Effects of all-on-four implant designs in mandible on implants and the surrounding bone: A 3-D finite element analysis.

AIMS: The purpose of this study was to observe the stresses of all-on-four implant designs in an edentulous mandible in the implant, surrounding bone, and monolithic ceramics. MATERIALS AND METHODS: In mandibular all-on-four implant models, anterior implants were placed vertically, and posterior implants were differently inclined. On the full-arch fixed prosthetic restoration monolithic zirconia framework, monolithic lithium disilicate was prepared as the superstructure. Model 1M (1M-15.5); posterior implants angled at 15° to the occlusion plane and a cantilever length of 5 mm, Model 2M; (2M-15.9), Model 3M; (3M-30.5), and Model 4M; (4M-30.9) were prepared. A total of 300 N bilateral force was applied at an angle of 30° and oblique to the occlusion plane. Stress values on dental implants, abutments, the surrounding bone, and prosthetic restorations were calculated. RESULTS: The highest stress concentration was observed in the 2nd connector region between the canine and the 1st premolar tooth in the monolithic zirconia frameworks (457.21 MPa). Stress concentration in the cortical bone was 60.93 MPa in posterior implants. Stress was higher in posterior angled implants than straight implants. Stress at posterior angulation increased by 21 MPa in implants angled at 15°. CONCLUSION: In bilateral loading, the force applied to anterior implants does not have a significant effect on the bone structure. Stress concentration increases in posterior angled implants and surrounding bone. Moreover, stress concentration increases as the length of the cantilever, the weakest part in all-on-four implants, increases. As posterior implant angulation increases, stress concentration level and localization are affected.

Discovery of a deeply divergent new lineage of vine snake (Colubridae: Ahaetuliinae: Proahaetulla gen. nov.) from the southern Western Ghats of Peninsular India with a revised key for Ahaetuliinae.

The Western Ghats are well known as a biodiversity hotspot, but the full extent of its snake diversity is yet to be uncovered. Here, we describe a new genus and species of vine snake Proahaetulla antiqua gen. et sp. nov., from the Agasthyamalai hills in the southern Western Ghats. It was found to be a member of the Ahaetuliinae clade, which currently comprises the arboreal snake genera Ahaetulla, Dryophiops, Dendrelaphis and Chrysopelea, distributed in South and Southeast Asia. Proahaetulla shows a sister relationship with all currently known taxa belonging to the genus Ahaetulla, and shares ancestry with Dryophiops. In addition to its phylogenetic position and significant genetic divergence, this new taxon is also different in morphology from members of Ahaetuliinae in a combination of characters, having 12-13 partially serrated keels on the dorsal scale rows, 20 maxillary teeth and 3 postocular scales. Divergence dating reveals that the new genus is ancient, dating back to the Mid-Oligocene, and is one of the oldest persisting monotypic lineages of snakes in the Western Ghats. This discovery adds to the growing list of ancient lineages endemic to the Agasthyamalai hills and underscores the biogeographic significance of this isolated massif in the southern Western Ghats.

Measuring the Complete-arch Distortion of an Optical Dental Impression.

Digital workflows have actively been used to produce dental restorations or oral appliances since dentists started to make digital impressions by acquiring 3D images with an intraoral scanner. Because of the nature of scanning the oral cavity in the patient's mouth, the intraoral scanner is a handheld device with a small optical window, stitching together small data to complete the entire image. During the complete-arch impression procedure, a deformation of the impression body can occur and affect the fit of the restoration or appliance. In order to measure these distortions, a master specimen was designed and produced with a metal 3D printer. Designed reference geometries allow setting independent coordinate systems for each impression and measure x, y, and z displacements of the cylinder top circle center where the distortion of the impression can be evaluated. In order to evaluate the reliability of this method, the coordinate values of the cylinder are calculated and compared between the original computer-aided design (CAD) data and the reference data acquired with the industrial scanner. The coordinate differences between the two groups were mostly less than 50 µm, but the deviations were high due to the tolerance of 3D printing in the z coordinates of the obliquely designed cylinder on the molar. However, since the printed model sets a new standard, it does not affect the results of the test evaluation. The reproducibility of the reference scanner is 11.0 ± 1.8 µm. This test method can be used to identify and improve upon the intrinsic problems of an intraoral scanner or to establish a scanning strategy by measuring the degree of distortion at each part of the complete-arch digital impression.

