GSDM: Historical Theses and Dissertations (BU access only)

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This is a historical collection of GSDM Theses and Dissertations that were originally submitted in print from 1964-2015. For more recent Dental School theses and dissertations, please go to the BU Theses & Dissertations Collection: https://open.bu.edu/handle/2144/8520.

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Description of media's influence on the retention of dental health messages among school-age children through the use of posters
(Boston University, 1982) Ziaii, Maryam
The purpose of this project was to assess the impact of the media on children's dental health awareness through the analysis of 400 posters constructed by selected school-age children. The posters were to contain messages of dental health in formation either obtained through the media or through classroom dental health education. In addition, this project examined the relationship of children participating in a fluoride mouthrinse program on the type of dental health message presented in the posters. Selected literature related to the area of investigation was reviewed. Results of the project indicated that there was a significant difference between posters with good oral health messages and poor oral health messages. In general, posters showing brushing and the use of fluoride toothpaste were the most popular. Almost half of the posters reviewed had messages that were received directly from television commercials. This project demonstrated that there was no significant difference between the posters from the group that participated in a fluoride mouthrinse program and the group that did not participate in the mouthrinse program. The results of this project show that television is a powerful vehicle for communication, because children came into more frequent contact with television than other form of mass media. It is recommended that more television time be made available for the presentation of useful dental health information in an interesting way in educating both children and adults.
A double-blind, placebo-controlled, single-dose parallel study of the analgesic safety and efficacy of oxycodone HCL/ibuprofen 5/400 mg compared to ibuprofen 400 mg alone and oxycodone HCL 5 mg alone in patients with moderate to severe pain following dental surgery
(Boston University, 2003) Zarringhalam, Nooshin Majd
In order to compare the efficacy and safety of a single-dose oral combination of oxycodone and ibuprofen to that of either drug alone and placebo for the treatment of acute postoperative pain, 498 patients were randomized in this double-blind, placebo and active-controlled, multicenter, parallel study. Patients with moderate to severe pain following surgical removal of at least 2 ipsilateral bony impacted third molars received a single dose of oxycodone/ibuprofen 5/400 rng combination or identical doses of either drug alone or placebo. The primary efficacy parameters were Total Pain Relief and Sum of Pain Intensity Difference over 6 hours (TOTPAR 6,SPID 6). Other endpoints included time to onset and a global evaluation score by the patient. Analysis of the data indicated that there was a significantly greater reduction in pain intensity and increased pain relief with oxycodone/ibuprofen treatment compared with ibuprofen alone over the entire 6- hour evaluation period(SPID 6, TOTPAR 6, P[less than]0.05), oxycodone alone (TOTPAR 6 and SPID 6, P[less than]0.001), or placebo (TOTPAR 6 and SPID 6, P[less than]0.001). Oxycodone/ibuprofen had an earlier onset of analgesia compared with ibuprofen(P[less than]0.01) or oxycodone alone (P[less than]0.001). The combination treatment had a 28% faster median time to onset of pain relief than did ibuprofen alone (21.4 vs. 29.7 minutes). Global Evaluation scores for patients receiving the combination treatment were significantly superior to those for patients receiving itouprofen (P[less than]0.01) or oxycodone (P[less than]0.001) alone. The most common treatment-emergent adverse events (TEAEs) were nausea and vomiting. There was no difference in the incidence of TEAEs among the combination, ibuprofen, and placebo groups. Patients receiving oxycodone alone had the highest incidence of TEAEs. It was concluded that oxycodone/ibuprofen combination provides statistically significant and clinically superior analgesia in acute postoperative pain compared with identical doses of each component alone or placebo. The combination drug was also safe and well tolerated.
