An in vitro assessment of the strength of porcelain veneers dependent on tooth preparation

Assessment of the Accuracy in Measuring the Enamel Thickness of Maxillary Incisors with Optical Coherence Tomography

Although the clinical assessment of enamel thickness is important, hardly any tools exist for accurate measurements. The purpose of this study was to verify the precision of enamel thickness measurements using swept-source optical coherence tomography (SS-OCT). Human extracted maxillary central and lateral incisors were used as specimens. Twenty-eight sites were measured in each specimen. The optical path length (OPL) at each measurement site was measured on the OCT images, and enamel thickness (e1) was calculated by dividing OPL by the mean refractive index of enamel, 1.63. The specimens were then sectioned, and a light microscope was used to measure enamel thickness (e2). e1 and e2 were then compared. Measurement errors between e1 and e2 for the central and lateral incisors were 0.04 (0.02; 0.06) mm and 0.04 (0.02; 0.07) mm [median value: (25%, 75% percentile)], respectively. No significant differences between measurement sites were noted for measurement errors between e1 and e2. These results demonstrate that OCT can be used for noninvasive, accurate measurements of enamel thickness.

Marginal discrepancy and load to fracture of monolithic zirconia laminate veneers: The effect of preparation design and sintering protocol

To investigate and analyze the impact of teeth preparation designs and sintering protocol on marginal fit and fracture resistance of monolithic translucent zirconia laminate veneers. A total of 40 extracted intact human maxillary central incisors were assigned into 4 groups (n=10/each group) to investigate 2 variables: (1) the design of tooth preparation (a 1.5 mm incisal reduction with or without palatal chamfer) and (2) the two different sintering programs used for translucent zirconia restoration (standard or speed sintering procedure). Marginal discrepancy was evaluated using a digital microscope. The specimens were loaded to failure in the compression mode, using a universal testing machine with a crosshead speed of 0.5 mm/min. Marginal adaptation of monolithic translucent zirconia laminates are affected by both tooth preparation design and sintering protocol. However, resistance to fracture of translucent zirconia laminates has affected mainly by sintering procedure regardless the teeth preparation design used.

The Success of Dental Veneers According To Preparation Design and Material Type

BACKGROUND:

Due to their high aesthetic outcome and long-term predictability, laminate veneers have become a common restorative procedure for anterior teeth. However, because of the variety in the preparation designs and the material types, the clinician faces a dilemma of which approach to use.

AIM:

To compare the survival rate of dental veneers according to different preparation designs and different material types. The sub-aim is to reach a favourable preparation design and material based on scientific evidence.

METHODS:

Comprehensive electronic search of the dental literature via PUBMED, MEDLINE and Scopus databases was performed using the following keywords: “porcelain veneers”, “composite veneers”, “all-ceramic veneers”, “success of porcelain veneers”, “preparation design”, “preparation geometry”, “patient’s satisfaction”. Additionally, references from the selected studies and reviews were searched for more information.

RESULTS:

Under the limitations of the available literature, the clinician preference is the decisive factor for choosing the preparation design. Nonetheless, incisal overlap preparation seems to have the most predictable outcome from all the preparation designs.

CONCLUSION:

Porcelain veneers show excellent aesthetic results and predictable longevity of the treatment, while composite veneers can be considered as a good conservative option, but with less durability.

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.

Thermal-stress analysis of ceramic laminate veneer restorations with different incisal preparations using micro-computed tomography-based 3D finite element models

Main objective of this study is to investigate the thermal behavior of ceramic laminate veneer restorations of the maxillary central incisor with different incisal preparations such as butt joint and palatinal chamfer using finite element method. In addition, it is also aimed to understand the effect of different thermal loads which simulates hot and cold liquid imbibing in the mouth. Three-dimensional solid models of the sound tooth and prepared veneer restorations were obtained using micro-computed tomography images. Each ceramic veneer restoration was made up of ceramic, luting resin cement and adhesive layer which were generated based on the scanned images using computer-aided design software. Our solid model also included the remaining dental tissues such as periodontal ligament and surrounding cortical and spongy bones. Time-dependent linear thermal analyses were carried out to compare temperature changes and stress distributions of the sound and restored tooth models. The liquid is firstly in contact with the crown area where the maximum stresses were obtained. For the restorations, stresses on palatinal surfaces were found larger than buccal surfaces. Through interior tissues, the effect of thermal load diminished and smaller stress distributions were obtained near pulp and root-dentin regions. We found that the palatinal chamfer restoration presents comparatively larger stresses than the butt joint preparation. In addition, cold thermal loading showed larger temperature changes and stress distributions than those of hot thermal loading independent from the restoration technique.

