Lingual Margin Research Articles

The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading.

This study aimed to investigate the effect of modified framework (MF) design on the fracture resistance of IPS e.max Press anterior single crown after thermocycling and cyclic loading. Two types of IPS e.max Press frameworks were designed (n = 10); standard framework (SF) with a 0.5 mm uniform thickness and MF with a lingual margin of 1 mm in thickness and 2 mm in height connected to a proximal strut of 4 mm height and a 0.3 mm wide facial collar. The crowns were cemented to resin dies, subjected to 5,000 cycles of thermocycling, and loaded 10,000 cycles at 100 N. A universal testing machine was used to load specimens to fracture, and the modes of failure were determined. The mean and standard deviation (SD) of fracture resistance were 219.24 ± 110.00 N and 216.54 ±120.02 N in the SF and MF groups. Thus, there was no significant difference (p = 0.96). Mixed fracture was the most common failure mode in both groups. We found no statistically significant difference between the groups (p = 0.58). The MF design did not increase the fracture resistance of IPS e.max Press crown. Framework design is an essential factor for the success of all-ceramic restorations and its modification might be regarded as an approach to increase fracture resistance. Furthermore, the modified design was evaluated in metal-ceramic or zirconia crowns while less attention was paid to the IPS e.max Press crowns. How to cite this article: Golrezaei M, Mahgoli HA, Yaghoobi N, et al. The Effect of Modified Framework Design on the Fracture Resistance of IPS e.max Press Crown after Thermocycling and Cyclic Loading. J Contemp Dent Pract 2024;25(1):79-84.

Accuracy of merging scans of definitive fixed prosthodontic impressions to obtain single, accurate digitized master casts.

Many elastomeric impressions sent to commercial laboratory dental technicians may include marginal defects. To fabricate accurate restorations, digital technology may be used to merge digital files of defective impressions into a single standard tessellation language (STL) file free of errors. This would save clinicians and patients time and may improve clinical care. The purpose of this study was to compare the accuracy of digital master casts reconstructed from merged STL files of defective impressions with the file of the original defect-free preparations. Ivorine teeth on a dentoform were prepared to receive a posterior fixed dental prosthesis (FDP) with complete coverage preparations. An impression was made in a stock tray using polyvinyl siloxane (PVS) impression material and an extraoral scanner (E3, 3Shape, Denmark) was used to digitize the impression; this was the reference cast. Wax was used to create defects on the buccal and lingual margins of the preparations. Fifteen PVS impressions were made of the FDP preparations with defects in the mesial and distal margins; another set of 15 PVS impressions was made of FDP preparations with defects in the buccal and palatal margins for a total of 30 impressions. All impressions were digitized using the same extraoral scanner (E3, 3Shape, Denmark). Corresponding STL files were paired and merged, and a master cast was created by eliminating the defects using the scanned data. This master cast was compared to the reference cast using reverse engineering software (Geomagic, Morrisville, NC, USA). The results were expressed as average errors and standard deviations in the master casts relative to the reference cast. To account for the presence of positive and negative values in the data set, in terms of errors, the root mean square (RMS) value was calculated for each sample. The mean average error in the sample was -0.4 μm. The average upper limit of 95% confidence interval was +36.5 μm, while the average lower limit of 95% confidence interval was -37.3 μm. The mean RMS of the errors found was 18.9 μm. The results of this study indicated that merging digitized definitive impressions to correct marginal defects resulted in master casts with a high level of accuracy relative to the reference cast.

Stevens-Johnson syndrome secondary to massive inflammatory hyperplasia of bilateral lingual margins: a case report and literature review.

