Multiunit Prosthesis Research Articles

Risk factors associated with screw loosening in CAD-CAM custom abutments: A 6-year retrospective study

Statement of ProblemCustom abutments made by using computer-aided design and computer-aided manufacturing (CAD-CAM) are often used for implant-supported prostheses. However, studies on screw loosening of implant prostheses using custom abutments are lacking. PurposeThe purpose of this retrospective study was to investigate the risk factors of screw loosening in implant-supported prostheses using custom abutments made with CAD-CAM. Material and methodsClinical charts, radiographic images, and CAD custom abutment design file data were collected and analyzed retrospectively. The study included 255 patients with 401 dental implants, and the follow-up duration was 6 years. Age, sex (male/female), type of unit (single-unit or multiunit), location of the implant (maxilla or mandible and anterior, premolar, or molar tooth), type of antagonist, and experience of the prosthodontist were reviewed, and implant angulation (mesiodistal and buccolingual), location of the screw access hole (mesiodistal and buccolingual distances from center), and attrition status (none, localized, or generalized) were measured by using a CAD file. The frequencies and percentages of risk factors were evaluated with the Fisher exact test, and the Bonferroni correction was used as a post hoc test. Multiple logistic regression with the Firth method was performed to calculate the odds ratios and their confidence intervals (α=.05). ResultsScrew loosening showed a correlation with the severity of attrition (P<.001). Single-unit prostheses had a higher risk of screw loosening than multiunit prostheses (P<.001). Experience of the prosthodontist (P<.001). Buccolingual angulation of the implant and abutment significantly influenced the incidence of screw loosening (P<.05). Age, sex, location of the implant, type of antagonist, mesiodistal implant angulation, and buccolingual and mesiodistal location of the screw access hole did not significantly influence the incidence of screw loosening (P>.05). ConclusionsThe degree of attrition, buccolingual angulation of the implant and abutment, type of unit, and experience of the prosthodontist (>3 years or <3 years) were risk factors in the incidence of screw loosening.

Prosthetic complications with monolithic or micro-veneered implant-supported zirconia single-unit, multiple-unit, and complete-arch prostheses on titanium base abutments: A single center retrospective study with mean follow-up period of 72.35 months.

The influence of prosthetic design on prosthetic complications when monolithic or micro-veneered zirconia prostheses are supported with titanium base (ti-base) abutments is not well-known. The purpose of this single center, retrospective study was to assess the prevalence of prosthetic complications with monolithic or micro-veneered single-unit, multi-unit, and complete-arch zirconia prostheses supported with ti-base abutments (implant level or multi-unit abutment level). This study retrospectively evaluated the electronic health record (EHR) of participants who received either monolithic or micro-veneered implant-supported single-unit, multi-unit, and/or complete-arch prostheses supported by ti-base or zirconia-ti-base hybrid abutments delivered between the years 2010 and 2021. Data were analyzed by using logistic regression and Exact Mantel-Haenszel chi-square test (α=0.05) to assess the clinical performance of prostheses and complications including crown decementation, feldspathic porcelain chipping, prosthesis fracture, zirconia-ti-base hybrid abutment decementation, abutment screw loosening, screw fracture, abutment fracture, implant loss, and prosthesis remake. The study included 94 participants (50 female, 44 male) with a mean age of 59.5 years (range: 24-101 years of age). The retrospective EHR evaluation yielded 82 single-unit, 51 multi-unit, and 20 complete-arch prostheses on 325 implants. Among 153 prostheses delivered, 108 were micro-veneered (47 single-unit, 41 multi-unit, and 20 complete-arch prostheses) and 45 were monolithic. The average duration was 72.35 months (6.02 years) with a follow-up period of 5-132 months. From the time of insertion to the time of EHR review, of 153 prostheses, 78.43% did not exhibit any prosthetic complication. However, 33 prostheses (21.57%) from 29 participants (30.85%) had at least one prosthetic complication. Only four patients (4.25%) experienced two or more prosthetic complications. Prosthetic design affected the probability of having a complication (p=0.005); complete-arch prostheses had higher probability (p ≤ 0.028). Single-unit prostheses had lower probability of complication than multi-unit prostheses (p=0.005). The most commonly observed complication was fracture of veneering material (5.88%) followed by prosthetic screw loosening (4.57%) and decementation between the zirconia and the ti-base abutment (2.61%). Micro-veneered complete-arch prostheses had higher probability of having chipping than that of not having (p < 0.001), and other micro-veneered prosthetic designs had similar probability of chipping with that of complete-arch prostheses (p ≥ 0.082). Frequency of chipping was affected by veneering (p < 0.001). Monolithic prostheses had lower probability of chipping than micro-veneered prostheses, regardless of the prosthetic design (p < 0.001). The frequency of prosthetic complications varied depending on prosthetic design. Complete-arch prostheses had the highest probability of complications while the single-unit prostheses had the lowest. Micro-veneered prostheses had higher probability for chipping than monolithic prostheses. Probability of chipping was similar for micro-veneered single-unit, multi-unit, and complete-arch zirconia prostheses.

