Soft tissue response to different abutment materials: A controlled and randomized human study using an experimental model.

OBJECTIVES: Aim of this study was to compare the soft tissue response to implant abutments made of titanium, zirconia, zirconia veneered with feldspar ceramics and PEEK by various clinical, histological, microbiological, and molecular biological markers in an experimental model. MATERIALS AND METHODS: A total of 40 experimental one-piece healing abutments of four different materials were mounted on bone level implants in 20 volunteering patients (split-mouth design). After a three-month period of open healing, clinical parameters at the abutments were assessed and adjacent mucosa was sampled for inflammatory cytokine mRNA concentrations and histological analysis by a novel method. In addition, PISF samples were obtained for the analysis of periodonto-pathogenic bacteria counts and active MMP-8 levels. Marginal bone level change was measured by intra oral radiographs. RESULTS: Abutments of the different materials did not exhibit significant differences regarding clinical parameters, pathogenic bacteria counts or pro-inflammatory cytokine concentrations. Likewise, no significant differences were detected regarding soft tissue morphology or bone level change. Compared to titanium abutments, significantly less mononuclear inflammatory cells were detected in the mucosa at abutments made of zirconia veneered with feldspar ceramics. CONCLUSIONS: All examined abutment materials exhibited a similar soft tissue response compared to titanium and histological data did not reveal early signs of elevated inflammation caused by PEEK- and feldspar-veneered zirconia abutments. Due to the short observation period and the small sample size, a final conclusion on the long-term suitability of those abutment materials cannot be drawn. However, based on the presented data, we consider further studies on that subject as appropriate.

Novel method to obtain human non-separated histological samples for the assessment of peri-implant soft tissue response: A feasibility study.

OBJECTIVES: To introduce a standardized and less invasive clinical model that provides histological information on the abutment-mucosa interface in humans. MATERIALS AND METHODS: New experimental healing abutments were left in an open healing position on bone-level implants in the interforaminal region of the mandibles in six edentulous patients. The one-piece abutments were hollow cylinder-shaped with two lateral openings that allow for ingrowth of the peri-implant mucosa into the central abutment cavity. After three months of healing, abutments and ingrown mucosa were sampled and processed for histological analysis in a non-separated resin-embedding technique. To test the validity of the new model, the ingrown tissue was compared to the peri-implant mucosa around the same samples. RESULTS: None of the experimental abutments exhibited signs of failure, and all samples showed mucosal ingrowth to the inner-abutment cavity. Comparison of ingrown tissue and peri-implant mucosa revealed no significant differences regarding the traits: tissue morphology, quality of collagen fibers, and adherence to the abutment. Ingrown mucosa exhibited a tendency for higher leukocyte infiltration. CONCLUSIONS: The presented model is a promising approach to reduce invasiveness during the sampling process for human non-separated abutment biopsies.

Corrosion behavior of dental alloys used for retention elements in prosthodontics.

The purpose of this study was to investigate the corrosion behavior of 10 different high noble gold-based dental alloys, used for prosthodontic retention elements, according to ISO 10271. Samples of 10 high-noble and noble gold-based dental alloys were subjected to: (i) static immersion tests with subsequent analysis of ion release for eight different elements using mass spectrometry; (ii) electrochemical tests, including open-circuit potential and potentiodynamic scans; and (iii) scanning electron microscopy, followed by energy-dispersive X-ray microscopy. The results were analyzed using one-way ANOVA and Sidak multiple-comparisons post-hoc test at a level of significance of α = 0.05. Significant differences were found among the 10 alloys studied for all ions (P < 0.001). The potentiodynamic analysis showed values from -82.5 to 102.8 mV for the open-circuit potential and from 566.7 to 1367.5 mV for the breakdown potential. Both the open-circuit and the breakdown potential varied considerably among these alloys. Scanning electron microscopy analysis confirmed the existence of typically small-diameter corrosion defects, whilst the energy-dispersive X-ray analysis found no significant alteration in the elemental composition of the alloys. The results of this study reveal the variability in the corrosive resistance among the materials used for retention elements in prosthodontics.

Possible implications of Ni(II) on oral IL-1ß-induced inflammatory processes.

