Clin Oral Invest DOI 10.1007/s00784-015-1475-7
ORIGINAL ARTICLE
First clinical experiences with CAD/CAM-fabricated PMMA-based fixed dental prostheses as long-term temporaries Fabian Huettig 1 & Andreas Prutscher 1 & Christoph Goldammer 1 & Curt A. Kreutzer 1 & Heiner Weber 1
Received: 2 September 2014 / Accepted: 9 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Objective The clinical performance of polymethylmethacrylate (PMMA)-based fixed dental prostheses (FDP) was evaluated in the indication of long-term temporaries. Materials and methods In the current indication of the applied machinable PMMA-based material (Vita CAD-Temp), i.e. temporary crowns and FDPs, 27 patients with compromised dentitions (uncertain dental prognosis or postponement of a removable treatment option) were recruited and 45 FDPs (3 or 4 units, 37 terminal-retained, 8 cantilevered) were inserted. Frameworks were computer-aided design (CAD)/computeraided manufacturing (CAM)-manufactured after conventional impression taking and labside scanning of stone master casts. A resin-modified hybrid cement material (RelyX Unicem) was used for luting in a conventional protocol. Clinical follow-up was performed biannually. Results Over an observation time from 2 to 26 months (median 13 months), 11 complications were found in 9 out of 45 PMMA restorations: 4 losses of retention, 5 complete fractures; two of these subsequent to a trepanation for endodontic treatment. Thereby, 3 out of 8 cantilevered FDPs had to be removed within 8 months. Thus, the statistical evaluation included FDPs with abutment at end, only. These standard design FDPs (n=37) showed a 90.4 % survival rate with a complication-free rate of 88.3 % estimated for an observation time of 16 months.
* Fabian Huettig [email protected] 1
Department of Prosthodontics with Section BMedical Materials and Technology^ at the Centre of Dentistry, Oral Medicine and Maxillofacial Surgery with Dental School, Tuebingen University Hospital, Osianderstr. 2-8, 72076 Tübingen, Germany
Conclusion Cantilevered FDPs and reconstructions on abutment teeth with markedly reduced biological prognosis or endodontic intervention yielded a high-failure rate. Terminal-retained FDPs performed clinically well in cases without compromised abutment teeth. Clinical relevance PMMA-based material might be used successfully for long-term temporization with 3- to 4-unit FDPs in a standard design over at least one year. Keywords CAD/CAM . Micro-reinforced polymers . Clinical study . Prospective . Temporization . Dental restorations
Introduction Over the last years, computer-aided design (CAD)/computeraided manufacturing (CAM) technology has made great achievements in prosthodontics [1]. Not only software-based design and tools have been improved, also the number of different machinable materials has raised [2]. Especially, low-priced polymers and composites for mainstream CAD/ CAM-Systems have come to market more and more. Their clinical indications range currently from onlays and single tooth crowns up to multiunit-fixed dental prostheses (FDPs) [3, 4]. But, indications of FDPs made from polymers are still limited to temporaries, exclusively [5]. So far, mechanical features found by in vitro testing and a zero monomer exposure of such materials are promising for clinical long-term application [6–8]. However, there is not enough in vitro data for sufficiently characterizing the physical properties and differences of machinable polymers and composites that are currently available. So far, these materials may offer reliable and aesthetic restorations on a lower cost level for the patient. The data about long-term behaviour in vivo is still limited to resin-
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based crowns [9–11]. Only case reports give some anecdotal information on the clinical application of composite FDPs [12]. Usually, temporaries are indicated for short- or midterm application, i.e. a couple of weeks up to 6 months. In fixed prosthodontics, the standard time span of temporization is about 1 to 2 weeks. A temporization for up to 6 months might be required for two-step surgical approaches in implant dentistry, for example. Extended wearing times (more than 6 months) made from semi-definite materials can be called Blong-term^ temporization. As stated by the German Society of Dental, Oral and Craniomandibular Sciences (DGZMK) [13], such long-term temporaries are indicated for treatment including changes of vertical dimension, aesthetics or phonetics, for palliative prosthodontic treatment in cancer patients and for bridging the time of healing or exploring potential abutment teeth with unclear prognosis for definitive restorative treatment later in time. All these objectives may need temporaries for about 1 year and or even longer time. For these indications—except for bridging the time of healing—the application of non-precious alloy framework veneered with resin composite is a standard recommendation. But, this is a rather expensive solution with costs close to that of a definitive fixed restoration. Thus, it seems worthwhile to find an option for providing long-term temporization that is technically and clinically reliable and at a reasonable cost level. There are resin-based materials that could be appropriate for long-term temporization and which are not limited to single-tooth restorations. Vita CAD-Temp (Vita Zahnfabrik, Bad Säckingen, Germany) was one of the first chemically improved polymers for CAD/CAM manufacturing. It was introduced into the market in 2005. Its certified indication for temporaries includes 3- to 4-unit bridges, but not for long-term use. Based on this information and through its 2-year human use history (also in our department), it was decided to run a clinical trial in order to test the clinical behaviour when applied as long-term temporary FDPs in patients with unclear prognosis of abutment teeth as well due to uncertainty about further prosthodontic treatment within the dentition of the patient (e.g. to postpone the decision for a removable partial denture in conjunction with compromised teeth in the same jaw and other than the retainers). Objective of this clinical study was the clinical performance of PMMA-based polymer for long-term temporary 3to 4-unit FDPs. Therefore, the study was designed as a controlled randomized trial with an intra-individual comparison of PMMA-based and metal-based FDPs. During recruitment, it turned out to be unrealistic to include a sufficient amount of such cases. Hence, the study was transferred in a prospectively followed patient cohort with PMMA-based FDPs only and no hypothesis was set. Furthermore, FDPs performance cannot be compared to available literature data, neither towards material nor patient selection.
