Clear aligners and open gingival embrasures: Retrospective study of epidemiology and risk factors

BACKGROUND: To investigate the epidemiology and risk factors of open gingival embrasures (OGE) in adult patients after clear aligner therapy (CAT). METHODS: A total of 518 adult patients were recruited to evaluate the prevalence and severity of OGE between central incisors through intraoral photographs; 281 patients with complete lateral cephalometric radiographs and cone-beam computed tomography (CBCT) were selected above to investigate mainly mesiodistal anatomical indicators regarding the occurrence and severity of OGE; and 186 non-extraction (NE) patients were selected from 281 patients to further investigate the relationship between tooth movement or labial-palatal/lingual anatomical indicators with OGE. RESULTS: The prevalence of OGE was relatively high and significantly associated with tooth extraction. The prevalence and severity of OGE decreased as follows: one-lower-incisor-extraction > two-premolar-extraction > NE types. The interproximal contact point-alveolar crest (ICP-AC) > 5 mm, ΔICP-AC > 0.5 mm, cemento-enamel junction-alveolar crest (CEJ-AC) > 2 mm, and ΔCEJ-AC > 0.2 mm were significantly associated with the occurrence of OGE. ΔCEJ-AC may more sensitively reflect bone loss, meanwhile, CEJ-AC in distal sites was significantly associated with moderate or severe OGE in mesial sites. Intrusion movement < 2 mm and labial inclination < 5° were the warning limits for incisor movement. Furthermore, we found that bone dehiscence and root resorption were significantly associated with OGE. CONCLUSION: OGE of varying severity could be accompanied by different degrees of three-dimensional alveolar bone resorption. Moderate-to-severe OGE may occur alongside other complications in orthodontic treatment. This research also provided valuable clinical insights and treatment guidance in CAT. PLAIN LANGUAGE SUMMARY: Clear aligner therapy (CAT) is a favored orthodontic choice for adults, yet it can carry hidden risks to periodontal health. Open gingival embrasure (OGE), or "black triangles" between teeth, can affect aesthetics, promote food impaction, and potentially relate to underlying bone loss. Our large-sample study investigated the incidence of OGE, identified the treatment alternatives associated with increased risk, how OGE related to alterations in tissue loss and tooth movement, and what risks OGE may indicate. The prevalence of OGE is relatively high in adult patients after CAT. Patients with a single lower incisor removed had the highest rates and severity of OGE, followed by those with two premolars extracted, and finally those with no extractions. Detailed imaging revealed that the occurrence and severity of OGE are significantly associated with bone loss, not only between teeth but also from the front-back directions. Additionally, specific thresholds for tooth movement that may elevate OGE risk include excessive incisor intrusion or forward tilting. Importantly, OGE often occurred along with other complications like bone dehiscence or root resorption. Our findings provide anatomical data on the potential three-dimensional tissue loss associated with different severities of OGE and further provide clinical guidance in CAT.