Minicavities were prepared in 26 caries-free teeth. Cavity preparation and the finishing of the occlusal area and the gingival floor was done with diamond burs (diameter 1 mm, grain sizes 90 μm and 15 μm, respectively). For the finishing of the axial box margin and the proximo-cervicaI curved border, a new set was developed: It is composed of an EVA-system with the total amplitude reduced to 0.34 mm, and a highly flexible file (Cavishape, grain 15 μm). The shape of this file had to be modified in order to follow the proximo-cervical curvature. The efficiency of the new device was compared with the axial margin trimmer by means of scanning electron microscopy and a score system.
The new device allowed a significantly better finishing of the proximo-cervical curvature and of the axial box margin

Gygax, M

Hotz, P.

Lussi, A.

Lüthi, D.

English

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Scanning Microscopy Volume 2 Number 3 Article 31 4-18-1988 A New Method for Finishing Minicavities A. Lussi University of Berne M Gygax University of Berne P. Hotz University of Berne D. Lüthi University of Berne Follow this and additional works at: https://digitalcommons.usu.edu/microscopy  Part of the Biology Commons Recommended Citation Lussi, A.; Gygax, M; Hotz, P.; and Lüthi, D. (1988) "A New Method for Finishing Minicavities," Scanning Microscopy: Vol. 2 : No. 3 , Article 31. Available at: https://digitalcommons.usu.edu/microscopy/vol2/iss3/31 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Scanning Microscopy by an authorized administrator of DigitalCommons@USU. For more information, please contact digitalcommons@usu.edu. Scanning Microscopy, Vol. 2, No. 3, 1988 (Pages 1553-1557) 0891-7035/88$3.00+.00 Scanning Microscopy International, Chicago (AMF O'Hare), IL 60666 USA A NEW METHOD FOR FINISHING M!N!CAVJTIES * A. Luss i , M. Gygax, P. Hotz, 0 . LUthi Department of Operative Dentistry , School of Dentistry Univer s ity of Berne, 3010 Berne, Switzerland (Received for publication March 23, 1987, and in revised form April 18, 1988) Abstract Minicavitie s were prepared in 26 caries-free teeth. Cavity preparation and the finishing of the occlusal area and the gingival floor was done with diamond burs (diameter I mm, grain s izes 90 .,um and 15 ,um, respectively). For the finishing of the axial box margin and the prox imo-cerv i ca I curved border , a new set was deve I oped: It is composed of an EVA-system with the total amp! itude reduced to 0.34 mm, and a highly flexible file (Cavishape, grain 15 ,,um). The shape of this file had to be modified in order to follow the proximo-cervical curvature. The efficiency of the new device was compared with the axial margin trimmer by means of scanning electron microscopy and a score system. The new device allowed a s ignificantly better fini shing of the proximo-cervi cal curv a-ture and of the ax ial box margin. KEY WORDS: Minicavities, finishing of prepara-tions, amalgam, diamond, EVA-system. *Address for correspondence: Adrian Lussi, Klinik fUr Zahnerhaltung, Freiburgstrasse 7, CH-3010 Bern, SWITZERLAND Phone No. (031) 64 25 80 1553 Introduction The prevalence of caries in Switzerland and other developed countries has been declining during the last decade (Marthaler 1977, 1979; Marthaler et al. 1982). This fact, combined with the more frequent recalls, has lead to the detection of caries in the earlier stages of development. Thus , Black's century-old principle that class 2 cavity preparations should extend beyond the carious lesion to prevent further decay is no longer valid (Bowen 1983). Many investigators (Markley 1951, Vale 1959, Nadal et al. 1961, Almquist et al. 1973, Jacobsen & Robinson 1980, Elderton 1984b) have suggested that smaller cavities (= "minicavitie s " , Fig. I) be prepared. Studie s have shown clearly that the smaller cavitie s have a longer service life (Almquist et al. 1973, O'Hara & Clark 1984). The reason s are: I) masticatory force s are borne by the tooth structure rather than the re storation; 2) the amalgam in the smaller cavities i s le ss susceptible to fracture. Therefore , Elderton (1984a) suggested a cavity width of I mm and an amalgam margin angle of at lea st 70° . Preparations of the minicavitie s and fini-shing of the occlusal area are easily accom-plished with commercially available instruments. The fini shing of the axial box margin and the prox imo-cerv i ca I curved border is another mat-ter. Instrument s , such as paper di sks and small bur s , can be used only when the old principle of cavity exten s ion i s employed. The gingival