Cementum thickening leads to lower whole tooth mobility and reduced root stresses: An in silico study on aging effects during mastication.

In the course of a lifetime the crowns of teeth wear off, cementum thickens and the pulp closes-in or may stiffen. Little is known about how these changes affect the tooth response to load. Using a series of finite element models of teeth attached to the jawbone, and by comparing these to a validated model of a 'young' pig 3-rooted tooth, the effects of these structural changes were studied. Models of altered teeth show a stiffer response to mastication even when material properties used are identical to those found in 'young' teeth. This stiffening response to occlusal loads is mostly caused by the thicker cementum found in 'old' teeth. Tensile stresses associated with bending of dentine in the roots fall into a narrower distribution range with lower peak values. It is speculated that this is a possible protective adaptation mechanism of the aging tooth to avoid fracture. The greatest reduction in lateral motion was seen in the bucco-lingual direction. We propose that greater tooth motion during mastication is typical for the young growing animal. This motion is reduced in adulthood, favoring less off-axis loading, possibly to counteract natural bone resorption and consequent compromised anchoring.

Starch Combined with Sucrose Provokes Greater Root Dentine Demineralization than Sucrose Alone.

Since there is no consensus about whether starch increases the cariogenic potential of sucrose, we used a validated 3-species biofilm model to evaluate if starch combined with sucrose provokes higher root dentine demineralization than sucrose alone. Biofilms (n = 18) composed by Streptococcus mutans (the most cariogenic bacteria), Actinomces naeslundii (which has amylolytic activity), and Streptococcus gordonii (which binds salivary amylase) were formed on root dentine slabs under exposure 8 ×/day to one of the following treatments: 0.9% NaCl, 1% starch, 10% sucrose, or a combination of 1% starch and 10% sucrose. Before each treatment, biofilms were pretreated with human whole saliva for 1 min. The pH of the culture medium was measured daily as an indicator of biofilm acidogenicity. After 96 h of growth, the biofilms were collected, and the biomass, bacteria viability, and polysaccharides were analyzed. Dentine demineralization was assessed by surface hardness loss (% SHL). Biofilm bioarchitecture was analyzed using confocal laser scanning microscopy. Treatment with a starch and sucrose combination provoked higher (p = 0.01) dentine demineralization than sucrose alone (% SHL = 53.2 ± 7.0 vs. 43.2 ± 8.7). This was supported by lower pH values (p = 0.007) of the culture medium after daily exposure to the starch and sucrose combination compared with sucrose (4.89 ± 0.29 vs. 5.19 ± 0.32). Microbiological and biochemical findings did not differ between biofilms treated with the combination of starch and sucrose and sucrose alone (p > 0.05). Our findings give support to the hypothesis that a starch and sucrose combination is more cariogenic for root dentine than sucrose alone.

Physical properties of root cementum: Part 26. Effects of micro-osteoperforations on orthodontic root resorption: A microcomputed tomography study.

INTRODUCTION: Studies have demonstrated the potential efficacy of micro-osteoperforations in accelerating tooth movement by amplifying the expression of inflammatory markers. The aim of this investigation was to examine the effects of micro-osteoperforations on orthodontic root resorption with microcomputed tomography. METHODS: This prospective controlled clinical trial involved 20 subjects requiring extraction of the maxillary first premolars as part of their orthodontic treatment. A buccal tipping force of 150 g was applied to both premolars. Using the Propel appliance (Propel Orthodontics, San Jose, Calif), micro-osteoperforations were applied at a depth of 5 mm on the mesial and distal aspects in the midroot region of the experimental side of the first premolar root; the contralateral side served as the control. After 28 days, both premolars were extracted. The teeth were scanned under microcomputed tomography, and the volumes of root resorption craters were calculated and compared. RESULTS: Premolars treated with micro-osteoperforation exhibited significantly greater average total amounts of root resorption than did the control teeth (0.576 vs 0.406 mm3). The total average volumetric root loss of premolars treated with micro-osteoperforation was 42% greater than that of the control teeth. CONCLUSIONS: This 28-day trial showed that micro-osteoperforations resulted in greater orthodontic root resorption. However, these results should be verified in patients who are undergoing full-length orthodontic treatment.

Torque differences according to tooth morphology and bracket placement: a finite element study.

