The effect of retainer design on the retention of filled resin in acid-etched fixed partial dentures

The effect of retainer design on the retention of filled resin in acid-etched fixed partial dentulres V. D. Williams, D.D.S., M.S.,* D. G. Drennon, L. M. Silverstone, D.D.Sc., Ph.D., B.Ch.D.*** University of Seattle, Wash.

Iowa, College of

Dentistry,

D.D.S., M.S.,**

Iowa City, Iowa, and University of Washington, School of Dentistry,

W

ith the development of composite resin (NPGGMA) by Bowen’ at the U.S. Bureau of Standards and the clinical applications of composite resin offered by Buonocore et al.,2 dentists have been provided with an adhesive restorative material. The problem of missing anterior teeth in young patients has been with dentistry for a long time. The use of acid-etch bonding for retainer fixation for anterior partial dentures has been explored with various techniques.

LITERATURE

REVIEW

The replacement of a tooth with a permanent removable partial denture, as reported by Bennington,3 was an improvement over the traditional “flipper” type removable partial denture. Ibsen’ and Portnoy’ advocated the use of an acrylic resin tooth or the patient’s own tooth as the pontic and acid-etching the pontic to the adjacent teeth. Scheer and Silverstone reported on 14 patients who had been treated similarly and had a relatively good retention rate of up to 24 months. Stolpa’ reported on a technique for making a small anterior fixed partial denture indirectly on a stone cast and then acid-etching the restoration to the adjacent abutment teeth. The esthetics of’ these acrylic resin restorations proved unacceptable within a few years. Staining and Presented at the Iowa Association of Dental Research Meeting, University of lowa, Iowa City, Iowa, and the International Association for Dental Research, Chicago, 111. This project was supported by U.S. Public HeaIth Service Grant No. S-507-RR5313-17, awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institute of Health. *Assistant Professor, Department of Family Dentistry. **Assistant Professor, Department of Restorative Dentistry. ***Professor and Head, Department of Cariology.

OOZZ-3913/82,‘100417

+ 07$00.70/0~

1982

The

and

C. V. Mosby

Co.

excessiveabrasion of the resin becameapparent. Even with these disadvantages,the retention rate has been remarkably good.Jordan et al.” reported on 86 restorations with a life spanof up to 1 year without pins in the adjacent teeth. With pins in the abutment teeth, retention was extended to 3 years. These restorations were acrylic resin pontics bondedto the abutment teeth with an acid-etch compositeresin. Others presentedtechniquesto improve the esthetics and permanenceusing a cast-metal framework.9-” The replacementtooth was a porcelain-fused-to-metal pontic attached to the adjacent teeth by a lingual plate of metal that was retained by acid-etchedcompositeresin. The advantages were (1) improved esthetics, (2) a prosthesisthat was more economicalthan a conventional fixed prosthesis,(3) no trauma to the pulp of young patients, (4) minimum chair time, (5) easy reattachment if needed, and (6) no permanent damageto the enamel.‘*,I3 Kuhlke and Drennon” reported that more than 20 of these restorations have been in service, with only two failures occurring in 3 years. Both of thesewere due to poor patient selection and cementation technique.

THE PROBLEM The rationale of the lingual retainer designhas been empirical. Rochette9usedsix holesmade with a sharp, pointed spatula in a wax pattern 0.8 mm thick, Howe and Denehy’Oadvocateda retainer casting 1 to 1.5 mm thick with as many retentive holesas possikrle,0.5 mm in diameter. Kuhlke and Drennon” recommended retainers 0.33 to 0.5 mm in thicknesswith holesdrilled with a No. % round bur. NewmanI bonded orthodontic brackets using a fine mesh screen.Given the many advantagesof this type of prosthesis,the purposeof this study was to determine which retainer design had the best retention capacity to enamel.

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WILLIAMS,

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No. W Burr No. 6 Burr

b Composite

, -7

mm

Diameter

4 Large Holes Lingual View 0.5-mm Thick

0.5mm

Fig. 3. Retainer desiglt C.

Fig. 1. Retainer design A.

No. 1 Burr

Lingual View 0.5 mm Thick Fig. 2. Retainer design B.