Materials and method Treated cohort The cohort was recruited from patients of the Department of Prosthodontics that needed prosthetic treatment and complied with predefined inclusion and exclusion criteria. Criterion for entering the study was fulfilling the indication for at least one long-term temporary FDP either on abutment teeth with unclear prognosis (periodontally or endodontically compromised or freshly treated teeth) or due to unclear prognosis of further prosthodontic treatment within the dentition of the patient (e.g. to postpone the decision for a removable partial denture). The patients were clinically examined and fully informed about the trial prior to entering the cohort. This examination encompassed a complete dental and hygiene status, a check of temporo-mandibular structures and function as well as X-rays, when necessary to approve indication and tooth prognosis. Patients had to be aged between 18 and 70 years at the time of treatment. Tooth mobility up to clinical grade 1 was allowed for periodontal-affected later retainers. Endondontic treatment or revision of a potential abutment tooth must have been finished by a dentist of the Centre for Dentistry at least 1 month ago, and patient reported no persisting pain in this period of time. In common, later abutment teeth had to be likely and expected to survive at least 1 year. This appraisal was upon the principal investigator, who was an experienced resident dentist. Medical exclusion criteria were as follows: reported poor general medical condition (i.e. oncologic, infectious, mental diseases) or pregnancy. Exclusion reasons in the stomatognathic system were as follows: clinical signs of bruxism, such as hypertrophic masseter muscle, attrited teeth or numerous wedge-shaped lesions (because early fracture of framework was observed in preceding treatments with this material in our clinic); poor oral hygiene evident by a visible dental plaque on more than 50 % of the buccal tooth surfaces; a potential retainer height less than 4 mm and an existing removable dental prosthesis or definite need for it in the same jaw (i.e. cases of reduced dentition in kinds of Kennedy subclass 3). Antagonist dentition had to ensure that the later FDP would be in static occlusion on at least 2 out of 3 units. Therefore, opposing natural, restored as well as prosthetic teeth were allowed. Following the modified CONSORT flowchart (see Fig. 1) during recruitment, 20 patients had to be excluded or dropped out (patient decided for other treatment or did not show up again). These patients were in potential need of at least 32 FDP, mostly in the posterior. Finally, 27 out of 47 patients were treated with 41 conventional and 11 cantilevered bridges (see Table 1). As primary planned in the study protocol, also 7 metal-based restorations (4 conventional, 3 cantilevered) were inserted as controls.
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inLab CAD/CAM system (Version 3.4 and 3.6, Sirona) using Cone Bur 14 (#59 99 771) on the left and Cylinder Pointed Bur (#58 55 734) on the right. Basic milling setting was as follows: −150 μm for occlusal offset, 75 μm for marginal thickness, −40 μm for spacer. The connector cross section was dimensioned ≥12 mm2 and at least 16 mm2 in FDPs with two pontics. Vita CAD-Temp CT-40 blocks were used for milling in full anatomical design according to the manufacturer’s instructions. Without preceding reduction, a compatible lightcuring composite (Vita VM LC, Vita Zahnfabrik) was added to finalize tooth colour and, for some FDPs, to optimize anatomical details and final shape. After a final try-in and check of clinical fit, function and aesthetics, the long-term temporaries were luted with RelyX Unicem (3 M ESPE) by a conventional protocol. Before luting, the retainers were cleaned with water-based pumice slurry using small, sonic-driven brushes (Sonicflex, KaVo Comp., Biberach, Germany), finally cleaned with water spray and relatively dry conditions were assured. No conditioning was applied to the restorations except for of a final cleaning with 70 % ethanol for a maximum of 45 seconds. Clinical follow-up
Fig. 1 Modified CONSORT flowchart declares the recruited, treated and evaluated patients towards their gender, age and number of FDPs
These were randomly assigned when a second FDP had to be inserted into the contralateral jaw region. The study was originally planned with such intra-individual controls, but the recruitment did not achieve the minimum cohort size required for a controlled design (n>15 patients with two FDPs). Thus, these 7 FDPs were excluded from clinical evaluation, later on.
After insertion, a biannual follow-up was consented due to the limited experiences and manufactures’ instruction for use. These examinations consisted of a complete dental and oral hygiene status as well as a clinical quality assessment of the restorations following modified Ryge criteria [14, 15]. A variable of main interest was the occurrence of any adverse event affecting clinical quality or long-term prognosis of both, restoration or abutment tooth. All clinical findings were recorded as source data in case report forms (CRF). Data was evaluated using statistical standard software (JMP 7, SAS Corporation, Cary, NC, USA).
Treatment and technical procedures Classification of events, entities and statistical approach Abutment teeth were prepared according to CAD/CAM standards, slightly adapting to a circular chamfer of 0.8 mm with an 8° convergance angle. Occlusal reduction was at least 1 mm and 1.5 mm whenever possible. Finally, all edges were blunted. Polyether material (Impregum Penta & Permadyne Garant 2:1, 3 M ESPE, Seefeld, Germany) was used for impression taking in a double-mixing technique using metal Rim-lock trays. Temporaries were made chair-side from BisGMA-Resin (ProTemp 3 Garant, 3 M ESPE) and luted with a non-eugenol temporary cement material (Temp Bond NE, Kerr Corp., Scafati, Italy). The preparations were scanned from the stone casts (inEOS, Sirona Dental Systems, Bensheim, Germany), and the FDPs were designed and manufactured with Cerec 3D
All biological and technical adverse events (AE) constraining intervention by the dentist were rated as complication. Survival was censored at the date, when the reconstruction was found clinically insufficient (serious adverse event, SAE) and had to be removed. Criteria for insufficiency were as follows: fracture of the reconstruction, loss of anatomical integrity (secondary caries, penetrable marginal gap) and wish of the patient. Using KaplanMeier method, both estimations are calculated, when at least one third of all reconstructions are still at risk. Additionally, one reconstruction was randomly selected from each patient to perform a validation of the described analyses because 12 out of 25 patients received two FDPs
