Marginal fit of indirect composite inlays using a new system for manual fabrication.

AIM: This in vitro study compares a new system for manual chair side fabrication of indirect composite restorations, which uses silicone models after alginate impressions, to CAD/CAM-technology and laboratory manual production techniques. MATRIALS AND METHODS: and study design Each 10 composite inlays were fabricated using different types of production techniques: CAD/CAM- technology (A), the new inlay system (B), plaster model after alginate impression (C) or silicone impression (D). The inlays were adapted into a metal tooth and silicone replicas of the cement gaps were made and measured. Statistical analysis was performed using ANOVA and Tukey's test. Results and Statistics In group A the biggest marginal gaps (174.9µm ± 106.2µm) were found. In group B the gaps were significantly smaller (119.5 µm ± 90.6 µm) than in group A (p=0.035). Between groups C (64.6 µm ± 68.0µm) and D (58.2 µm ± 61.7 µm) no significant differences could be found (p=0.998), but the gaps were significantly smaller compared with group B. Conclusion Chairside manufacturing of composite inlays resulted in better marginal precision than CAD/CAM technology. In comparison to build restorations in a laboratory, the new system is a timesaving and inexpensive alternative. Nevertheless, production of indirect composite restorations in the dental laboratory showed the highest precision.

Identification of psychological comorbidity in TMD-patients.

OBJECTIVES: The aim of the current study was to access the prevalence of depression among patients with Temporomandibular Joint Disorder (TMD) compared to patients with no current TMD. METHOD: Patients (92) and controls (90) answered questionnaires on subjective pain, severity of chronic pain, jaw disability, emotional well-being and depression, and a clinical examination was performed. RESULTS: Temporomandibular Joint Disorder patients reported higher disability of jaw function, compared to controls (p<0.001). The myoarthopathy subgroup (67.4%) had slightly more jaw disability than the myopathy subgroup (p>0.05). While 51% of TMD patients reported poor emotional well-being, only 7.8% of controls were affected (p<0.001). Clinical symptoms of depression were reported by 16% of TMD patients and not in the controls (p<0.001). Among TMD patients, a higher prevalence of depression was observed in the myopathy subgroup. DISCUSSION: A regular screening for psychological problems, using standardized questionnaires, should be integrated in clinical examination of TMD patients.

Load-bearing capacity of direct four unit provisional composite bridges with fibre reinforcement.

The aim of the current in vitro study was to evaluate the load-bearing capacity of provisional four-unit bridges with and without two different types of glass-fibre reinforcement produced in a direct technique with a silicon template from the composite materials Protemp, Luxatemp and CronMix. From each composite material, 30 bridges were manufactured, 10 without fibre reinforcement, 10 with Stick/StickNet and 10 with everStick/everStickNet reinforcement. After artificial aging by thermocycling samples were cemented onto a master model and subjected to load testing in a universal testing machine. Mean force at fracture for the groups without fibre reinforcement varied from 486 to 612 N. Depending on the material combination, fibre reinforcement resulted in a slightly increased or a reduced mean load-bearing capacity, varying from 674 N for the combination of Protemp and Stick to 262 N for CronMix and everStick. Position of fibres within the resin pontic was found to have an important influence on load-bearing capacity of reinforced bridges. Scanning electron microscopic investigation showed good adhesion of everStick fibres to the pre-impregnation resin whereas bonding of Stick fibres to the embedding polymer was incomplete. In conclusion, fibre reinforcement with Stick or everStick did not improve the load-bearing capacity of direct provisional bridges made from Protemp, Luxatemp, or CronMix as the position of fibres could not be controlled during the direct manufacturing process. To increase the load-bearing capacity of the provisional bridges, an exact positioning of fibres at the tension side in the dental laboratory is necessary.

Relationship between enamel erosion and liquid flow rate.