Semi-automatic and robust determination of dental arch form in dental cone-beam CT with B-spline approximation.

BACKGROUND AND OBJECTIVE: The dental arch form is generally used as a base for planning orthodontic treatments. It is, therefore, vital to determine the proper individual dental arch form for more accurate orthodontic treatment. We aimed to develop and validate a robust algorithm for semi-automatic determination of the dental arch form in dental cone-beam CT (CBCT) images with the cubic B-spline approximation. METHODS: Our algorithm consists of tooth segmentation, determination of an occlusal plane, and generation of intersection points between the teeth and the offset plane from the occlusal plane in CBCT images. By fitting a curve to the intersection points using the cubic B-spline curve approximation, the dental arch form was finally determined. The accuracy of the dental arch forms was evaluated by comparison with gold standards determined by an expert orthodontist. RESULTS: Thirteen dental CBCT scans from nine subjects were enrolled in this study. From the CBCT scans, 13 maxillary arch forms and 11 mandibular arch forms with Class I occlusion were determined by our proposed algorithm and evaluated for validation. The mean error between the dental arch forms of gold standards and our method using the cubic B-spline was 0.413 ± 0.092 mm (range, 0.264-0.587 mm). CONCLUSIONS: Our proposed method showed reliable accuracy of determining the dental arch forms for the maxilla and mandible. These results suggested that this method might be used for planning automatic tooth setup for individual patients.

Tongue pressure distribution of individual normal occlusions and exploration of related factors.

BACKGROUND: Tongue plays an important part in oral and maxillofacial system. Measurement of tongue pressure helps to evaluate the performance of tongue movement. OBJECTIVES: To establish a system for measuring tongue pressure against hard palate and to preliminarily explore pressure distribution of individual normal occlusions and the relationship with dental arch form. METHODS: A total of 19 volunteers of individual normal occlusions out of 189 dental students met inclusion criteria (nine males, ten females, aged 25.53 ± 0.96 years). A force-sensing resistor device was used to measure tongue pressure at rest and functional state (swallowing). We observed tongue pressure of four channel (anterior, posterior and lateral sides of hard palate) in sitting, supine position and swallowing. We analysed pressure differences according to gender and explored correlation relationship between tongue pressure and dental arch width and length using 3D digital maxillary image. RESULTS: In rest, tongue pressure against hard palate increased from front to back in both sitting and supine position, without gender differences. When swallowing saliva, the pressure at lateral sides of females was found significantly higher than that of males. Bivariate correlation analysis revealed duration of swallowing was positively correlated with BMI and weight at posterior region and positively correlated with palatal length at anterior palate. The greater the dental arch width, the smaller the pressure of swallowing in the anterior and lateral region. CONCLUSION: In rest, there was consistent pressure of tongue against hard palate. The pressure increased significantly during swallowing, especially in females. Tongue pressure was related to dental arch length, width, BMI and weight.

Maxillary arch dimensions associated with acoustic parameters in prepubertal children.

