Evaluation of the damping capacity of common CAD/CAM restorative materials.

OBJECTIVES: To evaluate and quantify the damping capacities of common CAD/CAM restorative materials (CRMs) and to assess their energy dissipation abilities by comparing loss tangent and Leeb hardness data. METHODS: Leeb hardness (HLD), together with its deduced energy dissipation data (HLDdis), and loss tangent values recorded via dynamic mechanical analysis (DMA) were determined for 4 ceramic, 13 composite, and 2 polymer-based CRMs as well as 1 metal. For Leeb hardness, ten indentations per material were performed on two separate specimens (12.0 × 12.0 × 3.5 mm3) after water storage (24 h; 37.0 ± 1.0 °C). For DMA, ten specimens (16.00 × 4.00 × 1.00 mm3 ± 0.05 mm) per material were investigated in distilled water (37.0 ± 0.5 °C) with a dynamic force of 1 N at 1.5 Hz. Each data set was analyzed using two-way analysis of variance (ANOVA) with material type and material nested in material type as factors. Post-ANOVA contrasts were performed using a Bonferroni adjustment for multiple comparisons (α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05). RESULTS: HLDdis data revealed the significantly highest damping capacity for metal and the lowest values for ceramics with composites and polymers in between. However, for loss tangent, the metal together with lithium disilicate glass-ceramics exhibited the lowest damping effects and polymer materials the highest results with composites likewise in between. A strong dependency of the loss tangent results on the filler content of the investigated CRMs was indicated (r = - 0.822, p < 0.001), while a positive and only moderate correlation between loss tangent and HLDdis was observed (r = 0.565, p < 0.001), which conversely revealed a very strong correlation (r = 0.911, p < 0.001) if the metal was excluded from the calculation. CONCLUSIONS: Although HLDdis and loss tangent values both allowed a distinct differentiation of the damping capabilities of various CRMs and the respective material types, HLDdis data appeared to more accurately describe the damping capacity of CRMs as the energy dissipation mechanism of permanent plastic material deformation, that is commonly observed for metals and some composite-based CRMs, is equally captured. This finding could be particularly interesting for the future development of new CRMs with improved mechanical properties as HLDdis data determination in principle is a very efficient and simple technique to entirely specify unknown damping capacities of materials.

New method to differentiate surface damping behavior and stress absorption capacities of common CAD/CAM restorative materials.

OBJECTIVES: To assess energy dissipation capacities and surface damping abilities of different CAD/CAM restorative materials (CRMs) to characterize stress resistance during load peaks. METHODS: Using instrumented indentation testing (IIT), Martens hardness (HM) together with its elastic (ηIT) and plastic index (ηITdis) and Leeb hardness (HLD) together with its deduced energy dissipation (HLDdis) were determined for eight ceramic, eight composite, and four polymer-based materials as well as three metals. The results were compared to those of bovine enamel. Ten indentations per material were performed at room temperature (23 ± 1 °C) on two separate specimens (12.0 × 12.0 × 3.5 mm3) after water storage (24 h; 37.0 ± 1.0 °C). Hardness parameters were recorded, and data were analyzed with one-way MANOVA (Games-Howell post hoc tests, α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05). RESULTS: Independently determined HLDdis, and ηITdis values substantiated different energy dissipation characteristics of CRM, whereby a strong correlation was observed for the two datasets (r = 0.956, p = 0.011). Ceramics had the significantly lowest values (p < 0.001) while both parameters revealed the highest surface damping effects for metals (p < 0.001), followed in both cases by bovine enamel. Energy dissipation of polymer and composite CRM was in between ceramics and bovine enamel (p < 0.001), whereas only for HLDdis did both show no significant difference (p > 0.05). SIGNIFICANCE: Promising new HLDdis and ηITdis data allow a reliable differentiation of energy dissipation and surface damping capacities of CRMs. Previously published rankings of edge chipping and loss tangent results were perfectly reproduced, especially by HLDdis.

Evaluation of the surface damage of dental implants caused by different surgical protocols: an in vitro study.

