Complex prosthetic rehabilitation due to severe dental wear

Complex prosthetic rehabilitation due to severe dental wear

 ITALIAN VERSION

 

In collaboration with Dr. Leonardo Bacherini

Several factors affect the life of a tooth and, consequently, different causes can lead to dental wear. Unfortunately, their effects are cumulative and irreversible and, despite its main cause, tooth wear starts immediately after tooth eruption. As a consequence, clinicians have to diagnose such a condition early, particularly when dental wear occurs suddenly and progressively in young patients. The processes causing tooth wear are attrition, erosion, abrasion, demastication, abfraction and non-carious cervical lesions.

 

Patient’s expectations

  • Remote pathological anamnesis: bulimia during youth
  • Recent pathological anamnesis: gastro-esophageal reflux disease (GERD)
  • Non smoker
  • Dental anamnesis: the patient complained about severe sensitivity on all teeth and wanted to improve the esthetics of her smile; the teeth were short and abraded

Localized Management of Sinus Floor

Localized Management of Sinus Floor

 

 

OBJECTIVES

The Localized Management of Sinus Floor is a surgical technique for transcrestal maxillary sinus floor elevation. Its aim is to create a surgical site for implants by displacing a portion of native residual below bone within the cavity of the maxillary sinus. This particular type of bone is usually found below the sinus floor and, through this technique, is displaced vertically in order to create a new implant alveolar portion. In the final configuration of the surgically created alveolus, the coronal portion of the crest must give primary implant stability. This will be completed by the coronal bone portion – pushed laterally and internally of the sinus cavity – from which, a sort of closed “tent” formed by the sinus membrane, will keep the cavity closed. The latter will be filled by blood produced by the alveolar walls.

Tissue repair of the peri-implant alveolus is totally entrusted to the physiological mechanism of bone repair on the site chosen for the implant osteotomy. 3-4-13-14

The goal is to change the height of available bone by creating an osteotomy tunnel starting from the crestal position and extending, initially transversally and medially, in a direction parallel to the palatine vault. This way, the osteotomy tunnel pushes the spongy bone against the floor of the maxillary sinus and avoids loss of the precious calcified structure.

The initially transverse direction (and not vertical, according to the normal prosthetic axis) is essential to:

1. Increase the height of native bone, interfacing the implant to improve primary stability;

2. Use the higher portion of the sinus floor which is normally found towards the medial side of the sinus cavity.

Preparation of the surgical field

According to the protocol, the preparation of the soft tissues is made with a partial thickness technique that has the objective to leave a thin layer of connective tissue which:

1. Ensures the integrity of the periosteum;

2. Allows to easily read the underlying bony anatomy.

The protection of the periosteum is critical, of course, to maintain the integrity of the blood supply15. Also the layer of connective tissue, and the interposed periosteum between tissue and bone, will be fundamental to promote the peri-implant tissue secondary intention healing. This is one of the main issues of the protocol.

This preparation enables to firmly anchor the keratinized tissue – using the sub-periosteal sutures – in an apical and vestibular position. This residual displaced tissue, previously covering the crest, has been displaced vestibularly14.

The flap preparation begins with a palatally beveled incision which slides along the bone plane, starting from the palatal angle of the crest, exactly where the palatal structure crosses the horizontal portion of the edentulous ridge. This has the aim of exposing the crest and displacing vestibularly the keratinized crestal residual tissue to the future implant emergency. This crestal tissue is the same one which has been previously moved from the palatal aspect of the surgical field. Fig. 01/05

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Fig. 01. Clinical aspect of the edentulous ridge of # 24 and # 25. The band of keratinized gingiva is now limited to the crestal position and the mucogingival line is now at the limit of the bucco-coronal angle.

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Fig. 02. Intraoral x-rays with the existing bridge and the descending position of the maxillary sinus floor. The latter greatly reduces crestal height in the anatomical position of # 25.
Less than 4mm height in section 17 of the Maxi-Scan Fig. 04a

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Fig. 03. Maxi Scan of the left maxilla from the palatal foramen to the distal portion of # 23.

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Fig. 04. Maxi Scan of the maxilla area from the left distal section at # 23. The sections involved in the insertion of the implants are the 12/13 for the implant in position # 24 and 15/16 for the implant in position # 25

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Fig. 05. The edentulous area was prepared according to the protocol described above, with a partial-thickness flap leaving a thin layer of connective tissue to ensure the periosteal continuity. The parasulcular incision of # 23 delimits the surgical field that can be used for the insertion of the implant and simultaneously maintains its anatomical integrity. An initial bone incision was carried out mesio-distally. The releasing palatal incisions are visible.

 

To overcome and loosen the muscle fibers over the muco-gingival line enables to completely release the flap.

The preparation on the buccal side of the flap is completed with parasulcular incisions around the adjacent natural teeth to delimit the osteotomy site and also to better mobilize the flap.

