Survival and success rates of soft-milled cobalt-chromium-ceramic full-arch screw-retained implant-supported prostheses: a 2- to 7-year follow-up retrospective study.

OBJECTIVES: To retrospectively assess implant and prosthesis survival and success and patient satisfaction in edentulous patients treated with soft-milled cobalt-chromium-ceramic full-arch screw-retained implant-supported prostheses (SCCSIPs) over a mean clinical follow-up period of 4 years. MATERIALS AND METHODS: Twenty-one edentulous patients, aged 47-80 years, underwent restoration with 27 SCCSIPs (210 implants, 349 crown units). After definitive prosthesis insertion, patients participated in a yearly dental check-up recall program, including clinical and radiographic examinations. All supporting implants were examined for biological and technical complications, and the restorations were evaluated using modified California Dental Association (CDA) criteria. Life table and Kaplan-Meier survival analyses were performed. Patient satisfaction regarding chewing, esthetics, comfort, and phonetics was evaluated using a visual analog scale (VAS). RESULTS: After a mean of 4 years, two implants (3.8%) failed, with no effect on prosthesis survival. The cumulative survival rate was 98.6% and 100% for implants and prostheses, respectively. The most frequent minor biological complication was soft tissue recession (11%). Porcelain fracture was the only major technical complication (0.6% of crown units), while the only minor technical complication was porcelain chipping (4% of crown units), which required only polishing. Overall, 66.7% of the prostheses were free of technical complications. Patient satisfaction was high to very high. Less satisfaction was noted with comfort due to soft tissue recession and food impaction. CONCLUSIONS: Within the limitations of this study, we conclude that the survival and success rates of SCCSIPs in edentulous patients were excellent. CLINICAL RELEVANCE: SCCSIPs should be considered when planning metal-ceramic implant-supported restorations.

[Examination of the mechanical properties of zirconia and porcelain blocks after grinding with smooth and coarse diamond burrs].

UNLABELLED: Porcelain and Zirconia are widely used materials in oral rehabilitation for fixed partial dentures, FPD. Among many important properties, A FPD should be able to resist bite forces, the harsh oral environment and to remain intact for a long period of time. When coming back from the dental laboratory, the mechanical properties of the FPD are optimal. But it is not uncommon for the dentist to perform a machining procedures on the restoration in order to achieve good fitting to the prepared teeth. In most cases these modifications are made using high speed dental hand piece, and diamond burs. The surface integrity of the restoration is an important parameter that influences on the restoration strength and durability. The more smooth the restoration surface is, it is less prone to fracture, and is less prone to coloring and plaque retention. Therefore, every modification the dentist makes on the restoration is not recommended. In some cases, the adjustments are made on a FPD which is already cemented to the teeth. If the teeth are vital, the implications of the machining of the restoration are even more destructive. As a result of the friction between the bur and the restoration, the temperature rises. There is a risk of pulp necrosis in temperature above 42 degrees C. The purpose of this study is to compare the mechanical properties of Zirconia and Porcelain blocks after grinding with smooth burs made in a new technology, Magic touch, Strauss co. (Ranana, Israel) and coarse burs. MATERIALS AND METHODS: blocks of Porcelain MARK II for CEREC (VIDENT), and Zirconia IPS e.max ZirCAD (Ivoclar Vivadent) were sliced to slices of 1mm and underwent drilling using the two kinds of burs, using thermocoupling--Almemo, Holzkirchen, Germany. So that the rise in temperature was measured through the drilling. Blocks of Porcelain and Zirconia were machined with the two kinds of burs, and their surface roughness was examined with Mitutoyo Surftest 402 Profilometer. Further examination was made with SEM micrographs. RESULTS: the samples machined with Magic touch burs, both on Porcelain and Zirconia, were significantly smoother than the samples machined with coarse burs (P 0.05). There was no significant rise in temperature (above 42 degrees C) using both kind of burs, on both Porcelain and Zirconia. The SEM microscopy demonstrates smoother surface of the porcelain and Zirconia which were grinded with Magic touch burs. CONCLUSIONS: Magic touch diamond burs, enables the dentist to perform fit adjustments on Porcelain or Zirconia FPD, leaving the restoration with minimum surface roughness, without elevating the temperature to high values, permitting both the tooth and the restoration to remain strong and durable for a longer period of time.

