Crestal bone loss due to abutment manipulation and an internal silver deposition implant design in a canine model.

OBJECTIVE: The study aimed to evaluate the effect of internal silver coating as a countermeasure to crestal bone loss around implants with or without multiple abutment disconnections/reconnections. MATERIALS AND METHODS: Following tooth extraction, 48 implants with connected healing abutments (24 implants internally coated with elemental silver) were placed in the mandible of eight beagle dogs. Two months after implant surgery one side of the mandible was randomly assigned to four abutment manipulations (disconnection/reconnection) on a weekly basis. At 4 months postoperative, biopsies were obtained and prepared for histomorphometric analysis. RESULTS: Healing abutment manipulation increased crestal bone remodeling when compared to no abutment manipulation (1.28 mm versus 0.92 mm, respectively), although the difference was not statistically significant (p = 0.0836). Overall, an internal silver coating did not provide a statistically sufficient implant treatment characteristic as a countermeasure to crestal bone loss (p = 0.7801). CONCLUSIONS: These findings indicate that the controlled variables explored here (abutment manipulation/internal silver coating) have a limited effect on initial crestal bone loss. CLINICAL RELEVANCE: Abutment manipulation during prosthetic work does not seem to harm the peri-implant soft and hard tissues.

Prospective clinical study of press-ceramic overlap and full veneer restorations: 7-year results.

The aim of this prospective clinical study was to investigate the long-term performance of all-ceramic veneers with overlap (OV) and full veneer (FV) preparation designs. Twenty-five patients were restored using 42 OV restorations (incisal/palatal butt-joint margin) and 24 FV restorations (palatal rounded shoulder margin). All restorations were leucite-reinforced glass-ceramic anterior veneers. The 7-year Kaplan-Meier survival rate was 100% for FV restorations and 97.6% for OV restorations. The all-ceramic veneers revealed significant deterioration over time according to United States Public Health Service criteria, irrespective of the preparation design. Based on the 7-year results of this study, both preparation designs can be considered reliable treatment options for anterior teeth with extended deficits.

Flapless postextraction socket implant placement in the esthetic zone: part 1. The effect of bone grafting and/or provisional restoration on facial-palatal ridge dimensional change-a retrospective cohort study.

The dental literature has reported vertical soft tissue changes that can occur with immediate implant placement, bone grafting, and provisional restoration ranging from a gain or loss of 1.0 mm. However, little is known of the effects of facial-palatal collapse of the ridge due to these clinical procedures. Based upon treatment modalities rendered, an ensuing contour change can occur with significant negative esthetic consequences. The results of a retrospective clinical cohort study evaluating the change in horizontal ridge dimension associated with implant placement in anterior postextraction sockets are presented for four treatment groups: (1) group no BGPR = no bone graft and no provisional restoration; (2) group PR = no bone graft, provisional restoration; (3) group BG = bone graft, no provisional restoration; and (4) group BGPR = bone graft, provisional restoration. Bone grafting at the time of implant placement into the gap in combination with a contoured healing abutment or a provisional restoration resulted in the smallest amount of ridge contour change. Therefore, it is recommended to place a bone graft and contoured healing abutment or provisional restoration at the time of flapless postextraction socket implant placement.

Early wound healing and patient morbidity after single-incision vs. trap-door graft harvesting from the palate--a clinical study.

OBJECTIVES: The aim of this study is to compare wound healing and patient pain perception of single-incision (single-incision, modified single-incision) and trap-door surgical techniques to harvest subepithelial connective tissue grafts from the palate. MATERIAL AND METHODS: Thirty-six patients were selected for root coverage procedures with subepithelial connective tissue grafts and randomly assigned to two single-incision groups or a trap-door group (n = 12/group). One week after surgery, a modified early-wound healing index (EHI), patient pain and painkiller intake were recorded. Follow-up was performed until complete epithelialization was achieved. RESULTS: Single-incision techniques showed significantly improved early healing over trap-door approaches. Specifically, the mean EHI was 2.50 ± 1.14 for single-incision techniques, as compared to 3.33 ± 1.30 for trap door. The incidence of secondary healing was significantly lower in the single-incision groups. Concomitantly, the cumulative dosage and duration of painkiller intake were significantly reduced, as compared to the trap-door group. CONCLUSION: Within the limits of this trial, single-incision techniques can lead to improved early healing and reduced patient pain after subepithelial connective tissue graft harvesting than trap-door techniques. CLINICAL RELEVANCE: Avoiding trap-door incisions for harvesting of connective tissue grafts may reduce patient morbidity.