The second incision mirrors the first, starting on the palatal edge of the bevel, and continuing through the connective palatal tissue, always running the blade tip on the bone plane with a cut parallel to the profile of the palatal arch. This incision is necessary in order to underline the profile of the palatal curve. Fig. 05

When no adjacent natural teeth are present, elongated relaxing incisions are made always with a large base for the mucosal flap. 14 Fig. 05

 

Implant site preparation

The thrust of the dislocated spongy bone against the sinus floor creates fault lines of the dome that, simultaneously and gradually, push up the sinus membrane. 3/4/12/14

All this is possible with a sequence of instruments that do not have a cutting, but primary a pushing, capacity. Therefore the correct term for these instruments is “expanders”, rather than “osteotomes”.

The surgical protocol defines a specific set of instruments for the purpose. The first three instruments actually do have cutting capacity and are used with the aim of creating an initial crestal osteotomy where the prosthetic implant palatal emergency is planned. The palatal implant position remains the stable reference point as the bone flap will be distracted in a final buccal position.

This entry point into the bone structure may safely receive the second set of instruments (expanders) that, unlike the first, have rounded tips and are intended to displace the largest possible surface area of bone within the maxillary sinus in the medio-lateral direction. 3/14 Fig. 05

Contrary to the first, the second set of instruments have a rounded tip and have the aim of displacing the largest possible bone surface within the maxillary cavity in a medio-lateral direction.

Crestal bone that will be pushed inside the cavity to create the apical portion of the implant site. So as to say, the intra-sinus native bone alveolus structure that forms the apical portion of the new surgical bone socket. Fig. 06/010

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Fig. 06. Intraoperative x-rays with probes in position. The plate is 10mm thick. The first probe has a connective disk of 3.8mm diameter and the second of 4.7 mm. The second probe is inserted with the larger rounder 3mm tip which produced the first disruption of the sinus floor. It is clear that the space between the two initial surgical tunnels must be increased of at least 3mm. This can be done essentially mesializing the # 24 tunnel.

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Fig. 07. The first implant of 3.8x13mm is almost in its final position. The second X-ray probe has been left in position so that it can be used as a stable reference point for defining the surgical site for the implant in position # 24.

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Fig. 08. Final position of the implants after removing the mounter. The implant in position # 24 is a 3.8x13mm and the implant in position # 25 is a 4.7×10.50mm. The amount of horizontal gain obtained by the combination of horizontal and vertical expansion is clearly visible.
The releasing bone incision comes from the inside of the first mesio-distal bone incision. It is beveled following the radial profile of the # 23 root prominence. This peculiar trace leaves the implant’s vestibular-mesial angle covered by the bone flap, thus maintaining the continuity of vascularization.

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Fig. 09. The 2mm high healing screws have been tightened, as required by the protocol to 20 N/cm. It is essential to block a portion of collagen sponge under the palatal incision to prevent bleeding. The keratinized tissue taken from the palatal side of the incision has been adapted buccally to the screws and fixed in that position with subperiosteal sutures. This avoids excessive suture traction.

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Fig. 010. Check X-ray with the healing screws and the cemented cantilever bridge. Excess cement under the bridge must be accurately removed. A portion of spongiosa displaced apically over the distal implant is clearly seen on the x-ray image. This creates a new peri-implant alveolus, displacing apically the native residual bone. This tissue was previously found lining the sinus floor.

 

The protocol does not require the use of burs.

The first cutting tool is the blade of the Beaver # 64 which will be used up to 1mm below the floor of the sinus. Fig. 05/06

After the Beaver # 64, two bone expanders with 90° cutting edges will be introduced in sequence:

1. the BE2 with the 1.5mm tip and, following, 2. the BE3 with the 1.9mm tip.

The BE2 and BE3 define a site for the emergence profile of the implant and an area of initial penetration that is used to guide the successive instruments with rounded tips8. The next bone expander is, in fact, the BE 45/15 with its 2.2mm rounded tip, which will be pushed below the floor of the sinus always transversally. The tunnel created with the BE 45/15 is then used to insert the 10mm length rounded 3mm diameter probe tip that will produce the first cracks in the medial side of sinus floor. Fig. 06/07

This probe will create a 10x3mm surgical tunnel parallel to the palatal vault. Reorientation towards the ideal (verticalized) prosthetic axis is obtained gradually when extracting this – and successive instruments – by forcing the tips of the instruments buccally during removal.

The following instruments, with a progressively increasing diameter, are inserted and then extracted with the same technique. It is very important that the final cavity must remain under dimensioned in both height and width, so that the final thrust is produced by the implant itself, which will be stabilized in the native bone available under the floor of the sinus. Fig 06/07

Before implant insertion, a portion of collagen is inserted and pushed using a Bone Expander in apical position, so that it remains interposed between the apex of the implant and the portion of displaced bone. This will create the apical, intra-sinus portion of the surgical alveolus5-10-11-12-14.

The extent of under sizing will be strictly conditioned by the quality of the bone and by the implant shape.

The changes induced in bone volume, are usually simultaneous to implant insertion.

The implant inserted into native bone will have the advantage of being functionalized at 70 days from insertion.

The reparative osteointegration can be easily followed-up with a clinical check and with a simple periapical x-rays7. Fig. 02/10/11/17/18

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Fig. 010. Check X-ray with the healing screws and the cemented cantilever bridge. Excess cement under the bridge must be accurately removed. A portion of spongiosa displaced apically over the distal implant is clearly seen on the x-ray image. This creates a new peri-implant alveolus, displacing apically the native residual bone. This tissue was previously found lining the sinus floor.

