Torsion and linear accuracy in intraoral scans obtained with different scanning principles

PurposeFew investigations have examined the production of single restorations using intraoral scanners (IOS). Data on full-arch scans are rare, and data regarding torsion within the entire arch are very sparsely reported. Therefore, the aim of this study was to examine the deviations of torsion and linear distances in full-arch scans of three IOS based on different scanning principles.MethodsA cobalt-chrome-molybdenum alloy master model (CCMM) with four hemispheres was fabricated by laser sintering. The CCMM was digitized using a laboratory scanner (ATOS-Core/GOM) and scanned with three IOS (Omnicam/Sirona(OC); True Definition/3M(TD); TriosII/Cara-Version/Kulzer(TR)). All scan data were exported in a standard STL-file format and were analyzed with GOM Inspect software (V7.5/GOM). Torsion between the right and left side of the arch and linear accuracy (trueness and precision) were evaluated. After normality was confirmed, all data were subjected to parametric statistical analyses.ResultsThe torsion ranged from 0.07 ± 0.03°(OC) to 0.29 ± 0.14°(TD). Pairwise comparisons showed significant differences between the OC and TD scanners and between the TR and TD scanners. The linear distances ranged from 6 ± 5 μm(OC) to 298 ± 317 μm(TD). Significant differences were observed among all investigated IOS (p = 0.05).ConclusionsAlthough the highest torsion was observed for the TD scanner, it is still not clear whether the differences between the IOS are related to the scanning principle or to the scanning algorithm. Due to the high clinical relevance of full-arch restorations, future studies should consider torsion. Regarding linear accuracy, no general difference related to the scanning principles of the IOSs was observed.     

Presurgical orthopedics by drink plates does not significantly normalize deglutition in infants with cleft lip and palate

Objective:To test the null hypothesis of no significant difference between intraoral pressure characteristics in infants with cleft lip and palate (CLP) with or without presurgical orthopedic (PSO) plates (groups CLP and CLP-PSO), compared with noncleft infants.Materials and Methods:Intraoral atmospheric pressure assessments were performed on 17 subjects with preoperative CLP (m/f, 11/6; mean/SD, 4.76/0.92 months) and a matched control group (n = 24; m/f, 15/9; mean/SD, 4.88/0.9 months), for 200 seconds, simultaneously at the vestibulum (vestibular space [VS]) and at the palate (subpalatal space [SPS]), using a prepared pacifier connected to a digital manometer. Areas under the pressure curves (AUC), frequencies, durations, and magnitudes of swallowing peaks and pressure resting plateaus were compared between trial groups and locations (VS, SPS) using a two-factor analysis of variance for repeated measures, Kruskal-Wallis test, and Mann-Whitney U-test (α = .05).Results:The null hypothesis was rejected: Globally, there were statistically significant differences in intraoral pressure characteristics between groups CLP, CLP-PSO, and control (all P < .01), with significantly higher negative pressures (AUC) in the control subjects compared with those of CLP or CLP-PSO. There were significant effects by the location of pressure recordings (VS, SPS) and their interaction with all treatment groups. Differences between noncleft and CLP subjects were more pronounced in the VS than in the SPS. There was no significant effect by PSO.Conclusion:PSO does not improve deviated swallowing characteristics during suction in CLP infants.     

Physical properties of self-, dual-, and light-cured direct core materials

The objective of this study is to evaluate flexural strength, flexural modulus, compressive strength, curing temperature, curing depth, volumetric shrinkage, water sorption, and hygroscopic expansion of two self-, three dual-, and three light-curing resin-based core materials. Flexural strength and water sorption were measured according to ISO 4049, flexural modulus, compressive strength, curing temperature, and curing depth according to well-proven, literature-known methods, and the volumetric behavior was determined by the Archimedes’ principle. ANOVA was calculated to find differences between the materials’ properties, and correlation of water sorption and hygroscopic expansion was analysed according to Pearson (p < 0.05). Clearfil Photo Core demonstrated the highest flexural strength (125 ± 12 MPa) and curing depth (15.2 ± 0.1 mm) and had the highest flexural modulus (≈12.6 ± 1.2 GPa) concertedly with Multicore HB. The best compressive strength was measured for Voco Rebilda SC and Clearfil DC Core Auto (≈260 ± 10 MPa). Encore SuperCure Contrast had the lowest water sorption (11.8 ± 3.3 μg mm⁻³) and hygroscopic expansion (0.0 ± 0.2 vol.%). Clearfil Photo Core and Encore SuperCure Contrast demonstrated the lowest shrinkage (≈2.1 ± 0.1 vol.%). Water sorption and hygroscopic expansion had a very strong positive correlation. The investigated core materials significantly differed in the tested properties. The performance of the materials depended on their formulation, as well as on the respective curing process.     

