The purpose of this clinical study was to evaluate the long-term outcome of three-unit posterior fixed partial dentures (FPDs) made of fiber-reinforced resin composite (FRC), and to identify design factors influencing the survival rate.
77 patients (52 females, 25 males) received 96 indirectly made FRC FPDs, using pre-impregnated unidirectional glass-fibers, requiring manual wetting, as framework material. FPDs were surface ( n = 31) inlay ( n = 45) or hybrid ( n = 20) retained and mainly located in the upper jaw. Hybrid FPDs consisted of a wing retainer at canine and an inlay retainer at distal abutment tooth. Surface FPDs consisted of uplay and wing combinations. Follow-up period was at minimum 4.5 years, with checkups at every 1–2 years. The study was carried out by six operators in three centers in the Netherlands, Finland and Sweden. Survival rates, including reparable defects of FPDs, and success rates were determined.
Kaplan–Meier survival rate at 5 years was 71.2% (SE 4.8%) for success and 77.5% (SE 4.4%) for survival. Differences were not significantly different. Main failure modes were delamination and fracture of the FPD. Only FPDs with surface retainers showed debonding.
A success rate of 71% and a survival rate of 78% after 5 years was found. Survival rates of inlay, hybrid and surface retained FPDs did not significantly differ.
The fixed partial denture (FPD) is a treatment modality offering tooth tissue conservation together with lower treatment costs. In a recent meta-analysis, the resin bonded FPD fabricated with a metal framework showed an estimated survival rate of 87.7% after 5 years . Complications like debonding of the framework from the luting cement were frequent and have been related to the unsatisfactory surface treatment of the metal alloy, due to difference in thermal expansion with regard to resin composite luting cements and the rigidity of the metal framework . Moreover, esthetic considerations may be a drawback. It is expected that fiber-reinforced composite (FRC) FPDs may provide an improved adhesive performance, because the material of the construction is similar to the luting material and FRC constructions are less rigid.
FRCs have recently been developed for dental applications and various types of fibers and fiber-products have been tested as reinforcing materials. Glass fibers are most often used because of their ability to withstand tensile stress and to prevent crack propagation in resin composite materials, and their esthetic character . Substantial improvements in flexural strength, fracture toughness and elastic modulus have been achieved in dental resin composites reinforced with fibers . The development of fiber products available for dental use has led from plain fibers to pre-impregnated fibers and finally fully resin impregnated fibers.
The retainer designs of an FRC prosthesis can be either full-coverage or partial coverage types, depending on the condition and amount of remaining sound tissue of the abutment teeth. The freedom in design of the FPD allows a tooth-conserving preparation when the abutment teeth are unrestored or have modest restorations. Fibers in the bridge construction run from the retainer at one end to the other, are preferably located in the tension side of the bridge and are completely covered by resin composite material. In addition, an FRC FPD can be fabricated either directly in the mouth or indirectly by a dental technician.
Two systematic reviews of all commercially available FRC products without discrimination between type of retainers or fabrication technique have been published . In both studies a limited number of published clinical studies was found, all of relatively limited duration, and few of the reported commercial products demonstrated robust clinical documentation to support their use. Problems specifically associated with a commonly used system include fractures of the veneering composite , but also wear and discoloration have been observed. Consequently, there is a need for data on other systems, preferably based on trials of longer duration.
In a recent study we reported 5-year follow-up data of three-unit anterior FRC FPDs, made of manually resin impregnated glass-FRC, which were placed in three academic centers in Finland, the Netherlands and Sweden . The purpose of the present study was to evaluate the long-term clinical outcome of three-unit FRC FPDs, but now applied in the posterior area. The FRC material was identical and all FPDs were indirectly made. Minimum service time was 4.5 years and design factors influencing survival were identified. Studies on metal resin-bonded FPDs showed lower survival rates in the posterior than in the anterior region, thus we expect that the survival rate of FRC FPDs shows the same difference.
