The Effect of Water Absorption on Acrylic Surface Properties

PURPOSE: The aim of the present study was to determine whether an increased water content during thermal cycling of hot water-treated acrylic was associated with a reduction in surface hardness and an increased opacity or whitening of the surface. MATERIALS AND METHODS: Ten acrylic samples were treated with 30 soak cycles (cycle duration, 24 hours), using warm water (40 degrees C) and an alkaline peroxide tablet (Efferdent control group); a further ten samples were treated with boiling water (100 degrees C) and one Efferdent tablet (experimental group). Indentation hardness of the acrylic specimens was measured prior to and immediately following the completion of the warm and hot water treatments, using an automated micro-indentation system. The hydrated acrylic specimens were then allowed to air dry at room temperature (20 degrees C) and were weighed weekly until they had obtained a constant dry weight. The loss in weight of the acrylic specimens represented the maximum water absorption. RESULTS: The hot water-treated specimens were much whiter than the warm water-treated specimens. The mean reduction in hardness (H(IT)) of the acrylic specimens following the treatment with hot water and alkaline peroxide tablet was 12.9%. Treatment with warm water and alkaline peroxide resulted in a slight increase in mean hardness (2.63%). There was a significant correlation between the water content of the acrylic specimens after treatment and the percentage of change in indentation hardness (r= 0.495, p= 0.026). CONCLUSIONS: The hot water treatment of the acrylic was associated with a significant reduction in hardness. We attribute the whitening and reduction in the hardness of the hot water-treated specimens to absorption of water and a disruption of the acrylic surface structure.     

Dental materials: 1979 literature review Part II

This paper, which is presented in two parts, reviews the work on dental materials published in 1979. Included in Part II are sections on impression materials, model, die and investment materials, waxes, acrylic resins, denture base polymers, soft lining materials and tissue conditioners, cast and wrought dental alloys, ceramics, implants and, finally, corrosion. Part I included sections on dental biomechanics, fissure sealants, cements, amalgam, composite filling materials, endodontic materials and microleakage.     

Gap measurement and bond strength of five selected adhesive systems bonded to tooth structure

The ability of a restorative material to bond and seal the interface with tooth structure is perhaps the most significant factor in determining resistance to marginal caries. Thus, the quality and durability of marginal seal and bond strength are major considerations in the selection of restorative materials. The purpose of this study was to compare the bond strength and marginal discrepancies of five adhesive systems: All-Bond 2, Clearfil Liner Bond, KB 200, ProBond and AELITE Bond. Twenty-five buccal and 25 lingual cavities were prepared in 25 caries-free extracted molar teeth, giving 10 cavities for each of the 5 adhesive systems. All teeth were restored with the resin composite Pertac Hybrid, or PRISMA Total Performance Hybrid with their appropriate adhesive systems. After restoration, the teeth were thermocycled, were stained with a 1.5% aqueous solution of a procion dye (reactive orange 14) and sectioned coronally with a saw microtome. Three sections of 200 μm thickness were prepared from each restoration which were then examined microscopically to measure marginal gap widths using a confocal tandem microscope. Shear bond strength measurements were carried out on the dentine bond using a universal testing machine. The All-Bond 2 adhesive system was found to have higher shear bond strength and to have the least gap with at the cementodentinal margin.     

Study of gypsum-bonded casting investments. Part 2

The simultaneous differential thermal analysis — thermogravimetry (DTA-TG) method used in Part 1 of this two-part study was extended to analyse two gypsum-bonded dental casting investments, Kerr Cristobalite Inlay and GC Cristobalite Micro. Both investments had a similar cristobalite content of about 70 per cent. The remaining 30 per cent was dental stone in GCM, and a mixture of plaster and dental stone in KCI. Inclusion of plaster in KCI appeared responsible for the greater amount of water required for mixing this investment. The DTA-TG method used in the present study can be applied to identify the type and amount of hemi-hydrate, and the type of silica, in currently available gypsum-bonded investments.     

The Influence of Surface Roughness on the Displacement of Osteogenic Bone Particles during Placement of Titanium Screw‐Type Implants

Background: Previously, we demonstrated that bone debris, which is translocated during dental implant placement, has osteogenic potential. Therefore, it was hypothesized that implant surface roughness can influence the amount of translocated bone debris/particles and thereby the osteogenic response. Material and Methods: Small titanium implants were left turned (smooth) or blasted and acid etched. The implants were placed in fresh cadaver bone. After explantation, the implants were incubated in a culture medium containing β‐glycerophosphate and dexamethasone up to 24 days. Subsequently, histology, scanning electron microscopy (SEM), DNA analysis, and calcium (Ca) content measurements were performed. Results: For both types of implant during implant placement, bone particles were translocated because of inherent roughness of the implant. SEM and histology confirmed the presence of a bone‐like tissue on the surface of both types of implants, as also confirmed by DNA and Ca measurements. However, the significantly higher roughness of the etched implants accounted for more bone debris and accordingly elevated osteogenic response. Control samples, which had not been placed into bone, did not show mineralization in the same medium. Conclusion: The present study, for the first time, demonstrated that implant surface roughness can increase the amount of the translocated bone particles and thereby also have a beneficial effect on the osteogenic response of these bone particles. It is hypothesized that these bone fragments behave like miniature auto‐grafts and thereby play a significant role to enhance peri‐implant osteogenesis. Optimization of surface topography should be evaluated to take advantage of this additional effect of surface roughness.     

Gender Differences in the Amount of Gingival Display During Smiling Using Two Intraoral Dental Biometric Measurements

Purpose: The aims of this study were to compare gender differences in the width and length of the maxillary right central incisor and the horizontal and vertical overlap of the anterior teeth and to determine the relationships of these two intraoral dental biometric measurements with the amount of gingival display during smiling. Materials and Methods: A total of 61 men and 66 women were included in this study. For each participant, the gingival tissue display during smiling was judged to be either visible or not, and the maximum mesiodistal and incisogingival dimensions of the maxillary right central incisor were measured, along with the amount of horizontal and vertical overlap of anterior teeth using a digital caliper. Gender differences in these parameters and the relationship between subjects showing gingival display when smiling and the two intraoral dental biometric measurements were determined. Statistical analyses of data were performed using SPSS (V11) software. The mean scores for gender were calculated, and a Student's t‐test was used to identify significant differences between both groups. Significance level was set to 0.05. Results: The age of the participants ranged between 23 and 52, with a mean of 33.47 ± 9.07 years. A relatively small percentage of the subjects (22.05%) displayed gingiva when smiling. More women displayed gingiva when smiling than men, with a 2:1 female:male ratio. Men exhibited significantly (p < 0.05) wider (8.76 ± 0.66 mm) and longer (10.28 ± 0.88 mm) central incisors compared to women (7.92 ± 0.72 mm; 9.27 ± 0.93 mm width and length, respectively). No gender differences were found in the width‐to‐length ratio. Subjects with gingival display had significantly more horizontal (4.28 ± 1.21 mm; p < 0.001), and vertical (3.52 ± 0.66 mm; p < 0.05) overlap of anterior teeth compared to those who did not display gingiva when smiling (2.40 ± 1.03 and 2.30 ± 0.93 mm, respectively). Conclusions: Significantly more women displayed gingiva in smiling. Men had significantly wider and longer central incisors. No differences were recorded between men and women relative to both the horizontal and vertical anterior tooth overlap. Subjects who displayed gingiva when smiling had more horizontal and vertical overlap of anterior teeth.