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Retentive Strength of Acid-Etched Anterior Fixed Partial Dentures: An in vitro Comparison of Attachment Techniques
A cid-etched fix e d partial dentures are a rational alternative to other form s o f rem ovable prostheses beca use additional strength and increa sed resistance to fra ctu re a re a ch ieved when the acrylic pontic is bonded with composite resin to natural tooth abutments.
Retentive strength of acid-etched anterior fixed partial dentures: an in vitro comparison of attachment techniques Edw ard J. Sweeney, DDS David L. M oore, DDS, MS John J. Dooner, DDS
I n som e cases, acid-etched fixed partial dentures provide an alternative to conventional fixed partial dentures or rem ovable prosthetic appliances. It has been reported that resin pontics, as w ell as natural tooth pontics, may be attached to abutm ent teeth w ith com posite resin m aterials w ithout m echanical p reparation of the ab u tm en ts.1 11 T h ese reports suggest that the life span of fixed partial dentures can range from several days to an ind efinite period, depending on the technique and location of the fixed partial denture in the mouth. The biting force of human dentition varies greatly; it increases from anterior to posterior. G uyton,12 D avenport,13 and A nderson14 reported that the bit ing force in the region of the incisors was in the range of 24 to 55 lb. K laffenboch15 said that molars could produce a force as high as 290 lb. The strength of acid -etched anterior fixed partial dentures was reported to vary betw een 41.5 to 55.8 lb with a mean strength of 4 8 .6 lb .16 It is evident that the strength of the attachm ent leaves som ething to be desired, even for anterior fixed partial dentures. T h is study was done to evaluate three attachm ent techniques that were designed to increase the strength of the fixed partial denture.
Materials and methods Eighteen fixed partial dentures that extended from the m axillary central incisors to the canines were constructed. R ecently extracted teeth were oriented 198 ■ JADA, Vol. 100, February 1980
6 mm apart in a rectangular silicone mold. A coldcuring acrylic resin was used to form a base. For all specim ens, a lateral incisor (Bioblend 21X ) was used as the pontic. Class III preparations were made in the m esial and distal surfaces of all pontics. These prep arations were 3 mm incisal-gingivally, 3 mm faciallingually, and 1.5 mm deep axially. M echanical re tention was made w ithin each preparation w ith a half-round bur. Preparations were connected across the lingual surface w ith a trench that was 1.5 mm wide. Specim ens were separated into three groups; six specim ens were in each group. GROUP A. Abutm ent teeth were acid-etched without m echanical preparation (Fig 1) and the pontic was attached w ith a photosensitive com posite resin sys tem (Nuva-Fil). GROUP B. Abutm ent teeth received Class III prepa rations w ith the same dim ensions and retention as the preparations in the pontics (Fig 2). To form a short bevel on the cavosurface, a no. 1-A diamond instrum ent was used. The axial wall was lined with a calcium hydroxide base (Pro-Cal). Teeth were then etched and the pontic was attached with com posite resin. GROUP C. Abutm ent teeth were prepared and treated as those in group B, except that a piece of ortho dontic arch w ire (Tru-Chrome, .019 x .026) was
Fig 1 ■ Abutment teeth in group A with pontic in position. Pontics were attached to abutment teeth with composite resin retained by acid-etched enamel retention alone.
Fig 2 ■ Abutment teeth in group B with pontic in position. Class III preparations were made in the abutment teeth that were pro tected with calcium hydroxide base before acid etching.
