Ceramic partial laminate veneers in anterior teeth: A literature review

STUDY SELECTION

Partial laminate veneers, defined as small ceramic restorations adhesively luted onto unprepared anterior teeth, are an interesting and conservative alternative to conventional ceramic and composite resin veneers in the anterior region. This literature review aimed to summarize the available laboratory and clinical data on ceramic partial laminate veneers. An electronic search of the MEDLINE/PubMed, EBSCO, and Web of Science databases was conducted. The keywords used were "partial veneer," "partial laminate veneer," "ceramic fragment," and "sectional veneer." The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. The risk of bias in the included studies was assessed using the QUIN tool.

RESULTS

Of the 266 identified articles, only 16 met the inclusion criteria (ten clinical reports, five laboratory studies, and one retrospective clinical study). To date, no randomized controlled clinical trials have been conducted. Most laboratory studies displayed a low risk of bias, with partial laminate veneers rendering adequate strength and color stability. Clinical reports have shown large variability in material selection, luting, and finishing/polishing protocols.

CONCLUSIONS

Low-quality evidence is available for ceramic partial laminate veneers. Available data from laboratory studies suggest good mechanical and optical performances comparable to those of conventional ceramic and composite resin veneers. Further clinical studies with longer follow-up periods are warranted.

Clinical report and fractographic analysis of a fractured partial laminate veneer

Ceramic partial laminate veneers represent a conservative option for the correction of morphological abnormalities, diastemas, and fractured anterior teeth, with minimal or no tooth preparation. The present clinical report describes the use of a partial laminate veneer to correct the shape of a maxillary right central incisor to match the restoration of the more damaged adjacent tooth. The failure of the partial laminate veneer after only 18 months was analyzed using a systematic fractographic approach, identifying critical considerations that should be addressed when providing this type of restoration.

Contemporary flowable bulk-fill resin-based composites: a systematic review

Flowable bulk-fill resin-based composites (BF-RBCs) represent a new and interesting alternative for the bulk-fill restorative techniques in the posterior region. However, they comprise a heterogeneous group of materials, with important differences in composition and design. Therefore, the aim of the present systematic review was to compare the main properties of flowable BF-RBCs, including their composition, degree of monomer conversion (DC), polymerization shrinkage and shrinkage stress, as well as flexural strength. The search was conducted following PRISMA guidelines in the Medline (PubMed), Scopus and Web of Science databases. In vitro articles reporting on the DC, polymerization shrinkage/shrinkage stress, and flexural strength of flowable BF-RBCs strength were included. The QUIN risk-of-bias (RoB) tool was used for assessing the study quality. From initially 684 found articles, 53 were included. Values for DC ranged between 19.41 and 93.71%, whereas polymerization shrinkage varied between 1.26 and 10.45%. Polymerization shrinkage stresses reported by most studies ranged between 2 and 3 MPa. Flexural strength was above 80 MPa for most materials. A moderate RoB was observed in most studies. Flowable BF-RBCs meet the requirements to be indicated for bulk fill restoration technique in the posterior region. However, important variations among composition and properties hinder extrapolation of the results to materials different from those reported here. Clinical studies are urgently required to assess their performance under a real working scenario.

Premature failure of a screw-retained ceramic single crown: A clinical report and fractographic analysis

Screw-retained implant-supported ceramic restorations have shown increased rates of technical complications compared with their cemented counterparts, including fracture and chipping of the ceramic structures. The present clinical report identified the causes leading to the catastrophic failure of a screw-retained lithium disilicate veneered crown cemented to a zirconia abutment with a titanium base by using a systematic fractographic approach. A combination of occlusal overloading, a deficient design and inadequate material selection was identified as being responsible for the fracture. These findings highlight the importance of a thorough analysis of the anatomic conditions and loading scenario of screw-retained implant-supported restorations.