Clinical anti-microbial efficacy of a new zinc citrate dentifrice

This crossover design clinical study compared the anti-microbial effects of a new 1% zinc citrate dentifrice with a control formulation. Thirty adults completed a washout phase and baseline samples of dental plaque, buccal mucosa, tongue, saliva, and plaque collected to enumerate anaerobes and streptococci. Subjects were randomly assigned a test dentifrice to use for the next 13 days. Oral samples similar to the baseline were collected on day 14 prior to oral hygiene for microbial analysis. The subject then placed a custom intra-oral stent with hydroxyapatite (HA) squares and brushed their teeth with their assigned dentifrice. Oral samples and HA squares were collected 5 h later for microbial analyses. This completed the study with one test dentifrice. The entire study was repeated with the alternate dentifrice after a second washout phase. Whereas baseline samples demonstrated no significant differences in microbial parameters between the two treatment groups (p > 0.05), subjects provided the zinc citrate dentifrice demonstrated 24–52% reductions in anaerobic bacteria and streptococci on day 14 versus the control paste (p < 0.05). In the 5-h post-brushing samples, subjects provided the zinc citrate toothpaste demonstrated 27–49% reductions for anaerobic bacteria and streptococci (p < 0.05). Additionally, in situ microbial biofilm formation on HA disks was significantly inhibited amongst the zinc citrate group (p < 0.05). Significant reductions in anaerobic bacteria and streptococci were observed amongst all intra-oral locations along with in situ biofilm formation after use of the zinc citrate dentifrice.     

Two years survival rate of class II composite resin restorations prepared by ART with and without a chemomechanical caries removal gel in primary molars

The aim was to test the null hypotheses that there is no difference: (1) in carious lesion development at the restoration margin between class II composite resin restorations in primary molars produced through the atraumatic restorative treatment (ART) with and without a chemomechanical caries removal gel and (2) in the survival rate of class II composite resin restorations between two treatment groups after 2 years. Three hundred twenty-seven children with 568 class II cavitated lesions were included in a parallel mouth study design. Four operators placed resin composite (Filtek Z 250) restorations bonded with a self-etch adhesive (Adper prompt L pop). Two independent examiners evaluated the restorations after 0.5, 1, and 2 years using the modified Ryge criteria. The Kaplan–Meier survival method was applied to estimate survival percentages. A high proportion of restorations were lost during the study period. Therefore, the first hypothesis could not be tested. No statistically significant difference was observed between the cumulative survival percentages of restorations produced by the two treatment approaches over the 2-year period (ART, 54.1 ± 3.4%; ART with Carisolv™, 46.0 ± 3.4%). This hypothesis was accepted. ART with chemomechanical gel might not provide an added benefit increasing the survival percentages of ART class II composite resin restorations in primary teeth.     

Interaction between deglutition,tongue posture,and malocclusion: A comparison of intraoral compartment formation in subjects with neutral occlusion or different types of malocclusion