Stevens-Johnson syndrome (SJS), also known as the multifactorial erythematous drug eruption, is a class of adverse reactions of the skin and mucous membranes primarily caused by drug allergy often involving the oral cavity, eyes, and external genital mucosa, generally accompanied by fever, and can be life-threatening in severe cases. In February 2022, the Department of Stomatology, the First Affiliated Hospital of Zhengzhou University admitted a patient with huge inflammatory hyperplasia of bilateral lingual margins secondary to SJS. Upon admission, no other obvious symptoms were observed except for tongue hyperplasia. The patient suffered from a severe adverse drug reaction caused by acetaminophen 2 months ago and was complicated by liver dysfunction and pulmonary infection. After 1 month of treatment and rehabilitation, he developed a secondary tongue mass and was subsequently admitted to Dept. of Oral and Maxillofacial Surgery Ward 2, the First Affiliated Hospital of Zhengzhou University. After completing the examination, the tongue mass was surgically removed. After a follow-up of 11 months, the patient's condition was satisfactory and no temporary discomfort was observed. The case of tongue mass secondary to SJS is extremely rare. If a stomatologist encounters a similar case, we should carefully inquire about the drug allergy history and recent medication history, and be alert to whether or not they had adverse drug reactions recently.

New bats in the tropical family Emballonuridae (Mammalia: Chiroptera) from the Oligocene and early Miocene of Florida

Three new genera and four new species in the tropical bat family Emballonuridae (Mammalia: Chiroptera) are described from the Oligocene and early Miocene of peninsular Florida. These are: a new genus Oligopteryx and two new species, O. floridanus and O. hamaxitos, from the late Oligocene (early Arikareean) Brooksville 2 Local Fauna in Hernando County, with referred specimens of each species from the early Oligocene (Whitneyan) I-75 Local Fauna in Alachua County; a new genus and species, Karstopteryx gunnelli, from the latest Oligocene (late Arikareean) Buda Local Fauna in Alachua County; and a new genus and species, Floridopteryx poyeri, from the early Miocene (early Hemingfordian) Thomas Farm Local Fauna in Gilchrist County. Characters that distinguish Oligopteryx from other emballonurid genera are: M1 with a much reduced parastylar region and a large talon with a triangular posterolingual extension; M1 and M2 with a prominent hypocone separated from the protocone by a deep, V-shaped notch in the postprotocrista, and deeply concave talon basin; small, single-rooted p3; m1 and m2 with the trigonid narrower and shorter than the talonid, the paraconid and metaconid located close together along the lingual margin, and the entocristid blade-like, V-shaped, and oriented labially. O. hamaxitos is distinguished from O. floridanus by its smaller size and well-developed paraloph and metaloph on M1 and M2. Karstopteryx gunnelli is separated from the two species of Oligopteryx by the prominent parastyle, anteriorly oriented preparacrista, and rounded talon. Floridopteryx poyeri is characterized by: M1 with a highly reduced parastylar region but with a well-developed parastyle, short preparacrista, small hypocone not separated from the protocone by a notch in the postprotocrista, and a squarish talon; m1/m2 with the talonid much broader than the trigonid, trigonid compressed, shorter than talonid, and with the paraconid and metaconid close together along the lingual margin, large hypoconulid, and anterior root flattened and compressed anteroposteriorly (m1 only). Oligopteryx and Karstopteryx are considered members of the subfamily Emballonurinae based on the reduced parastylar region of the M1 but are left unassigned at the tribal level. Oligopteryx differs from all living emballonurids in the presence of a p3. Floridopteryx has a reduced parastylar region on M1 and is also considered an emballonurine, but can be separated from Oligopteryx by the presence of a prominent parastyle and lack of a p3. Floridopteryx is placed in the monophyletic New World emballonurine tribe Diclidurini. Taphonomy indicates Oligopteryx was a colonial cave dweller, whereas Floridopteryx more likely roosted in trees, as do most living Neotropical emballonurids. A change from a tropical or subtropical climate in Florida in the Oligocene and early Miocene to a warm temperate climate from the middle Miocene to the present is reflected in the disappearance of emballonurids from Florida after the early Miocene. Molecular studies indicate the Emballonuridae dispersed from Africa to South America in the Oligocene, despite the oldest Western Hemisphere record of this family from the early Oligocene (~30 Ma) of Florida (Oligopteryx). We hypothesize emballonurids may have reached North America from Eurasia in the Eocene using an overland route and then dispersed overwater to the then-island continent of South America, with the oldest South American record of that family from the late Oligocene (~25 Ma) of Peru.

Asymptomatic and slow-growing lingual margin neoformation

Asymptomatic and slow-growing lingual margin neoformation

Large-sized fossil hamsters from the late Middle Pleistocene Locality 2 of Shanyangzhai, China, and discussion on the validity of Cricetinus and C. varians (Rodentia: Cricetidae).