Effect of lamination layer thickness and abutment preparation on the fit of Co-Cr multi-unit prostheses fabricated by additive manufacturing: An in vitro study

Statement of problemSelective laser melting has been increasingly used in the fabrication of metal-ceramic prostheses. The lamination layer thickness may influence the fit of the restoration. However, data regarding its impact remain scarce. PurposeThe purpose of this in vitro study was to evaluate the marginal and internal fit of cobalt-chromium (Co-Cr) 3-unit frameworks fabricated by additive manufacturing with different melting layer thicknesses on different abutments. Material and methodsThe first right maxillary premolar and molar from a typodont were prepared with a circumferential 1.2-mm chamfer, 2-mm occlusal reduction, and total taper of 8 degrees to receive 3-unit fixed partial dentures. After framework design, the data were sent to a laser machine, and 30 specimens were fabricated from Co-Cr metal powder (Mediloy S-Co) by selective laser melting. Specimens were assigned to 3 groups (n=10) with different lamination layer thicknesses of 25 (L25), 50 (L50), and 100 (L100) μm. Marginal fit and internal fit were evaluated. Results were compared among layer thickness groups and abutments. Data were compared by using the Levene test, t test, and ANOVA (α=.05). ResultsA statistical difference was found between different layer thickness groups (P=.016), but not between abutments (P=.429). On the abutment level, significant difference was found in the gap values for the molars (P=.049) between layer thickness groups, but not for the premolars (P=.126). Group L25 reported the smallest mean discrepancy values, and group L100 reported the highest, with statistical difference found between group L100 and groups L25 (P<.001) and L50 (P<.025), but not between groups L25 and L50 (P=.094). ConclusionsThe lamination layer thickness affected the adaptation of the metal frameworks. Framework fit did not significantly differ between abutments.

Evaluating the Frequency of Implant-Supported Fixed Prosthesis Complications in Yazd Dental School in 2020

Introduction: Evaluating the frequency of complications in implant supported prosthesis such as screw loosening and porcelain fracture is important for prevention and management of these problems. The purpose of this study was to evaluate the frequency of implant-supported fixed prosthesis complications in Yazd dental school in 2020. Methods: In this descriptive cross-sectional study, the patients treated with fixed implant-supported restorations in prosthodontic Department of Yazd Dental School, which at least 1 year passed from loading were recalled and examined by census sampling. Prosthetic complications, including porcelain chipping, open proximal contacts, screw loosening and repeated decementation was registered after inspection. The data were analyzed by SPSS 16 software and Chi-square and Fisher's exact tests. Prosthetic problems including porcelain pallor, open proximal contact, loosening of the abutment screw, and repeated loss of cement were recorded after examination and observation. Results: In 130 examined prosthesis, repeated decementation (8.5%), porcelain fracture (6.2%), open proximal contact (2.3%) and screw loosening (3.07%) was observed. Frequency of prosthetic complications according to sex, age, duration of implant loading and implant location were not statistically significant (p &gt;0.05). Frequency of repeated decementation was associated with prosthetic units and number of supporting implants (p &lt;0.05). Conclusion: Repeated decementation was the most frequent complication. Frequency of complications was not related to sex, age, duration of implant loading and implant location. Frequency of complications in single and multiunit prosthesis was different.