OBJECTIVES: To evaluate the association between maxillary arch dimensions and fundamental frequency and formants of voice in prepubertal subjects. MATERIALS AND METHODS: Thirty-five consecutive prepubertal patients seeking orthodontic treatment were recruited (mean age = 11.41 ± 1.46 years; range, 8 to 13.7 years). Participants with a history of respiratory infection, laryngeal manipulation, dysphonia, congenital facial malformations, or history of orthodontic treatment were excluded. Dental measurements included maxillary arch length, perimeter, depth, and width. Voice parameters comprising fundamental frequency (f0_sustained), Habitual pitch (f0_count), Jitter, Shimmer, and different formant frequencies (F1, F2, F3, and F4) were measured using acoustic analysis prior to initiation of any orthodontic treatment. Pearson's correlation coefficients were used to measure the strength of associations between different dental and voice parameters. Multiple linear regressions were computed for the predictions of different dental measurements. RESULTS: Arch width and arch depth had moderate significant negative correlations with f0 ( r = -0.52; P = .001 and r = -0.39; P = .022, respectively) and with habitual frequency ( r = -0.51; P = .0014 and r = -0.34; P = .04, respectively). Arch depth and arch length were significantly correlated with formant F3 and formant F4, respectively. Predictors of arch depth included frequencies of F3 vowels, with a significant regression equation ( P-value < .001; R2 = 0.49). Similarly, fundamental frequency f0 and frequencies of formant F3 vowels were predictors of arch width, with a significant regression equation ( P-value < .001; R2 = 0.37). CONCLUSIONS: There is a significant association between arch dimensions, particularly arch length and depth, and voice parameters. The formant most predictive of arch depth and width is the third formant, along with fundamental frequency of voice.

Curva de Spee: causas y tratamiento de su descompensación / Spee curve: causes and treatment of its discompensation

En el presente artículo se analiza y pasa revista a la bibliográfica acerca de la Curva de Spee: su etiología, los diferentes factores que pueden descompensarla, y los posibles tratamientos para corregirla en caso deestar alterada. Una mordida abierta esqueletal o dentaria, o una mordida profunda esqueletal o dentaria pueden modificarla, pudiendo utilizarse varios recursos y técnicas para tratar estos desórdenes, y así nivelar la curva.

In the present paper, the literature is analysed and reviewed the Curve of Spee: its aetiology, the different factors that can decompensate it, and the possible treatments to correct it in case of beingaltered. An open skeletal or dental bite, or a deep skeletal ordental bite can modify it, being able to use several resources and techniques to treat these disorders, and thus to level the curve.

Outcomes with a posterior reduced dental arch: a randomised controlled trial.

To compare function, patient satisfaction and quality of life of patients with a posterior reduced mandibular arch with those who had all missing teeth replaced with removable partial dentures. Patients with at least three and not more than six posterior occluding pairs of teeth were enrolled sequentially and randomised into one of two treatment groups: a denture and no-denture group. A research assistant allocated interventions; concealment was ensured using opaque-sealed envelopes. Analysis of data was performed in stages, adding samples of 10 incrementally, and stopping when the relevant statistical tests indicated a clear conclusion as judged by the power set at 80% or above. Study outcomes included patient satisfaction, function and survival of remaining teeth at 3 and 12 months post-intervention, using a visual analogue scale and the Oral Impacts on Daily Performance). Statistical analysis was performed by the 'intention-to-treat' principle. Age range of included patients was 23-55 years (mean = 42·3; s.d. = 9·2), with 78% being females. Most patients (70%) belonged to the low- or no-income group. Nine patients left the study, for different reasons. Primary outcomes for the denture group: 10% of the patients were not satisfied and 20% were unhappy with their function; for the no-denture group: 85% of the patients (with 15% having left the study) were satisfied with both their function and their non-denture status. Patients with posterior reduced mandibular dental arches reported greater perceived satisfaction, function and quality of life compared to those who had received a cobalt-chrome clasp-retained partial removable prosthesis.

Mechanical equilibrium of forces and moments applied on orthodontic brackets of a dental arch: Correlation with literature data on two and three adjacent teeth.

Although orthodontics have greatly improved over the years, understanding of its associated biomechanics remains incomplete and is mainly based on two dimensional (2D) mechanical equilibrium and long-time clinical experience. Little experimental information exists in three dimensions (3D) about the forces and moments developed on orthodontic brackets over more than two or three adjacent teeth. We define here a simplified methodology to quantify 3D forces and moments applied on orthodontic brackets fixed on a dental arch and validate our methodology using existing results from the literature by means of simplified hypotheses.

A comparison of three-dimensional stress distribution and displacement of naso-maxillary complex on application of forces using quad-helix and nickel titanium palatal expander 2 (NPE2): a FEM study.

