A natural tooth's stress distribution in occlusion with a dental implant

The loss of one or more teeth is normally treated with conventional fixed or removable partial dentures or with implant supported fixed or removable dentures. This study investigated stresses formed around the implant and the antagonist natural tooth under occlusal force in the substitution of a missing lower first molar with a rigid or resilient IMZ (Intra Mobil Zylinder) implant, using the finite element stress analysis method. The results indicate that a bite force of 143 N resulted in high compressive stresses around the roots of a natural tooth opposing a restoration supported by an IMZ implant with rigid type abutment. It is speculated that these high compressive stresses may contribute to intrusion of the tooth.     

The influence of medial implant location in three-unit posterior cantilever fixed partial dentures on stress distribution in surrounding mandibular bone

This study examined the influence of medial implant location in three-unit posterior cantilever fixed partial dentures (FPDs) on stress distribution in mandibular bone surrounding two implants. A three-dimensional finite element model that included three-unit FPD and two cylindrical-type implants (4 mm in diameter and 10 mm in length) osseointegrated in the posterior mandible, was digitized. Five different models were created according to the medial implant location between the missing second premolar and the first molar location. The distal implant was fixed at the missing second molar location. Oblique bite force of 100 N at 30 degrees buccal to the vertical direction was directed on each of three artificial teeth, respectively and simultaneously, while the lower surface of the mandible was fixed. The maximum equivalent stress in the cortical and the trabecular bone generally increased as the medial implant shifted to a distal position. Under the simultaneous bite force, relatively low maximum stresses within the cortical bone: between 55 MPa and 57 MPa, were shown in the models with the medial implant placed within the range of one implant diameter from the most medial position, while higher maximum stresses: between 64 MPa and 73 MPa, were demonstrated with more distally placed medial implants. The results suggest that reasonably low mechanical stress in the surrounding bone may be assured when the medial implant is placed in the range between the missing second premolar position and one implant diameter distal from that location.     

Location of main occluding areas and masticatory ability in patients with implant-supported prostheses

Background: The purpose of this study was to locate the main occluding area when the reduced posterior occlusal support was treated with an implant‐supported prosthesis and to evaluate the subsequent improvement in the masticatory ability as compared with removable partial dentures. Methods: Twenty‐six patients with implant prostheses and 24 patients with removable partial dentures were recruited for this study. All patients had partially lost their posterior occlusal support. The first molar region in any quadrant was always included in the prosthetic region. Each subject was instructed to clench a piece of temporary stopping as a test food on the occluding area that was preferably used during mastication. The main occluding area was judged by locating the tooth on which the temporary stopping rested during clenching. Subjective masticatory ability was self‐assessed by means of a questionnaire. Results: The main occluding area of the subjects in the implant group was located more posterior compared with the removable partial denture group. The level of masticatory ability in the implant group was the same as that in the control group. Conclusions:  The location of the main occluding area and the masticatory ability of the subjects with implants were equivalent to those with healthy natural dentition.     

A study of 184 consecutive patients referred for single‐tooth replacement

The aim of this investigation was to study the acceptance and the rejection of patients referred for single implant restorations based on data from referral, case history. clinical examination and therapy planning. The referrals comprised 184 patients with 251 missing single teeth. Sixty‐four per cent of the referred patients were accepted for treatment. There was difference in acceptance between men and women (75% and 54%, respectively). A negative relationship was noticed between age and acceptance. External trauma (33%), root fractures (16%) and congenitally missing teeth (15%) were the main reasons for lost or missing teeth. Anatomical limitations was the most frequent reason for rejection (76%). Most fillings and crowns on adjacent teeth to the edentulous space did not serve as a contraindication for an implant single‐tooth restoration, and thus extensive fillings or not acceptable crowns was the cause of rejection only for a minor group (13%). The great majority of the partially dentate patients showed a very high interest in treatment with single‐tooth implants, but some of the patients (4% in all, 11% of those rejected for treatment) did not want implant treatment after having received further information at the specialist clinic.     

