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science & practice 25th EAO Annual Scientific Meeting 14 to reduce any excess cement and to allow it to escape during setting, a 0.75 mm hole can be drilled on the palatal side in the incisal half of the temporary crown.11 Optimize the emergence profile by progressive modifi- cation of the temporary crown Taking impression In order to comply with OAOT, the ideal, provided that the abut- ment has not been adjusted, is to take an impression of the abutment. A resin impression coping fabri- cated over an abutment identical to the one seated in the mouth makes it possible to transfer the position of the abutment without unscrewing it (Figs. 7a & b). An abutment and a laboratory copy are positioned in the impression and, if it is thought that the abutment is not suitable for the permanent prosthesis, one could opt for a NobelProcera abutment (Nobel Biocare) or a modified abut- ment (Fig. 7c). Take an impression of the abutment without removing it Abutment Material According to several publica- tions,9, 12, 13 titanium and aluminum and zirconium oxides are the only materials that allow attachment of soft tissues on the abutment. For Van Brakel et al.,14 in a study on hu- mans, there is no difference be- tween titanium and zirconia regard- ing biology, with just a slight advan- tage in favor of zirconia for sulcular depth after three months. Gold al- loys cause apicalization of the at- tachment to the titanium12 of the im- plant, but this conclusion has been contested by Linkevicius and Apse.15 A gold alloy supports less dental plaque after 4 hours in vitro,16 but more than titanium or zirconia does after four days in vivo.17 Thus, there is no consensus yet in the medical literature concerning the superior- ity of one material over another in terms of biology. Zirconia and gold alloys have su- perior esthetic qualities when the abutment supports a glass-ceramic crown in vitro18 or in vivo19 , com- pared with titanium. When the im- plant site of the lateral incisor is wide (> 6.5 mm), selecting a 3.3 or 3.5 mm diameter implant makes it possible to use zirconia abutments. However, the majority of small-diam- eter implants on the market do not include zirconia abutments in their prosthetic ranges for reasons of me- chanical resistance. In such cases, commercial titanium abutments or abutments made by 3-D machining are used. In this situa- tion, the thick- ness of buccal soft tissue must ex- ceed 2 mm, which is the requisite di- mension specified by Van Brakel et al.20 to avoid there being any differ- ence in light reflection discernible by the human eye between a tita- nium and a zirconia abutment. Shape In cement-retained prostheses, excess ce- ment has been found to be a cause of periimplantitis.21–28 Linkevicius et al.29 have demon- strated in an in vitro experiment that there is a correlation between the depth of the abutment–crown joint and the amount of excess ce- ment on the surface of the abut- ment. This is an argument in favor of the use of NobelProcera individ- ual abutments. However, these indi- vidualized abutments often have significant undercut areas, which are recognized risk factors for the retention of intrasulcular cement.30 On small-diameter implants, the re- duced dimensions of the abutments diminish the friction surface of the implant-supported crown and the creation of two small mechani- cal retentions in the incisal zone of the abutment reduces any loosening (Fig. 8). Maximize retention of small-diameter abutments Crown Where edentulous gaps were narrow, 3 mm Nobel Active im- plants were placed and only tita- nium abutments, standard or Nobel- Procera, were used. Two types of crown are possible: metal–ceramic crowns or all-ceramic crowns. IPS e.max (Ivoclar Vivadent) If the abutment is titanium, us- ing an all- ceramic system can pres- ent restrictions related to the buc- co-palatal thickness of the lateral in- cisor. When the tooth is thick, this prosthetic solution makes it possi- ble to achieve an acceptable es- thetic out- come (Figs. 9a–d). Con- versely, when the thickness is less, this type of all-ceramic crown can sometimes result in more disadvan- tages than advantages from an esthetic perspective. In such a case, for the coping in lithium disilicate, one has to use high-opacity ceramic of significant thickness in order to hide the titanium abutment as much as possible. This has the effect of reducing the thickness of the cos- metic ceramic and thus reduces its ability to mimic the appearance of adjacent teeth (Figs. 10a–d). Metal–ceramic crowns Conversely,usingmetal-fused-to- porcelain crowns on narrow and small teeth makes it possible to re- duce the thickness of the copings made from precious alloys or palla- dium (to 0.3 mm or 0.4 mm) and in this way to increase stratification (Figs. 11a–c & Figs. 12a–d). However, the transgingival area remains the weak point in this type of restora- tion with a risk of the grey