Clinical complications in fixed prosthodontics

Immediate tooth replacement using fiber-reinforced composite and natural tooth pontic

The loss and replacement of anterior maxillary teeth poses several challenges. In patients refusing implant surgery, when minimal tooth reduction is desired, a fiber-reinforced composite fixed-partial denture may be used as a conservative alternative to a conventional fixed-partial denture for replacement of a single missing tooth. This article describes a clinical technique and six-year follow-up. The patient presented with a missing maxillary central incisor due to localized juvenile periodontitis. The abutment teeth were clinically stable. The advantage of supragingival margins and minimal tooth structure removal made the bonded bridge with a natural tooth pontic a viable procedure for this compromised restorative situation.

The Randomized Shortened Dental Arch Study

The evidence concerning the management of shortened dental arch (SDA) cases is sparse. This multi-center study was aimed at generating data on outcomes and survival rates for two common treatments, removable dental prostheses (RDP) for molar replacement or no replacement (SDA). The hypothesis was that the treatments lead to different incidences of tooth loss. We included 215 patients with complete molar loss in one jaw. Molars were either replaced by RDP or not replaced, according to the SDA concept. First tooth loss after treatment was the primary outcome measure. This event occurred in 13 patients in the RDP group and nine patients in the SDA group. The respective Kaplan-Meier survival rates at 38 months were 0.83 (95% CI: 0.74-0.91) in the RDP group and 0.86 (95% CI: 0.78-0.95) in the SDA group, the difference being non-significant.

In vitro evaluation of microleakage of various types of dental cements

Introduction. Microleakage is defined as the clinically undetectable seepage of oral fluids containing bacteria and debris between cement layer and tooth restoration. Objective. This in vitro study investigated the effect of different dental cements (zinc-phosphate, polycarboxylate, glass-ionomer and resin cement) on microleakage in different ceramic crown systems (metal ceramic crown, metal ceramic crown with a porcelain margin, Empress 2 and In Ceram all-ceramic crowns) fixed on extracted human teeth. Methods. One hundred and sixty intact human premolars were randomized to four groups of forty teeth each, according to the different ceramic crown systems. They were prepared in a standardized manner for metal-ceramic and all-ceramic crowns. Crowns were made following a standard laboratory technique, and each group of crowns were divided into four groups according to the different cement agents and cemented on their respective abutments. The specimens were subjected to thermocycling, placed in methylene blue solutions, embedded in resin blocks and vertically cut in the bucco-oral and meso-distal direction. The microleakage in the area of tooth-cement interface was defined as linear penetration of methylene blue and was determined with a microscope to assign microleakage scores using a five-point scale. Results. A significant association was found between a cement type and degree of microleakage (p=0.001). No statistically significant differences were found among the different ceramic crown systems luted with the same dental cement. The smallest degree of microleakage was observed in specimens luted with resin cement (X=1.73), followed by glass-ionomer cement (X=2.45) and polycarboxylate cement (X=3.20). The greatest degree of microleakage was detected in the crowns fixed with zincphosphate cement (X=3.33). Conclusion. The investigated dental cements revealed different sealing abilities. The use of resin cement resulted in the percentage of 0 microleakage scores. Due to this feature, the resin cement is to be recommended in everyday clinical practice.

All-ceramic and porcelain-fused-to-metal fixed partial dentures: a comparative study by 2D finite element analyses

All-ceramic fixed partial dentures (FPDs) have an esthetic approach for oral rehabilitation. However, metal-ceramic FPDs are best indicated in the posterior area where the follow-up studies found a lower failure rate. This 2D finite element study compared the stress distribution on 3-unit all-ceramic and metal-ceramic FPDs and identified the areas of major risk of failure. Three FPD models were designed: (1) metal-ceramic FPD; (2) All-ceramic FPD with the veneering porcelain on the occlusal and cervical surface of the abutment tooth; (3) All-ceramic FPD with the veneering porcelain only on the occlusal surface. A 100 N load was applied in an area of 0.5 mm² on the working cusps, following these simulations: (1) on the abutment teeth and the pontic; (2) only on the abutment teeth; and (3) only on the pontic. Relative to the maximum stress values found for the physiological load, all-ceramic FPD with only occlusal veneering porcelain produced the lowest stress value (220 MPa), followed by all-ceramic FPD with cervical veneering porcelain (322 MPa) and metal-ceramic FPD (387 MPa). The stress distribution of the load applied on the abutments was significantly better compared to the other two load simulations. The highest principal stress values were low and limited in a small area for the three types of models under this load. When the load was applied on the pontic, the highest stress values appeared on the connector areas between the abutments and pontic. In conclusion, the best stress values and distribution were found for the all-ceramic FPD with the veneering porcelain only on the occlusal surface. However, in under clinical conditions, fatigue conditions and restoration defects must be considered.