The influence of various attachment types in mandibular implant-retained overdentures on maximum bite force and EMG

The type of attachment that is used in oral rehabilitation by means of implant-retained mandibular overdentures may influence the retention and the stability of the denture. In this study, we examined the hypothesis that a better retention and stability of the denture improve the oral function. Eighteen edentulous subjects received 2 permucosal implants, a new denture, and, successively, 3 suprastructure modalities. Maximum bite force and electrical activity of the masseter and temporalis muscles were measured. The maximum bite force nearly doubled after treatment for each of the 3 attachments. However, the average bite force after treatment was still only two-thirds of the value obtained for dentate subjects. No large differences in maximum bite force and muscle activity were found among the 3 attachment types. Temporalis activity was significantly lower than masseter activity when subjects clenched without implant support. There was no difference in activity when subjects clenched with implant support.     

Influence of clenching intensity on bite force balance, occlusal contact area, and average bite pressure.

It has been difficult for investigators to simultaneously and reliably evaluate bite force in the intercuspal position with the area and location of occlusal contacts. This study was designed to investigate the variations in these parameters with respect to two factors: three levels of clenching and the preferred chewing side. Human subjects with normal occlusion were examined with a recently developed system (Dental Prescale Occluzer, Fuji Film, Tokyo, Japan). The three levels of clenching intensity were assessed by masseteric EMG activity and included the maximum voluntary contraction, and 30% and 60% of the maximum. The results indicated that the bite force and occlusal contact area on the whole dental arch increased with clenching intensity. In contrast, the average bite pressure, obtained by dividing the bite force by the contact area, remained unchanged regardless of the clenching intensity. As the clenching intensity increased, the medio-lateral position of the bite force balancing point shifted significantly (P<0.01) from the preferred chewing side toward the midline. The antero-posterior position remained stable in a range between the distal third of the first molar and the mesial third of the second molar. The bite force and occlusal contact area, which were mainly on the molars, increased with the clenching intensity, whereas the proportions of these two variables on each upper tooth usually did not change significantly. The exception was the second molar on the non-preferred chewing side. When comparisons were made between pairs of specific upper teeth of same name, usually no significant difference was found in bite force or occlusal contact area, regardless of the clenching level. Again, the exception to this observation was the second molar on the preferred chewing side, which had a larger area at the 30% clenching level. The results in normal subjects suggest that as the clenching intensity increases in the intercuspal position, the bite force adjusts to a position where it is well-balanced. This adjustment may prevent damage and overload to the teeth and temporomandibular joints.     

Localized edentulous ridge augmentation with upside down osteotomy prior to implant placement

Abstract –  Localized bone defects may be seen following the extraction of teeth with periapical lesion or advanced periodontal disease, or as a result of trauma. When these regions are considered for treatment with implants, localized ridge augmentation will be necessary. Autogenous bone grafts are used exclusively for ridge augmentation. This case report represents the treatment of a localized edentulous ridge with an upside down osteotomy technique at the symphysis region prior to implant placement. Systemically healthy 21-year-old female patient, who was missing a lower right incisor tooth, was scheduled for an implant treatment. However, the crestal width was only 1 mm. The augmentation was planned and the region was treated with an upside down osteotomy technique. Nine months after the augmentation procedure, the computed tomography (CT) examination of the area revealed that the width of the crest was 7 mm, and the height of the crest was in good relation with the cementoenamel junction of the adjacent teeth. Flipping a bone block graft, which was harvested from the edentulous area, upside down may provide a successful result in partially edentulous ridges, in both maxilla and mandible.     

Effect of implant‐supported prosthesis on the bite force and masticatory efficiency in subjects with shortened dental arches

The aim of the study was to assess changes in bite force and masticatory efficiency in shortened dental arch (SDA) subjects rehabilitated with implant‐supported restoration for 1st molar. Ten SDA subjects with bilaterally missing mandibular molars (experimental group) were recruited. In each subject, one tapered threaded implant was placed bilaterally in 1st mandibular molar region and restored. Masticatory efficiency was evaluated objectively by measuring the released dye from chewed raw carrots, with a ‘spectrophotometer’ at 530 nm preoperatively and at 3 months after restoration. Bite force was evaluated using ‘bite force measuring appliance’ preoperatively, at 6 weeks and at 3 months after restoration. Ten completely dentate‐matched subjects (in terms of age, sex, height and weight) acted as control. The results revealed that as compared with the control group, the experimental group showed significantly less (P < 0·05) mean maximum bite force at pre‐restoration and at 6 weeks after restoration. Although at 3 months the mean maximum bite force value was less than the control group but the mean difference was statistically insignificant. The mean difference of masticatory efficiency between control and experimental group was statistically significant (P < 0·05) before restoration, but was statistically insignificant at 3 months after restoration. Thus it was concluded that after the restoration of mandibular arch with implant‐supported prosthesis, both bite force and masticatory efficiency of all SDA subjects increased and were comparable to that of matched completely dentate subjects after 3 months.     

