In vitro 3D and gravimetric analysis of removed tooth structure for complete and partial preparations.

PURPOSE: To quantify and to compare a gravimetric and three-dimensional (3D) analysis of the removed tooth structure for different complete crown preparations. METHODS: A total of 80 molar resin teeth and 8 preparation finishing lines were chosen: 1 for metal ceramic crowns (MCC); 3 for zirconia all-ceramic crowns: knife edge (ZirKnE), chamfer (ZirCha), and shoulder (ZirSho); 4 for lithium disilicate: light chamfer (LDLCha), chamfer (LDCha), shoulder (LDSho) and table top. Teeth were individually weighed to high precision and then prepared following the preparation guidelines. The teeth were reweighed after preparation, and the amount of structural reduction was calculated. In addition, all teeth were scanned before and after preparation, and the 3D volume of removed dental tissue was calculated, superimposing the two .stl files, as a difference of the volumes before and after the preparation. Kruskal-Wallis statistical analysis was carried out to determine significant differences among the groups with a significance level of p<0.05. RESULTS: Both analyses showed that LDLCha, ZirKnE and table-top preparations produced the smallest amount of removed structure, whereas the preparations for MCC, ZirSho and LDSho were more destructive. For MCC, 2.6 times more tooth structure must be removed than for table top. ZirKnE was 17.82% and LDLCha was 21.51% more conservative than MCC. The data obtained through the volumetric method were similar with those obtained by gravimetric analysis. CONCLUSIONS: ZirKnE, LDLCha, and table-top preparations produced the least amount of tooth tissue removal. Three-dimensional volumetric analysis can be a possible alternative to gravimetric analysis.

Influence of preparation design and spacing parameters on the risk of chipping of crowns made with Cerec Bluecam before cementation.

PURPOSE: To evaluate the influence of the preparation design and spacing parameters on the risk of chipping of crowns made by CEREC Bluecam before cementation. METHODS: A knife-edge preparation and a chamfer preparation were made on upper premolars. The teeth were scanned and two Co-Cr alloy replicas were made. Fifteen full crowns were manufactured for four groups using CEREC. The groups differed in type of preparation (knife-edge (KE) or chamfer (CHA)) and spacing parameters: spacer (0 or 150µm), marginal adhesive gap (10 or 50 or 150µm) and margin thickness (0 or 300µm). The four groups were: CHA 150 (spacer)- 50 (marginal adhesive gap)- 0 (margin thickness), KE 150-50-0, KE 150-50-300 and KE 150-150-300. The crowns were loaded before cementation by using an Instron machine to simulate the masticatory load applied during a trial. Differences in means were compared using two-way ANOVA and a post-hoc test (Tukey Test). The level of significance was set at P=0.05. RESULTS: The fracture values, ordered from least to most resistant, were: KE 150-50-300 group, CHA 150-50-0 group, KE 150-50-0 group and KE 150-150-300 group. Two-way ANOVA revealed statistically significant differences between pairs of means (p<0.05). Tukey's test showed that restorations of the KE 150-150-300 group can withstand a load significantly higher than that of other groups (p<0.01). In this group, the failures were mostly minor chippings, while the other groups had mostly major chippings and fractures. CONCLUSIONS: Marginal adhesive gap can affect the trial of a full crown.

Retentive Strength of Y-TZP Crowns: Comparison of Different Silica Coating Methods on the Intaglio Surfaces.