Mesiodistal width of second primary molars in flush terminal plane occlusion :
(Boston University, 1990) Zafarmand, A Hamid
For years, it has been taught in dental schools that the mesiodistal width of lower primary molars in flush terminal plane type of occlusion are larger than of those in mesial step molar relationship. It has been proven that approximately in two thirds of cases, permanent occlusion can be predicted from molar relationship in primary dentition. This is an emphasis to the fact that primary molars potentially play an important role in establishment of molar relationship in the permanent dentition. Some investigators have shown that there are other factors that influence in determination of molar relationship. Growth of dental arches and path of eruption of tooth are the examples of those parameters that should be taken into consideration. For the purpose of this study, 25 patients were selected who only exhibited primary dentition, contributing 50 cases to this investigation. Each patient was evaluated as two cases of right and left side of the mouth if presented mesial step or flush terminal plane relationship. This study was performed to compare the mesiodistal size of upper and lower primary second molars in flush terminal plane cases with those in mesial step type of molar relationship. This comparison was made by measuring the anteroposterior size of the primary second molars of the above two samples of dental occlusion. The measures were obtained by a boley guage on the dental casts of maxillary and mandibular arches. Findings of this investigation indicate that a larger mesiodistal width of primary second molar exists in flush terminal plane relationship than in mesial step.
The effect of scanning device, spacer setting, and cementing on the marginal and internal fit of CADCAM milled all-ceramic full contour crowns
(Boston University, 2011) Wu, George Ding-Chun
Purpose: The purpose of this study was to evaluate the effect of cement, spacer setting, and three scanners on the marginal gap and internal fit of Sirona CAD/CAM all-ceramic full contour crowns. Materials and Methods: Prepared Ivorine typodont teeth were duplicated using poly-vinyl siloxane and poured with Type IV scannable dental stone. Four groups of twelve dies were divided into: inLab laser scanned dies with crowns milled at a 30 [mu]m spacer setting (in CEREC 3D), InEos red scanned dies with crowns milled at a 30 [mu]m spacer setting, Bluecam scanned dies with crowns milled at a 30 [mu]m spacer setting, and Bluecam scanned dies with crowns milled at a 80 [mu]m spacer setting. All-ceramic crowns were fabricated by a CEREC inLab milling unit using VITA Mark II blocks. Crowns needing adjustments for complete seating to their respective dies were recorded. After adjustments the marginal gap of the milled crowns to their respective dies were measured using an optical microscope. The crowns were then cemented on the dies using resin cement (3M Rely-X Unicem), set into epoxy resin, and sectioned. The marginal gap and internal fit after cementation were measured using an optical microscope. Results: Measurements for the CEREC inLab (30 [mu]m spacer setting) mean marginal gaps after adjustments were 58.00[mu]m±33 .13[mu]m, cemented crowns' marginal gaps 102.13[mu]m±44.64[mu]m, and cemented crowns' internal fit 169.16[mu]m±91.95[mu]m. Measurements for the CEREC Bluecam (30 [mu]m spacer) mean marginal gaps after adjustments were 26.6 l [mu]m±l 4.25[mu]m, cemented crowns' marginal gaps 79.58[mu]m±24 .98[mu]m, and cemented crowns' internal fit 126.26[mu]m±83.10[mu]m. Measurements for the CEREC inEos red (30 [mu]m spacer) mean marginal gaps after adjustments were 28.83[mu]m±l 5.29[mu]m, cemented crowns' marginal gaps l 18.20[mu]m±43.08[mu]m, and cemented crowns ' internal fit 138.49[mu]m±80.14[mu]m. Measurements for the CEREC Bluecam (80 [mu]m spacer) mean marginal gaps after adjustments were 3l. l 7[mu]m±l 1.79[mu]m, cemented crowns' marginal gaps 45.78[mu]m±l5.60[mu]m, and cemented crowns' internal fit 165.72[mu]m±73.58[mu]m. 8 of 12 crowns for the three scanner groups using a 30 [mu]m spacer setting needed adjustments. None of the crowns from the Bluecam (80 [mu]m spacer) group needed adjustments. Conclusion: CEREC CAD/CAM crowns fabricated with a 30 [mu]m