A scanning electron microscopy comparison of enamel polishing methods after air-rotor stripping

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1 A scanning electron microscopy comparison of enamel polishing methods after air-rotor stripping Cesare Piacentini, DMD, DDS," and Giuseppe Sfondrini, DMD, DDS ~ Pavia, Italy In the last few years, orthodontic literature has shown particular interest in the interproximal enamel reduction technique described as stripping or slenderizing. Most researchers have shown, by scanning electron microscopy (SEM) studies, the difficulties encountered while attempting to remove coarse abrasions left after stripping with the first instrument. The objective of this SEM study was to compare the different polishing methods proposed in the literature and to assess the efficiency of our own procedure. For this purpose, 48 healthy human teeth (premolars and molars) were used after removal for orthodontic or periodontal reasons. The teeth were divided into eight groups of six teeth each (two molars and four premolars), and mounted on a typodont to simulate a clinical situation. Each group underwent stripping according to one of the following techniques: 16-blade tungsten carbide bur and fine and ultrafine diamond burs; coarse diamond bur and fine and ultrafine diamond burs; coarse diamond disk and Sof-Lex disks (Dental products/3m, St. Paul, Minn.); 16-blade tungsten carbide bur and phosphoric acid on finishing strip; and 8-straight blade tungsten carbide diamond bur and Sof-Lex disks. The SEM investigations demonstrated that it is not possible to eliminate, with normal polishing and cleaning methods, the furrows left on the enamel both by the diamond burs and the diamond disks and the 16-blade tungsten carbide burs. Mechanical and chemical stripping as well did not prove to be effective. By contrast, with the use of a 8-straight blade tungsten carbide bur followed by Sof-Lex disks for polishing the enamel, it is possible to obtain well-polished surfaces that many times appear smoother than the intact or untreated enamel. (AM J ORTHOD DENTOFAC ORTHOP 1996;109:57-63.) In recent years, almost all orthodontic specialists have increasingly focused their interest on nonextraction therapy, a-7 Among the existing therapeutic methods to increase the maxillary and mandibular length, stripping or slenderizing is with no doubt the most popular. Such therapeutic procedures have been carefully tested and progressively improved and several researchers have been interested in the orthodontic aspect of this subject, as well as in the cariogenic and periodontal implications associated with this procedure. In 1985 Sheridan s introduced a stripping technique called the "ARS technique" that recommended: (1) positioning of a 0.20 wire in the interdental space to prevent damaging the papilla during stripping; (2) accomplishing enamel removal by means of a 16-blade tungsten carbide bur (699 L). Such reduction of the interproximal enamel could reach the 50% of the total, with an increase of each arch length of approximately 6.4 mm; the ~Researcher of Oral and Dental Research Institute. bhead of Department of Orthodontics. Copyright 1996 by the American Association of Orthodontists /96/$ /1/59560 stripping was only to be performed on the first molars and premolars. The reduction could reach 8.9 mm if the space obtainable by reducing the enamel in the anterior segments was also calculated; (3) following the first enamel reduction finish the area with finishing burs, disks, and polishing finishing strips; and (4) applying topical fluoride solutions after treatment to prevent the formation of secondary caries where the enamel had been removed. In 1987 the same author 9 presented a revision of his technique introducing some modifications and suggesting the following: (1) aligning of the dental elements; (2) opening the interproximal area by introducing a thick elastic separator in the contact point or using compressed coil springs; (3) positioning a 0.20 wire to prevent nicking the papilla and making the initial enamel reduction with a 16-blade tungsten carbide bur. The enamel surfaces could be reduced by 1 to 1.5 mm in thickness (calculating the amount of enamel removed from the mesial and distal aspects of the tooth) by working from posterior to anterior; and (4) polishing the abraded area with a stiletto-shaped ultrafine finishing diamond to give the contact point the optimum anatomic features. 57