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Overview to cohort and restorations
Patient (gender, age (year))
Individual reconstruction (code (#), design and material)
Region of FDP #
Time to complication‡ or removal† (months)
14 female, 13 male, age ∅ 51 years
31 3-unit FDPs (including 7 cantilever), 14 4-unit FDPs (including 1 cantilever)
6 anterior, 39 posterior, 19 maxilla, 26 mandible
2 endodontic problems (patient 1 and 3), 5 losses of retention, 5 fractures of framework, 2 fractures of veneering, 1 discomfort
1 (M, 52) 2 (M, 48) 3 (F, 42) 4 (M, 67) 5 (F, 63) 6 (F, 58) 7 (M, 67) 8 (M, 47) 9 (M, 63) 10 (F, 30) 11 (M, 50) 12 (F, 41) 13 (F, 52) 14 (M, 58) 15 (F, 56) 16 (F, 34) 17 (F, 53) 18 (M, 49)
#1: r-p-r-r* #2: r-p-p-r #1: r-p-r* #1: r-p-r* #1: r-p-p-r* #1: r-p-r #2: r-p-r* #1: r-p-r* #1: r-p-r* #1: [r-r-p] #2: r-r-p-r* #1: [r-r-p] #2: r-p-r* #1: r-p-r #2: r-p-r* #1: r-r-p-r* #1: r-p-r #2: r-p-r* #1: r-p-r* #1: r-p-r* #1: r-r-p-r #2: r-p-r* #1: [p-r-p-r] #1: r-r-p-r #2: [r-r-p] #3: r-p-r* #1: r-r-p-r #2: r-p-r*
A(2) P(1) P(1) P(1) P(1) A(1) P(2) P(1) P(1) A(2), P(1) P(1,3) P(1,2) P(1) A(1) P(2) P(1) P(1) P(1,2) P(1) P(1,2,3) A(1), P(2)
#2: ‡ (11), ‡,† (14)
19 (F, 57) 20 (M, 55) 21 (F, 53) 22 (F, 60) 23 (F, 51) 24 (F, 36) 25 (M, 28) 26 (M, 49) 27 (M, 58)
#1: r-p-r #2: r-p-r* #1: r-p-p-r* #1: [r-r-p] #2: [r-r-p] #3: r-p-r #4: r-p-r* #1: r-p-r #2: r-p-p-r* #1: r-r-p-r* #1: r-p-r #2: r-p-r* #1: r-p-p-r* #2: r-p-p-r #3: [p-r-r] #1: r-p-r* #1: [r-r-p]
P(1,2) P(1) A(3), P(1,2,4) P(2) P(1) P(1,2) P(1,2,3) P(1) P(1)
#1: ‡ (4), †(16) #2: ‡ (4)
[#1: ‡,†(8)] #2: ‡(3)
#1 ‡(0.6), †(4)
#2 ‡(24)
[#3 ‡(1)] [#1* ‡(0.5), †(2)]
Cantilevered FDPs are marked in square brackets. The FDPs assigned to random cohort are marked with asterisks. Number in curve brackets following BA^ and BP^ refers to reconstruction code of the preceding column. In Column 4, the reconstruction code is listed with double dagger indicating complication and dagger removal; in brackets the months till event A anterior, P posterior; Design code of the FDP is as follows: r retainer, p pontic.
(see Table 1) [16]. The mean of both estimations was regarded as favourable estimate. Prevalence of complications (Pc) and failure (Pf) is calculated as ratio of the number of observations to the number of inserted FDPs.
Results There was no loss to follow up. During a medium observation time of 13 months (range 2–26 months), 15 complications
were observed, affecting 11 constructions. In consequence, 6 FDPs (4 cantilevered, 2 standard design) had to be removed (Table 1). (a) Cantilevered PMMA FDPs: Five complications were found in 9 cantilevered bridges (Pc =0.55) within 0.5 to 11 months. Four FDPs failed (Pf =0.44), 3 due to fracture of framework and 1 due to loss of
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(b) PMMA FDPs with terminal abutments (standard design):
retention in a patient (#9) whom reported continuing discomfort with the FDP at the same time. The fractures always affected the connector of the pontic only and caused no exposure of tooth surface (see Fig. 4a). Three of these failed restorations had to be removed within 2 to 8 months. As it is obvious that these reconstructions underperform clinically, no further statistics were calculated. Two patients experienced complications (endodontic flare-up), later on followed by removal of the FDPs due to a complete fracture of the restoration. Speaking about one patient at 3 months, the other 12 months after the complication had occurred. The anterior FDP of patient #1 fractured at the connector between pontic and retainer (teeth 11/12). Furthermore, this FDP had lost retention 2 months after endodontic intervention. The posterior FDP of patient #3 fractured the endodontically treated retainer as well as straight through the pontic (see Fig. 4b). Three more losses of retention were observed in three other patients (after 3, 4 and 24 months). I n s u m m a r y, t h e Kaplan-Meier estimations for resin-based FDPs with terminal retainers showed a survival rate of 90.4 % and a complication-free rate of 88.3 % within 16 months. At this point of time, 15 out of 37 and 10 out of 25 randomized
restorations are at risk. (see Figs. 2 and 3). The prevalence of complications (P ) was estimated as 17 % c (8 events on 37 restorations and 4 events on 25 randomized restorations).
Discussion This study was planned with an intra-individual comparison of PMMA-based and metal-based FDPs. While running the design of a randomized controlled clinical trial, only 7 patients could be included and treated with metal-based controls. There was a lack of patients in need of two comparable FDPs. Furthermore—following the CONSORT flowchart (see Fig. 1)—the ratio of inclusion (27 out of 47 patients) shows that it was difficult at all to recruit comparable patients with the indication of at least one long-term temporary. No improvement of recruitment was possible, neither ethically (treatment without indication) nor financially (offering special concessions). Consequently, the 7 metal-based restorations were insufficient for the intended statistical evaluation and had to be closed out. That is why this clinical trial represents a prospective series of cases treated with PMMA-based CAD/CAMmanufactured FDPs. There was no loss to follow up. The recall of patients was not fully consistent with the planned 6-month follow-up interval, but more than 90 % of all patients were examined at least twice a year. If the indication was to bridge the time for a final prosthodontic treatment decision, the machinable polymers showed a good clinical survival for at least one year. This might be due to the foremost sound abutment teeth (no loosening, no massive decay) in such cases. For such a time span of clinical run, it might become cost-effective due to further cost reduction of CAD/CAM system and more and more implementation of digital workflow, polymers and composites [17]. Nevertheless, indication has to be limited towards bite force and design. Despite the exclusion criteria for bruxism, the cantileverdesigned FDPs showed early failure in this trial. This is in line with the general discussions of cantilever FPDs [18, 19]. Both features, signs of bruxism as well as cantilevered design, seem to exceed the mechanical properties of polymers [7, 20, 21]. Luting protocol & debondings Preceding clinical observations in our department revealed that the usage of temporary cements on PMMA-based FDPs
