Statistically significant vs Clinically Significant

Does statistically significant always mean clinically significant? What are the sensitivity and specificity of statistical significance when being used for clinical significance? Is it true that when something has been found to be statistically significant, it must be clinically significant too?

1. Does statistically significant always mean clinically significant?

No, statistical significance absolutely does not always equate to clinical significance.

• Statistical Significance merely indicates that the observed difference or effect in the study sample is unlikely to be due to chance, assuming the null hypothesis is true (typically indicated by a  p-value < 0.05) (Norman & Streiner, 2014). It is mathematically driven and heavily dependent on the sample size.

• Clinical Significance refers to the practical importance of a finding. It indicates whether an intervention makes a genuine, palpable difference in patient care, treatment efficiency, or functional/esthetic outcomes—often referred to as the Minimal Clinically Important Difference (MCID) (Pandis et al., 2010).

• Orthodontic Example: A study might find that a new aligner material corrects crowding 0.15 millimeters faster than a traditional material. If the study evaluates 5,000 patients, this 0.15 mm difference will likely be highly statistically significant (p < 0.001). However, 0.15 mm is imperceptible to both the orthodontist and the patient, rendering it completely clinically insignificant (Proffit et al., 2018).

Not all statistical differences are clinically significant, and sometimes differences that do not reach statistical significance nevertheless may indicate a clinical advance.

2. What are the sensitivity and specificity of statistical significance when being used for clinical significance?

If we evaluate "Statistical Significance" (SS) as if it were a diagnostic test for detecting true "Clinical Significance" (CS), the diagnostic performance metrics are skewed:

• Sensitivity (True Positive Rate) is High: If an orthodontic treatment truly has a massive, clinically significant effect (e.g., functional appliances reducing overjet by 6 mm), the statistical test will easily detect it. Thus, SS is highly sensitive to true clinical relevance, provided the study is adequately powered (Altman, 1991).

• Specificity (True Negative Rate) is Low: Specificity asks: If an effect is NOT clinically significant, will the statistical test correctly flag it as non-significant? In modern research with large sample sizes, the test fails at this. Large studies will frequently detect tiny, meaningless differences and label them as statistically significant. Therefore, relying purely on p-values produces many "false positives" for clinical relevance (Button et al., 2013).

3. Is it true that when something has been found to be statistically significant, it must be clinically significant too?

No, this is one of the most common epidemiological fallacies in dental research. As explained above, statistical significance only proves that a difference exists, not that the difference matters. To establish clinical significance, an orthodontist must look past the p-value and examine the effect size (magnitude of the change) and the confidence intervals to determine if the treatment alters clinical protocols in the real world (Johnston, 2002).

---

References:

• Altman DG (1991). Practical Statistics for Medical Research. Chapman and Hall/CRC.

• Button KS, et al. (2013). Power failure: why small sample size undermines the reliability of neuroscience. Nature Reviews Neuroscience.

• Johnston LE (2002). Clinical studies in orthodontics: art, science, or nonsense? American Journal of Orthodontics and Dentofacial Orthopedics.

• Norman GR, Streiner DL (2014). Biostatistics: The Bare Essentials. PMPH-USA.

• Pandis N, Polychronopoulou A, Eliades T (2010). Failure to establish a clinically significant difference... American Journal of Orthodontics and Dentofacial Orthopedics.

• Proffit WR, Fields HW, Larson BE, Sarver DM (2018). Contemporary Orthodontics, 6th Edition. Elsevier.

Are Burstone's six geometries applicable in all orthodontic appliances? Is there any difference between the six geometries of TPA and Bracket system?

1. Applicability of Burstone’s Six Geometries 

Burstone’s six geometries are fundamentally applicable to all orthodontic appliances that involve a wire segment connecting two attachments (brackets or tubes). Because these geometries are derived from the laws of physics and static equilibrium, they serve as a universal blueprint for predicting force systems.

• Universal Principle: These geometries describe the relationship between the angulation of the wire at each attachment and the resulting moments and forces.

• Static Equilibrium: They apply regardless of whether the appliance is a fixed bracket system, a Transpalatal Arch (TPA), or a lingual arch.

• Clinical Utility: They allow clinicians to predict the "force system" (the specific combination of forces and moments) that will be generated before the appliance is even activated.

2. Differences Between TPA and Bracket Systems

While the physical laws (the six geometries) remain constant, their clinical application and the "activation" of these geometries differ significantly between a Transpalatal Arch (TPA) and a standard Bracket System.

Comparison of TPA vs. Bracket Systems:

• Geometry Control: In a TPA, the clinician pre-shapes the wire to a specific geometry (e.g., Geometry VI) before insertion. In a Bracket System, the geometry is determined by the relative position of the malaligned teeth.

• Stability of Force: Force systems in a TPA remain relatively constant because the TPA utilizes a rigid, large-diameter wire. In Bracket Systems, force systems change dynamically as the teeth move and the wire deforms or rebounds.

• Activation Method: TPA activation is "active" (the wire is pre-bent). Bracket System activation is "reactive" (the wire is forced into a bracket, adopting the geometry of the tooth's current position).

• Friction/Binding: TPAs are generally frictionless as the wire is usually ligated or locked into lingual sheaths. Bracket systems are subject to friction and binding as the wire slides through bracket slots.

• Symmetry: TPAs are often used to create symmetric systems (e.g., Geometry I or VI) to maintain anchorage. Bracket systems frequently involve asymmetric geometries (e.g., Geometry II or III) during the leveling and aligning phases.

References

• Kharbanda, O. P. (2020). Orthodontics: Diagnosis and Management of Malocclusion and Dentofacial Deformities.

• Mulligan, T. F. (1979/1980). Common Sense Mechanics.

• Fleming, P. S., & Seehra, J. (2019). Fixed Orthodontic Appliances: A Practical Guide.

MCQs in Orthodontics - Later Stages of Development

Later Stages of Development

Adolescence: The Early Permanent Dentition Years, Growth Patterns in the Dentofacial Complex, Maturational and Aging Changes

0 / 50 Answered Score: 0%

Current Score

0 / 50

Accuracy

0%

MCQs in Orthodontics - Early stages of Development

Early Stages of Development

Late Fetal Development and Birth, Infancy and Early Childhood: The Primary Dentition Years, Late Childhood: The Mixed Dentition Years

MDS Orthodontics Board Review

Score: 0 / 0 (Total: 50)