The Value of Research

DF2 Uncategorized

Winter 2017

Fake News

We live in a blizzard of information. Most of it is bad. Any news, explanation, or argument has an infinite number of ways to be wrong, but a small (or single) way to be right. For example: Why does the Sun rise in the morning and set at night? It might be pulled by the chariot of Helios (Greek) or Sol (Norse) or Surya (Hindu). It might be driven by human sacrifice (Aztec). It might be the eye of Ra who travels in a boat across the sky every day (Egyptian). It might be spiraling around the Earth in complex patterns every day, month, and year (Ptolemy). There are many more assertions, all wrong. There is only one correct assertion, based on the fact that the Sun does not actually rise and set, but rather that the Earth rotates.

In our profession, there are endless assertions and explanations, and many of them are wrong too. How can we determine the truth? Our answer, which will be no surprise to anyone who knows us, is scientific research. But we live in a blizzard of research, and a lot of it can be misleading.

At a recent study club meeting we were asked about the effect of chlorhexidine (CHX) on fibroblasts. We routinely prescribe CHX after surgery, and sometimes for longer periods. The question was based on research findings that CHX reduces fibroblast viability, protein synthesis, and reproduction, and therefore on the concern that it could delay wound healing. But this research focuses on cell cultures. There are no clinical studies in humans showing a deleterious effect of CHX on wound healing. In fact, human clinical studies have shown that CHX reduces bacterial load and therefore improves post-surgical results. This apparent contradiction can guide us is assessing the value of studies cited by sales reps, specialists, direct marketing, or other studies. Here is the hierarchy of value, from lowest to highest:

  • Non-clinical studies. These include histology, microbiology, microscopy, molecular biology (DNA and RNA), chemistry, and cell cultures. While they may be of interest for explaining mechanisms behind clinical results, they are of little or no value alone. Examples are: LANAP studies showing histologic regeneration, microscopic studies of microgaps between implants and abutments, microscopic or physics-based abfraction hypotheses, and microbiology of caries and periodontal disease. If these do not correlate with clinical significance, they are mere curiosities. As another example, we are not restorative dentists but we are aware of a litany of materials (composites, bonding agents, porcelains) that have looked great in the lab but failed clinically.
  • Animal studies. Rats are not humans, nor are dogs or monkeys. Since ethical concerns preempt many human trials, animals are often used as proxies. But generalizing from another mammal is risky. For example, many studies implicating occlusal trauma in the progression of periodontal disease were performed in animals, and human studies have found little or no effect of occlusion on attachment loss.
  • Retrospective human clinical studies. Since these cases are chosen from patients who have already received treatment, there is a high risk for bias among researchers with an agenda. This is especially problematic if there is a single author with a vested interest in the study. For example, the only existing clinical study supporting the Pinhole Surgical Technique was published by its inventor and marketer using past cases he selected from his practice. However, when accomplished by disinterested researchers using double-blind, randomized, controlled protocols, retrospective studies may be of some value.
  • Prospective human clinical studies. These are the gold standard. They should be double-blind, randomized, and controlled. The larger the number of subjects, and the longer the term of the study, the better. Studies of only a handful of subjects or for only six months have little worth. And we need to distinguish between statistical significance and clinical significance. Half a millimeter might be statistically significant, but it means nothing from a clinical standpoint. Examples of valuable studies include support for grafting extraction sockets with bovine bone or FDBA to preserve volume, superiority of subepithelial CT grafts for root coverage, superiority of osseous resective surgery over open flap debridement or repeated scaling and root planing, requirement of 2 mm of facial bone around implants, benefit of alternating 3-month recalls following periodontal surgery, reduction of caries risk from topical fluoride exposure, safety of articaine (Septocaine) for mandibular blocks, and reduction of cardiovascular risk factors following periodontal treatment.

Those of us who have limited time or interest in studying research should limit our intake to long-term, large, double-blinded, controlled, randomized human clinical trials showing clinically significant results (or lack thereof). The next time someone selling their products or services shows you a histology study in rabbits or an article based on ultramicroscopy of cementum, ask to see a 5-year prospective study on dozens or hundreds of human patients. If none exists, smile, eat their free lunch, and move on.

Amy and David