Materials and methods
Between April 1998 and September 2002, 77 patients (52 females, 25 males) of the departments of Oral Function and the Centre of Special Dental Care of the Radboud University of Nijmegen (the Netherlands), the Institute of Dentistry University of Turku (Finland) and the Dental School Umeå (Sweden) were treated with 96 three-unit posterior indirect FRC FPDs. Approval of the University Medical Ethical Committee was obtained (the joint commission on the ethics of the Turku University and the Turku University Central Hospital, Resolution No. 264). Informed consent was given for each patient. The patients’ ages ranged from 12.4 to 77.5 years, with a mean age of 38.6 years. All FPDs replaced one missing tooth, which could be the first and second premolar or the first molar, and two adjacent abutment teeth were used for retention. No cantilever bridges were involved. Sixty-two patients received one FPD, thirteen patients received two FPDs and two patients received four FPDs. Among these, it concerned an FPD that was made after the first failed in four cases and these FPDs were included as new cases. The characteristics of the dentitions of subjects and FPDs made are presented in Table 1 . Patients were free of extensive periodontal disease and most of them had complete dental arches (except the missing tooth). X-rays to exclude periapical disease and loss of periodontal support of the abutment teeth were available.
|Gender of the patiënt||Male||33|
We aimed for conservation of tooth tissue and the FPD designs used depended on the level of restoration of the individual abutment teeth. The retainer designs of the two abutment teeth made can be divided into three categories: (1) uplay and wing combinations (surface retained), (2) both inlay retainers (inlay retained), and (3) wing retainer at palatal side of canine, inlay at distal abutment tooth (hybrid FPD) ( Fig. 1 ). Wing retainers (or so-called Maryland design surface retainers) were always provided with occlusal support. This could be designed as a minimal inlay-box preparation or, if there was any interocclusal space, without removal of tooth material. Uplay retainers were designed as an occlusal ‘wing’. In 12 cases the inlay retainer was provided with an additional wing at the buccal or lingual surface. The numbers of different FPD designs are described in Table 2 . Types of FPD designs were not evenly distributed between the three centers, with most of the surface retained FPDs made in Nijmegen, whereas the material of Turku and Umeå was predominantly of the inlay-type.
|Type of FPD||Mesial retainer||Distal retainer||n||Pontic type||Jaw|
|Surface retained||Uplay||Uplay||15||Premolar 14||Molar 1||Mandibula 11||Maxilla 4|
|Surface retained||Wing||Uplay||16||Premolar 16||Molar 0||Mandibula 10||Maxilla 6|
|Hybrid retained||Wing||Inlay||20||Premolar 20||Molar 0||Mandibula 6||Maxilla 14|
|Inlay retained||Inlay||Inlay||45||Premolar 25||Molar 20||Mandibula 18||Maxilla 27|
Treatment was performed by six experienced dentists, with adequate skills in adhesive techniques, according to a clinical protocol. Clinical procedures were performed during two treatment sessions: (1) tooth preparation, impressions and provisional restorations; and (2) try-in, placement of the FPD, and finishing. Tooth preparation involved removal of existing restorations and creating cavities with slight divergence of cavity walls and rounded angles. Inlay-cavities required adequate volume and support for the FRC substructure, at minimum 2 mm × 2 mm × 2 mm in size. Surface retainers with a minimal thickness of 0.4 mm at the canines were provided with palatal slots and distal grooves depending on the preference of the operator. Uplay retainers were made without tooth preparation in case occlusal space was available.
Impressions were made with a polyvinyl siloxane material. If present, cavities were protected with a provisional filling material for the period of the laboratory procedure.
FPDs were made in dental laboratories on full arch stone casts, which were isolated with separating agent. The fiber framework consisted of manual resin wetting requiring unidirectional pre-impregnated glass-fiber bundles (Stick™, Stick Tech Ltd., Finland). Each bundle consists of about 4000 glass fibers, with a diameter of 17 μm, embedded in a porous PMMA matrix. Glass-fiber reinforcements were manually impregnated with BisGMA–TEGDMA based light polymerizing monomer resin (Stick Resin, Stick Tech Ltd., Finland) to form a PMMA-dimethacrylate semi-inter polymer network (IPN) .