[Fiber reinforced composite posts: literature review].

FRC (Fiber-reinforced composite) posts have been used since the beginning of the 90s with the introduction of carbon fiber posts. Fiber posts are widely used to restore endodontically treated teeth that have insufficient coronal tooth structure. Many in vitro and in vivo studies have shown the advantage of using FRC over prefabricated and cast metal post especially indicated in narrow root canals which are prone to vertically root fracture. The most frequent failure of FRC is debonding of a post at the resin cement/dentin interface. Bonding to dentin may be achieved by using etch-and-rinse and self-etch adhesives. The bond strength formed by self-adhesive cements is noticeably lower in comparison to the bond strength formed with resin cements applied in combination with etch-and-rinse adhesives. In an attempt to maximize resin bonding to fiber posts, several surface treatments have been suggested. Sandblasting with alumina particles results in an increased surface roughness and surface area without affecting the integrity of the post as long as it is applied by 50 microm alumina particles at 2.5 bars for maximally 5 seconds at a distance of 30 mm. The efficiency of post salinization is controversial and its contribution to the retention is of minor importance. Hydrofluoric acid has recently been proposed for etching glass fiber posts but this technique produced substantial damage to the glass fibers and affected the integrity of the post. Delayed cementation of fiber post (at least 24h post endodontic treatment) resulted in higher retentive strengths in comparison to immediate cementation and the best results were obtained when the luting agent was brought into the post space with lentulo spirals or specific syringes. The resin cement film thickness also influences the pullout strengths of fiber-reinforced posts .The highest bond strength values were obtained when the cement layer oversized the post spaces but not larger than 0.3 mm. The use of core build-up materials as post luting cements is not recommended. The use of FRC post, combined with proper adhesive cementation technique can give an excellent solution when restoring endodontically treated teeth that are prone to fracture.

[Impressions techniques--Part 2].

A dental impression is a positive replica of the teeth, the surrounding gingiva and the border between them; the purpose of which is to create an accurate master model. Two major techniques for impressions exist today: The conventional and the digital impressions. The current article describes both techniques. In the conventional impressions, it is important to choose a proper tray, stock or custom, and to mix the material properly. The commonly used impression techniques for making a conventional impression are described with a review on the effect of the technique on its accuracy. The effect of the wash bulk on the accuracy of the stone dies and/or the restoration is discussed, as well. The digital impressions with their advantages and disadvantages are described in comparison to the conventional impressions. Although, digital impressions eliminate some of the negative characteristics of conventional impressions, proper soft-tissue management and isolation of tooth preparation margins is still mandatory.

[Tissue displacement and impression techniques--part 1].

In order to create an accurate model of the soft and hard tissues of the mouth, a complete control of the gingiva around the prepared teeth is needed. This gingiva must be displaced and bleeding must be avoided. This article describes the three techniques for tissue displacement: mechanical, chemicomechanical and surgical. Mechanical displacing the gingiva can be done by either the use of copper bands or with plain retraction cord. By combining chemical action with packing of a retraction cord a chemicomechanical displacement of the tissue can take place. The surgical retraction is possible by Laser, Electro surgery or Rotatory curettage. The advantages, disadvantages, and limitations of each of the different techniques are discussed. In addition, the different hemostatic agents are described with their mechanism of action, indications and contra-indications of each one of them.

Appropriateness of viscoelastic soft materials as in vitro simulators of the periodontal ligament.

