Prospective-Retrospective Comparison of Initial versus Final Biomechanical Score for Single-Unit Crowns supported by Implants Placed Using the Osteotome Technique Sinus Lift

Pages: 68-90

Radu Baston(1), Cristina Ilea-Peltecu(2), Mihaela Gaspar(3)

(1)medic dentist, chirurg oro-maxilo-facial, Peltecu Medical SRL, Bucureşti; (2)medic dentist, Peltecu Medical SRL, Bucureşti; (3)medic dentist, Clinica de Zâmbete Confident, Bucureşti

Abstract

Key words: prospective-retrospective study, single-unit implant-supported crown, osteotome sinus-lift technique, Renouard-Rangert biomechanical risk factors, initial biomechanical score, final biomechanical score.

The purpose of this paper is to investigate the prognostic value of the initial biomechanical score calculation for single-unit implant-supported crowns placed using the osteotome sinus-lift technique.

Materials and methods: from March 2004 to December 2018  we inserted in the load-bearing maxillary subsinusal areas 53 single-unit fixtures using  the  osteotome technique.  All fixtures have been loaded after 8 to 10 months with permanent single-unit crowns. Prior to every implant placement  we have calculated an initial biomechanical score, and biased it against a final one, e.g. after crown insertion.

Results: the initial biomechanical score matched the final one up to a maximal 1.5 – point deviation in 87% of the cases.

Discussion: the only  87% accuracy match is due to: (1) diverging from the initial treatment plan by changing implant length and/or diameter, (2) offset occlusal crown loading, (3) different subsinusal autologous basal bone heights, (4) different types of abutment-crown interfaces, e. g. cemented  versus  screw-retained and (5) a wide array of occlusal clearances ranging from 4 to 11mm. (!)

Conclusions: calculation of an initial biomechanic score seems to be an acceptable method for predicting the biomechanic outcome for single-tooth implant-supported crowns inserted using the osteotome sinus lift technique.

Introduction

Tooth removal is always followed by tridimensional bone loss. In the maxillary subsinusal, load-bearing area this phenomena, when associated with sinus pneu-matisation and periodontal defects leads to reduced basal bone heights seriously hampering implant placement without additional procedures1,4,5,6,7,8,9. “Crestal approach” is a general term encompassing different sinus-lift techniques which use osteotomes, (the osteotome technique sinus-lift) the fixture by itself,  piezo-surgery and sonic or rotary instruments9. If required, the created space can be filled with autologous bone, heterologous bone, artificial bone, a mixture of all these substances or can be left unfilled enabling  various degrees of spontaneous osteoinduction / osteoconduction. It is an already classic procedure for it has been demonstrated to be effective, less invasive, and associated with a reduced morbidity. All these techniques have in common a controlled modification and elevation of the sinus floor. (of the cortical bone layer plus the schneiderian membrane) When using the osteotome technique the sinus floor is fractured in a controlled manner with a set of osteotomes and subsequently lifted  up to a maximal height of 4mm, thus enabling placement of  screw-type fixtures. For the new-placed fixtures an immediate stability in an autologous bone height of at least 4mm is mandatory.  The present study can be defined as prospective-re-trospective because every single case data was picked up for some possible futu-re  study but its subject and data evaluation have been done only after data accumulation has been completed.

Purpose

The purpose of this article is to assess the prognostic value of the initial biome-chanical score for single-unit implant-supported crowns inserted on fixtures pla-ced using the osteotome sinus-lift technique.

For a  better purpose understanding we will review these two concepts:

  1. The Renouard-Rangert biomechanical risk factors10 are an analytical approach instrument for analyzing clinical data for predictable treatment of an implant-supported superstructure. (see fig.1) They are expressed by numbers and can be deployed to calculate its initial and/or final biome-chanical score.
  2. The Renouard-Rangert biomechanical score10 is the final algebraic sum resulting from the values assigned to each risk factor and depicts a spe-cific initial, final or an hypothetical final clinical situation. (see fig.2) It is divided into 3 areas, mimicking a traffic light.
Fig.1: Biomechanical risk factors. The four yellow lower right side paragraphs depict alarm signals that might be sent by an implant-supported rehabilitation after a certain period of occlusal loading. When one or more of the four signs appear the biomechanical score is worsening, respectively turns towards red, to the right. (see also fig.2)
FIG. 2 The “traffic light-like” Renouard-Rangert biomechanical score rating.