MATERIAL

AND

METHODS

Forty-five whole, unrestored, noncarious human canines were collected. All extraneous soft tissue and debris were removed from the roots of the teeth with a scaler. The teeth were then rinsed in tap water, placed for storage in distilled water and 1% thymol, and refrigerated at 4” C until ready for testing.15-” 418

Thick

Specimen

preparation

Each tooth was embeddedin improved dental stone (Velmix, Kerr Mfg. Co., Romulu i, Mich.) to the cementoenameljunction in a copper t Abe1.25 inchesin diameter and 1S inches in height.18I because one of the problems with in vitro experimenta ion with natural teeth has been embrittlement, a hole was cut in the bottom of the stoneto the apex of the t oath. The apex of the root was then removed to allow ‘vater penetration into the pulp chamber, dentinal tubul es,and enamelby diffusion. The teeth were randomly placed into five groups of nine teeth each. Each group received one retainer design (Figs. 1 to 5). Designs A, B, C, and E were rnzde by a vacuumpressure method. A Dentsply ‘lacu-Press Disk (Dentsply International, Inc., York, Pa.) 0.5 mm thick was adapted to the lingual surface of the Vacu-Press (Dentsply International, Inc.). Tl e patterns were trimmed to the appropriate lingu 11 form and the retentive holes placed. The patterns were cast in a nonprecious alloy (Fig. 6). Design D was made by cutting a polyester mesh screen,size No. 14/28, to fit the lingual surfaceof the natural too:h. The meshwas adapted to the lingual surface of tile tooth, and the periphery of the pattern was formed .n hard inlay wax (Corning Rubber Co., Inc., Brooklm, N.Y.). These patterns were also castin a nonprecicus alloy (Biobond C and B, Dentsply International, Inc ) by a commercial dental laboratory. OCTOBER

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DESIGN

‘Bevel ::‘, :;; ::’ A-

Reinforced Mesh Grid Lingual View 0.5 mm Thick Fig. 4. Retainer

design

Finger Design Lingual View 0.5-mm Thickness

After the sampleshad been submitted for testing, impressions were made of the interface side of the casting in a silicone impression material (Xantopren, Unitex Corp., Monrovia, Calif.) to facilitate a study of breakage patterns. In preparation for bonding the lingual surfaces,the teeth were pumiced with an oil-free, fine flour of pumice with a slow-speedhandpiece. The teeth were rinsed thoroughly with tap water and dried with a commercial hair dryer (Sears, Roebuck and Co., Chicago, ill.). The teeth were etched with a 35% phosphoric acid (Adaptic, Johnson and Johnson, East Windsor, N.J.) for the recommendedtime of 1 to 2 minutes.‘9V2’The crowns were rinsed for 1 minute in tap water and then dried with the hair dryer. On complete drying, the characteristic chalky white surface becameapparent. The unfilled resin (Adaptic) was mixed as directed by the manufacturer and spreadover the etchedenamel with a nylon brush.22-26 Before the unfilled resin had JOURNAL

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Fig. 5. Retainer

D.

Fig. 6. Castings

THE

Retainer

of different

design

E

designs.

Fig. 7. Retainers

attached

to teeth.

set, the filled resin was mixed and applied to the retainer. The retainer was seatedon the to& and held in place with a plastic strip (UNI-STRIPS, L. D. Caulk Co., Milford, Del.) until the compositeresin had set. Excess resin was removed to preven? the distur419

WILLIAMS,

Fig. 8. Aluminum

mounting

DRENNON,

LND

SILVERSTONE

jig.

\

45O fo ce applied to ratanar \

Lingual View

Fig. 9. Lingual view of force applied.

bance of the retainer and retentive areas(Fig. 7). The sampleswere then stored in distilled water and thymol for 7 days.

Testing

procedure

The Instron Testing Machine (Instron Corp., Canton, Mass.) was usedto measurethe retention capacity. The rings were placed in the aluminum mounting jig (Fig. 8) and aligned with the crosshead of the Instron.18 The mounting jig was then secured to the lower table of the Instron to prevent movement on loading. Each specimenof all the groups was subjectedto a compressive-shear-torqueforce. These are the more prevalent forces that probably occur in the retainertooth relationship of anterior teeth (Figs. 9 and 1O).27 A 45-degreeangle of impact was used in this study;

420

Fig. 10. Maxillomandibular sion.