Objective:To test the null hypothesis of no significant difference in terms of intraoral pressure curve characteristics assessed simultaneously at the subpalatal space (SPS) and the vestibular space (VS), during different oral postures, between four groups with either an Angle Class II/1 (II1), Angle Class II/2 (II2), anterior open bite (O) malocclusion, or a neutral occlusion control group (I).Materials and Methods:Intraoral pressure recordings were performed simultaneously in the VS and SPS of 69 consecutive subjects (n_II1  =  15; n_II2  =  17; n_O  =  17; n_I  =  20; mean age/standard deviation 18.43/6.60 years). Assessments included defined sections of open mouth posture (OMP, 30 seconds), anteriorly closed mouth condition (60 seconds), dynamics by a tongue-repositioning maneuver (TRM, 60 seconds), swallowing, and positive pressure generation (PP, 10 seconds). Interactions of malocclusion, compartment location, and posture on pressure curve characteristics were analyzed by Kruskal-Wallis and Mann-Whitney U-tests, adopting an α level of 5%.Results:Globally significant group differences were detected at the VS (plateau duration and median peak heights during TRM; area under pressure curve [AUC] during PP) and SPS (AUC during TRM and PP). Subjects with anteriorly nonopen dental configurations (groups I and II2) were able to keep negative pressure levels at the VS for longer time periods during TRM, compared to groups O and II1.Conclusions:The null hypothesis was rejected for mean VS plateau durations and peak heights and for SPS AUC. Negative pressures at the VS may stabilize outer soft tissues passively and may explain the dental arch form shaping effect by mimic muscles.     

Influence of bisphosphonates on the osteoblast RANKL and OPG gene expression in vitro

Bisphosphonates are widely used in the clinical treatment of bone diseases with increased bone resorption. In terms of side effects, they are widely known to be associated with osteonecrosis of the jaw (BONJ). The objective of this study was to evaluate the effect of bisphosphonates on the gene expression of receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) in vitro. Nitrogen-containing and non-nitrogen containing bisphosphonates have been compared. Human osteoblasts were stimulated with zoledronate and ibandronate at concentrations of 5 × 10⁻⁵ M, 5 × 10⁻⁶ M, and 5 × 10⁻⁷ M over the experimental period of 14 days. Furthermore, the hOB cell lines were stimulated by clodronate at concentrations of 5 × 10⁻³ M, 5 × 10⁻⁵ M, and 5 × 10⁻⁶ M. At each point in time, the gene expression levels of RANKL and OPG were quantified by real-time RT-PCR. The results showed a moderate enhancement of OPG gene expression whereas RANKL gene expression was strongly increased by nitrogen-containing bisphosphonates reaching a maximum after 14 days at high concentrations of 5 × 10⁻⁵ M. Lower concentrations did not enhance the RANKL and OPG expression considerably. The non-nitrogen-containing bisphosphonate clodronate, however, effected OPG and RANKL gene expression much less, even at higher concentrations of 5 × 10⁻³ M. The above-mentioned data suggest an enhanced RANKL/OPG gene expression after stimulation by bisphosphonates. Interestingly, clodronate might have little influence on osteoblast/osteoclast interaction with respect to OPG and RANKL gene expression.     

Thickness of softened human enamel removed by toothbrush abrasion: an in vitro study

The aim of the study was to assess the thickness of softened enamel removed by toothbrushing. Human enamel specimens were indented with a Knoop diamond. Softening was performed with citric acid or orange juice. The specimens were brushed in a brushing machine with a manual soft toothbrush in toothpaste slurry or in artificial saliva. Enamel loss was calculated from the change in indentation depth of the same indent before and after abrasion. Mean surface losses (95% confidence interval) were recorded in treatment groups (in nanometers): (1) citric acid, abrasion with slurry = 339 (280–398); (2) citric acid, abrasion with artificial saliva = 16 (5–27); (3) orange juice, abrasion with slurry = 268 (233–303); (4) orange juice, abrasion with artificial saliva = 14 (5–23); (5) no softening, abrasion with slurry = 28 (10–46). The calculated thickness of the softened enamel varied between 254 and 323 nm, depending on the acid used.     

