Automated Remodelling of Connectors in Fixed Partial Dentures

In this study, an approach for automated parametric remodelling of the connector cross-sectional area in a CAD model of a given fixed partial denture (FPD) geometry was developed and then applied to a 4-unit FPD. The remodelling algorithm was implemented using Rhinoceros and the Grasshopper plugin. The generated CAD models were used to perform a finite element analysis with Ansys to analyse the stress distribution in an implant-supported 4-unit FPD for different connector designs. The results showed that the type of connector adjustment matters and that the resulting stress can be significantly different even for connectors with the same cross-sectional area. For tensile stresses, a reduction in the connector cross-sectional area from the gingival side showed the highest influence on each connector type. It can be concluded that the developed algorithm is suitable for automatic connector detection and adjustment.

Effect of titanium implants along with silver ions and tetracycline on type I interferon-beta expression during implant-related infections in co-culture and mouse model

Type I interferon-beta (IFN-β) is a crucial component of innate and adaptive immune systems inside the host. The formation of bacterial biofilms on medical implants can lead to inflammatory diseases and implant failure. Biofilms elicit IFN-β production inside the host that, in turn, restrict bacterial growth. Biofilms pose strong antibiotic resistance, whereas surface modification of medical implants with antibacterial agents may demonstrate strong antimicrobial effects. Most of the previous investigations were focused on determining the antibacterial activities of implant surfaces modified with antibacterial agents. The present study, for the first time, measured antibacterial activities and IFN-β expression of titanium surfaces along with silver or tetracycline inside co-culture and mouse models. A periodontal pathogen: Aggregatibacter actinomycetemcomitans reported to induce strong inflammation, was used for infection. Silver and tetracycline were added to the titanium surface using the heat evaporation method. Macrophages showed reduced compatibility on titanium surfaces with silver, and IFN-β expression inside cultured cells significantly decreased. Macrophages showed compatibility on implant surfaces with tetracycline, but IFN-β production significantly decreased inside seeded cells. The decrease in IFN-β production inside macrophages cultured on implant surfaces with silver and tetracycline was not related to the downregulation of Ifn-β gene. Bacterial infection significantly upregulated mRNA expression levels of Isg15, Mx1, Mx2, Irf-3, Irf-7, Tlr-2, Tnf-α, Cxcl-1, and Il-6 genes. Notably, mRNA expression levels of Mx1, Irf7, Tlr2, Tnf-α, Cxcl1, and Il-6 genes inside macrophages significantly downregulated on implant surfaces with silver or tetracycline. Titanium with tetracycline showed higher antibacterial activities than silver. The in vivo evaluation of IFN-β expression around implants was measured inside transgenic mice constitutive for IFN-β expression. Of note, the non-invasive in vivo imaging revealed a significant decrease in IFN-β expression around subcutaneous implants with silver compared to titanium and titanium with tetracycline in sterile or infected situations. The histology of peri-implant tissue interfaces around infected implants with silver showed a thick interface with a significantly higher accumulation of inflammatory cells. Titanium implants with silver and tetracycline remained antibacterial in mice. Findings from this study unequivocally indicate that implant surfaces with silver decrease IFN-β expression, a crucial component of host immunity.

Semi-automated generation of bone loss defects around dental implants and its application in finite element analysis

This study aimed to develop an algorithm for modelling bone loss defects in a given mandibular geometry, with a user-defined depth, width, place, and defect type. The algorithm was implemented using Grasshopper and models with different bone loss types and depths around a dental implant were built. The models were used in a finite element analysis (FEA) to predict the stresses in peri-implant bone. The FEA showed that the stresses in peri-implant bone depend primarily on the depth of bone loss, whereas the type of bone loss showed no major influence.

Influence of VAC Therapy on Perfusion and Edema of Gracilis Flaps: Prospective Case-control Study

The gracilis muscle flap is a popular choice in reconstructive surgery to repair soft tissue defects or for functional restoration. Little is known on the influence of postoperative application of VAC (vacuum-assisted closure; Kinetic Concepts Inc., San Antonio, Tex.) therapy on perfusion and postoperative flap edema of free gracilis muscle flaps.

Methods

In total, 26 patients with soft tissue defects of lower extremity underwent gracilis muscle flap reconstruction. The study group (VAC, n = 13) was supplied with postoperative negative pressure therapy as a dressing; the control group (NVAC, n = 13) was supplied with conventional fat gauze dressing. Postoperative measurements of micro- and macroperfusion were performed intraoperatively, on postoperative day (POD) 3 and POD 5. Flap edema measurement was performed intraoperatively, on POD 5 and 2 weeks after operation.

Results

The VAC group showed significantly better macroflow during intraoperative VAC treatment, as well on POD 3 and POD 5. Venous outflow was also better with lower hemoglobin levels. Microflow was better in the NVAC group with higher measured oxygen levels. All gracilis muscle flaps of the VAC group showed significantly less flap edema compared with the control group.

Conclusions

VAC application on free gracilis muscle flaps leads to significantly less postoperative flap edema, improved arterial macroflow, and improved venous outflow. VAC therapy can be used without any danger for patient's safety, as flap survival is not endangered, and presents an easy to handle and pleasant dressing regimen for nursing staff and patients.

Fracture Resistance of Repaired 5Y-PSZ Zirconia Crowns after Endodontic Access

This study analyzed the fracture load before and after a chewing simulation of zirconia crowns that were trepanned and repaired using composite resin. Overall, 3 groups with 15 5Y-PSZ crowns in each group were tested. For group A, the fracture load of the unmodified crowns was evaluated. For group B, the crowns were trepanned and repaired using composite resin, also followed by a fracture test. For group C, crowns were prepared like in group B but received thermomechanical cycling before the final fracture tests. Furthermore, scanning electron microscopy (SEM) and X-ray microscopy (XRM) analysis were performed for group C. The mean fracture loads and standard deviation were 2260 N ± 410 N (group A), 1720 N ± 380 N (group B), and 1540 N ± 280 N (group C). Tukey-Kramer multiple comparisons showed a significant difference between groups A and B (p < 0.01) and groups A and C (p < 0.01). After ageing, surface fissures were detected via SEM, but no cracks that reached from the occlusal to the inner side of the crown were detected via XRM. Within the limitations of this study, it can be stated that trepanned and composite-repaired 5Y-PSZ crowns show lower fracture loads than 5Y-PSZ crowns without trepanation.