The periodontal ligament is a viscoelastic soft tissue that connects the tooth to the alveolar bone. This tissue should be simulated in numerical as well as in laboratory models. The mechanical properties of this tissue were previously determined ex vivo and in vivo. The aim of the study was to analyse the appropriateness of impression and reline materials used in dentistry to simulate viscoelastic behaviour of the periodontal ligament. Two reline [Durabase (Reliance Dental MFG, Co.) and Soft Liner (GC Corporation)] and two impression [President Plus (Coltene) and Prestige L (Vanini Dental Industry)] materials were examined in recovery and tensile relaxation tests. Recovery: This experiment simulated in vivo test. Roots of a pair of plastic maxillary premolar teeth were covered with each test material and embedded in acryl while maintaining the contact point. A 0·1-mm stainless steel strip, inserted at the contact point and maintained for 10 s, was used to tip the teeth. After removal, the tightness of dental contact point was measured over 30 min by determining the force needed to insert a 0·05-mm metal strip. Tensile relaxation: strips were elongated to 120%, 140% and 160% of their initial length and maintained at that length for 30 min. Two-phase decay function was applied. The results showed that elastic modulus and relaxation behaviour were significantly different between materials. Elastic modulus values were in the same range of those reported in the literature. However, the recovery values and behaviour showed that impression materials, especially President, are the materials of choice for this purpose because they simulated better the in vivo test.

[Elastomeric impression materials].

Elastomeric impression materials are in common use. The impression taken should be highly precise, thus, requiring specific care when manipulatingthese materials. There are 4 groups of elastomers; polysulfide, condensation silicone, addition silicone and polyether; each differ in their setting mechanism and their physical and chemical properties. This review elaborates the major properties of elastomers and its implications on their use. The impression material is inserted into the patient's mouth in a viscous state and transforms into viscoelastic state, upon withdrawal, influencing the residual deformation. The requirements are minimal residual deformation or maximal elastic recovery. As the mouth is a wet environment a major consideration is hydrophilicity. The wettability which is estimated by measuring either the contact angle of a droplet of water and the substrate post setting or the contact angle of a droplet of impression material and the wet tooth pre setting, determines the interaction of the material with both mouth fluids and gypsum. As the primary end target is to obtain a model depicting accurately the oral details, an attention to the impressions' compatibility with gypsum should also be given. Many studies were conducted to get a thorough understanding of the hydrophilic properties of each material, and the mechanism utilized, such as surfactants in hydrophilic PVS. Polyether is the only material that is truly hydrophilic; it exhibits the lowest contact angle, during and after setting. Recent studies show that during setting the Polyether hydrophilicity is increased compared to the condition after setting. Dimensional stability, a crucial property of the impression, is affected by the physical and chemical attributes of the material, such as its tear strength. Polysulfide has the highest tear strength. Tear Strength is affected by two major parameters, viscosity, a built-in property, and how fast the impression is pulled out of the mouth, the faster the impression is loaded and pulled out, the higher the tear strength is. The clinical use is dictated from the properties of each impression material, and the understanding of those enables the practitioner to minimize failures.

[Dentinal hypersensitivity].

Dentinal hypersensitivity is defined as short and transient painful response of exposed dentin, usually cervical, to different stimuli, such as thermal, mechanical osmotic or chemical. The etiology of dentinal hypersensitivity is open tubules (because of enamel loss or gingival recession), allowing painful stimulus to reach the pulp. The hydrodynamic theory explains the mechanism through which pain is aroused. When treating dentinal hypersensitivity, dentists always have to rule out other pathologies, such as carries, leakage, postoperative sensitivity, cracked tooth etc., and only then assess pain intensity and treat the tooth. Treatment always starts with prevention of both stimulus and exposure of dentin, and reducing predisposing factors. The treatment options include OTC products, such as fluoride and/or potassium enriched mouth washes and dentifrices, or in-office treatments, such as high content fluoride varnishes and gels, potassium oxalate chelating agents, Glutaraldehyde containing tissue fixating agents, bonding materials, low viscosity glass ionomers and even non-conservative treatments such as root canal therapy or mucogingival surgical interventions.

[Materials and technologies for fabricating denture bases].

