The Early Loading of Different Surface Modified Implants: A Prospective Clinical Study


 The early loading of different surface treated dental implants is compared in our clinical study. Patients were selected from the outpatient ward of the Department of Oro-Maxillofacial Surgery and Stomatology at the Semmelweis University. The secondary stability, that evolved after 6 weeks of healing, was measured on acid etched/sand blasted (SLA) and bio-hydroxyapatite coated implants. Osstell® and Periotest® were applied to determine this value. Periodontal probing depth appearing after 3 months of loading was checked on 6 points next to the implant supported prosthesis. Shapiro-Wilk and Mann-Whitney tests have been chosen to fulfil the statistical analysis. According to our results, a similar satisfying secondary stability can be obtained independently of the modality of the surface. The values were higher in the bio-hydroxyapatite group; however, this difference was not significant. The outcome of measuring the probing depth reflects the importance of frequent recalls of patients. The necessary ethical approval for our study has been provided by the National Institute of Pharmacy and Nutrition (reference number: OGYÉI/55197/2019 ).


Background
The direct integration of metal implants into the bone was discovered by Branemark et al in 1962. After numerous animal testing, dental implants that are based on the principle of osseointegration came into use in everyday dental practice (1965). The discovery of direct bone-implant contact (BIC) was an enormous invention in dental implantology. The de nition of osseointegration rst described in 1976 signi es the direct contact of the implant and the surrounding bone at an optical microscopy level. The su ciently modi ed surface has been described as one of the main conditions of osseointegration. This premise was also con rmed by Albrektsson et al in 1981. (1) The term of osseointegration has been changed and re-evaluated throughout time. It can be determined as a foreign body reaction of the organism (tissues) that evolves as a part of the physiological defence mechanism. The investigation of implant surfaces has an important place among basic research in implantology. The ideal form, the parameters, the biological indicator function and its effects are being increasingly searched for. (5,8,21) There is a vast literature in the topic, countless publications and scienti c presentations are currently being published. Dental implants can be de ned by the micro-and nanometre-sized parameters of their surfaces, by their chemical constitution, and by the physical and mechanical features of the implants.
Realising that a moderately rough surface, compared to the previously used fully rough or smooth surfaces, improves clinical results is considered to be one of the biggest ndings. (7,21) However, there is no clinically proved evidence on how and in what rate these nanometre-sized structures improve the osseointegration ability of an implant surface. The effect of micrometre-sized structures on cells is already clari ed, moreover, the bio lm forming ability of nanometre-sized structures is also proven with animal experiments, although the latter's mechanism is still unknown. (9,10,19,20) There is some ambiguity related to the hydrophilic surfaces as well. The data earned from animal tests clearly con rm the progress of the clinical outcome. This can be explained with the observation that using a hydrophilic surface reduces the deposition of the number of carbon, oxygen, and nitrogen compounds. Therefore, the extent of surface contamination decreases and the protein absorption of the implant surface increases.
Although the number of clinical evidence-based examinations in this topic is evanescent, the ultimate goal of surface development is to detect the quick, safe, and long-term formation of the seconder stability (osseointegration). (22) Present knowledge about the adequately modi ed surfaces is comprehensive, nonetheless there are some unexplained questions remaining. What does the ideal surface structure look like? What kind of effect does the surface have on the surrounding area? How and why does the shortterm success of some surfaces transform into failure? (8,22) The osseointegration stimulating effect of bone-like materials (e.g. tricalcium phosphate, hydroxyapatite) has been tried in many examinations. A vast amount of publications re ected on the promising short-term effect of biomaterial over-plated surfaces in the past, however, the anticipation of long-term success was rather disappointing. This observation has been explained with the phenomenon that the crystals peel off during the insertion of the implant, moreover after the absorption of these detached crystals, the surrounding bone cannot grow onto the implant's surface. Despite the failures, the application of various grain-sized (nowadays nanometre-sized) biomaterials onto the implant surface is still trying to be accomplished. (16,17) The sand blasted acid etched (combined) surface is one of the most frequently used surfaces nowadays, which has a positive in uence on osseointegration. The description of this effect has been published in several articles. (11,13,14) A few ndings can be found in the literature regarding the combination of combined surfaces and biomaterials, and its positive effect on osseointegration.