Dental Prosthetic Status and Prosthetic Needs of Geriatric Population: A Cross Sectional Study

Objective: Oral health is considered as an indicator for health and quality of life in geriatric patients. It becomes essential to assess the prosthetic status and need in order to promote oral health. Hence, a survey was conducted on geriatric patients visiting a dental teaching institute in India.Materials and Method: A cross-sectional survey was conducted among geriatric population aged above 60.The sample size was estimated to be 570. The information related to prosthetic status, prosthetic need was obtained using the World Health Organisation Oral Health Assessment Form 1997. Chi‑square test was used to analyse the data.Results: Out of 570 elderly people, 308 were males and 262 were females. The study results showed that 77% and 78% of the total subjects had no prostheses in maxillary and mandibular arch, respectively. Prosthetic status was better in males than in females. The level of prosthetic need was higher in females (82%) in mandibular arch compared to males (75%). In the age group of 80-85years need for complete denture was more. Requirement for single and multi unit prosthesis was higher in age groups of 60-65 years. Less percentage of subjects in the upper socio-economic categories needed prosthesis compared to those in the lower socio-economic categoriesConclusion: Unmet prosthetic needs were more in geriatric population attending the institutional outpatient department. There was no significant association of gender with prosthetic status and need and significant association was observed between age and socioeconomic status with prosthetic status and need.

Prosthetic Status and Needs among Head and Neck Cancer Irradiated Patients Suffering from Xerostomia in Delhi, India

Aim: To assess the prosthetic status and prosthetic needs of Head and Neck Cancer Irradiated Patientssuffering from Xerostomia in Delhi India.Materials and Method: A multi-centric, cross-sectional observational study was conducted among 120head and neck cancer irradiated patients suffering from xerostomia in Delhi. The information related tosocio-demographic data, the prosthetic status, and prosthetic need was obtained using a proforma based onWHO oral health assessment form 1997.Results: Out of 120 participants, 103 were males and 17 were females. The mean age of the study participantswas 47.68 + 10.26 years. Stage 1 carcinoma was diagnosed in 69 (57.5%) of the participants while stage 2carcinoma was diagnosed in 51 (42.5%) . Out of 120 individuals, 7 (5.8%) needed single unit prosthesis, 33(27.5%) needed multi-unit prosthesis, 48 (40%) needed a combination of a single and multi-unit prosthesis,and 18 (15%) needed a full prosthesis.Conclusion: The need for prosthesis was high among Head and Neck Cancer Irradiated Patients. There is aneed to emphasize dental service utilization among this group of people.

Impact of Oral Health on Quality of Life and Subjective Well-Being in Community-Dwelling Older Adults in Mexico

Objective: Associate the impact of oral health with quality of life and subjective well-being in the community-dwelling older adults in Mexico. Methods: Non-random sample; 326 subjects: age collected (60-69 / ≥ 70); gender (male / female); marital status (couple / no partner); schooling (0-6 years / ≥7); income for basic needs (yes / no); no depression (GDS-15), no cognitive impairment (MMSE) and comorbidity (no disease / ≥ 1 disease) to control biases. Oral conditions; Caries index (ICPOD) WHO criteria: Very low-Low; Moderate and High. Need for dental prostheses (WHO Manual): No prostheses needed (27-28 natural teeth or fixed / removable / total combination; Need prosthesis: 2-28 tooth without replacement. Xerostomia (Thomson Inventory); moderate to severe xerostomia > 17 points. Dependent variables: Quality of Life Related to Oral Health (GOHAI); 57-60 points: High perception. Subjective well-being: Moral Scale of the Geriatric Center of Philadelphia (PGCMS): Low score (0-11). Results: Age: 71.84 ± 7,278; female / male (70.9 / 29.1%). Controlling confounding factors, multiple logistic regression showed that the need for multi-unit or total prostheses; high CPOD index; severe xerostomia; and low perception of well-being subjective, were associated with low GOHAI scores: P = 0.000; P = 0.004; P = 0.003; P = 0.02 respectively. Subjective well-being only was associated with severe xerostomia and low CVRSO perception: P = 0.0 1; P = 0.02 respectively. Conclusion: Taking into account various confounding factors, the Quality of Life related to Oral Health was the most affected by the deterioration of oral health.

