Creating Space with Interproximal Reduction
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Earn 4 CE credits This course was written for dentists, dental hygienists, and assistants. Creating Space with Interproximal Reduction A Peer-Reviewed Publication Written by Michael Florman, DDS; Pablo Echarri Lobiondo, DDS; and Mahtab Partovi, DDS Go Green, Go Online to take your course This course has been made possible through an unrestricted educational grant. The cost of this CE course is $59.00 for 4 CE credits. Cancellation/Refund Policy: Any participant who is not 100% satisfied with this course can request a full refund by contacting PennWell in writing. Educational Objectives found a relationship between dental size (mesiodistal and Upon completion of this course, the clinician will be able to: labiolingual distances of the inferior incisors) and crowd- 1. List considerations of tooth anatomy and individual ing grade (PI index). Betteridge10 also found a relationship tooth shapes with respect to slenderization between dental size and crowding grade. 2. List the effect of slenderization on the periodontium Teeth vary in size between females and males, mostly 3. List instrumentation that can be used for slenderiza- in the permanent dentition, with men having larger teeth tion as well as their advantages and disadvantages and the maxillary centrals and canines showing the greatest 4. List the steps involved in slenderizing teeth. differences.11–16 Bolton17 analyzed the relationships between canine-to-canine widths and molar-to-molar widths in Abstract dental arches, and found tooth size discrepancies in approxi- One of the basic principles of orthodontics is the creation of mately 30% of patients. Freeman, Santoro and Alexander18 space to facilitate tooth movement. With appropriate case also observed similar percentages in their studies. Sassouni19 selection, slenderization offers the ability to safely obtain suf- found that Class III facial types and patients with deficient ficient space for tooth movement without the need for extrac- maxillary growth show a greater incidence of anterior tooth tions and without compromising slenderized teeth. shapes and agenesis. Cua-Benward20 found similar results in Class III subjects, and tooth deformities in the lower anterior Introduction region in Class II individuals. Creating space to facilitate tooth movement is one of the basic principles of orthodontics. As patients seek faster orthodontic Periodontal Considerations treatment, extraction is becoming reserved for cases where It is apparent from reviewing the literature that there is no there is severe crowding, a need for vertical change or control, negative or positive effect when teeth approximate after or where sagittal correction/compensation cannot otherwise slenderization. Investigators studying horizontal and vertical be accomplished. For less severe cases there has been an bony defects on posterior teeth found no evidence that narrow increasing trend towards expansion or interproximal reduc- spaces between roots were risk factors for periodontal disease. tion (IPR), with the choice depending on the case. IPR is also Other investigators found that teeth could function even known as enamel reduction, stripping, or slenderization.1 when the roots were touching and sharing a periodontal liga- ment. After reviewing several studies, Fillión21 concluded Historical and Anthropological Perspectives that periodontal state is improved even if slenderization is The natural interproximal abrasion of teeth was discussed performed on already aligned teeth and the interdental sep- by Black in 1902.2 Since then, numerous studies have ad- tum thickness is reduced as a result. Betteridge22 found that dressed interproximal abrasion and reduction. In 1944, fourteen of seventeen slenderization cases had an improved Ballard3 described the slenderization technique for the first gingival index. Boese23 compared forty patients’ radio- time. Sheridan4 in labial technique, and Fillión5 in lingual graphs taken four to nine years post-treatment and found no technique, among others, have contributed to the develop- significant differences in alveolar crest height. Crain24 and ment of the slenderization technique currently in use. An- Sheridan25 found no significant differences in the gingival thropologists have usually found little to no crowding in the index interproximally three to five years post-treatment. remains of primtive dental arches. The theory that primitive Enamel reductions in the above studies were maximum 0.5 humans wore down their teeth more rapidly is difficult to mm per proximal surface. dispute. Foods were much more difficult to masticate, of- ten contained abrasive particles such as sand or bone, and Contact Locations primitive people used their teeth to cut and shred foods. As cutting instruments remove enamel during slenderization, This tooth wear resulted in uncrowded dental arches. rounded contours are flattened. These need to be restored after enamel reduction to restore the contact back to the proper loca- The Need for