Solving color irregularities with a bioactive bulk-fill restorative system: Case report and 24-months follow up

Bulk-fill resin composites represent an excellent alternative to the conventional incremental layering technique for the reduction of polymerization stress on the adhesive interface. Marginal seal can be further improved by the incorporation of bioactive fillers, such as those encountered in Giomers. However, the high translucency required for the adequate polymerization of bulk-fill materials can seriously jeopardize the final aesthetic outcome of the restorations, especially in the presence of inhomogeneous or stained dentin substrates. The aim of this case report was to present the combined use of two bulk-fill Giomer materials (Beautifil Bulk Flowable and Beautifil II LS, Shofu) for the restoration of three posterior maxillary teeth displaying a black stained dentin substrate due to amalgam corrosion products. This technique allowed completion of the restorations with a satisfactory aesthetic and biomimetic outcome. The adequate preservation of the anatomy and function of the three restorations after 24-months follow-up, provides evidence of the enhanced marginal sealing capacity of these bioactive materials and the success of bulk-fill techniques over time.

A robust method for shift detection in time series

We present a robust and nonparametric test for the presence of a changepoint in a time series, based on the two-sample Hodges–Lehmann estimator. We develop new limit theory for a class of statistics based on two-sample U-quantile processes in the case of short-range dependent observations. Using this theory, we derive the asymptotic distribution of our test statistic under the null hypothesis of a constant level. The proposed test shows better overall performance under normal, heavy-tailed and skewed distributions than several other modifications of the popular cumulative sums test based on U-statistics, one-sample U-quantiles or M-estimation. The new theory does not involve moment conditions, so any transform of the observed process can be used to test the stability of higher-order characteristics such as variability, skewness and kurtosis.

Fractographic analysis of lithium silicate crown failures during sintering

The two-step production process of glass-ceramic dental restorations involves a computer-aided design/computer-aided machining step followed by a crystallization firing for the final material properties to be achieved. Certain firing parameters are believed to trigger spontaneous fracture of crowns during the cooling process. In this study, cooling fractures have been reproducibly observed and investigated using fractography combined with material (glass transition temperature) and process (cooling rate) characterization. Stress distribution was visualized using birefringence measurements. Fractographic observations revealed fracture starting at the intaglio side of the crowns specifically at contact points with the support firing pins. Further analysis showed that a fast cooling rate was applied during the glass transition region. Thermal stresses were concentrated around the firing pin supports and released the fracture. To prevent such fractures, a slow cooling protocol below the glass transition temperature is our recommendation to dental technicians. Furthermore, the use of planar firing pad or paste supports is advised over the use of point contact supports.

In vitro lifetime of zirconium dioxide-based crowns veneered using Rapid Layer Technology

Rapid Layer Technology (RLT) uses computer-aided design/computer-aided manufacturing (CAD/CAM) to manufacture a veneer layer that is adhesively bonded to the zirconia framework, avoiding firing steps during the fabrication process and thus preventing build-up of residual stresses. This work studied, using sliding contact fatigue, the in vitro lifetime of restorations produced using RLT compared with restorations produced using conventional veneering techniques. Zirconia copings were veneered with a conventional hand-layering method (VM9) using a fast (n = 16) or a slow (n = 16) cooling protocol, or with RLT. For the latter, the veneers were CAD/CAM fabricated using a feldspathic reinforced-glass (Vitablocs Mark II; n = 16) or a polymer-infiltrated reinforced-glass network (Enamic; n = 16) and adhesively bonded to the zirconia frameworks. Crowns thus obtained were submitted to sliding contact fatigue against a steatite indenter in a chewing simulator until failure. A Kaplan-Meier survival analysis was conducted. None of the hand-layered restorations survived after a 2 × 10⁶ -cycle interval, whereas no fractures in the RLT groups were observed. Vitablocs Mark II veneers survived for a longer testing period (3.5 × 10⁶ cycles) than their Enamic counterparts (2.5 × 10⁶ cycles) owing to their superior wear behavior. The RLT represents an efficient method to veneer zirconia frameworks by reducing processing steps and, more importantly, increasing the lifetime of the restorations.

Practical and theoretical considerations on the fracture toughness testing of dental restorative materials

BACKGROUND

An important tool in materials research, development and characterization regarding mechanical performance is the testing of fracture toughness. A high level of accuracy in executing this sort of test is necessary, with strict requirements given in extensive testing standard documents. Proficiency in quality specimen fabrication and test requires practice and a solid theoretical background, oftentimes overlooked in the dental community.