OBJECTIVE: To evaluate the effect of different methods of silica deposition on the intaglio surface of yttrium oxide stabilized zirconia polycrystal (Y-TZP) crowns on the retentive strength of the crowns. METHODS: One hundred simplified full-crown preparations produced from fiber-reinforced polymer material were scanned, and 100 Y-TZP crowns with occlusal retentions were milled. Crown/preparation assemblies were randomly allocated into five groups (n=20) according to the treatment of the intaglio surfaces: TBS = tribochemical silica coating via air-abrasion with 30-µm silica-coated alumina particles; GHF1 = application of thin glaze layer + hydrofluoric acid (HF) etching for 1 minute; GHF5 = glaze application + HF for 5 minutes; GHF15 = glaze application + HF for 15 minutes; NANO = silica nanofilm deposition (5 nm) via magnetron sputtering. All groups received a silane application. The surfaces of the preparations (polymer) were conditioned with 10% HF for 30 seconds and silanized. The crowns were cemented with resin cement, thermocycled (12,000 cycles; 5°C/55°C), stored for 60 days, and subjected to a retentive strength test (0.5 mm/min until failure). The retention data (MPa) were analyzed using one-way analysis of variance, Tukey tests, and Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown) and 50S (above 50% of cement on the substrate). RESULTS: The TBS (5.6±1.7 MPa) and NANO groups (5.5±1 MPa) had higher retentive strength than the other groups (p<0.0001) and had the highest values of characteristic strength. There was no difference in Weibull modulus, except for the GHF1 group (lower values). The TBS and GHF15 groups, respectively, had 60% and 70% of their failures classified as 50C, while most of the other groups had 50S failures. CONCLUSION: Tribochemical silica coating and silica nanofilm deposition on the inner surface of zirconia crowns promoted a higher retentive strength.

Fractographical Analysis and Biomechanical Considerations of a Tooth Restored With Intracanal Fiber Post: Report of the Fracture and Importance of the Fiber Arrangements.

OBJECTIVE: This article aims to present a fractographic analysis of an anterior tooth restored with a glass fiber post with parallel fiber arrangement, taking into account force vectors, finite element analysis, and scanning electron microscopy (SEM). METHODS: A patient presented at the Faculty of Dentistry (Federal University of Santa Maria, Brazil) with an endodontically treated tooth (ETT), a lateral incisor that had a restorable fracture. The treatment was performed, and the fractured piece was analyzed using stereomicroscopy, SEM, and finite element analysis. RESULTS: The absence of remaining coronal tooth structure might have been the main factor for the clinical failure. We observed different stresses actuating in an ETT restored with a fiber post as well as their relationship with the ultimate fracture. Tensile, compression, and shear stresses presented at different levels inside the restored tooth. Tensile and compressive stresses acted together and were at a maximum in the outer portions and a minimum in the inner portions. In contrast, shear stresses acted concomitantly with tensile and compressive stresses. Shear was higher in the inner portions (center of the post), and lower in the outer portions. This was confirmed by finite element analysis. The SEM analysis showed tensile and compression areas in the fiber post (exposed fibers=tensile areas=lingual surface; nonexposed fibers=compression areas=buccal surface) and shear areas inside the post (scallops and hackle lines). Stereomicroscopic analysis showed brown stains in the crown/root interface, indicating the presence of microleakage (tensile area=lingual surface). CONCLUSION: We concluded that glass fiber posts with parallel fibers (0°), when restoring anterior teeth, present a greater fracture potential by shear stress because parallel fibers are not mechanically resistant to support oblique occlusal loads. Factors such as the presence of remaining coronal tooth structure and occlusal stability assist in the biomechanical equilibrium of stresses that act upon anterior teeth.

A CAD/CAM-prototyped anatomical condylar prosthesis connected to a custom-made bone plate to support a fibula free flap.

This paper describes a new protocol for mandibular reconstruction. Computer-aided design/computer-aided manufacturing (CAD/CAM) technology was used to manufacture custom-made cutting guides for tumor ablation and reconstructive plates to support fibula free flaps. CT scan data from a patient with an odontogenic keratocyst on the left mandibular ramus were elaborated to produce a virtual surgical plan of mandibular osteotomy in safe tissue for complete ramus resection. The CAD/CAM procedure was used to construct a customized surgical device composed of a cutting guide and a titanium reconstructive bone plate. The cutting guide allowed the surgeon to precisely transfer the virtual planned osteotomy into the surgical environment. The bone plate, including a custom-made anatomical condylar prosthesis, was designed using the outer surface of the healthy side of the mandible to obtain an ideal contour and avoid the bone deformities present on the side affected by the tumor. Operation time was reduced in the demolition and reconstruction phases. Functional and aesthetic outcomes allowed patients to immediately recover their usual appearance and functionality. This new protocol for mandibular reconstruction using CAD/CAM to construct custom-made guides and plates may represent a viable way to reproduce the patient's anatomical contour, give the surgeon better procedural control, and reduce operation time.