Slenderization tion. Re-familiarizing dental shape and anatomy is important: Modern research has found that as we age, normal mesial contact points are more apical as the teeth move from the ante- drift of the teeth causes crowding in many individuals re- rior of the mouth to the posterior, and restoring them to their gardless of whether or not orthodontic treatment was per- proper position should be attempted. formed. Studies on the occlusions of Aboriginals found that they presented with interproximal wear with loss of up to Enamel Thickness 14–15 mm of hard tissue over a lifetime as a consequence of Tooth slicing studies have demonstrated that the enamel non-refined diets, and had no crowding.6,7 Sicher8 stated that thickness around teeth is similar in incisors, cuspids, molars, it was possible that tooth wear (attrition) has a positive func- and premolars. A study by Hall26 et al. demonstrated that tion and asked whether nature sacrifices tooth substance to mandibular lateral incisors have thicker enamel than central achieve an increase in functional potentiality. Peck and Peck9 incisors. Enamel thickness of the lower central incisor was 2 www.ineedce.com determined: 0.77 mm +/– 0.11 mm on the distal enamel tact. Several clinicians have provided their recommenda- thickness and 0.72 mm+/– 0.10 mm on the mesial. The tions for slenderization. Boese23 recommends slenderizing lower lateral incisor measured 0.96 mm +/– 0.14 mm on the half the enamel layer thickness. Berrer31 claims that lower distal and 0.80 mm +/– 0.11 mm on the mesial enamel thick- incisors can be stripped by 0.4 mm, which corresponds to a ness. Enamel thickness in premolars can be well over 1 mm. 0.5 mm slenderizing per proximal surface of the lower inci- Several enamel thickness studies allow us to draw the following sors. Paskow32 allows slenderizing of between 0.25 mm and conclusions27,28,29: The minimal enamel thickness, and not the 0.37 mm. Hudson27 suggests 0.20 mm for central incisors, average values, must be taken into account when determining 0.25 mm for the lateral ones, and 0.30 mm for the lower the enamel quantity that is going to be removed, since it is not cuspids, which gives a total of 3 mm for the whole ante- possible to know which teeth present minimal thickness. There rior group. Tuverson33 states 0.3 mm per proximal surface is no relationship between dental size and enamel thickness; of the lower incisors and 0.4 mm in cuspids, which gives, therefore, macrodontic teeth should not be stripped more than in total, the elimination of 4 mm in the anterior group. microdontic teeth (although aesthetically it is better to carry Alexander18 permits only 0.25 mm for all the teeth, and out the slenderizing on macrodontic teeth). Enamel thickness Sheridan34 defends a 0.8 mm slenderizing per each surface is slightly greater in the contact point, gradually decreasing in of posterior teeth and 0.25 mm in the anterior teeth, gaining thickness toward the cementoenamel junction. The enamel is in total some 8.9 mm. slightly thinner in distal than in mesial surfaces. In upper cus- The concept of removing half the enamel layer would pids and lower second bicuspids, these differences are greater. seem to be clinically acceptable. According to Fillión35, it is The exceptions are upper lateral incisors, whose thickness is possible to obtain 10.2 mm of space in the maxilla and 8.6 slightly greater distally. mm in the mandible if slenderizing is carried out from the mesial surface of the first right molar to the same surface of Tooth shape and enamel thickness the left molar. If slenderizing includes the second molar, an According to Bennett and McLaughlin30, we can distinguish additional 0.5 mm in distal surface of the first molar and 0.5 three main dental shapes: rectangular, triangular, and barrel- mm in mesial surface of the second molar can be obtained. shaped teeth. Studies reveal that there is no relationship be- When planning slenderizing, factors that must be considered tween dental shape and enamel thickness (Fig. 1). Therefore, include the degree of physiologic abrasion present (contact it is not possible to vary the amount of slenderization depend- tips or facets) (Fig. 2), whether the patient has already un- ing on dental shape and the only element of decision should dergone slenderizing, and the presence of over-dimensioned be the minimal enamel thickness. It is true, though, that more crowns or fillings. space is gained with minimal enamel wear in triangular- shaped teeth. Figure 2. Normal evolution increases the contact area into a contact surface. Figure 1. Triangular, “barrel-shaped” and rectangular teeth with different thicknesses of enamel Figure 3. Slenderizing from cuspid to cuspid must improve the midline and dental symmetry. How much enamel can be removed It is important to know how much enamel can be removed in individual teeth in order to know which cases can be slenderized and which require a different treatment plan. Generally, it is recommended to remove only up to approx- imately half of the enamel thickness on any surface being reduced.