The association of severe erosion with certain habits of consuming soft drinks prompted a study of erosion in relation to fluid flow. In the main experiments, citric acid solution (pH 3.2) was directed at polished enamel surfaces at flow rates of 26, 67 or 126 ml min(-1) through outlets of diameters 1.0, 2.6 or 5.0 mm for up to 20 min. Erosion depth increased with time of exposure and total volume of solution, with increasing flow rate and with decreasing outlet diameter. Scanning electron microscopy of acid-treated surfaces and of the subsurface enamel indicated that the clearance of dissolution products, rather than the mechanical dislodgement of partly dissolved crystal bundles, was the main process involved. For an exposure time of 20 min, erosion increased with (liquid velocity)(1/4). In a secondary experiment, it was found that the erosive potential of a low-erosive drink did not increase with increasing liquid velocity. The rapid increase in the rate of erosion caused by citric acid at low liquid velocities shows that reproducible stirring is essential for precision and intercomparison of in vitro studies. It also accounts for the rapid erosion seen when erosive drinks are consumed from a straw placed labial to the anterior teeth, or are "swished" between the teeth.

Scanning electron microscopy of softened enamel.

After exposing enamel specimens to 0.3% citric acid at pH 3.2 for various times, the acid was titrated to pH 7 before rinsing the specimens in water. After freeze-drying the specimens were examined by scanning electron microscopy. This procedure eliminates artefacts due to drying and mineral precipitation. The results showed that the outer region of softened enamel is much more delicate than previously thought, even after short (5- to 20-min) etching times. Mineral was lost from both prism boundaries and the prism bodies, resulting in a surface presenting thin, separate crystal bundles. In further studies, replicas of subsurface pores, created by resin impregnation, showed the softening depth to be several times greater than is suggested by techniques based on removing the softened enamel by physical forces. The results point to a need for improved methods of measuring softening depth. More importantly, it appears that the outer region of the softened layer remaining after an erosive challenge might be too fragile to resist frictional forces in vivo.

Influence of liquid temperature and flow rate on enamel erosion and surface softening.

Enamel erosion and softening are based on chemical processes which could be influenced by many factors including temperature and acid flow rate. Knowledge of the influence of these variables could have relevance to research experiments and clinical outcomes. Both parameters were investigated using an ultrasonication and profilometry method to assess erosion depth and surface softening of enamel. The influence of temperature was studied by eroding polished human enamel samples at 4, 20, 35 or 50 degrees C for 2 h. Secondly, different liquid flow conditions were established by varying acid agitation. Additionally, a slow laminar flow and a jet of citric acid, to simulate drinking through a straw, were applied to specimens. Erosion depth increased significantly with acid temperature from 11.0 microm at 4 degrees C to 35.8 microm at 50 degrees C. Surface softening increased much more slowly and plateaued at 2.9 microm to 3.5 microm after 35 degrees C. A strong dependence of erosion on liquid flow was revealed. In unstirred conditions only 8.6 microm erosion occurred, which increased to 22.2 microm with slow stirring and 40.9 microm with fast stirring. Surface softening did not increase correspondingly with its largest extent at slow stirring at 3.4 microm.The implication of these data are: first, the conditions for erosion experiments in vitro or in situ need to be specified for reliable comparisons between studies. Secondly, erosion of teeth by soft drinks are likely to be influenced both by the temperature of the drink and individual drinking habits.

Comparative study of wear of enamel induced by alternating and simultaneous combinations of abrasion and erosion in vitro.

Two types of interaction of erosive and abrasive forces with human enamel were analysed in an in vitro study. To simulate toothbrushing or chewing after an acidic challenge, enamel specimens were eroded in 0.3% citric acid (pH 3.2), then brushed with or without silica abrasive. To simulate simultaneous erosion and abrasion, as would occur during chewing of abrasive acidic food, enamel specimens were abraded in a toothbrushing machine, with and without silica abrasive, while immersed in citric acid. Enamel wear was measured by profilometry. In both experiments the combination of erosion and abrasion resulted in significantly greater wear than erosion alone, but no significant differences in wear after brushing with or without abrasive were found. Simultaneous erosion and abrasion resulted in about 50% more wear than alternating erosion and abrasion. It is concluded that softened enamel is highly unstable and potentially easily removed by short and relatively gentle physical action. Chewing of acidic foods with some abrasive properties might cause enhanced tooth wear.

Effect of toothpaste on the plaque inhibitory properties of a cetylpyridinium chloride mouth rinse.

