José Mondelli

Fracture strength of human teeth with cavity preparations

F ailure of dental restorations is a major concern. The most common causes are faulty cavity preparation and improper manipulation of restorative materials. Another cause of failure is the geometric form of the cavity preparation, which may lead to fracture of the tooth. The anatomic forms of posterior teeth with cusps and fossae present a design possessing a tendency to deflect the cusps under stress (Fig. 1, A).’ While sound teeth rarely fracture from the stresses of mastication, fracture of a cusp may occur in teeth which have been weakened by caries and the cavity preparation required for restoration. The typical intracoronal cavity preparation, especially in the maxillary premolars, exaggerates the height of the cusps (Fig. 1, B). The weakened or unsupported cusps are subjected to stresses which tend to deflect or fracture them at the buccopulpal or linguopulpal line angles (Fig., 1, C). While a fracture may not occur, deflection of a weakened cusp may open the tooth-restoration interface and lead to subsequent marginal leakage (Fig. 1, C). It is evident that the buccolingual width of the occlusal preparation may contribute toward weakening of the cusps. Cavity forms have been based on Black’s principles.’ For Class I and II cavity preparations, Black advocated an occlusal width of one-third the buccolingual intercuspal distance. Present-day equipment and restorative materials permit more conservative geometric forms. Modern cavity preparation permits narrow occlusal designs, one-fourth the buccolingual

Influence of some factors on the fit of cemented crowns

In the study, cast gold crowns were cemented similar to methods used for patients. Conclusions were that: 1. Fresh cement painted with a camel brush in the part of the crown to be cemented promotes a better fit than when the crown is completely filled with cement. 2. Mechanical vibration of the crown at cementation promotes a better fit. 3. Venting the crown, an internal relief by acid etching, or a combination of both these procedures improve the seating of the crown during cementation. 4. The association of one or numerous variables used in this study considerably improves the fit of the cemented crown.

Compromised bond strength after root dentin deproteinization reversed with ascorbic acid.

INTRODUCTIONnThe present study evaluated the effect of a reducing agent on the bond strength of deproteinized root canal dentin surfaces when using a self-adhesive versus dual-cured cement. Regional differences were also evaluated.nnnMETHODSnA total of 45 bovine incisor roots were divided into 3 groups: irrigation with physiologic solution (control), 10-minute deproteinization with 5% NaOCl, and 10-minute deproteinization with 5% NaOCl followed by 10 minutes of 10% ascorbic acid. Fiber posts were cemented with either RelyX U100 or RelyX ARC (with SingleBond 2 or Clearfil SE Bond). The push-out bond strength was evaluated after 24 hours of storage. Data were submitted to three-way analyses of variance and Dunnett T3 tests (alpha = 0.05).nnnRESULTSnNo differences between cements were observed within the testing conditions, regardless of the adhesive (P < .05). Deproteinization reduced bond strengths. Subsequent treatment with ascorbic acid was capable of reversing bond strength value changes to levels similar to those of controls. Regional radicular differences were also found, where coronal > middle > apical.nnnCONCLUSIONSnThe reducing agent was capable of reversing the effect of dentin deproteinization, and RelyX U100 behaved similarly to RelyX ARC.

Marginal microleakage in cemented complete crowns

An in vivo study was developed to observe the penetration of 131INa around the margins of complete crown castings cemented with zinc phosphate cement with and without the application of different protective agents, with the following results. 1. Complete crowns cemented with zinc phosphate cement showed 131INa marginal leakage differences depending on the protective material used prior to cementation. 2. The best protective agent against marginal leakage according to this study was two layers of cavity varnish applied to the margins. 3. The amount of marginal leakage can be influenced by crown adaptation and the film thickness of the cement. 4. There were no differences between test periods of 1 hour or 21 days after cementation.

FRACTURE RESISTANCE OF WEAKENED TEETH RESTORED WITH CONDENSABLE RESIN WITH AND WITHOUT CUSP COVERAGE

Objectives: This in vitro study evaluated the fracture resistance of weakened human premolars (MOD cavity preparation and pulp chamber roof removal) restored with condensable resin composite with and without cusp coverage. Material and Methods: Thirty human maxillary premolars were divided into three groups: Group A (control), sound teeth; Group B, wide MOD cavities prepared and the pulp chamber roof removed and restored with resin composite without cusp coverage; Group C, same as Group B with 2.0 mm of buccal and palatal cusps reduced and restored with the same resin. The teeth were included in metal rings with self-curing acrylic resin, stored in water for 24 h and thereafter subjected to a compressive axial load in a universal testing machine at 0.5 mm/min. Results: The mean fracture resistance values ± standart deviation (kgf) were: group A: 151.40 ± 55.32, group B: 60.54 ± 12.61, group C: 141.90 ± 30.82. Statistically significant differences were found only between Group B and the other groups (p<0.05). The condensable resin restoration of weakened human premolars with cusp coverage significantly increased the fracture resistance of the teeth as compared to teeth restored without cusp coverage. Conclusion: The results showed that cusp coverage with condensable resin might be a safe option for restoring weakened endodontically treated teeth.