The materials and technologies for fabrication of denture bases have developed during the last 150 years. The requirements of the ideal material are versatile and include functional, physical and esthetical demands. The current manuscript classifies denture base materials according to their chemical characteristics into polymers, reinforced polymers and light cured polymers. Poly Methyl Metacrylate (PMMA) was developed 70 years ago, and is still the major material for fabrication of denture bases due to its esthetic characteristics, high processing and polishing abilities, relining and rebasing possibility and low cost. The main disadvantages of PMMA are its dimensional changes during polymerization, porosity and allergic/cytotoxic effects. PMMA may be reinforced by metal, polyethylene or glass fibers. Other materials used for fabrication of denture bases are Nylon and Urethane dimethacrylate. Their advantages are better esthetics, low modulus of elasticity and reduced cytotoxicity. This review presents the advances in materials and techniques used for denture bases, the different materials, their advantages and disadvantages, the chemical reactions associated with their production, and their allergic and cytotoxic side effects.

[Fiber-reinforced composite in fixed prosthodontics].

Fiber reinforced composite (FRC) is composed of resin matrix and fibers filler. Common types of fibers: polyethylene, carbon and glass. Fibers can be continuous and aligned, discontinuous and aligned, discontinuous and randomly oriented. The architecture of the fibers is unidirectional, woven or braided. The two main types are: dry fibers or impregnated. Inclusion of fibers to resin composite increased its average flexural strength in 100-200 MPa. FRC can be utilized by the dentist in direct approach (splinting, temporary winged bridge) or indirect approach (laboratory made fixed partial denture). Laboratory fixed partial denture (FPD) is made from FRC substructure and Hybrid/Microfill particulate composite veneer. Main indications: interim temporary FPD or FPD in cases of questionable abutment teeth, in aesthetic cases where All Ceram FPD is not feasible. Retention is attained by adhesive cementation to minimally prepared teeth or to conventionally prepared teeth; other options are inlay-onlay bridges or hybrid bridges. Contraindications are: poor hygiene, inability to control humidity, parafunction habits, and more than two pontics. Survival rate of FRC FPD over 5 years is 75%, lower compared to porcelain fused to metal FPD which is 95%. Main reasons for failure are: fracture of framework and delamination of the veneer. Part of the failures is repairable.

Complete rehabilitation of patients with bruxism by veneered and non-veneered zirconia restorations with an increased vertical dimension of occlusion: an observational case-series study.

PURPOSE: To assess the clinical performance of the complete rehabilitation of a series of patients with bruxism treated by teeth- and implant-supported veneered and non-veneered zirconia restorations with an increased vertical dimension of occlusion (VDO). METHODS: Ten patients with bruxism, aged 62-70 years, were treated with 108 veneered and 142 non-veneered zirconia restorations and attended the recall appointment. The mean observation period was 28.2 (±16.8) months. The patients were identified from records, and clinical details were retrieved from their files. In the recall appointment, the restorations were evaluated using modified California Dental Association (CDA) criteria. The periodontal probing depth, bleeding index, presence of caries and implant survival and success rate were recorded. RESULTS: No biological complications were recorded for any restorations. The success and survival rate of all implants was 100%. The overall mean survival and success rate of all restorations was 99.6%. In the veneered group, the predominant complication was minor veneer chipping (13.9%) on the incisal edge, which required only polishing (grade 1); in the non-veneered group, the predominant failure was open proximal contacts between the implant restoration and adjacent teeth (9%); only one implant restoration needed repair. One restoration was replaced due to a horizontal tooth fracture. CONCLUSIONS: Within the limitations of this study, we conclude that the survival and success rate of monolithic zirconia restorations installed in patients with bruxism was excellent, although the veneered zirconia restorations showed a high rate of minor veneer chipping, which required only polishing.

Time-related PDL: viscoelastic response during initial orthodontic tooth movement of a tooth with functioning interproximal contact-a mathematical model.