Zygomatic Implants for Restoration of Complex Nasal Defects – A Case Report and Outcome

Total rhinectomy defects pose a challenge for the reconstructive surgeon, but since the introduction of osseointegrated implants, maxillofacial implant–retained prosthetic rehabilitation has provided the patient with an alternative option that has an excellent cosmetic result. Traditionally, zygomatic implants are used for prosthodontic restoration in patients with severely atrophic maxilla or to retain an obturator after tumor ablative surgery. More recently, the nonconventional use of zygomatic implants for retention of a nasal prosthesis has been reported in cases involving rhinectomy defects where the length of conventional dental implants is a limiting factor. In this article, we describe the use and value of transversely-oriented zygomatic implants in combination with an acrylic keeper and maxillary denture to optimize retention of a complex, multi-unit prosthesis in an edentulous patient with a total rhinectomy and upper lip defect.

Assessment of Periodontal Health and Necessity of Dental Treatment in the Institutionalized Elderly Population of East Godavari District, Andhra Pradesh.

Aim:To assess the periodontal health condition and treatment needs among elderly people aged 60–85 years residing as inmates in the eight old age homes in East Godavari district, Andhra Pradesh, India.Settings and Design:A cross-sectional descriptive study was conducted to verify the oral health condition and treatment needs among elderly people aged 60–85 years.Materials and Methods:Modified World Health Organization (WHO) 2013 oral health assessment pro forma for adults was used to assess the oral health status and treatment needs, the clinical assessment of oral mucosa, loss of attachment (LOA) , community periodontal index, dentition status, and treatment need. Prosthetic status and prosthetic needs and related oral health information were obtained from WHO Oral Health Assessment Questionnaire.Statistical Analysis Used:SPSS 23 was used for statistical analysis. Chi-square test was used for age- and gender-wise comparison. P < 0.05 was considered statistically significant.Results:Among the study subjects aged 60–74 years, there were 28.1% males and 25.9% females, and in 75–85 years, 30.6% were males 15.3% were females. In terms of periodontal status (pocket scores), 66.2% of elderly people have pocket scores 6 mm or more and presence of gingival bleeding in 75.9% of study subjects. Almost 24.4% had LOA scores of 12 mm or more. Comparison of LOA scores based on age and gender was statistically significant (P < 0.001). Of the study participants, 50.3% need prompt treatment (including scaling). Almost more than half of the study participants require one or multiunit prosthesis as only 10.93% of elderly population has ≥20 or more natural teeth present.Conclusion:The study showed poor periodontal health among institutionalized elderly inmates. Oral mucosal lesions were found to be higher and oral health status was very deprived among the study population.

Assessment of Oral Health Related Quality of Life Among the Institutionalised Elderly in Delhi, India.

To assess the oral health related quality of life (OHRQoL) among older people residing in old-age homes in Delhi, India. Oral health related quality of life was measured by using the Hindi version of Geriatric Oral Health Assessment Index (GOHAI) which was tested for its reliability and validity. Sociodemographic data were collected and questions regarding the self-perception of general health, oral health and perceived need for dental treatment were put forward. Clinical assessment was also performed. The mean additive-GOHAI score of the study population was found to be 41.57 ± 6.07. Statistically significant associations were found between GOHAI and perceived measures. GOHAI scores decreased with a decrease in the number of teeth present and a decrease in the number of teeth having coronal and root caries. Those subjects who were in need of multi-unit prostheses or full prostheses had significantly poorer OHRQoL compared to those without any prosthetic need or need of single-unit prostheses. This study revealed the extent of dental problems in old-age home residents and may help to plan appropriate preventive measures.

