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I industry report _ partial dentures

_Introduction

_The use of fibre-reinforced composite(FRC) to fabricate inlay-fixed partial dentures (IF-PDs) is an innovative therapeutic solution to re-store missing teeth.1 This new minimally-invasiveprosthetic approach has been made possible bydevelopments in the fields of adhesive dentistry,bonding systems, restorative materials, and con-servative preparation designs. Structurally, fibre-reinforced composite fixed partial dentures (FR-CFPDs) consist of two components: the fibres andthe resin matrix. The resin matrix serves as carrier,protector, and load-splicing medium around thefibres, which act as filler material.2 To improve themechanical properties of composite resins andoptimise the structures mechanical behaviour,specifically-oriented filler materials have beenproposed, such as glass fibres, aramid fibres, car-bon/graphite fibres, and ultra-high molecularweight polyethylene fibres. In-vitro studies havesuggested that glass fibres are the most suitable,

since they provide adequate adhesion to the poly-mer matrix.3

Glass-fibre-reinforced composite FPDs offer thepossibility of fabricating adhesive, aesthetic, andmetal-free tooth replacements at a reduced biologi-cal cost (Fig. 1).4 Compared to metal-ceramic and all-ceramic FPDs, the necessary preparation on abut-ment teeth is minimally invasive (Fig. 2).57 Moreover,the use of FRC reduces the risk of allergic or toxic sideeffects of metal alloys (Fig. 3).8 This therapeutic solu-tion is also specifically indicated in patients in whomimplant-surgery is contraindicated, because of, forexample, systemic diseases. Another significant ad-vantage of composite prosthetic solutions over otherrestorative materials is that they may be repaired in-tra-orally, without the risk of modifying aesthetic ormechanical performance (Figs. 4, 5).9

Owing to their good clinical performance1014, FRCsare increasingly used to restore missing teeth. Theclinical steps necessary for abutment preparation and

Fig. 1_Pre-op view of a patient who

rejected implant surgery. The maxil-

lary right first molar was extracted for

periodontal reasons approx. 3

months earlier.

Fig. 2_For the premolar, the exten-

sion of the preparation was deter-

mined by pre-existing restoration.

Where a tooth is intact, sound dental

tissues must be preserved as far as

possible, but no less than 3 mm

apico-coronally and 4 mm bucco-

palatally must be guaranteed for

preparation of the proximal box.

cosmeticdentistry 4_2008

Clinical and laboratoryprocedures to fabricate fibre-reinforced compositefixed partial denturesAuthors_ Giorgio Rappelli, Erminia Coccia & Daniele Rondoni, Italy

Fig. 1 Fig. 2

UtenzaG4Casella di testoBy kind permission of Cosmetic Dentistry International Edition n.4, 2008

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industry report _ partial dentures I


luting techniques have been documented1519, but lit-tle has been reported on the laboratory procedures in-volved in fabricating FRCFPDs. This report describesthe clinical and laboratory procedures entailed in fab-ricating fibre-reinforced composite inlay-fixed par-tial dentures (FRCIFPDs); the method can be used torestore missing teeth in an aesthetic, functional, andtime-saving manner, without any surgical steps. Inparticular, a laboratory technique is described thatuses a plexiglass flask; light-curing, pre-impregnatedglass fibres; and light-curing composites.

_Preparation of abutment teeth

Cavity design and preparation for FRCIFPDs aresimilar to those for inlay restorations (Figs. 6, 7).14

The buccal and palatal margins of both boxes mustbe flared apical-coronally, in order to ensure thecorrect position of the FPD during cementation. Fi-nite element (FE) analysis, employing two- andthree-dimensional models20,21, has indicated thatthe connector area is the critical zone for stress con-centration when vertical and lateral loads are ap-plied to the tooth-restoration complex. Moreover,Song et al.22 demonstrate the correlation betweenthe mechanical strength of FRCIFPDs and abutmentdesign; they highlight the need for abundant fibresto improve FPD strength. In order to provide optimalmechanical behaviour in the connector areas, theproximal boxes in abutment teeth must extend forapproximately 4 mm bucco-palatally, 1.5 mmmesio-distally, and 3 mm occluso-apically. The

Fig. 3_The final aspect of the FRCIFPD.