The implant surface must withstand high insertion torque during implant insertion. The aim of this study was to investigate the damage to implant surfaces caused by two different insertion protocols in vitro. Fifteen titanium implants per group were inserted in standardized polyurethane foam models, group 1 according to a non-threaded surgical protocol and group 2 according to a threaded surgical protocol. Before and after insertion, the surfaces were visualized by scanning electron microscopy (SEM) and non-contact laser profilometry. Different surface area parameters were evaluated and maximum torque during insertion was determined. SEM detected topographical changes such as deposition of the test block and smoothening of the surface in the region of the thread crests in both groups. The laser profilometry analysis revealed significant changes in the surface topography of the implants in both groups, but no differences between the groups. Insertion torque was significantly decreased in the threaded group. Both types of surgical intervention resulted in surface damage. Less damage was detected to the thread crests with the use of a thread cutter, and most of the surface was not visibly affected by the surgical protocol at the microscopic level. The surgical protocol seems to have a minor influence on preservation of the implant surface.

[Development and validation of the Mini Dental Assessment : A procedure for improved estimation of need for dental treatment in geriatrics]. / Entwicklung und Validierung des "Mini Dental Assessment" : Ein Verfahren zur besseren Einschätzung des zahnärztlichen Behandlungsbedarfes in der Geriatrie.

BACKGROUND: In the future there will be an increasing demand for professional care with simultaneous retention of the dentition in older people. Due to inadequate dental knowledge, it is often not possible for caregivers to adequately assess dental deficits. OBJECTIVE: The aim of the study was to develop and validate a simple tool (Mini Dental Assessment, MDA) to assess possible dental treatment needs (DTN) of residential geriatric facilities by nursing personnel. MATERIAL AND METHODS: In the study 169 patients (51 from the University Hospital Giessen, 118 from the Bonifatius Hospital Lingen) underwent a dental examination. The dental status was evaluated based on the California Dental Association (CDA) criteria and the DTN determined. In addition, the time since the patients last visit to a dentist (TLVD) and denture age (DA) were documented and a chewing function test (carrot eating test, CET) was carried out. In a second study 155 patients were examined (115 from the University Hospital Giessen, 40 from the Bonifatius Hospital Lingen) corresponding to the reference sample and including a further chewing function test (after Schimmel und Slavicek) and questionnaires on quality of life (Oral Health Impact Profile (OHIP), Denatl Impact on Daily Living (DiDDL)). RESULTS: A total of 108 patients required dental treatment. The mean value (±SD) for the TLVD was 2.5 ± 3.8 years and 10.8 ± 8.9 years for the DA. There was a positive correlation (Spearman, P < 0.005) between the DTN and degree of comminution in the CET (3.4 ± 1.8 grade). Based on the results an assessment tool was developed using the variables CET, TLVD and DA weighted by the respective regression coefficients (10:3:1). The resulting mean total MDA score was 51.32 ± 28.14. A sensitivity/specificity analysis was conducted and a receiver operating characteristic (ROC) curve calculated (area under curve, AUC: 0.805; 95% CI: 0.738-0.873). The ROC curve from the follow-up study showed a good agreement with the ROC curve from the reference study (AUC 0.829, 95% CI: 0.751-0.907). CONCLUSION: Based on the results of the study it could be shown that the MDA is a suitable instrument for making a valid statement on the assessment of DTN of patients in long-term care facilities. The validation study revealed the validity of the MDA in its originally developed form and the addition of two further chewing function tests did not significantly improve the validity of the MDA. Overall, the MDA appears to be an appropriate tool to help nursing home personnel to assess the necessity for nursing home residents to visit a dentist.

Mini dental assessment: a simple screening test for non-dental staff.

OBJECTIVE: The objective of this study was to develop a simple tool for the assessment of possible dental treatment needs (DTN) for non-dental professionals (Mini Dental Assessment, MDA). To keep the assessment universal, we aimed to base it on the patient's history and a simple chewing efficiency test (CET) as the dental status is a known determinant for chewing efficiency. MATERIALS & METHODS: The assessment was developed using data from 169 patients from two sites (University Hospital Giessen, St. Bonifatius Hospital Lingen, both Germany). In all patients, a dental examination was performed, the denture status was evaluated (based on the California Dental Association criteria; CDA criteria), and the DTN was determined. In addition, the time since the patient's last visit to a dentist (TLVD) and denture age (DA) were assessed. Furthermore, a CET was carried out and the comminution score was determined (CETS). RESULTS: In total, 108 patients required dental treatment. The mean value (±SD) was 2.9 ± 0.9 score points for the DTN, 2.5 ± 3.8 years for the TLVD, and 10.8 ± 8.9 years for the DA. There was a significant correlation (Spearman, P < .05) between the DTN and degree of comminution (3.4 ± 1.8). Based on the results of the statistical analysis, the intended assessment tool was developed using the variables CETS, TLVD, and DA weighed by their respective regression coefficients (10:3:1). Subsequently, the resulting MDA score (51.32 ± 28.14) was calculated. A sensitivity/specificity analysis was conducted and a receiver operating characteristic curve was calculated (SPSS 17.0, area under curve 0.805; 95 % CI 0.738-0.873). CONCLUSION: It can be concluded that the dental status of elderly patients is reflected in the outcome of the MDA. However, ongoing validation is needed. TRIAL REGISTRATION: DRKS00003219.