Case reports

The first case report explains why the final  biomechanical score shifted away from the initial one within an acceptable range of 1.5 points.

OPG filtru
Fig. 3. Panoramic x-ray excerpt before implant placing. The available bone height was 7mm.
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Fig. 4. Occlusal view before surgery in tooth area 14-16. The mesiodistal available space was 6 mm.

Fig. 5 The Initial biomechanical score was 0.
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Fig. 6. Periapical x-ray after implant placement in tooth area 15. The 3,7 mm diameter, 14 mm length fixture was placed using the osteotome sinus lift tech-nique. The sinusal floor was elevated by 4 mm. The created cavity was filled with Cerabone®.(yellow arrow)
IMG_0128
Fig. 7. Occlusal view in tooth area 14-16 immediately after crown cementation on a straight abutment.
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Fig. 8. Buccal view in tooth area 14-16 immediately after crown cementation.
Fig. 9. The final biomechanical score was 0.5. It insignificantly turned to the right, respectively towards red by 0.5 points only because initially a larger diameter implant was desired.

The second case report depicts why the final biomechanical score drifted away from the initial one way out of the acceptable range of 1.5 points.

Picture 007
Fig. 10. Panoramic x-ray excerpt before an immediate implant placing. The available bone height was 5mm. (yellow arrow)
Fig. 11. The initial biomechanical score was 1.

Fig. 12. Periapical x-ray after implant placement in tooth area 16. A 5.1mm diameter, 12mm length fixture was placed using the osteotome sinus lift tech-nique. The sinusal floor was elevated by 4 mm. The created cavity was filled with Cerabone®.(yellow arrows) It’s obvious that in the absence of a surgical guide the implant was positioned way too distal.
Fig. 13. Palatal view of the master cast with the crown in place. It is obvious that the implant is placed offset, e.g. distal from the center of the prostheses.
Fig. 14. Periapical x-ray after two years of occlusal loading. Notice the bone resorption reaching above the second fixture thread. (yellow arrow) This clear-cut alarm sign was ignored and the fixture was lost after another two months of occlusal loading. In order to establish a contact surface with the second premolar the prosthesis had to be built offset from the fixture axis. (red arrow)

Fig. 15. The final biomechanical score after two years of offset occlusal loading shifted drastically into red.
Fig. 16. Periapical x-ray two years after retreatment. A new fixture was placed mesial to the old site using a surgical guide. This time the implant is placed in the center of the prosthesis. (green arrow) The new fixture has a bioactive porous surface and is much less dependent on new formed bone.
IMG_3226
Fig. 17. Occlusal view after two years of occlusal loading. The prosthesis is a metal frame-free BelleGlass HP heat-and-presure processed polymer glass  crown. Although it was cured directly on an abutment for cemented superstructures it can be easily removed after removing the occlusal composite  layer covering the abutment screw,2,3. (green arrow)
Fig. 18. The final biomechanical score of the new prostheses accordingly shifted back to the left, respectively into green.

The third case report depicts a perfect match between an initial and a final biomechanical score.

Fig. 19. Occlusal view before surgery in tooth area 14-16. The intraoral mesiodistal available space was only 4mm.
Fig. 20. CT-scan excerpt before surgery. The available average bone height was 6mm. (yellow numbers)
Fig. 21. Periapical x-ray after implant placement in tooth area 15. No grafting material was used.
Fig. 22. Both initial and final biomechanical scores were 0.

