Standardizing failure, success, and survival decisions in clinical studies of ceramic and metal-ceramic fixed dental prostheses

Complete rehabilitation of compromised full dentitions with adhesively bonded all-ceramic single-tooth restorations: Long-term outcome in patients with and without amelogenesis imperfecta

OBJECTIVES

This clinical follow-up evaluated the long-term outcome of full-mouth rehabilitations with adhesively bonded all-ceramic restorations in patients suffering from amelogenesis imperfecta (AI) or affected by extensive tooth wear including a loss of the vertical dimension of occlusion.

MATERIALS AND METHODS

Included for evaluation were all patients treated with adhesively bonded monolithic single-tooth restorations made of silicate or lithium disilicate ceramics; allowing a maximum four missing teeth and a facial feldspathic veneering of LDS anterior crowns. After treatment, patients have been enrolled in a recall program for dental check-ups including quality assessment of the restorations. Patients answered the oral health impact profile (OHIP-14) at their last visit.

RESULTS

Seventeen patients (mean age = 35 ± 18 years) were observed up to 16.5 years (mean: 6.2 ± 3.8 years). 12 out of 450 restorations failed due to core fracture (n = 7), tooth fracture (n = 2), one secondary caries, one chip-off grade 3, and one fixed dental prosthesis due to discomfort. The overall mean survival rate of the single-tooth restorations was estimated 99.4% at 5 and 91.4% at 10 years. The overall mean success rate was estimated 92.6% at 5 and 81.4% at 10 years, mainly due to chip-offs and crack formation (27 out of 31 relative failures). The mean annual failure rates (AFR) range between 1.5 and 2% over the years, but non-AI patients were affected more frequently by early technical complications in the facial veneering of anteriors, resulting in an AFR ranging between 5.2 and 4%. Quality assessment revealed stable color, form and marginal integrity in all patients up to ten years. The distribution of OHIP values is comparable to the representative sample of healthy patients.

CONCLUSION

Adhesively bonded single-tooth restorations provided a high clinical quality in the long-run. However, while the survival and success were excellent in AI patients, restorations in non-AI patients were affected by a higher complication rate, likely related to a higher risk profile due to a history of bruxism and tooth wear.

Comparison of traditional and simplified methods for repairing CAD/CAM feldspathic ceramics

PURPOSE

To evaluate the adhesion to CAD/CAM feldspathic blocks by failure analysis and shear bond strength test (SBSt) of different restorative systems and different surface treatments, for purpose of moderate chipping repair.

MATERIALS AND METHODS

A self-adhering flowable composite (Vertise Flow, Kerr) containing bi-functional phosphate monomers and a conventional flowable resin composite (Premise Flow, Kerr) applied with and without adhesive system (Optibond Solo Plus, Kerr) were combined with three different surface treatments (Hydrofluoric Acid Etching, Sandblasting, combination of both) for repairing feldspathic ceramics. Two commercial systems for ceramic repairing were tested as controls (Porcelain Repair Kit, Ultradent, and CoJet System, 3M). SBSt was performed and failure mode was evaluated using a digital microscope. A One-Way ANOVA (Tukey test for post hoc) was applied to the SBSt data and the Fisher's Exact Test was applied to the failure analysis data.

RESULTS

The use of resin systems containing bi-functional phosphate monomers combined with hydrofluoric acid etching of the ceramic surface gave the highest values in terms of bond strength and of more favorable failure modalities.

CONCLUSION

The simplified repairing method based on self-adhering flowable resin combined with the use of hydrofluoric acid etching showed high bond strength values and a favorable failure mode. Repairing of ceramic chipping with a self-adhering flowable resin associated with hydrofluoric acid etching showed high bond strength with a less time consuming and technique-sensitive procedure compared to standard procedure.