BACKGROUND AND AIMS: Cetylpyridinium chloride (CPC) mouth rinses have moderate plaque inhibitory activity when used alone but rarely have shown adjunctive benefits to tooth brushing with toothpaste. Several explanations for this apparent anomaly can be proferred, including loss of antiseptic activity due to interactions with toothpaste ingredients. The aim of this study was to measure the effect of toothpaste on the plaque inhibitory properties of a CPC mouth rinse using paired rinses of CPC, toothpaste slurry (TP) and water (W). METHODS: The study was a single blind, randomised, seven-treatment, cross over design balanced for residual effects, involving 21 healthy, dentate subjects. The paired rinses were: W-CPC, CPC-W, TP-CPC, CPC-TP, W-TP, TP-W and W-W. Rinsing with solutions or slurries was done for 60 s twice per day. On day 1, subjects were rendered plaque free, suspended tooth cleaning and commenced the allocated rinse regimen. On day 5, plaque was scored by index. A 2(1/2) day wash out of normal oral hygiene was allowed between each regimen. RESULTS: The order from lowest to highest plaque scores was as follows: W-CPC = CPC-W < CPC-TP < TP-CPC < or = W-TP < TP-W < W-W. Several differences in pairs of treatments were statistically significant, the most relevant of which were significantly less plaque with W-CPC compared to TP-CPC, TP-W and W-TP, and significantly more plaque with W-W compared to all other regimens except TP-W. CONCLUSIONS: Toothpaste, whilst possessing some plaque inhibitory activity, when used immediately before a CPC mouth rinse adversely affected the plaque inhibitory action of this antiseptic. This in part may explain the reported lack of adjunctive benefits of CPC rinses to normal oral hygiene practices and supports the suggestion, made for chlorhexidine rinses, that their use should follow toothpaste by at least 60 min.

Acidic solubility of luting cements.

OBJECTIVES: Chemical disintegration of luting cements can adversely affect their long term success. The aim of the present study was to assess the susceptibility of zinc phosphate cement, glass ionomer cement and resin cement to erosion at various pH values. METHODS: Zinc phosphate and glass ionomer cement samples were eroded in 0.3% citric acid adjusted to pH 3.0, 4.0, 5.0, 6.0 and 7.0 at a temperature of 35 degrees C. A control group was stored in saline. Profilometric readings were performed after 30 min and 1h erosion time. Resin cement samples were eroded at pH 3.0 with measurements after 30 min, 6h, 24h and 7 days. A saline control group was measured after 7 days. RESULTS: Erosion of zinc phosphate cement was significantly higher at all pH values than erosion of glass ionomer cement with erosion depth increasing with decreasing citric acid pH. No erosion was seen in the control groups. The resin cement did not show any change in surface profile after the 7 day erosion period compared to the control group. Comparison to dental tissues revealed that erosion of glass ionomer cement in vitro was slightly lower than erosion of enamel and dentine. In contrast, erosion of zinc phosphate cement was much higher.

Cervical tooth wear and sensitivity: erosion, softening and rehardening of dentine; effects of pH, time and ultrasonication.

BACKGROUND: Cervical dentine wear is commonly observed and may be associated with dentine hypersensitivity. Erosion is thought to play a part in both conditions but compared to enamel has been little studied in dentine. AIM: The aims of these studies in vitro were to: (i) determine the effects of citric acid on dentine at different pH values and over time; (ii) measure the depth of dentine demineralisation or softening using ultrasonication; (iii) determine whether softened dentine can be remineralised or rehardened using artificial saliva. METHODS: Groups of flat dentine specimens prepared from unerupted human third molar teeth were: (a) exposed to citric acid at pH 3.2 for periods up to 4 h with mineral water as control; (b) exposed to citric acid at pH 2.54, 3.2, 4.5, 5.5 and 6.0 for 2 h and then subjected to ultrasonication stepwise up to 480 s; (c) exposed to citric acid at pH 2.54, 3.2, and 4.5, placed into artificial saliva for 24 h and then subjected to ultrasonication as in (b). Loss of dentine was measured by profilometry, after, each phase of erosion, ultrasonication and immersion in artificial saliva. RESULTS: Depth of erosion significantly increased non-linearly with time and significantly decreased with increasing pH. Ultrasonication had minimal albeit significant effects on control specimens. Removal of softened dentine increased with ultrasonication time. Depth of softening significantly increased with increasing erosion time to 2 h, plateauing at 2 microm. Depth of softening increased to 2 microm from pH 2.54 to pH 3.2 and decreased at higher pH values thereafter. 24 h in artificial saliva provided no protection to the soften zone against ultrasonicaion. Citric acid at all pH values and exposure times removed the dentine smear layer to expose tubules. Ultrasonication did not remove the smear layer on control specimens but removed all deposits formed after exposure to artificial saliva. CONCLUSION: It is concluded that dentine is susceptible to erosion even at relatively high pH, the tubule system is readily exposed and dentine, unlike enamel, shows little propensity to remineralise.