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Fig. 2 Kaplan-Meier plot estimating the complication-free rate of terminal-retained PMMA FDPs. A service time of 16 months in a complication rate of 88.3 % (95 % CI=0.96–0.73). This value derives from the mean of the estimates from the cohort and the random selection (one FDP out of each patient), depicted as a red and a blue line
led to both: frequent losses of retention and 100 % prevalence of fracture of the restorations after 3 months. Thus, a selfadhesive resin cement was chosen to diminish these adverse events and to enable the dentist to remove the restoration without harming the abutment teeth. However, thereby, a luted restoration is ruined due to slits and/or mechanical impact of removal. This can be regarded as a shortcoming compared to metal-based alternatives which are luted with temporary cement. Four out of five losses of retention were found in the posterior of the lower jaw. The other one occurred in a wide span anterior bridge, where the final retainer (tooth 12) showed heightened mobility (grade 3) at the date of complication. Fig. 3 Kaplan-Meier plot estimating the survival of terminal-retained PMMA FDPs. At a service time of 16 months, a 90.4 % (95% CI=0.97–0.65) survival rate is estimated. This value derives from the mean of the estimates from the cohort and the random selection (one FDP out of each patient), depicted as a red and a blue line
Fig. 4 a Exemplary clinical fracture of a cantilever pontic (patient #16). The fracture affected the connector only (arrow). No tooth substance of the retainer was exposed. b Fracture of the terminal-retained FDP in patient #3. One fracture followed the previously endodontically treated retainer (horizontal arrows on the left). Another fracture was found across the pontic. Both fractures did not follow the connector cross section (diagonal arrows on the right)
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Previously, this very retainer underwent apicectomy due to an apical endodontic flare-up. Fracture of this bridge followed the reattachment. If debonding occurs, the luting agent was found to be bonded to the reconstructions of inner lumina or the resin core built-ups of the teeth but not on the dentin. The authors found this quite practical because no further preparation was needed for subsequent treatment, which enables the use of existing CAD dataset for another construction or direct milling of a remake. Debonding might be due to distortional stress and weakening bonding of luting agent towards dentin [22–24]. It might also be due to the two-step approach, which requires a temporary luting affecting the later bonding towards dentin— even if thoroughly cleaned with pumice slurry before the final luting [25]. The authors assume that the biological movements of the lower jaw and higher functional load to the retainers (long span FDP and small root surface) stress the luting interface. As described for silicate ceramics on zirconia abutments, especially the low Young’s modulus of the PMMA, which is bonded to dentine, may cause these debondings [26]. An improvement might be possible by conditioning the resins [27] and an adhesive bonding protocol [28, 29]. This was described to be clinically successful even for onlays [30]. Therefore, another prerequisite would be to sandblast the intaglio surfaces of the restoration with alumina oxide prior to luting [31]. This was not applied to the restorations in this study. Furthermore, adhesion might be improved by an immediate dentin sealing as described by Magne for indirect singletooth restorations [32]. This assumption bears on the abovementioned observation that RelyX Unicem was found to bond to the composite core built-ups. In contrast, restorations fixed in a full-adhesive protocol might not be removed easily and will call for a completely new preparation in case of a failure or subsequent treatment. Finally, the preparation design might contribute to loosening and fractures. That is why preparation should follow the recommendations of Ohlmann for polymer crowns [33]. Biological prerequisites and complications Clinically, the failure plot (see Fig. 2) shows a culmination of early complications, which were mostly followed by further flaws (Table 1). Furthermore, interventions altering the reconstruction to fix biological problems (trepanation due to endodontic failure) led to later fracture of the framework (Fig. 4). Thus, high prevalence of events also has to be aligned with the compromised clinical situations treated in this study. This dependence might rather be a consequence to the succession of adverse events and not to the material itself. In cases where sound abutment teeth were treated with standard PMMA-based FDPs to postpone the decision of a fixed or removable denture, no adverse events and catastrophic failures were observed. However, metal-based and
temporarily luted FDPs have a lower susceptibility to fracture and can be removed and reluted to fix biological problems.
Conclusion and clinical implication With regard to the clinical situations restored in this study, it can be concluded that fixed dental prostheses made from Vita CAD-Temp in a standard design perform well under sound clinical conditions up to at least 1 year. Luting interface to the retainer was found as a weak point. Debonding of the selfadhesive luting resin accounts for one third of the complications, mainly in the lower jaw. Nevertheless, this material offers metal-free aesthetic restorations to the patient. But biological compromised abutment teeth, long span or cantilever designs are not recommended because of the high prevalence of early failures. In such cases, machinable polymers perform clinically inferior compared to metal-based and temporarily luted FDPs. Acknowledgments This clinical trial was approved by the Ethics Committee of Tuebingen University (30/2009MPG2) and is listed at the German Clinical Trials Register (DRKS00000644). The authors thank the following dental technicians of Tuebingen University Hospital’s Dental Lab: MDT Ekkehard Kroewerath, DT Volker Scheer and DT Karina Wuensch. The study was partially financed by Vita Zahnfabrik (Bad Säckingen, Germany) and by the Medical Faculty of Eberhard Karls University of Tuebingen. Conflict of interest The authors declare no personal conflict of interest, besides being involved in this clinical trial.
