Thermal cracks of implant-based zirconia four-unit restorations: A fractographic analysis of two restorations fractured during production.

Two zirconia-based 4-unit restorations intended for the same patient fractured during the veneering process even though the prolonged cooling protocol recommended by the manufacturers was used. Fractographic analyses revealed that both restorations fractured as a result of thermal shock, but at different times during production. Further investigation is necessary to optimize the firing protocols for large zirconia-based restorations and avoid fracture due to thermal shock.

Influence of misfit on the occurrence of veneering porcelain fractures (chipping) in implant-supported metal-ceramic fixed dental prostheses: an in vitro pilot trial.

OBJECTIVE: Technical complications such as veneer fractures are more common in implant-supported than tooth-supported restorations. The underlying causes have not been fully identified. The aim of this study was to evaluate whether misfit between the restoration and the implant may affect the risk of veneer fractures. MATERIALS AND METHODS: Twenty standardized five-unit implant-supported metal-ceramic fixed dental prostheses (FDP)s were manufactured and fixed in acrylic blocks. The test group consisted of ten FDPs fixed with a 150-µm misfit at the distal abutment. The remaining ten FDPs were fixed without misfit and acted as a control group. All FDPS underwent cyclic loading for a total of 100,000 cycles at 30-300 N. The FDPs were checked for cracks or chip-off fractures regularly. After cyclic load, the retorque value of all abutment screws was checked. RESULTS: Cracks within the veneering porcelain were noted in nine FDPs in the test group and one FDP in the control group. This difference was statistically significant (P < 0.001). Fractures of the veneering porcelain occurred in three FDPs in the test group. No fractures occurred in the control group. This difference was not statistically significant. There were no significant differences in retorque values neither between the groups nor between different abutment positions in the FDPs. CONCLUSIONS: Within the limitations of this in vitro pilot trial, it is suggested that misfit between a restoration and the supporting implant may increase the risk of cracking and/or chipping of the veneering porcelain for metal-ceramic FDPs.

Numeric simulation of occlusal interferences in molars restored with ultrathin occlusal veneers.

STATEMENT OF PROBLEM: Selecting material for a minimally invasive occlusal veneer reconstruction concept requires an understanding of how stresses are distributed during functional and parafunctional forces. PURPOSE: The purpose of this in vitro study was to investigate stress distribution in a maxillary molar restored with ultrathin occlusal veneers and subjected by an antagonistic mandibular molar to clenching and working and nonworking movements. MATERIAL AND METHODS: A maxillary first molar was modeled from microcomputed tomography (micro-CT) data, using medical image processing software, stereolithography editing/optimizing software, and finite element software. Simulated ultrathin occlusal veneer materials were used. The mandibular molar antagonist was a solid nondeformable geometric entity. Loads simulated clenching, working, and nonworking movements with loading of 500 N. The values of the maximum principal stress were recorded. RESULTS: In the clenching load situation, maximum tensile stresses were located at the occlusal veneer (52 MPa for composite resin versus 47 MPa for ceramic). In the working movement, significant additional tensile stresses were found on the palatal root (87 MPa for composite resin and 85 MPa for ceramic). In the nonworking movement, tensile stress on the ultrathin occlusal veneer increased to 118 MPa for composite resin and 143 MPa for ceramic veneers. Tensile stress peaks shifted to the mesiobuccal root (75 MPa for composite resin and 74 MPa for ceramic). CONCLUSIONS: The topography of stresses generated by the various occlusal interferences were clearly identified. Significant tensile stress concentrations were found within the restoration's occlusal topography and root, with the nonworking interference being the most harmful and also the most revealing of the difference between the composite resin and ceramic ultrathin occlusal veneers.

Identification of risk factors for fracture of veneering materials and screw loosening of implant-supported fixed partial dentures in partially edentulous cases.