AIMS

In this review we go through some fundamentals of the fracture mechanics concepts that are relevant to the understanding of fracture toughness testing, and draw attention to critical aspects of practical nature that must be fulfilled for validity and accuracy in results. We describe our experience with some testing methodologies for CAD/CAM materials and discuss advantages and shortcomings of different tests in terms of errors in testing the applicability of the concept of fracture toughness as a single-value material-specific property.

Mixed-mode fracture toughness of texturized LS2 glass-ceramics using the three-point bending with eccentric notch test

Here we use the 3-point bending with eccentric notch test (3-PBEN) to investigate the fracture behavior of a pressable and a CAD/CAM lithium disilicate (LS₂) glass-ceramics under combined mode-I and mode-II loading. The effect of the bulk texturization in the beams of the pressable LS₂ is made visible through the fracture trajectory following the most energetically favorable path dictated by the crystallite alignment. The CAD/CAM LS₂ shows an isotropic fracture mode but increasing fracture energy with mode-II contribution, similar to the pressable variant.

Chairside CAD/CAM materials. Part 2: Flexural strength testing

OBJECTIVE

Strength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory.

METHODS

Eight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12×12×1.2mm³) or round disc (Ø=12mm, thickness=1.2mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens.

RESULTS

A good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9MPa (Vitablocs Mark II) to 1303.21MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface.

SIGNIFICANCE

The B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry.

Repair Bond Strength of Aged Resin Composite after Different Surface and Bonding Treatments

The aim of this study was to compare the effect of different mechanical surface treatments and chemical bonding protocols on the tensile bond strength (TBS) of aged composite. Bar specimens were produced using a nanohybrid resin composite and aged in distilled water for 30 days. Different surface treatments (diamond bur, phosphoric acid, silane, and sandblasting with Al₂O₃ or CoJet Sand), as well as bonding protocols (Primer/Adhesive) were used prior to application of the repair composite. TBS of the specimens was measured and the results were analyzed using analysis of variance (ANOVA) and the Student-Newman-Keuls test (α = 0.05). Mechanically treated surfaces were characterized under SEM and by profilometry. The effect of water aging on the degree of conversion was measured by means of FTIR-ATR spectroscopy. An important increase in the degree of conversion was observed after aging. No significant differences in TBS were observed among the mechanical surface treatments, despite variations in surface roughness profiles. Phosphoric acid etching significantly improved repair bond strength values. The cohesive TBS of the material was only reached using resin bonding agents. Application of an intermediate bonding system plays a key role in achieving reliable repair bond strengths, whereas the kind of mechanical surface treatment appears to play a secondary role.

Students' and general practitioners' perceptions of a recently introduced clerkship in general practice. A survey from Austria

BACKGROUND

In autumn 2007, the Medical University of Graz (MUG) upgraded the status of general practice in medical training by integrating a compulsory five-week clerkship in general practice surgeries in the sixth and last year of the curriculum. In cooperation with the Styrian Academy of General Practice (STAFAM), more than 200 general practitioners (GPs) had been accredited to introduce medical students to the specific tasks, problems and decision-making process in general practice. Between October 2007 and June 2009, more than 300 students completed the clerkship.

OBJECTIVE

To explore the perceptions of students and GPs towards this new approach to undergraduate teaching in Austrian general practice.

METHODS

Between March and June 2009, we conducted a cross-sectional survey by using a self-administered questionnaire with 14 items for students as well as GPs. To limit recall bias, we gave the questionnaire to all students (n = 146) and GPs (n = 146) immediately after the clerkship. The response rates were 146/146 (100%) and 114/146 (78%) for students and GPs, respectively.

RESULTS

The study results show high satisfaction rates among students as well as GPs. Most of the students and GPs perceive the compulsory clerkship in general practice as an essential part of medical education. The organization of the clerkship had the least positive outcome.

CONCLUSION

Our survey shows that the clerkship is well accepted among Austrian medical students and GPs.

[Effect of surgery on inflammation parameters]

Of 27 patients undergoing major surgical procedures--mainly orthopaedic ones--we took the temperature, blood sedimentation rate, total white blood cell count, fraction of immature to total neutrophils (I:T proportion) and C-reactive protein. With the exception of the I:T proportion all unspecific indicators of inflammation showed an increase after the operation. Therefore, the I:T proportion is the most reliable parameter for the postoperative control of infections, since it is not subject to surgical trauma.