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Fig 011. The check x-ray after three months of load shows new apical bone structures above the implants. A new cortical line delimits the new sinus floor position. This is a typical functional response to osseointegration.
The implants were loaded, according to protocol, with a functional provisional at about 70 days from insertion, for a period of three months.
Please note that no filler materials are used in the Localized Management of Sinus Floor technique.

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Fig. 017. Radiographic appearance two years after implant insertion and after about 18 months of functional load. In the image it is possible to read the new bone density at both the apical and coronal levels, due to the physiological response of the bone to the functional load.

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Fig. 018. X-ray situation at four years from implant insertion. Radiographycally it is possible to visualize the new bone density in the zone between #23 and #24. This is also possible in the inter-implant space and in the new cortical line that profiles the sinus cavity.

 

Apical repositioning and suturing of the flap

After implant insertion the surgical screws are tightened to 20 N/cm to test primary stability and prevent accidental screw loosening. Fig. 09/10

The flap is adapted buccally and compressed for a few seconds to the emergence profile of the healing abutment in order to stabilize it in its final position. This position must be maintained.

The flap is firmly fixed in the desired position with sutures anchored to the periosteum. Fig. 09

The suturing technique must prevent ischemia and tension in the repositioned soft tissues so that the blood flow is not obstructed. This is especially important in the phase in which the post-operative edema reaches its apex.

The choice of the height of the healing abutment is made according to the thickness of the soft tissue; the height must be sufficient to stabilize buccally the keratinized mucosa repositioned from the palate.

The gap that remains between the buccal and palatal edges of the flaps will heal by secondary intention. This will also favor the regeneration of peri-implant keratinized mucosa that, as such, will stabilize itself over time. Fig. 012/013/014/015

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Fig. 012. Clinical appearance in an occlusal view at about a year after the insertion of the implants.

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Fig. 013. Enlarged view where we can note how the implant profile emergency lies within a volume of cheratinized tissue similar to the physiological one. The muco-gingival line is apically displaced in a position similar to that of the natural contiguous teeth.
The interproximal gingival space between # 23 e # 24, where a deep post-surgical depression was present, has been practically completely filled as a primary result of the secondary intention healing. Compare to Fig. 09a

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Fig. 014. Occlusal view with the implant abutments modified according to the Anatomically Modified Abutment (A.M.A.) technique before cementation of the final prosthesis.

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Fig. 015. Vestibular view with the A.M.A abutments ready for cementation.

 

Objectives of the flap technique

  • To adapt the keratinized tissue present on the crest to the implant emergence profile.
  • To increase the thickness and height of the keratinized tissue during implant insertion by avoiding a second surgical stage and probably establishing immediately the peri-implant biological width1-2-6-9.
  • To reduce the surgical trauma and simultaneously re-establish a normal depth of the fornix.
  • To preserve the natural anatomy of the contiguous teeth avoiding damage to the profile of the papillae.
  • To mimic the natural morphology of the gingiva. Fig. 013/014/15/16
  • To better cover the grey color titanium with thicker keratinized mucosa.
  • To facilitate a more effective home care.

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Fig. 016. Final crowns in position. The inter-papillar spaces are designed with an ideal emergency so as to enable the gum to adapt itself to the profile of the crowns.

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Fig. 017. 4 yrs follow-up.

 

References

Journals

1. Abrahamsson I, Berglundh T, Lindhe J . “The mucosal barrier following abutment dis/reconnection. An experimental study in dogs”, J Clin Periodont 1997;24 (8) : 568-72

2. Berlundh T, Lindhe J. “Dimension of the periimplant mucosa. Biological width revisited. J Clin Periodontol”, 1996 Oct;23(10):971-3

3. Bruschi GB, Scipioni A, Calesini G, Bruschi E. “Localized Management of Sinus Floor with Simultaneous Implant Placement. A Clinical Report”, Int J Oral Maxillofac Implants 1998;13:219-226

4. Bruschi GB, Crespi R, Capparè P, Bravi F, Bruschi E, Gherlone E. “Localized Management of Sinus Floor Technique for Implant Placement in Fresh Molar Sockets”, Clin. Implant Dent Relat Res. 2011 May 20

5. Buchter A, Kleinheinz J, Wiesmann HP et al. “Biological and Biomechanical evaluation of bone remodeling and implant stability after using an osteotome technique”, Clin. Oral Impl. Res. 16,2005; 1-8

6. Cocharan DL, Hermann JS, Schenk RK, Higginbottom FL, Buser D. “Biologic Width around Titanium Implant. A Histometric Analisis of the Implanto-gingival Junction around Unloaded and Loaded Nonsubmerged Impants in the Canine Mandible”, J Periodontol 1997 Feb; 68(2): 186-98

7. Friberg B.A Comparison between Cutting Torque and Reasonance frequency measurements of maxillary implants. A 20-month Clinical Study”, Int J Oral Maxillofac Surg 1999 Aug; 28 (4):297-303

8. Hartmann GA, Cocharan DL, “Initial implant position determines the magnitude of crestal bone remodeling”, J Periodontol 2004; 75: 572-577