OBJECTIVES: Nickel (Ni) is one of the main metal elements in orthodontic and prosthetic devices. Different effects of Ni are described ranging from an induction of local inflammation to allergy and cancerous/mutagenic properties. Inflammatory reactions are frequently observed in the oral cavity, but the interrelationship of Ni with those events is still unknown. Therefore, we focused on the impact of Ni on inflammation in vitro. METHODS: In accordance to previous immersion tests of our lab, human gingival fibroblasts (HGFs) (n=6) were exposed to a pro-inflammatory environment using interleukin-1 beta (IL-1ß) and additionally stimulated with different Ni(II) concentrations (400 and 4000ng/ml). At varying time points the expression of pro- and anti-inflammatory as well as matrix degeneration proteins, i.e. MMPs, were analyzed. Furthermore, proliferation assays, wound healing tests and the detection of NF-κB activation were conducted. Unstimulated HGFs served as control. RESULTS: Our experiments showed that low clinical average Ni(II) levels did not alter pro-inflammatory cytokines significantly compared to control (p>0.05). Instead, a 10-fold higher dose up-regulated these mediators significantly in a time-dependent manner (p<0.01). This was even more pronounced combining both Ni(II) concentrations with an inflammatory condition (p<0.001), MMP expressions were in line with our findings (p<0.001). The mRNA data were supported by proliferation and wound closure assays (p<0.001). However, the combination of both stimuli induced contradictory results. Analyzing NF-κB activation revealed that our results may be in part attributed to NF-κB. SIGNIFICANCE: Our in vitro study implicated that Ni(II) has various modifying effects on IL-1ß-induced inflammatory processes depending on the concentration.

Precision of fit and retention force of cast non-precious-crowns on standard titanium implant-abutment with different design and height.

OBJECTIVE: The cost-effectiveness of cast nonprecious frameworks has increased their prevalence in cemented implant crowns. The purpose of this study was to assess the effect of the design and height of the retentive component of a standard titanium implant abutment on the fit, possible horizontal rotation and retention forces of cast nonprecious alloy crowns prior to cementation. MATERIALS AND METHODS: Two abutment designs were examined: Type A with a 6° taper and 8 antirotation planes (Straumann Tissue-Level RN) and Type B with a 7.5° taper and 1 antirotation plane (SICace implant). Both types were analyzed using 60 crowns: 20 with a full abutment height (6 mm), 20 with a medium abutment height (4 mm), and 20 with a minimal (2.5 mm) abutment height. The marginal and internal fit and the degree of possible rotation were evaluated by using polyvinylsiloxane impressions under a light microscope (magnification of ×50). To measure the retention force, a custom force-measuring device was employed. STATISTICAL ANALYSIS: one-sided Wilcoxon rank-sum tests with Bonferroni-Holm corrections, Fisher's exact tests, and Spearman's rank correlation coefficient. RESULTS: Type A exhibited increased marginal gaps (primary end-point: 55 ± 20 µm vs. 138 ± 59 µm, P < 0.001) but less rotation (P < 0.001) than Type B. The internal fit was also better for Type A than for Type B (P < 0.001). The retention force of Type A (2.49 ± 3.2 N) was higher (P = 0.019) than that of Type B (1.27 ± 0.84 N). Reduction in abutment height did not affect the variables observed. CONCLUSION: Less-tapered abutments with more antirotation planes provide an increase in the retention force, which confines the horizontal rotation but widens the marginal gaps of the crowns. Thus, casting of nonprecious crowns with Type A abutments may result in clinically unfavorable marginal gaps.

Wear of double crown systems: electroplated vs. casted female part.

OBJECTIVES: The wear of telescopic crowns is a common problem often reducing the patient's satisfaction with the denture and resulting in a renewal of the denture. The study aims to compare the wear behavior of conical crowns using electroplated copings (group E ) with standard telescopic crowns with cast female parts (group C). MATERIAL AND METHODS: 10 conical crowns were milled for each group of a cast gold alloy. The specimen of group E had a conicity of 2º. The cast secondary crowns of group C had a 0º design. The electroplated coping was established by direct electroforming. An apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long term wear period. The retention force value and the force-distance integral of the first 0.33 mm of each cycle were calculated. RESULTS: The retentive forces were significantly higher for group E and the integrals were significantly lower for this group except the integral at cycle 10,000. The changes of retention force and integral did not differ significantly between both groups in all phases. The change of the integrals as well as the integral at the particular cycles showed higher interquartile distances for group C. CONCLUSIONS: Within the limitations of this study the tested conical crowns showed clinically acceptable retentive properties. The values reached a range comparable to retentive elements tested in recent literature. The values of group C showed higher ranges. The force measured for group E was significantly higher than for group C but the integrals showed an opposite tendency. The results indicate that an exclusive analysis of the force is not sufficient as the integral is not equivalent to the force although it describes the retentive property of the system in a better way than the force over a distance is described. Both systems seem to be suitable for clinical practice.

