Evaluation of Dental and Periodontal Health After IPR in Patients in Orthodontic Treatment With Clear Aligners

Interproximal enamel reduction (IPR) is a common procedure used during orthodontic treatment aimed to reduce mesio-distal tooth size dimensions to address lack of space (mild and moderate crowding), Bolton tooth-size discrepancy, correction of morphologic anomalies, tooth reshaping and management of gingival papilla. It is a practice that also offers an attractive alternative to overcome difficulty when extracting premolars and resolve the instability of overexpansion in non- extraction cases, improving the stability of the arches.

IPR may be exploited inconjunction with fixed appliance treatment, although its application with removable appliance treatment such as clear aligners is commonplace.

Clinically, the most accepted IPR techniques include air-rotor stripping with fine tungsten-carbide or diamond burs, handpiece or contra-angle-mounted diamond-coated disks, and handheld or motor- driven abrasive metal strips.

Some of these techniques can cause deep furrows and scratches that cannot be removed by polishing . In addition, these surface irregularities could promote the adherence of plaque bacteria and induce iatrogenic damage, such as dental caries, gingival inflammation, periodontal tissue breakdown, gingival recession and increased sensitivity of the shaped teeth to hot and cold temperatures.

Sometimes, after IPR, it is possible to have dentin hypersensitivity (DH), attributed to exposure to dentinal tubules. This clinical condition is influenced by various factors, including patient' s age, the severity of crowding, pathological tooth wear, hypersensitivity before treatment and the amount of the removed enamel.

DH can be defined as "short and sharp pain due to exposure of the dentinal tubules in response to thermal, evaporative, tactile, osmotic or chemical stimuli". The hydrodynamic theory proposed by Brännström is the most accepted theory to explain the DH mechanism. According to this theory, external stimuli, leading to fluid movement within the dentinal tubules and this movement indirectly stimulates the pulp nerve ends, causing a painful sensation.

Several methods can perform DH treatment. Based on the mode of their administration, the desensitizing treatment can be classified into at-home therapy or in-office therapy categories. At- home desensitizing products include toothpaste, mouthwashes and chewing gums. In contrast, in- office desensitizing products can be gels, solutions, varnishes, resin sealers, glass ionomers, dentin adhesives and more sophisticated laser techniques. In addition, eliminating of nociceptive stimuli, there are two main treatment strategies: modifying nervous response by preventing or reducing neuronal transmission and occluding the permeable dentinal tubules.

Potassium salts were thought to decrease the excitability of pulpal nerves and result in a reduction in DH. Still, clinical trials with sound design have failed to provide evidence that potassium is effective in desensitizing teeth. Potassium salts likely reduced the perception of dentin sensitivity through a placebo effect. The proposed mechanism for glutaraldehyde, another agent used for the treatment of DH, involves the reaction with serum albumin in dentinal tubule fluid, leading to precipitate formation within tubules and subsequent narrowing or blocking of the tubules. Strontium salts, fluoride, oxalate and arginine/calcium can occlude the tubules and form a protective layer on the dentin surface. Dental adhesives and resin sealants can occlude the dentinal tubules by forming a physical barrier thus blocking the movement of dentinal fluid and preventing direct stimulation of odontoblastic processes. The action of glass ionomers in the management of DH can also lead to occlusion of open dentinal tubules by precipitating a hydroxycarbonate apatite layer over the previously patent tubule openings. Laser treatment has been investigated as a prospective treatment for DH. Several studies suggest that the low-power laser could suppress the excitability of the pulpal nerves. Higher output laser is thought to reduce symptoms of DH by inducing the occlusion of dentin tubules.

Pain associated with DH may reduce the quality of life, but does not compromise people's health. Currently, no studies that have tested desensitizing substances to reduce or eliminate DH that can occur after IPR.

Inclusion criteria

• to be in orthodontic treatment with clear aligners and this treatment requires interproximal enamel reduction;
• permanent dentition;
• good oral and periodontal health.

Exclusion criteria

• enamel defects;
• cervical caries;
• periodontal disease;
• history of trauma or craniofacial anomalies;
• pregnancy.