The effect of surface treatments on the adhesive bond in all-ceramic dental crowns using four-point bending and dynamic loading tests

The aim of this study was to determine the effect of sandblasting, grinding and plasma treatment on the adhesive bond strength between framework ceramic (Y-TZP) and veneering ceramic (feldspar ceramic). Therefore, four-point bending specimens (n = 180) were cut from densely sintered 3Y-TZP blanks. Subsequently, 80 of these samples received surface treatment by sandblasting and 80 samples by grinding. A reference group (20 samples) was not processed. Half of the specimens that received a surface treatment were additionally exposed to an oxygen plasma treatment. After processing, all specimens were manually veneered with feldspar ceramic and examined with a four-point bending test to evaluate the strain energy release rate G. The surface treatment parameters that achieved the highest and lowest G were transferred to real geometries of a posterior crown (n = 45). The crowns' ceramic framework was sandblasted and veneered by hand. The all-ceramic crowns were tested in a dynamic loading test and Wöhler curves were evaluated. Four-point bending samples blasted at an angle of 90° at 6 bar and a working distance of 1.5 cm without plasma treatment achieved the highest energy release rate. Samples blasted at an angle of 90° at 2 bar and a working distance of 1 cm with plasma treatment achieved the lowest energy release rate. Overall, plasma treatment did not improve bond strength. In the dynamic loading test, the group blasted with 2 bar showed the best results.

Fracture load of 4-unit interim fixed partial dentures using 3D-printed and traditionally manufactured materials

STATEMENT OF PROBLEM

How the fracture strength of recently introduced 3-dimensionally (3D) printed interim materials compares with that of conventional materials is unclear.

PURPOSE

The purpose of this in vitro study was to compare the fracture load of 4-unit interim fixed partial dentures made from 3 different materials before and after mastication simulation.

MATERIAL AND METHODS

Based on a master model of a 4-unit fixed partial denture with maxillary left first premolar and second molar abutment teeth, interim restorations were fabricated from 3 different materials (3D-printed, Temporary CB Resin, milled, PMMA for brain, and manually manufactured, Luxatemp Plus). The fixed partial dentures (n=30 for each material) were cemented on 3D-printed model abutment teeth that were connected via a thin latex layer to a polyurethane base block. The fracture load of 15 fixed partial dentures of each material was tested without aging. Another 15 fixed partial dentures of each material were tested after thermomechanical aging.

RESULTS

The mean fracture load was between 186 N and 661 N, and all materials showed significant lower fracture loads after aging. Before and after aging (before/after ±standard deviation) milled (661 ±59/568 ±52 N) achieved the highest loads before manually manufactured (621 ±100/478 ±96 N) and 3D-printed (294 ±83/186 ±70).

CONCLUSIONS

The 3D-printed interim restoration material and the inherent manufacturing process show significant lower fracture loads than the tested alternatives. However, as the influence of geometric differences could not be quantified, whether this remains true after correcting for geometric differences remains unclear. For the tested interim materials, thermocycling and mastication simulation significantly reduced fracture loads over time, even at loads as low as 50 N.

Bacterial-Specific Induction of Inflammatory Cytokines Significantly Decreases upon Dual Species Infections of Implant Materials with Periodontal Pathogens in a Mouse Model

Cytokine profiles are often perturbed after infections of medical implants. With a non-invasive in vivo imaging system, we report in a mouse model that interferon expression after infection of subcutaneous implants with Streptococcus oralis, Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, and Treponema denticola (alone or as a combination) was species-specific, persisted longer in the presence of implants, and notably decreased upon dual species infections. This type I interferon expression disappeared within two weeks; however, histology of implant–tissue interface indicated high recruitment of immune cells even after three weeks. This was suggestive that biomaterial-associated infections could have prolonged effects, including the systemic stimulation of inflammatory cytokines. The present study investigated the systemic impact of this chronic peri-implant inflammation on the systemic expression of inflammatory cytokines (23) using a multiplex assay. Initially, the cytokine measurement in murine fibroblasts exposed to periodontal pathogens remained limited to the expression of five cytokines, namely, IL-6, G-CSF, CXCL-1/KC, MCP-1 (MCAF), and IL-12 (p40). The systemic determination of cytokines in mice increased to 19 cytokines (IL-1α, IL-2, IL-3, IL-5, IL-6, IL-9, IL-12 (p40), IL-12 (p70), IL-13, IL-17A, CCL-11/Eotaxin, G-CSF, IFN-γ, CXCL1/KC, MCP-1 (MCAF), MIP-1α/CCL3, MIP-1β/CCL4, CCL5/RANTES, and TNF-α). Systemic induction of cytokines was species-specific in the mouse model. The cytokine induction from infected implants differed significantly from sole tissue infections and sterile implants. Notably, systemic cytokine induction decreased after infections with dual species compared to single species infections. These findings describe the systemic effect of chronic peri-implant inflammation on the systemic induction of inflammatory cytokines, and this effect was strongly correlated to the type and composition of initial infection. Systemic modulations in cytokine expression upon dual species infections exhibit an exciting pattern that might explain the complications associated with biomaterial-related infection in patients. Moreover, these findings validate the requirement of multispecies infections for pre-clinical studies involving animal models.

Antimicrobial agents in dental restorative materials: Effect on long-term drug release and material properties

The present study reports on the long-term drug release and mechanical properties of bioactive dental filling materials based on chlorhexidine diacetate (CHX) or octinidine (di)hydrochloride (ODH) incorporated in a composite based on dimethacrylates or an ormocer. CHX or ODH were added to a nano-hybrid ormocer (O) and a nano-hybrid composite (C) with the amount of 2 wt% to achieve four matrix-drug combinations: O-CHX, O-ODH, C-CHX, and C-ODH. Drug extraction and release were measured using high-performance liquid chromatography with diode-array detection (HPLC-DAD), while drug distribution was assessed by using energy dispersive X-ray spectroscopy (EDX). Drug release in water at 37°C was observed over 87 d. To determine the material properties, the water absorption, water solubility, flexural strength and hardness were measured and compared to the reference materials. Persistent drug release over 87 d was observed for both ODH-based systems and both ormocer-systems, with the longest duration of activity seen for the O-ODH combination. Persistent drug release was achieved via the loosening of the polymer network indicated via decreasing polymerization enthalpies, enhanced water absorption, and water solubility. As a consequence, the flexural strengths of the materials were reduced. However, surface hardness was hardly reduced. ODH seems to be more adequate than CHX for the design of bioactive dental filling materials based on nano-hybrid ormocer and composites.