This retrospective study identified the risk factors for fracture of veneering materials and screw loosening of implant-supported fixed partial dentures in partially edentulous cases. The study group included a total of 182 patients who were installed 219 suprastructures at the Fixed Prosthodontic Clinic of Okayama University Dental Hospital between February 1990 and March 2005 and were subdivided in two subgroups: 120 patients (149 facing suprastructures) were included in the subgroup to investigate the risk factors of fracture of veneering materials, and 81 patients (92 suprastructures) were included in the subgroup to identify the risk factors of abutment screw loosening. Each patient was followed up from the day of suprastructure installation until March, 2005. A Cox proportional hazards regression model was used to identify the risk factors related to technical complications, and eight factors were regarded as candidate risk factors. Screw retention was the significant risk factor for fracture of veneering materials, whereas connection of suprastructures with natural tooth was the significant risk factor for screw loosening. It was suggested that screw retention was a significant risk factor for the fracture of veneering materials, and connection of suprastructures with natural tooth was a significant risk factor for screw loosening. Future studies, involving dynamic factors (e.g. bruxism) as predictors as well, are more helpful to discuss the risk factor of fracture of veneering materials and screw loosening.

Clinical fractures of veneered zirconia single crowns.

Crowns made from an yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) core with a porcelain veneer have shown high clinical failure rates. Manifestations of clinical failure in veneering ceramic ranges from a single chip to an extended fracture. Core failures are uncommon but usually are catastrophic. This article examines the possible causes of failure in zirconia systems and presents a case report involving the diagnosis and repair of three different types of failure in six 3Y-TZP/porcelain crowns.

Marginal Adaptation and Fracture Resistance of Lithium Disilicate Laminate Veneers on Teeth with Different Preparation Depths.

The purpose of this study was to evaluate the marginal adaptation and fracture load of ceramic laminate veneers on teeth with different preparation depths. A total of 75 extracted intact human maxillary central incisors were prepared with three different preparation depths (P) and assigned to the following five groups (n = 15): P1 (0.3-mm depth of preparation; preparation entirely in enamel); P2 (0.5-mm depth of preparation; preparation in enamel and dentin complex); P3 (1-mm depth of preparation; preparation entirely in dentin); P4 (no preparation, only surface roughening); and P5 (unrestored, intact teeth as control). A total of 60 lithium disilicate laminate veneers were fabricated. The marginal adaptation of the veneers was evaluated by light microscope and scanning electron microscope after cementation with resin cement. Finally, the veneers were loaded until fracture at a 90-degree angle to the lingual surface of the tooth. Statistical analyses were performed using analysis of variance and Tukey multiple range test. There was a significant difference between the marginal gap value of the distocervical measurement points of P1 and P2 and the distal measurement points of P3 and P4 (P = .33 and P = .017, respectively). The highest fracture resistance values were observed in the P5 group (mean: 389.55 ± 22 N) and the P2 group (mean: 322.86 ± 79.38 N), and the lowest values were observed in the P3 group (mean: 219.21 ± 60.74 N). The marginal adaptation of the laminate veneer restorations was not related to the depth of preparation. Mean fracture resistance of laminate veneers with 0.5-mm preparation depth was greater than that of the 0.3-mm and 1-mm preparation depth laminate veneers and those with no preparation.

Randomized controlled clinical study of veneered zirconia abutments for single implant crowns: Clinical, histological, and microbiological outcomes.

OBJECTIVES: To analyze the effect of veneering of the submucosal part of zirconia abutments and the type of retention (cemented vs screw-retained) on clinical, microbiological, and histological outcomes of single-tooth implant crowns. MATERIAL AND METHODS: A total of 44 patients with a single missing tooth to be replaced by an implant in the anterior region participated in the study. Implants were randomly assigned to receive zirconia-based CAD/CAM reconstructions using either one of four treatment modalities: cement-retained with submucosal veneering (CR-P), cement-retained without submucosal veneering (CR-W), screw-retained with submucosal veneering (SR-P), and screw-retained without submucosal veneering (SR-W). Clinical parameters were assessed at baseline (after crown insertion), at 6 and 12 months. Histological and microbiological analyses were performed at 6 months. Descriptive statistics and the Kruskal-Wallis test were applied. RESULTS: The clinical evaluation revealed, in general, stable peri-implant soft tissues with minimal differences for all measured parameters between the four groups, except for bleeding on probing with the two cemented groups exhibiting higher values at 12 months (35.0% ± 26.5% for CR-W and 25.0% ± 38.8% for CR-P versus 13.1 ± 14.8 for SR-W and 13.0 ± 18.2 for SR-P). The descriptive and semi-quantitative histology showed a trend for a higher inflammatory reaction in the two cemented (a medium to high number of inflammatory cells) compared to the screw-retained groups (low number of inflammatory cells) at 6 months. The microbiological test demonstrated low bacterial counts and a similar distribution in between the groups except for two species (Tannerella forsythia and Peptostreptococcus micros) that were found in higher counts in the cemented groups at 6 months. CONCLUSION: Submucosal veneering of zirconia abutments did not negatively affect the health of the peri-implant tissues. The cemented groups, though, did show a clinical and histological trend to higher levels of inflammation.