Influence of static and dynamic occlusal characteristics and muscle force on masticatory performance in dentate adults

Masticatory performance is the outcome of a complex interplay of several factors. This study was carried out to determine the relationship between masticatory performance and several muscular-related and occlusion-related factors in a population with a full or near-full complement of natural teeth. One-hundred dentate young adults participated in this cross-sectional study. Maximum muscular force with jaw, hand, tongue, and cheek were measured by means of a gnatodynamometer. Occlusal contact area and number of teeth in contact were determined in the maximal intercuspal position and in a 1.5-mm right and left lateral excursion by means of interocclusal registrations that were scanned and analysed using image software. Masticatory performance was determined by sieving the Optosil particles resulting from 20 chewing cycles. Stepwise multiple linear regression analysis showed that the maximum bite force in the region of the first molar had the best correlation with masticatory performance and explained 36% of its variation. Static occlusion characteristics such as occlusal contact area, the lack of lateral crossbite and the number of anterior teeth in contact explained an additional 9% of the variation in masticatory performance. These findings suggest that variables related to dynamic occlusion or tongue or cheek force do not enhance the prediction of masticatory performance.     

Interdisciplinary treatment planning for orthodontic‐prosthetic implant anchorage in a partially edentulous patient

Successful orthodontic treatment is characterized by optimal anchorage control. Teeth or groups of teeth are united to counteract biomechanical reactive forces during orthodontic treatment. These classic anchorage control mechanisms are less efficient or even non-existent in partially edentulous patients who are missing multiple posterior teeth. However, osseointegrated oral implants ad modum Br-vemark can provide optimal anchorage control for orthodontic tooth alignment and rehabilitation of occlusion through prosthetic implant restorations. Careful multidisciplinary planning based on complex diagnostic wax setup casts to determine exact implant location and orientation in line with future orthodontic tooth displacements and prosthetic implant crown restorations is the most important step in the overall treatment planning.     

Does long‐term use of unstable dentures weaken jaw muscles?

Summary Although it is well known that conventional denture wearers have lower maximum bite forces than dentate subjects, no previous studies have compared the strength of the jaw muscles between these two groups. This study compared maximum bite forces, electromyographic (EMG) activity and estimated jaw muscle strength among three groups: (i) 17 edentulous subjects using newly acquired implant‐retained overdentures (seven men, 10 women; mean age 60·3 ± 13·0 years); (ii) 10 age‐matched, fully dentate subjects (five men, five women; mean age 57·9 ± 11·0 years); and (iii) 39 young, fully dentate subjects (19 men, 20 women; mean age 24·4 ± 3·5 years). Electromyographic activity was recorded from subjects’ bilateral superficial masseter and anterior temporalis muscles while they generated maximum voluntary bite forces at the right central incisor, right first premolar and right first molar positions. Jaw muscle strength was estimated as the ratio of average EMG activity for all four muscles to the maximum bite force. At all three bite positions, edentulous subjects produced maximum bite forces that were less than half that of dentate subjects. Edentulous subjects also produced significantly less EMG activity and had significantly lower estimated jaw muscle strength. Our results suggest that weakened jaw muscles are one factor contributing to lower maximum bite forces among users of conventional dentures.     

Protraction of mandibular second and third molars into missing first molar spaces for a patient with an anterior open bite and anterior spacing