Wear of double crown systems: electroplated vs. casted female part

OBJECTIVES: The wear of telescopic crowns is a common problem often reducing the patient's satisfaction with the denture and resulting in a renewal of the denture. The study aims to compare the wear behavior of conical crowns using electroplated copings (group E ) with standard telescopic crowns with cast female parts (group C). MATERIAL AND METHODS: 10 conical crowns were milled for each group of a cast gold alloy. The specimen of group E had a conicity of 2º. The cast secondary crowns of group C had a 0º design. The electroplated coping was established by direct electroforming. An apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long term wear period. The retention force value and the force-distance integral of the first 0.33 mm of each cycle were calculated. RESULTS: The retentive forces were significantly higher for group E and the integrals were significantly lower for this group except the integral at cycle 10,000. The changes of retention force and integral did not differ significantly between both groups in all phases. The change of the integrals as well as the integral at the particular cycles showed higher interquartile distances for group C. CONCLUSIONS: Within the limitations of this study the tested conical crowns showed clinically acceptable retentive properties. The values reached a range comparable to retentive elements tested in recent literature. The values of group C showed higher ranges. The force measured for group E was significantly higher than for group C but the integrals showed an opposite tendency. The results indicate that an exclusive analysis of the force is not sufficient as the integral is not equivalent to the force although it describes the retentive property of the system in a better way than the force over a distance is described. Both systems seem to be suitable for clinical practice.

Changes in retention force with electroplated copings on conical crowns: a comparison of gold and zirconia primary crowns.

PURPOSE: The aim of this study was to examine the wear behavior of conical crowns with electroplated gold copings that are used to connect implants and teeth to a removable denture. Gold alloy and zirconium dioxide ceramic crowns were compared. MATERIALS AND METHODS: Fifteen crowns each were milled for two groups: gold alloy and zirconium dioxide. Each specimen had a 2-degree taper. The electroplated coping was established by direct electroforming. The retentive forces and the correlating distance during insertion and separation were measured after 10,000 wear cycles were applied. The wear testing was separated into a start phase, an initial wear phase, and the long-term wear period. The retention force value and the force-distance integral of the first 0.3 mm of each cycle were calculated. RESULTS: The changes in retention force and integral did not differ significantly between both groups in the start and the initial wear phase. No differences were seen in force development during the long-term wear period. Only the force-distance integral showed a significant difference: the median values of the gold crowns increased slightly, and they decreased slightly for the zirconia crowns. The median force values never fell below 6 N for gold and 4 N for zirconia. CONCLUSIONS: Within the limitations of this study, the tested conical crowns showed clinically acceptable retentive properties. As with other retentive elements for dentures, the specimens tested showed the greatest amount of change in retentive forces during the first 2,000 cycles. The development of retention force in both groups was not significantly different. However, the zirconia specimens showed reduced variability, which is preferable in clinical practice.

A cross-sectional analysis of the prevalence of dental anxiety and its relation to the oral health-related quality of life in patients with dental treatment needs at a university clinic in Switzerland.

OBJECTIVES: The aim of this observational, cross-sectional study was to analyse the relationship between dental anxiety (DA) and health-related quality of life aspects associated with oral conditions of a population with dental treatment needs in Switzerland. METHODS: The measurements of DA were collected by means of two questionnaires, the Dental Anxiety Scale (DAS) and a Visual Analogue Scale (VAS). Oral health-related quality of life (OHRQoL) was assessed with the Oral Health Impact Profile (OHIP). The sample included 223 patients enrolled at a university clinic which specialises in oral prosthetic rehabilitation and temporomandibular disorders. Of them, 78.9% were at or above the age of 50. RESULTS: No gender or age dependencies were observed. A comparison of answers regarding OHRQoL and DA revealed a significant interdependence (p = 0.0118); highly anxious patients were 3.55 times more likely to suffer from poor quality of life compared with less anxious ones. CONCLUSION: This cross-sectional study of mostly elderly patients seeking dental treatment in Switzerland found that increased DA was associated with an impaired OHRQoL. The average DA was slightly higher than the results of other industrialised countries and the average OHRQoL was reduced.

