Is All Minimally Invasive Dentistry Better Dentistry?

Just the other day a company car belonging to a local dentist drove by. It was plastered with advertising from the office, heralding the merits of bleaching, lasers, and minimally invasive dentistry (MID). It was at that moment that I realized that it is high time for the profession to quantify, legitimize, and provide research on the noble but troublesome topic of MID. The term minimally invasive has been embraced by the medical community—hospitals and surgeons are now marketing a wide array of MI medical treatments.
In this article, I will first review the ethics and politics of “naming” and “branding” in dentistry. Next, I will review the hierarchy of tooth needs, presenting a new concept in which not all structures and zones of the tooth have the same value. In turn, that will help to frame 3 cases—types where the dentists performed MID, but, in the end, the patients suffered with poor outcomes. I will conclude with the results of the 2009 Opinion Leaders’ Forum of Minimally Invasive/Minimally Traumatic Dentistry that I hosted. At the forum were some leading experts and forward thinkers, including Drs. Paul Belvedere, Bob Margeas, and Len Boksman.

THE NEW LEXICON OF DENTISTRY—WHAT EXACTLY IS MINIMALLY INVASIVE DENTISTRY?
Pogo once stated “We have met the enemy, and he is us.” Whenever we introduce a sub-“specialty” (or pseudo-“specialty”) such as cosmetic dentistry or a branding term such as laser dentistry or MID, there are serious concerns. Further compounding the problem are the advertising campaigns of the manufacturers that encourage the confusion by introduction of pseudoscience with terms like “nano technology” to describe a composite material that is actually a simple microfill.
Magnification is also an issue. Can a dentist perform MID with the naked eye? Most would argue no. In endodontics, the trend to use microscopes continues. We are now seeing a division of endodontic practitioners into 2 camps: microscope-based-visual endodontics and traditional-tactile endodontics. Tactile endodontics is what most general dentists and many endodontists rely upon—depending mainly on “feel” to find difficult canal systems. Conversely, routine exploration deep inside of the tooth at 20x magnification with perfect coaxial light allows for new possibilities in directed-dentin conservation. Can endodontics be MI without a microscope? Many would argue no.
Once we are able to recognize a definition of MID, which in its purest form is the preservation of tooth structure, it must be framed within a new concept—the Hierarchy of Tooth Needs. During patient treatment, the clinician needs to consider a multitude of factors that will affect the ultimate outcome. In simple terms, these factors can be grouped into 3 categories: operator needs, restoration needs, and tooth needs. These would be described as follows: operator needs being conditions that the clinician needs to treat the tooth; restoration needs being the prep dimensions and tooth conditions for optimal strength and longevity; and tooth needs being the biologic and structural limitations for a treated tooth to remain predictably functional.

THE HIERARCHY OF TOOTH NEEDS

Table 1 represents the hierarchy of needs to maintain optimal strength, fracture resistance, along with several other characteristics needed for long-term full function of the posterior and (Table 2) anterior tooth. This brief article is designed to simply introduce the reader to the reshuffling of the values assigned to different tooth structures and for the nuanced role of the importance of regional tissues. A full explanation of the new hierarchy will be presented in future articles to be published in Dentistry Today.

Table 1. Hierarchy of Tooth Needs for Posterior Teeth
Extremely High Axial wall Zone DEJ
Cervical Enamel
Pulp in Immature Teeth
High Coronal Zone DEJ
Coronal Dentin
Medium Coronal Enamel
Low 2o Dentin
No Value or Liability 3oDentin
Inflamed Pulp in Mature Teeth
Exposed Dentin (common in cusp tip areas)

 

Table 2. Hierarchy of Tooth Needs for Anterior Teeth
Extremely High Pericingulum dentin
Pulp in Immature Teeth
High Cingulum Enamel
Axial Wall DEJ
Cerical Enamel
Medium Peri-incisal Enamel
Low 2o Dentin
No Value or Liability 3o Dentin
Inflamed Pulp in Mature Teeth
Exposed Dentin in Incisal Area