Survival rates of porcelain laminate restoration based on different incisal preparation designs: An analysis

Background:

Veneer restorations provide a valid conservative alternative to complete coverage as they avoid aggressive dental preparation; thus, maintaining tooth structure. Initially, laminates were placed on the unprepared tooth surface. Although there is as yet no consensus as to whether or not teeth should be prepared for laminate veneers, currently, more conservative preparations have been advocated. Because of their esthetic appeal, biocompatibility and adherence to the physiology of minimal-invasive dentistry, porcelain laminate veneers have now become a restoration of choice. Currently, there is a lack of clinical consensus regarding the type of design preferred for laminates. Widely varying survival rates and methods for its estimation have been reported for porcelain veneers over approximately 2–10 years. Relatively few studies have been reported in the literature that use survival estimates, which allow for valid study comparisons between the types of preparation designs used. No survival analysis has been undertaken for the designs used. The purpose of this article is to attempt to review the survival rates of veneers based on different incisal preparation designs from both clinical and non-clinical studies.

Aims and Objectives:

The purpose of this study is to review both clinical and non-clinical studies to determine the survival rates of veneers based on different incisal preparation designs. A further objective of the study is to understand which is the most successful design in terms of preparation.

Materials and Methods

This study evaluated the existing literature – survival rates of veneers based on incisal preparation designs. The search strategy involved MEDLINE, BITTORRENT and other databases.

Statistical Analysis

Data were tabulated. Because of variability in the follow-up period in different studies, the follow-up period was extrapolated to 10 years in common for all of them. Accordingly, the failure rate was then estimated and The weighted mean was computed.

Conclusions

The study found that the window preparation was of the most conservative type. Incisal coverage was better than no incisal coverage and, in incisal coverage, two predictable designs – incisal overlap and butt were reported. In butt preparation, no long-term follow-up studies have been performed as yet. In general, incisal overlap was preferred for healthy normal tooth with sufficient thickness and incisal butt preparation was preferred for worn tooth and fractured teeth.

Alumina-reinforced zirconia implants: survival rate and fracture strength in a masticatory simulation trial

BACKGROUND

Alumina-toughened zirconia (ATZ) is a possible alternative material to titanium for oral implants. No data are available on the fracture strength of ATZ oral implants.

PURPOSE

The purpose of this study was to examine one-piece implants made of ATZ ceramic under artificial loading conditions and to compare the fracture strength of these implants with implants fabricated from tetragonal zirconium dioxide poylcrystal (TZP)-A.

MATERIALS AND METHODS

A total of 72 implants, 48 ATZ implants (groups A and B) and 24 TZP-A implants (group C), were investigated. A chamfer preparation at the implant heads was performed on all implants of groups B and C. Eight implants of each group underwent 1.2 or five million thermomechanical loading cycles in the chewing simulator (load value: 98 N). Further eight implants of each group were not cyclic loaded. Finally, the fracture strength of all implants was determined using a universal testing machine.

RESULTS

No implant fractured during loading in the chewing simulator. All implants were placed in the universal testing machine to evaluate fracture strength. The mean fracture strength values±standard deviations for the implants without artificial loading were 1734±165 N (ATZ, no preparation), 1220±85 N (ATZ, with preparation), and 578±49 N (TZP-A, with preparation); 1489±190 N (ATZ, no preparation), 1064±121 N (ATZ, with preparation), and 607±57 N (TZP-A, with preparation) with 1.2 million loading cycles; and 1358±187 N (ATZ, no preparation), 1098±97 N (ATZ, with preparation), and 516±45 N (TZP-A, with preparation) with five million cycles. The ATZ implants showed significantly higher mean fracture strengths compared with the TZP-A implants. Modification of the implant head using diamond burs and increased loading time also led to a significant decrease in fracture strength.

CONCLUSIONS

The ATZ implants showed an increased mechanical stability compared with the TZP-A. Modification of the implant head resulted in a decrease in fracture strength. However, within the limits of this in vitro investigation it can be concluded that ATZ implants will withstand functional loading over an estimated period of 20 years.

Compressive Fracture Resistance of Porcelain Laminates Bonded to Enamel or Dentin with Four Adhesive Systems

PURPOSE

To measure the compressive strength of porcelain laminates of 0.5 or 1.0 mm thickness when bonded to enamel or dentin using these resin cements: All-Bond 2 + Choice, Panavia 21, Scotchbond + Opal, and Super-Bond C&B.

MATERIALS AND METHODS

The buccal and lingual aspects of human molars were sectioned to prepare specimens at least 3 x 3 x 3 mm in size. Thirty horizontally flat enamel surfaces were prepared with a diamond disc for each group using a milling machine. Ten enamel specimens were randomly selected to test the fracture strength of 0.5-mm thick porcelain laminates without resin cement, and the data were recorded for a control group. The enamel specimens of each group were divided into two subgroups of 15 specimens to bond with either 0.5- or 1.0-mm thick porcelain laminates. Four resin cements were used for bonding of individual groups. All bonded specimens were stored in 37 degrees C for 24 hours before fracture testing. The horizontally flat dentin surfaces were prepared on the fractured bonded specimens using a diamond disc for each group. Ten 0.5 mm porcelain laminates were randomly selected to test the fracture strength on dentin (control group). The bonded laminates to dentin were prepared using the same procedure as for enamel. The fracture strengths were statistically analyzed at alpha= 0.05.

