Journal of Aligner Orthodontics, 02/2021

Mechanotransduction is defined as the molecular process of transmitting an extracellular physical cue into an intracellular biochemical signal. Throughout the history of dental science, mechanobiology, i.e., the study of tissue and cell responses to physical stimuli, has long been neglected. There is, however, increasing experimental evidence to suggest that the complex interplay between biophysical forces with traditional biochemical signalling is pivotal for tissue integrity and homeostasis in the oral cavity. Periodontal tissues, namely the gingiva, periodontal ligament, cementum and alveolar bone, are permanently subjected to mechanical stimuli. The latter can arise from natural processes like chewing, or orthodontic appliances. The term ‘orthodontic tooth movement’ describes the movement of teeth within the dental alveoli in response to forces exerted by orthodontic appliances. Orthodontic tooth movement is a macroscopic term that subsumes all the molecular, mechanobiology-related signalling cascades that enable the adaptation of the periodontium during orthodontic treatment. Here, cells such as mesenchymal stem cells and periodontal ligament fibroblasts respond to external forces by modulating the activity state and spatial distribution of mechanotransducing proteins like focal adhesion kinase and the cotranscriptional activator yes-associated protein. The signalling activity of these proteins leads to changes in cellular behaviour, inducing cellular responses like proliferation, differentiation and migration. In the future, exact determination of the fine-tuning and integration of mechanobiological and biochemical factors will help to achieve a better understanding of periodontal physiology and pathophysiology and improve clinical orthodontic treatment by considering the molecular principles of mechanotransduction. This mini review therefore summarises current findings in periodontal mechanobiology, with a special focus on the above-mentioned molecules. Keywords: extracellular matrix, mechanobiology, mechanotransduction, mesenchymal stem cells, periodontal ligament fibroblasts

Objective: To analyse the surface wear of four materials used in the fabrication of Invisalign attachments as a function of simulated aligner wear in vitro. Materials and methods: BracePaste Adhesive (American Orthodontics, Sheboygan, WI, USA), Filtek Supreme Ultra Flowable (3M ESPE, Seefeld, Germany), Tetric EvoFlow (Ivoclar Vivadent, Schaan, Liechtenstein) and Transbond XT Light Cure Adhesive (3M Unitek, Monrovia, CA, USA) were used to fabricate passive attachments on 32 typodont premolars. A total of 30 weeks of wear were simulated through repeated manual aligner placement and removal. Surface scans were taken at baseline (T0) and at five time points corresponding to 6, 12, 18, 24 and 30 weeks of simulated wear (T1, T2, T3, T4 and T5, respectively). The scans from each time point were superimposed onto the baseline scan taken prior to wear to quantify the dimensional changes at the surface of the attachments. Vickers hardness was also measured for each material. Results: Upon statistical analysis using a generalised linear mixed model, significant differences in negative dimensional deviation, a variable associated with material loss, were found among the four materials; however, time was not found to be a significant factor in the observed negative dimensional deviation. Significant differences in Vickers hardness values were observed among the four materials (P < 0.0001), with each one recording a different hardness value from all the others investigated. Conclusions: Although statistically significant differences were observed between the wear properties of the materials, each material appears to be suitable for use in the fabrication of Invisalign attachments under the conditions investigated. Keywords: attachment, biomaterials, Invisalign, materials

Objective: To use digital photographs to evaluate the attractiveness of Invisalign aligners (Align Technology, San Jose, CA, USA) with attachments that varied in number and shape compared with Sapphire brackets (Morelli, São Paulo, Brazil) and an aesthetic wire. Materials and methods: Seven digital photographs of the same smile were obtained: six with Invisalign aligners with different numbers and shapes of attachments, and one with Sapphire brackets and an aesthetic wire. The images were shown at random to 180 evaluators divided into three groups composed of laypeople, clinical dental practitioners and orthodontists, respectively, who were asked to rate the attractiveness of each image on a visual analogue scale. Results: The aligners with the fewest attachments were awarded the highest scores. Aligners with conventional attachments obtained higher scores than those with optimised attachments from all groups of evaluators; however, the difference between the shapes was statistically significant only for the aligner with six attachments in the group composed of laypeople. Conclusions: The greater the number of attachments was, the lower the attractiveness score the aligners received. Conventional attachments were shown to be more attractive than optimised attachments. All three groups of evaluators considered the Sapphire brackets with aesthetic wire to be more attractive than the aligner with eight conventional attachments; thus, this number of attachments appears to be the aesthetic limit for Invisalign aligners. Keywords: aesthetics, Invisalign, orthodontic appliances, orthodontic brackets, orthodontics, removable