simulation in protru-

this angle more nearly resemblestl e angle of forces that occurs in the incisor region during normal masticatory function. 27Downs28reported t aat the interincisal angle had a mean of 135.4 degrees with a range of 130 to 150.5 degrees(Fig. 10). The area of impact was also to one sideof the in&al edgeof the retainer to simulatethe sli:;ht torquing force that would be imparted to the retaincr from the pontic during protrusive movement (Fig. 9). For the purposesof this study, a crossheadspeedof 30 cm/min or 0.5 cm/set was usedtc simulate the rate of closure of the mandible in norma: incising of food. To record the event at higher speeds,an oscilloscope was attached to the 500 kg load cell ‘)f the Instron. At higher crossheadspeeds,the mechanicalgraph recorder of the Instron cannot respond fast enough. The variables controlled were (1) similar size tooth

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Table I. Tooth breakage

within

groups

Grouo

n

%

A B C D E Total

3 2 5 6 1 17

33 22 55 66 11 38 of total

01

sample

Table II. Compressive-shear forces of retainers that did not break teeth Group A

B C D E Total

n 6

7 4 3 8 28

139.3 174.4 220 129.3 116.2

Range (pounds)

SD

88-176 132-258.5 110-418 90.8-187 77-236.5

27.5 49.3 135.9 50.0 50.8

crowns, (2) similar retainer size, (3) storagein distilled water and thymol at a refrigerated temperature, (4) same kind and brand of metal for retainers, (5) standardized preparation of specimens,(6) 35% phosphoric acid for 1 to 2 minutes’ etching of the enamel (Adaptic-phosphoric acid), (7) identical batch of materials, and (8) standardized testing procedures.All sampleswere tested in random order, and the data were analyzed in two ways: (1) the retainer design having the best retention capacity and (2) the involved interface in retainer failure.

RESULTS Table I presentsthe relative tooth breakage within groups, and Table II exhibits the compressive-shear forcesexperienced by the retainers within their respective groups. A statistical analysis of variance was not used because(1) it was felt that the large amount of tooth breakage (38%) would bias the result toward the low end since the tooth broke before the retainer sheared, (2) someexperimenter error at the initial testing period left some values inadequately recorded at the maximum level, a situation that would also bias the results toward the low end of the normal distribution curve, and (3) some of the groups presented insufficient samplesto conduct a valid analysis of variance. There was no correlation between retainer design and tooth breakage in groups C and D, which exhibited a high degree of breakage.

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Fig. 11. Position of tooth breakage.

DISCUSSION The high tooth breakage (38%) was not anticipated at the beginning of this study. The mean load of tooth breakage for this study was 172 pounds. The breakage occurred at the neck of the tooth (Fig. 11). Group E had the lowest percentageof tooth breakage at 1l%, and groups C and D had the highest breakage at 55% and 66%, respectively. This could be clinically significant if one wishesthe retainer to shear from the tooth rather than fracture the crown with the application of a large force. The silicone impressions of the retainer castings were studied under the Zeiss stereomicroscopeIV (Carl Zeiss,Oberkochen, West Germany) to determine if there was any reasonfor the breakagepattern or high percentage, both within groups and individually. No demonstrablereasoncould be observedfor groups A, B, and E. A possibleexplanation for the large percentage of breakage in groups C and D could be the larger surface area available for retention. Table II exhibits the means, ranges, and standard deviations for all five groups. Possibly the most significant finding is that no retainer shearedunder a force of less than 75 pounds. Black,29 using the gnathodynamometer as the test instrument, reported that incisors received 50% to 33% of the force received by molars. “Rarely,” he stated, “do the anterior teeth need to withstand a force greater than 100 pounds.” The mean, maximum anterior bite force for a sampleof 40 subjects

