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Periodontitis is a widespread oral disease accompanied by uncontrolled inflammation-related tissue destruction. Periodontitis is related to various factors. Among them, occlusal trauma can aggravate the severity of periodontitis and has been attracting a great deal of attention. We systematically searched PubMed and Web of Science databases for related articles. Keywords for the search were "mechanical force", "mechanical stress", "occlusal trauma" and "periodontitis". This review focuses on the effect of mechanical forces on periodontitis and discusses the possible pivotal targets participating in this process. We elucidated and summarized 21 articles that reported on our topic. Several biological processes and pathways that participate in enhancing the inflammatory response to mechanical stress have been studied, including the regulation of osteogenesis and osteoclastic resorption balance, Yes-associated protein signaling, induction of collagen destruction, and regulation of programmed cell death. Mechanical force enhances the process of periodontitis in multiple ways. However, currently, no studies have further examined its underlying mechanism. Understanding the specific roles of mechanical forces may assist in the treatment of periodontitis with traumatic occlusal trauma., (© 2023 Wiley Periodicals LLC.)

Variation of the occlusal vertical dimension (OVD) has been discussed empirically for decades, but it has not been thoroughly explored with experimental data. In the present study, cone-beam computerized tomography (CBCT) of six selected patients was conducted to evaluate the bones of the lower facial structures. The anterior lower facial heights (ALFHs), alveolar process heights (APHs), vertical facial pattern (VFP), occluding dentition height (ODH) and condyle space (CS), which were evaluated by three-dimensional (3D) and two-dimensional (2D) lateral cephalometry derived from CBCT, were compared before and two years after the OVD increased full mouth rehabilitation. Consistent significant increases in ALFHs and the VFP indicated the OVD increase, while a significant decrease in the ΔODH indicated compressed dentition. In addition, 55 of the 56 sites (98.21%) of APH measurement illustrated no significant difference before and after treatment. The findings indicated that the increased OVD did not relapse to baseline and was sufficiently tolerated, with mostly constant APHs and an altered ODH after two years of observation in the six patients.

Objective: This study aims to systematically evaluate the effects of traumatic occlusion on the periodontal tissue of rats. The set of questions to be answered were-Can traumatic occlusion acting on a healthy and an unhealthy periodontium cause periodontal destruction?, Design: The protocols for systematic review were all developed, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement and applied to animal research. Reporting of In vivo experiment guidelines for reporting animal research to assess the risk of bias of the studies., Materials and Methods: A literature search was conducted using MEDLINE through PubMed and manual search from the reference lists of main articles related to the theme., Results: This search strategy identified 65 references, of which 33 were considered inappropriate. The full texts of 32 articles were read, 31 of which did not meet the eligibility criteria and were excluded. The final selection included 1 article for which data was extracted for further evaluation. The article included shows a strongest reaction in the periodontium in front of a secondary occlusal trauma as inflammation and apical migration of the junctional epithelium, bone degradation, and decrease in the quantity of collagen fiber. However, primary occlusal trauma also presents these alterations, with the exception of apical migration of the junctional epithelium., Conclusions: Although only one study was included in the systematic review of traumatic occlusion, there is some evidence from experimental studies on animals that shows a coherent picture of the effects of traumatic occlusion on the periodontium. However, new studies are needed to fully answer the questions posed by this systematic review., Competing Interests: None

Trauma from occlusion remains an important concept in dentistry. Traumatic occlusion affects the biological system through a series of events that induces an aseptic inflammatory response and bone resorption. Clinical evidence of these biological events is present in the form of active traumatic lesions or adaptive mechanisms. If these clinical signs are not identified prior to periodontal surgery, failure of the procedure could result due to an exacerbated leukocyte presence and unresolving wound. However, if traumatic occlusion is adjusted, evidence demonstrates that even large inflammatory events such as replantation of an avulsed tooth can be successful. Thus, harmony of occlusal contacts without interference is essential in achieving predictable periodontal/implant bone regeneration.

Purpose: Occlusal trauma, resulting in the destruction of alveolar bone, is a form of periodontal disease caused by excessive mechanical stress (MS) during hyperocclusion. Previously, we showed that CC chemokine ligand (CCL) 2/CCR2 receptor axis plays a crucial role in MS-dependent osteoclastogenesis. However, in the previous work, we were unable to precisely measure changes in alveolar bone profiles. In the present study, we sought to establish a precise method for evaluating alveolar bone resorption induced by hyperocclusion using micro-computed tomography., Methods: Under anesthesia, a stainless steel wire was attached to the molars of 5-week-old C57/BL6 wild-type (WT) mice, CCL2 -/- mice, and CCR2 -/- mice to induce occlusal force overload. At days 0 and 7, hard tissue samples were harvested and analyzed by micro-computed tomography., Results: In the WT mice, bone mineral density of the alveolar bone was significantly decreased at day 7 as compared with day 0, with marked alveolar bone resorption observed. Similarly, significant alveolar bone resorption was observed in the CCL2 -/- and CCR2 -/- mice at day 7 as compared with day 0., Conclusions: Micro-computed tomographic images can be used to measure changes in bone mineral density in a mouse model of hyperocclusion. This method may be useful for further investigating bone changes in other periodontal disease research fields., (Copyright © 2017 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.)

Introduction: The knowledge of the anatomy surrounding Bichat's fat pad, as well as its clinical applications, is essential to indicate and to safely perform its removal. This surgery is indicated not only for esthetic purposes, but also for functional reasons. When used properly, Bichat's fat pad is composed of stem cells that have a similar phenotype to adipose stem cells, useful in the treatment of pathologies and/or complications, such as maxillary sinus membrane perforation, oroantral/oronasal communications, peri-implantitis, ulcers, fibrosis of the oral mucosa, soft tissue reconstruction, among others. Due to its location, it is prone to suffer clinically significant pathologies, as well as constant trauma., Aim: The aim of this study is to report two clinical cases and subsequent follow-ups, where bichectomy was performed to avoid dental trauma to mucosal tissues during the masticatory function. Also, literature review on the application of Bichat's fat pad in dentistry is provided., Case Report: Two female patients (20 and 24 years) reported discomfort and constant pain in the oral mucosa caused by dental trauma. At the clinical examination, patient presented augmented and injured mucosa. The surgical sequence of Bichat's fat pad removal, as well as the extra-/intraoral photographic follow-up (8, 15, 30, and 180 days) of the patients is described., Conclusion: In order to indicate and/or accomplish surgical procedures involving Bichat's fat pad, it is fundamental to know its anatomy and possible applications, not only for esthetic purposes, but also for functional purposes. The patients showed evident improvements following the removal of Bichat's fat pad., Clinical Significance: Application of Bichat's fat and its removal should be evaluated, being an alternative in patients who constantly undergo mucosal injury during masticatory function.

