Mandibular complete denture impressions with fluid wax or polysulfide rubber: A comparative study

Some authors have stated that wax cannot be used to make impressions for complete dentures, while others have found that wax has some advantages over elastomeric impression materials. The purpose of this study was to compare mandibular impressions made with a fluid wax to those made with light-body polysulfide rubber. Fifteen maxillary and mandibular complete dentures were made using fluid wax as a final impression material. For comparison, 15 maxillary and mandibular complete dentures were made using light-body polysulfide rubber. The number of adjustments required over 1 year was recorded. No statistical difference in adjustments was noted between the two groups.     

Radiopacity and physical properties of titanium-polymethacrylate composite.

Titanium-polymethacrylate composite was prepared as an x-ray-opaque filler for composite core materials. The base monomers of the composite were 2,2-bis [4-(3-methacryloyloxy-2-hydroxypropoxy) phenyl] propane (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA). Pure titanium powder was used as a radiopaque element. Two functional methacrylates--isopropyl dimethacryloyl isostearoyl titanate (KR-7) and 4-methacryloyloxyethyl trimellitate anhydride (4-META)--were adopted as couplers of titanium powder. The radiopacity of composites was determined in terms of their equivalent thickness of aluminum per unit thickness of material. Compressive and transverse strengths of the composites were measured by use of coupled and untreated titanium fillers. The composites that contained 70% and 80% titanium by weight showed more radiopacity than enamel and less than amalgam. Radiopacity was controlled by the content of titanium filler in the composite. The decrease in compressive and transverse strengths of the composites was 0.7 to 15.9% and 43.7 to 52.9%, respectively, after one year's immersion in water. The decrease in transverse strength was remarkable; however, this deterioration was diminished by use of both KR-7 and 4-META as couplers for titanium. Thus, prepared titanium-polymethacrylate composite may be used as a radiopaque composite filler for self-curing composite core materials.     

Stimulation by carrageenan of arachidonate 12-lipoxygenase activity in dog gingival tissue

At 4 h after injection of carrageenan into the gingiva, the 12-lipoxygenase activity of the gingival homogenate was markedly increased. Activity in the cytosol and microsomal fractions was markedly increased when assessed as the specific activity based on nmol/min/mg of protein, and in the cytosol fraction as the percentage distribution of total activity. The 12-lipoxygenase activity in the homogenate from carrageenan-treated gingiva was not affected by either EDTA or calcium ion, or a combination of the two. 12-lipoxygenase activity in both carrageenan-treated and untreated gingiva was inhibited dose-dependently by AA861, a striking difference from its effect on platelet 12-lipoxygenase. There was a marked increase of 12-lipoxygenase activity in experimentally inflamed gingiva compared to the non-inflamed gingiva.     

DNA analysis of oral leukoplakia by flow cytometry.

DNA ploidy of 19 oral leukoplakias with and without epithelial dysplasia was investigated and the results were compared with 11 normal gingival biopsies, 14 oral benign tumours and 50 oral squamous cell carcinomas. The results suggest a possible relationship between DNA aneuploidy and oral leukoplakias or squamous cell carcinomas, as 32% of the oral leukoplakias and 48% of the oral squamous cell carcinomas were aneuploid although all the normal gingival biopsies and the benign oral tumours examined were diploid. No significant relationship was observed, however, between DNA ploidy and epithelial dysplasia in the leukoplakias.     