A detailed morphological description and comparative study were conducted on numerous large-sized hamster remains collected from the late Middle Pleistocene Locality 2 of Shanyangzhai (Syz 2), Hebei Province, China. The comparisons reveal that these fossils are highly similar to the extant Tscherskia triton in size and morphology, including the small degree of alternating between the main opposite cusps on M1-3, the presence of axioloph on M3, and mesolophids on m1-2 that are present but seldom reach the lingual margin of the teeth, among other features. However, minor differences between the two still exist. Consequently, all these fossils are designated as a chronosubspecies of the extant species, T. triton varians comb. nov. The skull and molar morphologies of Cricetinus varians and T. triton were meticulously compared to resolve the long-standing debate regarding the validity of Cricetinus Zdansky, 1928 and C. varians Zdansky, 1928. The findings indicate that the differences between the two are slight; as a result, C. varians can only be considered a chronosubspecies of T. triton, i.e., T. triton varians comb. nov., and Cricetinus should be recognized as a junior synonym of Tscherskia. We tentatively propose that, among the seven species once referred to Cricetinus, C. europaeus, C. gritzai, C. janossyi, and C. koufosi should be reassigned to Tscherskia, while C. beremendensis should be transferred to Allocricetus, and C. mesolophidos to Neocricetodon. Excluding Tscherskia sp. from the Late Pliocene Youhe fauna, there are no reliable Tscherskia fossils in China earlier than the Middle Pleistocene. Based on the current evidence, Tscherskia may have originated from Neocricetodon during the Early Pliocene in Europe and subsequently spread to Asia. T. triton is its sole surviving representative, which now exclusively inhabits East Asia.

Effect of CAD-CAM Framework Design Fabricated from Sintered Cobalt-Chromium Alloy on Fracture Resistance of Metal-Ceramic Restorations.

Porcelain fracture is a common problem of metal-ceramic restorations (MCRs). One suggested strategy to prevent it is to modify the metal framework design; however, the available information regarding the effect of framework design on porcelain fracture is scarce. This study aimed to assess the effect of computer-aided design and computer-aided manufacturing (CAD-CAM) framework design fabricated from sintered cobalt-chromium (Co-Cr) alloy on fracture resistance of MCRs. Twenty premolar metal dies were fabricated for this in vitro study. Ten standard frameworks were designed with 0.5 mm thickness, and 10 customized frameworks were designed with 1 mm thickness at the lingual margin and 0.5 mm thickness in all other areas. All specimens were fabricated from sintered Co-Cr alloy (Ceramill Sintron) using soft metal milling technology. After porcelain application, the specimens underwent thermocycling and cyclic loading for 3,000 cycles between 5 and 55°C. The fracture resistance was measured by a universal testing machine. The failure mode was also determined. Data were statistically analyzed by independent t-test (α = 0.05). The mean fracture resistance of porcelain was 2,379 ± 531 N in the standard and 2,557 ± 448 N in the customized group. No significant difference was found in fracture resistance of the two groups (P > 0.05). All specimens in both groups showed mixed failure. The fracture resistance of porcelain and the failure mode were not affected by the framework design of MCRs fabricated from sintered Co-Cr alloy (Ceramill Sintron).

Guttigomphus avilionis gen. et sp. nov., a trirachodontid cynodont from the upper Cynognathus Assemblage Zone, Burgersdorp Formation of South Africa.

The Burgersdorp Formation of South Africa is a richly fossiliferous rock sequence at the top of the Permian-Triassic Beaufort Group and is known for its abundance of Early-Middle Triassic vertebrate remains, particularly cynodonts. Fossils from the Burgersdorp Formation are referred biostratigraphically to the Cynognathus Assemblage Zone (CAZ), which is further divided into three subzones: Langbergia-Garjainia, Trirachodon-Kannemeyeria, and Cricodon-Ufudocyclops. Each subzone is characterised by the presence of a distinct species of trirachodontid, a group of gomphodont cynodonts found relatively abundantly throughout the CAZ, with the lower two subzones characterised by the medium-sized trirachodontids Langbergia and Trirachodon. The uppermost part of the formation, the Cricodon-Ufudocyclops subzone, yields trirachodontids of larger size. The majority of these trirachodontid specimens have previously been referred to Cricodon metabolus, a taxon also known from the Manda Beds of Tanzania and the Ntawere Formation of Zambia. Here we identify one of the specimens (BP/1/5538) previously referred to Cricodon as a new taxon, Guttigomphus avilionis. Guttigomphus can be distinguished from other gomphodont cynodonts by features of the upper postcanine teeth, such as an asymmetric crown in occlusal view (crown narrower along the lingual margin than the labial). Our phylogenetic analysis recovers Guttigomphus as a basal member of Trirachodontidae, outside of the clade including Cricodon, Langbergia and Trirachodon.