BACKGROUND: Our objectives are to analyse and to compare the stress distribution and displacement of the craniofacial structures, following the application of forces from quad-helix and Nickel Titanium Palatal Expander-2 (NPE2) using finite element analysis. METHODS: Three-dimensional finite element models of young dried human skull, quad-helix appliance and NPE2 were constructed, and the initial activation of the expanders was stimulated to carry out the analysis and to evaluate the Von Misses stresses and displacement. RESULTS: Both the models demonstrated the highest stresses at the mid-palatal suture, with maximum posterior dislocation. The second highest stress was recorded at the fronto-zygomatic suture. The pattern of stress distribution was almost similar in both the groups, but NPE2 revealed lower magnitude stresses than quad-helix. The only exception being quad-helix model showed high stress levels around pterygo-maxillary suture whereas minimal stress around pterygo-maxillary suture was noticed after NPE2 activation. The cusp of the erupting canine and the erupting mesiobuccal cusp of the second molar showed outward, backward and downward displacement signifying increase in their eruption pattern following maxillary expansion. CONCLUSIONS: Maxillary expansion using quad-helix and NPE2 can be used in posterior crossbite correction in cases where maximum skeletal changes are desirable at a younger age; it is furthermore effective in treating young patients with impacted or displaced teeth. Quad-helix and NPE2 produced acceptable forces for orthopaedic treatment even after being orthodontic appliances; their clinical application should be correctly planned as the effects of these appliances are largely age dependent.

An acoustic study of multiple lateral consonants in three Central Australian languages.

This study presents dental, alveolar, retroflex, and palatal lateral /̪ll ɭ ʎ/ data from three Central Australian languages: Arrernte, Pitjantjatjara, and Warlpiri. Formant results show that the laminal laterals (dental /̪l/ and palatal /ʎ/) have a relatively low F1, presumably due to a high jaw position for these sounds, as well as higher F4. In addition, the palatal /ʎ/ has very high F2. There is relatively little difference in F3 between the four lateral places of articulation. However, the retroflex /ɭ/ appears to have slightly lower F3 and F4 in comparison to the other lateral sounds. Importantly, spectral moment analyses suggest that centre of gravity and standard deviation (first and second spectral moments) are sufficient to characterize the four places of articulation. The retroflex has a concentration of energy at slightly lower frequencies than the alveolar, while the palatal has a concentration of energy at higher frequencies. The dental is characterized by a more even spread of energy. These various results are discussed in light of different acoustic models of lateral production, and the possibility of spectral cues to place of articulation across manners of articulation is considered.

Three-Dimensional Finite Element Analysis of the Biomechanical Behaviors of Implants with Different Connections, Lengths, and Diameters Placed in the Maxillary Anterior Region.

PURPOSE: To evaluate the biomechanical behaviors of multiple implant-supported prostheses with different implant lengths, connections, locations, and restoration materials in the maxillary anterior region using three-dimensional finite element analysis. MATERIALS AND METHODS: A finite element model of a maxillary image was created from a tomography data bank. The simulations were executed in two types of models based on the treatment plan: (1) two implants with 4.0-mm diameters placed in the maxillary central incisors to simulate an implant-supported fixed prosthesis with four elements with a cantilever of both maxillary lateral incisors; (2) two implants with 3.75-mm diameters placed in the maxillary lateral incisors to simulate a conventional fixed prosthesis with four elements with pontics for maxillary central incisors. Subsequently, the models created were subdivided into eight subgroups according to implant length, connection type, and restoration material. A total static oblique load of 150 N was applied to the cingulum area of the palatal surfaces of the four incisors at an angle of 45 degrees to the long axis of the implant in the palatal-labial direction. Bone stresses were analyzed through maximum and minimum principal stresses and ductile material as implant, framework, and abutments were analyzed using von Mises stress criterion. RESULTS: Regardless of implant diameter and type of treatment, the 8.5-mm-long implants exhibited the lowest tensile and compressive stresses. Maximum and minimum principal stresses were identified in the cortical bone. The lowest von Mises equivalent stress values were identified in the metal-ceramic prostheses, with the exception of the cantilever prosthesis model with flat top connection. Conical cone implant models exhibited maximum von Mises equivalent stress in contact with the abutment. CONCLUSION: The lowest principal stresses in the peri-implant bone were observed in implants with conical cone connection and 8.5 mm in length. Also, in most cases, the models with metal-ceramic restorations exhibited better stress distributions.