Fig 3 ■ Abutment teeth in group C with pontic and orthodontic arch wire (.019 x .026) in position. Cavity preparations were based before etching with acid.
placed betw een the two abutm ent preparations. T he .026 dim ension was vertical w ith the w ire through the lingual trench of the pontic (Fig 3). T h is was done as a possible reinforcem ent of the attachm ents. For all specim ens, the teeth were cleaned w ith a m ixture of pum ice and water. Surfaces were etched w ith 50% phosphoric acid for two m inutes, addi tion al acid was added, and specim ens were brushed ligh tly every 30 seconds. A cid was rem oved w ith a 30-second spray air and water; this was follow ed by a 30-second drying w ith air. Etched surfaces were im m ediately coated w ith a seal (Nuva-Seal) and cured w ith ultraviolet light. Pontic preparations were also coated w ith the seal and cured with ultraviolet light. Restorative m ate rial (Nuva-Fil) was then placed in the pontic prep arations and on the abutm ent teeth. T he pontic was positioned, and the restorative m aterial was adapted around the joint and tapered onto the facial and lingual surfaces to approxim ately 3 mm. Each join t was then cured w ith the ultraviolet light from the facial and lingual aspects. Restorative m aterial was applied again to bring the join t size to approxi m ately 5 mm incisal-gingivally and 4.5 mm faciallingually. This size of join t was chosen because it provided the maxim um bulk of com posite m aterial consistent with an aesthetic appearance and proper embrasure form. After curing, a diam ond in stru m ent was used to adjust the size of the join t to the required dim ension (± 0 .5 mm). A ll sam ples were stored at 100% hum idity before testing. Figure 4 shows the com pleted fixed partial denture. A testing m achine (Instron Universal Testing In strument) determ ined the force needed to displace the pontic. The load was applied through the long axis of the pontic w ith a crosshead speed of 0.1 cm/min on a small incisal notch placed in each pon tic. Sam ples rested on a metal platform that was seated on three m etal ball bearings (Fig 5). T he bear ings allow ed for a slight m ovem ent to align the specim en platform so that the force would be ver tically applied. T h is was done to elim inate horizon tal forces and externally applied m om ents. T he frac ture load in pounds required to displace each pon tic was recorded.
Results
Fig 4 ■ Bridge after placement of composite resin.
Results are presented in Table 1. A n overall com parison of the three groups was done, using one-factor analysis of variance (Table 2). Results of the a n a ly sis in d ica ted s ta tis tic a lly sig n ific a n t d if ferences between the three groups (P < .025). Com parisons betw een each pair of group m eans were then made using the Newman-Keuls m ultiple com parison technique. O utcom es of this analysis are reported in Table 3. Pairw ise com parison betw een groups B and C was considered statistically signifi-
Sweeney-Moore-Dooner : RETENTIVE STRENGTH OF ACID-ETCHED PARTIAL DENTURES ■ 199
Fig 5 ■ Test specimen ready for loading in testing instrument. Ball bear ings under specimen table allowed proper vertical alignment.
Table 1 ■ Load (in lb) required to displace pontic. Group A
No cavity preparation on abutments (acid-etched only)
B Class III cavity preparation on abutments (acid-etched) C
Class II preparation on abutments with arch wire reinforcement (acid-etched)
Force (lb)
Sample no.
103 100 104 102 92 86 132 170 152 88 112 108 105 77 100 104 90 70
1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6
Mean
SD
97.8
6.5
127.0
27.0
91.0
13.4
Table 2 ■ Sum m ary of analysis o f variance.* Source of variation Attachment techniques Error Total
df
Sums of squares
Means squares
F
4386.78 5950.83 10337.61
2193.39 396.72
5.53
2
15 17
* P < .025.
Table 3 ■ Newman-Keuls multiple com parison technique. Group means
C (91.0)
A (97.8)
B (127.0) A (97.8)
36.0*
29.2
6.8
* P < .05.
cant (P < .05). Com parison of groups A and C and A and B were not considered statistically significant. The greatest strength was achieved with group B in w hich Class III cavity preparations were made in the abutm ent teeth. A lthough not statistically signif icant w hen group means were com pared, greater 200 ■ JADA, Vol. 100, February 1980
Fig 6 ■ SEM photograph (original magnification, x 10) of one fracture site in group A. Notice smooth appearance of proximal surface. Fracture of labial composite resin extension is seen. Islands of unfilled resin (UR) remain attached to proximal enamel surface.
strength was achieved in five of the six specim ens. The reason for the low m ean strength of the one specim en was not determ ined. T he m ean load re quired to fracture the fixed partial denture in this group was 127.01b. Addition of the arch wire caused a significant decrease in strength w ith a m ean of 91.0 lb. T h is strength was less than that of group A in w hich cavity preparations were not made in the abutm ent teeth, although the difference was not sta tistically significant.