Antimicrobial agents in dental restorative materials: a on polymerization, short-term drug release and biological impact

With the aim to design bioactive dental restorative material, the present study investigated the influence of the antimicrobial agents chlorhexidine diacetate (CHX) and octinidine (di)hydrochloride (ODH) when incorporated in two different materials. Selected parameters were polymerization enthalpy, short-term drug release, and the effect on Streptococcus mutans as well as human gingival fibroblasts. Samples were made by mixing a nano-hybrid ormocer (O) and a methacrylate-based nano-hybrid composite (C), each with a mass fraction of 2% CHX or ODH. Release profiles and concentrations of active agents from the resins were assessed, and the cell proliferation of human gingival fibroblasts as well as Streptococcus mutans cultured with the eluates were evaluated. The influence on polymerization was assessed by means of differential scanning calorimetry. Both drugs, especially ODH, showed a decreasing effect on polymerization enthalpies associated with a lowered crosslinking degree. At the same time ODH appeared to be released more persistently than CHX. Moreover, ODH was more efficient with regard to bacteria growth inhibition but also more cytotoxic in terms of reduction of cell viability. ODH is deemed more appropriate for application in a dental resin-based drug delivery system, because of the more persistent drug release than seen for CHX.

Effect of sandblasting on the surface roughness and residual stress of 3Y-TZP (zirconia)

A defined surface roughness is important for the adhesive bonding of veneering ceramic to zirconia frameworks. Thus, we investigated the effects that sandblasting has upon the surface roughness and residual stress of zirconia. So as to achieve well-defined blasting parameters and also generate highly reproducible results; a custom-made, automated sandblasting machine was constructed (based on a 3D-printer construction kit). Thirty-two samples (measuring 30 mm × 35 mm × 0.2 mm) were cut from densely sintered 3Y-TZP blanks and then ground with a 45 µm grinding disc. After undergoing regeneration firing, the samples were sandblasted with varying working parameters: blasting angle (45°, 60° and 90°); blasting pressure (2 bar, 4 bar and 6 bar); and working distance (0.5 cm, 1.0 cm and 1.5 cm). The sandblasting path was chosen so as to create samples with an even surface roughness. Changes in blasting pressure resulted in the greatest changes in the surface roughness, the highest surface roughness values were achieved with sandblastings perpendicular to the sample surface. Furthermore, a correlation was found between the mean surface roughness and the residual stress.

The effect of adjuvant oral irrigation on self-administered oral care in the management of peri-implant mucositis: A randomized controlled clinical trial

OBJECTIVES

This single-blinded randomized clinical trial evaluated the effect of adjuvant oral irrigation in addition to self-administered oral care on prevalence and severity of peri-implant mucositis.

MATERIAL & METHODS

After randomization, patients suffering from peri-implant mucositis were assigned to the following: Group 1 (control) received oral hygiene instruction following a standardized protocol, including a sub- and supramucosal mechanical debridement. Group 2 and 3 additionally were instructed to use an oral irrigator with either water or 0.06% CHX solution. One implant per patient was considered for examination. Clinical examinations included Probing Depth, Bleeding on Probing (BOP-positive sites), and Modified Plaque and Gingival Index. A surrogate variable (mucositis severity score) was applied measuring severity of disease. Statistical analysis included linear regression models and sensitivity analysis.

RESULTS

Sixty periodontally healthy patients were examined for presence and severity of peri-implant mucositis. 70% of all patients reached complete resolution of disease after 12 weeks. The prevalence of peri-implant mucositis after 12 weeks was 50% in group 1, 35% in group 2, and 5% in group 3. Average BOP-positive sites were reduced in all groups after 12 weeks (mean change from baseline: group 1: -1.5; group 2: -1.8; group 3: -2.3).

CONCLUSION

Within the limits of the study, adjuvant use of an oral irrigator with 0.06% CHX in addition to mechanical biofilm removal and oral hygiene instruction can reduce the presence and severity of peri-implant mucositis after 12 weeks.

The effect of different occlusal contact situations on peri-implant bone stress - A contact finite element analysis of indirect axial loading

Implant restoration is one of the basic treatments in dentistry today, yet implant loss from occlusal overload is still a problem. Complex biomechanical problems such as occlusal overload are often analyzed by means of the finite element method. This numerical method makes it possible to analyze in detail the influence that different loading situations have upon implants and tissues, which is a key element in optimizing these dental procedures. This study was designed to investigate the stress distribution in peri-implant bone of a single-tooth implant crown using the finite element method. The load was applied indirectly via an occluding tooth through a three and five contact setup into the implant crown. The friction coefficient values between the crown and antagonist were varied between 0.1 and 1.0. Additionally, three crowns with cusp inclinations of 20°, 30° and 40° were modeled. Non-linear contact computations indicated that an increase in friction changed the direction and magnitude of contact forces, which also led to reduced stresses in the bone. Furthermore, the stress magnitudes were higher when cusps of a greater inclination were used. The intensity of stress alterations was strongly dependent on the distribution and number of contacts, and the contact force vector. In maximum intercuspation, a resulting axial load due to well-distributed contacts prevented high stresses in bone even with high cusp inclinations and low friction. Therefore for long-term clinical success, particular attention should be paid to occlusal adjustment so as to prevent oblique loading onto dental implant restorations.

Polish of interface areas between zirconia, silicate-ceramic, and composite with diamond-containing systems

PURPOSE

Fractures, occlusal adjustments, or marginal corrections after removing excess composite cements result in rough surfaces of all-ceramic FPDs. These have to be polished to prevent damage of the surrounding tissues. The aim of this study was to evaluate the roughness of zirconia, silicate-ceramic, and composite after polish with different systems for intraoral use.