In vitro color changes of soft tissues caused by restorative materials.

A crucial factor influencing implant esthetics is the color of the peri-implant mucosa. This in vitro study analyzed the effect of titanium and zirconia with and without veneering ceramic on the color of mucosa of three different thicknesses. Ten pig maxillae were used, and the palatal area was chosen as the test region. To simulate different mucosa thicknesses, connective tissue grafts, 0.5 mm and 1.0 mm thick, were harvested from three additional jaws. Defined mucosa thicknesses were created by placing the grafts under a palatal mucosa flap. Four different test specimens (titanium, titanium veneered with feldspathic ceramic, zirconia, and zirconia veneered with feldspathic ceramic) were placed under the mucosa, and the color of the tissue was evaluated with a spectrophotometer for three different soft tissue thicknesses (1.5, 2.0, and 3.0 mm). The color was compared to mucosa without test specimens, and the color difference (DeltaE) was calculated. All restorative materials induced overall color changes (DeltaE), which diminished with increases in soft tissue thickness. Titanium induced the most prominent color change. Zirconia did not induce visible color changes in 2.0-mm-thick and 3.0-mm-thick mucosa, regardless of whether it was veneered. However, with a mucosa thickness of 3.0 mm, no change in color could be distinguished by the human eye on any specimen. Mucosa thickness is a crucial factor in terms of discoloration caused by different restorative materials. In patients with thinner mucosa, zirconia will show the least color change.

Effect of Preparation Designs on the Prognosis of Porcelain Laminate Veneers: A Systematic Review and Meta-Analysis.

OBJECTIVE: To investigate the association between preparation designs and prognosis of porcelain laminate veneers (PLVs). METHODS: Electronic and manual literature searches were performed in Medline, Embase, CENTRAL, and Scopus databases for randomized controlled trials and retrospective and prospective cohort studies comparing any two of three preparation designs. The quality of the included studies was assessed using the Newcastle-Ottawa scale. Pooled hazard ratios and risk ratios were used to evaluate the difference between two preparation designs. Subgroup analyses, sensitivity analysis, and evaluation of publication bias were performed if possible. RESULTS: Of 415 screened articles, 10 studies with moderate to high quality were included in the meta-analysis. Comparison of preparations with incisal coverage to preparations without coverage revealed a significant result based on time-to-event data (hazard ratio=1.81, 95% confidence interval [CI]=1.18-2.78, I2=12.5%), but the result was insignificant based on dichotomous data (risk ratio=1.04, 95% CI=0.59-1.83, I2=42.3%). The other comparisons between any two of overlap, butt-joint, and window types revealed no statistically significant difference. Subgroup analyses regarding the porcelain materials, location of prosthesis, and tooth vitality could account for only part of the heterogeneity. No evidence of publication bias was observed. CONCLUSIONS: Within the limitation of the present study, it can be concluded that preparation design with incisal coverage for PLVs exhibits an increased failure risk compared to those without incisal coverage. The failure risk of the overlap type may be higher than the butt-joint type but must be validated in further studies.

Zirconia-based versus metal-based single crowns veneered with overpressing ceramic for restoration of posterior endodontically treated teeth: 5-year results of a randomized controlled clinical study.