Angiogenesis is the formation of new blood vessels based on a pre-existing vasculature. It comprises two processes, sprouting of endothelial cells and the division of vessels due to abnormal growth of the microvasculature. It has been demonstrated that substance P (SP) can induce angiogenesis either by modulating endothelial cell growth (direct mechanism) or by attracting cells with angiogenic potential to the injury site (indirect mechanism). Therefore, the purpose of this article is to review the angiogenic mechanisms that regulate mineralized tissue formation in human dental pulp tissue and their relationship with SP expression as a defence response to stimuli such as the masticatory function and occlusal trauma. Articles included in this review were searched in PubMed, Scopus and ISI Web of Science databases, combining the following keywords: human dentine pulp, angiogenesis, angiogenic growth factors, neuropeptides, substance P, neurogenic inflammation, dentine matrix, dentinogenesis, occlusal trauma and dental occlusion. It is concluded that human dental pulp tissue responds to occlusal trauma and masticatory function with a neurogenic inflammatory phenomenon in which SP plays an important role in the direct and indirect mechanisms of angiogenesis by the action evoked via NK1 receptors at different cells, such as fibroblasts, endothelial and inflammatory cells, leading to new blood vessel formation which are needed to stimulate mineralized tissue formation as a defence mechanism., (© 2016 International Endodontic Journal. Published by John Wiley & Sons Ltd.)

Using a model of experimental occlusal trauma in mice, we investigated cytological kinetics of periodontal ligament by means of histopathological, immunohistochemical, and photographical analysis methods. Periodontal ligament cells at furcation areas of molar teeth in the experimental group on day 4 showed a proliferation tendency of periodontal ligament cells. The cells with a round-shaped nucleus deeply stained the hematoxylin and increased within the day 4 specimens. Ki67 positive nuclei showed a prominent increase in the group on days 4 and 7. Green Fluorescent Protein (GFP) positivity also revealed cell movement but was slightly slow compared to Ki67. It indicated that restoration of mechanism seemed conspicuous by osteoclasts and macrophages from bone-marrow-derived cells for the periodontal ligament at the furcation area. It was suggested that the remodeling of periodontal ligament with cell acceleration was evoked from the experiment for the group on day 4 and after day 7. Periodontal ligament at the furcation area of the molar teeth in this experimental model recovered using the cells in situ and the bone-marrow-derived cells.

Purpose: The aim of this retrospective cohort study was to evaluate the clinical performance of zirconia-based implant-supported single crowns and fixed dental prostheses (FDPs) made by 15 members of the Italian Academy of Prosthetic Dentistry (AIOP) over a time period of up to 5 years., Materials and Methods: One hundred thirty-one patients were treated with a total of 210 zirconia-based single crowns and FDPs on implants in anterior and posterior regions. A cohort group with parafunctional habits was compared with patients without parafunctional habits according to the esthetic, functional, and biologic United States Public Health Service criteria modified by the FDI World Dental Federation., Results: The estimated cumulative survival (ECS) and standard error (SE) of all restorations on implants was 91.95% ± 1.39%, and the estimated cumulative success (ECSs) and SE was 88.37% ± 1.72%. The ECS of single crowns and FDPs was 91.25% ± 3.69% and 95.23% ± 2.28%, respectively, and the estimated cumulative success rates were 88.84% ± 2.05% and 87.96% ± 3.16%, respectively. Mechanical failures, including four zirconia core fractures, three hairline cracks, four chippings, and five delaminations of the ceramic veneering material, were recorded during a 1- to 5-year observation period. The odds ratio of 3.39 (95% confidence interval: 1.18 to 9.73) showed a moderate association between parafunction and failure., Conclusions: Zirconiabased implant-supported restorations showed encouraging clinical results over a period of up to 5 years, but more clinical data are needed before these restorations can be considered a viable treatment alternative. Mechanical failures were primarily observed in patients with parafunctions.

Purpose: The aim of this retrospective cohort study was to evaluate the clinical performance of tooth-supported zirconia-based fixed dental prostheses (FDPs) made by 15 members of the Italian Academy of Prosthetic Dentistry over a time period of up to 5 years., Materials and Methods: Ninety-eight patients were treated with a total of 137 zirconia-based FDPs in anterior and posterior regions using primarily chamfer or knife-edge tooth preparations. The cohort group with parafunctional habits was compared with patients without parafunctional habits according to the esthetic, functional, and biologic United States Public Health Service criteria modified by the FDI World Dental Federation., Results: The estimated cumulative survival of all restorations was 94.70% ± 1.25% standard error (SE), whereas the estimated cumulative success decreased to 89.78% ± 2.58 SE. Mechanical failures, including three zirconia framework fractures, two hairline cracks, nine chippings, and one delamination of the ceramic veneering, were recorded during the 1- to 5-year observation period. An odds ratio of 2.02 (95% confidence interval: 0.67 to 6.12) showed a moderate association between parafunction and failure., Conclusions: Zirconia-based tooth-supported FDPs showed promising clinical results over a period of up to 5 years. Technical complications were more commonly detected in patients with parafunctional habits.

Background: The purpose of this study was to use functional magnetic resonance imaging (fMRI) to quantify changes in brain activity during experimental occlusal interference., Methods: Fourteen healthy volunteers performed a rhythmical tapping occlusion task with experimental occlusal interference of the right molar tooth at 0 mm (no occlusion), 0.5 mm, and 0.75 mm. The blood-oxygen-level dependent (BOLD) signal was quantified using statistical parametric mapping and compared between rest periods and task periods., Results: In tapping tasks with experimental occlusal interference of 0.75 mm or 0.5 mm, there was clear activation of the contralateral teeth-related primary sensory cortex and Brodmann's area 46. At 0 and 30 minutes after removal of the experimental occlusal interference, the activation clearly appeared in the bilateral teeth-related primary sensory cortices and Brodmann's area 46. At 60 minutes after the removal of the experimental occlusal interference, the activation of Brodmann's area 46 had disappeared, and only the bilateral teeth-related primary sensory cortices were active., Conclusions: The present results suggest that adjustments for experimental occlusal interference can be objectively evaluated using fMRI. We expect that this method of evaluating adjustments in occlusal interference, combined with fMRI and the tapping task, could be applied clinically in the future.

