A comparison of the effects of incremental and snowplow techniques on the mechanical properties of composite restorations.

BACKGROUND: Glass fibre-reinforced composite (GFRC) has the potential to enhance the mechanical properties of resin-based restorations. Nevertheless, the application technique can influence the cervical margin porosity, potentially reducing the mechanical strength of restorations. METHODS: In an in vitro setup, mould specimens underwent six different treatments to assess the effects of snowplow and incremental curing techniques on the properties of GFRC (EverX) and universal resin composite (Filtek). Mechanical properties, namely flexural strength (FS), compressive strength (CS) and Vickers hardness (VH), were evaluated following ISO 4049 standards. Data interpretation utilized the Kruskal-Wallis tests. RESULTS: No significant difference emerged across groups for FS. CS in the snowplow method with lesser EverX thickness (SnPl_1) was comparable with only EverX and Filtek (P > 0.05). The CS was reduced in the snowplow technique with greater EverX thickness (SnPl_2) (P < 0.05) and further decreased with the incremental method (P < 0.001). VH results showed that EverX Posterior was consistently softer than Filtek, with specific patterns of hardness variations among different application methods. CONCLUSIONS: Applying EverX and Filtek using the snowplow technique delivers superior CS and VH for restorations in contrast to the incremental method. Utilizing the snowplow approach in high-stress areas can make restorations more fracture-resistant.

Effect of color shading procedures and cyclic loading on the biaxial flexural strength of zirconia.

PURPOSE: Zirconia is the most preferred ceramic restoration in posterior areas because of its flexural strength. The aim of the study is the evaluation of biaxial flexural strength of different colored zirconium oxide core materials after cyclic loading. MATERIAL AND METHODS: Zirconia discs (12 mm diameter and 1.2 mm thickness) were divided into 6 groups of 12 discs each. Groups were colored according to the Vita Classic shade guide: A3 and D4. One group was not colored and left as control. Each group was randomly divided into subgroups and subjected to mechanical cycling prior to biaxial flexural strength test. Cyclic loading was applied as 50 N loads for 20,000 times for the loaded groups. Samples were subjected to biaxial flexural strength test in a universal testing machine with a crosshead speed of 1 mm/min. Two-way analysis of variance (ANOVA) and Tukey's HSD tests were used for comparisons of the groups. RESULTS: Biaxial flexural strength values did not vary significantly depending on coloring procedure or loading process tested (p>.05). XRD analysis displayed that the monoclinic volume fraction of zirconia was highest in cyclic loaded D4 and was lowest in non-loaded control group. The SEM image revealed that A3 color solution created metallic coloring pigments at grain boundaries. CONCLUSIONS: Coloring procedures and cyclic loading did not affect the biaxial flexural strength of zirconia core material; however, microstructural analysis displays changes, which may weaken the zirconia structure on the long term.

The translucency effect of different colored resin cements used with zirconia core and titanium abutments.

PURPOSE: The purpose of this study was to evaluate the effect of the different color of resin cements and zirconia cores on the translucency parameter (TP) of the restoration that simulates the implant-supported fixed prosthesis using titanium base on the bottom. MATERIALS AND METHODS: Zirconia core plates (Zr-Zahn) were prepared in A2 shades (n = 11). Resin cement plates (3M ESPE) were prepared in A2, A1, translucent (TR) shades (n = 11). The initial color measurements and were measured on zirconia core plates, and resin cements plates using a spectrophotometer. Then, the resin cement plates were placed below the zirconia core plates, and the second measurements were done. The final measurements were done after placing the titanium discs in the bottom. The data were analyzed with two-way analysis of variance and Tukey honestly significant differences tests (α = 0.05). RESULTS: The highest TP values were recorded for A1-colored resin specimens and the lowest for zirconia core plates in the first measurement (P < 0.05). The addition of zirconia core decreased the TP values in all tested resin cement groups (P < 0.05). The highest TP value was recorded for A1-colored resin cement with zirconia core plates and the lowest for A2 and TR with zirconia core plates after second measurements (P < 0.05). The addition of titanium decreased the TP of the zirconia core plate and resin cement combination (P < 0.05). CONCLUSIONS: The addition of a zirconia core under the resin cement dramatically reduced the TP values, and the presence of a titanium layer decreased the TP value and caused a darker appearance.

Comparison of four different techniques for performing an osteotomy: a biomechanical, radiological and histological study on rabbits tibias.

