Secular Trends in Orthodontics: A Systematic Review of Growth Acceleration, Dentoalveolar Mismatch, and Clinical Implications

Background: Secular trends—defined as long-term changes in biological parameters across successive generations—have been documented across various domains of human growth and development. In orthodontics, understanding these trends is critical for accurate diagnosis, treatment timing, and outcome prediction. Objective: This systematic review synthesizes published evidence on secular trends in craniofacial growth, dental and skeletal maturation, tooth size, arch dimensions, malocclusion prevalence, and treatment demand, with emphasis on clinical implications for orthodontic practice. Methods: This systematic review followed PRISMA 2020 guidelines. PROSPERO registration was not performed because the review was initiated prior to protocol finalization and registration; however, the methodology adhered strictly to PRISMA 2020 guidelines, with predefined eligibility criteria and standardized data extraction to ensure transparency and reproducibility. Searches were conducted in PubMed, Google Scholar, and the Directory of Open Access Journals (DOAJ) from January 1990 to December 2021 using the Boolean search string: ("secular trend" OR "secular change" OR "cohort effect" OR "generational change") AND ("orthodontics" OR "craniofacial growth" OR "dental maturation" OR "tooth size" OR "dental arch" OR "malocclusion"). Studies were included if they compared two or more birth cohorts separated by at least one decade or compared historical with contemporary populations, assessed quantitative measures of dental development, skeletal maturation, tooth size, arch dimensions, or malocclusion, and were published in peer-reviewed journals. Risk of bias was assessed using an adapted Newcastle-Ottawa Scale (NOS), evaluating selection bias, comparability, and outcome assessment. A narrative synthesis was conducted due to substantial heterogeneity in outcomes and study designs; a meta-analysis was not performed because the included studies varied considerably in outcome measures (e.g., PHV age, tooth dimensions, leeway space, PAR Index), populations (different geographic and ethnic backgrounds), and assessment methods (e.g., Demirjian vs. CVM vs. hand-wrist), precluding meaningful statistical pooling. Results: Thirty-two studies were included, predominantly from European, North American, and East Asian populations. Findings indicate: (1) earlier peak height velocity (~0.5 years earlier) with increased growth velocity; (2) accelerated early dental maturation with prolonged mixed dentition; (3) increased posterior tooth dimensions (~1%); (4) reduced mandibular leeway space (~0.4 mm per quadrant); (5) narrower maxillary arches; (6) increased malocclusion severity (PAR Index nearly doubled over 100 years); and (7) increased orthodontic treatment prevalence (from <5% to ~30%). Findings regarding cervical vertebral maturation and non-European populations remain inconsistent. Collectively, these findings suggest the emergence of a dentoalveolar mismatch—a disproportion between tooth size and available arch space arising from asynchronous secular changes. When considered collectively, the increase in posterior tooth size (~0.7 mm combined) alongside a reduction in leeway space (~0.4 mm per quadrant) and narrowing arch dimensions suggests a cumulative space deficit that may be clinically significant. Conclusions: Secular trends may limit the applicability of historical normative data to contemporary patients, particularly in predominantly European and East Asian populations. A key emergent finding is a dentoalveolar mismatch—defined as a disproportion between tooth size and available arch space arising from asynchronous secular changes in dental and skeletal dimensions. These findings may reflect a transition from an evolutionarily adapted equilibrium between tooth size and jaw dimensions to an environmentally driven disequilibrium in modern populations. Orthodontists should consider adopting biological indicators of maturity rather than relying solely on chronological age, updating mixed dentition space analysis methods, accounting for population-specific variation, and recognizing the increased complexity of malocclusions in modern populations. Future orthodontic protocols should be recalibrated using contemporary biological data rather than historical growth standards.