Incisal Overlap Research Articles

EFFICACY OF INCISAL PREPARATION DESIGNS ON THE FRACTURE RESISTANCE OF TWO CAD/CAM LAMINATE VENEERS

Statement of problem: Mechanical properties are cardinal for the long-term clinical success of laminate veneer restorations. The most common failure is fracture and debonding, in which unfavorable occlusion and articulation play an important role. Nonetheless, the effect of different incisal preparations on the behavior of veneers remains controversial.Objective: The purpose of this study was to evaluate the fracture load of two different CAD/CAM laminate veneer materials: resin nano-ceramic [lava ultimate] and lithium disilicate glass ceramic [IPS e-max CAD], with two different incisal preparation designs [butt-Joint and incisal overlap]; using both in-vitro and finite element analysis studies. Materials and Methods: A total of 20 maxillary central incisors were used in this study. The samples were divided into two main groups (n=10), according to the CAD/CAM material used. Ten laminate restorations were constructed for each group following the manufacturer’s directions with the two preparation designs (5 samples each), then cemented on their corresponding teeth. Fracture load was recorded for each specimen using the universal testing machine. Meanwhile, Finite element analysis study was performed to assess the in-vitro observations. Results: The results revealed that incisal overlap design with Lava ultimate laminate veneers recorded the highest mean fracture strength value (395 ±37.18 N). This was supported by the finite element results that showed that the incisal overlap design with lava ultimate laminate veneers had the lowest Von Mises stress (30.75 MPa). Conclusions: Within the limitations of the present study, it was concluded that the butt-joint and incisal overlap designs demonstrated different mechanical behaviors with regard to the two different restorative materials. The incisal overlap design tolerated stresses better than the butt-joint design with both materials. Also, the incisal overlap design with resin nano-ceramic laminate veneers had the best stress distribution. Nevertheless, both types of CAD/CAM materials and different incisal preparation designs used could be considered strong enough to withstand the average anterior masticatory biting forces.

Evaluation of fracture resistance of ceramic veneers with different preparation designs and loading conditions: An in vitro study.

Purpose:The purpose of this study was to evaluate the effect of incisal butt joint and incisal overlap design on the fracture resistance of ceramic veneers under two different loading conditions, i.e., 125° and 60° representing protrusive and intercuspal movements, respectively.Materials and Methods:Thirty-two maxillary central incisors were divided into two groups of sixteen specimens each and were prepared with incisal butt joint and incisal overlap design. Ceramic veneers were fabricated and cemented. Both the groups were further divided and mechanical testing to evaluate the fracture resistance were done using the universal testing machine. The values were recorded in Newton along with the assessment of the failure mode of both veneer and the tooth.Results:Unpaired t-test showed a significant difference (P < 0.05) with butt joint design having higher fracture resistance than palatal overlap design with the mean value of 409.50N at 60° angle and 473.37N at 125° angle. Paired t-test depicted a significant difference for both the designs at 125° than at 60° angle (P < 0.05). Chi-square analysis showed more number of intact veneers with butt joint design; however, there was no significant difference (P > 0.05). Failure mode of teeth showed more number of coronal fracture followed by cervical fracture and root fracture, but there was no significant difference between the two groups (P > 0.05).Conclusion:Butt joint design had higher fracture resistance than palatal overlap design. Under functional loads for both designs, fracture resistance was higher at 125° than at 60° angle.

The Effect of Polymerization and Preparation Techniques on the Microleakage of Composite Laminate Veneers.