Aim: This study evaluates the relationship between occlusal interferences and premature contacts and bruxism by determining the relationship between unassisted and assisted nonworking interferences., Materials and Methods: In this study, 60 subjects (14 males and 46 females) that consisted of 30 bruxers (7 males, 23 females) and 30 nonbruxers (7 males, 23 females) were selected after completion of a questionnaire based on the exclusion criteria. Occlusal interferences in the centric relation and eccentric movements in the two groups were evaluated and recorded. Data were analyzed by SPSS software (version 16) using the Chi-square and paired t-tests., Results: The results showed a statistically significant relationship between bruxism and nonworking interferences (p < 0.05). There was no statistically significant relationship in the centric relation and other eccentric movements (p > 0.05). The number of assisted nonworking occlusal contacts was more than unassisted nonworking occlusal contacts., Conclusion: According to the results of this study, there is a relationship between certain types of occlusal interferences (nonworking interferences) and bruxism. Hence, it would be useful to examine occlusal contacts in bruxing patients to eliminate probable causative or contributing occlusal factors. Both assisted and unassisted nonworking occlusal contacts should be evaluated., Clinical Implication: Bruxism is an oral habit that consists of involuntary rhythmic or spasmodic nonfunctional gnashing, grinding or teeth clenching, other than chewing movements by the mandible. Bruxism may lead to occlusal trauma, tooth wear, fracture of the teeth and fillings, and hypertrophy of the masticatory muscles. Treatment of bruxism needs a correct diagnosis. Therefore, it is useful to determine the relationship between occlusal interferences and bruxism in order to prevent its development by adjusting for these interferences.

Objective: To evaluate the effect of subgingival scaling/root planning (SRP) and occlusal adjustment on clinical and occlusal parameters in teeth with chronic periodontitis and secondary occlusal trauma., Methods: Eighteen patients with chronic periodontitis and occlusal trauma were included and randomly divided into group A and group B. On day 0, group A was treated by full-mouth subgingival scaling and root planning, and group B was treated by occlusal adjustment in occlusal trauma site. On day 28, group A was treated by occlusal adjustment in occlusal trauma site, and group B was treated by full-mouth subgingival scaling and root planning. Probing depth (PD), attachment loss (AL), bleeding index (BI) were evaluated on 0, 28 and 56 d, and the occlusal time (OT) and the percentage of occlusal force were evaluated on 0, 28 and 56 d in occlusal trauma site. The data was statistically analyzed., Results: In baseline, the PD[(4.42 ± 1.41) mm vs (4.36 ± 1.38) mm], AL [(2.75 ± 1.32) mm vs (2.63 ± 1.37) mm] and BI [(2.20 ± 0.81) vs (2.24 ± 0.89)] of the full-mouth showed no significant difference between the two groups (P > 0.05). There was no significant difference in PD [(5.21 ± 1.21) mm vs (5.08 ± 1.12) mm], AL [(4.94 ± 1.47) mm vs (4.89 ± 1.32) mm], BI [(2.61 ± 0.92) vs 2.50 ± 0.79)], OT [(1.29 ± 0.39) s vs (1.34 ± 0.35) s] and the percentage of occlusal force [(6.8 ± 2.1)% vs (7.4 ± 1.7)%] in occlusal trauma site between the two groups(P > 0.05). After SRP therapy, the PD,AL,BI and OT were significantly decreased (P < 0.05).The clinical parameters exhibited no significant difference after only occlusal adjustment(P > 0.05).On 56 d, the reduction in clinical parameters was not significantly different between the two groups(P > 0.05),however the reduction of OT and the change of the percentage of occlusal force in group A [(0.85 ± 0.41) s, (2.2 ± 2.2)%] were more significant than those in group B [(0.70 ± 0.38) s; (1.5 ± 1.6)%] (P < 0.05). After occlusal adjustment, the increase of OT in group A [(0.21 ± 0.11) s] was lower than that in group B [(0.67 ± 0.37) s]through the 28-day observation period (P < 0.05)., Conclusions: Occlusal adjustment alone is inadequate for control and management of periodontitis.SRP therapy can eliminate the inflammation and decrease the OT of tooth with occlusal trauma.The combination of SRP and occlusal adjustment may achieve more stable results.

The aim of this review of the literature was to assess the biological effects of occlusal trauma on the stomatognathic system focusing on animal studies. However, there are no conclusive explanations on the association between occlusal trauma and disease of the stomatognathic system. A literature survey was performed using the Medline database, covering the period from 1967 to 2012. Over 300 abstracts were reviewed, and 70 manuscripts were selected. Additional references from citations within the articles were obtained, and current textbooks were also used. This review does not include the effects of occlusal trauma on dental implants or dental prostheses/appliances. A total of 70 full articles were included for the final analysis. The selected 70 articles were classified into the following five categories, including the effects of occlusal trauma on the pulp tissues, periodontal tissues, masticatory muscle, temporomandibular joint (TMJ) and central nervous system (CNS). It was demonstrated that occlusal trauma caused a variety of harmful biological effects on stomatognathic system. Additionally, occlusal trauma could lead to some pain substance changes in the pulp, periodontal tissues, masticatory muscle, TMJ and CNS, which was possibly related to the peripheral and the central neuronal sensitisation. However, these findings demonstrate that there are remaining disagreements by various authors. More randomised trials are needed to validate these effects., (© 2012 Blackwell Publishing Ltd.)

There are few review articles in the area of human research that focus on the interactions between occlusion and brain function. This systematic review discusses the effect of occlusion on the health of the entire body with a focus on brain function. Available relevant articles in English from 1999 to 2011 were assessed in an online database and as hard copies in libraries. The selected 19 articles were classified into the following five categories: chewing and tongue movements, clenching and grinding, occlusal splints and occlusal interference, prosthetic rehabilitation, and pain and stimulation. The relationships between the brain activity observed in the motor and sensory cortices and movements of the oral and maxillofacial area, such as those produced by gum chewing, tapping and clenching, were investigated. It was found that the sensorimotor cortex was also affected by the placement of the occlusal interference devices, splints and implant prostheses. Brain activity may change depending on the strength of the movements in the oral and maxillofacial area. Therefore, mastication and other movements stimulate the activity in the cerebral cortex and may be helpful in preventing degradation of a brain function. However, these findings must be verified by evidence gathered from more subjects., (© 2012 Blackwell Publishing Ltd.)

