Ife Disadvantages

The primary disadvantage associated with resin-bonded FPD" relates to the fact that the longevity of the prosthesis is less than for conventional prosthe-ses. This has been the subject of considerable investigation. Studies of first-generation etched metal FPD" at the University of Iowa (more anterior pros-theses than posterior) and the University of Maryland (more posterior prostheses than anterior), with an average service time of more than 10 years, have been relatively successful. The results estimate that 50% will fail after 250 months and 190 months, respectively (see Table 26-1).16 These studies also indicate that the rate of debonds does not increase with time.

In a study conducted in a private-practice setting, contemporary designs with a mean service time of 6 years achieved a 93% success rate . 3 This differs with the findings in a multicenter study in Europe, where debonding rates increased with the time after placement (almost 50% at 5 years) and were related to preparation design, luting agent selection, and the area of placement within the dental arch. 78 Another European study found retention rates of 60% at 10 years for early designs. In one study, posterior and mandibular resin-retained FPD" demonstrated higher dislodgment rates,79 which may have resulted from occlusal forces (see Chapter 4) and increased isolation difficulty during the bonding procedure.","' In light of these studies, the likelihood of eventual debonding should be discussed with the patient before treatment. By comparison, a meta-analysis of conventional FPD clinical studies indicated a doubling of the failure rate for every 5 years of service from 0 to 15 years."' When these results are projected from 15 years to 20 years, a 50% failure rate for conventional fixed partial dentures would take about 20 years."

Extensive enamel modifications are required with retentive design to the proximal and lingual surfaces of the abutment teeth (see Fig. 26-8, B). If the restoration is removed, composite resin bonding could restore the enamel contours, but transition to a more traditional prosthesis is likely. Enamel is limited in thickness, which requires precision in design and preparation with attention to detail ."2 Enamel lingual surfaces of anterior teeth are almost always thinner than 0.9 mm.83

Space correction is difficult with resin-retained FPDs. When the pontic space is greater or less than the dimensions of a normal tooth, achieving an esthetic result with this restoration is difficult. As with conventional fixed prostheses, treatment of diastemas is demanding, although a cantilever option may be appropriate.

Good alignment of abutment teeth is required because the prosthesis' path of insertion is limited by potential penetration of the enamel thickness. However, some posterior teeth, which are mesially or mesiolingually tilted, can be onlayed with a bonded retainer (see Figs. 26-19 and 26-21).

Esthetics is compromised on posterior teeth. Posterior resin-retained FPD design requires the extension or the metal framework onto the occlusal surface of posterior teeth. These occlusal rests and occasional onlaying of cusps are visible, which might be objectionable to some patients (see Fig. 26-19).

Clinical indications and contraindications are quite specific. In the presence of any contraindications, a conventional FPD or an implant-supported crown should be considered.

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