Clinical success of zirconia in dental applications

The application of ceramic materials for the fabrication of dental restorations is a focus of interest in esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. Zirconia was introduced into dentistry in the 1990s because of its good mechanical and chemical properties and is currently being used as a material for frameworks, dowels, implants, abutments, and orthodontic brackets. Many in vitro studies about zirconia use have been published, but clinical long-term studies are very important. This article presents data regarding the incidence of clinical success and complications of zirconia in these dental applications. Clinical studies published to date seem to indicate that zirconia is well tolerated and sufficiently resistant.

Two-year Clinical Evaluation of IPS Empress II Ceramic Onlays/Inlays

The two-year success rate of restorations reported in the current study demonstrates that IPS Empress II ceramics are clinically acceptable for onlay/inlay restorations on molars.

Competition of fracture mechanisms in monolithic dental ceramics: flat model systems

Monolithic (single layer) glass-ceramic restorations often fail from chipping and fracture. Using blunt indentation of a model flat porcelain-like brittle layer bonded onto a dentin-like polymer support system, a variety of fatigue fracture modes has been identified and analyzed: outer cone, inner cone, and median cracks developing in the near-contact region at the occlusal surface; radial cracks developing at the internal cementation surface along the loading axis. Our findings indicate that monolithic glass-ceramic layers are vulnerable to both occlusal surface damage and cementation internal surface fracture. Clinical issues in the longevity of ceramic restorations are discussed in relation to biting force, physical properties of ceramic crowns and luting cement, and thicknesses of ceramic and cement layers.

Correlation between margin fit and microleakage in complete crowns cemented with three luting agents

Microleakage can be related to margin misfit. Also, traditional microleakage techniques are time-consuming. This study evaluated the existence of correlation between in vitro margin fit and a new microleakage technique for complete crowns cemented with 3 different luting agents. Thirty human premolars were prepared for full-coverage crowns with a convergence angle of 6 degrees, chamfer margin of 1.2 mm circumferentially, and occlusal reduction of 1.5 mm. Ni-Cr cast crowns were cemented with either zinc phosphate (ZP) (S.S. White), resin-modified glass-ionomer (RMGI) (Rely X Luting Cement) or a resin-based luting agent (RC) (Enforce). Margin fit (seating discrepancy and margin gap) was evaluated according to criteria in the literature under microscope with 0.001 mm accuracy. After thermal cycling, crowns were longitudinally sectioned and microleakage scores at tooth-cement interface were obtained and recorded at x100 magnification. Margin fit parameters were compared with the one-way ANOVA test and microleakage scores with Kruskal-Wallis and Dunn's tests (alpha=0.05). Correlation between margin fit and microleakage was analyzed with the Spearman's test (alpha=0.05). Seating discrepancy and marginal gap values ranged from 81.82 microm to 137.22 microm (p=0.117), and from 75.42 microm to 78.49 microm (p=0.940), respectively. Marginal microleakage scores were ZP=3.02, RMGI=0.35 and RC=0.12 (p<0.001), with no differences between RMGI and RC scores. The correlation coefficient values ranged from -0.27 to 0.30 (p>0.05).

CONCLUSION

Margin fit parameters and microleakage showed no strong correlations; cast crowns cemented with RMGI and RC had lower microleakage scores than ZP cement.

In vitro exploration and finite element analysis of failure mechanisms of resin-bonded fixed partial dentures

PURPOSE

The purpose of this study was to explore the debonding mechanisms of two-unit cantilevered and straight and bent three-unit fixed-fixed resin-bonded fixed partial dentures (RBFPDs) and to measure the failure loads needed for debonding.

MATERIALS AND METHODS

Failure load tests were performed using Bondiloy beams simulating both cantilevered and fixed-fixed RBFPDs, luted onto flat-ground buccal surfaces of bovine teeth with RelyX ARC, Panavia F2.0, and UniFix resin cements. The failure loads were recorded, and the debonded surfaces of both the enamel and the restorations were examined for details of interest. Finite element analysis (FEA) was used to calculate the stress concentrations within the cement layers at failure.