Clinical investigation on axial versus tilted implants for immediate fixed rehabilitation of edentulous arches: preliminary results of a single cohort study.

PURPOSE: The purpose of this clinical investigation was to evaluate full-arch fixed-dental restorations supported by immediate loaded axial and tilted implants in a single-cohort study. Survival rate of axial and tilted implants was compared. MATERIALS AND METHODS: From 2006 to 2010, 30 patients were recruited and treated with dental implants. Provisional fixed-dental prostheses were screw-retained over axial or axial and tilted implants within 24 hours after surgery. Follow-ups at 6, 12, and 24 months and annually up to 5 years were scheduled, and radiographic evaluation of peri-implant bone level changes was conducted. RESULTS: Thirty patients (20 females and 10 males) were followed up for an average of 44 months (range 18-67 months). Six patients received both upper and lower implant rehabilitations, resulting in 36 restorations. A total of two hundred two implants were placed (maxilla = 118; mandible = 84) and 46% of the fixtures were evaluated at the 4-year recall. Four axial implants were lost in three patients, leading to 98.02% implant (97.56% axial implants and 100% tilted implants) and 100% prosthetic cumulative survival rate, respectively. No significant difference in marginal bone loss was found between tilted and axial implants in both jaws at 1-year evaluation. CONCLUSIONS: Midterm results confirmed that immediate loading of axial and tilted implants provides a viable treatment modality for the rehabilitation of edentulous arches.

Immediate fixed rehabilitation of the edentulous maxilla: a prospective clinical and radiological study after 3 years of loading.

PURPOSE: The aim of this study was to prospectively evaluate the clinical and radiographic outcomes of immediate full-arch fixed maxillary prosthesis supported by two axial and four tilted implants after 3 years of loading. MATERIALS AND METHODS: Thirty-two patients with atrophic maxilla were consecutively enrolled and treated. Each patient received a fixed full-arch maxillary rehabilitation supported by four tilted implants that engaged the posterior and the anterior sinus walls and two axial anterior implants. A total of 192 implants (30 Brånemark System MK IV and 162 NobelSpeedy Groovy, Nobel Biocare AB, Göteborg, Sweden) were inserted and immediately loaded. The definitive restorations were placed 6 months later, and follow-up visits were scheduled every 6 months. During follow-ups, marginal bone loss (MBL), plaque and bleeding scores, and patient's satisfaction were recorded. RESULTS: All patients reached at least 3-year follow-up examination (range 36-78, average 55.53 months). Two tilted implants failed before delivering the definitive restoration, resulting in a cumulative survival rate of 98.96%. All final prostheses were stable and functional, resulting in a cumulative survival and success rate of 100%. At the 3-year follow-up there was no significant difference in MBL between axial (1.55 ± 0.31 mm) and tilted implants (1.46 ± 0.19 mm) (p = .05). Plaque and bleeding scores decreased over time, while patient's satisfaction in both aesthetics and function increased. CONCLUSIONS: Implants placement with this configuration could be considered a predictable and cost- and time-effective alternative approach for the immediate restoration of the edentulous maxilla, avoiding bone grafting procedures, even with a medium-term follow-up.

Intraoral treatment of veneering porcelain chipping of fixed dental restorations: a review and clinical application.