This animal study compares different methods of performing an osteotomy, including using an Erbium-doped Yttrium Aluminum Garnet laser, histologically, radiologically and biomechanically. A total of 24 New Zealand rabbits were divided into four groups (Group I: multihole-drilling; Group II: Gigli saw; Group III: electrical saw blade and Group IV: laser). A proximal transverse diaphyseal osteotomy was performed on the right tibias of the rabbits after the application of a circular external fixator. The rabbits were killed six weeks after the procedure, the operated tibias were resected and radiographs taken. The specimens were tested biomechanically using three-point bending forces, and four tibias from each group were examined histologically. Outcome parameters were the biomechanical stability of the tibias as assessed by the failure to load and radiographic and histological examination of the osteotomy site. The osteotomies healed in all specimens both radiographically and histologically. The differences in the mean radiographic (p = 0.568) and histological (p = 0.71) scores, and in the mean failure loads (p = 0.180) were not statistically significant between the groups. Different methods of performing an osteotomy give similar quality of union. The laser osteotomy, which is not widely used in orthopaedics is an alternative to the current methods.

Is the value of oral health related to culture and environment, or function and aesthetics?

OBJECTIVE: To examine the disutility of tooth loss. It compared how people value their teeth in two countries which are culturally similar in order to explore the effect of culture on self-perceptions of oral health. BASIC RESEARCH DESIGN: Cross sectional study. PARTICIPANTS: Participants were recruited from subjects attending two hospitals in Turkey and in Iran. INTERVENTIONS: Nineteen descriptions of mouths with varying degrees and types of tooth loss were presented to the participants. They were shown mouth models of partially edentate dentitions and the teeth missing were explained in relation to the participants own mouth. The participants were specifically asked to consider the role their teeth played in function (chewing), communication (speech) and aesthetics (looks) along with "all the other things that make your mouth important". MAIN OUTCOME MEASURES: The participants were asked to indicate on a visual analogue scale how they would value the health of their mouth if they lost the tooth/teeth described and the resultant space was left unrestored. RESULTS: Overall 152 subjects participated, 78 in Turkey and 74 in Iran with 83 being female and 69 male. Their mean age was 29.5 years (SD 9.3), 62.5% had experienced tooth loss and 37.5% had complete (or completely restored) dentitions. Although there were no differences between the two countries in the degree of utility people attached to anterior teeth, Turkish participants attached significantly more disutility than Iranians to the loss of premolar and molar teeth (p < 0.003). CONCLUSION: Country of origin had an influence on the value placed on certain parts of the dentition and this effect is independent of the number of missing teeth, gender and age. This implies that attitudes to oral health are influenced by prevalent cultural attitudes more than by function.

Effect of dentin desensitizing procedures on methyl methacrylate diffusion through dentin.

BACKGROUND: Acrylic and bisacryl resins are widely used both during the temporization phase as well as for provisional restorations and the effect of external agents on dentin sensitivity can be reduced by the obliteration of the tubules. OBJECTIVE: The purpose of this study was to evaluate diffusion of methyl methacrylate monomer through dentin by high performance liquid chromatography (HPLC) after three different desensitizing procedures during the fabrication of two different provisional crown materials. MATERIALS AND METHODS: Forty extracted restoration and caries free human premolar teeth were used in this study. Thermoplastic vacuum formed material was used as a matrix to fabricate provisional restorations for each tooth before crown preparation. Teeth were prepared for a metal supported ceramic crown with 1 mm shoulder margins and then crown parts were separated from cementoenamel junction with a carborundum disk perpendicular to the long axis of the teeth. To the cementoenamel junction of each tooth a polypropylene chamber was attached that contains 1.5 cm 3 of deionized distilled water. Prepared teeth were divided into four groups ( n = 10) including control, desensitizing agent (DA) application, neodymium-doped yttrium aluminum garnet (Nd: YAG) laser irradiation (LI), and LI after DA application groups. After application of DA (except control) each group were divided into two subgroups for fabrication of provisional restorations ( n = 5). Two autopolymerizing provisional materials (Imident (Imicryl) and Systemp C and B (Ivoclar, vivadent)) were used to fabricate provisional restorations using the strips. Water elutes were analyzed by HPLC at 10 min and 24 h. RESULTS: The monomer diffusion values varied statistically according to desensitizing procedures, provisional resin systems, and the time periods. Monomer diffusion through dentin surfaces desensitized with Nd: YAG LI after DA application was the lowest. CONCLUSIONS: Nd: YAG LI in association with DA application is an effective combination to eliminate monomer diffusion through dentin to pulpal chamber.

The effect of repeated firings on the color of an alumina ceramic system with two different veneering porcelain shades.

