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Biomedical subjects

Matthias Kern

Publications and source records attributed to Matthias Kern.

32 records · Page 2Linked to original sources
PubMed2004

In vivo study of the marginal integrity of composite resin buildups after full crown preparation.

PURPOSE: The purpose of this in vivo study was to evaluate the marginal integrity of composite resin buildups after full crown preparation, and to identify possible changes during the provisional phase of the manufacturing process of the final restorations. MATERIALS AND METHODS: Two test groups were determined for the use of an autocuring (Clearfil New Bond, Kuraray) and a light-curing (Optibond FL, Kerr) dentin adhesive. After rubber-dam application, both dentin adhesives were used with the total-etch technique. Then, an autocuring composite resin was applied for the core buildup. Impressions of the built-up teeth were taken directly after preparation and before cementation of the final restorations. During the provisional phase, which lasted from 7 to 28 days, the prepared teeth were restored with cemented provisional crowns. Replicas of the built-up teeth were manufactured and examined with a scanning electron microscope. RESULTS: For the autocuring dentin adhesive, only one buildup showed a gap 10 microm wide and 100 microm long. For the light-curing dentin adhesive, two samples revealed gaps that were 10 microm wide and had lengths of 100 microm and 75 microm, respectively. No change could be perceived when comparing the state of the composite/tooth interface after preparation and before final cementation. CONCLUSION: The results show that when using an autocuring composite resin in combination with dentin adhesives, nearly gap-free margins of composite buildups can be achieved and therefore might serve as a sound basis for the final restoration.

Acid Etching, Dental↗
PubMed2003

Resin-ceramic bonding: a review of the literature.

Current ceramic materials offer preferred optical properties for highly esthetic restorations. The inherent brittleness of some ceramic materials, specific treatment modalities, and certain clinical situations require resin bonding of the completed ceramic restoration to the supporting tooth structures for long-term clinical success. This article presents a literature review on the resin bond to dental ceramics. A PubMed database search was conducted for in vitro studies pertaining to the resin bond to ceramic materials. The search was limited to peer-reviewed articles published in English between 1966 and 2001. Although the resin bond to silica-based ceramics is well researched and documented, few in vitro studies on the resin bond to high-strength ceramic materials were identified. Available data suggest that resin bonding to these materials is less predictable and requires substantially different bonding methods than to silica-based ceramics. Further in vitro studies, as well as controlled clinical trials, are needed.

Aluminum Oxide↗
PubMedDate not supplied

Investigation of the fracture resistance of three types of zirconia posts in all-ceramic post-and-core restorations.

PURPOSE: All-ceramic post-and-core restorations offer a number of advantages compared with systems that use metal cores. In certain clinical cases, however, fractures at the junction between the post and the core have been reported. The objective is therefore to improve the strength between the post and the core. MATERIALS AND METHODS: Three different methods were used to fabricate all-ceramic post-and-core restorations: pressing IPS Empress cores directly to CosmoPost zirconia posts, adhesively luting IPS Empress cores to CosmoPost zirconia posts, and Celay milling In-Ceram zirconia blanks to one-piece post-and-core restorations. Ten restorations were prepared with each of the three methods. The post-and-core complexes were tested to failure with the load applied perpendicular to the post axis. The load and deflection at fracture were recorded. RESULTS: The highest breaking load and highest deflection were recorded for the luting technique, with values of 25.3 N and 394 microns, respectively. The corresponding values for the pressed cores and the milled zirconia cores were 22 N and 301 microns, and 13 N and 160 microns. All differences were statistically significant at P < .05. Regarding the load dependence of the deflection, the luted cores again demonstrated the highest mean value, with 15.5 microns/N, while this value was 13.6 microns/N and 13 microns/N for the pressed-on and milled cores, respectively. These differences were not statistically significant. CONCLUSION: Adhesively luted all-ceramic cores on zirconia posts offer a viable alternative to the conventional pressed technique.

Aluminum Oxide↗
PubMedDate not supplied

Influence of framework design on fracture strength of mandibular anterior all-ceramic resin-bonded fixed partial dentures.