A revised approach of human mastication function rehabilitation through monotypical mastication analysis.

OBJECTIVE: The aim of the simulation was to find the forcing laws, which provide the close-to reality mastication motions of the components of the system and to investigate the contact zones, interaction forces and their action points as they vary in time. The loss of one or few elements of the mastication system can be restored without significant violations of the overall function provided the general correlations among the mastication system elements, which were influenced during the evolutionary development, have been determined in advance. MATERIALS AND METHODS: We present an approach based on the computer simulation of mastication biomechanics on the basis of finite element (FE) models. They were generated by using the data acquired with both optical and CT scanning systems, which enabled to obtain highly accurate three-dimensional geometrical models of all hard parts of the mastication system of a real dead goat. The surfaces of dental arcs of upper and lower jaws mechanically interacting one against another have been used as the main parts of the model. RESULTS: Using FE models we discovered that mastication forces are correlated directly between dental arches and TMJ surfaces. Factors influencing geometry of dental arches results a destroy jaw function. CONCLUSION: In the course of this analysis the mastication system of a goat has been considered as a representative of the ruminant individual and enabled to demonstrate the mechanics of the mastication process with insights for evaluation of the similarities and differences against the human mastication.

A field survey of the partially edentate elderly: Investigation of factors related to the usage rate of removable partial dentures.

Although the shortened dental arch (SDA) concept has been known to all over the world, acceptance of the SDA concept as an oral health standard can be questionable from the patients' point of view, even if it is biologically reasonable. Furthermore, because the health insurance system covers removable partial dentures (RPDs) for all citizens in Japan, SDA patients seem to prefer to receive prosthetic treatment to replace the missing teeth. However, there were few field surveys to investigate the usage rate of RPDs in Japan. The purpose of this study was to determine the usage rate of RPDs in older Japanese subjects and to investigate the factors related to the usage of RPDs. Partially edentate participants (n = 390) were included in this study. Oral examinations were conducted to record several indices. The Cochran-Armitage trend test was used to evaluate the relationship between the number of missing teeth and the usage rate of RPDs. Chi-squared tests and logistic regression analysis were conducted to evaluate the factors related to the usage rate of RPDs. Usage of RPDs had a significantly positive association with the number of missing distal extension teeth and bilaterally missing teeth. The usage rate of RPDs increased as the number of missing distal extension teeth increased (P for trend < 0·001). The conclusion of this study was that participants with missing distal extension teeth had higher usage rates of RPDs than other participants, and the usage rate increased as the number of missing distal extension teeth increased.

Effect of prosthodontic planning on lateral occlusion scheme: a comparison between conventional and digital planning.

UNLABELLED: Recently, digital wax-up is proposed as a tool to aid prosthodontic planning. However, there are no data about the effect of prosthodontic planning on lateral occlusion scheme. OBJECTIVE: This study aims to evaluate the impact of conventional and digital prosthodontic planning on lateral occlusion scheme. MATERIAL AND METHODS: Dental models of 10 patients were collected. All models had Angle Class I occlusion and were undergoing prosthodontic treatment that would influence the lateral occlusion scheme. Each set of models had received both conventional wax-up and digital wax-up. In relation to the lateral occlusion scheme, the following variables were evaluated: the prevalence of the different lateral occlusion scheme, number of contacting teeth and percentage of each contacting tooth. Four excursive positions on the working side were included: 0.5, 1.0, 2.0 and 3.0 mm from the maximal intercuspation position. RESULTS: The lateral occlusion scheme of the two wax-up models was subjected to alterations following excursion. There was a tendency for the prevalence of canine-guided occlusion to increase and for the prevalence of group function occlusion to decrease with increasing excursion. The number of contacting teeth was decreasing with the increasing magnitude of excursion. For the 0.5 mm and 1.0 mm positions, the two wax-ups had significantly greater contacts than the pre-treatment models, while at the 2.0 mm and 3.0 mm positions, all the models were similar. For all models, canines were the most commonly contacting teeth, followed by the teeth adjacent to them. No difference was observed between the two wax-ups in relation to the number of contacting teeth. CONCLUSION: Although the prosthodontic planning had influenced the pattern of the lateral occlusion scheme and contacts, there was no difference between the conventional and digital prosthodontic planning.