spacer setting needed adjustments (8 out of 12 crowns). Crowns fabricated with an 80 [mu]m spacer setting did not need any adjustments. ANOVA and Tukey test revealed that before cementation, full contour all-ceramic crowns milled using a 30 [mu]m spacer setting (in CEREC 3D) and generated by scanning dies with the inLab had marginal gaps that were significantly larger than marginal gaps from crowns milled using a 30 [mu]m spacer setting and generated by dies scanned with the Bluecam, crowns milled using an 80 [mu]m spacer setting and generated by dies scam1ed with the Bluecam, and crowns milled using a 30 [mu]m spacer setting and generated by dies scanned with the inEos Red. After cementation, full contour all-ceramic crowns milled using an 80 [mu]m spacer setting and generated by scanning dies with the Bluecam had marginal gaps that were significantly smaller than marginal gaps from crowns milled using a 30 [mu]m spacer setting and generated by dies scanned with the Bluecam, crowns milled using a 30 [mu]m spacer setting and generated by dies scanned with the inLab, and crowns milled using an 30 [mu]m spacer setting and generated by dies scanned with the inEos Red. Crowns fabricated using an 80 [mu]m spacer setting (Bluecam only) had marginal gaps that did not significantly increase after cementation. Crowns fabricated using a 30 [mu]m spacer setting had marginal gaps that significantly increased after cementation. After cementation, full contour all-ceramic crowns milled using a 80 [mu]m spacer setting and generated by scanning dies with the Bluecam had internal gaps that were similar to the crowns milled using a 30 [mu]m spacer setting and generated by scanning dies with the inLab. However, both these two groups had significantly larger marginal gaps than crowns milled using a 30 [mu]m spacer setting and generated by scanning dies with the Bluecam and crowns milled using a 30 [mu]m spacer setting and generated by scanning dies with the inEos Red. With the CEREC Bluecam, the 80 [mu]m spacer setting delivers better fitting crowns after cementation than those with a 30 [mu]m spacer setting.
The quality of the apical seal of teeth obturated using the System B HeatSource
(Boston University, 1997) Wu, Allen K.
A comparative study of the two techniques to fill the root canals of primary teeth
(Boston University, 1976) Weisz, Alex
A study of replantation of teeth in dogs using nuva-seal pit and fissure sealant and phosphoric acid as experimental agents
(Boston University, 1973) Wadlington, Lucian R.
Replantation has been a subject of interest for centuries, and innumerable case reports of replanted teeth have been published. For 200 years one of the main points of discussion has been whether the teeth should be replanted with or without the periodontal membrane which remains attached to the tooth after extraction. The vitality of the periodontal membrane is directly related to the rapidity of root resorption which is the main cause of tooth loss. The more current research has established that, if the time the tooth has been exposed to the extra-oral environm ent is minimal, the prognosis for the attached periodontal membrane is good. However, in most cases the extraoral exposure time for accidentally avulsed teeth is not minimal and precludes the survival of the ·periodontal membrane. In these instances other means should be investigated to improve the prognosis for these teeth. This study was directed toward preventing or retarding the resorption of the roots of replanted teeth. Nuva-seal pit and fissure sealant was selected as an agent to provide a thin plastic coating on the root surface to prevent resorption of the tooth structure. Phosphoric acid (50%) was the other agent to be applied to the roots of the teeth to produce a more porous surface and thus facilitate the reattachment of the periodontal fibers projecting from the alveolar socket walls. Also a new splinting technique was employed using Nuva-seal to attach replanted teeth to the adjacent teeth at their interproximal contacts and reinforcing this splint with acrylic bonding GAC cement. In general, it was hoped that this experiment would result in more information about the healing process of the periodontium and expand existing knowledge concerning the replantation of teeth.
