A study of primary dental enamel from preterm and full-term children using light and scanning electron microscopy

Purpose: The aim of this study was to examine the enamel thickness of the maxillary primary incisors of preterm children with very low birth weight (< 1,500 g) compared to full-term children with normal birth weight. Methods: A total of 90 exfoliated maxillary primary central incisors were investigated using light microscopy and scanning electron microscopy (SEM). Three serial buccolingual ground sections of each tooth were examined under light microscopy, and maximum dimensions of the prenatally and postnatally formed enamel were measured. Results: The enamel of preterm teeth was approximately 20% thinner than that for fullterm teeth. Most of the reduction was observed in the prenatally formed enamel. This was 5 to 13 times thinner than that for full-term children (P < .001). The catch-up thickness of postnatally formed enamel did not compensate fully for the decrease in prenatal enamel (P < .001). Although none of the teeth used in this study had enamel defects visible to the naked eye, 52% of preterm teeth showed enamel hypoplasia under SEM, compared with only 16% found on full-term teeth (P < .001). These defects were present as pits or irregular, shallow areas of missing enamel. Conclusions: Preterm primary dental enamel is abnormal in surface quality, and is significantly thinner compared to full-term enamel. The thinner enamel is due mainly to reduced prenatal growth and results in smaller dimensions of the primary dentition.

Stem and crown dimensions as predictors of thinning responses in a crowded tropical rainforest plantation of Flindersia brayleyana F. Muell.

A 67-year-old plantation of Flindersia brayleyana F. Muell. in the wet tropics of north-cast Queensland had developed with minimal management. Before thinning, the stand had a canopy stem density of 770 stems ha(-1) of which 564 were F brayleyana, a stand basal area of 78 m(2) ha(-1), a mean stem diameter at breast height (dbh) of 36 cm, and a mean dbh increment of 5.2 mm year(-1) over the life of the plantation and 0.5 mm year I at the time of thinning. Sixty-three percent of the trees had crown ratios (crown diameter determined from foliage projected area: dbh) of less than 12. Thinning treatments removed 57% of the canopy stems and 45% of the stand basal area. Mean dbh increment over 2.5 years after thinning on basaltic soil was 5.8 +/- 0.3 mm year(-1), but for trees with crown ratio

Rhizoctonia crown and root rot of the pasture legume, sulla (Hedysarum coronarium)

Rhizoctonia solani AG-2-2 was isolated from wilting and dying plants of sulla ( Hedysarum coronarium), which is currently being assessed in eastern and southern Australia for its potential as a pasture and forage legume. Infected plants in the field had extensive rotting of the taproot, lateral roots and crown. Koch's postulates were fulfilled using three inoculation methods. The disease may pose a considerable threat to the potential use of H. coronarium in the dryland, grazing farming systems of Australia, with resistance offering the most viable option for minimising its impact.

Determining the age of adult wild dogs (Canis lupus dingo, C-l. domesticus and their hybrids). I. Pulp cavity: tooth width ratios

In order to determine the age of adult wild dogs, we compared two methods ( that of Thomson and Rose (TR method) and that of Knowlton and Whittemore (KW method)) of measuring and calculating pulp cavity : tooth width ratios on upper and lower canine teeth from 68 mixed-sex, known-age wild dogs of 9 months to 13 years of age reared at two localities. Although significant relationships ( P = 0.0001) were found between age and pulp cavity ratios by both methods, the TR ratio calculation and measurement showed heteroscedasity in error variance whereas the KW ratios had a more stable error variance and were normally distributed. The KW method also found significant differences between pulp cavity ratios between teeth of the upper and lower jaws ( P < 0.0001) and sex ( P = 0.01) but not geographic origin ( P = 0.1). Regressions and formulae for fitted curves are presented separately for male and female wild dogs. Males show greater variability in pulp cavity decrements with age than do females, suggesting a physiological difference between the sexes. We conclude that the KW method of using pulp cavity as a proportion of tooth width, measured 15 mm from the root tip and averaged over both upper canines, is the more accurate method of estimating the age of adult wild dogs.

Tooth wear: diet analysis and advice

Diet analysis and advice for patients with tooth wear is potentially the most logical intervention to arrest attrition, erosion and abrasion. It is saliva that protects the teeth against corrosion by the acids which soften enamel and make it susceptible to wear. Thus the lifestyles and diet of patients at risk need to be analysed for sources of acid and reasons for lost salivary protection. Medical conditions which put patients at risk of tooth wear are principally: asthma, bulimia nervosa, caffeine addiction, diabetes mellitus, exercise dehydration, functional depression, gastroesophageal reflux in alcoholism, hypertension and syndromes with salivary hypofunction. The sources of acid are various, but loss of salivary protection is the common theme. In healthy young Australians, soft drinks are the main source of acid, and exercise dehydration the main reason for loss of salivary protection. In the medically compromised, diet acids and gastroesophageal reflux are the sources, but medications are the main reasons for lost salivary protection. Diet advice for patients with tooth wear must: promote a healthy lifestyle and diet strategy that conserves the teeth by natural means of salivary stimulation; and address the specific needs of the patients' oral and medical conditions. Individualised, patient-empowering erosion WATCH strategies; on Water, Acid, Taste, Calcium and Health, are urgently required to combat the emerging epidemic of tooth wear currently being experienced in westernised societies.