Assessment of human intraoral thermal sensitivity with simple devices in the clinic: implications for orofacial pain conditions.

AIMS: To use simple thermal devices with different diameters and temperatures to investigate reliability and magnitude of human intraoral thermal sensitivity. METHODS: Sixteen healthy volunteers participated. Six thermal devices with tapered circular ends (stimulus diameter 3, 5, and 10 mm) were used. Three different temperatures (room temperature, heat, and cold) were applied with each of the three diameters, ie, nine combinations. Participants were stimulated in randomized order at nine different sites: tongue, lip, maxillary attached gingiva adjacent to the left and right central incisors (without touching the lip) and to the left and right premolars (with or without touching the lip), and the left and right cheeks extraorally. Participants rated the perceived stimulus intensity on 0-50- 100 numeric rating scales (NRS). The number of paradoxical thermal sensations was also recorded. Ten volunteers were examined twice on the same day and recalled for a second session for assessment with the 5-mm-diameter device of within- and between-session reliability (interclass correlation coefficients [ICC]). The results were analyzed using a three-way analysis of variance. RESULTS: Reliability of NRS scores ranged from poor (ICC = 0.09, with cold stimulation at the premolar region) to excellent (ICC > 0.92, with cold stimulation at the cheek or tongue). NRS values varied with stimulus diameter (P < .050), temperature (P < .001), and sites (P < .001), with significant size x site and temperature x site interactions (P < .001). The tongue was the most sensitive site (P < .001) and the gingiva was the least sensitive site (P < .050). The 10-mm-diameter device produced higher NRS scores than the 3-mm-diameter device. CONCLUSION: The reliability of intraoral thermal sensitivity recorded with the 5-mm-diameter device varied greatly between different sites. Nonetheless, with this caveat in mind, the study did document that semiquantitative assessment of intraoral thermal sensitivity is feasible and applicable for clinical studies in different intraoral pain conditions.

The feeding biomechanics and dietary ecology of Paranthropus boisei.

The African Plio-Pleistocene hominins known as australopiths evolved derived craniodental features frequently interpreted as adaptations for feeding on either hard, or compliant/tough foods. Among australopiths, Paranthropus boisei is the most robust form, exhibiting traits traditionally hypothesized to produce high bite forces efficiently and strengthen the face against feeding stresses. However, recent mechanical analyses imply that P. boisei may not have been an efficient producer of bite force and that robust morphology in primates is not necessarily strong. Here we use an engineering method, finite element analysis, to show that the facial skeleton of P. boisei is structurally strong, exhibits a strain pattern different from that in chimpanzees (Pan troglodytes) and Australopithecus africanus, and efficiently produces high bite force. It has been suggested that P. boisei consumed a diet of compliant/tough foods like grass blades and sedge pith. However, the blunt occlusal topography of this and other species suggests that australopiths are adapted to consume hard foods, perhaps including grass and sedge seeds. A consideration of evolutionary trends in morphology relating to feeding mechanics suggests that food processing behaviors in gracile australopiths evidently were disrupted by environmental change, perhaps contributing to the eventual evolution of Homo and Paranthropus.

Covariation in the human masticatory apparatus.