PURPOSE: The purpose of this in vitro study was to evaluate the influence of the framework design on the fracture strength of all-ceramic resin-bonded fixed partial dentures (RBFPD) in the mandibular incisor region. MATERIALS AND METHODS: Twenty-four aluminum oxide ceramic frameworks were copy milled with the Celay system, glass infiltrated, and veneered with feldspathic porcelain to replace a mandibular incisor. Forty-eight extracted human incisors were used as abutments by embedding them in a polyester resin. The master casts were fabricated according to a typical clinical case. The sandblasted restorations were bonded to the acid-etched abutment teeth with a composite resin. Twelve RBFPDs had a conventional two-retainer design, and 12 had a cantilevered single-retainer design. Subgroups of eight specimens were subjected to a quasistatic load in the direction of the long axis of the abutment teeth in a universal testing machine. Additional subgroups of four specimens were subjected under 0 degrees to dynamic loading of 25 N in a dual-axis chewing simulator. RESULTS: The mean fracture strengths under quasistatic loading were 313 N (SD 42) for the two-retainer design and 291 N (SD 100) for the single-retainer design. The mean cycles sustained by specimens subjected to dynamic loading at 25 N were 50,081 (SD 42,705) for the two-retainer design and 297,099 (SD 508,439) for the single-retainer design. There was no statistically significant influence of the framework design on the fracture strength of the restorations under quasistatic or dynamic loading. CONCLUSION: The clinical application of cantilevered all-ceramic RBFPDs in the mandible may be an alternative to all-ceramic RBFPDs with two retainers.

Acid Etching, Dental↗
PubMedDate not supplied

Effect of different artificial aging conditions on ceramic-composite bond strength.

PURPOSE: The purpose of this study was to evaluate the influence of different storage conditions on the bond strength of adhesive bonding systems to yttria-partially stabilized zirconia ceramic. MATERIALS AND METHODS: Acrylic glass tubes filled with composite resin were bonded to ceramic disks. After sandblasting and ultrasonic cleansing of the ceramic samples, they were bonded using five bonding methods. Samples were tested for tensile bond strength following five different storage conditions: 3 days in distilled water at 37 degrees C, 31 days in distilled water at 37 degrees C, 37,500 thermocycles between 5 and 55 degrees C within 31 days, 150 days in distilled water at 37 degrees C, and 150 days in distilled water with 37,500 thermocycles performed at intervals. RESULTS: Mean resin bond strength values ranged from 7.7 to 41.9 MPa. There were statistically significant differences among groups, as revealed by the Kruskal-Wallis test. Some storage conditions influenced the resin bond strength statistically significantly, as revealed by the Wilcoxon rank sum test modified by Bonferroni-Holm. CONCLUSION: Thermocycling had a much higher impact on the durability of the resin bond strength to zirconia ceramic than did water storage at a constant temperature.

Adhesiveness↗
PubMedDate not supplied

Resin bond strength to densely sintered alumina ceramic.

PURPOSE: The aim of this in vitro study was to investigate the resin bond strength and durability of adhesive bonding systems to densely sintered, pure aluminum oxide ceramic. MATERIALS AND METHODS: Acrylic glass tubes filled with composite resin were bonded to industrially manufactured alumina ceramic disks with an ultrasonically machined surface. Groups of 20 samples were bonded in an alignment apparatus using five different bonding methods. Subgroups of 10 bonded samples were tested for tensile strength following storage in distilled water at 37 degrees C for either 3 or 150 days. In addition, the 150-day samples were thermocycled 37,500 times. The statistical analyses were made by the Kruskal-Wallis test, followed by multiple pairwise comparison of the groups using the Mann-Whitney test. RESULTS: The mean bond strength of a bis-GMA composite resin to sandblasted alumina ceramic was relatively high after 3 days, at 20 MPa. Additional silanization or tribochemical silica coating and silanization did not enhance the bond strength (18 to 20 MPa) and failed spontaneously over long-term storage. However, using a composite resin containing a special adhesive phosphate monomer, a statistically significantly higher and durable bond strength to the sandblasted alumina ceramic surface was achieved after 3 days (50 MPa) and after 150 days of storage (46 MPa). CONCLUSION: A durable bond strength to pure alumina ceramic was achieved only by using a composite resin containing an adhesive phosphate monomer after sandblasting the ceramic surface.

Aluminum Oxide↗
PubMedDate not supplied

Marginal discrepancies and leakage of all-ceramic crowns: influence of luting agents and aging conditions.

PURPOSE: This study evaluated the marginal discrepancies and leakage of all-ceramic crowns cemented with different luting agents after fatigue tests. MATERIALS AND METHODS: Forty-eight all-ceramic crowns were cemented onto natural molars. Zinc-phosphate cement, compomer cement, and an adhesive composite resin luting system were used in 16 specimens each. Sixteen metal-ceramic crowns were cemented with zinc-phosphate cement as a control. Half of the specimens in each group were fatigued in a chewing simulator for 600,000 loading cycles with 3,500 thermocycles. The others received the 3,500 thermocycles only. An impression-replica technique and SEM were used for evaluation of the marginal discrepancies. Leakage of the specimens was microscopically assessed. RESULTS: There were no significant differences between marginal discrepancies of the groups, with the exception of porcelain shoulder margins in the metal-ceramic group, which had significantly larger discrepancies (P < .01). There was no significant effect of the fatigue tests on marginal discrepancies. However, significant differences of leakage were found between the groups cemented with the different luting agents after both fatigue tests. The adhesive composite resin luting system demonstrated the least leakage. The compomer cement showed an intermediate level of leakage, and the zinc-phosphate cement showed severe leakage that extended through the dentinal tubules to the pulp chambers. No significantly different effect of the two fatigue tests on the leakage was found. CONCLUSION: The adhesive composite resin luting system showed clinically acceptable marginal discrepancies and an excellent ability to minimize leakage of all-ceramic crowns.