RESULTS

Statistically significant differences in mean fracture strengths between groups were revealed. No significant difference in fracture strengths of control specimens between enamel and dentin was found. Super-Bond C&B provided a higher fracture resistance of porcelain than the other resin cements. Increasing the thickness of porcelain laminate increased the fracture strength. The 0.5-mm thick porcelain bonded to enamel had higher fracture strength than that of 1.0-mm thick porcelain bonded to dentin when using Super-Bond C&B and Scotchbond + Opal cements.

CONCLUSIONS

Bonding techniques and curing systems of resin cements influenced the fracture resistance of porcelain laminates. Dry bonding with auto-polymerization of Super-Bond C&B resin provided the highest fracture resistance of porcelain. Porcelain bonded to enamel with this resin had a much higher fracture strength than when bonded to dentin.

Fracture strength of direct versus indirect laminates with and without fiber application at the cementation interface

OBJECTIVES

This study compared the fracture strength of direct and indirect resin composite laminate veneers and evaluated the effect of a bidirectional E-glass woven fiber application at different locations at the cementation interface.

METHODS

Standard preparations on canines (N=50, 10 per group) were made using a depth cutting bur (0.7mm depth) designed for laminate veneer restorations. Forty indirect laminates using a highly filled polymeric material (Estenia) and 10 direct laminates (Quadrant Anterior Shine) were prepared according to the manufacturer's instructions. Bidirectional E-glass woven-fiber sheet (0.06mm) (Everstick) was applied at different locations at the cementation interface. The control group received no fibers. The specimens were stored in water at 37 degrees C for 1 month prior to fracture testing performed in a universal testing machine where the load was applied from the incisal direction at 137 degrees (1mm/min).

RESULTS

No significant differences were found between the five groups (P>0.01) (one-way ANOVA). While indirect laminate veneers showed mean fracture strength of 247+/-47N, direct laminate veneers revealed 239+/-104N. The use of E-glass fibers at the cementation interface at different locations did not increase the fracture strength significantly (286-313N) (P>0.01). Failure analysis showed mainly cohesive fracture of the veneer restoration (20/50) and adhesive failure between the cementation interface and the laminate with fiber exposure (19/50) covering more than half of the restorations.

SIGNIFICANCE

Direct and indirect resin composite laminate veneers showed comparable mean fracture strengths. The use of E-glass woven-fiber sheet at the cementation interface did not increase the fracture strength of the polymeric laminate veneers.

Influence of tooth preparation design on the stress distribution in maxillary central incisors restored by means of alumina porcelain veneers: A 3D-finite element analysis

AIM

The present study aimed at providing 3D-FEA engineering tools for the understanding of the influence of tooth preparation design on the stress distribution and localization of critical sites in maxillary central incisors restored by means of alumina porcelain veneers under functional loading.

METHODS

A 3D-FEM model of a maxillary central incisor is presented. An arbitrary chewing static force of 10 N was applied with an angulation of 60 and 125 degrees to the tooth longitudinal axis at the palatal surface of the crown. The model was considered to be restored by means of alumina porcelain veneers with different tooth preparation designs. The differences in occlusal load transfer ability of the two restorative systems are discussed.

RESULTS

The maximum Von Mises equivalent stress values were observed in the window restorative system for both 125 and 60 degrees load angulations. When the chamfer with palatal overlap preparation was simulated, the stress distributed uniformly in the cement layer, whereas in the window preparation the stress mainly occurred in the incisal area of the cement layer.

SIGNIFICANCE

When restoring a tooth by means of porcelain veneers, the chamfer with palatal overlap preparation better restores the natural stress distribution under load than the window technique.

Survival rate and fracture strength of maxillary incisors, restored with different kinds of full veneers

This in vitro study evaluated the survival rate and fracture strength of different kinds of ceramic full veneers, fabricated with a new experimental press ceramic (EPC VP2117/TC2, Ivoclar-Vivadent AG, Schaan, Liechtenstein). Eighty, caries-free human maxillary central incisors were used as abutments and were randomly divided into one control group and four test-groups of 16 samples each. In group A, unprepared teeth served as control. In the test groups, four different types of full veneer preparations were performed. In test groups B/C, the preparation was maintained in enamel and the contact point was on the tooth/on the veneer, respectively. In test groups D/E, the preparation was extended into dentin and the contact point was on the tooth/on the veneer, respectively. All veneers were adhesively luted using Variolink II (Ivoclar-Vivadent AG). Then, the samples were exposed to the artificial mouth for 1.2 million chewing cycles (49 N). After exposure in the artificial mouth, a survival rate of the abutment teeth of 81-100% was reported among the different groups, but was not significantly different between the groups. However, no failures of the ceramic materials could be recognized. The median fracture strength of group A was 713.3 N, of group B 647.1 N, of group C 594.8 N, of group D 483.8 N and of group E 502.6 N. Among the different groups no significant difference was found. All mean values obtained were within the limits of clinical acceptance, indicating further clinical investigations on full veneers made out of the EPC.