Further modification to soft drinks to minimise erosion. A study in situ.

Soft drinks have been successfully modified to reduce enamel erosion. The aim of this study was to further modify an original low erosive blackcurrant drink product by the addition of a gum, to manipulate more favourably other drink parameters. The study was a single-blind, randomised four treatment crossover design involving 12 healthy volunteers. During 10 working-day study periods, subjects wore enamel samples in the mid palatal region of a removable appliance. Specimens were taped to expose a 2-mm enamel window. The drinks under test were: (1) Orange juice, (2) Original blackcurrant drink, (3) Water, and (4) Experimental blackcurrant drink. Drinks were imbibed at 250-ml volumes 4 times a day during appliance wearing from 09.00 to 17.00. Appliances were removed at lunchtime. Measurements of specimens were made at baseline, 2, 5 and 10 days using a profilometer. One 5-day and one 10-day specimen from each subject during each treatment were ultrasonicated. Significant differences, in erosion between drinks, were seen at days 5 and 10. Comparisons of preselected pairs of drinks of interest showed significantly reduced erosion by the two blackcurrant drinks compared to orange juice with no significant differences from water. The original blackcurrant drink produced significantly less erosion than the experimental drink. Ultrasonication removed enamel from the Orange juice specimens but very little from those exposed to water and the two blackcurrant drinks. Extrapolating the effects of both blackcurrant drinks suggested that alone they should not cause significant clinical erosion in a lifetime's intake of 1 litre per day.

Erosion and attrition of human enamel in vitro part II: influence of time and loading.

OBJECTIVES: To determine the influence of load and time on enamel wear by attrition under neutral and acid environments in vitro. METHODS: Groups of 10 enamel cusp and smooth surface specimens obtained from unerupted third molars were opposed in a wear machine under loads of 200, 400 and 600 g in citric acid at pH 3.2 and in physiological saline at 35 degrees C for 30 min (2280 wear cycles). The experiment was repeated with a load of 600 g for 10 and 20 min accompanied by 10 taped specimens to measure erosion only. Erosion and attrition of smooth surface specimens was determined by profilometry. RESULTS: At a load of 600 g attrition in saline increased with time from 7.9 microm (SD 3.7 microm) at 10 min, 10.2 microm (SD 4.8 microm) at 20-25.5 microm (SD 9.1 microm) after 30 min and combined attrition/erosion in citric acid from 1.5 microm (SD 0.4 microm) to 2.5 microm (SD 0.9 microm) to 6.0 microm (SD 3.7 microm). At a fixed time of 30 min, attrition in saline was 5.2 microm (SD 3.6 microm) at 200 g and 8.1 microm (SD 1.5 microm) at 400 g and combined attrition/erosion in citric acid 2.8 microm (SD 1.2 microm) and 3.6 microm (SD 0.7 microm). Comparison between both environments revealed significant differences at fixed load at all time points (p < 0.01) and at fixed time between 400 and 600 g (p < 0.01). CONCLUSIONS: Load and time significantly influence enamel wear both in acid and neutral conditions but the effects were not linear.

Erosion and attrition of human enamel in vitro part I: interaction effects.