Adhesives↗
PubMedDate not supplied

Clinical outcome of glass-fiber-reinforced crowns and fixed partial dentures: a three-year retrospective study.

OBJECTIVE: Glass-fiber-reinforced resin composites for the fabrication of esthetic single crowns and fixed partial dentures have been developed recently. However, little data on the clinical outcome of such restorations have been published. The purpose of this retrospective study was to evaluate the clinical outcome of crowns and fixed partial dentures made from the glass-fiber-reinforced resin composite material Targis/Vectris. METHOD AND MATERIALS: Between 1995 and 1997, 39 patients were treated with 67 single crowns and 83 fixed partial dentures. Twenty-five crowns and 28 fixed partial dentures were cemented with temporary cement, while 42 crowns and 55 fixed partial dentures were cemented with either zinc-phosphate cement or glass-ionomer cement. RESULTS: In September 2001, 57 restorations in 17 patients were still in function. The three-year survival rate calculated according to the Kaplan-Meier method was 58.8% for all restorations. However, after this time, it was 37.5% for crowns and 59.9% for fixed partial dentures cemented with temporary cement, and 55.1% for crowns and 67.9% for fixed partial dentures cemented with zinc phosphate or glass ionomer. The differences between the restoration groups were not statistically significant. CONCLUSION: Glass-fiber-reinforced crowns and fixed partial dentures made with the glass-fiber-reinforced resin composite material Targis/Vectris showed a lower survival rate than that published for metal-ceramic crowns and fixed partial dentures. Therefore, the use of this material for the fabrication of single crowns or fixed partial dentures as permanent restorations cannot be recommended.

Adult↗
PubMedDate not supplied

Clinical evaluation of marginal fit of a new experimental all-ceramic system before and after cementation.

PURPOSE: The purpose of this in vivo study was to evaluate the marginal fit of inlay and crown abutments for fixed partial dentures (FPD) made from a new all-ceramic material. MATERIALS AND METHODS: Sixteen patients were selected for the study. After abutment preparation, impressions were made and master dies were fabricated. FPDs were made with the experimental heat-pressed lithium-disilicate glass-ceramic following the manufacturer's recommendations. At random, one abutment of each FPD was chosen for evaluation (11 crown and 8 inlay abutments). Impressions of the restoration margins were taken before and after adhesive cementation. Replicas of the abutment margins were investigated by SEM. The marginal discrepancies were evaluated in sections of 200 microm. The highest value of each section was applied, and the mean of all sections of each replica was used for statistical analysis. RESULTS: The median of the marginal discrepancies before cementation was 96 microm for crowns and 89 microm for inlays. After adhesive cementation, the median increased for crowns to 130 microm and for inlays to 92 microm, a significant increase in the marginal discrepancies caused by cementation for crowns, but not for inlays. There were no significant differences between the discrepancies of crowns and inlays before or after cementation. CONCLUSION: The maximum marginal discrepancies found in this study were between 50 and 265 microm before cementation and between 70 and 285 microm after cementation, with no significant differences between the means for crowns and inlays. Adhesive cementation caused a significant increase of the marginal discrepancies for crown, but not inlay, abutments.

Cementation↗
PubMedDate not supplied

Assessment of dental appearance following changes in incisor angulation.

PURPOSE: This study evaluated the assessment of attractiveness of standardized changes in incisor angulation of different tooth arrangements. MATERIALS AND METHODS: Four sets of images showing the maxillary anterior teeth without lips against a black background were used for evaluation. Each set contained the original photograph, one computer-manipulated symmetric image, and four images with different standardized changes in incisor angulation (10 degrees). The judges, consisting of three groups (30 dental students, 30 medical students, 30 art students), ranked each photo set for attractiveness from 1 (most attractive) to 6 (most unattractive). RESULTS: The mean ranking (in parentheses) showed that symmetric teeth with ideal axes (2.5) and changes in the angulation of one (2.8) or both (2.5) lateral incisors were significantly more attractive than the angulation of one (4.2) or both (4.6) central incisors. There were no differences between the groups of participants. All findings were reproducible. CONCLUSION: Tooth arrangements showing central incisors with ideal axes were more attractive. Slight changes in the angulation of one or both lateral incisors did not influence attractiveness negatively.

Adult↗
PubMedDate not supplied

A preliminary prospective evaluation of all-ceramic crown-retained and inlay-retained fixed partial dentures.

