The study examined the effect of noninvasive crown retrieval/reuse process using an erbium-doped yttrium aluminum garnet laser (Er:YAG). Twenty-six extracted human teeth were prepared for a crown. The crown was milled using lithium disilicate (LD) and zirconia (Z) materials, n = 13 per group, with three for scanning electron microscopy (SEM). The crown was luted using composite resin cement and subjected to a laser retrieval process. After the retrieval process, the crown was cleaned, re-cemented and laser-retrieved two more times, without and with additional tooth reduction mimicking clinical refreshment of dentin. Retrieval time and temperature were analyzed using analysis of variance (ANOVA). Surface changes were observed through SEM. The retrieval times were 267.1 ± 130.43, 220 ± 79.09, 277.1 ± 126.44, 368.4 ± 136.14, 355 ± 159.39, and 419.2 ± 121.36 s for first, second, third LD and Z groups, respectively (p = 0.009). The maximal temperatures were 23.95.1 ± 1.89 °C, 24.86 ± 2.01 °C, 24.17 ± 1.53 °C, 22.88 ± 1.51 °C, 24.03 ± 1.74 °C, and 21.99 ± 1.32 °C for first, second, third LD and Z groups, respectively (p = 0.006). Er:YAG laser crown removal is an effective retrieval tool for all-ceramic crowns. Minimal changes to teeth and crowns were observed following laser irradiation.

Background. Reduced tooth structure in the pediatric and adolescent population is frequently restored with prefabricated zirconia crowns. On permanent teeth, these restorations may need to be removed and replaced with permanent restorations. Objectives.To explore and compare the use of 2 high-powered erbium lasers for removing prefabricated zirconia crowns from molar teeth as a non-invasive alternative to rotary instruments.Material and methods. Twenty-five permanent molars were prepared to dentin and prefabricated all-ceramic zirconia crowns were fitted and cemented with resin modified glass ionomer (RMGI) cement. The teeth were randomly assigned into one of the 2 retrieval treatment groups: the erbium-doped yttrium, aluminum and garnet (Er:YAG) laser group (G1; n = 12) or the erbium, chromium-doped yttrium, scandium, gallium and garnet laser (Er,Cr:YSGG) laser group (G2; n = 13). The laser operating parameters for the Er:YAG laser were 300 mJ, 15 Hz, 4.5 W, and 50-microsecond pulse duration (SSP mode); for the Er,Cr:YSGG laser, they were 4.5 W, 15 Hz, 20 water/20 air, and 5 W, 15 Hz, 50 water/50 air, and 60-microsecond pulse duration (H mode). The experiment was repeated twice. The surface area and the volume of teeth and crowns were measured and the cement space was calculated. The retrieval time and temperature changes were tested and recorded. The data were analyzed with the t-test. The surfaces of the dentin and the crown from each group were further examined using scanning electron microscopy (SEM).Results. The average time for crown removal using the Er:YAG laser was 1 min 32.7 s; for the Er,Cr:YSGG laser it was 3 min 13.9 s (p < 0.0001). The mean temperature changes were 1.41 ±1.36°C for the Er:YAG laser and 2.2 ±0.99°C for the Er,Cr:YSGG laser (p = 0.0321). The SEM examination showed no damage or major structural changes caused by treatment with either erbium-family laser.Conclusions. Both lasers are effective, non-invasive tools to remove prefabricated zirconia crowns cemented with resin cement and should be considered as viable alternatives to rotary instrumentation.

Introduction: Various guiding methods are used to place implants. This ex vivo pilot study used a convenience sample to examine time and accuracy for placement of two dental implants supporting a three-unit fixed prosthesis on a simulation model using a freehand and three guided placement techniques. Material and methods: Four operators with no prior implant placement experiences were randomly assigned placement of two maxillary or mandibular implants for a fixed prosthesis. Techniques included dynamic navigation (DN), static guide (SG), template-based guide (TBG) and freehand placement (FH). Preoperative and operative times were recorded. Discrepancies between the planned and placed implant positions were assessed by superimposing preoperative and postoperative CBCT scans. Data were analyzed with repeated measures regression with Tukey's adjusted pairwise comparisons (α = 0.05). Results: Dynamic navigation was associated with the longest operative time (13.5 mins vs 5-10.2, p=0.0001) but overall fastest when incorporating preoperative time (32.1 minutes vs. 143-181.5, p&lt;0.0001). All deviations measures were significantly associated with the placement method (p&lt;0.05) except apex vertical deviation (p=0.3925). Implants placed by SG had significantly lower entry 2D deviation than the other methods, particularly on the mandible. The DN and SG methods had significantly lower Apex 3D and overall angle deviations, again particularly on the mandible. The mandible had significantly higher deviations than maxilla. Conclusions: Within the limitations of this study, implant placement by novice operators is more accurate when using dynamic and static guidance in comparison to freehand and template-based techniques.

The study examined the effect of noninvasive crown retrieval/reuse process using erbium-doped yttrium aluminum garnet laser (Er:YAG). Twenty-six extracted human teeth were prepared for a crown. The crown was milled using lithium disilicate (LD) and zirconia (Z) materials, n=13 per group, 3 for scanning electron microscopy (SEM). The crown was luted using composite resin cement and subjected to a laser retrieval process. After the retrieval process, the crown was cleaned, recemented and laser-retrieved two more times, without and with additional tooth reduction mimicking clinical refreshment of dentin. Retrieval time and temperature were analyzed using analysis of variance (ANOVA). Surface changes were observed through SEM. The retrieval times were 267.1&plusmn;130.43, 220&plusmn;79.09, 277.1&plusmn;126.44, 368.4&plusmn;136.14, 355&plusmn;159.39, and 419.2&plusmn;121.36 seconds for first, second, third LD and Z groups, respectively (p=.009). The maximal temperatures were 23.95.1&plusmn;1.89&deg;C, 24.86&plusmn;2.01&deg;C, 24.17&plusmn;1.53&deg;C, 22.88&plusmn;1.51&deg;C, 24.03&plusmn;1.74&deg;C, and 21.99&plusmn;1.32&deg;C for for first, second, third LD and Z groups, respectively (p=.006). Er:YAG laser crown removal is an effective retrieval tool for all-ceramic crowns. Minimal changes to teeth and crowns were observed following laser irradiation.