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Biomedical subjects

H Moscovich

Publications and source records attributed to H Moscovich.

8 recordsLinked to original sources
PubMed2000

Time-and-motion study on class II copy-milled ceramic inlays.

OBJECTIVES: To obtain an estimate of working times of Class II copy-milled ceramic inlays as an indication of their efficiency, and to analyse factors of influence. METHODS: In a controlled clinical trial, 173 MO/DO or MOD ceramic inlays of the Celay system were constructed in 101 patients. Treatment was carried out by seven dentists. The inlays were replacements of existing amalgam restorations in both molar and premolar teeth. Net-times needed for the treatment and for the laboratory stage were registered. Variables of influence on the working time were assessed by using ln-working times in ANOVA. Differences of working times were expressed as the relative difference between the upper and lower value of each variable (Delta). RESULTS: The mean clinical treatment time was 67(+/-22)min. The laboratory stage required 60(+/-17)min working time. 'Cavity modification technique' (composite basing/conventional, Delta=17%), 'clinical operator' (seven dentists, Delta=57%), and 'size of the restoration' (large/medium, Delta=16%) significantly influenced the clinical treatment time (p<0.001). Although the dentists were familiar with inlay construction, they showed a 25% decrease in working time towards the end of the study. CONCLUSIONS: Class II copy-milled ceramic inlays in this time-and-motion study required about 125min of working time. Working time increased by applying composite basing and making large restorations. The dentist influenced working times, while efficiency increased over time. Dentists needed more laboratory time to produce an inlay than the dental technician.

Adult↗
PubMed1999

In vitro dentine hardness following gamma-irradiation and freezing.

OBJECTIVES: To investigate the short term effects of gamma-irradiation and conventional freezing on the hardness of human dentine. METHODS: Twenty-one dentine disks were produced by transverse sectioning 21 sound extracted human permanent molar teeth. The 2.1 mm thick disks were wet polished using 4000 grit polishing paper. Three lines were drawn dividing each disk into six symmetrical areas. Seven disks were randomly assigned for freezing in water at -18 degrees C for 12 days; seven were exposed to a single dose of 25.2 kGy gamma radiation in water; seven were kept in water at 20 degrees C for 12 days (control). Before treatment, three Vicker's indentations at a load of 30 kg and a dwelling time of 20 s were made in one half of each disk, at equal distances from its edge and centre. Using light microscopy and image analysis software, the indentation diagonals were measured 4 h after preparation. Vicker's hardness values (VHN = kg/mm2) were calculated for each indentation. Following the treatment, VHNs were calculated again, for three symmetrical indentations in the second half of each disk. A statistical analysis was performed using the Wilcoxon rank sum test. RESULTS: The frozen group showed no changes following the treatment (VHN = 58 +/- 6 before vs. 57 +/- 6 after). The irradiation and control groups showed some hardening (VHN = 53 +/- 7 vs. 59 +/- 8; 57 +/- 3 vs. 63 +/- 6, respectively), however all values were within the normal variation. CONCLUSION: Both conventional freezing at -18 degrees C for 12 days in water, and a single gamma-irradiation dose of 25.2 kGy in water, appeared to have no short term effects on the hardness of human coronal dentine.

Dentin↗
PubMed1999

[Human tooth tissue as dental restorative material].

With the recent development of copy-milling systems for porcelain, it has now become possible to construct fitting restorations from natural human tooth substance. This preliminary study aimed to find out whether it is possible to produce a well fitting Class II inlay from an extracted tooth using a copy-milling machine, so that the inlay produced will have enamel over its whole outer surface and dentine on its inner surface. Two pairs of matching sound extracted permanent molars were used. The molars were matched for mesio-distal size of the tooth crown and the convexity of the approximal surfaces. One tooth of each pair was assigned to be the 'donor' tooth, the other tooth being the 'host'. MO inlay preparations were made in the 'host' teeth. These were restored with the milled 'natural inlays' produced from the 'donor' teeth using the CELAY system. The restored 'host' teeth were sliced and examined using light-microscopy. All specimens showed a good fit and the desired location of enamel and dentine. The milling accuracy was assessed in a second experiment. This experiment showed similar marginal gaps for 'natural inlays' as for ceramic inlays. This study has shown that by using the CELAY milling machine it is possible to 'recycle' extracted teeth for the production of accurate restorations.

Dental Cavity Preparation↗
PubMed1998

The novel use of extracted teeth as a dental restorative material--the 'Natural Inlay'.