MATERIALS AND METHODS

Each set of 50 plates was made of zirconia, silicate-ceramic, and composite. All plates were ground automatically and were divided into 15 groups according to the treatment. Groups Zgrit, Sgrit, and Cgrit received no further treatment. Groups Zlab and Slab received glaze-baking, and group Clab was polished with a polishing device. In the experimental groups Zv, Sv, Cv, Zk, Sk, Ck, Zb, Sb, and Cb, the specimens were polished with ceramic-polishing systems “v”, “k”, and “b” for intraoral use. Roughness was measured using profilometry. Statistical analysis was performed with ANOVA and Scheffé-procedure with the level of significance set at P=.05.

RESULTS

All systems reduced the roughness of zirconia, but the differences from the controls Zgrit and Zlab were not statistically significant (P>.907). Roughness of silicate ceramic was reduced only in group Sv, but it did not differ significantly from both controls (P>.580). Groups Cv, Ck, and Cb had a significantly rougher surface than that of group Clab (P<.003).

CONCLUSION

Ceramic materials can be polished with the tested systems. Polishing of interface areas between ceramic and composite material should be performed with polishing systems for zirconia first, followed by systems for veneering materials and for composite materials.

Influence of nonthermal argon plasma on the shear bond strength between zirconia and different adhesives and luting composites after artificial aging

PURPOSE

Plasma activation of hydrophobic zirconia surfaces might be suitable to improve the bond strength of luting materials. The aim of this study was to analyze the influence of nonthermal argon-plasma on the shear bond strength (SBS) between zirconia and different combinations of 10-MDP adhesive systems and luting composites after artificial aging.

MATERIALS AND METHODS

Two hundred forty Y-TZP specimens were ground automatically with 165 µm grit and water cooling. Half of the specimens received surface activation with nonthermal argon-plasma. The specimens were evenly distributed into three groups according to the adhesive systems ([Futurabond U, Futurabond M, Futurabond M + DCA], VOCO GmbH, Germany, Cuxhaven) and into further two subgroups according to the luting materials ([Bifix SE, Bifix QM], VOCO GmbH). Each specimen underwent artificial aging by thermocycling and water storage. SBS was measured in a universal testing machine. Statistical analysis was performed using ANOVA and Scheffè procedure with the level of significance set to 0.05.

RESULTS

Surface activation with nonthermal plasma did not improve the bond strength between zirconia and the tested combinations of adhesive systems and luting materials. The plasma-activation trended to reveal higher bond strength if the self-etch luting material (Bifix SE) was used, irrespective of the adhesive system.

CONCLUSION

Plasma-activation seems to be suitable to improve bond strength between zirconia and self-etch resin materials. However, further research is necessary to identify the influence of varying plasma-parameters.

Survival rate of modern all-ceramic FPDs during an observation period from 2011 to 2016

PURPOSE

In literature, many studies compare survival rates of different types of FPDs. Most of them compared restorations, which originated from one university, but from different clinicians. Data about restoration survival rates by only one experienced dentist are very rare. The aim of this study was to evaluate the survival rate of allceramic FPDs without the blurring effects of different clinicians.

MATERIALS AND METHODS

153 veneeredzirconia FPDs were observed for follow-up. 22 patients received 131 single crowns and 22 bridges. Because of the different bridge lengths, one unit was defined as a restored or replaced tooth. In total, 201 units were included. Only the restorations performed by the same clinician and produced in the same dental laboratory from 2011 to 2016 were included. Considered factors were defined as “type of unit”, “type of abutment”, “intraoral region”, and “vitality”. Modified UHPHS criteria were used for evaluation. Statistical analysis was performed using cox-regression.

RESULTS

189 units (94.0%) showed no kind of failure. 5 chippings (2.4%) could be corrected by intraoral polishing. 4 units (1.9%) exhibited spontaneous decementation. These polishable and recementable restorations are still in clinical use. Chippings or decementations, which lead to total failure, did not occur. One unit was completely fractured (0.5 %). Biological failures (caries, periodontitis or periimplantitis) did not occur. The statistical analysis of the factors did not reveal any significant differences.

CONCLUSION

Modern all-ceramic FPDs seem to be an appropriate therapy not only for single restorations but for complex occlusal rehabilitations.

Influence of the material for preformed moulds on the polymerization temperature of resin materials for temporary FPDs

PURPOSE

Temperature increase of 5.5 ℃ can cause damage or necrosis of the pulp. Increasing temperature can be caused not only by mechanical factors, e.g. grinding, but also by exothermic polymerization reactions of resin materials. The aim of this study was to evaluate influences of the form material on the intrapulpal temperature during the polymerization of different self-curing resin materials for temporary restorations.

MATERIALS AND METHODS

30 provisonal bridges were made of 5 resin materials: Prevision Temp (Pre), Protemp 4 (Pro), Luxatemp Star (Lux), Structure 3 (Str) and an experimental material (Exp). Moulds made of alginate (A) and of silicone (S) and vacuum formed moulds (V) were used to build 10 bridges each on a special experimental setup. The intrapulpal temperatures of three abutment teeth (a canine, a premolar, and a molar,) were measured during the polymerization every second under isothermal conditions. Comparisons of the maximum temperature (T_Max) and the time until the maximum temperature (t_TMax) were performed using ANOVA and Tukey Test.

RESULTS

Using alginate as the mould material resulted in a cooling effect for every resin material. Using the vacuum formed mould, T_Max increased significantly compared to alginate (P<.001) and silicone (P<.001). In groups Lux, Pro, and Pre, t_TMax increased when the vacuum formed moulds were used. In groups Exp and Str, there was no influence of the mould material on t_TMax.

CONCLUSION

All of the mould materials are suitable for clinical use if the intraoral application time does not exceed the manufacturer's instructions for the resin materials.

The effect of direct and indirect force transmission on peri-implant bone stress - a contact finite element analysis

In almost all finite element (FE) studies in dentistry, virtual forces are applied directly to dentures. The purpose of this study was to develop a FE model with non-linear contact simulation using an antagonist as force transmitter and to compare this with a similar model that uses direct force transmission. Furthermore, five contact situations were created in order to examine their influence on the peri-implant bone stresses, which are relevant to the survival rate of implants. It was found that the peri-implant bone stresses were strongly influenced by the kind of force transmission and contact number.