Ceramic Fracture in Metal-Ceramic Restorations: The Aetiology

All dental restorations are liable to failure during function. Failure could be biologic, aesthetic, mechanical or a combination. Ceramic restorations in particular, including metal-ceramics, are prone to mechanical fracture, especially the fracture of veneering porcelain. Fracture of a metal-ceramic restoration jeopardizes function as well as aesthetics. It is equally onerous to manage for both patient and dentist. Optimal management of such cases requires a detailed knowledge of the aetiology behind this phenomenon. The current paper aims to highlight possible causative factors involved in the mechanical failures of metal-ceramic restorations. Clinical relevance: Ceramic fracture in metal-ceramic crowns and fixed partial dentures is routinely encountered in dental clinics. Knowledge of the aetiology is required to diagnose and manage such cases accurately as well as to avoid these errors in future.

Characterization of a Diamond Ground Y-TZP and Reversion of the Tetragonal to Monoclinic Transformation

PURPOSE

To characterize the surface of an yttria-stabilized zirconia (Y-TZP) ceramic after diamond grinding in terms of its crystalline phase, morphology, mean roughness (Ra), and wettability as well as to determine a thermal treatment to reverse the resulting tetragonal to monoclinic (t-m) transformation.

METHODS AND MATERIALS

Y-TZP specimens were distributed into different groups according to the actions (or no action) of grinding and irrigation. Grinding was accomplished using a diamond stone at a low speed. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy, goniometry, and profilometry. In situ high-temperature XRD was used to determine an annealing temperature to reverse the t-m transformation. Ra was submitted to the Kruskal-Wallis test, followed by the Dunn test (α=0.05). The volume fraction of the monoclinic phase and contact angle were submitted to one-way analysis of variance, followed by the Tukey test (α=0.05).

RESULTS

Monoclinic zirconia was observed on the surface of samples after dry and wet grinding with a diamond stone. The volume fraction of the monoclinic phase was smaller on the dry ground samples (3.6%±0.3%) than on the wet ground samples (5.6%±0.3%). High-temperature XRD showed reversion of the t-m phase transformation, which started at 700°C and completed at 800°C in a conventional oven.

CONCLUSIONS

Grinding with a diamond stone partially transformed the crystalline phase on the surface of a Y-TZP ceramic from tetragonal to monoclinic zirconia while simultaneously increasing the surface roughness and wettability. The t-m transformation could be reversed by heat treatment at 800°C or 900°C for 60 minutes or 1000°C for 30 minutes.

Comparison of the bond strength of ceramics to Co-Cr alloys made by casting and selective laser melting

PURPOSE

Considering the importance of metal-ceramic bond, the present study aimed to compare the bond strength of ceramics to cobalt-chrome (Co-Cr) alloys made by casting and selective laser melting (SLM).

MATERIALS AND METHODS

In this in-vitro experimental study, two sample groups were prepared, with one group comprising of 10 Co-Cr metal frameworks fabricated by SLM method and the other of 10 Co-Cr metal frameworks fabricated by lost wax cast method with the dimensions of 0.5 × 3 × 25 mm (following ISO standard 9693). Porcelain with the thickness of 1.1 mm was applied on a 3 × 8-mm central rectangular area of each sample. Afterwards, bond strengths of the samples were assessed with a Universal Testing Machine. Statistical analysis was performed with Kolmogorov-Smirnov test and T-test.

RESULTS

Bond strength in the conventionally cast group equaled 74.94 ± 16.06 MPa, while in SLM group, it equaled 69.02 ± 5.77 MPa. The difference was not statistically significant (P ≤ .05).

CONCLUSION

The results indicated that the bond strengths between ceramic and Co-Cr alloys made by casting and SLM methods were not statistically different.

Prospective cohort clinical study assessing the 5-year survival and success of anterior maxillary zirconia-based crowns with customized zirconia copings

STATEMENT OF PROBLEM

Studies evaluating anterior zirconia-based crowns are limited.

PURPOSE

The purpose of this prospective cohort clinical study was to assess the efficacy of zirconia-based anterior maxillary crowns with 0.3-mm customized copings at the cervical third and anatomical design elsewhere for up to 5 years of service.