INTRODUCTION: Torque of the maxillary incisors is essential in esthetics and proper occlusion, while torque expression is influenced by many factors. The aim of this finite element study was to assess the relative effect of tooth morphology, bracket prescription, and bracket positioning on tooth displacement and developed stresses/strains after torque application. METHODS: A three-dimensional upper right central incisor with its periodontal ligament (PDL) and alveolus was modelled. The tooth varied in the crown-root angle (CRA) between 156°, 170°, and 184°. An 0.018-inch slot discovery® (Dentaurum, Ispringen, Germany) bracket with a rectangular 0.018 × 0.025-inch ß-titanium wire was modelled. Bracket torque prescription varied between 0°, 12°, and 22°, with bracket placement at the centre of the middle, gingival or incisal third of the crown. A total of 27 models were generated and a buccal root torque of 30° was applied. Afterwards, crown and apex displacement, strains in the PDL, and stresses in the bracket were calculated and analysed statistically. RESULTS: The palatal crown displacement was significantly affected by bracket positioning (up to 94 per cent), while the buccal apex displacement was significantly affected by bracket prescription (up to 42 per cent) and bracket positioning (up to 23 per cent). Strains in the PDL were affected mainly by CRA (up to 54 per cent), followed by bracket positioning (up to 45 per cent). Finally, bracket prescription considerably affected the stresses in the bracket (up to 144 per cent). LIMITATIONS: These in silico results need to be validated in vivo before they can be clinically extrapolated. CONCLUSION: Tooth anatomy and the characteristics of the orthodontic appliance should be considered during torque application.

Stress distribution in root filled teeth restored with various post and core techniques: effect of post length and crown height.

AIM: To investigate interfacial stress distribution in restored root filled teeth with various post lengths and crown heights. METHODOLOGY: Three-dimensional mathematical models of a root filled mandibular premolar tooth were constructed. Parts of the tooth structures were replaced with ceramic crowns having three crown heights incorporating, either a cast post and core or a resin post and cores with fibre post or metallic post with four post lengths. Finite element linear analysis was performed to calculate equivalent and shear stress distribution at the interfaces between the teeth and post and cores under mesiodistal symmetrical boundary conditions and an oblique static load of 400 N. RESULTS: For the resin post and core with fibre and metallic posts, shear stress at the interface was greater in the cervical area than the post area, depending on the crown height. The resin post and core with metallic post had lower shear stress at the interface of cervical area than that of the fibre post model; however, the metallic post models produced a high concentration of shear stress at the interface between the post and resin composite. On the other hand, for the cast post and core, the shear stress at the interface was mainly produced in the post end area, which increased with decrease of post length. CONCLUSIONS: For the resin post and core, bonding integrity to the cervical area would play a critical role in the survival of the restored tooth, whereas for the cast post and core, the bond of the post would be essential.

Regenerative endodontic treatment of an immature tooth with a necrotic pulp and apical periodontitis using platelet-rich plasma (PRP) and mineral trioxide aggregate (MTA): a case report.

AIM: To report the successful clinical and radiographic outcome of a regenerative endodontic treatment. SUMMARY: A 16-year-old male patient presented with a discoloured, maxillary left lateral incisor with a necrotic pulp. Radiographic examination revealed an incompletely developed root with an open apex. Under local anaesthesia and rubber dam isolation, an access cavity was prepared and the necrotic pulpal remnants were removed. The canal was disinfected without mechanical instrumentation with 5.25% NaOCl solution and dried with sterile paper points. A triple antibiotic (metronidazole, ciprofloxacin and minocycline) mixed with distilled water was packed in the canal and left for 28 days. Ten millimetres of whole blood was drawn by venipuncture from the patients antecubital vein for preparation of platelet-rich plasma (PRP). After removal of the antibiotic mixture, the PRP was injected into the canal space up to the cementoenamel junction level. Three millimetres of white MTA was placed directly over the PRP clot. Two days later, the tooth was restored with permanent filling materials. The patient was recalled for 3, 6, 12, 24 and 36 months clinical/radiographic follow-up. A 3-year follow-up radiograph revealed resolution of the periapical lesion, increased thickening of the root walls, further root development and continued apical closure of the root apex. The tooth was not responsive to cold tests; however, sensitivity tests with an electric pulp tester (EPT) elicited a delayed positive response. KEY LEARNING POINTS: Regeneration is a viable treatment modality that allows continued root development of immature teeth with open apices and necrotic pulps. Platelet-rich plasma appears to be a suitable scaffold for regeneration of vital tissues in teeth with a necrotic pulps and an associated periapical lesion. Regenerative endodontic procedures may offer an effective treatment option to save teeth with compromised structural integrity.