Discussion The mean load required to dislodge the acrylic pontics in group A in w hich cavity preparation was not made in the abutment teeth was 9 7.8 lb. This is considerably higher than the load previously re ported in a sim ilar study in w hich the m ean fracture load was 48.6 lb .16 Increased retention in this study may have been caused by the larger preparations in the plastic pontic. The larger preparations provided a greater bulk of com posite resin and a greater area of attachm ent for the com posite m aterial to the abut m ent teeth. Figure 6 shows a scanning electron m iscoscope photograph of a fracture site in group A in w hich only acid-etched retention was used. T he fracture
------------► Fig 8 ■ Top, SEM photograph (original magnification, x 100) same site of fracture site enamel. Notice unfilled resin remaining in enamel pores of etched enamel surface as compared with figure below. Fracture appears to have occurred primarily within layer of unfilled resin. Bottom, SEM photograph (original magnifica tion, x 100) of etched enamel before unfilled resin was placed. Compare photograph with figure at top.
Fig 7 ■ SEM photograph (original magnification, x 500) of same area. Notice island of unfilled resin (UR). Adjacent enamel pores (E) appear to remain partially tilled with resin.
through the labial extension of the com posite resin is apparent. The interproxim al surface is smooth with small islands of unfilled resin adhering to the enamel. Figure 7 is an SEM photograph of one of the is lands of unfilled resin and adjacent enam el. The adjacent enam el pores appear to be partially filled w ith resin. Further m agnification of the enam el at the site of fracture shows unfilled resin rem aining in the enam el pores of the etched enam el (Fig 8, top). T h is photograph can be com pared with the photo graph of the etched enam el before the application of the unfilled resin (Fig 8, bottom). The fracture of the joint seem s to have occurred prim arily through the attachm ent of unfilled resin on the proxim al surfaces and through the labial and lingual extensions of the filled com posite resin. The liner of unfilled resin is obviously the weak link of
the attachm ent. However, w ithout u nfilled resin, filled resin would not penetrate as w ell into the m icropores of the etched enam el. The w eak link is probably necessary. Preparations in the abutm ent teeth further in creased the resistance to fracture (mean load, 127.0 lb). In this group, the weak link o f the attachm ent of unfilled resin was m inim ized. A bulk of the filled com posite resin extended from the pontic to w ithin the preparations on the abutm ent teeth. Fractures in this group occurred through the bulk of the filled com posite resin in the join t area. A ddition of the arch wire did not increase the resistance to fracture. Rather, the m ean load re quired to displace the pontic (91.0 lb) was less than w hen acid-etched retention alone was used (97.8 lb ). The w ire apparently interrupted the con tin uity of the bulk of com posite resin extending betw een the
Sweeney-Moore-Dooner RETENTIVE STRENGTH OF ACID-ETCHED PARTIAL DENTURES ■ 201
pontic and the abutment tooth. It would seem that, when acid-etched retention is used alone, the m axim um bulk of com posite m ate ria l sh o u ld be p la ce d in th e jo in t are a , w ith m axim um labial and lingual extension consistent with aesthetic appearance, embrasure form, and oc clusion. The reported m axim um biting force in the an terior area varies between 24 to 55 lb.1214 Therefore, acid-etched retention alone should be sufficient for the retention of m ost single replacem ents of anterior teeth. Cavity preparations in the abutment teeth may provide additional retention and might be indicated for longer spans or,for patients in whom acid-etched retention alone has failed.