Marginal Leakage of Two Composite Restorative Systems

The ability of sealants to seal margins of composite resins is demonstrated in this in vitro study which uses two composite resins and respective sealants under and over Class V restorations.

Network structures of Bis-GMA/TEGDMA resins differ in DC, shrinkage-strain, hardness and optical properties as a function of reducing agent.

OBJECTIVESnTo evaluate the influence of different tertiary amines on degree of conversion (DC), shrinkage-strain, shrinkage-strain rate, Knoop microhardness, and color and transmittance stabilities of experimental resins containing BisGMA/TEGDMA (3:1wt), 0.25wt% camphorquinone, 1wt% amine (DMAEMA, CEMA, DMPT, DEPT or DABE). Different light-curing protocols were also evaluated.nnnMETHODSnDC was evaluated with FTIR-ATR and shrinkage-strain with the bonded-disk method. Shrinkage-strain-rate data were obtained from numerical differentiation of shrinkage-strain data with respect to time. Color stability and transmittance were evaluated after different periods of artificial aging, according to ISO 7491:2000. Results were evaluated with ANOVA, Tukey, and Dunnetts T3 tests (α=0.05).nnnRESULTSnStudied properties were influenced by amines. DC and shrinkage-strain were maximum at the sequence: CQ<DEPT<DMPT≤CEMA≈DABE<DMAEMA. Both DC and shrinkage were also influenced by the curing protocol, with positive correlations between DC and shrinkage-strain and DC and shrinkage-strain rate. Materials generally decreased in L* and increased in b*. The strong exception was the resin containing DMAEMA that did not show dark and yellow shifts. Color varied in the sequence: DMAEMA<DEPT<DMPT<CEMA<DABE. Transmittance varied in the sequence: DEPT≈DABE<DABE≈DMPT≈CEMA<DMPT≈CEMA≈DMAEMA, being more evident at the wavelength of 400nm. No correlations between DC and optical properties were observed.nnnSIGNIFICANCEnThe resin containing DMAEMA showed higher DC, shrinkage-strain, shrinkage-strain rate, and microhardness, in addition to better optical properties.

Esthetic and functional restoration for an anterior open occlusal relationship with multiple diastemata: A multidisciplinary approach

An anterior open occlusal relationship and diastemata may negatively interfere with the harmony of the smile, often requiring a multidisciplinary intervention. This clinical report presents an integrated orthodontic, periodontal, and restorative solution for an anterior open occlusal relationship associated with multiple diastemata and discusses the most relevant aspects related to its etiology and treatment planning.

An acrylic resin pattern for a cast dowel and core

Abstract This report presented an orderly and effective method of preparing acrylic resin patterns for a cast dowel and core assembly.

Bond strength of resin-resin interfaces contaminated with saliva and submitted to different surface treatments

The purpose of this study was to investigate the effect of different surface treatments on shear bond strength of saliva-contaminated resin-resin interfaces. Flat resin surfaces were fabricated. In the control group, no contamination or surface treatment was performed. The resin surfaces of the experimental groups were contaminated with saliva and air-dried, and then submitted to: (G1) rinsing with water and drying; (G2) application of an adhesive system; (G3) rinsing and drying, abrasion with finishing disks, etching and application of adhesive system; (G4) rinsing and drying, etching, application of silane and adhesive system. Resin cylinders were placed over the treated surfaces. The specimens were stored in water or ethanol. Shear bond strength tests were performed and the mode of failure was evaluated. Data were submitted to two-way ANOVA and Dunnett T3 test. Contamination of resin-resin interfaces with saliva significantly reduced shear strength, especially after prolonged storage (p<0.05). Similar values to the original bond strength were obtained after abrasion and application of adhesive (G3) or etching and application of silane and adhesive (G4). If contamination occurs, a surface treatment is required to guarantee an adequate interaction between the resin increments.