STATEMENT OF PROBLEM: Possible sources of processing variables in porcelain firing include thickness and color of the opaque; thickness, color, and translucency of the body and enamel layers; firing temperature; and number of firings. PURPOSE: The purpose of this in vitro study was to investigate the color changes of an alumina ceramic system veneered with different veneering porcelain shades and fired different numbers of times. MATERIAL AND METHODS: Twenty disc-shaped ceramic specimens (10 mm in diameter, with a core thickness of 1 mm), with 2 different veneering porcelain shades (A1, A3), were fabricated from an alumina ceramic system (Turkom-Cera) (n=10). Repeated firings (3, 5, 7, or 9 firings) were performed, and color differences (ΔE) were determined using a spectrophotometer. Repeated-measures ANOVA was used to analyze the data (number of firings, veneering porcelain color). The Duncan test and paired 2-tailed tests were used for multiple comparisons (α=.05). RESULTS: The L*a*b* values of the ceramic system were affected by the number of firings (3, 5, 7, or 9) (P<.005) and veneering porcelain shade (P<.001). Significant interactions were present between the number of firings and the veneering porcelain shade for L* (P=.002), a* (P=.001), and b* (P=.001) values. A1 shade specimens maintained their L* value independent of the number of firings, whereas A3 shade specimens became lighter after an increased number of firings. For both A1 and A3 veneering porcelain shades, the a* value decreased after repeated firings, which resulted in less reddish specimens, and the b* value decreased after repeated firings, which resulted in less yellowish specimens. CONCLUSIONS: Imperceptible (ΔE<1.6) and clinically acceptable color changes (ΔE<3.7) were demonstrated by the alumina ceramic system tested.

Effects of cantilever design and material on stress distribution in fixed partial dentures--a finite element analysis.

The purpose of this study was to examine the stress distribution in distal cantilevered fixed partial dentures (FPDs) that are designed with different cantilever morphology and made from different restorative materials. The finite element (FE) method was used to create models of two restoration types; metal-ceramic and an all-ceramic FPDs. Both models were designed with distal cantilevers involving the first and second premolars as abutments and cantilever extension involving at the premolar or molar. The width of connector between the cantilever and the primary abutment restoration was 2.25 mm. The load applied during the FE analysis was positioned at the cusp tips of all teeth. The FE analysis of the models revealed that Von Mises stress values with maximum stress concentrations were observed on connectors of distal cantilevers. Stress concentration sites were also observed at the distal cervical area of the second premolar tooth. Models with premolar cantilever extensions restored with all-ceramic induced lower Von Mises stress values than metal-ceramic restorations, however models with molar cantilever extensions restored with all-ceramic restorations induced higher Von Misses stress values than metal-ceramic restorations. If the distal cantilever length and restorative material is appropriately chosen, the failure frequency may be reduced. All ceramic can be used as restorative material, when the cantilevers length is not more than the mesiodistal dimension of a premolar tooth and metal-ceramic restorations can be used in longer situations.

Effect of provisional restorations on the final bond strengths of porcelain laminate veneers.

The purpose of this in vitro study was to evaluate the effect of the different provisional restorations cementation techniques on the final bond strengths of porcelain laminate veneers (PLVs). Thirty-six extracted human central incisors were sectioned 2 mm below the cemento-enamel junction, and crown parts were embedded into self-cure acrylic resin. Standardized PLV preparations were carried out on labial surfaces of the teeth. Then the teeth were randomly divided into three groups of 12 each. In group 1, provisional restorations were cemented with eugenol-free cement. In group 2, prepared teeth surfaces were first coated with a desensitizing agent then provisional restorations were cemented with resin cement. In group 3, provisional restorations were not fabricated to serve as control. After specimens were stored in distilled water for 2 weeks, provisional restorations were removed and final IPS Empress 2 ceramic veneers were bonded with a dual-curing resin. Two microtensile samples from each tooth measuring 1.2 x 1.2 x 5 mm were prepared. These sections were subjected to microtensile testing and failure values were recorded. The data were analysed by one-way anova and Tukey HSD tests. The PLVs, placed on the tooth surface that had received a dentine desensitizer and provisional restorations luted with resin cement (group 2), showed the lowest bond strength in all test groups. But no statistically significant differences were found between the bond strength of PLVs in control group (no provisional restorations) and group 1 (provisional restorations cemented with eugenol-free cement before final cementations). Scanning electron microscopic (SEM) examination of this study also showed that the bonding to enamel surface was better in control group and group 1 than group 2.

Influence of different light sources on microtensile bond strength and gap formation of resin cement under porcelain inlay restorations.