In vitro comparison of microleakage with two different techniques of placing stainless steel crowns on mandibular deciduous first molar teeth with decreased mesiodistal width.

Background. Stainless steel crowns (SSCs) of the opposing maxillary deciduous molar teeth are used in mandibular deciduous first molars with decreased proximal surfaces due to caries. However, the SSCs of maxillary deciduous molar teeth are different from those of the mandibular deciduous molars in terms of the occlusal surface morphology, the buccal margin, and the proximal surface contour. Therefore, it is possible to prepare the buccal and lingual surfaces to use the SSC of the lower deciduous molar teeth and compare microleakage. Methods. Eighty extracted mandibular deciduous first molars were randomly assigned to two groups. In the case group (BLP), the buccal (B) and lingual (L) surfaces were prepared in addition to the proximal (P) surface, and an SSC was placed on the mandibular first deciduous teeth. Only the proximal surface was prepared in the control (P) group, and the SSC of the opposing tooth (maxillary deciduous first molar teeth) was placed. After dissecting the teeth, the extent of dye penetration was measured. Results. The difference in microleakage on the buccal aspect between the case and control groups was significant (P=0.02); however, the difference in microleakage on the lingual aspect between the case and control groups was not significant (P=0.89). Conclusion. Microleakage at the buccal margin of the SSC of mandibular deciduous first molars was less than the maxillary deciduous first molar SSC, with no significant differences in the lingual margin.

Tongue papillitis and volatile sulfur compounds (VSC) values in a COVID-19 patient.

A 30-years-old male patient in general good health came to my observation for a lingual checkup. The patient had tested positive for SARS-CoV-2 with a molecular swab about 1 month earlier, with mild symptoms of COVID-19: fever at 37.6°c for a day, mild sore throat. No alteration of flavors and odors. Upon physical examination, he showed excellent dento-periodontal health and very good oral hygiene. At the tip and lingual margins, there were asymptomatic red pinpoint spots, which the patient had noticed appearing from the first day of COVID-19 symptoms. A diagnosis of papillitis had been made and an examination with a gas chromatograph OralChroma™(Oral Chroma™, Abimedical, Abilit Corp., Osaka, Japan) was performed to evaluate tongue Volatile Sulfur Compounds (VSC) values with the aim to intercept any gastric or respiratory problems. The report showed very high levels of CH32S (735, when the maximum is 9) closely associated with gastric pathologies. An explanation of the phenomenon would lead to think that the SARS-CoV-2 virus had proliferated more in the gastric than in the respiratory field. The presence of papillitis in patients with COVID-19 has previously been documented in the scientific literature but has never been correlated with oral VSC values. Differential diagnosis includes: lingual irritation from savory or spicy foods, papillitis not linked to COVID-19 or mild alteration of the normal shape of the lingual mucosa in people who abuse alcohol.