Background:Marginal leakage is the important factor influencing the maintenance of dental esthetic.Aim:The purpose of this study was to evaluate the relationship between the preparation techniques and type of polymerization techniques on microleakage of composite laminate veneers.Materials and Methods:Ninety-one same sized, caries-free human maxillary central incisors were randomly assigned to 13 groups (n = 7) and were designed with four different preparation techniques (window type, feather type, bevel type, and incisal overlap type). One group determined as control group and any preparation was applied. Nanohybrid resin composite was used for restoration. Composite laminate veneers polymerized with three different techniques (direct light curing, indirect polymerization with a combination of pressure, light and heat using a light cup and heat cup, direct polymerization, and additionally heat cured in an oven). The specimens were thermocycled, and then immersed in 5% basic fuchsine solution. Following 24 h, all specimens were immersed in 65% nitric acid solutions for volumetric dye extraction test. Samples diluted with distilled water and centrifuged and microleakage determined by a spectrophotometer.Statistical Analysis Used:Data were analyzed with two-way ANOVA and Tukey honest significant difference post hoc multiple comparisons test (P < 0.05).Results:For comparing the microleakage value of preparation and polymerization techniques, Window type preparation showed a significant difference in direct polymerization + additional cured group (P < 0.05). Control group was statistically different from the other groups (P < 0.05).Conclusions:Window type laminate preparation can be preferred in indirect polymerization technique because it caused less leakage in this present study.

Fracture resistance of composite veneers with different preparation designs

Background: The aim of this in vitro study was to examine the fracture load of composite veneers using three different preparation designs. Material and methods: Fifteen extracted, intact, human maxillary central incisors were selected. Teeth were divided into three groups with different preparation design: 1) feather preparation, 2) bevel preparation, and 3) incisal overlap- palatal chamfer. Teeth were restored with composite veneers, and the specimens were loaded to failure. The localization of the fracture was recorded as incisal, gingival or combined. Results: Composite veneers with incisal overlap - palatal chamfer showed higher fracture resistance compared to feather preparation and bevel preparation. The mean (SD) fracture loads were: Group 1: 100.6±8.0 N, Group 2: 107.4±6.8 N, and Group 3: 122.0±8.8 N. The most common mode of failure was debonding for veneers with feather preparation and fracture when incisal edge is reduced. The most frequent localization of fracture was incisal. Conclusion: The type of preparation has a significant effect on fracture load for composite veneers. This study indicates that using an incisal overlap- palatal chamfer preparation design significantly increases the fracture resistance compared to feather and bevel preparation designs.

Survival of porcelain laminate veneers with different degrees of dentin exposure: 2-year clinical results.

To evaluate the clinical performance of porcelain laminate veneers (PLVs) after 2 years. Twenty-eight patients were treated with 125 PLVs. The experimental variables were preparation design (incisal overlap [IO] and incisal bevel [IB]) and adhesion surface (enamel [E], enamel with minimal dentin exposure [MDE], and enamel with severe dentin exposure (SDE)]. Marginal adaptation, marginal discoloration, secondary caries, postoperative sensitivity, and patient satisfaction were assessed according to the modified United States Public Health Service criteria. Each restoration was examined for fractures and debonding. In addition, gingival tissue health by gingival plaque, bleeding, and recession was recorded. An experienced clinician evaluated the restorations at baseline and after 6, 12, and 24 months, and survival rates evaluating relative and absolute failures were calculated (p = 0.05). Eleven (8.8%) veneers failed, and the overall cumulative survival rate was 91.2% after 2 years of followup. IB and IO preparation designs exhibited survival rates of 94% and 85.7%, respectively, but this difference was not statistically significant (p > 0.05). PLVs bonded to SDE were more likely to fail than those bonded to E and MDE (p < 0.05). There was no significant difference between the failure rate of PLVs bonded to E and those bonded to MDE (p > 0.05). PLVs have high survival rates when bonded to enamel only, as well as to enamel with minimal dentin exposure. However, extensive dentin exposure should be avoided during the preparation.

Randomized clinical trial of indirect resin composite and ceramic veneers: up to 3-year follow-up.