Marginal fit of indirect composite inlays using a new system for manual fabrication

This in vitro study compares a new system for manual chair side fabrication of indirect composite restorations, which uses silicone models after alginate impressions, to CAD/CAM-technology and laboratory manual production techniques. MATRIALS AND METHODS: and study design Each 10 composite inlays were fabricated using different types of production techniques: CAD/CAM- technology (A), the new inlay system (B), plaster model after alginate impression (C) or silicone impression (D). The inlays were adapted into a metal tooth and silicone replicas of the cement gaps were made and measured. Statistical analysis was performed using ANOVA and Tukey's test. Results and Statistics In group A the biggest marginal gaps (174.9μm ± 106.2μm) were found. In group B the gaps were significantly smaller (119.5 μm ± 90.6 μm) than in group A (p=0.035). Between groups C (64.6 μm ± 68.0μm) and D (58.2 μm ± 61.7 μm) no significant differences could be found (p=0.998), but the gaps were significantly smaller compared with group B. Conclusion Chairside manufacturing of composite inlays resulted in better marginal precision than CAD/CAM technology. In comparison to build restorations in a laboratory, the new system is a timesaving and inexpensive alternative. Nevertheless, production of indirect composite restorations in the dental laboratory showed the highest precision.

Introducing a semi-coated model to investigate antibacterial effects of biocompatible polymers on titanium surfaces

Peri-implant infections from bacterial biofilms on artificial surfaces are a common threat to all medical implants. They are a handicap for the patient and can lead to implant failure or even life-threatening complications. New implant surfaces have to be developed to reduce biofilm formation and to improve the long-term prognosis of medical implants. The aim of this study was (1) to develop a new method to test the antibacterial efficacy of implant surfaces by direct surface contact and (2) to elucidate whether an innovative antimicrobial copolymer coating of 4-vinyl-N-hexylpyridinium bromide and dimethyl(2-methacryloyloxyethyl) phosphonate (VP:DMMEP 30:70) on titanium is able to reduce the attachment of bacteria prevalent in peri-implant infections. With a new in vitro model with semi-coated titanium discs, we were able to show a dramatic reduction in the adhesion of various pathogenic bacteria (Streptococcus sanguinis, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis), completely independently of effects caused by soluble materials. In contrast, soft tissue cells (human gingival or dermis fibroblasts) were less affected by the same coating, despite a moderate reduction in initial adhesion of gingival fibroblasts. These data confirm the hypothesis that VP:DMMEP 30:70 is a promising antibacterial copolymer that may be of use in several clinical applications.

The effect of guidance elements on the rotation of cast crowns during cementation

The effect of guidance elements on the rotation of crowns was analyzed. Resin molars were prepared with curved or horizontal preparation lines. Further groups were formed with a groove or one or two boxes. Teeth were duplicated eightfold; crowns were produced and cemented with a rotational torque of 0.5 Ncm. The width of the cement gap was measured at 11 reference points. Having either one or two guidance boxes had a significant centering effect. No differences were found between both types of preparation lines. The use of a proximal guidance box may be considered to reduce torsion of a single crown during cementation.

Relationship between enamel erosion and liquid flow rate

The association of severe erosion with certain habits of consuming soft drinks prompted a study of erosion in relation to fluid flow. In the main experiments, citric acid solution (pH 3.2) was directed at polished enamel surfaces at flow rates of 26, 67 or 126 ml min(-1) through outlets of diameters 1.0, 2.6 or 5.0 mm for up to 20 min. Erosion depth increased with time of exposure and total volume of solution, with increasing flow rate and with decreasing outlet diameter. Scanning electron microscopy of acid-treated surfaces and of the subsurface enamel indicated that the clearance of dissolution products, rather than the mechanical dislodgement of partly dissolved crystal bundles, was the main process involved. For an exposure time of 20 min, erosion increased with (liquid velocity)(1/4). In a secondary experiment, it was found that the erosive potential of a low-erosive drink did not increase with increasing liquid velocity. The rapid increase in the rate of erosion caused by citric acid at low liquid velocities shows that reproducible stirring is essential for precision and intercomparison of in vitro studies. It also accounts for the rapid erosion seen when erosive drinks are consumed from a straw placed labial to the anterior teeth, or are "swished" between the teeth.

Scanning Electron Microscopy of Softened Enamel

After exposing enamel specimens to 0.3% citric acid at pH 3.2 for various times, the acid was titrated to pH 7 before rinsing the specimens in water. After freeze-drying the specimens were examined by scanning electron microscopy. This procedure eliminates artefacts due to drying and mineral precipitation. The results showed that the outer region of softened enamel is much more delicate than previously thought, even after short (5- to 20-min) etching times. Mineral was lost from both prism boundaries and the prism bodies, resulting in a surface presenting thin, separate crystal bundles. In further studies, replicas of subsurface pores, created by resin impregnation, showed the softening depth to be several times greater than is suggested by techniques based on removing the softened enamel by physical forces. The results point to a need for improved methods of measuring softening depth. More importantly, it appears that the outer region of the softened layer remaining after an erosive challenge might be too fragile to resist frictional forces in vivo.

Comparative Study of Wear of Enamel Induced by Alternating and Simultaneous Combinations of Abrasion and Erosion in vitro

Two types of interaction of erosive and abrasive forces with human enamel were analysed in an in vitro study. To simulate toothbrushing or chewing after an acidic challenge, enamel specimens were eroded in 0.3% citric acid (pH 3.2), then brushed with or without silica abrasive. To simulate simultaneous erosion and abrasion, as would occur during chewing of abrasive acidic food, enamel specimens were abraded in a toothbrushing machine, with and without silica abrasive, while immersed in citric acid. Enamel wear was measured by profilometry. In both experiments the combination of erosion and abrasion resulted in significantly greater wear than erosion alone, but no significant differences in wear after brushing with or without abrasive were found. Simultaneous erosion and abrasion resulted in about 50% more wear than alternating erosion and abrasion. It is concluded that softened enamel is highly unstable and potentially easily removed by short and relatively gentle physical action. Chewing of acidic foods with some abrasive properties might cause enhanced tooth wear.