ca-vity margin can be finished with the gingival margin trimmer. When the gingival floor was finished with a diamond bur (grain 15 .,um), it was shown that an additional finishing with a gingival margin trimmer did not improve this margin (Lussi et al. 1987). An axial margin trimmer can be used to finish the axial box margin and the proximo-cervical curved border (Fig. 2). However, preliminary clinical studies with severa I genera I pract i ti one rs showed that this finishing was unsatisfactory because the margins were too rough (Buzzi, unpublished). The aim of this study was, therefore, to develop a new instrument designed to satisfac-torily finish the axial box margins and the proximo-cervical curved borders of small cavity preparations(= "minicavities"). The finishing done with this new instrument was compared with that done with the axial margin trimmer. A. Lussi et al. __/ B ____/ A C Fig. I. A. Explorer locating caries on occlusal surface. Note lesion on proximal surface. B. Formation of enamel- lamella with diamond bur. C. Finishing with the new device. Note: curvature of file; 1 = axial box margin; 2 = proximo-cervi -cal curvature. Materials and Methods Minicavities were prepared on 26 caries-free extracted human premolars and molars. To s imulate the situation in the mouth, each tooth was embedded in a plaster block adjacent to another tooth. The cavity was prepared with a diamond bur (grain size 90 ,,um, diameter I mm, ISO). In order not to introduce a new variable only one investigator prepared the cavities. In all 26 cavities, the occ lu sa l area and the gingival floor were finished with the appropriate diamond bur (grain 15 ,,um, diameter I mm). To prevent damage to the adj a cent tooth while drilling the cavity, the final enamel-lamella could not be removed fully (Fig. lB). The remaining 52 unfini shed vertical borders were divided randomly into two groups. In one group the axial box margin and the proximo-cervical curved borders were treated with an unused sharp axial margin trimmer (Fig. 2), (tungsten carbide; LM, Michel & Cie AG, Schanzenstrasse I, CH-3008 Bern) . In the seco nd group the borders were finished with the new device. For further evaluations al I margins were coded, so that the investigator s did not know which instrument was used. 1554 The new instrument is composed of an EVA-system (Lutz et al. 1981) technically modified so that the tot a 1 amp Ii tude of vibration was reduced from 1.5 mm to 0.34 mm (KaVo, Innova-tionsgesel l schaft, 7950 Biberach, Germany). Thi s reduction was necessary to prevent damage to the border. The original EVA-system with i ts rigid diamond file has been used to eliminate over-hangs in restorations or to polish restorations (Small et al. 1987). The working surface of the orig inal file was replaced with a highly flexible file that has a curved end (Cavishape, grain 15 ,,um, Intensiv S.A. Via Mo! inazzo 11 , 6962 Vigane ll o, Swi tzer l and). The file was replaced so that the working surface conformed with the proximo-cervical curvature (Fig. 3). In both groups, the margins studied were finished for 20 ± 2 seconds, cleaned with Tubu-licid (Dental Therapeutics AB, Ektorpvagen 3, Fig. 2. The axia l margin trimmer (tungsten carbi-de). Fig. 3. The new device, a modified EVA-instrument (amplitude 0.34 mm) with a flexible file that is terminally curved. A new method for finishing minicavities 13145 Nacka, Sweden) , carefully washed with water and dried with air. Primary rep] icas were made with President light body (Coltene, 9450 Alt statte n, Switzerland). Secondary rep] ica s were made with an epoxy ( Stycast; Emerson and Cuming , 2431 Wester lo-0evel, Belgium), gold coated and evaluated using scanning electron micrographs (Cambridge, Stereoscan 200) and a score system. Prior to the study; it was found that independent scori ng of margins by the in-vestigators agreed in 95% of the cases. The scoring of the margins was done independently by two investigators (A.L and D.L) using a system s lightly modified from that of Tronstad and Lei-da! (1974) and Leida] and Tronstad (1975). Scores for the axial box margin Score 0: no chips at the enamel margin, perfect ma rg i n ( F i g . 