9. Linkevicius T. Apse P, Grybauskas S, Puisys A, “Influence of Thin Mucosal Tissues on Crestal Bone Stability around Implants with Platform Switching: A 1-year Pilot Study”, J Oral Maxillofac Surg 2010 Sep;68(9): 2272-7

10. Nkenke E, Kloss F, et al, “Histomorpfhometric and fluorescence microscopic analysis of bone remodeling after installation of implants using an osteotome technique”, Clin. Oral Impl. Res. 13, 2002; 595-602

11. Nobrega AR, Norton A, Siva JA, Silva JPD, Branco FM, Anitua E, “The osteotome Versus Conventional Drilling Technique for Implant Site Preparation: A Comparative Study in The Rabbit”, Int J Periodontics Rest 2013;32:e109-e115

12. Yilmaz HG, TÖzÜm TF, “Are Gingival Phenotype, Residual Ridge Height, and Membrane Thickness Critical for the Perforation of Maxillary Sinus?”, J Periodontol 2012; 83:420-425

13. Terheyden H, Lang NP, Bierbaum S, Stadlinger B, “Osseointegration – communication of cells”, Clin. Oral Impl. Res. 23, 2012, 1127–1135 doi: 10.1111/j.1600-0501.2011.02327.x

Books??

14. Bruschi GB, Crespi R, “Tecniche di espansione ossea in chirurgia implantare”, Quintessenza Edizioni 2012

Contributions to books

15. Wthinson SW. Ten Cate (ed), “Oral Histology”, 4th Edition.

16. Bruschi GB, Scipioni A, “Alveolar augmentation: New application for impants”, In: Heimke G. (ed), “Osseointegrated Implants, Vol I”, Boca Raton, FL CRC Press, 1990;2:35-61

 

CURRICULUM VITAE

DR. GIOVANNI BATTISTA BRUSCHI

M.D. University of Rome, D.M.D. (specialty in Dentistry) University of Rome. Assistant Professor at Boston University School of Graduate Dentistry Department of Prosthodontics directed by Prof. Martignoni. He has published numerous scientific articles in both national and international peer-reviewed journals. He is co-author of the book “Implantologia Orale” (Ed. Martina, Bologna, Italy). Co-author of the book “Implantoprotesi il ripristino dell’omeostasi tramiti restaurazioni singole” (Ed. Martina, Bologna, Italy). Co-author of the book “Techniques of bone expansion in implant surgery” (Quintessence International). Private practice in Rome limited to Oral Surgery and particularly Implantology and Endodontic Surgery.

E-mail: gbbruschi@gmail.com

 

For info: zerodonto@gmail.com

Esthetics in Total Removable Prosthodontics

Esthetics in Total Removable Prosthodontics

From the impression tray to the denture: techniques for fabrication

 

Patients feel teeth loss as a worsening of the quality of life. Although in the last years prevention in dentistry has reached more and more comfortable levels, the lengthening of average life is often associated with an increase in the incidence of periodontal disease and loss of tooth support, causing complete edentulism over time. The overcoming of problems related to edentulous patients requires specific skills for the clinicians and stimulates the research of innovative technique and restorative materials. In fact, each laboratory and clinical step has to be performed in the respect of traditional concepts, from the extension to the basal areas to the precision of the interface between soft tissues and the impression surface of the denture, from the border molding to the modelling of the prosthesis, from a proper and physiological record of the intermaxillary relationships to the optimal mounting of the artificial teeth.

CLINICAL CASE PRESENTATION
A 58-year old female patient presented with complete edentulism; she was not a smoker and was in good general health. The patient’s complaints regarded both function and communication, referring a severe discomfort in interpersonal relationships. Consequently, she requested for a radical rehabilitation of her mouth, paying particular attention to esthetics. Consequently, the aim of the prosthetic rehabilitation was the achievement of both optimal functional and esthetical results.
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TECHNICAL PROCEDURES
According to a conventional approach, the dentist took the study impressions by means of an irreversible hydrocolloid. The preliminary impressions have to be overextended, so as to record the whole extension of the maxillary and mandibular arch as well as of the adjacent soft tissues.

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The impressions were disinfected in the dental laboratory. The borders were covered with wax and the impressions were boxed in order to pour the dental stone; this allowed to achieve detailed and esthetically valid casts.
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According to the dentist’s indications, the Passamonti’s technique was chosen to fabricate the customized impression trays. The depth of the fornix was marked using a blue pencil.
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The project was completed designing the limits of the impression trays and the tissue stops.

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The preparation of the impression trays was completed covering the casts with a controlled thickness of dental wax.
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Then, the individual impression trays were fabricated.
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According to the conventional procedures, the dentist recorded the final, overextended impressions.
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The impressions were poured with Class IV dental stone.

Then, the registration bases were fabricated using light-curing resin; the polymer shrinkage was limited by means of a multi-step polymerization technique.
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Il medesimo materiale fotopolimerizzabile veniva, inoltre, utilizzato per produrre una placca per facilitare la registrazione dell’arco facciale con una struttura ritentiva per farla aderire alla forchetta occlusale
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The same light curing material was used to produce a maxillary registration base for the facial bow.