Summary and conclusions The force needed to dislodge an acrylic pontic bonded to natural tooth abutments with composite resin was determined for three attachm ent tech niques. Bulk of material in the joint area increased the resistance to fracture. Additional strength was obtained by Class III preparations in the abutment teeth. Addition of an arch wire fajled to reinforce the joints. The magnitude of the forces required to dislodge the pontics suggests that acid-etched fixed partial dentures provide a viable alternative to other fixed or removable prostheses replacing single anterior teeth. The additional strength obtained by cavity preparations in the abutment teeth suggests the pos sibility of fixed partial dentures with longer spans. A com posite material with greater linear strength w ould make application of the technique m ore widely used.
This project was supported in part by funds granted by the Research Service at the Veterans Administration Hospital, Leavenworth, Kan, pro ject no. 01-579-58-9133.
202 ■ JADA, Vol. 100, February 1980
The authors thank Drs. William Carson, chairman, department of me chanical engineering, University of Missouri, Columbia, and Dan Tira, coordinator of computer applications in instruction, University of Mis souri, Kansas City School of Dentistry, for assistance with the project. Dr. Sweeney, formerly a general practice resident at the Veterans Ad ministration Hospital, Leavenworth, Kan, where this study was con ducted, is currently a staff dentist, Jerry L. Pettis Memorial Veterans Hospi tal, 11202 Benton St, Loma Linda, Calif 92354, and is assistant professor, Loma Linda Dental School. Dr. Moore is professor and chairman, depart ment of operative dentistry, University of Missouri-Kansas City School of Dentistry, and consultant, operative dentistry, Veterans Administration Hospital, Leavenworth. Dr. Dooner is chief, dental service, Veterans Ad ministration Hospital, Leavenworth, and is associate professor, dentistry and director, graduate dental practice programs, University of MissouriKansas City School of Dentistry. Address requests for reprints to Dr. Sweeney. 1. Speiser, A.M. Transitional splinting with adhesive materials. J N] Dent Assoc 46(l):34-35, 1974. 2. Vogel, R.I. The use of a self-polymerizing resin with enamel etchant for temporary stabilization. J Periodontol 47(2):69-71, 1976. 3. Ibsen, R.L. Fixed prosthetics with a natural crown pontic using an adhesive composite. Case history. J South Calif State Dent Assoc 41:100102,1973. 4. Richmond, N.L. Acid-etch “bridge” technique. J Indiana State Dent Assoc 52:435-436, 1973. 5. McEvoy, S.A., and Mink, J.R. Acid-etched resin splinting for tem porarily stabilizing anterior teeth. J Dent Child 41(6):439-441, 1974. 6. Stuart, I.A. An unusual space maintainer retained by an acid-etched polymer resin. Br Dent J 137(ll):437-438, 1974. 7. Schwarz, M.S., and Sochat, P. The interim intracoronal wire and acrylic splint, J South Calif State Dent Assoc 40:1067-1069, 1972. 8. Light, E.I., and Rakow, B. Clinical evaluation of Nuva Fil. J NJ State Dent Soc 45:32-34, 1973. 9. Portnoy, L.L. Constructing a composite pontic in a single visit. Dent Surv 49:20, 1973. 10. Tucker, S.S. Repair of a loosened pontic in a single visit. Dent Surv 50:44, 1974. 11. Klassman, B., and Zucker, H.W. Combination wire-composite resin intracoronal splinting rationale and technique. J Periodontol 47(8):481486, 1976. 12. Guyton, A.C. Textbook of medical physiology. Philadelphia, W. B. Saunders Co., 1971, p 742. 13. Davenport, H.W. Physiology of the digestive tract: an introductory text. Chicago, Year Book Medical Publishers, 1966, p 11. 14. Anderson, D.J. Measurement of stress in mastication. J Dent Res 35:664-673, 1956. 15. Klaffenbach, A.O. Gnathodynamics. JADA 23:371-382, 1936. 16. Lambert, P.M.; Moore, D.L.; and Elletson, H.H. In vitro retentive strength of fixed bridges constructed with acrylic pontics and an ultraviolet-light-polymerized resin. JADA 92(4):740-743, 1976.