Telescopic crowns: extra-oral and intra-oral retention force measurement--in vitro/in vivo correlation.

OBJECTIVE: This study deals with the determination of the retentive forces of telescopic crowns measured extra- and intra-orally and the correlation of these values. BACKGROUND: The telescopic denture is a well-documented solution for prosthetic rehabilitation for a partially edentulous jaw. Acceptable retention forces are needed to avoid inadvertent removal of the denture during movement of the jaws. Recent literature suggests 3-7 N per attachment to be acceptable. These values are only supported by in vitro studies. In vivo data are scarce, and a correlation of the in vitro and in vivo values is lacking. MATERIAL AND METHODS: Twenty-five combined fixed-removable prostheses with a total of 72 double crowns were used for extra-oral retention force measurement prior to cementation (in vitro). The intra-oral measurement was performed at 72 defined measuring points of the dentures 4-6 weeks after prosthetic rehabilitation (in vivo). A specifically designed measuring device was used. RESULTS: The rank correlation showed that the in vitro and in vivo values correlate with each other (Spearman's ρ = 0.5052). Additionally, it was found that the median values measured before (1.97N) insertion of the dentures were significantly lower than after (4.70N) insertion (Mann-Whitney test, p ≤ 0.0001). CONCLUSION: The retention forces measured before and after insertion of the denture correlate with each other although their dimension is significantly higher after insertion. The reason for this behaviour might be some tilting during removal. Nevertheless, the correlation allows a prediction of the clinically relevant forces by a measurement of the extra-orally measured retentive values.

Vinylsiloxanether: a new impression material. Clinical study of implant impressions with vinylsiloxanether versus polyether materials.

AIM: The performance of three elastomeric materials for the open monophase implant impressions technique was tested under the following clinical conditions: polyether (IM) and vinylsiloxanether without (ID) and with additional simultaneous splinting of the implant impression copings with a higher shore hardness A-silicone (IDF). MATERIALS AND METHODS: The three test groups, IM, ID, and IDF, were randomly allocated 10 test subjects with three to five implants each. The impressions were analyzed regarding the subjective clinical assessments with 11-point rating scales by the dentist, the patient, and the dental technician, as well as to the comparison of these assessments with the objectified clinical fit of the manufactured crowns based on standard clinical evaluation criteria. The three groups were statistically analyzed on the basis of the hypothesis of non-inferiority of ID versus IM and IDF versus IM (alpha < 0.05). RESULTS: The results of the study showed the objective clinical fit of the dental prostheses made using ID being comparable to the results obtained with IM. Compared with ID and IM, the precision of fit attained with IDF was reduced, although the subjective dentist assessments of IDF were in parts significantly better than those of IM and ID (p = .015). A statistically significant superiority of ID in comparison with IM could be determined with regard to the subjective ratings of the taste by the test subject (p < .01), of the handling (p < .001) and of the precision details of impression (p = .012) by the dentist, and of removing the plaster model from the mold by the dental technician (p = .017). CONCLUSIONS: The overall results of the vinylsiloxanether material in terms of the patients', dentists', and dental technicians' assessments proved to be equivalent or superior to those of the polyether material. The IDF technique cannot be recommended for this application.

Tactile sensibility of single-tooth implants and natural teeth under local anesthesia of the natural antagonistic teeth.

INTRODUCTION AND AIM: The term osseoperception describes the capability of developing a subtle tactile sensibility over dental implants. The present clinical study aims at clarifying the question of how far tactile sensibility is to be attributed to the periodontium of the natural opposing tooth of the implant. MATERIAL AND METHOD: Thirty-two subjects with single-tooth implants with natural opposing teeth were included in this clinical, single-blind, split-mouth study. The natural antagonistic tooth of the implant and the corresponding natural contralateral tooth were anesthetized with a locally infiltrated articaine anesthetic. In a computer-assisted and randomized way, copper foils of varying thickness (0-100 µm) were placed interocclusally between the single-tooth implant and the natural opposing tooth, and between the contralateral pair of natural opposing teeth in order to investigate the active tactile sensibility according to the psychophysical method of constant stimuli and evaluate it statistically by the Weibull distribution. RESULTS: The average tactile sensibility of the implants with anesthetized antagonists at the 50% value calculated by means of the Weibull distribution was 20 ± 11 µm with a support area (90%-10% value) of 77 ± 89 µm. For the pair of natural teeth, the tactile sensibility at the 50% value was 16 ± 9 µm with a support area of 48.4 ± 93 µm. This resulted in an average intraindividual difference of 3.5 ± 7 µm at the 50% value and 29 ± 93 µm in the support area. The statistical calculations demonstrated an equivalent tactile sensibility (50% value) of the single-tooth implant and the contralateral natural control tooth with the natural antagonists being anesthetized in each case (double t-test, equivalence limit ± 8 µm, P < 0.01, power >80%). CONCLUSION: Apparently, the active tactile sensibility of single-tooth implants with natural opposing teeth is not only to be attributed to the periodontium of the opposing tooth but also to a perception over the implant itself. This could support the hypothesis according to which the implant may have a tactile sensibility of its own.