The measurement threshold and limitations of an intra-oral scanner on polished human enamel

ObjectiveTo investigate the measurement threshold of an intra-oral scanner (IOS) on polished human enamel.MethodsThe optical performance of an IOS was compared to a gold-standard non contacting laser profilometer (NCLP), on a painted microscope slide, compared to increasing particle size of silicon-carbide papers (21.8–269.0 μm) and separately on polished human enamel with increasing step-heights. The enamel samples were randomised (n = 80) and scanned using the IOS and NCLP at increasing step-height depths (μm) (1.87–86.46 μm) and quantified according to ISO:5436-1. The measurement threshold of the IOS was determined using a custom designed automated lesion localisation algorithm, corroborated by Gaussian skewness (Ssk) and kurtosis (Sku) analysis, to assess the minimum step-height measured on each enamel sample.ResultsThe NCLP showed statistically increased Sq surface roughness for all silicon carbide particle sizes compared to the microscope slide, whereas, the IOS Sq roughness discriminated silicon-carbide particles above 68.0 μm compared to the glass slide (p ≤ 0.02). On polished enamel, the automated minimum detectable step-height measurable on each sample was 44 μm. No statistically significantly different step-height enamel lesion measurements were observed between NCLP and IOS above this threshold (p > 0.05).SignificanceThis study revealed the fundamental optical metrological parameters for the IOS, was step-heights above 44 μm and this reflects the data acquisition of the system. These results highlight the limitations of IOS used in this study, mandating further research to optimise the performance of other IOS systems, for measuring wear of materials or tooth wear on human unpolished natural enamel surfaces.     

Pain levels in patients during periodontal probing and mechanical non-surgical therapy

The purpose of this study was to assess the degree of pain during periodontal probing and mechanical non-surgical therapy according to age, gender, and intersubject variation such as tooth type, tooth surfaces or regions of mouth, probing depth, and bleeding on probing. The study was carried out on 64 patients with chronic periodontitis. Pain/discomfort of patients during both periodontal probing and scaling and root planing (SRP) was measured using a visual analog scale (VAS). During periodontal probing and SRP, VAS scores decreased with increasing age for two procedures (Spearman ρ, −0.301 and −0.348, respectively; P < 0.01). VAS scores were considerably lower for oral sites than for facial sites. VAS scores in probing were significantly higher in sites ≥4 mm deep than sites <4 mm deep. Sites bleeding on probing had a significantly higher VAS scores than sites no bleeding on probing (p < 0.05). The results showed that although there is no difference between genders, the intensity of pain during periodontal probing and SRP was different dramatically between patients as well as vary between different locations in the same mouth. If pain responses for probing in different several regions in the same mouth during initial examination were noted into patient chart used for initial examination, the therapist will recognize patients with elevated pain responses. If need be, they will then apply some pain control medication or anesthetic for patients during probing and SRP.     

The variability of the curve of Spee

The aim of this study was to examine possible parameters correlating to the shape of the curve of Spee (COS) by analyzing multiple setups of the same Angle class I patient case. In all, 65 setups of the same Angle class I patient case were constructed. We measured the depth of the COS, length and width of the dental arch, steps, rotations, spaces and symmetry of the constructed setups. With a correlation analysis, possible relationships between the depth of the COS and measured parameters were evaluated. The COS in the constructed setups was more exaggerated than in the reference case but none of the measured parameters correlated to the depth of the COS. The largest deviation was found on the mesiobuccal cusp tip of the first molar (−0.5 ± 0.4 mm left side; −0.8 ± 0.5 mm right side). This study found a negative correlation between the length and width of the lower dental arch (r = −0.61). While maintaining Angle class I, a large spread width of the depth of the COS, the dental arch width and length was shown. The different manifestations of the COS in this study show the freedom of arrangement of the individual tooth morphology without exhibiting a correlation to parameters of the dental arch.     

In vitro comparison of chlorhexidine and povidone–iodine on the long-term proliferation and functional activity of human alveolar bone cells

This work reports the behaviour of osteoblastic human alveolar bone cells (first subculture) in the presence of chorhexidine (CHX) and povidone–iodine (PI). Short contact (2 min) of 24-h cultures with CHX, at 0.12 and 0.2%, and PI, at 5 and 10%, caused cell death within minutes; contact with 1% PI resulted in loss of the elongated characteristic cell shape. Cell adhesion was adversely affected at concentrations higher than 5 × 10⁻⁵% CHX or 0.05% PI. Long-term exposure to CHX at 10⁻⁵ and 10⁻⁴% or PI at 10⁻⁴% had little effect on cell growth and caused an induction in the synthesis of alkaline phosphatase (ALP). Concentrations of CHX and PI similar and higher than, respectively, 5 × 10⁻⁴% or 0.05% caused dose-dependent deleterious effects. CHX affected mainly the cell growth, whereas the effects of PI were observed mostly in ALP production and matrix mineralization. Considering the levels of CHX and PI used routinely in the oral cavity, results suggest that CHX has a higher cytotoxicity profile than PI. This observation might have some clinical relevance regarding the potential utility of PI in the prevention of alveolar osteitis.     