Retentive strength of acid-etched anterior fixed partial dentures: an in vitro comparison of attachment techniques Edw ard J. Sweeney, DDS David L. M oore, DDS, MS John J. Dooner, DDS
I n som e cases, acid-etched fixed partial dentures provide an alternative to conventional fixed partial dentures or rem ovable prosthetic appliances. It has been reported that resin pontics, as w ell as natural tooth pontics, may be attached to abutm ent teeth w ith com posite resin m aterials w ithout m echanical p reparation of the ab u tm en ts.1 11 T h ese reports suggest that the life span of fixed partial dentures can range from several days to an ind efinite period, depending on the technique and location of the fixed partial denture in the mouth. The biting force of human dentition varies greatly; it increases from anterior to posterior. G uyton,12 D avenport,13 and A nderson14 reported that the bit ing force in the region of the incisors was in the range of 24 to 55 lb. K laffenboch15 said that molars could produce a force as high as 290 lb. The strength of acid -etched anterior fixed partial dentures was reported to vary betw een 41.5 to 55.8 lb with a mean strength of 4 8 .6 lb .16 It is evident that the strength of the attachm ent leaves som ething to be desired, even for anterior fixed partial dentures. T h is study was done to evaluate three attachm ent techniques that were designed to increase the strength of the fixed partial denture.
Materials and methods Eighteen fixed partial dentures that extended from the m axillary central incisors to the canines were constructed. R ecently extracted teeth were oriented 198 ■ JADA, Vol. 100, February 1980
6 mm apart in a rectangular silicone mold. A coldcuring acrylic resin was used to form a base. For all specim ens, a lateral incisor (Bioblend 21X ) was used as the pontic. Class III preparations were made in the m esial and distal surfaces of all pontics. These prep arations were 3 mm incisal-gingivally, 3 mm faciallingually, and 1.5 mm deep axially. M echanical re tention was made w ithin each preparation w ith a half-round bur. Preparations were connected across the lingual surface w ith a trench that was 1.5 mm wide. Specim ens were separated into three groups; six specim ens were in each group. GROUP A. Abutm ent teeth were acid-etched without m echanical preparation (Fig 1) and the pontic was attached w ith a photosensitive com posite resin sys tem (Nuva-Fil). GROUP B. Abutm ent teeth received Class III prepa rations w ith the same dim ensions and retention as the preparations in the pontics (Fig 2). To form a short bevel on the cavosurface, a no. 1-A diamond instrum ent was used. The axial wall was lined with a calcium hydroxide base (Pro-Cal). Teeth were then etched and the pontic was attached with com posite resin. GROUP C. Abutm ent teeth were prepared and treated as those in group B, except that a piece of ortho dontic arch w ire (Tru-Chrome, .019 x .026) was
Fig 1 ■ Abutment teeth in group A with pontic in position. Pontics were attached to abutment teeth with composite resin retained by acid-etched enamel retention alone.
Fig 2 ■ Abutment teeth in group B with pontic in position. Class III preparations were made in the abutment teeth that were pro tected with calcium hydroxide base before acid etching.
Fig 3 ■ Abutment teeth in group C with pontic and orthodontic arch wire (.019 x .026) in position. Cavity preparations were based before etching with acid.