Figure 1. (Case 1) Low magnification view of a sealant on the occlusal of an upper second molar (orange arrow). Figure 2. (Case 1 continued.) Eight times magnification view of sealant. There are no visual clues that the sealant has failed.
Figure 3. (Case 1 continued.) The sealant was removed because of patient complaints of severe sweet sensitivity. Gross caries that extended near the pulp was present. This condition was masked by the sealant and even the use of a Diagnodent (KaVo) would have been of no value to diagnose the occult caries.
CASE 1
Sealants Gone Awry

This case features a sealant that looks clinically acceptable at low magnification (Figure 1). At high magnification, the seal­ant continues to exhibit acceptable margins (Figure 2). However, upon removal of said sealant, gross caries were present (Figure 3). This 22-year-old female patient reported sensitivity to sweets in the maxillary left quadrant. She is the daughter of a local endodontist. This endodontist expressed disappointment with the catastrophic failures found associated with this and other sealants placed on his daughter’s teeth by one of his referring general dentists. Unfortunately, his daughter may eventually need several root canal treatments as a result of the treatment. Yet another endodontist who performed endodontic therapy on his daughter after a failed sealant exclaimed, “Sealants are a sham, I am embarrassed for our profession. David, please send me some fissurotomy burs, some flowable and paste composite, and I will redo these things myself!” 
Figure 4a. Sectioned molar 4x and 24x magnification revealed a serious enamel defect that extends very near the dentin. This insidious defect is a perfect example of the unpredictable nature of occlusal morphology. The deep groove full of biofilm and caries activity is not part of the central groove and is also at an oblique angle to the long axis of the tooth. Figures 4b and 4c. Initial penetration was achieved with the original fissurotomy bur. The more aggressive taper on the 2.5 mm cutting surface of this bur allows a conical access to the enamel defect. This shape affords proper visualization of the myriad of directions that are possible. The most insidious types are the lateral and cul-de-sac types of defects that are often not discovered when parallel-sided cuts are made, compounded by insufficient magnification. Figure 4d. Once the extent of the defect and/or the lesion is ascertained, the more delicate and less tapered Fissurotomy NTF Bur can be utilized to finish removing stain and bacteria.

Where does the ADA stand on this issue? Divided! In March of 2008, the Journal of the American Dental Association published the recommendations and findings of the ADA Council on Scientific Affairs in an article promoting the value of traditional “painted on” sealants.1 In the article, it states “No mechanical preparation of the pits and fissures is recommended for noncavitated pits and fissures.” Only a few months later, the ADA Professional Product review2 completely contradicted that statement saying “The grooves and pits cannot be cleaned without mechanical devices. One needs something like a fissurotomy bur (Figures 4a to 4d) or air abrasion to do the job properly. Without mechanical preparation, the average penetration of a sealant is, perhaps, only 17% the depth of the groove on average.”3 It is no wonder that we as a profession are in chaos when it comes down to the 3 fundamental questions; should I cut, how much should I cut and how should I cut? To this end, my good friend Dr. Rella Christensen has made this re­search part of the mission for her new TRAC Research Foundation in Provo, Utah.

General Solution: Sealants Should Go in the Tooth, not on the Tooth
In my practice I balance patient age, and history of occult occlusal caries in the patient or other family members. Additionally, observation at 16X magnification is performed to evaluate pit and fissure staining, and the telltale enamel “halos” that indicate early dentinal caries. In the absence of a microscope, a laser caries detector (DIAGNOdent [KaVo]) is extremely helpful. An age-based diagnosis must be considered. A stained groove in a 45-year-old is a completely different situation than a stained groove in a 7-year-old. I do not seal over decay or stain in my practice. I use fissurotomy burs to remove all stain and caries. In adults, I monitor stained grooves unless I am restoring the tooth for other reasons.