2 58 Piacentini and Sfondrini American Journal of Orthodontics and Dentofacial Orthopedics January 1996 In 1989 Sheridan 1 considered the possibility of applying a resin composite to the stripped enamel surface for sealing the furrows. Scanning electron microscopic (SEM) observations of the interface between sealant and enamel surface after treatment with 16-blade tungsten carbide bur showed that the resin adhered strongly to the enamel. The treated surface, covered with the sealant, appeared smooth. The author inferred that possible secondary caries could be reduced. In 1990, Crain and Sheridan 11 did not find, from a statistical point of view, any relationship between interdental stripping (performed from 2 to 5 years earlier) and caries susceptibility or periodontal disease. Another author has shown interest in this subject. Radlanski in his 1988 investigations ~2 reported, through SEM investigations, the physiologic presence of abrasion areas on the interproximal enamel of healthy human teeth. In that area 30 to 40 ~m deep roughness was observed. According to the author this roughness could be attributed to masticatory forces or to bruxism phenomena. In additional research, the same author 13 reported on the interproximal surface of human teeth that underwent stripping with coarse and fine diamond burs, followed by fine and ultrafine finishing strips at SEM level. Radlanski emphasized the extreme difficulty involved in polishing the enamel, especially when eliminating the furrows left by the first bur. The author reported that, in general, the ridges and edges of the stripped areas evaluated after 12 weeks in vivo were more rounded compared with the samples stripped under in vitro conditions. According to the author, the structure of the areas where interproximal reduction was performed could favor adherence and, consequently, bacterial colonizations, with an increased risk of secondary caries. In later research Radlanski 14 reported the interproximal enamel structure at SEM level a year after stripping. He confirmed that it was impossible to polish those surfaces despite the careful use of fine and ultrafine strips, but he also observed the low incidence of caries in treated areas. In 1982 Brudevold et al. 4 reported that the iodide permeability of abraded bovine enamel increased after short exposure to an acid buffer and decreased after short exposure to a mineralizing solution. The rapid rate of initial phase of intraoral mineralization, according to the authors, 1~ reveals a powerful mechanism for protecting the dentition against demineralization. In 1991 Nagwa H. E1-Mangoury et al. 15 performed SEM research and concluded that the enamel interproximal reduction in the posterior segments did not expose the teeth to pathologic caries and that a spontaneous remineralization of the tissue followed after approximately a 9-month period of demineralization. Joseph et al. 16 proposed a mechanical stripping procedure, combined with the chemical action of 37% phosphoric acid. This procedure, according to the authors, produced enamel surfaces that encouraged "self-healing" on the basis of demineralization enhanced by the application of fluoridating/remineralizing solutions. Leclerc 17 carried out a complete analysis, using the SEM to investigate existing stripping procedures. The author proposed using a diamond disk, followed by a diamond bur, a 16- and 30-blade tungsten carbide bur and a polishing paste. Given the current interest in the subject and in light of recent literature, it seemed of value to carry out a morphological evaluation with the SEM of enamel surfaces resulting from the application of the most widely used stripping procedures proposed by various authors. The results obtained by means of these techniques were then compared with those obtained by using our personal procedures. MATERIALS AND METHODS Forty-eight healthy human teeth (permanent premolars and molars), extracted for orthodontic and periodontal reasons from patients aged under 40 years, were used. The samples were stored in 70% ethanol for no longer than 3 days and subdivided into eight groups of two molars and four premolars each. The teeth were mounted in typodonts, to be treated with the different stripping procedures and to simulate clinical conditions. To have comparable operative conditions, a single arch was used for each type of procedure to be assessed. The interproximal stripping was performed according to the following methods: Method 1: 16-blade tungsten carbide bur (Komet H284) and polishing by means of fine (Komet 862EF) and ultrafine (Komet 862UF) diamond burs (Komet burs made by Brasseler, Lemgo, West Germany); Method 2: coarse diamond bur (Komet 859) and polishing by means of fine and ultrafine diamond burs; Method 3: diamond disk (Komet 919) and polishing by means of medium, fine and ultrafine 3M Sof-Lex disks (Dental products/3m, St. Paul, Minn.); Method 4: tungsten carbide bur (Komet H28) and