Influence of liquid temperature and flow rate on enamel erosion and surface softening

Enamel erosion and softening are based on chemical processes which could be influenced by many factors including temperature and acid flow rate. Knowledge of the influence of these variables could have relevance to research experiments and clinical outcomes. Both parameters were investigated using an ultrasonication and profilometry method to assess erosion depth and surface softening of enamel. The influence of temperature was studied by eroding polished human enamel samples at 4, 20, 35 or 50 degrees C for 2 h. Secondly, different liquid flow conditions were established by varying acid agitation. Additionally, a slow laminar flow and a jet of citric acid, to simulate drinking through a straw, were applied to specimens. Erosion depth increased significantly with acid temperature from 11.0 microm at 4 degrees C to 35.8 microm at 50 degrees C. Surface softening increased much more slowly and plateaued at 2.9 microm to 3.5 microm after 35 degrees C. A strong dependence of erosion on liquid flow was revealed. In unstirred conditions only 8.6 microm erosion occurred, which increased to 22.2 microm with slow stirring and 40.9 microm with fast stirring. Surface softening did not increase correspondingly with its largest extent at slow stirring at 3.4 microm.The implication of these data are: first, the conditions for erosion experiments in vitro or in situ need to be specified for reliable comparisons between studies. Secondly, erosion of teeth by soft drinks are likely to be influenced both by the temperature of the drink and individual drinking habits.

Effect of toothpaste on the plaque inhibitory properties of a cetylpyridinium chloride mouth rinse

BACKGROUND AND AIMS

Cetylpyridinium chloride (CPC) mouth rinses have moderate plaque inhibitory activity when used alone but rarely have shown adjunctive benefits to tooth brushing with toothpaste. Several explanations for this apparent anomaly can be proferred, including loss of antiseptic activity due to interactions with toothpaste ingredients. The aim of this study was to measure the effect of toothpaste on the plaque inhibitory properties of a CPC mouth rinse using paired rinses of CPC, toothpaste slurry (TP) and water (W).

METHODS

The study was a single blind, randomised, seven-treatment, cross over design balanced for residual effects, involving 21 healthy, dentate subjects. The paired rinses were: W-CPC, CPC-W, TP-CPC, CPC-TP, W-TP, TP-W and W-W. Rinsing with solutions or slurries was done for 60 s twice per day. On day 1, subjects were rendered plaque free, suspended tooth cleaning and commenced the allocated rinse regimen. On day 5, plaque was scored by index. A 2(1/2) day wash out of normal oral hygiene was allowed between each regimen.

RESULTS

The order from lowest to highest plaque scores was as follows: W-CPC = CPC-W < CPC-TP < TP-CPC < or = W-TP < TP-W < W-W. Several differences in pairs of treatments were statistically significant, the most relevant of which were significantly less plaque with W-CPC compared to TP-CPC, TP-W and W-TP, and significantly more plaque with W-W compared to all other regimens except TP-W.

CONCLUSIONS

Toothpaste, whilst possessing some plaque inhibitory activity, when used immediately before a CPC mouth rinse adversely affected the plaque inhibitory action of this antiseptic. This in part may explain the reported lack of adjunctive benefits of CPC rinses to normal oral hygiene practices and supports the suggestion, made for chlorhexidine rinses, that their use should follow toothpaste by at least 60 min.

Acidic solubility of luting cements

OBJECTIVES

Chemical disintegration of luting cements can adversely affect their long term success. The aim of the present study was to assess the susceptibility of zinc phosphate cement, glass ionomer cement and resin cement to erosion at various pH values.

METHODS

Zinc phosphate and glass ionomer cement samples were eroded in 0.3% citric acid adjusted to pH 3.0, 4.0, 5.0, 6.0 and 7.0 at a temperature of 35 degrees C. A control group was stored in saline. Profilometric readings were performed after 30 min and 1h erosion time. Resin cement samples were eroded at pH 3.0 with measurements after 30 min, 6h, 24h and 7 days. A saline control group was measured after 7 days.

RESULTS

Erosion of zinc phosphate cement was significantly higher at all pH values than erosion of glass ionomer cement with erosion depth increasing with decreasing citric acid pH. No erosion was seen in the control groups. The resin cement did not show any change in surface profile after the 7 day erosion period compared to the control group. Comparison to dental tissues revealed that erosion of glass ionomer cement in vitro was slightly lower than erosion of enamel and dentine. In contrast, erosion of zinc phosphate cement was much higher.

Erosion and attrition of human enamel in vitro part II: influence of time and loading

OBJECTIVES

To determine the influence of load and time on enamel wear by attrition under neutral and acid environments in vitro.

METHODS

Groups of 10 enamel cusp and smooth surface specimens obtained from unerupted third molars were opposed in a wear machine under loads of 200, 400 and 600 g in citric acid at pH 3.2 and in physiological saline at 35 degrees C for 30 min (2280 wear cycles). The experiment was repeated with a load of 600 g for 10 and 20 min accompanied by 10 taped specimens to measure erosion only. Erosion and attrition of smooth surface specimens was determined by profilometry.

RESULTS

At a load of 600 g attrition in saline increased with time from 7.9 microm (SD 3.7 microm) at 10 min, 10.2 microm (SD 4.8 microm) at 20-25.5 microm (SD 9.1 microm) after 30 min and combined attrition/erosion in citric acid from 1.5 microm (SD 0.4 microm) to 2.5 microm (SD 0.9 microm) to 6.0 microm (SD 3.7 microm). At a fixed time of 30 min, attrition in saline was 5.2 microm (SD 3.6 microm) at 200 g and 8.1 microm (SD 1.5 microm) at 400 g and combined attrition/erosion in citric acid 2.8 microm (SD 1.2 microm) and 3.6 microm (SD 0.7 microm). Comparison between both environments revealed significant differences at fixed load at all time points (p < 0.01) and at fixed time between 400 and 600 g (p < 0.01).

CONCLUSIONS

Load and time significantly influence enamel wear both in acid and neutral conditions but the effects were not linear.

Erosion and attrition of human enamel in vitro part I: interaction effects

OBJECTIVE

The aim of the study in vitro was to measure the interplay of attrition and erosion of human enamel under several different pH conditions.