Outcome
The tooth was retreated with a “Cala Lilly” cusp tip to cusp tip Clark Class I composite (not pictured). (Visit Bio­clearmatrix.com or NDN.com [National Dental Network] to view the finished case.)

Discussion and Debate
Sealants (ultra MI) versus fissurotomy and flowable/paste composites (more invasive, requiring removal of enamel): Traditional painted on sealants, often performed by dental auxiliaries are a very cost-effective solution according to many studies.


Figure 5. (Case 2) The preoperative bite-wing depicted what appears to be a very shallow and MI Class I composite; yet the periapical radiograph revealed periapical infections indicating that the pulp must have been exposed at time of treatment.

Figure 6. (Case 2 continued.) Low magnification view of the occlusal surface of tooth No. 30.

Figure 7. (Case 2 continued.) High magnification view (8x) of occlusal surface. The composite restoration appeared to be “MI” and relatively well-sealed.

Figure 8. (Case 2 continued.) As a saucer shape was cut to explore the composite res­toration and to begin endodontic access, the bur was angled at 45º instead of parallel to the long axis of the tooth. Blue arrow on left highlights the carious activity in the untreated fissure adjoining the composite restoration. Green arrows on the right point out the lack of bond and carious invasion along the wall of the composite restoration. Carious invasion was so soft that no red dye uptake occurred in this spot, only the brown color and softness to explorer tip aid the diagnosis.

Figure 9. (Case 2 continued.) Previously ex­posed mesio-lingual pulp horn highlighted with red arrow.

Figure 10. (Case 2 continued.) 24x magnification revealing that there is no such thing as a “small” pulp exposure.

Figure 11. (Case 2 continued.) The pulp chamber was now accessed. The magnitude of the tooth loss for endodontic access is side-by-side with the tiny pulp horn exposure. A small sacrifice of additional enamel with a 45º enamel wall would have allowed an ideal restorative seal, and could have aided the clinician to avoid burrowing into and subsequently failing to recognize the pulp horn.

CASE 2
Minimally Invasive but Poorly Designed Class I (Posterior) Composites

In this tragic case, we see parallel-sided minimally enamel invasive Class I composites on the occlusal of tooth No. 30 (Figure 5 to 7). The radiographs demonstrate what appear to be very conservative Class I composites that could not possibly have involved the pulp, and yet there is a periapical abscess. As I cut a saucer to follow the restoration into the tooth, (Figure 8) we see that the untreated fissure to the left of the composite is wicking caries below the composite, and the parallel wall preparation has a poor seal and has allowed caries along the right side of the restoration. Low and high magnification (Figures 9 to 11) reveal the pulp horn that was inadvertently exposed previously. The accessed pulp chamber that does not incorporate the pulp horn exposure demonstrates the challenges of pulp horn anatomy in terms of avoidance during tooth preparation. A parallel-sided “minimally enamel invasive” preparation possesses 9 inherent problems (Table 3), some of which are general for all cavity preparations, others specific to composite resins. 

Table 3. Disadvantages of the Parallel-Sided Preparation
  1. The Parallel-Sided Preparation (PSP), designed by Dr. GV Black for amalgam; minimizes enamel removal but often inadvertently causes additional and unnecessary removal of dentin.

  2. The attrition of the all important DEJ is typically higher with the PSP than with the Clark class I.

  3. Inadvertent exposure of pulp horns is increased because of poor visibility and the logistics of shape of the PSP.

  4. Ignorance of pulp horn exposure and subsequent failure to take appropriate measures is greatly compounded with the PSP. Once again, obstructed vision is a major culprit. (In case 2, no pulp capping agent was placed, which is a good indication that the dentist was unaware of the pulp horn exposure. Because most dentists in the US and Canada are operating at low-to-no magnification [naked eye to 3.5X], every possible factor should be skewed to aid clinical visualization. If the dentist treating this case had been aware of the tiny pulpal exposure, at least hemostasis could have been established before placing the composite, which is a key to successful pulp capping.)4-6

  5. Crack initiation potential is maximized in continuous PSP’s.7,8 (The majority of dentinal fracturing initiates at line angles and at the 3 way intersection line angle where the interproximal joins the occlusal line angle in the classic class II preparation. In other words, most posterior teeth fracture from the inside out.)