Materials And Methods
In our study the effect on the osseointegration of SA (sand blasted -acid etched) and NH (biohydroxyapatite) surfaces of the Osstem® implants has been compared to Straumann SLA® (sand  By contrast, the NH surface (previously named as BA by the producer) of the Osstem® implants is a biohydroxyapatite surface. Its characteristic is that the sand blasted surface is covered with a 10 nm thick calcium phosphate (hydrophilic) layer, which has the ability of bio absorption in the human body (living tissues). Its Ra value is 2.5 ~ 3.0 µm. The nano calcium phosphate layer was found on the SA surface.
( Fig. 2a, 2b) The concept of inventing this surface was to combine the well working sand blasted -acid etched surface with the excellent osteoinductive featured HA surface.  an SLA surface, the BIC increases with 125% compared to the nothing but etched surfaces. Based on this knowledge, the SLA surface has been introduced to dental implantology. In the past few years, a work team from Gothenburg has been dealing with 3D optical pro lometry measurements, wherein Wennerberg et al analysed the most important surfaces available in trade. It can be accepted as a written result and a factual data that the Sa (in case of two dimension: Ra) value of the modern surfaces is between 0,9 and 1,4 µm. By the SLA surface this rate is 1,42 µm. (8,21) The aim of our clinical study was to compare the seconder stability of different surface modi ed implants on the 6th week after the implant insertion (in the event of loading). The rate of stability has been analysed both in women and men, however, done so non-exhaustively as there were divergences among various age groups, the general health of the patients, and discrepancy in their oral hygiene. Beyond that, with the measurement of the gingival sulcus depth, the most secure surfaces have been de ned from the perspective of plaque accumulation and the consequential formation of periimplantitis. Women and men of age 18-70 were included in the study, which was performed at the Department of Oro-Maxillofacial Surgery and Stomatology at the Semmelweis University. The recording the medical history of the participants was followed by extra-and intraoral examinations, and stomato-oncological screenings. Before the implant placement, all necessary dental treatments had been achieved, that may have included several conservative treatments and periodontal therapies. All the crucial consent forms and lea ets were ful lled and signed. To evaluate the quantity and quality of the bone, besides the conventional X-rays, the preoperative preparations were completed with taking a low-dosage Cone Beam CT (CBCT) scan. General diseases were not de ned as a disqualifying reason, but the non-controlled systematic diseases were. The medication of patients was registered as well. Controlled hypertension was the most commonly detected disease among the participants' medical history. The patients had not received neither bisphosphonate therapies, nor radio-or chemotherapy in the past years. Concerning the general oral hygiene, patients were ranged into 3 groups: good, moderate, proper. Bad oral hygiene was a contraindication not just for the participation in the study but also for receiving a dental implant. Patients who had had a previously done GBR-technique (Guided Bone Regeneration) in the correspondent area were excluded from the study. Smoking was not a disabling fact. 10% of the participants were light smokers (less than 10 cigarettes per day). There were no heavy smokers. Appearance of the patients on the controls were a vital factor. 75 implants (Osstem® SA 16, Osstem® NH 39, Straumann® SLA 20) were inserted according to this study. The operations were performed by 3 dento-alveolar surgeons (Joób, Körmöczi, Komlós).
Osstell® and Periotest® were used to measure the stability of the inserted implants. While using a Periotest® (PTV), an electrically driven tapping head percusses the implant and based on the parameters of repercussion, it shows the index proper to the stability. The Osstell® (ISQ) device measures by a resonance frequency analysis while using a special transducer. The device generates oscillation in the transducer via the piezoelectric effect, thus the index is given by the interactions of the implant and the quiver. On the 6th week after the implant placement, the value of the seconder stability was measured by different surface modi ed implants that had been inserted into various positions (front, premolar, molar). The gained data was compared. The loading of the implants (prosthetic rehabilitation) happened 6 weeks after the implant placement. Fix, metal-ceramic dentures were prepared in all of the cases.
Cemented and screw-retained crowns and bridges were applied. For the direct examination of stability, the rate of the insertion bending-moment was registered. The registration of the primary stability was necessary because the possibility of the early loading is dependent on its rate. After three months, the gingival sulcus depth was detected on 6 points next to the restorations. The necessary ethical approval for our study has been provided by the National Institute of Pharmacy and Nutrition (reference number: OGYÉI/55197/2019 ).