MATERIAL AND METHODS

Eighteen participants who required an anterior maxillary crown (n=20) and who had signed a consent form approved by the University of Washington Health Sciences Center Human Subjects Division were enrolled. All preparations were standardized and prepared with an occlusal reduction of 1.5 to 2 mm and an axial reduction of 1 to 1.5 mm with 10 degrees of convergence angle. All finish lines were located on the sound tooth structure. Zirconia copings (Lava; 3M ESPE) were custom designed and milled to a 0.3-mm thickness at the cervical third and with selective thickness elsewhere to support the veneering porcelain. All restorations were luted with self-etching self-adhesive composite resin cement. Recall appointments were at 2 weeks, 6 months, and 12 months, and annually thereafter for 5 years. Modified Ryge criteria were used to assess the clinical fracture measurements, esthetics, marginal discoloration, marginal adaptation, radiographic proximal recurrent caries, and periapical pathoses. Descriptive statistics and 95% confidence intervals were used to describe the number and rate of complications and self-reported satisfaction with the crowns.

RESULTS

Twenty crowns with a mean follow-up of 58.7 months were evaluated. All crowns were rated as Alfa for fracture measurements (smooth surface, no fracture/chipping). Twelve crowns were rated esthetically as Romeo (no mismatch in color and shade) and 8 as Sierra (mismatch in color and shade within normal range). Twelve crowns were rated as Alfa (no visible evidence of crevice) and 8 as Bravo (visible evidence of crevice, no penetration of explorer) for marginal integrity. Nineteen were rated as Alfa (no discoloration) and 1 as Bravo (superficial discoloration) for marginal discoloration. No proximal caries or periapical pathoses were detected in 5 years. Participants were highly satisfied with their crowns after 5 years (mean ±SD: 9.8 ±0.4 on 0 to 10 scale).

CONCLUSIONS

Zirconia-based anterior maxillary crowns with customized copings with 0.3-mm thickness at the cervical third and zirconia margins performed well after 5 years of service.

Low-Fusing Porcelain Glaze Application on 3Y-TZP Surfaces can Enhance Zirconia-Porcelain Adhesion

Abstract The aim of this study was to assess whether surface treatment improves zirconia-porcelain adhesion. The 3Y-TZP blocks were cut into squares, then polished and sintered. The zirconia surface treatments were performed as follows: no treatment (C); tribochemical silica coating (TBS); glaze application + hydrofluoric acid etching (GA); glaze application + hydrofluoric acid etching + silanization (GAS); deposition of silica nanofilm (NF). After treatments, veneering porcelain cylinders (3.3 x 3.3 mm) were built up on all specimens and fired. Then the specimens were subjected to thermal cycling (6000 cycles), and subjected to shear test. Fractures were analyzed by stereomicroscopy and SEM. Data were statistically analyzed by 1-way ANOVA and Tukey's test (5%). Zirconia-porcelain bond strength was affected by the ceramic surface treatments (p=0.0001). GA (19.5±3 MPa) and GAS (16.2±4 MPa) recorded the highest bond strength values, while control group had the lowest bond value (10.1±4 MPa). Adhesive failure of the samples predominated. Therefore, glaze application as 3Y-TZP treatment before veneering porcelain stratification may enhance zirconia-porcelain adhesion.

Intraoral Repair of Direct and Indirect Restorations: Procedures and Guidelines

The service life of defective direct or indirect restorations could be prolonged by repair or relayering actions where durable adhesion of resin-based composite materials is established for longevity of repairs. The advances in adhesive technologies have introduced several surface conditioning concepts to adhere resin composites onto different restorative materials. The purpose of this report is to summarize reasons for failure, survival of repaired reconstructions, elaborate upon types and mechanisms of available surface conditioning methods, and present operative dentists with practical guidelines for intraoral repair procedures.

Early complications and performance of 327 heat-pressed lithium disilicate crowns up to five years

PURPOSE

The prospective follow-up aimed to assess the performance of lithium disilicate crowns and clinical reasons of adverse events compromising survival and quality.

MATERIALS AND METHODS

58 patients were treated with 375 heat-pressed monolithic crowns, which were bonded with resin cement. Annual recalls up to five years included a complete dental examination as well as quality assessment using CDA-criteria. Any need for clinical intervention led to higher complication rate and any failure compromised the survival rate. Kaplan-Meier-method was applied to all crowns and a dataset containing one randomly selected crown from each patient.