Retention force of plastic clips on implant bars: a randomized controlled trial.

OBJECTIVES: Retention of overdentures is important for patients' satisfaction. The study tested whether the clinical performance of retentive clips made of poly-ether-ether-ketone (PEEK) is superior to those made of poly-oxy-methylene (POM). METHODS: A total of 30 patients received complete dentures with round bars (SFI-Bar) on two implants in a chairside technique. Two types of clip matrices (PEEK/POM) were used in a split-mouth technique. Retention forces were measured separately for both materials at baseline when the dentures were inserted and after 1, 3 and 6 months. The measurement was performed extraorally and intraorally by using a measuring stylus equipped, respectively, with an opposing matrix or bar part. Simultaneously, at each point in time the patient and the dentist judged the retention either to be good, or to be too high or too low. Statistical analysis involved performance of global non-parametric testing of dependence of retention force on time and material was performed with Brunner-Langer model; non-parametric 95% confidence intervals (CIs) were calculated. RESULTS: At baseline the median force for POM matrices was 6.89N (95% CI: 6.50-8.21) and for PEEK matrices 7.17N (95% CI: 6.97-7.93). After 6 months, the retention of POM decreased to 5.53N (95% CI: 4.81-7.00) and of PEEK to 6.42N (95% CI: 5.15-7.51). The retention force changed significantly over time (P = 0.004) without differences between POM and PEEK (P = 0.135). No significant alteration of the retention force over time was measured at the bar (P = 0.289). Retention was estimated to be good with 90% at baseline and with 80% after 6 months, equally by patients and dentist. CONCLUSIONS: POM as well as PEEK material fulfills the requirements of retentive clips on round bars.

Clinical retention force development of double crowns.

This study deals with the development of the retentive forces of double crowns intraorally measured. Twenty-five combined fixed-removable prostheses with a total of 84 double crowns were included in the study. The intraoral measurement was performed at 72 defined measuring points directly adjacent to the double crowns of the dentures. The measurement was performed 4-6 weeks (baseline), 6 months (recall 1), and 18 months (recall 2) after the insertion of the restoration. A specifically designed measuring device was used. The median values for the single measuring points reached 4.705 N at the baseline, 5.190 N after 6 months, and 3.740 N after 18 months. The measured values were analyzed according to differences between the median retention forces at the three defined points in time. The statistical analysis of the median values showed no statistical difference for the retention force change after 6 months but for the decrease until the second recall (Mann-Whitney test). The retention force per denture was calculated by a summation of the single measuring points. At the baseline, 12.9 N was reached. The forces did only decrease slightly and were not statistically significant. The results indicate that retention force values of double crowns, measured intraorally at the patient, do not relevantly change clinically within the first 1.5 years. Within the limitations of this study, it can be stated that wear does not influence the retentive forces of double crowns within the first 18 months. After this period the retention force should be still sufficient for denture retention.

Effect of platform switching on peri-implant bone levels: a randomized clinical trial.