Patients' and dentists' perception of dental appearance

The purpose of this study was to compare the patients' and dentists' perception of dental appearance. Based on internationally accepted guidelines about dental esthetics, a questionnaire was developed to measure “dental appearance” (QDA). Eleven items defined a QDA sum score (0 = “absolutely satisfied”, 44 = “absolutely dissatisfied”). The QDA was completed by 16 patients (eight women, eight men, mean age 63 ± 9 years) before and after a complete oral rehabilitation. Forty-two dentists evaluated the esthetics before and after rehabilitation on a visual analog scale (VAS, 0 = “absolutely unesthetic”, 100 = “absolutely esthetic”). The patients' quoting showed a significant esthetic improvement (QDA sum score) from 22 before treatment to 3.5 after treatment (P ≤ 0.001). Although most of the dentists judged an improvement in most of the patients dental appearances, no significant correlation could be found between patients' and dentists' judgment regarding dental appearance (r = −0.13–0.53, P > 0.05). When evaluating the influence of age, gender, and experience on rating dental appearance, no significant differences (P > 0.05) could be found.     

Histologic and histomorphometric results of three bone graft substitutes after sinus augmentation in humans

The aim of this study was to compare the histological behavior of three bone graft materials placed in human. The comparison was made among Bio-Oss? (BO), Engipore? (EP), and PepGen P-15? (P-15). Five biopsies for each group of biomaterial, retrieved 6 months after sinus lift augmentation, were analyzed. The investigation was carried out using light microscope (LM), scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), and circularly polarized light microscope (CPLM). Under LM, the amount of newly formed bone was significantly higher in BO than P-15 (P < .05), while the amount of residual graft material was significantly higher in P-15 than BO (P < .05). The extension of marrow spaces was significantly higher in EP than both BO and P-15 (P < .05). SEM-EDS analysis showed a Ca/P ratio of 1.8 for BO, 2.2 for EP, and 1.5 for P-15. Under CPLM, BO showed no significant difference for transverse (18.4 ± 2.7%) and longitudinal (16.3 ± 1.8%) bone collagen fibers (P = .195); EP showed a significant difference between transverse (4 ± 0.7%) and longitudinal (7.6 ± 2.5%) bone collagen fibers (P = .015); finally, P-15 showed no significant difference for transverse (3.8 ± 1.6%) and longitudinal (4.9 ± 1.2%) bone collagen fibers (P = .279). No investigated biomaterial was completely resorbed, but all the residual particles demonstrated a close bone integration to form a hybrid tissue. BO particles appeared perfectly osseointegrated in the trabecular bone. EP showed a tendency to concentrate the bone apposition into the microporosities; P-15 particles appeared bridged by newly formed bone trabeculae.     

Efficacy of tin-containing solutions on erosive mineral loss in enamel and dentine in situ

The addition of tin to mouth rinses is, at least in vitro, a promising strategy for symptomatic therapy of dental erosion. The aim of this study was to evaluate the in situ efficacy of an experimental tin-containing fluoride solution on erosive tissue loss in human enamel and dentine. The study was a three-cell (7 days each) crossover design involving eight healthy participants. Samples were mounted on buccal shields of mandibular mouth appliances, which were worn for 24 h except during meals and drinks. Specimens were demineralised extraorally with 0.05 M citric acid (pH 2.3) for 6 × 5 min daily and were treated with test solutions intraorally once per day for 30 s after the first demineralisation. Three solutions were used: placebo (negative control), a commercially available tin- and fluoride-containing (SnF₂) mouth rinse (positive control, 409 ppm Sn²⁺, 250 ppm F⁻, pH 4.2) and an experimental solution (pH 4.5) containing 1,900 ppm Sn²⁺ (SnCl₂) and 1,000 ppm F⁻ (AmF/NaF). Tissue loss (micrometre) was determined profilometrically. In enamel, tissue loss was 54.8 ± 8.6 in the placebo, 24.5 ± 14.4 in the positive control and 9.7 ± 4.1 in the experimental solution group. The respective values for dentine were 48.5 ± 13.0 in the placebo, 32.8 ± 9.6 in the positive control and 26.2 ± 6.7 in the experimental solution group. The experimental solution was notably effective for enamel but was less effective for dentine. The positive control solution was less effective than the experimental solution; its effects for enamel and dentine were similar.     

