Effect of Acidic Beverages on the Hardness, Elastic Modulus and Wear Resistance of Giomer and Nongiomer Bulk-fill Materials.

OBJECTIVES: The aim of this study was to evaluate and compare the effect of acidic beverages on the hardness, elastic modulus, and wear resistance of four different resin-based restorative materials. METHODS AND MATERIALS: A total of 128 specimens (10 mm diameter, 4 mm thickness) were prepared from a conventional resin composite (Filtek Z250 [Z250]), a giomer bulk-fill (Beautifil Bulk Restorative [BBR]) and two nongiomer bulk-fill materials (Tetric N-Ceram Bulk Fill [TNC] and SonicFill 2 [SF2]). Each material group was divided into four subgroups (n=8) according to the storage media: artificial saliva (control), orange juice, regular Coke, and sports drink. The experimental specimens were immersed in the solutions for 30 minutes, five times a day for 5 days and kept in artificial saliva for an hour between the immersion periods. Control specimens were stored in artificial saliva for 5 days. The nanoindentation test with a Berkovich diamond tip was used to determine the hardness and elastic modulus before and after the 5-day storage periods. Following the nanoindentation tests, the specimens were subjected to a chewing simulator for 120,000 cycles. The specimens were then scanned with a three-dimensional scanner. The wear resistance was analyzed by measuring the volume and height loss. Specimens were observed by environmental scanning electron microscopy. The statistical analyses were performed by analysis of variance, Tukey HDS test, and paired samples t-test (α=0.05). RESULTS: Z250 showed significantly higher elastic modulus in all groups (p<0.05). After erosive cycles, the greatest decrease in hardness and elastic modulus was observed for BBR. TNC showed higher wear resistance than the other resin-based materials (p<0.05). The BBR specimens immersed in acidic solutions showed higher wear rates than the artificial saliva group (p<0.05). CONCLUSIONS: Conventional resin composite showed higher hardness and elastic modulus than bulk-fill materials when exposed to acidic beverages but comparable or lower wear resistance. Degradation due to acidic beverages most affected the mechanical properties of giomer bulk-fill.

Pycnodysostosis: clinical, radiologic, and endocrine evaluation and linear growth after growth hormone therapy.

Pycnodysostosis is a rare hereditary bone abnormality with an autosomal recessive mode of inheritance. We report the clinical, radiologic, and endocrine status of 8 children with this rare disease. All patients had the characteristic phenotype of the disorder including short stature (8 of 8), increased bone density (7 of 8), separated cranial sutures (8 of 8), large fontanel with delayed closure (8 of 8), obtuse mandibular angle (8 of 8), delayed teeth eruption (8 of 8), enamel hypoplasia (7 of 8), dysplastic acromial ends of the clavicles (6 of 8), frontal bossing (6 of 8), ocular proptosis (8 of 8), and dysplastic nails (8 of 8). Developmental evaluation according to the revised Denever developmental screening showed normal motor, fine motor-adaptive language, and personal social abilities in all the children. All had normal hepatic and renal functions. Serum calcium and phosphorus concentrations were normal. Two children had low serum alkaline phosphatase concentration. Short stature is a characteristic feature of pycnodysostosis. Seven of the 8 children were born short (length standard deviation score [SDS] = -3 to -1.5). Deceleration of linear growth was significant during the first 3 years of life. All the children had height SDS below -3 at the end of their third year of life. Although short stature is a feature of this genetic disorder, defective growth hormone (GH) secretion in response to provocation with clonidine and glucagon was found in 4 of the 8 patients. These 4 patients had pituitary hypoplasia on the magnetic resonance imaging (MRI) of their brain. In addition, 3 of these 4 patients had demyelination of the cerebrum. Patients with pycnodysostosis (n = 8) had low circulating concentrations of insulin-like growth factor-1 (IGF-1) compared with normal age-matched short children with constitutional short stature (CSS). IGF-I increased significantly after injecting GH for 3 days in these patients. Physiologic replacement with GH (18 U/m(2)/week) divided in daily evening doses subcutaneously increased IGF-1 concentration and improved linear growth velocity and height standard deviation scores (HtSDS) in the 4 children with GH deficiency. These data ruled out GH resistance and proved the usefulness of GH therapy in the management of short stature in these patients. In summary, some patients with pycnodysostosis have partial GH deficiency and low IGF-1 concentration. GH therapy markedly increases IGF-I secretion and improves their linear growth. MRI study of the brain including the hypothalamic-pituitary area is recommended in these children because of the high incidence of pituitary hypoplasia and cerebral demyelination.