The effect of surface treatment on the Knoop hardness of Dicor.

One advantage cited for the use of Dicor over other ceramic materials is a reported Knoop hardness comparable to human enamel. However, when fabricating dental restorations, a Dicor glass-ceramic casting generally is subjected to several different surface treatments because of processing, esthetic, and functional requirements. Therefore, this study compared the Knoop hardness of Dicor specimens under three conditions: (1) cerammed, (2) cerammed and shaded, and (3) sectioned to reveal internal material. Knoop hardness differences between groups were significant (P less than or equal to .05). The cerammed surface was the hardest; it was harder than human enamel. Shaded specimens had a surface hardness comparable to dental porcelain. However, the internal glass-ceramic material, located beneath the shading porcelain and cerammed surface, had a Knoop hardness slightly higher than that of human enamel.     

Microscopic analysis of the effects of ultrasonic instrumentation on the root surface of molar furcations

Twenty molars, 10 from the maxilla and 10 from the mandible with furcation areas type II (Staffileno) were instrumented in their inter-radicular area with P10 instrument of Cavitron. It was established that the furcations of easier access instrumentation were the lingual o lower teeth and the buccal of the upper, and the most difficult accessibility were the distal of upper molars. The instrumentation can leave grooves or deformations, depending on the instrument to the area. It was concluded that ultrasonic instrument are useful removing supragingival calculus and bacterial plaque, and it must be limited to perform such procedures.     

Static frictional force and surface roughness of nickel-titanium arch wires

Surface roughness and static frictional force resistance of orthodontic arch wires were measured. Nine nickel-titanium alloy arch wires were studied. One beta-titanium alloy wire, one stainless steel alloy wire, and one cobalt-chromium alloy wire were included for comparison. Arithmetic average roughness in micrometers was measured with a profilometer. Frictional force resistance was quantified by pushing wire segments through the stainless steel self-ligating brackets of a four-tooth clinical model. The cobalt-chromium alloy and the nickel-titanium alloy wires, with the exception of Sentalloy and Orthonol, exhibited the lowest frictional resistance. The stainless steel alloy and the beta-titanium alloy wires showed the highest frictional resistance. The stainless steel alloy wire was the smoothest wire tested, whereas NiTi, Marsenol, and Orthonol were the roughest. No significant correlation was found between arithmetic average roughness and frictional force values.     

The mesh diagram for analysis of facial growth

Facial growth of twins by means of proportionate analysis of changes in the location of landmarks within a rectilinear coordinate system (mesh diagram) has been conducted, utilizing cephalometric data on 148 males and 128 females, observed annually from 8 to 16 years of age. Findings show relative consistence of the facial configuration during this 8 year time period, which includes the adolescent growth spurt. The median face in each sex shows little change in the location of soft and hard tissue landmarks, except for slight advancement of the chin as well as dorsal and caudad movement of Gonion. Nonetheless, individual variations in landmark location after 8 years of growth among the subjects studied signal the hazards of prediction within the precise framework that orthodontists seek.     

Evaluation of shear strength at the cement-endodontic post interface

The strength characteristics of the cement-implant interface were evaluated for smooth-tapered, threaded, and porous-surfaced endodontic implants with the use of different cements. Specifically, tensile and torsional shear strengths were measured for zinc phosphate, polycarboxylate, glass-ionomer, silicophosphate, and AH-26 cements. The results indicated superior shear strength characteristics for threaded endodontic implants on axial loading. However, this strength was diminished when torsional forces were applied. Porous-surfaced endodontic implants showed strong resistance to both axial and torsional loading.     

The position of the apical foramen of the permanent incisors

The position of the apical foramen in relation to the anatomical root apex is of considerable importance to the dentist, especially when the level of obturation of the root canal is determined through tooth length calculated radiologically. The main objective of this study was to determine in upper permanent incisor teeth, the position of foramen/foramina relative to the anatomical apex.
In 635 permanent upper incisors, the results of this study showed 54.3 per cent with the foramen coincident with the root apex, and 45.7 per cent where the root apex and the foramen were non-coincident. The average distance of the foramen from the root apex in the latter group was 0.35 mm and it ranged from 0.1 to 1.2 mm. The significance of these findings is discussed in relation to the apical termination of debridement and obturation of root canals.     

Blood group substances as differentiation markers in human dento-gingival epithelium

The level of cellular differentiation of human oral, sulcular, and junctional epithelium was compared by immunohistochemical analysis of cell membrane-associated blood group-specific carbohydrates. Identification of the blood group A-specific carbohydrate and its two immediate precursor substances, type 2 chain H and N-acetyllactosamine, was accomplished by an indirect immunofluorescence technique. Murine monoclonal antibodies reacting specifically with the antigenic determinants of the blood group substances were used as markers. The blood group A substance, indicating the highest level of cellular differentiation, was demonstrated on the cells in the upper layers of the oral epithelium. In the sulcular epithelium, the A substance was present on a few cells only, while type 2 chain H was observed frequently. This indicates an intermediate differentiation level of sulcular epithelium. The type 2 chain H precursor, N-acetyllactosamine, the indicator of the lowest level of cell differentiation among the tested substances, was the only blood group substance detected on the junctional epithelial cells and on the basal cells of the sulcular and oral epithelium. Based upon previous studies of cell renewal and differentiation in oral epithelium, the present results indicate that the variations in distribution of the different blood group substances correspond with the regional rates of cell division and the levels of cellular differentiation. The findings also suggest that the cells in the junctional epithelium differentiate to a level similar to that of basal cells in the oral epithelium.     

Pulp response to Streptococcus mutans

The maxillary molar pulps of germ-free rats were mechanically exposed, and suspensions of a strain of freshly grown Streptococcus mutans were applied to the pulp wounds. The pulps were left open to the oral environment, and the animals were maintained in the isolator until they were killed in groups after 2, 7, and 28 days. After 2 days there was little evidence of any pulp response. In the 7-day group early pulp necrosis was present. No evidence of inflammatory infiltration was detected in either the 2- or 7-day animals. After 28 days there was extensive pulp necrosis in many specimens. Dentine bridges were present in fewer than one fourth of the teeth.     

Multiple supernumerary teeth and possible implications

A case of an unusual number of supernumerary teeth is reported because patients who present with this symptom may be suffering from Gardner's syndrome or cleidocranial dysostosis.