staining with black tea. Re-polishing the stained specimens did not result in change of shade, indicating that the discoloration was intrinsic. Conclusion: Highly polymerized CAD/CAM PMMA materials showed better color stability than conventionally cold-cured or 3D printed provisional materials. Glazing does not improve color stability. Discoloration is dependent on the staining media used, resulting in intrinsic rather than extrinsic staining. Poster #: 31 Title: Effect of rotational misfit of implant components on marginal fit Name: Dan Lin Faculty Advisor: Winston Chee Background: With implant components, there is a need for a “non-rotational” feature to fix the components in a certain position, but also a necessary tolerance to allow parts to fit together. This intended “rotational misfit” between components can be between 1.6-5.3 and is commonly misunderstood. With greater rotational play, the fit of a multi-unit cemented prosthesis on the abutments may be adversely affected. Purpose: The purpose of this study is to demonstrate the effect of rotational misfit of pre-angled abutments that need to be precisely located from master cast to the oral cavity on the marginal fit of a multi-unit prosthesis. Methods: A pre-angled abutment and straight abutment were mounted in plaster and a 3-unit fixed prosthesis to these abutments fabricated. The prosthesis was cemented on the abutments and the marginal gap evaluated. Horizontal rotational differences of 0, 0.5, 1,1.5, and 2 between implant components were tested. Results: An increase in rotational misfit of the angled abutment caused a significant increase in marginal gap between the prosthesis and abutments. Conclusion: The rotational misfit of implant components will significantly impact the fit of a cement-retained restoration to the abutments. Due to the built-in tolerances of implant components, it is technically impossible to achieve precise relocation of the abutments. Therefore, it can be assumed that cemented multi-unit restorations often do not seat as intended on abutments. Poster #: 32 Title: Dimensional changes follow-
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ing extraction of maxillary molars Name: Peiman Mehirar Faculty Advisor: Homa Zadeh
olar bone can potentially compromise implant therapy, requiring additional augmentation procedures.
Poster #: 34 Title: Histological analysis of healing following ridge preservation with different biomaterials Name: Julio Moreno-Aleman Sanchez Faculty Advisor: Homa Zadeh
an inevitable consequence of tooth extraction. Atrophy of the alveolar ridge may cause aesthetic and functional problems, such as inadequate bone for the placement of dental implants. Ridge preservation has been proposed as a strategy to reduce post-extraction bone resorption. This study examined the histologic response of alveolar bone following ridge preservation. The biomaterial used included Biphasic Graft Material (BGM), which is a resorbable inorganic material derived from red marine algae. BGM consisted of 20% hydroxyapatite and 80% β- tricalciumphosphate. Leukocyte-platelet rich fibrin (L-PRF) was used in another group. Purpose: To examine the histologic response of alveolar bone following ridge preservation Methods: Thirty-six extraction sockets in 29 patients were randomly assigned to the following four treatment modalities: A: unassisted wound healing; B: L-PRF; C: collagen membrane alone; D: BGM+collagen membrane. Bone core was harvested at 4 months post-extraction for histologic and histomorphometric analysis of wound healing. Results: Histologic observations revealed no signs of inflammation. All groups demonstrated that distinct reversal lines were evident in the woven bone, and in areas of active apposition osteoblast-like cells as well as osteoclast-like cell were observed within Howship’s lacunae. Histomorphometric analysis revealed the percentage of bone volume relative to tissue volume (BV/TV) for unassisted wound healing, L-PRF, collagen membrane alone, and BGM+ collagen membrane were 44±20%, 46±26% 34±14%, and 29±21% respectively. The only statistically significant difference detected was between L-PRF and BGM+collagen membrane (p=0.04). Conclusion: The results of vital bone formation observed in the present study were consistent with previous publications. The application of L-PRF was associated with significantly more vital bone than sockets with BGM+collagen membrane. Data regarding the influence of dimensional changes of sockets in various groups is currently under analysis and will be necessary before clinical recommendations can be made.
Background: There is little evidence of dimensional changes of the alveolar crest following extraction of maxillary molars. Purpose: To investigate retrospectively the dimensional changes that occur in the alveolar crest following extraction of maxillary molars and unassisted healing by performing 3D measurements on cone beam computerized tomography (CBCT) scans. Methods: The population of patients who, between March of 2009 and June of 2015, had presented to the Ostrow School of Dentistry of USC for extraction of maxillary molars and had a CBCT taken at both pre- and post-extraction was included in this study. Only those sockets that had undergone unassisted healing were included. Twenty-two patients were identified who had required a total of twenty-four teeth to be extracted. Linear measurements were performed using SIMPLANT PRO 6.0 software. Fixed anatomic locations were used as reference points in order to compare pre- and post-extraction dimensions of the alveolar bone. Results: Quantitative analysis of CBCT images demonstrated that the mean (+SD) horizontal thickness of the alveolar bone in the maxillary molar area was 10.4+4.9, 12.1+3.8, 12.8+3.0, 13.4+1.6 mm at 1, 2, 3 and 5mm apical to the alveolar crest, respectively. Following a healing period of 10.9+11.5 months, post-op ridge remodeling was measured as being 84.6+29.3, 68.0+32.7, 49.8+30.8 and 29.1+32.0% of the original width of the alveolar bone at 1, 2, 3 and 5mm apical to the alveolar crest, respectively. The alveolar crest also underwent 2.4+1.4mm of vertical bone loss. Correlations between bone to cementoenamel junction distance on the palate and vertical palatal resorption (P=0.01); mean vertical resorption and mean horizontal resorption (P=0.05); and mean horizontal resorption and palatal plate thickness (P=0.01) correlations were statistically significant. Conclusion: Extraction of maxillary molar teeth without additional intervention led to extensive horizontal and vertical bone atrophy that extends at least up to 5mm apical to the original crest. The extensive loss of alve-
Poster #: 33 Title: Programmable orthodontic expander for treating cleft lip and palate Name: Ana Moneu Faculty Advisor: Stephen Yen
Background: Alveolar ridge resorption has been considered as
Poster #: 35 Title: Mouse model for orthodon-
Background: Orthodontic preparation for an alveolar bone graft in children with cleft lip and palate requires orthodontic repositioning of the cleft segments into a U-shaped arch that can coordinate with the lower dentition. Current methods for orthodontic expansion require multiple patient visits and orthodontic laboratory support to build the expanders. Purpose: The purpose of this study is to evaluate a nickel titanium expander that is reprogrammed by electric current to expand the maxillary segments to a target expansion position. Methods: Under an IRB approved protocol, 19 patients were expanded using nickel titanium expanders that required on average one visit to band and weld lingual sheaths and one visit to program the expander and insert the expander into the sheaths. After 2-3 months, the patients were expanded to ideal position based on intraoral measurements. The patients were grafted and followed with a study model and occlusal radiograph at 3 months post-surgery. At 6 months, a restricted-view conebeam CT will be taken. Results: Thus far, all 19 patients were expanded in preparation for the alveolar bone graft. Multiple adjustment visits were not necessary. Overall, this expander reduced patient visits, avoided laboratory costs and was accepted by young patients. Complications included breakage of the lingual sheaths, and embedding of the tall springs in palatal tissue. Conclusion: The programmable expander can expand the maxilla comparably with the current methods of rapid palatal expansion (RPE) and quad helices with fewer visits.
The Explorer Journal 2017