BACKGROUND: Every dental ceramic system can experience failure of the veneering porcelain. However, the increasing popularity of all-ceramic crowns and fixed dental prostheses (FDPs) seems to have led to an increasing need to repair chipped veneering porcelain. OBJECTIVES: The authors compared different methods to repair fractured ceramic restorations (porcelain-fused-to-metal and all-ceramic) and explain the basic principles of adhesion in these systems. They also evaluated the frequency and causes of failure in dental ceramic systems. METHODS: This review is based on the results of PubMed and Google Scholar searches, as well as on a hand search of the scientific literature, resulting in 300 articles from 1977 to 2012. The authors used multiple key words (ceramic, repair, bonding, hydrofluoric acid, air abrasion, silane, phosphates, silicon dioxide) and different strategies (connecting different key words with OR, NOR and AND and truncation of the stem of words) to search the databases. RESULTS: Because of differences in the material composition of ceramic systems (composed of metal, alumina or zirconia, glass-ceramics and feldspathic ceramics), different treatments are required for the exposed material surfaces after chipping. Use of hydrofluoric acid etching, air abrasion, tribochemical coating, silanization and metal primers or zirconia primers seem to be the most successful conditioning methods for durable bonding and repair. CONCLUSIONS AND CLINICAL IMPLICATIONS: Intraoral repair of a restoration offers a satisfying option for the patient when the restoration cannot be removed or replaced. Its success depends largely on the conditioning methods used for the fractured surfaces.

Effect of platform switching on collagen fiber orientation and bone resorption around dental implants: a preliminary histologic animal study.

PURPOSE: To show the presence and direction of the collagen fiber orientation around platform-switched (PS) and non-platform switched (NPS) implants at the crestal bone level. MATERIALS AND METHODS: Twelve implants (six PS and six NPS implants) were placed with single-stage surgery in three dogs. The implant abutments were disconnected and reconnected after 8, 10, 12, and 14 weeks. The animals were sacrificed in the 18 week. The specimens were stained with hematoxylin and eosin and examined using polarized light microscopy. RESULTS: The PS implant specimens showed circular fiber orientation at the implant platform level and the NPS implants showed similar fiber orientation at the bone level of the first implant thread. All specimens demonstrated a circular fiber orientation of the collagen fibers at the crestal bone level. CONCLUSIONS: The discrepancy in implantabutment diameter involving a change from a wider implant platform to a smaller abutment diameter, described as platform switching, seems to provoke a circular fiber orientation at the implant platform level. Similar circular fiber orientation was found at the first implant thread bone level for regular implants without platform switching. The histologic results support the hypothesis that platform switching can reduce crestal bone loss and can serve as a "mechanical retention factor" for periodontal fiber orientation. More clinical and histologic studies are needed to corroborate this preliminary finding.

Residual stresses in porcelain-veneered zirconia prostheses.

OBJECTIVES: Compressive stress has been intentionally introduced into the overlay porcelain of zirconia-ceramic prostheses to prevent veneer fracture. However, recent theoretical analysis has predicted that the residual stresses in the porcelain may be also tensile in nature. This study aims to determine the type and magnitude of the residual stresses in the porcelain veneers of full-contour fixed-dental prostheses (FDPs) with an anatomic zirconia coping design and in control porcelain with the zirconia removed using a well-established Vickers indentation method. METHODS: Six 3-unit zirconia FDPs were manufactured (NobelBiocare, Gothenburg, Sweden). Porcelain was hand-veneered using a slow cooling rate. Each FDP was sectioned parallel to the occlusal plane for Vickers indentations (n = 143; load = 9.8 N; dwell time = 5s). Tests were performed in the veneer of porcelain-zirconia specimens (bilayers, n=4) and porcelain specimens without zirconia cores (monolayers, n = 2). RESULTS: The average crack lengths and standard deviation, in the transverse and radial directions (i.e. parallel and perpendicular to the veneer/core interface, respectively), were 67 ± 12 µm and 52 ± 8 µm for the bilayers and 64 ± 8 µm and 64 ± 7 µm for the monolayers. These results indicated a major hoop compressive stress (~40-50 MPa) and a moderate radial tensile stress (~10 MPa) in the bulk of the porcelain veneer. SIGNIFICANCE: Vickers indentation is a powerful method to determine the residual stresses in veneered zirconia systems. Our findings revealed the presence of a radial tensile stress in the overlay porcelain, which may contribute to the large clinical chip fractures observed in these prostheses.

