Alexander Welk - Academia.edu (original) (raw)

Papers by Alexander Welk

PubMed, 2013

Dental plaque critically affects the etiology of caries, periodontitis and periimplantitis. The m... more Dental plaque critically affects the etiology of caries, periodontitis and periimplantitis. The mechanical removal of plaque can only be performed partially due to limited accessibility. Therefore, plaque still represents one of the major therapeutic challenges. Even though antiseptic mouth rinses reduce the extent of biofilm temporarily, plaque removal remains incomplete and continuous usage can even result in side effects. Here we tested argon plasma produced by kinpen09 as one option to inactivate microorganisms and to eliminate plaque. S. sanguinis biofilms cultivated in either the European Biofilm Reactor (EUREBI) or in 24 well plates were treated with argon plasma. In both test systems a homogeneous, good analyzable and stable biofilm was produced on the surface of titan plates within 72 h (>6,9 log10 CFU/ml). Despite the significantly more powerful biofilm production in EUREBI, the difference of 0.4 log10 CFU/ml between EUREBI and the 24 well plates was practically not relevant. For that reason both test models were equally qualified for the analysis of efficacy of cold atmospheric pressure plasma. We demonstrate a significant reduction of the biofilm compared to the control in both test models. After plasma application of 180 s the biofilm produced in EUREBI or in 24 well plates was decreased by 0.6 log10 CFU/ml or 0.5 log10 CFU/ml, respectively. In comparison to recently published studies analyzing the efficacy of kinpen09, S. sanguinis produces a hardly removable biofilm. Future investigations using reduced distances between plasma source and biofilm, various compositions of plasma and alternative plasma sources will contribute to further optimization of the efficacy against S. sanguinis biofilms.

PubMed, 2012

Objective: Many dental diseases are attributable to biofilms. The screening of antimicrobial subs... more Objective: Many dental diseases are attributable to biofilms. The screening of antimicrobial substances, in particular, requires a high sample throughput and a realistic model, the evaluation must be as quick and as simple as possible. For this purpose, a colorimetric assay of the tetrazolium salt XTT (sodium 3'-[1-[(phenylamino)-carbony]-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene-sulfonic acid hydrate) converted by saliva biofilms is recommended. Cleavage of XTT by dehydrogenase enzymes of metabolically active cells in biofilms yields a highly colored formazan product which is measured photometrically. Materials and method: The suitability of the XTT assay for detecting the vitality of ex vivo saliva biofilms was tested to determine the efficacy of chlorhexidine and ozone versus saliva biofilms grown on titanium discs. Results: The XTT method lends itself to testing the vitality of microorganisms in saliva biofilms. The sensitivity of the arrays requires a specific minimum number of pathogens, this number being different for planktonic bacteria and those occurring in biofilms. The antibacterial effect after treatment with chlorhexidine or ozone was measured by XTT conversion that was significantly reduced. The antimicrobial efficacy of 60 s 0.5% and 0.1% chlorhexidine treatment was equal and comparable with 60 s ozone treatment. Conclusion: The XTT assay is a suitable method to determine the vitality in saliva biofilms, permitting assessment of the efficacy of antimicrobial substances. Its quick and easy applicability renders it especially suitable for screening.