OBJECTIVE: This preliminary study aimed to find out whether it is possible to produce a well fitting Class II inlay from an extracted tooth using a copy-milling technique. METHODS: Two pairs of matching sound extracted permanent molar teeth were used. The molars were matched for mesio-distal size of the tooth crown and the convexity of the approximal surfaces. One tooth of each pair was assigned to be the 'donor' tooth, the other tooth being the 'host'. MO inlay preparations were made in the host teeth. These were restored with the milled 'Natural Inlays' produced from the donor teeth using the CELAY system. The restored host teeth were sliced and examined using light-microscopy. RESULTS: The specimens showed the desired location of enamel and dentine, and a clinically acceptable fit. CONCLUSION: This study has shown that by using the CELAY milling machine it is possible to 'recycle' extracted teeth for the production of dental restorations.

Cementation↗
PubMed1998

Effect of composite basing on the resistance to bulk fracture of industrial porcelain inlays.

OBJECTIVES: Bases are used in restorative dentistry for several reasons (i.e. isolation, elimination of undercuts, etc). Glass ionomers are the standard materials used as bases for porcelain inlays, despite the disadvantages of their mechanical properties. An alternative basing material is composite: a generous layer of posterior composite is cured and shaped in the cavity before an impression is taken. The composite basing technique has several clinical advantages. The aim of this study was to investigate the effect of the thickness of a composite base on the bulk fracture resistance of industrial porcelain, and to describe the procedure. METHODS: Fifteen porcelain (P) and 15 composite (C) bars, 1-, 2-, and 3-mm thick were joined to form 15 C/P bars, all 4-mm thick. Three groups were created: C 1 mm/P 3 mm (group 1), C 2 mm/P 2 mm (group 2), and C 3 mm/P 1 mm (group 3). The pairs were joined using Twinlook cement, subjected to a three-point bending test and loaded to fracture. The beam theory was used to support and explain the results. RESULTS: The fracture load means were: group 1, 197.7 +/- 18.7 N; group 2, 234.3 +/- 63.3 N, group 3, 336.3 +/- 31.3 N. Group 3 was significantly stronger than group 1 (P = 0.01) and group 2 (P = 0.03). Groups 1 and 2 were not statistically different. CONCLUSION: Composite basing is a tissue conserving method which may significantly increase the resistance to bulk fracture of adhesive porcelain inlays.

Acid Etching, Dental↗
PubMedDate not supplied

In vitro milling accuracy and fit of 'natural inlays'.

OBJECTIVE: This study aimed to investigate the milling behaviour of natural inlays (NI) dental restorations constructed from sound extracted teeth. This was done by comparing the milling accuracy and fit of NI to those of industrial porcelain inlays (PI), milled in the same way. METHODS: A calibration pro-inlay was used to mill three NI and three PI. These were cemented in six acrylic cavities reproduced from the calibration mould, using composite luting cement. No etching and bonding were done. After storage for 24 h in water at room temperature the specimens were sliced buccolingually in a standardised way. For each specimen, two sections were photographed under a light-microscope, resulting in enlarged pictures of the sections. An acetate matrix with the measurement points was placed over each picture in a standardised way. The interfaces between inlays and moulds were measured at 13 fixed points per section using computerised image analysis software. The mean vertical- and floor-interfaces were calculated for each picture, and the overall means were found for each group. Confidence intervals were used for comparison of the differences. The profiles of the milled materials were examined using scanning electron microscopy. RESULTS: There were no differences between NI and PI in the mean interfaces (NI, 102 +/- 8 micrometers; PI, 107 +/- 8 micrometers). Electron microscopy revealed no apparent differences in the profiles of the milled surfaces. CONCLUSION: These findings indicate that the milling accuracy and the fit of natural inlays and milled porcelain inlays are comparable.

Calibration↗
PubMedDate not supplied

Loss of sound tooth structure when replacing amalgam restorations by adhesive inlays.

The replacement of amalgam restorations by adhesive inlays requires an adjustment to the cavity form. This often necessitates the removal of sound tooth substance. Undercuts may be blocked out by a base, but an extensive use of glass ionomer for this purpose is not recommended due to the weak mechanical properties of this material. The present study estimated the amount of sound tissue removed when a given amalgam preparation was reshaped for an adhesive inlay without the use of a base. An MOD amalgam preparation was created in an acrylic tooth. Twenty copies were distributed among 20 operators, who were requested to transform the preparation into an adhesive inlay preparation, removing as little material as possible. One control preparation with parallel walls was produced. All teeth were weighed before and after the alteration. The preparations' volumes were calculated: original amalgam preparation 0.130 ml, parallel preparation 0.136 ml. The minimum removal necessary was therefore 0.006 ml. The amount removed by the operators varied, with a mean volume of 0.0138 +/- 0.004 ml. Statistical analysis showed that for the given preparation, significantly more material was removed than necessary for undercut elimination. On average, more than twice the minimal volume of material was lost. This loss can be minimized by developing alternative techniques for undercut elimination.

Dental Amalgam↗