A new method for assessing the accuracy of full arch impressions in patients.

OBJECTIVE: To evaluate a new method of measuring the real deviation (trueness) of full arch impressions intraorally and to investigate the trueness of digital full arch impressions in comparison to a conventional impression procedure in clinical use. METHODS: Four metal spheres were fixed with composite using a metal application aid to the lower teeth of 50 test subjects as reference structures. One conventional impression (Impregum Penta Soft) with subsequent type-IV gypsum model casting (CI) and three different digital impressions were performed in the lower jaw of each test person with the following intraoral scanners: Sirona CEREC Omnicam (OC), 3M True Definition (TD), Heraeus Cara TRIOS (cT). The digital and conventional (gypsum) models were analyzed relative to the spheres. Linear distance and angle measurements between the spheres, as well as digital superimpositions of the spheres with the reference data set were executed. RESULTS: With regard to the distance measurements, CI showed the smallest deviations followed by intraoral scanners TD, cT and OC. A digital superimposition procedure yielded the same order for the outcomes: CI (15±4µm), TD (23±9µm), cT (37±14µm), OC (214±38µm). Angle measurements revealed the smallest deviation for TD (0.06°±0,07°) followed by CI (0.07°±0.07°), cT (0.13°±0.15°) and OC (0.28°±0.21°). CONCLUSION: The new measuring method is suitable for measuring the dimensional accuracy of full arch impressions intraorally. CI is still significantly more accurate than full arch scans with intraoral scanners in clinical use. CLINICAL SIGNIFICANCE: Conventional full arch impressions with polyether impression materials are still more accurate than full arch digital impressions. Digital impression systems using powder application and active wavefront sampling technology achieve the most accurate results in comparison to other intraoral scanning systems (DRKS-ID: DRKS00009360, German Clinical Trials Register).

Management of shortened dental arches and periodontal health: 5-year results of a randomised trial.

In a multicentre randomised trial (German Research Association, grants DFG WA 831/2-1 to 2-6, WO 677/2-1.1 to 2-2.1.; controlled-trials.com ISRCTN97265367), patients with complete molar loss in one jaw received either a partial removable dental prosthesis (PRDP) with precision attachments or treatment according to the SDA concept aiming at pre-molar occlusion. The objective of this current analysis was to evaluate the influence of different treatments on periodontal health. Linear mixed regression models were fitted to quantify the differences between the treatment groups. The assessment at 5 years encompassed 59 patients (PRDP group) and 46 patients (SDA group). For the distal measuring sites of the posterior-most teeth of the study jaw, significant differences were found for the plaque index according to Silness and Löe, vertical clinical attachment loss (CAL-V), probing pocket depth (PPD) and bleeding on probing. These differences were small and showed a slightly more unfavourable course in the PRDP group. With CAL-V and PPD, significant differences were also found for the study jaw as a whole. For CAL-V, the estimated group differences over 5 years amounted to 0.27 mm (95% CI 0.05; 0.48; P = 0.016) for the study jaw and 0.25 mm (95% CI 0.05; 0.45; P = 0.014) for the distal sites of the posterior-most teeth. The respective values for PPD were 0.22 mm (95% CI 0.03; 0.41; P = 0.023) and 0.32 mm (95% CI 0.13; 0.5; P = 0.001). It can be concluded that even in a well-maintained.patient group statistically significant although minor detrimental effects of PRDPs on periodontal health are measurable.

The randomized shortened dental arch study: oral health-related quality of life.

