Sven Mühlemann

Cemented and screw‐retained implant reconstructions: a systematic review of the survival and complication rates

OBJECTIVES To assess the 5-year survival rates and incidences of complications of cemented and screw-retained implant reconstructions. METHODS An electronic Medline search complemented by manual searching was conducted to identify randomized controlled clinical trials (RCTs), and prospective and retrospective studies giving information on cemented and screw-retained single-unit and multiple-unit implant reconstructions with a mean follow-up time of at least 1 year. Assessment of the identified studies and data abstraction were performed independently by three reviewers. Failure rates were analyzed using Poisson regression models to obtain summary estimates and 95% confidence intervals of failure rates and 5-year survival proportions. RESULTS Fifty-nine clinical studies were selected from an initial yield of 4511 titles and the data were extracted. For cemented single crowns the estimated 5-year reconstruction survival was 96.5% (95% confidence interval (CI): 94.8-97.7%), for screw-retained single crowns it was 89.3% (95% CI: 64.9-97.1%) (P = 0.091 for difference). The 5-year survival for cemented partial fixed dental prostheses (FDPs) was 96.9% (95% CI: 90.8-99%), similar to the one for screw-retained partial FDPs with 98% (95% CI: 96.2-99%) (P = 0.47). For cemented full-arch FDPs the 5-year survival was 100% (95% CI: 88.9-100%), which was somewhat higher than that for screw-retained FDPs with 95.8% (95% CI: 91.9-97.9%) (P = 0.54). The estimated 5-year cumulative incidence of technical complications at cemented single crowns was 11.9% and 24.4% at screw-retained crowns. At the partial and full-arch FDPs, in contrast, a trend to less complication at the screw-retained was found than at the cemented ones (partial FDPs cemented 24.5%, screw-retained 22.1%; full-arch FDPs cemented 62.9%, screw-retained 54.1%). Biological complications like marginal bone loss >2 mm occurred more frequently at cemented crowns (5-year incidence: 2.8%) than at screw-retained ones (5-year incidence: 0%). CONCLUSION Both types of reconstructions influenced the clinical outcomes in different ways, none of the fixation methods was clearly advantageous over the other. Cemented reconstructions exhibited more serious biological complications (implant loss, bone loss >2 mm), screw-retained reconstructions exhibited more technical problems. Screw-retained reconstructions are more easily retrievable than cemented reconstructions and, therefore, technical and eventually biological complications can be treated more easily. For this reason and for their apparently higher biological compatibility, these reconstructions seem to be preferable.

Cognitive impairment in Gdi1-deficient mice is associated with altered synaptic vesicle pools and short-term synaptic plasticity, and can be corrected by appropriate learning training.

The GDI1 gene, responsible in human for X-linked non-specific mental retardation, encodes alphaGDI, a regulatory protein common to all GTPases of the Rab family. Its alteration, leading to membrane accumulation of different Rab GTPases, may affect multiple steps in neuronal intracellular traffic. Using electron microscopy and electrophysiology, we now report that lack of alphaGDI impairs several steps in synaptic vesicle (SV) biogenesis and recycling in the hippocampus. Alteration of the SV reserve pool (RP) and a 50% reduction in the total number of SV in adult synapses may be dependent on a defective endosomal-dependent recycling and may lead to the observed alterations in short-term plasticity. As predicted by the synaptic characteristics of the mutant mice, the short-term memory deficit, observed when using fear-conditioning protocols with short intervals between trials, disappeared when the Gdi1 mutants were allowed to have longer intervals between sessions. Likewise, previously observed deficits in radial maze learning could be corrected by providing less challenging pre-training. This implies that an intact RP of SVs is necessary for memory processing under challenging conditions in mice. The possibility to correct the learning deficit in mice may have clinical implication for future studies in human.

Critical soft-tissue dimensions with dental implants and treatment concepts

Dental implants have proven to be a successful treatment option in fully and partially edentulous patients, rendering long-term functional and esthetic outcomes. Various factors are crucial for predictable long-term peri-implant tissue stability, including the biologic width; the papilla height and the mucosal soft-tissue level; the amounts of soft-tissue volume and keratinized tissue; and the biotype of the mucosa. The biotype of the mucosa is congenitally set, whereas many other parameters can, to some extent, be influenced by the treatment itself. Clinically, the choice of the dental implant and the position in a vertical and horizontal direction can substantially influence the establishment of the biologic width and subsequently the location of the buccal mucosa and the papilla height. Current treatment concepts predominantly focus on providing optimized peri-implant soft-tissue conditions before the start of the prosthetic phase and insertion of the final reconstruction. These include refined surgical techniques and the use of materials from autogenous and xenogenic origins to augment soft-tissue volume and keratinized tissue around dental implants, thereby mimicking the appearance of natural teeth.

Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part I: digital versus conventional unilateral impressions

STATEMENT OF PROBLEM Trials comparing the overall performance of fully digital and conventional workflows in reconstructive dentistry are needed. PURPOSE The purpose of the first part of this randomized controlled clinical trial was to determine whether optical impressions produce different results from conventional impressions with respect to time efficiency and patient and operator perceptions of the clinical workflow. MATERIAL AND METHODS Three digital impressions and 1 conventional impression were made in each of 10 participants according to a randomly generated sequence. The digital systems were Lava COS, iTero, and Cerec Bluecam. The conventional impression was made with the closed-mouth technique and polyvinyl siloxane material. The time needed for powdering, impressions, and interocclusal record was recorded. Patient and clinician perceptions of the procedures were rated by means of visual analog scales. The paired t test with Bonferroni correction was applied to detect differences (α=.05/6=.0083). RESULTS The mean total working time ±standard deviation amounted to 260 ±66 seconds for the conventional impression, 493 ±193 seconds for Lava, 372 ±126 seconds for iTero, and 357 ±55 seconds for Cerec. The total working time for the conventional impression was significantly lower than that for Lava and Cerec. With regard to the working time without powdering, the differences between the methods were not statistically significant. The patient rating (very uncomfortable=0; comfortable=100) measured 61 ±34 for conventional impression, 71 ±18 for Lava, 66 ±20 for iTero, and 48 ±18 for Cerec. The differences were not statistically significant. The clinician rating (simple=0; very difficult=100) was 13 ±13 for the conventional impression, 54 ±27 for Lava, 22 ±11 for iTero, and 36 ±23 for Cerec. The differences between the conventional impression and Lava and between iTero and Lava were statistically significant. CONCLUSIONS The conventional impression was more time-effective than the digital impressions. In terms of patient comfort, no differences were found between the conventional and the digital techniques. With respect to the clinician perception of difficulty, the conventional impression and the digital impression with iTero revealed more favorable outcomes than the digital impression with Lava.

Systematic review of pre‐clinical models assessing implant integration in locally compromised sites and/or systemically compromised animals

OBJECTIVE The aim was to systematically search the dental literature for pre-clinical models assessing implant integration in locally compromised sites (part 1) and systemically compromised animals (part 2), and to evaluate the quality of reporting of included publications. METHODS A Medline search (1966-2011) was performed, complimented by additional hand searching. The quality of reporting of the included publications was evaluated using the 20 items of the ARRIVE (Animals in Research In Vivo Experiments) guidelines. RESULTS One-hundred and seventy-six (part 1; mean ARRIVE score = 15.6 ± 2.4) and 104 (part 2; 16.2 ± 1.9) studies met the inclusion criteria. The overall mean score for all included studies amounted to 15.8 ± 2.2. Housing (38.3%), allocation of animals (37.9%), numbers analysed (50%) and adverse events (51.4%) of the ARRIVE guidelines were the least reported. Statistically significant differences in mean ARRIVE scores were found depending on the publication date (p < 0.05), with the highest score of 16.7 ± 1.6 for studies published within the last 2 years. CONCLUSIONS A large number of studies met the inclusion criteria. The ARRIVE scores revealed heterogeneity and missing information for selected items in more than 50% of the publications. The quality of reporting shifted towards better-reported pre-clinical trials within recent years.

Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part II: CAD-CAM versus conventional laboratory procedures

Statement of problem. Clinical studies are needed to evaluate the entire digital and conventional workflows in prosthetic dentistry. Purpose. The purpose of the second part of this clinical study was to compare the laboratory production time for tooth‐supported single crowns made with 4 different digital workflows and 1 conventional workflow and to compare these crowns clinically. Material and methods. For each of 10 participants, a monolithic crown was fabricated in lithium disilicate‐reinforced glass ceramic (IPS e.max CAD). The computer‐aided design and computer‐aided manufacturing (CAD‐CAM) systems were Lava C.O.S. CAD software and centralized CAM (group L), Cares CAD software and centralized CAM (group iT), Cerec Connect CAD software and lab side CAM (group CiL), and Cerec Connect CAD software with centralized CAM (group CiD). The conventional fabrication (group K) included a wax pattern of the crown and heat pressing according to the lost‐wax technique (IPS e.max Press). The time for the fabrication of the casts and the crowns was recorded. Subsequently, the crowns were clinically evaluated and the corresponding treatment times were recorded. The Paired Wilcoxon test with the Bonferroni correction was applied to detect differences among treatment groups (&agr;=.05). Results. The total mean (±standard deviation) active working time for the dental technician was 88 ±6 minutes in group L, 74 ±12 minutes in group iT, 74 ±5 minutes in group CiL, 92 ±8 minutes in group CiD, and 148 ±11 minutes in group K. The dental technician spent significantly more working time for the conventional workflow than for the digital workflows (P<.001). No statistically significant differences were found between group L and group CiD or between group iT and group CiL. No statistical differences in time for the clinical evaluation were found among groups, indicating similar outcomes (P>.05). Conclusions. Irrespective of the CAD‐CAM system, the overall laboratory working time for a digital workflow was significantly shorter than for the conventional workflow, since the dental technician needed less active working time.

Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit

Statement of problem Trials comparing the overall performance of digital with that of conventional workflows in restorative dentistry are needed. Purpose The purpose of the third part of a series of investigations was to test whether the marginal and internal fit of monolithic crowns fabricated with fully digital workflows differed from that of crowns fabricated with the conventional workflow. Material and methods In each of 10 participants, 5 monolithic lithium disilicate crowns were fabricated for the same abutment tooth according to a randomly generated sequence. Digital workflows were applied for the fabrication of 4 crowns using the Lava, iTero, Cerec inLab, and Cerec infinident systems. The conventional workflow included a polyvinyl siloxane impression, manual waxing, and heat‐press technique. The discrepancy between the crown and the tooth was registered using the replica technique with polyvinyl siloxane material. The dimensions of the marginal discrepancy (Discrepancymarginal) and the internal discrepancy in 4 different regions of interest (Discrepancyshoulder, Discrepancyaxial, Discrepancycusp, and Discrepancyocclusal) were assessed using light microscopy. Post hoc Student t test with Bonferroni correction was applied to detect differences (&agr;=.05). Results Discrepancymarginal was 83.6 ±51.1 &mgr;m for the Cerec infinident, 90.4 ±66.1 &mgr;m for the conventional, 94.3 ±58.3 &mgr;m for the Lava, 127.8 ±58.3 &mgr;m for the iTero, and 141.5 ±106.2 &mgr;m for the Cerec inLab workflow. The differences between the treatment modalities were not statistically significant (P>.05). Discrepancyshoulder was 82.2 ±42.4 &mgr;m for the Cerec infinident, 97.2 ±63.8 &mgr;m for the conventional, 103.4 ±52.0 &mgr;m for the Lava, 133.5 ±73.0 &mgr;m for the iTero, and 140.0 ±86.6 &mgr;m for the Cerec inLab workflow. Only the differences between the Cerec infinident and the Cerec inLab were statistically significant (P=.036). The conventionally fabricated crowns revealed significantly lower values in Discrepancycusp and Discrepancyocclusal than all the crowns fabricated with digital workflows (P<.05). Conclusions In terms of marginal crown fit, no significant differences were found between the conventional and digital workflows for the fabrication of monolithic lithium disilicate crowns. In the occlusal regions, the conventionally manufactured crowns revealed better fit than the digitally fabricated crowns. Chairside milling resulted in less favorable crown fit than centralized milling production.

Criteria for the selection of restoration materials.

Selection of the appropriate material for dental restoration has become more and more difficult owing to the increasing variety of restoration materials. A decision flow chart is presented to guide the treatment team (dentist and dental technician) in the selection of the restoration material. This material selection is based on the available interocclusal space, esthetic aspects (eg, brightness value or translucency of the neighboring teeth), as well as clinical evidence extracted from survival rates.

Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic posterior fixed partial dentures. Part II: Time efficiency of CAD-CAM versus conventional laboratory procedures

Statement of problem. Clinical trials are needed to evaluate the digital and conventional fabrication technology for providing fixed partial dentures (FPDs). Purpose. The purpose of the second part of this clinical study was to compare the laboratory production time for tooth‐supported, 3‐unit FPDs by means of computer‐aided design and computer‐aided manufacturing (CAD‐CAM) systems and a conventional workflow. In addition, the quality of the 3‐unit framework of each treatment group was evaluated clinically. Material and methods. For each of 10 participants, a 3‐unit FPD was fabricated. Zirconia was used as the framework material in the CAD‐CAM systems and included Lava C.O.S. CAD software (3M) and centralized CAM (group L); CARES CAD software (Institut Straumann AG) and centralized CAM (group iT); and CEREC Connect CAD software (Dentsply Sirona) and centralized CAM (group C). The noble metal framework in the conventional workflow (group K) was fabricated by means of the traditional lost‐wax technique. All frameworks were evaluated clinically before veneering. The time for the fabrication of the cast, the 3‐unit framework, and the veneering process was recorded. In addition, chairside time during the clinical appointment for the evaluation of the framework was recorded. The paired Wilcoxon test together with appropriate Bonferroni correction was applied to detect differences among treatment groups (&agr;=.05). Results. The total effective working time (mean ±standard deviation) for the dental technician was 220 ±29 minutes in group L, 217 ±23 minutes in group iT, 262 ±22 minutes in group C, and 370 ±34 minutes in group K. The dental technician spent significantly more time in the conventional workflow than in the digital workflow, independent of the CAD‐CAM systems used (P<.001). Conclusions. Irrespective of the CAD‐CAM system, the overall laboratory time for the dental technician was significantly less for a digital workflow than for the conventional workflow.

Effect of Aging on Stained Monolithic Resin-Ceramic CAD/CAM Materials: Quantitative and Qualitative Analysis of Surface Roughness

PURPOSE The aim of this in vitro study was to measure the effect of staining and artificial aging on the surface roughness of commercially available resin-ceramic computer-aided design and computer-aided manufacturing (CAD/CAM) materials both quantitatively and qualitatively and to compare it to feldspathic material. MATERIALS AND METHODS Test specimens (n = 15 per material) were prepared of CAD/CAM ingots from a resin nanoceramic (Lava Ultimate, LVU), a polymer-infiltrated ceramic (Vita Enamic, ENA), and a resin nanoceramic (Cerasmart, CER). In the staining protocol, test specimens were (i) roughened in a standardized manner and (ii) stained with the manufacturers recommended staining kit by means of photo-polymerization (Bluephase Polywave). The control specimens were prepared out of a feldspathic ceramic (Vita Mark II,VM2) and stained in a ceramic furnace. As negative control of each group, 15 specimens were prepared and polished in a standardized manner. Surface roughness (Ra) was measured after finishing procedures and after simulation of clinical service up to 5 years by means of toothbrushing. After each year of aging, one specimen per group was randomly selected for scanning electron microscopy (SEM) analysis. Kruskal-Wallis test and paired post-hoc test were applied to detect differences between treatment groups (alpha = 0.05). RESULTS The mean roughness measurements of the stained CAD/CAM materials were 0.14 ± 0.04 μm (ENA), 0.15 ± 0.03 μm (LVU), 0.22 ± 0.03 μm (VM2), and 0.26 ± 0.12 μm (CER). In the polished CAD/CAM materials the measurements were 0.01 ± 0.01 μm (CER), 0.02 ± 0.01 μm (LVU), 0.02 ± 0.00 μm (VM2), and 0.03 ± 0.01μm (ENA). Irrespective of the restoration material, the applied staining protocol resulted in a higher surface roughness compared to the polished specimens (p < 0.001). After 5 years of simulated aging the mean surface roughness in the stained CAD/CAM materials were 0.22 ± 0.03 μm (VM2), 0.24 ± 0.09 μm (ENA), 0.25 ± 0.06 μm (CER), and 0.37 ± 0.09 μm (LVU). Aging had a significant effect on surface roughness in groups ENA and LVU (p < 0.001). SEM analysis showed that the staining layer on resin-ceramic CAD/CAM materials was partially removed over time. CONCLUSIONS The applied staining protocol significantly increased surface roughness of CAD/CAM materials. Instability of the staining layer on resin-ceramic CAD/CAM materials could be anticipated over time as a consequence of toothbrushing, whereas feldspathic ceramic did not suffer from such aging effect.