Marginal accuracy of three implant-ceramic abutment configurations.

PURPOSE: Microgaps at the implant-abutment interface allow for microbial colonization, which can lead to peri-implant tissue inflammation. This study sought to determine the marginal accuracy of three different implant-zirconium oxide (zirconia) abutment configurations and one implant?titanium abutment configuration. MATERIALS AND METHODS: Three combinations of implants with custom-made zirconia abutments were analyzed (n = 5/group): NobelProcera abutments/titanium inserts on Replace Select Tapered TiUnite implants (Nobel Biocare) (NP); Encode abutments/NanoTite Tapered Certain implants (Biomet 3i) (B3i); Astra Tech Dental Atlantis abutments/Biomet 3i NanoTite Tapered Certain implants (At). Five custom-made Encode titanium abutments/NanoTite Tapered Certain implants (Ti) were used as a control group. All abutments were fabricated with computer-aided design/computer-assisted manufacture. One-hundred twenty vertical gap measurements were made per sample using scanning electron microscopy (15 scans x 4 aspects of each specimen [buccal, mesial, palatal, distal] x 2 measurements). Analysis of variance was used to compare the marginal fit values among the four groups, the specimens within each group, and the four aspects of each specimen. RESULTS: Mean (± standard deviation) gap values were 8.4 ± 5.6 Μm (NP), 5.7 ± 1.9 Μm (B3i), 11.8 ± 2.6 Μm (At), and 1.6 ± 0.5 Μm (Ti). A significant difference was found between B3i and At. No difference resulted between NP with the other two groups. Gap values were significantly smaller for Ti relative to all zirconia systems. For each ceramic abutment configuration, the fit was significantly different among the five specimens. For 12 of the 15 ceramic abutment specimens, gap values sorted by aspect were significantly different. CONCLUSIONS: The implant?titanium abutment connection showed significantly better fit than all implant?zirconia abutment configurations, which demonstrated mean gaps that were approximately three to seven times larger than those in the titanium abutment system.

Reliability and fatigue failure modes of implant-supported aluminum-oxide fixed dental prostheses.

OBJECTIVES: To investigate failure modes and reliability of implant-supported aluminum-oxide three-unit fixed dental prostheses (FDPs) using two different veneering porcelains. MATERIAL AND METHODS: Thirty-six aluminum-oxide FDP frameworks were computer-aided designed and computer-aided manufactured and either hand-veneered(n = 18) or over-pressed(n = 18). All FDPs were adhesively luted to custom-made zirconium-oxide-abutments attached to dental implant fixtures (regular platform 4 × 13 mm). Specimens were stored in water before mechanical testing. A step-stress accelerated life test (SSALT) with three load/cycles varying profiles was developed based on initial single-load-to-failure testing. Failure was defined by veneer chipping or chipping in combination with framework fracture. SSALT was performed on each FDP inclined 30° with respect to the applied load direction. For all specimens, failure modes were analyzed using polarized reflected light microscopy and scanning electron microscopy. Reliability was computed using Weibull analysis software (Reliasoft). RESULTS: The dominant failure mode for the over-pressed FDPs was buccal chipping of the porcelain in the loading area of the pontic, while hand-veneered specimens failed mainly by combined failure modes in the veneering porcelain, framework, and abutments. Chipping of the porcelain occurred earlier in the over-pressed specimens (350 N/85 k, load/cycles) than in the hand-veneered ones (600 N/110 k) (profile I). Given a mission at 300 N load and 100 or 200 k cycles, the computed Weibull reliability (two-sided at 90% confidence bounds) was 0.99(1/0.98) and 0.99(1/0.98) for hand-veneered FDPs and 0.45(0.76/0.10) and 0.05(0.63/0) for over-pressed FDPs, respectively. CONCLUSIONS: In the range of average clinical loads (300-700 N), hand-veneered aluminum-oxide FDPs showed significantly less failure by chipping of the veneer than the over-pressed. Hand-veneered FDPs under fatigue loading failed at loads ≥600 N.