Results
One of the inserted 75 implants fell out spontaneously on the 4th week of the healing period. The success rate of the remained 74 implants was 100%. The results received by the registration of primary stabilities show that when inserting Straumann® SLA or Osstem® NH and SA surface modi ed implants, the value of stability was corresponding. (Table 1) According to this data, the early loading of the inserted implants were possible in every examined group. The measurement of the secondary stability was performed on the 6th week of the healing period. A Shapiro-Wilk test was used for testing the normality of the data. The presence of a signi cant difference between the examined groups was revealed with the Mann-Whitney test. The data of the Straumann® and the Osstem® implants (Table 2), moreover the data of the two different surface modi ed Osstem® implants (Table 3) were compared. There were no signi cant differences at all, although the rates of the secondary stability were higher in the Osstem NH® bio-hydroxyapatite group after 6 weeks of healing.   According to the results of the Shapiro-Wilk test, the distribution was not normal. Based on the results of the Mann-Whitney test, the only detected difference was shown in two values of the oral surface, two types of implants (Straumann® and Osstem®). In general, the gingival sulcus depth was smaller on the buccal surfaces. The lowest average was counted on the mid-buccal surface (0,63), in comparison to the disto-oral surface, where the average was the highest (0,86).

Discussion
According to our study, there was no signi cant difference on the secondary stability between the Staumann® and the Osstem® groups. There was also no signi cant difference between the two types of Osstem® implants (SA and NH), although the ISQ values of the NH surface implants were higher compared to the SA surface implants. In this study, the rates of the secondary stability was analysed comparatively early after the insertion of the implants, in the 6th week of the healing period. It can be concluded that in case of an early loading, the values of the secondary stabilities although not signi cantly, but were better of the bio-hydroxyapatite surface implants, with progressive osseointegration followed by the loading, thus a better long-term success can be achieved. This conclusion creates the possibility for further examination. The rates of the gingival sulcus depths, after three months, were higher on the oral surfaces compared to the buccal ones. This can be explained by the fact that the oral surfaces of the teeth are more di cult to clean. This observation re ects on how important the frequent recalls and the proper motivation is in order to achieve a long-term success and prevent the formation of periimplantitis. The aim of further research can be the in uence of the osseointegration process at its most critical period. The value of the primary stability (BIC) of the inserted implants dips and it approaches its original value after the fourth week. At this point, the secondary stability emerges. Presumably the physiological processes are positively in uenced by the different surfaces during the above mentioned two weeks.

Conclusion
Surface research is one of the fastest developing eld among basic implantology research. The aim of the modern surface modi cation procedure is to shorten the healing period, to achieve the osseointegration as soon as possible, and to create the possibility for earlier prosthetic restorations. The most important establishment of our clinical study is that decent results were observed by all the different surface modi ed groups and that the rates of the secondary stabilities gave the possibility for a prosthetic loading. Our ndings are equivalent with the data of the scienti c literature: the modern surface modi cation methods lead to good or even excellent results. Nonetheless, there are several questions relating to this topic, that could serve as ground for further research and thus should be answered.

Declarations
Ethics approval: The necessary ethical approval for our study has been consented by the National Institute of Pharmacy and Nutrition (reference number: OGYÉI/55197/2019).  a. The BA (Bio-HA) surface of the Osstem® implants in x4,000 micro magni cation. b. The BA (Bio-HA) surface of the Osstem® implants in x30,000 nano magni cation. On both gures the SA surface is coated with calcium phosphate in a 10 nm thick layer, which is visible on the surface as a nano coating layer.