Objective: To investigate the effects of an experimentally-induced increase in the occlusal vertical dimension (iOVD) on the functional characteristics of temporomandibular joint (TMJ) mechanoreceptors in rats., Materials and Methods: Sixty 13-week-old male albino Wistar rats were divided into control and iOVD groups (30 animals each). The vertical dimension between the maxillary and mandibular molars in the iOVD group was increased by 2.0 mm with a build-up of resin on the maxillary molars. Single-unit activities of TMJ mechanoreceptors were evoked by passive jaw movement. Recording was performed from the gasserian ganglion 1 day and 1, 3, 5, 7, and 9 weeks after the establishment of iOVD., Results: Compared with the control group, the firing threshold was significantly lower at 1, 3, and 5 weeks after iOVD in the iOVD group. There were no significant differences in the firing threshold at 1 day, or 7 or 9 weeks. The maximum instantaneous firing frequency was significantly higher at 1, 3, and 5 weeks after iOVD in the iOVD group, but there were no significant differences at 1 day, or 7 or 9 weeks. There were no significant differences in the average firing frequency during the experimental period., Conclusions: The present study findings suggest that TMJ mechanoreceptors in adult rats may ultimately adapt to iOVD.

Introduction: Mice with brachymorphism (bm) have defective chondrogenesis, including abnormal growth of the spheno-occipital synchondrosis. Malocclusion (anterior transverse crossbite) sometimes spontaneously occurs in inbred BALB/c-bm/bm mice, before the mandibular incisors erupt and make contact with the maxillary incisors. The aim of this study was to determine whether functional lateral loads to incisors promote anterior transverse crossbites in BALB/c-bm/bm mice., Methods: BALB/c-bm/bm mice with normal occlusion (normal group), BALB/c-bm/bm mice with malocclusion in which the incisors were not cut (mal group), and BALB/c-bm/bm mice in which the incisors had been cut to eliminate the functional lateral load during continued growth (mal-cut group) were used. We examined the amounts of shift of the maxillary and mandibular incisors in each group using radiographic images., Results: The amount of shift of the maxillary incisors in the mal group was significantly greater than that in normal group. The total amount of shift from the maxilla to the mandible in the mal group was significantly greater than in the normal and mal-cut groups., Conclusions: The results suggest that a continuous functional lateral load to the incisors is strongly related to promoting and worsening anterior transverse crossbite in BALB/c-bm/bm mice., (Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Purpose: The inter-relationships between various implant and bone parameters were evaluated for their influence on the von Mises stress distribution within the mandible using the finite element procedure. The maximum compressive stresses in cancellous and cortical bone were compared to the published stress-strain data to determine bone fracturing status when the maximum (traumatic) loading is applied., Materials and Methods: Parameters considered herein include the implant diameter and length. Also considered are Young's modulus of cancellous bone and that of cortical bone, along with its thickness. The implant-bone system was modeled using two-dimensional plane strain elements, 50% osseointegration between implant and cancellous bone was assumed, and linear relationships were assumed between the stress value and Young's modulus of both cancellous and cortical bone at any specific point within the mandible., Results: Implant length was more influential than implant diameter within cancellous bone, whereas implant diameter was more influential in cortical bone. A ranking of all the parameters indicated that the applied masticatory force had a more significant influence on the stress difference, in both cancellous and cortical bone, than all other parameters. Young's modulus of cortical bone and implant length were least influential in cancellous and cortical bone, respectively. Under traumatic loading, cancellous bone fractured for all parameter combinations. When all parameters were set to their average values, the cortical bone did not fracture under traumatic loading. However, it fractured if all the parameters were all set to the minimum values., Conclusion: Quantitative evaluation and ranking of the major implant and bone parameters will help provide practical guidelines that are useful for the design and testing of dental implants. The study may also be of interest to dental professionals in evaluating possible implant placement options under various clinical scenarios.

How 'control' characteristics of masticatory jaw movement, such as skilfulness of the movement, change after alteration in occlusion remains uncertain. For each of 10 healthy adults with good occlusion, an occlusal interference with artificial 'tooth-cusp' was introduced to the crown of the upper molar tooth on the non-working side of unilateral chewing. Mandibular incisor-point movements were then recorded by a 3D tracking device. The introduction of the occlusal interference induced a remarkable increase in the normalized jerk-cost (NJC), prolonged duration of the decelerative phase and lowered peak velocity for jaw closing movement during chewing. Overall, the NJC and velocity profile showed significant recoveries during the course of about 90 repetitive chewing cycles performed under the altered occlusal condition. These findings suggest that acute adaptive changes of jaw motion after introduction of occlusal interference might be characterized as the recovery process of movement skilfulness in terms of movement smoothness and velocity profile.

Background: The presence of the periodontal ligament (PDL) makes it possible to absorb and distribute loads produced during masticatory function and other tooth contacts into the alveolar process via the alveolar bone proper. However, several factors affect the integrity of periodontal structures causing the destruction of the connective matrix and cells, the loss of fibrous attachment, and the resorption of alveolar bone., Methods: The purpose of this study was to evaluate the stress distribution by finite element analysis in a PDL in three-dimensional models of the upper central incisor under three different load conditions: 100 N occlusal loading at 45 degrees (model 1: masticatory load); 500 N at the incisal edge at 45 degrees (model 2: parafunctional habit); and 800 N at the buccal surface at 90 degrees (model 3: trauma case). The models were built from computed tomography scans., Results: The stress distribution was quite different among the models. The most significant values (harmful) of tensile and compressive stresses were observed in models 2 and 3, with similarly distinct patterns of stress distributions along the PDL. Tensile stresses were observed along the internal and external aspects of the PDL, mostly at the cervical and middle thirds., Conclusions: The stress generation in these models may affect the integrity of periodontal structures. A better understanding of the biomechanical behavior of the PDL under physiologic and traumatic loading conditions might enhance the understanding of the biologic reaction of the PDL in health and disease.

An analysis of fracture and deformation modes in tooth enamel subjected to occlusal loading is presented. Several competing modes are identified: deformation by yield beneath the indenter; median cracking from the ensuing plastic zone and analogous radial cracking from the dentin-enamel junction along the load axis; and margin cracking from the cervical enamel-cement junction. The analysis, based on a simple model of tooth geometry, presents relations for the critical loads to initiate these damage modes within the enamel, and to drive ensuing cracks longitudinally around the tooth walls to failure. The relations are explicit in their dependence on characteristic tooth dimensions - enamel thickness and cuspal radius - and on material properties - modulus, hardness, toughness and strength. Provision is made to incorporate properties of the occlusal contact, whether from opposing dentition or intervening food particles. All these features are demonstrated on critical-load master diagrams. A characteristic feature of the damage evolution is the gradual evolution of each mode with increasing load, so that failure is generally a prolonged rather than abrupt event. This accounts for the remarkable damage tolerance of natural teeth. The equations may enable basic predictions of tooth responses for humans and animals under a variety of specified dietary and functional conditions.

