Linear polymers have been commonly used as dental composite. However the aim of this work is to use hyperbranched polymer in an attempt to produce dental composite. The reason is because the dendritic molecules have shown low viscosity at higher molecular weight compared to the linear counterparts. Therefore, this work attempts to substitute the linear polymer with as much of hyperbranched polymer in the dental composite that would pass the required ISO 4049:1998(E) "Dentistry - Resin-based filling material". Several formulations of dental composites were used, i.e. combinations of linear-linear and linear-hyperbranched polymers for comparison. Following this, physical and mechanical characterisation were conducted based on the ISO standards such as water sorption and water solubility. Other characterisation such as polymerisation shrinkage and Vickers hardness were also evaluated. It was found that different types of resins give different physical and mechanical properties. The maximum achievable hyperbranched polymer, which passes the required ISO standard, that can be incorporated in the linear polymer to form dental composite is 43% wt.
Acrylic Resins/*standards ; Biomechanics ; Composite Resins/*standards ; *Materials Testing ; Polymers/*standards ; Polyurethanes/*standards ; Reference Standards

OBJECTIVETo inspect the directionality of adhesive strength between composite resins and dental hard tissues.

METHODSTwo kinds of composite resins were bonded with their luting kits to the enamel and dentin surfaces of bovine teeth separately. The dead load shear and impact shear testing were performed from both of root apex direction and cutting edge direction.

RESULTSThe shear adhesive strength between the enamel and two kinds of composite resins was on the same behavior, that the shear adhesive strength of root apex direction was greater than that of cutting edge direction. In the dead load shear testing, the former was about two to three times of the latter (P < 0.05). In the impact shear testing, the former was about three to four times of the latter (P < 0.001). The effect of the direction of acting force was small on the shear adhesive strength between the dentin and two kinds of composite resins. In the both dead load shear testing and impact shear testing, there was no statistically significant difference between the datum of two directional loadings (P > 0.05, P > 0.5).

CONCLUSIONThe shear adhesive strength between the composite resins and enamel of bovine teeth is related to the acting direction of the shear force.

Adhesiveness ; Adhesives ; standards ; Animals ; Cattle ; Composite Resins ; standards ; Dental Bonding ; Dental Enamel ; Dentin ; Dentin-Bonding Agents ; standards ; Materials Testing ; methods ; Resin Cements ; standards ; Shear Strength

OBJECTIVETo assess effects of different class II cavities on stresses of amalgam and composite resin restoration.

METHODSFive kinds of class II MO cavities were prepared on the first molars of mandibles. The cavities were filled by amalgam and composite resin, respectively. The stresses were analyzed by using three-dimensional finite element method, after vertical and lateral pressures were loaded on the teeth.

RESULTSThe stresses were greater in traditional cavities than those in reformed cavities when 100 N vertical and lateral pressures were loaded on the teeth. But the pressing stress and shearing stress in cavities filled by amalgam were smaller in traditional cavities than those in reformed cavities. The stresses were smaller in cavities filled by resin than those in cavities filled by amalgam significantly, when the cavities were designed with slot retention groove, without slot retention groove and as plate form. The stresses were smaller in two kinds of slot and plate cavities than those in traditional and reformed cavities.

CONCLUSIONIt is better to design cavity with slot retention groove for amalgam restoration and to design cavity without slot retention groove for composite resin restoration.

Composite Resins ; standards ; Dental Amalgam ; standards ; Dental Cavity Preparation ; methods ; Dental Models ; Dental Restoration, Permanent ; methods ; Dental Stress Analysis ; methods ; Finite Element Analysis ; Humans ; Mandible ; Molar

This study examined the adhesive strength of two self-adhesive methacrylate resin-based sealers (MetaSEAL and RealSeal SE) to root dentin and compared them with RealSeal and AH Plus in properties. A total of 48 extracted human single-rooted teeth were used to prepare the 0.9-mm thick longitudinal tooth slice (each per tooth). Standardized simulated canal spaces of uniform dimensions were prepared in the middle of radicular dentin. After treated with 5.25% sodium hypochlorite (NaOCl) and 17% EDTA, tooth slices were allocated randomly to four groups (n=12) in terms of different sealers used: MetaSEAL, RealSeal SE, RealSeal, and AH plus groups. The simulated canal spaces were obturated with different sealers in each group. There were 10 slabs with 20 simulated canal spaces (n=20) used in each group for push-out testing. The failure modes and the ultrastructures of fractured sealer-dentin interfaces were examined. The remaining 2 slabs in each group underwent partial demineralization for observation of the ultrastructure of resin tags. The results showed that the push-out bond strength was 12.01±4.66 MPa in MetaSEAL group, significantly higher than that in the other three groups (P<0.05). Moreover, no statistically significant differences were noted in the push-out bond strength between RealSeal SE (5.43±3.68 MPa) and AH Plus (7.34±2.83 MPa) groups and between RealSeal SE and RealSeal (2.93±1.76 MPa) groups (P>0.05). Mixed failures were predominant in the fractured sealer-dentin interfaces in MetaSEAL and AH Plus groups, while adhesive failures were frequently seen in RealSeal SE and RealSeal groups. In conclusion, after complete removal of the smear layer, MetaSEAL showed superior bond ability to root dentin. The RealSeal SE is applicable in clinical practice, with its adhesive strength similar to that of AH Plus. The self-adhesive methacrylate resin-based sealer holds promise for use in endodontic treatment.
Adhesives ; standards ; Composite Resins ; standards ; Compressive Strength ; Dental Bonding ; Dental Pulp Cavity ; ultrastructure ; Dental Stress Analysis ; methods ; Dentin ; Dentin-Bonding Agents ; standards ; Epoxy Resins ; standards ; Humans ; Materials Testing ; methods ; Methacrylates ; standards ; Microscopy, Electron, Scanning ; Root Canal Filling Materials ; standards ; Root Canal Preparation ; Tooth Root