MATERIALS AND METHODS

Cusp and smooth surface enamel specimens were prepared from unerupted human third molar teeth. Cusp and smooth surface specimens opposed each other in a wear machine under a load of 600 g. The machine simulated tooth grinding for 30 min (2280 wear cycles). Six groups of 10 specimens were worn in the following environmental conditions: saline, citric acid at pH values of 3.2, 5.5 or 7.0 and two cycling groups (pH 3.2/saline or saline/pH 3.2). Additionally, 10 smooth surface specimens were exposed to the same fluids without attrition. Tissue loss on smooth surface specimens was determined by profilometry. The worn specimen surfaces were studied by SEM.

RESULTS

Attrition depth in saline and pH 7.0 citric acid was 25.5 microm. At pH 3.2 and 5.5 attrition depths were 6.0 and 4.3 microm, respectively. Cycling in saline/citric acid and vice versa produced attrition depths of 9.2 and 7.9 microm, respectively. In the erosion only specimens lesion depths were 3.0, 1.2 and 0 microm at pH 3.2, 5.5 and 7.0 and saline, respectively. Attrition specimens at pH 7.0 and in saline showed very rough surfaces. At low pH enamel surfaces appeared flat and smooth.

CONCLUSIONS

Enamel wear in neutral conditions is significantly higher than in acidic conditions (p < 0.05), apparently due to a smoothing effect of erosion on contacting surfaces.

Radiological examination of dental castings -- a review of the method and comparisons of the equipment

The mechanical stability of crowns or bridges as well as frameworks for removable partial dentures depends on factors like thickness and metal structure. The biological compatibility can be influenced by porosities and soldered joints. Radiological testing is a non-destructive method to check defects in dental castings. As dental precious metal alloys have high X-ray absorption, testing of high gold alloys should be performed with a suitable X-ray machine at a tube voltage of 120 kV since the X-ray penetration of dental X-ray units using a tube voltage of 70 to 80 kV is not high enough for these alloys. As the absorption of Co-Cr alloys and of titanium is much lower, these materials can be tested with a dental X-ray apparatus. The radiographs show location and size of metal defects. They enable an examination of metal thickness and content of porosities. Metal defects reducing the biological compatibility or cast stability can be detected prior to clinical fitting.

Cervical tooth wear and sensitivity: erosion, softening and rehardening of dentine; effects of pH, time and ultrasonication

BACKGROUND

Cervical dentine wear is commonly observed and may be associated with dentine hypersensitivity. Erosion is thought to play a part in both conditions but compared to enamel has been little studied in dentine.

AIM

The aims of these studies in vitro were to: (i) determine the effects of citric acid on dentine at different pH values and over time; (ii) measure the depth of dentine demineralisation or softening using ultrasonication; (iii) determine whether softened dentine can be remineralised or rehardened using artificial saliva.

METHODS

Groups of flat dentine specimens prepared from unerupted human third molar teeth were: (a) exposed to citric acid at pH 3.2 for periods up to 4 h with mineral water as control; (b) exposed to citric acid at pH 2.54, 3.2, 4.5, 5.5 and 6.0 for 2 h and then subjected to ultrasonication stepwise up to 480 s; (c) exposed to citric acid at pH 2.54, 3.2, and 4.5, placed into artificial saliva for 24 h and then subjected to ultrasonication as in (b). Loss of dentine was measured by profilometry, after, each phase of erosion, ultrasonication and immersion in artificial saliva.

RESULTS

Depth of erosion significantly increased non-linearly with time and significantly decreased with increasing pH. Ultrasonication had minimal albeit significant effects on control specimens. Removal of softened dentine increased with ultrasonication time. Depth of softening significantly increased with increasing erosion time to 2 h, plateauing at 2 microm. Depth of softening increased to 2 microm from pH 2.54 to pH 3.2 and decreased at higher pH values thereafter. 24 h in artificial saliva provided no protection to the soften zone against ultrasonicaion. Citric acid at all pH values and exposure times removed the dentine smear layer to expose tubules. Ultrasonication did not remove the smear layer on control specimens but removed all deposits formed after exposure to artificial saliva.

CONCLUSION

It is concluded that dentine is susceptible to erosion even at relatively high pH, the tubule system is readily exposed and dentine, unlike enamel, shows little propensity to remineralise.

Further modification to soft drinks to minimise erosion. A study in situ

Soft drinks have been successfully modified to reduce enamel erosion. The aim of this study was to further modify an original low erosive blackcurrant drink product by the addition of a gum, to manipulate more favourably other drink parameters. The study was a single-blind, randomised four treatment crossover design involving 12 healthy volunteers. During 10 working-day study periods, subjects wore enamel samples in the mid palatal region of a removable appliance. Specimens were taped to expose a 2-mm enamel window. The drinks under test were: (1) Orange juice, (2) Original blackcurrant drink, (3) Water, and (4) Experimental blackcurrant drink. Drinks were imbibed at 250-ml volumes 4 times a day during appliance wearing from 09.00 to 17.00. Appliances were removed at lunchtime. Measurements of specimens were made at baseline, 2, 5 and 10 days using a profilometer. One 5-day and one 10-day specimen from each subject during each treatment were ultrasonicated. Significant differences, in erosion between drinks, were seen at days 5 and 10. Comparisons of preselected pairs of drinks of interest showed significantly reduced erosion by the two blackcurrant drinks compared to orange juice with no significant differences from water. The original blackcurrant drink produced significantly less erosion than the experimental drink. Ultrasonication removed enamel from the Orange juice specimens but very little from those exposed to water and the two blackcurrant drinks. Extrapolating the effects of both blackcurrant drinks suggested that alone they should not cause significant clinical erosion in a lifetime's intake of 1 litre per day.

Evaluation of pH and erosion time on demineralisation

In the current study the effect of various pH values of citric acid and erosion time on erosion depth and subsurface demineralisation of human enamel was studied. In a laboratory investigation, six groups of 10 samples were eroded in 0.3% citric acid for 2 h at pH 2.54, for 2 h or 4 h at pH 3.2 and for 2 h, 4 h or 8 h at pH 4.5. The erosion depth was measured using a profilometer. The demineralised layer was then removed by ultrasonicating the samples with profilometric measurements taken at 5, 30, 120, 240 and 480 s ultrasonication time. The six test groups were classified by analysis of variance into four homogeneous groups according to their erosion depth and into three homogeneous groups according to their subsurface demineralisation. Erosion depth clearly depended on the pH value of the acid and the contact time. Depth of subsurface demineralisation and surface morphology did not depend on erosion depth. Similar subsurface demineralisation depths can be produced by appropriate combinations of pH and contact time.