78 - Effect of Bevels on Load Capacity of Composite-Restored Incisors

This study aimed to evaluate the effect of different bevel designs on the load capacity of incisors with a Class-IV resin-composite restoration under lingual loading. Eighty bovine incisors were randomly assigned to 4 groups of 20. They were all given Class-IV preparations, and restored with selective etching, an adhesive and a resin composite. The groups contained preparations with: 1) no bevel; 2) a buccal bevel; 3) a lingual bevel; or 4) a circumferential bevel. The teeth were tested for their load capacity under a lingual load on a universal testing machine. Finite element models were also used to examine the stresses in them to help interpret the experimental results. The buccal-bevel group had a higher mean load capacity than the no-bevel group, but the increase was not significant. The lingual and circumferential bevels significantly increased the fracture load of the restored incisors by 35.2% and 80.3%, respectively (p < 0.05). The fracture load of the circumferential-bevel group was also significantly higher than that of the lingual-bevel group. Fracture in the lingual and circumferential groups started predominantly from the resin composite and then deflected cohesively into the adjacent tooth structure. The other two groups had most of their fracture modes involving interfacial failure. Finite element analysis showed that the lingual and circumferential bevels reduced the fracture-causing tensile stress at the lingual margin of the restored interface. Class-IV preparations with a lingual or circumferential bevel increases the load capacity of incisors restored with resin composite under a lingual load.

Mylohyoid Muscle Revisited: Anatomic Features with Clinical Implications in Dentistry

The mylohyoid muscle, one of the suprahyoid group, forms the floor of the mouth. Its main function is swallowing. It is a margin between the sublingual and the submandibular spaces and is important in the pathway of oral and maxillofacial infection. In prosthodontics, it is one of anatomic landmarks that limits the lingual margin of the mandibular denture. Currently, the muscle receives much interest in the fields of maxillofacial reconstruction and rejuvenation. The hemorrhagic issue around the mandibular lingual region is usually involved with the mylohyoid especially in the dental implant installation. This review covers anatomic features of the mylohyoid muscle with diverse clinical implications.

Conservative Class II Foils.

Conservative Class II Foils.

Accessory cusp expression at the enamel-dentine junction of hominin mandibular molars.

Studies of hominin dental morphology frequently consider accessory cusps on the lower molars, in particular those on the distal margin of the tooth (C6 or distal accessory cusp) and the lingual margin of the tooth (C7 or lingual accessory cusp). They are often utilized in studies of hominin systematics, where their presence or absence is assessed at the outer enamel surface (OES). However, studies of the enamel-dentine junction (EDJ) suggest these traits may be more variable in development, morphology and position than previously thought. Building on these studies, we outline a scoring procedure for the EDJ expression of these accessory cusps that considers the relationship between these accessory cusps and the surrounding primary cusps. We apply this scoring system to a sample of Plio-Pleistocene hominin mandibular molars of Paranthropus robustus, Paranthropus boisei, Australopithecus afarensis, Australopithecus africanus, Homo sp., Homo habilis and Homo erectus from Africa and Asia (n = 132). We find that there are taxon-specific patterns in accessory cusp expression at the EDJ that are consistent with previous findings at the OES. For example, P. robustus M1s and M2s very often have a distal accessory cusp but no lingual accessory cusp, while H. habilis M1s and M2s show the opposite pattern. The EDJ also reveals a number of complicating factors; some apparent accessory cusps at the enamel surface are represented at the EDJ only by shouldering on the ridges associated with the main cusps, while other accessory cusps appear to have little or no EDJ expression at all. We also discuss the presence of double and triple accessory cusps, including the presence of a double lingual accessory cusp on the distal ridge of the metaconid in the type specimen of H. habilis (OH 7–M1) that is not clear at the OES due to occlusal wear. Overall, our observations, as well as our understanding of the developmental underpinnings of cusp patterning, suggest that we should be cautious in our comparisons of accessory cusps for taxonomic interpretations.

Effect of chamfer design on load capacity of reattached incisors

ObjectiveThis study aimed to evaluate the effect of different chamfer preparations on the load capacity of reattached fractured incisors under lingual loading. MethodsEighty #8 typodonts were randomly assigned to four groups (n = 20 each). They were sectioned to simulate crown fracture, and reattached with a self-etch adhesive and a resin composite. The preparation for each group was: (1) no chamfer; (2) buccal chamfer; (3) lingual chamfer; and (4) circumferential chamfer. Forty-eight human lower incisors were grouped and prepared similarly (n = 12 each). These teeth were tested for their load capacity under a lingual load on a universal testing machine. Finite element models were used to examine the stresses on the reattached surfaces to help interpret the experimental results. ResultsThe buccal chamfer did not increase the load capacity when compared with the no-chamfer group. Lingual and circumferential chamfers respectively increased the fracture load by 36.9% and 32.3% in typodonts, and 78.5% and 33.3% in human incisors. The increase was statistically significant (p < 0.05). A higher fracture load tended to be accompanied by a larger area of deflected cohesive fracture. Finite element analysis showed that lingual and circumferential chamfers reduced the fracture-causing tensile stress at the lingual margin of the reattachment interface by approximately 70% and 60%, respectively, in human upper incisors. SignificanceIt was the joint design, and not the size of the bond area, that affected the load capacity of reattached incisors. Among the preparations considered, only those with a lingual chamfer could increase the load capacity of reattached incisors under a lingual load.