421

WILLIAMS,

was 75.5 pounds (author’s calculation). Howell and ManlyW verified Black’s work, using the electronic strain gauge for measuring oral forces. The mean, maximum biting force for the canine was 51.4 pounds with a range of 24 to 75 pounds for all anterior teeth. They reported that not one anterior tooth had a bite force greater than 75 pounds. Anderson and Picton)’ reported that the teeth do make contact during chewing; the teeth came into contact during more than 50% of the thrusts of the mandible, with some subjects making contact during each thrust. Andersod2 measured the stress in mastication of three different foods. The mean, maximum, whole tooth load on the molars did not exceed 32.8 pounds. He concluded that maximal bite force is usually greater than needed for normal mastication. Carlsson33 stated that fixed partial dentures had the same value of bite force as natural teeth. In his study, natural canines developed values of 30.8 pounds, and fixed partial dentures on cuspids developed values of 44 pounds. Carlsson33 also stated that forces exerted during chewing are lower than maximal bite force. Because no retainer sheared below 75 pounds in this study, it appears that all retainer designs are retentive enough for acid-etched fixed partial dentures on anterior teeth. A comparison of the means of Table II with the high percentage of breakage in groups C and D in Table I would seem to indicate that groups C and D had a better retentive capacity, although this cannot be substantiated statistically because of the small sample size. The 27 samples that fractured cleanly were studied under the Zeiss stereomicroscope (Carl Zeiss) for mode of fracture. They were observed for (1) entirely tooth fracture, (2) primarily tooth fracture, (3) primarily retainer fracture, and (4) entirely retainer fracture. There were three failures entirely retainer-composite resin interface, 22 failures primarily retainercomposite resin interface, and two primarily toothcomposite resin interface. There were no failures entirely tooth-composite resin interface. This result was not totally unexpected since Terpstra” reported that, for all samples in his study of metal mesh orthodontic brackets acid-etched to teeth, the predominate location of failure was between the adhesive and backing, not between the adhesive and tooth. This study was aimed only at maximum retentive capacity. Because all samples were strong enough, future studies should be directed toward a minimum

422

DRENNON,

P ND SILVERSTONE

retentive capacity, ease of fabrication least damage to the tooth in case of trauma, and cost. Other recommendations for study should include oral problems in adhesion, such as capillary penetration between the composite resin ant1 retainer; water absorption; and exposure of the composite resin to the oral microbiota. In addition, the pas! ibility of chemically bonding the retainer to the camp Isite resin should not be overlooked.

CONCLUSIONS It can be stated that in this study (1) all designs may be retentive enough for anterior fo sees of occlusion generated by human beings, (2) group E had the lowest percentage of tooth breakage, and (3) most retainer failures occurred at the retainer- composite resin interface.

REFERENCES 1.

Bowen, R. L.: Adhesive bonding of various methods to hard tooth tissues. IV: Bonding to dentine, en: me1 and Auorapatite improved by use of a surface active col~onomer. J Dent Res 44906, 1965. 2. Buonocore, M. G., Matsui, H., and Gwimett, A. J.: Penetration of resin dentin materials into e:lamel surfaces with reference to bonding. Arch Oral Biol 13: 61, 1968. 3. Bennington, I. C.: The problem of ‘ellacement of the upper lateral incisor in the young patient Dent Pratt 22~405, 1972. 4. Ibsen, R. L.: Fixed prosthetics with a natural crown pontic using an adhesive composite. J S Cali’ Dent Assn 41:100, 1973. 5. Portnoy, L. L.: Constructing a compos te pontic in a single visit. Dent Surv 49~20, 1973. 6. Scheer, B., and Silverstone, L. M.: Re )lacement of missing anterior teeth by etch retained bridges. J Int Assoc Dent Child 6:17, 1975. 7. Stolpa, J. B.: An adhesive technique fo: small anterior fixed partial dentures. J PR~STHET DENT 34:! 13, 1975. 8. Jordan, R. E., Suzuki, M., Sills, P. S., Gratton, D. R., and Gwinnett, J. A.: Temporary fixed parti. 11dentures fabricated by means of the acid-etch resin technique : A report of 86 cases followed for up to three years. J Am Dent Assoc g&994, 1978. 9. Rochette, H. L.: Attachment of a splin: to enamel of lower anterior teeth. J PR~STHET DENT 30~41: 1, 1973. 10. Howe, D. F., and Denehy, G. E.: P nterior fixed partial dentures utilizing the acid-etch techniques and a cast-metal framework. J PROSTHET DENT 37:28, 1’ ‘75. 11. Kuhlke, K. L., and Drennon, D. G.: in alternative to the anterior single tooth removable partial denture. J Int Dent Child 8:11, 1977. 12. Newman, G. V.: Epoxy adhesives for ori nodontic attachments. Am J Orthod 51:901, 1965. 13. Wei, S. H. Y .: Electron microprobe anal fses of the remineralization of enamel. J Dent Res 49:621, 1970.

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14. 15.

16. 17 18.

19.

20.

21

22. 23.