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Working group 4 materials: cementation. Clin Oral Implants Res 18(Suppl 3):193–204. doi:10.1111/j.1600-0501.2007.01442.x 23. Hill EE, Lott J (2011) A clinically focused discussion of luting materials. Aust Dent J 56(Suppl 1):67–76. doi:10.1111/j.18347819.2010.01297.x 24. Breschi L, Mazzoni A, Ruggeri A, Cadenaro M, Di Lenarda R, De Stefano DE (2008) Dental adhesion review: aging and stability of the bonded interface. Dent Mater 24:90–101. doi:10.1016/j.dental. 2007.02.009 25. Frankenberger R, Kramer N, Appelt A, Lohbauer U, Naumann M, Roggendorf MJ (2011) Chairside vs. labside ceramic inlays: effect of temporary restoration and adhesive luting on enamel cracks and marginal integrity. Dent Mater 27:892–898. doi:10.1016/j.dental. 2011.05.007 26. Freitas AC Jr, Rocha EP, dos Santos PH, de Almeida EO, Anchieta RB (2010) All-ceramic crowns over single implant zircon abutment. Influence of young’s modulus on mechanics. Implant Dent 19:539–548. doi:10.1097/ID.0b013e31820030ca 27. Keul C, Muller-Hahl M, Eichberger M, Liebermann A, Roos M, Edelhoff D, Stawarczyk B (2014) Impact of different adhesives on work of adhesion between CAD/CAM polymers and resin composite cements. J Dent 42:1105–1114. doi:10.1016/j.jdent.2014.02.020 28. Hikita K, Van Meerbeek B, De Munck J, Ikeda T, Van Landuyt K, Maida T, Lambrechts P, Peumans M (2007) Bonding effectiveness of adhesive luting agents to enamel and dentin. Dent Mater 23:71– 80. doi:10.1016/j.dental.2005.12.002 29. Keul C, Kohen D, Eichberger M, Roos M, Gernet W, Stawarczyk B (2015) The effect of different pretreatment methods of PMMAbased crowns on the long-term tensile bond strength to dentin abutments. Clin Oral Investig 19:35–43. doi:10.1007/s00784-0141215-4 30. Edelhoff D, Schweiger J, Brix O et al (2011) Initial treatment of complex cases with CAD/CAM-generated restorations made from high-performance resins. Quintessenz 62:625–635 31. Wiegand A, Stucki L, Hoffmann R, Attin T, Stawarczyk B (2015) Repairability of CAD/CAM high-density PMMA- and compositebased polymers. Clin Oral Investig. doi:10.1007/s00784-0151411-x 32. Magne P, So WS, Cascione D (2007) Immediate dentin sealing supports delayed restoration placement. J Prosthet Dent 98:166– 174. doi:10.1016/S0022-3913(07)60052-3 33. Ohlmann B, Gruber R, Eickemeyer G, Rammelsberg P (2008) Optimizing preparation design for metal-free composite resin crowns. J Prosthet Dent 100:211–219. doi:10.1016/S00223913(08)60180-8
ORIGINAL ARTICLE
First clinical experiences with CAD/CAM-fabricated PMMA-based fixed dental prostheses as long-term temporaries Fabian Huettig 1 & Andreas Prutscher 1 & Christoph Goldammer 1 & Curt A. Kreutzer 1 & Heiner Weber 1
Received: 2 September 2014 / Accepted: 9 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Objective The clinical performance of polymethylmethacrylate (PMMA)-based fixed dental prostheses (FDP) was evaluated in the indication of long-term temporaries. Materials and methods In the current indication of the applied machinable PMMA-based material (Vita CAD-Temp), i.e. temporary crowns and FDPs, 27 patients with compromised dentitions (uncertain dental prognosis or postponement of a removable treatment option) were recruited and 45 FDPs (3 or 4 units, 37 terminal-retained, 8 cantilevered) were inserted. Frameworks were computer-aided design (CAD)/computeraided manufacturing (CAM)-manufactured after conventional impression taking and labside scanning of stone master casts. A resin-modified hybrid cement material (RelyX Unicem) was used for luting in a conventional protocol. Clinical follow-up was performed biannually. Results Over an observation time from 2 to 26 months (median 13 months), 11 complications were found in 9 out of 45 PMMA restorations: 4 losses of retention, 5 complete fractures; two of these subsequent to a trepanation for endodontic treatment. Thereby, 3 out of 8 cantilevered FDPs had to be removed within 8 months. Thus, the statistical evaluation included FDPs with abutment at end, only. These standard design FDPs (n=37) showed a 90.4 % survival rate with a complication-free rate of 88.3 % estimated for an observation time of 16 months.
* Fabian Huettig [email protected] 1
Department of Prosthodontics with Section BMedical Materials and Technology^ at the Centre of Dentistry, Oral Medicine and Maxillofacial Surgery with Dental School, Tuebingen University Hospital, Osianderstr. 2-8, 72076 Tübingen, Germany
Conclusion Cantilevered FDPs and reconstructions on abutment teeth with markedly reduced biological prognosis or endodontic intervention yielded a high-failure rate. Terminal-retained FDPs performed clinically well in cases without compromised abutment teeth. Clinical relevance PMMA-based material might be used successfully for long-term temporization with 3- to 4-unit FDPs in a standard design over at least one year. Keywords CAD/CAM . Micro-reinforced polymers . Clinical study . Prospective . Temporization . Dental restorations
Introduction Over the last years, computer-aided design (CAD)/computeraided manufacturing (CAM) technology has made great achievements in prosthodontics [1]. Not only software-based design and tools have been improved, also the number of different machinable materials has raised [2]. Especially, low-priced polymers and composites for mainstream CAD/ CAM-Systems have come to market more and more. Their clinical indications range currently from onlays and single tooth crowns up to multiunit-fixed dental prostheses (FDPs) [3, 4]. But, indications of FDPs made from polymers are still limited to temporaries, exclusively [5]. So far, mechanical features found by in vitro testing and a zero monomer exposure of such materials are promising for clinical long-term application [6–8]. However, there is not enough in vitro data for sufficiently characterizing the physical properties and differences of machinable polymers and composites that are currently available. So far, these materials may offer reliable and aesthetic restorations on a lower cost level for the patient. The data about long-term behaviour in vivo is still limited to resin-
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based crowns [9–11]. Only case reports give some anecdotal information on the clinical application of composite FDPs [12]. Usually, temporaries are indicated for short- or midterm application, i.e. a couple of weeks up to 6 months. In fixed prosthodontics, the standard time span of temporization is about 1 to 2 weeks. A temporization for up to 6 months might be required for two-step surgical approaches in implant dentistry, for example. Extended wearing times (more than 6 months) made from semi-definite materials can be called Blong-term^ temporization. As stated by the German Society of Dental, Oral and Craniomandibular Sciences (DGZMK) [13], such long-term temporaries are indicated for treatment including changes of vertical dimension, aesthetics or phonetics, for palliative prosthodontic treatment in cancer patients and for bridging the time of healing or exploring potential abutment teeth with unclear prognosis for definitive restorative treatment later in time. All these objectives may need temporaries for about 1 year and or even longer time. For these indications—except for bridging the time of healing—the application of non-precious alloy framework veneered with resin composite is a standard recommendation. But, this is a rather expensive solution with costs close to that of a definitive fixed restoration. Thus, it seems worthwhile to find an option for providing long-term temporization that is technically and clinically reliable and at a reasonable cost level. There are resin-based materials that could be appropriate for long-term temporization and which are not limited to single-tooth restorations. Vita CAD-Temp (Vita Zahnfabrik, Bad Säckingen, Germany) was one of the first chemically improved polymers for CAD/CAM manufacturing. It was introduced into the market in 2005. Its certified indication for temporaries includes 3- to 4-unit bridges, but not for long-term use. Based on this information and through its 2-year human use history (also in our department), it was decided to run a clinical trial in order to test the clinical behaviour when applied as long-term temporary FDPs in patients with unclear prognosis of abutment teeth as well due to uncertainty about further prosthodontic treatment within the dentition of the patient (e.g. to postpone the decision for a removable partial denture in conjunction with compromised teeth in the same jaw and other than the retainers). Objective of this clinical study was the clinical performance of PMMA-based polymer for long-term temporary 3to 4-unit FDPs. Therefore, the study was designed as a controlled randomized trial with an intra-individual comparison of PMMA-based and metal-based FDPs. During recruitment, it turned out to be unrealistic to include a sufficient amount of such cases. Hence, the study was transferred in a prospectively followed patient cohort with PMMA-based FDPs only and no hypothesis was set. Furthermore, FDPs performance cannot be compared to available literature data, neither towards material nor patient selection.