Contact fatigue response of porcelain-veneered alumina model systems.

Fatigue damage modes and reliability of hand-veneered (HV) and over-pressed (OP) aluminum-oxide layer structures were compared. Influence of luting cement thickness on mechanical performance was investigated. Sixty-four aluminum-oxide plates (10 × 10 × 0.5 mm) were veneered with hand built-up or pressed porcelain (0.7 mm) and adhesively luted (50- or 150-µm cement thickness) to water-aged composite resin blocks (12 × 12 × 4 mm). Single-load-to-failure and fatigue tests were performed with a spherical tungsten carbide indenter (d = 6.25 mm) applied in the center of the veneer layer. Specimens were inspected with polarized-reflected-light and scanning electron microscopy. Use-level probability Weibull curves were plotted with two-sided 90% confidence bounds, and reliability at 75,000 cycles and 250 N load was calculated. For all specimens but two OP with 50-µm cement thickness, failure was characterized by flexural radial cracks initiating at the bottom surface of the alumina core and propagating into the veneering porcelain before cone cracks could extend to the porcelain/alumina interface. HV specimens showed higher reliability compared to OP. Those with 50-µm cement thickness were more reliable relative to their 150-µm counterparts (HV_50 µm: 95% (0.99/0.67); HV_150 µm: 55% (0.92/0.01); OP_50 µm: 69% (0.84/0.48); OP_150 µm: 15% (0.53/0.004)). Similar failure modes were observed in HV and OP specimens. Radial cracks developing in the core and spreading into the veneer are suggested to cause bulk fracture, which is the characteristic failure mode for alumina core crowns. However, the highest resistance to fatigue loading was found for the HV specimens with thin cement thickness, while the lowest occurred for the OP with thick cement layer.

Reliability and failure modes of implant-supported zirconium-oxide fixed dental prostheses related to veneering techniques.

OBJECTIVES: To compare fatigue failure modes and reliability of hand-veneered and over-pressed implant-supported three-unit zirconium-oxide fixed-dental-prostheses(FDPs). METHODS: Sixty-four custom-made zirconium-oxide abutments (n=32/group) and thirty-two zirconium-oxide FDP-frameworks were CAD/CAM manufactured. Frameworks were veneered with hand-built up or over-pressed porcelain (n=16/group). Step-stress-accelerated-life-testing (SSALT) was performed in water applying a distributed contact load at the buccal cusp-pontic-area. Post failure examinations were carried out using optical (polarized-reflected-light) and scanning electron microscopy (SEM) to visualize crack propagation and failure modes. Reliability was compared using cumulative-damage step-stress analysis (Alta-7-Pro, Reliasoft). RESULTS: Crack propagation was observed in the veneering porcelain during fatigue. The majority of zirconium-oxide FDPs demonstrated porcelain chipping as the dominant failure mode. Nevertheless, fracture of the zirconium-oxide frameworks was also observed. Over-pressed FDPs failed earlier at a mean failure load of 696 ± 149N relative to hand-veneered at 882 ± 61N (profile I). Weibull-stress-number of cycles-unreliability-curves were generated. The reliability (2-sided at 90% confidence bounds) for a 400N load at 100K cycles indicated values of 0.84 (0.98-0.24) for the hand-veneered FDPs and 0.50 (0.82-0.09) for their over-pressed counterparts. CONCLUSIONS: Both zirconium-oxide FDP systems were resistant under accelerated-life-time-testing. Over-pressed specimens were more susceptible to fatigue loading with earlier veneer chipping.

Proximal contact areas of the maxillary anterior dentition.