This randomized controlled split-mouth clinical trial evaluated the short-term survival rate of indirect resin composite and ceramic laminate veneers. A total of 10 patients (mean age: 48.6 years) received 46 indirect resin composite (Estenia; n = 23) and ceramic laminate veneers (IPS Empress Esthetic; n = 23) on the maxillary anterior teeth. Veneer preparations with incisal overlap were performed and existing resin composite restorations of good quality were not removed but conditioned using silica coating (CoJet) and silanization (ESPE-Sil). Enamel and dentin were etched and rinsed; adhesive resin (ExciTE) was then applied. After cementation (Variolink Veneer), restorations were evaluated at baseline and thereafter every 6 months for up to 3 years using modified USPHS criteria. Seventeen laminate veneers were bonded onto intact teeth and 29 on teeth having existing resin composite restorations. In total, 3 failures were observed in the form of debonding (n = 1) and fracture (n = 2) in the group of resin composite laminate veneers. No significant difference was observed between the survival rates of composite and ceramic laminate veneers (Estenia: 87%, IPS Empress Esthetic: 100%; p > 0.05). The overall survival rate was 93.5% (Kaplan-Meier). Of the 43 laminate veneers, minor voids and defects were observed in 6 of the composite and 3 of the ceramic veneers. Slight staining at the margins (n = 3) and slightly rough surfaces were more frequently observed for the resin composite laminate veneers (n = 18) up to the final recall. Early findings of this clinical trial on two veneer materials showed statistically similar survival rates. Surface quality changes were more frequent in the composite veneer material.

Evaluation of the stress concentration of different incisal ridge preparations of porcelain veneers (Finite element analysis)

Background: Porcelain veneers are under a great deal of stress which may lead to clinical failure as fracture or dettachment. This study examined whether different finishing lines and lingual shoulder preparations in the incisal area of the maxillary central incisor affect the bond of the porcelain veneers. Materials and methods: A two- dimensional finite element model was made. Location and magnitude of maximum Von Mises stresses were calculated in porcelain veneer. Six types of preparations were drawn as:incisal overlap of 0.5mm, 1mm and 1.5mm depth and lingual shoulder, and incisal overlap of 0.5mm, 1mm and 1.5mm depth without shoulder preparation. Results: Stress formation is maximum in the incisal edge region. All the lingual shoulder preparations presented better stress distribution than the non shoulder preparations Conclusion: Stress is distributed more evenly when the tested preparation possesses a good thickness of porcelain and the more the surface area with incisal overlap the less possibility of bond failure.

Poster 41: Stability of Anterior Open Bite Correction in Class III Patients Using Bimaxillary Surgery Involving Intraoral Vertical Ramus Osteotomy

There is currently limited data on the use of intraoral vertical ramus osteotomy (IVRO) in the surgical treatment of anterior open bite and class three malocclusion. The purpose of this study is to investigate the stability of Le Fort I osteotomy with IVRO in the correction of anterior open bite with concomitant class III malocclusion. Chart reviews of patients who underwent surgical correction of anterior open bite with class three malocclusion were obtained from the years 2004-2009. Preoperative, postoperative, and 1 year postoperative lateral cephalograms were obtained. Anterior open bite was measured clinically from the edge of the maxillary central incisor to the edge of the mandibular central incisor along its axis. Angular measurements were used to evaluate jaw movement in the horizontal and vertical directions. Anterior-posterior movement of the jaws was determined by changes in the SNA and SNB angles. Vertical movements of the maxilla were calculated from changes in the Maxillary Occlusal Plane (MOP) and Palatal Plane (PP) angles to SN. Mandibular vertical movement was based on changes in the mandibular plane (MP) angle to SN. Dental compensation was determined by changes in MOP and MP angles. All cephalograms were traced and measured digitally with Dolphin© software. Statistical analysis was performed with the SAS procedure PROC MIXED (SAS/STAT software, SAS institute Inc., Cary, NC, USA). The accuracy of landmark identification, superimposition, and measurements were confirmed by retracing all cephalograms 7 days later by the same investigator. Sixty patient records were identified with 27 meeting the inclusion criteria. Six patients failed to have positive incisal overlap at 1 year postoperative (23%). Comparing preoperative data between the 2 groups, patients in the relapse group had a more significant open bite (OB −6.07 mm vs. −3.48 mm, p<0.05), overjet (−2.14 mm vs. −0.79 mm, p<0.05), maxillary posterior vertical excess (SN-PP: 0.75° vs. 3.74°, p<0.05), and a steeper mandibular plane angle (SN-MP: 41.98° vs. 36.35°, p<0.05). Surgically, the relapse group also had more maxillary clockwise movement compared to the non-relapse group (SN-PP +5.72° vs. +3.39°, p<0.05), but less mandibular counterclockwise movement (SN-MP −0.93° vs. −2.46°, p<0.05). When separating patients based on the severity of their preoperative open bite: no patients failed in the mild group (1–3 mm open bite; 0/9, 0%), 3 patients failed in the moderate group (3–6 mm open bite; 3/13, 23%), and 3 patients failed in the severe group (>6 mm open bite; 3/5, 60%). IVRO, when performed with maxillary Le Fort I osteotomy, has a success rate (78% positive incisal overlap at 1 year post operative) that is comparable to other surgical techniques when treating patients with anterior open bite and concomitant class III malocclusion. Patients likely to relapse have a severe preoperative open bite, a high preoperative mandibular plane angle, or inadequate mandibular counterclockwise movement during surgery. This study provides an evidence-based alternative to current techniques.