3 American Journal of Orthodontics and Dentofacial Orthopedics Volume 109,No. 1 Piacentini a n d Sfondrini 59 Fig. 1. Enamel structure after stripping with 16-blade tungsten carbide bur. (Magnification x372.) Fig. 3. Enamel structure after stripping with coarse diamond disk. (Magnification x372.) Fig. 2. Enamel surface after treatment with coarse diamond bur. (Magnification x372.) Fig. 4. Enamel surface after mechanical and chemical stripping. (Magnification x372.) polishing by means of medium, fine and ultrafine Sof-Lex disks; Method 5: coarse diamond bur and polishing by means of medium, fine and ultrafine Sof-Lex disks; Method 6: 16-blade tungsten carbide bur (Komet H284) and 20 passages of a medium and fine 3M finishing strip with phosphoric acid 37% gel on the surface (Phosphoric acid, jelly type, from "Concise Orthodontic Bonding System" Dental products 73M, St. Paul, Minn.); and Method 7:ET9 8-straight blade tungsten carbide bur (Komet-E.T. Carbide Set 4159 according to Dr. Ronald Goldstein, and polishing by means of fine and ultrafine Sof-Lex disks. All teeth were dehydrated and gold coated for SEM observation. OBSERVATIONS The photomicrographs were divided into two groups. The first group (Figs. 1 to 5) shows the enamel surface after the first stripping, and the second group (Figs. 7 to 14) shows the enamel morphologic features after polishing and the results of the different methods examined. The number on the lower left of the photograph refers to the method examined. Fig. 1 shows the enamel structure after stripping with a 16-blade tungsten carbide bur. Furrows that are the result of the passage of the bur are visible: they appear irregular and are uniformly distributed on the enamel surface.

4 60 Piacentini and Sfondrini American Journal of Orthodontics and Dentofacial Orthopedics January 1996 m i ~ b ~ Fig. 5. Enamel structure after stripping with a 8-blade tungsten carbide bur. (Magnification 372.) Fig. 6. Intact enamel surface. (Magnification x 372.) Fig. 7. Enamel surface after stripping according to method 1. -~ --I Fig. 8. Enamel surface after stripping according to method 2. (Magnification 1010.) Fig. 9. Enamel surface after stripping according to method 3. (Magnification x 1010,) Fig. 2 shows the enamel surface after treatment by means of a coarse diamond bur. The surface appears crossed by deep and irregular furrows that form hills and valleys. The enamel structure after stripping with a coarse diamond disk shows gross furrowing due to the use of a diamond disk. The furrows are regularly and uniformly distributed over the entire treated area (Fig. 3). Fig. 4 refers to the enamel surface after mechanical (16-blade tungsten carbide bur) and chemical (finishing strips and phosphoric acid) stripping. The grooves that are the result of the passage of the bur have almost completely disappeared, and the heads of the enamel prisms can be seen on the surface.

5 American Journal of Orthodontics and Dentofacial Orthopedics Volume 109,No. 1 Fig. 10. Enamel surface after stripping according to method 4. Fig. 11. Enamel surface after stripping according to method 5. Fig. 5 shows the different structure of the area between the Untreated enamel (top) and the area stripped with an 8-straight blade tungsten carbide bur (bottom). The surface appears finely rough and grooves or furrows cannot be seen. Fig. 6 shows the untreated enamel surface. A comparison with the previous images can be useful. Fig. 7 shows the enamel surface after stripping with tungsten carbide bur and polishing, using fine and ultrafine diamond burs (method 1). Furrows can be seen crossing the surface at different depths. After stripping with a coarse diamond bur and polishing with fine and ultrafine diamond burs (method 2), the enamel appears crossed by deep furrows, which alter its morphologic features (Fig. 8). Piacentini and Sfondrini 61 Fig. 12. Enamel surface after stripping according to method 6. Fig. 13. Enamel surface after stripping according to method 7. Fig. 14. Higher magnification of enamel surface after stripping according to method 7. (Magnification x2840.)