Mixed dentition orthodontic treatment aims to correct dental arch irregularities and abnormalities in occlusal relations, and to eliminate functional interferences. Proper management of space in the mixed dentition can prevent unnecessary loss of arch length, allowing for beneficial use of the leeway space. Invisalign First clear aligners (Align Technology, San Jose, CA, USA) are specifically designed to simplify the management of malocclusion in younger patients, who often present shorter clinical crowns, erupting dentition and dental arch expansion. The present study seeks to provide indications for successful digital planning and to describe a standardised treatment protocol for maxillary development with Invisalign First. Invisalign First aligners make it possible to treat a broad range of phase 1 orthodontic problems such as anterior crowding and spacing (mild to moderate), loss of arch length due to premature loss of primary teeth and mesial drift, constricted arches (up to edge-to-edge buccal horizontal overlap), anterior reverse articulation (usually one or two teeth), midline diastemas, mild to moderate deep bite, and flared/protruded incisors. It is also possible to treat patients with a mild Class II or Class III molar relationship by rotating and distalising the molars by ~1 mm. The clinical protocol described for phase 1 treatment with Invisalign First aligners has been designed to manage the developing occlusion, guiding the teeth into a proper maxillary arch form. The 10 steps outlined in the present study are intended to be easy to follow during digital planning to help practitioners to deliver such predictable therapies by developing the maxillary arch using clear aligners. Keywords: clear aligners, digital planning, early treatment, growing patients, maxillary arch expansion, mixed dentition

Clear aligners are, without doubt, the most popular option in current clinical orthodontic practice. As knowledge relating to the latter has increased, different treatment modalities have been proposed. The digital workflow plays a significant role in the treatment of malocclusion, giving a precise indication of how much and at what point each tooth will move; thus, it can be considered to provide the most individualised prescription possible. Many brands offer clear aligners, and the decision of which one to use depends entirely on the clinician; nevertheless, the option to fabricate them in one’s own clinic is a cost-effective and predictable process of which all clinicians should be aware. Keywords: 3D printing, clear aligners, digital workflow, in-office

An example of a developmental dental anomaly is a higher than normal number of teeth. Supernumerary teeth may be of different varieties, including mesiodens, distomolar and paramolar. The term ‘mesiodens’ refers to a supernumerary tooth present in the maxillary midline between the central incisors. Dental anomalies have the highest priority of treatment among orthodontic problems. Early diagnosis and treatment may help to prevent complications and improve self-perception and social integration. The present case report demonstrates that a properly intercepted case of mesiodens can be successfully treated with clear aligners because the Invisalign First (Align Technology, San Jose, CA, USA) system has specific features that are suitable for growing patients. Invisalign First is a new system of clear aligners designed to address a broad range of malocclusions in younger patients, for example through management of shorter clinical crowns and erupting dentition and predictable dental arch expansion. Keywords: dental anomalies, diastema, digital dentistry, growing patient, Invisalign, invisible orthodontics, mandibular advancement, oral health

Objective: To demonstrate how aligners were used to manage a displaced root of a mandibular canine in a male adult patient. Materials and methods: A 24-year-old man experienced relapse after a previous orthodontic treatment. He presented to a private dental clinic with a mandibular left canine root that was almost out of the bone. The present authors explained to the patient that they would like to attempt an innovative form of treatment with clear aligners to manage the movement of the root, and requested that a CBCT scan be taken. Results: The treatment goal was achieved and the canine root was restored back into the alveolar bone after 11 months of therapy. Conclusion: Root displacement can be managed with clear aligner therapy. Keywords: CBCT, clear aligner, fixed retainer, root control, torque