Scientific Reports, Apr 22, 2020

This study aimed to evaluate the effect of self-assembling peptide P 11-4 (SAP) in the therapy of... more This study aimed to evaluate the effect of self-assembling peptide P 11-4 (SAP) in the therapy of initial smooth surface caries (white spot lesions, WSL) following orthodontic multibracket treatment. Twentythree patients (13f/10m; average age 15.4 years) with at least two teeth with WSL were recruited for the randomised controlled clinical trial with split-mouth design. In opposite to the control teeth, the test teeth were treated with SAP on Day 0. The primary endpoint was the impedance measurement of WSL using customised tray to ensure reproducibility of the measurement location. The secondary endpoint was the morphometric measurement of WSL using a semi-automated approach to determine the WSL size in mm 2. Treatment effects were adjusted for site-specific baseline values using mixed models adapted from the cross-over design. Test WSL showed a mean baseline impedance value of 46.7, which decreased to 21.1, 18.4, and 19.7 after 45, 90, and 180 days, respectively. Control WSL showed a mean baseline value of 42.0, which decreased to 35.0, 29.5, and 33.7, respectively. The overall treatment contrast was −13.7 (95% CI: −19.6-−7.7; p < 0.001). For the secondary endpoint, the test WSL size decreased from 8.8 at baseline to 6.5 after 180 days. The control WSL decreased from 6.8 to 5.7, respectively. The related treatment contrast was −1.0 in favour of test WSL (95% CI: −1.6-−0.5; p = 0.004). The treatment of initial carious lesions with self-assembling peptide P 11 −4 leads to superior remineralisation of the subsurface lesions compared with the control teeth. Orthodontic treatments with fixed multibracket appliances hindering oral hygiene, support plaque accumulation, and caries progression 1,2. These orthodontic treatment-induced carious lesions are typically visible first as so-called white spot lesions (WSL) on the buccal surface of the tooth outlining the brackets 3-6. Modern treatment concepts for caries emphasise tooth preservation and remineralisation concepts especially for initial non-cavitated carious lesions, in order to hinder or to delay the first invasive intervention, meaning destruction of the natural tooth structure 7. Unique for buccal WSL is the addition of an aesthetic component to the cariological issue 3,8. Fluorides prevent the formation of so-called white spot lesions (WSL) but have shown little effect on the reduction of existing WSL 9-11. As their effect is restricted to the outer surface layer of the enamel (i.e. top 50 µm) and does not promote the remineralisation throughout the demineralised lesion body. The WSL persist visually almost unchanged 12-14. Other remineralisation agents, often based on calcium phosphate, have been investigated, but could not show clinically significant advantage over fluoride 10,11,15-17. As a consequence, new treatment approaches have been called for and biomimetic mineralisation seems to be one promising possibility 18-22. However, the only clinically available products at present are based on the self-assembling peptide P 11-4 (SAP P 11-4) 21. The mode of action for the treatment of initial caries with SAP P 11-4 is as follows 23,24. Monomeric P 11-4 diffuses into the subsurface lesion, self-assembles into fibres to form a 3D-matrix and attracts calcium-ions from saliva and templates the formation of hydroxyapatite crystals, thus supporting the natural remineralisation mechanism driven by saliva. Clinically, SAP P 11-4 has previously been investigated on buccal lesions. A first-in-man trial, mostly on inactive lesions, demonstrated regression of the WSL size and a trend toward remineralisation 25. Randomised clinical trials could show superior regression of the lesion as judged by morphometric analysis compared with

Journal of Oral Rehabilitation, Apr 23, 2011

In a cross-sectional analysis of data from the Study of Health in Pomerania (SHIP 0), temporomand... more In a cross-sectional analysis of data from the Study of Health in Pomerania (SHIP 0), temporomandibular disorders (TMD) were the strongest predictors for tinnitus beside headache. The aim of this study was to investigate whether signs and symptoms of TMD can be identified as risk factors for developing tinnitus. The SHIP 1 is a population-based 5-year longitudinal study intended to systematically describe the prevalence of and risk factors for diseases common in the population of Pomerania in northern Germany. A total of 3300 subjects (76% response) were reevaluated after 5 years for tinnitus and signs and symptoms of TMD using the same questionnaires and examination tools as baseline. To estimate the relative risk (RR) appropriately, a modified Poisson regression was used. After exclusion of prevalent cases with diagnosed tinnitus, 3134 subjects were analysed. Among the 191 exposed subjects with palpation pain in the temporomandibular joint (TMJ), 24 subjects (12·6%) received diagnosed tinnitus after 5 years, whereas among the 2643 unexposed subjects 142 subjects (5·8%) received tinnitus yielding a risk difference of 7·7% (95% confidence interval [CI]: 3·0%-12·5%) and a risk ratio of 2·60 (95% CI: 1·7-3·9). The risk ratio was 2·4 (95% CI: 1·6-3·7) after adjustment for gender, age, school education and frequent headache. Pain on palpation of the TMJ, however, did not worsen the prognosis for tinnitus in prevalent tinnitus cases (RR = 0·8, P = 0·288). Signs of TMD are a risk factor for the development of tinnitus.

MedEdPORTAL, Jul 27, 2010

Abstract Introduction DentSim is a web-based, interactive multimedia learning environment used fo... more Abstract Introduction DentSim is a web-based, interactive multimedia learning environment used for dental training and practice. The training program combines a virtual and clinical environment to ...