Mechanical fatigue cycling on teeth restored with fiber posts: impact of coronal grooves and diameter of glass fiber post on fracture resistance.

AIM: The aim of this paper was to evaluate the effect of different diameters and surface characteristics of a glass fiber post on the fracture resistance of teeth restored with fiber posts. METHODS: Eighty single-rooted bovine teeth were prepared, embedded in a PVC cylinder using acrylic resin, and allocated into 8 groups (N.=10) according to post diameter and shape: (smooth double-tapered fiber post) G1, G2, G3, and G4 with cervical diameters of 1.4 mm, 1.6 mm, 1.8 mm, and 2 mm, respectively; (double-tapered fiber posts with coronal grooves) G5, G6, G7, and G8 with cervical diameters of 1.4 mm, 1.6 mm, 1.8 mm, and 2 mm, respectively. A self-adhesive cement was used for post cementation, and the core build-up was standardized and made with composite resin. Specimens were stored for 7 days and then submitted to the mechanical fatigue testing (load=50 N., angle= 45°, frequency=1 Hz, temperature=37 ± 1 °C, number of cycles=1000000); the specimens that survived were submitted to static resistance testing (1 mm/min, 45°). The fracture loads and fracture modes was recorded. Data were submitted to 2-way ANOVA, post-hoc Tukey test and Pearson Correlation analysis. RESULTS: The cervical diameter of the post (P<0.0001) and surface characteristics (P=0.01013) significantly affected the fracture resistance (2-way ANOVA). Grooves reduced the fracture resistance when post diameter was 1.4 mm (G1 and G5). A moderate positive correlation was found between the fracture resistance and the fiber post diameter (r2=0.4445; P<0.0001) (Pearson correlation test). CONCLUSION: It appears that there is a direct relation between the diameter of the fiber post and the fracture strength of roots restored with fiber posts. But other factors may have influenced the fracture strength such as the reduction of intracanal dentin by the preparation for placement of wider fiber posts, since no difference was found for smooth fiber posts with different diameter. Otherwise, grooves at coronal part of the fiber post can damage the fracture resistance.

Surviving of bovine teeth adhesively restored with 3 types of fiber post after fatigue resistance.

AIM: Aim of this study was to evaluate the fatigue resistance of bovine roots adhesively restored with three fiber posts. METHODS: Twenty-four single-rooted bovine teeth were allocated into three groups (N.=8): Gr1- White Post DC; Gr2- DT Light Post; Gr3- FRC Postec Plus. Teeth were prepared using the preparation drill of the specific fiber post system for each group. After the specimen was embedded in a cylinder, using acrylic resin, up to 3 mm of the most coronal portion of the specimen, the posts were all cemented with same materials: Single Bond + Relyx CRA. After cementation, a standard core build-up was made with composite resin. The specimens were submitted to mechanical cycling (1.400.000, 50N, 8 Hz, 37°C). After fatigue testing, a score was given to each specimen. The scores were submitted to Kruskal-Wallis (α=0.05) and the fractures were observed. RESULTS: The performance after mechanical fatigue cycling was similar for the three fiber posts systems (P=0.366). Just one failure was noted from each group, a failure at the composite core. CONCLUSION: The tested fiber posts had good performance, but attention should be taken regard of the adhesion of composite core to fiber past.

Effect of cyclic loading on fracture strength and microleakage of a quartz fiber dowel with different adhesive, cement and resin core material combinations.