RESULTS

Due to drop-outs, 45 patients (31 females, 14 males) with the average age of 43 years (range = 17-73) who had 327 crowns (176 anterior, 151 posterior; 203 upper jaw, 124 lower jaw) were observed and evaluated for between 4 and 51 months (median = 28). Observation revealed 4 chippings, 3 losses of retention, 3 fractures, 3 secondary caries, 1 endodontic problem, and 1 tooth fracture. Four crowns had to be removed. Survival and complication rate was estimated 98.2% and 5.4% at 24 months, and 96.8% and 7.1% at 48 months. The complication rate was significantly higher for root canal treated teeth (12%, P<.01) at 24 months. At the last observation, over 90% of all crowns showed excellent ratings (CDA-rating Alfa) for color, marginal fit, and caries.

CONCLUSION

Heat pressed lithium disilicate crowns showed an excellent performance. Besides a careful luting, dentists should be aware of patients' biological prerequisites (grade of caries, oral hygiene) to reach full success with these crowns.

Topological design of all-ceramic dental bridges for enhancing fracture resistance

Layered all-ceramic systems have been increasingly adopted in major dental prostheses. However, ceramics are inherently brittle, and they often subject to premature failure under high occlusion forces especially in the posterior region. This study aimed to develop mechanically sound novel topological designs for all-ceramic dental bridges by minimizing the fracture incidence under given loading conditions. A bi-directional evolutionary structural optimization (BESO) technique is implemented within the extended finite element method (XFEM) framework. Extended finite element method allows modeling crack initiation and propagation inside all-ceramic restoration systems. Following this, BESO searches the optimum distribution of two different ceramic materials, namely porcelain and zirconia, for minimizing fracture incidence. A performance index, as per a ratio of peak tensile stress to material strength, is used as a design objective. In this study, the novel XFEM based BESO topology optimization significantly improved structural strength by minimizing performance index for suppressing fracture incidence in the structures. As expected, the fracture resistance and factor of safety of fixed partial dentures structure increased upon redistributing zirconia and porcelain in the optimal topological configuration. Dental CAD/CAM systems and the emerging 3D printing technology were commercially available to facilitate implementation of such a computational design, exhibiting considerable potential for clinical application in the future. Copyright © 2015 John Wiley & Sons, Ltd.

Influence of Different Framework Designs on the Fracture Properties of Ceria-Stabilized Tetragonal Zirconia/Alumina-Based All-Ceramic Crowns

The aim of this study was to evaluate the fracture load and failure mode of all-ceramic crowns with different ceria-stabilized tetragonal zirconia/alumina nanocomposite (Ce-TZP/A) framework designs. Four frameworks (anatomical shape: AS, with a buccal or lingual supporting structure: BS and LS, or buccal and lingual supporting structures: BLS) were fabricated. All frameworks were veneered with porcelain to fabricate all-ceramic crowns followed by cementation to tooth analogs. The fracture load of each crown either without or with pre-loading (1.2 million cycles, 49 N) was measured. The failure mode was classified into partial or complete fracture. Differences were tested for significance (p < 0.05) by a two-way Analysis of Variance (ANOVA), followed by Tukey’s test and by Fisher’s exact test, respectively. Without pre-loading, supporting structures did not influence the fracture load or failure mode. Partial fractures were the most common failure mode. Pre-loading promoted the severity of the failure mode, although the fracture load among the framework designs was not influenced. In the AS group, prefailures were observed during pre-loading, and complete fractures were significantly increased after pre-loading. In contrast, the failure mode of the BLS group remained unchanged, showing only partial fracture even after pre-loading. This Ce-TZP/A framework design, comprised of an anatomical shape with additional buccal and lingual structures, has the potential to reduce the chipping of the veneering porcelain.