Clinical longevity of ceramic laminate veneers bonded to teeth with and without existing composite restorations up to 40 months

This study evaluated the survival rate of ceramic laminate veneers bonded to teeth with and without existing composite restorations (ECR). Twenty patients (mean age: 49.7 years) received 92 feldspathic ceramic laminate veneers (Shofu Vintage AL) on the maxillary teeth (intact teeth: n = 26; teeth with ECR: n = 66). Preparations with incisal overlap were made, and ECR of good quality were not removed but conditioned using silica coating (CoJet) and silanization (ESPE-Sil). Enamel and dentin were etched with 38% H3PO4 for 15-30 s and rinsed 30 s; adhesive resin (Excite) was applied, and laminate veneers were then cemented (Variolink Veneer). Restorations were evaluated at baseline and thereafter every 6 months using modified United States Public Health Service criteria. Mean observation period was 21.6 months. Overall, five absolute failures were encountered (fractures: n = 3; chipping: n = 1; debonding: n = 1), resulting in a survival rate of 94.6% (Kaplan-Meier). Survival rates of the laminates bonded to teeth without (96%) and with ECR (93.5%) did not show significant differences (p > 0.05). Slight marginal defects (16 of 87 laminates) and slight marginal discoloration at the margins were noted (12 of 87 laminates) until the final recall. Secondary caries and endodontic complications were not detected in any of the teeth. The clinical survival of ceramic laminate veneers up to 40 months was not significantly influenced when they were bonded onto intact teeth or onto teeth with ECR. When no caries is present, it may not be necessary to replace existing composite restorations prior to cementation of ceramic laminate veneers.

Survival rates of porcelain laminate restoration based on different incisal preparation designs: An analysis

Background:Veneer restorations provide a valid conservative alternative to complete coverage as they avoid aggressive dental preparation; thus, maintaining tooth structure. Initially, laminates were placed on the unprepared tooth surface. Although there is as yet no consensus as to whether or not teeth should be prepared for laminate veneers, currently, more conservative preparations have been advocated. Because of their esthetic appeal, biocompatibility and adherence to the physiology of minimal-invasive dentistry, porcelain laminate veneers have now become a restoration of choice. Currently, there is a lack of clinical consensus regarding the type of design preferred for laminates. Widely varying survival rates and methods for its estimation have been reported for porcelain veneers over approximately 2–10 years. Relatively few studies have been reported in the literature that use survival estimates, which allow for valid study comparisons between the types of preparation designs used. No survival analysis has been undertaken for the designs used. The purpose of this article is to attempt to review the survival rates of veneers based on different incisal preparation designs from both clinical and non-clinical studies.Aims and Objectives:The purpose of this study is to review both clinical and non-clinical studies to determine the survival rates of veneers based on different incisal preparation designs. A further objective of the study is to understand which is the most successful design in terms of preparation.Materials and MethodsThis study evaluated the existing literature – survival rates of veneers based on incisal preparation designs. The search strategy involved MEDLINE, BITTORRENT and other databases.Statistical AnalysisData were tabulated. Because of variability in the follow-up period in different studies, the follow-up period was extrapolated to 10 years in common for all of them. Accordingly, the failure rate was then estimated and The weighted mean was computed.ConclusionsThe study found that the window preparation was of the most conservative type. Incisal coverage was better than no incisal coverage and, in incisal coverage, two predictable designs – incisal overlap and butt were reported. In butt preparation, no long-term follow-up studies have been performed as yet. In general, incisal overlap was preferred for healthy normal tooth with sufficient thickness and incisal butt preparation was preferred for worn tooth and fractured teeth.