Most anteroposterior orthodontic movements of posterior teeth have to overcome the "resistance" of adjacent teeth with functioning interproximal contacts. The aim of this study was to develop a mathematical model describing initial posterior tooth movement associated with functioning interproximal contacts in relation to the viscoelastic mechanical behavior of the human periodontal ligament (PDL). A linear viscoelastic 2D mathematical model was modified to depict tipping movement around the center of rotation (C(rot)) of a premolar where tipping is restrained by adjacent teeth. Equilibrium equations were applied taking into account the sagittal moment developed around the C(rot). The constants of the model were analyzed and applied to a numerical model that can simulate short-term tooth creep movement caused by a tipping force. Changes in force magnitude (0.5-3N) and crown length (6-10mm) were analyzed until no movement was observed (steady state). Premolar displacement in contact with adjacent teeth showed a non-linear progression over time with an initial sharp tipping movement followed by a transient period of 2.6-7.1min. As tipping force increased the transient period increased. A similar but smaller effect was observed with an increase in crown length. The premolar initial displacement within the arch (3.2-19.5microm) is about seven-fold smaller than retraction/protraction movement of an incisor. These suggest reduction in tooth displacement when functioning interproximal contact is present and clinically recommend establishing a space in the direction of tooth displacement before tooth movement.

Marginal Fit and Retention Strength of Zirconia Crowns Cemented by Self-adhesive Resin Cements.

The absolute marginal gap (AMG) precementation and postcementation and the retention of zirconia crowns cemented to standardized molar preparations (4×10) by self-adhesive resin cements (SARCs) were evaluated. The following SARCs were used: RelyX U-200 (RXU200; 3M ESPE, Seefeld, Germany), SmartCem 2 (SC2; Dentsply, Milford, DE, USA), and G-Cem Automix (GCA; GC, Alsip, IL, USA). The control adhesive resin cement was Panavia 21 (PAN; Kuraray Dental Co Ltd, Osaka, Japan). Twenty measuring locations at a constant interval along the margins were marked, and the AMG was measured by an image analysis system connected to a stereomicroscope (20×). The cemented copings were aged 270 days at 100% humidity and 37°C and then underwent 10,000 thermal cycles, 5°C-55°C. After aging, the crowns were tested for retention, and the debonded surfaces were examined at 3× magnification. The mean marginal gaps precementation and postcementation were 34.8 ± 17.4 µm and 72.1 ± 31 µm, respectively, with no statistically significant differences between the cements. A significant difference ( p≤0.001) in retention between the cements was found. The highest values were obtained for SC2 and GCA (1385 Pa and 1229 Pa, respectively), but these presented no statistically significant differences. The lowest values were found for PAN and RXU200 (738 Pa and 489 Pa, respectively), but these showed no statistically significant differences. The predominant mode of failure in all of the groups was mixed, and no correlations were found between marginal gap and retention.

Testosterone potentiation of ionophore and ADP induced platelet aggregation: relationship to arachidonic acid metabolism.

The role of arachidonic acid oxygenated products in human platelet aggregation induced by the ionophore A23187 was investigated. The ionophore produced an increased release of both saturated and unsaturated fatty acids and a concomitant increased formation of TxA2 and other arachidonate products. TxA2 (and possibly other cyclo oxygenase products) appears to have a significant role in ionophore-induced aggregation only when low concentrations (less than 1 micro M ) of the ionophore are employed. Testosterone added to rat or human platelet-rich plasma (PRP) was shown previously to potentiate platelet aggregation induced by ADP, adrenaline, collagen and arachidonic acid (1, 2). We show that testosterone also potentiates ionophore induced aggregation in washed platelets and in PRP. This potentiation was dose and time dependent and resulted form increased lipolysis and concomitant generation of TxA2 and other prostaglandin products. The testosterone potentiating effect was abolished by preincubation of the platelets with indomethacin.

A new muffle model system to study root canal morphology and instrumentation techniques.

A new muffle model system is presented using the principle of internal indexing. The system is composed of a metal stand, four pins, and a single Teflon mold that is used for the investment of all teeth. This system is very precise, reproducible, and versatile. The sectioned specimens can easily be stored assembled, as opposed to previous systems that rely on external indexing.

Furcation groove of buccal root of maxillary first premolars--a morphometric study.