RESULTS

Simulated two-unit cantilevered and straight three-unit fixed-fixed RBFPDs showed a significantly higher failure load than the simulated three-unit fixed-fixed RBFPDs with a curved appearance. The FEA models revealed the magnitude and stress locations within the cement layer, resulting in an explanation of the different failure modes.

CONCLUSIONS

The low failure loads for the three-unit bent fixed-fixed RPFPDs, compared with their straight counterparts and the two-unit cantilevered RBFPDs, indicate that clinically a reserved attitude needs to be maintained with regard to three-unit fixed-fixed RBFPDs spanning a clearly curved part of the dental arch. The FEA results make it clear which part of the tooth restoration interface is subject to the highest stress levels, making it possible to design abutment preparations that avoid high interfacial stresses to help prevent debonding.

[Effect of recasting on the thickness of metal-ceramic interface of nickel-chromium and cobalt-chromium alloys]

INTRODUCTION/AIM

This research was done to establish recasting effects of nickel-chromium and cobalt-chromium alloys on the thickness of their metal-ceramic interface in making fixed partial dentures. Metal-ceramic interface determines their functional integrity and prevents damages on ceramics during mastication. Investigation of metal-ceramic samples is supposed to show if base metal alloys for metal-ceramics are successfully recycled without any risk of reduction of metal-ceramic interface thickness.

METHODS

The research was performed as an experimental study. Per six metal-ceramic samples of nickel-chromium alloy (Wiron99) and cobalt-chromium alloy (Wirobond C) were made each. Alloy residues were recycled through twelve casting generations with the addition of 50% of new alloy on the occasion of every recasting. Analysis Energy Dispersive X-ray (EDX) (Oxford Instruments) and Scanning Electon Microscop (SEM) analysis (JEOL) were used to determine thickness of metal-ceramic interface together with PC Software for quantification of visual informations (KVI POPOVAC).

RESULTS

Results of this research introduced significant differences between thickness of metal-ceramic interface in every examined recycle generation. Recasting had negative effect on thickness of metal-ceramic interface of the examined alloys. This research showed almost linear reduction of elastic modulus up to the 12th generation of recycling.

CONCLUSION

Recasting of nickel-chromium and cobalt-chromium alloys is not recommended because of reduced thickness of metal-ceramic interface of these alloys. Instead of recycling, the alloy residues should be returned to the manufacturers.

Occlusion for fixed prosthodontics: a historical perspective of the gnathological influence

This article addresses the historical perspective of the gnathological influence upon the concepts of occlusion for fixed prosthodontics. A critical assessment and subsequent scientific validation of occlusal theories require an understanding of their evolution in the formative years and the subsequent development of effective models for clinical practice. While gnathological concepts offer a structured methodology for prosthodontic procedures, further research is needed to corroborate current occlusal treatment approaches. This review focuses on the "classic" fixed prosthodontic literature and the currently available scientific literature involving fixed prosthodontic dentate occlusion and gnathology. A MEDLINE search was performed to identify English-language peer-reviewed publications spanning the last 56 years, along with an extensive hand search for years prior. Electronic searches of the literature were performed in MEDLINE using the key words: case series, clinical trials, cohort studies, fixed partial denture occlusion, dental occlusion, dental occlusion research, centric relation, incisal guidance, maximal intercuspation, occlusal vertical dimension, and occlusion, in various combinations to obtain potential references for review. A total of 10,382 English-language nonduplicate titles were obtained for 1950-2006 for the key words "dental occlusion." Other key word searches produced smaller numbers of articles, many of which were duplicates due to multiple searches and were subsequently eliminated. Manual hand searching of the MEDLINE reference list and other journals of interest was performed to identify any articles missed in the original search. Articles were included for review if they contained emerging occlusal theories, new technologies, or occlusal studies that included multiple subjects in contrast to case reports.

The Procera Maryland Bridge: a case report

Although congenital partial hypodontia is widespread, and a variety of solutions for treating this condition in adolescents have been devised, all have had one or more significant drawbacks. A new treatment option that has recently become available, the Procera Maryland Bridge, appears to deliver excellent esthetics and strength. This article discusses that option and presents a case in which it was used successfully.