Three-dimensional finite element analysis of endodontically treated teeth with weakened radicular walls restored with different protocols.

STATEMENT OF PROBLEM: The restoration of weakened roots with glass fiber posts (GFPs) remains a challenge. PURPOSE: The purpose of this study was to evaluate the stress distribution of endodontically treated teeth with weakened radicular walls restored with different protocols by 3-dimensional finite element analysis (3D-FEA). MATERIAL AND METHODS: The following 4 models of endodontically treated maxillary canines restored with metal ceramic crowns were simulated on the basis of computed microtomographic images to characterize the groups: GNW (control), a nonweakened root restored with a GFP; GW, a weakened root restored with a GFP; GDA, a weakened root restored with a direct anatomic GFP; and GIA, a weakened root restored with an indirect anatomic GFP. Loads of 180 N were applied to the lingual surface on the incisal third of the teeth at 45 degrees. The models were supported by a periodontal ligament and fixed in 3 axes (x=y=z=0). The von Mises stress (VMS) was calculated. RESULTS: All models exhibited VMS concentrations at the loading area and were distributed along the proximal surfaces of the root. The GFP exhibited a homogeneous stress distribution, and similar VMS distributions were observed in all of the reconstructive techniques. CONCLUSIONS: Similar stress distributions were observed in the endodontically treated teeth, regardless of root weakness and the reconstructive technique for the radicular walls.

Fracture resistance of compromised endodontically treated teeth restored with bonded post and cores: An in vitro study.

STATEMENT OF PROBLEM: It is unclear which post and core system performs best when bonded to severely compromised endodontically treated teeth. PURPOSE: The purpose of this study was to investigate the fracture resistance and mode of failure of severely compromised teeth restored with 3 different adhesively bonded post and core systems. MATERIAL AND METHODS: Thirty extracted endodontically treated maxillary anterior teeth were randomly divided into 3 groups, CPC, gold cast post and core; TPC, titanium prefabricated post/composite resin core; and FPC, quartz fiber reinforced post/composite resin core. All posts were adhesively cemented. All cores resembled a central incisor preparation with no remaining tooth structure above the finish line. Cast gold crowns were fabricated and cemented adhesively. The specimens were aged with thermocycling and cyclic loading. Two specimens per group were randomly selected for micro-computed tomographic imaging before and after aging. Failure was induced with a universal testing machine. The mode of failure was characterized by the interface separation. Data were analyzed with 1-way ANOVA (α=.05) followed by post hoc tests (Bonferroni). RESULTS: A statistically significant difference was found among the 3 groups (P=.002). CPC was significantly different than TPC (P=.008) or FPC (P=.003). The primary mode of failure for CPC and TPC was root fracture, and for FPC post debonding. CONCLUSIONS: Severely compromised endodontically treated teeth restored with bonded gold cast post and cores showed significantly higher fracture resistance.

Effect of a zirconia primer on the push-out bond strength of zirconia ceramic posts to root canal dentin.

STATEMENT OF PROBLEM: The retention of zirconia ceramic posts to root canal dentin with resin-based luting cements is relatively poor. PURPOSE: The purpose of this in vitro study was to evaluate the effect of a new zirconia primer, a mixture of organophosphate and carboxylic acid monomers, on the push-out bond strength of zirconia posts to root canal dentin. MATERIAL AND METHODS: The root canals of 40 extracted human maxillary central incisors were endodontically treated and the post spaces were prepared. Zirconia posts were luted with 2 different resin luting agents (Panavia F and Clearfil SA luting cements) with and without the zirconia primer (Z-Prime Plus; Bisco). Three segments, each 2 mm high, were cut perpendicular to the post from each root. Bond strength was determined by pushing out the post with a universal testing machine. Three-way ANOVA and the Tukey HSD test was used to assess the effects of the zirconia primer, the 2 different resin luting cements, and different thirds of the root canal (α=.05). RESULTS: The zirconia primer significantly increased the push-out bond strength of zirconia posts to root canal dentin. Clearfil SA luting cement provided significantly higher bond strength than did Panavia F. For all experimental groups combined, bond strength decreased from the coronal to the apical section. CONCLUSIONS: A zirconia primer based on organophosphate/carboxylic acid monomers increased the bond strength of zirconia posts to root canal dentin bonded with both resin luting cements.

