The effect of calcium fluoride (CaF(2)) on the chemical solubility of an apatite-mullite glass-ceramic material.

OBJECTIVE: To assess the effect of varying CaF(2) on the chemical solubility of apatite-mullite glass-ceramic (G-C) materials in both the glassy and crystallized states. METHODS: Apatite-mullite forming glasses used in this study are ionomer cement derivatives based on the general formula (4.5SiO(2)-3Al(2)O(3)-1.5P(2)O(5)-3CaO-XCaF(2)). Six glass formulations were produced where X=0.5, 1, 1.5, 2, 2.5 and 3, and called HG1-6, respectively. Batches were melted in covered silliminite crucibles in a furnace overnight at 1050 degrees C, then at 1450 degrees C for 2h, before quenching in water. The six glass compositions were analyzed using differential thermal analysis (DTA), X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRF). Thirty discs (2mm thick and 12 mm diameter) were produced per glass using the lost wax casting technique. Ten were left as cast and 10 heat treated to either apatite or apatite-mullite. Solubility testing was carried out according to International Standard BS EN ISO 6872 1999 and the mass difference in solubility calculated as mug/cm(2). A lithium disilicate G-C system was used as a control material. RESULTS: All compositions formed glasses and on heat treatment could form apatite and apatite-mullite. The as-cast glass samples were the most soluble followed by the apatite samples. The apatite-mullite G-C was significantly less soluble than the other two phases (p<0.05) for all six compositions. The control material was significantly less soluble than all the HG glass-ceramic compositions for every phase (p<0.05). Decreasing the CaF(2) content (3-0.5 mol%) led to a decrease in solubility, without affecting the ability of the material to form apatite and apatite-mullite phases. SIGNIFICANCE: Increasing the CaF(2) content increases the chemical solubility for the glass, apatite G-C and apatite-mullite G-C phases. The solubility values obtained show that all the compositions, as cast and heat treated would be suitable for use as core ceramics.     

Cementum and dentin in hypophosphatasia

Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum.     

Plunging or cervical ranula. Review of the literature and report of 4 cases.

A review of the literature pertaining to plunging ranula is presented with special emphasis on the historical development of the various aetiological theories and treatment recommendations. Also 4 cases of plunging ranula are presented; three were treated by extirpation of the sublingual gland and one was treated by exteriorization of the ranula into the oral cavity. The treatment methods used here are discussed in relationship to the accepted aetiological theory.     

Effect of reducing frequency of augmented feedback on manual dexterity training and its retention

OBJECTIVE: The study addressed the impact of the frequency of tutorial-enriched augmented visual feedback, provided by a virtual simulation system (DentSim), on the skill acquisition for a cavity preparation task in novice dental students. METHODS: Thirty-six subjects were assigned to two training groups and a control group. The task consisted of a geometrical cross preparation on the lower left first molar. All subjects performed a pre-test to assess their basic skill level. The training groups received simulation feedback, enriched with tutorial information, across acquisition. One group trained under continuous augmented feedback, while a second group trained under an intermittent (66% of the time) feedback. At both 1-day and 4-month interval, subjects performed a retention test to explore learning specific effects. Two transfer tests were added to assess the extrapolation of the learned skills to an adjacent molar. All tests were performed in the absence of feedback. A control group performed all the tests, without preceding training. All preparations were graded by the simulation system. RESULTS: The training groups performed similarly across acquisition and improved with practice (ANOVA, P<0.001). After 1 day and 4 months of no practice, the training groups outperformed the control group on a retention test (ANOVA, P<0.001) and transfer test (ANOVA, P<0.001). CONCLUSIONS: Performance and learning of a cavity preparation task on a simulation unit was independent of the frequency of tutorial-enriched augmented visual feedback within the range tested. Training sessions on a simulation unit could be alternated with training sessions in the traditional phantom head laboratory.     

Oral lichen planus, amalgam and other restorative materials

Mucosal lesions in the oral cavity, identical to oral lichen planus (OLP), as a consequence of contact with in particular dental silver amalgam may be due to an allergic reaction to mercury or, possibly, a toxic effect on the oral mucosa. Substitution of amalgam preferably by gold--unless sensitisation to gold exists--often results in remission, which sustains a pathogenic role of amalgam in OLP. Substitution of amalgam should be considered if the mucosal lesions correspond topographically to the restorations and epicutaneous patch testing results in a positive reaction on mercury.     

Syndromes 22. Rieger's syndrome

Rieger syndrome is a rare autosomal-dominant disorder characterized by defects of the anterior chamber of the eye, failure of the periumbilical skin to involute, and developmental malformations of the dentition. Recognition of the dental anomalies may result in the early diagnosis of this syndrome and prevent progressive visual loss.     

The influence of surface free-energy on planimetric plaque growth in man

The purpose of this study was to examine the change in plaque area over nine days in vivo on four materials with different surface free-energies (s.f.e.). Twelve healthy dental students participated in a cross-over, split-mouth, double-blind study. Supragingival plaque formation was recorded over a nine-day period, on four different materials: fluorethylenepropylene (Teflon) (FEP), parafilm (PAR), cellulose acetate (CA), and enamel (E) with s.f.e. of 20, 26, 57, and 88 erg/cm2, respectively. Strips made from the first three materials were stuck to the buccal surface of an upper incisor. The remaining incisor was carefully polished and served as an enamel surface. The increase in plaque was evaluated after three, six, and nine days. A planimetrical analysis was used so that the plaque area could be expressed as a percentage of the total buccal tooth surface. This procedure was repeated on each subject, so that at the end, each pair of central or lateral incisors received the four tested materials. The results indicated that the adherence of micro-organisms on pellicle-coated substrata was influenced by the material's s.f.e.; there was an association between the s.f.e. of the substrata and the supragingival plaque extension in vivo. High surface free-energy substrata in the oral cavity attracted more micro-organisms than did low energetic materials. Additionally, the bacterial adhesion seemed very weak on surfaces with a low s.f.e.     

The combined use of two endosteal implants and iliac crest onlay grafts in the severely atrophic mandible by a modified surgical approach

Seventeen patients, who received an iliac crest onlay bone graft augmentation to their severely atrophic mandible with simultaneous placement of two endosteal implants by a modified surgical approach, were studied retrospectively. Follow-up ranged from 0.5 to 7.9 years after implant loading with an average follow-up of 4.3 years. Frequency of wound dehiscences and other postoperative complications, the extend of resorption of the initial graft, and the implant success rate were assessed. Two patients, who had a previous history of preprosthetic and implantological procedures at the surgical site, developed a serious wound dehiscence with loss of two implants in one patient and need for antibiotic treatment and sequestrectomy in the other patient. One implant was lost in two other patients with a negative surgical history, resulting in an implant success rate of 88.2%. The average resorption at the last follow up visit was 15% of the initial graft. Damage of the mental nerve was seen in 14.7% of nerves. Our preliminary data indicate that the procedure presented provides a reliable and predictable method for the construction of an implant-bearing overdenture in patients with a severely atrophic mandible. This one-step procedure can not be recommended for patients with a history of surgery in the anterior mandible.