A review of human skulls illustrating bone changes in periodontal disease
(Boston University, 1980) Visuddhidham, Thitima
Ceramic brackets : debonding effect on enamel
(Boston University, 2006) Virk, Mahadeep Singh
The purpose of this study was to evaluate the effect of orthodontic bracket debonding on the enamel surface using five different types of new ceramic bracket systems. A second objective was to evaluate the differences in the location of bond failure. Adhesive Remnant Index (ARI)was used to assess the amount of residual resin on the tooth surface after debonding. A new scale was designed to take the location and any damage to the enamel surface as well as to the bracket into consideration. The five types of Ceramic Brackets used in the project were designated into five categories denoted as follow: A. 20/40 ceramic bracket (American Orthodontics, WI), B. Inspire Ice (Ormco Corporation, CA), C. Mystique (GAC, NY), D. Fascination[R] (Dentaurum, Germany), E. Fascination[R] 2 (Dentaurum, Germany). Seventy five (75) extracted human molars were randomly selected. All the teeth were equally divided into five (5) groups of fifteen (15) teeth each for each ceramic bracket type. Pre and post debonding picture was taken at a 1OX magnification. Each sample was bonded using 3M Transbond XT adhesive. Each sample was subjected to thermocycling. Each sample was subjected to debonding force using Instron Testing Machine. Adhesive remnant index score was calculated and calculations were also done based on the new scale designed for this study. Statistical analysis of the debond strength results between all the groups was performed using one way ANOVA with post hoc test for multiple comparison at a significance level of [alpha]= 0.05. Descriptive statistics were also generated using Microsoft Excel XP. Additional analysis was performed to compare the debond type, new scale and ARJ among the different groups of ceramic brackets. The results showed that at a .05 significance level there is a statistically significant difference in the mean bond strengths of Fascination[R] and the rest of the sample groups, namely, 20/40, Inspire Ice, Mystique and Fascination[R] 2. There is no statistically significant difference in the mean debond strength between 20/40, Inspire Ice and Mystique. Fascination[R] 2 has statistically significance difference in mean debond strength from the rest of the sample groups at a .05 significance level. The high ARI score (4, 5) displayed by Fascination[R] and Fascination[R] 2 indicates primarily debonding at the Enamel-Adhesive interface. According to ARI score 20/40 ceramic bracket and Mystique have scores showing that approximately 60% of the samples ranging between 1 and 2. This means that approximately 60% of the samples had debonding interface of Bracket-Adhesive. Fascination[R] exhibited one sample with enamel damage (debond strength 503.87 kgf/cm2). Fascination[R] 2 ceramic bracket system exhibited four samples out of fourteen with enamel damage (mean debond strength 281.09 [plus or minus] 51.20 kgf/cm2). Approximately 46% of the 20/40 ceramic bracket samples exhibited bracket damage. Approximately 14% of the Mystique samples presented with bracket damage. Fascination[R] showed approximately 78% of samples with bracket damage. Inspire Ice exhibited neither enamel damage and nor bracket damage.
The efficacy of nonsurgical endodontic retreatment
(Boston University, 1984) Vilkin, Barry M.
The endodontic community is well aware that the future will produce a substantial number of retreatment cases. Practitioners who face cases requiring retreatment often choose a surgical approach, despite the lack of knowledge within the profession about the efficacy of nonsurgical remedies. A review of the literature produces a scant few articles that focus on nonsurgical retreatment techniques and success. This study was undertaken to evaluate the efficacy of non surgical retreatment approaches and, in particular, Schilder's cleaning, shaping and obturating techniques. Cases retreated nonsurgically in the endodontic clinic at Boston University School of Graduate Dentistry between 1975 and 1983 were recalled until a sample of 100 was obtained. The patient's records were reviewed to determine clinical symptomology and radiographic status at the- time of retreatment. Recall data was obtained from the clinical and radiographic examination given at the recall appointment. The study found a significant number (nine percent) of "lateral" rarefactions during the pretreatment radiographic evaluation. Upon recall, all of these cases exhibited complete or partial bone regeneration. In cases involving short-filled canals, the study found that nonsurgical retreatment could significantly improve the verticality of the fill 89 percent of the time. The study found that a high number of unfilled accessory canals exist in endodontic failures and that they can be filled successfully during retreatment. Eighty-three percent of the cases retreated evidenced complete or partial bone regeneration at the time of recall. The author concludes that nonsurgical retreatment can be utilized successfully in many cases where surgery is now employed and that the principles and techniques advocated by Schilder are particularly wellsuited towards retreating these failing cases.