Cadaveric Evaluation of Load to Failure in Canine Gingiva Apposed With Varied Suture Patterns Using Poliglecaprone 25.

The purpose of the study was to determine the effect of suture pattern and repair length on the load to failure in an ex vivo canine gingival model. Healthy mandibular gingiva and mucosa were harvested from fresh cadavers euthanized for purposes unrelated to the study. Samples were randomly assigned by length and pattern. Lingual and buccal free gingival margins were apposed using a simple interrupted (SI), cruciate (XT), simple continuous (SC), or unidirectional knotless continuous barbed suture (SF) closure technique with USP 4-0 poliglecaprone 25i, ii applied over 2 lengths (3 cm and 6 cm). A custom template was used to ensure uniform suture bite application. Surgical time was recorded. Using a soft tissue mechanical testing frame, samples were tensioned to failure. Testing was video recorded and reviewed in conjunction with the tension trace data for tension at initial failure (Tfail) and maximum tension sustained (Tmax). Two factor ANOVA by length and pattern was performed followed by individual one way T-tests. Statistically significant findings were XT-SC-SF patterns were quicker to perform than SI. SF was more likely to fail by suture breakage than tissue tearing, and SF withstood less tension at the 3 cm length than SI-XT-SC. No significant difference was detected in Tmax or Tfail between SI and SC or XT. The study demonstrates that SC and XT are comparable to SI in tension resistance and faster to perform suggesting that SC and XT could replace SI for extraction site closure although further in vivo testing is required.

Comparison of the Stress Distribution in Class I and Class II Amalgam and Bulk-Fill Composite Restorations Using CAD-FEM Modeling.

This study compares the mechanical strengths of bulk-fill composite resin and amalgam material to investigate the stress distribution and capacity to mitigate stress of restored Class I and Class II teeth under chewing loads, using finite element analysis. A 3D model of a human mandibular first molar and four Class I (C1) and Class II (C2) caries, including 95-degree cavity-margin angles, were created. Different material combinations were simulated: model C1-A and C2-A, with an amalgam material; and model C1-C and C2-C, with a bulk-fill composite resin. Solid 3D elements with four grid points were employed for modeling the tooth. A vertical occlusal load of 600 N was applied, and nodal displacements on the bottom cutting surfaces were constrained in all directions. All materials were assumed to be isotropic and elastic, and a static linear analysis was performed. The highest maximum principal stress was observed in C2-C, followed by C1-C, C2-A, and C1-A, respectively. The maximum principal stress load on the lingual cusp was recorded at the junction of the lingual margin (C1-C and C2-C), and stress was recorded on the line of restoration and enamel (C1-A and C2-A). Restoration materials and cavity preparations influence the stress distribution at the restoration-tooth interface and, consequently, the measured bond strength.

The functional role of the Carabelli trait in early and late hominins

The Carabelli trait is a dental feature that forms along the lingual margin of the protocone of deciduous and permanent maxillary molars. It is variably expressed, ranging from a small pit or furrow to a large cusp, and its development seems to be associated with crown size and molar cusp spatial configuration. The degree of expression of the Carabelli trait differs systematically between hominin taxa, and for this reason, it has been used extensively in the reconstruction of their phylogeny. However, the functional implications of having a large Carabelli trait remain unclear. In this study, we analyze the macrowear pattern of maxillary molars of early and late hominins using the occlusal fingerprint analysis method, an approach based on digital models of teeth that helps in reconstructing occlusal dynamics occurring during mastication. Tooth crowns with a small Carabelli cusp generally exhibit larger wear contact areas that extended cervically, while two additional new occlusal contact areas are common in teeth characterized by a large Carabelli cusp. These wear areas are created at the beginning of the chewing cycle, when occluding with the slopes of the lingual groove of the lower molars, between the metaconid and entoconid cusps. Advancing tooth wear leads to a slight enlargement of Carabelli occlusal contacts increasing their functional area. A steep inclination could be mechanically important in food reduction and in balancing the functional load distribution during mastication contacts. Steep wear areas are particularly developed in primates that process foods characterized by tough and fibrous textural properties. Future biomechanical and microwear texture analyses could provide additional information on the mechanical adaptation of this dental trait.