Correlation of RDC/TMD axis I diagnoses and axis II pain-related disability. A multicenter study

As part of an ongoing multicenter investigation involving four highly specialized tertiary clinics for temporomandibular disorders (TMD) treatment, retrospective analysis of Research Diagnostic Criteria for TMD (RDC/TMD) axis I and axis II data gathered on clinic and community cases were assessed with a twofold aim: (1) to search for a correlation between axis I diagnoses and axis II pain-related disability, and (2) to identify clinical (axis I) and psychosocial (axis II) predictors of high pain-related disability. Two samples of patients seeking treatment for TMD (clinic cases, N = 1,312) and a sample of general population subjects (community cases, N = 211) underwent a thorough assessment in accordance with the RDC/TMD version 1.0 [1] guidelines to receive both axis I and axis II diagnoses. Spearman’s test was performed to assess the level of correlation between axis I diagnoses and Graded Chronic Pain Scale (GCPS) pain-related disability. A stepwise multiple logistic regression model was used to identify the significant associations between 12 clinical and psychosocial predictors and the presence of high pain-related disability. Axis I findings were related with pain-related impairment (GCPS scores) in the overall study sample including both clinic community cases (Spearman correlation = 0.129, p = 0.000), but the results of the correlation analyses performed on the clinic sample alone were not significant (Spearman correlation = −0.018, p = 0.618). Predictors for high disability were related to axis II findings (severe depression and somatization) or psychosocial aspects related to the pain experience (pain lasting from more than 6 months; treatment-seeking behavior), while none of the axis I diagnoses remained in the final logistic regression model. The final model predicted the level of pain-related impairment at a fair level (R ² = 26.7%). The correlation between axis I diagnoses and pain-related impairment is not significant in the patients populations. Treatment-seeking behavior and other factors related with the pain experience are likely to be more important than the physical findings to determine the degree of psychosocial impairment.     

Influence of fluoride- or triclosan-based desensitizing agents on adhesion of resin cements to dentin

Effect of desensitizers on the bond strength of resin cements to dentin was evaluated. Intact premolars (N = 90) were embedded in polymethyl methacrylate; dentin surfaces were exposed, and they were randomly divided into two main groups of cements (Duolink (D), Variolink II (V); n = 45 per group) and then into three desensitizer subgroups (n = 15 per subgroup). Teeth in controls (C) were treated according to cements’ adhesion protocols; the other two groups received either fluoride- [Aqua-Prep F (F)] or triclosan-based [Seal&Protect (T)] desensitizers. Ceramic disks (Empress 2) were adhered; specimens were thermocycled (×5,000 cycles, 5–55 ± 1°C, dwell time 30 s) and subjected to shear bond strength test (MPa ± SD) in a universal testing machine (crosshead speed 1 mm/min). Failure types were classified using scanning electron microscope. For V, application of both desensitizers (29.6 ± 7.8 and 22.8 ± 2.8 for F and T, respectively) did not present significantly different results than that of the VC (21.2 ± 2.3; p > 0.05, one-way ANOVA). In D, F (20.6 ± 2.4) showed significantly higher results (p < 0.05) than those in T (16.1 ± 3.9) and DC group (15.2 ± 2.3). V showed significantly higher results than D (p < 0.05, Bonferroni). F and T did not negatively affect the bond strength results with D and V. Adhesive failures were more frequent with both T (84%) and F (66%) in D; cohesive failures in the cement (88%) were more commonly observed with F in V. Both F and T desensitizers can be safely used prior to final cementation but F in combination with V seems to be more reliable, considering both the bond strength and the failure types.     