OBJECTIVES: The aim of this 5-year randomized controlled trial was to compare the longevity and clinical behavior of single posterior crowns made with pressable ceramic on zirconia and on metal frameworks, and if failures occur, to delineate the contributing factors. METHODS: 72 patients, who needed the covering of at least a molar and/or premolar, were included in the study. All teeth were endodontically treated, with absence of periapical lesion or active periodontitis. Ninety single crowns were made with zirconia or metal framework and covered with pressable veneering ceramics. Two independent examiners assessed the survival of restorations at 6 months, 1-4 and 5 years after restoration placement including periapical radiographs, intraoral photographs, and USPHS modified criteria. The statistical analyses were performed with the Kaplan-Meier method. RESULTS: One core fracture occurred in Zircad/Zirpress crowns and one metal ceramic crown was lost for root fracture. Chipping fracture of the veneering ceramic was detected in 2 metal-ceramic crowns and in 3 zirconia-based crowns. The Estimate Cumulative Survival (ECS) and the Estimate Cumulative Success (ECSs) with standard deviation (SE) were respectively 97,73±2,19 and 92,64±4,14 for zirconia-based crowns whereas 97,44±2,39 and 91,11±4,27 for porcelain fused to metal crowns. CONCLUSIONS: The present randomized controlled trial shows that the survival of zirconia-based and metal-based single crowns is similar over a follow-up period of 5 years. No significant differences in esthetic, functional and biological outcomes were demonstrated between the two groups. The main failure mode was the chipping fracture of the veneering ceramic in both materials. Study number on ClinicalTrial.gov NCT02758457. CLINICAL SIGNIFICANCE: According to the results of this clinical study, zirconia-based rehabilitations with overpressing veneering technique represent a valid alternative to metal-based for posterior single crown restorations.

Facing the challenges of ceramic veneers.

Ceramic veneers are extremely popular and have been used for many years. In spite of their phenomenal success, they offer numerous challenges during service. In this column, I have identified and discussed several degenerative situations commonly observed, and I have described methods of preventing or reducing the problems. When properly placed, ceramic veneers are among the most beautiful and long-lasting of all dental restorations.

Direct anterior composite veneers in vital and non-vital teeth: a retrospective clinical evaluation.

OBJECTIVES: This retrospective, longitudinal clinical study investigated the performance of direct veneers using different composites (microfilled×universal) in vital or non-vital anterior teeth. METHODS: Records from 86 patients were retrieved from a Dental School clinic, comprising 196 direct veneers to be evaluated. The FDI criteria were used to assess the clinical evaluation. The survival analysis was done using Kaplan-Meier method and Log-Rank test. The multivariate Cox regression with shared frailty was used to investigate the factors associated with failure. RESULTS: A total of 196 veneers were evaluated, with 39 failures. The mean time of service for the veneers was 3.5 years, with a general survival rate of 80.1%. In the qualitative evaluation of the restorations, microfilled composite showed slighty better esthetics. The annual failure rates (AFR) were 4.9% for veneers in vital teeth and 9.8% for non-vital teeth with statistical significance (p=0.009). For microfilled and universal veneers the respective AFRs were 6.0% and 6.2% (p>0.05). Veneers made in non-vital teeth had a higher risk of failure over time compared to those made in vital teeth (HR 2.78; 95% CI 1.02-7.56), but the type of material was not a significant factor (p=0.991). The main reason for failure was fracture of the veneer. CONCLUSION: Direct composite veneers showed a satisfactory clinical performance. Veneers performed in vital teeth showed a better performance than those placed in non-vital teeth. No difference in the survival rate for different composites was found, although microfilled composites showed a slightly better esthetic appearance. CLINICAL SIGNIFICANCE: Direct composite veneers show good results in esthetic dentistry nowadays. Composite veneers in vital teeth have a lower risk of failure than those in non-vital teeth.

A randomized controlled clinical trial of 3-unit posterior zirconia-ceramic fixed dental prostheses (FDP) with layered or pressed veneering ceramics: 3-year results.

