dentistry’s radar at the time of this treatment. We treated his teeth. Now we would treat both his teeth an his apnea.
His budget did not allow the use of crowns, not to mention the difficulty of realizing decent aesthetics on very small teeth. As well,a high caries index made crowns inadvisable.
When I took x-rays, there was no sign of pulps in any of the teeth – they were all extremely calcified. Because nothing else could be done to stave off the collapse of this patient’s mouth, I took a deep breath and prepped into dentin on all the maxillary and mandibular incisors to a depth of 1.2mm- about 2/3 of the length of the blade of a 330 bur. I restored the teeth with Z100, the toughest kid on the block at the time, 1996.
A year later this patient returned. Unbelievably, 11 of 12 restorations were still intact. I re-restored the lost one, and five years later, these 12 were still intact! Incredible! I had discovered a new modality.
SUBSEQUENT EVOLUTION OF INCISAL TREATMENT
Since then I have placed over 4000 individual restorations. I have come to understand resins better,changed resins, and explored the application of this concept to the limit. I have lengthened worn maxillary teeth, and even restored vertical dimension in collapsed cases to full crown length against natural teeth and also against full dentures – i.e.- direct full mouth reconstruction. A case is detailed at the end of this article.
The case below was treated in 2006, and completed in one day without anesthesia. Since that time some of the restorations on the maxillary arch have de-coronated and evolved to conventional fixed crowns and bridges. In terms of the patient’s budget, this has been more acceptable than the same fees proposed en masse. This illustrates the value of this form of treatment in staging rehabilitation.
However, all of the restorations on the lower arch have endured! Three carious margins developed and required treatment.Beyond that, his lower arch is as it was left 14 years ago.
I think the composite maxillary teeth are too white in shade but the patient’s wife preferred it.
This case survived for 5 years without maintenance. Stepping back for perspective, this treatment has allowed the patient to retain his teeth, develop a relationship with a dental office, and avoid what would have become full dentures in most offices, or an implant-based and very expensive fixed restoration. In my value system, his one day in the office was money very well spent.The conventional treatment plan ,crown lengthening, elective endodontics and post/core buildups would have been delivered at many times the cost, all with attendant invasion and morbidity.
Some aesthetic re-contouring of evident imperfections seen in these photos was corrected the following day; but at the point of taking these pictures we were tired, and ready to go home!
CONFIDENCE IN THIS APPROACH
Obviously, I have a great deal of confidence in this approach to attrition. Its success has also altered preparation design for Class IV restorations that join a worn or compromised incisal edge. This is detailed in teh Handbook as well, see Mini-shoe
Properly executed, this approach produces durable, painless, conservative, attractive, and inexpensive restorations, which are endodonticly and periodontally innocuous.
For some time in these more extensive cases I worried about possible pulp encroachment when entering an already severely worn incisal edge, but there is a fortunate biological synergy, in that, typically, where there is no enamel on the incisal edge, the pulp immediately begins to calcify and retreat apically. In this way nature conveniently makes way for dentists to prepare into dentin with a bur.
In almost 25 years of using this procedure, preparing over four thousand teeth, I have never had a pulp exposure on an incisor.
To further reduce concern about pulpal effects, consider the downside: let us presume an exposure does take place. It will be a mechanical exposure without pre-existing pulpal pathology or caries. Thus, minimal bacterial invasion is involved. The prognosis for pulp survival with an MTA pulp cap will be excellent. Alternatively, prognosis with conventional RCT will be excellent.
It is prudent, however, to enter the dentin cautiously when preparing incisors, to maintain good control over these delicate preparations. Also, a typical depth of 1 mm. is all that is required for a lifespan of 10 to 20 years, making a number of assumptions about wear rate, of course.