Many studies have described shape variation of the modern human cranium in relation to subsistence; however, patterns of covariation within the masticatory apparatus (MA) remain largely unexplored. The patterns and intensity of shape covariation, and how this is related to diet, are essential for understanding the evolution of functional masticatory adaptations of the human cranium. Within a worldwide sample (n = 255) of 15 populations with different modes of subsistence, we use partial least squares analysis to study the relationships between three components of the MA: upper dental arch, masseter muscle, and temporalis muscle attachments. We show that the shape of the masseter muscle and the shape of the temporalis muscle clearly covary with one another, but that the shape of the dental arch seems to be rather independent of the masticatory muscles. On the contrary, when relative positioning, orientation, and size of the masticatory components is included in the analysis, the dental arch shows the highest covariation with the other cranial parts, indicating that these additional factors are more important than just shape with regard to covariation within the MA. Covariation patterns among these cranial regions differ mainly between hunting-fishing and gathering-agriculture groups, possibly relating to greater masticatory strains resulting from a large meat component in the diet. High-strain groups show stronger covariation between upper dental arch and masticatory muscle shape when compared with low-strain groups. These results help to provide a clearer understanding of constraints and interlinkage of shape variation within the human MA and allow for more realistic modeling and predictions in future biomechanical studies.

Biomechanical factors associated with mandibular cantilevers: analysis with three-dimensional finite element models.

PURPOSE: Although the risks of using a cantilever to treat missing teeth have been described, the mechanisms remain unclear. This study aimed to reveal these mechanisms from a biomechanical perspective. The effects of various implant sites, number of implants, and superstructural connections on stress distribution in the marginal bone were analyzed with three-dimensional finite element models based on mandibular computed tomography data. Forces from the masseter, temporalis, and internal pterygoid were applied as vectors. MATERIALS AND METHODS: Two three-dimensional finite element models were created with the edentulous mandible showing severe and relatively modest residual ridge resorption. Cantilevers of the premolar and molar were simulated in the superstructures in the models. The following conditions were also included as factors in the models to investigate changes: poor bone quality, shortened dental arch, posterior occlusion, lateral occlusion, double force of the masseter, and short implant. Multiple linear regression analysis with a forced-entry method was performed with stress values as the objective variable and the factors as the explanatory variable. RESULTS: When bone mass was high, stress around the implant caused by differences in implantation sites was reduced. When bone mass was low, the presence of a cantilever was a possible risk factor. The stress around the implant increased significantly if bone quality was poor or if increased force (eg, bruxism) was applied. CONCLUSION: The addition of a cantilever to the superstructure increased stress around implants. When large muscle forces were applied to a superstructure with cantilevers or if bone quality was poor, stress around the implants increased.

The effect of platform switching on stress distribution in implants and periimplant bone studied by nonlinear finite element analysis.

STATEMENT OF PROBLEM: It is unknown whether dental implant systems with a platform-switched configuration have better periimplant bone stress distribution and lead to less periimplant bone level changes. PURPOSE: The purpose of this study was to quantitatively investigate interfacial stress and stress distribution in implant bone in 2 implant abutment designs (platform-switched design and conventional diameter matching) by using a nonlinear finite element analysis method. MATERIAL AND METHODS: A finite element simulation study was applied to 2 commercially available dental implant systems: the Ankylos implant system with a reduced-diameter abutment (platform-switched implant) and the Anthogyr implant system with an abutment of the same diameter (regular platform implant). These 2 dental implant systems were positioned in a bone block, which was constructed based on a cross-sectional image of a human mandible in the molar region. In simulation, a single vertical load of 50 N, 100 N, or 150 N and horizontal loads of 50 N and 100 N were applied to the occlusal surface of the abutment. RESULTS: The finite element analysis found that the Ankylos implant system has a higher maximum von Mises stress in the implant abutment connection section and a lower maximum von Mises stress in the periimplant bone. The opposite results were found in the Anthogyr implant system. CONCLUSIONS: Lower stress levels in the periimplant bone with a more uniform stress distribution were found for the Ankylos implant system with a platform-switched configuration. Although relatively higher stress was found in the abutment, premature implant failure is not anticipated because of the high strength of titanium alloy.