Effect of time on the remineralisation of enamel by synthetic saliva after citric acid erosion

The aim of this in vitro study was to determine the influence of remineralisation time on rehardening of surface-softened enamel after citric acid erosion. Seven groups of 13 samples of human enamel were eroded in 0.3% citric acid at pH 3.2 for 2 h followed by profilometric measurements. Individual groups of specimens were placed in artificial saliva for 1, 2, 4, 6, 9 or 24 h. A control group was placed in isotonic saline for 24 h. After new profilometric measurements samples were ultrasonicated stepwise up to 480 s with profilometric measurements performed at 5, 30, 120, 240 and 480 s to measure the depth of surface softening. The control group had a softened surface layer of mean thickness 2.9 microm. Mineral deposition was seen at all remineralisation times by scanning electron microscopy. Exposure to artificial saliva for 1, 2 or 4 h produced a partial rehardening of the softened enamel; the additional surface losses produced by ultrasonication were lower and time delayed compared to the control group. Specimens remineralised for 6, 9 and 24 h showed little evidence of surface loss after ultrasonication. The data suggest that a complete rehardening of the softened enamel in vitro is reached after a remineralisation time of 6 h. These data are of clinical relevance to tooth wear. However, there is a need for studies in situ of enamel demineralisation and remineralisation.

The use of ultrasonication to study remineralisation of eroded enamel

The aim of this study was to use ultrasonication and profilometry as methods to study de- and remineralisation of citric acid-eroded enamel at different pH values. Seventy-eight polished human enamel samples were divided into three test and three control groups of 13 specimens each. Three specimens of each group were chosen for SEM examination. The samples were exposed to 0.3% citric acid at pH 2.54, 3.2 or 4.5 for 2 h. The depths of the resulting lesions were measured by profilometry. The test groups were placed in artificial saliva and the control groups were stored in saline (0.9% NaCl) for 24 h and new profiles recorded. Finally all specimens were ultrasonicated in water for 5, 30, 120, 240 and 480 s with profilometric measurements at each time point. Ultrasonication of the test groups after remineralisation showed little effect on the lesion depth, whereas the control groups had an enamel loss of 2.1 microm at pH 2.54, 2.9 microm at pH 3.2 and 0.4 microm at pH 4.5 after 30-second ultrasonication. These differences from respective test groups were statistically significant at pH 2.54 and 3.2 but not at pH 4.5. Ultrasonication of control pH 2.54 and 3.2 specimens removed an amorphous covering layer to reveal a flattened surface with prisms outlined by prism boundaries. It can be concluded that remineralisation in artificial saliva stabilises the surface softened enamel against ultrasonication.

Long-term results of telescopic crown retained dentures--a retrospective study

The clinical data for 250 telescopic crown retained dentures involving 617 abutment teeth preparations were collected and analysed in a retrospective study to ascertain the survival rate of the dentures and their abutment teeth. During the study period 10.6% of the abutment teeth had to be extracted. An increased number of telescopic crowns significantly improved the longevity of the prostheses and their associated abutment teeth in most denture designs, but this was not found to be the case with bilateral free-end saddle designs without an anterior bounded saddle. The use of more than four abutment teeth did not result in a higher survival rate.

Ultrasonication as a method to study enamel demineralisation during acid erosion

The aim of this study was to use ultrasonication as a method to measure subsurface demineralisation of enamel. Polished human enamel samples with surface profiles within +/-0.3 microm were divided into 6 groups of 10 specimens. The groups of specimens were exposed to 0. 3% citric acid (pH 3.2) for 30 min, 1, 2, 3 or 4 h. The depths of the resulting lesions were measured using a profilometer. A control group was stored in water for 4 h. Ultrasonication in water was performed on the specimen groups for 5, 30, 120, 240 and 480 s with profilometric measurements at each time point. The depth of the erosion increased linearly with the exposure time. Most of the additional loss of enamel occurred with the 5-second ultrasonication. The 30-min and 1-hour erosion lesions were further deepened by approximately 1 microm with 5 s of ultrasonication. The 2-, 3- and 4-hour lesions were deepened by 2-4 microm with 5 s of ultrasonication. There were no changes in the control group. It is concluded that ultrasonication removed softened enamel from the surface of the eroded enamel. Ultrasonication together with accurate measurement of lesion depth by profilometry offers a useful method for studying the depth of enamel softening associated with erosion.

The human mandibular intercondylar angle measured by computed tomography

In axial computed tomography it is possible to measure the intercondylar angle at the intersection of the longitudinal axes of the condyles. Published values range from 131 to 165 degrees. This angle was determined here in two groups of patients with (n = 22) and without (n = 12) temporomandibular joint dysfunction. A third group of children (n = 12) aged 4-9 years was included to investigate any age-related change in the angle. In the group of healthy individuals, a range of 105 to 165 degrees was found, with a mean intercondylar angle of 139 degrees. In the group with temporomandibular joint dysfunction the mean angle was 143 degrees with a range from 85 to 170 degrees. No statistically significant relation could be shown between intercondylar angle and joint dysfunction. In the group of children the mean angle was 138 degrees with values ranging from 90 to 180 degrees. No significant differences could be demonstrated among the groups. The absolute value of the intercondylar angle seems to be independent of factors such as sex, age and functional disorders of the joint.

Radiographic inspection of dental castings

Underdimensioning may adversely affect the clinical use of a crown or bridge. Insufficient dimensions may be due to inadequate modelling or deficiencies caused by the casting process. The dimensions of cast objects are measured mechanically using a calliper. This method has often proved to be insufficient in detecting areas of too small dimensions. This paper presents a non-destructive method of inspecting dental castings using radiography. The occlusal thickness of a random sample of 150 crowns made during regular clinical treatment in our department was inspected mechanically and radiographically. We found that 19% of the crowns were only 0.1 mm thick or less at the thinnest spot, 18% were between 0.1 and 0.2 mm and 9% were between 0.2 and 0.3 mm. In comparison to mechanical examination, radiographic inspection usually showed smaller values.