Role of EVC2 in hedgehog signaling and chondrocyte proliferation
(Boston University, 2016) Venkitapathi, Sundharamani
Ellis-van Creveld syndrome (EvC) is an autosomal recessive chondrodysplasia with dwarfism, characterized by short ribs/limbs, postaxial polydactyly, dysplastic nails, dysplastic teeth, delayed eruption of teeth and hyperplastic frena. Weyer's Acrofacial Dysostosis (WAD) is an autosomal dominant form of EvC with a milder phenotype caused due to mutations in EVC2. Mutations in either of the genes EVC or EVC2 lead to the manifestation of the same clinical phenotype identified as EvC. Evc2 knockout (KO) mice model characterized in our lab also demonstrated phenotypes similar to EvC. Reports suggest that EVC2 plays a key role in the processing of GLl3 to activator and repressor forms thereby modulating hedgehog signaling. Previous reports also show a decrease in BrdU labelled chondrocytes in the growth plates of Evc2 KO mice suggestive of decreased chondrocyte proliferation. The objective of the study is to investigate if EVC2 is required for GLl3 expression and analyze proliferation of Evc2 knockdown (KO) chondrogenic ATDC5 cells EVC and EVC2 proteins co-localized with the centrosomal marker pericentrin and localized to the base of cilia. Our results show that EVC interacts with EVC2 wild type (WT) and mutant proteins. EVC2's interaction with SMO to form a ciliary complex in the presence of WT and mutant EVC proteins was investigated by overexpression of plasmids in HEK 293 cells. Immunoblotting results from our study showed that EVC2 and EVC form a ciliary complex with SMO. To investigate the role of EVC2 in determining GLl3 levels, the expression of full length and truncated GLl3 proteins was analyzed in WT and Evc2 KO mouse embryonic fibroblasts (MEF) and chondrocytes by immunoblotting. Our data showed a decrease in the cytosolic expression of full length form of GLl3 in Evc2 KO MEF and chondrocytes demonstrating the importance of EVC2 in determining GLl3 levels. Our results show that stable knock down of Evc2 in ATDC5 cells leads to a decrease in cell proliferation in serum starvation/stimulation condition in comparison to control clones and parental ATDC5 cells. Our study shows no significant difference in cell proliferation between control and Evc2 knock down clones in the presence of serum. Also analysis of cell cycle progression by propidium iodide staining after serum starvation/stimulation revealed an absence of a distinct peak in "S" phase in Evc2 knock down clones in comparison to the control suggestive of a defect in the ability of the Evc2 knock down cells to progress through the G1-S phase of the cell cycle. Our data shows that EVC2 is required for expression of GLl3 protein and chondrocyte proliferation.
The effect of multidisciplinary approach to improving the oral hygiene of nursing home patients
(Boston University, 1977) Tynan, Edith P.
The purpose of this project is to study the effects of a multi disciplinary approach to the delivery of dental care on the oral health and hygiene of elderly institutionalized patients. An intensive, coordinated team approach to dental care and staff education will be evaluated. Evaluation will be made through the use of an original hygiene index of the patients and pre- and post tests of the staff. The use of dental students is justified by the benefits to both students and patients. The patients will receive the preventive dental care they require at no cost. The students will gain experience in working in a team outside the dental school as well as experience in working with a population which has specific dental needs.
Planning for extramural programs in geriatric dentistry: a multidisciplinary approach
(Boston University, 1980) Triolo, Kate
A cephalometric study of the relationship between the maxillary first permanent molar and the key ridge
(Boston University, 1970) Tichler, Howard M.
The maxillary first molar and the key ridge were investigated cephalometrically. The purpose of the study was to propose a guide for determining where to reposition the molar during orthodontic therapy. One hundred and eighty-twoindividuals (mean age, 10.2 years) with "normal occlusion" were used as a control group. This group was compared statistically to an experimental group of one hundred and fifty-nine patients (mean age, ll.0 years) with malocclusions. These individuals were primarily divided into Class I nonextraction and extraction groups and Class II, division 1 nonextraction and extraction groups. Each of these groups was statistically compared before treatment and at the end of active treatment. Four linear and four angular measurements were made on each tracing. In addition, the path of eruption of the molar was followed in a cross-sectional sample to illustrate the relative position of the molar to the key ridge during its eruption. The results showed that the key ridge can be identified and reproduced on a cephalometric tracing. The stability of the structure in relation to certain cranial landmarks is questionable. That is, changes in the position of the molar during treatment were accompanied by changes in the position of the key ridge. However, it was established, according to the method employed, that the angular relationship between the molar and the key ridge does not differ in normal and abnormal occlusions. In addition, the angular relationships of the molar and key ridge to the palatal and occlusal planes do not differ between the two groups. This suggests that perhaps the key ridge should be investigatedas a possible diagnostic aid in order to determine, cephalometrically, the proper position of the maxillary first molar.