In a young woman, aged 18 years 8 months, who had an anterior open bite and anterior spacing, the right and left mandibular first molar extraction spaces were closed by protraction of the second and third molars without reciprocal retraction of the incisors and the premolars. The amounts of protraction for the second molars were 12 mm on the right side and 11 mm on the left side. Two miniscrews were inserted into the mesiobuccal side of the edentulous spaces, and 2 more screws were inserted into the anterior sites after removing previous miniscrews. In addition, 4 miniscrews were inserted into the buccal and palatal sides between the first and second maxillary molars to intrude the maxillary posterior teeth, which had extruded into the missing mandibular spaces. Careful biomechanical consideration was used to prevent extrusion of the molars and worsening of the anterior open bite from protraction of the posterior teeth. Ultimately, the anterior open bite was corrected by both intrusion of the maxillary molars and extrusion of the maxillary anterior teeth. Excellent occlusion and correction of the anterior open bite were achieved without tipping, rotation of the posterior teeth, or other problems. The right mandibular third molar, which had been impacted at the beginning of treatment, erupted into the second molar space and functioned properly. At the 1-year follow-up examination, the patient had a slight anterior open bite, but closure of the first molar extraction spaces was well maintained.     

Short dental implants: a literature review and rationale for use

Implant prostheses are often used to restore partially or completely edentulous patients. The posterior regions of the mouth often have less available bone height than the anterior regions. The bone density of the remaining bone after tooth loss is often less in the posterior regions than the anterior region of the mouth. A review of the literature reveals implants shorter than 10 mm often have a higher failure rate than longer implants. These complications may be related to an increase in crown height, higher bite forces in the posterior regions, and less bone density. As a result, biomechanical methods to decrease stresses to the implant-bone interface are warranted. The forces to the implants may be reduced by eliminating lateral contacts in mandibular excursions and eliminating cantilevers on the prosthesis. The area of forces applied to the prosthesis may be increased by increasing the implant number, increasing the implant diameter, increasing the implant design surface area, and splinting the implants together. As a result of these biomechanical methods to decrease stress, Misch, et al reported a 99% implant survival with 7-mm and 9-mm implants in the posterior regions of the jaws. It is interesting to note that the natural teeth follow a similar biomechanical approach to accommodate the higher bite forces in the posterior regions of the mouth. The molar teeth do not become longer than the anterior teeth. The diameter is increased, the design of the roots is different, and the roots are splinted together. The anterior teeth have incisal guidance and eliminate posterior lateral forces to the posterior teeth in all mandibular excursions. A similar biomechanical approach is logical for posterior implants, especially when shorter implants are used to support the prosthesis.     

Pre- and post-implantation microbiota of the tongue, teeth, and newly placed implants

OBJECTIVES: This investigation sought intra-oral sources of species colonizing dental implants. MATERIALS AND METHODS: Plaque samples were taken pre- and post-successful osseointegration from implants, teeth, and from tongues of 10 edentulous and 11 partially dentate subjects. Samples were assayed using whole genomic DNA probes in a checkerboard assay to 42 subgingival species. RESULTS: Similar prevalences and mean levels (10(3) to 10(4)) of microorganisms colonized implants and teeth. Species levels from tongue samples were higher than those of teeth and implants, although species prevalence was similar, suggesting that larger samples were obtained from the tongue. No significant differences were observed between the microbiota from the tongue of edentulous and partially dentate subjects. Most implant species were detected on tongue pre-implantation. In individual edentulous subjects, there were positive associations between Capnocytophaga ochracea and Campylobacter rectus from tongue and implant samples. In individual partially dentate subjects, there were positive associations between Fusobacterium nucleatum subsp. vincentii from tongue and implant samples, and Treponema denticola from implant and tooth samples taken at the same visit. CONCLUSION: This study indicated that the tongue, in addition to teeth, can be a source for species colonizing new implants.     

Patient evaluation of treatment with fixed implant- supported partial dentures

The aim of this study was to analyse the patient evaluation of functional treatment outcome in 40 periodontally compromised patients who received implant-supported prostheses (ISPs) as part of the total treatment. The treatment protocol comprised periodontal treatment, extraction of teeth with poor prognosis, placement of dental titanium implants, and after healing, insertion of fixed ISPs. Five of the patients became edentulous in one jaw after extraction of all teeth and received a complete ISP, whereas 35 patients became partially edentulous after extraction of some teeth, 12 receiving a partial ISP on > or = 3 implants, and 23 one on two implants. The follow-up period was on average 1.8 years after the connection of the prostheses, which provided the patients a dentition with a mean of 12 occluding dental units. The first author (S.-W. Yi) performed all implant treatment. Patients' opinions on oral functions--mastication, phonetics, oral hygiene, chewing comfort and aesthetics--were evaluated by means of a questionnaire both before implant installation and at the last follow-up. A control group of 30 subjects with a healthy dentition of 14 occluding natural pairs of teeth answered the same questionnaire on one occasion. A great majority of the patients were extremely satisfied with the oral function after treatment and experienced the ISPs as 'natural teeth'. There was no significant difference between the three treatment groups and the control group for mastication, phonetics, chewing comfort and aesthetics. Patients with ISPs reported a small but significantly greater difficulty with oral hygiene procedures than the controls with natural teeth. Most patients said that they would undergo the treatment again, if necessary, and recommend it to others. It was concluded that the rehabilitation of the periodontally compromised patients, including ISPs on osseointegrated dental titanium implants, resulted in subjectively improved and satisfactory oral function.     

