Single tooth defects in the posterior quadrants

John Beumer III DDS, MS Robert Faulkner DDS

Division of Advanced Prosthodontics, UCLA This program of instruction is protected by copyright ©. No portion of this program of instruction may be reproduced, recorded or transferred by any means electronic, digital, photographic, mechanical etc., or by any information storage or retrieval system, without prior permission.

Single tooth defects – Posterior quadrants Fixed dental prostheses

Delivery 15 year follow-up

Fixed vs Implant

Implant is preferred when: l  Adjacent natural teeth are virgin or nearly virgin l  The long term prognosis of the abutments is

questionable due to previous endondotic treatment or periodontal compromise

Fixed is preferred l  Maxillary 1st molar defects -

l  Pneumatization of the maxillary sinus l  Higher failure rates

Restoration of endodonticallly treated teeth vs Implant crown

Endo is preferred (given a successful endodontic treatment outcome)

l  Reasonable volume of tooth structure remains l  Occlusion is ideal l  Parafunctional activity is minimal

Courtesy Dr. C. Goodacre

Mandible

Anatomic issues l  Buccal-lingual dimension. l  Thickness of the buccal plate

(immediate load) l  The lingual concavity l  Inferior alveolar nerve l  Mental nerve

Courtesy Dr. N. Barakat

Mandible

Anatomic issues l  Buccal-lingual dimension. l  Thickness of the buccal

plate (immediate load) l  The lingual concavity l  Inferior alveolar nerve l  Mental nerve

These structures are best appreciated with CT scans Courtesy Dr. N. Barakat

COURTESY DR N. GEHA

Anterior loop of the mental nerve

Courtesy Dr. N. Barakat

Anatomic issues •  Buccal-lingual

dimension. •  Thickness of the buccal

plate (immediate load) •  Maxillary sinus

Maxilla

Site enhancement

l Most commonly necessary in the maxillary premolar region

Timing for implant placement Immediate vs delayed vs staged

Immediate placement - placing the implant at the same time as extraction of the tooth ª  Delayed placement - placement of the implant 2-3 months following extraction. ª  Staged placement - placement of the implant 4-6 months after tooth extraction in

order to allow for bone healing of the extraction site.

The intent of these strategies is to minimize bone resorption, particularly on the facial surfaces of the implant.

ª  However, following tooth removal, resorption of labial and lingual bone occurs regardless of whether an implant is placed into the extraction site, whether placement of the implant is delayed for 2-3 months, or whether the socket is augmented with bone substitutes.

ª  Two hypotheses for resorption ª  Bone resorption is secondary to the contraction of the mucosal tissues

secondary to expression of the WIT genes (Suwanwela, et al, 2011) ª  Compromise of the blood supply to the facial bone following extraction

(DeRouk et al, 2008)

Timing for implant placement Immediate vs delayed vs staged implant placement

Immediate implant placement

ª  Tooth fracture, defects with no infection and intact labial plates

ª  Sufficient bone apical to the tooth socket to insure adequate primary stabilization

ª  Patients with significant bone loss are poor candidates. Those presenting with loss of labial bone with extended biologic width requiring bone augmentation are best treated with a staged technique

ª  Patients presenting with periodontal or peri-apical infections are poor candidates for immediate placement primarily because of the compromised blood supply associated with the potential implant site. They are best treated with “staged implant placement.”

Immediate placement

ª  Tooth fracture, defects with no infection and intact labial plates

ª  Sufficient bone apical to the tooth socket to insure adequate primary stabilization

ª  Immediate placement helps retain the levels of the interdental papilla, but will not preserve the bone on the labial side of the implant (Araugo et al, 2005; Botticelli et al, 2006; Araujo and Lindhe, 2009).

ª  If immediate placement is considered, there should be sufficient bone apical to the tooth socket order to insure adequate primary stabilization of the implant.

Delayed implant placement l  Delayed placement - placement of the implant 2-3

months following extraction.

Site enhancement ª Socket augmentation

ª Treatment of fresh extraction sockets with intact buccal and lingual bone walls.

ª Ridge preservation

ª Augmenting edentulous sites that are insufficient for implant placement.

ª Ridge reconstruction

Ridge preservation Defined as treatment of fresh extraction sockets with deficient

bone walls in order to maintain ridge contours.

When successful, these procedures permit placement of implants in ideal position and angulation. There is no evidence to indicate which particular approach might be the most efficacious (Chen and Buser, 2009).

Courtesy Dr. Krill

Site requirements and implant selection Premolars

Bone volumes necessary l  Implant diameters 4.0-4.5 mm

l  There should be sufficient volume of buccal-lingually and mesial-distally to encompass the implant with at least 2 mm of bone on each side

l  7 mm of mesial-distal space required

l  Implant lengths l  Mandible – 8-10mm l  Maxilla – 10-12 mm

Beware of the use of excessively wide implants in the premolar region. When the bone is excessively thin on the buccal side of the implant there is risk of loss of gthe facial plate and apical migration of bone and soft tissue.

10 year follow-up

Site requirements and implant selection Molars

Bone volumes necessary l  Implant diameters 5-6 mm

l  Two implants, 4 mm in diameter are preferred when the mesial – distal space permits l  Preferred in extension areas

l  Implant lengths l  Mandible – 8-10mm l  Maxilla – 10-12 mm

Solitary implants restoring single molars Avoid the use of 4mm implants - Cantilever effect

When the food bolus is applied to the marginal ridge (B), the restoration is easily tipped because the crown is supported by such a narrow platform.