Parameters affecting retentive force of electroformed double-crown systems

The aim of this study was to determine the values of retentive forces of double crowns. The effect of the abutment height, the material of the inner crown, and the taper were evaluated. Sixty inner crowns each were fabricated from zirconia and a gold alloy having three different abutment heights (5, 7, and 9 mm) and two different tapers (0° and 2°). All outer crowns were made with an electroforming system. The removal test was performed by a standardized setup using a universal testing machine at a crosshead speed of 1,000 mm min⁻¹. Ten separation cycles were performed of each specimen, and the mean was imported into a statistical program. The retention forces were in the range of 0.37 and 2.65 N. The abutment height (p < 0.001), the material of the inner crown (p = 0.035), and the taper (p < 0.001) showed statistical influence on the retention force in the two-way ANOVA. Zirconia primary crowns performed better than gold alloy in the 0° group, especially with short abutments. However, a taper of 0° and short abutments have clinical drawbacks that were not evaluated in this study. In situations with long abutment teeth and a 2° taper zirconia is an alternative to gold alloy primary crowns.     

Ex vivo radiographic tooth length measurements with the reference sphere method (RSM)

A reference-based radiographic “reference sphere method” (RSM) for accurate length measurements in (dental) projection radiographs for the assessment of tooth length in dry human mandible sections is evaluated. RSM determines the depth coordinates of reference spheres placed in the object plane from the elliptical distortion of their shadows. Two segments (one canine and one molar) of dry human mandibles were exposed 95 times at different angulations (0–40°) on a dental charge-coupled device receptor. Three steel spheres (diameters d ₁ = 2.00 mm, d ₂ = 3.00 mm) were attached roughly coplanar with the tooth’s main axis. Radiographs were assessed once by visual inspection plus manual landmark identification with a mouse-driven cursor. The results were compared to the true tooth length assessed after extraction and to a conventional method (C), i.e., the rule of proportion based on magnification of the sphere shadows. Mean relative length error was 2.28% (d ₁) and 0.46% (d ₂) for RSM and −13.58% (d ₁) and −9.90% (d ₂) for C. For both methods, length errors were significantly (p < 0.0001) correlated with the inclination relative to the receptor. RSM allows for complete a posteriori determination of the imaging geometry under the assumption of a known source-to-receptor distance. One specific application is foreshortening correction of objects coplanar with the reference spheres. Remaining errors are mainly due to incorrect landmark definition. In our setup, these were exaggerated by the visual/manual image-evaluation process. Automated image analysis has been shown for similar tasks to minimize these errors considerably.     

Interest in a new test for caries risk in adolescents undergoing orthodontic treatment

It has been reported that patients undergoing orthodontic treatment present a high risk of caries. Recently, an immediate chair-side test was proposed, displaying the intra-oral lactic acid production of cariogenic bacteria. The aim of this 12-month follow-up prospective cohort study was to evaluate the association between having a high score on this test and caries occurrence in 110 young patients scheduled for orthodontic treatment. Caries occurrence was studied by Kaplan–Meier curves and Multivariate Cox models allowed the examination of its association with covariates. Fifty four patients developed at least one carious lesion during the follow-up period. At baseline, approximately 70% of the patients presented a high risk of caries according to the test and this number came close to 80% by the study’s completion. According to the Kaplan–Meier estimator, 51% (CI_95% 0.40, 0.60) of the sample would have developed at least one carious lesion during the follow-up. The test score was then associated with age, DMFT, and caries occurrence. This study showed that a high test score at baseline associated with a high DMFT predicted a high risk of caries (RR = 2.6). Taking the patient’s age into consideration, an increase of 1 year resulted in a 10% decrease of the risk of caries occurrence (RR = 0.89). Within the limits of this longitudinal study, it may be concluded that this test is useful to evaluate the risk for dental caries in adolescents with orthodontic treatment. Furthermore, the distribution of the lesions in our sample suggests specific clinical approaches for this group of patients.