Materials and method Treated cohort The cohort was recruited from patients of the Department of Prosthodontics that needed prosthetic treatment and complied with predefined inclusion and exclusion criteria. Criterion for entering the study was fulfilling the indication for at least one long-term temporary FDP either on abutment teeth with unclear prognosis (periodontally or endodontically compromised or freshly treated teeth) or due to unclear prognosis of further prosthodontic treatment within the dentition of the patient (e.g. to postpone the decision for a removable partial denture). The patients were clinically examined and fully informed about the trial prior to entering the cohort. This examination encompassed a complete dental and hygiene status, a check of temporo-mandibular structures and function as well as X-rays, when necessary to approve indication and tooth prognosis. Patients had to be aged between 18 and 70 years at the time of treatment. Tooth mobility up to clinical grade 1 was allowed for periodontal-affected later retainers. Endondontic treatment or revision of a potential abutment tooth must have been finished by a dentist of the Centre for Dentistry at least 1 month ago, and patient reported no persisting pain in this period of time. In common, later abutment teeth had to be likely and expected to survive at least 1 year. This appraisal was upon the principal investigator, who was an experienced resident dentist. Medical exclusion criteria were as follows: reported poor general medical condition (i.e. oncologic, infectious, mental diseases) or pregnancy. Exclusion reasons in the stomatognathic system were as follows: clinical signs of bruxism, such as hypertrophic masseter muscle, attrited teeth or numerous wedge-shaped lesions (because early fracture of framework was observed in preceding treatments with this material in our clinic); poor oral hygiene evident by a visible dental plaque on more than 50 % of the buccal tooth surfaces; a potential retainer height less than 4 mm and an existing removable dental prosthesis or definite need for it in the same jaw (i.e. cases of reduced dentition in kinds of Kennedy subclass 3). Antagonist dentition had to ensure that the later FDP would be in static occlusion on at least 2 out of 3 units. Therefore, opposing natural, restored as well as prosthetic teeth were allowed. Following the modified CONSORT flowchart (see Fig. 1) during recruitment, 20 patients had to be excluded or dropped out (patient decided for other treatment or did not show up again). These patients were in potential need of at least 32 FDP, mostly in the posterior. Finally, 27 out of 47 patients were treated with 41 conventional and 11 cantilevered bridges (see Table 1). As primary planned in the study protocol, also 7 metal-based restorations (4 conventional, 3 cantilevered) were inserted as controls.
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inLab CAD/CAM system (Version 3.4 and 3.6, Sirona) using Cone Bur 14 (#59 99 771) on the left and Cylinder Pointed Bur (#58 55 734) on the right. Basic milling setting was as follows: −150 μm for occlusal offset, 75 μm for marginal thickness, −40 μm for spacer. The connector cross section was dimensioned ≥12 mm2 and at least 16 mm2 in FDPs with two pontics. Vita CAD-Temp CT-40 blocks were used for milling in full anatomical design according to the manufacturer’s instructions. Without preceding reduction, a compatible lightcuring composite (Vita VM LC, Vita Zahnfabrik) was added to finalize tooth colour and, for some FDPs, to optimize anatomical details and final shape. After a final try-in and check of clinical fit, function and aesthetics, the long-term temporaries were luted with RelyX Unicem (3 M ESPE) by a conventional protocol. Before luting, the retainers were cleaned with water-based pumice slurry using small, sonic-driven brushes (Sonicflex, KaVo Comp., Biberach, Germany), finally cleaned with water spray and relatively dry conditions were assured. No conditioning was applied to the restorations except for of a final cleaning with 70 % ethanol for a maximum of 45 seconds. Clinical follow-up
Fig. 1 Modified CONSORT flowchart declares the recruited, treated and evaluated patients towards their gender, age and number of FDPs
These were randomly assigned when a second FDP had to be inserted into the contralateral jaw region. The study was originally planned with such intra-individual controls, but the recruitment did not achieve the minimum cohort size required for a controlled design (n>15 patients with two FDPs). Thus, these 7 FDPs were excluded from clinical evaluation, later on.
After insertion, a biannual follow-up was consented due to the limited experiences and manufactures’ instruction for use. These examinations consisted of a complete dental and oral hygiene status as well as a clinical quality assessment of the restorations following modified Ryge criteria [14, 15]. A variable of main interest was the occurrence of any adverse event affecting clinical quality or long-term prognosis of both, restoration or abutment tooth. All clinical findings were recorded as source data in case report forms (CRF). Data was evaluated using statistical standard software (JMP 7, SAS Corporation, Cary, NC, USA).