Mongoloid features of the permanent mandibular second molar in Singaporean Chinese

The permanent mandibular second molar is usually described as four-cusped, two placed buccally and two lingually. It has been reported that five-cusp forms were more commonly present in dentitions of mongoloid origin. The prevalence and features of this tooth form were examined in a Singaporean sample of 380 subjects with bilateral presence of the mandibular second molars. One-hundred and sixty four cases (43.1 per cent) were found to have bilateral occurrence of five-cusp forms and thirty-four cases (8.9 per cent) with unilateral occurrence. Six-cusp forms were detected in three cases. There was almost equal prevalence in both sexes and both sides were equally involved in unilateral cases. The extra cusp was smallest, placed disto-buccally and sometimes midway at the distal border. The occlusal outline of five-cusp second molars was rectangular with a somewhat similar groove pattern to the first molar. There was an increase in the mesio-distal width of the crown. The high incidence was comparable with other studies of mongoloid dentitions and it could be considered as an important morphological and racial characteristic of the Singaporean Chinese.     

Relationship between sialographic findings of parotid glands and histopathologic finding of labial glands in Sj?gren's syndrome. Relation to clinical and immunologic findings.

We investigated a relationship between sialographic findings of parotid glands and histopathologic changes of labial glands, in relation to Sj?gren's syndrome. We examined 107 patients, suspected to have Sj?gren's syndrome because of dry mouth and dry eyes, in whom no other autoimmune diseases were diagnosed. Parotid sialography identified 37 patients with punctate, globular, cavitary, or destructive sialectasia (S-positive group). These sialographic findings were not seen in the other 70 patients (S-negative group). Among these patients, 54 demonstrated periductal lymphocytic infiltration in the labial glands (H-positive group), whereas the other 53 patients did not demonstrate this histologic finding (H-negative group). Significant differences in stimulated parotid salivary flow rate and incidence of keratoconjunctivitis sicca were observed between patients in the S-positive and the S-negative groups. Differences in the salivary flow rate and the incidence of keratoconjunctivitis sicca were also seen between patients in the H-positive and the H-negative groups, although the differences were not statistically significant. The rate of incidence of serum rheumatoid factor, anti-SS-A, and anti-SS-B antibodies were significantly higher in the S-positive and the H-positive groups than in their negative counterparts.     

Resin-bonded fixed partial dentures: A recall study

A clinical recall program was initiated at the University of Minnesota to evaluate the longevity and factors affecting longevity of resin-bonded fixed partial dentures (FPDs). Of the 49 resin-bonded FPDs evaluated in the clinic, 43 were acid-etched metal, resin-bonded FPDs, four were combinations of resin-bonded and conventional FPDs, and two were composite resin pontics. None of the combination FPDs and one of the two composite resin pontics were judged as failed at the examination. Of the 43 acid-etched metal resin-bonded FPDs, 15 were found to be debonded (failure rate = 34.9%). The average length of service for the 43 FPDs was 47.3 months. The average time of placement to debondment was 33 months for the 15 debonded FPDs. The failure rate for maxillary FPDs and FPDs with two retainers were significantly lower than the failure rate for mandibular FPDs and FPDs with more than two retainers (p greater than 0.05). The clinical significance of the present study was discussed.     

Cephalometric errors: A comparison between repeat measurements and retaken radiographs

This study compares landmark location errors in cephalometric radiography (when re-measuring radiographs) and radiographic errors (when retaking the radiograph). The samples comprised 32 remeasured and re-digitized radiographs and a further series of 22 retaken radiographs drawn from the same overall sample of 12-year-old Chinese children in Hong Kong. All radiographs were recorded in natural head posture with the lips in light contact. The relative size of the errors were assessed by calculating the 'error percentage' for both selected dento-skeletal and soft tissue profile measures. It is suggested that this index is clinically more meaningful than the usually used 'method error'. It expresses the variance of the method error (me2) as a percentage of the variance of the measurement under study (standard deviation2). This error percentage was found to be doubled, on average, for measurements on the retaken radiographs. In general, measures with most landmarks in the mid-sagittal plane showed the least increase in percentage error. The results suggest that errors arising from retaking cephalometric radiographs may effectively be greater than those usually reported. The Frankfort plane, the functional occlusal plane and the incisor long axes displayed poor reproducibility. For the soft tissues the lips served as poor angular landmarks and relatively acute angles with short 'arms' also displayed large errors.