color of the titanium abutment showing through when the periimplant mu- cosa is thin (see Fig. 33 in Russe & Limbour).31 Do not hesitate to use metal– ceramic crowns for small lateral incisors Monoblock screwed zirconia crown The use of hexagonal implants measuring 3.3 mm externally or with an internal connection measur- ing 3.5 mm makes it possible to use zirconia abutments. In these circum- stances, two options are possible, depending on the emergence posi- tion of the abutment screw: either a two-stage solution of a zirconia abut- ment supporting a cemented ce- ramic crown (Figs. 13a–d) or a mono- block crown screwed directly on to the implant (Figs. 14a & b). In these situations, the semitranslucent character of the material makes it possible to ensure optical continuity in both the coronal section and the gingival section, resulting in better esthetic integration. Cement In order to reduce the visibility of titanium showing through when a glass-ceramic crown is used, an opaque white cement should be em- ployed according to Dede et al.18 This involves a polycarboxylate ce- ment (Poly-F, DENTSPLY DeTrey), se- lected initially for its theoretical ability to potentially allow detach- ment of the crown. Recent studies have demonstrated that polycarbo- xylate has greater tensile strength than does zinc oxyphosphate or glass ionomer.32 At the time of ce- menting, the cement-coated crown is placed on a replica abutment; any excess is removed before placing the crown in the mouth.33 This clin- ical technique has been proven beneficial for both its qualities of re- tention and reducing excess ce- ment.34 If standard abutments are used, then the crown limit can be consid- erably subgingival and it is then vi- tal to use a minimum amount of ce- ment and to remove any excess im- mediately. The washable nature of polycarboxylate cement immedi- ately after placement can be an ad- vantage for its removal. Esthetic outcome When the esthetic outcome is evaluated according to the criteria specified by Fürhauser et al.35 and when particular attention is paid to the score for the papillae and the gingival level, use of small-diameter implants to replace lateral maxil- lary incisors appears to result in an improvement compared with wider implants. The margin of the papilla and the position of the collar, in re- lation to the contralateral incisor, are the two principal issues pre- sented by implant replacement of a lateral incisor (Fig. 15). In most cases, the mesial papilla, between the central incisor and the lateral in- cisor, is at an almost normal height, whereas the distal papilla, between the lateral incisor and the canine, is often shorter and displays a slight vertical deficit (Fig. 16). Initial evolution When the implants are well posi- tioned and the buccal soft and hard tissue are thick, the esthetic outcome is lasting. In the early years, an im- provement of the outcome may occur owing to the soft tissue filling the prosthetic embrasure (Figs. 17a & b). Continuous eruption Since the 1980s, authors such as Levers and Darling36 have described the phenomenon of continuous erup- tion, which results in a verticalization of the maxillary incisors. The osseoin- tegration of implants prevents them from following this migration and, over time, the lateral incisors can end up in a more apical and buccal posi- tion than the central incisors. This phenomenon is sometimes percepti- ble after some years have passed, whatever the age when the implants were placed (Figs. 18a & b). Thus, the organization of anterior guidance be- comes particularly important, since rapid movement of the central inci- sors can occur if these are not in occlusion when the implants are placed. During orthodontic treat- 5 Figs. 9a–d: IPS e.max high-opacity crown coping (a). Initial clinical result and radiograph (b & c). Result after one year (d). 5 Fig. 10a–c: Smile of female patient showing restoration of tooth #12 with IPS e.max (a). Close-up photo- graph: The opaque armature is visible (b). Ra- diograph (c). 5 Fig. 10d: The esthetic finish of the veneer on tooth #22 is superior to that of IPS e.max on tooth #12. 5 Figs. 11a–c: Metal– ceramic crown on master cast (a). Clinical result: The mesial and distal papillae are aligned (b). Radiographic result (c). 5 Figs. 12a–d: Master cast with the metal– ceramic crown on a modified abutment (a & b). Clinical result: The papillae are aligned (c). Radio- graphic result (d). Fig. 9a–c Fig. 9d Fig. 10d Fig. 10a–c Fig. 11a–c Fig. 12a–d 5 Figs. 13a–d: NobelProcera screwed zirconia abutment (a) and all-ceramic crown (b). Screwed abutment in the mouth (c). Esthetic outcome (d). 5 Figs. 14a & b: One-piece zirconia crown (a). Esthetic integration (b). 5 Fig. 15: The collar level of tooth #22 is ideal, but the papillae are slightly trun- cated. 5 Fig. 16: The distal papilla is slightly shorter than the mesial papilla (line shows difference in level). Figs. 13a–d Fig. 14a Fig. 14b Fig. 15 Fig. 16