The goal of this study was to quantify the apicoincisal extent of the proximal contact area (PCA) between the eight maxillary anterior teeth. A total of 140 PCA sites and 160 crown lengths were measured in 20 healthy patients. The percentage ratio of PCA to clinical crown length was computed and defined as the proximal contact area proportion (PCAP). Mean PCA dimensions between central incisors (CI/CI), central and lateral incisors (CI/LI), lateral incisors and canines (LI/CA), and canines and first premolars (CA/PM) were 4.2, 2.9, 2.0, and 1.5 mm, respectively. Mesial mean PCAPs were 41%, 32%, 20%, and 18%, respectively. The paired sample t test demonstrated significant differences between all PCAs (P < .0001), except for CA/PM sites (P = .24). Contact areas, not contact points, were observed between neighboring maxillary anterior teeth. Natural PCAPs emerged as well defined in the maxillary anterior dentition bilaterally. Therefore, PCAPs should be taken into consideration for clinical anterior restorations since they determine the papillary and incisal embrasures.

Papilla proportions in the maxillary anterior dentition.

Two hundred forty interdental papilla sites in 20 healthy patients were investigated. Interdental papilla heights of maxillary anterior teeth were measured from the gingival zenith, along with clinical crown lengths. Percentages of papilla height to crown length were computed and defined as papilla proportion, mesial papilla proportion (MPP), and distal papilla proportion (DPP). Mean interdental papilla heights of maxillary anterior teeth were 4 mm mesially and 4.1 mm distally. Mean MPP was 42% (n = 120), and mean DPP was 43% (n = 120). No significant differences were found between MPP and DPP for maxillary incisors (P >/= .5). Canines demonstrated a trend toward increased distal papilla heights. Papilla proportions were approximately 40% for all tooth groups. A more apical position of distal papilla heights from anterior to posterior teeth, mentioned in the literature, was not confirmed by the present data.

All-ceramic partial coverage restorations--midterm results of a 5-year prospective clinical splitmouth study.

OBJECTIVES: Midterm-evaluation of a 5-year prospective clinical splitmouth-investigation on survival rate and long-term behavior of all-ceramic partial coverage restorations (PCRs) on molars. Pressed ceramic and CAD/CAM fabricated PCRs were compared. METHODS: 80 vital molars of 25 patients were restored with all-ceramic PCRs (40 IPS e.max Press*[IP] and 40 ProCAD*[PC]). IP-PCRs were heat pressed following the lost-wax method. PC-PCRs were fabricated with Cerec 3** and Cerec InLab** CAD/CAM system (**Sirona Dental Systems, Bensheim, Germany). All PCRs were adhesively luted with a light-polymerizing composite (Syntac*/Tetric*) (*Ivoclar Vivadent, Schaan, Liechtenstein). Clinical reevaluations were performed at baseline and 13, 25, and 36 months after insertion of the PCRs according to the modified United States Public Health Services (USPHS) criteria. Absolute failures were demonstrated by Kaplan-Meier survival rate. RESULTS: After an observation time up to 3 years, survival rate of IP-PCRs was 100% and 97% for PC-PCRs due to one severe fracture. The PC-PCR had to be replaced after 9 months. Secondary caries and endodontic complications did not occur. Increased clinical service time resulted in significant decrease of marginal adaptation (p=0.031) and enhanced marginal discoloration (p<0.0001). Both PCR ceramic materials demonstrated significant deteriorations in color match (p<0.0001) and surface roughness (p<0.0001), IP-PCRs were significantly more affected (p< or =0.005). Regarding anatomic form IP-PCRs performed significantly better (p=0.0012). CONCLUSION: Pressed ceramic and CAD/CAM fabricated partial coverage restorations exhibited a reliable treatment option to restore larger defects in posterior teeth. Marginal degradation of the resin cement and deterioration of the all-ceramic materials during clinical function determine the clinical long-term performance of partial coverage restorations.

Gingival zenith positions and levels of the maxillary anterior dentition.