The intra- and extra-oral registrations were recorded using a facial bow, so as to check the correctness of the lip support and harmonize the oro-facial relationships.
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The casts were carefully blocked in the articulator, in order to not vary the inter-maxillary relationships recorded intraorally. First, the maxillary cast was blocked;
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then the mounting in the articulator was completed.

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After carefully checking the centric and non-centric movements of the mandible in the presence of total removable dentures, the bilaterally balanced occlusion was chosen as occlusal scheme to improve the stabilization of the prostheses.

On the basis of the intraoral records performed by the clinician on the wax blocks, it was possible to choose the proper dimensions of the maxillary anterior teeth as well as the correct length of each tooth.

Resin teeth Vitapan Plus were used; the customized line of the incisal margin, the natural appearance of the borders and the vitality of the surface texture allow these artificial teeth to be perceived as natural ones. The interdental embrasures allow not only to set a natural configuration of the papillae but also to achieve an easier cleaning of the denture by the patient. The palatal configuration supports the anterior guidance and contributes to a proper speech.

The “substitution” technique was used to mount the front teeth; consequently, the proper amount of was was removed to place the corresponding tooth,
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until the setting of the maxillary front teeth was completed.

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The mounting technique made the teeth 33 and 43 to be placed so as to guide the sliding of the maxillary canines on the mandibular ones, avoiding diastemata in the posterior segments and obtaining a correct proportion between over jet and overbite.

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Once the teeth 33 and 43 were set, the teeth 31 and 41 were placed respecting the midline of the maxillary central incisors.

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In the remaining room, the teeth 32 and 42 were finally set.

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The mounting was completed balancing the relationship between function and esthetic.
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A first intraoral try-in was performed to verify the correctness of the mounting of the front teeth by means of phonetic and esthetic procedures. During these steps, the trust gained by the patient is paramount to make the patient cowork with the dental team. In the respect of the functional parameters, it is even possible to allow the patient to suggest specific esthetic changes finalized to meet his/her expectations.

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Then, the mounting of the posterior teeth was performed in a bilaterally balanced occlusion.

The Vita Lingoform teeth were used to set the posterior segments. The univocal reproduction of the centric contacts and the spherical intersection of the interproximal surfaces allow for a controlled mounting of the Lingoform in any bite configuration. Being suitable for any mounting technique, even the lingualized one, particularly in full removable prosthodontics, the Vita Lingoform teeth can prevent the atrophy of the alveolar crests even in the presence of unfavorable static and dynamic mandibular relationships. The occlusal design is suitable for both one-to-one and one-to-two tooth contact. The possibility to widen the space for the tongue and to support the cheeks given by the Vita Lingoform teeth contributes to the patient’s comfort.

Then, the posterior teeth of both arches were mounted: the tooth 14 contacted with both cusps the plan of the mandibular wax block, the tooth 15 was in contact with only the palatal cusp and the tooth 16 with only the mesio-palatal cusp, so as both the Spee’s and Wilson’s curves were set.
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Similarly, the contralateral arch was mounted.
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Once the maxillary arch was completed, the mounting of the mandibular posterior sectors was performed starting with the tooth 36 in respect of the Angle’s class; then, the teeth 34 and 35 were placed in one-to-two tooth contact, so as to make the cusps of maxillary teeth close in the lower fossae.
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Similarly, the contralateral arch was mounted.
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Then, the dentist checked again the occlusion, the vertical dimension, the esthetic and phonetic procedures, achieving the best natural appearance and collaboration by the patient.

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Successively, the posterior limit of the maxillary denture was identified on the master cast, signing the sealing area and the gypsum to be removed.

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Once the amount of gypsum to be removed was quantitatively signed with “ + “ and “ – “ on the master cast, the procedure was carried on in the anterior-posterior direction.
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As reported above, in order to achieve the best esthetic result, particular care was dedicated to the proper integration between the gingival margins of the artificial teeth and their color. First, the gingival contours were modelled with wax, so as to imitate the morphology of the natural papillae and gingival scalloping.

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The mandibular denture and the posterior resin shields were modelled with the same technique.

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A metal brush was used to obtain a gingival stippling effect.

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The dentures modelled with wax were placed in a muffle one by one, in order to properly verify the final mounting in the articulator. Finally, the prostheses were polished and finished to carefully remove any debris.

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The esthetic finalization of the dentures was based on the creation of a micro-geography simulating the terminal blood vessels on surface of the artificial alveolar mucosa.

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The prosthetic shields were colored with composite materials. Controlled amounts of resin were removed and substituted with composites, in order to evidence the transition between the attached gingiva and the alveolar mucosa.

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The finishing of the dentures was carried on with a two-step approach, using both a cleaning machine and hand instruments.