6 62 Piacentini and Sfondrini American Journal of Orthodontics and Dentofacial Orthopedics January 1996 After treatment according to method 3 (coarse diamond disk and polishing with Sof-Lex), the surface appears smooth, although the furrows left by the diamond disk can still be seen (Fig. 9). Tungsten carbide bur stripping and polishing with Sof-Lex disks produce a finely rough surface where the furrows left by the first bur are still visible (method 4 and Fig. 10). Also in Fig. 11 (method 5) the surface is crossed by deep furrows despite the polishing with Sof-Lex disks. Mechanical-chemical stripping (method 6) partially alters the inorganic component of the enamel and the classical etch pattern is discernible (Fig. 12). Fig. 13 refers to the final result of stripping, using an 8-straight blade tungsten carbide bur and polishing with Sof-Lex (method 7). The enamel surface appears crossed by fine furrowing alternating with well-polished areas. At higher level magnification the furrows reveal themselves as fine and shallow (Fig. 14). CONCLUSIONS The morphologic analysis of the surfaces shows that the results obtained with the use of the different stripping methods proposed by the literature are comparable among themselves. All the different morphologic pictures, in fact, reveal the presence of furrowing and roughness, despite the use of careful polishing techniques. Therefore we can assume that polishing enamel after stripping to make it appear somewhat similar to the normal tissue before treatment is extremely difficult. This is essentially due to the difficulties, emphasized in the literature, when trying to eliminate furrowing and roughness left by the first bur. These abrasive areas might favor the adherence of bacterial plaque and offered little resistance to breakdown.is Joseph et al. x6 propose a combined mechanical and chemical technique. However, the result is an etched adamantine surface that, in our opinion, is susceptible to decalcification, despite the application of calcifying/fluoridating solutions as suggested by the authors. We believe that such a method may be risky because of rapid plaque accumulation on the enamel surface, which may result in greater exposure to carious agents. The clinician is unable to check whether the patients use calcifying/fluoridating solutions. We did not examine the procedure proposed by Leclerc because its clinical application seems to be very complicated. Given the high number of bur passages and the numerous burs required, the clinician might lose control of the quantity of the enamel removed or might be tempted to eliminate some steps of the procedure with negative effects on the final result. The morphologic analysis of our findings shows that satisfactory results may be achieved with a tungsten carbide bur as the first bur and polishing with Sof-Lex disks. Nevertheless, the best results were obtained with a method that uses the following: (1) 8-straight blade tungsten carbide bur for the first stripping, (2) fine Sof-Lex disk for first polishing, and (3) ultrafine Sof-Lex disk for final polishing. This method seems to be simple and clinically expedient as it involves only three steps. The 8-straight blade tungsten carbide bur allows a very precise first stripping and leaves very fine furrows, as it was made for polishing resin composite fillings. This fine roughness can then be easily removed with Sof-Lex disks. In conclusion, given the current emphasis on nonextraction treatment in orthodontics today, stripping is a technique that can increase space but it must be performed after a careful evaluation of the quantity of enamel that can be nonpathologically removed. It must accomplish this reduction with the best possible finishing of the interproximal enamel surface and meet the biologic requirements of the oral cavity. REFERENCES 1. Alexander RG, Sinclair PM, Goates LJ. Differential diagnosis and treatment planning for the adult. AM J ORTHOD 1986;89: Betteridge MA. The effects of interdental stripping on the labial segments evaluated one year out of retention. Br J Orthod 1981;8: Brudevold F, Tehrani A, Bakhos Y. Intraoral mineralization of abraded dental enamel. J Dental Res 1982;61: Bolton WA. Disharmony in tooth size and its relation to the analysis and treatment of malocclusion. Angle Orthod 1958; 28: Dibbets JNH, van der Weele LTH. Orthodontic treatment in relation to symptoms attributed to dysfunction of temporomandibular joint: a 10-year report of the University of Groningen study. AM J ORTHOD DENTOFAC ORTHOP 1987; 91: Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment first premolar extraction cases treated by traditional edgewise orthodontics. AM J ORTHOD 1981;80: Peck H, Peeh S. An index for the assessing tooth shape deviations as applied to the mandibular incisors. AM J ORTHOD 1972;61: Sheridan JJ. Air-rotor stripping. J Clin Orthod 1985;19:43-59.

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