CLINICAL SIGNIFICANCE

Congenitally missing lateral incisors always present a treatment dilemma for restorative dentists. Numerous treatment options exist; none of which are totally satisfactory. This article presents a potential alternative for these patients using a novel all-ceramic Maryland Bridge.

Classification system for conventional crown and fixed partial denture failures

The dental literature is replete with reports on the many aspects of failure encountered with traditional fixed prosthodontic treatment, including longitudinal survival studies of crowns and fixed partial dentures and reasons for failures. However, criteria for grading or classifying the type and severity of these failures are inadequate. A classification system for conventional fixed prosthodontic failures based on severity is presented.

[Effect of recasting on the elastic modulus of metal-ceramic systems from nickel-chromium and cobalt-chromium alloys]

BACKGROUND/AIM

Elastic modulus of metal-ceramic systems determines their flexural strenght and prevents damages on ceramics during mastication. Recycling of basic alloys is often a clinical practice, despite the possible effects on the quality of the future metal-ceramic dentures. This research was done to establish recasting effects of nickel-chromium and cobalt-chromium alloys on the elastic modulus of metal-ceramic systems in making fixed partial dentures.

METHODS

The research was performed as an experimental study. Six metal-ceramic samples of nickel-chromium alloy (Wiron 99) and cobalt-chromium alloy (Wirobond C) were made. Alloy residues were recycled through twelve casting generations with the addition of 50% of new alloy on the occasion of every recasting. Three- point bending test was used to determine elastic modulus, recommended by the standard ISO 9693:1999. Fracture load for damaging ceramic layer was recorded on the universal testing machine (Zwick, type 1464), with the speed of 0,05 mm/min.

RESULTS

The results of this research revealed significant differences between elasticity modules of metal-ceramic samples in every examined recycle generation. Recasting had negative effect on the elastic modulus of the examined alloys. This research showed the slight linear reduction of elastic modulus up to the 6th generation of recycling. After the 6th recycling there was a sudden fall of elastic modulus.

CONCLUSION

Recasting of nickel-chromium and cobalt-chromium alloys is not recommended because of the reduced elastic modulus of these alloys. Instead of reusing previously recasted alloys, the alloy residues should be returned to the manufacturer.

Factors that affect individual tooth prognosis and choices in contemporary treatment planning

A clinician evaluates a tooth for its quality of health. Once accomplished an estimate of longevity and survival is estimated. With current knowledge about the survival and success of implants a decision is made as to whether to extract or to treat and maintain the tooth. Questions and doubts abound in the decision making process in regards to the prognosis of an individual tooth. Unfortunately in dentistry, as in all biologic sciences, there are no straightforward answers to questions. This article will attempt to review the literature in this area to aid the practitioner in the decision making process with regards to the compromised tooth. The article will focus on the single tooth or implant restoration. Other factors such as the strategic value of a tooth and financial limitations in relation to long-term prognosis will also be discussed.

An evaluation of the performance of cast gold bonded restorations in clinical practice, a retrospective study

OBJECTIVES

To evaluate the performance of cast gold bonded restorations in clinical practice.

MATERIALS AND METHODS

The records of all patients treated with cast gold bonded restorations between 1997 and 2004 of The Dental Hospital of Newcastle upon Tyne were reviewed. The following data were recorded: sex of patient, location of teeth (anterior or posterior), position of teeth (upper or lower) and type of cement (glass ionomer, zinc phosphate or resin cement). The survival time was calculated for each restoration; and the reason for failure (either debond or change of treatment plan) identified for each case. The restorations were stratified according to the age of the patient into 10-year age bands and survival analysis was used to identify variables associated with increased risk of failure.

RESULTS

Restorations luted with resin cement showed the highest rate of survival after 7 years of follow-up. The alternative lutes had significantly worse survival (p<0.05). Restorations on anterior teeth had poorer survival than on posterior teeth but there were no differences between those placed in the mandible and the maxilla.

CONCLUSIONS

Within the limitations of this study resin cements are most appropriate for this type of restoration with 80% survival at 7 years. Restorations placed on posterior teeth survived better.

Root canal posts for the restoration of root filled teeth

BACKGROUND

The foundation for the reconstruction of endodontically-treated teeth can be provided by a metal or a non-metal post and core system but no guidelines exist for choosing one or the other in particular clinical cases.

