A four-year clinical evaluation of acid etched bridges

  A. R. Al-Shammery, BDS,MS,
H. I. Saeed, BDS
College of Dentistry, King Saud University, P.O.Box 60169, Riyadh 11545, Saudi Arabia.

Thirty six (36) three unit acid etched bridges (20 posterior and 16 anterior) were clinically evaluated in relation to retention, cracking in the porcelain and caries status of the abutment teeth. The results showed that after 4 years 26 bridges (72.2 %) were successfully retained, one porcalin facing had fractured and none of the abutments showed evidence of caries during the period of the study.

Rapid improvement in direct adhesive bonding between polymers and mineralized tooth structure has resulted in the development of a conservative method for tooth replacement, notably the acid etched bridge.1"5

Long term standardized clinical evaluation of this technique is still minimal but a number of reports on the longevity of such fixed partial dentures have been made.

Jordan et a!6 completed a 3-year study of 86 patients, and a 4-year study of 22 patients was reported by Jenkins.7 William and Denehy8 presented a study of 99 resin- bonded prostheses placed over a 10-year period. Failure rate of all prostheses in the latter study was 31 %.

Wiltshire and Ferreira9 showed that 34% of the resin-bonded bridges evaluated required recemen-tation  after  3  years  while  Al  Shammery  and Saeed00"11* reported a 91.6% clinical success rate after 12 months and a 72.2% success rate after 38 months follow up.

The purpose of this study was to clinically evaluate the longevity of posterior and anterior 3-unit acid-etched bridges relative to retention of the bridge, cracking on the porcelain facing, and caries incidence.

Thirty-six 3-unit acid-etched bridges (20 post­ erior and 16 anterior) were delivered to patients whose ages ranged between 18 and 55 years.

During the first visit, the protocol of the study was explained to the patients. The advantages and disadvantages of using this technique were also made clear to them. The criteria for patient selec­ tion were: healthy gingiva, good oral hygiene and sound abutment teeth, free from caries or any restorations. Edge-to-edge bite relation cases were excluded from the study. All patients lived or worked within Riyadh (Saudi Arabia) to ensure availability for recall evaluation.

During the second visit, the teeth were prepared by a previously standardized technique. Technique standardization was established by the two investigators making preparations for both the anterior and posterior restorations on typodont teeth. These preparations were then evaluated by an independent examiner, and differences were noted and reported to the investigators. The pro­ cess was considered standardized when the inde­ pendent examiner could not differentiate between the preparations of the two investigators.

The design for the preparation was as follows: a lingual and proximal reduction between 0.3 - 0.5 mm creating a chamfer finish line utilizing a tapered diamond. One proximal groove in the   namel of each abutment tooth was placed by using the same tapered diamond stone. All the margins of the preparations were placed 2-3 mm gingival from the incisal edge in the anterior and on occlusal cusps in the posterior. All were 2 mm from the free margin of the gingiva.

One occlusal rest was placed on each posterior abutment which one cingulum rest was placed on each anterior abutment. Vinyl polysiloxane impre­ ssion material was used for the final impression (President Coltene AG, Switzerland). Occlusal reg­ istrations were made utilizing 3M bite registration paste.

To minimize the variability, all restorations were fabricated by one technician. Frameworks were waxed up in with blue inlay wax and invested in phosphate bonded investment (DVP Whip Mix Co., Louisville, KY, USA).

Rexillium 111 [Nickel-Chromium-Beryllium] alloy (Jeneric Industries, Wallingford, CT, USA) was used to cast the frameworks and Vita porcelain was applied to the pontic areas (Vita Zahnfabrik, Bad Sackinjen, West Germany).

During the third visit, the unetched bridge was tried in the mouth and all the necessary adjust­ments were made. After estimating the surface area of the bridge, etching was accomplished in the lab­ oratory with 10% sulfuric acid for 3 minutes and 300 ma/cm2. Ultrasonic cleaning was done for 18 minutes.

During the fourth visit, all the abutment teeth were cleaned with a pumice-water mixture and etched for 60 seconds, washed thoroughly and dried in the usual way; bonding agent was applied to both the casting and the etched enamel of the abutment teeth.

Autopolymerizing luting resin Comspan (Caulk Dentsply Inc, Milford, Delaware, USA) was placed on the casting using a plastic instrument. In a previ-

ous study, Comspan provided a bond strength equal to that of Denmat.10

The bridge was seated and the excess luting resin was allowed to flow, care was being taken to pre­ vent any polymerized composite flash at the gingi­ val areas. After final set, excess material was removed with a flame-shaped No. 7901 finishing bur, and was completed with a rubber polishing point, thus enabling the finishing of the interproxi­
mal areas of the bridge. Patients were recalled at intervals of 6, 12, 24, 38, and 48-months.

During each recall visit, the retention of the fixed bridge, integrity of the porcelain facing and caries status of the abutment teeth were evaluated and recorded on a special evaluation form. All the 36 bridges were luted within the first two months of the study. The bridges which failed before or during the recall evaluation time were cleaned, then re-etched and luted following the identical previous protocol, but were excluded from the study. Figures 1 -4 depict pre- and post-operative views of
typical upper anterior bridges.

Table 1 shows the distribution of the 36 bridges, consisting of 20 posterior and 16 anterior. 23
bridges replaced maxillary teeth, and 13 bridges replaced mandibular teeth. Table 2 shows the longevity of the 36 bridges up to a 4-year follow-up.