Dental prostheses mimic the natural enamel behavior under functional loading: A review article

Alumina- and zirconia-based ceramic dental restorations are designed to repair functionality as well as esthetics of the failed teeth. However, these materials exhibited several performance deficiencies such as fracture, poor esthetic properties of ceramic cores (particularly zirconia cores), and difficulty in accomplishing a strong ceramic–resin-based cement bond. Therefore, improving the mechanical properties of these ceramic materials is of great interest in a wide range of disciplines. Consequently, spatial gradients in surface composition and structure can improve the mechanical integrity of ceramic dental restorations. Thus, this article reviews the current status of the functionally graded dental prostheses inspired by the dentino-enamel junction (DEJ) structures and the linear gradation in Young's modulus of the DEJ, as a new material design approach, to improve the performance compared to traditional dental prostheses. This is a remarkable example of nature's ability to engineer functionally graded dental prostheses. The current article opens a new avenue for recent researches aimed at the further development of new ceramic dental restorations for improving their clinical durability.

Zirconia based dental ceramics: structure, mechanical properties, biocompatibility and applications

Zirconia (ZrO₂) based dental ceramics have been considered to be advantageous materials with adequate mechanical properties for the manufacturing of medical devices.

Veneered anatomically designed zirconia FDPs resulting from digital intraoral scans: Preliminary results of a prospective clinical study

OBJECTIVES

The aim of this prospective clinical study was to evaluate the clinical performance of veneered anatomically designed zirconia fixed dental prostheses (FDPs) resulting from intraoral digital impressions.

METHODS

24 patients requiring treatment were provided with all-ceramic FDPs. Intraoral scans (iTero) were performed and veneered anatomically designed CAD/CAM-zirconia FDPs (Zerion/VitaVM9) were fabricated. A feldspar veneering ceramic following a slow cooling firing protocol was applied. A self-curing resin based luting material was used for adhesive cementation. Clinical evaluations were performed at baseline and 6, 12, and 18 months recalls according to the modified USPHS-criteria. Intraoral digital surface scans (iTero) were performed at each recall examination and were digitally superimposed (Geomagic) to evaluate potential veneer cohesive fractures. Kaplan-Meier survival analysis comprised secondary caries, clinically unacceptable fractures, root canal treatment and debonding. Kaplan-Meier success rate included restorations with minimal crevices, tolerable color deviations and clinically acceptable fractures. Data were statistically analyzed.

RESULTS

The Kaplan-Meier survival rate and success rate of the FDPs were 100% and 91.7%, respectively. Clinically acceptable veneer cohesive fractures and crevices at the restoration margin were observed in two patients. These shallow veneer fractures were only detected by overlapping baseline and recall scans. Ceramic surface roughness increased significantly over time (p<0.0001).

CONCLUSIONS

Veneered zirconia FDPs fabricated from digital intraoral scans showed a favorable clinical performance over an observation period of 18 months. Anatomical zirconia core design and slow cooling firing protocol of the veneering ceramic reduced the incidence of chip fractures to a level that could not be detected clinically.

CLINICAL SIGNIFICANCE

The digital workflow on the basis of intraoral digital impressions resulted in clinically satisfying outcomes for veneered zirconia FDPs.

Fracture of porcelain-veneered gold-alloy and zirconia molar crowns using a modified test set-up

Objective: The main aim of this study was to compare fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and metal-ceramic (MC) molar crowns using a modified test set-up to produce fractures similar to those seen in vivo, i.e. fractures of the veneering material rather than complete fractures.

Materials and methods: 13 high-noble-alloy MC and 13 Y-TZP molar crowns veneered with porcelain were manufactured. The crowns were artificially aged before final load to fracture. Load was applied using a 7 mm diameter steel ball exerting force on the cusps with stresses directed toward the core-veneer interface. Fracture surface analysis was performed using light- and scanning electron microscopy.

Results: The test design produced fractures of the veneering material rather than complete fractures. MC crowns withstood significantly (p > 0.001) higher loads (mean 2155 N) than Y-TZP (mean 1505 N) crowns, yet both endure loads sufficient for predictable clinical use. Fracture mode differed between MC and Y-TZP. MC crowns exhibited fractures involving the core-veneer interface but without core exposure. One Y-TZP crown suffered a complete fracture, all others except one displayed fractures of the veneering material involving the core-veneer interface with core exposure.

Conclusions: The test set-up produces fractures similar to those found in vivo and may be useful to evaluate the core-veneer interface of different material systems, both metals and ceramics. The study confirms suggestions from previous studies of a weaker core-veneer bond for Y-TZP compared to MC crowns.