placed betw een the two abutm ent preparations. T he .026 dim ension was vertical w ith the w ire through the lingual trench of the pontic (Fig 3). T h is was done as a possible reinforcem ent of the attachm ents. For all specim ens, the teeth were cleaned w ith a m ixture of pum ice and water. Surfaces were etched w ith 50% phosphoric acid for two m inutes, addi tion al acid was added, and specim ens were brushed ligh tly every 30 seconds. A cid was rem oved w ith a 30-second spray air and water; this was follow ed by a 30-second drying w ith air. Etched surfaces were im m ediately coated w ith a seal (Nuva-Seal) and cured w ith ultraviolet light. Pontic preparations were also coated w ith the seal and cured with ultraviolet light. Restorative m ate rial (Nuva-Fil) was then placed in the pontic prep arations and on the abutm ent teeth. T he pontic was positioned, and the restorative m aterial was adapted around the joint and tapered onto the facial and lingual surfaces to approxim ately 3 mm. Each join t was then cured w ith the ultraviolet light from the facial and lingual aspects. Restorative m aterial was applied again to bring the join t size to approxi m ately 5 mm incisal-gingivally and 4.5 mm faciallingually. This size of join t was chosen because it provided the maxim um bulk of com posite m aterial consistent with an aesthetic appearance and proper embrasure form. After curing, a diam ond in stru m ent was used to adjust the size of the join t to the required dim ension (± 0 .5 mm). A ll sam ples were stored at 100% hum idity before testing. Figure 4 shows the com pleted fixed partial denture. A testing m achine (Instron Universal Testing In strument) determ ined the force needed to displace the pontic. The load was applied through the long axis of the pontic w ith a crosshead speed of 0.1 cm/min on a small incisal notch placed in each pon tic. Sam ples rested on a metal platform that was seated on three m etal ball bearings (Fig 5). T he bear ings allow ed for a slight m ovem ent to align the specim en platform so that the force would be ver tically applied. T h is was done to elim inate horizon tal forces and externally applied m om ents. T he frac ture load in pounds required to displace each pon tic was recorded.
Results
Fig 4 ■ Bridge after placement of composite resin.
Results are presented in Table 1. A n overall com parison of the three groups was done, using one-factor analysis of variance (Table 2). Results of the a n a ly sis in d ica ted s ta tis tic a lly sig n ific a n t d if ferences between the three groups (P < .025). Com parisons betw een each pair of group m eans were then made using the Newman-Keuls m ultiple com parison technique. O utcom es of this analysis are reported in Table 3. Pairw ise com parison betw een groups B and C was considered statistically signifi-
Sweeney-Moore-Dooner : RETENTIVE STRENGTH OF ACID-ETCHED PARTIAL DENTURES ■ 199
Fig 5 ■ Test specimen ready for loading in testing instrument. Ball bear ings under specimen table allowed proper vertical alignment.
Table 1 ■ Load (in lb) required to displace pontic. Group A
No cavity preparation on abutments (acid-etched only)
B Class III cavity preparation on abutments (acid-etched) C
Class II preparation on abutments with arch wire reinforcement (acid-etched)
Force (lb)
Sample no.
103 100 104 102 92 86 132 170 152 88 112 108 105 77 100 104 90 70
1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6
Mean
SD
97.8
6.5
127.0
27.0
91.0
13.4
Table 2 ■ Sum m ary of analysis o f variance.* Source of variation Attachment techniques Error Total
df
Sums of squares
Means squares
F
4386.78 5950.83 10337.61
2193.39 396.72
5.53
2
15 17
* P < .025.
Table 3 ■ Newman-Keuls multiple com parison technique. Group means
C (91.0)
A (97.8)
B (127.0) A (97.8)
36.0*
29.2
6.8
* P < .05.
cant (P < .05). Com parison of groups A and C and A and B were not considered statistically significant. The greatest strength was achieved with group B in w hich Class III cavity preparations were made in the abutm ent teeth. A lthough not statistically signif icant w hen group means were com pared, greater 200 ■ JADA, Vol. 100, February 1980
Fig 6 ■ SEM photograph (original magnification, x 10) of one fracture site in group A. Notice smooth appearance of proximal surface. Fracture of labial composite resin extension is seen. Islands of unfilled resin (UR) remain attached to proximal enamel surface.
strength was achieved in five of the six specim ens. The reason for the low m ean strength of the one specim en was not determ ined. T he m ean load re quired to fracture the fixed partial denture in this group was 127.01b. Addition of the arch wire caused a significant decrease in strength w ith a m ean of 91.0 lb. T h is strength was less than that of group A in w hich cavity preparations were not made in the abutm ent teeth, although the difference was not sta tistically significant.