OBJECTIVE: The concept of platform switching has been introduced to implant dentistry based on observations of reduced peri-implant bone loss. However, randomized clinical trials are still lacking. This study aimed to test the hypothesis that platform switching has a positive impact on crestal bone-level changes. MATERIAL AND METHODS: Two implants with diameters of 4 mm were inserted epicrestally into one side of the posterior mandibles of 25 subjects. After 3 months of submerged healing, the reentry surgery was performed. On the randomly placed test implant, an abutment 3.3 mm in diameter was mounted, resulting in a horizontal circular step of 0.35 mm (platform switching). The control implant was straight, with an abutment 4 mm in diameter. Single-tooth crowns were cemented provisionally. All patients were monitored at short intervals over the course of 1 year. Standardized radiographs and microbiological samples from the implants' inner spaces were obtained at baseline (implant surgery), and after 3, 4, and 12 months. RESULTS: After 1 year, the mean radiographic vertical bone loss at the test implants was 0.53±0.35 mm and at the control implants, it was 0.58±0.55 mm. The mean intraindividual difference was 0.05±0.56 mm, which is significantly <0.35 mm (P=0.0093, post hoc power 79.9%). The crestal bone-level changes depended on time (P<0.001), but not on platform switching (P=0.4). The implants' internal spaces were contaminated by bacteria, with no significant differences in the total counts between the test and the control at any time point (P=0.98). CONCLUSIONS: The present randomized clinical trial could not confirm the hypothesis of a reduced peri-implant bone loss at implants restored according to the concept of platform switching.

Open or submerged healing of implants with platform switching: a randomized, controlled clinical trial.

AIM: The temporal pattern of bone-level alterations in conventionally restored implants is dependent upon healing mode (open or submerged). This study examined the influence of healing on marginal bone levels at implants with a medium-rough surface including the implant collar and a clearance-fit implant-abutment connection restored according to a platform-switching concept. MATERIAL AND METHODS: Two implants were placed in the posterior mandible of 21 test subjects, randomly assigned to open (OH) or submerged (SH) healing. Standardized radiographs were obtained after implant surgery, before re-entry, after crown mounting, 1 and 2 years after implant surgery, and evaluated for implant-bone-level alterations (ΔIBL). Bacterial samples of the implants' inner cavities were analysed by cultivation. STATISTICS: Brunner-Langer Model, equivalence testings by Wilcoxon's (equivalence range ±0.4mm). RESULTS: After 2 years, ΔIBL were -0.47±0.46mm (OH) and -0.54±0.38mm (SH). At the 1-year follow-up, all implants were contaminated with bacteria. ΔIBL (p<0.001) and the amount of bacterial contamination (p<0.001) significantly depended on time, but not on healing mode. ΔIBL of OH and SH were equivalent at all time points (all p0.044). CONCLUSIONS: Platform-switched implants showed very limited peri-implant bone-level alterations. The healing-mode neither affected the total amount nor the temporal patterns of ΔIBL. Thus, the results for the tested implants with a non-rigid implant-abutment connection were similar to results reported previously for implants with a rigid implant-abutment connection.

Conical crowns with electroplated gold copings: retention force changes caused by wear and combined off-axial load.

OBJECTIVES: The aim of this study was to examine the wear behavior of conical crowns of gold alloy and zirconium dioxide ceramics facing electroplated gold copings. METHODS: The conical crowns were milled in Group A of a cast gold alloy (Degunorm(®), DeguDent(®)) and B zirconium dioxide (Cercon(®), DeguDent(®)). Fifteen specimens were milled per group with a conicity of 2°. The electroplated coping was established by direct electroforming with the Solaris system (DeguDent(®)) and glued into a framework. An apparatus accomplishing 5000 wear cycles performed the wear test. After each of the cycles, extra axial forces (80 N) were loaded 1 million times on an extension of the framework. The retentive forces and the correlating distance during insertion and separation were measured. The wear test was separated in a start phase, an initial wear phase and the long-term wear period. The retention force value and the force-distance integral of the first 0.3 mm of each cycle were calculated. RESULTS: The changes of retention force (ΔF) and integral (ΔF(d)) differed significantly between both groups in the start phase (ΔF: A -1.85 N, B +1.39 N, P=0.0028; ΔF(d): A -0.155 N mm, B +0.2685 N mm, P=0.0378) and the initial wear phase. The long-term wear period showed no differences in force and integral development. As a statistical test for the comparison of the median values of the two groups, the Mann-Whitney test was used. The median force never fell below 4 N or exceeded 12 N. CONCLUSIONS: Within the limitations of this study, the conical crowns tested showed clinically acceptable retentive properties. The values of about 4-6 N mentioned as sufficient in the recent literature were always attained. As the most retentive elements for dentures, both groups showed the main changes in retentive forces during the first 2000 cycles. The retention force development of the zirconia group appears to be less excursive over the whole wear test.

Prevalence of findings compatible with carotid artery calcifications on dental panoramic radiographs.