Effect of Three-wall Bony Defect along Various Root Surfaces on Position of Center of Resistance: A 3D Finite Element Analysis.

INTRODUCTION: Increase in adult orthodontic patients has increased the challenges faced by orthodontists, as they often present themselves with a varying degree of dental and peri-odontal compromise, in which the entire orthodontic treatment planning will revolve around maintenance and augmentation of supporting apparatus. One of the many factors to be considered during treating an adult patient is the height of alveolar bone and its effect on center of resistance (CRes). MATERIALS AND METHODS: Eight 3D analytical models of upper central incisor were designed using 'Solid Works Office Premium'. The models were subjected to 3 and 6 mm bone loss along all four surfaces, i.e. labial, lingual, mesial and distal. One Newton of retraction force was applied on labial surface of tooth on model number 1, 2, 5 and 6 and 1N of distalization force was applied to model number 3, 4, 7 and 8. The relative location of the CRes to the total root length was taken as 41.8% of total root length from the root apex. The ANSYS software was used to evaluate the change in CRes on all the models. RESULTS: It was observed that CRes shifted apically from its relative location (41.8% from apex); however, this shift was clinically insignificant. Minimum deflection of CRes, 0.0122 mm, was seen when a distalization force was applied on model with 6 mm bone loss on distal surface, while maximum deflection of 0.0245 mm was seen when retraction force was applied on model with 6 mm bone loss on labial surface. CONCLUSION: The resultant displacement in position of center of resistance is negligible; hence, there is no need of changing biomechanics during orthodontic treatment for a tooth with three wall infrabony defects. However, it is necessary to further study other infrabony defects like two wall or one wall defect, and their effect on position of CRes.

The maxillary second molar - anatomical variations (case report).

To be acquainted with dental anatomical specificity is of great importance for dental endodontic treatment algorithm. The subject of present publication is 2 clinical cases of upper second molars, detailed characterization of, which is considered very important for enrichment of anatomical knowledge about dental anatomical variations. In one case, the reason for admission to the clinic of a 38-year-old woman was complains as of esthetic character as well as functional misbalance (disturbance of chewing function due to the damage of orthopedic construction). The patient indicated to the existence of coronary defects of large size aesthetic discomforts, damage and discolouration of old orthopedic construction (denture) in maxillary right molar area. According to the data obtained after clinical and visiographical examinations, chronic periodontitis of 17 teeth was identified as a result of incomplete endodontic treatment. According to the data obtained after clinical and visiographical examinations, the diagnosis of chronic periodontitis of 17 teeth was identified, tooth 17 with 2 roots and 2 canals. In the second clinical case, the reason for admission to the clinic of a 39-year-old woman was severe pain in the upper right molar area. The patient indicated to the caries on the tooth 17. After completion of proper survey clinical and visiographical examinations, acute pulpitis (K04.00) - with three roots and 4 canals was diagnosed. In both cases after the proper examinations and agreement with the patients a treatment plan envisaging: 17 teeth endodontic treatment, filling of caries defects and their preparation on one hand for orthopedic construction (denture) and on the other hand for restoration of anatomical integrity by light-cured composite, was scheduled. The present study is designed to prevent complications of endodontic treatment of the second molar, to optimize diagnosis and treatment algorithm, once again proving reliable information indicating to the individuality of treatment tactics.

Evaluation of different restorative techniques for filling flared root canals: fracture resistance and bond strength after mechanical fatigue.

PURPOSE: To evaluate the fracture resistance (FR) and bond strength (BS) after mechanical fatigue (MF) of flared root canals restored with different restorative techniques for fiber post cementation. MATERIALS AND METHODS: The root canals of 84 single-rooted premolars were endodontically treated and prepared in order to simulate an oversized root canal, except for the positive control group (PC), in which a prefabricated fiber post (PFP) with a diameter compatible with the post cavity was cemented. In the oversized root canals, alternative restorative techniques for post cementation were tested, as follows: NC: negative control (PFP with a diameter smaller than that of the root canal); AP: PFP + accessory posts; RR: root reinforcement with composite resin; DAP: direct anatomical post; IAP: indirect anatomical post. After the luting procedures using Excite DSC and Variolink II, indirect composite crowns were cemented on composite resin cores and the specimens were mechanically fatigued (1.2 x 106 cycles, 40 N). From each group, 8 specimens were subjected to the push-out BS test and the others 6 specimens to the FR test. For both tests, the data were subjected to ANOVA and Scheffe's tests (α = 0.05). RESULTS: In terms of FR, all alternative techniques showed intermediate performance, being similar to both control groups. In terms of BS, only the groups DAP and IAP were similar to the well-adapted condition (positive control group). CONCLUSION: The use of DAP and IAP should be the first choice for fiber post cementation in oversized root canals.