Furcation grooves on the palatal aspect of the buccal roots of 35 maxillary first premolars, randomly selected, were assessed and found to exist in 97% of the sample. The buccal roots were sectioned into slices, 1 mm thick, and morphometric horizontal and vertical measurements were taken by a Toolmaker Microscope. The slice with the deepest invaginations served as the reference plane. The deepest invaginations were found to be at a mean distance of 1.18 mm from the bifurcation, with a mean depth of 0.4 mm. The canal had a kidney-shaped appearance in cross-section, and the mean distance from the invagination to the canal wall was 0.81 mm. It is thus hazardous to use rotary instruments for flaring these roots and any circular-shaped post space preparation at this level is contraindicated. The outcome of such procedures might be root thinning, perforation, or vertical root fracture, thus causing a poor prognosis.

Residual dentin thickness in mandibular premolars prepared with hand and rotatory instruments.

The residual dentin thickness in the coronal part of root canals of mandibular premolars after stepback preparation and flaring with Gates Glidden (GG) drills was assessed sequentially in a newly designed muffle device. Twelve extracted teeth were embedded in clear polyester resin, sectioned horizontally (1, 3, and 5 mm apically to the cementoenamel junction), and reassembled in the muffle device. The sequence of canal preparation was K-files to #40, then GG-2 and GG-4. After each procedure, the slices were separated and residual dentin thickness measured by a toolmaker microscope in four directions (buccal, lingual, distal, and mesial) and reassembled in the muffle device. Statistical analysis by three-way analysis of variance with repeated measures was undertaken. The difference in residual dentin thickness was highly significant with regard to instrument (control, K-40, GG-2, GG-4; p < 0.0001), slice (upper, middle, and lower; p < 0.0003), and direction (B, L, M, and D; p < 0.001). In each slice, the width of the mesial side was similar to the distal side, as was the buccal to the lingual sides. Reduction of residual dentin thickness in the mesiodistal direction, from the unprepared upper slice to the GG-4 prepared lower slice, was appreciably greater (35%) than in the buccolingual direction (5%).

Effect of various mixing ratios on antibacterial properties and hardness of endodontic sealers.

Most chemically cured two-component dental materials, including endodontic sealers, are marketed with mixing instructions but with no strict mixing ratios. The present study evaluated the antibacterial properties and hardness of three endodontic sealers: Roth's cement (RC), CRCS, and AH26, mixed to four controlled consistencies within the range of the manufacturer recommendations. Using Enterococcus faecalis as the test microorganism, antibacterial activity was evaluated by agar diffusion and direct contact test. Surface hardness of sealers with the same consistency was evaluated on week-old specimens by the Knoop Hardness Number tester. In the agar diffusion test, light consistency of RC showed larger zones of inhibition than heavier consistency, whereas no significant differences were found with AH26 or CRCS. In the direct contact test, RC and CRCS exhibited complete inhibition of bacterial growth at all consistencies, whereas AH26 with the heavier consistencies did not inhibit bacterial growth at 24 h samples. The hardness of AH26 and CRCS was significantly lower with lighter consistencies. It is concluded that endodontic sealers possess different antibacterial and physical properties according to their mixing consistencies.

Post-irradiation polymerization of different anterior and posterior visible light-activated resin composites.

The Knoop hardness number was measured for bottom and top surfaces of 2 mm thick specimens of different anterior and posterior visible light-cured composites. The variables for this study included various exposure times and a series of time intervals from immediately after curing up to 72 h. Post-irradiation microhardness at the bottom and top surfaces increased rapidly over the first hour, was slower during 24 h and showed no further increase after 24 h. Increasing exposure time resulted in higher microhardness values at both surfaces. Magnitudes of change were larger for the bottom surface. Exposure times longer than those recommended by the manufacturers were needed, especially for the anterior microfilled composites, to achieve adequately photo-activated resin that had an optimum bottom/top surface microhardness of 80-90%. Maximum hardness values were found to be dependent on the volumetric fraction but not on the average inorganic filler size. The post-irradiation increase in hardness value was independent of composite parameters and is probably commensurate with polymerization kinetics.