Editor's Summary and Q&A: Orthodontic treatment of anterior open-bite malocclusion: Stability 10 years postretention

Introduction The postretention stability of open-bite treatment is a controversial topic in orthodontics. Methods In this study, the lateral cephalometric radiographs of 64 patients treated with orthodontics alone were evaluated to determine the amount of postretention change. The mean postretention interval was 14 years. The sample was divided into 3 groups based on the amounts of pretreatment overbite: (1) the contact group (n = 24), incisal overlap and incisal contact; (2) the overlap group (n = 25), incisal overlap and no incisal contact; and (3) the open-bite group (n = 15), no incisal overlap. The headfilms were digitized, and the values were analyzed. Results The 3 groups reacted differently. During the postretention period, mean overbite deepened in all groups, with the contact group deepening significantly more than the open-bite group. Overjet increased significantly more in the open-bite group than in the contact group. Pretreatment overjet correlated mildly with postretention overjet relapse in the open-bite group. Conclusions All 64 subjects had positive incisal overlap at the postretention recall. The postretention stability of open-bite treatment is a controversial topic in orthodontics. In this study, the lateral cephalometric radiographs of 64 patients treated with orthodontics alone were evaluated to determine the amount of postretention change. The mean postretention interval was 14 years. The sample was divided into 3 groups based on the amounts of pretreatment overbite: (1) the contact group (n = 24), incisal overlap and incisal contact; (2) the overlap group (n = 25), incisal overlap and no incisal contact; and (3) the open-bite group (n = 15), no incisal overlap. The headfilms were digitized, and the values were analyzed. The 3 groups reacted differently. During the postretention period, mean overbite deepened in all groups, with the contact group deepening significantly more than the open-bite group. Overjet increased significantly more in the open-bite group than in the contact group. Pretreatment overjet correlated mildly with postretention overjet relapse in the open-bite group. All 64 subjects had positive incisal overlap at the postretention recall.

Orthodontic treatment of anterior open-bite malocclusion: Stability 10 years postretention

The postretention stability of open-bite treatment is a controversial topic in orthodontics. In this study, the lateral cephalometric radiographs of 64 patients treated with orthodontics alone were evaluated to determine the amount of postretention change. The mean postretention interval was 14 years. The sample was divided into 3 groups based on the amounts of pretreatment overbite: (1) the contact group (n = 24), incisal overlap and incisal contact; (2) the overlap group (n = 25), incisal overlap and no incisal contact; and (3) the open-bite group (n = 15), no incisal overlap. The headfilms were digitized, and the values were analyzed. The 3 groups reacted differently. During the postretention period, mean overbite deepened in all groups, with the contact group deepening significantly more than the open-bite group. Overjet increased significantly more in the open-bite group than in the contact group. Pretreatment overjet correlated mildly with postretention overjet relapse in the open-bite group. All 64 subjects had positive incisal overlap at the postretention recall.

Restoring strength of incisors with veneers and full ceramic crowns.