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CONCLUSIONS

The criteria of esthetic evaluation could be different according to the viewpoint of the observer, being the dentist, the dental technician or the patient. Almost all the patients ask for white, completely straight and perfect teeth. Conversely, the operators look for color, surface texture, characterizations and anatomic modellation, in order to reproduce as closely as possible the natural tissues. Nonetheless, the treatment of completely edentulous patients necessitates to model and customize the prosthetic shields so as to improve the phonetics and to cover crest deformities.
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REFERENCES

1. Bortolotti L. Protesi mobile: tradizione e innnovazione. Masson, Milano, 2004..
2. Fradeani M. La riabilitazione estetica in protesi fissa. Quintessenza Edizioni Srl, Milano, 2004.
3. Hayakawa I. La protesi totale: principi e tecniche. Scienza e Tecnica Dentistica Edizioni Internazionali Milano, 2000.
4. Kinoshita S. Atlante a colori di parodontologia. Piccin-Nuova Libraria, Padova, 1987.
5. Linde J. Parodontologia 3a ed. Edi. Ermes, Milano, 1991.
6. Mutschelknauss RE. Testo atlante di parodontologia clinica. Scienza e Tecnica Dentistica Edizioni Internazionali s.n.c./Milano, 2000.
7. Preti G. Riabilitazione protesica. UTET, Torino, 2003.
8. Schärer P, Rinn LA, Kopp FR. Principi estetici nella ricostruzione protesica. Scienza e Tecnica Dentistica Edizioni Internazionali s.n.c./Milano, 1984.
9. Valletta G, Matarasso S. Atlante di parodontologia. Ed. Idelson, Napoli, 1984.
10.Carlo Montesarchio.Una solozione estetica in protesi totale Dental Labor .2000
11.Marino G. Cantoni A.: Guida al successo in protesi mobile completa . Ed. Saccardin, Martina Bologna1991
12.Lerch P. : Laprotesi totale. Resch. Ed. Verona 1987
13.Shay. J Contemp Dent Pract, 2000; 1:28-41.
14.Yeung et al. J Oral Rehabil, 2000; 27:183-189.
15.Carlsson. J Prosthet Dent, 1998; 79:17-23.
16.Orr et al. J Clin Periodontol, 1992; 19:589-594.
17.Jagger & Harrsion. Br Dent J, 1995; 178:413-417.

ACKNOWLEDGEMENTS

The author would like to thank Mr. Vincenzo D’Urso, Mr. Luca Di Maglie and Mr. Giovanni Martinelli for their scientific contribution.

CURRICULUM Carlo Montesarchio

Carlo Montesarchio was born in Naples in 1964. He took his Dental Technician certification in 1982; owner of his own dental laboratory since 1983. Author of publications on national and international journals, he participates in formation classes at the University “Federico II” of Naples. Lecturer for ANTLO.

He collaborates with dental industries for material and technology development. Lecturer at Master Courses of Removable Prosthodontics for VITA ZANFABRIK. He focuses all his activity on full removable dentures.

His formation is linked to several experiences dealt with national and international operators.

E-mail: cmontesarchio@alice.it

For Info: zerodonto@gmail.com

Digital impression by means of Itero intraoral scanning system to fabricate zirconia single crowns

Digital impression by means of Itero intraoral scanning system to fabricate zirconia single crowns


Stereomicroscopic analysis of the precision of fit of PFM frameworks fabricated with traditional impression vs zirconia prostheses produced using an optical impression technique

Case presentation
A 42 year-old female patient, unsatisfied by the esthetics of her smile, asked for the rehabilitation of the maxillary incisors by means of fixed prostheses, substituting 4 previous metal-ceramic single crowns.

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After the study of the case and the routinary clinical and laboratory analyses, the previous restorations were removed and the preparations of the abutment teeth were revised, making 1 mm circumferential chamfers.

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The periodontal tissues were conditioned to a healthy state using a temporary fixed acrylic resin prosthesis, that was relined so as to make the gingival tissues properly scalloped.

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After 3 weeks of provisionalization, the precision impressions were taken using the following techniques:
– conventional impression by means of polyethers;
– optical impression using the Itero intraoral scanning system.
Conventional impression
As to the conventional impression technique, the gingival tissues were displaced using two retraction cords; a #000 and a #2 cords were used to displace vertically and horizontally respectively the marginal tissues. The second cord was dipped in a 20% ferric sulfate astringent solution to improve hemostasis.

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Then, a conventional one-step two-phase precision impression was taken, using medium- and light-consistency polyether impression materials.

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The master cast was poured with class IV extra-hard stone and then it was duplicated.
With a merely speculative purpose, such a conventional impression was taken to compare the operative procedures with those of the optical impression, as well as to fabricate four gold alloy single frameworks, in order to relate the marginal and internal values of precision of fit with those achieved with zirconia cores fabricated using the optical impression workflow.

Digital impression
As regards the digital impression, the Itero intraoral scanning system was used.

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This system is based on a confocal laser scanning technique with focal planes at 50 microns, it records 300-350 images per abutment and it is provided with autofocus up to 3 cm. About 100-110 static shots per arch are taken and then they are merged by means of specific reference points identified by the software, which is able to reduce the mean error interpolating the images.

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The gingival tissues were displaced using a single #2 retraction cord without any astringent agent.
Subsequently, an optical impression was taken using the Itero system and a dedicated intraoral scanner. The impression procedure suggested by the software was followed: after gently removing each retraction cord, the three-dimensional morphology of each abutment was recorded. The image was taken as soon as the software interpolated correctly each abutment surface.