Fig. 4_Isolated with rubber dam to

ensure correct adhesive luting.

Fig. 5_Clinical check-up one week

after luting.

Fig. 6_A 75-year-old male presented

missing a maxillary right first premo-

lar. Because of systemic disease, the

patient rejected implant-supported

prosthesis, and a metal-free inlay

fixed partial denture was proposed.

Fig. 7_After occlusal analysis, box-

shaped proximal preparation was

performed on the premolar.

Figs. 8_After impression taking with

an elastomer material, die stone was

poured to obtain the working cast

(Fig. 8a). Wax-up of the final prosthe-

sis (Fig. 8b).

Fig. 6

Fig. 4

Fig. 8c

Fig. 8a

Fig. 8b

Fig. 7

Fig. 3

Fig. 5

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mesio-distal occlusal extension of the preparationappears not to be important for the mechanical be-haviour of the bridge20, but a minimal extension isrequired to provide sufficient adhesive retention.The cervical margins of the boxes should be placedsupra-gingivally, to facilitate removal of excess ce-ment. If the proximal margin is located on enamel,this provides better long-term marginal adaptationof the restoration.14

Dedicated diamond burs (no. 8113R, 8113NR,Intensiv SA; no. 3113R, 3117, Intensiv SA) in a high-speed hand piece with water irrigation can be usedfor cavity preparation. Preparations can be adhe-sively protected, to reduce post-operative sensi-tivity and avoid contamination of dentine duringtemporisation. The adhesive system should be ap-plied according to the manufacturers instruc-tions. An impression of the prepared teeth is thentaken using an elastomer material and an irre-versible hydrocolloid impression of the opposingarch is taken.

_FRCFPD fabrication

While fabricating the FRCIFPD, the technicianmust carefully plan each step, to optimise frame-work design. Several studies1,2,13,14 have shown thatsurvival of FRCIFPDs depends on the mechanicalperformance of the framework and on the qualityof adhesion between veneering material and fi-bres. Fracture of the principal structure in the con-nector areas and delamination of the compositeare the main causes of FRCIFPD failure.11,2326 Theframework design must be optimised: the frame-work should be the same shape as the final restora-tion but reduced in size.23,24 If it is designed thus,loads applied to the structure will be transferredfrom the veneering composite to the framework,averting the delamination due to tensile forcesacting on the composite-framework interface.26

The framework wax-up is the first and most criti-cal step in the entire procedure for FRCIFPD fabri-cation (Fig. 8). A specific silicone for stents (Tempputty, 95 shore, Micerium S.p.a., Italy) is placed in aplexiglass flask for composites (Tender flask,Micerium). Before the silicone hardens, the frame-work wax-up is immersed in the putty. In order toensure light polymerisation of the composite,transparent silicone (Temp Clear Silicone, 55 shore,Micerium) is used to fill the flask, which is immedi-ately closed. After about 15 minutes, the flask isopened and the two components are separated, inorder to remove the wax-up (Fig. 9). When the sili-cone stamps have dried completely, fabrication ofthe fibre framework may begin. An initial layer of

Fig. 9_The technician creates a

suitable silicone stamp applying

several types of silicone, in a dedi-

cated plexiglass flask, around the

framework wax-up.

Fig. 10_Dental floss can be used to

choose the required length of the fi-

bre, which must be cut with the den-

tists silicone.


Fig. 9c

Fig. 9a Fig. 9b

Fig. 9d

Fig. 10

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light-curing, pre-impregnated glass fibre (TF41,Tender Fiber Quattro, Micerium; Fig. 10) is placed inthe silicone and held in place by a small quantity offlow composite. The particular transparent sili-cone, provided in the fibre package, facilitates fibrehandling and enables glass fibres to be pushed tothe bottom of the framework stamp. The fibreframework is layered from the apical to the coro-nal zone, the first fibre being applied on the gingi-val surface of the pontic (Fig. 11).