AIM: This study evaluated the performance of different adhesive-cement-core combinations coupled with quartz fiber dowels after cyclic loading and fracture strength tests and assessed the microleakage using dye penetration method. METHODS: Forty maxillary canines (N=10 per group) were restored with fiber dowels (Quartz fiber DT Light Post) and four adhesive-cement-core material combinations (Group 1: All-Bond 2+C&B [root]/All-Bond 2+Biscore [core]; Group 2: All-Bond 2+Bisfil 2B [root]/All-Bond 2+Bisfil 2B [core]; Group 3: Scotchbond 1+RelyX ARC [root]/Scotchbond 1+Supreme [core]; Group 4: RelyX Unicem [root]/Scotchbond 1+Filtek Supreme [core]). The specimens were initially cyclic loaded (x2,000,000, 8 Hz, 3 to 100 N at 45 °C under 37±3 °C water irrigation) and then immersed in 0.5% basic fuchsine at 37 °C for 24 hours for dye penetration and interface failure detection. The failure surfaces were observed under the stereomicroscope (x100 magnification). Circumferential and centripetal dye penetration was scored at the buccal and lingual sites. RESULTS: Only three specimens failed macroscopically during cyclic loading. No significant difference was found among the groups for the number of resisted cycles (P=0.9). Mean fracture strength between the groups were also not statistically significant (213±63-245±71 N) (P=0.740) (ANOVA). All four groups showed high values of dye penetration along the restoration interfaces being not significant from each other (P=0.224) (Kruskal-Wallis). The lingual sides of the teeth where the load applied, showed significantly higher incidence of detachment between the core and the dentin (100%, 90%, 100%, 90% for groups 1, 2, 3, 4, respectively) compared to the buccal side (30%, 30%, 60%, 40%) (P=0.032, c2 test). In 13 specimens (32.5%) crack lines at the coronal area were observed. Fracture strength was not significantly correlated with dye penetration (P=0.1803, r=-0.2162, Linear Regression and Correlation test). CONCLUSION: Different combinations of adhesive-cement-composite core materials for the fiber post tested performed similar under cyclic loading and fracture strength tests.

Biocompatibility of various root canal filling materials ex vivo.

AIM: To evaluate the biocompatibility of a resin-based endodontic filler (RealSeal) using the indirect cytotoxicity test. METHODOLOGY: Human gingival fibroblasts were cultured ex vivo. Pellets of the materials to be tested were incubated for 24, 48, and 72 h at 37 degrees C under sterile conditions to obtain their eluates. The fibroblasts were exposed to either diluted (50%) or undiluted eluates for 24 h. A culture medium with foetal calf serum was added to the control wells. Cell viability was estimated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide method. The data concerning cell viability were statistically analyzed using one-way anova test and Bonferroni multiple comparisons test. RESULTS: Eluates obtained after 24 h of incubation with the resin filler did not reduce cellular viability. An increase in cellular viability, as compared with control cells, was observed in the gutta-percha group. The undiluted eluate from the polyether material was cytotoxic, causing an 82 +/- 4% decrease in cellular viability. Eluates obtained after 48 h of incubation with the resin filler increased cellular viability, whereas the polyether significantly reduced viability. Gutta-percha did not cause any detectable change. After 72 h of incubation the eluate of the resin filler caused an increase in cellular viability, as did gutta-percha, whereas polyether caused a significant decrease. CONCLUSIONS: RealSeal resin filler was nontoxic in this laboratory model. Further investigations are necessary to verify its usefulness in clinical applications.

The prosthetically guided osteodistraction of the mandible in the microvascular bone reconstruction after cancer surgery.

The rehabilitation of the mandible after ablation cancer surgery is a challenge. Furthermore, osteodistraction in the microvascular fibula flap makes it difficult to predict adequate bone lengthening. The aim of this article is to evaluate a protocol used to manufacture templates for measuring osteodistraction, in terms of force vectors and definitive height. An accurate prosthetic wax-up with guide pins measuring the quantity of bone lengthening must be performed to manufacture the template. This device may be used to establish the end of the osteo-distraction in respect to the vertical dimension of the definitive occlusion.

Short-term clinical evaluation of inlay and onlay restorations made with a ceromer.

PURPOSE: This prospective clinical trial evaluated the clinical acceptability of a new material, ceromer, used for inlay and onlay restorations in single- or multisurface cavities of posterior teeth. MATERIALS AND METHODS: Forty-three Targis inlay and onlay restorations were placed in 25 patients and evaluated using the United States Public Health Service criteria. The laboratory work was conducted by three dental technicians according to the manufacturer's recommendations. Twenty-five restorations were luted with Syntac bonding system and Variolink II, and 18 were luted with Scotchbond Multi Purpose and Opal Luting Composite. The recalls were done at 6, 12, and 18 months. Restorations were evaluated for six parameters and scored as ideal (A), clinically acceptable (B), or clinically unacceptable (C). RESULTS: Indirect restorations received, after 18 months, scores of A at the following rates: color match 77%; marginal discoloration 93%; secondary caries 100%; anatomic form 93%; and marginal integrity 95%. For these parameters, statistical analysis indicated no significant differences at baseline and after 18 months. Postoperative hypersensitivity was reported by seven patients at baseline, but it decreased and there was no hypersensitivity at 12- and 18-month follow-ups. CONCLUSION: Over an 18-month period the Targis restorative system yielded good clinical service.