PURPOSE: The purpose of this preliminary prospective study was to evaluate the clinical outcome of crown-retained and inlay-retained fixed partial dentures (FPDs) made from a new lithium-disilicate glass-ceramic (IPS e.max Press, Ivoclar Vivadent). MATERIALS AND METHODS: Eighty-one 3-unit FPDs were placed in 68 patients. The FPDs replaced teeth in the anterior (8%) and posterior region (92%). All teeth were prepared according to a standardized protocol. The size of the proximal connector of the FPDs was 12 mm2 (anterior) or 16 mm2 (posterior), respectively. Crown-retained FPDs were cemented either with glass ionomer (n = 20) or resin composite (n = 16), while all inlay-retained FPDs (n = 45) were cemented with resin composite. Initial follow-up was performed at 6 and 12 months and annually thereafter. RESULTS: The mean observation periods were 48 months (for crown-retained FPDs) and 37 months (for inlay-retained FPDs). None of the crown-retained FPDs failed during the observation period, while 6 inlay-retained FPDs (13%) had to be replaced. Six cases failed because of debonding (n = 3) or a combination of debonding and fracture (n = 3). During the observation period, 2 patients died and the status of another 5 patients is unknown. The 4-year survival rate according to Kaplan-Meier was 100% for crown-retained FPDs and 89% for inlay-retained FPDs. The differences between the groups were statistically significant. CONCLUSION: Crown-retained 3-unit FPDs made from a new glass-ceramic have a significantly better outcome up to 5 years than inlay-retained 3-unit FPDs over the observation period.

Adult↗
PubMedDate not supplied

In vitro evaluation of bacterial leakage along the implant-abutment interface of different implant systems.

PURPOSE: Microbial leakage and colonization between implants and their abutments may cause inflammatory reactions in the peri-implant tissues. This study evaluated microbial leakage at the implant-abutment interface with a new in vitro model. MATERIALS AND METHODS: Bacterial leakage was tested during dynamic loading in a 2-axis chewing simulator. The authors theorized that dynamic loading would decrease the stability of the implant-abutment connections and thereby lead to bacterial penetration along the gap. Five different implant systems with 8 standard implant-abutment combinations for single molar crowns were tested. The internal aspects of the implants were inoculated with a bacterial suspension and connected to the superstructure with the recommended torque. The specimens were immersed in a nutrient solution and loaded with 1,200,000 cycles of 120 N in the chewing simulator. RESULTS: Statistically significant differences (P < or = .05) between implant systems with respect to number of chewing cycles until bacterial penetration were found. DISCUSSION: The degree of penetration in a specific implant system presumably is a multifactorial condition dependent on the precision of fit between the implant and the abutment, the degree of micromovement between the components, and the torque forces used to connect them. CONCLUSION: It was concluded that the newly developed test model is a sensitive tool for the detection of differences between current implant systems with respect to their ability to prevent bacterial penetration at the implant-abutment interface under dynamic loading conditions.

Dental Abutments↗
PubMedDate not supplied

Retention forces and seating discrepancies of implant-retained castings after cementation.

PURPOSE: The purpose of this in vitro study was to evaluate the influence of cement type and application technique on seating discrepancies and retention forces of noble alloy castings cemented on titanium abutments. MATERIALS AND METHODS: Eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (KetacCem), polycarboxylate (Durelon), and self-adhesive resin (RelyX Unicem) cements were used. The inner surfaces of the castings were either completely coated or half-coated with cement. Abutments were used as delivered with a machined surface for the first part of the study. Groups of 8 castings were cemented in both ways. For the second part of the study, the abutments were air-abraded (aluminum oxide, 50 microm particle size), and groups of 8 completely coated castings were cemented with all cements. Marginal discrepancies were measured before and immediately after cementation. Tensile tests were conducted to measure the retention forces. Statistical analysis was performed with pair-wise comparison using the Wilcoxon rank sum test modified by Bonferroni-Holm. RESULTS: Change in seating discrepancies did not differ significantly among the different application techniques. The median retention forces for completely-coated castings were 177 N for eugenol-free zinc oxide, 346 N for zinc phosphate, 469 N for glass ionomer, 813 N for polycarboxylate, and 653 N for self-adhesive resin. With respect to retention force, 3 significantly different groups (P < .05) were identified: (1) zinc oxide, (2) zinc phosphate/glass ionomer, and (3) polycarboxylate/self-adhesive resin. No differences in retention between the 2 coating techniques were found for any cement. However, air abrading the abutments resulted in increased retention of the castings for some of the cements. CONCLUSIONS: Half-coating of the restorations with cements did not result in reduced retention values compared to the complete coating technique, but air abrasion resulted in increased retention with some cements.

Air Abrasion, Dental↗