The number of fibre layers depends on theshape of the framework wax-up, fibre stratifica-tion is continued, to fill the available space in theputty. The flask is then closed and placed inside aspecific device that provides complete light cur-ing (within four minutes) of the fibre framework.The polymerised FRC framework is then finishedand its adaptation to the working cast is checked(Fig. 12).

A silane coupling agent is applied to the frame-work surface prior to composite resin veneering.The first layer consists of opaque dentine (EnamelPlus HFO Tender, Micerium), which reduces thetransparency of the glass fibre (Fig. 13). Variousdentine shades and brown stains are then appliedso that the restoration and the surrounding intactteeth are aesthetically similar. Veneering is com-pleted with enamel composites and characterisa-tion (Enamel Plus HFO dentine stain and enamel,Micerium). Finishing and polishing procedures,using diamond burs, dedicated brushes, gums,and diamond pastes, must be performed verycarefully (Fig. 14).

_FRCFPD adhesive luting

Adhesive procedures are used for cementingthe FRCFPD in place. The operating field must beisolated with a rubber dam, to prevent contami-

Fig. 11_After fabrication of the

stamp, 4 layers of pre-impregnated

glass fibre are stratified into the

framework space. A flowable com-

posite can be used to fill the air voids

and facilitate linkage between the

different layers of fibres.

Fig. 12_Adaptation of the framework

is checked in the working cast. This

particular shape, known as an

anatomical framework, is similar to

that of the wax-up, and ensures uni-

form stress distribution throughout

the prosthesis-teeth complex.

Fig. 13_During layering of the differ-

ent shades of Enamel Plus HFO com-

posite, the initial silicone mock-up can

be used to check the correct amounts

of dentine and enamel composites.

Fig. 11b

Fig. 11dFig. 11c

Fig. 11a

Fig. 13Fig. 12

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nation by saliva or gingival fluids (Fig. 15). Thetooth surfaces must be cleaned, taking care not totouch the preparation margins, after which thesurfaces are etched and sealed with the same ad-hesive system used before the impression wastaken. Air abrasion systems ensure better cleaningof the cavity preparations than traditional proce-dures.14,27 The inner surfaces of the FRCFPD canalso be sandblasted, after which they must besilanated.

A dual-cure composite cement (EnaCem,Micerium) is used for luting. The cement is appliedto the inner cavity surface, and seating of the FR-CFPD must be performed carefully, to allow pro-gressive removal of excess cement. The lutingcomposite must be cured for 60 seconds on eachside of the abutment, to ensure complete poly-merisation of the cement. After removing the rub-ber dam, the occlusion is checked with articulatingpaper. Finishing and polishing may be necessary, ifocclusal retouching is required, or if excess cementis present at the margins; these are performed withthe same materials and techniques used for direct

restorations (Fig. 16). One week after luting, thepatient is recalled for a check-up of the occlusion,aesthetics, and excess cement (Fig. 17).

_Discussion

Currently, interest in using FRCs for many den-tal applications is growing11, and acceptable suc-cess rates in long-term FRC prosthetic solutions,such as crowns and FPDs, have been reported.1013

The main causes of failure of FRC devices in highstress-bearing applications are fracture5,12, de-lamination of veneering composite, and de-ce-mentation of the prosthesis.28 In order to increasethe survival rate of the FRCs structure, clinical andlaboratory procedures need to be optimised to re-duce the risk of mechanical failure. In vivo studiesand FE analyses have shown that FRCFPD connec-tors are the most critical areas with regard tostress concentration.20,21 Repeated, strong masti-catory forces can contribute to formation of mi-cro-cracks, eventually leading to fracture of thecomposite, especially in the connector areas. Inorder to reduce this risk, the clinician should in-

Fig. 14_The IFPD is finished and

polished with the same burs and

brushes used for direct restorations.