OBJECTIVES: Although the shortened dental arch (SDA) concept is a widely accepted strategy to avoid overtreatment, little is known on its impact on oral health-related quality of life (OHRQoL). This multicenter randomized controlled trial aimed to investigate the OHRQoL for removable partial dental prostheses (RPDP) with molar replacement versus the SDA concept. MATERIAL AND METHODS: In both groups, missing anterior teeth were replaced with fixed dental prosthesis. Two hundred fifteen patients with bilateral molar loss in at least one jaw were included. The Oral Health Impact Profile (OHIP-49) was completed before; 6 weeks (baseline), 6 months, and 12 months after treatment; and thereafter annually until 5 years. RESULTS: Of the initial cohort, 81 patients were assigned to the RPDP group and 71 to the SDA group (age, 34 to 86 years). Before treatment, the median OHIP score was similar in both groups (RPDP, 38.0; SDA, 40.0; n.s.). Results indicate marked improvements in OHRQoL in both groups between pretreatment and baseline (RPDP, 27.0; SDA, 19.0; p ≤ 0.0001) which continued in the RPDP group until the 1-year follow-up (p = 0.0002). These significant reductions in OHIP scores are reflected in its subscales. No further differences were seen within and between groups during the remainder observation period. CONCLUSION: Both treatments show a significant improvement in OHRQoL which continued in the RPDP group until the 1-year follow-up. No significant differences were seen between groups. CLINICAL RELEVANCE: For improving OHRQoL, it is not necessary to replace missing molars with a RPDP.

The randomized shortened dental arch study: tooth loss over five years.

OBJECTIVES: The study was designed to provide clinical outcome data for two treatments of the shortened dental arch (SDA). MATERIAL AND METHODS: In a multicenter randomized controlled clinical trial, patients with complete molar loss in one jaw were provided with either a partial removable dental prosthesis (PRDP) retained with precision attachments or treated according to the SDA concept preserving or restoring a premolar occlusion. No implants were placed. The primary outcome was tooth loss. RESULTS: Of 152 treated patients, 132 patients reached the 5-year examination. Over 5 years, 38 patients experienced tooth loss. For the primary outcome tooth loss, the Kaplan-Meier survival rates at 5 years were 0.74 (95% CI 0.64, 0.84) in the PRDP group and 0.74 (95% CI 0.63, 0.85) in the SDA group. For tooth loss in the study jaw, the survival rates at 5 years were 0.88 (95% CI 0.80, 0.95) in the PRDP group and 0.84 (95% CI 0.74, 0.93) in the SDA group. The differences were not significant. No Cox regression models of appropriate fit explaining tooth loss on the patient level could be found. CONCLUSIONS: The overall treatment goals of a sustainable oral rehabilitation and the avoidance of further tooth loss over longer periods were not reliably achievable. The influence of the type of prosthetic treatment on tooth loss might have been overestimated. CLINICAL RELEVANCE: Regarding our results, the patient's view will gain even more importance in the clinical decision between removable and fixed restorations in SDAs.

The randomized shortened dental arch study: 5-year maintenance.

The scientific evidence concerning prosthodontic care for the shortened dental arch (SDA) is sparse. This randomized multicenter study aimed to compare two common treatment options: removable partial dental prostheses (RPDPs) for molar replacement vs. no replacement (SDA). One of the hypotheses was that the follow-up treatment differs between patients with RPDPs and patients with SDAs during the 5-year follow-up period. Two hundred and fifteen patients with complete molar loss in one jaw were included in the study. Molars were either replaced by RPDPs or not replaced according to the SDA concept. A mean number of 4.2 (RPDP) and 2.8 (SDA) treatments for biological or technical reasons occurred during the 5-year observation time per patient. Concerning the biological aspect, no significant differences between the groups could be shown, whereas treatment arising from technical reasons was significantly more frequent for the RPDP group. When the severity of treatment was analyzed, a change over time was evident. When, at baseline, only follow-up treatment with minimal effort is required, over time there is a continuous increase to moderate and extensive effort observed for both groups (Controlled-trials.com number ISRCTN97265367).

[Preventive strategies in prosthetic dentistry]. / Präventionsorientierte Strategien in der prothetischen Zahnmedizin.

Despite the success in preventing oral diseases, the prevalence of tooth loss in the German population remains high and increases with age. Today, the advances in prosthetic dentistry allow necessary tooth replacement following preventive strategies-after considering benefits and risks. Modern treatment options improve the overall prognosis of the stomatognathic system and the quality of life of the affected patients significantly. Hereby, adverse iatrogenic effects can be minimized or even completely avoided by extending the traditional treatment spectrum, e.g., using adhesively fixed restorations and implant-supported restorations, and refraining from placing restorations that are unnecessary from the medical point of view. Generally, patients benefit greatly from prosthetic treatment and the achieved health gain is remarkably high. It encompasses not only the recovery of the impaired oral functions but also extends to the whole human organism, including nutrition, digestion, musculoskeletal system, as well as mental and social well-being.