Effect of the coating material on root dentin remineralization in vitro.

PURPOSE: A fluoride-releasing coating material containing surface pre-reacted glass-ionomer (S-PRG) filler has become commercially available. However, there has been no detailed investigation of its remineralization effects at various tooth surface regions. The remineralization effects of S-PRG filler-containing coating material at different sites of demineralized dentin surfaces in vitro were evaluated. METHODS: Baseline lesions were prepared on bovine root dentin surfaces by immersion in demineralization buffer and divided into four groups: (B)--baseline lesion; (P)--S-PRG filler-containing material; (V)--S-PRG filler-free coating material as negative control; and (X)--resin-modified glass- ionomer as positive control. Material was applied to half the lesion surface, then P, V and X were remineralized in a gel system. Mineral profiles, integrated mineral loss (IML) and lesion depth (LD) at four regions, i.e. 1--exposed dentin surface adjacent to the material; 2--at a distance from the material; 3--beneath the material near to the edge; and 4--at a distance from the edge, were analyzed by transversal microradiography. Data were analyzed using ANOVA and Games-Howell test with α = 0.05. RESULTS: B showed typical artificial demineralized lesion. The IMLs of V, P and X at regions 1 and 2, and P and X at region 3 were significantly lower than that of B, however, those of V at region 3 and the other three groups at region 4 were not significantly different from that of B. At region 1, P and X showed significantly lower IMLs than V. At region 2, the IML of X showed significantly lower IML than V. There was no significant difference between P and X. The LD values of V, P and X at all regions were not significantly different from that of B. Fluoride, strontium and silicate ions released from the S-PRG filler would provide a favorable environment for remineralization of the demineralized dentin in P.

Effect of root morphology on biomechanical behaviour of premolars associated with abfraction lesions and different loading types.

The aim of this study was to investigate the biomechanical behaviour of maxillary premolar teeth regarding root morphology and abfraction depth, submitted to axial and oblique occlusal load. The investigation was conducted using 3D finite element analysis and strain gauge test. Sound maxillary premolar single and double root were selected for 3D model generation. The teeth were scanned for external morphology data acquisition. The 3D geometry was stored in *.STL and exported to Bio-CAD software (Rhinoceros-3D) to model generation. Mesh generation, mechanical properties and boundary conditions were performed in finite element software (Femap, Noran Engineering, USA). Twelve models were generated: sound tooth, 1.25 and 2.5 mm abfraction teeth. 100N compressive static load was applied: axially and 45° angle to the long axis on the palatine surface of the buccal cusp. Two strain gauges were bonded on the teeth mounted in a mechanical testing machine. Von Mises criterion showed that the double-root teeth associated with 2.5 mm abfraction and oblique loading presented higher stress values. Axial loading associated with single-root teeth propitiated the lowest stress rates. Double root sound 1.25 and 2.5 mm abfraction teeth associated with oblique loading showed the highest strain values (µS): 692.6, 1043.31 and 1236.14, respectively. Single root sound 1.25 and 2.5 mm abfraction teeth associated with oblique loading showed 467.10, 401.51 and 420.98 strain values, respectively. Axial loading showed lower strain rates, ranging from 136.12 to 366.91. The association of deep lesions, oblique loading and double-root tooth promoted higher stress and strain concentration.

Effect of the crown, post, and remaining coronal dentin on the biomechanical behavior of endodontically treated maxillary central incisors.