Objective: Since there is no consensus on the association between occlusion and temporomandibular disorders (TMDs), the aim of the present paper was to conduct a review of electromyographic studies, in order to asses the relationship between various occlusal features and masticatory muscles' activity., Material and Methods: An exhaustive MEDLINE computer search was performed to identify all experimental studies present in the English literature describing the relationship between the electromyographyc evaluation of patients and their occlusal morphology., Results: The search methodology provided a total of 102 abstracts and from these 11 full reports were required as full text. Of the 11 articles selected, 8 studied the variation of the muscular activity as a consequence of the experimental introduction of occlusal disturbances whereas the remaining three studies estimated the electrical muscular characteristics without any artificial alteration of the occlusal morphology., Conclusion: The results obtained seem to suggest that occlusal features can affect the electrical signals recordings of masticatory muscles. Further researches are strongly requested to realize if this altered muscular activity can turns in the occurrence of TMDs.

The biological mechanisms that maintain the position of teeth in their sockets establish a dynamic equilibrium between bone resorption and apposition. In order to reveal some of the dynamics involved in the tissue responses towards occlusal forces on periodontal ligament (PDL) and alveolar bone homeostasis, we developed the first mouse model of hyperocclusion. Swiss-Webster mice were kept in hyperocclusion for 0, 3, 6, and 9 d. Morphological and histological changes in the periodontium were assessed using micro-computed tomography (micro-CT) and ground sections with fluorescent detection of vital dye labels. Sections were stained for tartrate-resistant acid phosphatase, and the expression of receptor activator of nuclear factor-kappaB ligand (RANKL) and osteopontin (OPN) was analyzed by immunohistochemistry and real-time polymerase chain reaction (PCR). Traumatic occlusion resulted in enamel surface abrasion, inhibition of alveolar bone apposition, significant formation of osteoclasts at 3, 6 and 9 d, and upregulation of OPN and RANKL. Data from this study suggest that both OPN and RANKL contribute to the stimulation of bone resorption in the hyperocclusive state. In addition, we propose that the inhibition of alveolar bone apposition by occlusal forces is an important mechanism for the control of occlusal height that might work in synergy with RANKL-induced bone resorption to maintain normal occlusion.

Objective: To investigate the short-term and long-term effects of occlusal rehabilitation on the co-contractration patterns of masticatory muscles of patients with extensive tooth wear., Methods: Twenty-nine patients with severe tooth wear were selected and conducted with occlusal rehabilitation. The surface electromyography (EMG) of masseter (MM), anterior temporalis (TA) and posterior temporalis (TP) at rest position, during clenching and chewing were separately recorded in the stage of pre-treatment, 1 month after temporary restoration, 1 month after permanent restoration and long-term observation (mean 3.5 years). The Asymmetry Indexes (AI) of bilateral muscles, Activity Indexes of MM/TA, MM/TP and TA/TP were compared in each stage., Results: (1) After occlusal rehabilitation, all the AIs of bilateral MM, TA and TP at rest position, during clenching and chewing showed obvious decrements. (2) In every stage of occlusal rehabilitation, all of the Activity Indexes of MM/TA at rest position, during clenching and chewing had no obvious changes. (3) The Activity Indexes of MM/TP and TA/TP during clenching and chewing significantly increased after occlusal rehabilitation., Conclusion: The treatment of occlusal rehabilitation can significantly improve the bilateral symmetry of masticatory muscles in patients with extensive tooth wear, and also change the coordinated EMG activity of different masticatory muscles.

Background: There is limited knowledge relating to the influence of mechanical stress on the temporomandibular joint (TMJ) and the degree of damage this stress can induce in the case of an altered occlusal plane on the extracellular matrix cartilage and chondrocytes. The aim of this study was to examine the histopathological influence of an altered occlusal plane on rabbit TMJ cartilage., Methods: Fifteen male Japanese white rabbits were used in this study. In 12 cases, the upper right and lower left teeth were ground to their cervical level so that the occlusal plane was tilted right side up. Their temporomandibular joints (TMJs) harvested at 3 days, 1, 2 and 4 weeks were analyzed immunocytochemically and immunohistochemically. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick endlabeling (TUNEL) method was used for immunocytochemical study to detect DNA fragmentation in chondrocytes. An immunohistochemical study was also performed to evaluate the metabolism of type 2 collagen in the extracellular matrix in the TMJ cartilage., Results: The number of apoptotic cells increased in all experimental animals. More apoptotic cells were observed in the articular eminences than in the condyles. The type 2 collagen-positive area in the condyles was reduced at the beginning but recovered within 4 weeks, and remained small throughout this experimental period in the articular eminences., Conclusions: These findings suggest that histopathological changes occurred in response to alteration of the occlusal plane. The influence decreased as the occlusal plane recovered in the condyles, but the immunocytochemical and immunohistochemical influence continued in the articular eminences.

Objective: To assess the impact of overloading on peri-implant bone level and the bone-to-implant contact (BIC) in the presence of healthy or inflamed peri-implant tissues., Materials and Methods: Four screw-shaped machined implants were placed bilaterally in the mandible of four beagle dogs and left submerged for 3 months. Prosthetic abutments were connected either in supra-occlusal contact with the opposite teeth (overloaded) or in infra-occlusal position (unloaded). In each dog, cotton floss ligatures were placed unilaterally around abutments to promote plaque accumulation; the contralateral side was brushed three times a week. There were four experimental sites, two implants in each: loaded uninflamed (LU), loaded inflamed (LI), unloaded uninflamed (UU), and unloaded inflamed (UI). Clinical and radiographic parameters were recorded at baseline and every 3 months throughout the observation period. At 12 months, the dogs were sacrificed and histomorphometric analysis was performed., Results: Implants with ligature-induced peri-implantitis presented high inflammatory indices throughout the observation period. Clinical parameters did not change from baseline for both LU and UU. Loading significantly increased the percentage of BIC (BIC%) (P<0.05) and slightly increased crestal bone resorption, but not apical to the implant neck. Both LI and UI groups showed significant peri-implant bone loss (P<0.01), mostly horizontal on the buccal aspect and angular on the lingual aspect, which exposed implant threads. Loading significantly (P<0.05) increased implant thread exposure due to buccal and lingual vertical bone resorption., Conclusions: In the presence of uninflamed peri-implant mucosa, overloading of implants in the dog model increased BIC% and slightly reduced marginal bone level. However, resorption did not progress beyond the implant neck. Overloading aggravated the plaque-induced bone resorption when peri-implant inflammation was present.