Result: Cantilever forces lead to screw loosening, implant fracture and overload the bone anchoring the implant.

Immediate loading Generally discouraged in the posterior quadrants

Immediate placement into extraction sites

Generally discouraged in the molaer sites Possible in premolar sites

Selection of implants

External hex vs internal interlocking l  Internal interlocking is preferred but

both have been used successfully

Tapered implants l  In extraction sites

l  Semi-guided or fully guided site preparation using surgical drill guides is preferred

Surgical placement

Prosthodontic Issues - Single tooth defects Posterior quadrants

ª  Internal connections are favored as opposed the external hex

ª  Custom abutments must be designed with appropriate resistance and retention form if cement retention is planned

ª  Avoid ridge laps ª  Occlusal surfaces

ª  Metal vs ceramic

ª  Screw retention preferred over cement retention ª  Occlusion is centric only contact

ª  Lingualized or buccalized

l  Internal connections are favored as opposed the external hex although external hex designs have been used effectively, especially in premolar sites

External hex vs internal connections

Custom abutments CAD-CAM vs Hand Milled

l  Hand milled when retention is with cross linking scews

l  CAD-CAM when cement retention is used

Abutment materials

l Titanium

l Metal ceramic

l Zirconia l  Not recommended

because of the risk of fracture

Custom abutments Retention and resistance form

l  3 degree taper l Add grooves for additional resistance form

Custom abutments Retention and resistance form

l  Note the groove l  Important even for crowns

retained with cross linking screws

l Hygiene becomes problematic

Avoid ridge laps

Maxillary premolars

l  Ridge lapping is discouraged except in the esthetic zone

Smooth emergence profiles preferred

Occlusal materials Metal vs ceramic

Laminated porcelain occlusal surfaces are at risk for chipping and fracture

Avoid buccal and lingual cantilevers

The occlusal table must be narrowed to avoid buccal and lingual cantilevers. Molars should be no wider than premolars as shown in these two examples.

Occlusion Centric only contact (during clenching)

Occlusion contacts

l  Occlusal adjustment l  Two thicknesses of mylar should pass through the implant contact

when the natural teeth hold one thickness

Proximal contacts

Proximal adjustments Two thicknesses of mylar

Premolar Sites  4 mm diameter

implants are ideal for premolar sites  Occlusion should

be centric only contact  This 1st premolar

site was restored with a 4 mm implant fixture and a UCLA abutment

Premolar Sites  This mandibular 1st premolar site was restored

with a 4 mm implant fixture and a conical abutment

Single Tooth Restorations Distal Extension Defects

Distal Extension Defects

ª  Two implants are recommended when restoring a single molar in an edentulous extension area.

ª  Note the access for a proxy brush

Restoration of single molar sites

Custom abutment Lingual set screw

In this patient, two 4 mm diameter implant were used to restore the first molar. The width of the occlusal table was limited to the width of the natural premolar, thereby eliminating any possible buccal or lingual cantilevers.

Restoration of single molar sites Note:   Hygiene access for proxy brush   Note width of occlusal table

Restoration of single molar sites - Solutions

In this patient a wide diameter implant was used to restore the first molar.

When there is insufficient space for two implants, a wide diameter implant is preferred

Cement vs screw retention

l Screw retention preferred l Cement retention

Problem - Insufficient interocclusal space to design an abutment with appropriate resistance and retention form. Solution – Screw retention

l  Another advantage is with screw retention the emergence profile of the crown is improved

Courtesy G. Perri

Lack of interocclusal space

Challenges of cementation Platform reduction (platform switching) l  If the cement becomes impacted below the margin, its

removal is problematic l  Access is extremely difficult if not impossible without

laying a soft tissue flap

Courtesy Dr. G. Perri

Challenges of cementation

l  How will you remove the cement if it becomes impacted beneath the margins of this implant crown?

l  More than likely, you will not given the severity of the undercut associated with the custom abutment.

l  Therefore, under these circumstances it is advisable to place the margins supra-gingival.

Avoid the use of preformed non-preparable abutments

Issues of concern v Position of the cement margin

in relation to the gingival margin v Particularly significant in the

anterior region v Impaction of cement into the

gingival sulcus is highly likely v Difficulty in seating the crown

because of hydraulic pressure

Avoid the use of preformed non-preparable abutments

l  Cementing crowns with platform reduction

l  Cement the crown extra-orally

Cement retention with platform reduction

Complications

l  Implant fracture l  Implant overload l Recurrent screw loosening l Subgingival cement accumulation leading

to peri-implantitis and loss of the implant

The combination of a small diameter implant, restoring a large mesial – distal space leads to either screw loosening, implant fracture or resorption of bone anchoring the implant.

Fracture Implant fractured after 30 months of function

Solitary implants restoring single molars Cantilever effect

Solitary implants restoring single molars Cantilever effect

Fracture l  Implant fractured after 18 months of function

Single tooth restorations in the molar region – Cantilever effect

This implant was too short and too narrow to withstand occlusal loads and bone loss caused by the resorptive remodeling response led to its loss.

4 mm diameter implant

Mesial cantilever

Subgingival cement accumulation and implant loss

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