An analysis of projective drawings done by children in the dental environment
(Boston University, 1976) Thompson, Oswald N.
Effects of covering marginal gingival tissue with acrylic removable partial denture
(Boston University, 1969) Thiel, James N.
The purpose of this investigation is to determine the effects of covering marginal gingival tissue with plastic removable appliances. The study was undertaken from both a clinical and histologic aspect. A recent study done for the Clark-Cleveland Company showed that approximately 12 million people are wearing partial dentures of one form or another. This figure has increased 400% since 1944 when approximately three million people were wearing partial dentures. Because the number of patients has increased so rapidly it is hoped that a study of this nature will encourage more research in the field of prosthetics. Today more than ever before, people are requesting replacements for missing teeth. However, not all are financially able to undertake fixed bridgework. Partial dentures will be used until a more economical method of replacement is found. It would therefore stand to reason that partial dentures should be improved and the problems of this appliance understood. A number of plastic removable partial dentures were fabricated using the Hawley design methods. These were inserted into the mouths of 17-19 year old dental assistants to determine the effects on the marginal tissue. The inadequacies of using human subjects are many and unfortunately not all could be overcome. The greatest shortcomings were: 1) uncooperativeness of the patient 2) temperament and attitude 3) cost of fabrication and materials 4) availability and control of the patient Other problems were considered minor enough to be negligible.
Histological study of laterally repositioned mucoperiosteal pedicle grafts and laterally repositioned "stimulated" osteoperiosteal pedicle grafts in the treatment of denuded roots
(Boston University, 1980) Swart, Jacobus N. J.; Lugo-Romeu, Ferdinand
It has been suggested by Melcher [20] that activated "osteoperiosteal" flaps in which the periosteum is nudged into fibrogenic and osteogenic activity by means of controlled injury should, by virtue of their intrinsic osteogenic, fibrogenic and vascular proliferative properties, provide superior donor tissue. Melcher hypothesized that osteoperiosteal flaps rather than mucoperiosteal flaps might be more effectively utilized as a treatment modality in periodontal surgery. Goldman [21] has recently demonstrated in animals, as well as in humans, that dormant adult periosteum may be reactivated by controlled surgical trauma. He considers that stimulated osteo-periosteal pedicle grafts might provide superior donor tissue in the treatment of denuded roots. This clinical and histological study was initiated to compare the use of stimulated osteoperiosteal and mucoperiosteal pedicle grafts in the treatment of surgically induced denuded roots in dogs. This study should provide histologic information on the mode of attachment between the soft tissue-root interface of both laterally repositioned mucoperiosteal pedicle grafts (Part I) and laterally repositioned stimulated osteoperiosteal pedicle grafts (Part II).
Maxillary third molar impactions: a comparison of edgewise and Begg noextraction and extraction cases
(Boston University, 1976) Susman, John L.
A modified bioassay system for measuring bone resorption in tissue culture and a study of the effects of a hypoglycemic agent 5-bromo-2-thisphenecarboxaldhyde on prostaglandings E2 and parathyroid hormone induced bone resorption
(Boston University, 1983) Sun, Arthur Fang-Shuo
Opaque modifiers have been widely used in the intrinsic staining technique to enhance the esthetics of ceramometal restorations. The opaque modifiers are especially useful when adequate reduction of tooth structure for ceramometal restorations is not feasible. Despite the fact that opaque modifiers have become an indispensable part of ceramometal technology very little is known as to their color behavior and effect on the ceramometal bond. The object of this research was to study the color stability of the opaque modifiers and their effect on the ceramometal bond after repeated firings. Two types of alloys, a noble alloy (Eclipse)* and a base alloy (Neydium+Be)*, were used to fabricate the samples. A ten-time repeated firings (Table 2, page 81) were conducted to fire the samples. The opaque modifiers (SMO and SMBG)** to be tested were applied to the samples according to the two methods described below. These two methods are simulations of the practical methods employed by most dentists and dental technologists. Method I. The opaque modifiers were applied on a layer of regular opaque. Method II. The opaque modifiers were applied and fired directly to the metal castings. The experimental design of this research was to provide information