The aim was to determine the in vitro fracture resistance of incisors restored with veneers and full ceramic crowns compared to unrestored teeth. Seventy intact, extracted human maxillary central incisors were randomized and assigned to 7 groups (n = 10). The teeth in group 1 remained intact (control). The teeth in groups 2 to 6 were prepared and IPS Empress restorations were conditioned and bonded using an adhesive luting cement, Variolink II/Syntac (group 2: labial veneer with incisal overlap, group 3: 3/4 veneer with margin in enamel, group 4: 3/4 veneer with margin in dentin, group 5: crown with margin in enamel, group 6: crown with margin in dentin group 7: veneer on worn tooth. After finishing and polishing, specimens were stored in water and thermocycled for 2000 cycles between 5 degrees C and 55 degrees C. The maximal fracture load of the specimens (40-degree inclination) was determined using the universal testing machine (Zwick) at a constant crosshead speed (0.5 mm/min). The statistical analysis was performed using the Kruskal-Wallis test with Bonferroni correction (p < 0.05). Fracture surfaces were qualitatively analyzed by SEM. All restored teeth with cervical preparation margins in enamel showed a fracture load not significantly different from the intact teeth (control). Restored teeth with cervical preparation margins in dentin showed a significantly lower fracture load. All restorations showed a fracture load far above 400 N, serving as functional reference for anterior teeth. The failures were predominantly cohesive. For the restoration of tooth strength, defining the finishing lines of veneers and crowns in enamel is recommended. Restorations with finishing lines in dentin resulted in significant loss of strength. Three-quarter veneers with finishing lines in enamel are functionally equal to crowns with the advantage of conserving tooth structure.

Longevity and failure load of ceramic veneers with different preparation designs after exposure to masticatory simulation

Laminate veneers are widely used in the management of unesthetic anterior teeth. However, limited information is available regarding the influence of preparation design on longevity of ceramic veneers. This study evaluated the influence of preparation design on longevity and failure load of ceramic veneers bonded to human maxillary central incisors after cyclic loading and thermal cycling in a dual-axis masticatory simulator. Sixty-four caries-free maxillary central incisors were divided into 4 groups (n = 16). The control group remained unprepared (NP). For Group WP, a window preparation was made. Specimens in Group IOP were prepared with an incisal overlap of 2 mm without palatal chamfer. For Group CVP, specimens were prepared with a complete-veneer design of 3-mm incisal reduction and 2-mm palatal extension. Forty-eight IPS Empress 1 ceramic veneers were bonded adhesively with dual-polymerizing composite (Variolink II). All specimens were subjected to cyclic mechanical loading (1.2 million cycles, cycle frequency 1.3 Hz, invariable palatal load 49 N) and thermal cycling (5 degrees C-55 degrees C, dwell time 60 seconds, 5500 cycles) in a masticatory simulator. Failure was defined by bulk fracture of a specimen. Subcritical crack patterns were observed. Surviving specimens were loaded in a universal testing machine until fracture. The failure-load values (N) (1.5 mm/min crosshead speed) were automatically recorded by controlling software. Statistical analysis of data was performed by Kruskal-Wallis analysis of variance (alpha = .05) and pairwise Wilcoxon rank sum tests (alpha = .05). Three specimens from group NP, 1 specimen each from the WP and CVP groups, and 2 specimens from group IOP fractured during fatigue. After 1.2 million cycles, the highest crack rates were observed for complete veneers and originated in the palatal concavity extending to the facial surface. The median (interquartile range = x .25 - x .75 ) failure loads (N) were as follows: NP 713.3 (404.4-777.1), WP 549.5 (477.5-597.7), IOP 695.3 (400.0-804.6), and CVP 519.2 (406.1-732.9). No significant differences in longevity and failure load were demonstrated between natural teeth and teeth restored with ceramic veneers ( P = .555). Maxillary teeth restored with the 3 types of IPS Empress 1 veneers showed fracture resistance similar to that of unprepared incisors ( P = .555).

Bases epidemiológicas para análise das más oclusões morfológicas como fatores de risco no desenvolvimento das desordens temporomandibulares de origem articular