Research Square (Research Square), Jul 14, 2020

Background The aim of the study was to compare a 2D and 3D color system concerning a variety of s... more Background The aim of the study was to compare a 2D and 3D color system concerning a variety of statistical and graphical methods to assess validity and reliability of color measurements, and to give some guidance when to use which system and how to interpret color distance measures, including ΔE and d(0M1). Methods The tooth color of teeth 14 to 24 of 35 patients with a regular bleaching treatment (BT) was visually assessed and electronically measured with the spectrophotometer Shade Inspector™. Tooth color was recorded before BT (T 1 /T 2-Baseline), 14d (T 3 /T 4) and 6 months (T 5 /T 6) after BT. VITAPAN® Classical (VC) and VITA-3D-Master® (3D) served as reference systems. Results Intra-rater variability. The 2D system is better than the 3D system both visually and electronically in terms of ΔE and d(0M1) for statistics of agreement and reliability. All four methods show strong patterns of disagreement between repeated measurements in Bland-Altman plots. The 3D system lacks reliability of hue compared with that of lightness and chroma, which is more pronounced visually than electronically. The smallest detectable color difference (SDCD) differs by the four methods used and is most favorable in the electronical 2D system. Inter-rater variability. The agreement between the 2D and 3D system in terms of ΔE is not good according to Byrt's classi cation. It is lower within the electronical method than within the visual method. Comparability of the 2D and 3D system is uncertain because

Quintessence International, Jul 1, 2007

Objective: To compare the effectiveness of polymer burs (SmartPrep, SS White) and conventional ca... more Objective: To compare the effectiveness of polymer burs (SmartPrep, SS White) and conventional carbide burs in removing dentin caries. Method and materials: Thirty extracted permanent teeth were assigned to 2 groups according to the caries removal technique. One experienced clinician performed all excavation procedures, monitoring the caries removal by checking the hardness of the dentin with a dental explorer. The excavation working time was documented and stopped in each group when a leather-hard texture was reached. After the teeth were embedded and sectioned (400 Microm), the caries in the remaining dentin was assessed using a caries detector. On microscope images of the samples, the mean stain depth of the remaining carious tissue per tooth was measured by AnalySIS computer software. Results: Mean carious surface areas differed minimally but not statistically significantly after use of polymer burs (31.5 mm2 +/- 0.18) and carbide burs (38.1 mm2 +/- 0.15). Mean carious surface staining depth was slightly smaller with carbide burs (0.26 mm +/- 1.38) than with polymer burs (0.40 mm +/- 1.15). The mean-quartile test for the total carious surface (P = .363) and the carious margin (P = .681) showed no statistically significant differences. Of the carbide bur-treated samples, 84.5% were caries free as opposed to 93.0% in the polymer bur group. The results also showed no significant difference between the mean working time of the polymer burs (5.11 minutes) and the carbide burs (4.99 minutes). Conclusion: Under these experimental conditions, polymer burs and tungsten carbide burs were similarly effective for caries removal.

BMC Microbiology, 2021

Background Antimicrobial agents are considered valuable adjuncts to mechanical methods of plaque ... more Background Antimicrobial agents are considered valuable adjuncts to mechanical methods of plaque control. However, their long-term use can be limited because of side effects. Therefore, using physiological substances is promising due to no risk of development, for example, of microbial resistances, allergies or DNA damaging. The lactoperoxidase-thiocyanate-hydrogen peroxide system (LPO-system) is a highly effective antimicrobial system. This study aimed to evaluate in a randomized study with a four-replicate cross-over design the effectiveness of two oral hygiene lozenges containing LPO-system in oral hygiene. Results After using the mouth rinse as positive control (A) and allocated test lozenges (B) (0.083% H2O2) & (C) (0.04% H2O2) for 4 days instead of the normal oral hygiene procedures (tooth brushing etc.), Listerine rinse (A) was statistically significantly more effective than the LPO-system-lozenge with 0.083% H2O2, the LPO-system-lozenge with 0.04% H2O2, and the placebo lozen...

