Fixed partial denture (FPD) prostheses restore esthetics and function by connecting and fixing to adjacent teeth. Conventional FPDs require, for better retention and resistance, extensive preparations. Those preparations include buccal, palatal or lingual coverage, proximal guide planes, chamfers and /or grooves to optimize retention.^1–4 The removing of such large amount of tooth structure increases the risk of periodontal complications and pulp exposure.^1,3 In 1973, Rochette introduced resin bonded FPDs as a less invasive therapeutic option. He pioneered the use of lingual perforated cast alloy framework with acid etch composite for periodontal splinting of the anterior region.⁵ However, early Rochette bridges presented high failure rates. Since then, resin bonded FPDs have evolved with different framework materials and designs. Even though metal frameworks are highly resistant, they do have esthetical and mechanical limits such as the greyish appearance of the abutment teeth and dislodgment by the early loss of retention.^2–4,7 This led to introducing metal free FPDs, also widely developed thanks to adhesive dentistry. The preparation designs for RBFPDs were strictly limited to the enamel. Studies revealed a survival rate of 86% after 3 years without retentive preparation.⁶ All Ceramic RBFPDs have been introduced in the early nineties of the last century as a treatment option for missing incisors. Adhesive dentistry has undergone major transformations in current concepts. It has launched new resin bonded FPD designs that allowed to be more conservative such as single unit cantilevered ceramic bridges which become the most commonly used design when replacing lateral incisor especially when implant supported crowns cannot be indicated.⁸ Placing an implant is not always possible in cases where there is an insufficient bone height or width or for patients with general pathologies that may limit implant indications. That is why in some cases it is compulsory to indicate an FPD. Anterior ceramic RBFPDs showed promising results and high survival rates. They have proved to be viable and reliable alternative.⁸

Keywords: oligodentia, lateral incisor, implant, orthodontia, fixed partial denture, cantilevered bridge, bonding

Tooth agenesis is a frequent congenital human craniofacial abnormality that may be caused by genetic variations and/or environmental factors.^9,10 However, the extent to which genetic and/or environmental factors are involved remains unknown.^11,12 Studies reported a different prevalence of dental agenesis according to the type of dentition, group of teeth, and race.^13,14 It has also been described that it affects 1.37 times females more than males.^16,17 After third molars, maxillary lateral incisors (MLI) have been documented to be the most frequently missing teeth among permanent teeth.^18–20 According to a retrospective study that has been conducted on a sample including 1000 patients during a 6 year period , in the Department of Orthodontics at the Dental Medicine Clinic in Monastir, the congenital absence of MLI was about 3.6% over 7.8% of general tooth agenesis.²¹

The management for agenesis of the MLI primarily offers an alternative between two options: either space closure or space opening via orthodontic treatment. Prosthodontic treatment is often required as an adjunct to orthodontic therapy. The ideal treatment should be the most conservative option that satisfies both esthetic and functional requirements. Space opening for missing MLI is reported to be advantageous, as it provides harmonious facial and tooth development, respects the arch symmetry and allows an ideal intercuspation of canines.²² In addition, creating an orthodontic space requires minimal equilibration and reshaping on sound teeth.^23,24 When enough space is available in the maxillary arch, an implant-supported replacement should be considered as the most conservative treatment option.

A 24-year-old healthy female patient with congenitally missing both upper lateral incisors was referred to the department of fixed prosthodontics in the dental clinic of Monastir. She had recently completed orthodontic treatment that included space opening for eventual dental implants. However, radiographic showed insufficient apical inter dental bone volume which did not allow implant placement. Clinical examination revealed bilateral missing maxillary lateral incisors, short edentulous span, a slight deep bite and bilateral class I molar and canine relationships with canine guidance (Figure 1, 2).

Figure 1 Pre-operative extra-oral view.

Figure 2 Pre-operative intra-oral view.

Since the occlusal bite in the anterior teeth was located in the third incisal of the palatal surface of maxillary teeth, we have retained the indication of a cantilevered RBFPD. We selected central incisors as abutment teeth since they provide sufficient surface area for bonding with their overall length. The occlusal scheme was marked with an articulator paper to identify impact points. Our preparation limits were then located behind these impact points. (Figure 3) Teeth preparation was entirely restricted to the enamel surface. Palatal surfaces of maxillary central incisors are reduced with a round shaped bur about 0.7mm of the enamel are removed with a supra-gingival finish line (Figure 4).

Figure 3 Palatal scheme of the preparation.

Figure 4 Palatal limits of the preparation.

Palatal preparation is extended to interproximal surfaces to optimize retention. Interproximal preparations adjacent to edentulous sites included interproximal contacts (Figure 5, 6). All line and angles are rounded and prepared for digital impression. A silicone impression was conducted then transferred to dental laboratory. The FPD was manufactured. Prior to cementing, IPS emax RBFPDs were carefully positioned with try-in pastes to verify marginal adaptation, shape, color and occlusion (Figure 7). Internal surfaces of the restorations were conditioned with an 8% hydrofluoric acid for 20 seconds, washed with water and air-dried to be then, silaned (Figure 8, 9). Abutement surfaces of the teeth were etched with a 37% phosphoric acid for 30s then washed and dried (Figure 10, 11). A total etch adhesive system was applied with a 20 s photoactivation. (Figure 12)

Figure 5 Proximal limits of the preparation.