OBJECTIVES

To assess the effectiveness of different post and core systems for the restoration of endodontically-treated teeth. The primary objective of this review was to compare the clinical failure rates of the different types of posts.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2005, Issue 3), MEDLINE (from 1966 to September 2005), Scopus (from January 1985 to December 2004) and EMBASE (until December 2004). We looked through reference lists of articles and dental conference proceedings. We contacted researchers in the field and manufacturers.

SELECTION CRITERIA

Randomised or quasi-randomised clinical trials (RCTs) comparing failures on endodontically-treated permanent teeth with different types of post. The outcomes were loss of retention, post fracture and root fracture.

DATA COLLECTION AND ANALYSIS

Two review authors (Michele Muller-Bolla (MMB) and Cybele Borg (CB)) independently assessed the quality of trials and extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Two trials involving 317 participants were included but only one of them, involving 200 participants, compared metal to non-metal posts. The other answered to the secondary objective. The risk of failure was greater with metal-cast posts (9/98) compared to carbon fibre posts (0/97) (risk ratio (RR) = 0.05 (95% confidence interval (CI) 0.00 to 0.90)) but the study was at high risk of bias. Thus fewer failures occurred when using non-metal posts but the evidence is unreliable.

AUTHORS' CONCLUSIONS

Our systematic review could not specify which type of post and core system should be used when two or three dentine walls remain. More RCTs are needed to confirm whether fibre-reinforced post and core systems are superior and to clarify the influence of the remaining tooth structure on the treatment outcome of the different post and core systems available. Well-defined inclusion criteria focusing on the number of dentine walls (two or three) should be used.

Mechanical properties of metal-ceramic systems from nickel-chromium and cobalt-chromium alloys

Background/Aim. Metal-ceramic bond strength and alloys' elastic modulus clearly determine the potential of alloy application, because the ceramic integrity during mastication depends on these two characteristics. The aim of this study was to evaluate metal-ceramic bond strength and elastic modulus of cobalt-chromium alloys in making porcelainfused- to-metal restorations, regarding the application of the most frequent nickel-chromium alloy. Methods. The research was performed as an experimental study. Six metalceramic samples were made from nickel-chromium alloy (Wiron 99) and cobalt-chromium alloy (Wirobond C), according to the manufactures manuals and instructions from ISO 9693: 1996. Three-point bending test was performed up to the ceramic fracture. The fracture load was measured on an universal testing machine (Zwick, type 1464), with cross-head speed of 0,05mm/min. Results. The results of this study confirmed the significant differences between the metal-ceramic bond strength (p < 0.01) and elastic modulus (p < 0.001) of nickel-chromium and cobalt-chromium alloys, where cobalt-chromium alloys showed higher values for both tested parameters. Conclusion. Cobalt-chromium metal-ceramic alloys can successfully replace nickel-chromium alloys, especially for fabrication of long-span metal-ceramic bridges due to the great flexural strength.

Complications associated with fixed partial dentures with a loose retainer

STATEMENT OF PROBLEM

When 1 retainer of a definitive fixed partial denture (FPD) becomes loose, the clinician has the option of either sectioning and removing the FPD or attempting removal of the intact cemented retainer. Excessive force during attempted FPD removal may irreversibly damage dentition.

PURPOSE

This study evaluated the type and frequency of complications that may accompany the removal of definitive cemented FPDs with a single loose retainer.

MATERIAL AND METHODS

Participants included 22 patients with a definitive cemented FPD with complete cast crown coverage castings in which 1 retainer became loose and the other retainer remained cemented. Cemented FPD retainers were removed using 1 of 2 attachments supplied with a crown removal system (Dentco). The patient and FPD characteristics, type of attachment, number of attempts before removal, condition of removed FPD, and condition of the abutment teeth were recorded. Descriptive statistics were used to analyze the data.

RESULTS

Clinical findings recorded prior to FPD removal showed that 41% of patients were unaware they had a loose FPD retainer and 82% reported no discomfort associated with the loose retainer. Caries were noted on 50% of the teeth with a loose retainer. Damage resulting from attempted removal of the cemented retainer included minor porcelain fracture (9%), minor core chipping (14%), minor incisal edge chipping of tooth preparations (27%), and major damage to the abutment tooth (4%).

CONCLUSION

Retrieval of an intact FPD and recementation was possible 64% of the time.