[Heat-induced symptomatology in human teeth. An in-vitro study]. / Sintomatologia indotta dal calore su denti umani. Studio in vivo.

OBJECTIVE: Various dental procedures can generate thermal increase in the dental pulp, in particular if they are incorrectly conducted. In literature the pulp cells are considered very heat sensitive. In this study the symptomatological response of patients during and after thermal administration to the dental crown has been recorded. The analysis of the symptomatology was used as an indication for the definition of the threshold of thermal damage. EXPERIMENTAL DESIGN: Twelve healthy teeth of four patients programmed for extraction were subdivided into six couples of homologous teeth. One tooth out of each couple was used for the immediate in vivo recording of the symptoms; the other, once extracted, was used to determine the thermal increase applied through the insertion of a thermocouple sensor. In each couple of teeth the thermal stimulus was equal. RESULTS: The average thermal increase was 11.2 degrees C. Pain starts at temperatures ranging from 39.5 to 50.4 degrees C with an average of 44.6 degrees C. This agrees with classical physiological data which reports the threshold of pain at 45 degrees C. CONCLUSIONS: The threshold of pain registered suggests that at temperatures below 44.6 degrees C damage to the dental pulp is improbable, at least in healthy teeth. The limit of 45 degrees C appears, therefore, to be a probable safe threshold, contrary to what is reported in literature.

[The construction of plates for intraoral registration with photopolymerizing resins. An original method]. / Costruzione di placche per la registrazione intraorale con resine fotopolimerizzabili. Metodica originale.

The recording of maxillo-mandibular relationships using Gothic arch assembly in dentulous subjects is useful not only in prosthetic rehabilitation, but also in the analysis of mandibular range of motion on patients with temporomandibular disorders. The traditional methodology to assemble Gothic arch plate is too long and elaborate, so it is remitted to the laboratory. This study describes a quick and simplified technique utilizing photopolymerizing resins which can be used by the dentist in his own office, in order to permit a greater use in the clinical practice.

Comparative study of the marginal microleakage of six cements in fixed provisional crowns.

STATEMENT OF PROBLEM: In many situations, provisional restorations require a long-term permanence in the oral cavity. During this period, the abutments need the best possible biologic and mechanical protection. In this way, the vitality of the pulp and the integrity of mineralized tissues can be preserved. The luting cement used to fix interim restorations should have good mechanical properties, low solubility, and good adhesion to resist bacterial and molecular penetration. However, because of its provisional nature, the prosthesis should be easy to remove from the abutments. These contrasting requirements may lead to a compromise in cement behavior, particularly in its mechanical properties. PURPOSE: This in vitro study evaluated the marginal microleakage of 4 provisional cements, a cavity base compound and a zinc-phosphate luting cement in provisional acrylic resin crowns fixed on extracted human teeth. MATERIAL AND METHODS: Thirty acrylic resin crowns were made and fitted on intact human premolars with the 6 cements. All restorations were applied in a standardized manner by means of an axial load of 10 kg. Specimens were thermocycled then submerged in a 5% basic fuchsin solution, then sectioned and observed under a light stereomicroscope. A 5-level scale was used to score dye penetration in the tooth/cement interface. RESULTS: A high dye penetration in the tooth/cement interface was present in all 4 provisional cements. Microleakage existed in specimens where zinc-phosphate and cavity base compounds were used; however, it was lower than the other materials. A significant difference (P < .05) was found between zinc-phosphate and one eugenol-free cement and between cavity base and the same eugenol-free cement. CONCLUSIONS: All materials tested demonstrated different degrees of microleakage. Zinc-phosphate and cavity base compound cements had the best sealing properties. This latter, even if conceived as a cavity base, may be considered a good provisional cement as far as microleakage is concerned.

