Creating Space with Interproximal Reduction

One of the basic principles of orthodontics is the creation of space to facilitate tooth movement. With appropriate case selection, slenderization offers the ability to safely obtain sufficient space for tooth movement without the need for extractions and without compromising slenderized teeth. Introduction Creating space to facilitate tooth movement is one of the basic principles of orthodontics. As patients seek faster orthodontic treatment, extraction is becoming reserved for cases where there is severe crowding, a need for vertical change or control, or where sagittal correction/compensation cannot otherwise be accomplished. For less severe cases there has been an increasing trend towards expansion or interproximal reduction (IPR), with the choice depending on the case. IPR is also known as enamel reduction, stripping, or slenderization.1 Historical and Anthropological Perspectives The natural interproximal abrasion of teeth was discussed by Black in 1902.2 Since then, numerous studies have addressed interproximal abrasion and reduction. In 1944, Ballard3 described the slenderization technique for the first time. Sheridan4 in labial technique, and Fillión5 in lingual technique, among others, have contributed to the development of the slenderization technique currently in use. Anthropologists have usually found little to no crowding in the remains of primtive dental arches. The theory that primitive humans wore down their teeth more rapidly is difficult to dispute. Foods were much more difficult to masticate, often contained abrasive particles such as sand or bone, and primitive people used their teeth to cut and shred foods. This tooth wear resulted in uncrowded dental arches. The Need for Slenderization Modern research has found that as we age, normal mesial drift of the teeth causes crowding in many individuals regardless of whether or not orthodontic treatment was performed. Studies on the occlusions of Aboriginals found that they presented with interproximal wear with loss of up to 14–15 mm of hard tissue over a lifetime as a consequence of non-refined diets, and had no crowding.6,7 Sicher8 stated that it was possible that tooth wear (attrition) has a positive function and asked whether nature sacrifices tooth substance to achieve an increase in functional potentiality. Peck and Peck9 found a relationship between dental size (mesiodistal and labiolingual distances of the inferior incisors) and crowding grade (PI index). Betteridge10 also found a relationship between dental size and crowding grade. Teeth vary in size between females and males, mostly in the permanent dentition, with men having larger teeth and the maxillary centrals and canines showing the greatest differences.11–16 Bolton17 analyzed the relationships between canine-to-canine widths and molar-to-molar widths in dental arches, and found tooth size discrepancies in approximately 30% of patients. Freeman, Santoro and Alexander18 also observed similar percentages in their studies. Sassouni19 found that Class III facial types and patients with deficient maxillary growth show a greater incidence of anterior tooth shapes and agenesis. Cua-Benward20 found similar results in Class III subjects, and tooth deformities in the lower anterior region in Class II individuals. Periodontal Considerations It is apparent from reviewing the literature that there is no negative or positive effect when teeth approximate after slenderization. Investigators studying horizontal and vertical bony defects on posterior teeth found no evidence that narrow spaces between roots were risk factors for periodontal disease. Other investigators found that teeth could function even when the roots were touching and sharing a periodontal ligament. After reviewing several studies, Fillión21 concluded that periodontal state is improved even if slenderization is performed on already aligned teeth and the interdental septum thickness is reduced as a result. Betteridge22 found that fourteen of seventeen slenderization cases had an improved gingival index. Boese23 compared forty patients’ radiographs taken four to nine years post-treatment and found no significant differences in alveolar crest height. Crain24 and Sheridan25 found no significant differences in the gingival index interproximally three to five years post-treatment. Enamel reductions in the above studies were maximum 0.5 mm per proximal surface. Contact Locations As cutting instruments remove enamel during slenderization, rounded contours are flattened. These need to be restored after enamel reduction to restore the contact back to the proper location. Re-familiarizing dental shape and anatomy is important: contact points are more apical as the teeth move from the anterior of the mouth to the posterior, and restoring them to their proper position should be attempted. Enamel Thickness Tooth slicing studies have demonstrated that the enamel thickness around teeth is similar in incisors, cuspids, molars, and premolars. A study by Hall26 et al. demonstrated that mandibular lateral incisors have thicker enamel than central incisors. Enamel thickness of the lower central incisor was