ZWR - Das Deutsche Zahnärzteblatt, 2011

Minimalinvasive nichtoperative Methoden in der Gesichtsästhetik, 2019

Journal of Oral Microbiology

Background: Dental plaque consists of a diverse microbial community embedded in a complex structu... more Background: Dental plaque consists of a diverse microbial community embedded in a complex structure of exopolysaccharides. Dental biofilms form a natural barrier against pathogens but lead to oral diseases in a dysbiotic state. Objective: Using a metaproteome approach combined with a standard plaque-regrowth study, this pilot study examined the impact of different concentrations of lactoperoxidase (LPO) on early plaque formation, and active biological processes. Design: Sixteen orally healthy subjects received four local treatments as a randomized singleblind study based on a cross-over design. Two lozenges containing components of the LPOsystem in different concentrations were compared to a placebo and Listerine®. The newly formed dental plaque was analyzed by mass spectrometry (nLC-MS/MS). Results: On average 1,916 metaproteins per sample were identified, which could be assigned to 116 genera and 1,316 protein functions. Listerine® reduced the number of metaproteins and their relative abundance, confirming the plaque inhibiting effect. The LPO-lozenges triggered mainly higher metaprotein abundances of early and secondary colonizers as well as bacteria associated with dental health but also periodontitis. Functional information indicated plaque biofilm growth. Conclusion: In conclusion, the mechanisms on plaque biofilm formation of Listerine® and the LPO-system containing lozenges are different. In contrast to Listerine®, the lozenges led to a higher bacterial diversity.

Clinical Oral Investigations

Objective To compare the effectiveness and complications of intraligamentary anesthesia (ILA) wit... more Objective To compare the effectiveness and complications of intraligamentary anesthesia (ILA) with conventional inferior alveolar nerve block (IANB) during injection and dental treatment of mandibular posterior teeth. Materials and methods In this randomized, prospective clinical trial, 72 patients (39 males, 33 females), scheduled for dental treatment of mandibular posterior teeth, were randomly allocated to ILA group (n = 35) received ILA injection or IANB group (n = 37) received the conventional IANB. Our primary outcome was to assess pain and stress (discomfort) during the injection and dental treatment, using the numeric rating scale (NRS) from 0 to 10 (0 = no pain, 10= the worst pain imaginable), whereas recording 24-h postoperative complications was our secondary outcomes. Results Patients in ILA group reported significantly less pain during injection when compared with IANB group (p = 0.03), while pain during dental treatment was similar in both groups (p = 0.2). Patients in...

Journal of Clinical Periodontology

European Journal of Dental Education, 2006

Compared with its potential, computer technology use is still lacking in medical/dental education... more Compared with its potential, computer technology use is still lacking in medical/dental education. To investigate the primary advantages of computer-assisted learning (CAL) systems in German dental education, as well as the reasons for their relatively low degree of use correlated with personal and professional profiles of respondents. A questionnaire was mailed to heads in the departments of conservative dentistry and prosthetic dentistry in all dental schools in Germany. Besides investigating the advantages and barriers to the use of computer technology, the questionnaire also contained questions regarding each respondent&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s gender, age, academic rank, experience in academia and computer skills. The response rate to the questionnaire was 90% (112 of 125). The results indicated a distinct discrepancy between the desire for and actual occurrence of lectures, seminars, etc. to instruct students in ways to search for and acquire knowledge, especially using computer technology. The highest-ranked advantages of CAL systems in order, as seen by respondents, were the possibilities for individual learning, increased motivation, and both objective theoretical tests and practical tests. The highest-ranked reasons for the low degree of usage of CAL systems in order were the inability to finance, followed equally by a lack of studies of CAL and poor cost-advantage ratio, and too much effort required to integrate CAL into the curriculum. Moreover, the higher the computer skills of the respondents, the more they noted insufficient quality of CAL systems (r = 0.200, P = 0.035) and content differences from their own dental faculty&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s expert opinions (r = 0.228, P = 0.016) as reasons for low use. The correlations of the attitudes towards CAL with the personal and professional profiles showed not only statistical significant reinforcements of, but also interesting deviations from, the average responses.

Community Dentistry and Oral Epidemiology, 2000

In a prospective, randomised and blinded cohort study, the acceptance and effectiveness of a 3-mo... more In a prospective, randomised and blinded cohort study, the acceptance and effectiveness of a 3-monthly chlorhexidine-thymol varnish application was assessed in 8-to 10-yr-old children (nΩ29) with high caries incidence after brushing with a 1.23% fluoride gel. The children of the control group (nΩ25) brushed with a fluoride gel only. The standardised interview showed good acceptance of the varnish applications in spite of the bitter taste. Caries incidence in one year was 1.2 DMFS (SD 1.5, median 1; 95% confidence interval 0-1) for the test group and 2.1 DMFS (SD 2.3, median 2; 95% confidence interval 0-3) for the control Key words: children; chlorhexidine; high group. Due to a slightly lower reduction in caries incidence (42.3%) than in other caries risk studies and a higher standard deviation than in unselected study groups, the pow-Christian Splieth, Department of Operative er of the present study was not high enough to prove this difference in caries Dentistry, Periodontology and Pediatric Dentistry, Ernst Moritz Arndt University, incidence to be statistically significant in the Mann-Whitney test (PΩ0.11). This Rotgerberstr. 8, D-17487 Greifswald, was also found for the difference of 0.4 initial lesions. The distribution patterns Germany of caries incidence for tooth groups (70% in the first permanent molar) and surfaces Tel: π49 3834 867169 (58% on occlusal surfaces) did not differ between the test and the control group.