Cortical bone thickness in dentate and edentulous human cadavers

BACKGROUND: A critical component of treatment planning in dental implant therapy is the amount of available bone. Thick cortical plates have been the primary way to achieve primary implant stability. However, information about cortical bone thickness in various regions of the maxilla and mandible is largely missing. Hence, it was the purpose of this cadaver study to determine an average cortical bone thickness in different tooth locations. METHODS: To determine the average thickness of buccal and lingual plates, 28 cadaver heads (68% male and 32% female) with an average age of 73.1 years were measured at various locations correlating to molar (M), premolar (PM), and anterior (A) regions. Edentulous and dentate regions also were recorded. RESULTS: Average buccal cortical thicknesses were 1.69 mm (M), 1.43 mm (PM), and 1.04 mm (A) in the edentulous maxilla; 2.06 mm (M), 1.78 mm (PM), and 1.36 mm (A) in the edentulous mandible; 2.23 mm (M), 1.62 mm (PM), and 1.59 mm (A) in the dentate maxilla; and 1.98 mm (M), 1.20 mm (PM), and 0.99 mm (A) in the dentate mandible. Average lingual cortical thicknesses were 2.06 mm (M), 1.60 mm (PM), and 1.36 mm (A) in the edentulous maxilla; 2.39 mm (M), 1.88 mm (PM), and 1.66 mm (A) in the edentulous mandible; 2.35 mm (M), 2.0 mm (PM), and 1.95 mm (A) in the dentate maxilla; and 2.51 mm (M), 1.92 mm (PM), and 1.24 mm (A) in the dentate mandible. CONCLUSIONS: The average cortical thickness of the buccal plates ranged from 1.0 to 2.1 mm in the edentulous maxilla and mandible, with the thinnest area in the anterior maxilla and the thickest area in the posterior mandible. The buccal plate of the dentate maxilla and mandible ranged from 1.6 to 2.2 mm in thickness, with the thinnest area in the lower anterior region and the thickest area in the upper posterior region.     

Chewing side, bite force symmetry, and occlusal contact area of subjects with different facial vertical patterns

Craniofacial dimensions influence oral functions; however, it is not known whether they are associated with function asymmetry. The objective of this study was to evaluate chewing side preference and lateral asymmetry of occlusal contact area and bite force of individuals with different craniofacial patterns. Seventy-eight dentate subjects were divided into 3 groups according to the VERT index as follows: (1) mesofacial, (2) brachyfacial and (3) dolichofacial. Chewing side preference was evaluated using jaw tracking equipment, occlusal contact area was measured by silicon registration of posterior teeth, and bite force was measured unilaterally on molar regions using 2.25 mm-thick sensors. Statistical analysis was performed using ANOVA on Ranks, Student's t-test, and Mann-Whitney tests at a 5% significance level. Mesofacial, brachyfacial, and dolichofacial subjects presented more occlusal contact area on the left side. Only dolichofacial subjects showed lateral asymmetry for bite force, presenting higher force on the left side. No statistically significant differences were found for chewing side preference among all groups. Within the limitations of this study, it can be concluded that craniofacial dimensions play a role in asymmetry of bite force. ClinicalTrials.gov ID: NCT01286363.     