Dental prosthetic status and prosthetic needs of geriatric patients attending the College of Dentistry, Al Jouf University, Kingdom of Saudi Arabia.

Objective:To evaluate the dental prosthetic status and prosthetic needs of geriatric patients attending the College of Dentistry, Al Jouf University, Kingdom of Saudi Arabia.Materials and Methods:Patients aged 60 years and above were included in this study. The World Health Organization oral health assessment pro forma was employed to record the data pertaining to the prosthetic status and prosthetic treatment needs of participants. Data obtained were analyzed using the Statistical Package for the Social Sciences (SPSS, Chicago, IL, USA) Version 20.0. Differences in proportions were compared using the Chi-square test.Results:Out of 286 edentulous patients, 69.06% needed some form of prosthetic treatment, 73.77% did not have any prosthesis in upper arch, and 80.06% did not have any prosthesis in lower arch. Out of 162 males, 32.09% and 26.54% had prosthesis in upper and lower arch, respectively. Among 124 females, 18.54% and 19.35% had prosthesis in upper and lower arch, respectively. In males, the need for any type of prosthesis in upper and lower arch was 68.51% and 75.92%, respectively. In females, the need for prosthesis in upper and lower arch was 57.25% and 72.58%, respectively. The need for multiunit prosthesis was more in both arches in both genders. The need for complete denture and combination of single- or multiunit prosthesis was more among the males as compared to females in maxilla and vice versa for mandible.Conclusion:The observations of this study propose that the greater part of the prosthetic needs were insufficient among the geriatric people.

An evaluation of prosthetic status and treatment needs among institutionalized elderly individuals of Delhi, India

Context: Oral health is essential for elderly person's general health and well-being. The most common oral problem in elderly is tooth loss which results due to periodontal diseases and caries. Prosthetic status is very important as it is related to dietary intake and maintaining nutritional status. Hence, to promote the oral health of the elderly, we need to know their prosthetic status and need. Aims: The aim of this study is to find the prosthetic status and need of 65–74 years old elderly residing in old age homes of Delhi, India. Settings and Design: A cross-sectional study was conducted among a total of 464 residents of 20 old age homes of Delhi, India. Material and Methods: Residents with age group of 64–75 were included in the study. The prosthetic status with treatment need was recorded using the World Health Organization Oral Health Assessment Form (1997). Statistical Analysis Used: Chi-square test and t-test were used to find significance of variables. P < 0.05 was considered significant. Results: Full removable dentures were worn by 7.30% of participants with predominance in upper arch, and one bridge was seen in 9.10% of participants with predominance in lower arch. Full removable denture was required in 25.20% of participants. Most of participants required multiunit prosthesis in both upper as well as lower arch (42.20% and 36.20%, respectively). Conclusion: The present study underlines a considerable need for dental treatment in elderly as the prosthetic status of participants was poor, and prosthetic needs were high.

A Newly Designed Screw- and Cement-Retained Prosthesis and Its Abutments.

The degree of misfit between a prosthesis and its supporting implants is a major concern in screw-retained prostheses because it can lead to screw loosening or mechanical failure of implant components. On the other hand, the difficulty of removing subgingival excess cement and the irretrievability of the superstructure are major drawbacks to cement-retained prostheses. A newly designed screw- and cement-retained prosthesis (SCRP) may solve these problems with its passivity, retrievability, and ease in the complete removal of excess cement, giving it the advantages of both screw-retained and cement-retained prostheses. This prosthetic system is mainly composed of a cement-retained framework with screw holes on the occlusal surface and specially designed cementable abutments for multiunit prostheses. The principle and structure of the SCRP system is described in this article.

Intraorale reparatie en correctie van kronen en bruggen

In cases of a fracture of the porcelain or non-aesthetic margin of a correctly functioning single- or multi-unit dental prosthesis, an intra-oral restoration or correction using a resin composite can generally be chosen. To establish adhesion to metal, porcelain, resin and composite, macro-mechanical, micromechanical and/or chemical retention methods are available. In order to achieve macro-mechanical retention, the preparation ofpits, grooves and/or undercuts is necessary. Micromechanical retention indicates surface roughening of the prosthodontic material at microscopic level through etching or sand-blasting. For chemical retention methods, special primers are used which may react chemically with the several prosthodontic materials. The treatment of choice is determined by the prosthodontic material and the feasibility of the retention method.