Dentre as pesquisas empreendidas no campo da epidemiologia, um grupo específico aborda patologias de etiologia desconhecida ou não totalmente compreendidas. É dentro deste grupo que estão situadas as desordens temporomandibulares (DTM). Três estratégias observacionais básicas têm sido utilizadas para abordar o papel etiológico da má oclusão no desenvolvimento das DTM, dentro do repertório epidemiológico. São elas: estudos do tipo transversal, estudos de caso controle e estudos de coorte. Alguns experimentos clínicos são realizados com base na remoção do fator etiológico suspeito. Com base em uma revisão estruturada da literatura, a partir da metodologia empregada nos estudos selecionados, podemos concluir que a definição dos possíveis fatores etiológicos relacionados a subgrupos específicos de DTM é fundamental para que o papel das más oclusões no desenvolvimento destas desordens, embora pareça pequeno quando baseado nas evidências disponíveis, não seja subestimado. Pode ser útil a caracterização de uma oclusão normal como aquela associada como o menor risco para o desenvolvimento de problemas de DTM, mas é provavelmente inapropriada a aplicação destes parâmetros para reverter um problema intra-capsular já estabelecido. O conceito de uma oclusão de baixo fator de risco implicaria em um pequeno desvio entre RC e MIH, pequeno transpasse horizontal, transpasse vertical positivo e ausência de mordida cruzada posterior. Este conceito é compatível com o conceito de oclusão normal defendido por décadas, embora uma variação do normal ao invés de um critério absoluto deva ser permitida. Embora provavelmente seja prudente estabelecer metas morfológicas terapêuticas que busquem o que é observado em oclusões não tratadas julgadas normais ou ideais, o estabelecimento de uma oclusão que alcance todos os critérios gnatológicos, por meio de tratamento ortodôntico, talvez seja impossível e provavelmente desnecessário.

Stresses within porcelain veneers and the composite lute using different preparation designs

The purpose of this study was to investigate compressive and tensile stresses in porcelain and composite at the labial marginal region of porcelain veneer restorations using chamfer, shoulder, or knife-edge labial margin designs with labial window or incisal overlap incisal preparation designs. Porcelain veneer models were constructed and loaded with (1) a 200-N, 45 degrees palatal load to simulate functional loading, and (2) a horizontal labial loading of 200 N to mimic trauma. Maximum tensile and compressive stresses were recorded within the labial marginal region of both porcelain and composite lute. Under the 45 degrees palatal load, stresses within the palatal marginal porcelain were chiefly compressive, and stresses for the knife-edge designs as much as 42% less than for shoulder designs. Incisal overlap preparations were generally associated with less compressive stress within both porcelain and composite than the window preparation. When a labial load was applied, tensile stresses were as much as 25 times greater for the chamfer and shoulder designs compared with the knife-edge design. Labial loading also resulted in an increase in tensile stresses within the composite lute, and stresses were again lowest within the knife-edge margin design. Under the limitations of this study, using the incisal overlap preparation, porcelain veneers with knife-edge labial margins could better sustain occlusal loading without fracture. J Prosthodont 2001;10:16-21.

Survival of three types of veneer restorations in a clinical trial: a 2.5-year interim evaluation

Objectives: In this clinical trial, 180 veneer restorations (VRs) were evaluated. The purpose of the study was to collect survival data and to find possible relations between survival and (1) `type of VR', (2) `preparation design', (3) `operator' and (4) the patient-related variables `tooth-type' and `vitality of the tooth'. Methods: The restorations were provided by seven dentists in 112 patients on central and lateral maxillary incisors. Experimental variables were: `type of VR' (either direct resin composite (DC), indirect resin composite (IC) or porcelain (P)), `preparation design' (with and without incisal overlap) and `operator'. Failures were recorded at two levels: absolute failure (need for new restoration) and relative failure (need for repair). Survival was defined at three levels: (1) s!urvival of original restoration (S r, endpoints: `absolute' failures), (2) functional survival (S f, endpoints: `relative' failures) and (3) overall survival (S o, endpoints: both `absolute-' and `relative failures'). Results: The variable `type of VR' showed significant influence on S f and S o but not on S r. S f and S o rates of P, IC and DC were, respectively: S f-P, 94%; S o-P, 94%; S f-IC, 94%; S o-IC, 90%; S f-DC, 80%; S o-DC, 74%. VRs on vital teeth showed a significantly better survival than VRs on non-vital teeth at all survival levels. Conclusions: Preparation of the incisal edge for incisal coverage is considered to be unnecessary to assure or improve the strength of VRs. c non-vital teeth showed higher risk to fail than veneers placed on vital teeth. Porcelain veneers showed the best overall survival.