OBJECTIVES: The aim of the present pilot study was to test whether or not posterior zirconia-ceramic fixed dental prostheses (FDPs) with pressed veneering ceramic exhibit less chipping than FDPs with layered veneering ceramics. METHODS: Forty patients (13 female, 27 male; mean age 54 years (range 26.1-80.7 years) in need of one maxillary or mandibular three-unit FDP in the second premolar or molar region were recruited and treated at two separate centers at the University of Zurich according to the same study protocol. The frameworks were made out of zirconia using a CAD/CAM system (Cerec Sirona, Bensheim, Germany). The patients were randomly assigned to either the test group (zirconia frameworks veneered with pressed ceramic; IPS e.max ZirPress, Ivoclar Vivadent AG, Schaan, Liechtenstein; n=20) or the control group (layered veneering ceramic; IPS e.max Ceram, Ivoclar Vivadent AG, Schaan, Liechtenstein; n=20). All FDPs were adhesively cemented and evaluated at baseline (i.e., cementation), at 6 months and at 1 and 3 years of clinical service. The survival of the reconstruction was recorded. The technical outcome was assessed using modified United States Public Health Services (USPHS) criteria. The biologic parameters analyzed at abutment teeth and analogous non-restored teeth included probing pocket depth (PPD), plaque control record (PCR), bleeding on probing (BOP), and tooth vitality (CO2). Data was descriptively analyzed and survival was calculated using Kaplan-Meier statistics. RESULTS: 36 patients (25 female, 11 male; mean age 52.3 years) with 18 test and 18 control FDPs were examined after a mean follow-up of 36 months (95% CI: 32.6-39.1 months). Comparison of groups was done by Crosstabulation showing even distribution of the respective restored teeth amidst the groups. Survival rate was 100% for both test and control FDPs. Chipping of the veneering ceramic tended to occur more frequently in test (n=8; 40%) than in control (n=4; 20%) FDPs, albeit not significantly (p=0.3). No further differences of the technical outcomes of test and control FDPs occurred.In both test and control group healthy conditions and no difference of the biologic parameters at the abutment and un-restored teeth was found. CONCLUSION: Zirconia FDPs with pressed and layered veneering ceramics exhibited similar outcomes at 3 years. A trend to more chipping of the pressed veneering ceramic, however, was observed. CLINICAL SIGNIFICANCE: Posterior restorations with zirconia frameworks are a viable treatment method. When restoring posterior teeth with all-ceramic restorations, care providers should be aware of the higher rate of chipping compared to the published data on conventional metal-ceramic restorations.

Balancing the risks and benefits associated with cosmetic dentistry - a joint statement by UK specialist dental societies.

Cosmetic dentistry has become increasingly popular, largely as a result of social trends and increased media coverage. This understandable desire for the alleged 'perfect smile' needs to be tempered with an appropriate awareness of the significant risks associated with invasive cosmetic procedures such as veneers and crowns. Patients need to be properly informed that elective removal of healthy enamel and dentine can result in pulpal injury and poorer periodontal health in the longer term, particularly if they are young. The duty of candour means that they ought to be informed that aggressive reduction of sound tooth tissue is not biologically neutral and results in structural weakening of their teeth. Less invasive procedures such as bleaching on its own or for example, combined with direct resin composite bonding, can satisfy many patient's demands, while still being kinder to teeth and having much better fall-back positions for their future requirements. It is the opinion of the British Endodontic Society, British Society for Restorative Dentistry, Restorative Dentistry UK, Dental Trauma UK, British Society of Prosthodontics and the British Society of Paediatric Dentistry that elective invasive cosmetic dental treatments can result in great benefit to patients, but that some aggressive treatments used to achieve them can produce significant morbidities in teeth which were previously healthy. This is a worrying and growing problem with many ethical, legal and biologic aspects, but many adverse outcomes for patients who request cosmetic dental improvements are preventable by using biologically safer initial approaches to treatment planning and its provision.

The influence of direct composite additions for the correction of tooth form and/or position on periodontal health. A retrospective study.