4 ) Score 1: few, isolated small chips at the enamel margin, imperfect margin (Fig. 5) Score 2: large chips at the enamel margin, unac-ceptable margin (Fig. 6) Scores for the proximo-cervical curvature Score 0: no chips at the enamel margin, perfect margin (Fig. 7) Score I: few, i solated small chips at the enamel margin, imperfect margin (Fig. 8) Score 2: large chips at the enamel margin, unac-ceptable margin (Fig. 9) Statistica l evaluation The statistical s ignificance of the diffe-rences between the methods was determined using the Chi- square test. A sig nifi cance level of P -< 0.05 was employed. Results Axial box margin (Table 1). The margins of the axial box were signifi-cantly better, when finished with the modified EVA-instrument and the highly flexible file com-pared to the axia l margin trimmer (P-< 0.05). A zero score (0; indicating a perfect margin) was found more frequently (21 to 13) with the new device than with the hand instrument. Unaccep-table margins (i.e., score 2) were recognized 5 times with the margin trimmer, while this oc-curred 3 times with the EVA-instrume nt. Proximo-cervical curvature Table 2 clearly shows the sig nificant bet-ter finishing of the proximo-cervical curvature of the new device compared to the axial margin trimmer . The margin was perfect in 4 of the 26 cases using the trimmer, while this occurred in 17 of 26 cases using the new instrument. Im-perfect and unacceptab I e margins were detected more than twice as often with the hand instru-ment as with the modified EVA-instr ument. 1555 Table Grading of the axial box margin Score EVA-instrument with file Axial margin trimmer 0 21 13 2 8 *=significant difference, P-< 0 .05 2 3 5 * Table 2 Grading of the proximo-cervical curvature Score EVA- instrument with file Axial margin trimmer 0 17 5 4 13 *=significant difference, P-< 0.05 Discussion 2 4 9 * Minipreparations of class 2 cavities often are not employed in daily practice mainly be-cause adequate instruments for finishing the axial box margin and the proximo-cervical curva-ture were not availab le. Proper fini shing of the proximo-cervical curvature i s important because secondary caries often start at this site (Vale 1959). In small cavities, paper disks cannot be used because they are too large. Small burs can cause a s lice in the preparation (e.g., a long gingival bevel) which is not desirable for amalgam restorations. The axial margin trimmer i s small enough to finish the whole border. However, it l eaves a rough margin. Additionally, in daily practice there i s the problem of the axial margin trimmer becoming dull, the difficul-ty to sharpen it and the expense of replacing it (Buzzi, unpublished). This study shows that the new device is clearly superior to the axial margin trimmer. In the proximo-cervical curvature the new device led to a perfect finishing more than four times as frequently as the axia l margin trimmer. The large amount of enamel chips lost in the curva-ture when the axial margin trimmer i s employed could be due to the higher force exerted by the operator to start movement in the curvature. The Cavishape-file, however, fits close to the whole margin causing a uniform applicat ion of force. Additionally, the small amplitude of the modi-fied EVA-instrument (0.34 mm) and the flexible, curved file that fits well to the anatomy of the cavity are ideal for finishing the proximo-cervica l curvature . The new in stru ment was also super ior to the axial margin trimmer in finishing the axial box margin. The modified EVA-instrument and the Cavishape-fi le produced perfect margins more than 1.5 times compared to the margin trimmer. Additionally, the new device is easier to use . Further applications of the EVA instrument with the reduced amplitude and the high flexible file under study are in the preparation of inac-cessib le minislices and in the treatment of root surfa ces. Fig. 4. Perfect axial box margin finished with the new instrument. No enamel chips can be found at the margin, arrow (Score = 0). Bar = 200 ,Um Fig. 7. Perfect proximo-cervical curvature finished with the axial margin trim-mer. No enamel chips can be found at the margin, arrow (Score= 0). Bar= 200 Mm A. Lussi et al. Fig. 5. Imperfect axia l box margin finished with the new instrument. Few enamel chips can be found at the margin, arrow (Score = I). Bar = 200 Mm Fig. 8. Imperfect proximo-cervical curvature finished with the axial margin trim-mer. Few ename I chips can be found at the margin, arrow (Score = I ). Bar = 200 ,.um 1556 Fig. 6. Unacceptable axial box margin finished with the new instrument. Large chips can be found at the margin, arrow (Score = 2). Bar = 200 ,um Fig. 9. Unacceptable proxi-mo-cervical curvature finished with the axial margin trimmer. Large chips can be found at the margin, arrow (Score = 2). Bar = 200 ,.um A new method for fini sh ing minicavitie s Acknowledgements We wish to thank Prof. Dr. M.A. Crenshaw for hi s help in preparing this manuscript in Eng Ii