The purpose of this study was to investigate changes in the periodontal masseteric reflex (PMR) after experimentally induced occlusal hypofunction. Wistar rats were divided into control groups (CGs) and hypofunction groups (HGs). Rats in the HGs had their lower incisors cut down every other day for 6 weeks. Electrical stimulation was given to the periodontal ligaments of an upper incisor or the left trigeminal mesencephalic nucleus (MeV) in the CGs and HGs. Recordings of masseter motor unit responses were performed at 0, 1, 2, 4 and 6 weeks after hypofunction. Compared with the CGs, significant longer latencies in the PMR were found in the 4w- and 6w- HGs. After MeV stimulation, no significant difference in latency was found between HGs and CGs. After periodontal stimulation, the threshold value of masseteric motor-unit responses was higher in HGs than in CGs in 4and 6 weeks respectively. These results suggest that the PMR can be changed by periodontal sensory modification during occlusal hypofunction.

While many studies reported the structural changes in the periodontal ligament (PDL) under hypofunctional conditions, the associations of cytokine growth factors are still unclear. They are known to take part in inflammation, and may affect the biological properties of hypofunctional tooth. To investigate the hypofunctional PDL and the recovery from this condition, we focused on interleukin-1 beta (IL-1beta) and basic fibroblast growth factor (FGF-2). Male Wistar rats were divided into occluded, non-occluded, and recovery groups. An anterior bite plate was used to eliminate the occlusal contact of molars in the non-occluded group, and was then removed for the recovery group. After occlusal stimuli were eliminated for 7 and 14 days, and after 3 and 7 days of recovery from 7 days in the hypofunctional condition, the PDLs of the lower first molars were investigated immunohistochemically. The lack of occlusal stimuli caused atrophic changes in the PDL with the upregulation of IL-1beta and decreased expression of FGF-2, while decreased IL-1beta and enhanced FGF-2 expression were observed in the recovery process. These results suggest that occlusal stimuli regulate IL-1beta and FGF-2 expression, and the nature of this regulation may differ from that in the healing process of an inflammatory reaction.

Background and Objective: Despite little evidence regarding the relationship between tooth mobility and nonworking contact, the evaluation of occlusion is performed mainly by the detection of premature and/or nonworking contacts during tapping movements and lateral excursion. The hypothesis of this study is that occlusal contact during mastication is potentially traumatic to periodontal tissue. It clarifies the relationship between chewing patterns and the status of periodontal tissue., Material and Methods: Subjects included 73 adults, 20-29 years of age (39 men and 34 women), with complete sets of teeth and no history of orthodontic treatment or periodontal disease. The closing chewing patterns of each subject were classified into three groups by the Masticatory Deviation Index, which depicts the deviation from the normal chewing patterns within 5 mm from the intercuspal position. Periotest was used to diagnose teeth mobility and the values were compared among the three groups., Results: The present study indicates that the chewing movements which deviated from the normal chewing movements increased the mobility of specific types of teeth., Conclusion: The results of this study imply a relationship between chewing movements and tooth mobility and indicate that functional evaluation of occlusion is necessary for the examination of periodontal tissue. Occlusal evaluation with border and tapping movements might be insufficient, and functional occlusal evaluation during chewing movements can be clinically useful for using to evaluate periodontal tissue.

Clinical effects of forces applied by dental occlusion on the periodontium have been evaluated for decades. Historically, trauma from occlusion has been considered as a major etiologic factor of inflammatory periodontal diseases, while some researchers have interpreted it to be of less importance or without any detectable importance in periodontics. In this study, five three-dimensional models of a maxillary central incisor were created using ANSYS 5.40. The only difference in each model was the height of the alveolar bone that showed from normal height (13 mm of alveolar bone height) to 8 mm of alveolar bone loss (5 mm of alveolar bone height). Five-point forces of 0.3 N summing up to 1.5 N were applied in a parallel line, 1 mm apical to the incisal edge on the palatal side in a palatolabial direction. The maximum (S1) and minimum (S3) principal stresses in the nodes of the labial side of the periodontal ligament (apical to the alveolar crest) were assessed. Analysis was done using the finite element method. An increase of S1 (up to 16 times in the cervical and 11.25 times in the apical area) and S3 (up to 17.13 times in the cervical and 9.9 times in the apical area) in comparison to the normal model was shown. The highest stress levels were traced in the subcervical area, except for the last model (8 mm of the alveolar bone loss). According to the results of this study, 2.5 mm of alveolar bone loss can be considered as a limit beyond which stress alterations were accelerated. Based on the FEM analysis, alveolar bone loss increases stress (S1 and S3) produced in the PDL, in spite of applying the same force vector.

Objective: PPTA and c-fos mRNA expression were detected in dog caudalis subnucleus of trigeminal spinal tract nucleus (VC) induced by trauma occlusion in order to investigate orofacial pain mechanism., Methods: The occlusal surface of the first and second maxillary right molars in 15 dogs were unilaterally raised 1.5 mm with casting Ni-Cr inlay which were fixed in Class I hole. On days 3, 7, 14, 30 and 60 after teeth operation, the VC of right and left sides were removed. PPTA and c-fos mRNAs were detected in experimental and control groups with reverse transcription-polymerase chain reaction (RT-PCR)., Results: (1) The basal levels of PPTA and c-fos mRNAs were extremely low and poorly detectable in VC in control animals. (2) The expression of PPTA mRNA in VC of traumatic side was up regulated from 3 days after inlay was fixed in molar and reached peak level during 14 to 30 days and then down-regulated gradually and no significant difference was noted between 60 days group and control group. (3) c-fos mRNA expression was more intense during 3 to 7 days compared with the control group but undetectable in the other experimental period. (4) Both PPTA and c-fos mRNAs expression in VC of trauma occlusal side were more intense than that in the contralateral side., Conclusions: The present results show that both PPTA and c-fos mRNA expression are elevated in dog's VC induced by traumatic occlusion. The primary afferent terminal of orofacial area is sensitized, which suggest one kind of mechanism of orofacial pain in the condition of traumatic occlusion.