PURPOSE: The location of the gingival zenith in a medial-lateral position relative to the vertical tooth axis of the maxillary anterior teeth remains to be clearly defined. In addition, the apex of the free gingival margin of the lateral incisor teeth relative to the gingival zeniths of the adjacent proximal teeth remains undetermined. Therefore, this investigation evaluated two clinical parameters: (1) the gingival zenith position (GZP) from the vertical bisected midline (VBM) along the long axis of each individual maxillary anterior tooth; and (2) the gingival zenith level (GZL) of the lateral incisors in an apical-coronal direction relative to the gingival line joining the tangents of the GZP of the adjacent central incisor and canine teeth under healthy conditions. MATERIALS AND METHODS: A total of 240 sites in 20 healthy patients (13 females, 7 males) with an average age of 27.7 years were evaluated. The inclusion patient criteria were absence of periodontal disease, gingival recession, or gingival hypertrophy as well as teeth without loss of interdental papillae, spacing, crowding, existing restorations, and incisal attrition. GZP dimensions were measured with calibrated digital calipers for each individual tooth and within each tooth group in a medial-lateral direction from the VBM. GZLs were measured in an apical-coronal direction from a tangent line drawn on the diagnostic casts from the GZPs of the adjacent teeth. RESULTS: This study demonstrated that all central incisors displayed a distal GZP from the VBM, with a mean average of 1 mm. Lateral incisors showed a deviation of the gingival zenith by a mean of 0.4 mm. In 97.5% of the canine population, the GZP was centralized along the long axis of the canine. The mean distance of the contour of the gingival margin in an apical-coronal direction of the lateral incisors (GZL) relative to gingival line joining the tangent of the adjacent central and canine GZPs was approximately 1 mm. CONCLUSION: This investigation revealed a GZP mean value of 1 mm distal from the VBM for the central incisor tooth group. The lateral incisors showed a mean average of 0.4 mm. The canine tooth group demonstrated almost no deviations of the GZP from the VBM. The GZL of the lateral incisors relative to the adjacent central incisor and canine teeth were more coronal by approximately 1 mm. These data could be used as reference points during esthetic anterior oral rehabilitation. CLINICAL SIGNIFICANCE: The information presented in this article can be clinically applied to reestablish the proper intratooth GZPs of the maxillary anterior teeth during periodontal crown lengthening or root coverage procedures. In addition, the intra-arch gingival level of the lateral incisor gingival zenith relative to the adjacent central and canine teeth can be appropriately established.

Dimensional changes of the alveolar ridge contour after different socket preservation techniques.

OBJECTIVES: The aim of the following study was to assess contour changes after socket preservation techniques. MATERIAL AND METHODS: In five beagle dogs, the distal root of the third and fourth mandibular premolars was extracted. The following treatments (Tx) were randomly assigned for the extraction socket. Tx 1: BioOss Collagen. Tx 2: BioOss Collagen and a free soft tissue graft. Tx 3: No treatment. Tx 4: The internal buccal aspect was covered with an experimental collagen membrane, the extraction socket was filled with BioOss Collagen and the membrane folded on top of the graft. Impressions were obtained at baseline, 2 and 4 months after surgery. Bucco-lingual measurements were performed using digital imaging analysis. RESULTS: All groups displayed contour shrinkage at the buccal aspect. Only the differences between the two test groups (Tx 1, Tx 2) and the control group (Tx 3) were significant at the buccal aspect (p< or =0.001). No measurements of the Tx 4 group could be performed. CONCLUSION: Socket preservation techniques, used in the present experiment, were not able to entirely compensate for the alterations after tooth extraction. Yet, incorporation of BioOss Collagen seems to have the potential to limit but not avoid the post-operative contour shrinkage.

Effect of mouth-motion fatigue and thermal cycling on the marginal accuracy of partial coverage restorations made of various dental materials.