The aim of this in vivo study was to evaluate the influence of 5- to 6-year-old direct composite additions on the marginal periodontal tissues. Composite additions were directly placed on 79 intact maxillary anterior teeth in 19 patients (12 to 19 years) by one operator using an ultrafine midway-filled densified resin composite. All patients were recalled 5 to 6 years later for a periodontal evaluation. Plaque index, gingivitis index, and probing depth were measured at the buccal-approximal sites of all unilaterally restored teeth (n=51). An intra-individual comparison was made between the periodontal health of the treated versus the intact sites. The plaque index (P=0.029) and gingivitis index (P=0.008) were significantly higher for the treated sites compared to the intact sites. The difference in probing depth nearly reached the level of significance (P=0.059). In conclusion, 5-to 6-year-old direct composite additions have a negative influence on marginal periodontal health, which consisted of increased plaque retention, gingival inflammation, and periodontal destruction.

Porcelain veneers: a review of the literature.

OBJECTIVES: Porcelain veneers are steadily increasing in popularity among today's dental practitioners for conservative restoration of unaesthetic anterior teeth. As with any new procedure, in vitro and in vivo investigations are required to assess the ultimate clinical efficacy of these restorations. The current literature was therefore reviewed in search for the most important parameters determining the long-term success of porcelain veneers. DATA SOURCES: Laboratory studies focusing on parameters in prediction of the clinical efficacy of porcelain veneers such as the tooth preparation for porcelain veneers, the selection and type of the adhesive system, the quality of marginal adaptation, the resistance against microleakage, the periodontal response, and the aesthetic characteristics of the restorations have been reviewed. The clinical relevance of these parameters was then determined by reviewing the results of short and medium to long-term in vivo studies involving porcelain veneers performed during the last 10 years. CONCLUSIONS: The adhesive porcelain veneer complex has been proven to be a very strong complex in vitro and in vivo. An optimal bonded restoration was achieved especially if the preparation was located completely in enamel, if correct adhesive treatment procedures were carried out and if a suitable luting composite was selected. The maintenance of aesthetics of porcelain veneers in the medium to long term was excellent, patient satisfaction was high and porcelain veneers had no adverse effects on gingival health inpatients with an optimal oral hygiene. Major shortcomings of the porcelain veneer system were described as a relatively large marginal discrepancy, and an insufficient wear resistance of the luting composite. Although these shortcomings had no direct impact on the clinical success of porcelain veneers in the medium term, their influence on the overall clinical performance in the long term is still unknown and therefore needs further study.

Six-year follow-up with Empress veneers.

This study reports on 6 years experience with IPS Empress laminate veneers. A total of 83 anterior veneers were positioned in 21 patients from January 1991 to December 1996 in the author's private practice. Final evaluation was carried out in May and June 1997. Color match, marginal discoloration, recurrent caries, contour, and marginal integrity were evaluated using the modified U.S. Public Health Service criteria at baseline and subsequent recall appointments. On the basis of the criteria used, a large percentage of veneers were rated Alfa. Only one failure was recorded, resulting in a success rate of 98.8%. A thorough description of clinical procedures and laboratory techniques through which anterior teeth can be successfully treated with ceramic veneers is supplied. A clinical case is presented to demonstrate the satisfactory esthetic results obtained using this very conservative restorative technique.

The microleakage between alloy and polymeric materials in veneer crowns.

OBJECTIVE: This study investigated the cervical microleakage between a cobalt-chromium (Co-Cr) alloy and four indirect polymeric veneering materials using different adhesive systems. METHOD AND MATERIALS: The Co-Cr-based alloy for fixed prosthesis used in this study (Biosil F, Degussa) was veneered with four different polymeric materials: Artglass, Chromasit, Solidex, and Superacryl. RESULTS: Superacryl produced the highest microleakage score (4 +/- 0.0). The least microleakage at the interface was produced by Artglass (1 +/- 0.816), followed by Chromasit (2 +/- 1.414) and Solidex (2.5 +/- 1.0). Only the differences between Artglass and Superacryl were significant. CONCLUSION: Within the limitations of this in vitro study, cervical microleakage between the coping and the veneer depended on the particular polymeric material used for veneering. Leakage was significantly lower when resin materials were used together with a chemical conditioning system (ie, Artglass/Siloc).