sh and Mrs. Regu I a Aeb i for the preparation of the manuscript. References Almquist TC, Cowan RD, Lambert RL (1973). Conservative amalgam restorations. J Prosthet Dent 29, 524-528. Bowen WH (1983). Impact on Research. In: Cariology Today, B. Guggenheim (ed). Karger, Basel 1984, 49-55. Elderton RJ (1984a). Cava-surface angles, amalgam margin angles and occlusal cavity pre-parations. Br Dent J 156, 319-324. Elderton RJ ( 1984D). New approaches to ca-vity design. Br Dent J 157: 421-427. Jacobsen PH, RobTrison PB (1980). Basic techniques and materi a Is for conservative den-tistry: I. Cavity preparation. J Dent 8, 283-291. -Leida I TI, Tronstad L ( 1975). electron microscopy of cavity margin s with ultra-speed instruments. J Dent 152-159. Scanning finished Res 54, Lussi A, Gygax M, Hotz P (1987). Die Mini-Praparation approxima ler Kavitaten. Schweiz Mschr Zahnmed 97, 186-190. Lutz F, Curilovic z, Mormann W (1981). In -terdenta le RestorationsOberhange rationelle Entfernung mit neuentwickelten Masch inenin st ru -menten. Acta Parodonto I in Sch we i z Mschr Zahn-he ilk 91, 969-982. Markley MR (1951). Restorations of s ilver amalgam. J Am Dent Assn. 43, 133-146. Marthaler TM ( 1977) .Dental caries 12 years after introduction of preventive program-pre Ii -minary report from seven communities. Schweiz Mschr Zahnheilk 87, 823-828. Marthaler rrq-( 1979). Was kann eine praven-ti v orientierte Jugendzahnheilkunde erreichen 7 Ergebn i sse l 5j ahr i ger .;ystemat i scher BemUhungen in der Schweiz. Dtsch zahnarztl Z 34, 76-84. Marthaler TM, Wiesner V, BanaT A ( 1982). A reevaluation of DMF-data obtained in the Canton of Zurich 1963-1972. Schwei z Mschr Zahnmed 92, 1159-1165. -Nadal R, Phillips RW, Swartz ML (1961). Clinical investigation on the relation of mer-cury to the ama I gam restoration: I I. J Am Dent Assn. 63, 488-496. O'Hara JW, Clark LL ( 1984). The evolution of the contemporary cav ity preparation. J Am Dent Assn. 108, 993-997. Small KL, Goldfogel MH, Hicks MJ ( 1987). Marginal finishing for cast gold restorations: Reciprocal-action instrumentation. J Prosthet Dent 58, 403-408. Tronstad L, Leida! TI (1974). electron microscopy of cavity margins with chise ls or rotating instruments speed. J Dent Res 53, 1167-1174. Scanning finished at low Vale WA (J95gr:- Cavity preparation and fur-ther thoughts on high speed. Br Dent J .!.QI_, 333-340. 1557 Disc ussion with Reviewer s Reviewer IV: Do the authors feel that it would be possible to make some of these distinctions between the two techniques using a hand magni-fier or the naked eye, or is thi s far too diffi -cult to discern on a "white" colored tooth? Authors: Sometimes, it was possible to distin-guish grade 2 from grade O by a hand magnifier. However, the hand lens is not adequate for quan-tification with a score system. Reviewer IV: Was a "fresh" axial margin trimmer used for each cavity? I 'm sure that the authors would agree that dulling of the trimmer would influence the results if the same one was used throughout the study. Authors: For all 26 margins the same file and the same margin trimmer (with two working sides) were used. It would be unusual in daily practice to sharpen the axial margin trimmer (tungsten carbide) after using it for only one margin or to replace the file after each margin finishing. It is our experience that the trimmer does not dull as easily as the reviewer suggests. Reviewer IV: Since the two score systems are identical , it would be proper to combine them into one, i.e. , there i s no reason to repeat the same inf ormatio n twice. Authors: The scoring system is repeated because of the need to refer to the mi crographs. ( see Fig s . 4-9). J.C. Punwani: Were mini cavities prepared by only one investigator? How was the potential bias controlled in the use of hand in st rument s (margin trimmers)? Reviewer IV: Si nee the authors comment in the Discussion on the operator variab les that make the axial margin trimmer le ss efficient, it would be beneficia l for them to explain why they did not compare the results from several opera-tors in this study? Authors: In this first report, all minicavities were prepared by one investigator. In our opinion, it is virtua ll y impossib le to e limin ate operator bias because the devices are so di f-ferent. However, we have been aware of this pro-blem and therefore a study with different prac-titioners i s in progress. 

A New Method for Finishing Minicavities

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A New Method for Finishing Minicavities

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