Survival rate of lithium disilicate restorations at 4 years: A retrospective study

STATEMENT OF PROBLEM

Ceramic restorations are frequently being placed due to the esthetic demand and the cost of noble metals that has increased considerably. One major disadvantage of ceramic restoration is failure of the material due to fracture by crack propagation. In vitro studies are of little clinical significance and in vivo studies are too short to support clinical success.

PURPOSE

The purpose of this retrospective study was to evaluate the failure rate of lithium disilicate restorations (monolithic and layered) at 4 years.

MATERIAL AND METHODS

Data were collected over 45 months from 2 commercial laboratories. Restorations were categorized into monolithic restorations and layered restorations. Each category was further classified into complete coverage single crowns, fixed dental prostheses, e.max veneers, and inlay/onlay restorations. Failure rates were compared and analyzed using Chi-square (α=.05).

RESULTS

A total of 21,340 restorations were evaluated in this study and included 15,802 monolithic restorations and 5538 layered restorations. The failure rate for single crown monolithic restorations was 0.91% and was 1.83% for single crown layered restorations. For fixed dental prostheses, 4.55% of monolithic restorations failed. For e.max veneers, 1.3% of monolithic veneers fractured and 1.53% of layered veneers fractured. Of the inlay/onlay restorations group, 1.01% of monolithic restorations fractured.

CONCLUSION

In the short term (45 months), restorations fabricated with the lithium disilicate material (IPS e.max) had relatively low fracture rates. Layered single crowns fractured at approximately 2 times the rate of monolithic crowns.

Influence of surface preparation on fracture load of resin composite-based repairs

The purpose of the present study is to evaluate the fracture load of composite-based repairs to fractured zirconium oxide (Z) crowns and to ceramic-fused-to-metal (CM) crowns, comparing different mechanical surface preparation methods. A total of 75 crowns were repaired; samples then underwent dynamic loading and thermocycling. Final fracture load values for failure of the repaired crowns were measured and the type of fracture registered. Group I: CM: Surface preparation with a diamond bur + 9.5% Hydrofluoric Acid (HF) etching; Group II): CM: air-particle (Al2O3) + 9.5% HF; Group III: CM: Silica coating (SiO2); Group IV): Z: air-particle (Al2O3) + HF 9.5%; Group V) Z: Silica coating (SiO2). Of the three CM groups, Group I (CM-diamond bur) showed the highest mean failure value, with significant difference in comparison with Group III (CM-silica coating). For the zirconia groups, the highest value was obtained by Group V (silica coating).

Key words:Crown, ceramic-fused-to-metal, zirconia, resin-composite, ceramic covering.

Outcome of zirconia single crowns made by predoctoral dental students: a clinical retrospective study after 2 to 6 years of clinical service

STATEMENT OF PROBLEM

Zirconia has established its role as a reliable ceramic material for fixed prostheses.

PURPOSE

The purpose of this retrospective study was to evaluate the outcome of zirconia single crowns made by predoctoral students after 2 to 6 years of clinical service.

MATERIAL AND METHODS

A cohort of 88 patients treated with zirconia single crowns (mean 3 crowns per patient, range 1 to 12 crowns) from 2007 to 2010 by predoctoral dental students was identified. The patients were invited to attend a clinical examination.

RESULTS

Sixty-six participants (75%) took part in the clinical follow-up (30 women and 36 men; mean age 60.4 years, range 19 to 81 years). Altogether, 190 teeth with single crowns were examined, and the mean follow-up time was 3.88 years (1.85 to 6.04 years). The most common complications were chipping of veneering porcelain (4%) and loss of cementation (4%). The success rate of the zirconia single crowns after 2 to 6 years was 80% and the survival rate 89%.

CONCLUSIONS

Zirconia crowns can be successfully used in predoctoral dental education. The success rate of zirconia single crowns after 2 to 6 years was 80% and the survival rate was 89%, in accordance with previous studies.