Discussion The mean load required to dislodge the acrylic pontics in group A in w hich cavity preparation was not made in the abutment teeth was 9 7.8 lb. This is considerably higher than the load previously re ported in a sim ilar study in w hich the m ean fracture load was 48.6 lb .16 Increased retention in this study may have been caused by the larger preparations in the plastic pontic. The larger preparations provided a greater bulk of com posite resin and a greater area of attachm ent for the com posite m aterial to the abut m ent teeth. Figure 6 shows a scanning electron m iscoscope photograph of a fracture site in group A in w hich only acid-etched retention was used. T he fracture
------------► Fig 8 ■ Top, SEM photograph (original magnification, x 100) same site of fracture site enamel. Notice unfilled resin remaining in enamel pores of etched enamel surface as compared with figure below. Fracture appears to have occurred primarily within layer of unfilled resin. Bottom, SEM photograph (original magnifica tion, x 100) of etched enamel before unfilled resin was placed. Compare photograph with figure at top.
Fig 7 ■ SEM photograph (original magnification, x 500) of same area. Notice island of unfilled resin (UR). Adjacent enamel pores (E) appear to remain partially tilled with resin.
through the labial extension of the com posite resin is apparent. The interproxim al surface is smooth with small islands of unfilled resin adhering to the enamel. Figure 7 is an SEM photograph of one of the is lands of unfilled resin and adjacent enam el. The adjacent enam el pores appear to be partially filled w ith resin. Further m agnification of the enam el at the site of fracture shows unfilled resin rem aining in the enam el pores of the etched enam el (Fig 8, top). T h is photograph can be com pared with the photo graph of the etched enam el before the application of the unfilled resin (Fig 8, bottom). The fracture of the joint seem s to have occurred prim arily through the attachm ent of unfilled resin on the proxim al surfaces and through the labial and lingual extensions of the filled com posite resin. The liner of unfilled resin is obviously the weak link of
the attachm ent. However, w ithout u nfilled resin, filled resin would not penetrate as w ell into the m icropores of the etched enam el. The w eak link is probably necessary. Preparations in the abutm ent teeth further in creased the resistance to fracture (mean load, 127.0 lb). In this group, the weak link o f the attachm ent of unfilled resin was m inim ized. A bulk of the filled com posite resin extended from the pontic to w ithin the preparations on the abutm ent teeth. Fractures in this group occurred through the bulk of the filled com posite resin in the join t area. A ddition of the arch wire did not increase the resistance to fracture. Rather, the m ean load re quired to displace the pontic (91.0 lb) was less than w hen acid-etched retention alone was used (97.8 lb ). The w ire apparently interrupted the con tin uity of the bulk of com posite resin extending betw een the
Sweeney-Moore-Dooner RETENTIVE STRENGTH OF ACID-ETCHED PARTIAL DENTURES ■ 201
pontic and the abutment tooth. It would seem that, when acid-etched retention is used alone, the m axim um bulk of com posite m ate ria l sh o u ld be p la ce d in th e jo in t are a , w ith m axim um labial and lingual extension consistent with aesthetic appearance, embrasure form, and oc clusion. The reported m axim um biting force in the an terior area varies between 24 to 55 lb.1214 Therefore, acid-etched retention alone should be sufficient for the retention of m ost single replacem ents of anterior teeth. Cavity preparations in the abutment teeth may provide additional retention and might be indicated for longer spans or,for patients in whom acid-etched retention alone has failed.