Figure 6 IPS emax single-unit cantilevered bridges.

Figure 7 Intra-oral trying of the restorations.

Figure 8 Etching of the internal surfaces of restorations.

Figure 9 Silanization of the restorations.

Figure 10,11,12 Teeth condoning with a Total-Etch system.

VARIOLINK dual resin cement was applied on the internal surfaces of the restorations and carefully positioned on the preparations (Figure 13). The resin bonded bridge was cemented using bonding resin cement after isolation of the teeth with a light cured isolation (Figure 14). Excess was removed and proceeded to an occlusion control. The patient was instructed to clinical controls every 6months (Figure 15).

Figure 13,14 Final cementation of the restorations.

Figure 15 Final result after a two-weeks control.

Oligodentia condition can affect physical, intellectual and psychological maturation of the patient.²⁵ Its prosthodontic management is important for functional and esthetic rehabilitation. Opening of the space with orthodontic means provides excellent esthetic outcomes and maintains or creates canine guidance. Canine guidance is biologically desirable and has predictable functional results as it protects the future prostheses.²⁶ Advocates of space closure would argue periodontal conditions with dental or implant supported prostheses.

They have reported the worst periodontal conditions caused by bacterial plaque retention on teeth abutting conventional fixed denture due to excessive contours and maladaptation.²⁷ Implant supported prostheses in the anterior region could be responsible of major esthetic defects such as gingival retraction,²⁸ interdental black triangles²⁹ and infracclusion.^28,30–34 Moreover, a canine-protected occlusion may not be considered as completely stable. It tends to be replaced by group function because of the inevitable physiological wear.^27,34,35 However, Clinicians have to recognize, that space closure is not always possible and that alternative strategies will be needed.^36,37

Once a suitable sized space has been achieved, different prosthetic options can be available such as implant supported crowns, conventional or adhesive fixed partial denture and even removable prostheses. At this point of the treatment, it is important to discuss different treatment options with the patient. Our patient agreed to an implant treatment.

However, her CBCT showed an insufficient apical bone volume due to the close proximity of the adjacent roots.³⁸ Among tooth-supported restorations, conventional fixed bridges are considered as the most invasive option. It has been reported that peripheral preparation removes 63% to 72% of the total sound tooth structures.^39,40 Which increases the risk of endodontic treatment for young patients with an important pulp volume.^40,41 RBFDP was first described by Rochette as a technique for splinting mandibular anterior teeth with compromised periodontal state.^40,42

Metal frame RBFPDs were introduced in the mid-1970s. Howe and Denehy advocated the use of perforated metallic retainers to optimize retention of the luting agent.⁴³ In early 1980s, Metal-ceramic RBFDP, widely known as Maryland, were presented with an electrolytic etching of the metal surface.⁴⁰ Livaditis and Thompson developed a method for etching non perforated metal alloys in order to protect the resin interface from abrasion and leakage.^44,45 Is has been reported that RBFPDs with two-retainer design were responsible of dramatic decays mainly caused by frequent partial unilateral debonding.^43,47 Authors explained partial debonding by the difference of dental mobility between the abutement teeth.^48,49

In order to prevent premature failure, preparation strategies have changed. Tooth preparation should provide a definite outline form and path of insertion for the restoration, therefore optimizing resistance and retention forms. It included slots,⁵⁰ grooves,⁵¹ seats,..^52,53 to promote mechanical resistance. However, such preparations scarified additional tooth structure which lowers the value of the abutment teeth and made them prone to developing caries and fracture. RBFPDs with two retainer design demonstrated a high incidence of unilateral fracture lefting the pontic bonded to a single retainer.^53,54 Debond rates of RBFDP supporting more than one pontic (52%) was double that the frameworks supporting a single pontic.⁵⁵

Kern et al reported a 5-year survival rate reaching 92% for cantilevered RBFPD compared to a 74% rate for traditional two-retainer designs.⁵⁶ All-ceramic RBFPDs demonstrated higher resin bond strengths than fracture strengths.^53,57,58 In order to enhance mechanical properties of RBFPDs, they were transformed into cantilevered designs that provide to be able to minimize shear and torque forces caused by differential movement on the abutements during function.^53,59,60 Metal-ceramic cantilevered RBFPDs recorded high success rates.^53,61,62 However, its main esthetic problem was related to the greyish aspect of the metal framework when bonded to the lingual surface.⁶³ All-ceramic cantivered RBFPDs proved to be a reliable conservative prosthetic design that serves either as a minimally invasive definitive prosthesis therapy.⁵³ They offer better esthetics and less biological damage. This type of bridge provides a similar quality of life that of those with implants. Analysis of the failure modes on zirconia RBFPDs showed 100% adhesive fractures located at the interface of resin-zirconia. Alumina or zirconia ceramics contain lower or non-existent glass phase which may be responsible for inadequate adhesion.^62,63

The progress in adhesive dentistry has brought us to reconsider tooth preparation designs. Cantilevered, all-ceramic RBFPDs combine minimally invasive preparation and bond strength. Those restorations should be presented to the patients as a sustainable alternative to implant therapy.

None.

The authors declare that there are no conflicts of interest.

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