Development of silicon nitride ceramic for CAD/CAM restoration.

White Silicon nitride (Si3N4) ceramic has unique characteristics. Because of its high fracture toughness, strength, and biocompatibility, it can therefore be used to fabricate dental restorations. The purpose of this study was to produce partially-sintered block of Si3N4 for fabrication of CAD/CAM dental restorations. The related properties of this novel Si3N4 were evaluated including sintered shrinkage, flexural strength and fracture toughness. Partially sintered Si3N4 ceramic blocks were prepared by heating at 1,400°C for 2 h under N2 gas. After full sintering at 1,650oC for 2 h, the linear shrinkage value was recorded at 19.88±0.56%. The flexural strength and fracture toughness were measured, the results were 891.21±37.25 MPa and 6.33±0.30 MPa•m1/2, respectively. These results showed that flexural strength and fracture toughness of Si3N4 were more than 800 MPa and 5 MPa•m1/2, the white Si3N4 developed in this study can be used to fabricate multi-unit dental restorations According to ISO 6872.

Trephination-based, guided surgical implant placement: A clinical study.

STATEMENT OF PROBLEM: Conventional guided implant surgery promises clinical success through implant placement accuracy; however, it requires multiple drills along with surgical sleeves and sleeve adapters for the horizontal and vertical control of osteotomy drills. This results in cumbersome surgery, problems with patients having limited mouth opening, and restriction to specific drill or implant manufacturers. A protocol for using trephination drills to simplify guided surgery and accommodate multiple implant systems is introduced. PURPOSE: The purpose of this clinical study was to evaluate the accuracy of implant placement using this novel guided trephine drill protocol with and without a surgical sleeve. MATERIAL AND METHODS: Intraoral scanning and preoperative cone beam computed tomography (CBCT) scans were used for implant treatment planning. Surgical guides were fabricated using stereolithography. Implant surgery was performed using the guided trephination protocol with and without a surgical sleeve. Postoperative CBCT scans were used to measure the implant placement deviations rather than the implant planning position. Surgical placement time and patient satisfaction were also documented. One-tailed t test and F-test (P=.01) were used to determine statistical significance. RESULTS: Thirty-five implants in 17 participants were included in this study. With a surgical sleeve, implant positional deviations were 0.51 ±0.13 mm vertically, 0.32 ±0.10 mm facially, 0.11 ±0.11 mm lingually, and 0.38 ±0.13 mm mesially. Without a surgical sleeve, implant positional deviations were 0.58 ±0.27 mm vertically, 0.3 ±0.14 mm facially, 0.39 ±0.16 mm lingually, and 0.41 ±0.12 mm mesially. No statistically significant difference was found between the 2 protocols (P>.01), except that the sleeve group had greater vertical control precision (F-test, P=.006), reduced placement time, and the time variation was reduced (t test, P=.003; F-test, P<.001). CONCLUSIONS: This trephination-based, guided implant surgery protocol produces accurate surgical guides that permit guided surgery in limited vertical access and with the same guided surgery protocol for multiple implant systems. Guided sleeves, although not always necessary, improve depth control and reduce surgical time in implant placement.

Comparison of excursive occlusal force parameters in post-orthodontic and non-orthodontic subjects using T-Scan® III.

OBJECTIVE: Published studies indicate that orthodontically treated patients demonstrate increased posterior occlusal friction contributing to temporomandibular disorder (TMD) symptoms. This study investigated measured excursive movement occlusal contact parameters and their association with TMD symptoms between non- and post-orthodontic subjects. METHODS: Twenty-five post-orthodontic and 25 non-orthodontic subjects underwent T-Scan® computerized occlusal analysis to determine their disclusion time (DT), the excursive frictional contacts, and occlusal scheme. Each subject answered a TMD questionnaire to determine the presence or absence of TMD symptoms. Statistical analysis compared the within group and between group differences (p < 0.05). RESULTS: Statistically significant differences were observed in the disclusion time: DT = 2.69 s in the post-orthodontic and 1.36 s in the non-orthodontic group. In the non-orthodontic group, 72.7% working and 27.3% non-working side contacts were seen, while in the post-orthodontic group, (near equal) 54.7% working and 45.3% non-working side contacts were seen. Presence of canine guidance was seen in 60% of the non-orthodontic group and 24% in the post-orthodontic group. Seventy-two percent of the post orthodontics subjects presented with one or more TMD symptoms. CONCLUSION: Significantly longer disclusion time, higher posterior frictional contacts, and more TMD symptoms were observed in the post-orthodontic group, suggesting that orthodontic treatment increases posterior tooth friction. Computerized occlusal analysis is an objective diagnostic tool determining the quality of excursive movements following orthodontic treatment.