Impronta digitale con sistema Itero

Moreover, the system needed to record the morphology of the teeth adjacent to the abutments (2 per each emiarch) as well as of the antagonist teeth, in order to acquire the occlusal reference points necessary to the CAD phase.

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Case finalization
Four gold alloy single frameworks were fabricated from the stone master cast poured from the conventional impression, according to the traditional lost wax technique.

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Differently, a stereolitographic working model of the scanned area was obtained from the digital impression.

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Then, two sets of zirconia single cores with a thickness of 0.5 mm were produced: one set was automatically modelled by the Cares software (Straumann) while the other one was anatomically modeled using the Katana system (Noritake).

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The fit of the frameworks was checked intraorally using a white silicon disclosing agent inside the metal copings and a black one in the zirconia cores, so as to highlight any pressure spot on the internal surface of each crown.

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In all systems, the passive fit was considered clinically optimal.
A Cares copingAB KatanaABC Zirconia oro ceramica

 

Then, the marginal precision of each coping was checked using a stereomicroscope (30x), gently displacing the marginal tissues apically by means of metal anatomical gingival divaricators. In all systems no clinically relevant marginal misfit was noticed.

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Both sets of zirconia copings were veneered by means of dedicated ceramics; after the intraoral tryin, the esthetic evaluation was made in accordance with the patient.

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Finally, it was decided to cement the zirconia-ceramic single crowns fabricated with the Katana system using a resin luting agent.

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The cement excesses were carefully removed using teflon tips on a sonic handpiece under a stereomicroscope, so as not to wound the gingival tissues.

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The occlusal contacts were carefully checked and balanced both in centric occlusion and in lateral and protrusive movements.

Analysis of the marginal and internal precision of fit
The marginal precision and internal fit of both the metal (considered in the literature as the gold standard for marginal fit) and the zirconia cores were checked by means of a stereomicroscopical analysis (40x) of the longitudinal section of each coping. Consequently, both the sets of zirconia frameworks were duplicated using the same files: a first set was veneered for the subsequent clinical procedures while a second one was used to fabricate the specimens to be sectioned.
Viceversa, the metal cores were not duplicated, since they had not to be veneered.
Within the limits due to the absence of a reference metal master cast, the present clinical study was performed to verify the in vivo precision of prosthetic single crowns; thus, it was necessary to seat each coping on the relative working model.
The metal frameworks were cemented using a zinc-phosphate cement while the zirconia cores were luted with the same resin cement used for the clinical cementation of the crowns. Then, each coping was embedded in resin blocks and the longitudinal sections of the cores were made, in order to evaluate the marginal and internal precision of fit of the frameworks. The cut was made along the longitudinal axis of the tooth, from the middle area of the buccal cervical convexity to the middle area of the incisal margin. Finally, the measurements of the marginal precision at the finish line (MO: Marginal Opening, AMO: Absolute Marginal Opening) and of the internal fit in the axial (coronal, mid, incisal) and incisal areas (buccal, mid, palatal) were made using a point-to-point micrometric measuring software.

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Accordingly to literature data, the metal frameworks showed lower marginal gaps (16.9 microns) than the zirconia copings (21.1-28.4 microns). Nonetheless, all the values recorded on the all ceramic restorations were comparable to the clinically acceptable values of fit stated by the American Dental Association. Particularly, the marginal gaps were between 21.1 e 28.4 micron.
Similarly, the values of internal adaptation were lower in the metal cores; this was probably due to the minimum dimensions of the burs used in CAD-CAM systems to drill the internal surfaces of the all-ceramic cores, determining unsatisfactory values of internal fit at level of the incisal areas (138.8-220-3 micron). Nonetheless, as reported in literature, these parameters do not affect the clinical reliability of all-ceramic cores.

Statistical analysis
Although with merely speculative purpose because of the limited number of specimens, the marginal and internal values of fit were statistically analyzed by means of univariate ANOVA and Tukey’s post-hoc test (p<0.05).
Statistically significant differences were noticed both between the metal and zirconia copings and between the Noritake and Cares zirconia cores..
Furthermore, statistically significant differences were recorded in all measurement points, as shown in the table.

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Conclusions
The digital impression technique proved to be reliable in terms of precision and detail reproduction.
The impression software was very user friendly during both the clinical procedures and the digital prescription phases.
Nonetheless, a few drawbacks were evidenced and should be implemented in the future. The dimensions of the intraoral scanner were quite big and not very comfortable to reach all intraoral sites; moreover, the weight of the scanner should be reduced in order to make its handling easier.
Although intraoral powders were not required by the system, the Itero scanner, as well as other intraoral cameras, still requires the use of retraction cords to displace gingival tissues. To date, this still represents the real limit in the clinical use of optical impression techniques, that will become a really revolutionary tool as soon as innovative technologies will allow clinicians to scan
iuxtagingival and intrasulcular areas directly, making the impression even more comfortable for patients and avoiding any operator-sensitive variable in dental impression making. By the way, it is worth noticing that optical impression techniques allow to scan the impression of single abutments at different times, interpolating multiple partial impressions by stitching; although this reduces the discomfort of patients, such a procedure could negatively affect the precision of scanning in transition areas.
The precision of fit of zirconia copings fabricated using the digital workflow completely satisfied the parameters of marginal precision and internal adaptation reported as clinically valid by scientific literature.