Fig. 23. Buccal view immediately after temporary cementation of the permanent crown. The periimplantar “half-papillae” are not regenerated yet.
Fig. 24. Occlusal view immediately after temporary cementation of the permanent crown. The large interproximal contact surfaces significantly reduce the risk of abutment screw loosening.
Fig 25. Periapical x-ray after a three-year occlusal loading following crown removal for permanent cementation. There is no detectable periimplantar bone loss.

   

Fig. 26. Buccal view after permanent cementation. The periimplantar “half-papillae” regeneration process reached about 50 percent.

After three years of occlusal loading the biomechanical score remained unchanged, “in green”, without any alarm sign in sight. (look for fig. 22)

Materials and methods

From March 2004 to December 2018  we inserted in the load-bearing maxillary subsinusal areas 53 single-unit fixtures using  the osteotome sinus-lift technique. The lowest vertical bone height was 4mm. The sinusal floor was fractured in a controlled manner and the schneiderian membrane was elevated up to 4mm. In only ten cases we introduced grafting material (Cerabone®) through the socket. All fixtures have been submerged for 6 to 9 months. No fixture was lost during the osseointegration period nor during the uncovering procedure. All fixtures have been loaded after 8 to 10 months with permanent single-unit crowns. Twenty-one crowns were cemented and 32 were screw-retained. Eighteen crowns had BelleGlass occlusal surfaces and 35 had standard PFM occlusal surfaces. One cemented PFM fixture has been lost after two years of occlusal loading and a second cemented PFM crown after four years of occlusal loading. Both cases featured single-unit implants placed in free-end positions. Both cases  have been retreated by placing an implant mesial to the removed one. Both new implant-supported crowns had BelleGlass occlusal surfaces and were screw-retained. For each clinical case we created a Power Point Presentation file (PPT file) in which we stored: (1) standardized parallel technique periapical radio-graphs before implant placement, (2) after implant placement, (3) after pros-thesis delivery, (4) standardized intraoral buccal views before implant place-ment, (6) and after prosthesis delivery, (7) standardized intraoral occlusal views before implant placement, (8) and after prosthesis delivery. Prior to every im-plant placement  we have calculated an initial biomechanical score and biased it against a final one, e.g. calculated immediatelly after crown insertion. A bio-mechanical score shift below 1.5 points was considered irrelevant.

Fig. 27. Distribution of single-unit crowns in the load bearing maxillary areas.

Results

The initial biomechanical score matched the final one up to a maximal 1.5-point shift in 87% of the cases.

 Discussion

The only  87% accuracy match is probably due to: (1) diverging from the initial treatment plan by changing implant length and/or diameter, (2) offset occlusal crown loading, (3) different subsinusal basal, respectively autologous bone heights, (4) different types of abutment-crown interfaces, e. g. cemented  versus  screw-retained, (5) a wide array of occlusal clearances ranging from 4 to 11mm, (!) and (5) different occlusal surface materials.

The main shortage of this study is that due to low patient compliance we were unable to assess the biomechanical score shift at standardized periods of time (at 5 and 10 years) following  crown placement. The main accomplishment is that it establishes a prognostic value for the initial biomechanical score. (calculated be-fore treatment start) 

Conclusions:

  1. Calculation of an initial biomechanic score seems to be an acceptable method for predicting the biomechanic outcome for single-tooth crowns supported by fixtures inserted using the osteotome sinus lift technique.
  2. The osteotome technique sinus lift is indicated only if the initial biome-chanical score is “in green”.
  3. An initial biomechanical score will probably match the final one only if both clinical indication and procedure protocol are strictly taken into account, e. g.:  an initial bone height of at least 4mm yielding good im-plant primary stability, deployment of  a dedicated surgical guide, a corti-cal bone/schneiderian membrane lift of no more than 4 mm.
  4. When lifting the sinus floor up to 4mm bone grafting material seems to be unnecessary.
  5. Screw-retained crowns with non-ceramic occlusal surfaces are of superior performance compared to PFM crowns featuring ceramic occlusal surfa-ces or full-ceramic crowns. 

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