regarding the following issues which have long been a concern to the dental profession: (1) Do the repeated firings affect the color stability of the opaque modifiers and the ceramometal bond of the ceramometal restoration? (2) Do the methods (methods I & II described above) for applying the opaque modifiers affect the color stability of the opaque modifiers and the stability of the ceramometal bond? (3) Do the metal alloys (noble & base alloys) for casting the metal substructures of ceramometal restorations affect the color stability of opaque modifiers and the stability of the ceramometal bond? The spectrophotometric result of this research indicated a significant trend of color (Hue, Value & Chroma) shift of the ceramometal samples during repeated firing procedures. The color shift could be attributed to the combined effect of the firings, the metal alloys and the methods for applying the opaque modifiers. There was a significant interaction among the effects from the firings, the metal alloys and the methods of opaque modifier application. This interaction was very complicated since the magnitude of the individual affect on the color shift from all three factors was not only inconsistent but also interrelated. [TRUNCATED]
A comparison of the accuracy of torch soldering, laser welding, and casting in one piece for implant-supported fixed partial dentures
(Boston University, 1996) Sudhinaraset, Pornphan
Accuracy of fit and adequacy of strength are major concerns for implant supported fixed partial dentures (ISFPDs). The first objective of this study was to measure the relative accuracy of four-unit, ISFPDs that have been joined by using: (1) soldering with a torch, (2) laser welding, and (3) casting in one piece. The second objective was to evaluate the strength of the joints of rectangular alloy bar specimens that have been joined by using the same methods as described above. Part I Four-unit ISFPDs were used as samples in this part of the study. A group of five ISFPDs was indexed and connected with conventional torch soldering. A second group of five castings was laser-welded. A third group of five solid, one-piece, cast ISFPDs served as controls. The ISFPDs were cast from a palladium alloy that includes palladium 78 %, gold 2% (ULTIMA gold, J.M. Ney Corp., Bloomfield, CT). The solder recommended by the manufacturer for a palladium alloy (Ney 2 white, J.M. Ney Corp.) was used. Soldered ISFPDs were indexed on the working model with the use of a cyanoacrylate adhesive (Zaplt, Dental Ventures of America, Inc., Anaheim Hills, CA), then attached to soldering analogs (31, West Palm Beach, FL) and invested in a conventional soldering investment (Hi Heat, Whip Mix Corp., Louisville, KY). Laser welded ISFPDs were welded directly on the working models with the use of a laser welding machine (Laser Welder, Exel Technology, Inc., Hauppauge, NY). One-piece castings were also fabricated on the working model. Each four-unit ISFPD was firmly attached to the master model with the use of implant screws (31) and a torque-controlled wrench (31). Accuracy of the fit of each ISFPD was compared by measuring the gap distances between the laboratory analogue and gold coping interface at predetermined points with the use of a video micrometer (JV 6000. Javelin System Inc., Torrance CA) before and after connecting the two gold cylinders. The values obtained were subjected to an analysis of variance (ANOVA). Results indicated statistically significant differences in the marginal gap distances between the soldered group, laser-welded group and one piece group (p[less than] 0.01). Mean marginal gap distance and standard deviation for the soldered group was 53.60 ± 23.2677 [mu]m., mean marginal gap distance and standard deviations for the laser-welded group was 8.7920 ± 1.8070 [mu]m., and mean marginal gap distance and standard deviation for the one-piece casting group was 79.8160 ± 7.0575 [mu]m. Part II Thirty rectangular bars were cast from a palladium alloy that includes palladium 78%, gold 2% (ULTIMA gold, J.M. Ney Corp.) and divided into three groups. Ten bars were indexed and connected with conventional torch soldering. A second group of ten castings was laser-welded. Ten solid, one-piece, cast bars served as controls. All thirty specimens were subjected to a four-point bending test with the use of a universal testing machine (Instron, model 4202, Instron Co., Canton, MA). Yield strengths were calculated from the load at yield point. The statistical evaluation revealed a significant difference between the laser-welded group and the soldered group. The laser-welded group had a statistically significant higher yield strength than the soldered group (p[less than]0.05). There was no statistically significant difference between the laser-welded group and the one-piece casting group (p[less than]0.05).

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