Retention of CAD/CAM resin composite crowns following different bonding protocols.

PURPOSE: To evaluate the effect of different surface treatments and primers with a CAD/CAM resin composite block on its crown retention. METHODS: 120 human molars were prepared with a 24° total convergence angle, 1.5 mm height, and axial walls in dentin. Surface area was measured by digital microscopy. Crowns were machined from CAD/CAM resin composite blocks. Teeth were randomly allocated to 12 groups (n= 10) based on possible combinations of three surface treatments: [Control, Alumina air abrasion (50-µm Al2O3 at 0.28 MPa) ]; 5% hydrofluoric acid etch (20-second scrub); silane application (with or without Kerr Silane primer); and adhesive application (with or without Optibond XTR Adhesive). Optibond XTR Adhesive was applied to the tooth preparations and crowns were bonded with MaxCem Elite cement. Crowns were fatigued for 100,000 cycles at 100 N in water and debonded in tension (1 mm/minute). Crown retention strength (maximum load/surface area) values were analyzed using a three-way ANOVA with Tukey's post-hoc tests (α= 0.05). RESULTS: Surface treatment, silane and adhesive applications independently affect retention force (P< 0.05). All interactions were not significant (P> 0.05). Alumina airborne abrasion surface treatment, silane and adhesive applications all improve retention strength. Therefore, CAD/CAM resin composite crowns can withstand debonding while undergoing mechanical fatigue. Although all forms of surface treatment and primer application improve bond strength, the highest mean retention strength values were recorded when the crowns were alumina particle abraded and coated with adhesive (with or without silane). CLINICAL SIGNIFICANCE: In order to improve the bonding of resin composite crowns, application of alumina airborne particle abrasion and a coat of adhesive (proceeded by an optional coat of silane) is recommended. If hydrofluoric acid is utilized, the crowns should be treated with a coat of silane followed by adhesive application.

Machinability of CAD-CAM materials.

STATEMENT OF PROBLEM: Although new materials are available for computer-aided design and computer-aided manufacturing (CAD-CAM) fabrication, limited information is available regarding their machinability. The depth of penetration of a milling tool into a material during a timed milling cycle may indicate its machinability. PURPOSE: The purpose of this in vitro study was to compare the tool penetration rate for 2 polymer-containing CAD-CAM materials (Lava Ultimate and Enamic) and 2 ceramic-based CAD-CAM materials (e.max CAD and Celtra Duo). MATERIAL AND METHODS: The materials were sectioned into 4-mm-thick specimens (n=5/material) and polished with 320-grit SiC paper. Each specimen was loaded into a custom milling apparatus. The apparatus pushed the specimens against a milling tool (E4D Tapered 2016000) rotating at 40 000 RPM with a constant force of 0.98 N. After a 6-minute timed milling cycle, the length of each milling cut was measured with image analysis software under a digital light microscope. Representative specimens and milling tools were examined with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy. RESULTS: The penetration rate of Lava Ultimate (3.21 ±0.46 mm/min) and Enamic (2.53 ±0.57 mm/min) was significantly greater than that of e.max CAD (1.12 ±0.32 mm/min) or Celtra Duo (0.80 ±0.21 mm/min) materials. SEM observations showed little tool damage, regardless of material type. Residual material was found on the tools used with polymer-containing materials, and wear of the embedding medium was seen on the tools used with the ceramic-based materials. Edge chipping was noted on cuts made in the ceramic-based materials. CONCLUSIONS: Lava Ultimate and Enamic have greater machinability and less edge chipping than e.max CAD and Celtra Duo.

Evaluation of Different Polishing Systems and Speeds for Dental Zirconia.