Occlusal and TMJ loads in subjects with experimentally shortened dental arches

To determine whether shortened dental arches (SDAs) cause functional overloading of the teeth and the temporomandibular joints, which has been implicated in periodontal diseases and temporomandibular disorders, we investigated the influences of SDA on occlusal and joint loads. Bite force and masticatory muscle electromyograms were recorded in five dentate subjects who clenched maximally on intra-oral appliances, creating symmetrical SDAs experimentally. Muscular forces estimated from the recorded electromyograms were fed into a finite element jaw model for calculating bite forces and joint loads. Comparison between the measured and the calculated bite forces ensured that the joint loads were representative. The bite force on each tooth increased with missing molar occlusions, while joint loads decreased. The bite force per root surface area was always greatest on the most posterior tooth, and these values were most constant. The findings provide no evidence that SDA causes overloading of the joints and the teeth, which suggests that neuromuscular regulatory systems are controlling maximum clenching strength under various occlusal conditions.     

The evaluation of vertical heights of maxillary and mandibular bones and the location of anatomic landmarks in panoramic radiographs of edentulous patients for implant dentistry

The purpose of this study was to determine variations in the vertical height measurements in the edentulous maxilla and mandible, and to assess positions of the maxillary sinus, mandibular foramen, and the mandibular canal, which are important for implant length selection and planning using panoramic radiographs. The study sample included 346 edentulous alveolar ridges of 90 men and 83 women. Sixty-three dentate patients' panoramic radiographs were used for location of the first premolar and molar area. Panoramic radiographs were made with a Siemens Orthophos panoramic machine which had been standardized previously. All radiographs were made using a standardized manner by the same technician. Fourteen sites were measured on every panoramic radiograph whenever possible, eight sites in the maxilla and six sites in the mandible. Correlation analyses were performed between age groups and all measurements to determine if age is significant as a covariate. In order to examine the effect of gender the statistical analysis of differences between men and women was performed with Student t-test. The 5% significance level was used for statistical significancy. The height of the maxilla and the mandible in the anterior, first premolar, and first molar regions were significantly greater in men than in women. A majority of the most inferior border of the maxillary sinuses was located anterior to the first molar area (premolar regions) both in men (48.9%) and women (55.4%). Although, there was no statistically significant difference between edentulous men and women for the vertical distances from the mental foramen to the alveolar crest, and horizontal distances from mental foramen to midline, there were statistically significant differences between edentulous men and edentulous women for the vertical distances from the upper border of the mandibular canal to the alveolar crest in the first molar area. Mental foramens were located at the crest of the ridge in 7.2% of the edentulous women, and 6.7% of the edentulous men. The results of this study may guide clinicians to make primer decision of implant insertion area for implant supported prosthesis in edentulous patients.     

第一磨牙缺失不同修复方法的咬合接触特征研究

目的 针对单个第一磨牙缺失的病例,研究种植及可摘局部义齿（RPD）种不同修复方法所恢复的牙列咬合接触特征。方法 选择15名单个第一磨牙缺失的患者作为实验组,15名正常牙列人群作为对照组,其中,实验组每位患者同时进行种植及RPD修复,应用TeeTester咬合分析仪,测试对照组和实验组在未修复、RPD修复及种植义齿修复后3种状态下分别做正中咬合及咀嚼运动,分析其咬合接触特征(总咬合力、总接触面积、不平衡指数、单次咀嚼循环时间,OT/DT比值),并进行统计学分析。结果 患者做正中咬合时,在总咬合力、总接触面积、不平衡指数方面,患者未修复时分别为（48.76±12.82）kg,（317.59±58.47）mm2,（24.78±7.40）,行RPD修复时分别为（54.36±10.59）kg,（355.81±77.43）mm2,（18.29±8.42）,行种植修复时分别为（61.94±12.36）kg,（398.17±83.86）mm2,（17.80±6.69）;患者咀嚼运动时在总咬合力、总接触面积、不平衡指数、单次咀嚼循环时间及T0/Td方面,患者行种植修复时分别为（52.14±16.53）kg,（348.08±81.76）mm2,（15.69±9.16）,（0.4072±0.10）s,（1.718±0.26）。统计学分析表明,RPD、种植义齿修复和对照组的部分咬合接触特征结果无显著性差异,但与未修复前结果有显著性差异。单次咀嚼循环时间及T0/Td在各组间均无显著性差异。结论 在恢复咬合力及咬合接触面积方面,种植义齿优于RPD,较接近天然牙列,并明显优于不修复。正中咬合时全牙列的总咬合力及总接触面积明显大于咀嚼运动时,但不平衡指数无明显统计学差异。