The randomized shortened dental arch study: tooth loss.

The evidence concerning the management of shortened dental arch (SDA) cases is sparse. This multi-center study was aimed at generating data on outcomes and survival rates for two common treatments, removable dental prostheses (RDP) for molar replacement or no replacement (SDA). The hypothesis was that the treatments lead to different incidences of tooth loss. We included 215 patients with complete molar loss in one jaw. Molars were either replaced by RDP or not replaced, according to the SDA concept. First tooth loss after treatment was the primary outcome measure. This event occurred in 13 patients in the RDP group and nine patients in the SDA group. The respective Kaplan-Meier survival rates at 38 months were 0.83 (95% CI: 0.74-0.91) in the RDP group and 0.86 (95% CI: 0.78-0.95) in the SDA group, the difference being non-significant.

Surfactant release from hydrophilized vinylpolysiloxanes.

Vinylpolysiloxane impression materials (VPS) exhibit an apolar (hydrophobic) backbone chemistry. Hence, surfactants are added to improve their hydrophilicity for impression-taking in moist environments. However, the mechanisms at the liquid-VPS-interface regarding the surfactant are unknown. We hypothesized that surfactant is leached from the VPS. Four experimental VPS formulations were fabricated containing 0 (control), 1.5, 3, and 5 wt% non-ionic surfactant. Samples were prepared (n = 6) and contact angles determined 30 min after mixing. After 60 sec, droplets were transferred onto the control. Mass spectrometry was used to analyze the droplets. Contact angles were inversely correlated with the surfactant concentration (p < 0.05). Droplets transferred from hydrophilized specimens onto the control showed similar contact angles. Surfactant could be clearly identified inside the droplets from the hydrophilized samples, however, not inside the control. Surfactants reduced the surface tension of the liquid in contact and did not change the surface properties of the VPS itself.

Repairability of cross-linked biopolymers.

Repair of biopolymers is a critical issue, especially with aged restorations. Obtaining a chemical bond to the repair surface might solve this problem. We hypothesized that certain repair liquids are suitable to establish a strong bond to an artificially aged dimethacrylate-based biopolymer for temporary restorations. Specimens made of a self-curing temporary crown-and-bridge material were prepared and thermocycled for 7 days (5000x, 5-55 degrees C). Cylinders made of light-curing composites (n=10) were bonded onto the specimen surface, either after grinding or after the application of 4 different experimental repair liquids (Bis-GMA:TEGDMA mixture=bonding, methylmethacrylate=MMA, bonding & acetone, bonding & MMA). A shear bond strength test was performed 24 hrs after repair. The highest bond strength was obtained with the bonding & acetone liquid (20.1+/-2.2 MPa). The use of MMA significantly affected the bond strength (6.8+/-1.9 MPa). MMA is inadequate as a repair liquid on aged composite-based biopolymers.

Effects of prosthetic treatment for shortened dental arches on oral health-related quality of life, self-reports of pain and jaw disability: results from the pilot-phase of a randomized multicentre trial.

A multi-centre randomized clinical trial is under way at 14 university dental schools in Germany to compare prosthodontic treatments for the shortened dental arch (SDA). One of the aims of this pilot-study was to measure the effect of two treatment options of the SDA on oral health-related quality of life and on the Research Diagnostic Criteria (RDC) for temporomandibular disorders (TMD). Thirty-four patients participated in the pilot-study. Inclusion criteria were: all molars were missing and the presence of at least both canines and one premolar in each quadrant. Participants were randomly assigned to receive either removable partial dentures including molar replacement (RPD_group) or retain a premolar occlusion (PROC_group). The Oral Health Impact Profile (OHIP-49) and the RDC for TMD were completed by participants before treatment (pre-treatment), 6 weeks (6 wks), 6 months (6m) and 12 months (12 m) after treatment. At the 12-month follow up, data of 10 women and 11 men (mean age: 62 +/- 10 years) were available. Medians of the OHIP total-scores were as follows: RPD (n = 10), 43.5 (pre-treatment), 18.2 (6 wks), 13.3 (6m), 14.7 (12 m). PROC (n = 11): 31.8 (pre-treatment), 27.1 (6 wks), 8.8 (6m), 8.3 (12 m). Significant differences were shown for RPD_group between pre-treatment and 6m/12 m and for PROC_group between pre-treatment and 6m. There were no significant differences between treatment groups at any time. Within each group, an improvement of life-quality was observed. No significant difference could be reported between the two therapy concepts. This may be due to the low sample size within the pilot study.