Treatment and technical procedures Classification of events, entities and statistical approach Abutment teeth were prepared according to CAD/CAM standards, slightly adapting to a circular chamfer of 0.8 mm with an 8° convergance angle. Occlusal reduction was at least 1 mm and 1.5 mm whenever possible. Finally, all edges were blunted. Polyether material (Impregum Penta & Permadyne Garant 2:1, 3 M ESPE, Seefeld, Germany) was used for impression taking in a double-mixing technique using metal Rim-lock trays. Temporaries were made chair-side from BisGMA-Resin (ProTemp 3 Garant, 3 M ESPE) and luted with a non-eugenol temporary cement material (Temp Bond NE, Kerr Corp., Scafati, Italy). The preparations were scanned from the stone casts (inEOS, Sirona Dental Systems, Bensheim, Germany), and the FDPs were designed and manufactured with Cerec 3D
All biological and technical adverse events (AE) constraining intervention by the dentist were rated as complication. Survival was censored at the date, when the reconstruction was found clinically insufficient (serious adverse event, SAE) and had to be removed. Criteria for insufficiency were as follows: fracture of the reconstruction, loss of anatomical integrity (secondary caries, penetrable marginal gap) and wish of the patient. Using KaplanMeier method, both estimations are calculated, when at least one third of all reconstructions are still at risk. Additionally, one reconstruction was randomly selected from each patient to perform a validation of the described analyses because 12 out of 25 patients received two FDPs
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Overview to cohort and restorations
Patient (gender, age (year))
Individual reconstruction (code (#), design and material)
Region of FDP #
Time to complication‡ or removal† (months)
14 female, 13 male, age ∅ 51 years
31 3-unit FDPs (including 7 cantilever), 14 4-unit FDPs (including 1 cantilever)
6 anterior, 39 posterior, 19 maxilla, 26 mandible
2 endodontic problems (patient 1 and 3), 5 losses of retention, 5 fractures of framework, 2 fractures of veneering, 1 discomfort
1 (M, 52) 2 (M, 48) 3 (F, 42) 4 (M, 67) 5 (F, 63) 6 (F, 58) 7 (M, 67) 8 (M, 47) 9 (M, 63) 10 (F, 30) 11 (M, 50) 12 (F, 41) 13 (F, 52) 14 (M, 58) 15 (F, 56) 16 (F, 34) 17 (F, 53) 18 (M, 49)
#1: r-p-r-r* #2: r-p-p-r #1: r-p-r* #1: r-p-r* #1: r-p-p-r* #1: r-p-r #2: r-p-r* #1: r-p-r* #1: r-p-r* #1: [r-r-p] #2: r-r-p-r* #1: [r-r-p] #2: r-p-r* #1: r-p-r #2: r-p-r* #1: r-r-p-r* #1: r-p-r #2: r-p-r* #1: r-p-r* #1: r-p-r* #1: r-r-p-r #2: r-p-r* #1: [p-r-p-r] #1: r-r-p-r #2: [r-r-p] #3: r-p-r* #1: r-r-p-r #2: r-p-r*
A(2) P(1) P(1) P(1) P(1) A(1) P(2) P(1) P(1) A(2), P(1) P(1,3) P(1,2) P(1) A(1) P(2) P(1) P(1) P(1,2) P(1) P(1,2,3) A(1), P(2)
#2: ‡ (11), ‡,† (14)
19 (F, 57) 20 (M, 55) 21 (F, 53) 22 (F, 60) 23 (F, 51) 24 (F, 36) 25 (M, 28) 26 (M, 49) 27 (M, 58)
#1: r-p-r #2: r-p-r* #1: r-p-p-r* #1: [r-r-p] #2: [r-r-p] #3: r-p-r #4: r-p-r* #1: r-p-r #2: r-p-p-r* #1: r-r-p-r* #1: r-p-r #2: r-p-r* #1: r-p-p-r* #2: r-p-p-r #3: [p-r-r] #1: r-p-r* #1: [r-r-p]
P(1,2) P(1) A(3), P(1,2,4) P(2) P(1) P(1,2) P(1,2,3) P(1) P(1)
#1: ‡ (4), †(16) #2: ‡ (4)
[#1: ‡,†(8)] #2: ‡(3)
#1 ‡(0.6), †(4)
#2 ‡(24)
[#3 ‡(1)] [#1* ‡(0.5), †(2)]
Cantilevered FDPs are marked in square brackets. The FDPs assigned to random cohort are marked with asterisks. Number in curve brackets following BA^ and BP^ refers to reconstruction code of the preceding column. In Column 4, the reconstruction code is listed with double dagger indicating complication and dagger removal; in brackets the months till event A anterior, P posterior; Design code of the FDP is as follows: r retainer, p pontic.
(see Table 1) [16]. The mean of both estimations was regarded as favourable estimate. Prevalence of complications (Pc) and failure (Pf) is calculated as ratio of the number of observations to the number of inserted FDPs.
Results There was no loss to follow up. During a medium observation time of 13 months (range 2–26 months), 15 complications
were observed, affecting 11 constructions. In consequence, 6 FDPs (4 cantilevered, 2 standard design) had to be removed (Table 1). (a) Cantilevered PMMA FDPs: Five complications were found in 9 cantilevered bridges (Pc =0.55) within 0.5 to 11 months. Four FDPs failed (Pf =0.44), 3 due to fracture of framework and 1 due to loss of
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(b) PMMA FDPs with terminal abutments (standard design):
retention in a patient (#9) whom reported continuing discomfort with the FDP at the same time. The fractures always affected the connector of the pontic only and caused no exposure of tooth surface (see Fig. 4a). Three of these failed restorations had to be removed within 2 to 8 months. As it is obvious that these reconstructions underperform clinically, no further statistics were calculated. Two patients experienced complications (endodontic flare-up), later on followed by removal of the FDPs due to a complete fracture of the restoration. Speaking about one patient at 3 months, the other 12 months after the complication had occurred. The anterior FDP of patient #1 fractured at the connector between pontic and retainer (teeth 11/12). Furthermore, this FDP had lost retention 2 months after endodontic intervention. The posterior FDP of patient #3 fractured the endodontically treated retainer as well as straight through the pontic (see Fig. 4b). Three more losses of retention were observed in three other patients (after 3, 4 and 24 months). I n s u m m a r y, t h e Kaplan-Meier estimations for resin-based FDPs with terminal retainers showed a survival rate of 90.4 % and a complication-free rate of 88.3 % within 16 months. At this point of time, 15 out of 37 and 10 out of 25 randomized
restorations are at risk. (see Figs. 2 and 3). The prevalence of complications (P ) was estimated as 17 % c (8 events on 37 restorations and 4 events on 25 randomized restorations).