OBJECTIVES: To investigate the influence of mouth-motion fatigue on marginal-accuracy of partial-coverage-restorations-(PCRs) of various dental materials. METHODS: Eighty molars were prepared equally and divided into five groups (n=16). PCRs were fabricated of following dental materials: Group-GO=Gold-Pontor-MPF(double dagger), Group-TA=Targis*, Group-EX=IPS-e.max-Press*, Group-EM=IPS-Empress*, Group-PC=ProCAD*/Cerec 3(dagger) ((double dagger)Metalor/*Ivoclar-Vivadent/(dagger)Sirona-Dental-System). Gold-PCRs were cemented conventionally. Residual 64 PCRs were adhesively luted and subjected to masticatory loading (1.2million-cycles, 1.6Hz, 49N) and thermal cycling (5 degrees C/55 degrees C, 60s, dwell-time, 5500cycles). Discrepancies in marginal-accuracy were examined on epoxy replicas (200 x magnification). Statistical analysis was performed by unpaired and paired t-tests (alpha=0.05). RESULTS: After cementing, marginal-accuracy (geometrical mean)[95% confidence limits] was recorded: GO-47[43-51]microm, TA-42[38-45]microm, EX-60[52-67]microm, EM-52[45-60]microm and PC-75[59-94]microm. No significant differences were found between groups GO, TA and EM. Values of Group-EX were significantly higher compared to Group-TA (p=0.04). Group-PC demonstrated significantly decreased marginal-accuracy towards groups GO (p=0.03) and TA (p=0.02). Except for Group-GO (p=0.01), no significant changes in marginal-accuracy were observed after mouth-motion fatigue and thermal cycling (GO-42[38-45]microm, TA-42[38-47]microm, EX-56[49-65]microm, EM-54[46-64]microm and PC-71[59-84]microm). However, Group-GO and Group-EM showed significant deviations in marginal-accuracy after aging (p=0.04). Marginal discrepancies of groups EX and EM were similar (p=1.0). Values of Group-PC were significantly higher when compared to groups GO (p=0.01) and TA (p=0.02). Buccal-lingual marginal discrepancies were significantly higher than mesial-distal in all groups and stages. SIGNIFICANCE: Cast-gold-PCRs demonstrated superior marginal-accuracy, followed by indirect ceromer PCRs. All-ceramic PCRs showed in vitro clinical acceptable marginal widths, even though CAD/CAM fabrication slightly compromised marginal-accuracy. Since preparation margins were not exposed to occlusal loading directly, increased marginal discrepancies due to marginal chipping during mouth-motion fatigue were not experienced.

Masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial crowns with and without coverage of compromised cusps.

PURPOSE: To evaluate preparation designs of compromised cusps and whether or not they influence masticatory fatigue, fracture resistance, and marginal discrepancy of ceramic partial-coverage restorations (PCRs) luted on mandibular molars. MATERIALS AND METHODS: Sixty-four caries-free molars were equally divided into four groups. Control group NP received no preparation (NP). Group B-IN received a basic inlay (IN) preparation with buccal (B) cusp conservation and occlusal reduction of both lingual cusps. Group B-ON was prepared in the same way, except buccal cusps were prepared with an angle of 45 degrees to the occlusal plane (buccal onlay). Group B-OV preparation was similar to group B-ON, but buccal cusps received a further shoulder preparation on the buccal aspect (buccal overlap). Forty-eight all-ceramic IPS e.max Press PCRs were fabricated and luted adhesively. Specimens underwent mouth-motion fatigue (1.2 million cycles, 1.6 Hz, 49 N) and 5500 thermal cycles (5 degrees C/55 degrees C). Fracture patterns were observed. Surviving specimens were loaded until fracture. Marginal discrepancies were examined. RESULTS: Only one specimen of group B-ON fractured during fatigue. Median fracture loads (N) [IQR = x(.25) - x(.75)]: group NP = 1604 N [1182-1851 N], group B-IN = 1307 N [1262-1587N], group B-ON = 1396 N [817-1750N], group B-OV = 1205 N [1096-1542N]. No significant differences in fracture resistance were found between restored molars and unprepared teeth (p _ 0.18). Different preparation designs showed no significant influence on PCR fracture resistance. Mouth-motion fatigue caused a significanty decrease of marginal accuracy in groups B-IN (p = 0.009) and B-ON (p = 0.008). Marginal discrepancy values of groups B-IN and B-OV were significantly different after fatigue (p = 0.045). CONCLUSION: Ceramic coverage of compromised cusps did not demonstrate an increase of fracture resistance after fatigue when compared to less invasive partial-coverage restorations. However, enhanced exposure of restoration margins to occlusal wear could result in more extensive marginal discrepancies.