Tetanus in an adult dog originating from a tooth root abscess

A three-and-a-half-year-old entire male Staffordshire Bull Terrier was presented with a cough and difficulty in swallowing. Two days later the dog was re-presented and a diagnosis of tetanus was made. An abscessed canine tooth was extracted and submitted for culture. Clostridium tetani was cultured from the pulp chamber of the tooth. The dog was treated with tetanus antitoxin, antibiotics and supportive care and made a complete recovery.

Microstructure of Pharyngeal Tooth Enameloid in the Parrotfish Scarus rivulatus (Pisces:Scaridae)

The microstructure of parrotfish pharyngeal teeth was examined using scanning electron microscopy to infer possible mechanical properties of the dentition with respect to their function. Parrotfish tooth enameloid is formed from fluorapatite crystals grouped into bundles. In the upper and lower pharyngeal jaw, the majority of the crystal bundles are orientated either perpendicularly or vertically to the enameloid surface. The only exception is in the trailing apical enameloid in which the majority of bundles are orientated perpendicularly or horizontally to the trailing surface. A distinct transition occurs through the middle of the apex between the leading and trailing enameloid in teeth of the lower pharyngeal jaw. This transition appears less distinct in the teeth of the upper pharyngeal jaw. Enameloid microstructure indicates that shear forces predominate at the apex of the teeth. In the remainder of the enameloid, the microstructure indicates that wear is predominant, and the shear forces are of less importance.

Genetic and environmental influences on dentofacial structures and oral health: studies of Australian twins and their families

Our studies of the teeth and faces of Australian twins commenced at the School of Dentistry, The University of Adelaide in the early 1980s. There are now over 900 pairs of twins enrolled in our continuing investigations, together with 1200 relatives. There are 3 main cohorts of participants. The first cohort comprises around 300 pairs of teenage twins for whom various records have been collected, including dental casts, facial photographs, finger and palm prints and information on laterality, including handedness. The second cohort comprises around 300 pairs of twins who have been examined at 3 stages of dental development from approximately 4 years of age to about 14 years: at primary, mixed, and permanent dentition (excluding 3rd molars) stages. The most recent study of tooth emergence and oral health, for which we are currently recruiting twins, will provide a third cohort of around 500 twin pairs aged from around birth to 3 to 4 years of age. Our broad aim in these studies has been to improve our understanding of how genetic and environmental factors contribute to variation in dental and facial features, and to oral health. We have also used our data to investigate aspects of the determination of laterality, particularly the fascinating phenomenon of mirror imaging. We plan to maximize the use of the longitudinal data and DNA we have collected, and continue to collect, by performing genome-wide scans for putative genetic linkage peaks for a range of dental features, and then to test for association between a series of likely candidate genes and our phenotypes.

Methyl jasmonate induced gene expression in wheat delays symptom development by the crown rot pathogen Fusarium pseudograminearum

The necrotrophic fungal pathogen Fusarium pseudograminearum (F. pseudograminearum) causes crown rot disease (CR) in wheat. This host-pathogen interaction has not been studied previously at the molecular level. In this study. using real-time quantitative PCR, the expression of 26 selected wheat genes was examined 1, 2 and 4 days after inoculation of wheat seedlings of the CR susceptible cultivar Kennedy and the partially field-resistant cultivar Sunco. Reproducible induction of eight defence genes consisting of PR1.1, PR2 (beta,1-3 glucanase), PR3 (chitinase), PR4 (wheativin), PR5 (thaumatin-like protein). TaPERO (peroxidase), PR10 and TaGLP2a (germin-like) was observed. These genes were induced in both cultivars, however. some genes were induced more rapidly in Sunco than in Kennedy. MJ treatment also induced the above pathogen responsive defence genes in both cultivars while benzo(1,2,3)thiadiazole-7-carbothionic acid S-methyl ester (BTH) treatment weakly induced them in Kennedy only. Similarly. treatment with MJ before inoculation significantly delayed the development of necrotic symptoms for 2 weeks in both wheat cultivars, while BTH pre-treatments delayed symptom development in Kennedy only. The chemically induced protection, therefore, correlated with induction of the F. pseudograminearum-responsive genes. These results support the emerging role of jasmonate signalling in defence against necrotrophic fungal pathogens in monocots and future manipulation of this pathway may improve CR resistance in wheat. (c) 2006 Elsevier Ltd. All rights reserved.

Orthodontic tooth movement in the prednisolone-treated rat

Adverse effects of corticosteroids on bone metabolism raise concerns as to whether steroid treatment may influence orthodontic movement. This study examined the effect of prednisolone on orthodontic movement using an established rat model. The corticosteroid treated group (N = 6) was administered prednisolone (1 mg/kg) daily, for a 12-day induction period; the control group (N = 6) received equivalent volumes of saline. On day 12, an orthodontic appliance was placed which exerted 30 g of mesial force to the maxillary first molar. Animals were sacrificed on day 24 and tooth movement was measured. Sagittal sections of the molars were stained with haematoxylin and eosin, and for tartrate-resistant acid phosphatase (TRAP) activity. While there were no significant differences in the magnitude of tooth movement between the 2 groups, steroid-treated rats displayed significantly less root resorption on the compression side and fewer TRAP-positive cells within the PDL space on the same side. This suggests steroid treatment suppressed elastic activity.