Objective: To investigate changes of two sodium channels, PN(3) and NaN, during orofacial pain by occlusal trauma in rat., Methods: Expressions of PN(3) mRNA and NaN mRNA in trigeminal ganglion were tested during various periods of persistent occlusal trauma with reverse transcription-polymerase chain reaction (RT-PCR)., Results: In groups, including control, occlusal trauma groups, PN(3) mRNA and NaN mRNA were all expressed in trigeminal ganglion neurons. In the control group, there were similar density values bilaterally. In the occlusal trauma group, the density values in gel electrophoresis of PN(3) mRNA and NaN mRNA on the intervention side were slightly greater than those on the control side., Conclusions: The stimulation of occlusal trauma upregulates expressions of PN(3) mRNA and NaN mRNA, which suggests the signal occurring and conduction of chronic pain by occlusal trauma have the same molecular mechanism of sodium channel as inflammatory pain.

The aim of the present study was to establish whether the early signs of various orofacial dysfunctions, malocclusions, or occlusal interferences can predict the development of temporomandibular dysfunction (TMD) in young adults. Forty-eight subjects referred for speech therapy and 49 controls participated in all four stages of this longitudinal study. The subjects were examined at the ages of 7, 10, 15, and 19 years. The phoniatrician diagnosed errors in place of articulation and problems in the movement and co-ordination of the speech articulators. Occlusion, TMD signs (palpatory tenderness of the masticatory muscles, and of temporomandibular joints (TMJ), jaw deviation on opening, and clicking), mandibular movement capacity and occlusal interferences were registered by the orthodontist. Multiple logistic regression models were applied in order to evaluate whether single signs of TMD at the age of 19 years were related to previous/present malocclusions or interferences, to misarticulations of speech, problems in oral motor skills, or other signs of TMD. The effect of gender was also considered. The results showed that excessive overjet was the only variable which seemed to consistently increase the risk of TMD. In addition, girls seemed to be more prone to the development of TMD than boys. Although, during growth, there were both local and central factors associated occasionally with TMD development, the predictive value of those variables in the estimation of the individual risk of TMD was rather small.

The hypothesis of a functional coupling between the muscles of the craniomandibular system and the muscles of other body areas is still controversial. The purpose of this pilot study was to examine whether there is a relationship between the craniomandibular system, the craniocervical system and the sacropelvic region. To test this hypothesis, the prevalence and localization of dysfunction of the cervical spine and the sacroiliac joint were examined in a prospective, experimental trial. Twenty healthy students underwent an artificial occlusal interference, which caused an occlusal interference. The upper cervical spine (CO-C3) and the sacroiliac joint were examined before, during and after this experimental test. The primary outcome with these experimental conditions was the occurrence of hypomobile functional abnormalities. In the presence of occlusal interference, functional abnormalities were detected in both regions examined and these changes were statistically significant. The clinical implications of these findings may be that a complementary examination of these areas in CMD patients could be useful.

During orthodontic treatment, it is often necessary to move the hypofunctional teeth. In this study, we revealed an influence of orthodontic forces in the hypofunctional periodontal ligament, and focused on the distribution of proteoglycans, major extracellular matrix molecules. Five-week-old rats were divided into normal group and hypofunctional group. To induce occlusal hypofunction, occluding teeth of the mandibular first molar were extracted. At 8-week-old, orthodontic force by 15 or 2 gf titanium-nickel alloy closed coil spring was applied to the mandibular first molar toward the mesial direction. Immunohistochemical analysis was performed using antibodies for chondroitin sulfate (CS) and heparan sulfate (HS). In normal group, CS was observed throughout the extracellular matrix, while HS was observed on the endothelial cells and the osteoclastic cells on compressive side. In hypofunctional group without orthodontic appliance, CS and HS were detected in less amounts. With 15 gf, CS was observed at the compressive area where no cells and fibers were present, and HS was observed at the periphery of this area. With 2 gf, however, the distribution of CS and HS was similar to the normal control. These findings indicate that CS and HS were affected by orthodontic forces, and suggest their distinct functions in tissue remodeling.

In humans, the inappropriate occlusal vertical dimension (OVD) causes several orofacial disorders, such as bruxism and pain in the masticatory muscles and temporomandibular joint. However, it is still unclear how strictly the OVD is adjusted. To answer this question, we studied the temporal change of the OVD in bite-raised young guinea pigs. The OVD was raised by fixation of a bite-raising appliance to the lower incisors, and increased by either 3 or 1.5 mm at the first molars. After the space produced between the upper and lower molars was filled within 10 days due to eruption of the molars, the appliance was removed. In the bite-raised animals, the raised OVD was reduced until it attained that observed in the control animals, after which the OVD increased according to cranial growth. These results show that the OVD is developmentally changed and strictly controlled.

Different opinions have been expressed concerning the effect of orthodontic treatment on mandibular function. One factor discussed is occlusal interferences. The aim of this study was to establish the prevalence of occlusal interferences in 210 orthodontic patients before (mean age 12 years 8 months) and after (mean age 16 years 10 months) treatment and to compare them with subjects with minor orthodontic treatment need. The results showed a decrease in retruded contact position/intercuspal position (RCP/ICP) interferences in all morphological deviations, age, and gender groups. The prevalence of mediotrusion interferences decreased in some types of malocclusions whilst in others there was no change. One reason for this is that treatment was started when the majority of the patients had no second or third molars erupted. At the final registration, the second molars were erupted in all patients, and the third molars were erupted in approximately 25 per cent. Mediotrusion interferences were more consistent with basal morphological deviations, for example, Class III relationships and anterior open bite were more consistent in the same person, and more difficult to eliminate than RCP/ICP interferences. RCP/ICP interferences, often caused by dental deviation in position, size, and shape, were easier to correct. Optimal orthodontic treatment, if necessary, including selective grinding, will decrease the prevalence of occlusal interferences.

Associations between articulatory speech disorders and mandibular movement capacity, as well as between malocclusions and jaw movements, were examined in two groups of adolescents, i.e. 52 individuals with and 45 without misarticulations of speech. The mean age of the whole sample was 19.2 years. Articulatory speech disorders and functioning of the speech articulators were diagnosed by a phoniatrician. Mandibular movement capacity, malocclusions, occlusal interferences, and signs of temporomandibular dysfunction were recorded by an orthodontist. Multiple regression analyses showed that subjects with articulatory speech disorders were likely to have smaller opening capacity than subjects with a correct speech articulation. Excessive overjet, lateral cross bite, and a tendency to anterior open bite were associated with large movements of the jaw. These results suggest that in young adulthood mandibular movement capacity seems to vary depending on occlusion and is related to misarticulations of speech.