24

DESIGN

Newman, G. V.: Current status of bonding attachments. J Clin Orthod 7~433, 1973. Silverstone, L. M.: The Histopathology of Enamel Lesions Produced in Vitro and Their Relation to Enamel Caries, vol. 1. Thesis, University of Bristol, England, 1967. Linden, I,. A.: Microscopic observations of fluid flow through enamel in vitro. Odontol Revy 19:349, 1968. Muhlrman. H. R.: Storage medium and enamel hardness. Helv Odont Arta 8:112, 1964. IIermrs, II. H.: A Comparative Study of the Effect of the Pin I)epth in Dentin on the Retention of Pin-Retained Composite Crown Bases. Thesis, University of Iowa, 1977. Silverstone. I,. M.: The acid-etch technique: In vitro studies wtih special reference to the enamel surface and the enamelresin Interface. In Proceedings, International Symposium on ihe Arid Etch Technique. St. Paul, Minn., 1975, North (:entr:d Publishing Co.. pp 13-38. Rock. W. P.: The effect of etching of human enamel upon bond strengths with fissure sealant resins. Arch Oral Biol 19~873, 1974. ~Jiirgensen, K. I).: Matono, R., and Shimokobe, H.: Deformation of cavities and resin fillings in loaded teeth. Stand J Dent Res 84~46, 1976. Phillips, R. W.: Composite restorative resins. J Am Dent Assoc 80~357. 1970. Short, G. M., Hembree, Jr., J. H., and McKnight, J. P.: The bond strengths of resin systems to etched enamel. J PROSTHET hNT 36~538, 1976. Reisbick. M. H., and Brodsky, J. F.: Strength parameters of composite resins. J PROSTHET DENT 26~178, 1971.

ARTICLES

26. 27.

28.

29. 30. 31. 32. 33. 34.

Keprini

reque.st.r

DR VINCENT

to.

D. WILLIAMS

THE UNIVERSITY OF IOWA COLLEGE OF DENTISTRY IOWA

CITY,

IA

52242

TO APPEAR IN FUTURE ISSUES

The conversion Lynda

Forster, L.. and Valiaho, M. I,.: Transverse and bond strength of restorative resins. Acta Odontol Stand 29:5.?7. 197 1. Hembree, J. H.: Abrasion of composite restorativr material. Arkansas Dent J till, 1973. Shore, N. A.: Temporomandibular Joint Dysfunction and Occlusal Equilibration, ed 2. Philadelphia. IoTii, .I B. I.lppincott co., p 15. Downs, W.: Variations in facial relationships: Their significance in treatment and prognosis. Am J Orthod 34:812, 1948. Black, G. V.: The force exerted in the closure tli the jaws. Dent Cosmos 37~474, 1895. Howell, H. H., and Manly, R. S.: An electronic strain qauae for measuring oral forces. J Dent Res 27:710 1948. Anderson, D. J., and Picton, D. C. A.: Tooth contact during chewing. J Dent Res 36:26, 1957. Anderson, D. J.: Measurement of stress in mastication. II. .J Dent Res 35672, 1956. Carlsson, G. E.: Bite force and chewing efficiency. Front Oral Physiol 1:265, 1974. Terpstra, D. W.: An Investigation of the Shear and Tensile Strength of Direct Bond Bracket Backings. Thesis. University of Iowa, 1978.

25.

K. Bangtson,

of Chromascan designations D.D.S., MS.,

and Richard J. Goodkind,

to CIE tristimulus D.M.D.,

values

M.S.

Caries, periodontal, and prosthetic findings in patients with removable partial dentures: A ten-year longitudinal study Bo Bergman, D.D.S., Odont.Dr., Carl-Olof

Olsson,

Anders Hugoson, D.D.S., Odont. Dr., and

D.D.S.

Delayed onset of masseter muscle pain in experimental L. V. Christensen,

D.D.S., S. E. Mohamed,

A sot2 palate desensitization prostheses

D.D.S., and J. D. Harrison,

tooth clenching D.D.S.

procedure for patients requiring

pal&al lift

Billie Daniel, M.A.

Physical therapy as an adjunct to temporomandibular William

N. Danzig,

joint therapy

D.D.S., and Arlyn R. Van Dyke

Isolation of pathogenic microorganisms from denkxres and denture-soaking containers of myelosuppre%@d cancer patients Louis

THE

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G. DePaola,

OF PROSTHETIC

D.D.S., M.S., and Glenn E. Minah,

DENTISTRY

D.D.S., M.S., Ph.D.

423