Before the fibers were placed on the cast, a thin layer of flowable composite was applied at the retainer area, which was not light-cured upon placement of the fiber bundle. After light polymerization, the framework was veneered with composite resin (in Turku and Umeå: Sinfony (3M ESPE, Germany); in Nijmegen: Artglass (Hereaus Kulzer, Germany)). The composite resin was built incrementally using a heat-light polymerization oven (in Turku and Umeå the 3M ESPE oven; in Nijmegen the Heraflash).
In the second treatment session, provisional restorations were removed and the abutment teeth were cleaned from debris. In most cases the fit of the FPD was checked using a silicon material (Fit Checker, GC, Japan); if needed the fit was adapted using diamond burs. Rubberdam was used in Nijmegen only, in about 50% of the cases. The bonding surface of the FPD was treated with the monomer resin. The resin was left unpolymerized, shielded from light, for at least 3 min to allow the resin to penetrate and activate the semi-IPN-phase of the polymethylmethacrylate polymer matrix of the FRC framework. FPDs were luted with resin composite cement (Turku and Umeå: Compolute (3M ESPE, Germany) and Variolink (Ivoclar Vivadent, Liechtenstein); in Nijmegen: Twinlook (Hereaus Kulzer, Germany) and Panavia F (Kuraray, Japan)) according to the manufacturer’s instructions. After removal of excess material, the resin composite cement was light cured for 20 s per surface. After polymerization, restoration margins were finished. Occlusion was adjusted with fine diamond-burs and the restoration was polished using rubbers and polishing discs. Patients received individual instructions to maintain plaque control.
For specific evaluation of the FRC FPDs, the majority of patients were invited for a check-up once a year, up to 5 years at minimum. Besides these check-ups, patients were advised to contact the dentist from the university clinic in case an event occurred concerning their FPD. The performance of the restorations was evaluated by clinical examination. Caries and periodontal status, wear of the restoration, discoloration, fractures and dislodgements were recorded. During the years 2005–2007 all patients with FPDs that were at least 4.5 years old and whose records did not already indicate a failure or removal of the restoration, were invited to participate in a clinical examination.
During the follow-up period, all interventions were recorded. Interventions may vary from finishing in case of chip fractures through repair by adding resin composite to renewal of the restoration. When records indicated interventions, the date and type of repair were recorded. If FPDs were repaired more than once, the first date of repair was used. The FPDs that could be rebonded after dislodgement were rebonded using the same procedure as had been used originally. Modes of failure were recorded as: (1) fracture of framework; (2) debonding one end; (3) dislodgement; (4) delamination of the veneering composite; (5) combination of problems. Fracture of the pontic, while the framework was still intact, was recorded as delamination.
All restorations were included as individual cases. Two failure categorizations were used:
Repaired needed: Includes interventions, such as polishing and finishing after chipping of small fragments of the veneering resin composite, repair of small delaminations with restorative resin composite, or adding fibers at the connector area of the fiber framework, during follow-up. Also rebonding of FPD after dislodgement or debonding of one retainer was considered a repair.
Failure occurred: An FPD was considered failed, when problems, such as fracture of the restoration, unreparable delamination of the veneering resin composite, and combination of problems, that could not be repaired with the FPD in situ, occurred during follow-up.
Survival was analyzed at different levels: on the level of ‘success’ and on the level of ‘survival’ using the two criteria of failure as endpoints. In both cases, restorations not meeting the criterion of failure at the end of the observation period were labeled “censored”. Reasons for drop-out were traced.
Kaplan–Meier survival analyses were done for the complete group of FPDs and discriminated according to retainer type and preparation form. The 95% confidence intervals for survival probability at 5 years were calculated. Correlations between variables were crosschecked and possibilities for Cox regression analyses were omitted because there are two many variables. The analyses were performed with SPSS version 16.0 (SPSS Inc., Chigaco, IL, USA).