  6. Angle of enamel rod engagement is poorest in the PSP. Enamel rods that are cut obliquely, from 45º to 90º have been shown to have up to 85% stronger resin bonds than the enamel rods in the PSP which have an angle of intersection near 0º. (This principal is well demonstrated with the enamel rod engagement angle of porcelain veneers, where the angle of engagement is the ideal 90º and supports the predictable bond of millions of porcelain veneers, a comforting asset.9 Conversely, undermined enamel typical in the box shape class II is not strengthened by composite resins.10)

  7. When subjected to occlusal forces, marginal ditching is maximized with the PSP. (It is interesting that amalgam is the only dental material that appears to hold up well to occlusal wear and avoid ditching at the margin when paired with a PSP. Porcelain inlays, posterior composites, even gold inlays show marginal ditching when paired with the PSP. Conversely, an infinity edge margin with 45º cavity walls shows excellent wear resistance for both gold and some microfilled composites (3M ESPE’s Filtek Supreme and Kerr’s included in the study).4 Marginal ditching is much more than an annoyance. Ditching is a point where vertical fracturing can initiate and is also a starting point for microleakage and recurrent decay. For fracture initiation, the simple formula of Stress/Surface Area = Crack Initiation Potential must be understood. When an occlusal surface is stressed, a tiny weakness begins to accumulate most of the stress of the entire occlusal surface, and the crack initiates easily.)

  8. PSP surface areas: Total surface area of enamel is minimized while dentin surface area is maximized. (Bear in mind that on average there are 10,000 tubules per square millimeter of cut dentin. Let’s ignore the pulpal issues for a moment and ask ourselves, “Is dentin bonding as permanent as enamel bonding?” Not yet! Every attempt should be made to increase the enamel/dentin percentage when it comes to cavity preparation surface area. Sacrificing selected areas of enamel while simultaneously protecting the DEJ and dentin can dramatically improve the enamel/dentin surface area percentage. In addition, the Hierarchy of tooth needs is better satisfied.)

  9. C-factor or configuration factor is poor with the PSP. (“Everything that makes a preparation good for amalgam makes it bad for C-factor.” Composite fillings should go “on the tooth,” not “in the tooth.”)

This case now has 2 big strikes against it. First, the pulp is dead. Secondly, and more serious, there is a large periapical lesion on each root apex. Risk of failure of root canal therapy increases with both the presence and size of a periapical infections.11 This is a tragic example of MID creating a maximally traumatic outcome.

General Solutions: Fillings Should Go On The Tooth, Not In The Tooth
Dr. Paul Belvedere says it best: “We cannot be MI in the strict sense if we want to achieve excellence with composite dentistry. That is because enamel driven composites are not adhesive, but cohesive in nature.” The design of the saucer shapes recommended for the occlusal when the fissurotomy reveals significant dentinal caries are shown in case 3.

Outcome
The tooth No. 30 is currently under­going calcium hydroxide intracanal disinfection for 6 weeks. It will then be obturated with gutta-percha and restored with a buccal-occlusal-lingual composite onlay. (Completed case summaries are available at Bioclearmatrix.com.)

Figure 12. (Case 3) Preoperative views at low and high magnification of an upper molar; the interproximal portion of the composite has broken away and fallen out despite good mechanical undercuts. The neighboring class II amalgams with boxy shapes have served well for decades.