Effect of tooth preparation design on marginal adaptation of composite resin CAD-CAM onlays

Statement of problemAlthough different preparation designs have been proposed for onlays fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM), their effect on marginal adaptation is unclear. PurposeThe purpose of this in vitro study was to investigate the effect of tooth preparation designs on the marginal and internal adaptation of ceramic-reinforced composite resin CAD-CAM onlays. Material and methodsA traditional preparation with a heavy chamfer on the functional cusp and a contrabevel on the nonfunctional cusp and a shoulder preparation with equal reduction on all cusps were used for mesial-occlusal-distal (MOD) onlay preparations. Ceramic-reinforced composite resin onlays were designed and milled based on the scanned prepared teeth. A digital silicone replica technique was used to determine marginal discrepancies between preparations and onlay restorations. A total of 100 numeric distances (representations of the fit in each region) were measured in 3 distinct regions: the buccal margin, lingual margin, and internal area. Independent Student t tests were used to determine significant differences (α=.05). ResultsTraditional preparation designs resulted in significantly smaller overall discrepancies (50.9 ±0.5 μm and 139.1 ±5.4 μm, P<.001) and smaller marginal discrepancies in the buccal (49.7 ±1.4 μm and 135.8 ±2.2 μm, P<.001) and lingual areas (47.1 ±1.0 μm and 133.4 ±1.1 μm, P<.001). ConclusionsThe marginal adaptation of ceramic-reinforced composite resin CAD-CAM onlays was affected by the preparation design. The traditional preparation design offered better marginal adaptation; therefore, it is recommended in clinical practice.

Effect of finish line design and metal alloy on the marginal and internal gaps of selective laser melting printed copings

Statement of problemSelective laser melting (SLM) technology has been introduced for printing metal dental restorations from Co-Cr base alloys or Au-Pt high noble alloys. However, information regarding the fit of restorations fabricated by using this technique is limited. PurposeThe purpose of this in vitro study was to determine the effect of 3 different finish line designs on the marginal and internal gaps of metal copings made from a base (Co-Cr), high noble (Au-Pd-Ag), and noble alloy (Co-Pd) by using the SLM technology. Material and methodsThree Ivorine right maxillary central incisors were prepared with a chamfer, deep chamfer, or shoulder finish line. The preparations were scanned by using a TRIOS scanner, and a total of 90 dies were printed using DPR 10 Resin (30×3 finish line designs). Ten SLM copings were fabricated for each margin design and metal alloy combination for a total of 90 copings (10×3 finish line designs×3 alloys). Copings were cemented onto dies using an autopolymerizing composite-resin luting material. All coping-die assemblies were sectioned buccolingually by using a low-speed diamond saw, and images were obtained by using an inverted bright field metallurgical microscope at ×100 magnification. Marginal and internal gaps were measured at 5 locations: buccal margin, midfacial, incisal, midlingual, and lingual margin. After gap measurements, representative specimens were embedded in autopolymerizing resin and prepared for metallographic examination. A 2-way multivariate analysis of variance (MANOVA) was conducted to determine the overall significance, followed by ANOVA for each dependent variable (α=.05). ResultsThe results indicated that alloy type and finish line had a significant influence on marginal gap of copings (P<.001). Relative to the internal gap, alloy type had a significant effect (P<.001), but the type of finish line had no statistically significant influence (P=.337). No statistically significant interactions occurred. Base alloys were printed with almost no observable porosity, whereas noble and high noble alloys exhibited hot tears and porosity. ConclusionsThefinish line type did not influence the internal gap between copings and dies, whereas the alloy type influenced the marginal gap between copings and dies. SLM-fabricated Co-Cr copings on teeth prepared with a deep chamfer finish line demonstrated the lowest marginal gap.