Dental Prosthetic Status and Prosthetic Needs of Institutionalised Elderly Population in Oldage Homes of Jabalpur City, Madhya Pradesh, India

Oral disorders are cumulative throughout life and hence unfavourable outcomes are likely to be greatest among the elderly. A descriptive cross-sectional study was conducted among institutionalized geriatric population in old-age homes of Jabalpur city, Madhya Pradesh, to assess their prosthetic status and prosthetic needs. A cross-sectional survey was conducted in all the four old-age homes of Jabalpur city, Madhya Pradesh state, India. All residents aged 60years and above formed the study population. The recording of prosthetic status and prosthetic needs was carried out according to the World Health Organisation (WHO) Oral Health Assessment Form (1997). A total of 224 individuals were included in the study of which 123 were females and 101 were males. Seventy five percent of the females and 55% of the males had no prostheses in their upper arch and 61% of the females and 76% of the males had no prostheses in their lower arch. More number of males presented with 'Bridges' in their upper arch when compared to females (P value=0.006). Highest prosthetic need in males was multi-unit prosthesis (42% in upper arch and 41% in lower arch) whereas, females' required full prosthesis (39% in both the upper arch and lower arches). Ageing presents some formidable challenges, particularly with the institutionalised. This study clearly demonstrates a high insufficiency of prosthetic care among the institutionalized elderly population. Any preparation towards the provision of oral health care should not be limited to treatment alone but, more importantly focus on empowering this elderly community with information and education programmes.

Soldering in Prosthodontics-An Overview, Part I

The fit of fixed multiunit dental prostheses (FDP), traditionally termed fixed partial dentures (FPDs), is an ongoing problem. Poorly fitting restorations may hasten mechanical failure, due to abutment caries or screw failure. Soldering and welding play an important role in trying to overcome misfit of fixed multiunit prostheses. The term FPD will be used to denote multiunit fixed dental prostheses in this review. This is the first of a series of articles that review the state of the art and science of soldering and welding in relation to the fit of cemented or screw-retained multiunit prostheses. A comprehensive archive of background information and scientific findings is presented. Texts in dental materials and prosthodontics were reviewed. Scientific data were drawn from the numerous laboratory studies up to and including 2009. The background, theory, terminology, and working principles, along with the applied research, are presented. This first article focuses on soldering principles and dimensional accuracy in soldering. There is some discussion and suggestions for future research and development. Soldering may improve dimensional accuracy or reduce the distortion of multiunit fixed prostheses. Many variables can affect the outcome in soldering technique. Research science has developed some helpful guidelines. Research projects are disconnected and limited in scope.

Survival Rates of All-Ceramic Systems Differ by Clinical Indication and Fabrication Method