CASE 3
Dislodged Traditional Box Shaped Class II Composite that was Restored With a Metal Matrix 

In previous articles I have discussed the myriad of problems that we see with traditional “conservative” Class II composites. We know that posterior composites have up to a 50% higher failure rate than do amalgams.12-14 The assumption has always been that composite broke down under the heavier occlusal forces typical in bicuspids and molars. Our studies will show that the real problem is the cavity shape and the filling/matrix technique, not the composite material per se. Figure 12 shows a Class II composite that has broken at the isthmus and has fallen out. One of the biggest controversies to be solved in the next century is: Do Class II composites, bounded by enamel margins, require mechanical undercuts? We have eliminated the need for mech­anical undercuts in our practice with great success (seen in a 1 to 6 year follow-up of hundreds of cases) with the Clark Class II saucer shape. There are many reasons why we should not create an undercut boxy (interproximal) shape; and yet dentistry remains mired in this cavity preparation. Sadly for this patient, the composite restoration suffered recurrent decay and then broke out after a few years of service, while the amalgams lasted for decades. 
We can at last break free of the boxy Class II and rely on enamel margins with a true hermetic seal. The long margins of the Clark Class II shape, along with clean, lightly abraded enamel past the margins cannot be fully light-cured with a metal matrix. It relies instead on translucent matrices, separators and wedging systems to fully cure the long infinity edge margins; just like we have done with anterior restorations—with great success!


Figure 13. (Case 3 continued.) The case was retreated with a cusp tip-to-cusp tip Calla Lilly occlusal preparation to help splint the tooth—protecting against fracture and minimizing marginal ditching. Note that wedges or “prewedges were present in the interproximal to help control/retract the interproximal tissue and rubber dam.

Figure 14. (Case 3 continued.) Removal of carious dentin has been completed, followed by 1 min application of full strength sodium hypo­chlorite to disinfect and lighten the color of the affected but structurally sound dark dentin.

Figure 15a. Unfavorable C-factor and poor enamel rod engagement are typically present when removing old amalgam or composite restorations. Figure 15b. The enamel was cut back with a Cala Lilly shape. This modified preparation then allowed engagement of nearly the entire occlusal surface.

Figure 16. (Case 3 continued.) Although not mandatory for the Clark Class II, the teeth are re-prepared in the interproximal after the occlusal is restored when large occlusal and large interproximal areas are involved. C-factor problems are mitigated and the injection molding of the interproximal is simplified, however, when the interproximal is isolated from the occlusal during composite placement.

Figure 17. Diagrams of the Clark Class II (left), the slot preparation created by Simonson and others (center), and the original GV Black class II (right).

Figure 18. The Bioclear average curved molar. The Bioclear Matrix, with its translucent and fully anatomic shape, allows single-phase injection molding of the composite material along with long infinity edge margins accessed by full light curing—even past the finish lines.

Figure 19. (Case 3 continued.) Clear anatomic matrices are present along with soft silicone interproximators, allowing buccal-lingual curing and full and rounded embrasure shapes.

Figure 20. (Case 3 continued.) For the first time in history, a potential long-term hermetic seal of the margins (especially the gingival margin) is possible. That is very unlikely when there is a minimally enamel invasive, parallel-sided preparation present. Inadequate light curing at, and slightly past the margins (because of a metal matrix), is a significant problem.

Outcome

The case is retreated with a cusp tip-to-cusp tip Calla Lilly occlusal preparation (Figures 13 to 15b) to help splint the tooth to protect against fracturing, and also to minimize marginal ditching. Dentin disinfection with sodium hypochlorite has the ad­ditional benefit of lessening the amount of discoloration of the healthy but dark affected dentin. (Figure 14) The occlusal is restored independently of the interproximal to simplify the restoration phase and to control C-factor; and the interproximal zones are then prepared with a large saucer shape (Figures 16 to 17). The Bioclear Matrix with its translucent and fully anatomic shape (Figures 18 to 19) a