STATEMENT OF PROBLEM: It is unclear how the amount of remaining coronal dentin and the type of post and core rehabilitation affect the strain, stress distribution, and fracture resistance of endodontically treated teeth. PURPOSE: The purpose of this study was to evaluate the effects of the type of post, type of crown, and the amount of remaining coronal dentin on the biomechanical behavior of endodontically treated teeth. MATERIAL AND METHODS: The investigation was conducted by using 3-dimensional finite element analysis and laboratory tests. Three-dimensional models of a maxillary central incisor were generated: without remaining coronal dentin, with 1.0 mm of remaining coronal dentin, with 2.0 mm of remaining coronal dentin, and restored with a glass-fiber post or a cast post and core in combination with a metal crown or an alumina-reinforced ceramic crown. The results were evaluated by using the von Mises criterion and Maximum Principal Stress. One hundred twenty bovine incisors were selected and divided into 12 treatment groups (n=10). Specimens were loaded at a 135-degree angle to perform strain measurements and were then loaded until fracture. The strain and fracture resistance results were analyzed with 3-way analysis of variance and the Tukey honestly significant difference test (α=.05). RESULTS: The alumina-reinforced ceramic crowns and metal crowns associated with a glass-fiber post showed a homogeneous stress distribution within the root. The cast post and core concentrated higher stresses at the post-dentin interface. Significant differences were found among the mean fracture resistance values for all groups (P<.05). The presence of 2.0 mm of coronal remnants resulted in lower strains and higher fracture resistance for both the metal and ceramic crowns. Roots restored with glass-fiber posts exhibited more favorable fractures. CONCLUSIONS: The presence of 2 mm of remaining coronal dentin improved the mechanical behavior of the endodontically treated maxillary incisors. Teeth restored with glass-fiber posts and composite resin cores showed a homogeneous stress distribution within the root dentin.

Fracture strength and nanoleakage of weakened roots reconstructed using relined glass fiber-reinforced dowels combined with a novel prefabricated core system.

PURPOSE: The aim of this study was to evaluate fracture strength and nanoleakage of endodontically treated weakened teeth after being restored with relined glass fiber-reinforced dowels and two types of cores. MATERIALS AND METHODS: Sixty sound human decoronated and endodontically treated teeth were embedded in epoxy resin blocks, then divided into three groups (n = 20) according to the method of root reconstruction. Group 1 (control): nonweakened roots were restored with glass fiber-reinforced dowels (UNIC); group 2: weakened roots restored with glass fiber-reinforced dowels relined with composite resin; group 3: weakened roots restored with glass fiber-reinforced dowels and a thick layer of luting cement. Dowels were cemented using Corposit, a dual-cured adhesive resin cement, then each group was assigned into two subgroups (n = 10) according to the type of core used; subgroup a: custom-made core using the same luting cement, subgroup b: prefabricated glass fiber-reinforced core (UNIC). Half the specimens of each subgroup were individually mounted at 45° angles and statically compressed until fracture at a 0.5 mm/min crosshead speed with a 5 kN load cell. The type of failure was assessed using a magnification lens. The other half of the specimens were removed from the block, placed in silver nitrate solution for 24 hours followed by photo developer for 8 hours, then examined using environmental scanning electron microscope/energy dispersive analytical X-ray for nanoleakage evaluation. Data were statistically analyzed. RESULTS: The nonweakened group recorded the highest fracture strength values. The composite relined group showed significantly higher fracture strength values than the cement group. The prefabricated core yielded higher fracture strength values than the custom-made core. All groups showed a degree of nanoleakage, with higher scores recorded for the composite group. CONCLUSIONS: The fracture resistance of wide root canals can be improved by using glass fiber-reinforced dowels relined with composite resin as an alternative to increasing the thickness of luting cement; however, the percentage nanoleakage would increase. On the other hand, the recently introduced prefabricated glass fiber-reinforced core can be considered a promising technique, but further investigations are necessary.

Effects of 980-nm diode laser on the ultrastructure and fracture resistance of dentine.

Few reports have addressed the effects of diode laser irradiation at 980 nm on the morphology and fracture resistance of dentine. The purpose of this study is to evaluate the effects of 980-nm diode laser on the ultrastructure and fracture resistance of root dentine. The roots of 90 extracted canine teeth were divided into three groups according to the type of irrigating solution (water, NaOCl, and NaOCl/EDTA) and subdivided into three subgroups (n = 10) according to the amount of laser irradiation (without irradiation, 1.5 W/100 Hz and 3.0 W/100 Hz). The roots were filled with an epoxy resin-based sealer and gutta-percha and then subjected to a fracture resistance test. Data were analyzed by ANOVA and the Tukey test (p < 0.05). Additionally, 18 canine teeth were prepared using the same irrigation/irradiation protocols and evaluated by scanning electron microscopy (SEM). The SEM showed greater changes when the laser power increased, and the changes also varied according to the irrigating solution. A modified smear layer was observed in specimens that were treated with water and then laser-irradiated. The laser treatment did not alter the fracture resistance of roots treated with 1.5 W/100 Hz (246.3 ± 29.5 N) and 3.0 W/100 Hz (215.3 ± 25.1 N) laser power. The roots treated with NaOCl were more susceptible to fracture (199.4 ± 15.1 N) than those irrigated with water (254.2 ± 23.0 N) (p < 0.05). The 980-nm diode laser altered the morphology of the dentine but did not affect the fracture resistance of the roots.