Caries Research, 2005

To be able to generalize studies, it is important to know whether responders and nonresponders di... more To be able to generalize studies, it is important to know whether responders and nonresponders differ significantly. These data are usually not available. To assess whether responders and nonresponders differed significantly, 319 first and second graders in Greifswald, Germany took part in a compulsory dental school examination. Their parents completed a questionnaire on oral health topics and were asked to decide about their children’s participation in a school-based caries prevention program plus anonymous scientific evaluation. The 91 children who were not allowed to participate (nonresponders) were older (mean 8.5 years) than the 228 responders (mean 8.1 years; p < 0.001), mostly because of a few older children having repeated a grade. In an age-adjusted analysis, nonresponders exhibited in 21 of 30 indices of higher caries and plaque values, less preventive measures and a lower rate of participation. The difference in caries in the permanent dentition and fluorosis reached s...

Journal of Clinical Periodontology, 2019

Periodontitis and caries are the most commonly occurring dental diseases worldwide (Marcenes et a... more Periodontitis and caries are the most commonly occurring dental diseases worldwide (Marcenes et al., 2013) and account for about 60% of tooth loss (Glockmann, Panzner, Huhn, Sigusch, & Glockmann, 2011). The main aetiology for both diseases is accumulation of bacterial plaque on tooth surfaces (Löe, Theilade, &

Clinical Oral Investigations, 2022

Objectives During the corona pandemic, dental practices temporarily closed their doors to patient... more Objectives During the corona pandemic, dental practices temporarily closed their doors to patients except for emergency treatments. Due to the daily occupational exposure, the risk of SARS-CoV-2 transmission among dentists and their team is presumed to be higher than that in the general population. This study examined this issue among dental teams across Germany. Materials and methods In total, 2784 participants provided usable questionnaires and dry blood samples. Dry blood samples were used to detect IgG antibodies against SARS-CoV-2. The questionnaires were analyzed to investigate demographic data and working conditions during the pandemic. Multivariable logistic mixed-effects models were applied. Results We observed 146 participants with positive SARS-CoV-2 IgG antibodies (5.2%) and 30 subjects with a borderline finding (1.1%). Seventy-four out of the 146 participants with SARS-CoV-2 IgG antibodies did not report a positive SARS-CoV-2 PCR test (50.7%), while 27 participants with...

Clinical Oral Investigations, 2013

Objectives Studies on indirect pulp treatment (IPT) show varying success rates of 73 to 97 %. The... more Objectives Studies on indirect pulp treatment (IPT) show varying success rates of 73 to 97 %. The necessity of reopening the cavity and the question of the optimal capping material is still under debate. The aim of this prospective in vivo study was to compare the clinical and microbiological outcomes of mineral trioxide aggregate (MTA), medical Portland cement, and calcium hydroxide on the dentin-pulp complex of permanent and primary teeth treated with two-step IPT. Materials and methods In 86 regular patients (51 % men; 49 % women; age 17.2 years ±13.8), one deep carious lesion each was treated with incomplete caries removal, randomly selected capping with either calcium hydroxide (n =31), medical Portland cement (29) or white MTA (26), and re-entry (6.3 months ±1.0). Clinical (color, humidity, and consistency of dentin) and microbiological (Lactobacilli/Mutans Strep. counts) parameters were recorded at the first and second treatment. Results The IPT had a high success rate of 90.3 % regardless of the material used (p =0.72). The arrested lesions showed consistently darker, dry, and therefore, sclerotic dentine (p <0.05) as well as a decrease in bacterial counts at re-entry (Lactobacilli p =0.01/Mutans Strep. p =0.07). Conclusions The findings of this study support the use of the IPT as a treatment for deep carious lesions preferably with nonresorbing materials such as MTA or medical Portland cement. Clinical relevance The findings of this study could promote the improvement of the IPT as a one-step treatment of deep carious lesions when the remaining demineralized dentin would be sealed with durable restorations.