Fig. 15_Prior to adhesive cementation,

the prepared surfaces of the abutment

teeth are cleaned with care.

Fig. 16_The use of a dual composite

enabled extended working time, and

facilitated the removal of excess ce-

ment.

Fig. 17_Post-op view: aesthetic inte-

gration between dental tissues and

the FRCIFPD.

Fig. 18_A 65-year-old female pre-

sented missing a mandibular right

first molar. For economical reasons,

a FRCIFPD was programmed.

Fig. 19_Two inlay cavities with the

same preparation axis were made in

the abutment teeth.


Fig. 18 Fig. 19

Fig. 16

Fig. 14

Fig. 17

Fig. 15

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crease the space available to the technician, en-abling him or her to apply the correct amount offibre and composite on the abutment teeth.5

Fracture of veneering composite at the connec-tors is thus correlated to box preparation design(Figs. 18, 19). When space is inadequate, compos-ite wear may result in early failure of the restora-tion or in fibre exposure, which may lead to plaqueaccumulation and hydrolysis of the fibre.29 An-other important strategy to reduce fracture at theconnector areas is to optimise the concentrationof fibres. The manufacturing processes and spe-cific equipment described in this report, if appliedwith care, enable fibre compaction to be max-imised, decreasing voids in the framework, andmaking the technique more predictable.30 In addi-tion, use of the flask allows an anatomic frame-work design to be created, ensuring better stressdistribution within the tooth-restoration com-plex. This is very important, not only to reduce therisk of composite fracture at the connectors, butalso to prevent delamination of the veneering ma-terial in the pontic element.

Separation between fibre and composite resinmay be due to tensile forces acting on the com-posite-fibre interface.23,31 If the shape of theframework is optimised, this should reduce tensileloads and increase the probability that the forcesapplied over the structure act to compress thecomposite-fibre interface. Xie et al.23 have shownthat the optimised framework shape should be thesame as that of the final restoration but reducedin size, to distribute masticatory forces on thecomposite-fibre interface, both when the load isapplied at the occlusal fossa and when it is appliedat the buccal cusp of the pontic (Fig. 20).

Another important cause of FRCFPD failure isde-cementation. Adhesive luting requires specialclinical care, especially in isolating the operativefield (Figs. 2123). De-cementation appears also tobe correlated with excessive mesio-distal length ofthe FPD, especially in posterior teeth. Thus, eachFRCFPD must be limited to singular edentulous ar-eas of the mouth (Fig. 24).

_Conclusion

The clinical and laboratory procedures requiredto fabricate FRCFPDs are described, paying partic-ular attention to strategies that can reduce the riskof failure. Prospective clinical trials will be required,to investigate long-term survival of this prostheticsolution._

Editorial Note: A complete list of references isavailable from the publisher.

Fig. 20_Prior to luting, the inner part

of the inlay retainers must be sand-

blasted and silanated.

Fig. 21_In-enamel location of the

apical margins of the proximal boxes

provides better adhesion and a more

predictable, long-term adaptation.

Fig. 22_Prior to cementing, the

FRCIFPD was evaluated intra-orally.

Fig. 23_Total acid etching of the

cavity preparations.

Fig. 24_The FRCIFPD offers aesthetic

and less-invasive restoration.

Dr Erminia Coccia is a lecturer at the Department of Prosthodontics,School of Dentistryat the Politechnic University of Marche, Italy.

Dr Daniele Rondoni has a private practice in Savona, Italy.

Prof. Giorgio Rappelli is Associate Professor at the Department of Prosthodontics,School of Dentistry at the Politechnic University of Marche, Italy.He can be contacted at:

Politechnic University of MarcheVia Tronto 10 Tel.: +39 07122 0622760020 Ancona Fax: +39 07122 06221Italy E-mail: [email protected]

cosmeticdentistry_author info

Fig. 24

Fig. 22

Fig. 21

Fig. 20

Fig. 23

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