Peri-implant complications for posterior endosteal implants

OBJECTIVES

(1) To assess whether there is evidence of an association between the number of peri-implant tissue complications and patient characteristics such as gender, diabetes status, smoking status, and bite force; (2) To assess whether there is evidence of an association between the number of peri-implant tissue complications and location of the implant, surgical technique used, bone graft status and sinus lift status.

MATERIALS AND METHODS

This randomized, controlled clinical trial included a total of 176 implants (OsseoSpeed, DENTSPLY) in 67 participants with 88 fixed dental prostheses. Information was obtained from health histories, a baseline exam, surgical notes, and post-operative exams. The data were analyzed using Fisher's exact and Mann-Whitney tests and generalized estimating equations using logistic regression with a significance level set at 0.05.

RESULTS

All 176 implants survived within a recall period of 3 years, but 11 implants demonstrated peri-implant tissue complications. Ten sites showed dehiscence and one case exhibited vertical bone loss. There was a statistically significant association between surgical technique used (1-stage or 2-stage) and the presence of soft tissue complications (P = 0.005), where 2-stage surgery was associated with a higher frequency of peri-implant soft tissue complications. A correlation, although not statistically significant (P = 0.077), was noted, between peri-implant tissue complications and bone grafting, suggesting a possible role for this factor as well.

CONCLUSIONS

Participants who did not require any second-stage surgery at the implant sites experienced fewer complications. Therefore, additional surgical procedures should be performed judiciously considering their possible effects on peri-implant tissue health.

CLINICAL SIGNIFICANCE

The clinical implication of this research study is that secondary surgery should be considered with caution during implant placement and it should be performed only when other options have been exhausted, as it has been shown to have a direct adverse effect on the long-term peri-implant tissue health.

Advances in dental materials

The dental market is replete with new resorative materials marketed on the basis of novel technological advances in materials chemistry, bonding capability or reduced operator time and/or technique sensitivity. This paper aims to consider advances in current materials, with an emphasis on their role in supporting contemporary clinical practice.

A systematic review of outcome measurements and quality of studies evaluating fixed tooth-supported restorations

PURPOSE

The purpose of this systematic review was to review clinical studies of fixed tooth-supported prostheses, and to assess the quality of evidence with an emphasis on the assessment of the reporting of outcome measurements. Multiple hypotheses were generated to compare the effect of study type on different outcome modifiers and to compare the quality of publications before and after January 2005.

MATERIALS AND METHODS

An electronic search was conducted using specific databases (MEDLINE via Ovid, EMBASE via Ovid, Cochrane Library) through July 2012. This was complemented by hand searching the past 10 years of issues of the Journal of Oral Rehabilitation, Journal of Prosthetic Dentistry, Journal of Prosthodontics, and the International Journal of Prosthodontics. All experimental and observational clinical studies evaluating survival, success, failure, and complications of tooth-supported extracoronal fixed partial dentures, crowns, and onlays were included. No restrictions on age or follow-up time were placed.

RESULTS

The electronic search generated 14,869 papers, of which 206 papers were included for full-text review. Hand-searching added 23 papers. Inclusion criteria were met by 182 papers and were included for the review. The majority were retrospective studies. Only 8 (4.4%) were randomized controlled trials. The majority of the studies measured survival and failure, and few studies recorded data on success; however, more than 60% of the studies failed to define survival, success, and failure. Many studies did not use any standardized criteria for assessment of the quality of the restorations and, when standardized criteria were used, they were modified, thereby not allowing for comparisons with other studies. There was an increase of 21.8% in the number of studies evaluating outcome measurements of all-ceramic restorations in past 8 years.

CONCLUSIONS

Prosthodontic literature presents with a reduced percentage of RCTs compared to other disciplines in dentistry. The overall quality of recording prosthodontic outcome measurements has not improved greatly in the past 8 years.

Fracture analysis of randomized implant-supported fixed dental prostheses

OBJECTIVE

Fractures of posterior fixed dental all-ceramic prostheses can be caused by one or more factors including prosthesis design, flaw distribution, direction and magnitude of occlusal loading, nature of supporting infrastructure (tooth root/implant), and presence of adjacent teeth. This clinical study of implant-supported, all-ceramic fixed dental prostheses, determined the effects of (1) presence of a tooth distal to the most distal retainer; (2) prosthesis loading either along the non-load bearing or load bearing areas; (3) presence of excursive contacts or maximum intercuspation contacts in the prosthesis; and (4) magnitude of bite force on the occurrence of veneer ceramic fracture.