Summary and conclusions The force needed to dislodge an acrylic pontic bonded to natural tooth abutments with composite resin was determined for three attachm ent tech niques. Bulk of material in the joint area increased the resistance to fracture. Additional strength was obtained by Class III preparations in the abutment teeth. Addition of an arch wire fajled to reinforce the joints. The magnitude of the forces required to dislodge the pontics suggests that acid-etched fixed partial dentures provide a viable alternative to other fixed or removable prostheses replacing single anterior teeth. The additional strength obtained by cavity preparations in the abutment teeth suggests the pos sibility of fixed partial dentures with longer spans. A com posite material with greater linear strength w ould make application of the technique m ore widely used.
This project was supported in part by funds granted by the Research Service at the Veterans Administration Hospital, Leavenworth, Kan, pro ject no. 01-579-58-9133.
202 ■ JADA, Vol. 100, February 1980
The authors thank Drs. William Carson, chairman, department of me chanical engineering, University of Missouri, Columbia, and Dan Tira, coordinator of computer applications in instruction, University of Mis souri, Kansas City School of Dentistry, for assistance with the project. Dr. Sweeney, formerly a general practice resident at the Veterans Ad ministration Hospital, Leavenworth, Kan, where this study was con ducted, is currently a staff dentist, Jerry L. Pettis Memorial Veterans Hospi tal, 11202 Benton St, Loma Linda, Calif 92354, and is assistant professor, Loma Linda Dental School. Dr. Moore is professor and chairman, depart ment of operative dentistry, University of Missouri-Kansas City School of Dentistry, and consultant, operative dentistry, Veterans Administration Hospital, Leavenworth. Dr. Dooner is chief, dental service, Veterans Ad ministration Hospital, Leavenworth, and is associate professor, dentistry and director, graduate dental practice programs, University of MissouriKansas City School of Dentistry. Address requests for reprints to Dr. Sweeney. 1. Speiser, A.M. Transitional splinting with adhesive materials. J N] Dent Assoc 46(l):34-35, 1974. 2. Vogel, R.I. The use of a self-polymerizing resin with enamel etchant for temporary stabilization. J Periodontol 47(2):69-71, 1976. 3. Ibsen, R.L. Fixed prosthetics with a natural crown pontic using an adhesive composite. Case history. J South Calif State Dent Assoc 41:100102,1973. 4. Richmond, N.L. Acid-etch “bridge” technique. J Indiana State Dent Assoc 52:435-436, 1973. 5. McEvoy, S.A., and Mink, J.R. Acid-etched resin splinting for tem porarily stabilizing anterior teeth. J Dent Child 41(6):439-441, 1974. 6. Stuart, I.A. An unusual space maintainer retained by an acid-etched polymer resin. Br Dent J 137(ll):437-438, 1974. 7. Schwarz, M.S., and Sochat, P. The interim intracoronal wire and acrylic splint, J South Calif State Dent Assoc 40:1067-1069, 1972. 8. Light, E.I., and Rakow, B. Clinical evaluation of Nuva Fil. J NJ State Dent Soc 45:32-34, 1973. 9. Portnoy, L.L. Constructing a composite pontic in a single visit. Dent Surv 49:20, 1973. 10. Tucker, S.S. Repair of a loosened pontic in a single visit. Dent Surv 50:44, 1974. 11. Klassman, B., and Zucker, H.W. Combination wire-composite resin intracoronal splinting rationale and technique. J Periodontol 47(8):481486, 1976. 12. Guyton, A.C. Textbook of medical physiology. Philadelphia, W. B. Saunders Co., 1971, p 742. 13. Davenport, H.W. Physiology of the digestive tract: an introductory text. Chicago, Year Book Medical Publishers, 1966, p 11. 14. Anderson, D.J. Measurement of stress in mastication. J Dent Res 35:664-673, 1956. 15. Klaffenbach, A.O. Gnathodynamics. JADA 23:371-382, 1936. 16. Lambert, P.M.; Moore, D.L.; and Elletson, H.H. In vitro retentive strength of fixed bridges constructed with acrylic pontics and an ultraviolet-light-polymerized resin. JADA 92(4):740-743, 1976.