PURPOSE: To evaluate two polishing systems and three polishing speeds on the gloss, roughness, and heat production of yttria stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS: A Y-TZP block (Zenostar Zr Translucent) was sectioned into 4-mm-thick sections. Specimens (n = 30 per polishing system) were first wet ground with a fine diamond bur at 200,000 RPM for 15 seconds. The baseline gloss of all specimens was measured in a glossmeter (60° angle) in a direction perpendicular to grinding. Initial surface roughness (Ra ) was determined on an optical profilometer in a direction perpendicular to grinding. The specimens were then polished with either a Dialite ZR Polishing Kit or a CeraMaster Polishing Kit. All grinding and polishing was performed by the same operator calibrated to apply approximately 2 N pressure. The medium grit polisher was used for 30 seconds, repeated for 30 seconds, and then the fine grit polisher was used. After each step, the gloss and roughness of each specimen was remeasured as described previously. Each polishing system was used at 5000, 15,000, and 40,000 RPM (n = 10 for each polish system/speed combination). A group of glazed specimens (n = 10) was evaluated for gloss and roughness as a control. The heat generated for each polishing step was measured with a thermocouple. The gloss and roughness of the specimens were analyzed using a linear mixed model and Tukey-Kramer post-hoc tests. Each step of polishing was compared to the glazed control group with an ANOVA and Dunnett's test. RESULTS: Polishing step, system, and speed were significant (p < 0.05) for gloss and roughness. Examination of system and step interaction was significant for gloss only. Post-hoc analysis revealed that 15,000 RPM produced higher gloss and lower roughness than other speeds. Each progressive step produced an improvement in gloss except for initial 30 seconds with the CeraMaster Coarse (medium polisher; p = 0.34). Roughness was also reduced at each progressive step. No polishing speed/system produced an increase in temperature above 41°C. Both polishing systems were capable of achieving a similar or superior roughness and gloss as the glazed control specimens after the final polishing step at 15,000 RPM. CONCLUSIONS: Fifteen thousand RPM is an optimal polishing speed. Progressing through the polishing sequence significantly improves gloss and roughness and can create similar values as glazed zirconia.

Bonding a veneered zirconia anterior fixed partial denture.

This case report documents the rationale and procedure for bonding a veneered zirconia restoration. A three-unit zirconia fixed partial denture (FPD) was fabricated with facial and incisal porcelain veneering. The intaglio surface of the prosthesis was abraded with 50-µm aluminum oxide (Al2O3) particles and coated with one layer of a 10-methacryloxydecyl dihydrogen phosphate (MDP) primer. The FPD was tried into the mouth and occlusal adjustment was performed with a fine grit diamond, and then it was polished with zirconia polishing points. The intaglio surfaces of the abutment crowns were cleaned with 37% phosphoric acid and rinsed. A self-etch adhesive was applied to the tooth preparations and light-cured, and the crowns were filled with cement and seated. Excess cement was immediately wiped away with a brush, followed by spot-curing of the margins. The case demonstrates that, when properly designed, veneered zirconia restorations offer acceptable esthetic and mechanical properties for anterior FPDs.

A residual granuloma in association with a dental implant.

At times, dental implants are placed into sites with a history of periapical pathology. Sometimes the infection is active, and other times the tooth may have been extracted years before implant placement. In either case, the possibility exists for long-term residual cysts or infections that can negatively impact the prognosis of the implant. In this case report, an implant is placed into a healed mandibular ridge several months after extraction of the tooth. A radiolucency was noted on routine radiographic examination 2 years later. Surgical inspection and histology revealed a periapical granuloma with acute and chronic inflammatory cells. After surgical curettage of the site, the patient healed without complication. Implants may develop apical pathology as a result of a preexisting long-term residual infection.

Bone associated with implants in diabetic and insulin-treated rats.

OBJECTIVES: Diabetes is an increasingly prevalent disease with oral health manifestations. While diabetes clearly has an affect on bone, its impact on the healing of bone associated with dental implants is not completely understood. The purpose of this study was to measure bone response to implants in uncontrolled and insulin-controlled diabetic rats. MATERIAL AND METHODS: One hundred and fifty-two rats were divided into control, diabetic, and insulin groups. Rats received streptozotocin (65 mg/kg) to induce diabetes; animals in the insulin group also received a subcutaneous slow-release insulin implant. Titanium alloy implants (1.5 x 8 mm) were placed in the proximal tibiae of animals. Implants were harvested at 2, 7, 14, and 24 days and examined histologically. Bone or bone-like tissue adjacent to implants was quantified as a percent. Data were compared using a two-way analysis is variance (ANOVA) with time and treatment as primary independent factors. RESULTS: Time and treatment were significant factors in predicting bone response to implants (P<0.0001). Mean bone volume peaked at day 7 and decreased over time to day 24. Mean bone volume percent at 2, 7, 14, and 24 days (+/-SD) was 8.2 (+/-8), 22.9 (+/-8), 18.8 (+/-10), and 14.9 (+/-9), respectively. Mean total bone volume percent (adjusted for day) for control, diabetic, and insulin groups (+/-SD) was 12.4 (+/-9), 22.6 (+/-10), and 17 (+/-7), respectively. Bone volume adjacent to implants in diabetic rats was significantly greater than controls (P<0.05). Diabetic animals treated with insulin were not statistically different from controls. CONCLUSIONS: Induction of diabetes with STZ is associated with increased bone response compared with controls. This response was mediated by treatment with insulin.