Proper management of the occlusal plane is an essential consideration when multiple long-span posterior restorations are designed. When restorations are added to an existing tooth arrangement characterized by rotated, tipped, or extruded teeth, excursive interferences may be incorporated, resulting in detrimental sequelae. The curve of Spee, which exists in the ideal natural dentition, allows harmony to exist between the anterior tooth and condylar guidance. An instrument called the Broadrick flag has been used to assist in the reproduction of tooth morphology that is commensurate with the curve of Spee when posterior restorations are designed; its use prevents the introduction of protrusive interferences. Consideration also must be given to lateral excursive movements when the occlusal plane is designed. In this article, the importance of the curve of Spee in prosthodontic and restorative dentistry is discussed, and a patient treatment demonstrating use of the Broadrick flag is described.

A primary goal in the reconstruction of the dental implant patient is to achieve the lowest stress possible on the abutments, both artificial and natural. Bidez and Misch use the formula [figure: see text] [formula: see text] to explain that the stress can be easily lowered by increasing "A," by using larger implants, or by using additional implants. Another equally important method of lowering the stress is to reduce and manage the force application (F). The majority of completed implant cases can well tolerate applied forces from mastication and swallowing, both of which are close to 50 pounds per square inch, but it is the destructive power from DCS that can easily range from 500 to 1,000 pounds per square inch with which this article is concerned.

It has been suggested that occlusal interference results in masticatory muscle dysfunction. In our previous study, occlusal interference reduced the rat masseter energy level during masticatory movements. The purpose of this study was to investigate the histological alterations of rat masseter muscles following experimental occlusal alteration with unilateral bite-raising. A total of eight male adult Wistar rats were equally divided into control and experimental groups. The experimental rats wore bite-raising splints on the unilateral upper molar. However, 4 weeks after the operation, the anterior deep masseter muscles were removed and then stained for succinic acid dehydrogenase (SDH), haematoxylin eosin (HE) and myofibrillar ATPase. Most of the muscle fibres in experimental rats remained intact, although partial histological changes were observed, such as extended connective tissue, appearance of inflammatory cells in the muscle fibres and existence of muscle fibres with central nuclei and central cores. Moreover, the fibre area-fibre frequency histograms of experimental muscle indicated a broad pattern than that of controls. These results indicated that occlusal interference caused histological changes in masseter muscles and that this may be related to the fact that the masseter energy level was reduced during masticatory movements in unilateral bite-raised rats.

The features that constitute an "ideal" functional occlusion have not been conclusively established. Orthodontic treatment has the capacity to change static and functional occlusal relationships fundamentally. In this article, we present the evidence on which features of the occlusion are reported to be detrimental to the teeth and masticatory system Deficiencies in this research area are highlighted, together with the need for prospective longitudinal trials to clarify the requirements of an ideal functional occlusion Based on the existing evidence this paper suggests which occlusal features may be significant in producing an "ideal" functional occlusion As no long-term studies exist to measure the impact of non-ideal occlusal relationships on the dentition, it is debatable whether orthodontic treatment should be prolonged in order to ensure that "ideal" occlusal contacts are achieved As the occlusion tends to "settle" in the period following appliance removal, we propose that it may be more appropriate to examine the functional occlusal relationships after retention has ceased rather than prolong active orthodontic treatment to achieve "ideal" functional occlusal goals.

Purpose: The aim of this study was to investigate the effect of experimental alterations of nonworking-side occlusal contacts on jaw-elevator muscle activity., Materials and Methods: Individual devices were fabricated to simulate various lateral occlusal relationships. Twelve human subjects were asked to carry out submaximal lateral clenching, and electromyographic (EMG) activity of the masseter and anterior and posterior temporalis muscles was measured., Results: Clenching in a lateral mandibular position under natural conditions induced an activity pattern with a clear dominance of the anterior and posterior temporalis muscles on the working side. Working-side dominance in the anterior temporalis was reduced moderately when an experimental nonworking-side occlusal contact was added. Dominance decreased dramatically when an experimental nonworking-side interference was added. The working-side activity in the posterior temporalis was also reduced dramatically by an experimental nonworking-side interference, but not by a nonworking-side occlusal contact. None of the experimental contact patterns had a significant effect on the masseter activity., Conclusion: These results suggest that the nonworking-side occlusal contacts have a significant effect on clenching-induced temporalis muscle activity.

The aim of this study was to investigate the relationships between occlusal contacts, responses of muscles, and jaw movements during simulated clenching. Seven healthy human males who possessed complete natural dental arches with normal occlusion, ranging from 24 to 29 years of age, volunteered for this study. Acrylic occlusal stops were fabricated for the lower jaw to simulate various occlusal conditions. Vertical movements of the lower jaw were measured by four sets of linear variable differential transformers. Simultaneously, electromyographic (EMG) activity from the bilateral masseter and anterior temporal muscles was measured. Under experimentally altered occlusal conditions, the subjects performed clenching tasks at 50% of their maximal voluntary contraction level. Analysis of EMG responses revealed clenching on the unilateral occlusal support tended to cause a unilateral activity of the ipsilateral anterior temporalis. Analysis of the movement amplitude revealed a significant difference between the experimental occlusal conditions (P < 0.05). Clenching on unilateral occlusal stops caused a larger upward movement on the contralateral side. Bilateral first premolar clenching without molar support caused a larger upward movement of the mandible in the posterior region, whereas bilateral second molar clenching did not cause a significant upward movement.

Adverse occlusal forces can result in mechanical complications of implant components. While unacceptably high incidences of mechanical failures have been reported for the two-stage external hex screw-type implant systems, the standard-diameter ITI solid-screw implant does not seem to be vulnerable to these problems. The 8 degrees Morse taper has eliminated abutment screw loosening and fracture. The incidence of prosthetic screw loosening has been minimized by the 45 degrees bevel on the implant shoulder and by the 1.5 mm vertical abutment walls. The design of the standard-diameter solid-screw ITI implant and the material used in its fabrication (cold worked type IV cp titanium) have eliminated fixture fracture. However, because there have been some reported instances of fractures involving reduced-diameter and hollow implants, these designs should be used with caution.