METHODS

89 implant-supported FDPs were randomized as either a three-unit posterior metal-ceramic (Au-Pd-Ag alloy and InLine POM, Ivoclar, Vivadent) FDP or a ceramic-ceramic (ZirCAD and ZirPress, Ivoclar, Vivadent) FDP. Two implants (Osseospeed, Dentsply) and custom abutments (Atlantis, Dentsply) supported these FDPs, which were cemented with resin cement (RelyX Universal Cement). Baseline photographs were made with markings of teeth from maximum intercuspation (MI) and excursive function. Patients were recalled at 6 months and 1-3 years. Fractures were observed, their locations recorded, and images compared with baseline photographs of occlusal contacts.

CONCLUSION

No significant relationship existed between the occurrence of fracture and: (1) the magnitude of bite force; (2) a tooth distal to the most distal retainer; and (3) contacts in load-bearing or non-load-bearing areas. However, there was a significantly higher likelihood of fracture in areas with MI contacts only.

CLINICAL SIGNIFICANCE

Because of the absence of a periodontal ligament, this clinical study demonstrates that there is a need to evaluate occlusion differently with implant-supported prostheses than with natural tooth supported prostheses. Implant supported prostheses should have minimal occlusion and lighter contacts than those supported by natural dentition.

CLINICAL TRIALSGOV NO

K23 D2007-46.

Size-dependent strength of dental adhesive systems

OBJECTIVE

The aim of this study is to explain the influence of peripheral interface stress singularities on the testing of tensile bond strength. The relationships between these theoretically predicted singularities and the effect of specimen size on the measured bond strength are evaluated.

METHODS

Finite element method (FEM) and boundary element method (BEM) analyses of microtensile bond strength test specimens were performed and the presence of localized high stress concentrations and singularities was analyzed. The specimen size effect predicted by the models was compared to previously published experimental data.

RESULTS

FEM analysis of single-material trimmed hour-glass versus cast cylindrical specimens showed different theoretical stress distributions, with the dumbbell or cylindrical specimens showing a more homogeneous distribution of the stress on the critical symmetry plane. For multi-material specimens, mathematical singularities at the free edge of the bonded interface posed a computational challenge that resulted in mesh-dependence in the standard FEM analysis. A specialized weighted-traction BEM analysis, designed to eliminate mesh-dependence by capturing the effect of the singularity, predicted a specimen size effect that corresponds to that published previously in the literature.

SIGNIFICANCE

The results presented here further support the attention to specimen dimensions that has already broadened the empirical use of the microtensile test methods. FEM and BEM analyses that identify stress concentrations and especially marginal stress singularities must be accounted for in reliable bonding strength assessments. Size-dependent strength variations generally attributed to the effects of flaw distributions throughout the interfacial region are not as relevant as the presence of singularities at bonded joint boundaries - as revealed by both FEM and BEM analyses, when interpreted from a generalized fracture mechanics perspective. Furthermore, this size-dependence must be considered when evaluating or designing dental adhesive systems.

Interfacial adhesion of zirconia/veneer bilayers with different thermal characteristics

The aim of this study was to investigate how changes in the thermal characteristics of veneer ceramics with almost identical chemical and mechanical properties but with different coefficients of thermal expansion (CTE) can modify their interfacial adhesion to zirconia. 48 bilayers made of one Y-TZP ceramic and four veneer ceramics were fabricated (n=12). Thermal residual stresses were calculated on the basis of the CTE and glass transition temperatures. After defined notching all specimens were loaded in a four-point bending test and the critical loads were recorded which induced stable crack extension at the adhesion interface. The strain energy release rate (G, J/m(2)) was calculated and was taken as a measure of interfacial adhesion. The CTE of the veneer ceramics were significantly correlated with their adhesion to Y-TZP (p<0.001). Interfacial adhesion in zirconia/veneer bilayers is predominantly affected by the thermal characteristics of the veneer ceramic.