Approximately 50 articles were included in this review based on a MEDLINE and PubMed search of English-language peer-reviewed literature focused on research published between 1993 and 2008. The authors also hand searched relevant dental journals. Randomized controlled trials, nonrandomized controlled trials, longitudinal experimental clinical studies, longitudinal prospective studies, and longitudinal retrospective studies were all eligible for inclusion in this review. Treatment of teeth with an all-ceramic restoration in the form of a veneer, inlay, onlay, crown, or fixed dental prosthesis, and the subsequent clinical success or failure of these restorations. Restoration survival rate (in percent) as a function of observation period and fabrication method, reported by restoration type. Specific fabrication methods for single-tooth restorations included InCeram Alumina, InCeram Spinell, Procera, IPS Empress, IPS Empress 2, and Dicor crowns. Fabrication methods for fixed partial dentures included InCeram, InCeram Zr, IPS Empress 2, and Cercon Zr, respectively. The reported Kaplan-Meier survival rates were grouped by restoration type rather than by ceramic system. For porcelain veneers, less than 5% failure was reported at 5 years and less than 10% failure rate at 10 years (n ranging from 83 to 3047). For ceramic inlay and onlay restorations, 10-year failure rates were found to be less than 10% (n ranging from 200 to 1588). Greater success rates were reported for anterior crowns. Kaplan-Meier survival rates were calculated for end points ranging in duration from 1 to 4 years (6 studies), 5 to 6 years (12 studies), 7 to 8 years (5 studies), and 10 years or more (2 studies). The results for multiunit prostheses included 11 studies, fewer prostheses, and generally higher failure rates. As with single crowns, failure rates for multiunit prostheses were reported to be consistently higher in the posterior region than anteriorly. Kaplan-Meier survival rates were reported for 3-unit fixed partial dentures for end points ranging from 1 to 10 years, with a mean end point of approximately 5.6 years. The authors suggest that many all-ceramic restorations were found to demonstrate acceptable longevity compared with conventional restorations (eg, metal-ceramic crowns). For single-rooted anterior teeth, broad support was found for the premise that clinicians may select from any all-ceramic system for laminate veneers, intracoronal restorations such as inlays and onlays, and for full-coverage restorations. For restoration of molar teeth, the review suggests that relatively few all-ceramic systems will provide predictable long-term success. The number of clinical complications with all-ceramic fixed dental prostheses (multiunit) remains high, even with increased connector size. Although zirconium systems offer the advantage of favorable material characteristics for substructures, the clinical problem of chipping of the weaker esthetic veneer persists.

Different bone loading patterns due to fixation of three‐unit and five‐unit implant prostheses

It has been considered that implant prostheses ought to display passive fit. The objective of this finite element analysis (FEA) was to simulate the bone loading resulting from the fixation of implant-supported three and five-unit fixed partial dentures (FPDs). Based on a patient case, six different FPD-groups were fabricated using either two or three implants for support. Strain gauges on the pontics of the prostheses were used for in vivo measurements. Based on the values obtained, bone loading models were simulated using three-dimensional finite element analysis and the results obtained were represented as von Mises equivalent stress. The mean strain (epsilon) values ranged from 15 micro epsilon to 170 micro epsilon for the three-unit FPDs and from 32 micro epsilon to 302 micro epsilon for the five-unit FPDs. FEA revealed von Mises stresses up to 30 MPa in the cortical area, while in trabecular bone values up to 5 MPa were observed. Static implant loading of similar magnitude can be provoked through 200 N axial load. Although the in vivo measured strain levels (epsilon) were of higher magnitude for the five-unit prostheses, FEA revealed bone loading of comparable magnitude for both three- and five-unit FPDs. Multi-unit prostheses may demonstrate greater inaccuracies compared with single implant restorations, but due to the absence of moment loading the multi-implant configuration appears to compensate for the higher strain development.

The response of bone in primates around unloaded dental implants supporting prostheses with different levels of fit

Implant failure as a consequence of prosthetic loading following clinical determination of successful stage I healing is poorly understood. A basic premise of accepted prosthetic protocol is passive connection of multiunit prostheses to the implant support. To better understand mechanical factors related to implant failure, this basic passivity premise was experimentally tested prior to study of functional loading research. The purpose of this preliminary study was to measure the bone response around implants placed in the mandible of baboons that supported prostheses exhibiting two levels of fit and not loaded occlusally. Screw-retained prostheses that exhibited a mean linear distortion of 38 microns and 345 microns made up the fit and misfit groups respectively. The results failed to distinguish a difference in bone response between the two levels of prosthetic fit. Although the finding can be argued as a sample size limitation, the data strongly suggest an opposite response than is clinically expected and, consequently, does not warrant the use of additional animals in this initial study. Because the design of this study does not mimic the clinical application of misfitting prostheses (where dynamic functional loads are superimposed with misfit loads), it cannot be inferred that, in clinical application, fit does not alter the osseointegrated interface. Ongoing investigation of failure due to nonpassive connections under dynamic loading conditions of mastication will help clarify the clinical significance of passivity.