[Pharmacologic therapy of cranio-cervico-mandibular disorders. Review of the literature]. / Approccio alla terapia farmacologica dei disordini cranio-cervico-mandibolari. Rassegna della letteratura.

The recommended treatments of craniomandibular disorders (CMD) are drug therapy, physiotherapy, relaxation procedures, occlusal therapy with and without splint. The purpose of this study is to carry out a survey of the literature on drug therapy in patients affected by CMD. It is essential to recognize the cause of pain (muscular or articular) and the phase of disorder (acute or chronic) in order to establish an adequate pharmacological protocol for each type of CMD. Non-steroidal anti-inflammatory drugs (NSAID) are generally accepted for treatment of internal derangement and myofacial pain, sometimes in association with benzodiazepine.

[Short-term effects of the Michigan splint on muscular and joint pain]. / Effetti a breve termine della placca di Michigan sul dolore muscolare ed articolare.

BACKGROUND: In 1966 Ramfjord and Ash proposed the Michigan's splint that, at present, is one of the splints widely accepted for the treatment of craniomandibular disorders (CMD). METHODS: For this study, thirty-one subjects were examined according to the protocol of the European Academy of CMD; each patient indicated the intensity of pain using a Visual Analogue Scale (VAS). After therapy with Michigan's splint, the visit was repeated and the patient indicated again the VAS. RESULTS: The results showed that the splint has short-term benefit effects on the muscular and articular pain, even if the effects are lesser on the articular pain. CONCLUSIONS: The Michigan's splint is a valid device for therapy of CMD, moreover it is very cheap, very easy to use and without contraindications.

Reliability of tactile perception using sharp and dull explorers in marginal opening identification.

PURPOSE: The most direct method to clinically evaluate marginal openings in fixed partial dentures is to use manual explorers for tactile perception. The purpose of this in vitro study was to establish the reliability of different instruments for discovering marginal openings. MATERIALS AND METHODS: The materials used in this study included a dull stylet and a sharp-tipped explorer as well as a metal cylinder surface featuring 9 "V"-shaped circumferential grooves ranging in size from 20 to 165 microns. A group of 42 subjects were asked to discover the grooves using both instruments. RESULTS: The data revealed high reliability in the use of the sharp-tipped explorer. With this instrument, a defect of 36 microns could be perceived by 95% of the subjects. The dull, worn instrument gave significantly inferior results (P < 0.05). CONCLUSION: Using a sharp-tipped explorer on a smooth metal surface, tactile perception is a reliable means of detecting open margin defects up to 36 microns wide. As has been suggested in previous studies, the difficulty seems to be not in defect detection but in the evaluation of the clinical acceptability once it is detected.

Clinical and histological evaluation of thermal injury thresholds in human teeth: a preliminary study.

The effect on healthy dental pulp of thermal increases ranging from 8.9 to 14.7 degrees C was evaluated. These temperature increases correspond approximately to those caused by certain restorative procedures, such as tooth preparation with high-speed instruments and the fabrication of direct provisional crowns. Two criteria of evaluation have been used in conjunction, a clinical (symptomatic) and a histological one, to assert with greater precision potential damage to the pulp. The results suggest a low susceptibility of cells to heat, which does not appear to be a major factor of injury, at least in the short term. The main cause of postoperative inflammation or necrosis of the pulp is probably the injury of the dentine, a tissue in direct functional and physiological connection with the pulp.

[An experimental clinical evaluation of the influence of the blood circulation on the parapulpal thermal levels]. / Valutazione clinica sperimentale dell'influenza del circolo ematico sui livelli termici parapulpari.

The aim of this study is the evaluation of pulpal blood flow effect on the thermal levels measured at the pulpodentin junction in human anesthetized premolars. The value have been recorded as discrepancies between peak temperatures caused by a thermal stimulus applied on the same tooth in two different conditions: with and without pulpal blood supply. Thermal stimuli ranged from 3 to 9 degrees C on a total of twelve teeth giving a mean peak difference of 1.3 degrees C. This result has been interpreted as the effect of thermal dissipation produced by pulpal blood flow. The small magnitude of the value suggests, however, that anesthetized pulp fails to protect itself from injurious heat by increasing pulpal blood flow.