Clinical success with ceramic inlays/onlays has been assisted by the ability to develop a reliable bond of composite resin to dental tissues. The purpose of this study was to test the efficiency of two different light sources on microtensile bond strength and the gap formation of resin cement under class II porcelain inlay restorations. Standardized mesio-occlusal cavities were prepared in 30 freshly extracted, intact human premolar teeth. Then impressions were made and ceramic inlays were fabricated. In the cementation process, the resin cement/inlay combinations were exposed to two different photopolymerization units. The polymerizations through 15 specimens were performed with a conventional halogen light source for 60 s, and the other specimens were cured by a plasma arc light for 9 s. After the cementation process, two 1.2 x 1.2 mm wide 'I' shape sections per tooth were produced with a sectioning machine and sections were subjected to microtensile testing after 24 h or 1 week. Gap formation of specimens cured by different photopolymerization units were evaluated with scanning electron microscopy (SEM). Statistically significant differences were found between the microtensile bond strength of inlays exposed to conventional light and plasma arc curing unit (P < 0.001). Plasma arc curing units make it possible to polymerize composite in much shorter times than conventional curing unit. However, the samples polymerized with conventional halogen light produced better microtensile bond strength than the plasma arc unit.

The effect of dentin desensitizers on thermal changes in the pulp chamber during fabrication of provisional restorations.

The purpose of this study was to evaluate the effect of two dentin desensitizers on the pulp chamber temperature increase during fabrication of provisional restorations by a direct method. Sixty intact extracted mandibular third molars were prepared for a metal-ceramic complete crown. Then the teeth were randomly divided into three groups of 20 each. Group 1, no dentin desensitizer was used as the control group; group 2, a resin-based dentin desensitizer was selected; and group 3, the prepared teeth surfaces were coated with polyurethane cyanoacrylate adhesive. Each of the three groups was further divided into two polymerizing systems (autopolymerizing and a photopolymerizing) of 10 each. After insertion of the resin-filled matrix, the temperature change in the pulpal chamber was recorded with thermocouple connected to a data logger. anova indicated no significant differences for all combinations of desensitizing agents and curing methods (P > 0.05). When light cured composite or chemical curing acrylics were used to make temporary crowns, the presence of desensitizing agent did not reduce the temperature transmitted from the provisional material; the residual temperature rise transmitted was of such a magnitude as to cause concern regarding possible thermal injury to pulp.

Influence of different light sources on microleakage of class V composite resin restorations.

UNLABELLED: The aim of this study was to evaluate the effect of three different curing units on microleakage of class V composite restorations. Class V cavities were prepared on the buccal surfaces of 45 extracted premolar teeth. The teeth were randomly divided into three groups of 15 each. A conventional halogen curing unit (Hilux 350), a high intensity halogen curing unit (Optilux 501) and plasma arc curing unit (Power Pac) were used to polymerize composite resin (Vitalesence). After restoration, the teeth were thermocycled for 100 cycles between 5 degrees and 55 degrees C using a dwell time of 30 s and exposed to a dye. Results showed that there was no significant difference among three different curing units (P > 0.05), however the microleakage at the dentin margins was greater than the enamel margins (P < 0.05). CLINICAL RELEVANCE: Plasma arc curing or fast halogen units cure composite materials at a faster rate than conventional curing units because of the high light intensity. High intensity halogen curing units and plasma arc curing units might be useful alternatives in composite polymerization. Therefore, these units are suggested for clinical use to save chair side time.

The efficiency of different light sources to polymerize resin cement beneath porcelain laminate veneers.

Plasma arc light units for curing resin composites have been introduced with the claim of relatively short curing times. The purpose of this study was to evaluate the efficiency of two different light sources to polymerize dual curing resin cement beneath porcelain laminate veneers. Twenty extracted healthy human maxillary centrals were used. Teeth were sectioned 2 mm below the cemento-enamel junction and crown parts were embedded into self-cure acrylic resin, labial surface facing up. Cavity preparation was carried out on labial surfaces. These teeth were divided into two groups of 10 each. The resin cement/veneer combination was exposed to two different photo polymerization units. A conventional halogen light (Hilux 350, Express Dental Products) and a plasma arc light (Power PAC, ADT) were used to polymerize resin cement. Ten specimens were polymerized conventionally (40 s) and the other specimens by plasma arc curing (PAC) (6 s). Two samples from each tooth measuring 1.2 x 1.2 x 5 mm were prepared. These sections were subjected to microshear testing and failure values were recorded. Statistically significant differences were found between the bond strength of veneers exposed to conventional light and PAC unit (P < 0.001). Samples polymerized with halogen light showed better bond strength. The results of this study suggest that the curing efficiency of PAC through ceramic was lower compared with conventional polymerization for the exposure durations tested in this study.