OBJECTIVE: The aim of the study in vitro was to measure the interplay of attrition and erosion of human enamel under several different pH conditions. MATERIALS AND METHODS: Cusp and smooth surface enamel specimens were prepared from unerupted human third molar teeth. Cusp and smooth surface specimens opposed each other in a wear machine under a load of 600 g. The machine simulated tooth grinding for 30 min (2280 wear cycles). Six groups of 10 specimens were worn in the following environmental conditions: saline, citric acid at pH values of 3.2, 5.5 or 7.0 and two cycling groups (pH 3.2/saline or saline/pH 3.2). Additionally, 10 smooth surface specimens were exposed to the same fluids without attrition. Tissue loss on smooth surface specimens was determined by profilometry. The worn specimen surfaces were studied by SEM. RESULTS: Attrition depth in saline and pH 7.0 citric acid was 25.5 microm. At pH 3.2 and 5.5 attrition depths were 6.0 and 4.3 microm, respectively. Cycling in saline/citric acid and vice versa produced attrition depths of 9.2 and 7.9 microm, respectively. In the erosion only specimens lesion depths were 3.0, 1.2 and 0 microm at pH 3.2, 5.5 and 7.0 and saline, respectively. Attrition specimens at pH 7.0 and in saline showed very rough surfaces. At low pH enamel surfaces appeared flat and smooth. CONCLUSIONS: Enamel wear in neutral conditions is significantly higher than in acidic conditions (p < 0.05), apparently due to a smoothing effect of erosion on contacting surfaces.

Evaluation of pH and erosion time on demineralisation.

In the current study the effect of various pH values of citric acid and erosion time on erosion depth and subsurface demineralisation of human enamel was studied. In a laboratory investigation, six groups of 10 samples were eroded in 0.3% citric acid for 2 h at pH 2.54, for 2 h or 4 h at pH 3.2 and for 2 h, 4 h or 8 h at pH 4.5. The erosion depth was measured using a profilometer. The demineralised layer was then removed by ultrasonicating the samples with profilometric measurements taken at 5, 30, 120, 240 and 480 s ultrasonication time. The six test groups were classified by analysis of variance into four homogeneous groups according to their erosion depth and into three homogeneous groups according to their subsurface demineralisation. Erosion depth clearly depended on the pH value of the acid and the contact time. Depth of subsurface demineralisation and surface morphology did not depend on erosion depth. Similar subsurface demineralisation depths can be produced by appropriate combinations of pH and contact time.

Effect of time on the remineralisation of enamel by synthetic saliva after citric acid erosion.

The aim of this in vitro study was to determine the influence of remineralisation time on rehardening of surface-softened enamel after citric acid erosion. Seven groups of 13 samples of human enamel were eroded in 0.3% citric acid at pH 3.2 for 2 h followed by profilometric measurements. Individual groups of specimens were placed in artificial saliva for 1, 2, 4, 6, 9 or 24 h. A control group was placed in isotonic saline for 24 h. After new profilometric measurements samples were ultrasonicated stepwise up to 480 s with profilometric measurements performed at 5, 30, 120, 240 and 480 s to measure the depth of surface softening. The control group had a softened surface layer of mean thickness 2.9 microm. Mineral deposition was seen at all remineralisation times by scanning electron microscopy. Exposure to artificial saliva for 1, 2 or 4 h produced a partial rehardening of the softened enamel; the additional surface losses produced by ultrasonication were lower and time delayed compared to the control group. Specimens remineralised for 6, 9 and 24 h showed little evidence of surface loss after ultrasonication. The data suggest that a complete rehardening of the softened enamel in vitro is reached after a remineralisation time of 6 h. These data are of clinical relevance to tooth wear. However, there is a need for studies in situ of enamel demineralisation and remineralisation.

The use of ultrasonication to study remineralisation of eroded enamel.