Retention

As shown in Table 2, 6 bridges failed within the first 6 months recall period. Failure represented 16.6% of the total number of bridges in the study (30% of the total number of posterior bridges, and 30.7% of the total number of the mandibular bridges). Retention results, for the period 6-12 months, indicated a further 3 poste'riorfailure. Thus the failure rate increased to 25% of the total number of bridges {45% of the posterior bridges and 53% of the mandibular bridges).

The recall period between 12-24 months showed one failure of a maxillary posterior bridge. Increasing the failure rate to 27.7% of the total Oumber of the bridges (50% failure of the posterior bridges and 13.04% of the total of maxillary bridges). Up to the 4 years recall period, none of the remaining bridges failed.

Cracking in the Porcelain Facings

The porcelain facings of all the restorations were in excellent condition, except for one mandibular premolar facing that had a fracture of less than 25% of the surface area of the buccal surface.

Caries status of the abutment teeth

None of the abutments developed any evidence of caries during the 4-year period of study.

Success of any restoration is significantly affected by the operator's careful attention and by proper patient selection. The majority of failures in this study were in replacements of mandibular premo­ lars and molars.

On examination of the failed prosthesis, it was evident that the bonding agent remained attached to the metal framework and not on the teeth. This pattern suggested that failures were adhesive in nature between the etched enamel and the luting resin. Such failure could possibly be due to saliva contamination during the bonding procedure.

The results of William and Denehy8 showed that the failure rate among the 99 resin- bonded prosth­ eses from all causes was 31 %. In the current study, the failure rate was 27% for all the bridges. The study of Wiltshire and Ferreira9 showed that 34% of resin-bonded bridges required recementation after 1 -3 years follow-up, which is also in consistent with the results of the current study.

This study differed from the two previous studies,89 in that it investigated only 3-unit acid-etched bridges. Also, this study specifies the loca­tion of the failure while the previous studies8'9 did not.

Caries occurrence on the abutment teeth, in the previous studies89 was 3% in one study8 and 0% in the other study9, which is in agreement with the results of this study. It is felt that isolation, with a rubber dam during cementation of the mandibular acid-etched restoration, is far more effective than the use of cotton rolls in the mandibular area. These results showed that high failure rate occurred dur­
ing the first six months of placement of the restora­ tions, followed by a reduced rate of failure by the end of the fourth year,

Acid-etched bridges can be successfully retained in patients in whom exert excessive pressures on the restoration are unlikely to occur during normal masticatory function. The abutment teeth should be periodontally sound and free from extensive caries or restorations. This will facilitate an optimum bond­ ing area between the etched enamel and the resin.

A four-year report of the clinical status of 36 acid-etched fixed restorations was presented. The study indicated that the longevity of the restoration was clearly dependent on the area of replacement of the missing tooth. There was a high failure rate in the retention of those restorations placed in man­ dibular molar and premolar areas. There was a higher success rate for the maxillary restorations for both the anterior and posterior teeth.

The acid-etched bridge can be considered as a permanent restoration to replace a single missing tooth in the maxillary arch, or in the anterior area of the mandibular arch.

This research study was supported by the College of Dentistry Research Center (CDRC), King Saud University-Grant No. 1009.

1. Thomson VP. Electrolytic etching modes of various non-precious alloys for resin bonding. J Prosthet Dent (special issueA)1982;61:186.
2. 2.   Tanaka T, Atsutz M, Uchiyama Y, Kawashima I. Pitting corrosion for retaining acrylic resin facings. J Prosthet       11  % Dent 1979;42:293-291.
3. Rochette AL. Attachment of a splint to enamel of lower anterior teeth.) Prosthet Dent 1973,30:418-423.
4. Howe DF, Denehy GE. Anterior fixed partial dentures utilizing the acid etch technique and a cast metal framework. J Prosthet Dent 1977;37:28-31.
5. Thomson, VP, del Castillo E, Lividitis GJ. Resin bond to electrolytically etched non-precious alloys for resin-bonded prosthesis. J Dent Re5 (special issue A) 1981;60:377.
6. Jordan RE, Suzukim, Sills PS, Craton DR, Gwinnett jA. Temporary fixed partial dentures fabricated by means of the acid-etch resin techniques. A report of 86 cases fol­lowed up to three years. J Amer Dent Assoc 1978,-96:994.
7. Jenkins CBG. Etched-retained anterior pontics. Brit Dent J 1978;144:206.
8. Williams VD, Denehy GE, Thayer KE, Boyer DB. Resin bonded prostheses: a ten-year retrospective study. J Dent Res (special issue) 1987;66:739.
9. Wiltshire WA, Ferreira MR, Nel JC. Clinical evaluation of resin-bonded bridges at 1 to 3 years, j Dent Res (special issue) 1987;66:740.
10. Al-Shammery AR, Saeed Hi. Acid etched bridge; one year clinical evaluation. Tropical Dent. J 1987;10:175-179.
11. Al-Shammery AR, Saeed HI. Acis etched bridge. 36 cases report in 38 months follow- up. J. Dent. Res. (special issue) 1988;67:1545.
12. Al-Shammery AR. In vitro: Effect of different electrolytic etching times and luting media for two non-precious alloys upon shear bond strengths to human enamel. Thesis submitted to the Faculty of Graduate School of the University of Minnesota, June 1984

Address reprint requests to

 Dr. Al-Shammery, College of Dentistry

 King Saud University, P.O.Box 60169,

Riyadh 11545, Saudi Arabia.