References
1. Almeida E Silva JS, Erdelt K, Edelhoff D, Araújo E, Stimmelmayr M, Vieira LC, Güth JF. Marginal and internal fit of four-unit zirconia fixed dental prostheses based on digital and conventional impression techniques. Clin Oral Investig. 2013 May 29. [Epub ahead of print]
2. Brawek PK, Wolfart S, Endres L, Kirsten A, Reich S. The clinical accuracy of single crowns exclusively fabricated by digital workflow–the comparison of two systems. Clin Oral Investig. 2013 Dec;17(9):2119-25. doi: 10.1007/s00784-013-0923-5. Epub 2013 Jan 31.
3. Seelbach P, Brueckel C, Wöstmann B. Accuracy of digital and conventional impression techniques and workflow. Clin Oral Investig. 2013 Sep;17(7):1759-64. doi: 10.1007/s00784-012-0864-4. Epub 2012 Oct 21.
4. Scotti R, Cardelli P, Baldissara P, Monaco C. Clinical fitting of CAD/CAM zirconia single crowns generated from digital intraoral impressions based on active wavefront sampling. J Dent. 2011 Oct 17. [Epub ahead of print]

Controlled Split Crest and Guided Bone Regeneration (GBR) with contemporary implant placement: rationale and limits of the clinical application in esthetic areas.

Controlled Split Crest and Guided Bone Regeneration (GBR) with contemporary implant placement: rationale and limits of the clinical application in esthetic areas.

The authors’ experience in the medium term.

 

Introduction

According to the current scientific literature, a prosthetically-guided approach should be the first choice for implant placement, even in case of horizontal/vertical alveolar bone resorption. In the last decade, different reconstructive techniques were described with the aim of restoring bone volume.

Among the available techniques, the authors widely experienced and achieved very satisfactory clinical outcomes with the “Edentulous Ridge Expansion” (E.R.E.), introduced by Dr. Bruschi and Scipioni in 1994.

This technique relies upon the healing potential of the spongy bone, associated with the elevation of a partial thickness flap to preserve the periosteum. The intra-bony gap is initially filled by a blood clot that turns into osteoid tissue in about 40 days. After about 90-120 days, the extracellular matrix progressively mineralizes and the osteoblasts mature into osteocytes.

In this technique, the preservation of an optimal trophism of the bone is paramount, leaving a thickness of at least 1-1.5 mm to the buccal bone; an extensive periosteal blood supply is required as well. This approach limits the risk of fenestrations, dehiscences or necrosis of the buccal bone during implant insertion and healing.

The E.R.E. technique is suitable in case of knife-edge alveolar ridges with at least a height of 10 mm and a width of 4 mm. Its main drawback is the risk of fracture during the displacement of the buccal bone plate; therefore, its predictability is not absolute. Such risk can be limited using a partial thickness flap, in order to ensure a better cortical blood supply in case of fracture.

If, on the one hand, a partial thickness flap is advisable, on the other hand, periosteal preservation does not allow to associate bone regeneration techniques that may be required during surgery, especially when a prosthetically-guided implant positioning is aimed. For this purpose, in recent years, the authors have developed a modified split-crest technique associated to a contextual guided bone regeneration (GBR), in order to compensate any dehiscence and/or fenestration, minimize the marginal bone loss and fill the gap between bone and implant. This approach is particularly important in the esthetic zone, where the stability of the buccal bone is critical for the success.

In a systematic review of the literature (Donos et al., 2008), the survival rate of implants placed in sites augmented with the split-crest technique ranged from 86.2 % to 100% after 12 months to 5 years in different studies. The success rate of the split osteotomy, measured as the achievement of adequate ridge dimensions for placement of implants, varied from 87.5% to 97.8% from 18 to 20.4 months post-loading, respectively.

The present article aimed at analyzing the clinical factors influencing the reliability of the split-crest technique as well as discussing its limits and rationale by the presentation of two clinical cases.

The technique: rationale and anatomic considerations

 

Comparing an atrophic ridge with its normal anatomy in sagittal view (Fig. 1), it can be noted that the bone volume is evidently resorbed, particularly on the buccal side. Differences in bone resorption rates between the buccal and lingual aspects are due to the greater amount of bundle-bone present on the buccal side of the alveolar ridge. The bundle-bone is strictly related to the presence of teeth, so a greater resorption rate occurs on the buccal aspect after tooth loss (Araujo & Lindhe 2005).
Frequently, in edentulous ridges an hourglass shaped alveolar process is found, due to the presence of an undercut at the base of the ridge. This anatomical peculiarity should not be underestimated in case of implants in the esthetic zone, as the drills can create fenestrations in the apical part of the implant site. Small fenestrations are not a big issue for osseointegration but can affect the achievement of optimal soft tissues esthetics, resulting in a grayish tissue transparency, particularly unpleasant in the anterior maxilla.

atrofia processo alveolare anatomia mascellare superiore  hourglass shaped alveolar bone riassorbimento post estrattivo dr. dott. dario mari sac ITI impianti in zona estetica cresta alveolare bundle bone osso fibroso araujo lindhe classificazione Cawood Howell