Discussion This study was planned with an intra-individual comparison of PMMA-based and metal-based FDPs. While running the design of a randomized controlled clinical trial, only 7 patients could be included and treated with metal-based controls. There was a lack of patients in need of two comparable FDPs. Furthermore—following the CONSORT flowchart (see Fig. 1)—the ratio of inclusion (27 out of 47 patients) shows that it was difficult at all to recruit comparable patients with the indication of at least one long-term temporary. No improvement of recruitment was possible, neither ethically (treatment without indication) nor financially (offering special concessions). Consequently, the 7 metal-based restorations were insufficient for the intended statistical evaluation and had to be closed out. That is why this clinical trial represents a prospective series of cases treated with PMMA-based CAD/CAMmanufactured FDPs. There was no loss to follow up. The recall of patients was not fully consistent with the planned 6-month follow-up interval, but more than 90 % of all patients were examined at least twice a year. If the indication was to bridge the time for a final prosthodontic treatment decision, the machinable polymers showed a good clinical survival for at least one year. This might be due to the foremost sound abutment teeth (no loosening, no massive decay) in such cases. For such a time span of clinical run, it might become cost-effective due to further cost reduction of CAD/CAM system and more and more implementation of digital workflow, polymers and composites [17]. Nevertheless, indication has to be limited towards bite force and design. Despite the exclusion criteria for bruxism, the cantileverdesigned FDPs showed early failure in this trial. This is in line with the general discussions of cantilever FPDs [18, 19]. Both features, signs of bruxism as well as cantilevered design, seem to exceed the mechanical properties of polymers [7, 20, 21]. Luting protocol & debondings Preceding clinical observations in our department revealed that the usage of temporary cements on PMMA-based FDPs
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Fig. 2 Kaplan-Meier plot estimating the complication-free rate of terminal-retained PMMA FDPs. A service time of 16 months in a complication rate of 88.3 % (95 % CI=0.96–0.73). This value derives from the mean of the estimates from the cohort and the random selection (one FDP out of each patient), depicted as a red and a blue line
led to both: frequent losses of retention and 100 % prevalence of fracture of the restorations after 3 months. Thus, a selfadhesive resin cement was chosen to diminish these adverse events and to enable the dentist to remove the restoration without harming the abutment teeth. However, thereby, a luted restoration is ruined due to slits and/or mechanical impact of removal. This can be regarded as a shortcoming compared to metal-based alternatives which are luted with temporary cement. Four out of five losses of retention were found in the posterior of the lower jaw. The other one occurred in a wide span anterior bridge, where the final retainer (tooth 12) showed heightened mobility (grade 3) at the date of complication. Fig. 3 Kaplan-Meier plot estimating the survival of terminal-retained PMMA FDPs. At a service time of 16 months, a 90.4 % (95% CI=0.97–0.65) survival rate is estimated. This value derives from the mean of the estimates from the cohort and the random selection (one FDP out of each patient), depicted as a red and a blue line
Fig. 4 a Exemplary clinical fracture of a cantilever pontic (patient #16). The fracture affected the connector only (arrow). No tooth substance of the retainer was exposed. b Fracture of the terminal-retained FDP in patient #3. One fracture followed the previously endodontically treated retainer (horizontal arrows on the left). Another fracture was found across the pontic. Both fractures did not follow the connector cross section (diagonal arrows on the right)
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Previously, this very retainer underwent apicectomy due to an apical endodontic flare-up. Fracture of this bridge followed the reattachment. If debonding occurs, the luting agent was found to be bonded to the reconstructions of inner lumina or the resin core built-ups of the teeth but not on the dentin. The authors found this quite practical because no further preparation was needed for subsequent treatment, which enables the use of existing CAD dataset for another construction or direct milling of a remake. Debonding might be due to distortional stress and weakening bonding of luting agent towards dentin [22–24]. It might also be due to the two-step approach, which requires a temporary luting affecting the later bonding towards dentin— even if thoroughly cleaned with pumice slurry before the final luting [25]. The authors assume that the biological movements of the lower jaw and higher functional load to the retainers (long span FDP and small root surface) stress the luting interface. As described for silicate ceramics on zirconia abutments, especially the low Young’s modulus of the PMMA, which is bonded to dentine, may cause these debondings [26]. An improvement might be possible by conditioning the resins [27] and an adhesive bonding protocol [28, 29]. This was described to be clinically successful even for onlays [30]. Therefore, another prerequisite would be to sandblast the intaglio surfaces of the restoration with alumina oxide prior to luting [31]. This was not applied to the restorations in this study. Furthermore, adhesion might be improved by an immediate dentin sealing as described by Magne for indirect singletooth restorations [32]. This assumption bears on the abovementioned observation that RelyX Unicem was found to bond to the composite core built-ups. In contrast, restorations fixed in a full-adhesive protocol might not be removed easily and will call for a completely new preparation in case of a failure or subsequent treatment. Finally, the preparation design might contribute to loosening and fractures. That is why preparation should follow the recommendations of Ohlmann for polymer crowns [33]. Biological prerequisites and complications Clinically, the failure plot (see Fig. 2) shows a culmination of early complications, which were mostly followed by further flaws (Table 1). Furthermore, interventions altering the reconstruction to fix biological problems (trepanation due to endodontic failure) led to later fracture of the framework (Fig. 4). Thus, high prevalence of events also has to be aligned with the compromised clinical situations treated in this study. This dependence might rather be a consequence to the succession of adverse events and not to the material itself. In cases where sound abutment teeth were treated with standard PMMA-based FDPs to postpone the decision of a fixed or removable denture, no adverse events and catastrophic failures were observed. However, metal-based and
temporarily luted FDPs have a lower susceptibility to fracture and can be removed and reluted to fix biological problems.
Conclusion and clinical implication With regard to the clinical situations restored in this study, it can be concluded that fixed dental prostheses made from Vita CAD-Temp in a standard design perform well under sound clinical conditions up to at least 1 year. Luting interface to the retainer was found as a weak point. Debonding of the selfadhesive luting resin accounts for one third of the complications, mainly in the lower jaw. Nevertheless, this material offers metal-free aesthetic restorations to the patient. But biological compromised abutment teeth, long span or cantilever designs are not recommended because of the high prevalence of early failures. In such cases, machinable polymers perform clinically inferior compared to metal-based and temporarily luted FDPs. Acknowledgments This clinical trial was approved by the Ethics Committee of Tuebingen University (30/2009MPG2) and is listed at the German Clinical Trials Register (DRKS00000644). The authors thank the following dental technicians of Tuebingen University Hospital’s Dental Lab: MDT Ekkehard Kroewerath, DT Volker Scheer and DT Karina Wuensch. The study was partially financed by Vita Zahnfabrik (Bad Säckingen, Germany) and by the Medical Faculty of Eberhard Karls University of Tuebingen. Conflict of interest The authors declare no personal conflict of interest, besides being involved in this clinical trial.
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