The effect of type of restoration on the stress field developed in terminal abutments with severely reduced periodontal support and coronal structure.

STATEMENT OF PROBLEM: Periodontally compromised teeth (PCT) that serve as terminal abutments (TAs) are often challenging depending on the post-and-core treatment, the type of partial fixed dental prosthesis (PFDP), and the periodontal support. PURPOSE: The purpose of this study was to investigate the biomechanical impact of 3 types of PFDP supported by cast post-and-cores on PCT serving as terminal abutments. MATERIAL AND METHODS: A 3-dimensional (3D) model of a human mandible was fabricated by using computed tomography (CT) images and parameterized in a computer-aided design (CAD) environment as follows: Right premolar preparation geometries were designed. The second premolar was assembled with 7-mm or 10-mm cast post-and-core models. Both premolar-models were designed to support single, splinted, or 1-unit cantilever splinted crowns. In each situation, their periodontium geometries were designed to be reduced by 10%, 50%, and 70%. All models were imported into a 3D finite element analysis (FEA) environment and loaded; von Mises stress values and distribution patterns were evaluated. RESULTS: Insertion of the post primarily affected the apical areas of both the root and post; the type of PFDP and periodontal support mainly affected stress distribution. In patients with a normal periodontium, splinting the teeth did not contribute to their stress relief. By extending the post length, a stressful area close to the apex of the post was developed. Splinting mitigated the stress field of the coronal part of the 50% PCT (up to 98.9%); the 30% PCT experienced a substantial decrease (up to 215.9%) in stress in the radical part as well. The increase in the length of the post produced negligible stress-related differences in the apical part of the 50% PCT (0.2% to 2.6%). The use of the 7-mm post effectively relieved the radical part of the splinted 30% PCT. The magnitude of the stress on the radical part of post-restored PCT was considerably increased in the presence of a cantilever. CONCLUSIONS: Splinted crowns supported by a 7-mm cast post-and-core are a favorable biomechanical approach for the restoration of PCT with severe loss of coronal structure. The use of a cantilever greatly aggravates the biomechanical response, especially of post-restored PCT.

Revascularization for a necrotic immature permanent lateral incisor: a case report and literature review.

BACKGROUND: Revascularization is a valuable treatment in immature necrotic teeth that allows the continuation of root development. CASE REPORT: This article describes the successful revascularization treatment of an immature maxillary lateral incisor that was initially diagnosed with apical periodontitis. The tooth was asymptomatic and functional clinically and radiographically during the follow-up period of 5 years. CONCLUSION: The follow-up showed evidence of progressive thickening of the dentinal walls, development of root length and apical closure. The article also discusses the currently available literature regarding revascularization of immature permanent teeth.

The role of orthodontic tooth movement in bone and root mineral density: a study of patients submitted and not submitted to orthodontic treatment.

BACKGROUND: Orthodontic force application to the teeth is responsible for a series of biological responses in the bone and dentin, which lead to some alterations of the mineral density of the tissues. Our objective was determine, through cone-beam computed tomography (CBCT), the mineral density of the apical third of the roots of the upper central incisors and of the periapical bone portion surrounding these teeth, in patients submitted to orthodontic treated and untreated individuals. MATERIAL/METHODS: 30 untreated individuals and 15 treated ones (treatment cessation at least 1 year before the study) underwent CBCT. Mineral density was assessed in the apical third of the root of the upper central incisors and in the alveolar bone in the periapical region of these teeth. In order to reduce CBCT-related mineral density variability, we standardized the cone-beam tomography device, the image-acquisition settings and the field of view positioning and size. Student's t test was used for the analyses. RESULTS: bone mineral density (BMD) and root mineral density (RMD), in Hounsfield Units, were 674.84 and 1282.26 for the untreated group and 630.28 and 1370.29 for the treated group, respectively. The differences between the group means were statistically significant for RMD (p<0.05). CONCLUSIONS: untreated individuals had a significant lower mean RMD in comparison with those submitted to orthodontic treatment.