The aim of this study was to use ultrasonication and profilometry as methods to study de- and remineralisation of citric acid-eroded enamel at different pH values. Seventy-eight polished human enamel samples were divided into three test and three control groups of 13 specimens each. Three specimens of each group were chosen for SEM examination. The samples were exposed to 0.3% citric acid at pH 2.54, 3.2 or 4.5 for 2 h. The depths of the resulting lesions were measured by profilometry. The test groups were placed in artificial saliva and the control groups were stored in saline (0.9% NaCl) for 24 h and new profiles recorded. Finally all specimens were ultrasonicated in water for 5, 30, 120, 240 and 480 s with profilometric measurements at each time point. Ultrasonication of the test groups after remineralisation showed little effect on the lesion depth, whereas the control groups had an enamel loss of 2.1 microm at pH 2.54, 2.9 microm at pH 3.2 and 0.4 microm at pH 4.5 after 30-second ultrasonication. These differences from respective test groups were statistically significant at pH 2.54 and 3.2 but not at pH 4.5. Ultrasonication of control pH 2.54 and 3.2 specimens removed an amorphous covering layer to reveal a flattened surface with prisms outlined by prism boundaries. It can be concluded that remineralisation in artificial saliva stabilises the surface softened enamel against ultrasonication.

Ultrasonication as a method to study enamel demineralisation during acid erosion.

The aim of this study was to use ultrasonication as a method to measure subsurface demineralisation of enamel. Polished human enamel samples with surface profiles within +/-0.3 microm were divided into 6 groups of 10 specimens. The groups of specimens were exposed to 0. 3% citric acid (pH 3.2) for 30 min, 1, 2, 3 or 4 h. The depths of the resulting lesions were measured using a profilometer. A control group was stored in water for 4 h. Ultrasonication in water was performed on the specimen groups for 5, 30, 120, 240 and 480 s with profilometric measurements at each time point. The depth of the erosion increased linearly with the exposure time. Most of the additional loss of enamel occurred with the 5-second ultrasonication. The 30-min and 1-hour erosion lesions were further deepened by approximately 1 microm with 5 s of ultrasonication. The 2-, 3- and 4-hour lesions were deepened by 2-4 microm with 5 s of ultrasonication. There were no changes in the control group. It is concluded that ultrasonication removed softened enamel from the surface of the eroded enamel. Ultrasonication together with accurate measurement of lesion depth by profilometry offers a useful method for studying the depth of enamel softening associated with erosion.

Long-term results of telescopic crown retained dentures--a retrospective study.

The clinical data for 250 telescopic crown retained dentures involving 617 abutment teeth preparations were collected and analysed in a retrospective study to ascertain the survival rate of the dentures and their abutment teeth. During the study period 10.6% of the abutment teeth had to be extracted. An increased number of telescopic crowns significantly improved the longevity of the prostheses and their associated abutment teeth in most denture designs, but this was not found to be the case with bilateral free-end saddle designs without an anterior bounded saddle. The use of more than four abutment teeth did not result in a higher survival rate.

The human mandibular intercondylar angle measured by computed tomography.

In axial computed tomography it is possible to measure the intercondylar angle at the intersection of the longitudinal axes of the condyles. Published values range from 131 to 165 degrees. This angle was determined here in two groups of patients with (n = 22) and without (n = 12) temporomandibular joint dysfunction. A third group of children (n = 12) aged 4-9 years was included to investigate any age-related change in the angle. In the group of healthy individuals, a range of 105 to 165 degrees was found, with a mean intercondylar angle of 139 degrees. In the group with temporomandibular joint dysfunction the mean angle was 143 degrees with a range from 85 to 170 degrees. No statistically significant relation could be shown between intercondylar angle and joint dysfunction. In the group of children the mean angle was 138 degrees with values ranging from 90 to 180 degrees. No significant differences could be demonstrated among the groups. The absolute value of the intercondylar angle seems to be independent of factors such as sex, age and functional disorders of the joint.

Radiographic inspection of dental castings.

Underdimensioning may adversely affect the clinical use of a crown or bridge. Insufficient dimensions may be due to inadequate modelling or deficiencies caused by the casting process. The dimensions of cast objects are measured mechanically using a calliper. This method has often proved to be insufficient in detecting areas of too small dimensions. This paper presents a non-destructive method of inspecting dental castings using radiography. The occlusal thickness of a random sample of 150 crowns made during regular clinical treatment in our department was inspected mechanically and radiographically. We found that 19% of the crowns were only 0.1 mm thick or less at the thinnest spot, 18% were between 0.1 and 0.2 mm and 9% were between 0.2 and 0.3 mm. In comparison to mechanical examination, radiographic inspection usually showed smaller values.