Cerebrovascular accidents are responsible for killing or disabling more than half a million Americans every year. They are the third leading cause of death in this country. In Germany, the annual stroke incidence reaches 182 cases per 100,000 inhabitants. Stroke there is the fourth leading cause of death. There is a need of finding cost-effective means of decreasing stroke mortality and morbidity. Instruments for early diagnosis are of great humanitarian and economic importance. All possible clinical findings should be taken into account. It is not the demand of this study to present the panoramic radiograph as a screening test method for early diagnosis of atherosclerosis. The aim is to show the potential of this radiograph used in everyday clinical dental practice by the prevalence of radiopaque findings in the carotid region. This study included panoramic dental radiographs of 2,557 patients older than 30 years of age. Fifty-nine percent of the patients were women and 41% were men. The radiographs were adjudged for signs compatible with carotid arterial calcifications appearing as a radiopaque nodular mass adjacent to the cervical vertebrae at or below the intervertebral space C3-4. Of all these radiographs, 4.8% showed radiopaque findings compatible with atherosclerotic lesions. The proportion of women reached 64.8% and that of men reached 35.2%. In accordance to recent literature, the results of this study show that about 5% of the patients show radiological findings compatible with carotid arterial calcifications. Some of these patients at risk for a cerebrovascular accident may be identified in the dentist's office by appropriate review of the panoramic dental radiograph. The suspicion of carotid artery calcifications demands an impetuous referral to an appropriate practitioner who can assist in the control of risk factors and if necessary arrange surgical removal of the carotid arterial plaque. So, the dentist should be aware of this problem and able to make a contribution to stroke prevention.

Influence of the lubricant and the alloy on the wear behaviour of attachments.

OBJECTIVES: Wear of attachments leads to a loss of retention and reduces the function of overdentures. This study evaluated the retention force changes of an attachment system for overdentures. The influence of the lubricant and the alloy on wear constancy was examined. METHODS: Cylindrical anchors of the Dalbo(®) -Z system were tested (Cendres+Métaux SA). Three groups of alloy-lubricant combinations were generated 1.Elitor(®) /NaCl-solution (EN) 2.Elitor(®) /Glandosane(®) aquadest. (EG) and 3.Valor(®) /Glandosane(®) /aquadest. (VG). Ten samples of each group were subjected to 10 000 insertion-separation cycles. RESULTS: For the EN-group, this led to a large increase in retention force. The EG- and VG-group showed a constant decrease after an initial increase in retention force at the beginning of the wear simulation. The change of the alloy caused no statistically significant differences. The use of a more viscous lubricant reduced the retention force increase significantly. CONCLUSIONS: The use of a lubricant which simulates clinical conditions is an absolute need for wear simulation because the retention force changes are influenced enormously. The change of the alloy at the Dalbo(®) -Z system did not influence the wear behaviour. As a slight decrease in retention force was recorded, it is useful for an attachment system to allow compensation with an adjustable matrix.

Osseoperception: active tactile sensibility of osseointegrated dental implants.

PURPOSE: The phenomenon of developing a certain tactile sensibility through osseointegrated dental implants is called osseoperception. Active tactile sensibility can be tested by having the subject bite on test bodies. The aim of the study was to describe the active tactile sensibility of single-tooth implants based on the 50% value and the slope of the sensibility curve at the 50% value. MATERIALS AND METHODS: Sixty-two subjects with single-tooth implants with natural opposing teeth were included in the study. In a computer-assisted and randomized way, copper foils of varying thickness (0 to 200 Μm) were placed inter?occlusally between the single-tooth implant and the natural opposing tooth, and the active tactile perception was studied according to the psychophysical method of constant stimuli and statistically evaluated by logistic regression. RESULTS: Tactile perception of the implants at the 50% value estimated by logistic regression was 20.2 ± 10.9 Μm on average, and the slope was 29 ± 15. Regarding implant surface structure, significant differences were observed. The sandblasted and acid-etched surface was significantly more sensitive than the titanium plasma-sprayed surface, and the machined surface was similar to the titanium plasma-sprayed surface. CONCLUSIONS: Active tactile sensibility of implants with natural antagonistic teeth is very similar to that of teeth, but the slope of the tactile sensibility curve is flatter. Significant differences in tactile sensibility as a function of different implant surfaces may indicate that receptors near the implant form the basis of osseoperception.