Effects of captopril on fibrinolytic function in healthy humans.

Several lines of evidence point to an interrelation of the renin angiotensin system (RAS) with the endogenous fibrinolytic system. In the present study, we have therefore investigated the effect of the ACE-inhibitor captopril on various parameters of the fibrinolytic system in healthy volunteer subjects. 10 male subjects aged 28-38 years were given captopril 25 mg b.i.d. over 2 weeks. Venous blood was drawn before and at the end of the treatment period at 09.00 AM, after the volunteers had received their last dose of captopril by 07. 30 AM. Blood samples were processed for the determination of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1). Both parameters were determined with respect to their abundance (as antigen concentrations) and function (activity). In addition, the concentration and activity of the von Willebrand factor were also determined. Two weeks of captopril treatment had no significant effect on any of the above mentioned parameters. Our results thus show that short-term treatment with the ACE-inhibitor captopril, at least in healthy subjects on an unrestricted NaCl intake, does not affect the fibrinolytic balance between t-PA and PAI-1 or the von Willebrand factor.

Antihypertensive drug treatment and fibrinolytic function.

Thromboembolic complications such as ischemic stroke and myocardial infarction are significantly more frequent in patients with arterial hypertension. From the available intervention studies, it appears that pharmacologic treatment of hypertension-at least with diuretics and beta-blockers-may more effectively protect against cerebrovascular as compared to coronary thromboembolic events. Whether other antihypertensive substances provide a more effective protection with respect to cardiac morbidity and mortality is the subject of numerous studies presently underway. These studies will help to answer the question of whether the extent of protection from coronary events during antihypertensive treatment depends on factors beyond blood pressure control. The fibrinolytic system is crucially involved in the pathogenesis of thromboembolic events. One determinant of this system is the balance between plasminogen activators (tissue-type plasminogen activator [t-PA]) and inhibitors (plasminogen activator inhibitor 1 [PAI-1]). Experimental and clinical evidence suggests that at least some of the drugs used in the treatment of hypertension may alter the activity of the fibrinolytic system. Scarce and controversial data with respect to such an interaction exist with respect to diuretics, beta-blockers, and calcium antagonists. In addition, experimental evidence demonstrates that PAI-1 is stimulated by angiotensin II (A II), whereas t-PA is activated by bradykinin. Thus, antihypertensive drugs acting within the renin angiotensin system should exert effects also within the fibrinolytic system. However, results from clinical studies with angiotensin converting enzyme (ACE) inhibitors and A II receptor antagonists do not unequivocally support such a concept. The discrepancy in the results may, at least in part, be explained by studies performed in healthy volunteer subjects showing that ACE inhibition profoundly affected fibrinolysis only during stimulation of the renin angiotensin system by NaCL restriction.

Serum zinc in aging germ-free and conventional rats.

Zinc nutritional status appears to decline with age in humans and rodents. Since germ-free rats outlive their conventional counterparts in better health, serum Zn levels were determined in male germ-free and conventional Lobund Wistar rats in samples originating from the Lobund Aging Study. Starting at 5 months of age, germ-free rats showed significantly higher serum Zn levels than did their conventional counterparts. In conventional rats sacrificed up to 30 months of age in apparently good health, serum Zn levels showed no effect of age, while a slight but significant increase with age was observed in the germ-free rats. In healthy germ-free adults (6-24 months of age), serum Zn concentrations were approximately 25% higher than those in comparable conventional animals. In conventional rats 18-30 months of age (average, 24.5 months), sacrificed because of an obvious moribund condition, serum Zn levels were significantly lower than those in rats of the same age range (average, 24.9 months) that were obviously healthy. Results suggest that the often observed higher absorptive capacity of the germ-free gut might have contributed to higher serum Zn levels, and that a decline in serum Zn concentration with age may be a consequence, rather than a causative factor, of declining health.

[The attachments of the IMZ system in full denture prosthodontics]. / Die Attachments des IMZ-Systems in der Totalprothetik.

With the aid of a photoelastic model it was possible to visualize the transmission of forces from four different types of attachment (parallel bar, round bar, RS- and O-ring attachment) onto IMZ implants. The parallel bar produced the highest stresses between the implants. By contrast, the round bar mainly transmitted transverse forces. RS- and O-ring attachments transmitted the least forces onto the implants. The retentive power of the attachments has also been measured. The round bar proved to be almost twice as retentive as the RS attachment and nearly three times as retentive as the O-ring.